xvEPA
United States May 2006
EPW600
-------
EPA/600/R-05/144aB
May 2006
Air Quality Criteria for Lead
Volume I
National Center for Environmental Assessment-RTF Office
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC
-------
DISCLAIMER
This document is a second external review draft being released for review purposes only
and does not constitute U.S. Environmental Protection Agency policy. Mention of trade names
or commercial products does not constitute endorsement or recommendation for use.
PREFACE
National Ambient Air Quality Standards (NAAQS) are promulgated by the United States
Environmental Protection Agency (EPA) to meet requirements set forth in Sections 108 and 109
of the U.S. Clean Air Act. Those two Clean Air Act sections require the EPA Administrator
(1) to list widespread air pollutants that reasonably may be expected to endanger public health or
welfare; (2) to issue air quality criteria for them that assess the latest available scientific
information on nature and effects of ambient exposure to them; (3) to set "primary" NAAQS to
protect human health with adequate margin of safety and to set "secondary" NAAQS to protect
against welfare effects (e.g., effects on vegetation, ecosystems, visibility, climate, manmade
materials, etc); and (5) to periodically review and revise, as appropriate, the criteria and NAAQS
for a given listed pollutant or class of pollutants.
Lead was first listed in the mid-1970's as a "criteria air pollutant" requiring NAAQS
regulation. The scientific information pertinent to Lead NAAQS development available at the
time was assessed in the EPA document Air Quality Criteria for Lead; published in 1977. Based
on the scientific assessments contained in that 1977 lead air quality criteria document (1977 Lead
AQCD), EPA established a 1.5 |ig/m3 (90-day average) Lead NAAQS in 1978.
To meet Clean Air Act requirements noted above for periodic review of criteria and
NAAQS, new scientific information published since the 1977 Lead AQCD was later assessed in
a revised Lead AQCD and Addendum published in 1986 and in a Supplement to the 1986
AQCD/Addendum published by EPA in 1990. A 1990 Lead Staff Paper, prepared by EPA's
Office of Air Quality Planning and Standards (OPQPS), drew upon key findings and conclusions
from the 1986 Lead AQCD/Addendum and 1990 Supplement (as well as other OAQPS-
sponsored lead exposure/risk analyses) in posing options for the EPA Administrator to consider
with regard to possible revision of the Lead NAAQS. However, EPA decided not to revise the
lead NAAQS at that time.
I-ii
-------
The purpose of this revised Lead AQCD is to critically evaluate and assess the latest
scientific information that has become available since the literature assessed in the above 1986
Lead AQCD/Addendum and 1990 Supplement, with the main focus being on pertinent new
information useful in evaluating health and environmental effects of ambient air lead exposures.
This includes discussion in this document of information regarding: the nature, sources,
distribution, measurement, and concentrations of lead in the environment; multimedia lead
exposure (via air, food, water, etc.) and biokinetic modeling of contributions of such exposures
to concentrations of lead in brain, kidney, and other tissues (e.g., blood and bone concentrations,
as key indices of lead exposure).; characterization of lead health effects and associated exposure-
response relationships; and delineation of environmental (ecological) effects of lead. This
Second External Review Draft of the revised Lead AQCD mainly assesses pertinent literature
published or accepted for publication through June, 2004.
The First External Review Draft (dated December 2005) of the revised Lead AQCD
underwent public comment and was reviewed by the Clean Air Scientific Advisory Committee
(CASAC) at a public meeting held in Durham, NC on February 28-March, 2006. The public
comments received and CASAC recommendations were taken into account in making
appropriate revisions to this document and incorporating them into this Second External Review
Draft (dated May, 2006) which is being released for further public comment and CASAC review
at a public meeting to be held June 28-29, 2006. Public comments and CASAC advice received
on these Second External Review Draft materials will be taken into account in incorporating
further revisions into the final version of this Lead AQCD, which must be completed and issued
by October 1, 2006. Evaluations contained in the present document will be drawn on to provide
inputs to an associated Lead Staff Paper prepared by EPA's Office of Air Quality Planning and
Standards (OAQPS), which will pose options for consideration by the EPA Administrator with
regard to proposal and, ultimately, promulgation of decisions on potential retention or revision,
as appropriate, of the current Lead NAAQS.
Preparation of this document has been coordinated by staff of EPA's National Center for
Environmental Assessment in Research Triangle Park (NCEA-RTP). NCEA-RTP scientific
staff, together with experts from academia, contributed to writing of document chapters. Earlier
drafts of document materials were reviewed by scientists from other EPA units and by non-EPA
experts in several public peer consultation workshops held by EPA in July/August 2005.
I-iii
-------
NCEA acknowledges the valuable contributions provided by authors, contributors, and
reviewers and the diligence of its staff and contractors in the preparation of this draft document.
I-iv
-------
Air Quality Criteria for Lead
(Second External Review Draft)
VOLUME I
EXECUTIVE SUMMARY E-l
1. INTRODUCTION 1-1
2. CHEMISTRY, SOURCES, AND TRANSPORT OF LEAD 2-1
3. ROUTES OF HUMAN EXPOSURE TO LEAD AND OBSERVED
ENVIRONMENTAL CONCENTRATIONS 3-1
4. LEAD TOXICOKINETICS AND MEASUREMENT/MODELING OF HUMAN
EXPOSURE IMPACTS ON INTERNAL TISSUE DISTRIBUTION OF LEAD 4-1
5. TOXICOLOGICAL EFFECTS OF LEAD IN LABORATORY ANIMALS,
HUMANS, AND IN VITRO TEST SYSTEMS 5-1
6. EPIDEMIOLOGIC STUDIES OF HUMAN HEALTH EFFECTS
ASSOCIATED WITH LEAD EXPOSURE 6-1
7. INTEGRATIVE SYNTHESIS OF LEAD EXPOSURE/HEALTH
EFFECTS INFORMATION 7-1
INSERT (To be included in the final draft)
8. ENVIRONMENTAL EFFECTS OF LEAD 8-1
VOLUME II
CHAPTER 5 ANNEX (TOXICOLOGICAL EFFECTS OF LEAD IN
LABORATORY ANIMALS, HUMANS, AND IN VITRO TEST SYSTEMS) AX5-1
CHAPTER 6 ANNEX (EPIDEMIOLOGIC STUDIES OF HUMAN HEALTH
EFFECTS ASSOCIATED WITH LEAD EXPOSURE) AX6-1
CHAPTER 8 ANNEX (ENVIRONMENTAL EFFECTS OF LEAD) AX8-1
I-v
-------
Table of Contents
Page
List of Tables I-xxii
List of Figures I-xxviii
Authors, Contributors, and Reviewers I-xxxvi
U.S. Environmental Protection Agency Project Team I-xlviii
U.S. Environmental Protection Agency Science Advisory Board (SAB)
Staff Office Clean Air Scientific Advisory Committee (CASAC) 1-1
Abbreviations and Acronyms I-lii
EXECUTIVE SUMMARY E-l
1. INTRODUCTION 1-1
1.1 LEGAL AND HISTORICAL BACKGROUND 1-1
1.1.1 Legislative Requirements 1-1
1.1.2 Criteria and NAAQS Review Process 1-3
1.1.3 Regulatory Chronology 1-4
1.2 CURRENT LEAD CRITERIA AND NAAQS RE VIEW 1-7
1.2.1 Procedures and Key Milestones for Document Preparation 1-7
1.3 ORGANIZATIONAL STRUCTURE AND CONTENT OF
THE DOCUMENT 1-9
1.3.1 Ascertainment of Literature and General Document Format 1-9
1.3.2 Organization and Content of the Document 1-10
REFERENCES 1-12
2. CHEMISTRY, SOURCES, AND TRANSPORT OF LEAD 2-1
2.1 PHYSICAL AND CHEMICAL PROPERTIES OF LEAD 2-1
2.2 SOURCES OF LEAD 2-13
2.2.1 Natural Sources 2-13
2.2.2 Lead Emission in the U.S 2-16
2.2.3 Stationary Sources 2-19
2.2.4 Mobile Sources 2-44
2.3 TRANSPORT WITHIN THE ENVIRONMENT 2-52
2.3.1 Atmospheric Transport of Lead Particles 2-52
2.3.2 Deposition of Airborne Particles 2-54
2.3.3 Resuspension of Lead-Containing Soil and Dust Particles 2-58
2.3.4 Runoff from Impervious Surfaces 2-64
2.3.5 Leaching of Soil Lead 2-68
2.3.6 Transport in Aquatic Systems 2-72
2.3.7 Plant Uptake 2-75
2.3.8 Routes of Exposure for Livestock and Wildlife 2-75
2.4 METHODS FOR MEASURING ENVIRONMENTAL LEAD 2-77
2.5 SUMMARY 2-79
REFERENCES 2-83
I-vi
-------
Table of Contents
(cont'd)
3. ROUTES OF HUMAN EXPOSURE TO LEAD AND OBSERVED
ENVIRONMENTAL CONCENTRATIONS 3-1
3.1 EXPOSURE: AIR 3-2
3.1.1 Routine Monitoring of Lead Within the U.S 3-2
3.1.2 Observed Concentrations - Ambient Air 3-7
3.1.3 Observed Concentrations- Indoor Air 3-12
3.1.4 Observed Concentrations - Occupational 3-13
3.2 EXPOSURE: SOIL AND DUST 3-15
3.2.1 Urban Background Concentrations of Soil Lead 3-16
3.2.2 Soil Concentrations Near Stationary Sources 3-19
3.2.3 Observed Concentrations - House Dust 3-24
3.2.4 Concentrations of Lead in Road Dust 3-30
3.3 EXPOSURE: DRINKING WATER 3-31
3.4 EXPOSURE: FOOD INGESTION 3-38
3.5 OTHER ROUTES OF EXPOSURE 3-45
3.5.1 Lead-Based Paint 3-45
3.5.2 Calcium Supplements 3-46
3.5.3 Glazes 3-46
3.5.4 Miniblinds 3-47
3.5.5 Hair Dye 3-47
3.5.6 Other Potential Sources of Lead Exposure 3-47
3.6 MEASUREMENT METHODS 3-48
3.7 SUMMARY 3-49
REFERENCES 3-50
4. LEAD TOXICOKINETICS AND MEASUREMENT/MODELING OF HUMAN
EXPOSURE IMPACTS ON INTERNAL TISSUE DISTRIBUTION OF LEAD 4-1
4.1 INTRODUCTION 4-1
4.2 TOXICOKINETICS OF LEAD 4-2
4.2.1 Absorption of Lead 4-3
4.2.2 Distribution 4-12
4.2.3 Metabolism 4-16
4.2.4 Excretion 4-17
4.3 BIOLOGICAL MARKERS OF LEAD BODY BURDENS
AND EXPOSURE 4-19
4.3.1 Lead in Blood 4-19
4.3.1.1 Summary of Key Findings from the 1986
LeadAQCD 4-19
4.3.1.2 Analytical Methods for Measuring Lead in Blood 4-19
4.3.1.3 Levels of Lead in Blood 4-20
4.3.1.4 Blood Lead as aBiomarker of Lead Body Burden 4-22
4.3.1.5 Blood Lead as aBiomarker of Lead Exposure 4-28
I-vii
-------
Table of Contents
(cont'd)
4.3.1.6 Summary of Blood Lead as a Biomarker of Lead
Body Burden and Exposure 4-32
4.3.2 Lead in Bone 4-33
4.3.2.1 Summary of Key Findings from the 1986
LeadAQCD 4-33
4.3.2.2 Methodology of Bone Lead Analysis 4-33
4.3.2.3 Bone Lead as a Biomarker of Lead Body Burden 4-39
4.3.2.4 Distribution of Lead from Bone into Blood
and Plasma 4-42
4.3.2.5 Mobilization of Lead From Bone 4-46
4.3.2.6 Summary of Bone Lead as a Biomarker of Lead
Body Burden and Exposure 4-51
4.3.3 Lead in Teeth 4-51
4.3.3.1 Summary of Key Findings from the 1986
LeadAQCD 4-51
4.3.3.2 Analytical Methods for Measuring Lead in Teeth 4-51
4.3.3.3 Tooth Lead as a Biomarker of Lead Body Burden 4-52
4.3.3.4 Relationship between Tooth Lead and Blood Lead 4-53
4.3.3.5 Mobilization of Lead from Teeth 4-54
4.3.3.6 Summary of Tooth Lead as a Biomarker of
Lead Body Burden and Exposure 4-54
4.3.4 Lead in Urine 4-55
4.3.4.1 Summary of Key Findings from the 1986
LeadAQCD 4-55
4.3.4.2 Analytical Methods for Measuring Lead in Urine 4-55
4.3.4.3 Levels of Lead in Urine 4-55
4.3.4.4 Urine Lead as a Biomarker of Lead Body Burden 4-56
4.3.4.5 Relationship Between Lead in Blood and Urine 4-57
4.3.4.6 Summary of Urine Lead as a Biomarker of Lead
Body Burden and Exposure 4-61
4.3.5 Lead in Hair 4-62
4.3.5.1 Summary of Key Findings from the 1986
LeadAQCD 4-62
4.3.5.2 Analytical Methods for Measuring Lead in Hair 4-62
4.3.5.3 Levels of Lead in Hair 4-62
4.3.5.4 Hair Lead as a Biomarker of Lead Body Burden 4-63
4.3.5.5 Hair Lead as a Biomarker of Lead Exposure 4-63
4.3.5.6 Summary of Hair Lead as a Biomarker of Lead
Body Burden and Exposure 4-64
4.4 MODELING LEAD EXPOSURE AND TISSUE DISTRIBUTION
OF LEAD 4-64
4.4.1 Introduction 4-64
I-viii
-------
Table of Contents
(cont'd)
4.4.2 Empirical Models of Lead Exposure Blood Lead Relationships 4-67
4.4.3 Historic Overview of Mechanistic Models of Lead Biokinetics 4-83
4.4.3.1 Rabinowitz Model 4-83
4.4.3.2 Marcus Model(s) 4-85
4.4.3.3 Bert Model 4-86
4.43 A Contemporary Models 4-87
4.4.4 Integrated Exposure Uptake Biokinetic (IEUBK) Model for
Lead in Children 4-90
4.4.4.1 Model Structure 4-90
4.4.4.2 Model Calibration and Evaluation 4-97
4.4.4.3 Model Applications 4-97
4.4.4.4 Implementation Code 4-99
4.4.5 Leggett Model 4-100
4.4.5.1 Model Structure 4-100
4.4.5.2 Model Calibration and Evaluation 4-103
4.4.5.3 Model Applications 4-104
4.4.5.4 Implementation Code 4-105
4.4.6 O'Flaherty Model 4-105
4.4.6.1 Model Structure 4-105
4.4.6.2 Model Calibration and Evaluation 4-109
4.4.6.3 Model Applications 4-109
4.4.6.4 Implementation Code 4-110
4.4.7 EPA All Ages Lead Model 4-111
4.4.7.1 Model Structure 4-111
4.4.8 Slope Factor Models 4-113
4.4.9 Model Comparisons 4-114
4.4.10 Conclusions and Future Directions 4-123
REFERENCES 4-125
5. TOXICOLOGICAL EFFECTS OF LEAD IN LABORATORY ANIMALS,
HUMANS, AND IN VITRO TEST SYSTEMS 5-1
5.1 INTRODUCTION 5-1
5.2 EFFECTS OF LEAD ON HEME SYNTHESIS 5-2
5.2.1 Effects of Lead on Erythrocyte Biology and Function 5-2
5.2.2 Effects of Lead on Erythrocyte Functions 5-3
5.2.3 Effect of Lead on Erythrocyte Heme Metabolism 5-8
5.2.4 Effect of Lead on Other Hematological Parameters 5-11
5.2.5 Effects of Lead on Erythrocyte Enzymes 5-12
5.2.6 Erythrocyte Lipid Peroxidation and Antioxidant Defense 5-15
5.3 NEUROLOGIC/NEUROBEHAVIORAL EFFECTS OF LEAD 5-17
5.3.1 Neurotoxi col ogi c/Neurob ehavi oral Effects of Lead
in Animals 5-17
I-ix
-------
Table of Contents
(cont'd)
5.3.1.1 Introduction 5-17
5.3.1.2 Neurochemical Alterations Resulting from
Lead Exposure 5-19
5.3.1.3 Actions of Lead Exposure Defined by
Neurophysiologic Approaches 5-28
5.3.1.4 Lead Exposure and Sensory Organ Function 5-32
5.3.1.5 Neurobehavioral Toxicity Resulting from
Pb Exposure 5-35
5.3.1.6 Lead-Induced Changes in Cellular Development
and Disposition of the Metal 5-61
5.3.1.7 Susceptibility and Vulnerability Factors Modifying
Pb Exposure and Thresholds for CNS Effects 5-66
5.3.1.8 Summary 5-72
5.3.2 Neurotoxi col ogical/Neurobehavi oral Effects of Lead
in Humans 5-74
5.3.2.1 Effects of Lead in Young Children to
Mid-Adolescence 5-74
5.3.2.2 Clinical Manifestations in Adults with Childhood
Lead Poisoning 5-81
5.3.2.3 Adults with Ambient Exposures to Lead 5-81
5.4 REPRODUCTIVE AND DEVELOPMENTAL EFFECTS OF LEAD 5-82
5.4.1 Summary of Key Findings on the Developmental and
Reproductive Effects of Lead in Animals from the 1986
LeadAQCD 5-82
5.4.2 Effects on Male Reproductive Function 5-84
5.4.2.1 Effects on Male Sexual Development
and Maturation 5-85
5.4.2.2 Effects on Male Fertility: Effects on Sperm
Production and Function 5-89
5.4.2.3 Effects on Male Sex Endocrine System 5-91
5.4.2.4 Effects on Morphology and Histology of Male
Sex Organs 5-91
5.4.3 Effects on Female Reproductive Function 5-93
5.4.3.1 Effects on Female Sexual Development and
Maturation 5-93
5.4.3.2 Effects on Female Fertility 5-94
5.4.3.3 Effects on the Female Sex Endocrine System
and Menstrual Cycle 5-94
5.4.3.4 Effects on Morphology and Histology of Female
Sex Organs and the Placenta 5-98
5.4.4 Effects on Embryogenesis 5-99
5.4.4.1 Embryo/Fetal Mortality 5-99
I-x
-------
Table of Contents
(cont'd)
5.4.4.2 Effects on embryo/fetal morphology 5-105
5.4.5 Effects on Growth and Endocrine Regulation of Growth 5-105
5.4.6 Effects on Other Endocrine Systems during Development 5-106
5.4.7 Effects on Other Organ Systems during Development 5-107
5.4.7.1 Developmental Effects on Blood and Liver 5-107
5.4.7.2 Developmental Effects on Skin 5-108
5.4.7.3 Developmental Effects on the Retina 5-108
5.5 CARDIOVASCULAR EFFECTS OF LEAD 5-111
5.5.1 Introduction 5-111
5.5.2 Lead Exposure and Arterial Pressure in Experimental
Animals 5-111
5.5.2.1 Effect of Lead on Production of Reactive
Oxygen Species and Nitric Oxide Metabolism 5-112
5.5.2.2 Protein Kinase C, Inflammation, NFKB
Activation and Apoptosis 5-118
5.5.2.3 Effect of Lead Exposure on the Adrenergic
System 5-120
5.5.2.4 Effects of Lead on the Renin-Angiotensin-
Aldosterone (RAAS) and Kininergic Systems 5-122
5.5.3 Effects of Lead Exposure on Vasomodulators 5-123
5.5.4 Effects of Lead on Vascular Reactivity 5-124
5.5.5 Lead-Calcium Interactions in Vascular Tissue 5-126
5.5.6 Cardiotoxicity and Atherogenesis 5-127
5.5.7 Effects of Lead on Endothelial Cells 5-127
5.5.8 Effects of Lead on Vascular Smooth Muscle Cells 5-131
5.6 GENOTOXIC AND CARCINOGENIC EFFECTS OF LEAD 5-133
5.6.1 Introduction 5-133
5.6.2 Carcinogenesis Studies 5-134
5.6.2.1 Human Studies 5-134
5.6.2.2 Laboratory Animal Studies 5-135
5.6.2.3 Cell Culture Studies 5-137
5.6.2.4 Organ-Specific Studies 5-140
5.6.2.5 Carcinogenesis Summary 5-140
5.6.3 Genotoxicity Studies 5-140
5.6.3.1 Human Studies 5-141
5.6.3.2 Laboratory Animal Studies 5-142
5.6.3.3 Cell Culture Studies 5-145
5.6.3.4 Animal Cell Cultures 5-147
5.6.3.5 Cell-Free Studies 5-149
5.6.3.6 Organ-Specific Studies 5-149
5.6.3.7 Genotoxicity Section Summary 5-149
I-xi
-------
Table of Contents
(cont'd)
5.6.4 Genotoxicity as it Pertains to Potential Developmental
Effects 5-149
5.6.5 Epigenetic Effects and Mixture Interactions 5-150
5.6.5.1 Gene Expression 5-150
5.6.5.2 DNA Repair 5-151
5.6.5.3 Mitogenesis 5-152
5.6.5.4 Epigenetic Mechanisms Summary 5-153
5.7 LEAD AND THE KIDNEY 5-155
5.7.1 Review of Earlier Work 5-155
5.7.2 Markers of Renal Toxicity 5-157
5.7.3 Biochemical Mechanisms of Lead Toxicity 5-158
5.7.4 Animal Studies 5-160
5.7.4.1 Lead Toxicokinetics 5-160
5.7.4.2 Pathology, Ultrastructural, and Functional
Studies 5-161
5.7.4.3 Biochemical Mechanisms of Lead Toxicity 5-167
5.7.4.4 Effect of Age on Lead Toxicity 5-184
5.8 EFFECTS ON BONE AND TEETH 5-187
5.8.1 Biology ofBone and Bone Cells 5-187
5.8.2 Summary of Information Presented in the 1986
LeadAQCD 5-189
5.8.3 Bone Growth in Lead-Exposed Animals 5-189
5.8.4 Regulation of Bone Cell Function in Animals - Systemic
Effects of Lead 5-192
5.8.4.1 Hypercalcemia/Hyperphosphatemia 5-192
5.8.4.2 Vitamin D[1,25-(OH2)D3] 5-193
5.8.4.3 Parathyroid Hormone 5-193
5.8.4.4 Growth Hormone 5-194
5.8.5 Bone Cell Cultures Utilized to Test the Effects of Lead 5-195
5.8.5.1 Bone Organ Culture 5-195
5.8.5.2 Primary Cultures of Osteoclasts and
Osteoblasts 5-195
5.8.5.3 Rat Osteosarcoma Cell Line (ROS 17/2.8) 5-196
5.8.5.4 Human Osteosarcoma Cells (HOS TE 85) 5-199
5.8.5.5 Chick Chondrocytes 5-199
5.8.6 Bone Lead as a Potential Source of Toxicity in Altered
Metabolic Conditions 5-200
5.8.6.1 Pregnancy and Lactation 5-201
5.8.6.2 Age/Osteoporosis 5-205
5.8.6.3 Weight Loss 5-207
I-xii
-------
Table of Contents
(cont'd)
5.8.7 Teeth - Introduction 5-208
5.8.8 Uptake of Lead by Teeth 5-210
5.8.9 Effects of Lead on Enamel and Dentine Formation 5-211
5.8.10 Effects of Lead on Dental Pulp Cells 5-212
5.8.11 Adverse Effects of Lead on Teeth—Dental Caries 5-213
5.8.12 Lead from Teeth as a Potential Source of Toxicity 5-214
5.9 EFFECTS OF LEAD ON THE IMMUNE SYSTEM 5-216
5.9.1 Introduction 5-216
5.9.2 Host Resistance 5-216
5.9.2.1 Viral Diseases 5-217
5.9.2.2 Bacterial Diseases 5-217
5.9.2.3 Parasitic Diseases 5-219
5.9.2.4 Tumors 5-219
5.9.3 Humoral Immunity 5-219
5.9.3.1 General Effects on B lymphocytes and
Immunoglobulins 5-220
5.9.3.2 IgE Alterations 5-221
5.9.4 General Effects on Thymocytes and T lymphocytes 5-224
5.9.4.1 Delayed Type Hypersensitivity 5-226
5.9.4.2 Other T-Dependent Cell-Mediated
Immune Changes 5-228
5.9.5 Lymphocyte Activation and Responses 5-230
5.9.5.1 Activation by Mitogens 5-230
5.9.5.2 Activation via Other Receptors 5-231
5.9.5.3 Cytokine Production 5-232
5.9.6 Macrophage Function 5-235
5.9.6.1 Nitric Oxide (NO) Production 5-237
5.9.7 Granulocytes and Natural Killer (NK) Cells 5-244
5.9.8 Hypersensitivity and Autoimmunity 5-245
5.9.9 Mechanism of Lead-Based Immunomodulation 5-247
5.9.10 Age-Based Differences in Sensitivity 5-249
5.10 EFFECTS OF LEAD ON OTHER ORGAN SYSTEMS 5-254
5.10.1 Effects of Lead on the Hepatic System 5-255
5.10.1.1 Hepatic Drug Metabolism 5-255
5.10.1.2 Biochemical and Molecular Perturbations
in Lead-Induced Liver Tissue Injury 5-260
5.10.1.3 Effects of Lead Exposure on Hepatic
Cholesterol Metabolism 5-262
5.10.1.4 Effect of Lead on Hepatic Oxidative Stress 5-263
5.10.1.5 Lead-Induced Liver Hyperplasia: Mediators
and Molecular Mechanisms 5-265
5.10.1.6 Effects of Lead on Liver Heme Synthesis 5-269
I-xiii
-------
Table of Contents
(cont'd)
5.10.2 Gastrointestinal System and Lead Absorption 5-272
5.10.2.1 Lead and In vitro Cytotoxicity in Intestinal
Cells 5-273
5.10.2.2 Alterations in Intestinal Physiology and
Ultrastructure 5-273
5.10.2.3 Intestinal Uptake and Transport 5-274
5.10.2.4 Alterations in Gastrointestinal Motility/
Gastrointestinal Transit and Function 5-276
5.10.2.5 Lead, Calcium, and Vitamin D Interactions
in the Intestine 5-276
5.10.2.6 Lead and Intestinal Enzymes 5-278
5.11 LEAD-BINDING PROTEINS 5-279
5.11.1 Lead-Binding Proteins within Intranuclear Inclusion Bodies
in Kidney 5-279
5.11.2 Cytoplasmic Lead-Binding Proteins in Kidney and Brain 5-281
5.11.3 Lead-Binding Proteins in Erythrocytes 5-283
5.11.4 Lead-Binding Proteins in Rat Liver 5-286
5.11.5 Lead-Binding Proteins in Intestine 5-287
5.11.6 Lead-binding Protein in Lung 5-289
5.11.7 Relationship of Lead-Binding Protein to Metallothionein 5-289
5.11.8 Is ALAD an Inducible Enzyme and Is It the Principal Lead-
Binding Protein in the Erythrocyte? 5-290
REFERENCES 5-294
6. EPIDEMIC-LOGIC STUDIES OF HUMAN HEALTH EFFECTS ASSOCIATED
WITH LEAD EXPOSURE 6-1
6.1 INTRODUCTION 6-1
6.1.1 Approach to Identifying Lead Epidemiologic Studies 6-2
6.1.2 Approach to Assessing Epidemiologic Evidence 6-2
6.1.3 Considerations in the Interpretation of Epidemiologic Studies
of Lead Health Effects 6-4
6.1.4 Approach to Presenting Lead Epidemiologic Evidence 6-6
6.2 NEUROTOXIC EFFECTS OF LEAD IN CHILDREN 6-8
6.2.1 Summary of Key Findings on Neurotoxic Effects of Lead
in Children from 1986 Lead AQCD/Addendum and
1990 Supplement 6-8
6.2.2 Introduction to Neurotoxic Effects of Lead in Children 6-10
6.2.3 Neurocognitive Ability 6-11
6.2.3.1 Prospective Longitudinal Cohort Studies of
Neurocognitive Ability 6-11
6.2.3.2 Cross-Sectional Studies of Neurocognitive
Ability 6-32
I-xiv
-------
Table of Contents
(cont'd)
6.2.3.3 Meta-Analyses of Studies of Neurocognitive
Abilities 6-34
6.2.4 Measures of Academic Achievement 6-36
6.2.5 Measures of Specific Cognitive Abilities 6-41
6.2.6 Disturbances in Behavior, Mood, and Social Conduct 6-44
6.2.7 Sensory Acuities 6-50
6.2.8 Neuromotor Function 6-51
6.2.9 Brain Anatomical Development and Activity 6-52
6.2.10 Gene-Environment Interactions in the Expression of Lead-
Associated Neurodevelopmental Deficits 6-54
6.2.11 Reversibility of Lead-Related Neurodevelopmental Deficits
Associated with Prenatal and Postnatal Exposure 6-56
6.2.12 Periods of Enhanced Developmental Susceptibility to Central
Nervous System Effects of Environmental Lead 6-60
6.2.13 Effect of Environmental Lead Exposure on Neurodevelopment
at the Lower Concentration Range 6-64
6.2.14 Selection and Validity of Neuropsychological Outcomes
in Children 6-69
6.2.15 Confounding, Causal Inference, and Effect Modification of
the Neurotoxic Effects of Lead in Children 6-72
6.2.16 Summary of the Epidemiologic Evidence for the Neurotoxic
Effects of Lead in Children 6-74
6.3 NEUROTOXIC EFFECTS OF LEAD IN ADULTS 6-76
6.3.1 Summary of Key Findings on the Neurotoxic Effects of Lead
in Adults from the 1986 Lead AQCD 6-76
6.3.2 Overview of Cognitive and Psychomotor Tests Associated
with Adult Lead Exposure 6-76
6.3.3 Adult Environmental Lead Exposure Effects 6-79
6.3.3.1 Neurobehavioral Effects Associated with
Environmental Lead Exposure 6-79
6.3.3.2 Summary of Adult Environmental Lead Exposure
Effects 6-82
6.3.4 Adult Occupational Lead Exposure Effects 6-83
6.3.4.1 Neurological Symptoms Associated with
Occupational Lead Exposure 6-83
6.3.4.2 Neurobehavioral Effects Associated with
Occupational Lead Exposure 6-83
6.3.4.3 Neurophysiological Function and Occupational
Lead Exposure 6-87
6.3.4.4 Evoked Potentials and Occupational Lead
Exposure 6-88
I-xv
-------
Table of Contents
(cont'd)
6.3.4.5 Postural Stability, Autonomic Testing, and
Electroencephalogram (EEG) and Occupational
Lead Exposure 6-89
6.3.4.6 Occupational Exposure to Organolead and
Inorganic Lead 6-90
6.3.5 Amyotrophic Lateral Sclerosis and Other Neurological
Outcomes Associated with Lead in Adults 6-91
6.3.6 Summary of the Epidemiologic Evidence for the Neurotoxic
Effects of Lead in Adults 6-94
6.4 RENAL EFFECTS OF LEAD 6-95
6.4.1 Summary of Key Findings on the Renal Effects of Lead from
the 1986 Lead AQCD 6-95
6.4.2 Renal Outcome Definitions 6-96
6.4.3 Lead Exposure Measure Definitions 6-97
6.4.4 Lead Nephrotoxicity in Adults 6-98
6.4.4.1 General Population Studies 6-98
6.4.4.2 Occupational Studies 6-109
6.4.4.3 Patient Population Studies 6-111
6.4.4.4 Mortality Studies 6-116
6.4.5 Lead Nephrotoxicity in Children 6-117
6.4.5.1 Studies in Adults Following Childhood Lead
Poisoning 6-117
6.4.5.2 Lead Body Burden in Children with Chronic
Renal Disease 6-118
6.4.5.3 Environmental Studies in Children 6-118
6.4.6 Mechanisms for Lead Nephrotoxicity 6-119
6.4.7 Susceptible Populations for Lead Nephrotoxicity 6-121
6.4.7.1 Chronic Medical Diseases 6-121
6.4.7.2 Age 6-121
6.4.7.3 Genetic Polymorphisms 6-122
6.4.8 Confounding of the Renal Effects of Lead by Other Potential
Risk Factors 6-124
6.4.8.1 Cadmium 6-124
6.4.9 Summary of the Epidemiologic Evidence for the Renal
Effects of Lead 6-127
6.5 CARDIOVASCULAR EFFECTS OF LEAD 6-129
6.5.1 Summary of Key Findings of the Cardiovascular Effects
of Lead from the 1985 Lead AQCD and Addendum, and
1990 Supplement 6-129
6.5.2 Effects of Lead on Blood Pressure and Hypertension 6-131
6.5.2.1 Introduction 6-131
I-xvi
-------
Table of Contents
(cont'd)
6.5.2.2 Blood Pressure and Hypertension Studies Using
Blood Lead as Exposure Index 6-133
6.5.2.3 Blood Pressure and Hypertension Studies Using
Bone Lead as Exposure Index 6-150
6.5.3 Other Cardiovascular Outcomes 6-153
6.5.3.1 Ischemic Heart Disease 6-153
6.5.3.2 Cardiovascular/Circulatory Mortality
(including stroke) 6-155
6.5.3.3 Other Cardiovascular Effects 6-157
6.5.4 Lead and Cardiovascular Function in Children 6-158
6.5.5 Potential Confounding of the Cardiovascular Effects of Lead 6-160
6.5.5.1 Confounding by Copollutants 6-160
6.5.5.2 Confounding by Smoking Status 6-161
6.5.5.3 Confounding by Alcohol Consumption 6-161
6.5.5.4 Confounding by Dietary Calcium Intake 6-162
6.5.5.5 Summary of Potential Confounding of the Lead
Effect on Cardiovascular Health 6-164
6.5.6 Gene-Lead Interactions 6-164
6.5.7 Summary of the Epi demi ol ogi c Evi dence for the
Cardiovascular Effects of Lead 6-167
6.6 REPRODUCTIVE AND DEVELOPMENTAL EFFECTS OF LEAD 6-170
6.6.1 Summary of Key Findings of the Reproductive and
Developmental Effects of Lead from the 1986 Lead AQCD 6-170
6.6.2 Placental Transfer of Lead 6-171
6.6.3 Effects of Lead on Reproductive Function 6-173
6.6.3.1 Effects on Male Reproductive Function 6-173
6.6.3.2 Genotoxicity and Chromosomal Aberrations 6-178
6.6.3.3 Effects on Female Reproductive Function 6-181
6.6.4 Spontaneous Abortion 6-181
6.6.4.1 Spontaneous Abortion and Maternal Exposure
to Lead 6-181
6.6.4.2 Spontaneous Abortion and Paternal Exposure
to Lead 6-184
6.6.5 Fetal Growth 6-185
6.6.6 Preterm Delivery 6-190
6.6.7 Congenital Abnormalities 6-192
6.6.8 Summary of the Epi demi ol ogi c Evi dence for the Reproductive
and Developmental Effects of Lead 6-194
6.7 Genotoxic and Carcinogenic Effects of Lead 6-195
6.7.1 Summary of Key Findings from the 1986 Lead AQCD 6-195
I-xvii
-------
Table of Contents
(cont'd)
6.7.2 Summary of Key Findings by the International Agency for
Research on Cancer and the National Toxicology Program 6-196
6.7.3 Meta-Analyses of Lead and Cancer 6-198
6.7.4 Genotoxicity of Lead 6-200
6.7.5 Review of Specific Studies on the Carcinogenicity of Lead
Since the 1986 Lead AQCD 6-201
6.7.5.1 Introduction 6-201
6.7.5.2 Key Studies of Occupational Populations in
theU.S 6-204
6.7.5.3 Key Studies of the General Population 6-217
6.7.5.4 Other Lead Studies 6-219
6.7.6 Confounding of Occupational Lead Studies Due to Other
Occupational Exposures: Arsenic, Cadmium 6-220
6.7.7 Confounding of Lead Studies: Smoking and Other Factors 6-221
6.7.8 Summary of Epidemiologic Evidence for the Genotoxic and
Carcinogenic Effects of Lead 6-222
6.8 EFFECTS OF LEAD ON THE IMMUNE SYSTEM 6-223
6.8.1 Summary of Key Findings of the Effects of Lead on the
Immune System from the 1986 Lead AQCD 6-223
6.8.2 Host Resistance, Hypersensitivity, and Autoimmunity 6-224
6.8.3 Humoral Immunity 6-225
6.8.4 Cell-Mediated Immunity 6-232
6.8.5 Lymphocyte Function 6-237
6.8.6 Phagocyte (Macrophage and Neutrophil) Function 6-240
6.8.7 Summary of the Epi demi ol ogi c Evi dence for the Effects of
Lead on the Immune System 6-241
6.9 EFFECTS OF LEAD ON OTHER ORGAN SYSTEMS 6-243
6.9.1 Biochemical Effects of Lead 6-243
6.9.1.1 Summary of Key Findings of the Biochemical
Effects of Lead from the 1986 Lead AQCD 6-243
6.9.1.2 Heme Biosynthesis 6-247
6.9.1.3 Effects on Blood Lipids: Cholesterol 6-248
6.9.2 Effects of Lead on the Hematopoietic System 6-250
6.9.2.1 Summary of Key Findings of the Effects of
Lead on the Hematopoietic System from the
1986 Lead AQCD 6-250
6.9.2.2 Blood Hemoglobin Levels 6-250
6.9.2.3 Erythrocyte Volume and Number 6-253
6.9.2.4 Erythropoiesis 6-256
6.9.2.5 Other Effects on Erythrocyte Metabolism
and Physiology 6-260
I-xviii
-------
Table of Contents
(cont'd)
6.9.3 Effects of Lead on the Endocrine System 6-261
6.9.3.1 Summary of Key Findings of the Effects of
Lead on the Endocrine System from the
1986 Lead AQCD 6-261
6.9.3.2 Thyroid Endocrine Function 6-262
6.9.3.3 Reproductive Endocrine Function 6-266
6.9.3.4 Pituitary and Adrenal Endocrine Function 6-270
6.9.3.5 Calcitropic Endocrine Function 6-270
6.9.4 Effects of Lead on the Hepatic System 6-273
6.9.4.1 Summary of Key Findings of the Effects of
Lead on the Hepatic System from the 1986
Lead AQCD 6-273
6.9.4.2 Nonspecific Hepatic Injury 6-274
6.9.4.3 Hepatic Cytochrome P450 Function 6-275
6.9.5 Effects of Lead on the Gastrointestinal System 6-276
6.9.5.1 Summary of Key Findings of the Effects of
Lead on the Gastrointestinal System from the
1986 Lead AQCD 6-276
6.9.5.2 Gastrointestinal Colic 6-276
6.9.6 Effects of Lead on the Respiratory System 6-278
6.9.6.1 Summary of Key Findings of the Effects of
Lead on the Respiratory System from the
1986 Lead AQCD 6-278
6.9.6.2 Pulmonary Function 6-278
6.9.7 Effects of Lead on Bone and Teeth 6-278
6.9.7.1 Summary of Key Findings of the Effects of Lead
on Bone and Teeth from the 1986 Lead AQCD 6-278
6.9.7.2 BoneToxicity 6-279
6.9.7.3 Dental Health 6-280
6.9.8 Effects of Lead on Ocular Health 6-283
6.9.8.1 Summary of Key Findings of the Effects of Lead
on Ocular Health from the 1986 Lead AQCD 6-283
6.9.8.2 Ocular Effects 6-284
6.9.9 Summary of the Epidemiologic Evidence for the Effects of
Lead on Other Organ Systems 6-285
6.10 INTERPRETIVE ASSESSMENT OF THE EVIDENCE IN
EPIDEMIOLOGIC STUDIES OF LEAD HEALTH EFFECTS 6-287
6.10.1 Introduction 6-287
6.10.2 Exposure and Outcome Assessment in Lead Epidemiologic
Studies 6-288
I-xix
-------
Table of Contents
(cont'd)
6.10.2.1 Assessment of Lead Exposure and Body Burdens
Using Biomarkers 6-288
6.10.2.2 Assessment of Health Outcomes 6-292
6.10.3 Concentration-Response Relationship of Lead Health Effects 6-293
6.10.4 Interindividual Variability in Susceptibility to Lead Toxicity 6-298
6.10.4.1 Influence of Genetic Polymorphisms on Risk 6-299
6.10.4.2 Influence of Nutritional Status on Risk 6-300
6.10.4.3 Influence of Health Status on Risk 6-300
6.10.4.4 Influence of Coexposures on Risk 6-301
6.10.4.5 Influence of Timing of Exposure on Risk 6-301
6.10.5 Reversibility of Lead Health Effects 6-304
6.10.5.1 Natural History of Effects 6-304
6.10.5.2 Medical Interventions 6-306
6.10.6 Confounding of Lead Health Effects 6-306
6.10.6.1 Adjustment for Confounding in Epidemiologic
Studies of Lead 6-306
6.10.6.2 Confounding Adjustment on Lead Health Effect
Estimates 6-307
6.10.7 Inferences of Causality 6-310
6.10.8 Effects on the Individual Versus Effects on the Population 6-311
6.10.8.1 Effects of Lead on Intelligence 6-313
6.10.8.2 Cardiovascular Effects of Lead 6-317
6.10.9 Summary of Key Findings and Conclusions Derived from
Lead Epidemiology Studies 6-323
REFERENCES 6-329
ENVIRONMENTAL EFFECTS OF LEAD 8-1
8.1 TERRESTRIAL ECOSYSTEMS 8-1
8.1.1 Methodologies Used in Terrestrial Ecosystem Research 8-2
8.1.2 Distribution of Atmospherically Delivered Lead in
Terrestrial Ecosystems 8-4
8.1.3 Species Response/Mode of Action 8-8
8.1.4 Exposure/Response of Terrestrial Species 8-10
8.1.5 Effects of Lead on Natural Terrestrial Ecosystems 8-12
8.2 AQUATIC ECOSYSTEMS 8-15
8.2.1 Methodologies Used in Aquatic Ecosystem Research 8-16
8.2.2 Distribution of Lead in Aquatic Ecosystems 8-18
8.2.3 Species Response/Mode of Action 8-21
8.2.4 Exposure/Response of Aquatic Species 8-25
8.2.5 Effects of Lead on Natural Aquatic Ecosystems 8-27
I-xx
-------
Table of Contents
(cont'd)
8.3 CRITICAL LOADS FOR LEAD IN TERRESTRIAL AND
AQUATIC ECOSYSTEMS 8-28
8.3.1 Definitions 8-29
8.3.2 Historical Perspective 8-29
8.3.3 Application of Critical Loads to Terrestrial and
Aquatic Ecosystems 8-31
8.3.4 Calculation of Critical Loads 8-31
8.3.4.1 Critical Limits 8-33
8.3.4.2 Models 8-33
8.3.5 Critical Loads in Terrestrial Ecosystems 8-37
8.3.6 Critical Loads in Aquatic Ecosystems 8-39
8.3.7 Limitations and Uncertainties 8-40
8.3.8 Conclusions 8-41
REFERENCES 8-42
I-xxi
-------
List of Tables
Number Page
1-1 Key Milestones and Projected Schedule for Development of Revised Lead
Air Quality Criteria Document (Lead AQCD) 1-8
2-1 Lead Alloys and Their Industrial Applications 2-3
2-2 Physical Properties of Elemental Lead 2-4
2-3 Lead Salts: Names, Formulae, Physical Characteristics, and Uses 2-6
2-4 Lead Oxides: Names, Formulae, Physical Characteristics, and Uses 2-7
2-5 Lead Compounds Observed in the Environment 2-8
2-6 Annual, Worldwide Emissions of Lead from Natural Sources 2-13
2-7 Naturally Occurring Lead Concentrations in Maj or Rock Types 2-15
2-8 The Mass-Median Aerodynamic Diameters for Particles During Various
Processes at Primary Lead Smelters 2-22
2-9 The Emissions of Lead from Non-Lead Metallurgical Processes 2-24
2-10 The Range of Lead Concentrations in Coal Lithotypes 2-28
2-11 Emission Factors of Lead for Coal Combustion in Three Different Furnaces 2-30
2-12 The Emissions of Lead from Industrial, Commercial, and Residential
Coal Combustion 2-31
2-13 Emission Factors for Oil-Fired Utility Boilers 2-32
2-14 The Concentrations of Lead in Biomass, Char, and Ash Samples from
Spruce, Beech, Oak, Pine, and of Ailanthus Trees 2-34
2-15 Emission Factors of Lead From Processes Used in Cement Manufacture by
Control Device 2-41
2-16 Rate of Lead Compound Emissions from Glass-Melting Furnaces 2-42
2-17 Emission Factors of Lead for Automobiles with Model Years Between
1971 and 1996 2-45
I-xxii
-------
List of Tables
(cont'd)
Number Page
2-18 Emission Factors of Lead for Automobiles with Model Years Between
1971 and 1996 2-46
2-19 The Concentration of Lead in Particulate Matter Emissions and Emissions
Factors for Lead from Buses and Trucks Fueled with Diesel No. 2 and
Jet A Fuel 2-48
2-20 Dry Deposition Velocities for Lead Particles 2-56
2-21 Concentrations of Lead in Rainwater in the United States 2-59
2-22 The Percentage of Lead in Resuspended Paniculate Matter 2-63
2-23 The Concentrations of Lead in Runoff From Building Surfaces 2-67
2-24 Soil/Water Partition Coefficients for Several Different Soils and Conditions 2-71
3-1 Examples of Airborne Concentrations of Lead at Selected Sites Around the
World During 1985 to 2005 3-10
3-2 Airborne Concentrations Surrounding Residential Lead-Based
Paint Abatement 3-14
3-3 Concentration of Soil Lead in Urban Areas 3-18
3-4 Concentrations of Soil Lead with Distance from Lead Smelters 3-20
3-5 Soil Lead Concentration Profile Measured Near a Lead Smelter in
Northern France 3-21
3-6 Soil Concentrations Measured Near Mining Sites 3-23
3-7 Concentrations of Lead in Soils Grouped by Soil Grain Size 3-24
3-8 Examples of Lead Concentrations in Indoor Dust 3-28
3-9 The Concentration of Lead in Road Dust 3-31
3-10 Examples of Tap Water Concentrations of Lead 3-37
3-11 90th Percentile Tap Water Pb Concentrations for a Selection of U.S. Cities
Exceeding the EPA Pb Action Level 3-39
I-xxiii
-------
List of Tables
(cont'd)
Number Page
3-12 Examples of Lead Concentrations in Food Products 3-41
4-1 Blood Lead Concentrations in United States by Age, NHANES IV
(1999-2002) 4-21
4-2 Blood Lead Concentrations in United States by Gender, NHANES IV
(1999-2002) 4-21
4-3 Blood Lead Concentrations by Occupation, NHANES III (1988-1994) 4-23
4-4 Urine Lead Concentrations in U.S. by Age, NHANES IV (1999-2002) 4-56
4-5 General Linear Model Relating Blood Lead Concentration in Children and
Environmental Lead Levels—Bunker Hill Superfund Site 4-69
4-6 Structural Equation Model (1) Relating Blood Lead Concentration in
Children and Environmental Lead Levels—Bunker Hill Superfund Site 4-71
4-7 Structural Equation Model (2) Relating Blood Lead Concentration in
Children and Environmental Lead Levels—Bunker Hill Superfund Site 4-72
4-8 General Linear Model Relating Blood Lead Concentration in Children and
Environmental Lead Levels—Coeur d'Alene Basin 4-73
4-9 Multivariate Regression Model Relating Blood Lead Concentration in
Children and Environmental Lead Levels -Multi-Study Pooled Analysis 4-74
4-10 Children's Predicted Blood Lead Levels for Floor Dust Lead Loading
(|ig/ft2) and Exterior Lead Exposures (ppm) 4-76
4-11 Likelihood of a Child's Blood Lead > 10 |ig/dL for Floor Dust Lead
Loadings and Exterior Exposure Levels (ppm) 4-77
4-12 Meta-Analysis of the Relationship Between Log-Transformed Blood
Lead and Various Environmental Lead Sources 4-79
4-13 Structural Equation Models Relating Blood Lead Concentration in
Children and Pre-abatement Environmental Lead Levels—Lead in
Urban Soil Abatement Demonstration Project 4-84
4-14 Basis for Absorption Fraction of Inhaled Lead in the IEUBK Model for
Lead in Children 4-95
I-xxiv
-------
List of Tables
(cont'd)
Number Page
4-15 Comparison of Observed and Predicted Geometric Mean Blood Lead
for Three Community Blood Lead Studies 4-98
4-16 Comparison of Observed and Predicted Probability of Exceeding a
Blood Lead Concentration of 10 |ig/dL Lead for Three Community Blood
Lead Studies 4-98
4-17 Summary of Models of Human Exposure that Predict Tissue Distribution
of Lead 4-115
4-18 Inputs and Results of Simulations Comparing the U.S. EPA Adult Lead
Methodology (ALM) With Multicompartmental Models 4-122
5-3.1 Chronic Lead Exposure and LTP 5-29
5-3.2 Mechanisms of Pb-Induced Impairment of Retinal Function 5-36
5-4.1 Selected Studies Showing the Effects of Lead on Reproductive Function
in Males 5-86
5-4.2 Selected Studies Showing the Effects of Lead on Reproductive Function
in Females 5-95
5-4.3 Selected Studies Showing the Effects of Lead on Mammalian Embryogenesis
and Development 5-100
5-9.1 Recent Studies Reporting Lead-Induced Increase in IgE 5-223
5-9.2 Studies Reporting Lead-Induced Shifts in Thl vs. Th2 Cytokines 5-233
5-9.3 Suggested Mechanisms of Lead-Induced Immunotoxicity 5-248
5-9.4 Immunomodulation Associated with Low Blood Lead Levels in Animals 5-250
5-9.5 Comparisons of Age-Based Sensitivity to Lead-Induced Immunotoxicity 5-251
6-2.1 Covariate-Adjusted Changes in IQ per 1 |ig/dL Increase in Blood
Lead Concentration 6-26
6-2.2 Summary of Studies with Quantitative Relationships of IQ and Blood Lead
for Blood Lead Levels Less than 10 |ig/dL 6-65
I-xxv
-------
List of Tables
(cont'd)
Number Page
6-3.1 Key Neurobehaviorial Effects Studies of Occupational Lead Exposures 6-84
6-4.1 Summary of Key Studies on the Renal Effects of Environmental
Lead Exposure 6-99
6-5.1 Summary of Studies with Quantitative Relationships of Systolic Blood
Pressure and Blood Lead 6-134
6-7.1 Results of Meta-Analyses Addressing the Association Between Lead
Exposure and Cancer 6-199
6-7.2 Results of Epidemiologic Studies on the Genotoxicity of Lead Exposure 6-201
6-7.3 Epidemiologic Studies of Lead Exposure and Cancer in Specific Populations,
by Geographic Region and Study Design 6-202
6-7.4 Summary of Key Studies on Lead Exposure and Cancer Occurrence in
Human Populations 6-205
6-8.1 Summary of Results of Selected Studies of Associations Between Lead
Exposure and Serum Immunoglobulin Levels 6-226
6-8.2 Summary of Results of Selected Studies of Associations Between Lead
Exposure and Serum Lymphocyte Abundances 6-234
6-9.1 Blood Lead-Response Relationships for Heme Synthesis Biomarkers in
Adults and Children 6-245
6-9.2 Summary of Results of Selected Studies of Associations Between Lead
Exposure and Blood Hemoglobin Levels 6-251
6-9.3 Summary of Results of Selected Studies of Associations Between Lead
Exposure and Serum Erythropoietin 6-257
6-9.4 Summary of Results of Selected Studies of Associations Between Lead
Exposure and Thyroid Hormone Levels 6-264
6-9.5 Summary of Results of Selected Studies of Associations Between Lead
Exposure and Male Sex Hormone Levels in Adults 6-267
6-9.6 Summary of Results of Selected Studies of Associations Between Lead
Exposure and Calcitropic Hormones 6-271
I-xxvi
-------
List of Tables
(cont'd)
Number Page
6-10.1 Summary of Studies with Quantitative Relationships for IQ and Blood Lead 6-314
8-2.1 Summary of Lead Ambient Water Quality Criteria for Freshwater Organisms
at Different Hardness Levels 8-17
8-2.2 Summary of Sediment Quality Benchmarks and Guidelines for Lead 8-18
8-2.3 Summary of Lead Concentrations in United States Surface Water, Sediment,
and Fish Tissue 8-20
I-xxvii
-------
List of Figures
Number Page
2-1 Multiple possible molecular targets for interference by Pb2+ ion at
nerve synapses 2-12
2-2 Lead emissions sources and rates for the U.S. (1990) 2-17
2-3 Lead emissions sources and rates for the U.S. (2002) 2-18
2-4 Percentage volatility of Pb during combustion of plastics at four temperatures 2-37
2-5 The deposition velocity plotted against the geometric mean Stokes diameter
for particles with a density of 6 g/cm"3 (i.e., lead) 2-57
2-6 The modeled soil concentrations of lead in the South Coast Air Basin of
California based on four resuspension rates 2-64
2-7 The modeled and measured airborne concentrations of lead in the South
Coast Air Basin of California based on two resuspension rates 2-65
2-8 Annual lead production and use in the U.S. (1968 and 2003) 2-80
2-9 Trends in U.S. air lead emissions, 1982-2002 2-81
2-10 Transport pathways for lead in the environment 2-82
3-la Lead TSP monitoring sites from 2000-2006 3-3
3-lb Airborne concentrations of lead, averaged across the U.S., shown in relation
to the current NAAQS, for the years 1983 through 2002 3-3
3-2a Locations monitored by the Speciation Trends Network (STN) 3-4
3-2b The average maximum quarterly mean Pb concentrations observed in PM2.5
by the STN 3-4
3-3a The IMPROVE network of PM2.5 monitors 3-5
3-3b IMPROVE sites with Pb PM2.5 concentrations at or above 0.0008 |lg/m3
between 2000 and 2005 3-6
3-4a The National Air Toxics Trends Stations (NATTS) network 3-7
I-xxviii
-------
List of Figures
(cont'd)
Number Page
3-4b Average maximum quarterly mean Pb concentrations measured at
NATTS network sites (2002-2005) 3-8
3-5 The changes in lead concentration with depth in two peat cores 3-25
3-6 The change in lead concentration versus stagnation time 3-35
3-7 The change in lead concentration versus stagnation time 3-36
4-1 Relative bioavailability (RBA) is the bioavailability of the lead in the test
material compared to that of lead acetate (test material/lead acetate) 4-9
4-2 Estimated relative bioavailability (RBA, compared to lead acetate) of ingested
lead in mineral groups, based on results from juvenile swine assays 4-10
4-3 Blood lead concentrations in U.S. children, 1-5 years of age 4-22
4-4 Simulation of relationship between blood lead concentration and body burden
in adults 4-25
4-5 Simulation of relationship between blood lead concentration and body burden
in children 4-27
4-6 Simulation of temporal relationships between lead exposure and blood lead
concentration in children 4-30
4-7 Simulation of relationships between lead intake and blood lead concentration
in adults and children 4-31
4-8 Cortical lead to blood leads ratios for occupationally-exposed subjects
(both active and retired) and referents 4-44
4-9 Tibia leads to blood lead ratios for environmentally-exposed pregnancy-related
subj ects, middle-aged to elderly subj ects, and younger subj ects 4-45
4-10 Simulation of relationship between urinary lead excretion and body
burden in adults 4-58
4-11 Simulation of relationship between lead intake and urinary lead excretion in
adults and children 4-60
I-xxix
-------
List of Figures
(cont'd)
Number Page
4-12 Structural equation model for relationships between dust and soil lead and
blood lead concentration in children, based on data collected at the Bunker
Hill Superfund Site (1988-1999) 4-70
4-13 Structural equation model for relationships between dust and soil lead and
blood lead concentration in children 4-78
4-14 Structural equation model for relationships between dust and soil lead and
blood lead concentration in children, based on data collected in the Rochester
(NY) Lead in Dust Study 4-80
4-15 Structural equation model for relationships between dust and soil lead
and blood lead concentration in children, based on data collected in the
Cincinnati (OH) Prospective Child Study 4-81
4-16 Structural equation model for relationships between dust and soil lead and
blood lead concentration in children, based on pre-abatement cross-sectional
data collected in the Urban Soil Lead Abatement Demonstration Project 4-83
4-17 Lead biokinetics based on Rabinowitz et al. (1976) 4-85
4-18 Lead biokinectics based on Marcus (1985a) 4-86
4-19 Lead biokinetics based on Marcus (1985b) 4-87
4-20 Lead biokinetics based on Marcus (1985c) 4-88
4-21 Lead biokinetics based on Bert etal. (1989) 4-89
4-22 Structure of the integrated exposure uptake biokinetics model for lead
in children 4-91
4-23 Age-dependency of absorption fraction for ingested lead in the IEUBK
model for lead in children 4-94
4-24 Structure of the Leggett Lead Biokinetic Model 4-101
4-25 Age-dependency of absorption fraction for ingested lead in the Leggett and
O'Flaherty models 4-104
4-26 Structure of the O'Flaherty Lead Exposure Biokinetics Model 4-106
I-xxx
-------
List of Figures
(cont'd)
Number Page
4-27 Bone growth as simulated by the O'Flaherty Lead Exposure
Biokinetics Model 4-108
4-28 Structure of the All Ages Lead Model 4-112
4-29 Model comparison of predicted lead uptake-blood lead concentration
relationship in children 4-117
4-30 Model comparison of predicted lead uptake-blood lead concentration
relationships in adults 4-119
4-31 Model comparison of predicted of lead uptake-bone and soft tissue lead
burden relationship in adults 4-120
4-32 Comparison of model predictions for childhood lead exposure 4-121
4-33 Comparison of model predictions for adult lead exposure 4-121
5-2.1 Schematic presentation of heme synthesis pathway 5-9
5-3.1 Time course and magnitude of response of extracellular GLU concentration
as a result of chronic lead exposure 5-22
5-3.2 Simplified diagram showing the actions ofPb at a synapse 5-25
5-3.3 PKC activity as a function of Ca2+ andPb2+ concentrations 5-26
5-3.4 Difference score measure of population spike amplitude 5-30
5-3.5 Dose-effect function for lead-induced changes in fixed-interval performance 5-42
5-4.1 Data from male and female experimental animals suggests that Pb has
multiple targets in the hypothalmic-pituitary-gonadal axis 5-84
5-5.1 This illustration depicts some of the potential mechanisms by which
oxidative stress may participate in the pathogenesis of Pb-induced
HTN and cardiovascular complications 5-119
5-7.1 Changes in GFR of experimental high-dose lead and control animals with
duration of exposure to lead 5-162
I-xxxi
-------
List of Figures
(cont'd)
Number Page
5-7.2 Correlation between GFR and blood lead during the first 6 months of
high-dose lead exposure 5-162
5-7.3 GFR in high-lead and low-lead experimental discontinuous (ED6) and
DMSA-treated rats (DMSA) as compared to controls (C12) 5-164
5-7.4 Changes in GFR in experimental and control rats, at various time periods 5-164
5-7.5 Urinary NAG concentration in experimental and control rats at various
time periods 5-165
5-7.6 Kidney, liver, brain, and bone Pb levels in 56 Pb-exposed rats 5-166
5-7.7 Percentage of moderate and severe hypertrophy and vacuolization lesions
in small and medium sized arteries in the kidney of lead-exposed rats 5-168
5-7.8 Percentage of moderate and severe muscular hypertrophy lesions in
arterioles of the kidney in lead-exposed rats 5-168
5-9.1 Windows during prenatal development (days postconception for rat)
or embryonic development (days postincubation initiation for chicken)
during which sensitivity of DTH to lead emerges 5-228
5-9.2 This figure shows the fundamental alterations to the immune system and to
immunological response and recognition induced by exposure to lead 5-253
5-10.1 Flow diagram indicating the Pb effects on the cholesterol synthesis pathway 5-264
5-10.2 Schematic diagram illustrating the mode of Pb-induced lipid peroxidation 5-264
5-10.3 Hypothesis of chemical-induced liver injury generated primarily on the
basis of different types of inhibitors 5-269
5-11.1 Sephadex G-75 gel filtration of RBC hemolysate from lead-exposed
individual 5-284
5-11.2 SDS-polyacrylamide gel electrophoresis of RBC hemolysates from normal
control (A) and lead-exposed individuals (B), and of low-mol-wt. lead-
binding protein (C) stained with coomassie blue 5-285
5-11.3 Chromatographic profiles of protein, ALAD activity and Pb in human
erythrocytes incubated with 5% glucose solution containing Pb acetate 5-287
I-xxxii
-------
List of Figures
(cont'd)
Number Page
5-11.4 Chromatic profiles of protein, ALAD activity, Pb, and Se in the erythrocytes
of lead exposed workers 5-288
6-2.1 Unadjusted and adjusted relationships between average lifetime blood lead
concentrations and Wechsler Scale performance IQ 6-16
6-2.2 Linear models for the 7 cohort studies in the pooled analysis, adjusted for
maternal IQ, HOME score, maternal education, and birth weight 6-31
6-2.3 Golgi-stained section of human cerebral cortex taken from equivalent areas
of the anterior portion of the middle frontal gyrus at different ages 6-61
6-2.4 Full scale IQ test scores by previous or concurrent blood lead concentration 6-63
6-2.5 Restricted cubic splines and log-linear model for concurrent blood
lead concentration 6-67
6-2.6 Log-linear model (95% CI shaded) for concurrent blood lead concentration
adjusted for HOME score, maternal education, maternal IQ, and birth weight 6-68
6-2.7 Log-linear model for concurrent blood lead concentration along with linear
models for concurrent blood lead levels among children with peak blood
lead levels above and below 10 |ig/dL 6-68
6-4.1 Creatinine Clearance Versus Blood Lead Slope at a Blood Lead of 5 |ig/dL 6-107
6-4.2 Effect on associations between lead dose and renal function depending on
whether effect modification (age in this example) is assessed 6-111
6-4.3 Estimated mean (+2 SE) glomerular filtration rate according to time in
the chelation group (n = 31) and the control group (n = 30) during the
observation and intervention periods 6-115
6-5.1 Change in the systolic pressure (effect estimate in mm Hg) associated
with a doubling of the blood lead concentration 6-146
6-5.2 Change in the diastolic pressure (effect estimate in mm Hg) associated
with a doubling of the blood lead concentration 6-147
6-5.3 Effect of doubling mean blood lead on estimate of blood pressure change
with95%CIs 6-149
I-xxxiii
-------
List of Figures
(cont'd)
Number Page
6-10.4 Effect of blood lead on fraction of population with IQ level <70 or
<50 points 6-318
6-10.5 Distribution of systolic blood pressure in women and men aged 35 to
64 years from the Framingham Heart Study (Kannel, 2000a) 6-320
6-10.6 Relationship of cardiovascular events (coronary disease, stroke, peripheral
artery disease, cardiac failure) to systolic blood pressure in women and men
aged 35 to 64 years from the Framingham Heart Study (Kannel, 2000a) 6-321
6-10.7 Effect of blood lead on expected annual risk of cardiovascular events per
1,000 person-years 6-322
6-10.8 Relationship of blood lead levels to personal air lead concentrations in five
occupational cohorts, including office workers, cab drivers, and plant
workers (Azar et al., 1975) 6-322
8-3.1 The predicted development of metal concentrations in ecosystems for
four cases of exceedance or non-exceedance of critical limits and critical
loads, respectively 8-32
I-xxxv
-------
Authors, Contributors, and Reviewers
CHAPTER 1 - INTRODUCTION
Principal Author
Dr. Lester D. Grant—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
CHAPTER 2 - CHEMISTRY, SOURCES, TRANSPORT OF LEAD
Chapter Manager/Editor
Dr. Brooke L. Hemming—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Principal Authors
Dr. Brooke L. Hemming—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (Section 2.1)
Ms. Allison Harris—Department of Civil and Environmental Engineering, Carnegie-Mellon
University, Pittsburgh, PA 15213 (Sections 2.2 - 2.4)
Professor Cliff Davidson—Department of Civil and Environmental Engineering,
Carnegie-Mellon University, Pittsburgh, PA 15213 (Sections 2.2 - 2.4)
Contributors and Reviewers
Professor Brian Gulson—Graduate School of the Environment, Macquarie University
Sydney, NSW 2109, Australia
Professor John W. Winchester (Emeritus)—Dept. of Oceanography, Florida State University,
Tallahassee, FL 32306-4320
Ms. Rosemary Mattuck—Gradient Corporation, 20 University Road, Cambridge, MA 02138
Professor Russell Flegal— Department of Environmental Toxicology, University of California,
Santa Cruz, 1156 High Street, Santa Cruz, CA 95064
I-xxxvi
-------
Authors, Contributors, and Reviewers
(cont'd)
Contributors and Reviewers
(cont'd)
Dr. Mary Ross—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Ms. Beth Hassett-Sipple—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. Zachary Pekar—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Ms. Anne Pope—Office of Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711
Mr. Douglas Solomon—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. Joseph Touma—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. John Vandenberg—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
CHAPTER 3 - ROUTES OF HUMAN EXPOSURE AND OBSERVED
ENVIRONMENTAL CONCENTRATIONS
Chapter Manager/Editor
Dr. Brooke L. Hemming—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Principal Authors
Ms. Allison Harris—Department of Civil and Environmental Engineering, Carnegie-Mellon
University, Pittsburgh, PA 15213 (Sections 3.1-3.5)
Professor Cliff Davidson—Department of Civil and Environmental Engineering, Carnegie-
Mellon University, Pittsburgh, PA 15213 (Sections 3.1-3.5)
I-xxxvii
-------
Authors, Contributors, and Reviewers
(cont'd)
Contributors and Reviewers
(cont'd)
Mr. Kevin Cavender—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Professor Brian Gulson—Graduate School of the Environment, Macquarie University
Sydney, NSW 2109, Australia
Professor John W. Winchester (Emeritus)—Department of Oceanography, Florida State
University, Tallahassee, FL 32306-4320
Ms. Rosemary Mattuck—Gradient Corporation, 20 University Road, Cambridge, MA 02138
Professor Russell Flegal— Department of Environmental Toxicology, University of California,
1156 High Street, Santa Cruz, CA 95064
Dr. Sharon Harper—National Exposure Research Laboratory (D205-05), U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. Mary Ross— National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Mr. Tom Helms—Office of Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711
Mr. James Hemby—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Ms. Beth Hassett-Sipple—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Mr. Phil Lorang—Office of Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711
Mr. David Mintz—Office of Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711
Dr. Zachary Pekar—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
I-xxxviii
-------
Authors, Contributors, and Reviewers
(cont'd)
Contributors and Reviewers
(cont'd)
Dr. Michael Rizzo—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Mr. Mark Schmidt—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. John Vandenberg—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
CHAPTER 4 - LEAD TOXICOKINETICS AND MEASUREMENT
MODELING OF HUMAN EXPOSURE IMPACTS ON INTERNAL
TISSUE DISTRIBUTION OF LEAD
Chapter Managers/Editors
Dr. James Brown—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Robert Elias—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (Retired)
Principal Authors
Dr. Gary Diamond—Syracuse Research Corporation, 8191 Cedar Street, Akron, NY 14001
(Section 4.2-4.4)
Dr. Brian Gulson—Graduate School of the Environment, Macquarie University
Sydney, NSW 2109, Australia (Section 4.3)
Contributors and Reviewers
Dr. Lester D. Grant—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Ms. Rosemary Mattuck—Gradient Corporation, 20 University Road, Cambridge, MA 02138
I-xxxix
-------
Authors, Contributors, and Reviewers
(cont'd)
Contributors and Reviewers
(cont'd)
Professor Russell Flegal—Department of Environmental Toxicology, University of California,
1156 High Street, Santa Cruz, CA 95064
Dr. Zachary Pekar—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Ms. Beth Hassett-Sipple—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. John Vandenberg—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
CHAPTER 5 - TOXICOLOGICAL EFFECTS OF LEAD IN LABORATORY ANIMALS,
HUMANS, AND IN VITRO TEST SYSTEMS
Chapter Managers/Editors
Dr. Anuradha Mudipalli—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Srikanth Nadadur—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Lori White—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Principal Authors
Dr. Anuradha Mudipalli—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (Sections 5-2, 5-10)
Dr. Stephen Lasley—Dept. of Biomedical and Therapeutic Sciences, Univ. of Illinois College of
Medicine, PO Box 1649, Peoria, IL 61656 (Section 5.3.1)
Dr. Lori White—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (Section 5.3.1)
I-xl
-------
Authors, Contributors, and Reviewers
(cont'd)
Principal Authors
(cont'd)
Dr. John Rosen—Division of Environmental Sciences, The Children's Hospital at Montefiore,
The Albert Einstein College of Medicine, 111 E. 210th St. Room 401, Bronx, NY 10467
(Section 5.3.2)
Dr. Gary Diamond— Syracuse Research Corporation, 8191 Cedar Street, Akron, NY 14001
(Section 5.4)
Dr. N.D. Vaziri—Division of Nephrology and Hypertension, University of California - Irvine
Medical Center, 101, The City Drive, Bldg 53, Room #125. Orange, CA 92868 (Section 5.5)
Dr. John Pierce Wise, Sr.—Maine Center for Toxicology and Environmental Health,
Department of Applied Medical Sciences, 96 Falmouth Street, PO Box 9300, Portland, ME
04104-9300 (Section 5.6)
Dr. Harvey C. Gonick—David Geffen School of Medicine, University of California at
Los Angeles, CA (201 Tavistock Ave, Los Angeles, CA 90049) (Sections 5.7, 5.11)
Dr. Gene E. Watson—University of Rochester Medical Center, Box 705, Rochester, NY 14642
(Section 5.8)
Dr. Rodney Dietert—Institute for Comparative and Environmental Toxicology, College of
Veterinary Medicine, Cornell University, Ithaca, NY 14853 (Section 5.9)
Contributors and Reviewers
Dr. Lester D. Grant—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Paul Reinhart—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. David A. Lawrence—Dept of Environmental and Clinical Immunology, Empire State Plaza
P.O. Box 509, Albany, NY 12201
Dr. Michael J. McCabe, Jr.—Dept of Environmental Medicine, University of Rochester,
575 Elmwood Avenue, Rochester, NY 14642
Dr. Theodore I. Lidsky—New York State Institute for Basic Research, 1050 Forest RD,
Staten Island, NY 10314
I-xli
-------
Authors, Contributors, and Reviewers
(cont'd)
Contributors and Reviewers
(cont'd)
Dr. Mark H. Follansbee—Syracuse Research Corporation, 8191 Cedar St. Akron, NY 14001
Dr. William K. Boyes—National Health and Environmental Effects Research Laboratory,
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Philip J. Bushnell—National Health and Environmental Effects Research Laboratory,
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Ms. Beth Hassett-Sipple—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. Zachary Pekar—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. John Vandenberg—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
CHAPTER 6 - EPIDEMIOLOGICAL STUDIES OF HUMAN HEALTH EFFECTS
ASSOCIATED WITH LEAD EXPOSURE
Chapter Managers/Editors
Dr. Jee Young Kim—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Dennis Kotchmar—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. David Svendsgaard—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Principal Authors
Dr. David Bellinger—Children's Hospital, Farley Basement, Box 127, 300 Longwood Avenue,
Boston, MA 02115 (Section 6.10)
I-xlii
-------
Authors, Contributors, and Reviewers
(cont'd)
Principal Authors
(cont'd)
Dr. Margit Bleecker—Center for Occupational and Environmental Neurology, 3901
Greenspring Ave., Suite 101, Baltimore, MD 21211 (Section 6.3)
Dr. Gary Diamond— Syracuse Research Corporation, 8191 Cedar Street.
Akron, NY 14001 (Section 6.8, 6.9)
Dr. Kim Dietrich—University of Cincinnati College of Medicine, 3223 Eden Avenue,
Kettering Laboratory, Room G31, Cincinnati, OH 45267 (Section 6.2)
Dr. Pam Factor-Litvak—Columbia University Mailman School of Public Health, 722 West
168tt Street, Room 1614, New York, NY 10032 (Section 6.6)
Dr. Vic Hasselblad—Duke University Medical Center, Durham, NC 27713 (Section 6.10)
Dr. Steve Rothenberg—CINVESTAV-IPN, Merida, Yucatan, Mexico & National Institute of
Public Health, Cuernavaca, Morelos, Mexico (Section 6.5)
Dr. Neal Simonsen—Louisiana State University Health Sciences Center, School of Public Health
& Stanley S Scott Cancer Center, 1600 Canal Street, Suite 800, New Orleans, LA 70112
(Section 6.7)
Dr. Kyle Steenland—Rollins School of Public Health, Emory University, 1518 Clifton Road,
Room 268, Atlanta, GA 30322 (Section 6.7)
Dr. Virginia Weaver—Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe
Street, Room 7041, Baltimore, MD 21205 (Section 6.4)
Contributors and Reviewers
Dr. J. Michael Davis—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Lester D. Grant—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Kaz Ito—School of Medicine, New York University, Tuxedo, NY 10917
Dr. Kathryn Mahaffey—Office of Prevention, Pesticides and Toxic Substances,
U.S. Environmental Protection Agency, Washington, DC 20460
I-xliii
-------
Authors, Contributors, and Reviewers
(cont'd)
Contributors and Reviewers
(cont'd)
Dr. Karen Martin—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. Zachary Pekar—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Ms. Beth Hassett-Sipple—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. John Vandenberg—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
CHAPTER 7- INTEGRATIVE SYNTHESIS: INTEGRATIVE SYNTHESIS:
LEAD EXPOSURE AND HEALTH EFFECTS
Chapter Manager/Editor
Dr. Lester D. Grant—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Principal Authors
Dr. Lester D. Grant—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Lori White—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Contributors and Reviewers
Dr. James Brown—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Brooke L. Hemming—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
I-xliv
-------
Authors, Contributors, and Reviewers
(cont'd)
Contributors and Reviewers
(cont'd)
Dr. Jee Young Kim—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Dennis J. Kotchmar—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Anuradha Mudipalli—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Srikanth S. Nadadur—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Mary Ross— National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. David Svendsgaard—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. John Vandenberg—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
CHAPTER 8 - ENVIRONMENTAL EFFECTS OF LEAD
Chapter Manager/Editor
Dr. Timothy Lewis—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Principle Authors
Dr. Ruth Hull—Cantox Environmental Inc., 1900 Minnesota Court, Suite 130, Mississauga,
Ontario, L5N 3C9 Canada (Section 8.1)
Dr. James Kaste—Department of Earth Sciences, Dartmouth College, 352 Main Street, Hanover,
NH03755 (Section 8.1)
I-xlv
-------
Authors, Contributors, and Reviewers
(cont'd)
Principle Authors
(cont'd)
Dr. John Drexler—Department of Geological Sciences, University of Colorado, 1216 Gillespie
Drive, Boulder, CO 80305 (Section 8.1)
Dr. Chris Johnson—Department of Civil and Environmental Engineering, Syracuse University,
365 Link Hall, Syracuse, NY 13244 (Section 8.1)
Dr. William Stubblefield—Parametrix, Inc. 33972 Texas St. SW, Albany, OR 97321
(Section 8.2)
Dr. Dwayne Moore—Cantox Environmental, Inc., 1550ALaperriere Avenue, Suite 103,
Ottawa, Ontario, K1Z 7T2 Canada (Section 8.2)
Dr. David Mayfield—Parametrix, Inc., 411 108th Ave NE, Suite 1800, Bellevue, WA 98004
(Section 8.2)
Dr. Barbara Southworth—Menzie-Cura & Associates, Inc., 8 Winchester Place, Suite 202,
Winchester, MA 01890 (Section 8.3)
Dr. Katherine Von Stackleberg—Menzie-Cura & Associates, Inc., 8 Winchester Place, Suite
202, Winchester, MA 01890 (Section 8.3)
Contributors and Reviewers
Dr. Jerome Nriagu—Department of Environmental Health Sciences, 109 South Observatory,
University of Michigan, Ann Arbor, MI 48109
Dr. Judith Weis—Department of Biology, Rutgers University, Newark, NJ 07102
Dr. Sharon Harper—National Exposure Research Laboratory (D205-05), U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. Karen Bradham—National Research Exposure Laboratory (D205-05), U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
Dr. Ginger Tennant—Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711
I-xlvi
-------
Authors, Contributors, and Reviewers
(cont'd)
Ms. Gail Lacey—Office of Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711
Dr. John Vandenberg—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
[Note: Any inadvertently omitted names of authors/reviewers will be inserted in the final version
of this LeadAQCD, as will more complete addresses for all authors/reviewers.]
I-xlvii
-------
U.S. Environmental Protection Agency Project Team
for Development of Air Quality Criteria for Lead
Executive Direction
Dr. Lester D. Grant (Director)—National Center for Environmental Assessment-RTF Division,
(B243-01), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Scientific Staff
Dr. Lori White (Lead Team Leader)—National Center for Environmental Assessment
(B243-01), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. James S. Brown—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Robert Elias—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (Retired)
Dr. Brooke Hemming—National Center for Environmental Assessment (B243-01), U.S.
Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Jee Young Kim—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Dennis Kotchmar—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Timothy Lewis—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Anuradha Muldipalli—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Srikanth Nadadur—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Paul Reinhart—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. Mary Ross— National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Dr. David Svendsgaard—National Center for Environmental Assessment (B243-01),
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
I-xlviii
-------
U.S. Environmental Protection Agency Project Team
for Development of Air Quality Criteria for Lead
(cont'd)
Technical Support Staff
Mr. Douglas B. Fennell—Technical Information Specialist, National Center for Environmental
Assessment (B243-01), U.S. Environmental Protection Agency, Research Triangle Park, NC
27711
Ms. Emily R. Lee—Management Analyst, National Center for Environmental Assessment
(B243-01), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Ms. Diane H. Ray—Program Specialist, National Center for Environmental Assessment
(B243-01), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711
Ms. Donna Wicker—Administrative Officer, National Center for Environmental Assessment
(B243-01), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (Retired)
Mr. Richard Wilson—Clerk, National Center for Environmental Assessment (B243-01), U.S.
Environmental Protection Agency, Research Triangle Park, NC 27711
Document Production Staff
Ms. Carolyn T. Perry—Task Order Manager, Computer Sciences Corporation, 2803 Slater Road,
Suite 220, Morrisville, NC 27560
Mr. John A. Bennett—Technical Information Specialist, Library Associates of Maryland,
11820 Parklawn Drive, Suite 400, Rockville, MD 20852
Mr. William Ellis—Records Management Technician, InfoPro, Inc., 8200 Greensboro Drive,
Suite 1450, McLean, VA 22102
Ms. Sandra L. Hughey—Technical Information Specialist, Library Associates of Maryland,
11820 Parklawn Drive, Suite 400, Rockville, MD 20852
Dr. Barbara Liljequist—Technical Editor, Computer Sciences Corporation, 2803 Slater Road,
Suite 220, Morrisville, NC 27560
Ms. Michelle Partridge-Doerr—Publication/Graphics Specialist, TekSystems, 1201 Edwards
Mill Road, Suite 201, Raleigh, NC 27607
Mr. Carlton Witherspoon—Graphic Artist, Computer Sciences Corporation, 2803 Slater Road,
Suite 220, Morrisville, NC 27560
I-xlix
-------
U.S. Environmental Protection Agency
Science Advisory Board (SAB) Staff Office
Clean Air Scientific Advisory Committee (CASAC)
Chair
Dr. Rogene Henderson*—Scientist Emeritus, Lovelace Respiratory Research Institute,
Albuquerque, NM
Members
Dr. Joshua Cohen—Faculty, Center for the Evaluation of Value and Risk, Institute for Clinical
Research and Health Policy Studies, Tufts New England Medical Center, Boston, MA
Dr. Deborah Cory-Slechta—Director, University of Medicine and Dentistry of New Jersey and
Rutgers State University, Piscataway, NJ
Dr. Ellis Cowling*—University Distinguished Professor-at-Large, North Carolina State
University, Colleges of Natural Resources and Agriculture and Life Sciences, North Carolina
State University, Raleigh, NC
Dr. James D. Crapo [M.D.]*—Professor, Department of Medicine, National Jewish Medical
and Research Center, Denver, CO
Dr. Bruce Fowler—Assistant Director for Science, Division of Toxicology and Environmental
Medicine, Office of the Director, Agency for Toxic Substances and Disease Registry, U.S.
Centers for Disease Control and Prevention (ATSDR/CDC), Chamblee, GA
Dr. Andrew Friedland—Professor and Chair, Environmental Studies Program, Dartmouth
College, Hanover, NH
Dr. Robert Goyer [M.D.]—Emeritus Professor of Pathology, Faculty of Medicine, University
of Western Ontario (Canada), Chapel Hill, NC
Mr. Sean Hays—President, Summit Toxicology, Allenspark, CO
Dr. Bruce Lanphear [M.D.]—Sloan Professor of Children's Environmental Health, and the
Director of the Cincinnati Children's Environmental Health Center at Cincinnati Children's
Hospital Medical Center and the University of Cincinnati, Cincinnati, OH
Dr. Samuel Luoma—Senior Research Hydrologist, U.S. Geological Survey (USGS),
Menlo Park, CA
1-1
-------
U.S. Environmental Protection Agency
Science Advisory Board (SAB) Staff Office
Clean Air Scientific Advisory Committee (CASAC)
(cont'd)
Members
(cont'd)
Dr. Frederick J. Miller*—Consultant, Gary, NC
Dr. Paul Mushak—Principal, PB Associates, and Visiting Professor, Albert Einstein College of
Medicine (New York, NY), Durham, NC
Dr. Michael Newman—Professor of Marine Science, School of Marine Sciences, Virginia
Institute of Marine Science, College of William & Mary, Gloucester Point, VA
Mr. Richard L. Poirot*—Environmental Analyst, Air Pollution Control Division, Department
of Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT
Dr. Michael Rabinowitz—Geochemist, Marine Biological Laboratory, Woods Hole, MA
Dr. Joel Schwartz—Professor, Environmental Health, Harvard University School of Public
Health, Boston, MA
Dr. Frank Speizer [M.D.]*—Edward Kass Professor of Medicine, Channing Laboratory,
Harvard Medical School, Boston, MA
Dr. Ian von Lindern—Senior Scientist, TerraGraphics Environmental Engineering, Inc.,
Moscow, ID
Dr. Barbara Zielinska*—Research Professor, Division of Atmospheric Science, Desert
Research Institute, Reno, NV
SCIENCE ADVISORY BOARD STAFF
Mr. Fred Butterfield—CASAC Designated Federal Officer, 1200 Pennsylvania Avenue, N.W.,
Washington, DC, 20460, Phone: 202-343-9994, Fax: 202-233-0643 (butterfield.fred@epa.gov)
(Physical/Courier/FedEx Address: Fred A. Butterfield, III, EPA Science Advisory Board Staff
Office (Mail Code 1400F), Woodies Building, 1025 F Street, N.W., Room 3604, Washington,
DC 20004, Telephone: 202-343-9994)
*Members of the statutory Clean Air Scientific Advisory Committee (CASAC) appointed by the
EPA Administrator
I-li
-------
Abbreviations and Acronyms
aFGF
AA
AAL
AALM
AAS
ACBP
ACE
AChE
ACSL
ADCC
ADHD
ADP
AF
A horizon
AHR
ALA
ALAD
ALAS
ALAU
ALM
ALS
ALT
AMD
AMP
ANF
ANOVA
AP
AP-1
APE
ApoE
APP
AQCD
a-fibroblast growth factor
arachidonic acid; atomic absorption
active avoidance learning
All Ages Lead Model
atomic absorption spectroscopy
Achenbach Child Behavior Profile
angiotensin converting enzyme
acetylcholinesterase
Advanced Continuous Simulation Language
antibody-dependent cellular cytotoxicity
attention deficit/hyperactivity disorder
adenosine dinucleotide phosphate
absorption fraction
uppermost layer of soil (litter and humus)
aryl hydrocarbon receptor
5-aminolevulinic acid; 5-aminolevulinic acid
5-aminolevulinic acid dehydratase
aminolevulinic acid synthase
5-aminolevulinic acid dehydratase
Adult Lead Methodology
amyotrophic lateral sclerosis
alanine aminotransferase; alanine transferase
activity mean diameter
adenosine monophosphate
atrial natriuretic factor
analysis of variance
alkaline phosphatase
activator protein-1
apurinic endonuclease
apolipoprotein E
amyloid precursor protein
Air Quality Criteria Document
I-lii
-------
ASA
AST
ASV
ATP
ATP1A2
ATPase
ATSDR
ATV
AVS
AWQC
P
PFGF
6-p-OH-cortisol
BAEP
BBB
Bcell
BCF
BDNF
BLL
BLM
BMDM
BMI
BMP
BRHS
BSID
BTQ
BUN
BW
CA
45Ca, 47Ca
CA1
CAS
CAA
Ca-ATPase
arylsulfatase
aspartate aminotransferase
anode stripping voltammetry
adenosine triphosphate
sodium-potassium adenosine triphosphase a2
adenosine triphosphate synthase
Agency for Toxic Substances and Disease Research
all-terrain vehicle
acid volatile sulfide
ambient water quality criteria
beta-coefficient; slope of an equation
P-fibroblast growth factor
6-p-hydroxycortisol
brainstem auditory-evoked potentials
blood-brain barrier
B lymphocyte
bioconcentration factor
brain-derived neurotrophic growth factor
blood lead level
biotic ligand model
bone marrow-derived macrophages
body mass index
bone morphogenic protein
British Regional Heart Study
Bayley Scales of Infant Development
Boston Teacher Questionnaire
blood urea nitrogen
body weight
chromosomal aberration
calcium-45 and -47 radionuclides
cornu ammonis 1 region of hippocampus
cornu ammonis 3 region of hippocampus
Clean Air Act
calcium-dependent adenosine triphosphatase
I-liii
-------
43CaCl2
CaCO3
CaEDTA
CAL
CAMKII
cAMP
CaNa2 EDTA
CANTAB
CAP
Caio(P04)6(OH)2
CASAC
CBCL
CCE
CD
CDC
CERR
CESD, CES-D
cGMP
CI
CKD
CLRTAP
CMI
CNS
C02
ConA
COX-2
CP
CPT
CRAC
CREB
CRT
CSF
CSF-1
calcium-43 radionuclide-labeled calcium chloride
calcium carbonate
calcium disodium ethylenediaminetetraacetic acid
calcitonin
calcium/calmodulin-dependent protein kinase
cyclic adenosinemonophosphate
calcium disodium ethylenediaminetetraacetic acid
Cambridge Neuropsychological Testing Automated Battery
criteria air pollutant
hydroxyapatite
Clean Air Scientific Advisory Committee
Achenbach Child Behavior Checklist
Coordination Center for Effects
Sprague-Dawley CD (rat)
Centers for Disease Control and Prevention
Consolidated Emissions Reporting Rule
Center for Epidemiologic Studies Depression (scale)
cyclic guanosine-3',5'-monophosphate; cyclic
guanylylmonophosphate
confidence interval
chronic kidney disease
Convention on Long-range Transboundary of Air Pollution
cell-mediated immunity
central nervous system
carbon dioxide
concanavalin A
cyclooxygenase-2
coproporphyrin
current perception threshold
calcium release activated calcium reflux
cyclic-AMP response element binding protein
chronic renal insufficiency
cerebrospinal fluid
colony-stimulating factor-1
I-liv
-------
CTL
CuZnSOD
CWA
CYP
DA
DET
DPS
dfs
DOT
DIAL
DMEM
DMFS
DMSA
DMTU
DNA
DNTC
DOC
DOM
DOS
DPH
DRL
DSA
DTC
DTK
E
E2
EBE
EC
ECF
Eco-SSL
EDRF
EDTA
EEDQ
cytotoxic T lymphocyte
copper and zinc-dependent superoxide dismutase
Clean Water Act
cytochrome (e.g., CYP1 A, CYP-2A6, CYP3A4, CYP450)
dopamine; dopaminergic
diffusive equilibrium thin films
decayed or filled surfaces, permanent teeth
covariate-adjusted number of caries
diffusive gradient thin films
dialkyllead
Dulbecco's Modified Eagle Medium
decayed, missing, or filled surfaces, permanent teeth
2,3-dimercaptosuccinic acid; dimethyl succinic acid
dimethyl thio urea
deoxyribonucleic acid
diffuse neurofibrillary tangles with calcification
dissolved organic carbon
dissolved organic matter
Disk Operating System
1, 6-diphenyl-l,3,5-hexatriene
differential reinforcement of low rate (schedule)
delayed spatial alternation
dithiocarbamate
delayed type hypersensitivity
embryonic day; epinephrine
estradiol
early biological effect
coronary endothelial (cells)
effect concentration for 50% of test population
extracellular fluid
ecological soil screening level
endothelium-derived relaxing factor
ethylenediaminetetraacetic acid
7V-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinone
I-lv
-------
EEG
EOF
EGTA
eNOS
EOD
EP
EPA
EPMA
EPSP
EqP
ERG
ERL
ERM
EROD
ESP
ESRD
ET
ET-AAS
EXAFS
EXANES
F344
FA
FCS
FDA
FEF
FEP
FEVi
FGF
FI
FMLP
fMRI
foe
FPLC
FR
el ectroencephal ogram
epidermal growth factor
ethyleneglycoltetraacetic acid
endothelial nitric oxide synthase
explosive ordnance disposal
erythrocyte protoporphyrin
U.S. Environmental Protection Agency
electron probe microanalysis
excitatory postsynaptic potential
equilibrium partitioning (theory)
electroretinogram
effects range - low
effects range - median
ethoxyresorufin-0-deethylase
electrostatic precipitator
end-stage renal disease
endothelein; essential tremor
electrothermal atomic absorption spectroscopy
extended X-ray absorption fine structure
extended X-ray absorption near edge spectroscopy
Fischer 344 (rat)
fatty acid
fetal calf serum
Food and Drug Administration
forced expiratory flow
iron protoporphyrin
forced expiratory volume in one second
fibroblast growth factor (e.g., PFGF, aFGF)
fixed-interval (operant conditioning)
7V-formy 1 -L-methi ony 1 -L-l eucy 1 -L-pheny 1 al anine
functional magnetic resonance imaging
fraction organic carbon
fast protein liquid chromatography
Federal Register; fixed-ratio operant conditioning
I-lvi
-------
FSH
FT3
FT4
FVC
Y-GT
GABA
GAG
GCI
GD
GDP
GEE
GFAAS
GFAP
GFR
GH
GI
GL
GLU
GM
GMP
GnRH
goc
G6PD
GPEI
G-R
GRP78
GSD
GSD;
GSH
GSHPx
GSSG
GST
GTP
GvH
follicle stimulating hormone
free triiodothyronine
free thyroxine
forced vital capacity
y-glutamyl transferase
gamma aminobutyric acid
glycosaminoglycan
General Cognitive Index
gestational day
guanosine diphosphate
generalized estimating equations
graphite furnace atomic absorption spectroscopy
glial fibrillary acidic protein
glomerular filtration rate
growth hormone
gastrointestinal
gestation and lactation
glutamate
geometric mean
guanosine monophosphate
gonadotropin releasing hormone
grams organic carbon
glucose-6-phosphate dehydrogenase
glutathione S-transferase P enhancer element
Graham-Rosenblith Behavioral Examination for Newborns
glucose-regulated protein 78
geometric standard deviation
individual geometric standard deviation
glutathione; reduced glutathione
glutathione peroxidase
oxidized glutathione
glutathione transferase; glutathione S-transferase
guanosine triphosphate
graft versus host (reaction)
I-lvii
-------
H+
HAP
Hb
HBEF
H2C03
Hct
HDL
HFE
HFF
HH
HHANES
HHC
HLA
HNO3
H202
HOC1
HOME
HOS-TE-85
HPG
HPLC
H3P04
HPRT
HSAB
H2SO4
HSPG
HTN
HUD
HY-SPLIT
IARC
IBL
ICD
ICP
ICP-AES
ICP-MS
acidity
hazardous air pollutant
hemoglobin
Hubbard Brook Experimental Forest
carbonic acid
hematocrit
high-density lipoprotein (cholesterol)
hemochromatosis gene
human foreskin fibroblasts
hydroxylamine hydrochloride
Hispanic Health and Nutrition Examination Survey
hereditary hemochromatosis
human leukocyte antigen
nitric acid
hydrogen peroxide
hypochlorous acid
Home Observation for Measurement of Environment
human osteosarcoma cells
hypothalamic-pituitary-gonadal (axi s)
high-pressure liquid chromatography
phosphoric acid
hypoxanthine guanine phosphoribosyl transferase
Hard-Soft Acid-Base (model)
sulfuric acid
heparan sulfate proteoglycan
hypertension
U.S. Department of Housing and Urban Development
hybrid single-particle Lagrangian integrated trajectory (model)
International Agency for Research on Cancer
integrated blood lead index
International Classification of Diseases
inductively coupled plasma
inductively coupled plasma atomic emission spectroscopy
inductively coupled plasma mass spectrometry
I-lviii
-------
ICRP
IDMS
IEC
IEUBK
IFN
Ig
IGFi
IL
IMPROVE
iNOS
i.p., IP
IQ
IRT
ISCST
IT
i.v., IV
KABC
KID
KLH
K-pNPPase
KTEA
K-XRF
L
LAA ICP-MS
LCso
LDH
LDL
L-dopa
LE
LH
LISREL
LMW
LNAME, L-NAME
International Commission on Radiological Protection
isotope dilution mass spectrometry
intestinal epithelial cells
Integrated Exposure Uptake Biokinetic (model)
interferon (e.g., IFN-y)
immunoglobulin (e.g., IgA, IgE, IgG, IgM)
insulin-like growth factor 1
interleukin (e.g., IL-1, IL-lp, IL-4, IL-6, IL-12)
Interagency Monitoring of Protected Visual Environments
(network)
inducible nitric oxide synthase
intraperitoneal
intelligence quotient
interresponse time
Industrial Source Complex Short Term (model)
intrathecal
intravenous
Kaufman Assessment Battery for Children
Kent Infant Development Scale
keyhole limpet hemocyanin
potassium-stimulated p-nitrophenylphosphatase
Kaufman Test of Educational Achievement
K-shell X-ray fluorescence
lactation
laser ablation inductively coupled plasma mass spectrometry
lethal concentration (at which 50% of exposed animals die)
lactate dehydrogenase
low-density lipoprotein (cholesterol)
3,4-dihydroxyphenylalanine (precursor of dopamine)
Long Evans (rat)
luteinizing hormone
linear structural relationships (model)
low molecular weight
L-7V°-nitroarginine methyl ester
I-lix
-------
LOAEL
LOWES S
LPO
LPS
LT50
LTD
LTP
LVH
liPIXE
MAO
MAPK
MCH
MCHC
MCV
MDA
MDA-TBA
MDI
MDRD
meso-DMSA
Mg-ATPase
MHC
MK-801
MLR
MMAD
MMSE
MN
Mn-SOD
MRFIT
MRI
mRNA
MRS
MSV
MT
MVV
lowest-observed adverse effect level
locally weighted scatter plot smoother
lipid peroxide; lipid peroxidation
lipopolysaccharide
time to reach 50% mortality
long-term depression
long-term potentiation
left ventricular hypertrophy
microfocused particle induced X-ray emission
monoaminoxidase
mitogen-activated protein kinase
mean corpuscular hemoglobin
mean corpuscular hemoglobin concentration
mean corpuscular volume
malondialdehyde
malondialdehyde-thiobarbituric acid
Mental Development Index
Modification of Diet in Renal Disease (study)
w-2,3-dimercaptosuccinic acid
magnesium-dependent adenosine triphosphatase
major histocompatibility complex
NMD A receptor antagonist
mixed lymphocyte response
mass median aerodynamic diameters
Mini-Mental State Examination
micronuclei formation
manganese-dependent superoxide dismutase
Multiple Risk Factor Intervention Trial
magnetic resonance imaging
messenger ribonucleic acid
magnetic resonance spectroscopy
Moloney sarcoma virus
metallothionein
maximum voluntary ventilation
I-lx
-------
N, n
NA, N/A
NAA
NAAQS
NAC
NAD
NADH
NADP
NAD(P)H, NADPH
NADS
NAG
Na-K-ATPase
NART
NAS
NASCAR
NAT
NAWQA
NBAS
NCEA-RTP
ND
NE
NEI
NEPSY
NES
NF-KB
NHANES
NHEXAS
NIOSH
NIST
NK
NMDA
NMDAR
number of observations
not available
TV-acetylaspartate; neutron activation analysis
National Ambient Air Quality Standards
TV-acetyl cysteine; nucleus accumbens
nicotinamide adenine nucleotide
reduced nicotinamide adenine dinucleotide; nicotinamide adenine
dinucleotide dehydrogenase
nicotinamide adenine dinucleotide phosphate
reduced nicotinamide adenine dinucleotide phosphate
nicotinamide adenine dinucleotide synthase
7V-acetyl-p-D-glucosaminidase
sodium-potassium-dependent adenosine triphosphatase
North American Reading Test
Normative Aging Study
National Association for Stock Car Automobile Racing
TV-acetyltransferases
National Water-Quality Assessment
Brazelton Neonatal Behavioral Assessment Scale
National Center for Experimental Assessment Division in
Research Triangle Park, NC
non-detectable; not detected; not determined; not done
norepinephrine
National Emissions Inventory
Developmental Neuropsychological Assessment
Neurobehavioral Evaluation System
nuclear transcription factor-KB
National Health and Nutrition Examination Survey
National Human Exposure Assessment Survey
National Institute for Occupational Safety and Health
National Institute for Standards and Technology
natural killer
7V-methyl-D-aspartate
7V-methyl-D-aspartate receptor
I-lxi
-------
NO
NO2
N03
NOD
NOEC
NOM
NOS
NOX
NPL
NR
NRC
NTP
NTR
02
OAQPS
OAR
OC
OH
1,25-OH-D, 1,25-OHD3
25-OH-D, 25-OH D3
O horizon
ONOO
OR
ORD
OS
OSHA
P
Pio
PAD
PAH
PAI-1
Pb
203
Pb
nitric oxide
nitrogen dioxide
nitrate
autoimmune diabetes prone strain of mice
no-observed-effect concentration
natural organic matter
nitric oxide synthase; not otherwise specified
nitrogen oxide metabolites
National Priorities List
not reported
National Research Council
National Toxicology Program
neurotrophin receptor
superoxide ion
Office of Air Quality Planning and Standards
Office of Air and Radiation
organic carbon
hydroxyl
1,25-dihydroxyvitamin D
25-hydroxyvitamin D
forest floor
peroxynitrate ion
odds ratio
Office of Research and Development
oxidative stress
Occupational Safety and Health Administration
probability value
probability for the occurrence of a blood lead concentration
exceeding 10 |ig/dL
peripheral arterial disease
polycyclic aromatic hydrocarbon
plasminogen activator inhibitor-1
lead
lead-203 radionuclide
I-lxii
-------
20
4pb, 206pb, 207pb, 208pb
PbB
PbBPs
PbCl2
PbCO3
PbD
PBG-S
PbH
Pb(N03)2
PbO
Pb(OH)2
PbS
PbSO4
PC12
PCV
PDE
PDI
PEC
PFCs
PG
PHA
Pi
PIXE
PKA
PKC
PM
PM2.5
PMN
PMNL
P5N
PND
POMS
stable isotopes of lead-204, -206, -207, -208 respectively
lead-210 radionuclide
blood lead; blood lead concentration
lead binding proteins
lead choride
lead carbonate
interior dust lead concentration
porphobilinogen synthase
hand lead concentration
lead nitrate
lead oxide
lead hydroxide
galena
lead sulfate
pheochromocytoma cell
packed cell volume
phosphodiesterase
Psychomotor Index
probably effect concentration
plaque forming cells
prostaglandin (e.g., PGE2 ,PGF2)
phytohemagglutinin A
inorganic phosphorus
particle induced X-ray emission
protein kinase A
protein kinase C
particulate matter
combination of coarse and fine particulate matter
fine particulate matter
polymorphonuclear leukocyte
polymorphonuclear leukocyte
pyrimidine 5'-nucleotidase
postnatal day
Profile of Mood States
I-lxiii
-------
ppb
PPD
ppm
PRL
PTH
PTHrP
PUFA
PVC
PWM
R2
r
r2
RAAS
RAS
RBA
RBC
RBP
222Rn
ROI
ROS
ROS 17.2.8
RR
ZSEM
SAB
S-BIQ
SBIS-4
s.c., SC
SCAN
SCE
SD
SDS-PAGE
SE
SEM
parts per billion
purified protein derivative
parts per million
prolactin
parathyroid hormone
parathyroid hormone-related protein
polyunsaturated fatty acid
polyvinyl chloride
pokeweed mitogen
multiple correlation coefficient
Pearson correlation coefficient
correlation coefficient
renin-angiotensin-aldosterone system
renin-angiotensin system
relative bioavailablity
red blood cell; erythrocyte
retinol binding protein
most stable isotope of radon
reactive oxygen intermediate
reactive oxygen species
rat osteosarcoma cell line
relative risk
sum of the molar concentrations of simultaneously
extracted metal
Science Advisory Board
Standford-Binet Intelligence Quotient
Stanford-Binet Intelligence Scale-4th Edition
subcutaneous
test of central auditory processing
sister chromatid exchange
standard deviation; Spraque-Dawley (rat)
sodium dodecyl sulfate-polyacrylamide gel electrophoresis
standard error; Staphylococcus aureus enterotoxin
simultaneously extracted metal; standard error of the mean
I-lxiv
-------
SES
sGC
SHBG
SIMS
SIR
SLE
SMR
SNAP
S02
SOD
SOILCHEM
SRA
SRBC
SRC
SRD
SRE
SRIXE
SULT
T3
T4
T&E
TB
TEA
TEARS
Tc
Tcell
TEC
TEL
TES
TF
TGF
TH
232^
ThO
socioeconomic status
soluble guanylate cyclase
sex hormone binding globulin
secondary ion mass spectrometry
standardized incidence ratio
systemic lupus erythmatosus
standardized mortality ratio
Schneider Neonatal Assessment for Primates
sulfur dioxide
superoxide dismutase
chemical species equilibrium model
Self Reported Antisocial Behavior scale
sheep red blood cell
Syracuse Research Corporation
Self Report of Delinquent Behavior
sterol regulatory element
synchrotron radiation induced X-ray emission
sulfotransferases
triiodothyronine
thyroxine
threatened and endangered (species)
tuberculosis
thiobarbituric acid
thiobarbituric acid-reactive species
cytotoxic T lymphocyte
T lymphocyte
threshold effect concentration
tetraethyllead; triethyl lead chloride
testosterone
transferrin
transforming growth factor (e.g., TGF-a ,TGF-P, TGF-P1)
T-helper lymphocyte
stable isotope of thorium-232
precursor T lymphocyte
I-lxv
-------
Thl
Th2
THC
TIMS
TLC
TM
TML
TNF
tPA
TPALL
TPBS
TPY
TRH
TRI
TriAL
Trk
TSH
TSP
TSS
TT3
TT4
TTR
TWA
TX
235-rj 238-rj
UC1P
UDP
UGT
UNECE
USGS
UV
VC
VCS
Vd
T-derived lymphocyte helper 1
T-derived lymphocyte helper 2
CD4,CD8-positive T lymphocytes
thermal ionization mass spectrometry
Treatment of Lead-exposed Children (study)
T-memory lymphocyte
tetramethyllead
tumor necrosis factor (e.g., TNF-a, TNF-P1)
plasminogen activator
transfer rate from diffusible plasma to all destinations
Total Problem Behavior Score
tons per year
thyroid releasing hormone
Toxics Release Inventory
trialkyllead
tyrosine kinase receptor
thyroid stimulating hormone
total suspended particulates
total suspended solids
total triiodothyronine
serum total thyroxine
transthyretin
time-weighted average
tromboxane (e.g., TXB2)
uranium-234 and -238 radionuclides
plasma-to-urine clearance
uridine diphosphate
uridine diphosphate-glucuronyl transferases
United Nations Economic Commission for Europe
United States Geological Survey
ultraviolet
vital capacity
vinyl chloride stabilizer
deposition velocity
I-lxvi
-------
VDR
VEP
VI
VLDL
VMI
VP
VSMC
WHO
WIC
WISC-III
WISC-R
WPPSI
WRAT-R
w/v
XAS
XPS
X-rays
XRD
XRF
ZPP
vitamin D receptor
visual-evoked potential
variable-interval
very low density lipoprotein (cholesterol)
visual motor integration
plasma volume
vascular smooth muscle cells
World Health Organization
Women, Infants, and Children (program)
Wechsler Intelligence Scale for Children-Ill
Wechsler Intelligence Scale for Children-Revised
Wechsler Preschool and Primary Scale of Intelligence
Wide Range Achievement Test-Revised
weight per volume
X-ray absorption spectroscopy
X-ray photoelectron spectroscopy
synchrotron radiation
X-ray diffraction
X-ray fluorescence
zinc protoporphyrin
I-lxvii
-------
i 1. INTRODUCTION
2
3
4 The present document critically assesses the latest scientific information concerning
5 health and welfare effects associated with the presence of various concentrations of lead (Pb)
6 in ambient air, as pertinent to providing updated scientific bases for EPA's current periodic
7 review of the National Ambient Air Quality Standards for Lead (Pb NAAQS). As such, this
8 document builds upon previous assessments published by the U.S. Environmental Protection
9 Agency (EPA), including: (a) the document, Air Quality Criteria for Lead (U.S. Environmental
10 Protection Agency, 1977); (b) an updated revision of that Lead Air Quality Criteria Document
11 (Lead AQCD) and an accompanying Addendum published in 1986 (U.S. Environmental
12 Protection Agency, 1986a,b); as well as (c) an associated 1990 Supplement (U.S. Environmental
13 Protection Agency, 1990). This document focuses on evaluation and integration of information
14 relevant to Pb NAAQS criteria development that has become available mainly since that covered
15 by the 1986 and 1990 criteria assessments.
16 This introductory chapter (Chapter 1) of the revised Lead AQCD presents:
17 (a) background information on pertinent Clean Air Act legislative requirements, the criteria and
18 NAAQS review process, and the history of previous Pb criteria reviews; (b) an overview of the
19 current Pb criteria review process, associated key milestones, and projected schedule; and
20 (c) an orientation to the general organizational structure and content of this revised Lead AQCD.
21
22
23 1.1 LEGAL AND HISTORICAL BACKGROUND
24 1.1.1 Legislative Requirements
25 Two sections of the Clean Air Act (CAA) govern the establishment, review, and revision
26 of NAAQS. Section 108 (42 U.S.C. 7408) directs the Administrator of the U.S. Environmental
27 Protection Agency (EPA) to identify ambient air pollutants that may be reasonably anticipated to
28 endanger public health or welfare and to issue air quality criteria for them (U.S. Code, 2003a).
29 These air quality criteria are to reflect the latest scientific information useful in indicating the
30 kind and extent of all identifiable effects on public health or welfare that may be expected from
31 the presence of a given pollutant in ambient air.
May 2006 1-1 DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
7
8
9
10
1 1
12
13
14
15
16
17
18
19
20
21
Section 109(a) of the CAA (42 U.S.C. 7409) directs the Administrator of EPA to propose
and promulgate primary and secondary NAAQS for pollutants identified under Section 108 (U.S.
Code, 2003b). Section 109(b)(l) defines a primary standard as one that, in the judgment of the
Administrator, is requisite to protect the public health (see inset below) based on the criteria and
allowing for an adequate margin of safety. The secondary standard, as defined in Section
109(b)(2), must specify a level of air quality that, in the judgment of the Administrator, is
requisite to protect the public welfare (see inset below) from any known or anticipated adverse
effects associated with the presence of the pollutant in ambient air, based on the criteria.
EXAMPLES OF PUBLIC
HEALTH EFFECTS
Effects on the health of the general
population, or identifiable groups within the
population, who are exposed to pollutants in
ambient air
Effects on mortality
Effects on morbidity
Effects on other health conditions including
indicators of:
• pre-morbid processes,
• risk factors, and
• disease
EXAMPLES OF PUBLIC
WELFARE EFFECTS
Effects on personal comfort and well-being
Effects on economic values
Deterioration of property
Hazards to transportation
Effects on the environment, including:
animals
climate
crops
materials
soils
vegetation
visibility
water
weather
wildlife
Section 109(d) of the CAA (42 U.S.C. 7409) requires periodic review and, if appropriate,
revision of existing criteria and standards (U.S. Code, 2003b). If, in the Administrator's
judgment, the Agency's review and revision of criteria make appropriate the proposal of new or
revised standards, such standards are to be revised and promulgated in accordance with Section
109(b). Alternatively, the Administrator may find that revision of the standards is inappropriate
and conclude the review by leaving the existing standards unchanged. Section 109(d)(2) of the
1977 CAA Amendments also requires that an independent scientific review committee be
established to advise the EPA Administrator on NAAQS matters, including the scientific
soundness of criteria (scientific bases) supporting NAAQS decisions. This role is fulfilled by the
Clean Air Scientific Advisory Committee (CASAC), which is administratively supported by
EPA's Science Advisory Board (SAB).
May 2006
1-2
DRAFT-DO NOT QUOTE OR CITE
-------
1 1.1.2 Criteria and NAAQS Review Process
2 Periodic reviews by EPA of criteria and NAAQS for a given criteria air pollutant progress
3 through a number of steps, beginning with preparation of an air quality criteria document
4 (AQCD) by the National Center for Environmental Assessment Division in Research Triangle
5 Park, NC (NCEA-RTP), a unit within EPA's Office of Research and Development (ORD). The
6 AQCD provides a critical assessment of the latest available scientific information upon which
7 the NAAQS are to be based. Drawing upon the AQCD, the Office of Air Quality Planning and
8 Standards (OAQPS), a unit within EPA's Office of Air and Radiation (OAR), prepares a Staff
9 Paper that (a) evaluates policy implications of the key studies and scientific information
10 contained in the AQCD; (b) presents relevant exposure and risk analyses; and (c) presents EPA
11 staff conclusions and recommendations for standard-setting options for the EPA Administrator to
12 consider. The Staff Paper is intended to help "bridge the gap" between the scientific assessment
13 contained in the AQCD and the judgments required of the Administrator in determining whether
14 it is appropriate to retain or to revise the NAAQS.
15 Iterative drafts of both the AQCD and the Staff Paper (as well as other analyses, such as
16 associated exposure and/or risk assessments supporting the Staff Paper) are made available for
17 public comment and CAS AC review. Final versions of the AQCD and Staff Paper incorporate
18 changes in response to CAS AC review and public comment. Based on the information in these
19 documents, the EPA Administrator proposes decisions on whether to retain or revise the subject
20 NAAQS, taking into account public comments and CASAC advice and recommendations. The
21 Administrator's proposed decisions are published in the Federal Register, with a preamble that
22 delineates the rationale for the decisions and solicits public comment. After considering
23 comments received on the proposed decisions, the Administrator makes a final decision, which is
24 promulgated via a Federal Register notice that addresses significant comments received on the
25 proposal.
26 Promulgated NAAQS decisions involve consideration of the four basic elements of a
27 standard: indicator, averaging time, form, and level. The indicator defines the pollutant to be
28 measured in the ambient air for the purpose of determining compliance with the standard. The
29 averaging time defines the time period over which air quality measurements are to be obtained
30 and averaged, considering evidence of effects associated with various time periods of exposure.
31 The form of a standard defines the air quality statistic that is to be compared to the level of the
May 2006 1 -3 DRAFT-DO NOT QUOTE OR CITE
-------
1 standard (i.e., an ambient concentration of the indicator pollutant) in determining whether an area
2 attains the standard. The form of the standard specifies the air quality measurements that are to
3 be used for compliance purposes (e.g., the 98th percentile of an annual distribution of daily
4 concentrations; the annual arithmetic average), the monitors from which the measurements are to
5 be obtained (e.g., one or more population-oriented monitors in an area), and whether the statistic
6 is to be averaged across multiple years. These basic elements of a standard are the primary focus
7 of the staff conclusions and recommendations posed in the Staff Paper and are explicitly
8 specified in the ensuing NAAQS rulemaking, building upon the policy-relevant scientific
9 information assessed in the AQCD and on the policy analyses contained in the Staff Paper.
10 These four elements taken together determine the degree of public health and welfare protection
11 afforded by the NAAQS.
12
13 1.1.3 Regulatory Chronology
14 In 1971, U.S. EPA promulgated national ambient air standards for several major "criteria"
15 pollutants (see Federal Register, 1971), but did not include lead among them at that time. Later,
16 on October 5, 1978, the EPA promulgated primary and secondary NAAQS for lead, under
17 Section 109 of the CAA (43 FR 46258), as announced in the Federal Register (1979). The
18 primary standard and the secondary standard are the same: 1.5 |ig/m3 as a quarterly average
19 (maximum arithmetic mean averaged over 90 days). The standards were based on the EPA's
20 1977 Air Quality Criteria for Lead (U.S. Environmental Protection Agency, 1977).
21 In 1986, the EPA published a revised Air Quality Criteria Document for Lead (U.S.
22 Environmental Protection Agency, 1986a). The 1986 AQCD assessed newly available scientific
23 information on the health and welfare effects associated with exposure to various concentrations
24 of lead in ambient air, based on literature published through 1985. The 1986 document was
25 principally concerned with the health and welfare effects of lead, but other scientific data were
26 also discussed in order to provide a better understanding of the pollutant in the environment.
27 Thus, the 1986 document included chapters that discussed the atmospheric chemistry and
28 physics of the pollutant; analytical approaches; environmental concentrations; human exposure
29 and dosimetry; physiological, lexicological, clinical, and epidemiological aspects of lead health
30 effects; and lead effects on ecosystems. An Addendum to the 1986 Lead AQCD was also
31 published along with it (U.S. Environmental Protection Agency, 1986b). Subsequently,
May 2006 1 -4 DRAFT-DO NOT QUOTE OR CITE
-------
1 a Supplement to the 1986 Lead AQCD/Addendum was published by EPA in 1990 (U.S.
2 Environmental Protection Agency, 1990a). That 1990 Supplement evaluated still newer
3 information emerging in the published literature concerning (a) lead effects on blood pressure
4 and other cardiovascular endpoints and (b) the effects of lead exposure during pregnancy or
5 during the early postnatal period on birth outcomes and/or on the neonatal physical and
6 neuropsychological development of affected infants and children.
7 The evaluations contained in the 1986 Lead AQCD/Addendum and the 1990 Supplement
8 provided scientific inputs to support decision-making regarding periodic review and, as
9 appropriate, revision of the Lead NAAQS; and they were drawn upon by EPA's Office of Air
10 Quality Planning and Standards in preparation of an associated OAQPS Lead Staff Paper (U.S.
11 Environmental Protection Agency, 1990b). However, after consideration of evaluations
12 contained in these documents, EPA chose not to propose revision of the Lead NAAQS.
13 Changes in relative contributions of various lead sources and exposure pathways to
14 human exposures in the United States, and EPA actions to reduce such exposures, provide
15 important background for this current lead criteria and NAAQS review. Since 1978, the amount
16 of lead emitted into the air nationally has markedly declined. For example, as illustrated in
17 Chapters 2 and 3 of this document, from 1982 to 2002 lead emissions into the air decreased by
18 93% and the average air quality concentration of lead decreased by 94% from 1983 to 2002
19 (http://www.epa.gov/airtrends/lead2.html). Total lead emissions into the air decreased from
20 about 220,000 tons in 1970 to less than 4,000 in 1999. This decline is mainly attributable to
21 EPA's regulatory efforts to reduce the content of lead in gasoline (see, for example,
22 50 FR 9386), which substantially altered basic patterns of air lead emissions in the United States
23 (http://www.epa.gov/airtrends/lead2.html). Emissions from stationary sources have also been
24 greatly reduced (http://www.epa.gov/airtrends/lead2.html, Figure 2-11); but, given the even
25 greater reductions in emissions from transportation sources, industrial processes (including
26 smelters and battery manufacturers) now constitute a larger percentage of remaining lead
27 emissions to the atmosphere (http://www.epa.gov/airtrends/lead2.html, Figure 2-12). In short,
28 lead emissions into the atmosphere decreased greatly in the 1980's and 1990's, a trend that has
29 continued on through to the present. As a consequence, airborne lead now represents only a
30 relatively small component of total exposure to lead in the United States, such that the principal
31 sources and pathways for U.S. lead exposure among the classically-defined most sensitive
May 2006 1 -5 DRAFT-DO NOT QUOTE OR CITE
-------
1 population group (young children) involve non-inhalation pathways, e.g., ingestion of lead from
2 deteriorating paint, food, drinking water, dust, and historically contaminated soil. While these
3 downward trends in air lead exposures nationwide are encouraging, several important sources of
4 air lead exposure may still persist in some localities. Lead emissions from specific stationary
5 sources and/or reentrainment of lead-contaminated soils (including from past deposition of
6 airborne lead) may still have significant impacts on a local level. Recognition of the multimedia
7 nature of lead exposure of the general population has been important historically and sorting out
8 relative contributions to total lead exposure burdens represents an important input to the current
9 periodic Lead NAAQS review effort.
10 Since the 1980's, EPA has played a major, effective role in working to reduce the main
11 sources of lead exposure for most children, including deteriorating lead-based paint, lead-
12 contaminated dust, and lead-contaminated residential soil (http://www.epa.gov/lead/).
13 For example, EPA has established standards for lead-based paint hazards and lead dust cleanup
14 levels in most pre-1978 housing and child-occupied facilities, and is now developing standards
15 for those conducting renovation activities that create lead-based paint hazards and for the
16 management and disposal of lead-based debris (http://www.epa.gov/lead/regulation.htm). Also,
17 EPA has developed standards for management of lead in solid and hazardous waste, continues to
18 oversee the cleanup of lead contamination at Superfund facilities, and has issued regulations to
19 reduce lead in drinking water (http://www.epa.gov/lead/sources.htm). Beyond taking specific
20 regulatory actions, the Agency's Lead Awareness Program also continues to work to
21 protect human health and the environment against the dangers of lead by conducting research
22 and designing educational outreach efforts and materials (http://www.epa.gov/lead/).
23 Since the 1980's, EPA has also promulgated regulations under section 112 of the Clean
24 Air Act (42 U.S.C. § 7412), to address emissions of lead components and other toxic pollutants
25 from both primary lead smelters and secondary lead smelters (40 CFR Subparts X and TTT).
26 Under section 112(d), these emission standards are to require "the maximum degree of reduction
27 in emissions" that are "achievable." Thus, EPA promulgated section 112(d) standards for
28 secondary lead smelters on June 23, 1995 (60 Fed. Reg. 3587) and revised them on June 13,
29 1997 (62 Fed. Reg. 32209), followed by promulgation of section 112(d) standards for primary
30 lead smelters on June 4, 1999 (64 Fed. Reg. 30194).
May 2006 1 -6 DRAFT-DO NOT QUOTE OR CITE
-------
1 1.2 CURRENT LEAD CRITERIA AND NAAQS REVIEW
2 1.2.1 Procedures and Key Milestones for Document Preparation
3 It is important to emphasize at the outset that development of the present document has
4 and will continue to include substantial external (non-EPA) expert inputs and opportunities for
5 public input through (a) public workshops involving the general scientific community,
6 (b) iterative reviews of successive drafts of this document by CASAC, and (c) comments from
7 the public on successive drafts. Extensive external inputs received through such reviews will
8 help to ensure that the review of the Lead NAAQS will be based on critical assessment in this
9 document of the latest available pertinent science.
10 The procedures for developing this revised Lead AQCD build on experience derived from
11 other recent criteria document preparation efforts. These include close coordination between
12 NCEA-RTP and OAQPS staff, as well as with others, throughout the document
13 preparation/review process. Briefly, the respective responsibilities for production of the
14 document and meeting key milestones are as follows. An NCEA-RTP Lead Team has been
15 designated as being responsible for creation and implementation of a proj ect plan for developing
16 the Lead AQCD, taking into account input from individuals in other ORD units, OAQPS, and
17 other EPA program/policy offices identified as part of the EPA Lead Work Group. The Lead
18 Team defines critical issues and topics to be addressed by the authors and provides direction in
19 order to focus on evaluation of those studies most clearly identified as likely being important for
20 U.S. air standard setting purposes. Criteria document materials are authored in part by
21 NCEA-RTP Lead Team staff with appropriate expertise in particular areas and by non-EPA
22 consultants to EPA who are recognized experts in pertinent specific areas (e.g., lead biokinetic
23 modeling, toxicology, epidemiology, etc.).
24 Key milestones for development of this Lead AQCD are listed in Table 1-1. As a first
25 step, EPA announced on November 9, 2004 official initiation of the current periodic review of
26 air quality criteria for lead. More specifically, under processes established in Sections 108 and
27 109 of the Clean Air Act, U.S. EPA began by announcing in the Federal Register (69 FR 64,926)
28 the formal commencement of the current review process with a call for information (see Federal
29 Register, 2004). In addition, EPA prepared a January 2005 draft Lead AQCD Work Plan, which
30 was made available for public comment and was the subject of teleconsultation with CASAC on
31 March 28, 2005 as a means by which to communicate the process and timeline for development
May 2006 1 -7 DRAFT-DO NOT QUOTE OR CITE
-------
Table 1-1. Key Milestones and Projected Schedule for Development of Revised Lead Air
Quality Criteria Document (Lead AQCD)1
Major Milestones Target Dates
1. Literature Search Ongoing
2. Federal Register Call for Information November 9. 2004
3. Prepare Draft Lead AQCD Project Work Plan Nov-Dec 2004
4. Release Draft Project Plan for Public Comment/CASAC Review January 2005
5. Public Comment Period Jan/Feb 2005
6. CASAC Teleconsultation on Project Work Plan March 28, 2005
7. Workshop Drafts of Lead AQCD Chapters May/June 2005
8. Peer Consultative-Review Workshop(s) July/August 2005
9. Release First External Review Draft December 1, 2005
10. Public Comment Period Dec 2005-Feb 2006
11. CASAC/SAB Public Review Meeting (First Ext. Rev. Draft) Feb. 28-Mar 1, 2006
12. Release Second External Review Draft May 2006
13. Public Comment Period May/June 2006
14. CASAC/SAB Public Review Meeting (Second Ext. Rev. Draft) June 28-29,2006
15. Final Lead AQCD October 1,2006
1 Schedule may be modified from time to time, as necessary, to reflect actual project requirements and progress,
but EPA is under court order to produce a final Lead AQCD by October 1, 2006. Missouri Coalition for the
Environment v. EPA. Civil Action No. 4:04-CV-00660 (ERW) (E.D. Mo. Sept. 14, 2005). Also, note that
materials contributed by non-EPA authors, at times, have been and will continue to be modified by EPA staff
in response to internal and/or external review comments and that EPA is responsible for the ultimate content
of this Lead AQCD.
1 of a revised Lead AQCD. Next, expert consultants to NCEA-RTP and NCEA-RTP staff
2 (a) carefully evaluated pertinent new studies obtained via the call for information and via
3 ongoing literature searches conducted by NCEA-RTP information retrieval specialists and
4 (b) prepared preliminary draft chapter materials for inclusion in this revised Lead AQCD. Those
5 preliminary draft materials then underwent expert peer discussion at public workshops organized
6 and conducted by NCEA-RTP in July/August, 2005. After consideration of comments received
7 at the workshops, appropriate revisions were made in the draft materials and incorporated into
8 the First External Review Draft of the Lead AQCD, which was made available for public
9 comment (for 90 days) and CASAC review at a public meeting on February 28-March 1, 2006.
May 2006 1 -8 DRAFT-DO NOT QUOTE OR CITE
-------
1 EPA, after taking into account CASAC and public comments, is releasing this Second External
2 Review Draft of this revised Lead AQCD for further review by the public and CASAC before
3 completing the final version of it for issuance by October 1, 2006. Publication of the final
4 document and its availability to the public will be announced in the Federal Register.
5 Drawing upon evaluations in the Lead AQCD and other lead exposure/risk analyses, the
6 EPA's Office of Air Quality Planning and Standards (OAQPS) staff will prepare a draft Lead
7 Staff Paper that assesses policy implications of key information in the Lead AQCD, report
8 pertinent exposure and risk analyses, and poses possible options for the EPA Administrator to
9 consider with regard to whether to retain or, if appropriate, revise the Lead NAAQS. The draft
10 Lead Staff Paper and analyses will also be made available for review by the public and CASAC.
11 Taking into account CASAC and public comments, EPA expects to produce revised exposure
12 and risk analyses as well as a revised draft Lead Staff Paper for public comment and CASAC
13 review before making final revisions in that Staff Paper, to inform the decisions to be made by
14 the EPA Administrator regarding possible retention or revision of the Lead NAAQS. The
15 proposed NAAQS decisions will then be made available via the Federal Register for public
16 comment and, following consideration of comments received, the EPA Administrator will
17 ultimately promulgate final Lead NAAQS decisions via their announcement in the Federal
18 Register.
19
20
21 1.3 ORGANIZATIONAL STRUCTURE AND CONTENT OF
22 THE DOCUMENT
23 1.3.1 Ascertainment of Literature and General Document Format
24 Lists of references published since completion of the 1986 Lead AQCD/Addendum and
25 1990 Supplement were made available to the authors. The references were mainly selected from
26 information data base (e.g., Pub Med) searches conducted by EPA. However, additional
27 references have been added as work has proceeded in creating the present draft document
28 materials. As an aid in selecting pertinent new literature, the authors were also provided with a
29 summary of issues to be addressed in this revised Lead AQCD. Many such issues identified in
30 the course of previous lead criteria assessments, through interactions between EPA Lead Team
31 and Lead Work Group members, and via workshop discussions.
May 2006 1 -9 DRAFT-DO NOT QUOTE OR CITE
-------
1 The general format used in this draft document is to open each new chapter (or main
2 section) for the updated Lead AQCD with concise summary of key findings/conclusions from
3 the previous lead criteria assessments, especially the 1986 Lead AQCD/Addendum (U.S.
4 Environmental Protection Agency, 1986a,b) and 1990 Supplement (U.S. Environmental
5 Protection Agency, 1990). After presentation of such background information, the remainder of
6 each chapter or section typically provides an updated discussion of newer literature and resulting
7 key conclusions. In some cases where no new information is available, the summary of key
8 findings and conclusions from the previous lead criteria assessment(s) must suffice as the basis
9 for current key conclusions. Increased emphasis is placed in the main chapters of this revised
10 Lead AQCD on interpretative evaluation and integration of evidence pertaining to a given topic
11 than was typical of many previous EPA air quality criteria documents, with more detailed
12 descriptions of individual studies or other supportive information being provided in a series of
13 accompanying annexes.
14
15 1.3.2 Organization and Content of the Document
16 This updated Lead AQCD critically assesses scientific information on the health and
17 welfare effects associated with exposure to the concentrations of lead in ambient air. The
18 document is not intended to be a detailed, exhaustive review of the literature. Rather, the cited
19 references reflect the current state of knowledge issues pertinent to decisions regarding possible
20 revision by EPA of the Lead NAAQS. Although emphasis is placed mainly on the discussion of
21 health and welfare effects data, other scientific information also is evaluated in order to provide a
22 better understanding of the nature, sources, distribution, and concentrations of lead in ambient
23 air, as well as the measurement of human exposure to lead.
24 The focus of discussion is on assessment of selected pertinent scientific information
25 published since the last prior assessments of air quality criteria for lead contained in the 1986
26 Lead AQCD/Addendum or 1990 Supplement. Emphasis is placed on studies conducted at or
27 near lead concentrations found in ambient air. Other studies are included if they contain unique
28 data (e.g., the documentation of a previously unreported effect or of a mechanism for an
29 observed effect) or if they are multiple-concentration studies designed to characterize exposure-
30 or dose-response relationships.
May 2006 1-10 DRAFT-DO NOT QUOTE OR CITE
-------
1 As noted earlier, key findings and conclusions from the 1986 Lead AQCD/Addendum and
2 1990 Supplement are typically first briefly summarized at the outset of discussion of a given
3 topic, with appropriate reference back to the previous criteria assessment materials. Typically,
4 important prior studies are more specifically discussed only if they are open to reinterpretation in
5 light of newer data and/or are judged to be potentially useful in decisions on revision of the
6 standards for lead. Generally, only information that has undergone scientific peer review and has
7 been published (or accepted for publication) in the open literature through December 31, 2005
8 has been considered in this revised Lead AQCD. Certain other unpublished analyses (e.g., EPA
9 analyses of recently available U.S. lead air quality data) is also considered, depending on the
10 importance of the subject information and its pertinence to criteria development for Lead
11 NAAQS, as determined in consultation with CASAC.
12 This Lead AQCD consists of two volumes. Volume 1 consists of eight chapters that
13 comprise the main body of the revised Lead AQCD and an Executive Summary for all chapters.
14 In Volume I of this draft document, this introductory chapter (Chapter 1): (a) provides brief
15 statements regarding the purpose of the document; (b) presents information on the legislative
16 background and regulatory chronology of lead criteria reviews; and (c) presents an overview of
17 the organization of the document. Chapter 2 provides information on the physics and chemistry
18 of lead, as well as sources, emissions, transport and deposition/fate. Chapter 3 discusses
19 environmental concentrations, dispersal patterns, and multimedia exposure pathways. Chapter 4
20 focuses on the measurement of concentrations of lead in biological samples and the modeling of
21 multimedia exposure impacts on human internal lead burdens, especially as indexed by blood or
22 bone lead concentrations. Then, Chapter 5 discusses toxicologic studies of lead health effects in
23 humans, laboratory animals, and in vitro test systems; whereas Chapter 6 assesses lead-related
24 epidemiologic (observational) studies of human population groups. Chapter 7 provides an
25 integrative synthesis of key information drawn from the earlier chapters to delineate human lead
26 exposure and health effect findings and conclusions of most importance for derivation of primary
27 Pb NAAQS. Lastly, Chapter 8 deals with ecological and other environmental effects of lead as
28 key types of welfare effects pertinent to the derivation of secondary Pb NAAQS. Volume II of
29 this revised Lead AQCD includes several annexes containing more detailed descriptive materials
30 supporting the interpretative evaluations highlighted in the main chapters dealing with health and
31 vegetation/ecological effects.
May 2006 1-11 DRAFT-DO NOT QUOTE OR CITE
-------
1 REFERENCES
2 Federal Register. (1971) National primary and secondary ambient air quality standards. F. R. (April 30)
3 36:8186-8201.
4 Federal Register. (1979) National primary and secondary ambient air quality standards: revisions to the National
5 Ambient Air Quality Standards for lead. F. R. (February 8) 44: 8202-8237.
6 Federal Register. (2004) Air quality Criteria Document for Lead: Call for Information. F. R. (November 9)
7 69:64926-64928.
8 U.S. Code. (2003a) Clean Air Act, §108, air quality criteria and control techniques.. U. S. C. 42: §7408.
9 U.S. Code. (2003b) Clean Air Act, § 109, national ambient air quality standards. U. S. C. 42: §7409.
10 U.S. Environmental Protection Agency. (1977) Air quality criteria for lead. Research Triangle Park, NC: Health
11 Effects Research Laboratory, Criteria and Special Studies Office; EPA report no. EPA/600/8-77-017.
12 Available from NTIS, Springfield, VA; PB-280411.
13 U.S. Environmental Protection Agency. (1986a) Air quality criteria for lead. Research Triangle Park, NC: Office of
14 Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no.
15 EPA/600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
16 U.S. Environmental Protection Agency. (1986b) Lead effects on cardiovascular function, early development, and
17 stature: an addendum to U.S. EPA Air quality criteria for lead. In: Air quality criteria for lead, v. 1. Research
18 Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and Assessment
19 Office; pp. A1-A67; EPA report no. EPA/600/8-83/028aF. Available from: NTIS, Springfield, VA;
20 PB87-142378.
21 U.S. Environmental Protection Agency. (1990a) Summary of selected new information on effects of lead on health
22 and supplement to 1986 air quality criteria for lead. Research Triangle Park, NC: Office of Health and
23 Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA/600/8-89.
24 Available from NTIS, Springfield, VA; PB92-235670.
25 U.S. Environmental Protection Agency. (1990b) Review of the national ambient air quality standards for lead:
26 assessment of scientific and technical information: OAQPS staff paper. Research Triangle Park, NC:
27 Office of Air Quality Planning and Standards; report no. EPA-450/2-89/022. Available from: NTIS,
28 Springfield, VA; PB91-206185.
May 2006 1-12 DRAFT-DO NOT QUOTE OR CITE
-------
i 2. CHEMISTRY, SOURCES, AND TRANSPORT
2 OF LEAD
3
4 The purpose of this chapter is to provide background information on the chemical
5 properties of Pb that are relevant to its transport within the environment, its transport into
6 ecosystems and its impact on human health; to discuss the known sources of Pb in the
7 environment; and to outline the mechanisms by which Pb is transported within the environment.
8 The chapter does not provide a comprehensive list of all sources of lead, nor does it provide
9 emission rates or emission factors for all source categories, since such information is available
10 for only a limited number of sources. Rather, the chapter provides data on the chemistry,
11 sources, and transport of lead where information is available in the literature. Particle size
12 distribution data for lead are even scarcer than total lead emissions from sources; particle size
13 data are presented where such data are available.
14
15
16 2.1 PHYSICAL AND CHEMICAL PROPERTIES OF LEAD
17 Properties of Elemental Lead
18 Elemental Pb possesses an array of useful physical and chemical properties, making it
19 among the first metals to be extracted and used by humankind. It has a relatively low melting
20 point (327.51), is a soft, malleable, and ductile metal, a poor electrical conductor, and is easily
21 cast, rolled and extruded. While sensitive to environmental acids, after exposure to
22 environmental sulfuric acid (H2SO4), metallic Pb becomes impervious to corrosion due to
23 weathering and submersion in water. This effect is due to lead sulfate (PbSO4), the relatively
24 insoluble precipitate produced by reaction of Pb with H2SO4, forms a protective barrier against
25 further chemical reactions (Schweitzer, 2003). This aspect of its chemistry made Pb especially
26 convenient for roofing, containment of corrosive liquids, and until the discovery of its adverse
27 health effects, construction of water supply systems.
28 Lead is readily extracted from galena, a widely available sulfide mineral form of lead
29 (PbS), by froth flotation, followed by roasting in the presence of a limited amount of oxygen to
30 form litharge, one of two forms of lead oxide (PbO). Elemental Pb is then isolated by reducing
May 2006 2-1 DRAFT-DO NOT QUOTE OR CITE
-------
1 PbO by way of heating in the presence of elemental carbon (coke, charcoal) (Greenwood and
2 Earnshaw, 1984). This and other extraction and recovery processes will be discussed in greater
3 detail, later in this chapter.
4 Lead alloys constitute 60% of lead used in industry (Prengaman, 2003). The major
5 alloying elements are antimony, calcium, tin, copper, tellurium, arsenic, and silver. Selenium,
6 sulfur, bismuth, cadmium, indium, aluminum, and strontium are also sometimes used. Lead
7 alloys are found primarily in lead acid batteries, solder, ammunition, and cable sheathing
8 (Prengaman, 2003). Table 2-1 provides a list of Pb alloys in use by industry.
9 Some of the physical properties of elemental Pb are listed in Table 2-2. The most
10 important of these properties, when evaluating the transport routes for Pb within the atmosphere,
11 is its boiling point. As indicated, Pb will only exist in the vapor phase at or above 1750 °C.
12 Therefore, at ambient atmospheric temperatures, elemental Pb will deposit to surfaces or exist in
13 the atmosphere as a component of atmospheric aerosol.
14
15 Oxidation States of Lead
16 Lead is the heaviest congener of carbon, and shares many properties with the other
17 elements found in the same column of the periodic chart (silicon, germanium, and tin).
18 As Group IV elements, these elements have four valence electrons (2p and 2 s), allowing for
19 both divalent and tetravalent compounds.
20 Due to its high atomic number (82), the valence electron orbitals of the Pb atom exist at a
21 comparatively large distance from its nucleus. As with s and/? orbitals at any quantum level,
22 electrons in the 6s orbital tend to occupy space near the nucleus with greater probability than
23 those in the 6p orbital. The strong attraction produced by the large Pb nucleus combined with
24 the long distance that the 6s electrons must travel result in electron accelerations to relativistic
25 speeds. The Theory of Relativity states that as the velocity of matter approaches the speed of
26 light, its apparent mass increases. In this instance, the electrons in the Pb 6s orbital experience
27 an increase in weight, which increases the attractive effect of the positive nuclear charge, which
28 contracts the diameter of the Pb 6s orbital (Pitzer, 1979). This "relativistic effect" on valence
29 electrons is proportional to the square of atomic number, and manifests within the Group IV
30 elements as a distinctly increasing trend in the stability of the divalent state from Si down to Pb.
31 In the case of Pb, the two 6s electrons behave as if they were chemically inert, leaving only the
May 2006 2-2 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-1. Lead Alloys and Their Industrial Applications
Lead Alloy
Uses
Lead-Antimony
Lead-Calcium
Lead-Tin
Lead-Copper
Lead-Silver
Lead-Tellurium
Lead-Bismuth
Lead-Cadmium
Lead-Indium
Lead-Strontium
Lead-Lithium
Lead-Antimony-Tin
Lead-Calcium-Aluminum
Lead-Calcium-Tin
Lead-Calcium-Silver
Lead-Antimony-Silver
Lead-Silver-Tin
Lead-Strontium-Tin
Lead-Lithium-Tin
Grids, posts, and connectors for lead-acid batteries, ammunition, cable
sheathing, anodes, tank linings, pumps, valves, and heating and cooling coils
Automotive, standby power, submarines, and specialty sealed batteries,
electrowinning anodes, cable sheathing, sleeving, specialty boat keels, and lead
alloy tapes
Soldering for electronics, general purposes, automobile radiators, and heat
exchangers, corrosion resistant coatings on steel and copper, cable sheathing,
fuses, sprinkler system alloys, foundry pattern alloys, molds, dies, punches,
cores, mandrels, replication of human body parts, and filters for tube bonding
Lead sheet, pipe, cable sheathing, wire, fabricated products, tank linings, tubes
for acid-mist precipitators, steam heating pipes for sulfuric acid or chromate
plating baths, and lead sheathing for roofs
Anodes, high-temperature solders, insoluble anodes in the electrowinning of
zinc and manganese, and soft solders
Pipes, sheets, shielding for nuclear reactors, and cable sheathing
Fuses, sprinkler system alloys, foundry pattern alloys, molds, dies, punches,
cores, mandrels, solders, replication of human body parts, and filters for tube
bonding
Fuses, sprinkler system alloys, foundry pattern alloys, molds, dies, punches,
cores, mandrels, solders, replication of human body parts, and filters for
tube bonding
Fuses, sprinkler system alloys, foundry pattern alloys, molds, dies, punches,
cores, mandrels, solders, replication of human body parts, filters for tube
bonding, and joining metals to glass
Battery grids
Bearings, lead-acid battery grids
Printing, bearings, solders, slush castings, and specialty castings
Negative battery grids of lead-acid batteries
Positive grids of lead-calcium batteries, and lead anodes for electrowinning
Zinc electrowinning
Anodes used for the production of thin copper foil in electronics, and anodes in
cathodic protection of steel pipes and structures in water
Anodes in cathodic protection of steel pipes and structures in water, and soft
solders
Anodes for copper electrowinning
Lead-acid battery grids
Source: Prengaman (2003).
May 2006
2-3
DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-2. Physical Properties of Elemental Lead
Physical Property
Atomic number 82
Atomic weight 207.2
Valence electrons [Xe]4f145d106s26p
Melting point 328 °C
Boiling point 1750 °C
Density 11.34 g/cm3
Atomic radius 146 pm
Standard reduction potential - 0.126V
Oxidation numbers +2, +4
lonization Energy 715.6 kJ/mol
Source: Kotz and Purcell (1991).
1 two 6p electrons available for bonding or oxidation under ordinary conditions. For this reason,
2 the relativistic effect is also known as the "inert pair effect." Consequently, Pb(II) is the most
3 common oxidation state in which Pb is found in the environment (King, 1995; Claudio et al.,
4 2003).
5 Lead is distinguished from other elements that are subject to relativistic effects by its
6 preference for forming tetravalent (Pb(IV) organometallic compounds, however. In fact, it is
7 only with rare exception that Pb(II) organometallic compounds form (Pelletier, 1995;
8 Greenwood and Earnshaw, 1984). All simple alkyllead compounds, such as the well-known fuel
9 additives, tetramethyllead (TML) and tetraethyllead (TEL) are composed of Pb(IV). In contrast,
10 inorganic Pb(IV) compounds, such as PbC>2 are strong oxidants, and unstable with respect to
11 their Pb(II) analogs. There are, overall, more than 200 known organolead compounds
12 (Harrison, 1985).
13 In relation to the other Group IV metals, however, Pb forms the least stable and most
14 reactive organometallic derivatives. This is largely due to the weak bond between lead and
15 carbon, consistent with its large atomic size, and the influence of the relativistic effect on its
16 valence orbitals. Specifically, the mean bond dissociation energies of the metal-carbon bonds for
May 2006 2-4 DRAFT-DO NOT QUOTE OR CITE
-------
1 Group IV elements are 56.7 kcal/mol for germanium, 46.2 kcal/mol for tin, and 30.8 kcal/mol for
2 lead (Shapiro & Frey, 1968). Organolead compounds are thermally unstable and will decompose
3 to metallic lead and free radicals at relatively low temperatures (Willemsen and van der Kerk,
4 1965). For example, TML decomposes at temperatures above 200°C, and TEL decomposes at
5 temperatures above 110°C (King, 1995). In solution, organolead compounds decompose in the
6 presence of UV radiation (1 hr/254 nm) and sunlight (Gomez Ariza et al., 2000).
7 Tetralkyllead compounds have atmospheric residence times ranging from a few hours to a
8 few days (Pelletier, 1995). TML and TEL react with OH in the gas-phase, following pseudo-first
9 order kinetics, to form a variety of products that include ionic trialkyllead (TriAL), dialkyllead
10 (DiAL) and metallic Pb. Trialkyllead is slow to react with OH and is quite persistent in the
11 atmosphere (Hewitt and Harrison, 1986; Harrison and Laxen, 1980).
12
13 Lead Oxides, Chalcogenides, and Salts
14 A rich variety of inorganic Pb compounds and complex salts can be prepared in the
15 laboratory under conditions of temperature and pressure not usually seen in the environment.
16 Information on the many possible organic and inorganic Pb compounds can be found in the text
17 by Greenwood and Earnshaw (1984). Several representative Pb salts and oxides are described in
18 Tables 2-3 and 2-4. Inorganic Pb compounds that can be found in the environment are the focus
19 of this discussion.
20 As explained earlier, Pb exists preferentially in its +2 oxidation state in the environment.
21 Under aqueous acidic conditions, Pb readily oxidizes, with a strongly positive electrochemical
22 potential (E° =1.355 V), and a large equilibrium constant (K = 10 916), to form Pb(II) (Singley,
23 1994):
24
25 2Pb + O2 + 4H+ -» 2Pb2+ + 2H2O (2-1)
26
27 Table 2-5 lists the various Pb compounds and salts that are present naturally or are
28 introduced into the environment by anthropogenic activities. From this list, it is clear that only a
29 relatively limited number of salts and covalently-bound Pb compounds are of significance in
30 the environment, i.e., sulfates (PbSO4), chlorides (PbCl2), carbonates (PbCO3, Pb(HCO3) 2),
31 hydroxides (Pb(OH) 2), nitrates (Pb(NO3) 2), phosphates (PbPO4, Pb(HPO4) 2), silicates, oxides
May 2006 2-5 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-3. Lead Salts: Names, Formulae, Physical Characteristics, and Uses
Category
Compound
Name
Formula
Form
Uses
Lead Acetates Anhydrous Lead Pb(C2H3O2)2
Acetate
Basic Lead 2Pb(OH)2
Acetate Pb(C2H3O2)2
Lead Acetate Pb(C2H3O2)2
Trihydrate
Lead Tetraacetate Pb(C2H3O2)4
Lead Lead Carbonate PbCO3
Carbonates
Basic Lead
Carbonate
2PbC03
Lead Halides Lead Fluoride PbF2
Lead Chloride PbCl,
Lead Bromide
Lead Iodide
PbBr,
PbI2
White, crystalline Preparing other lead salts
solid
Heavy, white Sugar analysis
powder
White, Making other lead compounds, mordant for
monoclinic cotton dyes, water repellant, processing agent
crystalline solid for cosmetics, perfumes, and toiletries
Colorless, Oxidizing agent in organic synthesis, cleaving
monoclinic of a-hydroxy acids, introducing acetyl groups
crystalline solid in organic molecules
Colorless, Catalytic polymerization of formaldehyde,
orthorhombic improving the bonding of polychloroprene to
crystals metals in wire-reinforced hoses, a component
of high-pressure lubricating greases, and a
lubricant for poly vinyl chloride
White, hexagonal Ceramic glazes, a curing agent with peroxides
crystals to form polyethylene wire insulation, a color-
changing component of temperature-sensitive
inks, a component of lubricating grease, and a
component of weighted nylon-reinforced fish
nets made of poly vinyl chloride libers
Colorless, Glass sealing disks for IR sensors, wear-
orthorhombic resistant automotive shock absorbers,
crystals electrolytic deposition of lead, flux for
brazing of aluminum and its alloys, optical
glass libers for IR transmission, and thin film
batteries
White, Artist's pigment, precursor of organolead
orthorhombic compounds, seawater-activated batteries,
needles expanding polymer mortar, flux for soldering
cast iron and cast brass, sound-insulating
rubber sealants, corrosion inhibitor for
galvanized steel, and infrared-transmitting
glasses for CO2 lasers
White, Filler for flame-resistant polypropylene, glass
orthorhombic optical waveguides for infrared thermometers
crystals and catalysts for producing polyesters
Powdery, yellow, Aerosols for cloud seeding, making high-
hexagonal contrast photographic images of laser
crystals radiation, high capacity cathodes in lithium
batteries, and low-temperature thermographic
copying materials
Lead Silicates
Lead Sulfates
Lead
Monosilicate
Lead Bisilicate
Tribasic Lead
Silicate
Tribasic Lead
Sulfate
3PbO-
2Si02
PbO
0.03A12O3-
1.95SiO2
3PbO-Si02
3PbO
PbSO4
H20
White, trigonal
crystalline
powder
Pale yellow
powder
Reddish-yellow
powder
Fine, white
powder
Formulating lead-bearing glazes for ceramics,
source of PbO in glass manufacturing
Ceramic glazes
Glass and frit production
Providing long-term heat stability to PVC,
electrical insulation, activation for
azodicarbonamide blowing agents for vinyl
foam
Source: Carr(2003).
May 2006
2-6
DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-4. Lead Oxides: Names, Formulae, Physical Characteristics, and Uses
Name
Formula
Form
Uses
Lead Monoxide
PbO
Lead Dioxide
PbO2
Lead
Sesquioxide
Red Lead
Pb3O4
Reddish below 489°C,
yellow at high
temperatures
Brownish-black
crystalline powder of
fine flakes
Amorphous, orange-
yellow powder
Brilliant orange-red
pigment
Pastes for the grids of lead-acid batteries, optical,
electrical, and electronic glasses, glazes for fine
tableware, vulcanizing agent for rubber, lead soaps
used in driers as varnishes, high-temperature
lubricants, neutralizing agent in organic synthesis,
heat stabilizer in plastics, and starting material in
the production of pigments
Active material of the positive plates in lead-acid
batteries, oxidizing agent in the manufacture of
chemicals, dyes, matches, pyrotechnics, and liquid
polysulfide polymers, antifriction agent for plastic
sliding bearings, ballistic modifiers in high-energy
propellants, electrodes for seawater electrolysis,
filters for desulfurization of waste gases,
vulcanizing agents for butyl-rubber puncture-
sealing layers inside tires
Ballistic modifier for high-energy propellants,
cathode material in lithium batteries, additive to
increase the shattering force of explosives
Pigment in anticorrosion paints for steel surfaces,
lead oxide pastes for tubular lead-acid batteries,
ballistic modifiers for high-energy propellants,
ceramic glazes for porcelain, lubricants for hot
pressing metals, radiation-shielding foam coatings
in clinical x-ray exposures, and rubber adhesives
for roadway joints
Source: Carr(2003).
1 (PbO, PbsO^, and PbS. With the exception of the covalently-bound sulfide and oxide, these
2 compounds are derived from acids (or the related anions) that are common in the environment,
3 such as sulfuric acid (H2SO4), nitric acid (HNO3), carbonic acid (H2CO3), an acid that forms
4 when CO2 dissolves in water), and phosphoric acid (HsPO^. Lead salts, once formed, tend to be
5 only slightly soluble in neutral solutions, but are quite soluble in the presence of acid (Weast
6 etal, 1988).
May 2006
2-7
DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-5. Lead Compounds Observed in the Environment
Location
Observed Pb Compounds
Minerals
Smelting Aerosols
Coal Combustion Aerosols
Coal Combustion Flue Gases
Wood Combustion
Waste Incineration Aerosols
Soils Near Mining Operations
Motor vehicle exhaust (combustion of leaded fuel)
Roadside dust
Other mobile sources:
Brake wear, wheel weights
NASCAR vehicle emissions
Aircraft engine wear
Lawn mowers
PbS (Galena)
PbO (Litharge, Massicot)
Pb3O4 (Minium or "Red Lead")
PbCO3 (Cerussite)
PbSO4 (Anglesite)
Pb°, PbS
PbSO4,PbO,PbSO4.PbO
PbCO3
Pb silicates
PbS
PbSe
Pb°, PbO, PbO2 (Above 1150K)
PbCl2 (Law rank coals, above 1150K)
Pb$O4 (Below 1150 K)
PbCO3
PbCl2
PbO
PbCO3
PbSO4
[PbFe6(S04)4(OH)12]
[Pb5(P04)3Cl]
[Pb4S04(C03)2(OH)3]
PbS-Bi2S3
Pb oxides, silicates
PbBrCl
PbBrCl-2NH4Cl
PbBrCl-NH4Cl
PbSO4, Pb°, PbSO4 (NH4)SO4, Pb3O4,
PbO-PbSO4 and 2PbCO3-Pb(OH)2,PbSO4
Pb°
Pb halides
Pb°
Pb halides (Battery leakage)
aSource: Biggins and Harrison (1979, 1980).
1 Lead Coordination Chemistry, and Its Role in Biochemistry
2 The formation of coordinate covalent complexes represents a different class of chemical
3 interaction from the formation of simple covalent compounds and salts. "Coordinate covalent"
4 bonds form when anions or neutral molecules interact with metal ions in solution that are capable
May 2006
2-8
DRAFT-DO NOT QUOTE OR CITE
-------
1 of donating both of the electrons required to form a covalent bond. These molecules (or anions)
2 are called, "ligands," or "electron donors." Ligands possess a filled valence orbital with a
3 geometry that allows it to overlap to a substantial degree with an empty orbital associated with
4 the metal ion. In the case of Pb, its large atomic size is associated with several out-lying empty
5 atomic orbitals leading to a tendency to form a large number of coordinate covalent bonds
6 (Claudio et al., 2003). This is suggested by the coordination number (9) of PbCb, in its
7 crystalline form, which is able to share electrons with 9 adjacent chloride ions (Cl") (Douglas
8 etal., 1983).
9 Molecules capable of serving as ligands for metal ions in solution take many forms.
10 "Monodentate" ligands are molecules capable of providing 2 electrons to form a single
11 coordinate bond, such as water (H2O), ammonia (NH3); "multidentate" ligands can participate in
12 more than one coordinate bond. A common term for the binding of a metal ion by a multidentate
13 ligand is "chelation." The chelating agent, ethylenediaminetetraacetic acid (EDTA), is a well
14 known, hexadentate ligand, containing 6 functional groups capable of forming 6-coordinate
15 bonds with metal ions in aqueous solution. Proteins, particularly the active sites of enzymes,
16 contain functional groups—ususally associated with amino acid side chains—that can serve as
17 ligands for metal ions. In fact, the zinc finger proteins must form coordinate complexes with
18 Zn2+ ions to stabilize their active conformations (Claudio et al., 2003).
19 Several types of equilibrium constants for ligand-metal interactions can be derived,
20 depending on the property of interest. One formulation, the "binding constant (Kb)," between the
21 free metal ion and ligands in- solution, with the ligand-metal complex, is derived below, for a
22 negatively charged ligand:
23
[ML ""'l
24 Kb = binding constant = rAJT n*irT_., (2-2)
25 Where:
26 Kbl =-
27
28 Kb2 =
29
30 Etc.
May 2006 2-9 DRAFT-DO NOT QUOTE OR CITE
-------
1 KM provides a measure of the stability of a solution of the free metal ion, Mn+ and an
2 individual ligand, L, compared to the complex of MLn+. Alternatively, KM gives an indication of
3 the strength of the interaction between Mn+ and L. Thus, Kb2 indicates the strength of the
4 interaction between the MLn+ complex and an additional ligand, L. Subsequent additions of
5 ligands to the complex are described following the same convention. Binding constants are
6 useful, in particular, for evaluating the strength of interactions between metals and small
7 (monodentate) ligands. The form typically used to evaluate binding between metals and proteins
8 is the "dissociation" constant, Kd. The example given here is for a neutral ligand:
9
10 Kd = dissociatbn constant =- x"' \ (2-3)
[MLxn+]
11 Where:
dl~ [MLn+] '
13
14 K,, =
[ML2n+] '
15
16 Etc.
17
18 Kd is the inverse of Kb, in that it refers to stability of the existing complex between ligand
19 and metal, versus the free metal ion and the free ligand. K
-------
1 "hard bases," and soft acids prefer ligands based on larger atoms, such as sulfur and selenium,
2 i.e., "soft bases."
3 The HSAB concept is useful for understanding the behavior of Pb in the biological
4 context. Lead forms coordinate covalent bonds with ligand atoms with effectiveness that
5 declines with atomic size. For example, Pb forms especially stable bonds with sulfur and sulfur-
6 containing compounds, and somewhat less so with carboxylic acids (O-based ligands) and
7 imidazoles (N-based ligands) (Claudio et al., 2003).
8 In biological systems, Pb competes very effectively with native or homeostatic metal ions
9 for binding with the sulphahydryl, carboxyl and imidazole side-chains comprising enzyme active
10 sites. This competition leads to inhibition of enzyme activity, as well as the replacement of
11 calcium in bone and, ultimately, to a substantial list of negative human health effects. The
12 relative strength of these different interactions appears to be reasonably well-predicted by the
13 HSAB model.
14 By far, the most effective biological ligands for Pb are amino acid side-chains containing
15 sulfur and selenium. Smaller electron donors (hard bases), such as carboxylic acids that bind Pb
16 via electrons associated with oxygen, form weaker bonds. These complexes are generally more
17 labile, i.e., bonds form and break rapidly, thus allowing more effective competition at protein
18 binding sites amongst metals available in solution. Example simple ligands in this case are the
19 amine functional group, -NH, and the thiol functional group, -SH. The amine group has a Pb
20 binding constant on the order of 100, while the thiol group binding constant is on the order of
21 107. Example proteins in this instance are carboxypeptidase A, a zinc-binding protein, with
22 carboxylate and histidine side-chains, and the four cysteine zinc finger consensus peptide, CP-
23 CCC. Carboxypeptidase A has a Pb dissociation constant of approximately 10"4 M, versus that
24 of the zinc finger protein, which is 3.9 X 10"14 M. Claudio et al. (2003) concluded, on the basis
25 of these values, that carboxypeptidase A is unlikely to be a protein associated with Pb poisoning,
26 while cysteine-rich proteins, including the zinc enzyme, d-aminolevulinic acid dehydratase
27 (ALAD), the second enzyme in the heme biosynthetic pathway, are more likely targets. ALAD
28 active site, with its Cyss active site, is known to be inhibited at femtomolar (10"15 M)
29 concentrations of Pb in vitro.
30 Figure 2-1 illustrates the wide array of possible inhibitory interactions between Pb2+ and
31 proteins responsible for transduction at nerve synapses. Targets for Pb2+ interference at the
May 2006 2-11 DRAFT-DO NOT QUOTE OR CITE
-------
Figure 2.1 Multiple possible molecular targets for interference by Pb + ion at
nerve synapses.
Source: Nihei and Guilarte (2002).
4
5
6
7
8
9
10
presynaptic terminal include synaptic vesicles, ionotropic receptors, Ca2+ and other channel
proteins, and kinase proteins. At the postsynaptic interface, ionotropic proteins, dopamine
receptors, protein kinase-C isoenzymes and ion channel proteins are amongst the proteins subject
to interference by Pb2+ (Nihei and Guliarte, 2002).
Additional information concerning the physical aspects of Pb coordination chemistry and
its role in biological systems can be gotten from the substantial review by Claudio et al. (2003).
A complete discussion of the neuro- and other toxic effects associated with exposure to Pb can
be found in Chapter 5 of this document.
May 2006
2-12
DRAFT-DO NOT QUOTE OR CITE
-------
4
5
6
7
8
9
10
11
12
13
14
15
16
2.2 SOURCES OF LEAD
In this section, we summarize information on a number of major sources of lead,
categorized as natural sources, stationary point sources, and mobile sources. In addition to these
categories, fugitive emissions such as resuspension of lead in soil and dust can be important.
Resuspension is considered a transport route and is therefore discussed in Section 2.3.
2.2.1 Natural Sources
The common sources of natural Pb include volcanoes, sea-salt spray, biogenic sources,
wild forest fires, and wind-borne soil particles in rural areas with background soil concentrations.
Natural sources combined contribute an estimated 19,000 metric tons of Pb to the air each year
(Nriagu and Pacyna, 1988). However, there is significant variability in the Pb emissions from
volcanoes and forest fires and considerable uncertainty in biogenic and sea-salt emissions of Pb
(Nriagu, 1989). Table 2-6 shows the median value and the range of annual emissions worldwide
for natural sources of airborne Pb.
Table 2-6. Annual, Worldwide Emissions of Lead from Natural Sources
Amount Emitted: Range
Source (thousands of metric tons/yr)
Wind-borne soil particles
Seasalt Spray
Volcanoes
Wild Forest Fires
Biogenic, continental particulates
Biogenic, continental volatiles
Biogenic marine sources
Total
0.3-7.5
0.02-2.8
0.54-6.0
0.06-3.8
0.02-2.5
0.01-0.038
0.02-0.45
0.97-23
Amount Emitted: Median
(thousands of metric tons/yr)
3.9
1.4
3.3
1.9
1.3
0.20
0.24
12
Source: Nriagu (1989).
May 2006
2-13
DRAFT-DO NOT QUOTE OR CITE
-------
1 The natural lead emissions worldwide are somewhat greater than the estimated
2 3800 metric tons/year of lead emitted from anthropogenic stationary and mobile sources in the
3 U.S. in the year 2000 (U.S. Environmental Protection Agency, 2003). However, many countries
4 around the world have much greater lead emissions than the U.S. from stationary and mobile
5 sources, including several countries that still use leaded gasoline. Furthermore, the EPA estimate
6 does not account for emissions of lead in resuspended soil. Harris and Davidson (2005) estimate
7 that stationary and mobile source emissions account for only about 10% of the total lead
8 emissions in the South Coast Air Basin of California; the remaining 90% of the emissions are
9 from resuspended soil. The soil contains elevated lead levels because of the many decades of
10 leaded gasoline use. Therefore, on a worldwide basis, the anthropogenic emissions of lead are
11 expected to be much greater than natural emissions.
12 There are four stable isotopes of Pb: 204Pb, 206Pb, 207Pb, and 208Pb. The last three of these
13 isotopes are produced by decay of 238U, 235U, and 232Th respectively. The concentrations of
14 natural vs. anthropogenically derived Pb in environmental media are often determined through
15 isotopic ratios. Most minable Pb ores exhibit ratios of 206Pb/207Pb between 0.92 and 1.20
16 (Erel et al., 1997). Rock released or "natural" Pb, however, generally exhibits a higher
17 206Pb/207Pb ratio.
18 Deep soil samples converge to ratios of 206Pb/207Pb ~ 1.21 and 208Pb/206Pb ~ 2.05 which
19 are considerably different than the natural ratios found in adjacent bedrock (Erel et al., 1997).
20 For more information on isotopic ratios of lead and their uses as environmental tracers, see
21 Chapter 8 of this document.
22 Natural aerosol Pb tends to have large particle sizes (Reuer and Weiss, 2002). As a result,
23 it deposits rapidly and has an atmospheric residence time of a few hours to -10 days (Reuer and
24 Weiss, 2002). The average downward flux is estimated as 0.012 mg nT2 yr"1 for natural Pb in all
25 forms (Hindier et al., 1999).
26 Concentrations of lead in the air and soil have most likely been elevated by anthropogenic
27 activities at least since the rise of the Greek and Roman societies, both of which used Pb
28 extensively. The natural, background concentration of Pb in soil is approximately 10 to 15 ppm
29 (Bindler et al. 1999; Erel et al., 1997). This is significantly higher than the adjacent bedrock but
30 is approximately equal to concentrations found in bedrock residues such as quartz and clay (Erel
31 et al., 1997). An estimated 3.1 x 1014 metric tons of Pb are dispersed within the continental crust
May 2006 2-14 DRAFT-DO NOT QUOTE OR CITE
-------
1 (Reuer and Weiss, 2002). Of this, approximately 9.3 x 107 metric tons of Pb are found in Pb
2 ores. Table 2-7 lists the naturally occurring concentrations of Pb in bedrocks, ocean crusts, and
3 continental crusts. Spatially, background levels of lead vary considerably.
Table 2-7. Naturally Occurring Lead Concentrations in Major Rock Types
Lithology Natural Lead Concentration (ppm)
Continental Crust 15.0
Oceanic Crust 0.9
Basalts, Gabbros 3.5
Limestones 5.0
Granulites 9.8
Greywackes 14.0
Gneisses, Mica Schists 22.0
Shales 22.0
Granites 32.0
Source: Reuer and Weiss (2002).
4 Natural Pb in surface water is derived from four different sources: biogenic material,
5 aeolian particles, fluvial particles, and erosion (Ritson et al., 1994). About 90% of natural Pb in
6 surface waters is in the dissolved phase (Reuer and Weiss, 2002). Organic ligands are
7 complexed with 50 to 70% of this Pb with the balance found in inorganic compounds (Reuer and
8 Weiss, 2002). Biological particles in the open ocean scavenge a significant portion of the Pb
9 complexes, which have an estimated two-year residence time in the surface waters (Reuer and
10 Weiss, 2002).
11 A naturally occurring, radioactive isotope of Pb, 210Pb, is commonly studied as a tracer to
12 determine how particles are transported through the environment. The source of 210Pb is the 238U
13 decay series. In this process, gaseous 222Rn is produced, which escapes from the soil and enters
14 the atmosphere. As radon decays into 210Pb, the particulate Pb deposits onto soils and surface
May 2006 2-15 DRAFT-DO NOT QUOTE OR CITE
-------
1 waters all over the world. The surfaces of all soils have been exposed to atmospherically derived
2 Pb particles (Bindler et al., 1999).
3 Particles of 210Pb tend to be submicron, with an average size of 0.53 jim AMD (Winkler
4 et al., 1998). The mean residence time for 210Pb in the air is approximately 4 to 5 days but has
5 been estimated as long as 8 days with some seasonal variability (Winkler et al., 1998). The
6 downward flux has been estimated as 136 Bq nT2 yr"1 for 210Pb (Joshi et al., 1991). This results
7 in natural, background concentrations in the soil of <0.1 |ig/g (Bindler et al., 1999).
8 Atmospheric deposition is likely the largest source of 210Pb to water bodies. Leaching
9 of Pb naturally contained in host rock is a very small source to water (Toner et al., 2003).
10 In surface waters, 210Pb is primarily in particulate form, while dissolved Pb is transported more
11 readily (Joshi et al., 1991). Dissolved 210Pb is scavenged by suspended matter (Carvalho, 1997).
12 The residence time of dissolved 210Pb is approximately 30 days although partial re-dissolution
13 from bottom sediments probably occurs (Carvalho, 1997). One estimate found that -56% of
14 atmospherically derived 210Pb in lakes of the Canadian Shield was retained in the sediment
15 (Joshi etal., 1991).
16 Many authors have measured concentrations of 210Pb in plants (including foodstuffs) and
17 animals (including humans). Holtzman (1978) summarized these measurements. Concentrations
18 in United States vegetation range between 30 pCi/kg and 70,000 pCi/kg for wheat and lichens
19 respectively. The estimated human consumption of 210Pb from vegetation averages 1.4 pCi/day
20 in the United States. Overall the concentrations of 210Pb in animals vary significantly depending
21 on the type of tissue or organ measured. However, concentrations are generally higher in
22 animals with higher rates of Pb intake.
23
24 2.2.2 Lead Emission in the U.S.
25 Figures 2-2 and 2-3 show annual air emissions rates for U.S. Pb sources (10 tons per year
26 [TPY] or greater) for 1990 and 2002. These data were extracted from the National Emissions
27 Inventory (NEI), the database of hazardous air pollutant (HAPs) and criteria air pollutant (CAPs)
28 sources and annual emissions rates (U.S. Environmental Protection Agency, 2006b). EPA
29 collects NEI CAP data under the Consolidated Emissions Reporting Rule (CERR) (40 CFR
30 Part 51). The CERR specifies two sets of reporting thresholds for CAPs. Type A (large sources)
31 must report annually, while Type B sources must report every three years. For the 2002 NEI,
May 2006 2-16 DRAFT-DO NOT QUOTE OR CITE
-------
1990 Pb Sources Emitting 10 Tons/year or More
_| Mobile Sources
pH Primary Lead Smelting
[] Integrated Iron and Steel Manufacturing
r il Muncipal Waste Combustors
I' J Iron and Steel Forging
|| Inorganic Pigments Manufacturing
| Pulp and Paper Production
III Secondary Lead Smelting
[-1-3 Secondary Copper Smelting
|~l| Industrial/Commercial/ Institutional Boilers Process Heaters
Erf Iron and Steel Foundries
n A Hazardous Waste Incineration
J Secondary Nonferrous Metals
| Primary Copper Smelting
] Utility Boilers: Coal
F^TI Medical Waste Incinerators
\ | Lead Acid Battery Manufacturing
LJ Pressed and Blown Glass and Glassware Manufacturing
B_J Primary Nonferrous Metals—Zinc. Cadmium and Beryllium
^3 Aulobody Refinishing Paint Shops
^^ Sewage Sludge Incineration
Q| Asphalt Processing and Asphalt Roofing Manufacturing
I Hydrochloric Acid Production
rt\ Petroleum Refineries - Catalytic Cracking. Catalytic Reforming, & Sulfur Plant Units
[ \] Secondary Aluminum Production
^| Paints and Allied Products Manufacturing
rS I Fabricated Structural Metal Manufacturing
PJ Clay Ceramics Manufacturing
f\\ Synthetic Organic Chemical Manufacturing (HON)
| | Utility Boilers: Oil
fiy Motor Vehicle Parts and Accessories
| Nonferrous Foundries, Not Elsewhere Classified
J Portland Cement Manufacturing
F3 Copper Ores
Figure 2-2. Lead emissions sources and rates for the U.S. (1990). Emissions, including all
sources in 1990, totaled 3598 tons.
May 2006
2-17
DRAFT-DO NOT QUOTE OR CITE
-------
2002 Pb Sources Emitting 10 Tons/year or More
K-:-l Iron and Steel Foundries
I —I Industrial/Commercial/ Institutional Boilers Process Heaters
tM Utility Boilers: Coal
['/| Mobile Sources
pj Portland Cement Manufacturing
J Hazardous Waste Incineration
[ 11 Electric Services
i J National Security
| ] Muncipal Waste Combustors
II Integrated Iron and Steel Manufacturing
f^^ Pressed and Blown Glass and Glassware Manufacturing
A Secondary Nonferrous Metals
\ Lead and Zinc Ores
Lead Acid Battery Manufacturing
Stainless and Nonstainless Steel Manufacturing: Electric Arc Furnaces (EAF)
Primary Copper Smelting
Primary Metal Products Manufacturing
Utility Boilers: Oil
Industrial Inorganic Chemical Manufacturing
Airports. Flying Fields, and Airport Terminal Services
Refuse Systems
Electric and Other Services Combined
Minerals and Earths, Ground or Otherwise Treated
Pulp and Paper Production
Secondary Copper Smelting
Ferroalloys Production: Ferromanganese and Silicomanganese
Figure 2-3. Lead emissions sources and rates for the U.S. (2002). Emissions, including all
sources in 2002, totaled 1726 tons.
4
5
EPA collected information on both Type A and Type B sources. (For more information
on the CERR, see:/www.epa.gov/ttnchiel/cerr/index.html). EPA collects NEI HAP data from
State, local and tribal air agencies every three years on a voluntary basis.
The NEI contains estimates of facility-specific HAP and CAP emissions and their source-
specific parameters necessary for modeling such as location and facility characteristics (stack
May 2006
2-18
DRAFT-DO NOT QUOTE OR CITE
-------
1 height, exit velocity, temperature, etc.). Complete source category coverage is needed, and the
2 NEI contains estimates of emissions from stationary point and nonpoint (stationary sources such
3 as residential heating that are inventoried at the county level) and mobile source categories. The
4 NEI contains individual stack and fugitive estimates at individual geocoordinates for point
5 sources. County level estimates are provided in the NEI for nonpoint and mobile sources. Point
6 source categories of HAPs include major and area sources as defined in Section 112 of the CAA.
7 Nonpoint source categories of HAPs include area sources and other stationary sources that may
8 be more appropriately addressed by other programs rather than through regulations developed
9 under certain air toxics provisions (Sections 112 or!29) in the CAA.
10 Another source of information on Pb emissions within the U.S. is the EPA Toxics Release
11 Inventory (TRI) (U.S. Environmental Protection Agency, 2006a). Reported emissions in the air
12 in 2004, including fugitive and point source emissions from facilities, total over 1 million
13 pounds. Further information about the TRI can be found at (http://www.epa.gov/ebtpages/
14 emerreportingtoxicsreleaseinventorytri.html).
15 The TRI is updated annually and provides a rough estimate of temporal and spatial trends
16 in lead emissions. The NEI is somewhat more comprehensive but is updated less frequently.
17 Temporal and spatial analyses of lead emissions nationwide are presented at the end of this
18 chapter.
19
20 2.2.3 Stationary Sources
21 Emissions estimates and measurements on a per facility basis are scarce. The AP-42
22 document of the EPA includes emission factors for many different processes and operations.
23 For lead-processing facilities, these emission factors are usually expressed as grams of Pb
24 emitted per kg of Pb processed (U.S. Environmental Protection Agency, 2005). In general,
25 AP-42 data are not listed in the following sections except in the absence of newer, more robust or
26 peer-reviewed data on process emissions. Although AP-42 emission factors can provide a first
27 order estimate, they are limited in that they are often derived from one individual source and do
28 not reflect the variability between sources (U.S. Environmental Protection Agency, 2006c).
29 Also, in many cases, AP-42 emission factors do not account for process parameters. In some
30 cases, AP-42 may complement the data listed below, and the reader is referred there for emission
May 2006 2-19 DRAFT-DO NOT QUOTE OR CITE
-------
1 factors not given in this chapter. Up-to-date, accurate emissions estimates are critical as inputs
2 to models predicting airborne concentrations, and more research in this area is needed.
3
4 Primary and Secondary Lead Smelters
5 Primary Pb smelting is the process by which elemental Pb is recovered from Pb ore.
6 Lead ore is primarily in the form of galena (PbS) but can also occur as plattnerite (PbO2),
7 cerussite (PbCOs), and anglesite (PbSO4) (Reuer and Weiss, 2002). Producing elemental Pb
8 from ore involves three processes - sintering, reduction, and refining - each with its own
9 characteristic emissions. Primary Pb production in the United States emitted about 565 metric
10 tons of Pb in 2000, approximately 14.7% of total anthropogenic Pb emissions in the United
11 States (U.S. Environmental Protection Agency, 2003).
12 Secondary Pb smelters reclaim scrap Pb. Both the principal input to and the principal
13 major product market of secondary smelters are lead-acid batteries. Secondary Pb production
14 contributed 82% of total Pb production in 2003 (USGS, 2003). Secondary Pb production in the
15 United States emitted about 422 metric tons of Pb in 2000, approximately 11.0% of total
16 anthropogenic Pb emissions in the United States (U.S. Environmental Protection Agency, 2003).
17 Although recycling of lead-acid batteries with minimal emissions may be possible (Socolow and
18 Thomas, 1997) secondary smelters and battery recycling facilities are still one of the most
19 significant stationary sources of airborne lead emissions.
20 The quantity of Pb emitted from a given facility is highly variable and depends on facility
21 processes and meteorological conditions such as wind speed and ambient temperature.
22 Emissions estimates are typically performed through direct measurements, mass balances,
23 process models, inverse inferences, or emissions factors (Frey and Small, 2003).
24 Emissions from smelters have been measured in several cases. A survey of approximately
25 50 European Pb smelters had mean emission factors of 0.1 grams and 0.05 grams of Pb emitted
26 per kg of Pb processed for primary and secondary Pb smelters respectively (Baldasano et al.,
27 1997). Measurements of emissions from the blast furnace of a primary smelter were between
28 1.2 and 3.8 kg Pb/hr (Bennett and Knapp, 1989). The acid-sinter at the same plant emitted
29 between 0.4 and 8.5 kg Pb/hr (Bennett and Knapp, 1989). Emissions occur during every stage of
30 the overall smelting process. Because the process emissions mostly are controlled to conserve
31 raw materials, the largest source of emissions is likely to be fugitive dust from the transport,
May 2006 2-20 DRAFT-DO NOT QUOTE OR CITE
-------
1 grinding, and storage of battery scrap (Kimbrough and Suffet, 1995), which by definition is
2 uncontrolled.
3 Much work has been done to determine the species of Pb emitted from the various
4 smelting processes. The fraction of Pb in particulate matter (PM) emissions varies significantly
5 between processes and depends on the type of furnace used. However, Pb is often the dominant
6 element in smelter emissions. Lead can be emitted either in PM or in fumes. Lead fume
7 emissions are particularly high if Pb blast furnace bullion is transferred in an open ladle (Wang
8 and Morris, 1995). Major components of particulate Pb emissions are PbS, PbSC>4, PbSCVPbO,
9 and elemental Pb, and minor species are PbCOs, PbO, Pb silicates, and PbO litharge (Batonneau
10 et al, 2004; Harrison and Williams, 1983; Ohmsen, 2001; Sobanska et al, 1999; Rieuwarts and
11 Farago, 1995).
12 The distribution of particle sizes varies depending on temperature, process, and the
13 conditions of each facility. Ohmsen (2001) found that Pb emissions from a blast furnace tend to
14 be less than 1 jim in size and have a smaller diameter than particulate emissions from either the
15 sintering process or storage areas. Higher temperatures (>600 °C) in the blast furnace tend to
16 produce emissions with finer particle sizes. Dusts from the raw materials area tend to fall
17 between 10 and 100 |im, while dusts from the refinery tend to fall between 1 and 30 |im
18 (Ohmsen, 2001). Sobanska et al (1999) found that just 15% of dust particles by mass emitted
19 from a "water jacket" furnace were smaller than 10 jim and the remaining 85% fell between
20 10 and 100 |im. The measurements of Harrison et al. (1981) at a primary smelter found that
21 particles derived from combustion processes were typically between 0.1 and 2 jim, but particle
22 size measurements showed that these particles could agglomerate to more than 10 jim if they are
23 confined to ventilation ducts. Reported sizes from primary smelting processes are shown in
24 Table 2-8.
25 The concentrations of Pb in stack outlets have been measured in several cases.
26 Measurements taken at the stack of a blast furnace at a primary smelter ranged between 3.67 and
27 7.32 mg/m3 (Bennett and Knapp, 1989). Stack concentrations at the sinter plant of the same
28 facility ranged between 4.48 and 71.0 mg/m3 (Bennett and Knapp, 1989). Two stacks on a blast
29 furnace at a secondary smelting facility had Pb concentrations of 0.002 and 0.0137 mg/m3
30 (Sturges and Harrison, 1986). The average values of approximately 50 European smelters were
31 2 mg/m3 for both primary and secondary smelters (Baldasano, et al., 1997).
May 2006 2-21 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-8. The Mass-Median Aerodynamic Diameters for Particles During Various
Processes at Primary Lead Smelters
Primary Smelter
Process
Raw Materials
Sinter
Blast Furnace
Copper Drosser
Refinery
Harrison et al.
(1981)
—
5.1 um
3.4 um
9.4 um
—
Average Particle Size
Ohm sen
(2001)
40 um (range = 10-100 um)
range = 10-300 um
90% of particles were <1 um
range = 10-300 um
range = -1-100 um,
mostly <20 um
Bennett and Knapp
(1989)
—
0.91 um, 80% of
particles <10 um
1.1 um, 88% of
particles <10 um
—
—
Note: Where there were multiple data points, geometric means were used. Data for Harrison et al. (1981) were
occasionally given as >11 um. These values were replaced with 11 um before calculating the geometric mean.
Thus, these values represent a lower limit.
Source: Harrison et al. (1981), Ohmsen (2001), Bennett and Knapp (1989).
1 The ambient air concentrations in the immediate vicinity of smelters tend to be elevated to
2 varying degrees depending on facility operations and meteorological conditions. In the UK, an
3 increase of 15 |ig/m3 in the local ambient air was attributed to the emissions of a single
4 secondary Pb smelter (Sturges and Harrison, 1986). Harrison and Williams (1983) measured
5 concentrations of 15.8 |ig/m3, 0.691-5.1 |ig/m3, and 0.151-4.54 |ig/m3 at sites 500 m, 700 m, and
6 1200 m from the stacks of a primary smelter respectively. Fenceline measurements at two
7 secondary smelters located in California ranged between 0.85 and 4.0 |ig/m3 (Kimbrough and
8 Suffet, 1995). Air concentration data measured at 50 m, 500 m, and 800 m from the plant were
9 slightly lower but generally the same order of magnitude as the fenceline values. Ambient
10 concentrations measured at 12 sites within several hundred meters of three secondary Pb
11 smelters in Manitoba were elevated (Tsai, 1987). The geometric means of these samples, which
12 were taken over three month time spans, ranged between 0.107 and 1.69 |ig/m3. Additionally,
13 the area was shown to be much less likely to meet the Manitoba guideline of <5 |ig/m3 for a
14 24-hour average when the smelters were operating than when they were not.
15
May 2006 2-22 DRAFT-DO NOT QUOTE OR CITE
-------
1 Non-Lead Metallurgical Processes
2 Emissions of Pb from non-lead smelters can be significant. Emissions from smelters,
3 metal works, and metal refineries depend on the type of equipment used to process the metals,
4 the concentrations of Pb in the initial material (ore, recycled material, or alloy), the type and
5 effectiveness of pollution controls at the facility, and the temperature of operations (Pacyna,
6 1986). Little work has been done to speciate Pb emissions from metallurgical facilities, although
7 Pb emissions from a primary copper-nickel smelter are primarily in the form of PbO (Barcan,
8 2002). The emissions of Pb from non-lead metallurgical processes are summarized in Table 2-9.
9
10 Ore Mining and Processing
11 Lead mining occurs in 47 countries, although primary Pb production is on the decline
12 (Dudka and Adriano, 1997). World mine production of Pb is approximately 2.8 million metric
13 tons per year (Wernick and Themelis, 1998). The reserve base of Pb is estimated to be about
14 120 million metric tons, which will sustain current rates of mine production for 43 years
15 (Wernick and Themelis, 1998).
16 Mines can be a significant source of metal emissions to the atmosphere. Lead and zinc
17 ores, which are often mined together, frequently contain high concentrations of cadmium and
18 arsenic (Pacyna, 1986). An emission factor for Pb mines has been reported as 0.91 grams of Pb
19 emitted to the air per kg of Pb mined (Pacyna, 1986).
20 Since Pb is mined in the form of galena (PbS), emissions from Pb mines tend also to be in
21 the form of galena (Dudka and Adriano, 1997). However, other species have been detected.
22 In mine spoils, Pb is typically galena and secondary alternation products such as plumbojarosite
23 [PbFe6(SO4)4(OH)i2] (Rieuwerts and Farago, 1995). Other Pb forms detected in the vicinity of
24 mines are pyromorphite [Pbs^O^Cl], which has a low bioavailability, PbCOs which is formed
25 from the weathering of galena in the soil, leadhillite [Pb4SO4(CO3)2(OH)2], PbS'Bi2S3, Pb
26 oxides, Pb silicates, and PbSC>4 (Rieuwerts and Farago, 1995).
27 Although mining can be considered a point source to air, mine wastes can have a major
28 widespread effect on soil and water (Riewerts and Farago, 1995). Mines produce four different
29 types of large-volume waste: mine waste, which consists of overburden and barren rocks,
30 tailings, dump heap leachate, and mine water (Dudka and Adriano, 1997). Tailings especially
31 are major sources of metal contamination to soil and water (Bridge, 2004). Acid mine drainage
May 2006 2-23 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-9. The Emissions of Lead from Non-Lead Metallurgical Processes
to
o
o
Metallurgical Plant
Lead Emissions
Particle Sizes
MMAD = Mass median
aerodynamic diameter
Location
Source
O
O
2
O
H
O
c
o
H
W
O
V
O
Aluminum (secondary)
Aluminum (secondary)
Aluminum (secondary) -
burning drying
Aluminum (secondary) -
reverberatory furnace
Antimony
Antimony
Brass/Bronze refinery
Brass/Bronze refinery - blast
furnace
0.81±0.014% of PM emissions
0.098±0.031% of PM emissions
1.01x10-3-3.52x10-3 kg/mt
produced (venturi scrubber)
3.38x10-6-7.40x10-6 kg/mt
produced (baghouse)
1.05x10-2-1.13x10-2 kg/mt
produced (multiple cyclones)
5.0xlO"4-l.lxlO"3 kg/mt processed
(baghouse)
0.17±0.04% of PM emissions
0.11±0.02% of PM emissions
0.01-1% of PM emissions
16 g/ton produced
Brass/Bronze refinery - crucible 10 g/ton produced
furnace
Brass/Bronze refinery - cupola 65 g/ton produced
furnace
Brass/Bronze refinery -
reverberatory furnace
60 g/ton produced
Fine (< 2.5 um)
Coarse (2.5-10 um)
Brass/Bronze refinery - rotary 60 g/ton produced
furnace
n.a.
n.a.
Fine (< 2.5 um)
Coarse (2.5-10 um)
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
Philadelphia, USA
Philadelphia, USA
US
US
Philadelphia, USA
Philadelphia, USA
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
Olmezetal. (1988)
Olmezetal. (1988)
U.S. EPA (1998)
U.S. EPA (1998)
Olmezetal. (1988)
Olmezetal. (1988)
Lee & VonLehmden (1973)
Pacyna (1986)
Pacyna (1986)
Pacyna (1986)
Pacyna (1986)
Pacyna (1986)
-------
Table 2-9 (cont'd). The Emissions of Lead from Non-Lead Metallurgical Processes
to
o
o
Metallurgical Plant
Lead Emissions
Particle Sizes
MMAD = Mass median
aerodynamic diameter
Location
Source
O
O
2
O
H
O
c
o
H
W
O
V
O
Brass/Bronze production
Copper-Nickel
Copper-Nickel
Copper-Nickel (primary)
Copper-Nickel (primary)
Copper-Nickel (primary)
Copper (primary) smelter
Copper (primary) converter
Copper (secondary)
reverberatory furnace
Copper (secondary) smelter
Copper Smelter - furnace
Copper Smelter - sinter
Copper Smelter (secondary)
Iron Ore Recovery and
Ni refinery
25 kg/mt produced (high-leaded
alloys)
6.6 kg/mt produced (red and
yellow lead alloys)
2.5 kg/mt produced (other alloys)
184mt/yr, 21 kg/hr
13.4 mt/year
0.6-1.4% of PM emissions
2.3-3.6 kg/ton produced
3.1 kg/ton produced
3.0x 10~2 kg/ton produced
0.27 kg/ton produced
2.5 - 25 kg/mt produced
5.0*10~4 kg/mt processed
0.24-0.52 kg/hr
below detection
54-214 g/ton produced
6 mt/year
n.a.
1.2 urn MMAD
0.9 urn MMAD
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
0.87 urn MMAD
<0.10 urn MMAD
n.a.
Coarse (2.5-10 urn)
US U.S. EPA (1998)
Copper Cliff, Ontario Chan & Lusis (1986)
Falconbridge, Ontario Chan & Lusis (1986)
Monchegorsk, Russia Barcan (2002)
Poland Pacyna (1986)
n.a. Pacyna (1986)
US U.S. EPA (1998)
US U.S. EPA (1998)
US U.S. EPA (1998)
US
n.a.
n.a.
n.a.
U.S. EPA (1998)
Bennett &Knapp( 1989)
Bennett &Knapp (1989)
Pacyna (1986)
Copper Cliff, Ontario Chan & Lusis (1986)
-------
Table 2-9 (cont'd). The Emissions of Lead from Non-Lead Metallurgical Processes
to
o
o
Metallurgical Plant
Lead Emissions
Particle Sizes
MMAD = Mass median
aerodynamic diameter
Location
Source
O
O
2
O
H
O
c
o
H
W
O
V
O
Iron foundry cupola
Iron foundry -reverberatory
furnace
Iron foundry - electric induction
furnace
Iron foundry - casting
Iron and Steel foundry
Steel works - electric-arc
furnace
Zinc-Cadmium (primary)
Zinc Smelter - furnace
Zinc Smelter - sinter
0.05-1.10 kg/mt produced
(no control device)
7.80xlO"4 kg/mt processed
(afterburner, venturi scrubber)
6.95x10-4-2.23x10-3 kg/mt
produced (baghouse)
6.00xlO"3-7.00xlO"2kg/mt
produced (no control device)
4.45 xlO'3-5.00xlO-2 kg/mt
produced (no control device)
2.40x 10"3 kg/mt processed
(afterburner, venturi scrubber)
0.01-0.1% of PM emissions
4.1-16.3 g/ton produced
1.2-25 kg/ton produced
0.86-1.5 kg/hr
3.6-6.0 kg/hr
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
1.8-2.2 urn MMAD
0.9-2.1 urn MMAD
U.S.
U.S.
U.S.
U.S.
n.a.
n.a.
n.a.
n.a.
n.a.
U.S. EPA (1998)
U.S. EPA (1998)
U.S. EPA (1998)
U.S. EPA (1998)
Lee & Von Lehmden (1973)
Pacyna (1986)
Pacyna (1986)
Bennett & Knapp (1989)
Bennett & Knapp (1989)
Source: Olmez et al. (1988), Lee and Von Lehmden (1973), Pacyna (1986), Chan and Lusis (1986), Barcan (2002), Bennett and Knapp (1989).
-------
1 can contain highly elevated levels of Pb, >3000 |ig/L, and can contaminate vast areas (Bridge,
2 2004; Kurkjian et al., 2004). Soil contamination from both active and abandoned mines can be a
3 significant source of airborne lead from fugitive or wind blown matter. Resuspension of
4 contaminated soil is addressed later in this chapter, and soil lead concentrations near mines are
5 discussed in Chapter 3.
6 Mining of materials other than Pb can also release Pb to the atmosphere. Zinc-copper
7 ores, for example, contain Pb in the range of 100-100,000 ppm (Lee and Von Lehmden, 1973),
8 and about 6.1% of all Pb in the United States is extracted from "zinc mines" (Dudka and
9 Adriano, 1997).
10 In an underground gold mine, high lead-particulate concentrations were associated with
11 blasting (Annegarn et al., 1988). These particles were primarily Pb oxides and submicron in
12 size. A source apportionment analysis on airborne PM in an underground gold mine found that
13 the significant sources of Pb were rock dust and diesel exhaust (McDonald et al., 2003).
14 Concentrations of airborne Pb inside the mine were measured at 0.21 |ig/m3.
15
16 Stationary External Combustion: Coal Combustion
17 Coal is commonly burned as a fuel for utilities, industries, and commercial and
18 institutional facilities. Coal combustion can be a significant local source of Pb emissions as well
19 as a considerable regional source of airborne Pb.
20 Coal is pulverized, fluidized, or gasified before combustion. Generally, Pb impurities will
21 volatilize early in the combustion process although the precise rate of vaporization depends on
22 the distribution of Pb particles in the coal and the particle sizes (Lockwood and Yousif, 2000).
23 As Pb vapors cool they will condense, either forming individual particles or condensing on the
24 surface of ash particles (Lockwood and Yousif, 2000; Furimsky, 2000; Clarke, 1993; Pacyna,
25 1986). A high surface area to volume ratio makes fine ash particles better candidates for surface
26 sorption than coarse particles. Additionally, recondensed Pb particles tend to be fine, with an
27 average size of 0.2 jim (Lockwood and Yousif, 2000). The fine fraction of PM from coal
28 combustion has an enrichment factor of approximately 22 (Lockwood and Yousif, 2000).
29 The primary contributor of Pb emissions from coal combustion is the Pb content of the
30 coal itself. Lead is present in all coal samples in varying amounts, depending on the location of
31 the coalfield and even the location of the coal sample within a coalfield. Generally, Pb is present
May 2006 2-27 DRAFT-DO NOT QUOTE OR CITE
-------
1 in trace amounts in the form of PbS, but can also be present as pyrite and PbSe (Lockwood and
2 Yousif, 2000; Mukherjee and Srivastava, 2005). The rank of the coal - either bituminous,
3 subbituminous, or lignite - does not seem to correlate with the quantity of trace elements
4 (Mukherjee and Srivastava, 2005). The age of the coal also does not seem to impact the
5 concentration of Pb (Ghosh et al., 1987). The most important factors contributing to Pb content
6 of uncombusted coal seems to be local environmental conditions at the time the coal formed and
7 the relative proportions of organic and inorganic matter (Pacyna, 1986; Ghosh et al., 1987).
8 Globally, the concentrations of Pb in coal range between 2 and 80 ppm (Mukherjee and
9 Srivastava, 2005). Table 2-10 lists the range of Pb concentrations measured in four different
10 coal components.
Table 2-10. The Range of Lead Concentrations in Coal Lithotypes
Coal Lithotype Range of Lead Concentrations (ppm)
Vitrain 0.30-16.17
Clarain 4.84-17.55
Durain 4.10-11.76
Fusain 3.64 - 15.60
Source: Ghosh etal. (1987).
11 Coal is often combined with limestone to attenuate sulfur dioxide emissions. However,
12 limestone can contain trace elements and has been shown to increase emissions of Pb by four to
13 six times in a fluidized bed system compared to tests performed without a limestone addition
14 (Clarke, 1993). Other measurements performed on a fluidized bed system found that increasing
15 limestone increased particulate emissions of Pb but decreased gaseous emissions of Pb. The
16 overall emissions of Pb (gaseous + particulate) remained relatively constant (Furimsky, 2000).
17 Limestone had a negligible effect on pressurized fluidized bed systems although Pb emissions
18 from gasification systems may increase with limestone additions (Clarke, 1993).
19 Emissions from coal combustion depend a great deal on the process conditions at a given
20 facility. In addition to the type of boiler, conditions such as temperature, heating rate, exposure
21 time at elevated temperatures, and whether the environment is oxidizing or reducing can affect
May 2006 2-28 DRAFT-DO NOT QUOTE OR CITE
-------
1 emissions (Pacyna, 1986). For Pb, changes in the temperature affect the size of particles, the
2 amount of Pb in the vaporized fraction, and the species of the emissions. At combustion
3 temperatures of 1800 K, about 0.1% of the total ash produced was vaporized (Lockwood and
4 Yousif, 2000). At 2800 K the vaporized fraction of the ash was increased to 20%. Additionally
5 the ratio of air to coal during combustion can have a major effect on emissions (Furimsky, 2000).
6 In a fluidized bed system, increasing the air to coal ratio from 1.0 to 1.10 decreased the gas to
7 solid ratio for Pb emissions from 1.5 to 0.18 (Furimsky, 2000).
8 Uncontrolled combustion of coal can occur - usually as natural, in-ground coal fires - and
9 such combustion can emit Pb (Finkelman, 2004). Although such fires may have local
10 importance, they are not discussed in detail here.
11 Controlled combustion is the norm for industries and utilities. The major pollution
12 control systems are electrostatic precipitators (ESP), wet scrubbers, and baghouses. In general,
13 pollution control systems are most effective at removing large particles and are least effective at
14 removing submicron particles. ESPs are highly efficient and can remove particulates with
15 >99.9% efficiency depending on particle size, ash resistivity, flue gas temperature, and moisture
16 content (Clarke, 1993). ESPs are used at more than 90% of coal-fired utility boilers in the
17 United States (Senior et al., 2000). Particles that escape EPSs are typically in the range of
18 0.1-1.0 |im in diameter (Senior et al., 2000). Wet scrubbers are also more than 99% efficient
19 (Pacyna, 1986). The majority of particles that escape are <2 jim in size (Pacyna, 1986).
20 Wet scrubbers are used less commonly than ESPs and baghouses (Senior et al., 2000).
21 Baghouses or fabric filters are frequently used by coal-fired utilities. As with ESPs and wet
22 scrubbers, the collection efficiency of baghouses is a function of particle size (Senior et al.
23 2000). Baghouses are >99% effective with mass emissions averaging <20 mg/m3 (Clarke,
24 1993).
25 Very little information is published regarding the actual quantity of Pb emitted from coal-
26 fired boilers. The EPA AP-42 program publishes emission factors for typical coal-fired boilers,
27 although using process data specific to a given facility is likely to be more accurate. Clarke
28 (1993) reports emissions from fluidized beds. Of the processes tested, the emissions of Pb were
29 highest from a 0.5 m bed with a limestone sorbent, second highest with a 1.0 m bed without a
30 limestone sorbent, and lowest with a 0.5 m bed without a limestone sorbent (Clarke, 1993).
31 Reducing the depth of the fluidized bed by 50% decreased the emissions of trace elements by
May 2006 2-29 DRAFT-DO NOT QUOTE OR CITE
-------
1 ~5 to 50% probably because deeper beds undergo attrition of ash (Clarke, 1993). Olmez et al.
2 (1988) report the Pb mass fractions of PM in a stack of a coal-fired power plant. For fine
3 particles, Pb constituted 0.04 ± 0.004%. For coarse particles, Pb constituted 0.03 ± 0.002%.
4 Coal combustion products that underwent long-range transport from the coal-fired power plants
5 of the Midwest contributed an estimated 0.05 |ig/m3 to the ambient air in Boston (Thurston and
6 Spengler, 1985). Table 2-11 lists the emission factors for three different types of coal, in three
7 different types of power plants.
Table 2-11. Emission Factors of Lead for Coal Combustion in Three Different Furnaces.
Rank
Bituminous with control
device
Bituminous without
control device
Subbituminous with
control device
Lignite with control
device
Pulverized coal
Anthracite
Cyclone Furnace
8.5xlO"14kg/J
2.10xlO"4kg/mt
2.18xl(T13kg/J
1.03xl(r13kg/J
1.44xl(r14kg/J
507 lb/1012 Btu
Stoker Furnace
128xlO"13kg/J
2.18xl(r13kg/J
1.56xl(r13kg/J
2.17xl(r14kg/J
4.45xlO"3kg/mt
Pulverized Furnace
5.5xlO"14kg/J
2.10xlO"4kg/mt
2.18xl(r13kg/J
6.2xl(T14kg/J
92xl(T13kg/J
Source
Pacyna (1986)
U.S. EPA (1998)
U.S. EPA (1998)
Pacyna (1986)
Pacyna (1986)
U.S. EPA (2005)
U.S. EPA (1998)
Source: Pacyna (1986), U.S. Environmental Protection Agency (1998, 2005).
10 The species of Pb emitted from coal depend on process conditions. PbSCu was found to
11 be the dominant lead compound in flue gas up to 1150 K (Lockwood and Yousif, 2000).
12 Above this temperature, elemental Pb and PbO, both in the vapor phase, dominate. As the
13 temperature increases, the equilibrium shifts toward elemental Pb (Lockwood and Yousif, 2000).
14 In pulverized coal combustion at 1800K, the lead species found in the gas phase were PbO,
15 elemental Pb, PbCl, and PbCb (Furimksy, 2000). The solid phase was comprised of PbO,
16 PbO»SiO2, elemental Pb, and PbO2 (Furimksy, 2000). As the flue gas cools, the composition of
17 lead changes. PbCb increases and is the main constituent of the gas phase before condensation
18 occurs at 900K. If low rank low chlorine coal is used, then PbO and elemental Pb will dominate
May 2006
2-30
DRAFT-DO NOT QUOTE OR CITE
-------
1 the gas phase. At 1500K, PbSC>4 dominates the particulate phase; at 1800K PbO2 was the
2 predominant lead compound in the particulate phase (Furimksy, 2000).
3 The emissions of lead from coal combustion in industrial, commercial, and residential
4 boilers are similar to the values listed above for utility boilers. Table 2-12 lists emission factors
5 for coal combustion.
Table 2-12. The Emissions of Lead from Industrial, Commercial,
and Residential Coal Combustion
Coal-fired unit Emission factor (g/metric ton)
Industrial cyclone boiler 1.2
Industrial stoker boiler 7.7
Industrial pulverized coal boiler 4.5
Commercial/Residential boiler
(stoker or hand-fired) 2.7
Note: Data for industrial boilers assuming 10% ash fraction and 85% efficient control devices.
Source: Pacyna (1986).
6 Stationary External Combustion: Fuel Oil Combustion
1 Fuel oil combustion constitutes 15% of fossil fuel energy production in the United States.
8 (U.S. Environmental Protection Agency, 1998). As with coal, fuel oil is used to generate energy
9 for utilities, industries, and commercial and residential boilers. The discussion below focuses on
10 electric power utilities, which are the largest users of fuel oil.
11 Fuel oil is generally combusted in tangentially-fired or wall-fired boilers. Emissions of
12 Pb from oil combustion depend on the process conditions, the amount of Pb in the oil, and the
13 amount of sulfur in the oil (Pacyna, 1986) (see Table 2-13).
14 The Pb concentration in the oil is the most important factor for determining the eventual
15 emissions from combustion. The concentration of Pb in crude oil ranges between 0.001 to
16 0.31 ppm (Pacyna, 1986). The heavy fractions of crude oil tend to possess higher metal
May 2006 2-31 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-13. Emission Factors for Oil-Fired Utility Boilers
Boiler Type
Emission Factor
Control Device
Residual oil-fired boiler, No. 6 oil, normal firing
Residual oil-fired boiler, No. 6 oil, normal firing
Residual oil-fired boiler, No. 6 oil, tangential firing
Residual oil-fired boiler, No. 5 oil, normal firing
Distillate oil grades 1 and 2
Oil-fired utilityboiler
Oil-fired utility boiler
4.33xlO'15kg/J
9.35xlO"15kg/J
5.43xlO-15-1.22xlO"14kg/J
4.33xlO'15kg/J
6.89xlO"15kg/J
3.84xlO"15kg/J
2.61b/trillionBtu
9.01b/trillionBtu
none
Flue gas recirculation
none
none
None
PM control
PM/SO2 control
Source: U.S. Environmental Protection Agency (1998).
1 concentrations, trending to larger concentrations metal concentrations with increasing weight.
2 Refining oil removes about 10% of metals (Pacyna, 1986).
3 As with coal, process conditions and the presence of pollution control devices greatly
4 affect the rate and characteristics of emissions from fuel oil combustion. Emissions from oil-
5 fired boilers depend on the efficiency of combustion and how much deposited material has built
6 up in the boiler (Pacyna, 1986). Additionally, poor mixing, low flame temperatures, and a short
7 residence time in the combustion zone cause overall paniculate emissions to be greater and
8 individual particle sizes to be larger (Pacyna, 1986). Oil, which is typically atomized prior to
9 combustion, will emit larger particles and have a higher particulate loading when atomization is
10 done at low pressures. Conversely, high pressure atomization leads to smaller particles and
11 lower particulate loadings (Pacyna, 1986). In general, about 90% of PM mass is <2.5 jim in
12 diameter (Olmez et al., 1988).
13 Emission factors published in the literature are limited. An average emission factor for
14 European oil-fired power plants was reported as 126 jig Pb/MJ for oil containing 1% sulfur
15 (Pacyna, 1986). Lead emissions are higher for oils with greater sulfur contents. Olmez et al.
16 (1988) report Pb mass fractions for two oil-fired power plants in Philadelphia. Lead was found
17 to be 1.0% ± 0.2% and 1.8% ± 0.6% in the fine fraction in these two plants, respectively, and
May 2006
2-32
DRAFT-DO NOT QUOTE OR CITE
-------
1 0.48% ± 0.2% and 3% ± 0.4% in the coarse fraction. Lead in PM at the Philadelphia plants was
2 enriched by more than a factor of 1000 compared to the Pb concentration in the fuel oil. Lead in
3 PM for seven other oil-fired power plants was enriched by more than a factor of 100 (Olmez
4 et al., 1988). A plant in Boston increased the ambient concentration of fine Pb aerosols by an
5 estimated 0.05 |ig/m3 and the ambient concentration of coarse Pb aerosols by 0.003 |ig/m3
6 (Thurston and Spengler, 1985).
7 The combustion of used oil is also common. About 75% of used oil, which is generated
8 in the transportation, construction, and industrial sectors, is burned as fuel oil (Boughton and
9 Horvath, 2004). The Pb concentration of used oils is markedly higher than that of low-sulfur
10 crude-based heavy fuel oils (Boughton and Horvath, 2004). Emissions from used oil combustion
11 are estimated at approximately 30 mg of Pb from the combustion of 1 L of used oil. This is 50 to
12 100 times higher than emissions from crude-derived fuel oils.
13 Emission rates for industrial boilers are similar to those of utility boilers. Industrial oil-
14 fired boilers are not usually equipped with pollution control devices. Approximately 6.4 g of Pb
15 are emitted for 1000 L of fuel oil burned with a sulfur content of 1% (Pacyna, 1986).
16 Commercial and residential boilers, which are also not typically equipped with pollution
17 control devices, have emissions of approximately 3.3 g of Pb emitted per 1000 L of fuel oil
18 (Pacyna, 1986).
19
20 Stationary External Combustion: Wood Combustion
21 Wood-fired boilers are used almost exclusively by industries that produce wood or wood
22 products. These include pulp and paper mills, lumber production facilities, and furniture
23 manufacturers (U.S. Environmental Protection Agency, 1998). The materials used as fuel may
24 include bark, slabs, logs, cuttings, shavings, pellets, and sawdust.
25 During combustion, elemental pollutants such as Pb are converted to their oxide forms.
26 These are hydrated and later carbonated under atmospheric conditions (Demirbas, 2003a).
27 As with coal and oil, the largest factor affecting emissions from wood combustion is the
28 concentration of Pb in the fuel. Lead concentrations tend to be very low for virgin wood. The
29 median Pb concentration in 24 pine and spruce samples was 0.069 ppm (Krook et al., 2004).
30 The concentrations of Pb in spruce, beech, oak, pine, and ailanthus are listed in Table 2-14.
31
May 2006 2-33 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-14. The Concentrations of Lead in Biomass, Char, and Ash Samples
from Spruce, Beech, Oak, Pine, and of Ailanthus Trees
Wood
Spruce trunk wood
Beech trunk wood
Oak trunk wood
Pine trunk wood
Ailanthus trunk wood
Spruce bark
Beech bark
Oak bark
Pine bark
Ailanthus bark
Biomass (ppm)
0.32a
0.36a
0.27a
n.a.
n.a.
0.38a
0.43a
0.31a
n.a.
n.a.
Char (ppm)
2.5a
2.6a
2.1a
n.a.
n.a.
3.r
3.3a
2.5a
n.a.
n.a.
Ash (ppm)
33.2a'b
35.0a'b
28.4a'b
34.9b
32.7b
5.2a, 36.2b
3.8a,40.8b
4.0a, 34.0b
38.7b
35.7b
"Source: Demirbas (2003a).
b Source: Demirbas (2003b).
1 Waste wood recovered from construction and demolition sites is increasingly used as fuel.
2 Although most of this wood is untreated, some can have elevated levels of metals from surface
3 treatment of the wood or industrial preservatives (Krook et al., 2004). Additionally, waste wood
4 commonly contains contaminants such as metal pieces, concrete, stone, gravel, glass, and soil,
5 which may increase metal emissions during combustion. Lead has been measured in waste wood
6 at levels -40 times higher than levels found in virgin wood. The median concentration of Pb in
7 recovered waste wood in Sweden was 33 ppm (Krook et al., 2004). Lead in recovered waste
8 wood from Germany and the Netherlands had a median value of 110 ppm.
9 Emissions of metals from wood are affected by process conditions. Good air-fuel mixing
10 and high furnace temperatures keep emissions low (Demirbas, 2003a). Additionally emissions
11 depend on whether or not the wood was combined with other fuels, the feed rate, the physical
12 state of the wood, the stack temperature, the geometry of the boiler which can act as an inertial
13 particulate collector, the draft setting, and the amount of moisture in the fuel (Demirbas, 2003a;
14 Pels et al., 1990; Pacyna, 1986).
May 2006 2-34 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pollution control devices may be present with large-scale wood-fired boilers. These can
2 greatly reduce paniculate emissions. However, in a wood-burner installation in Ontario, a
3 cyclone was found to have an efficiency of just 53% for total PM mass (Pels et al., 1990). For
4 particles <2 jim in diameter, the concentrations downstream of the cyclone were actually greater
5 than those upstream, probably indicating that larger particles were breaking apart during passage
6 through the cyclone. The emissions of Pb from wood combustion are highly variable. The
7 emission factor for wet fuel at a large-scale wood burner was 0.0006 g Pb/kg fuel (Pels et al.,
8 1990). For dry fuel, emission factors were in the range <0.00035 to 0.0014 g Pb/kg fuel burned
9 with an average of 0.00056 g Pb/kg fuel (Pels et al., 1990). Emissions from a wood stove and a
10 fireplace are estimated as 0.007 g Pb and 0.0047 g Pb per kg of wood burned, respectively
11 (Pacyna, 1986). The recently updated AP-42 emission factor for lead from wood residue
12 combustion in boilers is 4.8x10-5 Ib/MMBtu (U.S. Environmental Protection Agency, 2005).
13 Emissions from the combustion of waste wood are higher than emissions from
14 combustion of virgin wood. Although emission factors are not available, the concentration of Pb
15 in ash from waste wood combustion is elevated above that from the combustion of virgin wood
16 (Krook et al., 2004).
17 Data on particle sizes and species of emitted aerosols from wood combustion are not
18 readily available.
19
20 Stationary Combustion Sources: Solid Waste Incineration
21 Incineration of municipal waste is on the decline in the United States. Historically it has
22 been an important source of Pb emissions and locally it is still a concern in some places (Walsh
23 et al., 2001). In New York City in the late 1960s, emissions from refuse incineration were
24 between 602 and 827 tons per year, an appreciable fraction of the emissions from cars, which
25 totaled -1752 metric tons in the same area (Walsh et al., 2001).
26 Incinerator residue is partitioned into bottom ash, fly ash, and flue gas. Here we focus on
27 Pb in flue gas, due to its importance in increasing airborne Pb concentrations (Chang et al.,
28 1999). Lead in incinerator effluents is derived primarily from the noncombustible materials that
29 end up in refuse (Pacyna, 1986). These incinerators may be equipped with pollution control
30 devices such as cyclones, baghouses, ESPs, electrified gravel beds, and venturi scrubbers (U.S.
31 Environmental Protection Agency, 1998).
May 2006 2-3 5 DRAFT-DO NOT QUOTE OR CITE
-------
1 Factors that affect the quantity of Pb emitted from incinerators include combustion
2 temperature, the amount of Pb in the refuse, process conditions, moisture content, the addition of
3 reactive species such as calcium, magnesium, and aluminum, and the addition of sorbents. Of all
4 these factors, temperature seems to have the greatest impact on metal volatility (Chen and Yang,
5 1998). Metal volatilization is fast during the initial stages of combustion but levels off after
6 about 15 minutes (Ho et al., 1993; Chen and Yang, 1998). When plastics only were burned, Pb
7 volatility was at 18% at 600 °C, 61% at 800 °C, and 91% at 1000 °C (Chen and Yang, 1998).
8 Figure 2-4 shows the percent volatility for Pb at four different combustion temperatures over
9 25 minutes of combustion time. Chang et al. (1999) derived the following relationship for Pb
10 emissions from a fixed bed refuse incinerator in Taiwan:
11
12 ln£(w/%) = -3.083r+3.659 (2-4)
13
14 where E is the weight percent of Pb in particulate emissions, and T is the combustion
15 temperature in Kelvin.
16 The amount of Pb emitted is dependent on the quantity of Pb in refuse. Typical sources of
17 Pb include paper, inks, batteries, cans and other metal scrap, and plastics. Plastics are the most
18 important source of Pb in municipal solid waste since lead is used in plastic dyes and stabilizers,
19 and plastics constitute a large portion of the waste stream (U.S. Environmental Protection
20 Agency, 1998; Wagner and Carabello, 1997). For United States municipal solid waste, Pb
21 concentrations vary between 110 and 1500 ppm with an average of about 330 ppm (Durlak et al.,
22 1997). Since other countries have very different waste compositions, Pb concentrations
23 elsewhere can vary greatly.
24 Additionally, process conditions can affect Pb emissions. Increasing the amount of
25 oxygen accelerates the rate of metal volatilization but does not seem to affect the overall amount
26 of metal volatilized (Ho et al., 1993). Similarly, Chen and Yang (1998) observed that changing
27 the N2:C>2 ratio from 4: 1 to 1 :4 increased Pb volatility. An increase in the gas velocity can also
28 increase Pb emissions although this is a relatively minor effect (Chang et al., 1999; Chen and
29 Yang, 1998).
May 2006 2-36 DRAFT-DO NOT QUOTE OR CITE
-------
_
$
100
90 -
80
70
60
50
40
30
20 -
10 -
Symbol
•e-
*
*
-*
Temp.
600°C
800°C
900°C
1000°C
10
15
Time (min.)
20
25
Figure 2-4. Percentage volatility of Pb during combustion of plastics at four temperatures.
Source: Chen and Yang (1998).
1 The moisture content in an incinerator can affect the behavior of Pb. At a typical
2 temperature of 950 °C, decreasing the moisture level from 37% to 5% increased Pb in the fly ash
3 from 54% to 58% (Durlak et al., 1997). Similarly, decreasing the relative humidity from 60% to
4 40% at 900 °C increased the Pb volatility from 67% to 76%, respectively (Chen and Yang,
5 1998). In addition to these direct effects, moisture can indirectly affect emissions by altering the
6 combustion temperature (Durlak et al., 1997).
7 Additives can reduce metal emissions from incinerators. Additives such as calcium,
8 magnesium, and aluminum react with metals and bind them. This has been shown to reduce the
9 formation of metal particulates. Adding A1(NC>3)3, for example, reduced quantities of PbCb
10 emitted (Ho et al., 1993). The addition of Ca(OH)2 did not affect volatility at 600 °C (lower
May 2006
2-37
DRAFT-DO NOT QUOTE OR CITE
-------
1 limit for combustion temperature) or at 1000 °C (upper limit for combustion temperature)
2 (Chen and Yang, 1998). However, Ca(OH)2 did appreciably limit Pb emissions at intermediate
3 temperatures.
4 Sorbents can also reduce metal emissions. Sorbents function by binding metal vapors
5 through heterogeneous chemical absorption and/or condensation before vaporized metals are
6 able to form particulates (Ho et al., 1993). In a fluidized bed incinerator, the efficiency of metal
7 capture with sorbents varied between 4.9% and 94.5% (Ho et al., 1993). The efficiency was
8 dependent on temperature. Low efficiencies were observed at high and low temperatures; the
9 optimal efficiency was observed in the intermediate range of-600 to 800 °C. Limestone was
10 shown to be a more effective sorbent than sand.
11 Emissions from refuse incinerators have been reported as 0.018 g of Pb emitted per kg of
12 refuse, assuming a control device with 85% efficiency (Pacyna, 1986). A source apportionment
13 study showed that refuse incineration increased the ambient concentration of Pb by an estimated
14 0.008 |ig/m3 (Thurston and Spengler, 1985). This was observed after incinerators had been
15 banned in the area probably indicating prohibited, residential refuse combustion. Lead in PM
16 emissions has been reported to be between 6.9% and 8.9%, with an average of 8.1% (Pacyna,
17 1986). Three United States incinerators had emissions in which Pb constituted 8.2 ± 1.6% of the
18 PM (Olmez et al., 1988).
19 Chlorine plays a critical role in determining the speciation of Pb emissions. Lead in the
20 incineration system exists primarily as chlorine species (either PbCl or PbCb) (Durlak et al.,
21 1997). However an increase in moisture content decreases the levels of free chlorine, which has
22 the subsequent effect of shifting Pb from gaseous PbCb to PbO in particulate form. PbCl2(g) is
23 completely volatilized at 430 °C (Chen and Yang, 1998; Chang et al., 1999). Above 800 °C
24 PbCb slowly decomposes and PbO(g) and PbCl(g) are present in greater concentrations.
25 The presence of sodium can also affect speciation. Sodium has a greater affinity for
26 binding with chlorine than Pb (Durlak et al., 1997). Thus increasing the sodium content
27 effectively shifts the dominant Pb compound from PbCb to PbO. Decreasing the sodium content
28 from 6560 ppm to 4500 ppm (the average value observed in municipal solid waste) was
29 responsible for increasing Pb in the fly ash from 35% to 60% at average moisture levels (Durlak
30 et al., 1997). High concentrations of sodium attenuate the influence of moisture on Pb
31 emissions.
May 2006 2-3 8 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead emissions tend to concentrate in the submicron size range (Chang et al., 1999;
2 Olmez et al., 1988). Lead in the fine fraction was enriched by a factor of more than 105 at
3 several United States incinerators compared with the concentration of Pb in the solid waste
4 (Olmez et al., 1988). Lead in the coarse fraction was enriched by a factor of more than 1000.
5
6 Stationary Combustion Sources: Sewage Sludge Combustion
1 Sewage sludge incinerators exist at approximately 200 sites in the United States (U.S.
8 Environmental Protection Agency, 1998). Lead can enter the sewage waste stream through car
9 washes, galvanized material, pipe erosion, pigments, food, processed chemicals, and roofs
10 (Krook et al., 2004). As in other combustion processes, Pb impurities vaporize during
11 incineration and then condense.
12 The Pb content of dry sludge varies between 80 and 26,000 ppm, with an average of
13 1,940 ppm (Pacyna, 1986). Sludge taken from an industrial wastewater treatment plant in
14 Taiwan had Pb levels of 1,500 ppm (Chang et al., 1999). Prior to combustion, Pb is either bound
15 to organic matter in sludge or is present as a carbonate (Lockwood and Yousif, 2000).
16 In sewage sludge incinerators, higher temperatures are associated with higher Pb
17 emissions (Pacyna, 1986). Additionally, sewage sludge incinerators tend to be equipped with
18 venturi scrubbers with efficiencies of 90 to 99% (Pacyna, 1986). Other pollution control devices
19 are less common.
20 Sorbents can be effective pollution controls. Kaolinite, in particular, was shown to reduce
21 Pb emissions significantly (Lockwood and Yousif, 2000).
22 Emissions have been estimated as 0.14 g Pb emitted per kg of sludge combusted (Pacyna,
23 1986). The fine fraction of particulate emissions in an experimental setup was enriched with Pb
24 by a factor of 2.5 (Lockwood and Yousif, 2000).
25
26 Stationary Combustion Sources: Scrap Tire Combustion
27 Waste tires are increasingly used as a fuel although uncontrolled burning as a result of
28 accidents or illegal activity is common (U.S. Environmental Protection Agency, 1998). One
29 analysis showed that uncontrolled combustion resulted in Pb emissions on the order of 0.47 mg
30 Pb/kg tire for tires that had been cut into four to six pieces (Lemieux and Ryan, 1993).
31 Emissions were lower for shredded tires, at 0.10 mg Pb/kg tire, probably because of greater
May 2006 2-39 DRAFT-DO NOT QUOTE OR CITE
-------
1 oxygen transport between tire pieces. Another analysis detected trace amounts of Pb in the
2 smoke from the combustion of tire bodies but did not detect Pb emissions when the tread was
3 burned (Wagner and Caraballo, 1997).
4
5 Lead-acid Battery Manufacturing
6 Lead-acid batteries constituted 84% of Pb consumed in 2003 (USGS, 2003). Lead-acid
7 batteries are manufactured from Pb alloy ingots and Pb oxide. Lead alloy ingots are produced by
8 smelters, the emissions of which are characterized earlier in this chapter. Lead oxide is either
9 produced on-site or is outsourced (U.S. Environmental Protection Agency, 1998).
10 Lead-acid battery manufacture consists of the following processes: grid casting or
11 stamping, paste mixing, plate stacking, plate burning, and assembly into the battery case (U.S.
12 Environmental Protection Agency, 1998). Each process has its own characteristic emissions of
13 Pb. Emissions from Pb oxide manufacture tend also to be in the form of Pb oxides. These
14 emissions are usually attenuated through a baghouse. The sites of other processes are usually
15 equipped with baghouses or impingement wet scrubbers (U.S. Environmental Protection
16 Agency, 1998).
17
18 Cement Manufacturing
19 The manufacture of Portland cement emits relatively low quantities of Pb. Trace amounts
20 of Pb are present in the raw materials of calcium, silicon, aluminum, and iron (U.S.
21 Environmental Protection Agency, 1998). As the raw materials are thermo-treated, most of the
22 Pb is trapped in the resulting clinker, although some is released as PM (U.S. Environmental
23 Protection Agency, 1998). Additionally, emissions result from the combustion of the coal,
24 natural gas, or waste tires used to fire the kiln (Pacyna, 1986; U.S. Environmental Protection
25 Agency, 1998).
26 Emissions are reduced significantly through the use of pollution control devices. ESPs
27 and baghouses are both common although baghouses tend to be more effective. Lead is present
28 in the emitted PM in the range of 100 to 1000 ppm (Lee and Von Lehmden, 1973). Emission
29 factors for cement production are listed in Table 2-15.
May 2006 2-40 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-15. Emission Factors of Lead From Processes Used in
Cement Manufacture by Control Device.
Pollution Control Device
Process
Dry Process (total)
Kiln/cooler
Dryer/grinder
Wet Process (total)
Kiln/cooler
Dryer/grinder
Multi-cyclones
16.0
12.0
4.0
12.0
10.0
2.0
ESP
4.0
3.0
1.0
3.0
2.5
0.5
Baghouse
0.16
0.12
0.04
0.12
0.10
0.02
Note: Units are g Pb/metric ton cement.
Source: Pacyna (1986).
1 Glass Manufacturing
2 The production of leaded glass emits significant quantities of Pb. Its uses primarily
3 include Pb crystal, cathode ray tubes for televisions, and optical glasses such as binoculars,
4 microscopes, and telescopes (U.S. Environmental Protection Agency, 1998). Leaded glass is
5 composed of silica sand and Pb oxide. Lead oxide concentrations in U.S.-produced leaded glass
6 typically range between 12% and 60% but can be as high as 92% (U.S. Environmental Protection
7 Agency, 1998).
8 The basic process of glass manufacturing includes blending the raw materials, melting,
9 and forming and finishing. Lead emissions can occur during all of these processes. During
10 blending, forming, and finishing, Pb is emitted as part of fugitive dust emissions in minor
11 quantities (Shapilova and Alimova, 2000; U.S. Environmental Protection Agency, 1998).
12 The major source of Pb emissions derives from the melting process. Emissions from
13 melting depend mostly on the amount of Pb oxide in the raw material (Shapilova and Alimova,
14 2000; U.S. Environmental Protection Agency, 1998). Other factors are the type and efficiency of
15 the furnace, the waste-gas volume, the smoke-flue length, and the efficiency of pollution control
16 devices (Shapilova and Alimova, 2000). Electric furnaces emit significantly less Pb than gas-
17 flame furnaces. One analysis found that the rate of Pb emissions from a gas-flame regenerative
May 2006 2-41 DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
7
8
furnace was more than seven times higher than the rate of emissions from a deep tank electric
furnace (Shapilova and Alimova, 2000). Baghouses are the most efficient pollution control
device for glass manufacturing operations (U.S. Environmental Protection Agency, 1998).
Wet scrubbers are relatively ineffective, and ESPs are between 80% and 90% effective (U.S.
Environmental Protection Agency, 1998). Rates of Pb emissions from several types of furnaces
are listed in Table 2-16.
Table 2-16. Rate of Lead Compound Emissions from Glass-Melting Furnaces
_ .
Lquipment
_
Product
Lead Compound
^ . . , .
Emissions g/sec)
Electric tank furnace with gas-heated
.. a &
working zone
Electric tank furnace with gas-heated
,.
working zone
Gas-flame potter furnace3
Slag-lining electric furnace with gas-
, ° , , . &
heated working zone
._,, .^ . ,„, „, „
Glass with 16% PbO
„, ... , ,0/ _, „
Glass with 16% PbO
Glass with 16% PbO
._,, .^ ,„ ,„, „, „
Glass with 64.5% PbO
nn^
0.134
„ „ „,
0.002
0.004
nf\r\A
0.004
a Fitted with a "cassette pulse filter" designed specifically to capture paniculate emissions from small-sized,
glass-melting furnaces.
Source: Shapilova and Alimova (2000).
9 Ammunition Production and Shooting Ranges
10 In 2003, 48,800 metric tons of Pb were consumed in the United States for the production
11 of ammunition (USGS, 2003). Additionally, some Pb is used to produce Pb azide or Pb
12 styphnate, which is a detonating agent. Small arms manufacturing plants are likely emitters of
13 Pb although the actual quantity is unknown.
14 Shooting ranges, both outdoor and indoor, may have a local impact on airborne Pb
15 concentrations. Lead is emitted from cast Pb bullets and lead-based primers (Gulson et al.,
16 2002). The propellants contain <2 ppm lead and seem to have a negligible effect on air
17 concentrations. A 97% reduction in the air Pb concentrations was observed when Cu-jacketed
18 bullets replaced cast Pb bullets (Gulson et al., 2002). In comparing the Pb exposure of
May 2006
2-42
DRAFT-DO NOT QUOTE OR CITE
-------
1 personnel, there seems to be little difference between indoor and outdoor firing ranges (Gulson
2 et al., 2002). One study found that soil Pb concentrations at an outdoor firing range were
3 elevated by up to 2600 times background concentrations, indicating significant atmospheric
4 deposition (DeShields et al., 1998).
5 An additional source of Pb emissions may be explosive ordnance disposal (EOD) (U.S.
6 Environmental Protection Agency, 1998). Emissions from EOD are either from the combustion
7 or detonation of the propellant and primer material or from nonenergetic wastes such as
8 containers and other wastes associated with the propellant (U.S. Environmental Protection
9 Agency, 1998).
10
11 Demolition
12 A study of Pb dust-fall during the demolition and debris removal of urban row houses
13 found that Pb was released in very large quantities (Farfel et al., 2003). Many of the row houses
14 demolished at three sites in Baltimore, MD contained lead-based paint in addition to being near
15 sites with elevated levels of Pb in street dust (-700 ppm), sidewalk dust (-2000 ppm), and
16 residential entryway mat dust (-750 ppm). The results of the study showed that dust fall within
17 10m of the demolition sites was much higher than baseline measurements and was highly
18 enriched with Pb (Farfel et al., 2003). The geometric mean Pb dust fall rate increased to 410 jig
19 Pb/m2/hr during demolition and to 61 jig Pb/m2/hr during debris removal. The baseline rate is
20 just 10 jig Pb/m2/hr. The Pb concentration in dust fall was 2600 ppm during demolition,
21 1500 ppm during debris removal, and 950 ppm at baseline (Farfel et al., 2003). Thus, demolition
22 and debris removal can be a major source of airborne lead under some conditions.
23
24 Other Stationary Sources of Lead Emissions
25 There are additional stationary sources of Pb emissions that have not been mentioned
26 above. Each of these sources are relatively small, but may be an important local source.
27 Previously unmentioned Pb sources include: medical waste incineration, hazardous waste
28 incineration, drum and barrel reclamation, crematories, pulp and paper mills, pigment
29 production, Pb cable coating production, frit manufacturing, ceramics and glaze production, type
30 metal production, pipe and sheet Pb production, abrasive grain processing, solder manufacturing,
May 2006 2-43 DRAFT-DO NOT QUOTE OR CITE
-------
1 electroplating, resin stabilizer production, asphalt concrete production, paint application, and
2 rubber production.
3
4 2.2.4 Mobile Sources
5 Automotive Sources of Lead Emissions
6 Lead is used to manufacture many components in on-road vehicles including the battery,
7 bearings, paint primers, corrosion-resistant gas tanks, and some plastic and ceramic electrical
8 components (U.S. Environmental Protection Agency, 1998). The major sources of Pb
9 emissions—fuel combustion and vehicle wear—are considered below.
10
11 Emissions from Combustion of Unleaded Gasoline
12 Although its phase out began in 1975, Pb was still added to gasoline in the United States
13 as an anti-knock additive at the time of the last Criteria Document (U.S. Environmental
14 Protection Agency, 1986). The United States completed its phase out of Pb additives in 1990,
15 and airborne concentrations have fallen dramatically nationwide. This is considered one of the
16 great successes for public and environmental health (Nriagu, 1990). Airborne concentrations in
17 the United States fell an average of 94% between 1983 and 2002 and 57% between 1993 and
18 2002 (U.S. Environmental Protection Agency, 2003).
19 Most countries have made a similar move away from leaded fuel, but a few continue the
20 practice of adding tetraethyl Pb to automotive gasoline. Worldwide Pb consumption for gasoline
21 peaked in the 1970s at just under 400,000 metric tons, but by 1993, this value fell to about
22 70,000 metric tons (Socolow and Thomas, 1997). Leaded gasoline was the largest source of air
23 emissions throughout the 1970s and 1980s (Socolow and Thomas, 1997). In Pakistan, a country
24 that continues to use leaded fuel, the airborne concentrations in the urban center of Karachi range
25 between 2.0 and 19 jig Pb/m3 (Parekh et al., 2002). This is 2 to 3 orders of magnitude higher
26 than typical urban concentrations in the United States.
27 In the absence of tetraethyl Pb additives, Pb is emitted from automobiles as a trace
28 element in PM. Metals enter the vehicle in trace amounts, naturally occurring in gasoline.
29 The amount of PM that is emitted from the car depends on a number of variables including the
30 ambient temperature, the cruising speed, the amount of stop-and-go activity, the type of catalyst,
May 2006 2-44 DRAFT-DO NOT QUOTE OR CITE
-------
1 the fuel quality, the phase of driving, and the age, size, maintenance level, and engine type of the
2 vehicle.
3 The amount of Pb that naturally occurs in gasoline is approximately 0.00005 g/L (Harris
4 and Davidson, 2005). An estimated 30 to 40% of this Pb deposits in the engine and exhaust
5 system; the balance is emitted (Huntzicker et al., 1975; Loranger and Zayed, 1994).
6 Particulate matter emissions have been shown to be higher in older vehicles than in newer
7 vehicles (Gillies et al., 2001; Cadle et al., 1999). Gillies et al. (2001) compared emission factors
8 from several studies, and found that emission factors from car models between the years 1964
9 and 1983 had emission factors for PM that were about an order of magnitude higher than models
10 from the 1990s. This was true even of catalyst-equipped vehicles. Similarly, Cadle et al. (1999)
11 tested 195 cars with model years between 1971 and 1996. Their results, which are listed in
12 Table 2-17, show an increase in emission rates with automobile age.
13
14
Table 2-17. Emission Factors of Lead for Automobiles with Model Years
Between 1971 and 1996
Vehicle Category
1991-1996
1986-1990
1981-1985
1971-1980
Smokers
Diesel
Summer
0.003
0.027
0.006
0.043
0.035
0.15
Emission Factors in mg/mile
Winter
0.019
0.019
0.103
0.222
0.282
0.142
Note: "Diesel" denotes diesel automobiles, "Smokers" denotes automobiles with visible emissions.
Source: Cadle etal. (1999).
15 Vehicles that have visible tailpipe emissions are known as "smokers." The emissions of
16 almost all pollutants are elevated from smoking vehicles compared to their non-smoking
17 counterparts. Emission rates of Pb from smokers are an order of magnitude higher than typical
18 cars manufactured in the 1990s, as shown in Table 2-17. Interestingly, another study found that
19 smoking and other high-emitting vehicles emitted more Pb after undergoing repair than before
May 2006 2-45 DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
(Cadle et al., 1997). The emission rate of Pb before repair had an average value of 0.029 mg/mi
with a standard deviation of 0.047 mg/mi. After repair, the emission rate for Pb increased to
0.161 mg/mi with a standard deviation of 0.346 mg/mi. The authors explain this surprising result
by suggesting that either changes in combustion conditions caused elemental deposits from the
engine and exhaust system to be released, or PM deposited during repair and testing was not
removed before emissions testing (Cadle et al., 1997).
Table 2-17 also shows the effect of the ambient temperature on emission rates of Pb.
Emissions tend to be higher during cold months than during warm months (Cadle et al., 1999).
The rate of emissions is largely dependent on the phase of driving. The Federal Test
Procedure analyzes three phases: cold start, hot stabilized, and hot start, the results of which are
shown in Table 2-18. Driving cycles that are not included are the highway fuel economy test,
and a high speed, high load cycle known as US06 (Cadle et al., 1999). Emissions were
significantly higher during cold start than during the hot stabilized and hot start phases.
Table 2-18. Emission Factors of Lead for Automobiles with Model Years
Between 1971 and 1996
Vehicle Category
1991-1996
1986-1990
1981-1985
1971-1980
Smokers
Diesel
Cold Start
0.005
0.041
0.016
0.112
0.116
0.190
Summer Emission Factors in mg/mile
Hot Stabilized
0.002
0.020
0.002
0.015
0.010
0.048
Hot Start
0.002
0.031
0.006
0.044
0.031
0.313
Source: Cadle etal. (1999).
16 Despite the large variability in Pb emissions, several studies describe average on-road
17 emission factors for a typical fleet. Sternbeck et al. (2002) measured metal concentrations
18 in two tunnels in Gothenburg, Sweden. The emission factors subsequently derived were
19 0.036 ± 0.0077 mg/km per vehicle and 0.035 ± 0.014 mg/km per vehicle for the two tunnels,
May 2006
2-46
DRAFT-DO NOT QUOTE OR CITE
-------
1 respectively. Another tunnel study was performed on a fleet comprised of 97.4% light-duty
2 vehicles and 2.6% heavy-duty vehicles in the Sepulveda Tunnel in California (Gillies et al.,
3 2001). The emission factors for Pb were 0.08 mg/km per vehicle and 0.03 mg/km per vehicle in
4 the PMio and PM2.5 fractions respectively. Lough et al. (2005) analyzed emissions from on-road
5 vehicles in two tunnels in Milwaukee, Wisconsin. Trucks constituted between 1.5% and 9.4% of
6 the vehicles, with the balance comprised of passenger cars. Lead emission rates were on the
7 order of 0.01 mg/km per vehicle and 0.1 mg/km per vehicle in the summer and winter
8 respectively. Cadle et al. (1999) analyzed 195 in-use, light-duty vehicles using two
9 dynamometers. Their results are shown in Tables 2-17 and 2-18. A test on noncatalyst-
10 equipped, light-duty vehicles found that Pb constituted about 0.03% of the fine particle mass
11 emitted from these vehicles (Kleeman et al., 2000).
12 Vehicle-derived Pb seems to have a bimodal size distribution. The submicron mode is
13 likely the product of combustion or high temperatures, and therefore probably came from the
14 tailpipe (Lough et al., 2005; Harrison et al., 2003; Abu-Allaban et al., 2003). The coarse mode,
15 with an approximate size range of 1.0 to 18 jim in diameter, is likely a product of physical
16 processes such as road dust resuspension and tire or brake wear (Lough et al., 2005; Abu-
17 Allaban et al., 2003). More than 80% of the airborne Pb particles near a roadway were
-------
Table 2-19. The Concentration of Lead in Particulate Matter Emissions and Emissions
Factors for Lead from Buses and Trucks Fueled with Diesel No. 2 and Jet A Fuel
Fuel and Vehicle Type
Truck, Diesel No. 2
Truck and Bus, Diesel
No. 2
Truck and Bus, Jet A
Bus, Jet A and Diesel No. 2
with paniculate trap
Concentration of
Pb in PM (%)
0.0007
0.0006
0.0010
0.0009
Uncertainty
(%)
0.0028
0.0025
0.0055
0.0052
Emission Factor
(mg/km)
0.0053
0.0045
0.0050
0.0016
Uncertainty
(mg/km)
0.0187
0.0188
0.0214
0.0100
Bus, Jet A with paniculate
trap
Phoenix PM10 study
0.0028
0.0147
0.0132
0.0294
0.0018
n.a.
0.0085
n.a.
The results of Chow et al. (1991) on heavy-duty paniculate emissions in Phoenix are listed in the last row
for comparison.
Source: Lowenthal et al. (1994).
1 Emissions from Vehicle Wear
2 Vehicle wear and loss of Pb wheel weights are considered as sources of roadside Pb
3 contamination. Brake wear, in particular may emit significant quantities of Pb in PM. Harrison
4 et al. (2003) note that Pb is poorly correlated with emissions of NOX, which is emitted from
5 tailpipes. These authors therefore suggest that brake wear contributes the additional quantities of
6 Pb observed in ambient air. Sternbeck et al. (2002) compare emission factors derived in other
7 studies. Estimates of Pb emissions from brake pads in Sweden were just under 200 jig/km per
8 vehicle (Sternbeck et al., 2002). This is an order of magnitude higher than the tailpipe emissions
9 measured by Cadle et al. (1999).
10 Up to 35% of brake pad mass loss is emitted as airborne PM (Garg et al., 2000). One
11 study that analyzed particulate emissions from seven different brake pad formulations found that
12 only one type of brake pad described as "potassium titanate, aramid, and copper fiber" emitted
13 PM with a measurable Pb fraction (Garg et al., 2000).
14 A joint study in Reno, NV and Durham/Research Triangle Park, NC found that the
15 dominant contributors to roadside PM were resuspended road dust and tailpipe emissions (Abu-
May 2006
2-48
DRAFT-DO NOT QUOTE OR CITE
-------
1 Allaban et al., 2003). However, brake wear was a significant source of PM in places where
2 strong braking occurred, such as at freeway exits (Abu-Allaban et al., 2003).
3 Particulate matter emissions from brake pads were primarily in the fine fraction. Eighty-
4 six percent and 63% of airborne PM was smaller than 10 and 2.5 |im, respectively (Garg et al.,
5 2000). It is expected that Pb particles from mechanical processes such as brake wear would be in
6 the coarse fraction. However, smaller particles may be observed if Pb is vaporized from hot
7 brake surfaces (Harrison et al., 2003; Lough et al., 2005).
8 Lead weights used to balance vehicle wheels may be an additional source of elevated
9 roadside concentrations of Pb. In Albuquerque, NM deposition of Pb wheel weights was
10 estimated to be between 50 and 70 kg/km per year (Root, 2000). Wheel weights are 95% Pb, 5%
11 antimony, and typically weigh between 7 and 113 grams. These wheel weights can become
12 dislodged during quick stops. Although deposited pieces of wheel weights are quite large, Pb is
13 very malleable and can be worn away into respirable particles by being run over by vehicles
14 (Root, 2000).
15
16 Emissions from Racing Vehicles
17 Vehicles used in racing (including cars, trucks, and boats) are not regulated by the EPA
18 according to the Clean Air Act and can therefore use alkyl-lead additives to boost octane. Data
19 on Pb levels in racing fuel and rates of Pb emissions are scarce. The U.S. Department of Energy
20 stopped tracking information on the production of leaded gasoline for non-aviation use in 1990
21 (U.S. Environmental Protection Agency, 2002). However, the National Motor Sports Council
22 reports that approximately 100,000 gallons of leaded gasoline were used by National Association
23 for Stock Car Automobile Racing (NASCAR) vehicles in 1998 (U.S. Environmental Protection
24 Agency, 2002).
25 As was the case with on-road emissions during the time of universal leaded gasoline use,
26 the combustion of racing fuel likely elevates airborne Pb concentrations in the nearby area. This
27 may pose some health risk for some subpopulations, such as residents living in the vicinity of
28 racetracks, fuel attendants, racing crew and staff, and spectators. However, EPA has formed a
29 voluntary partnership with NASCAR with the goal of permanently removing alkyl-Pb from
30 racing fuels used in the Busch, Winston Cup, and Craftsman Truck Series (U.S. Environmental
May 2006 2-49 DRAFT-DO NOT QUOTE OR CITE
-------
1 Protection Agency, 2002). In January of 2006, NASCAR agreed to switch to unleaded fuel in its
2 racecars and trucks beginning in 2008.
3 In addition to racing vehicles and piston engine aircraft, legally permitted uses of leaded
4 fuel include construction machinery, agricultural equipment, logging equipment, industrial and
5 light commercial equipment, airport service equipment, lawn and garden equipment, and
6 recreation equipment including boats, ATVs, jet skis, snowmobiles, etc., (U.S. Environmental
7 Protection Agency, 2000). Given the relative unavailability of leaded fuel, it is unlikely that it is
8 commonly used for any of these purposes other than racing vehicles.
9 Emissions from the combustion of leaded fuel are generally in the form of submicron
10 particles of inorganic Pb halides.
11
12 Aircraft
13 Piston-engine aircraft use leaded fuel. Aviation fuel or avgas contains between 0.1 and
14 1.0 g of tetraethyllead additives per liter. About 32.7% of general aviation aircraft use avgas, the
15 remainder use jet fuel, which does not contain Pb additives (U.S. FAA, 1996). The overall
16 fraction of aviation fuel containing Pb additives is unknown.
17 In the South Coast Air Basin of California, emissions of Pb from general aviation aircraft
18 was estimated as 634 ±110 kg/year (Harris and Davidson, 2005). This corresponds to
19 0.54 grams of Pb released per flight. Approximately 267 kg of the total was emitted below the
20 mixing height in 2001, which could be a local source of Pb exposure.
21 Commercial jet aircraft do not use leaded fuel. However, they are also likely sources of
22 Pb emissions. In-flight sampling of contrails from a DC-8 and a 757 showed that metals
23 constituted more than 11% and 5.2% of PM, respectively (Twohy and Gandrud, 1998). This is a
24 lower limit for the fraction of metals in emissions since almost half of the particles in contrails
25 are from the ambient air (Twohy and Gandrud, 1998).
26 No known estimates have been made of the quantity of Pb in commercial aircraft
27 emissions. However, the dominant metals seem to be Fe, Cr, and Ni (Karcher, 1999). These are
28 the primary components of stainless steel and indicate that engine erosion is a significant source
29 of metal emissions (Karcher, 1999).
May 2006 2-50 DRAFT-DO NOT QUOTE OR CITE
-------
1 Metal particles in contrails have two modes. One is submicron with an average diameter
2 of about 0.36 jim (Karcher, 1999; Twohy and Gandrud, 1998). The larger mode is ~1 |im in
3 diameter and has a morphology that suggests mechanical generation (Karcher, 1999).
4
5 Lawn-Care Equipment
6 A life cycle assessment used to compare gasoline-, electricity-, and battery-powered lawn
7 mowers found that electricity-powered mowers had the fewest overall emissions over its lifetime
8 (Sivaraman and Lindner, 2004).
9 Battery powered mowers are fitted with a lead-acid battery. The total amount of Pb
10 released to the environment from the battery over its lifetime is approximately 0.052 kg Pb
11 which includes consideration of raw material extraction and refining, energy production, Pb
12 mining and refining, battery manufacture, and battery recycling (Sivaraman and Lindner, 2004).
13 Electricity-powered lawn mowers presumably emit less PM and Pb than gasoline-
14 powered mowers. This is a reasonable assumption since utility generation plants tend to be fitted
15 with pollution control devices and internal combustion engines of gasoline-powered mowers
16 do not.
17
18 Other Sources of Lead Emissions
19 Lead emissions are associated with the combustion of any fossil fuel. Thus, any of the
20 following may be additional mobile sources of Pb emissions that are not addressed above:
21 construction equipment, off-road recreational vehicles, generators, marine vessels, locomotives,
22 agricultural equipment, logging equipment, and lawn and garden equipment. However, detailed
23 data on these sources are not readily available.
24 Additionally, the resuspension of lead-contaminated soil and dust is a major source of
25 airborne lead. Since fugitive dust emissions are not considered a primary source of airborne lead
26 a discussion of resuspended soil particles is omitted here and covered in Section 2.3.3 as a mode
27 of transport for lead particles through the environment.
28
29
May 2006 2-51 DRAFT-DO NOT QUOTE OR CITE
-------
1 2.3 TRANSPORT WITHIN THE ENVIRONMENT
2 2.3.1 Atmospheric Transport of Lead Particles
3 Atmospheric Dispersion
4 The atmosphere is the major environmental transport pathway for anthropogenic lead
5 (Reuer and Weiss, 2002).
6 Airborne lead tends to be in the form of submicron aerosols (Davidson and Rabinowitz,
7 1992; Davidson and Osborn, 1986; Harrison, 1986; Lin et al., 1993). The mass median diameter
8 averaged for several studies is 0.55 jim (Milford and Davidson, 1985). A study performed in
9 1991, after leaded gasoline was no longer the predominant source of lead in the atmosphere,
10 showed a bimodal distribution for lead particles with the larger peak in the fine fraction (Lin
11 et al., 1993). The mass median diameter for lead samples was 0.38 ± 0.06 jim in the fine fraction
12 and 8.3 ± 0.6 jim in the coarse fraction. Since small particles are much slower to deposit than
13 larger particles, lead can be transported great distances in the atmosphere. Detectable quantities
14 of lead have been found even in the most remote places on earth. Because much of the airborne
15 lead is generally associated with fine particles, atmospheric dispersion models used for gaseous
16 pollutants can be applied to estimate atmospheric flows of lead under certain conditions. Use of
17 such dispersion models is more accurate for submicron lead emitted from stacks than it is for
18 larger particles resulting from fugitive emissions, such as resuspended soil particles.
19 The airborne concentration of a species emitted from a point source is frequently
20 described with a Gaussian distribution. This simple description holds true only when turbulence
21 is stationary and homogeneous. However, the Gaussian model can be modified to account for
22 more complex atmospheric conditions. For a thorough discussion of assorted Gaussian plume
23 models and parameters, the reader is directed toward the work of Seinfeld and Pandis (1998).
24 Gaussian models are in general reasonably accurate for small-scale work - within approximately
25 100 km of the source.
26 The rate and direction of dispersion are dependent both on pollutant characteristics and
27 meteorological conditions. Important meteorological factors include windspeed, surface
28 roughness, inversion frequency, inversion duration, and the temperature.
29 A Gaussian dispersion model (EMITEA-AIR) was applied to theoretical primary and
30 secondary lead smelters in Europe (Baldasano et al., 1997). This model accounts for plume rise
31 as well as interactions between the plume and terrain. Two sites were modeled. Conditions in
May 2006 2-52 DRAFT-DO NOT QUOTE OR CITE
-------
1 Copenhagen, Denmark included flat terrain, dominant strong winds, neutral or stable turbulence,
2 and an annual mean temperature of 10°C. Conditions in Catalunya, Spain had a complex terrain,
3 weak winds, unstable turbulence, and an annual mean temperature of 15°C.
4 The results of these modeling efforts showed that airborne concentrations of lead were
5 both lower and more symmetric surrounding the Copenhagen site than surrounding the
6 Catalunya site (Baldasano et al., 1997). Concentrations at the Copenhagen site had a maximum
7 value of 0.004 |ig/m3. Concentrations at the Catalunya site ranged between 0.065 and 0.3 |ig/m3.
8 The prevalence of calm winds and the complex terrain were the most important factors
9 contributing to high lead concentrations surrounding the Catalunya smelter.
10 Modeling efforts for an abandoned battery recycling facility using the EPA Industrial
11 Source Complex Short Term (ISCST) model, based on Gaussian equations, showed good
12 agreement with measured concentrations (Small et al., 1995). Model predictions at three sites at
13 distances between 240 and 310m from the stack were between 3.8 and 4.4 |ig/m3, whereas
14 measured concentrations taken when the plant was in full operation had averages between
15 4.1 and 5.2 |ig/m3.
16 For long-range transport modeling, Lagrangian trajectory or Eulerian grid models are
17 commonly employed. These models determine how a parcel of air moves relative to the moving
18 fluid and a fixed coordinate system, respectively.
19 Two Lagrangian experiments were performed in the Azores in the northern Atlantic
20 (Veron and Church, 1997). Retrospective air mass trajectories based on the hybrid single-
21 particle Lagrangian integrated trajectory (HY-SPLIT) model found that air masses enriched with
22 lead had been over continental regions ten days prior to testing. This is consistent with current
23 understanding that most lead emissions are from sources on continents, not from oceanic
24 sources. Airborne lead at this remote location was transported from several different countries
25 (Veron and Church, 1997).
26 Similarly, backward air mass trajectories estimated for Greenland showed that the highest
27 air concentrations of metals were in air parcels that had been over continental regions five days
28 earlier (Davidson et al., 1993). The model used in this study employed a constant acceleration
29 formulation of the trajectory equations and encompassed air parcel movements affected by
30 terrain and meteorology. The air masses with the highest metal concentrations were traced back
May 2006 2-53 DRAFT-DO NOT QUOTE OR CITE
-------
1 to polluted regions, including the Arctic Basin, eastern North America, and Western Europe
2 (Davidson etal., 1993).
3 A numerical model that combined weather system modeling with three-dimensional
4 Lagrangian transport and diffusion modeling was used to determine the foreign contributions of
5 lead to airborne concentrations in Israel (Erel et al., 2002). These predictions, in conjunction
6 with isotopic measurements, indicated that Israel received significant amounts of lead from
7 Egypt, North Africa, the United Arab Emirates, Jordan, Turkey, and Eastern Europe (Erel et al.,
8 2002).
9
10 Historical Records of A tmospheric Lead Transport and Deposition
11 An important field of research involves analyzing natural records of lead deposited from
12 the atmosphere. Lead concentrations are measured in media such as soil, sediments, ocean
13 water, peat bogs, plants, snowpacks, or ice cores. Based on concentrations, ratios to other
14 pollutants, or isotopic compositions, an airborne concentration is back calculated and in some
15 cases the major emitters can be identified. Sediments can provide records dating back several
16 million years, peat bogs can reach back to the late glacial period (-15000 years ago), corals and
17 trees can record up to several hundred years, and lichens and mosses can provide recent
18 deposition data (Weiss et al., 1999). Additionally, some applications can yield data showing
19 variation with seasons or climate. These methods have been used to monitor both short and
20 long-range transport. For a comprehensive look at natural historical records, the reader is
21 referred to review articles by Weiss et al. (1999), Boutron et al. (1994), and Garty (2001).
22
23 2.3.2 Deposition of Airborne Particles
24 Deposition (both dry and wet) is the major removal mechanism for atmospheric
25 pollutants. Here we focus on deposition data published specifically for lead aerosols, although
26 the literature on particle deposition is extensive.
27
28 Dry Deposition
29 Dry deposition is the process by which pollutants are removed from the atmosphere in the
30 absence of precipitation. The downward flux,-F, is characterized by:
31
May 2006 2-54 DRAFT-DO NOT QUOTE OR CITE
-------
1 -F = VdC (2-5)
2
3 where C is the airborne concentration in |ig/m3 and Vd is the deposition velocity in m/second.
4 The deposition velocity is an empirical quantity defined by Equation 2-5 as the ratio of F to C
5 with units of m/s. It should be noted that both the airborne concentration and the deposition
6 velocity are dependent on vertical height.
7 The physical factors governing dry deposition are often described in a manner analogous
8 to electronic resistances (Davidson and Wu, 1990). The parameters of aerodynamic resistance,
9 boundary layer resistance, and surface resistance run in parallel with sedimentation resistance or
10 gravity. The relative importance of each of these resistances varies with particle size and
11 meteorological conditions (Wu et al., 1992a).
12 The size of depositing particles is arguably the most important factor affecting deposition
13 rates. For very small particles, Brownian motion is the dominant mechanism that transports
14 particles through the viscous sublayer that borders surfaces (Nicholson, 1988a). For large
15 particles, sedimentation is the most important process governing particle deposition.
16 For intermediate particles, impaction and interception largely determine deposition rates.
17 The deposition velocity has the most uncertainty for these intermediate sized particles
18 (Nicholson, 1988a). Although most of the airborne lead mass was associated with submicron
19 particles, only about 0.5% of the lead particle mass undergoing dry deposition in Chicago was
20 <2.5 |im in diameter (Lin et al., 1993). Additionally, more than 90% of lead particle mass that
21 undergoes dry deposition is in an insoluble chemical form (Gatz and Chu, 1986).
22 Deposition velocities for lead are in the range of 0.05 to 1.3 cm/s. Table 2-20 is a
23 compilation of data from the literature. Figure 2-5 shows the variation of deposition velocity for
24 lead as a function of particle size.
25
26 Wet Deposition
27 Wet deposition is the process by which airborne pollutants are scavenged by precipitation
28 and removed from the atmosphere. The flux of a depositing species can be defined through the
29 following equation:
30
31 F=VPCP (2-6)
32
May 2006 2-55 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-20. Dry Deposition Velocities for Lead Particles
pj
to
o
o
ON
to
1
ON
O
f?
H
6
o
0
H
O
o
H
W
O
O
w
Vd (cm/s)
0.26
0.56
0.06 ±0.02
0.06 ± 0.02
0.09 ±0.03
0.26
0.14±0.13
0.15 ±0.07
0.41
0.43
0.19
0.33 ±0.03
0.31 ±0.02
0.37 ±0.04
0.31 ±0.02
0.28 ±0.05
0.34 ±0.05
0.9 ±0.3
1.3±0.5
0.05
0.005
0.06 ±0.01
0.46
0.06
0.13
MMAD(um)
all
all
all
all
all
all
10% >4
0.87
0.68
0.75
0.70
0.79
0.79
0.5
0.5
0.5
0.3
82%<1
Surface
water
orchard grass
all
teflon plates
teflon plates
water
water
land
alfalfa + oil
alfalfa + oil
grass + oil
grass + oil
soil
soil
beech canopy
spruce canopy
polyethylene petri dish
oak
polyethylene petri dish
filter paper
bucket
water
Other
model of Rojas et al.(1993)
model of Slinn & Slinn (1 980)
model of Williams (1982)
mass balance model
stable conditions
unstable conditions
stable conditions
unstable conditions
stable conditions
unstable conditions
throughfall
throughfall
foliar extraction
aerometric mass balance
Reference
Davidson and Rabinowitz (1992)
Davidson and Rabinowitz (1992)
Rojas etal. (1993)
Rojas etal. (1993)
Rojas etal. (1993)
Friedlander etal. (1986)
Davidson and Wu (1990)
Davidson et al. (1985)
Davidson and Wu (1 990)
Davidson and Wu (1990)
Davidson and Wu( 1990)
El-Shobokshy(1985)
El-Shobokshy(1985)
El-Shobokshy(1985)
El-Shobokshy(1985)
El-Shobokshy(1985)
El-Shobokshy(1985)
Davidson and Wu (1990)
Davidson and Wu (1 990)
Davidson and Wu (1990)
Davidson and Wu( 1990)
Davidson and Wu( 1990)
Davidson and Wu( 1990)
Davidson and Wu (1 990)
Davidson and Wu( 1990)
taken from Dedeurwaerder et al. (1983)
taken from Dedeurwaerder et al. (1983)
taken from Dedeurwaerder et al. (1 983)
taken from Hofken et al. (1983)
taken from Hofken et al. (1983)
taken from Lindberg and Harriss (1981)
taken from Lindberg and Harriss (1981)
taken from Lindberg and Harriss (1981)
taken from Pattenden et al. (1982)
taken from Rohbock (1982)
taken from Sievering et al. (1979)
Source: Davidson and Rabinowitz (1992), Rojas et al. (1993), Friedlander et al. (1986), Davidson and Wu (1990), Davidson et al. (1985), and El-Shobokshy (1985).
-------
Deposition Velocity
ilUUU
^ 1000
E
u
>•
o 0.100
o
0)
c
5 0.010
v>
0
Q.
Q)
Q
n nn-i
1
a
-s
-t
_\
. \
- '
~
: .
_
r
-
~_
~
/*""'*
/
k
\
X
\
*v
\
1 ^
\
t
/
{ i
/ \l
S
^ Density = 6 g cm"3
*~ ~""
/
1 1 I 11 1 1 1 1 1 1 1 1 1 i 11 1 1 1 1 1 1 1
0.01 0.10 1.00 8.00
Mean Stokes Diameter ((jm)
Figure 2-5. The deposition velocity plotted against the geometric mean Stokes diameter
for particles with a density of 6 g/cm 3 (i.e., lead). Error bars are shown and
the arrow indicates a negative value for the lower limit of uncertainty.
Source: Reprinted from Main and Friedlander (1990).
1 where Vp is the rate of precipitation in cm/s and Cp is the concentration of the chemical species
2 in the precipitation in |ig/L (Miller and Friedland, 1994).
3 The size of particles can influence wet deposition rates. Large particles are scavenged
4 more efficiently. Lead, which is found primarily in the submicron size range, does not undergo
5 wet deposition as easily as many of the crustal elements (Davidson and Rabinowitz, 1992).
6 Conko et al. (2004) note a seasonal trend in wet deposition rates for lead. The highest
7 concentrations were observed in the summer months, which the authors attribute to increased
8 emissions from electric power plants. This contradicts the findings of Gelinas and Schmit
9 (1998), who found the lowest deposition of lead occurred in the summer. The authors suspect
10 that this is due to decreased traffic in the summer months.
11 Regional differences may affect deposition rates. Miller and Freidland (1994) observed
12 wet deposition fluxes at an elevation of 1200 m that were almost twice as high as fluxes
13 observed at low altitudes. This effect is observed because wet deposition of lead occurs almost
May 2006
2-57
DRAFT-DO NOT QUOTE OR CITE
-------
1 exclusively through rainfall at low elevations, but cloudwater interception is an important factor
2 at high elevations in addition to rainfall. Comparing values for urban and rural sites, similar
3 rates of wet deposition were observed indicating that lead is widely disbursed and is emitted by
4 area sources (Conko et al., 1994).
5 Precipitation activity has been linked to variability in wet deposition rates. Intense rain
6 showers had lower lead concentrations than slow, even rainfalls (Chow, 1978). Thunderstorms
7 typically did not have detectable quantities of lead but occasionally produced very high levels.
8 The concentration of lead in rainfall does not appear to be correlated to the amount of
9 time between rainfalls, but meteorological conditions such as a thermal inversion preceding a
10 rainfall may affect the lead content (Chow, 1978).
11 Lead in rainwater includes both dissolved and particulate material. Approximately 83%
12 of lead in wet deposition samples was in a soluble form, compared to less than 10% in dry
13 deposition samples (Gatz and Chu, 1986).
14 Typical concentrations of lead in precipitation are listed in Table 2-21. The table shows a
15 pronounced downward trend with time presumably due to the phase out of leaded fuel.
16
17 Bulk Deposition
18 Bulk deposition is the rate of dry and wet deposition combined. It is typically sampled in
19 open buckets or other open containers. This is often used to estimate the overall rate of
20 atmospheric input to soil, surface water, or other terrestrial media. However, it is understood
21 that dry deposition onto surrogate surfaces may differ greatly from dry deposition onto natural
22 surfaces. The ratio of dry to wet deposition is 1.5, 0.4, and 0.25 in marine, rural, and urban areas
23 respectively (Galloway et al., 1982). The ratio of dry deposition to wet deposition ranged
24 between 0.1 and 0.5 in arctic regions (Davidson and Rabinowitz, 1992). In a literature survey,
25 Hicks (1986) found that this ratio varied between 0.4 and 1.8.
26
27 2.3.3 Resuspension of Lead-Containing Soil and Dust Particles
28 The resuspension of soil-bound lead particles and contaminated road dust is a significant
29 source of airborne lead. Here we focus on resuspension by wind and vehicular traffic although
30 resuspension through other mechanical processes such as pedestrian traffic, agricultural
31 operations, construction, and even raindrop impaction is possible. In general, mechanical
May 2006 2-58 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-21. Concentrations of Lead in Rainwater in the United States
Dates of
Testing
1966-1967
1971-1972
1975-1976
1977-1978
1982
pre-1982
pre-1982
pre-1982
1988-1989
1998
Precipitation
concentration
(Mg/L)
32.7
31.2
25.2
15.6
17.0
44
5.4-147
12
0.59-64
0.09
0.02-0.41
1.9
0.47 ±0.55
Cloudwater
concentration
(jig/L) Location
98.1 Northeastern US
93.6 Northeastern US
75.6 Northeastern US
46.8 Northeastern US
5 1 Northeastern US
n.a. Urban areas
n.a. Rural areas
n.a. Remote areas
5.4 Northeastern US
n.a. Reston, VA
Source
Lazrusetal. (1970)a
Schlesinger and Reiners (1974)a
Smith and Siccama (1981)a
Smith and Siccama (1981)a
Scherbatskoy and Bliss (1984)a
Galloway etal. (1982)b
Galloway etal. (1982)b
Galloway etal. (1982)b
Miller and Friedland (1991)a
Conko et al. (2004)
Source: a Cited in Miller and Friedland (1994), b cited in Davidson and Rabinowitz (1992), and Conko et al. (2004).
1
2
3
4
5
6
7
0
o
9
10
11
12
stresses are more effective
1988b).
Rapid
at resuspending particles than wind (Sehmel, 1980; Nicholson,
calculations of ambient, respirable concentrations of lead from resuspension can
performed through the use
PMio can be
of fugitive dust emission factors. The
estimated through the following equation (Cowherd
where RIO is the emission
contaminant
RIO — a EIQ A
be
emission rate of a pollutant as
etal., 1985):
(2-7)
rate of a contaminant as PMio (units of mass/time), a is the fraction
in the PMio size range (mass/mass), E10 is the PMio
of
emission factor (mass/source
extent), and A is the source extent (in source dependent units, which are typically area but can
volume).
be
May 2006
2-59
DRAFT-DO NOT QUOTE OR CITE
-------
1 Emission factors for fugitive dust depend on whether the predominant force of
2 resuspension is traffic or other mechanical disturbance, or wind. Emission factors are not
3 recommended for detailed calculations but can provide order of magnitude assessments with
4 minimal effort. Condition specific equations for fugitive dust emissions are provided by
5 Cowherd et al. (1985) and AP-42 (U.S. Environmental Protection Agency, 2005).
6 Understanding the physics of resuspension from natural winds requires analyzing the
7 wind stresses on individual particles, including frictional drag, form drag, gravitation, and the
8 Bernoulli effect (Sehmel, 1980). Although this analysis can be accurate on a small scale,
9 predicting resuspension on a large scale generally focuses on empirical data for continual soil
10 movement due to three processes: saltation, surface creep, and suspension (Sehmel, 1980;
11 Nicholson, 1988b). Saltation is the process by which particles in the 100 to 500 |im size range
12 bounce or jump close to the surface. The low angle at which these particles strike the surface
13 can transfer momentum to smaller particles allowing them to be suspended into the atmosphere
14 (Sehmel, 1980; Nicholson, 1988b). Depending on soil conditions, saltation can be responsible
15 for moving 50 to 75% of surface particles. Surface creep is the rolling or sliding motion of
16 particles, which is induced by wind stress or momentum exchanged from other moving particles.
17 This generally applies to large particles 500 to 1000 jim in diameter and moves 5 to 25% of soil
18 by weight (Sehmel, 1980; Nicholson, 1988b). Suspension is the process that actually ejects
19 particles into the air. This affects particles smaller than 100 jim in diameter and moves 3 to 40%
20 of soil by weight (Sehmel, 1980; Nicholson, 1988b).
21 Resuspension is often defined in terms of a resuspension factor, K, with units of m"1, or a
22 resuspension rate (A), with units of sec"1. The resuspension factor was used in early research on
23 reentrainment and is defined by:
24
25 K= """-^-"Y (2-8)
26
27 where Ca;r is the airborne concentration of a chemical species and Csoii is the surface soil
28 concentration of the same species. K has significant limitations, in that it is dependent both on
29 the height at which Ca;r is measured and the depth to which Csoii is measured. This factor also
30 assumes that all airborne material is a direct result of resuspended soil-bound material, which is
May 2006 2-60 DRAFT-DO NOT QUOTE OR CITE
-------
1 not the case in most situations (Sehmel, 1980; Nicholson, 1988b). Additionally, K cannot be
2 used if soil concentrations are not uniform across the area of interest (Nicholson, 1988b).
3 The resuspension rate, A, is the fraction of a surface contaminant that is released per time
4 and is defined by:
5
6 A= R
-------
1 driven by saltation and not the direct pick-up by wind, the size distribution of resuspended
2 particles does not change with windspeed (Young et al., 2002).
3 Vehicular resuspension is the result either of shearing stress of the tires or turbulence
4 generated by the passing vehicle (Nicholson, 1988b; Nicholson et al., 1989). This process can be
5 particularly important, since the most contaminated roadways tend to have the most traffic.
6 As with wind resuspension, a number of factors can affect the rate of resuspension from
7 vehicular motion. These factors include vehicle size, vehicle speed, moisture, and particle size.
8 Lead in street dust appears to have a bimodal distribution. The fine mode is likely from
9 vapor phase condensation from combustion engines, while the coarse mode is from either vehicle
10 wear or significant coagulation of smaller particles. Al-Chalabi and Hawker (1997) observed
11 that in roadways with significant resuspension, lead concentrations were lower indicating either
12 dispersion from the source or the scavenging of smaller lead particles by coarser particles.
13 Abu-Allaban et al. (2003) similarly observed that lead in road dust tended to be in the coarse
14 mode. Measurements performed in tunnel tests indicated that < 17% of PMio lead was smaller
15 than 2.5 |im (Lough et al., 2005).
16 Resuspension may occur as a series of events. Short episodes of high windspeeds, dry
17 conditions, and other factors conducive to resuspension may dominate annual averages of
18 upward flux (Nicholson, 1988b, 1993).
19 The concentrations of lead in suspended soil and dust vary significantly. In suspended
20 soils sampled near industrial emitters of lead, PMio-bound lead varied between 0.012 and 1.2 mg
21 Pb/ kg of bulk soil (Young et al., 2002). Tsai and Wu (1995) measured lead in airborne particles
22 that was 30 times higher than lead in road dust. This enrichment factor was much higher than for
23 other pollutants, which may indicate that lead is more easily resuspended than other
24 contaminants. The fractions of lead in suspended dusts and soils are listed in Table 2-22.
25 The contribution of resuspended soil and dust to the airborne burden may be significant,
26 particularly from highly contaminated sites. A source apportionment study in Boston indicated
27 that soil resuspension increased the airborne concentration of lead by as much as 0.02 |ig/m3 in
28 the fine mode (Thurston and Spengler, 1985). Isotopic measurements in Yerevan, Armenia
29 credited resuspension of contaminated soil with 75% of the atmospheric lead in 1998 (Kurkjian
30 et al., 2002). Calculations based on road dust emissions and lead weight fractions indicate that
31 resuspension was responsible for -40% of overall lead emissions to the South Coast Air Basin of
May 2006 2-62 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-22. The Percentage of Lead in Resuspended Particulate Matter
Source
Paved road dust
Paved road dust
Paved road dust
Paved road dust
Unpaved road dust
Unpaved road dust
Unpaved road dust
Unpaved road dust
Agricultural soil
Agricultural soil
Agricultural soil
Agricultural soil
Agricultural soil
Agricultural soil
Playa dust
Sand & gravel storage
Construction site
Location
Urban
San Joaquin
Valley
Urban
Fresno, CA
Urban
Reno and
Sparks, NV
Rural
San Joaquin
Valley
Rural
San Joaquin
Valley
Rural
Bakersfield, CA
Residential
San Joaquin
Valley
Staging area
San Joaquin
Valley
San Joaquin
Valley
San Joaquin
Valley
San Joaquin
Valley
San Joaquin
Valley
San Joaquin
Valley
Stockton, CA
Rural
Reno and
Sparks, NV
Visalia, CA
Urban
Reno and
Sparks, NV
Pb fraction of
PM10 mass (%)
0.0161 ±0.0031
0.3 ±0.03
0.0057 ±0.0028
0.0058 ±0.0073
0.01
0.0203 ±0.0133
0.0043 ± 0.0008
0.0063 ±0.0059
0.0031 ±0.0025
0.0062 ± 0.0034
0.0024 ± 0.0082
0.003 ± 0.0025
0.01
0.02
Pb fraction of
PM2.5 mass (%) Reference
Chow etal. (2003)
0.4 Chow etal. (1994)
l.E-02 Gillies etal. (1999)
Chow etal. (2003)
Chow etal. (2003)
Chow etal. (1994)
Chow etal. (2003)
Chow etal. (2003)
Chow etal. (2003)
Chow etal. (2003)
Chow etal. (2003)
Chow etal. (2003)
Chow etal. (2003)
Chow etal. (1994)
l.E-03 Gillies etal. (1999)
Chow etal. (1994)
l.E-03 Gillies etal. (1999)
Source: Chow et al. (1994, 2003) and Gillies et al. (1999).
May 2006
2-63
DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
California in 1989 (Lankey et al., 1998). Resuspension estimates based on modeling efforts for
the same area suggest that resuspension contributed -90% of overall lead emissions in 2001
(Harris and Davidson, 2005). Figures 2-6 and 2-7 demonstrate how air and soil concentrations
are affected by long-term resuspension.
0.010
CM
£
"B)
c
0
4J
re
4->
c
o
o
c
0
o
o o
= 1x1(r10/s
A = 1x1(T9/s
A = 1x1CT8/s
0.000 \
1970 1975
1980 1985
Year
1990 1995 2000
Figure 2-6. The modeled soil concentrations of lead in the South Coast Air Basin of
California based on four resuspension rates.
Source: Reprinted from Harris and Davidson (2005).
7 2.3.4 Runoff from Impervious Surfaces
8 The runoff of water from impervious surfaces may be a significant transport route for lead
9 from urban areas to soil, waterways, and catchment basins. As water runs off roadways and
10 buildings, it can become laden with dissolved and suspended matter. Dust on roadways contains
11 a significant fraction of lead due to vehicle wear, vehicle emissions, road wear, fluid leakage,
12 and atmospheric deposition. Lead in road dust is discussed in further detail in Sections 2.3.3 and
13 3.2 of this document. Additionally, lead-containing paints, gutters, roofing materials, and other
14 housing materials may leach with rainfall.
May 2006
2-64
DRAFT-DO NOT QUOTE OR CITE
-------
1975
1980 1985 1990 1995 2000
Year
Figure 2-7. The modeled and measured airborne concentrations of lead in the South
Coast Air Basin of California based on two resuspension rates.
Source: reprinted from Harris and Davidson (2005).
1 Urban catchments in Fresno, California had highly elevated soil lead concentrations,
2 suggesting high concentrations of lead in runoff waters (Nightengale, 1987). Basins in use since
3 1962, 1965, and 1969 had surface soil concentrations of 570, 670, and 1400 ppm, respectively.
4 Nearby control soils had surface concentrations between 8.3 and 107 ppm.
5 Urban runoff released into a stream in State College, Pennsylvania caused significant
6 spikes in lead concentrations (Lieb and Carline, 2000). Concentrations upstream of the release
7 point were 1.5 |ig/L. Downstream concentrations were 1.8 |ig/L when there was no precipitation
8 and averaged 14.6 |ig/L during storm events.
9 The amount of lead that is removed from roadways and buildings by rainwater depends
10 somewhat on the intensity of the storm. Experiments performed by Davis and Burns (1999)
11 indicated that high intensity storms washed away significantly more exterior house paint than
12 low-intensity storms. A separate set of experiments showed that the amount of lead contained in
13 roadway runoff increased significantly with the length of the dry period prior to a rain event
14 (Hewitt and Rashed, 1992).
May 2006
2-65
DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead in runoff water is primarily in the particulate form, with a very small fraction in the
2 dissolved form (Hewitt and Rashed, 1992; Davis and Burns, 1999; Roger et al., 1998). Between
3 69% and 93% of lead washed from painted structures was in paniculate form (Davis and Burns,
4 1999). More than 90% of lead in highway runoff from a rural highway in the UK was in the
5 particulate phase (Hewitt and Rashed, 1992). Roger et al. (1998) observed that lead particles in a
6 motorway catchment in France were typically <50 jim in diameter. Samples taken from road
7 water samples also in France showed that most lead was in an inorganic, non-bioavailable form
8 (Flores-Rodriguez et al., 1994).
9 The amount of lead from roadways varies by region, the rainfall intensity, maximum
10 inflow, rainfall duration, and the antecedent dry weather period (Shinya et al., 2000).
11 Measurements taken near a roadway in France showed that in runoff water, concentrations
12 ranged between 0.46 and 4.57 g Pb/kg of suspended PM (Roger et al., 1998). Another study of
13 French roadways had an average lead content of 2.36 g Pb/kg of dried material (Flores-
14 Rodriguez et al., 1994). Thirteen storm events studied at a heavily trafficked, rural highway in
15 England showed mean lead contents of 181 jig/L (Hewitt and Rashed, 1992). Of this total, 16.2
16 ±6.9 |ig/L was in the dissolved phase and 165 ± 101 jig/L in the particulate phase. An
17 additional 0.36 |ig/L was in an organic form. The mean concentrations of lead during four rain
18 events studied near a roadway in Japan ranged between 17 and 39 jig/L (Shinya et al., 2000).
19 The initial concentrations were higher, ranging from 130 to 567 |ig/L. This indicates the
20 presence of a first flush effect in which much of the contamination is removed within the initial
21 period of rainfall. Hewitt and Rashed (1992) observed a similar downward trend in the lead
22 concentration with time. However, no first flush phenomenon was observed in the study
23 performed by Taebi and Droste (2004), which evaluated combined urban runoff transported to a
24 mixed residential and commercial urban catchment in Iran. The concentrations of lead for each
25 of 10 major rainfall events ranged between 0.018 and 0.558 |ig/L. The arithmetic mean for all
26 10 events was 0.278 |ig/L.
27 Studies of runoff from building materials showed high lead concentrations from painted
28 wood and painted brick, particularly if the paint is more than 10 years old (Davis and Burns,
29 1999; Davis et al., 2001). The maximum concentrations of lead were 1900 |ig/L and 28000 |ig/L
30 associated with painted exterior wood and brick surfaces, respectively (Davis and Burns, 1999).
May 2006 2-66 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead from paint is released into waters in both particulate and dissolved form. The
2 concentrations in runoff from building surfaces are listed in Table 2-23.
Table 2-23. The Concentrations of Lead in Runoff From Building Surfaces
Geometric
Substance Mean (jig/L)
Block (painted)
Brick (painted)
Wood (painted)
0-5 yr. old paint
5-10 yr. old paint
>10yr. old paint
Roofs
Residential roofs
Commercial roofs
Institutional roofs
9.2
22
43
8.0
18
81
6.0
Median
(Mg/L)
8.0
16
49
8.1
14
88
5.2
2
12
64
Mean
Hg/L)
38
580
170
27
120
810
38
1.5
62
64
Range (jig/L)
<2-590
<2-28000
<2-1900
<2-370
<2-2600
<2-28000
<2-590
Reference
Davis and Burns (1999)
Davis and Burns (1999)
Davis and Burns (1999)
Davis and Burns (1999)
Davis and Burns (1999)
Davis and Burns (1999)
Davis and Burns (1999)
Davis etal. (2001)
Davis etal. (2001)
Davis etal. (2001)
Source: Davis and Burns (1999) and Davis et al. (2001).
3 Matthes et al. (2002) studied runoff from lead sheet to simulate lead in gutters, roofs,
4 piping, siding, and sculptures. Typical concentrations in runoff ranged between 700 and
5 3700 mg/L. This was attributed to the solubility of cerrusite (lead carbonate) and hydrocerrusite
6 (lead hydroxy carbonate), which form on the surface of air-exposed lead. Lead corrosion
7 (cerrusite and hydrocerrusite) dissolution rates from lead sheets were measured at 14.3 to
8 19.6 millimoles of lead/m2 per year (Matthes et al., 2002).
9 The amount of lead removed by runoff events varies. Hewitt and Rashed (1992) estimate
10 that approximately 8% of lead and 5% of organic lead emitted from vehicles is removed by
11 highway drainage waters. Shinya et al. (2000) estimate that total lead loads for a roadway in
12 Japan prior to four storm events ranged between 0.053 and 0.771 mg Pb/m2. These storm events
13 removed half of the load in 0.07 to 3.18 hours after the start of the rainfall event.
May 2006
2-67
DRAFT-DO NOT QUOTE OR CITE
-------
1 Davis et al. (2001) estimate the total annual loading of lead from all sources to be between
2 0.069 and 0.18 kg Pb/ha. They estimate that 80 to 90% of this is derived from runoff from
3 buildings.
4
5 2.3.5 Leaching of Soil Lead
6 Soil lead has some capacity to leach through the soil column, potentially contaminating
7 ground water. Lead sorbs strongly to constituents of the soil matrix and is only weakly soluble
8 in pore water, so the leaching of lead is a much slower process than the leaching of many other
9 contaminants (Marcos et al., 2002; Zhang and Xu, 2003; Unlii, 1998; Pang et al., 2002). The
10 sorbing capacity of the soil and the solubility of the contaminants can be affected by the
11 hydraulic conductivity of the soil, the composition of the soil solution, the content of the soil
12 organic matter, the content of the soil clay minerals, soil pH, microbial activity, preferential flow
13 through plant root channels and animal holes, and geochemical reactions (Rhue et al., 1992;
14 Elzahabi and Yong, 2001). The experiments of Erel et al. (1997) on soil columns indicate that
15 anthropogenic lead is more readily available for leaching than lead that naturally occurs in
16 the soil.
17 Lead can bind to many different surfaces in the heterogeneous soil matrix. This
18 adsorption greatly affects mobility and is dependent on the characteristics of the soil and lead
19 compounds. Lead is partitioned between the soil water solution, precipitated forms, secondary
20 Fe or Mn oxides, carbonates, organic matter, sulfides, or the surfaces of clay, humus, or silicate
21 particles (Badawy et al., 2002; Venditti et al., 2000; Cajuste et al., 2000; Erel and Patterson,
22 1994). The most labile fraction of lead is adsorbed to the surfaces of colloid soil particles, which
23 may include organic matter, clay, oxides, or carbonates (Erel et al., 1997). Lead leached from a
24 limestone soil during a sequential fractionation procedure was exclusively in the iron/manganese
25 oxide form (Hee, 1994). A study of industrially contaminated soils found that between
26 approximately 50% and 60% of the lead was not susceptible to leaching during any phase of a
27 sequential fractionation procedure (Cajuste et al., 2000). The remaining lead was found
28 primarily in the carbonate and Fe-Mn oxide fractions, with sizeable amounts in the organic and
29 exchangeable phases. None of the lead was water soluble. Maskall and Thornton (1998) also
30 observed a high fraction of lead in the carbonate form in highly contaminated soil. The unusual
31 presence of carbonate-bound lead is probably due to the formation of cerrusite (PbCOs) in soils
May 2006 2-68 DRAFT-DO NOT QUOTE OR CITE
-------
1 contaminated with calcareous slag wastes (Maskall and Thornton, 1998). Lead migration in this
2 contaminated soil was associated with Fe-Mn oxides. A third contaminated site was tested by
3 Jing et al. (2004). These soils showed 57% of lead in the Fe-Mn oxide form, 29% in the
4 carbonate form, and just 5% in the residual, soil-bound form.
5 High chlorine content in soil has been shown to increase lead leaching (Urdu, 1998).
6 Chloride complexation with lead enhances lead solubility.
7 The pore-water velocity is inversely proportional to sorption rates. At low flow, the
8 longer retention times lead to more complete sorption of lead to soil particles (Pang et al., 2002).
9 In laboratory experiments on soil columns, transport of lead was enhanced by the
10 introduction of soil colloid suspensions (Karathanasis, 2000). Colloids increased transport of not
11 only colloid-bound lead but also dissolved lead. Colloid transport was enhanced by increasing
12 the colloid surface charge, increasing the pH, increasing the amount of organic carbon,
13 increasing the soil macroposity, decreasing the colloid size, and decreasing the Al, Fe, and quartz
14 contents (Karathanasis, 2000). Colloid binding and co-transport of lead are important
15 mechanisms for lead migration, but colloids also enhance the flow of lead through physical
16 blockage from exchange sites, competitive sorption, and organic complexation (Karathanasis,
17 2000). Denaix et al. (2001) observed that most of the lead-transporting colloids in an acidic,
18 loamy soil were biological in nature. The lead concentration in the colloid fraction was not
19 correlated with pH, colloidal organic carbon contents, or colloidal silicon concentrations (Denaix
20 et al., 2001). Approximately 50% of the total lead transfer in these experiments was attributed to
21 colloidal transfer.
22 At low pH, metal species bound to carbonates, hydroxides, and other soil matrix
23 components are more likely to dissolve into solution (Maskall and Thornton, 1998; Elzahabi and
24 Yong, 2001; Badawy et al., 2002). This increases the rate of lead migration through the soil.
25 The experiments of Jing et al. (2004), which followed eight different leaching protocols, suggest
26 that pH is the primary factor in determining the concentration of lead in leached solution. At pH
27 >12, lead forms soluble hydroxide anion complexes and leaches out of the soil column. At pH
28 between 6 and 12, lead leachibility is low due to adsorption and precipitation. At pH <6 free Pb
29 ions leach into the pore water and are removed from the soil columns. Rhue et al. (1992)
30 observed that organic lead species (Me2?b2+ and Et2Pb2+) were best absorbed at pH 6.2 and 7.2,
31 respectively. Sorption decreased at pH <5 and >8.2 (Rhue et al., 1992).
May 2006 2-69 DRAFT-DO NOT QUOTE OR CITE
-------
1 A partition coefficient, Kd, is often used to describe the susceptibility of lead to leaching.
2 This value is used to compare the fractionation of a contaminant between liquid and solid forms.
3 Kd is defined by the following equation:
4
5 Kd = S/C' (2-10)
6
7 where S is the total concentration of lead adsorbed in the solid phase and C' is the concentration
8 of lead in pore water solution (Elzahabi and Yong, 2001). Kd increases with increasing pH
9 (up to 7.0) and increasing distance from the leachate source (Elzahabi and Yong, 2001; Sheppard
10 and Sheppard, 1991). Kd decreases with an increase in the influent heavy metal concentration
11 and the degree of saturation (Elzahabi and Yong, 2001). The highest value of Kd appears to be
12 near the source of lead contamination. Values of Kd in the literature cover many orders of
13 magnitude between 1.20 L/kg and "infinity" (when no lead can be detected in pore water).
14 These values are listed in Table 2-24. For more information on lead solid-solution partitioning
15 see Chapter 8.
16 The rate of migration through the soil has been estimated in many different studies. Using
17 lead isotopes, Erel et al. (1997) estimate the rate of lead migration to be 0.5 cm/year in soils
18 collected from rural locations in Israel. Sheppard and Sheppard (1991) measured the rate of flow
19 through spiked soils, which were highly acidic and had a low organic matter content. These
20 soils, which were especially susceptible to leaching, exhibited migration rates of 0.3 cm/day
21 during the first year of experiments. The migration rate appeared to slow down in subsequent
22 years. Cores taken at smelting sites used during the Roman era, medieval times, and the
23 18th century underwent sequential extraction (Maskall and Thornton, 1998). The estimated lead
24 migration rates at the Roman, medieval, and 18th century sites were 0.07 to 0.54 cm/year, 0.31 to
25 1.44 cm/year, and 0.11 to 1.48 cm/year, respectively.
26 Mass balance calculations of Miller and Friedland (1994) suggest migration rates of
27 0.11 cm/year and 0.29 cm/year through the organic horizons of spruce-fir and northern hardwood
28 forests, respectively. Similar calculations by Kaste et al. (2003) at the same site predicted that
29 anthropogenic lead will take -60 and -150 years to be transported through the organic horizon in
30 the deciduous and spruce-fir forests, respectively. The difference in response times for the two
31 forests may be due to differences in the litter depth and/or in the rate of litter decomposition.
May 2006 2-70 DRAFT-DO NOT QUOTE OR CITE
-------
Table 2-24. Soil/Water Partition Coefficients for Several Different Soils and Conditions
Kd
(L/kg)
12.68
3.23
1.20
1.36
-6000
-3000
-5000
20
9000
92.99
14.25
125.58
95.51
1330±200
pH
4.0
4.0
3.5
3.5
n.a.
n.a.
n.a.
4.9
4.8
4.45
4.45
5.01
5.01
3.0-4.0
Beginning Soil
Water Content
(%)
26.69
28.20
26.29
26.32
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
Soil Type
illitic (spiked)
illitic (spiked)
illitic (spiked)
illitic (spiked)
brown pseudopodzolic
rendzina
gley podzolic
acidic (low-organic-matter sand)
sphagnum peat
mining site
mining site
mining site
mining site
acidic (high-organic-matter peat)
Reference
Elzahabi and Yong (2001)
Elzahabi and Yong (2001)
Elzahabi and Yong (2001)
Elzahabi and Yong (2001)
Alumaa et al. (2002)
Alumaa et al. (2002)
Alumaa et al. (2002)
Sheppard and Sheppard (1991)
Sheppard and Sheppard (1991)
Merrington and Alloway
(1994)
Merrington and Alloway
(1994)
Merrington and Alloway
(1994)
Merrington and Alloway
(1994)
Deiss et al. (2004)
Source: Elzahabi and Yong (2001), Alumaa et al. (2002), Sheppard and Sheppard (1991), Merrington and
Alloway (1994), and Deiss et al. (2004).
1 Soil tested from a car battery salvage facility showed a significantly greater lead
2 concentration in the leached solution than in a reference soil (Jensen et al., 2000).
3 Concentrations in the leached solution went as high as 8000 |ig/L. Other industrially
4 contaminated soils did not show such high rates of leaching, but these other soils had nearly
5 neutral pHs.
6 Isotopic ratios in soil cores in the Sierra Nevada, California showed that 21% of lead at a
7 depth of 30 cm had anthropogenic origins and had migrated from the surface (Erel and Patterson,
8 1994). The remaining 79% of lead at this depth was naturally occurring.
May 2006
2-71
DRAFT-DO NOT QUOTE OR CITE
-------
1 Physical mixing of soils through animal activity may also increase the rate of lead
2 migration. Mace et al. (1997) observed a significant decrease in lead transport time through soil
3 as a result of rodent activity in a southern California location.
4 Vilomet et al. (2003) used isotopes to trace the leaching of lead from a landfill into
5 groundwater in France. The active landfill has been in use since 1900 and has no bottom liner.
6 Detectable quantities of leached lead were observed as far as 4600 m downgradient (Vilomet
7 et al., 2003).
8
9 2.3.6 Transport in Aquatic Systems
10 Chemical, biological, and mechanical processes govern the cycling of lead in aquatic
11 environments. Here we focus on the exchange between sediment and surface water, which is
12 affected by many different factors including salinity, the formation of organic complexes, redox
13 conditions, and pH (Arakel and Hongjun, 1992).
14 Lead enters surface waters from a number of sources. Atmospheric deposition is the
15 largest source, but urban runoff and industrial discharge are also significant (Peltier et al., 2003;
16 Hagner, 2002; Perkins et al., 2000). As expected, concentrations in surface waters are highest
17 near sources of pollution.
18 The dispersal of lead in waterways is relatively quick. If lead is emitted into waterways as
19 a point source, water concentrations decrease rapidly downstream of the source (Rhoads and
20 Cahill, 1999; Hagner, 2002; Kurkjian et al., 2004; Peltier et al., 2003). Lead is removed from the
21 water column through flushing, evaporation, or sedimentation (Schell and Barnes, 1986).
22 Kurkjian et al. (2004) note that first order approximations of concentrations of non-conservative
23 pollutants (such as lead) can be made by using the exponential decay curve:
24
25 C = C0ekx (2-11)
26
27 where C is the pollutant concentration, C0 is the concentration at the source, x is the downstream
28 distance from the source, and k is the decay rate in km1. For the Debed River in Armenia,
29 Kurkjian et al. (2004) found that a decay rate of 0.57 km1 provided the best fit to measured lead
30 concentrations.
May 2006 2-72 DRAFT-DO NOT QUOTE OR CITE
-------
1 Metals in waterways are transported primarily as soluble chelates and ions, constituents of
2 PM, or by adsorption onto suspended organic or inorganic colloids (Arakel and Hongjun, 1992).
3 The last two are the most important for lead. The predominant chemical forms of lead that
4 interact with aqueous ecosystems are PbO and PbCOs (Schell and Barnes, 1986). Lead is
5 adsorbed on colloids that are typically secondary clay minerals, Fe-Mn oxides or hydroxides, or
6 organic compounds (Arakel and Hongjun, 1992). The concentration of lead appears to increase
7 with increasing salinity (Arakel and Hongjun, 1992).
8 Schell and Barnes (1986) describe water columns as "transient reservoirs" for pollutants.
9 They found mean residence times for lead in two lakes and a reservoir to be between 77 and
10 250 days, although it should be noted that residence times tend to be shorter in turbulent
11 waterways. Lead concentrations in water are attenuated by the presence of A1(OH)3
12 precipitation, which is responsible for an estimated 54% of total lead loss, and by the adsorption
13 of lead onto other particles which settle out of the water column, which makes up the other 46%
14 of lead loss (Kurkjian et al., 2004). Schell and Barnes (1986) measured sedimentation rates for
15 anthropogenic lead, which ranged between 0.0360 g cm2 a1 and 0.0644 g cm2 a1.
16 The concentration of lead in sediment roughly follows the concentration of lead in
17 overlying water (Kurkjian et al., 2004; Rhoads and Cahill, 1999). Thus, lead concentrations in
18 sediment are highest near sources and decrease downstream.
19 Lead preferentially sorbs onto small particles rather than large particles. Small grain sizes
20 and the larger surface area per unit weight lead to greater potential for adsorption (Rhoads and
21 Cahill, 1999). Concentrations of metals increase approximately logarithmically with decreasing
22 particle size.
23 Organic matter in sediment has a high capacity to accumulate trace elements. High humic
24 levels may lead to greater lead contamination in sediments (Rhoads and Cahill, 1999; Kiratli and
25 Ergin, 1996).
26 Sulfides are another potential source of lead adsorption. This is especially true under
27 anoxic conditions (Kiratli and Ergin, 1996; Perkins et al., 2000). An increase in the amount of
28 sulfide in pore water was shown to decrease the dissolved concentration of lead (Peltier et al.,
29 2003).
May 2006 2-73 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead in sediment can also be sequestered on iron or manganese oxides (Peltier et al.,
2 2003; Gallon et al., 2004; Schintu et al., 1991). These forms may make lead susceptible to
3 recycling into the overlying water column (Schintu et al., 1991).
4 Lead appears to be relatively stable in sediment. It has a very long residence time, and
5 many studies suggest that lead is not mobile in the sediment. However, many other studies
6 suggest that lead-containing particles can be remobilized into the water column (Ritson et al.,
7 1999; Steding et al., 2000; Hlavay et al., 2001; Kurkjian et al., 2004; Peltier et al., 2003; Gallon
8 et al., 2004). For example, Steding et al. (2000) observe that isotopic concentrations of lead in
9 the San Francisco Bay match those of leaded gasoline from the 1960s and 1970s, suggesting that
10 recontamination by sediment may be a significant source of lead to overlying waters. Ritson
11 et al. (1999) similarly observed that there was a negligible reduction in lead concentrations in the
12 San Francisco Bay despite the closing of a nearby lead smelter, the implementation of municipal
13 effluent controls, and the elimination of lead additives to gasoline. That concentrations have
14 remained high may suggest recycling of sediment lead. Similarly, in a study of water lead
15 concentrations in the North Sea, concentrations of lead did not decrease significantly with the
16 elimination of major sources (Hagner, 2002). This also may indicate continued high rates of
17 atmospheric deposition or cycling of lead stored temporarily in sediment.
18 Modeling efforts of Gallon et al. (2004) indicate that processes that resuspend sediment
19 (such as diffusion, bioturbation, and bioirrigation) are small compared to sedimentation of
20 colloidal particles. Kurkjian et al. (2004) suggest a correction factor for equation (9) to account
21 for the contribution of lead from sediment.
22
23 C = C0ekx + Is (2-12)
24
25 where Is is the amount of lead that is resuspended into the water column. Depending on
26 the region of the river under discussion, the authors extrapolated Is values in the range of
27 1.3-2.8 |igPb/L.
28
29
May 2006 2-74 DRAFT-DO NOT QUOTE OR CITE
-------
1 2.3.7 Plant Uptake
2 Plants that take up lead can be a source of lead exposure for wildlife, livestock, and
3 humans that consume contaminated plants. More thorough discussion of soil lead extraction by
4 plants and subsequent effects on ecosystem health can be found in Chapter 8.
5 Plants grown in soils contaminated by mine spoils (e.g., Cobb et al., 2000), smelting
6 operations (e.g., Barcan et al., 1998), sludge amendments (e.g., Dudka and Miller, 1999),
7 contaminated irrigation water (e.g., Al-Subu et al., 2003), or lead-containing agrochemicals (e.g.,
8 Azimi et al., 2004) have higher than natural concentrations of lead. In general, higher lead
9 concentrations in soils results in increased lead levels in plants.
10 Although the transfer of soil lead to plants and direct stomatal uptake of atmospherically
11 deposited lead are generally small, all plants accumulate lead to some degree (Finster et al.,
12 2004). The rate of uptake is affected by plant species, soil conditions, and lead species.
13 Of all the factors affecting root uptake, pH is believed to have the strongest effect (Dudka
14 and Miller, 1999). Acidic soils are more likely to have lead in solution and therefore available
15 for absorption. This is sometimes attenuated by liming.
16 Most lead in plants is stored in roots and very little is stored in fruits (e.g., Finster et al.,
17 2004; Cobb et al., 2000). Of 33 edible plants grown in urban gardens, roots had a median
18 concentration that was 12% of the soil lead concentration (Finster et al., 2004). Shoot lead, when
19 it was detectable, was just 27% of root lead. Root vegetables seem the most prone to lead uptake
20 followed by leafy vegetables (Dudka and Miller, 1999; Finster et al., 2004). Fruits and grains do
21 not seem as susceptible to lead contamination.
22 Metals that are applied to soil as salts (usually as sulfate, chloride, or nitrate salt) are
23 accumulated more readily than the same quantity of metal added via sewage sludge, flue dust, or
24 fly ash (Dudka and Miller, 1999). This is likely because metal salts lead to the formation of
25 metal chloride complexes and ion pairs, which can increase metal diffusion and subsequent root
26 uptake.
27
28 2.3.8 Routes of Exposure for Livestock and Wildlife
29 There are many routes of exposure, including food ingestion, drinking water, and
30 inhalation for terrestrial organisms. For aquatic organisms, the main routes of exposure are food
31 ingestion and water intake. A few representative studies which have analyzed routes of lead
May 2006 2-75 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposure for livestock and wildlife are summarized here. For a discussion of health effects,
2 toxicity, and lead concentrations in animal tissue, the reader is directed to Chapter 8.
3 Lead concentration of plants ingested by animals is primarily a result of atmospheric
4 deposition of lead particles onto plant surfaces rather than uptake of soil lead through plant roots
5 (Steinnes, 2001; Palacios et al., 2002; Dudka and Miller, 1999). The uptake of lead by the
6 lowest trophic levels - invertebrates, phytoplankton, and krill for example - are some of the most
7 important avenues for introducing lead into food chains (Pilgrim and Hughes, 1994; Sanchez-
8 Hernandez, 2000; Hagner, 2002).
9 Some of the highest levels of lead exposure in animals occur near major sources like
10 smelters. In two studies of horses living near smelters, the estimated ingestion rate was in the
11 range of 2.4 to 99.5 mg Pb/kg body weight per day (Palacios et al., 2002) and 6.0 mg Pb/kg body
12 weight per day (Liu, 2003). Both exposure rates were well above the estimated fatal dose for
13 horses. Sheep grazing near smelters were similarly poisoned (Liu, 2003; Pilgrim and Hughes,
14 1994). Installation of pollution controls at a lead smelter in Slovenia greatly reduced the amount
15 of lead in nearby vegetation and the blood lead levels of cows grazing on this vegetation
16 (Zadnik, 2004). Lead concentrations in topsoil at this site have not declined in the 20 years since
17 the pollution controls were implemented.
18 The amount of lead entering the food chain depends highly on the species of the animal,
19 the species of their food, and where the organisms live. A study of sheep living in the
20 southernmost part of Norway, which is the most polluted part of the country, showed a strong
21 correlation between liver lead concentrations and moss concentrations (Steinnes, 2001). The
22 sheep fed almost exclusively on a grass that picks up atmospherically deposited lead easily.
23 Correspondingly high levels were also observed in hare and black grouse in this region.
24 Similarly, a study of lead concentrations in raccoon tissues showed much higher concentrations
25 in urban raccoons that rural raccoons (Khan et al., 1995). This may be because urban raccoons
26 are exposed to higher air concentrations, ingest human refuse, or frequently visit storm sewers.
27 In general, ruminant animals appear to be more resistant to lead ingestion than monogastric
28 animals (Humphreys, 1991).
29 Lead levels are somewhat elevated even in Antarctic animals (Sanchez-Hernandez, 2000).
30 Antarctic food systems are supported by krill (Euphausia superbd), which is the primary food
31 source for organisms in higher trophic levels. Lead concentrations measured in E. superba were
May 2006 2-76 DRAFT-DO NOT QUOTE OR CITE
-------
1 in the range of 0.17-12.0 ppm by dry weight. This is probably elevated above natural levels due
2 anthropogenic input (Sanchez-Hernandez, 2000).
3 Acute lead poisoning observed in Laysan albatross (Phoebastria immutabilis) chicks was
4 traced to the direct ingestion of paint chips by using isotopic analysis (Finkelstein et al., 2003).
5 Blood lead levels in P. immutabilis at the Midway Island National Wildlife Refuge had a
6 geometric mean of 190 |ig/dL. P. immutabilis chicks at a reference site had blood lead levels of
7 4.5 |ig/dL.
8 Contamination in mammals and fish livers was shown to be higher in highly polluted
9 coastal zones than in the open sea (Hagner, 2002). In foraminifers, which are meiobenthic
10 organisms, high sediment concentrations corresponded to high tissue concentrations. Sediment
11 concentrations were 10 to 20 times higher than foraminifer concentrations. Fish take in lead
12 either in their food or in water through their gills. The relative importance of these two
13 mechanisms depends largely on the fish species. A literature survey suggests that there has been
14 no observable decrease in fish muscle and liver concentrations of lead in twenty years in marine
15 or freshwater environments (Hagner, 2002). Lead concentrations in the harbor porpoise
16 (Phocoenaphocoena) appear to increase with the age of the animal. This was not true for the
17 common seal (Phoca vitulina) (Hagner, 2002). Shrimp (Palaemonetes varians) were shown to
18 absorb 4 to 8% of the lead content of its prey (Boisson et al., 2003). Between 52% and 57% of
19 the lead accumulated from food was irreversibly retained in P. varians tissue. Just 2% of
20 dissolved lead accumulated from water was retained in tissue (Boisson et al., 2003).
21
22
23 2.4 METHODS FOR MEASURING ENVIRONMENTAL LEAD
24 The previous 1986 AQCD (U.S. Environmental Protection Agency, 1986) contained a
25 detailed review of sampling and analytical methods for lead in environmental media. Included in
26 that document were discussions of site selection criteria, sampling methods, sample preparation,
27 and analysis techniques. Furthermore, the document included discussion of sampling of lead
28 emissions from mobile and stationary sources. In this section, we present a brief summary of
29 sampling and analysis of lead. For a more comprehensive discussion, the reader is referred to the
30 1986 Lead AQCD.
May 2006 2-77 DRAFT-DO NOT QUOTE OR CITE
-------
1 Emissions can be estimated from measurements at sources using grab samples, periodic
2 samples, or continuous monitoring. Determining the rate of emissions requires knowing both the
3 fluid flow rate and the concentration of lead in the fluid, usually air or water. Thus it is much
4 easier to measure emissions from stacks than it is to measure fugitive, diffuse, or nonpoint
5 emissions (Frey and Small, 2003).
6 Much of the recent improvement in measurement of lead emissions from sources is due to
7 better sampling and analytical equipment. For example, better dilution tunnels can provide
8 reliable samples from in-stack sampling, and improved analytical methods such as inductively
9 couple plasma mass spectrometry permit determination of lead at lower levels than in years past.
10 This means it is possible to obtain data from short sampling runs, permitting better time
11 resolution.
12 Wet deposition can be collected using precipitation buckets that seal tightly immediately
13 before and after rain. Dry deposition on land can be sampled using surrogate surfaces such as
14 Teflon plates (Davidson et al., 1985; Davidson and Wu, 1990), or alternatively by leaf-washing
15 (Lindberg and Lovett, 1985) or sampling throughfall precipitation that washes previously
16 deposited lead off the vegetation and onto the forest floor (Wu et al., 1992b). Dry deposition
17 onto bodies of water is more difficult to estimate, usually requiring airborne concentrations used
18 with deposition velocity estimates (Zufall and Davidson, 1997). Subsequent analysis of all of
19 these samples can be performed by atomic absorption spectrometry, neutron activation analysis,
20 x-ray fluorescence, or proton-induced x-ray emission (Koutrakis and Sioutas, 1996), or by
21 inductively-coupled plasma mass spectrometry (ICP-MS) (U.S. Environmental Protection
22 Agency, 1991).
23 Recently developed single-particle instruments can identify which particles contain lead,
24 and what other elements are present in the same particle. Information on the size of the particle
25 is also provided (Pekney et al., 2006; Silva and Prather, 1997). Although such instruments are
26 not able to determine the precise mass of lead in each particle, they can provide valuable data on
27 the characteristics of particles that contain lead from individual sources or source categories.
28 Such "fingerprinting" methods can be used to identify sources of lead-containing particles in the
29 environment.
30
May 2006 2-78 DRAFT-DO NOT QUOTE OR CITE
-------
1 2.5 SUMMARY
2 The sources of airborne lead have been considered in three categories: natural sources,
3 stationary sources, and mobile sources. Nationwide, lead emissions fell 98% between 1970 and
4 2003 (U.S. Environmental Protection Agency, 2003). The elimination of alkyllead additives to
5 automotive gasoline was principally responsible for the drop, although lead emissions fell 5%
6 between 1993 and 2002 after the total phase-out of leaded fuel (U.S. Environmental Protection
7 Agency, 2003).
8 For most of the past 50 to 60 years, the primary use of Pb was as additives for gasoline.
9 Leaded gasoline use peaked in the 1970s, and worldwide consumption has declined since
10 (Nriagu, 1990). In 1970, on-road vehicles were responsible for 73% of lead emissions (U.S.
11 Environmental Protection Agency, 1994). In 2002, on-road vehicles contributed less than half
12 of a percent (U.S. Environmental Protection Agency, 2003). In every case where the lead
13 standard has been exceeded since 2002, stationary point sources were responsible
14 (www.epa.gov/air/oaqps/greenbk/inte.html).
15 Natural processes contribute a small amount to the overall load of lead in the
16 environment. Nriagu and Pacyna (1988) estimate mean global emissions are at least an order of
17 magnitude smaller than anthropogenic emissions. Natural sources include volcanoes, seasalt
18 spray, wild forest fires, wind-borne soil particles, and biogenic processes (Nriagu, 1989).
19 Stationary sources emitted an estimated 1,662,000 kilograms nationwide in 2000 (U.S.
20 Environmental Protection Agency, 2003). Currently, the major use of Pb in the United States is
21 in lead-acid batteries, for which the demand is increasing (Socolow and Thomas, 1997). Other
22 major uses are for glass, paints, pigments, and ammunition. United States consumption of Pb by
23 industry is shown in Figure 2-8. The consumption reached -1.4 million metric tons per year in
24 the mid 1990s (Socolow and Thomas, 1997). Approximately 910,000 metric tons of this was
25 secondary production, indicating high rates of Pb recycling.
26 The largest source of Pb emissions was leaded gasoline throughout the 1970s and 1980s.
27 The largest emitters are now in the manufacturing sector, which includes lead-acid battery plants,
28 smelters, lead-alloy production facilities, and others (Harris and Davidson, 2005). These
29 emissions are not confined to the air—approximately 90 facilities nationwide generate 90% of
30 the lead-containing solid hazardous waste (Chadha et al., 1998). Nationwide air emissions in
31 2000 were estimated as 1885 metric tons from metals processing, 758 metric tons from
May 2006 2-79 DRAFT-DO NOT QUOTE OR CITE
-------
1,600,000
1,400,000
j£ 1,200,000
"~ 1,000,000
-§ 800,000
^ 600,000
400,000
200,000
0
1—
L
r
HJ Other
g] Bearing Metals
^ Brass and Bronze
M Casting Metal
H Type metal
• Pipe and Sheet Lead
O Caulking Lead
@ Cable Coverings
Q Solder
E3 Ammunition
§ Pigments and paints
ED Gasoline additives
d Batteries
1968 1972 1976 1980 1984 1989 1993 1997 2001 2003
Year
Figure 2-8. Annual lead production and use in the U.S. (1968 and 2003).
Source: U.S. Bureau of Mines, 1968-1995 and USGS, 1996-2003.
1 incineration, 513 metric tons from transportation, primarily from avgas-fueled aircraft,
2 439 metric tons from fuel combustion for utility generation as well as industrial and commercial
3 purposes, 198 metric tons from Pb oxide and pigment production, and 48 metric tons from other
4 processes (U.S. Environmental Protection Agency, 2003).
5 Emission inventories for Pb have significant omissions and discrepancies (Harris et al.,
6 2006; Chadha et al., 1998). An analysis of four emission inventories for lead in southern
7 California showed that major emitters of lead were missed by all four databases, and that the
8 databases were not consistent with one another nor updated regularly (Harris et al., 2006). Thus,
9 the data above are probably a lower limit for Pb emissions. Efforts to develop accurate databases
10 of Pb emissions are needed.
11 The EPA Trends Report provides analysis of the available data on Pb emissions through
12 the year 2002 (http://www.epa.gov/airtrends/lead2/html) (U.S. Environmental Protection
13 Agency, 2003). Figure 2-9 shows the decline in estimated Pb emissions.
14
May 2006
2-80
DRAFT-DO NOT QUOTE OR CITE
-------
80,000
60,000
in 1985, EPA refined its methods for estimating emissions
| Transportation
Q] Industrial Processes
n Fuel Combustion
1982-02: 93% decrease
1993-02: 5% decrease
85
92 93 94 95 96 97 98 99 00 01 02
Year
Figure 2-9. Trends in U.S. air lead emissions, 1982-2002.
Source: U.S. Environmental Protection Agency (2003).
1 Air is the major transport route for lead emissions. Deposition of airborne pollutants to
2 surfaces has been observed in the most remote places on Earth, including the Arctic and
3 Antarctic. Mass balance calculations performed on an agricultural plot in France indicate that
4 atmospheric deposition is the dominant source of lead to soil even when lead-containing
5 fertilizer is applied (Azimi et al., 2004). However, on a local scale, solid waste disposal or mine
6 tailings may be the predominant source of soil lead.
1 A rigorous comparison of resuspension, leaching, and plant uptake "removal" rates for
8 soil lead has not been undertaken. Resuspension of lead-containing particles is likely the
9 dominant removal mechanism from surface soil when soil pH is high. Leaching may dominate
10 when soil pH is low. Leaching of lead through soil occurs more rapidly than uptake to pea or
11 wheat crops (Azimi et al., 2004). More research is needed to compare removal rates for other
12 plants with soil lead migration and resuspension rates.
13
May 2006
2-81
DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
7
10
11
Surface waters are contaminated through several routes. On a global scale, sediment
resuspension and wet and dry deposition are the predominant contributors to lead concentrations
in surface water. On a local scale industrial effluent and urban runoff may dominate.
The major routes of lead transport into the food chain appear to be ingestion of
contaminated plants, ingestion of contaminated water, and inhalation of contaminated air.
Research into the relative importance of each of these transport routes is needed.
Measurements conducted in any ecosystem worldwide show some level of lead
contamination. Anthropogenic Pb reaches these ecosystems through many possible transport
routes, which are shown in Figure 2-10.
Paints (weathering,
burning, sanding)
Oil & Coal
combustion
Smelting, refining
Cement production
Mining
Incineration
Sewage sludge
Municipal waste
ATMOSPHERE
Battery
Manufacturing/
recycling
Aircraft
Lead pipes
Storage tanks
Sewage effluent
Industrial effluent
Solid waste
disposal
Sewage sludge
Inorganic phosphatic
fertilizer
Paint
Figure 2-10. Transport pathways for lead in the environment.
Source: Modified from Zabel (1993).
May 2006
2-82
DRAFT-DO NOT QUOTE OR CITE
-------
1 REFERENCES
2 Abu-Allaban, M; Gillies, J. A.; Gertler, A. W.; Clayton, R.; Proffitt, D. (2003) Tailpipe, resuspended road dust, and
3 brake-wear emission factors from on-road vehicles. Atmos. Environ. 37: 5283-5293.
4 Al-Chalabi, A. S.; Hawker, D. (1997) Response of vehicular lead to the presence of street dust in the atmospheric
5 environment of major roads. Sci. Total Environ. 206: 195-202.
6 Al-Subu, M. M.; Haddad, M.; Mizyed, N.; Mizyed, I. (2003) Impacts of irrigation with water containing heavy
7 metals on soil and groundwater—a simulation study. Water, Air, Soil Pollut. 146: 141-152.
8 Alumaa, P.; Kirso, U.; Petersell, V.; Steinnes, E. (2002) Sorption of toxic heavy metals to soil. Int. J. Hyg. Environ.
9 Health 204: 375-376.
10 Annegarn, H. J.; Zucchiatti, A.; Sellschop, J. P. F.; Kusko, B. (1988) Composition and size of dust in a gold mine
11 atmosphere. J. Mine Vent. Soc. S. Afr. 41: 1-10.
12 Arakel, A. V.; Hongjun, T. (1992) Heavy-metal geochemistry and dispersion pattern in coastal sediments, soil, and
13 water of Kedron Brook floodplain area, Brisbane, Australia. Environ. Geol. Water Sci. 20: 219-231.
14 Azimi, S.; Cambier, P.; Lecuyer, I.; Thevenot, D. (2004) Heavy metal determination in atmospheric deposition and
15 otherfluxes in northern France agrosystems. Water Air Soil Pollut. 157: 295-313.
16 Badawy, S. H.; Helal, M. I. D.; Chaudri, A. M.; Lawlor, K.; McGrath, S. P. (2002) Soil solid-phase controls lead
17 activity in soil solution. J. Environ. Qual. 31: 162-167.
18 Baldasano, J. M.; Calbo, J.; Puig, O.; Guinart, X. (1997) Climatological modeling of lead particles dispersion from
19 typical primary and secondary lead smelters. In: Power, H.; Tirabassi, T.; Brebbia, C. A., eds. Air pollution
20 modelling, monitoring and management. Boston, MA: Computational Mechanics Publications;
21 pp. 259-267.
22 Barcan, V. (2002) Nature and origin of multicomponent aerial emissions of the copper-nickel smelter complex.
23 Environ. Int. 28: 451-456.
24 Barcan, V. S.; Kovnatsky, E. F.; Smetannikova, M. S. (1998) Absorption of heavy metals in wild berries and edible
25 mushrooms in an area affected by smelter emissions. Water Air Soil Pollut. 103: 173-195.
26 Batonneau, Y.; Bremard, C.; Gengembre, L.; Laureyns, J.; Le Maguer, A.; Le Maguer, D.; Perdrix, E.; Sobanska, S.
27 (2004) Speciation of PM10 sources of airborne nonferrous metals within the 3-km zone of lead/zinc
28 smelters. Environ. Sci. Technol. 38: 5281-5289.
29 Bennett, R. L.; Knapp, K. T. (1989) Characterization of paniculate emissions from non-ferrous smelters. JAPCA
30 39: 169-174.
31 Biggins, P. D. E.; Harrison, R. M. (1979) Atmospheric chemistry of automotive lead. Environ. Sci. Technol.
32 13:558-565.
33 Biggins, P. D. E.; Harrison, R. M. (1980) Chemical speciation of lead compounds in street dusts. Environ. Sci.
34 Technol. 14: 336-339.
35 Bindler, R.; Brannvall, M.-L.;Renberg, I. (1999) Natural lead concentrations in pristine boreal forest soils and past
36 pollution trends: a reference for critical load models. Environ. Sci. Technol. 33: 3362-3367.
37 Boisson, F.; Cotret, O.; Teyssie, J.-L.; El-Baradei', M.; Fowler, S. W. (2003) Relative importance of dissolved and
3 8 food pathways for lead contamination in shrimp. Mar. Pollut. Bull. 46: 1549-1557.
39 Boughton, B.; Horvath, A. (2004) Environmental assessment of used oil management methods. Environ. Sci.
40 Technol. 38: 353-358.
41 Boutron, C. F.; Candelone, J.-P.; Hong, S. M. (1994) Past and recent changes in the large-scale tropospheric cycles
42 of lead and other heavy metals as documented in Antarctic and Greenland snow and ice: a review.
43 Geochim. Cosmochim. Acta 58: 3217-3225.
44 Bridge, G. (2004) Contested terrain: mining and the environment. Annu. Rev. Energy Environ. 29: 205-259.
45 Cadle, S. H.; Mulawa, P. H.; Ball, J.; Donase, C.; Weibel, A.; Sagebiel, J. C.; Knapp, K. T.; Snow, R. (1997)
46 Paniculate emission rates from in-use high-emitting vehicles recruited in Orange County, California.
47 Environ. Sci. Technol. 31: 3405-3412.
48 Cadle, S. H.; Mulawa, P. A.; Hunsanger, E. C.; Nelson, K.; Ragazzi, R. A.; Barrett, R.; Gallagher, G. L.; Lawson,
49 D. R.; Knapp, K. T.; Snow, R. (1999) Composition of light-duty motor vehicle exhaust paniculate matter in
50 the Denver, Colorado area. Environ. Sci. Technol. 33: 2328-2339.
51 Cajuste, L. J.; Cruz-Diaz, J.; Garcia-Osorio, C. (2000) Extraction of heavy metals from contaminated soils: I.
52 Sequential extraction in surface soils and their relationships to DTP A extractable metals and metal plant
53 uptake. J. Environ. Sci. Health Part A: Toxic/Hazard. Subst. Environ. Eng. A3 5: 1141-1152.
54 Carr, D. S. (2003) Lead compounds. In: Ullman's encyclopedia of industrial chemistry. 6th ed. New York, NY:
55 Wiley.
May 2006 2-83 DRAFT-DO NOT QUOTE OR CITE
-------
1 Carvalho, F. P. (1997) Distribution, cycling and mean residence time of 226Ra, 210Pb and 210Po in the Tagus estuary.
2 Sci. Total Environ. 196: 151-161.
3 Chadha, A.; McKelvey, L. D.; Mangis, J. K. (1998) Targeting lead in the multimedia environment in the continental
4 United States. J. Air Waste Manage. Assoc. 48: 3-15.
5 Chan, W. H.; Lusis, M. A. (1986) Smelting operations and trace metals in air and precipitation in the Sudbury Basin.
6 In: Nriagu, J. O.; Davidson, C. L, eds. Toxic metals in the atmosphere. New York, NY: John Wiley
7 & Sons, Inc.; pp. 113-143. (Advances in environmental science and technology: v. 17).
8 Chang, Y.-M; Chang; T.-C.; Lin, J.-P. (1999) Effect of incineration temperature on lead emission from a fixed bed
9 incinerator. J. Chem. Eng. Jpn. 32: 626-634.
10 Chen, C.-N.; Yang, W.-F. (1998) Metal volatility during plastic combustion. J. Environ. Sci. Health Part A:
11 Toxic/Hazard. Subst. Environ. Eng. A33: 783-799.
12 Chow, T. J. (1978) Lead in natural waters. In: Nriagu, J. O., ed. The biogeochemistry of lead in the environment;
13 part A. Ecological cycles. Amsterdam, The Netherlands: Elsevier/North-Holland Biomedical Press;
14 pp. 185-218. (Topics in environemntal health: v. 1A).
15 Chow, J. C.; Watson, J. G.; Richards, L. W.; Haase, D. L.; McDade, C.; Dietrich, D. L.; Moon, D.; Sloane, C.
16 (1991) The 1989-90 Phoenix PM10 study. Volume II: source apportionment. Final report. Phoenix, AZ:
17 Arizona Department of Environmental Quality; Desert Research Institute document no. 8931.6F1.
18 Chow, J. C.; Watson, J. G.; Houck, J. E.; Pritchett, L. C.; Rogers, C. F.; Frazier, C. A.; Egami, R. T.; Ball, B. M.
19 (1994) A laboratory resuspension chamber to measure fugitive dust size distributions and chemical
20 compositions. Atmos. Environ. 28: 3463-3481.
21 Chow, J. C.; Watson, J. G.; Ashbaugh, L. L.; Magliano, K. L. (2003) Similarities and differences inPM10 chemical
22 source profiles for geological dust from the San Joaquin Valley, California. Atmos. Environ.
23 37: 1317-1340.
24 Clarke, L. B. (1993) The fate of trace elements during coal combustion and gasification: an overview. Fuel
25 72:731-736.
26 Claudio, E. S.; Godwin, H. A.; Magyar, J. S. (2003) Fundamental coordination chemistry, environmental chemistry,
27 and biochemistry of lead(II). In: Karlin, K. D., ed. Progress in inorganic chemistry, volume 51. Hoboken,
28 NY: John Wiley & Sons; pp. 1-144.
29 Cobb, G. P.; Sands, K.; Waters, M.; Wixson, E.G.; Dorward-King, E. (2000) Accumulation of heavy metals by
30 vegetables grown in mine wastes. Environ. Toxicol. Chem. 19: 600-607.
31 Conko, K. M.; Rice, K. C.; Kennedy, M. M. (2004) Atmospheric wet deposition of trace elements to a suburban
32 environment, Reston, Virginia, USA. Atmos. Environ. 38: 4025-4033.
33 Cowherd, C.; Muleski, G. E.; Englehart, P. J.; Gillette, D. A. (1985) Rapid assessment of exposure to paniculate
34 emissions from surface contamination sites. Washington, DC: U.S. Environmental Protection Agency,
3 5 Office of Health and Environmental Assessment; report no. EPA/600/8-85/002.
36 Davidson, C. I.; Osborn, J. F. (1986) The sizes of airborne trace metal containing particles. In: Nriagu, J. O.;
37 Davidson, C. I., eds. Toxic metals in the atmosphere. New York, NY: John Wiley & Sons; pp. 355-390.
3 8 (Advances in environmental science and technology: v. 17).
39 Davidson, C.; Rabonowitz, M. (1992) Lead in the environment: from sources to human receptors. In: Needleman,
40 H. L., Human lead exposure. Ann Arbor, MI: CRC Press; pp. 65-88.
41 Davidson, C. I.; Wu, Y.-L. (1990) Dry deposition of particles and vapors. In: Lindberg, S. E.; Page, A. L.; Norton,
42 S. A., eds. Acidic precipitation: v. 3, sources, deposition, and canopy interactions. New York, NY:
43 Springer-Verlag; pp. 103-216.
44 Davidson, C. I.; Goold, W. D.; Mathison, T. P.; Wiersma, G. B.; Brown, K. W.; Reilly, M. T. (1985) Airborne trace
45 elements in Great Smokey Mountains, Olympic and Glacier National Parks. Environ. Sci. Technol.
46 19:27-35.
47 Davidson, C. I.; Jaffrezo, J. L.; Small, M. J.; Summers, P. W.; Olson, M. P.; Borys, R. D. (1993) Trajectory analysis
48 of source regions influencing the south Greenland Ice Sheet during the Dye 3 gas and aerosol sampling
49 program Atmos. Environ. 27A: 2739-2749.
50 Davis, A. P.; Burns, M. (1999) Evaluation of lead concentration in runoff from painted structures. Water Res.
51 33:2949-2958.
52 Davis, A. P.; Shokouhian, M.; Ni, S. (2001) Loading estimates of lead, copper, cadmium, and zinc in urban runoff
53 from specific sources. Chemosphere 44: 997-1009.
May 2006 2-84 DRAFT-DO NOT QUOTE OR CITE
-------
1 Dedeurwaerder, H. L.; Dehairs, F. A.; Decadt, G. G.; Baeyens, W. F. (1983) Estimates of dry and wet deposition
2 and resuspension fluxes of several trace metals in the southern bight of the North Sea. In: Pruppacher,
3 H. R.; Semonin, R. G.; Slinn, W. G. N., eds. Precipitation scavenging, dry deposition, and resuspension.
4 New York, NY: Elsevier; pp. 1219-1231.
5 Deiss, I; Byers, C.; Clover, D.; D'Amore, D.; Love, A.; Menzies, M. A.; Powell, I; Walter, T. M. (2004) Transport
6 of lead and diesel fuel through a peat soil near Juneau, AK: a pilot study. J. Contam. Hydrol. 74: 1-18.
7 Demirbas,, A. (2003a) Toxic air emissions from biomass combustion. Energy Sources 25: 419-427.
8 Demirbas., A. (2003b) Trace metal concentrations in ashes from various types of biomass species. Energy Sources
9 25:743-751.
10 Denaix, L.; Semlali, R. M.; Douay, F. (2001) Dissolved and colloidal transport of Cd, Pb, and Zn in a silt loam soil
11 affected by atmospheric industrial deposition. Environ. Pollut. 114: 29-38.
12 DeShields, B. R.; Meredith, R. W.; Griffin, D.; Laughlin, T.; Collins, W. (1998) The use of field methods to
13 evaluate the toxicity of lead to plants at a small arms firing range. In: Little, E. E.; Greenberg, B. M.;
14 DeLonay, A. J., eds. Environmental toxicology and risk assessment: seventh volume; ASTM STP
15 1333. West Conshohocken, PA: American Society of Testing and Materials; pp 166-183.
16 Douglas, B. E.; McDaniel, D. H.; Alexander, J. J., eds. (1983) Concepts and models of inorganic chemistry. 2nd ed.
17 New York, NY: John Wiley & Sons, Inc.
18 Dudka, S.; Adriano, D. C. (1997) Environmental impacts of metal ore mining and processing: a review. J. Environ.
19 Qual. 26: 590-602.
20 Dudka, S.; Miller, W. P. (1999) Accumulation of potentially toxic elements in plants and their transfer to human
21 food chain. J. Environ. Sci. Health Part B 34: 681-708.
22 Durlak, S. K.; Biswas, P.; Shi, J. (1997) Equilibrium analysis of the affect of temperature, moisture and sodium
23 content on heavy metal emissions from municipal solid waste incinerators. J. Hazard. Mat. 56: 1-20.
24 El-Shobokshy, M. S. (1985) The dependence of airborne paniculate deposition on atmospheric stability and surface
25 conditions. Atmos. Environ. 19: 1191-1197.
26 Elzahabi, M.; Yong, R. N. (200 l)pH influence on sorption characteristics of heavy metal in the vadose zone. Eng.
27 Geol. 60: 61-68.
28 Erel, Y.; Patterson, C. C. (1994) Leakage of industrial lead into the hydrocycle. Geochim. Cosmochim. Acta
29 58: 3289-3296.
30 Erel, Y.; Veron, A.; Halicz, L. (1997) Tracing the transport of anthropogenic lead in the atmosphere and in soils
31 using isotopic ratios. Geochim. Cosmochim. Acta 61: 4495-4505.
32 Erel, Y.; Axelrod, T.; Veron, A.; Mahrer, Y.; Katsafados, P.; Dayan, U. (2002) Transboundary atmospheric lead
33 pollution. Environ. Sci. Technol. 36: 3230-3233.
34 Farfel, M. R.; Orlova, A. O.; Lees, P. S. J.; Rohde, C.; Ashley, P. J.; Chisolm, J. J., Jr. (2003) A study of urban
3 5 housing demolitions as sources of lead in ambient dust: demolition practices and exterior dust fall. Environ.
36 HealthPerspect. Ill: 1228-1234.
37 Pels, M.; Cooper, D. F.; Patterson, M. N. (1990) An analysis of wood-burning installations from an environmental
38 aspect. Energy Convers. Manage. 30: 235-244.
39 Finkelman, R. B. (2004) Potential health impacts of burning coal beds and waste banks. Int. J. Coal Geol. 59: 19-24.
40 Finkelstein, M. E.; Gwiazda, R. H.; Smith, D. R. (2003) Lead poisoning of seabirds: environmental risks from
41 leaded paint at a decommissioned military base. Environ. Sci. Technol. 37: 3256-3260.
42 Finster, M. E., Gray, K. A.; Binns, H. J. (2004) Lead levels of edibles grown in contaminated residential soils: a
43 field survey. Sci. Total Environ. 320: 245-257.
44 Flores-Rodriguez, J.; Bussy, A.-L.; Thevenot, D. R. (1994) Toxic metals in urban runoff: physico-chemical mobility
45 assessment using speciation schemes. Water Sci. Tech. 29(1-2): 83-93.
46 Frey, H. C.; Small, M. J. (2003) Integrated environmental assessment, part I: estimating emissions. J. Ind. Ecol.
47 7:9-11.
48 Friedlander, S. K.; Turner, J. R.; Hering, S. V. (1986) A new method for estimating dry deposition velocities for
49 atmospheric aerosols. J. Aerosol Sci. 17: 240-244.
50 Furimsky, E. (2000) Characterization of trace element emissions from coal combustion by equilibrium calculations.
51 Fuel Proc. Technol. 63: 29-44.
52 Gallon, C.; Tessier, A.; Gobeil, C.; Alfaro-De La Torre, M. C. (2004) Modeling diagenesis of lead in sediments of a
53 Canadian Shield lake. Geochim. Cosmochim. Acta 68: 3531-3545.
54 Galloway, J. N.; Thornton, J. D.; Norton, S. A.; Volchok, H. L.; McLean, R. A. N. (1982) Trace metals in
55 atmospheric deposition: a review and assessment. Atmos. Environ. 16: 1677-1700.
May 2006 2-85 DRAFT-DO NOT QUOTE OR CITE
-------
1 Garg, B. D.; Cadle, S. H.; Mulawa, P. A.; Groblicki, P. J. (2000) Brake wear paniculate matter emissions. Environ.
2 Sci. Technol. 34: 4463-4469.
3 Garry, J. (2001) Biomonitoring atmospheric heavy metals with lichens: theory and application. Crit. Rev. Plant Sci.
4 20(4): 309-371.
5 Gatz, D. F.; Chu, L.-C. (1986) Metal solubility in atmospheric deposition. In: Nriagu, J. O.; Davidson, C. I., eds.
6 Toxic metals in the atmosphere. New York, NY: John Wiley & Sons, Inc.; pp. 391-408. (Advances in
7 environmental science and technology: v. 17).
8 Gelinas, Y.; Schmidt, J. -P. (1998) Estimation of the bult atmospheric deposition of major and trace elements to a
9 rural watershed. Atmos. Environ. 32: 1473-1483.
10 Ghosh, R.; Majumder, T.; Ghosh, D. N. (1987) A study of trace elements inlithotypes of some selected Indian coals.
11 Int. J. Coal Geol. 8: 269-278.
12 Gillies, J. A.; O'Connor, C. M; Mamane, Y.; Gertler, A. W. (1999) Chemical profiles for characterizing dust
13 sources in an urban area, western Nevada, USA. In: Livingstone, I., ed. Aeolian geomorphology: papers
14 from the 4th international conference on aeolian research; 1998; Oxford, United Kingdom. Z. Geomorphol.
15 116(suppl.): 19-44.
16 Gillies, J. A.; Gertler, A. W.; Sagebiel, J. C.; Dippel, W. A. (2001) On-roadpaniculate matter (PM25 and PM10)
17 emissions in the Sepulveda Tunnel, Los Angeles, California. Environ. Sci. Technol. 35: 1054-1063.
18 Gomez Ariza, J. L.; Morales, E.; Sanchez-Rodas, D.; Giraldez, I. (2000) Stability of chemical species in
19 environmental matrices. TrAC Trends Anal. Chem. 19: 200-209.
20 Greenwood, N. N.; Earnshaw, A. (1984) Chemistry of the elements. New York, NY: Pergamon Press.
21 Gulson, B. L.; Palmer, J. M.; Bryce, A. (2002) Changes in blood lead in a recreational shooter. Sci. Total Environ.
22 293: 143-150.
23 Hagner, C. (2002) Regional and long-term patterns of lead concentrations in riverine, marine and terrestrial systems
24 and humans in northwest Europe. Water Air Soil Pollut. 134: 1-39.
25 Harris, A. R.; Davidson, C. I. (2005) The role of resuspended soil in lead flows in the California South Coast Air
26 Basin. Environ. Sci. Technol. 39: 7410-7415.
27 Harris, A. R.; Fifarek, B. J.; Davidson, C. I.; Blackmon, R. L. (2006) Stationary sources of airborne lead: a
28 comparison of emissions data for southern California. J. Air Waste Manage. Assoc. 56: 512-517.
29 Harrison, P. G. (1985) Pb lead. In: Harrison, P. G., ed. Organometallic compounds of germanium, tin, and lead. New
30 York, NY: Chapman and Hall; pp. 41-68.
31 Harrison, R. M. (1986) Chemical speciation and reaction pathways of metals in the atmosphere. In: Davidson, J. O.;
32 Nriagu, C. I., eds. Toxic metals in the atmosphere, New York, NY: John Wiley & Sons, Inc.; pp. 319-333.
33 (Advances in environmental science and technology: v. 17).
34 Harrison, R. M.; Laxen, D. P. H. (1980) Metals in the environment. 1. Chemistry. Chem. Br. 16: 316-320.
3 5 Harrison, R. M.; Williams, C. R. (1983) Physico-chemical characterization of atmospheric trace metal emissions
36 fromaprimary zinc-lead smelter. Sci. Total Environ. 31: 129-140.
37 Harrison, R. M.; Williams, C. R.; O'Neill, I. K. (1981) Characterization of airborne heavy-metals within a primary
38 zinc-lead smelting works. Environ. Sci. Technol. 15: 1197-1204.
39 Harrison, R. M.; Tilling, R.; Callen Romero, M. S.; Harrad, S.; Jarvis, K. (2003) A study of trace metals and
40 polycyclic aromatic hydrocarbons in the roadside environment. Atmos. Environ. 37: 2391-2402.
41 Hee, S. S. Q. (1994) Availability of elements in leaded/unleaded automobile exhausts, a leaded paint, a soil, and
42 some mixtures. Arch. Environ. Contam. Toxicol. 27: 145-153.
43 Hewitt, C. N.; Harrison, R. M. (1986) Formation and decomposition of trialkyllead compounds in the atmosphere.
44 Environ. Sci. Technol. 20: 797-802.
45 Hewitt, C. N.; Rashed, M. B. (1992) Removal rates of selected pollutants in the runoff waters from a major rural
46 highway. Water Res. 26:311-319.
47 Hicks, B. B. (1986) Measuring dry deposition: a re-assessment of the state of the art. Water Air Soil Pollut.
48 30:75-90.
49 Hlavay, J.; Polyak, K.; Weisz, M. (2001) Monitoring of the natural environment by chemical speciation of elements
50 in aerosol and sediment samples. J. Environ. Monit. 3: 74-80.
51 Ho, T. C.; Chu, H. W.; Hopper, J. R. (1993) Metal volatilization and separation during incineration. Waste Manage.
52 13:455-466.
53 Hofken, K. D.; Meixner, F. X.; Ehhalt, D. H. (1983) Deposition of atmospheric trace constituents onto different
54 natural surfaces. In: Pruppacher, H. R.; Semonin, R. G.; Slinn, W. G. N., eds. Precipitation scavenging, dry
55 deposition, and resuspension: v. 2, dry deposition and resuspension: proceedings of the fourth international
56 conference; November-December 1982; Santa Monica, CA. New York, NY: Elsevier; pp. 825-835.
May 2006 2-86 DRAFT-DO NOT QUOTE OR CITE
-------
1 Holtzman, R. B. (1978) Application of radio lead to metabolic studies. In: Nriagu, J. O., ed. The biogeochemistry of
2 lead in the environment; part B. Biological effects. Amsterdam, The Netherlands: Elsevier/North-Holland
3 Biomeical Press; pp. 37-96. (Topics in environmental health: v. IB).
4 Humphreys, D. J. (1991) Effectsof exposure to excessive quantitiesof lead onanimals. Br. Vet. J. 147: 18-30.
5 Huntzicker, J. J.; Friedlander, S. K.; Davidson, C. I. (1975) Material balance for automobile-emitted lead in Los
6 Angeles basin. Environ. Sci. Technol. 9: 448-457.
7 Jensen, D. L.; Holm, P. E.; Christensen, T. H. (2000) Leachability of heavy metals from scrap dirt sampled at two
8 scrap iron and metal recycling facilities. Waste Manage. Res. 18: 367-379.
9 Jing, C.; Meng, X.; Korfiatis, G. P. (2004) Lead leachability in stabilized/solidified soil samples evaluated with
10 different leaching tests. J. Hazard. Mater. B114: 101-110.
11 Joshi, S. R.; McCrea, R. C.; Shukla, B. S.; Roy, J.-C. (1991) Partitioning and transport of lead-210 in the Ottawa
12 River watershed. Water Air Soil Pollut. 59: 311-320.
13 Karathanasis, A. D. (2000) Colloid-mediated transport of Pb through soil porous media. Int. J. Environ. Studies
14 57(5): 579-596.
15 Karcher, B. (1999) Aviation-produced aerosols and contrails. Surv. Geophys. 20: 113-167.
16 Kaste, J.; Friedland, A.; Stirrup, S. (2003) Using stable and radioactive isotopes to trace atmospherically deposited
17 Pb in montane forest soils. Environ. Sci. Technol. 37: 3560-3567.
18 Khan, A. T.; Thompson, S. J.; Mielke, H. W. (1995) Lead and mercury levels in raccoons from Macon County,
19 Alabama. Bull. Environ. Contam. Toxicol. 54: 812-816.
20 Kimbrough, D. E.; Suffet, I. H. (1995) Off-site forensic determination of airborne elemental emissions by multi-
21 media analysis: a case study at two secondary lead smelters. Environ. Sci. Technol. 29: 2217-2221.
22 King, R. B. (1995) Silicon, germanium, tin, and lead. In: Inorganic chemistry of main group elements. New York,
23 NY: VCH Publishers Inc.; pp. 43-65.
24 Kiratli, N.; Ergin, M. (1996) Partitioning of heavy metals in surface Black Sea sediments. Appl. Geochem.
25 11:775-788.
26 Kleeman, M. J.; Schauer, J. J.; Cass, G. R. (2000) Size and composition distribution of fine paniculate matter
27 emitted from motor vehicles. Environ. Sci. Technol. 34: 1132-1142.
28 Kotz, J. C.; Purcell, K. F., eds. (1991) Chemistry and chemical reactivity. 2nd ed. Philadelphia, PA: Saunders
29 College Publishing; pp. 953-968.
30 Koutrakis, P.; Sioutas, C. (1996) Physico-chemical properties and measurement of ambient particles. In: Wilson, R.;
31 Spengler, J. D., eds. Particles in our air: concentrations and health effects. Cambridge, MA: Harvard
32 University Press; pp 15-39.
33 Krook, J.; Martensson, A.; Eklund, M. (2004) Metal contamination in recovered waste wood used as energy source
34 in Sweden. Resour. Conserv. Recycl. 41: 1-14.
35 Kurkjian, R.; Dunlap, C.; Flegal, A. R. (2002) Lead isotope tracking of atmospheric response to post-industrial
36 conditions in Yerevan, Armenia. Atmos. Environ. 36: 1421-1429.
37 Kurkjian, R.; Dunlap, C.; Flegal, A. R. (2004) Long-range downstream effects of urban runoff and acid mine
3 8 drainage in the Debed River, Armenia: insights from lead isotope modeling. Appl. Geochem.
39 19: 1567-1580.
40 Lankey, R. L.; Davidson, C. I.; McMichael, F. C. (1998) Mass balance for lead in the California south coast air
41 basin: an update. Environ. Res. 78: 86-93.
42 Lazrus, A. L.; Lorange, E.; Lodge, J. P., Jr. (1970) Lead and other metal ions in United States precipitation. Environ.
43 Sci. Technol. 4: 55-58.
44 Lee, R. E., Jr.; Von Lehmden, D. J. (1973) Trace metal pollution in the environment. J. Air Pollut. Control Assoc.
45 23: 853-857.
46 Lemieux, P. M.; Ryan, J. V. (1993) Characterization of air pollutants emitted from a simulated scrap tire fire. J. Air
47 Waste Manage. Assoc. 43: 1106-1115.
48 Lieb, D. A.; Carline R. F. (2000) Effects of urban runoff from a detention pond on water quality, temperature and
49 caged Gammams minus (Say) (Amphipoda) in a headwater stream. Hydrobiologia441: 107-116.
50 Lin, J.-M.; Fang, G.-C.; Holsen, T. M.; Noll, K. E. (1993) A comparison of dry deposition modeled from size
51 distribution data and measured with a smooth surface for total particle mass, lead and calcium in Chicago.
52 Atmos. Environ. Part A 27: 1131-1138.
53 Lindberg, S. E.; Harriss, R. C. (1981) The role of atmospheric deposition in an eastern U.S. deciduous forest. Water
54 Air Soil Pollut. 16: 13-31.
55 Lindberg, S. E.; Lovett, G. M. (1985) Field measurements of particle dry deposition rates to foliage and inert
56 surfaces in a forest canopy. Environ. Sci. Technol. 19: 238-244.
May 2006 2-87 DRAFT-DO NOT QUOTE OR CITE
-------
1 Liu, Z. P. (2003) Lead poisoning combined with cadmium in sheep and horses in the vicinity of non-ferrous metal
2 smelters. Sci. Total Environ. 309: 117-126.
3 Lockwood, F. C.; Yousif, S. (2000) A model for the paniculate matter enrichment with toxic metals in solid fuel
4 flames. Fuel Process. Technol. 65-66: 439-457.
5 Loranger, S.; Zayed, J. (1994) Manganese and lead concentrations in ambient air and emission rates from unleaded
6 and leaded gasoline between 1981 and 1992 in Canada: a comparative study. Atmos. Environ.
7 28: 1645-1651.
8 Lough, G. C.; Schauer, J. J.; Park, J.-S.; Shafer, M. M; Deminter, J. T.; Weinstein, J. P. (2005) Emissions of metals
9 associated with motor vehicle roadways. Environ. Sci. Technol. 39: 826-836.
10 Lowenthal, D. H.; Zielinska, B.; Chow, J. C.; Watson, J. G.; Gautam, M.; Ferguson, D. H.; Neuroth, G. R.; Stevens,
11 K. D. (1994) Characterization of heavy-duty diesel vehicle emissions. Atmos. Environ. 28: 731-743.
12 Mace, J. E.; Graham, R. C.; Amrhein, C. (1997) Anthropogenic lead distribution in rodent-affected and undisturbed
13 soils in southern California. Soil Sci. 162: 46-50.
14 Main, H. H.; Friedlander, S. K. (1990) Dry deposition of atmospheric aerosols by dual tracer method-I. area source.
15 Atmos. Environ. 24A: 103-108.
16 Marcos L.; Legret M.; Raimbault G.; Le Cloirec P. (2002) Experimental study and modelling of zinc and lead
17 migration in sandy soils due to stormwater infiltration. Water Sci. Technol. 45: 57-64.
18 Maskall, J. E.; Thornton, I. (1998) Chemical partitioning of heavy metals in soils, clays and rocks at historical lead
19 smelting sites. Water Air Soil Pollut. 108: 391-409.
20 Matthes, S. A.; Cramer, S. D.; Covino Jr., B. S.; Bullard, S. J.; Holcomb, G. R. (2002) Precipitation runoff from
21 lead. In: Townsend, H. E., ed. Outdoor Atmospheric Corrosion. West Conshocken, PA: American Society
22 for Testing and materials International, pp. 265-274. (ASTM STP 1421).
23 McDonald, J. D.; Zielinska, B.; Sagebiel, J. C.; McDaniel, M. R.; Mousset-Jones, P. (2003) Source apportionment
24 of airborne fine paniculate matter in an underground mine. J. Air Waste Manage. Assoc. 53: 386-395.
25 Merrington, G.; Alloway, B. J. (1994) The flux of Cd, Cu, Pb and Zn in mining polluted soils. Water Air Soil Pollut.
26 73: 333-344.
27 Milford, J. B.; Davidson, C. I. (1985) The sizes of paniculate trace elements in the atmosphere-a review. J. Air
28 Pollut. Control Assoc. 35: 1249-1260.
29 Miller, E. K.; Friedland, A. J. (1991) Recent reductions of the atmospheric lead flux to high-elevation forests of the
30 northeastern USA. In: Farmer, J. G., ed. Heavy metals in the environment (8th international conference);
31 September; Edinburgh, Scotland, UK. Edinburgh, UK: CEP Consultants Ltd.; pp 86-89.
32 Miller, E. K.; Friedland, A. J. (1994) Lead migration in forest soils: response to changing atmospheric inputs.
33 Environ. Sci. Technol. 28: 662-669.
34 Mukherjee, S.; Srivastava, S. K. (2005) Trace elements in high-sulfur Assam coals from the Makum Coalfield in the
3 5 northeastern region of India. Energy Fuels 19: 882-891.
36 Nicholson, K. W. (1988a) The dry deposition of small particles: a review of experimental measurements. Atmos.
37 Environ. 22: 2653-2666.
38 Nicholson, K. W. (1988b) A review of particle resuspension. Atmos. Environ. 22: 2639-2651.
39 Nicholson, K. W. (1993) Wind tunnel experiments on the resuspension of paniculate matter. Atmos. Environ.
40 27A: 181-188.
41 Nicholson, K. W.; Branson, J. R.; Giess, P.; Cannell, R. J. (1989) The effects of vehicle activity on particle
42 resuspension. J. Aerosol Sci. 20: 1425-1428.
43 Nightingale, H. I. (1987) Accumulation of As, Ni, Cu, and Pb in retention and recharge basins soils from urban
44 runoff. Water Resour. Bull. 23: 663-672.
45 Nihei, M. K.; Guilarte, T. R. (2002) Molecular mechanisms of low-level Pb2+ neurotoxicity. In: Massaro, E. J., ed.
46 Handbook of Neurotoxicology, v. 1. Totowa, NJ: Humana Press, Inc.; pp. 107-133.
47 Nriagu, J. O. (1989) A global assessment of natural sources of atmospheric trace metals. Nature (London)
48 338:47-49.
49 Nriagu, J. O. (1990) The rise and fall of leaded gasoline. Sci. Total Environ. 92: 13-28.
50 Nriagu, J. O.; Pacyna, J. M. (1988) Quantitative assessment of worldwide contamination of air, water and soils by
51 trace metals. Nature (London) 333: 134-139.
52 Ohmsen, G. S. (2001) Characterization of fugitive material within a primary lead smelter. J. Air Waste Manage.
53 Assoc. 51: 1443-1451.
54 Olmez, I.; Sheffield, A. E.; Gordon, G. E.; Houck, J. E.; Pritchett, L. C.; Cooper, J. A.; Dzubay, T. G.; Bennett, R. L.
55 (1988) Compositions of particles from selected sources in Philadelphia for receptor modeling applications.
56 JAPCA 38: 1392-1402.
May 2006 2-88 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pacyna, J. M. (1986) Emission factors of atmospheric elements. In: Nriagu, J. O.; Davidson, C. I., eds. Toxic metals
2 in the atmosphere. New York, NY: John Wiley & Sons, Inc.; pp 1-32. (Advances in environmental science
3 and technology: v. 17).
4 Palacios, H.; Iribarren, I.; Olalla, M. J.; Cala, V. (2002) Lead poisoning of horses in the vicinity of a battery
5 recycling plant. Sci. Total Environ. 290: 81-89.
6 Pang, L.; Close, M.; Schneider, D.; Stanton, G. (2002) Effect of pore-water velocity on chemical nonequilibrium
7 transport of Cd, Zn, and Pb in alluvial gravel columns. J. Contam. Hydrol. 57: 241-258.
8 Parekh, P. P.; Khwaja, H. A.; Khan, A. R.; Naqvi, R. R.; Malik, A.; Khan, K.; Hussain, G. (2002) Lead content of
9 petrol and diesel and its assessment in an urban environment. Environ. Monitor. Assess. 74: 255-262.
10 Pattenden, N. J.; Branson, J. R.; Fisher, E. M. R. (1982) Trace element measurements in wet and dry deposition and
11 airborne paniculate at an urban site. In: Georgii, H. W.; Pankrath, J., eds. Deposition of atmospheric
12 pollutants. Dordrecht, The Netherlands: Reidel; pp. 173-184.
13 Pekney, N. J.; Davidson, C. I. ; Bein, K. J. ; Wexler, A. S. ; Johnston, M. V. (2006) Identification of sources of
14 atmospheric PM at the Pittsburgh supersite, part I: single particle analysis and filter-based positive matrix
15 factorization. Aerosol Sci. Technol.: in press.
16 Pelletier, E. (1995) Environmental organometallic chemistry of mercury, tin, and lead: present status and
17 perspectives. In: Tessier, A.; Turner, D. R., eds. Metal speciation and bioavailability in aquatic systems.
18 New York, NY: John Wiley & Sons; pp. 103-148. (Analytical and Physical Chemistry of Environmental
19 Systems series: v. 3)
20 Peltier, E. F.; Webb, S. M.; Gaillard, J.-F. (2003) Zinc and lead sequestration in an impacted wetland system. Adv.
21 Environ. Res. 8: 103-112.
22 Perkins, S. M.; Filippelli, G. M.; Souch, C. J. (2000) Airborne trace metal contamination of wetland sediments at
23 Indiana Dunes National Lakeshore. Water Air Soil Pollut. 122: 231-260.
24 Pilgrim, W.; Hughes, R. N. (1994) Lead, cadmium, arsenic and zinc in the ecosystem surrounding a lead smelter.
25 Environ. Monit. Assess. 32: 1-20.
26 Pitzer, K. S. (1979) Relativistic effects on chemical properties. Ace. Chem. Res. 12: 271-276.
27 Prengaman, R. D. (2003) Lead alloys. In: Ullman's encyclopedia of industrial chemistry. 6th ed. New York, NY:
28 Wiley-VCH.
29 Reuer, M. K.; Weiss, D. J. (2002) Anthropogenic lead dynamics in the terrestrial and marine environment. Philos.
30 Trans. R. Soc. London Ser. A 360: 2889-2904.
31 Rhoads, B. L.; Cahill, R. A. (1999) Geomorphological assessment of sediment contamination in an urban stream
32 system. Appl. Geochem. 14: 459-483.
33 Rhue, R. D.; Mansell, R. S.; Ou, L.-T.; Cox, R.; Tang, S. R.; Ouyang, Y. (1992) The fate and behavior of lead alkyls
34 in the environment: a review. Crit. Rev. Environ. Control 22: 169-193.
35 Rieuwerts, J. S.; Farago, M. E. (1995) Lead contamination in smelting and mining environments and variations in
36 chemical forms and bioavailability. Chem. Speciation Bioavailability 7: 113-123.
37 Ritson, P. I.; Esser, B. K.; Niemeyer, S.; Flegal, A. R. (1994) Lead isotopic determination of historical sources of
38 lead to Lake Erie, North America. Geochim. Cosmochim. Acta 58: 3297-3305.
39 Ritson, P. I.; Bouse, R. M.; Flegal, A. R.; Luoma, S. N. (1999) Stable lead isotopic analyses of historic and
40 contemporary lead contamination of San Francisco Bay estuary. Marine Chem. 64: 71-83.
41 Roger, S.; Montrejaud-Vignoles, M.; Andral, M. C.; Herremans, L.; Fortune, J. P., (1998) Mineral, physical and
42 chemical analysis of the solid matter carried by motorway runoff water. Water Res. 32: 1119-1125.
43 Rohbock, E. (1982) In: Georgii, H. W.; Pankrath, J., eds. Deposition of atmospheric pollutants. Dordrecht, The
44 Netherlands: Reidel; pp. 159-171.
45 Rojas, C. M.; Van Grieken, R. E.; Laane, R. W. (1993) Comparison of three dry deposition models applied to field
46 measurements in the southern bight of the North Sea. Atmos. Environ. 27A: 363-370.
47 Root, R. A. (2000) Lead loading of urban streets by motor vehicle wheel weights. Environ. Health Perspect.
48 108:937-940.
49 Sanchez-Hernandez, J. C. (2000) Trace element contamination in Antarctic ecosystems. Rev. Environ. Contam.
50 Toxicol. 166: 83-127.
51 Schell, W. R.; Barnes, R. S. (1986) Environmental isotope and anthropogenic tracers of recent lake sedimentation.
52 In: Fritz, P.; Fontes, J. C., eds. Handbook of environmental isotope geochemistry, the terrestrial
53 environment, B. Vol. 2. New York, NY: Elsevier Science Publishers; pp. 169-206.
54 Scherbatskoy, T.; Bliss, M. (1984) Occurrence of acidic rain and cloud water in high elevation ecosystems in the
55 Green Mountains of Vermont. In: Samson, P. J., ed. The meteorology of acid deposition. Pittsburgh, PA:
56 Air Pollution Control Association; pp. 449-463.
May 2006 2-89 DRAFT-DO NOT QUOTE OR CITE
-------
1 Schintu, M; Kudo, A.; Sarritzu, G.; Contu, A. (1991) Heavy metal distribution and mobilization in sediments from a
2 drinking water reservoir near a mining area. Water Air Soil Pollut. 57: 329-338.
3 Schlesinger, W. H.; Reiners, W. A. (1974) Deposition of water and cations on artificial foliar collectors in Fir
4 krummholz of New England mountains. Ecology 55: 378-386.
5 Schweitzer, P. A. (2003) Lead and lead alloys. In: Schweitzer, P. A. Metallic materials: physical, mechanical, and
6 corrosion properties. New York, NY: Marcel Dekker Inc.; pp. 695-698.
7 Sehmel, G. A. (1980) Particle resuspension: a review. Environ. Int. 4: 107-127.
8 Seinfeld, J. H.; Pandis, S. N. (1998) Atmospheric chemistry and physics: from air pollution to climate change.
9 New York, NY: John Wiley & Sons, Inc.
10 Senior, C. L.; Helble, J. J.; Sarofim, A. F. (2000) Emissions of mercury, trace elements, and fine particles from
11 stationary combustion sources. Fuel Process. Technol. 65-66: 263-288.
12 Shah, S. D.; Cocker, D. R., Ill; Miller, J. W.; Norbeck, J. M. (2004) Emission rates of paniculate matter and
13 elemental and organic carbon from in-use diesel engines. Environ. Sci. Technol. 38: 2544-2550.
14 Shapilova, M. V.; Alimova, S. I. (2000) Environmental problems in the production of household and crystal glass.
15 Glass Ceram. 57: 293-295.
16 Shapiro, H.; Frey, F. W. (1968) Valence states and nature of bonding. In: The organic compounds of lead.
17 New York, NY: John Wiley & Sons, Inc.; pp. 5-8.
18 Sheppard, S. C.; Sheppard, M. I. (1991) Lead in boreal soils and food plants. In: Adriano, D. C., ed. Metals in soils,
19 waters, plants and animals: proceedings of an international conference; April 1990; Orlando, FL. Water Air
20 Soil Pollut. 57-58: 79-81.
21 Shinya, M.; Tsuchinaga, T.; Kitano, M.; Yamada, Y.; Ishikawa, M., (2000) Characterization of heavy metals and
22 polycyclic aromatic hydrocarbons in urban highway runoff. Water Sci. Tech. 42: 201-208.
23 Sievering, H.; Dave, M.; McCoy, P.; Sutton, N. (1979) Deposition of sulfate during stable atmospheric transport
24 over Lake Michigan. Atmos. Environ. 13: 1717-1718.
25 Silva, P. J.; Prather, K. A. (1997) On-line characterization of individual particles from automobile emissions.
26 Environ. Sci. Technol. 31: 3074-3080.
27 Singley, J. E. (1994) Electrochemical nature of lead contamination. J. Am. Water Works Assoc. 86: 91-96.
28 Sivaraman, D.; Lindner, A. S. (2004) A comparative life cycle analysis of gasoline-, battery-, and electricity-
29 powered lawn mowers. Environ. Eng. Sci. 21: 768-785.
30 Slinn, S. A.; Slinn, W. G. N. (1980) Predictions for particle deposition on natural waters. Atmos. Environ.
31 14:1013-1016.
32 Small, M. J.; Nunn, A. B., Ill; Forslund, B. L.; Daily, D. A. (1995) Source attribution of elevated residential soil
33 lead near a battery recycling site. Environ. Sci. Technol. 29: 883-895.
34 Smith, W. H.; Siccama, T. G. (1981) The Hubbard Brook ecosystem study: biogeochemistry of lead in the northern
35 hardwood forest. J. Environ. Qual. 10: 323-333.
36 Sobanska, S.; Ricq, N.; Laboudigue, A.; Guillermo, R.; Bremard, C.; Laureyns, J.; Merlin, J. C.; Wignacourt, J. P.
37 (1999) Microchemical investigations of dust emitted by a lead smelter. Environ. Sci. Technol.
38 33: 1334-1339.
39 Socolow, R.; Thomas, V. (1997) The industrial ecology of lead and electric vehicles. J. Ind. Ecol. 1: 13-36.
40 Steding, D. J.; Dunlap, C. E.; Flegal, A. R. (2000) New isotopic evidence for chronic lead contamination in the San
41 Francisco Bay estuary system: implications for the persistence of past industrial lead emissions in the
42 biosphere. Proc. Natl. Acad. Sci. U. S. A. 97: 11181-11186.
43 Steinnes, E. (2001) Metal contamination of the natural environment in Norway from long range atmospheric
44 transport. Water Air Soil Pollut. 1(3/4): 449-460.
45 Sternbeck, J.; Sjodin, A.; Andreasson, K. (2002) Metal emissions from road traffic and the influence of
46 resuspension—results from two tunnel studies. Atmos. Environ. 36: 4735-4744.
47 Sturges, W. T.; Harrison, R. M. (1986) The use of Br/Pb ratios in atmospheric particles to discriminate between
48 vehicular and industrial lead sources in the vicinity of a lead works—I. Thorpe, West Yorkshire. Atmos.
49 Environ. 20: 833-843.
50 Taebi, A.; Droste, R. L. (2004) First flush pollution load of urban stormwater runoff. J. Environ. Eng. Sci.
51 3:301-309.
52 Thurston, G. D.; Spengler, J. D. (1985) A quantitative assessment of source contributions to inhalable paniculate
53 matter pollution in metropolitan Boston. Atmos. Environ. 19: 9-25.
54 Toner, R. N.; Frost, C. D.; Chamberlain, K. R. (2003) Isotopic identification of natural vs. anthropogenic sources of
55 Pb in Laramie basin groundwaters, Wyoming, USA. Environ. Geol. 43: 580-591.
May 2006 2-90 DRAFT-DO NOT QUOTE OR CITE
-------
1 Tsai, E. C.-E. (1987) Analysis of ambient lead concentrations around three secondary lead smelters. Water Air Soil
2 Pollut. 33:321-329.
3 Tsai, J.-H.; Wu, Y.-L. (1995) Contributions of road dust resuspension to the airborne particle concentrations in
4 Taipei. Part. Sci. Technol. 13: 55-67.
5 Twohy, C. H.; Gandrud, B. W. (1998) Electron microscope analysis of residual particles from aircraft contrails.
6 Geophys. Res. Lett. 25: 1359-1362.
7 U.S. Environmental Protection Agency. (1986) Air quality criteria for lead. Research Triangle Park, NC: Office of
8 Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no.
9 EPA-600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
10 U.S. Environmental Protection Agency. (1991) Methods for the determination of metals in environmental samples.
11 Washington, DC: U.S. Environmental Protection Agency; EPA/600/4-91-010.
12 U.S. Environmental Protection Agency. (1998) Locating and estimating air emissions from sources of lead and lead
13 compounds. Washington, DC: Office of Air Quality; report no. EPA-454/R-98-006. Available:
14 http://www.epa.gov/ttn/chief/le/lead.pdf [13 October, 2005].
15 U.S. Environmental Protection Agency. (2000) Great Lakes binational toxics strategy report on alkyl-lead: sources,
16 regulations and options. Ann Arbor, MI: Great Lakes National Program Office. Available:
17 http://www.epa.gov/glnpo/bns/lead/Step%20Report/steps.pdf [12 October, 2005].
18 U.S. Environmental Protection Agency. (2002) PBT national action plan for alkyl-Pb. Washington, DC: Persistent,
19 Bioaccumulative, and Toxic Pollutants (Pbt) Program. Available:
20 http://www.epa.gov/opptintr/pbt/cheminfo.htm [13 October, 2005].
21 U.S. Environmental Protection Agency. (2003) National air quality and emissions trends report. 2003 special studies
22 edition. Research Triangle Park, NC: Office of Air Quality Standards; Emissions Monitoring and Analysis
23 Division; report no. EPA 454/R-03-005. Available: http://www.epa.gov/air/airtrends/aqtrnd03/toc.html
24 (27 August, 2004).
25 U.S. Environmental Protection Agency. (2005) AP 42: Compilation of air pollutant emission factors.
26 Washington, DC: Office of Information Analysis and Assessment. Available:
27 http://www.epa.gov/ttn/chief/ap42/index.html (17 August 2005).
28 U.S. Environmental Protection Agency. (2006a) Toxic release inventory program. Washington, DC: Toxic Release
29 Inventory Program. Available: http://www.epa.gov/tri (11 March 2006).
30 U.S. Environmental Protection Agency. (2006b) National emissions inventories for the U.S. Washington, DC: Toxic
31 Release Inventory Program. Available: http://www.epa.gov/ttn/chief/net (11 March 2006).
32 U.S. Environmental Protection Agency. (2006c) Introduction to emission factors. Washington, DC: Introduction to
33 emission factors. Available: http://www.epa.gov/oar/oaqps/efactors.html (13 March 2006).
34 U.S. Federal Aviation Administration. (1996) General aviation and air taxi activity survey annual summary report
3 5 data: 1996. Washington, DC: U.S. Department of the Transportation; report no. FAA APO-98-5.
36 U.S. Geological Survey (USGS). (2003) Minerals yearbook 2003: lead. Washington, DC: U. S. Department of the
37 Interior. Available: http://minerals.usgs.gov/minerals/pubs/commodity/lead/ [13 October, 2005].
3 8 Unlii, K. (1998) Transport of metals leaching from land-disposed oil field wastes. Waste Manage. Res.
39 16(6): 541-554.
40 Van Borm, W.; Keersmaekers, T.; Adams, F. (1988) Characteristics of resuspended soil particles with high
41 concentrations of Cu, Zn, Cd, and Pb as a function of particle size. J. Aerosol. Sci. 19: 1287-1289.
42 Venditti, D.; Durecu, S.; Berthelin, J. (2000) A multidisciplinary approach to assess history, environmental risks,
43 and remediation feasibility of soils contaminated by metallurgical activities. Part A: chemical and physical
44 properties of metals and leaching ability. Arch. Environ. Contain. Toxicol. 38: 411-420.
45 Veron, A. J.; Church, T. M. (1997) Use of stable lead isotopes and trace metals to characterize air mass sources into
46 the eastern North Atlantic. J. Geophys. Res. [Atmos.] 102: 28,049-28,058.
47 Vilomet, J. D.; Veron, A.; Ambrosi, J. P.; Moustier, S.; Bottero, J. Y.; Chatelet-Snidaro, L. (2003) Isotopic tracing
48 of landfill leachates and pollutant lead mobility in soil and groundwater. Environ. Sci. Technol.
49 37:4586-4591.
50 Wagner, J. P.; Caraballo, S. A. (1997) Toxic species emissions from controlled combustion of selected rubber and
51 plastic consumer products. Polym. Plast. Technol. Eng. 36: 189-224.
52 Walsh, D. C.; Chillrud, S. N.; Simpson, H. J.; Bopp, R. F. (2001) Refuse incinerator paniculate emissions and
53 combustion residues for New York City during the 20th century. Environ. Sci. Technol. 35: 2441-2447.
54 Wang, L.; Morris, A. E. (1995) A process engineering approach to remedy an environmental problem of fugitive
55 lead emissions during lead refining. J. Mater. Res. 10: 538-544.
May 2006 2-91 DRAFT-DO NOT QUOTE OR CITE
-------
1 Weast, R. C.; Astle, M. I; Beyer, W. H., eds. (1988) CRC handbook of chemistry and physics. 69th ed. Boca Raton,
2 FL: CRC Press, Inc.Weiss, D.; Shotyk, W.; Kempf, O. (1999) Archives of atmospheric lead pollution.
3 Naturwissenschaften 86: 262-275.
4 Wernick, I. K.; Themelis, N. J. (1998) Recycling metals for the environment. Annu. Rev. Energy Environ.
5 23:465-497.
6 Willemsens, L. C.; VanDerKerk, G. J. M. (1965) General introduction to organolead chemistry. In: Willemsens,
7 L. C.; Van Der Kerk, G. J. M. Investigations in the field of organolead chemistry. Utrecht, The
8 Netherlands: International Lead Zinc Research Organization, Inc.; pp. 1-13.
9 Williams, R. (1982) A model for the dry deposition of particles to natural water surfaces. Atmos. Environ.
10 16: 1933-1938.
11 Winkler, R.; Dietl, F.; Frank, G.; Tschiersch, J. (1998) Temporal variation of 7Be and 210Pb size distributions in
12 ambient aerosol. Atmos. Environ. 32: 983-991.
13 Wu, Y.-L.; Davidson, C. L; Dolske, D. A.; Sherwood, S. I. (1992a) Dry deposition of atmospheric contaminants: the
14 relative importance of aerodynamic, boundary layer, and surface resistances. Aerosol Sci. Technol.
15 16:65-81.
16 Wu, Y.-L.; Davidson, C. I.; Lindberg, S. E.; Russell, A. G. (1992b) Resuspension of paniculate chemical species at
17 forested sites. Environ. Sci. Technol. 26: 2428-2435.
18 Young, T. M.; Heeraman, D. A.; Sirin, G.; Ashbaugh, L. L. (2002) Resuspension of soil as a source of airborne lead
19 near industrial facilities and highways. Environ. Sci. Technol. 36: 2484-2490.
20 Zabel, T. F. (1993) Diffuse sources of pollution by heavy metals. J. Inst. Water Environ. Manage. 7: 513-520.
21 Zadnik, T. (2004) Lead in topsoil, hay, silage and blood of cows from farms near a former lead mine and current
22 smelting plant before and after installation of filters. Vet. Hum. Toxicol. 46: 287-290.
23 Zhang, M. K.; Xu, J. M. (2003) Difference of lead, copper and zinc concentrations between interiors and exteriors of
24 peds in some contaminated soils. Chemosphere 50: 733-738.
25 Zufall, M. J.; Davidson, C. I. (1997) Dry deposition of particles to water surfaces. In: Baker, J. E., ed. Atmospheric
26 deposition of contaminants to the Great Lakes and coastal waters: proceedings from a session at SETAC's
27 15th annual meeting; October-November, Denver, CO. Pensacola, FL: SETAC Press; pp. 1-15. (SETAC
28 technical publications series).
May 2006 2-92 DRAFT-DO NOT QUOTE OR CITE
-------
i 3. ROUTES OF HUMAN EXPOSURE TO LEAD AND
2 OBSERVED ENVIRONMENTAL CONCENTRATIONS
3
4 Introduction
5 Lead has been observed in measurable quantities in nearly every environmental media all
6 over the world. Thus, the routes of exposure and their relative contributions to body burden are
7 difficult to characterize fully. The relative contributions of lead sources to a person's blood lead
8 level depend on the proximity of major sources to the workplace and residence of that individual,
9 the condition of the residence (especially the presence and condition of lead-based paint), and
10 whether the housing is located in an urban, suburban, or rural location.
11 In general, lead exposure has fallen with the elimination of leaded gasoline, lead-based
12 paint, and lead solder in cans. However, lead intake is cumulative, and lead poisoning is not
13 uncommon. Blood lead and bone lead are the common biomarkers for lead exposure that are
14 used in this chapter as biological indicators of human lead exposure.
15 A comprehensive analysis of multimedia concentrations of lead showed that people in
16 cities, especially in poor and minority-dominated neighborhoods, are the most at risk for lead
17 exposure (Chadha et al., 1998). In the Third National Health and Nutrition Examination Survey
18 (NHANES III), high blood lead levels were correlated with non-Hispanic black race/ethnicity,
19 low-income, and residence in older housing (Pirkle et al., 1998). These elevated lead levels were
20 associated with exposure to lead-based paint and lead-contaminated soil and dust. Another study
21 showed that the racial disparity in blood lead is likely due to differences in housing conditions
22 and environmental exposures (Lanphear et al., 1996). Higher blood lead levels in black children
23 were linked to higher rates of paint deterioration and higher levels of lead-contaminated dust
24 compared to residences housing white children. The authors conclude that the main reason for
25 the racial disparity in blood lead levels was that African American children were exposed to both
26 interior and exterior sources of lead, whereas white children were exposed primarily to exterior
27 sources of lead. Similarly, exposure analyses in Arizona showed that Hispanic populations were
28 exposed to more lead on a daily basis than non-Hispanics in the same sampling area (O'Rourke
29 etal., 1999).
30
May 2006 3-1 DRAFT-DO NOT QUOTE OR CITE
-------
1 3.1 EXPOSURE: AIR
2 3.1.1 Routine Monitoring of Lead Within the U.S.
3 There are four long-term networks in the United States that provide data on ambient air
4 concentrations of lead, all funded in whole or in part by EPA. The first is the network of official
5 state/local lead monitoring stations which measure lead in total suspended particulate matter
6 (TSP), i.e., particles up to about 30 microns. These stations use samplers and laboratory analysis
7 methods which have either Federal Reference Method (FRM) or Federal Equivalence Method
8 (FEM) status. The FRM and FEM method descriptions can be found in 40 CFR part 50,
9 Appendix G. Sampling is conducted for 24-hour periods, with a typical sampling schedule of
10 1 in 6 days. About 250 sampling sites operated during 2005. These sites provide a total lead
11 measurement and are intended to be used for determining compliance with the lead NAAQS.
12 The locations of these sites are shown in Figure 3-la. The state/local agencies which operate
13 these sites report the data to EPA's Air Quality System where they are accessible via several
14 web-based tools. Many of the stations in this network have been in operation since the 1970s.
15 EPA's series of annual air quality trends reports have used data from this network to quantify
16 trends in ambient concentrations of lead. The most recent Trends report for lead can be found at
17 http://www.epa.gov/airtrends/lead.html. Based data meeting strict requirements for
18 completeness, Figure 3-lb shows a sharply declining trend in overall U.S. airborne Pb
19 concentrations since 1983.
20 The second is a network of about 200 PM2.5 speciation sites. This network consists of
21 54 long-term trends sites [commonly referred to as the Speciation Trends Network (STN)] and
22 about 150 supplemental sites. Nearly all of these state/local sites are in urban areas, often at the
23 location of highest known PM2.5 concentrations. Sites in this network determine the lead
24 concentration in a PM2.5 sample and, as such, do not measure lead in the size fraction >2.5 jim in
25 diameter. Lead is quantified via the XRF method. The standard operating procedure for metals
26 by XRF is available at: http://www.epa.gov/ttnamtil/files/ambient/pm25/spec/xrfsop.pdf. Data are
27 managed through the Air Quality System. These sites generally began operation around 2000.
28 The locations of these sites are shown in Figure 3-2a and Figure 3-2b shows the average
29 maximum quarterly mean concentrations of Pb observed at those sites that were at or above
30 0.005 |ig/m3 for 2002-2005.
May 2006 3-2 DRAFT-DO NOT QUOTE OR CITE
-------
o
o .Active Sites
• Inactive Sites
Figure 3-la. Lead TSP monitoring sites from 2000-2006.
2
•*-*
c
0)
o
c
o
o
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
- 90% of sites have concentrations below this line
42 Sites
NAAQS
1983-02: 94% decrease
1993-02: 57% decrease
10% of sites have concentrations below this line
83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02
Year
Figure 3-lb. Airborne concentrations of lead, averaged across the U.S., shown in relation
to the current NAAQS, for the years 1983 through 2002.
May 2006
3-3 DRAFT-DO NOT QUOTE OR CITE
-------
o Trends
: Supplemental
• Tribal
Figure 3-2a. Locations monitored by the Speciation Trends Network (STN).
• > .030 ug/m3 (2 monitor-methods)
• .010 -.030 ug/m3 (30)
o .005 -.010 ug/m3 (73)
. <,005 ug/m3 (167)
Figure 3-2b. The average maximum quarterly mean Pb concentrations observed in
by the STN.
May 2006
J-4
DRAFT-DO NOT QUOTE OR CITE
-------
1 The third network is the Interagency Monitoring of Protected Visual Environments
2 (IMPROVE) network, which measures PM2.5 air lead concentrations mainly in rural (Class 1)
3 areas. This network is administered by the National Park Service, largely with funding from
4 EPA on behalf of state air agencies that use the data to track trends in rural visibility. Lead in the
5 PM2.5 is again quantified via the XRF method. Data are managed and are accessible through the
6 IMPROVE website but are available through the Air Quality System. The oldest of these sites
7 began operation in 1988, while many others began operation in the mid 1990s. The locations of
8 these sites are shown in Figure 3-3 a. There are 110 formally designated "IMPROVE" sites
9 located in or near national parks and other Class I visibility areas; virtually all of these are rural.
10 Approximately 80 additional sites at various urban and rural locations, requested and funded by
11 various parties, are also informally treated as part of the network. Samplers are operated on the
12 same 1 in 3 day schedule as the STN by several different federal, state, and tribal host agencies
13 (see: http://vista.cira.colostate.edu/IMPROVE/). Figure 3-3b shows IMPROVE sites that detect
14 air Pb concentrations in PM2.5 at or above 0.0008 |lg/m3 between 2000 and 2005.
15
16
€1
, *
%"
Figure 3-3a. The IMPROVE network of PM2.5 monitors.
May 2006 3-5 DRAFT-DO NOT QUOTE OR CITE
-------
• > .030 |jg/m3 (2 monitor-methods)
« .010-.030Mg/m3<30)
o .005-.010|jg/m3(73)
o <.005(jg/m3(167)
Figure 3-3b. IMPROVE sites with Pb PM2.5 concentrations at or above 0.0008
between 2000 and 2005.
1 Finally, the National Air Toxics Trends Stations (NATTS) network of 23 sites monitors
2 urban and some rural areas. These sites are also operated by 22 state or local host agencies.
3 All collect paniculate matter as PMio for toxic metals analysis and, as such, do not measure lead
4 in the size fraction >10 |im in diameter. Lead in the collected sample is quantified via the
5 ICP/MS method. The standard operating procedure for metals by ICP/MS is available at:
6 http://www.epa.gov/ttn/amtic/airtox.html. Data are managed through the Air Quality System.
7 These sites are relatively new, with 2004 being the first year in which all were operating. The
8 Air Quality System can be accessed at http://www.epa.gov/ttn/airs/airsaqs/ (see Figure 3-4a for
9 the locations of the NATTS monitoring sites). Figure 3-4b shows the most recent average
10 maximum quarterly mean concentrations of Pb observed in PMio collected at the NATTS sites.
11
May 2006
DRAFT-DO NOT QUOTE OR CITE
-------
Figure 3-4a. The National Air Toxics Trends Stations (NATTS) network.
1 In addition to these four long-term networks, various organizations have operated other
2 sampling sites yielding data on ambient air concentrations of lead, often for limited periods
3 and/or for primary purposes other than quantification of lead itself. Much but not all of these
4 data is accessible via the Air Quality System. In an effort to gather as much air toxics data,
5 including lead, into one database, the EPA and STAPPA/ALAPCO created the Air Toxics Data
6 Archive. The Air Toxics Data Archive can be accessed at: http://vista.cira.colostate.edu/atda/.
7
8 3.1.2 Observed Concentrations - Ambient Air
9 Widespread emissions from stationary and mobile sources, as well as resuspended soil,
10 have contributed to elevated airborne lead concentrations as described in Chapter 2. In fact,
11 airborne lead concentrations in many places throughout the world have been several orders of
12 magnitude higher than natural background levels for the past seventy years (Miller and
13 Friedland, 1994). The lowest concentrations measured are at the South Pole, where an average
14 concentration of 0.076 ng/m3 was recorded (Maenhaut et al., 1979). Even at this remote
May 2006 3-7 DRAFT-DO NOT QUOTE OR CITE
-------
> .012 pg/m3 (2 monitor-methods)
.006-.012M9/m3(9)
.003-.006pg/m3(11)
< .003 M9/m3 (4)
Figure 3-4b. Average maximum quarterly mean Pb concentrations measured at NATTS
network sites (2002-2005).
1 location, it is likely that the airborne lead levels are elevated above natural background. This is
2 evidenced by lead concentrations in Arctic ice sheets that have risen from <1 ng/kg in 800 BC to
3 200 ng/kg in the 1960's (Murozumi et al., 1969).
4 Airborne concentrations of lead in the U.S. have fallen dramatically over the last 30 years
5 due largely to the phase out of leaded gasoline additives. Major declines over several orders of
6 magnitude have been observed not only in urban areas, but also in rural regions and remote
7 locations. Data taken at rural sites throughout the United States since 1979 showed a similar
8 decline (Eldred and Cahill, 1994).
9 The United States has not been the only country to experience a significant drop in lead
10 concentrations. In the early 1980's, 5% of Europe's urban population was exposed to
11 concentrations above the World Health Organization's (WHO) recommended limit of 0.5 |ig/m3
May 2006
DRAFT-DO NOT QUOTE OR CITE
-------
1 for an annual average (Fenger, 1999; WHO, 2000). By the late 1980s, this value had fallen, and
2 very few locations reported concentrations above 0.5 |ig/m3. These areas were primarily near
3 large, uncontrolled metal industries (Fenger, 1999). Notable decreases in airborne lead have
4 even been seen in remote locations. For example, measurements made in Bermuda between
5 1993 and 1994 showed that, despite its remote location, airborne lead concentrations had fallen
6 by an order of magnitude since the 1970s and by a factor of four since the 1980s (Huang, 1996).
7 Similarly, measurements taken at the South Pole were routinely below the detection limit in
8 2000-2001, which indicates a significant improvement in Antarctic air quality since the 1970s
9 (Arimoto et al., 2004). Table 3-1 lists examples of airborne lead concentrations at various
10 locations around the world during 1985 to 2005. It should be noted that concentrations are not
11 directly comparable due to different measurement time scales, sampling equipment, and
12 analytical methods.
13 Concentrations of airborne lead are sometimes several orders of magnitude higher in
14 urban areas compared to remote regions (Schroeder et al., 1987; Malm and Sisler, 2000). Rural
15 areas tend to have concentrations falling somewhere between those of urban and remote areas.
16 A comprehensive review of airborne lead concentrations throughout the U.S. showed that urban
17 areas had air lead concentrations up to 96,270 ng/m3, rural areas had air lead concentrations up to
18 1700 ng/m3, and remote areas had air lead concentrations up to 64 ng/m3. Thus, urban
19 populations are typically exposed to distinctly higher levels of airborne lead than rural or remote
20 residents.
21 According to the 1978 NAAQS, quarterly average airborne concentration of lead are not
22 to exceed 1.5 |ig/m3. Between September 2001 and September 2002, there were just four areas
23 in the United States not in attainment of this standard: Liberty-Acadia, MO; Herculaneum, MO;
24 East Helena, MT; and Lame Deer, MT (U.S. Environmental Protection Agency, 2003). In 2004,
25 there were only two areas out of attainment (www.epa.gov/air/oaqps/greenbk/inte.html).
26 Some seasonal variability is common for lead concentrations. However, whether seasonal
27 variability is present depends on precipitation trends, changes in wind direction, and mixing
28 height variability for a given area. For example, a relative maximum was observed in the winter
29 in the Arctic because of the lack of precipitation during winter months (Heidam, 1986), whereas
30 a relative maximum was observed in the summer in Bermuda when winds come predominantly
31 from Africa and Europe (Huang, 1996). Chiaradia and Cupelin (2000) observed no seasonality
May 2006 3-9 DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-1. Examples of Airborne Concentrations of Lead at Selected Sites Around the
World During 1985 to 2005.
Airborne Concentrations
(ng/m3)
Location
Reference
Urban
326 ± 15.6 in
fine mode
75.6 ±5.95 in
coarse mode
O O f\
330
52
64
12 ±6
10 ±8
64 ±47
110 ±65
4-444
758
45 ±16
49 ±43
13.1
15.4-18.9
6.9
22 ±17
<40
230-650
400-1000
127-173
46-113
27.4
Boston, MA
Boston, MA
Clemson, SC
Akron, Oh
Norfolk, VA
Chicago, IL
Cadiz, Spain
Bari, Italy
Malta, Malta
Eleusis, Greece
Caesarea, Israel
Jerusalem-Tel Aviv freeway, Israel
Geneva, Switzerland
Vancouver, BC
Riverside, CA
Los Angeles, CA
San Francisco, CA
Jerusalem, Israel
Yerevan, Armenia
St. Louis, MO
Australia roadsides
Hong Kong roadsides
Gothenburg, Sweden roadsides
Birmingham, UK roadside
Thurston and Spengler (1985)
Thurston and Spengler (1985)
Del Delumyea and Kalivretenos
(1987)
Del Delumyea and Kalivretenos
(1987)
Del Delumyea and Kalivretenos
(1987)
Del Delumyea and Kalivretenos
(1987)
Torts and Van Grieken (1997)
Torfs and Van Grieken (1997)
Torfs and Van Grieken (1997)
Torfs and Van Grieken (1997)
Ereletal. (1997)
Ereletal. (1997)
Chiaradia and Cupelin (2000)
Brewer and Belzer (2001)
Hui (2002)
Hui (2002)
Hui (2002)
Erel et al. (2002)
Kurkjian et al. (2002)
Kim et al. (2005)
Al-Chalabi and Hawker (1997)
Chan et al. (2000)
Sternbeck et al. (2002)
Harrison et al. (2003)
Near Sources of Lead Emissions
1700-4000 Fenceline of a lead smelter, CA, downwind Kimbrough and Suffet (1995)
960-1200 Fenceline of a lead smelter, CA, upwind Kimbrough and Suffet (1995)
May 2006
3-10
DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-1 (cont'd). Examples of Airborne Concentrations of Lead at Selected Sites
Around the World During 1985 to 2005
Airborne Concentrations
(ng/m3) Location Reference
Rural (cont'd)
16
9
2.5
0.54-6.34
28.6
Remote
2.2
4.6
15
0.04-3.2
0.032
Packwood, WA
Whiteface Mountain, NY
IMPROVE network
IMPROVE network
Lake Balaton, Hungary
Olympic National Park
Glacier National Park
Great Smoky Mt. National Park
Bermuda
Antarctica
Davidson et al. (1985)
Miller and Friedland (1994)
Eldred and Cahill (1994)
Malm and Sisler (2000)
Hlavayetal. (2001)
Davidson etal. (1985)
Davidson etal. (1985)
Davidson etal. (1985)
Huang etal. (1996)
Arimoto et al. (2004)
1 in lead concentrations in Geneva, Switzerland. Measurements taken at a number of U.S. and
2 French cities suggest some variation, based on seasonal differences in mixing height (Delumyea
3 and Kalivretenos, 1987).
4 Measurements made in Riverside, CA show diurnal trends (Singh et al., 2002). Lead
5 concentrations are high in the morning (6 a.m.-10 a.m.) and the late afternoon (4 p.m.-8 p.m.).
6 This is probably indicative of heavy traffic, despite the use of unleaded gasoline, a depressed
7 atmospheric mixing height in the morning, and advection from Los Angeles traffic. Lead
8 concentrations in Riverside are significantly lower during midday (10 a.m.-4 p.m.) and night
9 (8p.m.-6a.m.).
10 Concentrations of lead are dependent on height. This is particularly true if lead is emitted
11 at street level from traffic. Measurements performed at roadsides in Hong Kong in 1997 show
12 much higher concentrations at breathing level than at rooftop level (Chan et al., 2000).
13 Similarly, lead concentrations measured at four elevations in Berne, Switzerland show a
14 pronounced decrease with height (Gaelli and Nyffeler, 1987). Some leaded gasoline was still
May 2006
3-11
DRAFT-DO NOT QUOTE OR CITE
-------
1 used in Hong Kong and Switzerland during these two studies. Measurements made in an urban
2 street canyon in Lahti, Finland show that concentrations declined by a factor of five between
3 street level (1.5m) and rooftop level (25m) (Vakeva et al., 1999).
4 As airborne concentrations of lead have fallen in the United States a corresponding
5 decrease in blood lead levels of the U.S. population has been observed. In a meta-analysis of
6 19 studies from six continents, a strong linear correlation was observed between blood lead
7 levels and gasoline lead levels (Thomas et al., 1999). As gasoline lead was reduced to zero in
8 the study countries, airborne lead concentrations declined and converged to less than 0.2 |ig/m3,
9 and blood lead levels also declined, converging to a median of 3 |ig/dL.
10
11 3.1.3 Observed Concentrations - Indoor Air
12 Concentrations of lead can be elevated indoors. Lead in indoor air is directly related to
13 lead in housedust, which poses both an inhalation and an ingestion risk and is discussed in more
14 detail in Section 3.2. Strong correlations have been observed in a Boston study between indoor
15 air, floor dust, and soil lead concentrations (Rabinowitz et al., 1985a). In the National Human
16 Exposure Assessment Survey (NHEXAS) study of six Midwestern states, concentrations of lead
17 in personal air were significantly higher than either indoor or outdoor concentrations of air lead
18 (Clayton et al., 1999). The predominant sources of indoor air lead are thought to be outdoor air
19 and degraded lead-based paint.
20 Lead concentrations are likely elevated somewhat in houses of smokers. In a nationwide
21 U.S. study, blood lead levels were 38% higher in children who exhibited high cotinine levels,
22 which reflect high secondhand smoke exposure (Mannino et al., 2003). Lead is present both in
23 tobacco and in tobacco smoke, although tobacco lead concentrations have fallen in parallel with
24 decreases in airborne lead concentrations (Mannino et al., 2003).
25 Another source of lead in residential air is metal-cored candlewicks. The U.S. Consumer
26 Product Safety Commission banned the use of metal-cored candlewicks that contain more than
27 0.06% lead as of October 15, 2003 (USGS, 2003). However, prior to this time, emissions of lead
28 from metal-core wicks were measured in the range of 0.5 to 66 jig/hour according to one study
29 (Nriagu and Kim, 2000) and 100 to 1700 jig/hour according to another study (Wassan et al.,
30 2002). In homes where such candles were burned, airborne concentrations could have been well
31 above ambient levels.
May 2006 3-12 DRAFT-DO NOT QUOTE OR CITE
-------
1 3.1.4 Observed Concentrations - Occupational
2 Lead concentrations inside work places can also be elevated. Thus, inhalation of lead
3 during work hours is an additional route of exposure for some subpopulations.
4 Feng and Barratt (1994) measured concentrations of lead in two office buildings in the
5 United Kingdom. In general, concentrations in the UK office buildings were higher than
6 concentrations in nearby houses. Office dust was concentrated in the organic and residual
7 fractions, unlike house dust which was bound to carbonate and Fe-Mn oxides. This indicates
8 that offices and houses may have different lead sources. Office building lead also tends to be in
9 the coarse mode, unlike house dust that predominantly occurs in fine particles (Feng and Barratt,
10 1994).
11 As expected, concentrations of lead tend to be highly elevated within manufacturing
12 facilities for lead-based products (Rieuwerts et al., 1999; Harrison et al., 1981; Tsai et al., 1997).
13 Thus, occupational exposure can represent a major lead exposure route for employees working in
14 such facilities. For example, measurements taken in a battery manufacturing plant found lead
15 concentrations in floor dust to be 47,700 pprn outside of the assembly plant, 39,200 ppm inside
16 the assembly plant, and 73,700 ppm in the battery grid storage area (Rieuwerts et al., 1999).
17 In another study, airborne concentrations of lead in a battery manufacturing plant, a metallic film
18 capacitor plant, and a lead powder plant were 140 ± 112 |ig/m3, 281 ± 114 |ig/m3, and 485 ± 245
19 |ig/m3 respectively (Tsai et al., 1997). Work sites that use mechanical actions such as abrasion,
20 friction, and cutting typically generate large particles. However, work sites that use high
21 temperature operations generate small, respirable particles. At the three sites listed above,
22 particle sizes were predominantly >10 |im in diameter (Tsai et al., 1997). A Pb-Zn smelter in the
23 UK similarly showed much larger lead particle sizes inside the facility than outside of the facility
24 (Harrison et al., 1981). This may be because concentrations are high enough indoors to
25 coagulate. Floor dusts (<60 jim) taken from each process site in the overall smelting process
26 contained the same lead species as the aerosols emitted from each process, which are discussed
27 in Section 2.2.
28 Residential renovation and paint removal are major sources of lead exposure for both
29 workers and residents. Dry sanding, abrasive blasting, and burning, welding, or heating surfaces
30 covered with lead-based paint typically generate highly dangerous levels of lead (Jacobs, 1998).
31 Geometric mean and maximum air lead concentrations observed during each of these processes
May 2006 3-13 DRAFT-DO NOT QUOTE OR CITE
-------
1 (as reported by Jacobs, 1998) are listed in Table 3-2. Daniels et al. (2001) measured airborne
2 concentrations of lead during exterior paint removal from residences via wet abrasive blasting
3 technology. The eight-hour, time-weighted average (TWA) air exposures measured via personal
4 monitors ranged between 55.1 and 81.5 |ig/m3. Area air concentrations were between 20.5 and
5 26.9 |ig/m3.
Table 3-2. Airborne Concentrations Surrounding Residential
Lead-Based Paint Abatement
Abatement Technique
Preparation (e.g., carpet removal)
Abrasion
Chemical stripping
Encapsulation
Heat gun
Component replacement
Cleaning
Geometric Mean
Oig/m3)
2
8
o
3
2
7
o
3
2
Maximum Exposure
Oig/m3)
206
403
476
72
915
121
590
Source: Jacobs (1998).
6 Lead-based paints were the predominant coating for U.S. highway bridges for many years.
7 Paint removal during bridge renovation projects has also been cited as a major source of lead
8 exposure for workers. As with residential renovation, lead concentrations during industrial paint
9 removal depend largely on the technology used. Generally, abrasive blasting techniques are
10 used, which breaks lead coatings into small particles that can be inhaled or ingested if hands are
11 not washed prior to eating or smoking (Chute and Mostaghim, 1991). Vacuum blasting may
12 reduce occupational exposures. Personal monitors worn during vacuum blasting on a bridge
13 registered air lead concentrations between 27 and 76 |ig/m3 with a geometric mean of 55 |ig/m3
14 (Mickelson and Johnston, 1995). Concentrations measured eleven meters from the removal
15 processes fell to 0.1 and 2 |ig/m3 over an eight-hour TWA.
16 Certain types of mining operations can also result in occupational exposure to lead.
17 For example, lead concentrations measured in underground gold mines were somewhat elevated,
18 but comparable to ambient concentrations due to adequate air exchange (Annegarn et al., 1988).
May 2006 3-14 DRAFT-DO NOT QUOTE OR CITE
-------
1 Air lead concentrations ranged between 1.4 |ig/m3 and 800 |ig/m3 and were highly dependent on
2 the process being undertaken (Annegarn et al., 1988). A source apportionment study in a
3 Nevada gold mine measured lead concentrations that averaged 0.21 |ig/m3 (McDonald et al.,
4 2003).
5 Children of lead workers are also at increased risk for lead exposure. In a meta-analysis
6 of take-home lead exposure, the geometric mean blood lead level of children was 9.3 |ig/dL
7 (Roscoe et al., 1999). This was significantly higher than the geometric mean of 3.6 |ig/dL for
8 children overall. Similarly, 52% of children of lead workers had blood lead levels at or above
9 10 |ig/dL, compared with just 8.9% of children nationwide (Roscoe et al., 1999). Having a
10 parent in an automobile body or maintenance occupation also appears to raise children's blood
11 lead levels (Murgueytio et al., 1998a).
12
13
14 3.2 EXPOSURE: SOIL AND DUST
15 Contaminated soil can be a potential source of lead exposure for humans. Soil lead can be
16 directly ingested through hand-to-mouth behavior common in children, indirectly ingested
17 through contaminated food, or inhaled when breathing air containing resuspended soil particles.
18 Soil ingestion, as reported by parents, peaks during the second year of life and diminishes
19 thereafter (Lanphear et al., 2002).
20 Soil lead concentrations measured in urban, residential, and industrial areas are discussed
21 here. Soil lead concentrations in rural and remote areas, agricultural soils, and sediment are
22 addressed in Chapter 8 of this document. Information on the distribution of soil lead throughout
23 natural ecosystems is also covered in Chapter 8.
24 The natural background concentration of lead in soil is estimated to be in the range of 1 to
25 200 ppm, with an average of 15 ppm (Zimdahl and Skogerboe, 1977). It should be noted that
26 soil lead measurements are difficult to compare given the variety of extraction techniques and
27 depths of soil cores analyzed in each study.
28 The dominant source of lead to soil is atmospheric deposition both from local sources and
29 long-range transport (Erel et al., 1997; Markus and McBratney, 2001; Sheets et al., 2001).
30 In general soil in urban and residential areas is contaminated primarily via atmospheric
31 deposition, direct application of agricultural chemicals, and natural mineral weathering of parent
May 2006 3-15 DRAFT-DO NOT QUOTE OR CITE
-------
1 rock (Paces, 1998). At a local level, soil lead contamination can be derived from agricultural and
2 food wastes, animal wastes and manure, logging and other wood-cutting activities, urban refuse,
3 municipal sewage sludge, miscellaneous organic wastes including excreta, solid wastes from
4 metal manufacturing, coal fly ash and bottom fly ash, peat for agricultural and fuel uses, wastage
5 of commercial products, mine tailings, and smelter slags and wastes (Nriagu and Pacyna, 1988).
6 Flaking and peeling of lead-based paint can also be a significant source of soil lead near old
7 structures (Small et al., 1995; Finkelstein et al., 2003).
8
9 Soil Response Times
10 The retention time for lead in the soil is much longer than it is in the air. The only
11 "removal" mechanisms for soil lead are resuspension, mechanical mixing from tilling,
12 landscaping and animals, and leaching, the last of which is known to be a slow process (see
13 Chapter 2 of this document for details). The retention time, or the amount of time required to
14 reduce the soil lead concentration by half, is estimated to be on the order of hundreds to
15 thousands of years (Dudka and Adriano, 1997). Box model estimates based on data for an
16 agricultural catchment in the Czech Republic predict that steady state concentrations for soil lead
17 will not be achieved for 980 years (Paces, 1998). Modeling efforts by Harris and Davidson
18 (2005) in southern California similarly predict that steady state concentrations of soil lead will
19 not be achieved for hundreds of years, assuming emission rates stay constant. The lowest
20 estimates of a response time are given by Miller and Friedland (1994) in the northeastern United
21 States. They estimate that soil lead concentrations in a northern hardwood forest zone will
22 stabilize in just 17 years and soil lead concentrations in a subalpine spruce-fir forest zone will
23 stabilize in 77 years. A later study in the same region estimated the response times as 60 years
24 and 150 years for the two forests, respectively (Kaste et al., 2003).
25
26 3.2.1 Urban Background Concentrations of Soil Lead
27 The concentration of soil lead varies significantly throughout urban areas depending on
28 proximity to stationary sources and roadways and on wind speed and direction.
29 The major sources of lead in urban soils are automotive traffic from the days of leaded
30 gasoline (Sheets et al., 2001; Mielke, 1993; Sutherland, 2000) and deteriorating exterior lead-
31 based paint. Soil concentrations decrease both with depth and distance from roadways. In one
May 2006 3-16 DRAFT-DO NOT QUOTE OR CITE
-------
1 study of 831 homes in the U.S., 24% of housing units that had deteriorated, exterior, lead-based
2 paint had bare soil lead levels in excess of 1200 ppm (Jacobs et al., 2002). For housing units
3 without deteriorating paint, just 4% of homes had soil lead levels greater than 1200 ppm. In one
4 study of several urban areas, there was little correlation between soil lead and the age of nearby
5 houses, which suggests that lead-based paint may not be as significant of a source as automotive
6 lead under some conditions (Mielke, 1993).
7 Concentrations of lead in soil depend primarily on the size of the city and the location
8 within the city (Mielke, 1991, 1993). Extensive lead studies in Baltimore, New Orleans, and
9 cities throughout Minnesota found the highest concentrations of lead in the central sections of
10 each city, where traffic and population density are greatest (Mielke, 1991, 1993). The lowest
11 concentrations were found in the outskirts of these cities and in smaller cities. In all of these
12 studies, the age of housing did not seem to be a major factor, which suggests that the impacts of
13 lead-based paint may be dominated by historic emissions of leaded gasoline additives. However,
14 given that the highest concentrations are typically found in the inner city, generally
15 disproportionately populated by minorities and the poor, suggests that these groups are likely
16 most at risk for lead exposure from contaminated soil.
17 Some of the highest concentrations of soil lead are observed near major roadways.
18 Surface soil lead concentrations measured near a major freeway in Cincinnati, OH, fell between
19 59 ppm and 1980 ppm, which is well above background (Turer et al., 2001). These
20 concentrations dropped off dramatically with depth. An estimated 40% of lead from automobile
21 exhaust is retained in the nearby soil (Turer et al., 2001).
22 Measurements of Erel et al. (1997) in Israel show that soil lead concentrations decrease
23 more rapidly with depth near roadways than far from roadways. In a soil profile extracted near a
24 local road, lead concentrations fell by a factor of 42 between the surface and 30 to 36 cm from
25 the surface. However, far from the roadway, lead concentrations fell by about a factor of
26 3 between the surface and 30 to 36 cm below the surface.
27 Several authors making measurements during the days of leaded gasoline usage reported
28 elevated lead concentrations in soil that decrease with distance from roadways. For example,
29 Pierson and Brachaczek (1976) reported soil lead levels that decreased from >1000 ppm adjacent
30 to the road down to less than 200 ppm at 12.5 m from the roadway edge. These concentrations
31 have likely stayed high despite the elimination of leaded gasoline use. Harris and Davidson
May 2006 3-17 DRAFT-DO NOT QUOTE OR CITE
-------
1 (2005) have also shown through use of a mass balance model that elevated lead concentrations in
2 soil are likely to remain high for hundreds of years; and this is consistent with other studies
3 showing similarly long residence times in soil (e.g., Dudka and Adriano, 1997).
4 Soil lead concentrations in urban areas are generally higher than soil lead concentrations
5 in rural or remote areas. The average concentrations of soil lead in urban areas are shown in
6 Table 3-3. In many cases, these data represent averages of soil lead levels across commercial,
7 residential, and public areas, which include a wide range of concentrations.
Table 3-3. Concentration of Soil Lead in Urban Areas
Location
S pringfield, MO
Urban locations throughout Egypt
southern California
central New Orleans, LA
outer New Orleans, LA
suburban New Orleans, LA
Baton Rouge, LA
Monroe, LA
Alexandria, LA
Lafayette, LA
Natchitoches, LA
Reno-Sparks, NV
Manoa, Hawaii
Gainesville, FL
Miami, FL
5 oil cone, (ppm)
107 ± 8
23-200
65.2, 66.3, 99.4
4-69000
1-24400
2-5650
2-6680
8-1 1600
6-2590
6-886O
6-143O
-10
58 ± 27
-16
-93
Depth (cm)
0-15
0-30
0-10
0-2.5
0-2.5
0-2.5
0-2.5
0-2.5
0-2.5
O-2.5
O-2.5
0-1
O-2.5
O-2O
O-1O
R eference
Sheets et al., 2OO1
Badawy et al., 2OO2
Young et al., 2002
Mielke, 1993
Mielke, 1993
Mielke, 1993
Mielke, 1993
Mielke, 1993
Mielke, 1993
Mielke, 1993
Mielke, 1993
Gillies et al., 1999
Sutherland, 2OOO
Chirenje etal., 2OO4
Chirenje etal., 2O04
9 Several studies have assessed the impact of soil lead concentrations on blood lead levels.
10 Without accounting for other sources of lead intake, Duggan and Inskip (1985) estimated that,
11 for every 1000 ppm increase in soil lead concentration, children's blood lead levels increase
12 5 |ig/dL. Aschengrau et al. (1994) reported decreases in blood lead levels of 1.12 to 1.35 |ig/dL
13 for 1000 ppm reductions in soil lead concentrations during a randomized control trial. The
14 results of a pooled analysis of 12 studies showed a 3.8 |ig/dL increase in blood lead levels per
15 1000 ppm increase in soil lead levels (Lanphear et al., 1998). Soil abatement at a Superfund site
16 resulted in a 3.5 |ig/dL decrease in blood lead levels for 6 to 36 month old children (Lanphear
17 et al., 2003). A smaller reduction in blood lead levels was observed for 36 to 72 month old
18 children because of age differences, lead intake from other sources, and mouthing behaviors.
19 Murgueytio et al. (1998b) observed a 2.8 |ig/dL increase in blood lead levels with increases in
May 2006
3-18
DRAFT-DO NOT QUOTE OR CITE
-------
1 soil concentrations of 1000 ppm. Accounting for age differences and, therefore, the
2 redistribution of bone lead stores, (Gwiazda et al., 2005) reconciles many of the apparent
3 differences between the results of the Lanphear et al. (1998, 2003), Murgueytio et al. (1998b),
4 and Aschengrau et al. (1994) studies.
5
6 3.2.2 Soil Concentrations Near Stationary Sources
7 Concentrations Near Lead Smelters
8 Lead in soil is highly elevated near sources of lead emissions. In particular, areas around
9 stationary facilities such as smelters and battery disposal sites can have very high levels of soil
10 lead.
11 Major smelter deposits exist primarily within a 0.5 km radius of the stack (Chatterjee and
12 Banerjee, 1999; Rieuwerts et al., 1999) although some studies observe elevated concentrations of
13 lead as far away as 30 km (Liu, 2003). Franssens et al. (2004) used isotopic measurements to
14 show that between 50% and 80% of dry depositing lead within a 3 to 4 km radius of a lead-zinc
15 smelter had an industrial origin.
16 Soil concentrations of lead decrease dramatically with distance from the source and
17 depend greatly on windspeed and direction (Kimbrough and Suffet, 1995; Palacios et al., 2002;
18 Suchara and Sucharova, 2004). Godin et al. (1985) measured soil lead concentrations that were
19 almost proportional to the inverse of the distance from the source and the square root of the wind
20 direction frequency. Suchara and Sucharova (2004) estimated an exponential decrease in soil
21 lead concentration with distance from a lead smelter in the Czech Republic. Data collected
22 within a 14 km radius showed an exponential decrease in soil lead concentration with distance
23 from the source. Exponential decreases in soil concentrations have been suggested elsewhere, as
24 well (e.g., Chatterjee and Banerjee, 1999; Rieuwerts et al., 1999). Results of Chatterjee and
25 Banerjee (1999) indicate that lead concentrations remain relatively constant within about 250
26 meters of the source and decrease with distance after this. Examples of data showing decreases
27 in soil concentration with distance from major sources are shown in Table 3-4.
28 As in the case for urban soils, lead concentrations decrease significantly with depth near
29 industrial sites. As an example, Table 3-5 lists a lead concentration profile measured near a lead
30 smelter in northern France.
May 2006 3-19 DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-4. Concentrations of Soil Lead with Distance from Lead Smelters
Distance from
Smelter (m)
Fence line
20
30
40
100
123-256
250
400
500
700
1500
3000
5000
10000
20000
30000
Concentration
(ppm, dry weight)
2300a'4, 46700 ± 2100a'5, 12650b'6
5657dJ
3937dJ
3253d'1
783d'1'312.8±98.7e'2'1800a'4
636 ± 522C'8
22941 , 20200 ± 1100a'5
12741
400 ± 20a'5
792ej
519C'3
242C'3
216.7 ±87.6e'2, 137C'3
110.3±76.4e'2
57.4 ± 24.9e'2
32.9±21.4e'2
Note: In cases where multiple transects were sampled, only the downwind transects are shown.
Values are given as mean ± standard deviation.
aDepth sampled was not defined
bSample depth was 0-5 cm
°Sample depth was 0-10 cm
dSample depth was 0-15 cm
eSample depth was 0-30 cm
'Palacios et al. (2002)
2Liu (2003)
3Godinetal. (1985)
4Kimbrough and Suffet (1995)
5Chatterjee and Banerjee (1999)
6Rieuwerts et al. (1999)
7Venditti et al. (2000)
8Young et al. (2002)
May 2006
3-20
DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-5. Soil Lead Concentration Profile Measured Near a
Lead Smelter in Northern France
Depth (cm)
0-6
6-9
9-36
36-50
50-70
70-85
85-120
120-165
Soil Horizon
Oi
Oa
Ag
ABg
BAg
Bg
HC2g
HC3g
Soil Cone, (ppm)
2340
4480
383
21.7
18.2
17.1
12.4
10.2
Source: Denaix et al. (2001).
1 The species of metals found near smelters vary depending on soil conditions. One study
2 observed lead in topsoil that was either in the form Pb5(PO4)3Cl or Pb(II) compounds that were
3 adsorbed onto Fe(II) oxides or associated with clay particles (Batonneau et al., 2004). Other
4 measurements at a site contaminated with automotive battery wastes showed lead species in the
5 soil to be Pb(CO)3, Pb(CO3)2, Pb(OH)2, PbO, and PbSO4 (Pichtel et al., 2000). Additional
6 studies have shown lead contamination bonded to bacteria (Denaix et al., 2001), carbonate
7 (Maskall and Thornton, 1998; Pichtel et al., 2000; Venditti et al., 2000), sulfide phases (Pichtel
8 et al., 2000; Venditti et al., 2000), organic phases (Pichtel et al., 2000; Venditti et al., 2000) and
9 Fe-Mn oxides (Venditti et al., 2000). The prevalence of carbonate forms in contaminated soil is
10 due to coinciding contamination with calcareous slag wastes (Maskall and Thornton, 1998).
11 Lead concentrations do not appear to have decreased in areas surrounding smelters despite
12 the implementation of pollution controls. A smelter in Slovenia was fitted with protective filters
13 in 1978 (Zadnik, 2004). Since that time, concentrations have fallen dramatically in hay samples
14 and cow blood within 10 km of the smelter; however, soil concentrations in areas around the
15 smelter did not decrease between 1978 and 2003 (Zadnik, 2004). Similarly, a lead-zinc smelter
16 in British Columbia, Canada was replaced by a new smelting facility in 1997 (Hilts, 2003).
17 Airborne concentrations fell by nearly 75%, and lead concentrations fell by 50% in outdoor
18 dustfall, street dust, and indoor dustfall. However, no statistically significant decline was
May 2006 3-21 DRAFT-DO NOT QUOTE OR CITE
-------
1 observed in soil lead concentrations nor in lead concentrations in carpeting inside nearby
2 residences (Hilts, 2003). Soil lead concentrations at five U.S. factory sites, which had closed
3 decades ago, were elevated as well (Rabinowitz, 2005). Also, many sites where smelters had
4 previously operated and are unrecognized as such (Eckel et al., 2001) may represent a previously
5 unidentified exposure risk for nearby populations.
6
7 Concentrations Near Mines
8 Concentrations of lead are highly elevated near mines as well. Lead and zinc mines in
9 particular have large deposits of lead in nearby soil, but mines used for extracting other metals
10 can also have lead-contaminated soil. Mine sites are contaminated by the disposal of mine
11 tailings, acid mine drainage, and atmospheric deposition of airborne emissions (Dudka and
12 Adriano, 1997). Mines in the United States produced an estimated 480 Tg of lead tailings and
13 50 Tg of lead mine wastes between 1910 and 1981 (Dudka and Adriano, 1997).
14 Lead is widely dispersed in areas surrounding mining sites (Dudka and Adriano, 1997;
15 Rieuwerts and Farago, 1995). Thus, it is not easy to determine a relationship between distance
16 and soil concentration, as is the case for smelting emissions. However, a study of an abandoned
17 lead-zinc mine in Tyndrum, Scotland located near a river showed that fluvial transport had
18 carried lead contamination at least as far as 6.5 km, although contamination is suspected as far as
19 25 km downstream (MacKenzie and Pulford, 2002). Examples of soil concentrations measured
20 near mining sites are shown in Table 3-6.
21 Lead is found in many different forms near mining sites. It is commonly found in its
22 mineral form of galena (Rieuwerts and Farago, 1995; Dudka and Adriano, 1997). However,
23 in mine spoils, lead is also found as plumbojarosite [PbFe6(SO4)4(OH)i2], pyromorphite
24 [Pb5(PO4)3Cl], lead carbonate [PbCO3], leadhillite [Pb4SO4(CO3)2(OH)2], PbS'Bi2S3, lead
25 oxides, lead silicates, and lead sulfate [PbSO4] (Rieuwerts and Farago, 1995; Mbila and
26 Thompson, 2004).
27 Lead tends to be more heavily concentrated in smaller soil grain sizes than in larger grain
28 sizes (MacKenzie and Pulford, 2002). Results of one study are listed in Table 3-7. Young et al.
29 (2002) observed that the lead concentration was much higher in the < 38 |im size range than in
30 the 300 |im to 2 mm size range in contaminated soils. This is likely due to the higher specific
31 surface area of smaller soil particles and the fact that lead tends to bond with organic matter and
May 2006 3-22 DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-6. Soil Concentrations Measured Near Mining Sites
Location
Wales, UK
Halkyn, UK
Shipham, UK
Shipham, UK
Derbys, UK
Winster, UK
Leadville, US
Derbys, UK
Shipham, UK
Pribram, Czech
Republic
Tyndrum,
Scotland
Goldenville,
Canada
Sao Domingos,
Portugal
Jasper County,
Missouri, U.S.
Dubuque, Iowa,
U.S.
Type of
Mine
Pb
Pb-Zn
Zn,Pb
Zn,Pb
Pb
Pb
Pb
Pb
Zn,Pb
Pb
Pb-Zn
Au
Cu
Pb
Zn,Pb
Main Period of
Operation
historic,
not specified
1845-1938
1700-1850
1650-1850
18th and
19th cent.
Up to end of
18th cent.
1860s-1960s
18th and
19th cent.
18th and
19th cent.
18th-20thcent.
Up to 1862
1869-1927
Pre-Roman-
Roman times
1850-1957
19th century
Depth
(cm)
0-15
0-15
0-15
0-5
0-5
0-5
n.a.
0-15
0-15
0-5
n.a.
n.a.
0-30
n.a.
0-20
Mean
cone.
(ppm)
1159
1127
7900
2002
5610
7140
1110
1800
7360
(max)
1451
13000
70-120
2694
574 ±691
791
Reference
Gallacher et al. (1984) (taken from
Rieuwerts and Farago, 1995)
Davies et al. (1985) (taken from
Rieuwerts and Farago, 1995)
Mattigod et al. (1986) (taken from
Rieuwerts and Farago, 1995)
Thornton et al. (1988) (taken from
Rieuwerts and Farago, 1995)
Thornton (1990) (taken from
Rieuwerts and Farago, 1995
Cotter-Howells and Thornton
(1991) (taken from Rieuwerts and
Farago, 1995)
Cook et al. (1993) (taken from
Rieuwerts and Farago, 1995
Li and Thornton (1993) (taken from
Rieuwerts and Farago, 1995)
Li and Thornton (1993) (taken from
Rieuwerts and Farago, 1995)
Rieuwerts and Farago (1996)
(taken from Rieuwerts and
Farago, 1995)
MacKenzie and Pulford (2002)
Wong et al. (2002)
Freitas et al. (2004)
Murgueytio et al. (1998b)
Mbila and Thompson (2004)
May 2006
3-23
DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-7. Concentrations of Lead in Soils Grouped by Soil Grain Size
Size Fraction
>180(im
53-180 nm
<53 (im
Pb cone, of main
mine waste
0.91%
1.5%
4.5%
Pb cone, of processing
site waste
17%
14%
18%
Source: MacKenzie and Pulford (2002).
1 Fe/Al oxides, which can also concentrate in smaller size particles (Young et al., 2002).
2 Additionally, Rieuwerts and Farago (1995) note that soil lead particles are typically larger in
3 mining areas than in smelting areas.
4 Lead concentrations in peat have also been shown to decrease with depth. Figure 3-5
5 illustrates two peat profiles sampled near an abandoned lead mine.
6 Blood lead levels are typically elevated for people living near lead mines. Soil collected
7 at residences near the Tar Creek Superfund Site, which is a lead mining area in northeastern
8 Oklahoma, showed wind-dispersed mine wastes (Lynch et al., 2000). More than 20% of soils
9 exceeded the EPA action level of 500 ppm and children's blood lead levels tended to be higher
10 when compared to children living outside the Superfund towns. In this same area, Malcoe et al.
11 (2002) showed that blood lead levels were highest among African American, Mexican American,
12 and poor children. Blood lead levels were most commonly correlated with mean floor dust lead
13 loading and with soil lead, especially front yard soil (Malcoe et al., 2002). At the Jasper County
14 Superfund Site in southwestern Missouri, homes had significantly higher soil and dust lead levels
15 and significantly higher blood lead levels than areas outside of the Superfund site (Murgueytio
16 et al., 1998b). There was a strong statistical relationship observed there between blood lead
17 levels and dust, soil, and paint lead.
18
19 3.2.3 Observed Concentrations - House Dust
20 Given the large amount of time people spend indoors, exposure to lead in dusts and indoor
21 air can be significant. For children, dust ingested via hand-to-mouth activity may be a more
May 2006 3-24 DRAFT-DO NOT QUOTE OR CITE
-------
(i) Pb concentration (ing kg'l
3000 4000 1000 IBM
chronology
1966
1921
ill*
1IS2
1829
14 1.16 1.11
b atom ratio
(b)
6 ""*"
1.12
conccnirition (rag kg"1)
HO
2M
300
ebronolofy
IM1
1*12
11)2
1172
1.14 Lit
|tom
I. II
Figure 3-5. The changes in lead concentration with depth in two peat cores. Core A was
taken at a location adjacent to the ore processing area of the abandoned lead
mine in Tyndrum, Scotland. Core B was taken 0.5 km from the main mine
waste dump at the same site.
Source: MacKenzie and Pulford (2002).
1 important source of lead exposure than inhalation (Adgate et al., 1998; Oliver et al., 1999).
2 However, dust can be resuspended through household activities (e.g., Ferro et al., 2004), thereby
3 posing an inhalation risk as well. The particle size of "dust" is not well defined, although 50 jim
4 or 75 |im in diameter is sometimes given as an upper limit. In a study performed in the UK, lead
5 in housedust tended to be bound to the carbonate or Fe-Mn oxides (Feng and Barratt, 1994).
6 Lead in housedust can derive from a number of different sources. Lead appears both to
7 come from sources outside the home (Jones et al., 2000; Adgate et al., 1998) and from lead-
8 based paint (Hunt et al., 1993; Lanphear et al., 1996). A chemical mass balance study in Jersey
9 City, NJ observed that crustal sources contributed almost half of the lead in residences, lead-
May 2006
3-25
DRAFT-DO NOT QUOTE OR CITE
-------
1 based paint contributed about a third, and deposition of airborne lead contributed the remainder
2 (Adgate et al., 1998). Residential concentrations measured at the Bunker Hill Superfund Site in
3 northern Idaho indicate that the concentration in houses depends primarily on the neighborhood
4 soil concentration (von Lindern et al., 2003a, 2003b). However, factors such as household
5 hygiene, the number of adults living in the house, and the number of hours children spend
6 playing outside were also shown to affect concentrations. Using a classification scheme, Hunt
7 et al. (1993) identified sources of lead in housedust in London for various particle size ranges.
8 In the 64 to 1000 jim size range, the predominant source of lead was lead-based paint. However,
9 in the <64 jim size bin, paint, road dust, and garden soil were significant contributors. Lead
10 deposition measured on an interior plate near an open window, an unsheltered exterior plate, and
11 a sheltered exterior plate in New York City were 4.8, 14.2, and 32.3 |ig/(ft2 week) (52, 153, and
12 348 |ig/(m2 week)), respectively (Caravanos et al., 2006). Data from a control (interior plate,
13 closed window) showed deposition that was primarily from exterior, environmental sources
14 as well.
15 Living near a smelter or a mine contributes significantly to the lead load in residences
16 (Rieuwerts and Farago, 1995; Rieuwerts et al., 1999; Sterling et al., 1998). Homes of mine and
17 smelter employees tend to have lead levels elevated above those of nearby houses indicating that
18 lead can be transported into homes via workers (Rieuwerts et al., 1999). In a US study, mining
19 wastes, paint, and soil were all shown to contribute to housedust (Sterling et al., 1998). Soil and
20 mining wastes accounted for more than 50% of lead in housedust. Lead-based paint contributed
21 16-23% of lead in housedust in a mining community (Sterling et al., 1998).
22 Renovation, and especially old paint removal, can greatly increase lead levels inside the
23 home (Mielke et al., 2001; Laxen et al., 1987; Jacobs, 1998). Removal of exterior paint via
24 power sanding released an estimated 7.4 kg of lead as dust, causing lead levels inside one house
25 to be well above safe levels (Mielke et al., 2001). Remaining in a residence during the deleading
26 procedure can be acutely dangerous (Rey-Alvarez and Menke-Hargrave, 1987). Deleading by
27 dry-scraping and sanding has been shown to raise children's blood lead levels during the process,
28 but deleading by covering or replacing painted surfaces decreased children's blood lead levels
29 during the abatement process (Amitai et al., 1991). Excessive lead exposure can occur even after
30 lead abatement. In one prospective controlled study, an average blood lead increase of 6.5 |ig/dL
31 was observed among children whose homes had undergone lead-based paint abatement
May 2006 3-26 DRAFT-DO NOT QUOTE OR CITE
-------
1 (Aschengrau et al., 1997). Clark et al. (2004) found that despite adherence to US Department of
2 Housing and Urban Development (HUD) post-abatement standards, six month old children who
3 lived in houses that had recently undergone lead abatement were eleven times more likely to
4 have blood lead levels increase by 5 |ig/dL or more compared to a control group. These studies
5 suggest that existing clearance standards may be inadequate to protect children from lead
6 following abatement or other lead hazard controls (Clark et al., 2004).
7 Examples of lead concentrations measured in house dust, school dust, and nursing home
8 dust are shown in Table 3-8. It should be noted that dust lead loadings may be better predictors
9 of blood lead levels than dust concentrations (Lanphear et al., 1995, 1998). Standards for
10 residential lead loadings of housedust were set by EPA in 2001 to be 40 |ig/ft2 (430 |ig/m2) for
11 floors and 250 |ig/ft2 (2690 |ig/m2) for windowsills.
12 An additional concern is attic dust or dust found in roof cavities. Significant deposits of
13 atmospheric lead can build up in these spaces. This dust can seep into living spaces through
14 ceiling decorative artwork, cracks between the wall and ceiling, electric light fittings, wall vents,
15 or exhaust, roof, and ceiling fans (Davis and Gulson, 2005). Additionally, renovations, housing
16 additions, ceiling collapses, and storm damage can produce large plumes of attic dust (Davis and
17 Gulson, 2005).
18 Studies comparing lead concentrations in attic dust with house age showed an excellent
19 correlation between attic dust lead levels and ambient air concentration data measured
20 throughout the lifetime of the house (Chiaradia et al., 1997; Ilacqua et al., 2003). Attic dust may
21 even serve as a proxy for estimating historic ambient concentrations, although the resolution on
22 such calculations would be low. Attic dust lead concentrations measured in Australia were an
23 order of magnitude higher in houses near a copper smelter compared with houses far from the
24 smelter (Chiaradia et al., 1997). However, isotopic analyses showed that alkyl-lead additives
25 were the dominant source of lead contamination in attic dust, overall suggesting that gasoline
26 emissions had a greater influence than the smelter. The geometric mean concentration of lead
27 measured in attics in Sydney was 1660 ppm near industrial sites, 1173 ppm near semi-industrial
28 sites, 447 ppm in non-industrial sites, and 16 ppm in background crustal materials (Davis and
29 Gulson, 2005).
30 Even at low concentrations, lead in housedust can have an effect on children's blood lead
.2
31 levels. Epidemiological studies show that, at a median floor dust lead level of 5 |ig/ft
May 2006 3-27 DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-8. Examples of Lead Concentrations in Indoor Dust
to
o
o
ON
Concentration of Lead
(ppm unless otherwise indicated)
503 (mean)
308 (median)
43-13,600
9 (geometric mean)
1.5-48.9
117-362
1598
Location
Edinburgh Scotland
Edinburgh Scotland
Edinburgh Scotland
Various parts of Denmark
Various parts of Denmark
UK
Helena and Silver Valleys, US
Surface
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Reference
Laxenetal. (1987)
Laxenetal. (1987)
Laxenetal. (1987)
Jensen (1992)
Jensen (1992)
Feng and Barratt( 1994)
Schilling and Bain (1988)a
OJ
i
to
oo
o
^
H
I
0
o
2|
0
H
O
Cj
o
H
W
O
O
1 — I
H
W
3025-4140
1283
114-185
1984
348
340
786
1870
1560
726
435
857±91ppminPM60
1133±119ppminPM10
975 ppm in PM53
481 ppminPM25o
(near 2 Pb smelters)
Trail, B.C. Canada (near Pb smelter)
Illinois (near Pb smelter)
Landskrona, Sweden (near Pb smelter)
Pribram, Czech Republic (near Pb smelter)
Wales, UK (near a mining site)
Halkyn, UK (near a mining site)
Shipham, UK (near a mining site)
Derbys, UK (near a mining site)
Winster, UK (near a mining site)
Leadville, US (near a mining site)
Pribram, Czech Republic (near a mining site)
Jersey City, NJ
Jersey City, NJ
Public school in Port Pirie, Australia
Public school in Port Pirie, Australia
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Hertzmanetal. (1991)a
Kimbroughetal. (1994)a
Faragoetal. (1999)a
Rieuwerts and Farago (1996)a
Gallacheretal. (1984)a
Daviesetal. (1985)a
Thornton (1988)a
Thornton etal. (1990)a
Cotter-Howells and Thornton (1991)a
Cook etal. (1993)a
Rieuwerts and Farago (1996)a
Adgate et al. (1998)
Adgate et al. (1998)
Oliver etal. (1999)
Oliver etal. (1999)
-------
Table 3-8 (cont). Examples of Lead Concentrations in Indoor Dust
to
o
o
Concentration of Lead
(ppm unless otherwise indicated)
Location
Surface
Reference
to
VO
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
1693-6799 ppm in PM53
1407-4590 ppm in PM250
954
14.4 (ng/m3)
26.8 (ng/m3)
558 ± 544 ppm in TSP
612±518ppminPM10
547 ± 512 ppm in PM2 5
5140 (ng/m2)
18230 (ng/m2)
24,6 (ng/m2)
3158 (ng/m2)
219.3 (ng/m2)
89.3 (ng/m2)
191.5 (ng/m2)
26.9 (ng/m2)
20.7 (ng/m2)
50.9 (ng/m2)
95.5 (ng/m2)
65.8 (ng/m2)
39.6 (ng/m2)
63.6 (ng/m2)
Houses in Port Pirie, Australia
Houses in Port Pirie, Australia
Households in Midwest, US
Households in Midwest, US
Households in Midwest, US
Nursing homes in Vienna
Nursing homes in Vienna
Nursing homes in Vienna
Households in Midwest, US
Households in Midwest, US
Boston, MA
Cincinnati, OH
Cincinnati, OH
Rochester, NY
Rochester, NY
Butte, MT
Bingham Creek, UT
Leadville, CO
Magna, UT
Sandy, UT
Midvale, UT
Palmerton, PA
Floor dust
Floor dust
Windowsill dust
Airborne
Airborne, personal air
Airborne
Airborne
Airborne
Surface dust
Windowsill dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Floor dust
Oliver etal. (1999)
Oliver etal. (1999)
Clayton etal. (1999)
Clayton etal. (1999)
Clayton etal. (1999)
Komarnicki (2005)
Komarnicki (2005)
Komarnicki (2005)
Clayton etal. (1999)
Clayton etal. (1999)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
cited in Lanphear et al. (1998)
aCited in Rieuwerts and Farago (1995).
-------
1 (54 |ig/m2), approximately 5% of children have blood lead levels > 10 |ig/dL (Lanphear et al.,
2 1998, 2005; Malcoe et al., 2002). At a floor dust lead loading of 50 |ig/ft2 (540 |ig/m2), the
3 percentage of children with blood lead levels > 10 |ig/dL rose to 20% (Lanphear et al., 1998).
4 In another study, children exposed to floor dust lead loadings in excess of 25 |ig/ft2 (270 |ig/m2)
5 were at eight times greater risk of having blood lead levels > 10 |ig/dL compared to children
6 exposed to levels below 2.5 |ig/ft2 (27 |ig/m2) (Lanphear et al., 2005).
7 Throughout early childhood, floor dust lead contamination is a source of exposure. Lead-
8 contaminated windowsill dust becomes an additional source of lead intake during the second
9 year of life when children stand upright. Because of normal mouthing behaviors and increased
10 mobility, the highest blood lead levels are seen in children between 18 and 36 months of age
11 (Clark et al., 1991). This peak is observed after a rapid rise in blood lead levels between 6 and
12 12 months.
13
14 3.2.4 Concentrations of Lead in Road Dust
15 Elevated concentrations of lead in road dust pose an important exposure risk through wind
16 and traffic resuspension, as outlined in Chapter 2 of this document.
17 The primary source of lead in road dust is adjacent soil (de Miguel et al., 1997). However
18 traffic emissions, the weathering and corrosion of building materials (de Miguel et al., 1997), and
19 brake pad wear (Garg et al., 2000) are additional sources. Between 60 to 90% of the mass of
20 road dust consists of soil particles (Adgate et al., 1998). Soil is still an important reservoir for
21 lead emitted from vehicles despite the widespread phase out of leaded gasoline. The
22 concentration of lead in road dust is generally elevated above background. This is particularly
23 true in urban areas. Additionally, measurements reported in 2003 in the San Joaquin Valley of
24 California show concentrations that are significantly lower than concentrations measured in the
25 same area in 1987 (Chow et al., 2003). Examples of road dust lead data reported in the literature
26 are listed in Table 3-9.
27 Metals in road dust tend to be associated with small size grains. Measurements of Kuang
28 et al. (2004) show that metals are concentrated in grains smaller than 0.125 mm in diameter.
29 De Miguel et al. (1997) observe a steep gradient in road dust concentrations of lead in the
30 north-south direction in Oslo, Norway. This indicates that lead concentrations are much higher
31 in the highly urbanized areas and lower in the suburban and residential areas. This is consistent
May 2006 3-30 DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-9. The Concentration of Lead in Road Dust
Cone, of Lead (ppm)
Location
Land Use
Reference
180±14
1927 ±508
536 ±39
57,2 ±27.3
-100
1209 ±170 (PM2.5)
1061 ±155 (PM10)
588+688
470 ±524
151 ±124
161 ±31
57 ±28
109 + 74
58 ±73
203 ±133
43 ±8
101 ±88
Oslo, Norway
Madrid, Spain
Calcutta, India
Beijing, Chinga
Reno-Sparks, NV
Hong Kong
Hong Kong
Honolulu, HI
Honolulu, HI
Honolulu, HI
S an J oaquin Valley, C A
San Joaquin Valley, CA
S an J oaquin Valley, C A
S an J oaquin Valley, C A
San Joaquin Valley, CA
S an J oaquin Valley, C A
San Joaquin Valley, CA
urban, paved road
urban, paved road
near lead smelter, paved
urban, paved road
urban, paved road
urban, paved road
urban, paved road
urban, paved road
urban, paved road
urban, paved road
urban, paved road
rural, paved road
composite, paved road
agricultural unpaved road
residential unpaved road
staging area soil
unpaved composite
de Miguel etal., 1997
de Miguel etal., 1997
Chatterjee and Banerjee, 1999
Kuang etal., 2004
Gillies etal., 1999
Ho etal,, 2003
Ho etal,, 2003
Sutherland etal., 2003
Sutherland etal., 2003
Sutherland etal,, 2003
Chow eta I., 2003
Chow eta I., 2003
Chow etal., 2003
Chow etal., 2003
Chow eta I., 2003
Chow eta I., 2003
Chow etal,, 2003
1 with traffic and building construction, renovation, and weathering of building materials being the
2 dominant source of lead to soil and subsequently road dust (de Miguel et al., 1997).
O
4
5 3.3 EXPOSURE: DRINKING WATER
6 Lead in drinking water is primarily a result of corrosion from lead pipes, lead-based
7 solder, or brass or bronze fixtures within a residence (Lee et al., 1989; Singley, 1994; Isaac et al.,
8 1997). Very little lead in drinking water comes from utility supplies. Experiments of Gulson
9 et al. (1994) confirm this by using isotopic analysis. Tap water analyses for a public school,
10 apartments, and free standing houses also indicate that the indoor plumbing is a greater source of
11 lead in drinking water than the utility, even for residences and schools serviced by lead-pipe
12 water mains (Moir et al., 1996). Ratios of influent lead concentration to tap concentrations in
13 homes in four municipalities in Massachusetts ranged between 0.17 to 0.69, providing further
14 confirmation that in-home lead corrosion dominates the trace quantities of lead in municipal
15 water supplies (Isaac et al., 1997). The information in this section addresses lead concentrations
16 in water intended for human consumption only. However, this water comes from the natural
17 environment, and concentrations of lead found in natural systems are discussed in Chapter 8.
May 2006
3-31
DRAFT-DO NOT QUOTE OR CITE
-------
1 The chemical composition of water distribution pipes is of great importance when
2 considering how much lead is leached into drinking water. Copper piping with lead-based solder
3 has largely replaced pure lead piping in the United States. A survey of 94 water companies
4 nationwide in 1988 revealed that copper pipe was present in 73% of homes, galvanized pipe was
5 present in 13% of homes, a mixture of galvanized and copper was present in 11% of homes, and
6 plastic pipes were present in 2% of homes (Lee et al., 1989). An analysis of PVC pipes indicated
7 that some lead is leached from PVC in measurable amounts (Sadiq et al., 1997). PVC, which
8 contains -1% lead, increased the tap water concentration to an average of 0.017 ± 0.038 mg/L,
9 which was a statistically significant increase over the influent concentration of 0.011 ± 0.026
10 mg/L (Sadiq et al., 1997). Guo et al. (1997) suggested that lead may be leached from cement-
11 mortar lined pipes in significant quantities if the cement was made from clinker derived from
12 combusted, hazardous materials.
13 In addition to piping, lead may leach from faucets. Water lead measurements performed
14 for 12 faucets of different compositions typically found in homes indicated that new cast-brass
15 faucets leached more lead than any of the other designs (Gardels and Sorg, 1989). Water lead
16 levels were below the detection limit from a plastic faucet. In houses with copper piping and
17 lead-based solder, brass fixtures may contribute as much as 50% of lead in drinking water (Lee
18 etal., 1989).
19 The primary type of solder used in the United States was 50-50 tin-lead solder (50% tin,
20 50% lead) before the Safe Drinking Water Act amendments of 1986 were enacted (U.S. EPA
21 2006). Although new or repaired pipes may not use solder containing more than 0.2% lead,
22 50-50 solder still exists in many older structures. In comparing lead leached from 50-50 tin-lead
23 solder, 95-5 tin-antimony solder, and a liquefied 50-50 tin-lead formulation that contained a
24 flux, Birden et al. (1985) showed that the liquefied 50-50 formulation leached the most lead into
25 drinking water. The 95-5 tin-antimony solder was the safest with respect to drinking water
26 quality. Measurements of metals leached from four, nonlead-based solders in copper pipes were
27 undertaken by Subramanian et al. (1991, 1994). Of the four solders tested (95-5 Sn-Sb, 96-4
28 Sn-Ag, 94-6 Sn-Ag, and 95.5-4.0-0.5 Sn-Cu-Ag), all showed that metals (Ag, Cd, Cu, Sb, Sn,
29 and Zn) were leached in small enough quantities to make these solders safe alternatives to lead-
30 based solders.
May 2006 3-32 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead corrosion is essentially an electrochemical process. Electrons may be transferred
2 from the metal (lead) to the solution (drinking water) where the major electron acceptors are
3 dissolved oxygen, hydrogen ions, or disinfectant residuals (Singley, 1994). Alternatively, when
4 two different metals are in contact, there is a difference in potential, and the difference in
5 electron demand may increase corrosion (Singley, 1994). In either case, lowering the pH and
6 increasing the dissolved oxygen demand are known to increase rates of corrosion. The corrosion
7 process occurs faster at high temperatures than at low temperatures (e.g., Thompson and Sosnin,
8 1985; Lee etal., 1989).
9 The combined pH and alkalinity of water are sometimes described as the aggressiveness
10 of the water and is measured using the Langelier Index. A pH above 8.0 is generally considered
11 safe for lead leaching (e.g., Lee et al., 1989; Frey, 1989).
12 There are conflicting reports on the effect of chlorine in water. Chlorine, which is
13 typically used as a disinfectant in municipal supplies, may increase the rate of corrosion by
14 providing a source of electron acceptors (Singley, 1994). However, measurements of Lee et al.
15 (1989) show an absence of statistically significant change in lead levels with increasing
16 concentration of free chlorine. Laboratory tests of Edwards and Dudi (2004) show that chlorine
17 reacts with soluble Pb2+ to precipitate a red-brown colored lead solid. This solid is highly
18 insoluble, even at a pH of 1.9 for twelve weeks. Thus, chlorine may actually lessen the overall
19 quantity of lead in drinking water. Elevated levels of lead in drinking water in Washington DC
20 in 2000 were traced to a change from chlorine to chloramine disinfectant. The red-brown lead
21 solid does not form in the presence of chloramines, and the data suggest that chloramines
22 dramatically increase the amount of lead leached from brass (Edwards and Dudi, 2004).
23 Flouridating water does not seem to affect the solubility or reactivity of lead compounds
24 (Urbansky and Schock, 2000).
25 Corrosion inhibitors are sometimes added to water to inhibit scaling or iron precipitation.
26 Zinc orthophosphate in the range of 0.4-0.6 mg/L is an effective inhibitor for lead corrosion
27 (Lee et al., 1989). Results indicate that zinc orthophosphate is more effective at reducing lead
28 levels than increasing the pH. Soluble lead release is reduced by up to 70% with the addition of
29 orthophosphate (Edwards and McNeill, 2002). Other proposed corrosion inhibitors such as
30 sodium zinc hexametaphosphate or sodium hexametaphosphate are not effective at reducing lead
31 corrosion (Lee et al., 1989). In fact, results of McNeill and Edwards (2004) indicate that
May 2006 3-33 DRAFT-DO NOT QUOTE OR CITE
-------
1 hexametaphosphate increased the levels of soluble lead in drinking water. Each milligram per
2 liter of hexametaphosphate increased the lead content by ~1.6 mg/L after a 72 hour stagnation
3 period in pure lead pipes (Edwards and McNeill, 2002).
4 The length of time that drinking water remains in a pipe also affects the water lead
5 concentration. Thus, a first flush phenomenon is generally observed in the morning after water
6 has stayed in the pipe through the night. An estimated 47% of total leached lead was observed in
7 the first 500 mL of water after prolonged stagnation (Singh and Mavinic, 1991). Gardels and
8 Sorg (1989) demonstrated that 60 to 75% of total lead leached appeared in the first 125 mL of
9 water after prolonged stagnation. For cold water, the peak lead concentrations occurred in the
10 first or second 25 mL sample and decreased exponentially with time thereafter. For hot water
11 the peak lead concentration occurred in the second or third 25 mL sample before decreasing
12 exponentially (Gardels and Sorg, 1989). In a system where fully flushed water had a lead
13 content of 1.7 |ig/L, removing just 125 mL of water from the tap every hour kept lead
14 concentrations elevated (35 to 52 |ig/L) throughout the day (Gulson et al., 1997). Lytle and
15 Schock (2000) showed a temporary exponential increase in lead concentration with stagnation
16 time before the rate leveled off. After 10 hours of stagnation, -50 to 70% of the maximum lead
17 concentration had been achieved, although, lead levels continued to increase even after 90 hours
18 of stagnation. Their results are shown in Figures 3-6 and 3-7. It should be noted that the shape
19 of the stagnation-concentration curves was the same for all situations regardless of water quality.
20 Some examples of concentrations of lead in drinking water are shown in Table 3-10. The
21 lead standard for drinking water was set by the U.S. EPA in 1988, with a maximum allowable
22 limit of 5 |ig/L for water entering the distribution system (Frey, 1989). Longitudinal
23 observations suggest that temporal variation is small for individual households compared to
24 between-home variation (Clayton et al., 1999).
25 Lead in drinking water can be either in paniculate or soluble form. Lead can be in the
26 form of aqueous ions or complexes, particularly when pH is low. Solids are the product of
27 nonadherent corrosion deposits, eroded pieces of plumbing material, or background inputs from
28 the distribution system (Lytle et al., 1993). Lead particles are released when pH and alkalinity
29 are low, and they typically occur in the form of hydrocerrusite scales (McNeill and Edwards,
30 2004). The lead products of corrosion are CaCO3, PbCO3, Pb3(CO3)2(OH)2,
31 PblO(CO3)6(OH)6O, Pb5(PO4)3OH, and PbO (Lytle et al., 1993; McNeill and Edwards, 2004).
May 2006 3-34 DRAFT-DO NOT QUOTE OR CITE
-------
too
0.90
0.70
O.«0
0.50
0.40
O.JO
0.20
0.10
0.00-
NQ
I 1 t
Eh
1
1
2 £
0 10 20 30 40 50 60 70 80 90
Stagnation Lirncih)
Impact of stagnation time on lead and dissolved oxygen concentration in lead pipe
(13 mm diameter) exposed to softened water in Study A.
Figure 3-6. The change in lead concentration versus stagnation time. (Reprinted from
Lytle and Schock, 2000).
1 Based on the conditions described above, models to predict drinking water lead concentrations
2 have been proposed (e.g., Clement et al., 2000; Van Der Leer et al., 2002). Lead in water,
3 although it is typically found at low concentrations in the U.S., has been linked to elevated blood
4 lead concentrations. In a study of mothers and infants in Glasgow, Scotland tap water was the
5 main correlate of raised maternal blood lead levels (Watt et al., 1996). In a prospective study
6 children exposed to water with lead concentrations greater than 5 ppb had blood lead levels -1.0
1 |ig/dL higher than children with water lead levels less than 5 ppb (Lanphear et al., 2002). Thus,
8 water may not be a trivial source of lead under some conditions.
May 2006
3-35
DRAFT-DO NOT QUOTE OR CITE
-------
LOO
0.90
I.I Hit
0.70
~ 0.60
M
§ Q.SO
0.44)
OJO
0.20
0.10
o.oo H
Aged 16L-184 days
Aged 455-41,2 days
4 _
1
s
1
I 5
f^
if
0 102030405060708090
i;;U, i i.jf >. .1, l.; 111- : I).
Impact of stagnation time on lead and dissolved oxygen concentration in lead pipe (13 mm diameter)
exposed to non-softened water in Study A.
Figure 3-7. The change in lead concentration versus stagnation time. (Reprinted from
Lytle and Schock, 2000).
1
2
3
4
5
6
1
8
9
10
The 1991 EPA Lead and Copper Rule requires that public water utilities conduct
monitoring of lead from customer taps - generally every six months, annually, or triennially,
depending on the levels of lead observed in drinking water. Less frequent monitoring is required
if levels are low. The rule established a tap water limit ("action level") of 0.015 mg/L (15 ppb)
for Pb, based on the 90th percentile concentration, above which corrective action is required
(see http://www.epa.gov/safewater/lcrmr/implement.html). The Safe Drinking Water
Information System/Federal Version (SDWIS/FED) maintains a database to which public water
utilities are required to submit monitoring data. States have been required to report to EPA the
90th percentile lead concentrations reported by water systems serving more than 3,300 people.
The data available up through 2005 show that about 96% of the utilities that monitored and
May 2006
3-36
DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-10. Examples of Tap Water Concentrations of Lead
^<:
to
o
o
OJ
OJ
O
^
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Water Concentration
20
13
0.70
0.32
16
8
3
2
6
5
17
7.7
25.0
15.3
11.6
3.92
0.84
Location
Vancouver, Canada
Vancouver, Canada
Arizona
Mexico/US border
Halifax, Canada
Halifax, Canada
Halifax, Canada
Halifax, Canada
Halifax, Canada
Halifax, Canada
Dharan, Saudi Arabia
Clinton, MA
Gardner, MA
Fall River, MA
New Bedford, MA
Midwest, US
Midwest, US
Residence Type
Apartments
Houses
Residences
Residences
Houses
Houses
Apartments
Apartments
Public School
Public School
Community sites
Residences
Residences
Residences
Residences
Residences
Residences
Description
copper or plastic pipes
copper or plastic pipes
-D
-D
standing water
running water
standing water
running water
standing water
running water
PVC pipes
standing water
standing water
standing water
standing water
standing water
flushed water
Reference
Singh and Manivic (1991)
Singh and Manivic (1991)
Sofuoglu et al. (2003)
Sofuoglu et al. (2003)
Moiretal. (1996)
Moiretal. (1996)
Moiretal. (1996)
Moiretal. (1996)
Moiretal. (1996)
Moiretal. (1996)
Sadiq etal. (1997)
Isaac etal. (1997)
Isaac etal. (1997)
Isaac etal. (1997)
Isaac etal. (1997)
Clayton etal. (1999);
Thomas etal. (1999)
Clayton etal. (1999);
Thomas etal. (1999)
-------
1 reported 90th percentile results are below the action level (see http://www.epa.gov/safewater/
2 Icrmr/lead data.html). For illustrative purposes, Table 3-11 shows 90th percentile drinking water
3 lead concentrations for a selection of large US cities reported in 1992, 1993 and in more recent
4 years. These are examples of high tap water concentrations that exceed the action level for Pb in
5 tap water and are thusly notably higher than the mean concentrations reported in Table 3-10.
6
7
8 3.4 EXPOSURE: FOOD INGESTION
9 Lead contaminated food continues to be a major route of lead exposure. In a detailed
10 study of lead ingestion in food, Flegal et al. (1990) showed that North Americans ingest an
11 estimated 50 jig of lead each day through food, beverages, and dust, and -30 to 50% of this
12 amount is through food and beverages. The global average daily intake is about 80 |ig/day from
13 food and 40 |ig/day from drinking water, according to estimates made by the UN Environment
14 Program (Juberg et al., 1997). In Australia, women between 20 and 39 years of age ingest
15 between 7.3 and 9.7 |ig/day (Gulson et al., 2001a). Infants that are breast-fed take in
16 -0.73 |ig/day compared to 1.8 |ig/day for formula-fed infants (Gulson et al., 2001a). Australian
17 children ingest approximately 6.4 |ig/day. A duplicate diet study shows that most diets also
18 contain a large amount of house dust (Manton et al., 2005). Other significant sources of dietary
19 lead are calcium-supplemented food where calcium is derived from limestone and tin coatings
20 that contain lead. In the Midwest, lead concentrations in foods consumed by children 0 to
21 6 years old were similar or lower than adults, but on a body weight basis lead intake rates were
22 1.5 to 2.5 times higher for young children (0.26 |ig/kg body weight/day for children 0 to 7 yrs
23 and 0.10 |ig/kg body weight for people overall) (Thomas et al., 1999). Overall, a small
24 percentage of the population exceeded health-based intake levels set by FAO/WHO (Thomas
25 et al., 1999). During the NHEXAS study in Maryland, the mean intake of lead in the diet was
26 7.6 |ig/day (Scanlon et al., 1999). The accompanying longitudinal study showed that lead
27 dietary exposures vary little over time. For U.S. children age 0 to 12 months, 13 to 24 months,
28 2 to 6 years, and their mothers, the estimated rate of lead ingestion was 1.8 jig/day, 3.3 jig/day,
29 4.1 |ig/day and 7.5 jig/day, respectively (Manton et al., 2005). This is significantly lower than
30 the value reported above by Flegal et al. (1990), which may reflect the reduction in lead
May 2006 3-38 DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-11. 90* Percentile Tap Water Pb Concentrations for a Selection of U.S. Cities
Exceeding the EPA Pb Action Level
90th %ile 90th %ile
1
2
O
4
5
6
7
8
9
State
AZ
DC
FL
IA
IL
MI
MN
MN
NJ
NY
NY
OH
OR
PA
SC
TX
VA
WA
Water system
Phoenix Municipal
Washington Aqueduct
Miami Beach, City of
Cedar Rapids
Chicago
Detroit
Minneapolis
St. Paul
Bayonne Water Dept.
Syracuse
Yonkers
Columbus
Portland
Philadelphia Water Dept.
Columbia, City of
Galveston
City of Richmond
Tacoma
(ppb)
1993
19
18
27
80
10
21
19
54
18
50
68
15
41
322
40
18
16
32
(ppb)
1992
11
39
4
42
20
15
32
28
25
40
110
16
53
15
114
6
25
17
emissions since the late 1980s. It should also be noted that
absorption
rates.
Since the elimination of lead
U.S. food is atmospheric deposition
solder in U.S.
(Flegal et al.,
90th %ile
(ppb) Recent Monitoring
Recent Period
1
63
8
6
7
12
6
11
18
25
18
1
8
13
6
2
4
12
1/1/2003
7/1/2003
1/1/2001
1/1/2003
1/1/1999
1/1/2002
1/1/2002
1/1/2003
7/1/2001
1/1/2003
1/1/2003
1/1/2002
7/1/2003
1/1/2002
1/1/2002
1/1/2000
1/1/2000
1/1/2001
nutrition and fasting can
-12/31/2003
-12/31/2003
-12/31/2001
-12/31/2003
-12/31/2001
-12/31/2002
-12/31/2002
-12/31/2003
-12/31/2001
- 6/30/2003
- 6/30/2003
-12/31/2002
- 6/30/2006
-12/31/2002
-12/31/2002
-12/31/2002
-12/31/2002
-12/31/2003
affect
canned food, the primary source of lead in
1990). Overall, anthropogenic aerosols
account for an estimated 40% of lead in food, while the bulk of the remainder is derived from
harvesting,
etal., 1997
transporting, processing,
packaging, or
preparing the food
; Dudka and Miller, 1999). Lead contamination
primarily atmospheric in origin. Lead deposits on
ingested (Flegal et al., 1990). Lead concentrations
in poultry
(Flegal et al.,
and livestock
forage or feed or onto soil that is
in food
have been
1990; Juberg
is also
directly
reported to increase by a
May 2006
3-39
DRAFT-DO NOT QUOTE OR CITE
-------
1 factor of 2 to 12 between harvest and consumption (Flegal et al., 1990). A food production
2 facility in Turkey was shown to contaminate pasta with lead (Demirozii and Saldamli, 2002), as
3 indicated by lead concentrations in the semolina being 14.2 to 36.5 ng/g compared with the
4 finished pasta product where concentrations ranged from 107.1 to 147.6 ng/g (Demirozii and
5 Saldamli, 2002). An increase (from an average value <0.5 ng/g to average values between 11.9
6 and 69.8 ng/g) between raw and finished cocoa products has also been observed (Rankin et al.,
7 2005). In this case, contamination seems to occur during shipping and/or processing.
8 Lead concentrations measured in households throughout the Midwest were significantly
9 higher in solid food compared to beverages and tap water (Clayton et al., 1999; Thomas et al.,
10 1999). However, beverages appeared to be the dominant dietary pathway for lead according to
11 the statistical analysis (Clayton et al., 1999), possibly indicating greater bodily absorption of lead
12 from liquid sources (Thomas et al., 1999). Dietary intakes of lead were greater than those
13 calculated for intake from home tap water or inhalation on a |ig/day basis (Thomas et al., 1999).
14 The NHEXAS study in Arizona showed that for adults ingestion was a more important lead
15 exposure route than inhalation (O'Rourke et al., 1999).
16 Lead concentrations in vegetables may be increased by soil amendments such as mine
17 wastes, slag, or fly ash. Historically, mine tailings were often disposed in streambeds, and this
18 poses an exposure risk when stream sediments are used to boost productivity in gardens (Cobb
19 et al., 2000). Slag is sometimes used for constructing agricultural and forestry roads or for
20 landfill. This can be an additional source of lead contamination for nearby crops (Bunzl et al.,
21 2001). Fly ash is applied to land infrequently for alkaline adjustment, as cover for landfills, or to
22 amend agricultural soils. Elevated lead levels in fly ash can subsequently contaminate crops
23 (Brake et al., 2004). Although soil contamination may be important on a local scale, overall
24 atmospheric deposition is a more significant source of food lead than uptake from soil. For
25 example, more than 52% of the total lead present in citrus fruits was removed by washing,
26 indicating that surface deposits make up the bulk of lead contamination in unprocessed fruit
27 (Caselles, 1998).
28 Examples of lead concentrations measured in several foods are shown in Table 3-12.
29 In general, food lead concentrations have decreased as a direct result of the decrease in airborne
30 emissions of lead from automotive gasoline. This has been directly shown through
31 measurements performed on vintage wines (Lobinski, 1995; Medina et al., 2000). The
May 2006 3-40 DRAFT-DO NOT QUOTE OR CITE
-------
Table 3-12. Examples of Lead Concentrations in Food Products
to
o
o
Food
Concentration
Location
Description
Reference
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Barley, grain
Barley, grain
Potato tubers, peeled
Potato tubers, peeled
Lettuce
Spinach
Potatoes
Wheat
Rice
Sweet corn
Field corn
Carrots
Onions
Tomatoes
Peanuts
Soybeans
Applesauce, canned
Fruit cocktail, canned
Spinach, fresh
Peaches, canned
0.4 ppm
2.0 ppm
0.21 ppm
0.89 ppm
0.19 ppm
0.53 ppm
0.03 ppm
0.02 ppm
0.01 ppm
0.01 ppm
0.01 ppm
0.05 ppm
0.04 ppm
0.03 ppm
0.01 ppm
0.04 ppm
8.5 ug/serving
7.1 ug/serving
2.4 ug/serving
6.0 ug/serving
Uncontaminated soil
Zn-Pb smelter contaminated
Uncontaminated soil
Zn-Pb smelter contaminated
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
Edible portion, untreated soil
FDA Total Diet Study
FDA Total Diet Study
FDA Total Diet Study
FDA Total Diet Study
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Dudka and Miller (1999)
Jubergetal. (1997)
Jubergetal. (1997)
Jubergetal. (1997)
Jubergetal. (1997)
-------
Table 3-12 (cont'd). Examples of Lead Concentrations in Food Products
to
o
o
Food
Concentration
Location
Description
Reference
to
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Pears, canned
Strawberries, fresh
Apple juice, bottled
Wine
Vaccinium vitis-idaea
Vaccinium myrtillus
Rubus chamaemoms
Empetmm hermaphroditum
Leccinum auranticcum
Leccinum sacbrum
Russul vesea
Xerocomus subtomentosus
Suillus luteus
Lactarius trivialis
Lactarius torminosus
Lettuce
Lettuce
Lettuce
Carrots
Carrots
4.9 ng/serving
1 . 1 ug/serving
2.6 ug/serving
7.7 ug/serving
0.4-2.3 ppm
0.7-1.6 ppm
0.3-4.7 ppm
0.3-1.5 ppm
0.8-2.3 ppm
1.1-5.2 ppm
1.1-3.4 ppm
1.3-3.1 ppm
2.0-2.3 ppm
1.1-3.1 ppm
0.6-3. 5 ppm
0.65-1. 3 ppm
0.15-0.46 ppm
0.36 ppm
0.07-0.28 ppm
<0.02-0.09 ppm
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Monchegorsk, Russia
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
FDA Total Diet Study
FDA Total Diet Study
FDA Total Diet Study
FDA Total Diet Study
Berry, near Ni-Cu smelter
Berry, near Ni-Cu smelter
Berry, near Ni-Cu smelter
Berry, near Ni-Cu smelter
Mushroom, near Ni-Cu smelter
Mushroom, near Ni-Cu smelter
Mushroom, near Ni-Cu smelter
Mushroom, near Ni-Cu smelter
Mushroom, near Ni-Cu smelter
Mushroom, near Ni-Cu smelter
Mushroom, near Ni-Cu smelter
Close to lead smelter
Far from lead smelter
Background concentration
Close to lead smelter
Far from lead smelter
Jubergetal. (1997)
Jubergetal. (1997)
Jubergetal. (1997)
Jubergetal. (1997)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Barcanetal. (1998)
Moseholm et al. (1992))
Moseholm et al. (1992))
Moseholm et al. (1992))
Moseholm etal. (1992))
Moseholm etal. (1992))
-------
Table 3-12 (cont'd). Examples of Lead Concentrations Food Products
to
o
o
Food
Concentration
Location
Description
Reference
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Carrots
Potatoes
Potatoes
Potatoes
Kale
Kale
Kale
Wine
Breast milk
Infant formula
Baby food
Brassica juncea
Triticum aestivum L.
Basil
Cabbage
Cilantro
Collard greens
Coriander
Ipasote
Lemon balm
0.02-0.03 ppm
<0.02-0.12ppm
O.02-0.06 ppm
O.02 ppm
1.4-9.3 ppm
0.58-2.4 ppm
0.52-0.72 ppm
65ug/L
0.55 ug/kg
1.6 ug/kg
2.9 ug/kg
298.3 ppm
19.2 ppm
<10 ppm
<10 ppm
49 ppm
12 ppm
39 ppm
14 ppm
20 ppm
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
France
Australia
Australia
Australia
Taihe, China
Taihe, China
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Background concentration
Close to lead smelter
Far from lead smelter
Background concentration
Close to lead smelter
Far from lead smelter
Background concentration
Vintage 1990-1995
Indian mustard, near lead smelter
Common wheat, near lead smelter
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Moseholmetal. (1992))
Moseholmetal. (1992))
Moseholmetal. (1992))
Moseholmetal. (1992))
Moseholmetal. (1992))
Moseholmetal. (1992))
Moseholmetal. (1992))
Medina et al. (2000)
Gulsonetal. (200 Ib)
Gulsonetal. (200 Ib)
Gulsonetal. (200Ib)
Cui et al. (2003)
Cui et al. (2003)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
-------
Table 3-12 (cont'd). Examples of Lead Concentrations in Food Products
to
o
o
ON
OJ
i
r\
r\
O
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Food
Mint
Mustard greens
Parsley
Red chard
Rhubarb
Sage
Swiss chard
Thyme
Carrot
Onion
Radish
Tuna, canned
Sardines, canned
Blue mussel, canned
Balsamic vinegar
Wine vinegar
Tea leaves
Cocoa beans
Cocoa, manufactured
Chocolate products
Concentration
<10 - 60 ppm
<10 ppm
<10 ppm
<10 ppm
<10 - 36 ppm
<10 ppm
22-24 ppm
<10 ppm
10 ppm
21 ppm
12-18 ppm
0.1 ppm (max.)
0.2 ppm (max.)
0.3 ppm (max.)
15-307 ug/L
36-50 ug/L
0.59-4.49 ppm
0.5 ng/g
230 ng/g
70 ng/g
Location
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Chicago, IL
Zhejiang Province, China
Nigeria
Nigeria
Nigeria
Description
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Edible portion, urban garden
Commercial tea producing areas
Reference
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Finster et al. (2004)
Lourenco et al. (2004)
Lourenco et al. (2004)
Lourenco et al. (2004)
Ndung'u et al. (2004)
Ndung'u et al. (2004)
Jin et al. (2005)
Rankin et al. (2005)
Rankin et al. (2005)
Rankin et al. (2005)
-------
1 organolead concentration in French, Californian, Australian, and Argentinean wines peaked in
2 1978 (Lobinski, 1995). The maximum concentration was -0.5 |ig/L which was 10 to 100 times
3 higher than lead concentrations in drinking water. Conversely, Medina et al. (2000) observed a
4 peak lead concentration in French wine in the early 1950s. Isotopic analyses indicate that
5 automotive emissions were the dominant source of lead contamination since 1950. It is not clear
6 why French wine concentrations decreased through the late 1970s while automotive emissions
7 were still increasing. It should be noted that concentrations in food can be very low and are
8 frequently below detection limits. For concentrations of lead in non-edible plants, see Chapter 8.
9
10
11 3.5 OTHER ROUTES OF EXPOSURE
12 3.5.1 Lead-Based Paint
13 Lead-based paint was the dominant form of house paint for many decades, and a
14 significant percentage of homes still contain lead-based paint on some surfaces. Lead-based
15 paint poses a potential exposure risk due to inhalation during renovation or demolition projects,
16 or due to ingestion from hand-to-mouth activities and pica, which are common in children.
17 Lead-based paint exposure is one of the most common causes of clinical lead toxicity.
18 In a 1970 study, it was observed that for children with blood lead levels greater than
19 50 |ig/dL, more than 80% were reported to ingest paint chips or broken plaster (Sachs et al.,
20 1970). A later study by McElvaine et al. (1992) showed that children with blood lead levels
21 above 55 |ig/dL were ten times more likely to have paint chips observable on abdominal
22 radiographs than children with blood lead below this value. Shannon and Greaf (1992) noted
23 that the majority of preschool-aged children with blood lead over 25 |ig/dL were reported to put
24 paint chips in their mouth.
25 As lead-based paint degrades, it becomes incorporated into house dust, which was
26 discussed in depth earlier in this chapter. Lead-based paint can pose an inhalation risk during
27 renovation and demolition activities. As described in Section 3.1 of this document, renovation
28 projects often involve abrasive blasting techniques to remove old layers of paint. This forms
29 lead particles that are easily inhaled (Chute and Mostaghim, 1991; Mickelson and Johnston,
30 1995; Jacobs et al., 1998; Mielke et al., 2001). At industrial sites, exposure is limited primarily
31 to workers. However, during residential renovation or abatement projects, residents may be
May 2006 3-45 DRAFT-DO NOT QUOTE OR CITE
-------
1 unduly exposed to very high levels of airborne lead. Blood lead levels were shown to increase in
2 children who lived in houses with a significant (>1.5 mg/cm2 on at least one surface) amount of
3 lead paint that had undergone some sanding, scraping, or other indoor surface refinishing in the
4 preceding six months (Rabinowitz, 1985b).
5 Additionally, exterior lead-based paint can degrade and contaminate nearby soil. Paint
6 and surface soil samples collected in and around Oakland, CA households of children having
7 elevated blood lead levels had nearly identical isotopic ratios as the children's blood (Yaffe
8 et al., 1983). This suggests that weathered, lead-based paint was a major exposure route for
9 these children who played outside near the most highly contaminated areas.
10
11 3.5.2 Calcium Supplements
12 Potentially toxic levels of lead were measured in calcium supplements in studies
13 undertaken in the 1960s through the early 1990s (Scelfo and Flegal, 2000). An analysis of
14 136 different brands of supplements showed that two-thirds of the supplements did not meet the
15 1999 California criteria for acceptable lead levels: 1.5 jig Pb/daily dose of calcium (Scelfo and
16 Flegal, 2000). The lowest concentrations were observed in calcium products that were
17 nonchelated synthesized and/or refined. These corresponded to antacids and infant formulas.
18 Antacids and infant formulas had lead concentrations ranging from below the detection limit to
19 2.9 jig Pb/g calcium (Scelfo and Flegal, 2000). Natural calcium supplements derived from
20 bonemeal, dolomite, or oyster shell were much more likely to be in exceedance of the 1999
21 standard. Lead levels reported elsewhere showed comparable lead levels in supplements and
22 cow milk (Juberg et al., 1997). Whole milk, 2% milk, and calcium supplements had lead
23 concentrations in the range of 1.7 to 6.7 jig Pb/g calcium, 0.8 to 9.0 jig Pb/g calcium, and 3.1 to
24 6.9 jig Pb/g calcium, respectively (Juberg et al., 1997). A clamshell powder commonly known
25 as hai gen fan that is added to tea has shown detectable levels of lead contamination as well
26 (MMWR, 1999).
27
28 3.5.3 Glazes
29 Lead glazes have been commonly used throughout history. Kitchen glassware cannot
30 have a lead solubility in excess of 2.5 to 7 |ig/mL according to a 1980 rule by the U.S. Food and
31 Drug Administration (Flegal et al., 1990). However, lead glazes on imported pottery may
May 2006 3-46 DRAFT-DO NOT QUOTE OR CITE
-------
1 persist. Foods with low pH (acidic ones) are particularly susceptible to solubilizing lead and
2 contaminating food during storage in lead glazed glassware. Lead glazes may be especially
3 problematic when low temperature fluxes and glazes are used. This is more common in
4 traditional charcoal kilns than gas-fired kilns.
5
6 3.5.4 Miniblinds
7 Some imported vinyl miniblinds form lead dust upon disintegration (Juberg et al., 1997).
8 This exposure route was responsible for several cases of lead poisoning in Arizona and North
9 Carolina in the mid 1990s. Lead stabilizers are not used in vinyl miniblinds manufactured in the
10 United States (Juberg et al., 1997).
11
12 3.5.5 Hair Dye
13 The analysis of Mielke et al. (1997) shows that some hair dyes contain lead acetate in the
14 range of 2300 to 6000 jig Pb/g of product. This lead can be easily transferred via hand-to-mouth
15 and hand-to-surf ace activity, and an estimated 3 to 5% of lead acetate can be transferred through
16 the skin. Hair dyes tested in this study contain 3 to 10 times more lead than is allowable for
17 paint (Mielke et al., 1997).
18
19 3.5.6 Other Potential Sources of Lead Exposure
20 Additional consumer products that may pose a risk of lead exposure include lead crystal,
21 pool cue chalk (Miller et al., 1996), cosmetics, and folk remedies, which purposefully contain
22 lead (such as alarcon, alkohl, azarcon, bali goli, coral, gliasard, greta, kohl, KooSo or KooSar
23 pills, liga, pay-loo-ah, rueda, and surma of East Indian, Pakistani, Chinese, and Latin American
24 origins) (CDC, 1999). Unintentional or malicious lead contamination has also been found for the
25 following products: ground paprika, ayurvedic metal-mineral tonics, and Deshi Dewa (a fertility
26 drug) (CDC, 1999; Kakosky et al., 1996).
27
May 2006 3-47 DRAFT-DO NOT QUOTE OR CITE
-------
1 3.6 MEASUREMENT METHODS
2 Methods for measurement of lead in environmental media were discussed in the 1986 Pb
3 AQCD and the reader is referred to that document for details regarding the main methods
4 employed and associated detection limits. Some of the most commonly employed methods are
5 concisely noted below.
6 The concentration of lead in air can be measured through several different methods.
7 Use of filter media and inertial impactors are two of the most common methods, and in both
8 cases particles can be separated by size. An additional method involves mounting a particle
9 separation device in the stack along with gas flow control and metering equipment. The
10 collected particles are then analyzed for mass and lead content (Clarke and Bartle, 1998).
11 Sampling of airborne particles to determine concentration and chemical species can be
12 performed via direct-reading instruments, which include optical counters, electrical counters,
13 resonant oscillation aerosol mass monitors, and beta radiation detectors (Koutrakis and Sioutas,
14 1996). Additionally, particles may be collected in cyclones and denuder systems.
15 Collected particles can be analyzed for lead using x-ray fluorescence analysis (XRF),
16 proton-induced x-ray emission (PIXE), neutron activation analysis (NAA), atomic absorption
17 (AA), or inductively-coupled plasma mass spectrometry (ICP-MS) (Koutrakis and Sioutas,
18 1996).
19 Lead concentrations in soil, dust, food, and other environmental media are determined
20 using similar techniques. Generally, substances undergo acid digestion in an HC1 or HNOs
21 solution before analysis via XRF, PIXE, NAA, AA, or ICP-MS. Special care should be taken in
22 all cases to avoid external contamination of samples, especially when measuring very low
23 concentrations of lead.
24 For detailed discussions of methods for determining lead speciation and isotopic ratios,
25 see Chapter 8 of this document. Also, see Chapter 4 for information related to measurement of
26 lead in biological tissues.
27
28
May 2006 3-48 DRAFT-DO NOT QUOTE OR CITE
-------
1 3.7 SUMMARY
2 Lead concentrations in environmental media have been presented throughout this chapter.
3 Concentrations of lead in all environmental media are present in detectable quantities. However,
4 the bioavailability and bioaccessibility of this lead may vary significantly. See Chapter 8 for a
5 discussion of bioavailable and bioaccessible forms of lead.
6 The highest air, soil, and road dust concentrations are found near major lead sources, such
7 as smelters, mines, and heavily trafficked roadways. Airborne concentrations have declined
8 dramatically with the phase out of leaded gasoline. Soil concentrations have remained relatively
9 constant.
10 Drinking water is susceptible to lead contamination primarily through leaching from
11 pipes, solder, and faucets. Water that has been stagnant in pipes, has been disinfected with
12 chloramines, has a low pH, or has a low alkalinity is particularly high risk for leaching lead.
13 Lead-contaminated food is a major exposure route. Deposition of airborne lead and house
14 dust are the major sources of lead in food. Significant quantities of lead are ingested by certain
15 populations every day.
16 Lead-based paint is still prevalent in older homes. This can be a major exposure route if
17 paint has deteriorated or undergone careless renovation.
18 Other sources of lead exposure vary in their prevalence and potential risk. These include
19 calcium supplements, lead-based glazes, certain types of miniblinds, hair dye, and other
20 consumer products.
May 2006 3-49 DRAFT-DO NOT QUOTE OR CITE
-------
1 REFERENCES
2 Adgate, J. L.; Willis, R. D.; Buckley, T. I; Chow, J. C; Watson, J. G.; Rhoads, G. G.; Lioy, P. J. (1998) Chemical
3 mass balance source apportionment of lead in house dust. Environ. Sci. Technol. 32: 108-114.
4 Al-Chalabi, A. S.; Hawker, D. (1997) Response of vehicular lead to the presence of street dust in the atmospheric
5 environment of major roads. Sci. Total Environ. 206: 195-202.
6 Amitai, Y.; Brown, M. J.; Graef, J. W.; Cosgrove, E. (1991) Residential deleading: effects on the blood lead levels
7 of lead-poisoned children. Pediatrics 88: 893-897.
8 Annegarn, H. J.; Zucchiatti, A.; Sellschop, J. P. F.; Kusko, B. (1988) Composition and size of dust in a gold mine
9 atmosphere. J. Mine Vent. Soc. S. Afr. 41: 1-10.
10 Arimoto, R.; Schloesslin, C.; Davis, D.; Hogan, A.; Grube, P.; Fitzgerald, W.; Lamborg, C. (2004) Lead and
11 mercury in aerosol particles collected over the South Pole during ISCAT-2000. Atmos. Environ.
12 38: 5485-5491.
13 Aschengrau, A.; Beiser, A.; Bellinger, D.; Copenhafer, D.; Weitzman, M. (1994) The impact of soil lead abatement
14 on urban children's blood lead levels: phase II results from the Boston lead-in-soil demonstration project.
15 Environ. Res. 67: 125-148.
16 Aschengrau, A.; Beiser, A.; Bellinger, D.; Copenhafer, D.; Weitzman, M. (1997) Residential lead-based-paint
17 hazard remediation and soil lead abatement: their impact among children with mildly elevated blood lead
18 levels. Am. J. Public Health 87: 1698-1702.
19 Badawy, S. H.; Helal, M. I. D.; Chaudri, A. M.; Lawlor, K.; McGrath, S. P. (2002) Soil solid-phase controls lead
20 activity in soil solution. J. Environ. Qual. 31: 162-167.
21 Barcan, V. S.; Kovnatsky, E. F.; Smetannikova, M. S. (1998) Absorption of heavy metals in wild berries and edible
22 mushrooms in an area affected by smelter emissions. Water Air Soil Pollut. 103: 173-195.
23 Batonneau, Y.; Bremard, C.; Gengembre, L.; Laureyns, J.; Le Maguer, A.; Le Maguer, D.; Perdrix, E.; Sobanska, S.
24 (2004) Speciationof PM10 sources of airborne nonferrous metals within the 3-km zone of lead/zinc smelters.
25 Environ. Sci. Technol. 38: 5281-5289.
26 Birden, H. H., Jr.; Calabrese, E. J.; Stoddard, A. (1985) Lead dissolution from soldered joints. J. Am. Water Works
27 Assoc. 77: 66-70.
28 Brake, S. S.; Jensen, R. R.; Mattox, J. M. (2004) Effects of coal fly ash amended soils on trace element uptake in
29 plants. Environ. Geol. 45: 680-689.
30 Brewer, R.; Belzer, W. (2001) Assessment of metal concentrations in atmospheric particles fromBurnaby Lake,
31 British Columbia, Canada. Atmos. Environ. 35: 5223-5233.
32 Bunzl, K.; Trautmannsheimer, M.; Schramel, P.; Reifenhauser, W. (2001) Availability of arsenic, copper, lead,
33 thallium, and zinc to various vegetables grown in slag-contaminated soils. J. Environ. Qual. 30: 934-939.
34 Caravanos, J.; Weiss, A. L.; Jaeger, R. J. (2006) An exterior and interior leaded dust deposition survey in New York
35 City: results of a 2-year study. Environ. Res. 100: 159-164.
36 Caselles, J. (1998) Levels of lead and other metals in citrus alongside a motor road. Water Air Soil Pollut.
37 105:593-602.
3 8 Centers for Disease Control and Prevention (1999) Adult lead poisoning from an Asian remedy for menstrual
39 cramps—Connecticut, 1997. Morb. Mortal. Wkly Rep. (MMWR) 48: 27-29.
40 Chadha, A.; McKelvey, L. D.; Mangis, J. K. (1998) Targeting lead in the multimedia environment in the continental
41 United States. J. Air Waste Manage. Assoc. 48: 3-15.
42 Chan, L. Y.; Kwok, W. S.; Chan, C. Y. (2000) Human exposure to respirable suspended paniculate and airborne
43 lead in different roadside microenvironments. Chemosphere 41: 93-99.
44 Chatterjee, A.; Banerjee, R. N. (1999) Determination of lead and other metals in a residential area of greater
45 Calcutta. Sci. Total Environ. 227: 175-185.
46 Chiaradia, M.; Cupelin, F. (2000) Behaviour of airborne lead and temporal variations of its source effects in Geneva
47 (Switzerland): comparison of anthropogenic versus natural processes. Atmos. Environ. 34: 959-971.
48 Chiaradia, M.; Chenhall, B. E.; Depers, A. M.; Gulson, B. L.; Jones, B. G. (1997) Identification of historical lead
49 sources in roof dusts and recent lake sediments from an industrialized area: indications from lead isotopes.
50 Sci. Total Environ. 205: 107-128.
51 Chirenje, T.; Ma, L. Q.; Reeves, M.; Szulczewski, M. (2004) Lead distribution in near-surface soils of two Florida
52 cities: Gainesville and Miami. Geoderma 119: 113-120.
53 Chow, J. C.; Watson, J. G.; Ashbaugh, L. L.; Magliano, K. L. (2003) Similarities and differences inPM10 chemical
54 source profiles for geological dust from the San Joaquin Valley, California. Atmos. Environ. 37: 1317-1340.
May 2006 3-50 DRAFT-DO NOT QUOTE OR CITE
-------
1 Chute, D. O.; Mostaghim, N. L. (1991) Protecting workers from lead. A review of regulations and practices. J. Prot.
2 Coat. Linings 8(4): 36-43.
3 Clark, S.; Bornschein, R.; Succop, P.; Roda, S.; Peace, B. (1991) Urban lead exposures of children in Cincinnati,
4 Ohio. Chem. Speciation Bioavailability 3(3-4): 163-171.
5 Clark, S.; Grote, J.; Wilson, J.; Succop, P.; Chen, M; Galke, W.; McLaine, P. (2004) Occurrence and determinants
6 of increases in blood lead levels in children shortly after lead hazard control activities. Environ. Res.
7 96: 196-205.
8 Clarke, A. G.; Bartle, G. (1998) Paniculate emissions by extractive sampling. In: Clark, A. G., ed. Industrial air
9 pollution monitoring. New York, NY: Chapman & Hall; pp. 33-60. (Environmental management series: v.
10 8).
11 Clayton, C. A.; Pellizzari, E. D.; Whitmore, R. W.; Perritt, R. L., Quackenboss, J. J. (1999) National human
12 exposure assessment survey (NHEXAS): distributions and associations of lead, arsenic, and volatile organic
13 compounds in EPA Region 5. J. Exposure Anal. Environ. Epidemiol. 9: 381-392.
14 Clement, M.; Seux, R.; Rabarot, S. (2000) A practical model for estimating total lead intake from drinking water.
15 Water Res. 34: 1533-1542.
16 Cobb, G. P.; Sands, K.; Waters, M.; Wixson, E.G.; Dorward-King, E. (2000) Accumulation of heavy metals by
17 vegetables grown in mine wastes. Environ. Toxicol. Chem. 19: 600-607.
18 Cook, M.; Chappell, W. R.; Hoffman, R. E.; Mangione, E. J. (1993) Assessment of blood lead levels in children
19 living in a historic mining and smelting community. Am. J. Epidemiol. 137: 447-455.
20 Cotter-Howells, J.; Thornton, I. (1991) Sources and pathways of environmental lead to children in a Derbyshire
21 mining village. Environ. Geochem. Health 13: 127-135.
22 Cui, Y.; Wang, Q.; Dong, Y.; Li, H. (2003) Elemental sulfur effects on Pb and Zn uptake by Indian mustard and
23 winter wheat. J. Environ. Sci. (China) 15: 836-841.
24 Daniels, A. E.; Kominsky, J. R.; Clark, P. J. (2001) Evaluation of two lead-based paint removal and waste
25 stabilization technology combinations on typical exterior surfaces. J. Hazard. Mater. 87: 117-126.
26 Davidson, C. I.; Goold, W. D.; Mathison, T. P.; Wiersma, G. B.; Brown, K. W.; Reilly, M. T. (1985) Airborne trace
27 elements in Great Smokey Mountains, Olympic and Glacier National Parks. Environ. Sci. Technol.
28 19:27-35.
29 Davies, B. E.; Elwood, P. C.; Gallacher, J.; Ginnever, R. C. (1985) The relationships between heavy metals in
30 garden soils and house dusts in an old lead mining area of North Wales, Great Britain. Environ. Pollut. Ser.
31 B 9: 255-266.
32 Davis, J. J.; Gulson, B. L. (2005) Ceiling (attic) dust: a "museum" of contamination and potential hazard. Environ
33 Res. 99: 177-194.
34 De Miguel, E.; Llamas, J. F.; Chacon, E.; Berg, T.; Larssen, S.; Royset, O.; Vadset, M. (1997) Origin and patterns of
35 distribution of trace elements in street dust: unleaded petrol and urban lead. Atmos. Environ. 31: 2733-2740.
36 Del Delumyea, R.; Kalivretenos, A. (1987) Elemental carbon and lead content of fine particles from American and
37 French cities of comparable size and industry, 1985. Atmos. Environ. 21: 1643-1647.
3 8 Demirozu, B.; Saldamli, 1. (2002) Metallic contamination problem in a pasta production plant. Turk. J. Eng. Env.
39 Sci. 26: 361-365.
40 Denaix, L.; Semlali, R. M.; Douay, F. (2001) Dissolved and colloidal transport of Cd, Pb, and Zn in a silt loam soil
41 affected by atmospheric industrial deposition. Environ. Pollut. 114: 29-38.
42 Dudka, S.; Adriano, D. C. (1997) Environmental impacts of metal ore mining and processing: a review. J. Environ.
43 Qual. 26: 590-602.
44 Dudka, S.; Miller, W. P. (1999) Accumulation of potentially toxic elements in plants and their transfer to human
45 food chain. J. Environ. Sci. Health B 34(4): 681-708.
46 Duggan, M. J.; Inskip, M. J. (1985) Childhood exposure to lead in surface dust and soil: a community health
47 problem. Public Health Rev. 13: 1-54.
48 Eckel, W. P.; Rabinowitz, M. B.; Foster, G. D. (2001) Discovering unrecognized lead smelting sites by historical
49 methods. Am. J. Public Health 91: 625-627.
50 Edwards, M.; Dudi, A. (2004) Role of chlorine and chloramine in corrosion of lead-bearing plumbing materials.
51 J. Am. Water Works Assoc. 96: 69-81.
52 Edwards, M.; McNeill, L. S. (2002) Effect of phosphate inhibitors on lead release from pipes. J. Am. Water Works
53 Assoc. 94: 79-90.
54 Eldred, R. A.; Cahill, T. A. (1994) Trends in elemental concentrations of fine particles at remote sites in the
55 United States of America. Atmos. Environ. 28: 1009-1019.
May 2006 3-51 DRAFT-DO NOT QUOTE OR CITE
-------
1 Erel, Y.; Veron, A.; Halicz, L. (1997) Tracing the transport of anthropogenic lead in the atmosphere and in soils
2 using isotopic ratios. Geochim. Cosmochim. Acta61: 4495-4505.
3 Erel, Y.; Axelrod, T.; Veron, A.; Mahrer, Y.; Katsafados, P.; Dayan, U. (2002) Transboundary atmospheric lead
4 pollution. Environ. Sci. Technol. 36: 3230-3233.
5 Farago, M. E.; Thornton, L; White, N. D.; Tell, L; Martensson, M.-B. (1999) Environmental impacts of a secondary
6 lead smelter in Landskrona, southern Sweden. Environ. Geochem. Health 21: 67-82.
7 Feng, Y.; Barratt, R. S. (1994) Lead and cadmium composition in indoor dust. Sci. Total Environ. 152: 261-267.
8 Fenger, J. (1999) Urban air quality. Atmos. Environ. 33: 4877-4900.
9 Ferro, A. R.; Kopperud, R. J.; Hildemann, L. M. (2004) Source strengths for indoor human activities that resuspend
10 paniculate matter. Environ. Sci. Technol. 38: 1759-1764.
11 Finkelstein, M. E.; Gwiazda, R. H.; Smith, D. R. (2003) Lead poisoning of seabirds: environmental risks from
12 leaded paint at a decommissioned military base. Environ. Sci. Technol. 37: 3256-3260.
13 Finster, M. E., Gray, K. A.; Binns, H. J. (2004) Lead levels of edibles grown in contaminated residential soils:
14 a field survey. Sci. Total Environ. 320: 245-257.
15 Flegal, A. R.; Smith, D. R.; Elias, R. W. (1990) Lead contamination in food. In: Nriagu, J. O.; Simmons, M. S., eds.
16 Food contamination from environmental sources. New York, NY: John Wiley & Sons, Inc.; pp. 85-120.
17 Franssens, M.; Flament, P.; Deboudt, K.; Weis, D.; Perdrix, E. (2004) Evidencing lead deposition at the urban scale
18 using "short-lived" isotopic signatures of the source term (Pb-Zn refinery). Atmos. Environ. 38: 5157-5168.
19 Freitas, H.; Prasad, M. N. V.; Pratas, J. (2004) Plant community tolerant to trace elements growing on the degraded
20 soils of Sao Domingos mine in the south east of Portugal: environmental implications. Environ. Int.
21 30:65-72.
22 Frey, M. M. (1989) The AWWA lead information survey: a final report. J. Am. Water Works Assoc. 81: 64-68.
23 Frey, H. C.; Small, M. J. (2003) Integrated environmental assessment, Part I: estimating emissions. J. Ind. Ecol.
24 7:9-11.
25 Gallacher, J. E. J.; Elwood, P. C.; Phillips, K. M.; Davies, B. E.; Jones, D. T. (1984) Relation between pica and
26 blood lead in areas of differing lead exposure. Arch. Dis. Child. 59: 40-44.
27 Galli, B. C.; Nyffeler, U. P. (1987) Height dependence of heavy metal size distribution and concentration on
28 aerosols. J. Aerosol Sci. 18: 813-816.
29 Gardels, M. C.; Sorg, T. J. (1989) A laboratory study of the leaching of lead from water faucets. J.- Am. Water
30 Works Assoc. 81: 101-113.
31 Garg, B. D.; Cadle, S. H.; Mulawa, P. A.; Groblicki, P. J. (2000) Brake wear paniculate matter emissions. Environ.
32 Sci. Technol. 34: 4463-4469.
33 Gillies, J. A.; O'Connor, C. M.; Mamane, Y.; Gertler, A. W. (1999) Chemical profiles for characterizing dust
34 sources in an urban area, western Nevada, USA. In: Livingstone, I., ed. Aeolian geomorphology: papers
3 5 from the 4th international conference on aeolian research; 1998; Oxford, United Kingdom. Z. Geomorphol.
36 116(suppl.): 19-44.
37 Godin, P. M.; Feinberg, M. H.; Ducauze, C. J. (1985) Modelling of soil contamination by airborne lead and
3 8 cadmium around several emission sources. Environ. Pollut. Ser. B 10: 97-114.
39 Gulson, B. L.; Law, A. J.; Korsch, M. J.; Mizon, K. J. (1994) Effect of plumbing systems on lead content of drinking
40 water and contribution to lead body burden. Sci. Total Environ. 144: 279-284.
41 Gulson, B. L.; James, M.; Giblin, A. M.; Sheehan, A.; Mitchell, P. (1997) Maintenance of elevated lead levels in
42 drinking water from occasional use and potential impact on blood leads in children. Sci. Total Environ.
43 205:271-275.
44 Gulson, B. L.; Mizon, K. J.; Palmer, J. M.; Patison, N.; Law, A. J.; Korsch, M. J.; Mahaffey, K. R.; Donnelly, J. B.
45 (200 la) Longitudinal study of daily intake and excretion of lead in newly born infants. Environ. Res.
46 85:232-245.
47 Gulson, B. L.; Mizon, K. J.; Korsch, M. J.; Mahaffey, K. R.; Taylor, A. J. (200Ib) Dietary intakes of selected
48 elements from longitudinal 6-day duplicate diets for pregnant and nonpregnant subjects and elemental
49 concentrations of breast milk and infant formula. Environ. Res. 87: 160-174.
50 Guo, Q. (1997) Increases of lead and chromium in drinking water from using cement-mortar-lined pipes: initial
51 modeling and assessment. J. Hazard. Mater. 56: 181-213.
52 Gwiazda, R.; Campbell, C.; Smith, D. (2005) A noninvasive isotopic approach to estimate the bone lead
53 contribution to blood in children: implications for assessing the efficacy of lead abatement. Environ. Health
54 Perspect. 113: 104-110.
55 Harris, A. R.; Davidson, C. I. (2005) The role of resuspended soil in lead flows in the California South Coast Air
56 Basin. Environ. Sci. Technol. 39: 7410-7415.
May 2006 3-52 DRAFT-DO NOT QUOTE OR CITE
-------
1 Harrison, R. M; Williams, C. R.; O'Neill, I. K. (1981) Characterization of airborne heavy-metals within a primary
2 zinc-lead smelting works. Environ. Sci. Technol. 15: 1197-1204.
3 Harrison, R. M.; Tilling, R.; Callen Romero, M. S.; Harrad, S.; Jarvis, K. (2003) A study of trace metals and
4 polycyclic aromatic hydrocarbons in the roadside environment. Atmos. Environ. 37: 2391-2402.
5 Heidam, N. Z. (1986) Trace metals in the Arctic aerosol. In: Nriagu, J. O.; Davidson, C. I., eds. Toxic metals in the
6 atmosphere. New York, NY: John Wiley & Sons; pp. 267-293. (Advances in environmental science and
7 technology: v. 17).
8 Hertzman, C.; Ward, H.; Ames, N.; Kelly, S.; Yates, C. (1991) Childhood lead exposure in trail revisited. Can. J.
9 Public Health 82: 385-391.
10 Hilts, S. R. (2003) Effect of smelter emission reductions on children's blood lead levels. Sci. Total Environ.
11 303:51-58.
12 Hlavay, J.; Polyak, K.; Weisz, M. (2001) Monitoring of the natural environment by chemical speciation of elements
13 in aerosol and sediment samples. J. Environ. Monit. 3: 74-80.
14 Ho, K. F.; Lee, S. C.; Chow, J. C.; Watson, J. G. (2003) Characterization of PM10 and PM25 source profiles for
15 fugitive dust in Hong Kong. Atmos. Environ. 37: 1023-1032.
16 Huang, S. L.; Arimoto, R.; Rahn, K. A. (1996) Changes in atmospheric lead and other pollution elements at
17 Bermuda. J. Geophys. Res. [Atmos.] 101: 21,033-21,040.
18 Hui, C. A. (2002) Concentrations of chromium, manganese, and lead in air and in avian eggs. Environ. Pollut.
19 120:201-206.
20 Hunt, A.; Johnson, D. L.; Thornton, L; Watt, J. M. (1993) Apportioning the sources of lead in house dusts in the
21 London borough of Richmond, England. Sci. Total Environ. 138: 183-206.
22 Ilacqua, V.; Freeman, N. C. J.; Fagliano, J.; Lioy, P. J. (2003) The historical record of air pollution as defined by
23 attic dust. Atmos. Environ. 37: 2379-2389.
24 Isaac, R. A.; Gil, L.; Cooperman, A. N.; Hulme, K.; Eddy, B.; Ruiz, M.; Jacobson, K.; Larson, C.; Pancorbo, O. C.
25 (1997) Corrosion in drinking water distribution systems: a major contributor of copper and lead to
26 wastewaters and effluents. Environ. Sci. Technol. 31: 3198-3203.
27 Jacobs, D. E. (1998) Occupational exposures to lead-based paint in structural steel demolition and residential
28 renovation work. Int. J. Environ. Pollut. 9: 126-139.
29 Jacobs, D. E.; Clickner, R. P.; Zhou, J. Y.; Viet, S. M.; Marker, D. A.; Rogers, J. W.; Zeldin, D. C.; Broene, P.;
30 Friedman, W. (2002) The prevalence of lead-based paint hazards in U.S. housing. Environ. Health Perspect.
31 110: A599-A606.
32 Jensen, H. (1992) Lead in household dust. Sci. Total. Environ. 114: 1-6.
33 Jin, C. W.; Zhang, S. J.; He, Y. F.; Zhou, G. D.; Zhou, Z. X. (2005) Lead contamination in tea garden soils and
34 factors affecting its bioavailability. Chemosphere 59: 1151-1159.
35 Jones, N. C.; Thornton, C. A.; Mark, D.; Harrison, R. M. (2000) Indoor/outdoor relationships of paniculate matter in
36 domestic homes with roadside, urban and rural locations. Atmos. Environ. 34: 2603-2612.
37 Juberg, D. R.; Kleiman, C. F.; Kwon, S. C. (1997) Position paper of the American Council on Science and Health:
38 lead and human health. Ecotoxicol. Environ. Saf. 38: 162-180.
39 Kakosy, T.; Hudak, A.; Naray, M. (1996) Lead intoxication epidemic caused by ingestion of contaminated ground
40 paprika. J. Toxicol. Clin. Toxicol. 34: 507-511.
41 Kaste, J.; Friedland, A.; Stirrup, S. (2003) Using stable and radioactive isotopes to trace atmospherically deposited
42 Pb in montane forest soils. Environ. Sci. Technol. 37: 3560-3567.
43 Kim, E.; Hopke, P. K.; Pinto, J. P.; Wilson, W. E. (2005) Spatial variability of fine particle mass, components, and
44 source contributions during the regional air pollution study in St. Louis. Environ. Sci. Technol.
45 39:4172-4179.
46 Kimbrough, D. E.; Suffet, I. H. (1995) Off-site forensic determination of airborne elemental emissions by multi-
47 media analysis: a case study at two secondary lead smelters. Environ. Sci. Technol. 29: 2217-2221.
48 Kimbrough, R. D.; LeVois, M.; Webb, D. R. (1994) Management of children with slightly elevated blood lead
49 levels. Pediatrics 93: 188-191.
50 Komarnicki, G. J. K. (2005) Lead and Cadmium in indoor air and the urban environment. Environ. Pollut.
51 136:47-61.
52 Koutrakis, P.; Sioutas, C. (1996) Physico-chemical properties and measurement of ambient particles. In: Wilson, R.;
53 Spengler, J. D., eds. Particles in our air: concentrations and health effects. Cambridge, MA: Harvard
54 University Press; pp 15-39.
55 Kuang, C.; Min, H.; Neumann, T.; Norra, S.; Stiiben, D. (2004) Chemical composition of urban street sediments and
56 its sources. J. China Univ. Geosci. 15: 75-83.
May 2006 3-53 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kurkjian, R.; Dunlap, C.; Flegal, A. R. (2002) Lead isotope tracking of atmospheric response to post-industrial
2 conditions in Yerevan, Armenia. Atmos. Environ. 36: 1421-1429.
3 Lanphear, B. P.; Emond, M; Jacobs, D. E.; Weitzman, M; Tanner, M; Winter, N. L.; Yakir, B.; Eberly, S. (1995)
4 A side-by-side comparison of dust collection methods for sampling lead-contaminated house dust. Environ.
5 Res. 68: 114-123.
6 Lanphear, B. P.; Weitzman, M.; Eberly, S. (1996) Racial differences in urban children's environmental exposures to
7 lead. Am. J. Public Health 86: 1460-1463.
8 Lanphear, B. P.; Matte, T. D.; Rogers, J.; Clickner, R. P.; Dietz, B.; Bornschein, R. L.; Succop, P.; Mahaffey, K. R.;
9 Dixon, S.; Galke, W.; Rabinowitz, M.; Farfel, M.; Rohde, C.; Schwartz, J.; Ashley, P.; Jacobs, D. E. (1998)
10 The contribution of lead-contaminated house dust and residential soil to children's blood lead levels.
11 Environ. Res. 79:51-68.
12 Lanphear, B. P.; Hornung, R.; Ho, M.; Howard, C. R.; Eberly, S.; Knauf, K. (2002) Environmental lead exposure
13 during early childhood. J. Pediatr. 140: 40-47.
14 Lanphear, B. P.; Succop, P.; Roda, S.; Henningsen, G. (2003) The effect of soil abatement on blood lead levels in
15 children living near a former smelting and milling operation. Public Health Rep. 118: 83-90.
16 Lanphear, B. P.; Hornung, R.; Ho, M. (2005) Screening housing to prevent lead toxicity in children. Public Health
17 Rep. 120:305-310.
18 Laxen, D. P. H.; Raab, G. M.; Fulton, M. (1987) Children's blood lead and exposure to lead in household dust and
19 water - a basis for an environmental standard for lead in dust. Sci. Total Environ. 66: 235-244.
20 Lee, R. G.; Becker, W. C.; Collins, D. W. (1989) Lead at the tap: sources and control. J. Am. Water Works Assoc.
21 81:52-62.
22 Li, X.; Thornton, I. (1993) Multi-element contamination of soils and plants in old mining areas, UK. Appl.
23 Geochem. Suppl. 2: 51-56.
24 Liu, Z. P. (2003) Lead poisoning combined with cadmium in sheep and horses in the vicinity of non-ferrous metal
25 smelters. Sci. Total Environ. 309: 117-126.
26 Lobinski, R. (1995) Organolead compounds in archives of environmental pollution. Analyst (Cambridge, U. K.)
27 120:615-621.
28 Lourengo, H. M.; Afonso, C.; Martins, M. F.; Lino, A. R.; Nunes, M L. (2004) Levels of toxic metals in canned
29 seafood. J. Aquat. Food Prod. Technol. 13: 117-125.
30 Lynch, P. A.; Malcoe, L. H.; Skaggs, V. J.; Kegler, M. C. (2000) The relationship between residential lead
31 exposures and elevated blood lead levels in a rural mining community. J. Environ. Health 63: 9-15.
32 Lytle, D. A.; Schock, M. R. (2000) Impact of stagnation time on metal dissolution from plumbing materials in
33 drinking water. Aqua 49: 243-257.
34 Lytle, D. A.; Schock, M. R.; Dues, N. R.; Clark, P. J. (1993) Investigating the preferential dissolution of lead from
35 solder particulates. J. Am. Waterworks Assoc. 85: 104-110.
36 MacKenzie, A. B.; Pulford, I. D. (2002) Investigation of contaminant metal dispersal from a disused mine site at
37 Tyndrum, Scotland, using concentration gradients and stable Pb isotope ratios. Appl. Geochem.
38 17: 1093-1103.
39 Maenhaut, W.; Zoller, W. H.; Duce, R. A.; Hoffman, G. L. (1979) Concentration and size distribution of paniculate
40 trace elements in the south polar atmosphere. J. Geophys. Res. 84: 2421-2431.
41 Malcoe, L. H.; Lynch, R. A.; Kegler, M. C.; Skaggs, V. J. (2002) Lead sources, behaviors, and socioeconomic
42 factors in relation to blood lead of Native American and white children: a community-based assessment of a
43 former mining area. Environ. Health Perspect. Suppl. 110(2): 221-231.
44 Malm, W. C.; Sisler, J. F. (2000) Spatial patterns of major aerosol species and selected heavy metals in the United
45 States. Fuel Process. Technol. 65: 473-501.
46 Mannino, D. M.; Albalak, R.; Grosse, S.; Repace, J. (2003) Second-hand smoke exposure and blood lead levels in
47 U.S. children. Epidemiology 14: 719-727.
48 Manton, W. I.; Angle, C. R.; Krogstrand, K. L. S. (2005) Origin of lead in the United States diet. Environ. Sci.
49 Technol.: 10.1021/es051145e.
50 Markus, J.: McBratney, A. B. (2001) A review of the contamination of soil with lead: II. Spatial distribution and risk
51 assessment of soil lead. Environ. Int. 27: 399-411.
52 Maskall, J. E.; Thornton, I. (1998) Chemical partitioning of heavy metals in soils, clays and rocks at historical lead
53 smelting sites. Water Air Soil Pollut. 108: 391-409.
54 Mattigod, S. V.; Page, A. L.; Thornton, I. (1986) Identification of some trace metal minerals in a mine-waste
55 contaminated soil. Soil Sci. Soc. Am. J. 50: 254-258.
May 2006 3-54 DRAFT-DO NOT QUOTE OR CITE
-------
1 Mbila, M. O.; Thompson, M. L. (2004) Plant-available zinc and lead in mine spoils and soils at the Mines of Spain,
2 Iowa. J. Environ. Qual. 33: 553-558.
3 McDonald, J. D.; Zielinska, B.; Sagebiel, J. C.; McDaniel, M. R.; Mousset-Jones, P. (2003) Source apportionment
4 of airborne fine paniculate matter in an underground mine. J. Air Waste Manage. Assoc. 53: 386-395.
5 McElvaine, M. D.; DeUngria, E. G.; Matte, T. D.; Copley, C. G.; Binder, S. (1992) Prevalence of radiographic
6 evidence of paint chip ingestion among children with moderate to severe lead poisoning, St. Louis,
7 Missouri, 1989 through 1990. Pediatrics 89(suppl. 4): 740-742.
8 McNeill, L. S.; Edwards, M. (2004) Importance of Pb and Cu paniculate species for corrosion control. J. Environ.
9 Eng. 130: 136-144.
10 Medina, B.; Augagneur, S.; Barbaste, M.; Grouset, F. E.; Buat-Menard, P. (2000) Influence of atmospheric pollution
11 on the lead content of wines. Food Addit. Contam. 17: 435-445.
12 Mickelson, R. L.; Johnston, O. E. (1995) Lead exposure during removal of lead-based paint using vacuum blasting.
13 J. Prot. Coat. Linings 12: 78-84.
14 Mielke, H. W. (1991) Lead in residential soils: background and preliminary results of New Orleans. In: Adriano,
15 D. C., ed. Metals in soils, waters, plants and animals: proceedings of an international conference; April
16 1990; Orlando, FL. Water Air Soil Pollut. 57-58: 111-119.
17 Mielke, H. W. (1993) Lead dust contaminated USA communities: comparison of Louisiana and Minnesota. Appl.
18 Geochem. Suppl. 2: 257-261.
19 Mielke, H. W.; Taylor, M. D.; Gonzales, C. R.; Smith, M. K.; Daniels, P. V.; Buckner, A. V. (1997) Lead-based hair
20 coloring products: too hazardous for household use. J. Am. Pharm. Assoc. 37: 85-89.
21 Mielke, H. W.; Powell, E. T.; Shah, A.; Gonzales, C. R.; Mielke, P. W. (2001) Multiple metal contamination from
22 house paints: consequences of power sanding and paint scraping in New Orleans. Environ. Health Perspect.
23 109:973-978.
24 Miller, E. K.; Fnedland, A. J. (1994) Lead migration in forest soils: response to changing atmosphenc inputs.
25 Environ. Sci. Technol. 28: 662-669.
26 Miller, M. B.; Curry, S. C.; Kunkel, D. B.; Arreola, P.; Arvizu, E.; Schaller, K.; Salmen, D. (1996) Pool cue chalk:
27 a source of environmental lead. Pediatrics 97: 916-917.
28 Moir, C. M.; Freedman, B.; McCurdy, R. (1996) Metal mobilization from water-distnbution systems of buildings
29 serviced by lead-pipe mains. Can. Water Resour. J. 21: 45-52.
30 Moseholm, L.; Larsen, E. H.; Andersen, B.; Nielsen, M. M. (1992) Atmospheric deposition of trace elements around
31 point sources and human health risk assessment. I. Impact zones near a source of lead emissions. Sci. Total
32 Environ. 126: 243-262.
33 Murgueytio, A. M.; Evans, R. G.; Sterling, D. A.; Clardy, S. A.; Shadel, B. N.; Clements, B. W. (1998a)
34 Relationship between lead mining and blood lead levels in children. Arch. Environ. Health 53: 414-423.
35 Murgueytio, A. M.; Evans, R. G.; Daryl, R. (1998b) Relationship between soil and dust lead in a lead mining area
36 and blood lead levels. J. Exposure Anal. Environ. Epidemiol. 8: 173-186.
37 Murozumi, M.; Chow, T. J.; Patterson, C. (1969) Chemical concentrations of pollutant lead aerosols, terrestrial dusts
38 and sea salts in Greenland and Antarctic snow strata. Geochim. Cosmochim. Acta 33: 1247-1294.
3 9 Ndung'u, K.; Hibdon, S.; Flegal, A. R. (2004) Determination of lead in vinegar by ICP-MS and GFAAS: evaluation
40 of different sample preparation procedures. Talanta 64: 258-263.
41 Nriagu, J. O.; Kim, M.-J. (2000) Emissions of lead and zinc from candles with metal-core wicks. Sci. Total Environ.
42 250:37-41.
43 Nriagu, J. O.; Pacyna, J. M. (1988) Quantitative assessment of worldwide contamination of air, water and soils by
44 trace metals. Nature (London) 333: 134-139.
45 Oliver, D. P.; McLaughlin, M. J.; Naidu, R.; Smith, L. H.; Maynard, E. J.; Calder, I. C. (1999) Measuring Pb
46 bioavailability from household dusts using an in vitro model. Environ. Sci. Technol. 33: 4434-4439.
47 O'Rourke, M. K.; VanDe Water, P. K.; Jin, S.; Rogan, S. P.; Weiss, A. D.; Gordon, S. M.; Moschandreas, D. M.;
48 Lebowitz, M. D. (1999) Evaluations of primary metals fromNHEXAS Arizona: distributions and
49 preliminary exposures. J. Exp. Anal. Environ. Epidemiol. 9: 435-444.
50 Paces, T. (1998) Critical loads of trace metals in soils: a method of calculation. Water Air Soil Pollut. 105: 451-458.
51 Palacios, H.; Iribarren, I.; Olalla, M. J.; Cala, V. (2002) Lead poisoning of horses in the vicinity of a battery
52 recycling plant. Sci. Total Environ. 290: 81-89.
53 Pichtel, J.; Kuroiwa, K.; Sawyer, H. T. (2000) Distribution of Pb, Cd and Ba in soils and plants of two contaminated
54 sites. Environ. Pollut. 110: 171-178.
May 2006 3-55 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pierson, W. R.; Brachaczek, W. W. (1976) Paniculate matter associated with vehicles on the road. Presented at:
2 SAE automotive engineering congress and exposition; February; Detroit, MI. Warrendale, PA: Society of
3 Automotive Engineers; SAE technical paper no. 760039.
4 Pirkle, J. L.; Kaufmann, R. B.; Brody, D. I; Hickman, T.; Gunter, E. W.; Paschal, D. C. (1998) Exposure of the U.S.
5 population to lead, 1991-1994. Environ. Health Perspect. 106: 745-750.
6 Rabinowitz, M. B. (2005) Lead isotopes in soils near five historic American lead smelters and refineries. Sci. Total
7 Environ. 346: 138-148.
8 Rabinowitz, M.; Leviton, A.; Needleman, H.; Bellinger, D.; Waternaux, C. (1985a) Environmental correlates of
9 infant blood lead levels in Boston. Environ. Res. 38: 96-107.
10 Rabinowitz, M.; Leviton, A.; Bellinger, D. (1985b) Home refinishing lead paint and infant blood lead levels. Am. J.
11 Public Health 75: 403-404.
12 Rankin, C.; Nriagu, J. O.; Aggarwal, J. K.; Arowolo, T. A.; Adebayo, K.; Flegal, A. R. (2005) Lead contamination
13 in cocoa and cocoa products: isotopic evidence of globan contamination. Environ. Health Perspect.
14 113: 1344-1348.
15 Rey-Alvarez, S.; Menke-Hargrave, T. (1987) Deleading dilemma: pitfall in the management of childhood lead
16 poisoning. Pediatrics 79: 214-217.
17 Rieuwerts, J. S.; Farago, M. E. (1995) Lead contamination in smelting and mining environments and variations in
18 chemical forms andbioavailability. Chem. SpeciationBioavailability 7: 113-123.
19 Rieuwerts, J.; Farago, M. (1996) Heavy metal pollution in the vicinity of a secondary lead smelter in the Czech
20 Republic. Appl. Geochem. 11: 17-23.
21 Rieuwerts, J. S.; Farago, M.;Bencko, V. (1999) Topsoil and housedust metal concentrations in the vicinity of a lead
22 battery manufacturing plant. Environ. Monit. Assess. 59: 1-13.
23 Roscoe, R. J.; Gittleman, J. L.; Deddens, J. A.; Petersen, M. R.; Halperin, W. E. (1999) Blood lead levels among
24 children of lead-exposed workers: a meta-analysis. Am. J. Ind. Med. 36: 475-481.
25 Sachs, H. K.; Blanksma, L. A.; Murray, E. F.; O'Connell, M. J. (1970) Ambulatory treatment of lead poisoning:
26 report of 1,155 cases. Pediatrics 46: 389-396.
27 Sadiq, M.; Zaidi, T. H.; Al Muhanna, H.; Mian, A. A. (1997) Effect of distribution network pipe material on
28 drinking water quality. J. Environ. Sci. Health A32: 445-454.
29 Scanlon, K. A.; Macintosh, D. L.; Hammerstrom, K. A.; Ryan, P. B. (1999) A longitudinal investigation of solid-
30 food based dietary exposure to selected elements. J. Exposure Anal. Environ. Epidemiol. 9: 485-493.
31 Scelfo, G. M.; Flegal, A. R. (2000) Lead in calcium supplements. Environ. Health Perspect. 108: 309-313.
32 Schilling, R. J.; Bain, R. P. (1988) Prediction of children's blood lead levels on the basis of household-specific soil
33 lead levels. Am. J. Epidemiol. 128: 197-205.
34 Schroeder, W. H.; Dobson, M.; Kane, D. M.; Johnson, N. D. (1987) Toxic trace elements associated with airborne
35 paniculate matter: a review. JAPCA 37: 1267-1285.
36 Shannon, M. W.; Graef, J. W. (1992) Lead intoxication in infancy. Pediatrics 89: 87-90.
37 Sheets, R. W.; Kyger, J. R.; Biagioni, R. N.; Probst, S.; Boyer, R.; Barke, K. (2001) Relationship between soil lead
38 and airborne lead concentrations at Springfield, Missouri, USA. Sci. Total Environ. 271: 79-85.
39 Singh, I.; Mavinic, D. S. (1991) Significance of building and plumbing specifics on trace metal concentrations in
40 drinking water. Can. J. Civil Eng. 18: 893-903.
41 Singh, M.; Jaques, P. A.; Sioutas, C. (2002) Size distribution and diurnal characteristics of particle-bound metals in
42 source and receptor sites of the Los Angeles Basin. Atmos. Environ. 36: 1675-1689.
43 Singley, J. E. (1994) Electrochemical nature of lead contamination. J. Am. Water Works Assoc. 86: 91-96.
44 Small, M. J.; Nunn, A. B., Ill; Forslund, B. L.; Daily, D. A. (1995) Source attribution of elevated residential soil
45 lead near a battery recycling site. Environ. Sci. Technol. 29: 883-895.
46 Sofuoglu, S. C.; Lebowitz, M. D.; O'Rourke, M. K.; Robertson, G. L.; Dellarco, M.; Moschandreas, D. J. (2003)
47 Exposure and risk estimates for Arizona drinking water. J. Am. Water Works Assoc. 95: 67-79.
48 Sterling, D. A.; Johnson, D. L.; Murgueytio, A. M.; Evans, R. G. (1998) Source contribution of lead in house dust
49 from a lead mining waste superfund site. J. Exposure Anal. Environ. Epidemiol. 8: 359-373.
50 Sternbeck, J.; Sjodin, A.; Andreasson, K. (2002) Metal emissions from road traffic and the influence of
51 resuspension—results from two tunnel studies. Atmos. Environ. 36: 4735-4744.
52 Subramanian, K. S.; Connor, J. W.; Meranger, J. C. (1991) Leaching of antimony, cadmium, copper, lead, silver,
53 tin and zinc from copper piping with non-lead-based soldered joints. J. Environ. Sci. Health Part A:
54 Environ. Sci. Eng. A26: 911-929.
55 Subramanian, K. S.; Sastri, V. S.; Connor, J. W. (1994) Drinking water quality: impact of non-lead-based plumbing
56 solders. Toxicol. Environ. Chem. 44: 11-20.
May 2006 3-56 DRAFT-DO NOT QUOTE OR CITE
-------
1 Suchara, I.; Sucharova, J. (2004) Distribution of 36 element deposition rates in a historic mining and smelting area
2 as determined through fine-scale biomonitoring techniques. Part II: relative long-term accumulated
3 atmospheric deposition levels. Water Air Soil Pollut. 153: 229-252.
4 Sutherland, R. A. (2000) Depth variation in copper, lead, and zinc concentrations and mass enrichment ratios in soils
5 of an urban watershed. J. Environ. Qual. 29: 1414-1422.
6 Sutherland, R. A.; Day, J. P.; Bussen, J. O. (2003) Lead concentrations, isotope ratios, and source apportionment in
7 road deposited sediments, Honolulu, Oahu, Hawaii. Water Air Soil Pollut. 142: 165-186.
8 Thomas, V. M; Socolow, R. H.; Fanelli, J. J.; Spiro, T. G. (1999) Effects of reducing lead in gasoline: an analysis of
9 the international experience. Environ. Sci. Technol. 33: 3942-3948.
10 Thompson, N. G.; Sosnin, H. A. (1985) Corrosion of 50-50 tin-lead solder in household plumbing. Weld. J. (Miami,
11 FL, U.S.) 64(4): 20-24.
12 Thornton, I. (1988) Metal content of soils and dusts. Sci. Total Environ. 75: 21-39.
13 Thornton, I.; Davies, D. J. A.; Watt, J. M.; Quinn, M. J. (1990) Lead exposure in young children from dust and soil
14 in the United Kingdom. In: Conference on advances in lead research: implications for environmental health;
15 January 1989; Research Triangle Park, NC. Environ. Health Perspect. 89: 55-60.
16 Thurston, G. D.; Spengler, J. D. (1985) A quantitative assessment of source contributions to inhalable paniculate
17 matter pollution in metropolitan Boston. Atmos. Environ. 19: 9-25.
18 Torts, K.; Van Grieken, R. (1997) Chemical relations between atmospheric aerosols, deposition and stone decay
19 layers on historic buildings at the Mediterranean coast. Atmos. Environ. 31: 2179-2192.
20 Tsai, C.-J.; Shih, T.-S.; Sheu, R.-N. (1997) Characteristics of lead aerosols in different work environments. Am. Ind.
21 Hyg. Assoc. J. 58: 650-656.
22 Turer, D.; Maynard, J. B.; Sansalone, J. J. (2001) Heavy metal contamination in soils of urban highways:
23 comparison between runoff and soil concentrations at Cincinnati, Ohio. Water Air Soil Pollut.
24 132:293-314.
25 U.S. Environmental Protection Agency. (2003) National air quality and emissions trends report. 2003 special studies
26 edition. Research Triangle Park, NC: Office of Air Quality Standards; Emissions Monitoring and Analysis
27 Division; report no. EPA 454/R-03-005. Available:
28 http: //www.epa .gov/air/airtrends/aqtrnd03/toc .html (27 August, 2004).
29 U.S. Environmental Protection Agency. (2006) Safe Drinking Water Act. Available:
30 http://www.epa.gov/region5/defs/html/sdwa.htm (8 May, 2006).
31 U.S. Geological Survey (USGS). (2003) Minerals yearbook 2003: lead. Washington, DC: U. S. Department of the
32 Interior. Available: http://minerals.usgs.gov/minerals/pubs/commodity/lead/ [13 October, 2005].
33 Urbansky, E. T.; Schock, M. R. (2000) Can flouridation affect lead(II) in potable water? Int. J. Environ. Stud.
34 57: 597-637.
35 Vakeva, M.; Ha'meri, K.; Kulmala, M.; Lahdes, R.; Ruuskanen, J.; Laitinen, T. (1999) Street level versus rooftop
3 6 concentrations of submicron aerosol particles and gaseous pollutants in an urban street canyon. Atmos.
37 Environ. 33: 1385-1397.
38 Van Der Leer, D.; Weatherill, N. P.; Sharp, R. J.; Hayes, C. R. (2002) Modelling the diffusion of lead into drinking
39 water. Appl. Math. Modell. 26: 681-699.
40 Venditti, D.; Durecu, S.; Berthelin, J. (2000) A multidisciplinary approach to assess history, environmental risks,
41 and remediation feasibility of soils contaminated by metallurgical activities. Part A: chemical and physical
42 properties of metals and leaching ability. Arch. Environ. Contam. Toxicol. 38: 411-420.
43 Von Lindern, I. H.; Spalinger, S. M.; Bero, B. N.; Petrosyan, V.; Von Braun, M. C. (2003a) The influence of soil
44 remediation on lead in house dust. Sci. Total Environ. 303: 59-78.
45 Von Lindern, I.; Spalinger, S.; Petroysan, V.; Von Braun, M. (2003b) Assessing remedial effectiveness through the
46 blood lead soil/dust lead relationship at the Bunker Hill Superfund site in the Silver Valley of Idaho.
47 Sci. Total Environ. 303: 139-170.
48 Wassan, S. J.; Guo, Z.; McBrian, J. A.; Beach, L. O. (2002) Lead in candle emissions. Sci. Total Environ.
49 296: 159-174.
50 Watt, G. C. M.; Britton, A.; Gilmore, W. H.; Moore, M. R.; Murray, G. D.; Robertson, S. J.; Womersley, J. (1996)
51 Is lead in tap water still a public health problem? An observational study in Glasgow. Br. Med. J.
52 313:979981.
53 Wong, H. K. T.; Gauthier, A.; Beauchamp, S.; Tordon, R. (2002) Impact of toxic metals and metalloids from the
54 Caribou gold-mining areas in Nova Scotia, Canada. Geochem: Explor. Environ. Anal. 2: 235-241.
May 2006 3-57 DRAFT-DO NOT QUOTE OR CITE
-------
1 World Health Organization. (2000) Air quality guidelines for Europe. 2nd. ed. Copenhagen, Denmark: Regional
2 Office for Europe. (WHO regional publications, European series no. 91). Available:
3 http://www.euro.who.int/air/activities/20050223_4 [29 November, 2005].
4 Yaffe, Y.; Flessel, C. P.; Wesolowski, J. I; del Rosario, A.; Guirguis, G. N.; Matias, V.; Gramlich, J. W.; Kelly,
5 W. R.; DeGarmo, T. E.; Coleman, G. C. (1983) Identification of lead sources in California children using
6 the stable isotope ratio technique. Arch. Environ. Health 38: 237-245.
7 Young, T. M; Heeraman, D. A.; Sirin, G.; Ashbaugh, L. L. (2002) Resuspension of soil as a source of airborne lead
8 near industrial facilities and highways. Environ. Sci. Technol. 36: 2484-2490.
9 Zadnik, T. (2004) Lead in topsoil, hay, silage and blood of cows from farms near a former lead mine and current
10 smelting plant before and after installation of filters. Vet. Hum. Toxicol. 46: 287-290.
11 Zimdahl, R. L.; Skogerboe, R. K. (1977) Behavior of lead in soil. Environ. Sci. Technol. 11: 1202-1207.
12 Zinati, G. M.; Li, Y.; Bryan, H. H.; Mylavarapu, R. S.; Codallo, M. (2004) Distribution and fractionation of
13 phosphorus, cadmium, nickel, and lead in calcareous soils amended with composts. J. Environ. Sci. Health
14 Part 639:209-223.
15
May 2006 3-58 DRAFT-DO NOT QUOTE OR CITE
-------
i 4. LEAD TOXICOKINETICS AND MEASUREMENT/
2 MODELING OF HUMAN EXPOSURE IMPACTS ON
3 INTERNAL TISSUE DISTRIBUTION OF LEAD
4
5 4.1 INTRODUCTION
6 The preceding two chapters presented important background information on: physical
7 and chemical properties of lead (Pb) and its inorganic and organic compounds; sources and
8 emissions of lead into the ambient air and other environmental media; and concentrations of lead
9 in ambient air and other components of multimedia human exposure pathways (e.g., water, food,
10 soil, exterior and interior/dusts, etc.) This chapter deals predominately with the relationship
11 between human exposure to lead and lead burden in the body.
12 With exposure, mainly by ingestion and inhalation, a portion of lead is absorbed and
13 distributed to various body compartments from which it is eliminated at various rates.
14 Conceptually, the burden of lead in the body may be considered divided between a fast
15 compartment (soft tissues) and a slow compartment (skeletal). Lead in blood is exchanged with
16 both of these compartments. The contribution of bone lead to the blood lead changes with the
17 duration and intensity of the exposure, age, and various physiological variables (e.g., nutritional
18 status, pregnancy, menopause).
19 In lead toxicologic and epidemiologic studies, dose-response relationships for nearly all of
20 the major health effects of lead are typically expressed in terms of an index of internal Pb dose.
21 Blood lead concentration is extensively used in epidemiologic studies as an index of exposure
22 and body burden due mainly the feasibility of incorporating its measurement into human studies
23 relative to other potential dose indicators, e.g., lead in kidney, plasma, urine, or bone. Blood lead
24 is determined by both the recent exposure history of the individual, as well as the long-term
25 exposure history that leads to accumulation in bone. The benefits and limitations of blood lead
26 concentration as an indicator of lead body burden were discussed in Section 13.3.2 of the 1986
27 Lead AQCD. Application of internal dose-response information to the assessment of risks from
28 lead exposures requires means for estimating the resultant internal doses. Approaches to
29 estimating external lead exposure impacts on internal tissue concentrations, including various
May 2006 4-1 DRAFT-DO NOT QUOTE OR CITE
-------
1 types of regression analyses and complex biokinetic modeling are thusly topics of much
2 importance here.
3 This chapter begins by providing an overview the toxicokinetics of lead which focuses on
4 our current understanding of the routes of lead exposure, uptake, distribution, and elimination in
5 humans. Next, there is a detailed discussion of biological markers used to assess human lead
6 burden and exposure. Subsequently, models for assessing lead exposure-burden relationships in
7 humans are presented. The modeling discussion begins with recent developments in
8 epidemiological models of lead exposure-blood lead concentration relationships in humans.
9 The evolution of lead biokinetics modeling and other major modeling advances during the past
10 25 years or so is then presented.
11
12
13 4.2 TOXICOKINETICS OF LEAD
14 The toxicokinetics of lead was extensively summarized in the 1986 AQCD and has been
15 the subject of several recent reviews (e.g., ATSDR, 2005; Mushak, 1991, 1993). Since the
16 completion of the 1986 AQCD, knowledge of the toxicokinetics of lead has been advanced in
17 several areas. New studies have been published on the kinetics of lead movement into and out of
18 bone (based on analysis of stable lead isotope profiles) which have demonstrated the importance
19 of bone lead stores as a source of lead to the blood, fetus and nursing infant. New animal and
20 human experimental models have been developed for studying dermal and gastrointestinal
21 bioavailability of lead; the latter studies have provided a more quantitative understanding of the
22 gastrointestinal bioavailability of lead in soils. Several new models of the toxicokinetics of lead
23 in humans have been developed which incorporate simulations of bone growth and resorption in
24 the distributional kinetics of lead in humans.
25 The summary provided below discusses the major features of absorption, distribution,
26 metabolism, and excretion of lead. Information specific to route of exposure (e.g., inhalation,
27 oral, dermal) are discussed under separate subsections. Distinguishing features of inorganic and
28 organic lead (e.g., alkyl lead compounds) are also discussed.
29
May 2006 4-2 DRAFT-DO NOT QUOTE OR CITE
-------
1 4.2.1 Absorption of Lead
2 Inhalation Exposure
3 Inorganic Lead
4 Inorganic lead in ambient air consists of aerosols of lead-bearing particulate matter.
5 Amounts and patterns of deposition of inhaled particulate aerosols in the respiratory tract are
6 affected by the size of the inhaled particles, age-related factors that determine breathing patterns
7 (e.g., relative contributions of nose and mouth breathing), airway geometry, and air-stream
8 velocity within the respiratory tract (James et al., 1994). Absorption of lead deposited in the
9 respiratory tract is influenced by particle size and solubility, as well as the pattern of regional
10 deposition within the respiratory tract. Fine particles (<1 |im) deposited in the bronchiolar and
11 alveolar region can be absorbed after extracellular dissolution or can be ingested by phagocytic
12 cells and transported from the respiratory tract (Bailey and Roy, 1994). Larger particles
13 (>2.5 |im) that are deposited, primarily, in the ciliated airways (nasopharyngeal and
14 tracheobronchial regions) can be transferred by mucociliary transport into the esophagus and
15 swallowed.
16 Quantitative studies of the deposition and clearance of inhaled inorganic lead in humans
17 have been limited to studies of adults and to exposures to relatively small particles (Chamberlain
18 et al., 1978; Hursh and Mercer, 1970; Hursh et al., 1969; Morrow et al., 1980; Wells et al.,
19 1977). In these studies, exposures were to lead-bearing particles having mass median
20 aerodynamic diameters (MMAD) below 1 |im. Deposition of inhaled lead particles of this size
21 can be assumed to have been primarily in the bronchi olar and alveolar regions of the respiratory
22 tract (James et al., 1994), where mucociliary transport is likely to have been a relatively minor
23 component of particle clearance (Hursh et al., 1969), compared to the fate of larger particles.
24 Approximately 25% of inhaled lead chloride or lead hydroxide (MMAD 0.26 and 0.24 |im,
25 respectively) was deposited in the respiratory tract in adult subjects who inhaled an inorganic
26 lead aerosol through a standard respiratory mouthpiece for 5 minutes (Morrow et al., 1980).
27 Approximately 95% of deposited inorganic lead, inhaled as submicron particles, was absorbed
28 (Hursh et al., 1969; Wells et al., 1977). Clearance from the respiratory tract of inorganic lead
29 inhaled as submicron particles of lead oxide, or lead nitrate, was multiphasic, with approximate
30 half-times of 0.8 hours (22%), 2.5 hours (34%), 9 hours (33%), and 44 hours (12%)
31 (Chamberlain et al., 1978). Given the submicron particle size of the exposure, these rates are
May 2006 4-3 DRAFT-DO NOT QUOTE OR CITE
-------
1 thought to represent, primarily, absorption from the bronchiolar and alveolar regions of the
2 respiratory tract. As noted previously, amounts and rates of absorption of inhaled lead particles
3 that are larger than 2.5 jim, and which may be more typical of certain human exposure scenarios,
4 will be determined, primarily, by rates of mucociliary transport to the gastrointestinal tract.
5 While no quantitative studies of the deposition and absorption of inhaled lead in children
6 have been reported, age-related differences in airway geometry and physiology can be expected
7 to contribute to higher total particle deposition in the respiratory tract of children compared to
8 adults inhaling similar particle sizes (James et al., 1994; Xu and Yu, 1986).
9
10 Organic Lead
11 Alkyl lead compounds can exist in ambient air as vapors. Inhaled tetraalkyl lead vapor is
12 nearly completely absorbed following deposition in the respiratory tract. Following a single
13 exposure to vapors of radioactive (203Pb) tetraethyl lead (approximately 1 mg/m3 breathed
14 through a mouthpiece for 1 to 2 minutes) in four male subjects, 37% of inhaled 203Pb was
15 initially deposited in the respiratory tract, of which approximately 20% was exhaled in the
16 subsequent 48 hours (Heard et al., 1979). One hour after the exposure, approximately 50% of
17 the 203Pb burden was associated with liver, 5% with kidney, and the remaining burden widely
18 distributed throughout the body, suggesting near complete absorption of the lead that was not
19 exhaled. In a similar experiment conducted with (203Pb) tetramethyl lead, 51% of the inhaled
20 203Pb dose was initially deposited in the respiratory tract, of which approximately 40% was
21 exhaled in 48 hours. The distribution of 203Pb 1 hour after the exposure was similar to that
22 observed following exposure to tetraethyl lead.
23
24 Oral Exposure
25 Inorganic Lead
26 The extent and rate of gastrointestinal absorption of ingested inorganic lead are influenced
27 by physiological states of the exposed individual (e.g., age, fasting, nutritional calcium and iron
28 status, pregnancy) and physicochemical characteristics of the lead bearing material ingested
29 (e.g., particle size, mineralogy, solubility, and lead species). Lead absorption may also vary with
30 the amount of lead ingested.
May 2006 4-4 DRAFT-DO NOT QUOTE OR CITE
-------
1 Effect of Age. Gastrointestinal absorption of water-soluble lead appears to be higher in
2 children than in adults. Estimates derived from dietary balance studies conducted in infants and
3 children (ages 2 weeks to 8 years) indicate that -40 to 50% of ingested lead is absorbed
4 (Alexander et al., 1974; Ziegler et al., 1978). In adults, estimates of absorption of ingested
5 water-soluble lead compounds (e.g., lead chloride, lead nitrate, lead acetate) ranged from 3 to
6 10% in fed subjects (Heard and Chamberlain 1982; James et al., 1985; Rabinowitz et al., 1980;
7 Watson et al., 1986). Data available on lead absorption between childhood and adulthood ages
8 are very limited. While no absorption studies have been conducted on subjects in this age group,
9 the kinetics of the change in stable isotope signatures of blood lead in mothers and their children
10 as both come into equilibrium with a novel environmental lead isotope profile, suggest that
11 children ages 6 to 11 years and their mothers may absorb a similar percentage of ingested lead
12 (Gulson et al., 1997).
13 Studies in experimental animals provide additional evidence for an age-dependency of
14 gastrointestinal absorption of lead. Absorption of lead, administered as lead acetate (6.37 mg
15 lead/kg, oral gavage), was higher in juvenile Rhesus monkeys (38% of dose) compared to adult
16 female monkeys (26% of the dose) (Pounds et al., 1978). Rat pups absorb -40 to 50 times more
17 lead via the diet than do adult rats (Aungst et al., 1981; Forbes and Reina, 1972; Kostial et al.,
18 1978). This age difference in absorption may be due, in part, to the shift from the neonatal to
19 adult diet, and to postnatal physiological development of intestine (Weis and LaVelle, 1991).
20 Effect of Fasting. The presence of food in the gastrointestinal tract decreases absorption
21 of water-soluble lead (Blake and Mann, 1983; Blake et al., 1983; Heard and Chamberlain, 1982;
22 James et al., 1985; Maddaloni et al., 1998; Rabinowitz et al., 1980). In adults, absorption of a
23 tracer dose of lead acetate in water was -63% when ingested by fasted subjects and 3% when
24 ingested with a meal (James et al., 1985). Heard and Chamberlain (1982) reported nearly
25 identical results. The arithmetic mean of reported estimates of absorption in fasted adults was
26 57% (based on Blake et al., 1983; Heard and Chamberlain, 1982; James et al., 1985; Rabinowitz
27 et al., 1980). Reported fed/fasted ratios for absorption in adults range from 0.04 to 0.2 (Blake
28 et al., 1983; Heard and Chamberlain, 1983; James et al., 1985; Rabinowitz, et al., 1980).
29 Mineral content is one contributing factor to the lower absorption of lead when lead is ingested
30 with a meal; that is, the presence of calcium and phosphate in a meal depress the absorption of
31 ingested lead (Blake and Mann, 1983; Blake et al., 1983; Heard and Chamberlain, 1982).
May 2006 4-5 DRAFT-DO NOT QUOTE OR CITE
-------
1 Effect of Nutrition. Lead absorption in children is affected by nutritional iron status.
2 Children who are iron-deficient have higher blood lead concentrations than similarly exposed
3 iron-replete children, which suggest that iron deficiency may result in higher lead absorption or,
4 possibly, other changes in lead biokinetics that contribute to altered blood lead concentrations
5 (Mahaffey and Annest, 1986; Marcus and Schwartz, 1987). Evidence for the effect of iron
6 deficiency on lead absorption has been derived from animal studies. In rats, iron deficiency
7 increases the gastrointestinal absorption of lead, possibly by enhancing binding of lead to iron
8 binding proteins in the intestine (Bannon et al., 2003; Barton et al., 1978a; Morrison and
9 Quatermann, 1987).
10 Dietary calcium intake also appears to affect lead absorption. An inverse relationship has
11 been observed between dietary calcium intake and blood lead concentration in children,
12 suggesting that children who are calcium-deficient may absorb more lead than calcium-replete
13 children (Mahaffey et al., 1986; Ziegler et al., 1978). An effect of calcium on lead absorption is
14 also evident in adults. In experimental studies of adults, absorption of a single dose of lead
15 (100 to 300 jig lead chloride) was lower when the lead was ingested together with calcium
16 carbonate (0.2 g calcium carbonate) than when the lead was ingested without additional calcium
17 (Blake and Mann, 1983; Heard and Chamberlain, 1982). A similar effect of calcium occurs in
18 rats (Barton et al., 1978b). In other experimental animal models, absorption of lead from the
19 gastrointestinal tract has been shown to be enhanced by dietary calcium depletion or
20 administration of vitamin D (Mykkanen and Wasserman, 1981, 1982).
21 Effect of Pregnancy. Absorption of lead may increase during pregnancy. Although there
22 is no direct evidence for this in humans, an increase in lead absorption may contribute, along
23 with other mechanisms (e.g., increased mobilization of bone lead), to the increase in blood lead
24 concentration observed during the later half of pregnancy (Gulson et al., 1997, 1998b, 2004;
25 Lagerkvist et al., 1996; Rothenberg et al., 1994; Schuhmacher et al., 1996).
26 Effect of Dose. Lead absorption in humans may be a capacity limited process, in which
27 case the percentage of ingested lead that is absorbed may decrease with increasing rate of lead
28 intake. However, available studies to date, do not provide a firm basis for discerning if the
29 gastrointestinal absorption of lead is limited by dose. Numerous observations of nonlinear
30 relationships between blood lead concentration and lead intake in humans provide support for the
31 likely existence of a saturable absorption mechanism or some other capacity-limited process in
May 2006 4-6 DRAFT-DO NOT QUOTE OR CITE
-------
1 the distribution of lead in humans (Pocock et al., 1983; Sherlock et al., 1984, 1986). However, in
2 immature swine that received oral doses of lead in soil, lead dose-blood lead relationships were
3 curvilinear, whereas dose-tissue lead relationships for bone, kidney, and liver were linear
4 (Casteel et al., 2006). The same pattern (nonlinearity for blood lead concentration and linearity
5 for tissues) was observed in swine administered lead acetate intravenously (Casteel et al., 1997).
6 These results suggest that the nonlinearity in the lead dose-blood lead concentration relationship
7 may derive from an effect of lead dose on some aspect of the biokinetics of lead other than
8 absorption (e.g., saturation of binding of lead in red blood cells). In fasted rats, absorption was
9 estimated at 42 and 2% following single oral administration of 1 and 100 mg lead/kg,
10 respectively, as lead acetate, suggesting a limitation on absorption imposed by dose (Aungst
11 et al., 1981). Saturable mechanisms of absorption have been inferred from measurements of net
12 flux kinetics of lead in the in situ perfused mouse intestine, the in situ ligated chicken intestine,
13 and the in vitro isolated segments of rat intestine (Aungst and Fung, 1981; Barton, 1984;
14 Flanagan et al., 1979; Mykkanen and Wasserman, 1981). While evidence for capacity-limited
15 processes at the level of the intestinal epithelium is compelling, the dose at which absorption
16 becomes appreciably limited in humans is not known.
17 Effect of Particle Size. Particle size influences the degree of gastrointestinal absorption
18 (Ruby et al., 1999). In rats, an inverse relationship was found between absorption and particle
19 size of lead in diets containing metallic lead particles that were <250 jim in diameter (Barltrop
20 and Meek, 1979). Tissue lead concentration was a 2.3 fold higher when rats ingested an acute
21 dose (37.5 mg Pb/kg) of lead particles that were <38 jim in diameter, than when rats ingested
22 particles having diameters in the range of 150 to 250 |im (Barltrop and Meek, 1979).
23 Dissolution kinetics experiments with lead-bearing mine waste soil suggest that surface area
24 effects control dissolution rates for particles sizes of <90 jim diameter; however, dissolution of
25 90 to 250 |im particle size fractions appeared to be controlled more by surface morphology
26 (Davis et al., 1994). Similarly, Healy et al. (1992) found that the solubility of lead sulfide in
27 gastric acid in vitro was much greater for particles 30 jim in diameter than for particles 100 jim
28 in diameter.
29 Absorption from Soil. Lead in soil can exist in a variety of mineralogical contexts,
30 which can effect lead solubility in the gastrointestinal tract and, potentially, lead absorption from
31 the gastrointestinal tract. In adult subjects who ingested soil (particle size <250 jim) collected
May 2006 4-7 DRAFT-DO NOT QUOTE OR CITE
-------
1 from the Bunker Hill NPL site, 26% (SD: 8.1) of the resulting 250 |ig/70 kg body weight lead
2 dose was absorbed when the soil was ingested in the fasted state, and 2.5% (SD: 1.7) was
3 absorbed when the same soil lead dose was ingested with a meal (Maddaloni et al., 1998).
4 The dominant lead minerals in the sample (relative lead mass) contained lead oxides (-40%),
5 lead sulfates (-25%), and lead sulfides (-11%). Absorption reported for fasted subjects (26%)
6 was approximately half that reported for soluble lead ingested by fasting adults, i.e., -60%
7 (Blake et al., 1983; Heard and Chamberlain, 1983; James et al., 1985; Rabinowitz et al., 1980).
8 Measurements of the absorption of ingested soil lead in infants or children have not been
9 reported.
10 Relative bioavailability (RBA) of lead in soils (i.e., ratio of estimated absorbed fraction of
11 ingested soil lead to that of a water soluble form of lead, based on measurements of ingested lead
12 recovered in blood and/or other tissues) has been more extensively studied in animal models.
13 In immature swine that received oral doses of soil-like materials from various mine waste sites
14 (75 or 225 jig Pb/kg body weight), relative bioavailability of soil-borne lead ranged from 6 to
15 100%, compared to that of a similar dose of highly water-soluble lead acetate (Figure 4-1;
16 Casteel et al., 2006). Electron microprobe analyses of lead-bearing grains in the various test
17 materials revealed that the grains ranged from as small as 1 to 2 jim up to a maximum of 250 jim
18 (the sieve size used in preparation of the samples) and that the lead was present in a wide range
19 of different mineral associations (phases), including various oxides, sulfides, sulfates, and
20 phosphates. These variations in size and mineral content of the lead-bearing grains are the
21 suspected cause of variations in the rate and extent of gastrointestinal absorption of lead from
22 different samples of soil. Based on these very limited data, the relative oral bioavailability of
23 lead mineral phases were categorized into "low" (<0.25), "medium" (0.25 to 0.75), and "high"
24 (>0.75) relative bioavailability categories (Figure 4-2; Casteel et al., 2006).
25 Studies conducted in rats also indicate that the bioavailability of lead in soils can be lower
26 than that of water-soluble forms of lead (e.g., lead acetate) and that the ingestion of soil can
27 lower the bioavailability of water-soluble lead (Freeman et al., 1992; 1994, 1996). Estimates of
28 relative bioavailability of lead in soil (compared to lead acetate) in rats ranged from 7 to 28%.
29 The absolute bioavailability of ingested lead acetate in rats was estimated to be -15% (Freeman
30 et al., 1994); therefore, the above range for relative bioavailability (7 to 28%) corresponds to an
31 absolute bioavailability range of-1 to 4%. The addition of "uncontaminated soil" (having a lead
May 2006 4-8 DRAFT-DO NOT QUOTE OR CITE
-------
5 10
15
20
Test
1 California Gulch Fe/Mn PbO
2 Jasper Co Low Lead Yard
3 Jasper Co High Lead Mill
4 Aspen Residential
5 Aspen Berm
6 California Gulch Phase 1 Residential Soil
7 NIST Paint
8 Jasper Co High Lead Smeiter
9 Palmerfon Location 2
10 Murray Smelter Soil
11 Palmerton Location 4
12 Murray Smeiter Slag
13 Bingham Creek Residential
14 Bingham Creek Channel
15 Gulch AV Slag
16 Midvale Slag
17ButteSoil
18 California Gulch Oregon Gulch Tailings
19 Galena-enriched Soil
Figure 4-1. Relative bioavailability (RBA) is the bioavailability of the lead in the test
material compared to that of lead acetate (test material/lead acetate).
Source: Casteel et al. (2006).
concentration of 54 ± 3 mg lead/kg soil) to diets containing lead acetate decreased the
bioavailability of lead acetate by -76% (Freeman et al., 1996).
4
5
6
7
8
9
10
11
12
13
Dermal Exposure
Inorganic Lead
Dermal absorption of inorganic lead compounds is generally considered to be much less
than absorption by inhalation or oral routes of exposure; however, few studies have provided
quantitative estimates of dermal absorption of inorganic lead in humans, and the quantitative
significance of the dermal absorption pathway as a contributor to lead body burden in humans
remains an uncertainty. Lead was detected in the upper layers of the stratum corneum of lead-
battery workers prior to their shifts and after cleaning of the skin surface (Sun et al., 2002),
suggesting adherence and/or possible dermal penetration of lead. Following skin application of
203Pb-labeled lead acetate in cosmetic preparations (0.12 mg Pb in 0.1 mL or 0.18 mg Pb in
May 2006
4-9
DRAFT-DO NOT QUOTE OR CITE
-------
QQ
•a
to
.y 0.8-'
Q.
(0
Q.
3
o
O
TJ
0)
13
£
"^
to
Group
Figure 4-2. Estimated relative bioavailability (RBA, compared to lead acetate) of ingested
lead in mineral groups, based on results from juvenile swine assays.
Source: Casteel et al. (2006).
1 0.1 g of a cream) to eight male volunteers for 12 hours, absorption was <0.3%, based on whole-
2 body, urine and blood 203Pb measurements, and was predicted to be 0.06% during normal use of
3 such preparations (Moore et al., 1980). Most of the absorption took place within 12 hours of
4 exposure. Lead also appears to be absorbed across human skin when applied to the skin as lead
5 nitrate; however, quantitative estimates of absorption have not been reported. Lead (4.4 mg,
6 as lead nitrate) was applied (vehicle or solvent not reported) to an occluded filter placed on the
7 forearm of an adult subject for 24 hours, after which the patch was removed, the site cover and
8 the forearm were rinsed with water, and total lead was quantified in the cover material and rinse
9 (Stauber et al., 1994). The amount of lead recovered from the cover material and rinse was
10 3.1 mg (70% of the applied dose). Based on this recovery measurement, 1.3 mg (30%) of the
11 applied dose remained either in the skin or had been absorbed in 24 hours; the amount that
12 remained in or on the skin and the fate of this lead (e.g., exfoliation) was not determined.
May 2006
4-10
DRAFT-DO NOT QUOTE OR CITE
-------
1 Exfoliation has been implicated as an important pathway of elimination of other metals
2 from skin (e.g., inorganic mercury; Hursh et al., 1989). The concentrations of lead in sweat
3 collected from the right arm increased 4 fold following the application of lead to the left arm,
4 indicating that some lead had been absorbed (amounts of sweat collected or total lead recovered
5 in sweat were not reported). In similar experiments with three subjects, measurements of 203Pb
6 in blood, sweat and urine, made over a 24-h period following dermal exposures to 5 mg Pb as
7 203Pb nitrate or acetate, accounted for <1% of the applied (or adsorbed) dose. This study also
8 reported that absorption of lead could not be detected from measurements of lead in sweat
9 following dermal exposure to lead as lead carbonate.
10 Studies conducted in animals suggest that dermal penetration of inorganic lead may vary
11 with lead species. Dermal absorption of lead applied as lead arsenate appeared to be less that of
12 lead acetate, based on measurements of kidney lead levels following application of either
13 compound to the shaved skin of rats (Laug and Kunze, 1948).
14
15 Organic Lead
16 Relative to inorganic lead and organic lead salts, tetraalkyl lead compounds have been
17 shown to be rapidly and extensively absorbed through the skin of rabbits and rats (Kehoe and
18 Thamann, 1931; Laug and Kunze, 1948). A 0.75 mL amount of tetraethyl lead, which was
19 allowed to spread uniformly over an area of 25 cm2 on the abdominal skin of rabbits, resulted in
20 10.6 mg of lead in the carcass at 0.5 hours and 4.4 mg at 6 hours (Kehoe and Thamann, 1931).
21 In a comparative study of dermal absorption of inorganic and organic salts of lead conducted in
22 rats, -100 mg of lead was applied in an occluded patch to the shaved backs of rats. Based on
23 urinary lead measurements made prior to and for 12 days following exposure, lead compounds
24 could be ranked according to the relative amounts absorbed (i.e., percent of dose recovered in
25 urine): lead naphthalene (0.17%), lead nitrate (0.03%), lead stearate (0.006%), lead sulfate
26 (0.006%), lead oxide (0.005%), and metal lead powder (0.002%). This rank order (i.e., lead
27 naphthalene > lead oxide) is consistent with a rank ordering of penetration rates of inorganic and
28 organic lead salts through excised skin from humans and guinea pigs: lead nuolate (lead linoleic
29 and oleic acid complex) > lead naphthanate > lead acetate > lead oxide (nondetectable) (Bress
30 and Bidanset, 1991).
31
May 2006 4-11 DRAFT-DO NOT QUOTE OR CITE
-------
1 4.2.2 Distribution
2 Inorganic Lead
3 Lead in Blood. Blood lead concentrations vary considerably with age, physiological state
4 (e.g., pregnancy, lactation, menopause), and numerous factors that affect exposure to lead. The
5 NHANES provide estimates for average blood lead concentrations in various demographic strata
6 of the U.S. population. Samples for Phase 2 of NHANES III were collected during 1991 to
7 1994. Geometric mean blood lead concentration of U.S. adults, ages 20 to 49 years, estimated
8 from the NHANES III Phase 2, were 2.1 jig/dL (95% CI, 2.0, 2.2) (Pirkle et al., 1998). Among
9 adults, blood lead concentrations were highest in the strata that included ages 70 years and older
10 (3.4 |ig/dL; 95% CI, 3.3, 3.6). Geometric mean blood lead concentration of children, ages 1 to
11 5 years, were 2.7 (95% CI, 2.5, 3.0) for the 1991 to 1994 survey period; however, the mean
12 varied with socioeconomic status and other demographic characteristics that have been linked to
13 lead exposure (e.g., age of housing) (Pirkle et al., 1998). Central estimates from the NHANES
14 III Phase 2 (1991 to 1994), when compared to those from Phase 1 of the NHANES III (1988 to
15 1991) and the NHANES II (1976 to 1980), indicate a downward temporal trend in blood lead
16 concentrations in the United States, over this period. Data from the most recent survey
17 (NHANES IV, Centers for Disease Control, 2005) are discussed in Section 4.3 (see Tables 4-1
18 and 4-2). For survey years 2001 to 2002, the geometric mean blood lead concentration for ages
19 >1 year (n = 8,945) was 1.45 |ig/dL (95% CI: 1.39, 1.52); with the geometric mean in males
20 (n = 4,339) being 1.78 |ig/dL (95% CI: 1.71, 1.86) and in females (n = 4,606) being 1.19 |ig/dL
21 (95% CI: 1.14, 1.25).
22 Lead in blood is found primarily (-99%) in the red blood cells (Bergdahl et al., 1997b,
23 1998, 1999; Hernandez-Avila et al., 1998; Manton et al., 2001; Schutz et al., 1996; Smith et al.,
24 2002). Most of the lead found in red blood cells is bound to proteins within the cell rather than
25 the erythrocyte membrane. ALAD is the primary binding ligand for lead in erythrocytes
26 (Bergdahl et al., 1997b, 1998; Sakai et al., 1982; Xie et al., 1998). Lead binding to ALAD
27 is saturable; the binding capacity has been estimated to be -850 |ig/dL red blood cells (or
28 -40 |ig/dL whole blood) and the apparent dissociation constant has been estimated to be
29 -1.5 |ig/L (Bergdahl et al., 1998). Two other lead-binding proteins have been identified in the
30 red cell, a 45 kDa protein (Kd 5.5 |ig/L) and a smaller protein(s) having a molecular weight
31 <10 kDa (Bergdahl et al., 1996, 1997b, 1998). Of the three principal lead-binding proteins
May 2006 4-12 DRAFT-DO NOT QUOTE OR CITE
-------
1 identified in red blood cells, ALAD has the strongest affinity for lead (Bergdahl et al., 1998) and
2 appears to dominate the ligand distribution of lead (35 to 84% of total erythrocyte lead) at blood
3 lead levels below 40 jig/dL (Bergdahl et al., 1996, 1998; Sakai et al., 1982).
4 Approximately 40 to 75% of lead in the plasma is bound to plasma proteins, of which
5 albumin appears to be the dominant ligand (Al-Modhefer et al., 1991; Ong and Lee, 1980). Lead
6 may also bind to y globulins (Ong and Lee, 1980). Lead in serum that is not bound to protein
7 exists largely as complexes with low molecular weight sulfhydryl compounds (e.g., cysteine,
8 homocysteine) and other ligands (Al-Modhefer et al., 1991). Free ionized lead (i.e., Pb2+) in
9 plasma represents an extremely small percentage of total plasma lead. The concentration of Pb2+
10 in fresh serum, as measured by an ion-selective lead electrode, was reported to be 1/5,000 of the
11 total serum lead (Al-Modhefer et al., 1991).
12 In human adults, -94% of the total body burden of lead is found in the bones. In contrast,
13 bone lead accounts for 73% of the body burden in children (Barry 1975). Lead concentrations in
14 bone increase with age throughout the lifetime, indicative of a relatively slow turnover of lead in
15 adult bone (Barry 1975, 1981; Gross et al., 1975; Schroeder and Tipton, 1968). This large pool
16 of lead in adult bone can serve to maintain blood lead levels long after external exposure has
17 ended (Fleming et al., 1997; Inskip et al., 1996; Kehoe, 1987; O'Flaherty et al., 1982; Smith
18 et al., 1996). It can also serve as a source of lead transfer to the fetus when maternal bone is
19 resorbed for the production of the fetal skeleton (Franklin et al., 1997; Gulson et al., 1997,
20 1999b, 2003) (see Section 4.3.2.3 for a more complete discussion of these topics).
21 Lead is not distributed uniformly in bone. Lead accumulates in those bone regions
22 undergoing the most active calcification at the time of exposure. During infancy and childhood,
23 bone calcification is most active in trabecular bone; whereas, in adulthood, calcification occurs at
24 sites of remodeling in cortical and trabecular bone. This suggests that lead accumulation will
25 occur predominantly in trabecular bone during childhood, but in both cortical and trabecular
26 bone in adulthood (Aufderheide and Wittmers, 1992). A portion of lead in mature bone is
27 essentially inert, having an elimination half-time of several decades. A labile compartment
28 exists as well that allows for maintenance of an equilibrium between bone and soft tissue or
29 blood (Rabinowitz et al., 1976). Although a high bone formation rate in early childhood results
30 in the rapid uptake of circulating lead into mineralizing bone, bone lead is also recycled to other
31 tissue compartments or excreted in accordance with a high bone resorption rate (O'Flaherty
May 2006 4-13 DRAFT-DO NOT QUOTE OR CITE
-------
1 1995). Thus, most of the lead acquired early in life is not permanently fixed in the bone
2 (O'Flaherty, 1995). In general, bone turnover rates decrease as a function of age, resulting in
3 slowly increasing bone lead levels among adults (Barry, 1975; Gross et al., 1975; Schroeder and
4 Tipton, 1968). An X ray fluorescence study of tibial lead concentrations in individuals older
5 than 10 years showed a gradual increase in bone lead after age 20 (Kosnett et al., 1994). In 60 to
6 70 year-old men, the total bone lead burden may be >200 mg, while children <16 years old have
7 been shown to have a total bone lead burden of 8 mg (Barry, 1975). However, in some bones
8 (i.e., mid femur and pelvic bone), the increase in lead content plateaus at middle age and then
9 decreases at higher ages (Drasch et al., 1987). This decrease is most pronounced in females and
10 may be due to osteoporosis and release of lead from resorbed bone to blood (Gulson et al., 2002).
11 Bone lead burdens in adults are slowly lost by diffusion (heteroionic exchange) as well as by
12 resorption (O'Flaherty, 1995). Bone lead stores can contribute substantially to blood lead, and
13 maternal bone lead can be transferred to the fetus during pregnancy, and to breast milk and
14 nursing infants during lactation (see Sections 4.3.2.4, 4.3.2.5 for further discussion).
15 Lead in Soft Tissues. Several studies have compared soft tissue concentrations of lead in
16 autopsy samples of soft tissues (Barry, 1975, 1981; Gross et al., 1975; Schroeder and Tipton,
17 1968). These studies were conducted in the 1960s and 1970s and, therefore, reflect burdens
18 accrued during periods when ambient and occupational exposure levels where much higher than
19 current levels. Average blood lead concentrations reported in the adults subjects were -20 |ig/dL
20 in the Barry (1975) and Gross et al. (1975) studies, whereas more current estimates of the
21 average for adults in the United States are below 5 |ig/dL (Centers for Disease Control, 2005).
22 Levels in other soft tissues also appear to have decreased substantially since these studies were
23 reported. For example, average lead concentrations in kidney cortex of male adults were
24 0.78 |ig/g wet tissue and 0.79 |ig/g, as reported by Barry (1975) and Gross et al. (1975),
25 respectively (samples in the Barry study were from subjects who had no known occupational
26 exposures). In a more recent analysis of kidney biopsy samples collected in Sweden, the mean
27 level of lead in kidney cortex among subjects not occupationally exposed to lead was 0.18 jig/g
28 (maximum, 0.56 |ig/g) (Barregard et al., 1999). In spite of the downward trends in soft tissue
29 lead levels, the autopsy studies provide a basis for describing the relative soft tissue distribution
30 of lead in adults and children. Most of the lead in soft tissue is in liver. Relative amounts of lead
31 in soft tissues as reported by Schroeder and Tipton (1968), expressed as percent of total soft
May 2006 4-14 DRAFT-DO NOT QUOTE OR CITE
-------
1 tissue lead, were: liver, 33%; skeletal muscle, 18%; skin, 16%; dense connective tissue, 11%;
2 fat, 6.4%; kidney, 4%; lung, 4%; aorta, 2%; and brain, 2% (other tissues were <1%). The highest
3 soft tissue concentrations in adults also occur in liver and kidney cortex (Barry, 1975;
4 Gerhardsson et al., 1986, 1995b; Gross et al., 1975; Oldereid et al., 1993). The relative
5 distribution of lead in soft tissues, in males and females, expressed in terms of tissue:liver
6 concentration ratios, were: liver, 1.0 (~1 |ig/g wet weight); kidney cortex, 0.8; kidney medulla,
7 0.5; pancreas, 0.4; ovary, 0.4; spleen, 0.3; prostate, 0.2; adrenal gland, 0.2; brain, 0.1; fat, 0.1;
8 testis, 0.08; heart, 0.07; and skeletal muscle, 0.05 (Barry, 1975; Gross et al., 1975). In contrast to
9 lead in bone, which accumulates lead with continued exposure in adulthood, concentrations in
10 soft tissues (e.g., liver and kidney) are relatively constant in adults (Barry 1975; Treble and
11 Thompson 1997), reflecting a faster turnover of lead in soft tissue, relative to bone.
12 Maternal-Fetal-Infant Transfer. The maternal/fetal blood lead concentration ratio,
13 indicated from cord blood lead measurements, is -0.9 (Carbone et al., 1998; Goyer, 1990;
14 Graziano et al., 1990). In one of the larger studies of fetal blood lead concentration, maternal
15 and cord blood lead concentration were measured at delivery in 888 mother-infant pairs; the
16 cord/maternal ratio was relatively constant, 0.93, over a blood lead concentration range of ~3 to
17 40 |ig/dL (Graziano et al., 1990). A study of 159 mother-infant pairs also found a relatively
18 constant cord/maternal ratio (0.84) over a maternal blood lead range of ~1 to 12 |ig/dL (Carbone
19 et al., 1998). As noted in the discussion of the distribution of lead in bone, maternal bone lead is
20 transferred to the fetus during pregnancy and can be transferred to breast milk and nursing
21 infants during lactation (see Sections 4.3.2.4, 4.3.2.5 for further discussion). Breast
22 milk/maternal blood concentration ratios are, in general, <0.1, although values of 0.9 have been
23 reported (Gulson et al., 1998b).
24
25 Organic Lead
26 Information on the distribution of lead in humans following exposures to organic lead is
27 extremely limited. One hour following 1 to 2 minute inhalation exposures to 203Pb tetraethyl or
28 tetramethyl lead (1 mg/m3), -50% of the 203Pb body burden was associated with liver and 5%
29 with kidney; the remaining 203Pb was widely distributed throughout the body (Heard et al.,
30 1979). The kinetics of 203Pb in blood of these subjects showed an initial declining phase during
31 the first 4 hours (tetramethyl lead) or 10 hours (tetraethyl lead) after the exposure, followed by a
May 2006 4-15 DRAFT-DO NOT QUOTE OR CITE
-------
1 phase of gradual increase in blood lead concentration that lasted for up to 500 hours after the
2 exposure. Radioactive lead in blood was highly volatile immediately after the exposure and
3 transitioned to a nonvolatile state thereafter. These observations may reflect an early distribution
4 of organic lead from the respiratory tract, followed by a redistribution of de-alkylated lead
5 compounds.
6 In a man and woman who accidentally inhaled a solvent containing 31% tetraethyl lead
7 (17.6% lead by weight), lead concentrations in the tissues, from highest to lowest, were liver,
8 kidney, brain, pancreas, muscle, and heart (Bolanowska et al., 1967). In another incident, a man
9 ingested a chemical containing 59% tetraethyl lead (38% lead w/w); lead concentration was
10 highest in the liver followed by kidney, pancreas, brain, and heart (Bolanowska et al., 1967).
11
12 4.2.3 Metabolism
13 Inorganic Lead
14 Metabolism of inorganic lead consists of formation of complexes with a variety of protein
15 and nonprotein ligands. Major extracellular ligands include albumen and nonprotein sulfhydryls.
16 The major intracellular ligand in red blood cells is ALAD. Lead in other soft tissues such as
17 kidney, liver, and brain exists predominantly bound to protein. High affinity cytosolic lead
18 binding proteins (PbBPs) have been identified in rat kidney and brain (DuVal and Fowler, 1989;
19 Fowler, 1989). The PbBPs of rat are cleavage products of a2|i globulin, a member of the protein
20 superfamily known as retinol-binding proteins (Fowler and DuVal, 1991). Other high-affinity
21 lead binding proteins (Kd approximately 14 nM) have been isolated in human kidney, two of
22 which have been identified as a 5 kD peptide, thymosin 4 and a 9 kD peptide, acyl-CoA binding
23 protein (Smith et al., 1998). Lead also binds to metallothionein, but does not appear to be a
24 significant inducer of the protein in comparison with the inducers of cadmium and zinc (Eaton
25 et al., 1980; Waalkes and Klaassen, 1985). In vivo, only a small fraction of the lead in the
26 kidney is bound to metallothionein, and appears to have a binding affinity that is less than Cd2+,
27 but higher than Zn2+ (Ulmer and Vallee, 1969); thus, lead will more readily displace zinc from
28 metallothionein than cadmium (Goering and Fowler, 1987; Nielson et al., 1985; Waalkes et al.,
29 1984).
30
31
May 2006 4-16 DRAFT-DO NOT QUOTE OR CITE
-------
1 Organic Lead
2 Alkyl lead compounds undergo oxidative dealkylation catalyzed by cytochrome P 450 in
3 liver and, possibly, in other tissues. Few studies of the metabolism of alkyl lead compounds in
4 humans have been reported. Occupational monitoring studies of workers who were exposed to
5 tetraethyl lead have shown that tetraethyl lead is excreted in the urine as diethyl lead, ethyl lead,
6 and inorganic lead (Turlakiewicz and Chmielnicka, 1985; Vural and Duydu, 1995; Zhang et al.,
7 1994). Trialkyl lead metabolites were found in the liver, kidney, and brain following exposure to
8 the tetraalkyl compounds in workers; these metabolites have also been detected in brain tissue of
9 nonoccupational subjects (Bolanowska et al., 1967; Nielsen et al., 1978). In volunteers exposed
10 by inhalation to 0.64 and 0.78 mg lead/m3 of 203Pb labeled tetraethyl and tetramethyl lead,
11 respectively, lead was cleared from the blood within 10 hours, followed by a re appearance of
12 radioactivity back into the blood after -20 hours (Heard et al., 1979). The high level of
13 radioactivity initially in the plasma indicates the presence of tetraalkyl/trialkyl lead. The
14 subsequent rise in blood radioactivity, however, probably represents water-soluble inorganic lead
15 and trialkyl and dialkyl lead compounds that were formed from the metabolic conversion of the
16 volatile parent compounds (Heard et al., 1979).
17
18 4.2.4 Excretion
19 Inorganic Lead
20 The kinetics of elimination of lead from the body reflects the existence fast and slow
21 pools of lead in the body. Blood, which comprises -1% of body burden, exchanges with both
22 slow and fast pools, and exhibits multiphasic elimination kinetics. The dominant phase,
23 exhibited shortly after a change in exposure occurs, has a half-life of-20 to 30 days. A slower
24 phase becomes evident with longer observation periods following a decrease in exposure. The
25 half-life of this slow phase has been estimated to be -3 to 30 years and appears to correlate with
26 finger bone lead levels and is thought to reflect the release of lead from bone stores to blood.
27 Independent of the route of exposure, absorbed lead is excreted primarily in urine and
28 feces; sweat, saliva, hair and nails, and breast milk are minor routes of excretion (Chamberlain
29 et al., 1978; Griffin et al., 1975; Hursh and Suomela, 1968; Hursh et al., 1969; Kehoe, 1987;
30 Moore et al., 1980; Rabinowitz et al., 1976; Stauber et al., 1994). Fecal excretion accounts for
31 -one-third of total excretion of absorbed lead (fecal/urinary excretion ratio of-0.5), based on
May 2006 4-17 DRAFT-DO NOT QUOTE OR CITE
-------
1 intravenous injection studies conducted in humans (Chamberlain et al., 1978). A similar value
2 for fecal/urinary excretion ratio, -0.5, has been observed following inhalation of submicron lead
3 particles (Chamberlain et al., 1978; Hursh et al., 1969). Estimates of blood-to-urine clearance
4 range from 0.03 to 0.3 L/day with a mean of 0.12 L/day (Araki et al., 1990; Berger et al., 1990;
5 Chamberlain et al., 1978; Gulson et al., 2000; Koster et al., 1989; Manton and Malloy, 1983;
6 Rabinowitz et al., 1973, 1976; Ryu et al., 1983; see Diamond, 1992 for an analysis of these data.
7 Much of the available information on the excretion of ingested lead in adults derives from
8 studies conducted on five male adults who received daily doses of 207Pb nitrate for periods up to
9 210 days (Rabinowitz et al., 1976). The dietary intakes of the subjects were reduced to
10 accommodate the tracer doses of 207Pb without increasing daily intake, thus preserving a steady
11 state with respect to total lead intake and excretion. Total lead intakes (diet plus tracer) ranged
12 from -210 to 360 jig/day. Urinary excretion accounted for -12% of the daily intake (range for
13 five subjects: 7 to 17%) and fecal excretion, -90% of the daily intake (range, 87 to 94%).
14 Based on measurements of tracer and total lead in saliva, gastric secretions, bile, and pancreatic
15 secretions (samples collected from three subjects by intubation), gastrointestinal secretion of lead
16 was estimated to be -2.4% of intake (range, 1.9 to 3.3%). In studies conducted at higher
17 ingestion intakes, 1 to 3 mg/day for up to 208 weeks, urinary lead excretion accounted for
18 -5% of the ingested dose (Kehoe, 1987).
19
20 Organic Lead
21 Lead absorbed after inhalation of tetraethyl and tetramethyl lead is excreted in exhaled air,
22 urine, and feces (Heard et al., 1979). Following 1 to 2 minute inhalation exposures to 203Pb
23 tetraethyl (1 mg/m3), in four male subjects, 37% of inhaled 203Pb was initially deposited in the
24 respiratory tract, of which -20% was exhaled in the subsequent 48 hours (Heard et al., 1979).
25 In a similar experiment conducted with (203Pb) tetramethyl lead, 51% of the inhaled 203Pb dose
26 was initially deposited in the respiratory tract, of which -40% was exhaled in 48 hours. Lead
27 that was not exhaled was excreted in urine and feces. Fecal/urinary excretion ratios were
28 1.8 following exposure to tetraethyl lead and 1.0 following exposure to tetramethyl lead (Heard
29 et al., 1979). Occupational monitoring studies of workers who were exposed to tetraethyl lead
30 have shown that tetraethyl lead is excreted in the urine as diethyl lead, ethyl lead, and inorganic
31 lead (Turlakiewicz and Chmielnicka, 1985; Vural and Duydu, 1995; Zhang et al., 1994).
May 2006 4-18 DRAFT-DO NOT QUOTE OR CITE
-------
1 4.3 BIOLOGICAL MARKERS OF LEAD BODY BURDENS
2 AND EXPOSURE
3 4.3.1 Lead in Blood
4 4.3.1.1 Summary of Key Findings from the 1986 Lead AQCD
5 The extensive use of blood lead concentration as a dose metric reflects mainly the greater
6 feasibility of incorporating blood lead measurements into clinical or epidemiologic studies,
7 compared to other potential dose indicators, such as lead in kidney, plasma, urine, or bone
8 (Flegal and Smith, 1995; Graziano, 1994; Skerfving, 1988). However, blood lead measurements
9 have several limitations as measures of lead body burden (Mushak, 1989, 1993), as were noted in
10 Section 13.3.2 of the 1986 Lead AQCD, which discussed attributes and limitations of blood lead
11 concentration as an indicator of internal exposure. Since the 1986 Lead AQCD was completed
12 relevant developments include numerous studies of determinants of lead levels in bone (see
13 Section 4.3.2), which further support the importance of bone lead on blood lead as an index of
14 lead exposure. The enhanced understanding of lead biokinetics has also been consolidated into
15 exposure-biokinetics models, which not only serve to illustrate exposure-blood-body burden
16 relationships, but also provide a means for making predictions about these relationships that can
17 be tested experimentally or in epidemiologic studies. The basic concepts laid out in the 1986
18 Lead AQCD, that the concentration of lead in blood is largely determined by the relatively recent
19 exposure history of the individual and that it reflects the level of lead in a relatively mobile and
20 small compartment, remain valid. In children, who experience a more rapid turnover of bone
21 mineral than adults, blood lead concentrations closely parallel changes in total body burden.
22
23 4.3.1.2 Analytical Methods for Measuring Lead in Blood
24 Analytical methods for measuring lead in blood include flame atomic absorption
25 spectrometry (AAS), graphite furnace atomic absorption spectrometry (GFAAS), anode stripping
26 voltammetry (ASV), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and
27 inductively coupled plasma-mass spectrometry (ICP-MS). GFAAS and ASV are generally
28 considered to be the methods of choice (Flegal and Smith, 1995). Background correction, such
29 as Zeeman background correction that minimizes the impact of the absorbance of molecular
30 species, must be applied. Limits of detection for lead using AAS are on the order of 5-10 |ig/dL
31 for flame AAS measurements, approximately 0.1 |ig/dL for flameless AAS measurements, and
May 2006 4-19 DRAFT-DO NOT QUOTE OR CITE
-------
1 0.005 |ig/dL for GFAAS (Flegal and Smith, 1995; National Institute for Occupational Safety and
2 Health, 1994). Standard methods that have been reported for blood lead analysis are summarized
3 in Annex Table AX4-2.1. Sample preparation usually consists of wet ashing in heated strong
4 acid (National Institute for Occupational Safety and Health, 1977a,b,c,d,e); however, preparation
5 methods not requiring wet ashing have also been reported (Aguilera de Benzo et al., 1989;
6 Delves and Campbell, 1988; Manton and Cook, 1984; National Institute for Occupational Safety
7 and Health, 1977f; Que Hee et al., 1985; Zhang et al., 1997). The presence of phosphate,
8 ethylenediaminetetraacetic acid (EDTA), or oxalate can sequester lead and cause low readings in
9 flame AAS (National Institute for Occupational Safety and Health, 1984). A comparison of
10 IDMS, ASV, and GFAAS showed that all three of these methods can be used to quantify lead
11 levels in blood (Que Hee et al., 1985).
12
13 4.3.1.3 Levels of Lead in Blood
14 Blood lead concentrations in the U.S. general population have been monitored in the
15 National Health and Nutrition Examination Survey (NHANES) conducted by the Centers for
16 Disease Control and Prevention. Data from the most recent survey (NHANES IV, Centers for
17 Disease Control, 2005) are shown in Tables 4-1 and 4-2. For survey years 2001-2002, the
18 geometric mean blood lead concentration for ages >1 year (n = 8,945) was 1.45 |ig/dL (95% CI:
19 1.39, 1.52); with the geometric mean in males (n = 4,339) being 1.78 |ig/dL (95% CI: 1.71,
20 1.86) and in females (n = 4,606) being 1.19 |ig/dL (95% CI: 1.14, 1.25). Blood lead
21 concentrations in the U.S. general population have decreased over the past three decades as
22 regulations regarding lead paint, leaded fuels, and lead-containing plumbing materials have
23 decreased exposure. Changes in children over time are shown in Figure 4-3.
24 Yassin et al. (2004) analyzed occupational category strata from NHANES III (1988-1994;
25 Table 4-3). The geometric mean for all adults (n = 11,126) included in the analysis was
26 2.42 |ig/dL (GSD 6.93), with the highest means estimated for vehicle mechanics (n = 169;
27 M 4.80 |ig/dL [GSD 3.88]) and construction workers (n = 122; GM 4.44 |ig/dL [GSD 7.84]).
28 See Annex Table AX4-2.2 for a summary of selected measurements of blood lead levels in
29 humans.
30
May 2006 4-20 DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-1. Blood Lead Concentrations in United States by Age, NHANES IV (1999-2002)
Age
Survey Period
N
Blood Lead
(Mg/dL)a
1-5 years
1999-2000 2001-2002
723 898
2.23 1.70
(1.96,2.53) (1.55,1.87)
6-11 years
1999-2000 2001-2002
909 1,044
1.51 1.25
(1.36, 1.66) (1.14, 1.36)
12-19 years
1999-2000 2001-2002
2,135 2,231
1.10 0.94
(1.04,1.17) (0.90,0.99)
^20 years
1999-2000 2001-2002
4,207 4,772
1.75 1.56
(1.68, 1.81) (1.49, 1.62)
to
o
o
aBlood lead concentrations presented are geometric means (95% CI).
to
Table 4-2. Blood Lead Concentrations in United States by Gender, NHANES IV (1999-2002)
Gender
Survey
n
Blood
(Mg/dL
Period
Lead
Males
1999-2000
3,913
2.01
(1.93,2.09)
2001-2002
4,339
1.78
(1.71, 1.86)
Females
1999-2000
4,057
1.37
(1.32, 1.43)
2001-2002
4,606
1.19
(1.14, 1.25)
H
6
o
o
H
O
O
H
W
O
O
HH
H
W
aBlood lead concentrations presented are geometric means (95% CI).
-------
0)
T3
O
_O
CO
18
16
14^
12-
10-
8
6
2
0
1976-1980 1988-1991 1991-1994 1999-2000
Survey Period
2001-2002
Figure 4-3. Blood lead concentrations in U.S. children, 1-5 years of age. Shown are
geometric means and 95% confidence intervals as reported from the
NHANES II (1976-1980) and NHANES III Phase 1 (1988-1991; Pirkle et al.,
1994); NHANES III Phase 2 (1991-1994; Pirkle et al., 1998); and NHANES IV
(1999-2000, 2001-2002; Centers for Disease Control, 2005).
1 4.3.1.4 Blood Lead as a Biomarker of Lead Body Burden
2 Considerable recent effort has been directed at evaluating possible associations between
3 lead body burden and health outcomes, including neurodevelopmental outcomes in children
4 (Wasserman et al., 1994) and renal cardiovascular outcomes in adults (Cheng et al., 2001; Gerr
5 et al., 2002; Glenn et al., 2003; Hu et al., 1996; Korrick et al., 1999; Rothenberg et al., 2002;
6 Tsaih et al., 2004). Conceptually, measurement of long-term lead body burden may be a
7 preferred dose metric if the effects of lead on a particular outcome are lasting and cumulative.
8 However, if the effects of lead on the outcome represent the acute effects of current exposure,
9 then long-term body burden may not the preferred exposure metric. In the absence of clear
10 evidence as to which averaging time (current versus long-term) is most relevant to a particular
11 outcome, both long-term and short-term dose metrics need be explored.
12 A simple conceptual representation of the lead body burden is that it is comprised of a fast
13 turnover pool, comprised mainly of soft tissue, and a slow pool, comprised mainly of skeletal
May 2006
4-22
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-3. Blood Lead Concentrations by Occupation, NHANES III (1988-1994)
to
o
o
Oi
^
to
OJ
DRAFT-DO I
^
0
H
O
O
H
W
O
O
HH
H
W
Blood Lead (ug/dL)
Occupation
Vehicle mechanics
Food service workers
Management, professional, technical, and sales workers
Personal service workers
Agricultural workers
Production workers: machine operators, material movers, etc.
Laborers other than in construction
Transportation workers
Mechanics other than vehicle mechanics
Construction trades people
Construction laborers
Health service workers
All workers
Data from Yassin et al. (2004).
n
169
700
4,768
1,130
498
1,876
137
530
227
470
122
499
11,126
GM
4.80
2.00
2.13
2.48
2.76
2.88
3.47
3.49
3.50
3.66
4.44
1.76
2.42
GSD
3.88
2.69
4.05
4.52
4.02
4.24
3.36
5.19
4.91
4.64
7.84
2.24
6.93
Maximum
28.1
27.0
39.4
25.9
23.4
52.9
21.8
22.3
16.6
16.9
36.0
22.4
52.9
-------
1 tissues (Rabinowitz et al., 1976). The rapid pool has an elimination half-life of-28 days and
2 comprises <1% of the lead body burden. The slow pool has an elimination half-life of several
3 decades and comprises >90% of the total lead body burden. Blood, which comprises -1% of
4 body burden, exchanges with both the slow and fast pools, and exhibits multiphasic elimination
5 kinetics. The dominant phase, exhibited shortly after a change in exposure occurs, has a half-life
6 of-20-30 days. A slower phase becomes evident with longer observation periods following a
7 decrease in exposure. The half-life of this slow phase has been estimated to be -3 to 30 years
8 and appears to correlate with finger bone lead levels and is thought to reflect the release of lead
9 from bone stores to blood. This characterization is supported by measurements of lead content
10 of cadaver tissues (Barry, 1975; Schroeder and Tipton, 1968), lead isotope kinetics in adults
11 (Chamberlain et al., 1978; Rabinowitz et al., 1976; Griffin et al., 1975), and measurements of
12 blood and bone lead levels in retired lead workers (Schiitz et al., 1987a; Christoffersson et al.,
13 1986).
14 As a consequence of a relatively large fraction of the body burden having a relatively slow
15 turnover compared to blood, a constant lead uptake (or constant intake and fractional absorption)
16 gives rise to a quasi-steady state blood lead concentration, while the body burden continues to
17 increase, largely as a consequence of retention of lead in bone (Figure 4-4). As a result, the
18 contribution of blood lead to body burden decreases over time. An abrupt change in lead uptake
19 gives rise to a relatively rapid change in blood lead, to a new quasi-steady state, achieved in
20 -75-100 days (i.e., 3-4 times the blood elimination half-life). In the hypothetical simulation
21 shown in Figure 4-4, body burden has approximately doubled (from 5 to 10 mg) as a result of a
22 5-year period of increased lead uptake; however, the blood lead concentration prior to and 1 year
23 following cessation of the increased uptake has not changed (-2 jig/dL). Therefore, a single
24 blood lead concentration measurement, or a series of measurements taken over a short-time span,
25 can be expected to be a relatively poor index of lead body burden unless exposure over the
26 lifetime and, thereby, body burden has been constant. On the other hand, an average of
27 individual blood lead concentrations measured over a longer period of time (long-term average
28 blood lead concentrations) can be expected to be a better index of body burden. In the
29 hypothetical simulation shown in Figure 4-4, both the long-term average blood lead
30 concentration and the body burden have approximately doubled.
31
May 2006 4-24 DRAFT-DO NOT QUOTE OR CITE
-------
00
30 40
Age (year)
50
30
40
Age {year)
50
Figure 4-4. Simulation of relationship between blood lead concentration and body burden
in adults. A constant baseline intake gives rise to a quasi-steady state blood
lead concentration, while the body burden continues to increase, largely as a
consequence of retention of lead in bone (upper panel). An abrupt change
in lead uptake gives rise to a relatively rapid change in blood lead, to a new
quasi-steady state, and a relatively small change in body burden. The long-
term average blood lead concentration more closely tracks the pattern of
change in body burden (lower panel). Simulation based on lead biokinetics
model of Leggett (1993).
May 2006
4-25
DRAFT-DO NOT QUOTE OR CITE
-------
1 The disparity in the kinetics of blood lead and body burden has important implications for
2 the interpretation of blood lead concentration measurements in epidemiology studies. Cross-
3 sectional studies, by design, sample blood lead concentration at one time or over relatively
4 narrow windows of time. In these samples, the blood lead concentration may or may not reflect
5 well the body burden; it is more likely to do so if the measured value is a reflection of the long-
6 term average blood lead concentration. However, in cross-sectional samples, this cannot be
7 ascertained. Longitudinal sampling provides a means for estimating average blood lead
8 concentrations over time, and such estimates are more likely to be more strongly influenced by
9 differences in body burden, than by differences in short-term variability in exposure. The degree
10 to which repeated sampling will reflect the actual long-term time-weighted average blood lead
11 concentration will depend on the sampling frequency in relation to variability in exposure. High
12 frequency variability in exposures can produce episodic (or periodic) oscillations in blood lead
13 concentration and body burden that may not be captured with low sampling frequencies.
14 The same basic concepts described above regarding lead biokinetics of adults also apply
15 to children. The empirical basis for the understanding of the biokinetics of lead in children is
16 much weaker than that for adults. However, based on the understanding of bone mineral kinetics
17 and its importance as a mechanism for uptake and loss of lead from bone (Leggett, 1993;
18 O'Flaherty, 1991a,b,c, 1993, 1995), the slow pool, described above for adults, is thought to be
19 much more labile in children, reflecting a more rapid turnover of bone mineral in children. As a
20 result, while bone growth will contribute to accumulation of lead in bone in children, changes in
21 blood lead concentration in children are thought to more closely parallel changes in total body
22 burden (Figure 4-5). Empirical evidence in support of this comes from longitudinal studies in
23 which relatively high correlations (r = 0.85) were found between concurrent (r = 0.75) or lifetime
24 average blood lead concentrations (r = 0.85) and tibia bone lead concentrations (measured by
25 XRF) in a sample of children in which average blood lead concentrations exceeded 20 |ig/dL;
26 the correlations was much weaker (r < 0.15) among children who had average blood lead
27 concentration < 10 |ig/dL (Wasserman et al., 1994). Nevertheless, in children, as in adults, the
28 long-term time-weighted average blood lead concentration is more likely to provide a better
29 reflection of lead body burden than a single sample (the exception to this would be if exposure
30 and, thereby, body burden was relatively constant throughout the lifetime).
31
May 2006 4-26 DRAFT-DO NOT QUOTE OR CITE
-------
25
-T 20
: 15
T3
TO
"O
o
_o
DQ
10-
5-
0
0
4 6
Age (year)
8
CO
o
o.
*<
CO
c
a.
o
13
0
10
o
23456
Age (year)
8 9 10
Figure 4-5. Simulation of relationship between blood lead concentration and body burden
in children. Blood lead concentration is thought to parallel body burden more
closely in children than in adults, due to more rapid turnover of bone and
bone-lead stores in children (upper panel). Nevertheless, the long-term
average blood lead concentration more closely tracks the pattern of change
in body burden (lower panel). Simulation based on Leggett (1993) lead
biokinetics model.
May 2006
4-27
DRAFT-DO NOT QUOTE OR CITE
-------
1 4.3.1.5 Blood Lead as a Biomarker of Lead Exposure
2 Characterizing quantitative relationships between external lead exposures and blood lead
3 concentrations has become central to concentration-response analyses for human populations
4 exposed to lead. The 1986 Lead AQCD summarized the empirical basis for this as it stood at the
5 time. A summary of empirically-derived regression slope factors relating lead exposures and
6 blood lead is provided in Abadin and Wheeler (1993). More recent meta-analyses, based on
7 structure equation modeling, provide further support for quantitative relationships between lead
8 exposures and blood lead concentrations in children (e.g., U.S. Environmental Protection
9 Agency, 2001; Lanphear et al., 1998; Succop et al., 1998).
10 The elimination half-time of lead from blood has been estimated to be -25 to 30 days in
11 adult males whose blood lead concentrations were >20 |ig/dL (Chamberlain et al., 1978;
12 Rabinowitz et al., 1976; Griffin et al., 1975). In the latter studies, the elimination half-times
13 were estimated from measurements of the time to achieve a new quasi-steady state blood lead
14 concentration following an increase in exposure (Griffin et al., 1975), or from measurement of
15 the rate of change in blood concentration of an administered isotope of lead (Chamberlain et al.,
16 1978; Rabinowitz et al., 1976). However, the half-time for a change in blood lead concentration
17 (or stable isotope ratio) after an abrupt change in exposure can be much longer. Gulson et al.
18 (1995, 1999a) estimated the half-time for the change in stable lead isotope ratio (206Pb/204Pb) in
19 blood, after an abrupt change instable isotope exposure, to be approximately 25 to 80 days in
20 adult females (blood lead concentration range 3 to 20 jig/dL). Manton et al (2000) estimated the
21 half-time for the decline in blood lead concentration after an abrupt decrease in exposure to be
22 -200 to 1000 days in children (age range: 8 to 60 months, blood lead concentration: 7 to
23 5 |ig/dL). The longer half-times measured under the latter conditions, reflect the contribution of
24 bone lead stores to blood lead following a change in exposure. Based on these observations,
25 a single blood lead concentration may reflect the near-term or longer-term history of the
26 individual to varying degrees, depending on the relative contributions of internal (e.g., bone) and
27 external sources of lead to blood lead, which, in turn, will depend on the exposure history and,
28 possibly age-related characteristics of bone turnover.
29 Analyses of serial blood lead concentrations measured in longitudinal epidemiologic
30 studies have found relatively strong correlations (e.g., r = 0.5 to 0.8) between individual blood
31 Pb concentrations measured after 6 to 12 months of age (Dietrich et al., 1993; McMichael et al.,
May 2006 4-28 DRAFT-DO NOT QUOTE OR CITE
-------
1 1988; Otto et al., 1985; Rabinowitz et al., 1984; Schnaas et al, 2000). These observations
2 suggest that, in general, exposure characteristics of an individual child (e.g., exposure levels
3 and/or exposure behaviors) tend to be relatively constant across age. However, a single blood
4 lead measurement may not distinguish between a history of long-term lower level lead exposure
5 from a history that includes higher acute exposures (Mushak, 1998). This is illustrated in
6 Figure 4-6. Two hypothetical children are simulated. Child A has a relatively constant lead
7 intake from birth; whereas Child B has the same long-term lead intake as Child A, with a 1-year
8 elevated intake which begins at age 24 months (Figure 4-6, upper panel). The absorption
9 fraction is assumed to be the same for both children. Blood lead samples 1 and 5, or 2 and 4,
10 will yield similar blood lead concentrations (~3 or 10 |ig/dL, respectively), yet the exposure
11 contexts for these samples are very different. Two samples (e.g., 1 and 2, or 4 and 5), at a
12 minimum, are needed to ascertain if the blood lead concentration is changing over time. The rate
13 of change can provide information about the magnitude of change in exposure, but not
14 necessarily about the time history of the change (Figure 4-6, lower panel). Here again, time-
15 integrated measurements of lead concentration may provide a means for accounting for some of
16 these factors and, thereby, provide a better measure of long-term exposure. The same concepts
17 apply to estimation of long-term exposure based on blood lead measurements in adults
18 (Gerhardsson et al., 1992, 1995a; Roels et al., 1995).
19 An additional complication is that the relationship between lead intake and blood lead
20 concentration is curvilinear; that is, the increment in blood lead concentration per unit of lead
21 intake decreases with increasing blood lead concentration, both in children (Lacey et al., 1985;
22 Ryu et al., 1983; Sherlock and Quinn, 1986) and in adults (Kehoe, 1987; Laxen et al., 1987;
23 Pocock et al., 1983; Sherlock et al., 1982, 1984). The nonlinearity is evident even at blood lead
24 concentrations below 25 |ig/dL (Figure 4-7). The nonlinearity in the lead intake-blood lead
25 concentration relationship is derived, at least in part, from a capacity limitation in the
26 accumulation of lead in erythrocytes (Bergdahl et al., 1997a, 1998, 1999; Manton et al., 2001;
27 Smith et al., 2002). A capacity-limited process may also reside at the level of intestinal
28 absorption; however, the dose at which absorption becomes appreciably limited in humans is not
29 known. Lead intake-blood lead relationships also vary (a) with age, as a result of age-
30 dependency of gastrointestinal absorption of lead, and (b) with diet and nutritional status
31 (Mushak, 1991).
May 2006 4-29 DRAFT-DO NOT QUOTE OR CITE
-------
0 12 24 36 48 60 72 84
Age (months)
40
O)
3.
T3
re
30-
20 -I
o
5 10-1
DO
0
0 12 24 36 48 60 72 84
Age (months)
Figure 4-6. Simulation of temporal relationships between lead exposure and blood lead
concentration in children. Child A and Child B have a relatively constant
basal lead intake (ug/day/kg body weight) from birth; Child B experiences
1-year elevated intake which begins at age 24 months (upper panel). Blood
lead samples 1 and 5, or 2 and 4, will yield similar blood lead concentrations
(~3 or 10 ug/dL, respectively), yet the exposure scenarios for these samples are
very different. As shown in the example of Child C and Child D, two samples
can provide information about the magnitude of change in exposure, but not
necessarily the temporal history of the change (lower panel).
May 2006
4-30
DRAFT-DO NOT QUOTE OR CITE
-------
70
60
35 50
O)
3= 40
"13
TO
% 30 H
CD
10
0
0
Adult
Child
5 10 15
Lead Intake (jjg/kg/day)
20
80
70
32 60
a 50-
i 40
E 30
| 20
10
0
0
Adult
Child
10 20 30
Lead Intake ([jg/kg/day)
40
Figure 4-7. Simulation of relationships between lead intake and blood lead concentration
in adults and children. The relationship between lead intake and blood lead
concentration is curvilinear in adults and children. Predictions are for a
2-year-old child and 30-year-old adult, for a constant lead intake (jig/kg/day).
Predictions are based on Leggett (1993, upper panel) and O'Flaherty (1993,
1995, lower panel).
May 2006
4-31
DRAFT-DO NOT QUOTE OR CITE
-------
1 The blood lead concentration is also influenced by lead in bone. Evidence for the
2 exchange of bone lead and soft tissue lead stores comes from analyses of stable lead isotope
3 signatures of lead in bone and blood. As noted earlier, bone lead likely contributes to the slow
4 phase of elimination of lead from blood that has been observed in retired lead workers
5 (Christoffersson et al., 1986; Schiitz et al., 1987a). Bone lead stores may contribute 40 to 70% of
6 the lead in blood (Manton, 1985; Gulson et al., 1995; Smith et al., 1996). This contribution
7 increases during pregnancy, when mobilization of bone lead increases, apparently as the bone is
8 resorbed to produce the fetal skeleton (Gulson et al., 2003). The mobilization of bone lead
9 during pregnancy may contribute, along with other mechanisms (e.g., increased absorption),
10 to the increase in lead concentration that has been observed during the later stages of pregnancy
11 (Gulson et al., 1997; Lagerkvist et al., 1996; Schuhmacher et al., 1996). In addition to
12 pregnancy, other states of increased bone resorption appear to result in release of bone lead to
13 blood; these include lactation, osteoporosis, and menopause (Gulson et al., 2003). These
14 observations are consistent with epidemiologic studies that have shown increases in blood lead
15 concentration after menopause and in association with decreasing bone density in
16 postmenopausal women (Hernandez-Avila et al., 2000; Nash et al., 2004; Symanski and Hertz-
17 Picciotto, 1995). The relationship between blood and bone lead is discussed further in Section
18 4.3.2 on bone lead as a biomarker of lead exposure.
19
20 4.3.1.6 Summary of Blood Lead as a Biomarker of Lead Body Burden and Exposure
21 The blood lead concentration measured in an individual will be determined by the recent
22 exposure history of the individual, as well as the long-term exposure history that gives rise to
23 accumulated bone lead stores. The contribution of the latter to blood lead may change with the
24 duration and intensity of the exposure, age, and various physiological variables (e.g., nutritional
25 status, pregnancy, menopause). Longitudinal measurements of blood lead can be expected to
26 provide a more reliable measure of exposure history of an individual (and will more closely
27 parallel body burden) compared to a single measurement; however, the degree to which this will
28 apply will depend on the sampling frequency with respect to the temporal pattern of exposure.
29 In general, higher blood lead concentrations can be interpreted as indicating higher
30 exposures (or lead uptakes); however, they do not necessarily predict appreciably higher body
May 2006 4-32 DRAFT-DO NOT QUOTE OR CITE
-------
1 burdens. Similar blood lead concentrations in two individuals (or populations) do not necessarily
2 translate to similar body burdens or similar exposure histories.
3
4 4.3.2 Lead in Bone
5 4.3.2.1 Summary of Key Findings from the 1986 Lead AQCD
6 In the 1986 Lead AQCD, the discussion on the distribution of lead in bone was fairly
7 limited and mostly based on postmortem studies. The distribution between the two major
8 compartments of cortical and trabecular bone were addressed especially based on the pioneering
9 isotopic work of Rabinowitz et al. (1977). Estimates of the amount of lead in bone were also
10 provided. There was limited discussion of the half-life of lead in bone as being on the order of
11 several decades.
12 One of the major conclusions of the 1986 Lead AQCD regarding bone lead was that the
13 traditional view that the skeletal system was a total sink for body lead was now giving way to the
14 notion that there were at least several bone compartments for lead, with different mobility
15 profiles. The possibility of bone lead serving as a source of long-term internal exposure was also
16 considered.
17 Since 1986, the main focus of lead in bone studies has been on occupationally-exposed
18 subjects, because of concern, until more recent times, about the ability to measure lower levels of
19 lead in bone from environmentally-exposed subjects. Furthermore most of the focus has been on
20 adult males, with very few studies on females and children. The newly available studies of lead
21 in bone are discussed in the following sections.
22
23 4.3.2.2 Methodology of Bone Lead Analysis
24 Analytical Methods for Measuring Lead in Bone
25 Bone is comprised of two main types (cortical and trabecular) that have distinct rates of
26 turnover and lead release, resulting in potential differences in implications with respect to
27 toxicity aspects (further discussed in Section 4.3.2.3). The most commonly measured bones are
28 the tibia, calcaneus, patella, and finger bone. For cortical bone, the midpoint of the tibia is
29 measured. For trabecular bone, both the patella and calcaneus are measured. Recent studies
30 favor measurement of the patella, because it has more bone mass and may afford better
31 measurement precision than the calcaneus. The advantages and disadvantages of patella and
May 2006 4-33 DRAFT-DO NOT QUOTE OR CITE
-------
1 calcaneus sites have not been thoroughly investigated. Bone lead measurements in cadavers,
2 environmentally-exposed subjects, and occupationally-exposed subjects are presented in Annex
3 Tables AX4-2.3, AX4-2.4, and AX4-2.5, respectively.
4 Bone analysis methods for in vivo measurements have included AAS, ASV, ICP-AES,
5 ICP-MS, laser ablation inductively coupled plasma mass spectrometry (LAAICP-MS), thermal
6 ionization mass spectrometry (TIMS), synchrotron radiation induced X-ray emission (SRIXE),
7 particle induced X-ray emission (PIXE), and X-ray fluorescence (XRF). Since the 1986 Lead
8 AQCD, there have been many new papers published on bone lead using XRF. The upsurge in
9 popularity of the XRF method has paralleled a decline in the use of the other methods.
10 In the past, two main approaches for XRF measurements have been used to measure lead
11 concentrations in bone, the K-shell and L-shell methods. The K-shell method is now the most
12 widely used, as there have been no further developments in L-shell devices since the early 1990s.
13 The K-shell methods using 57Cd and 109Cd have been described in detail by Somervaille et al.
14 (1989). Briefly, the K-shell XRF method uses 88.034 keV gamma rays from 109Cd to fluoresce
15 the K-shell X-rays of lead.
16 Plaster-of-Paris "phantoms" with varying lead concentrations measured by ICP-MS or
17 AAS are used to calibrate the K shell systems. Differences and corrections in the use of the
18 phantoms have been discussed in for example, Gordon et al. (1994), Kondrashov and Rothenberg
19 (2001a), Todd et al. (2000), Todd and Chettle (2003), and Chettle et al. (2003). Todd et al.
20 (2002) also commented that the calibration of 109Cd based K shell XRF equipment with
21 standards that consist of a lead-doped Plaster-of-Paris matrix are not valid because Plaster-of-
22 Paris is not true bone matrix. The problem of contamination from various sources (external or
23 the matrix of the Plaster-of-Paris phantom) and its impact on variance was addressed by Todd
24 (2000).
25 There have been several publications focused on the calculating estimates of lead
26 concentrations and uncertainties for XRF measurements (Kondrashov and Rothenberg, 2001a,b;
27 Gordon et al. 1993; Todd, 2000; Todd and Chettle, 2003; Chettle et al., 2003; Todd et al., 2003)
28 culminating in an agreed position in 2003 for these uncertainties (Chettle et al., 2003). Todd
29 et al. (2000) provide a detailed discussion of the influences on the variability and measurement
30 uncertainty including: repositioning, sample measurement duration, overlying tissue, operator
31 expertise, detector resolution, and changes to measurement process over time. Some of these
May 2006 4-34 DRAFT-DO NOT QUOTE OR CITE
-------
1 aspects were also discussed by Hu et al. (1995). In a K shell XRF study of 210 children aged
2 11 to 12!/2 years from a smelter town in Yugoslavia, Todd et al. (2001) (ER) decided that the
3 methodological uncertainty in children was comparable to that in adults.
4 Apart from the recent study into the L shell method by Todd et al. (2002a), there have
5 been several investigations into the reproducibility and accuracy of the K shell method. The
6 main approaches have been repeated measurements on the same individuals within a limited
7 timeframe, repeat measurements on the same individuals over an extended time frame, repeat
8 measurements of cadaver legs at the same location (and compared with AAS analyses), and
9 extended measuring times (Somervaille et al., 1986; Aro et al., 2000; Gordon et al., 1994;
10 Hoppin et al., 2000; Todd et al., 2000). In one of the earliest validation studies, Somervaille et al.
11 (1986) compared K shell and AAS measurements of 30 dissected tibia whose lead values ranged
12 from 6.5 to 83 jig/g of ashed bone. They found no evidence of a systematic difference between
13 the two measurement techniques of more than 1 |ig/g.
14 Short term variability of XRF results was investigated in two recent studies of cadaver
15 legs. In the first study, Aro et al (2000) compared lead levels in 8 cadaver legs: XRF measures
16 of intact bone with skin and hair, bare bones and then ashed bone by ICP-MS. The XRF
17 measurements involved 10 consecutive 30 minute measurements on each bone. In the tibia, lead
18 concentrations by XRF showed standard deviations for each bone ranging from 6 to 58% for
19 intact bone (mean 27%) and 13 to 36% for bare bone. Patella lead concentrations had standard
20 deviations ranging from 9 to 88% (mean 36%) for intact bone and 6 to 64% (mean 19%) for bare
21 bone. ANOVA results showed that after controlling for sampling variation contributed by age,
22 gender and leg sections, no significant difference was found for mean lead concentrations
23 measured on intact bone and bare bone and by ICP-MS methods.
24 In the other cadaver study, Todd et al. (2000) measured 10 intact adult legs and the bare
25 tibia dissected from 9 of these legs for investigation of the short term variability in XRF results.
26 Each bare tibia was measured 6 times over 3 hours (without repositioning the tibia
27 measurements) at the same location as when measured intact. In addition, 4 volunteers
28 underwent monthly single measurements of the left tibia for 1 year. As a further check or
29 reproducibility, half-hour measurements on the standard bone - NIST 1400 -were measured:
30 30 measurements were taken over a period of four days repositioning the sample between each
31 measurement, and 60 consecutive measurements acquired over and 30-hour period without
May 2006 4-3 5 DRAFT-DO NOT QUOTE OR CITE
-------
1 repositioning the sample. They concluded that: "the uncertainty in an individual measurement is
2 an underestimate of the standard deviation of replicate measurements, suggesting a
3 methodological deficiency probably shared by most current 109Cd-based K-shell XRF lead
4 measurement systems."
5 As part of the same study of cadaver legs, 9 tibia were divided into cross-sectional
6 segments 2 cm apart which were further separated into the tibia core and surface samples for the
7 AAS measurements (Todd et al. 2002b). The authors found no statistically significant difference
8 between mean XRF measured concentrations and mean surface lead concentrations measured by
9 AAS but the XRF measurements for tibia core lead concentrations were significantly
10 overestimated by between 5 and 8 jig/g bone mineral. That is, XRF more closely reflects lead
11 concentrations at tibia surface than in tibia core.
12 In another aspect of the cadaver studies of Todd and colleagues (Todd et al., 2001)
13 measured multiple locations on the 10 intact legs and on the 9 bare tibiae. For example, each
14 intact leg underwent single XRF measurements at each of 10 locations along a middle track,
15 extending to 10 cm above and below the vertical mid point of the tibia. Each of the 9 bare tibia
16 underwent at least 6 XRF measurements without repositioning the tibia between measurements
17 at each centimeter location on a 9 cm x 3 cm grid that covered the upper half of the tibia
18 (27 locations). In bare tibia mean XRF results increased up-and-down from the vertical midpoint
19 of the tibia, consistent with the idea that the ends of tibia contain a larger component of
20 trabecular bone than the middle section thereby increasing the 109Cd based XRF result. This
21 finding contrasted with those of Hoppin et al. (2000); Todd et al. (2001) attributed the difference
22 to the smaller range of vertical displacement (±1 cm) in 4 bare bones measured by Hoppin et al.
23 (2000). However, in single XRF spectra taken at multiple locations on intact limbs, there was no
24 detectable effect of vertical location on XRF result; Todd et al. (2000) suggested that measuring
25 away from the vertical midpoint of the tibia should not be of practical concern when performing
26 in vivo XRF measurements. Aro et al. (2000) also concluded that bone lead was reasonably
27 homogeneously distributed.
28 A comparison of lead concentrations between right and left tibia in 12 human skeletons to
29 assess natural homogeneity of lead content revealed natural symmetry with a calculated
30 correlation coefficient of 0.9 (Wittmers et al., 1988). K shell XRF measurements on left and
31 right tibia in 14 subjects showed no significant differences between legs (Gordon et al., 1994).
May 2006 4-36 DRAFT-DO NOT QUOTE OR CITE
-------
1 The reproducibility of XRF measurements over extended intervals has been investigated
2 in several studies. Gordon et al. (1994) measured 5 subjects 5 times on 2 occasions 10 months
3 apart and found mean standard deviations of 3.4 and 5.1 jig/g bone mineral for males and
4 females respectively. Armstrong et al. (1992) measured tibia lead concentrations on two
5 occasions separated by 5 years of a group of workers occupationally exposed to lead. In 1983,
6 the average uncertainty in a single measurement was 9.3 jig/g bone mineral with a mean lead
7 concentration in 15 subjects of 54.4 |ig/g bone mineral. In 1988, the uncertainty was 4.9 |ig/g
8 and mean value for 11 subjects was 44.2 jig/g. They suggested that the difference in
9 measurements separated by 5 years could be accounted for by counting statistics. Todd
10 et al. (2000) performed 27 replicate measurements on 10 intact cadaver legs on the same location
11 over a period of 4% months. The found the average difference between the (average) XRF
12 results from short term and longer term measurements was 1.2 |ig/g "showing there is a
13 reassuringly small amount of variability in the XRF results over a sustained period of time"
14 (p. 3743). They also performed monthly measurements on 4 adult volunteers (2 male, 2 female)
15 over 1 year. Tibia lead varied from 6.4 to 12.9 jig/g bone mineral and standard deviations of the
16 measurements ranged from 4.9 to 9.9 |ig/g.
17 Attenuation of X-rays by skin and hair can affect the bone lead measurements. For
18 example, normalization of the lead X-rays to the elastic scatter was considered to render the
19 accuracy of measurements insensitive to variations in overlying tissue thickness (Chettle et al.,
20 1991; Hu et al., 1995). Todd et al. (2000, p 3737) state that: "The principal factor influencing a
21 human subject's bone lead measurement uncertainty is the thickness of tissue overlying the bone
22 that is measured" but concluded (page 3742) from the difference in average XRF results for
23 intact and bare bone that the bone lead measurements were qualitatively independent of the
24 presence of overlying tissues.
25 However, in a study of young adults, McNeill et al. (1999) found that the measurement
26 uncertainties were greater than uncertainties for occupationally exposed males and attributed this
27 to inclusion of obese subjects and females in their study; uncertainties increased with bone body
28 mass index and were poorer for females than males.
29 In a study of 108 former female smelter employees and 99 referents, Popovic et al. (2005)
30 suggest that a high body mass index can give distorted values.
May 2006 4-37 DRAFT-DO NOT QUOTE OR CITE
-------
1 In the most recent study using nine leg phantoms of different soft tissue thickness, Ahmed
2 et al. (2006) found that by increasing the overlying tissue thickness from 3.2 to 14.6 mm, there
3 was an increase in average measurement uncertainty by a factor of 2.4 and an increase in
4 minimum detectable limit by a factor of 2.46.
5 Since 1986, several investigators have reported refinements to hardware and software to
6 improve the precision and accuracy of XRF measurements and there have been a number of
7 investigations into the precision, accuracy and variability in XRF measurements (e.g., Aro et al.,
8 2000; Todd et al., 2000, 2001, 2002). Todd et al. (2000) provided a detailed discussion of
9 factors that influence the variability and measurement uncertainty, including repositioning,
10 sample measurement duration, overlying tissue, operator expertise, detector resolution, and
11 changes to measurement process over time. Some of these aspects were also discussed by
12 Hu et al. (1995). From their cadaver and in vivo measurements, Todd et al. (2000) concluded
13 that the uncertainty in an individual measurement was an underestimate of the standard deviation
14 of replicate measurements, suggesting a methodological deficiency probably shared by most
15 current 109Cd-based K-shell XRF lead measurement systems. In examining the reproducibility of
16 the bone lead measurements over a 41/2 month period, Todd et al. found the average difference
17 between the XRF results from short term and longer term measurements was 1.2 |ig/g, indicating
18 only a small amount of variability in the XRF results over a sustained period of time.
19
20 Statistical Methods for Analyzing Bone Lead Concentrations in Epidenriologic Studies
21 In the literature, XRF bone data has typically been reported in two ways: one involving a
22 methodological approach to assessing the minimum detection limit and the other termed an
23 epidemiologic approach by Rosen and Pounds (1998). In the methodological approach, a
24 minimum detection limit is defined using various methods, including two or three times the
25 square root of the background counts; one, two, or three times the SD of the background; and
26 two times the observed median error. This approach relies upon the minimum detection limit to
27 define a quantitative estimate that is of sufficient precision to be included in the statistical
28 analysis. The following are examples of methodological minimum detection limits for bone lead
29 analyses. Bellinger et al. (1994) observed minimum detection limits, equivalent to the SD, of
30 5.4 |ig/g for tibia and 9.2 jig/g for patella. Using twice the median observed error, Gerhardsson
31 et al. (1993) observed minimum detection limits of 9.8 |ig/g for tibia and 19.1 |ig/g for
May 2006 4-3 8 DRAFT-DO NOT QUOTE OR CITE
-------
1 calcaneus. For finger bone lead measurements, Chri staffers son et al. (1986) observed a
2 minimum detectable limit of 20 |ig/g, which was equivalent to three times the square root of the
3 background counts.
4 With the epidemiologic approach, to determine the minimum detection limit of an
5 instrument all values are used (including negative values), which results in extremely low
6 detection limits. Rosen and Pounds (1998) noted that this approach yields population bone lead
7 averages that they considered artificially low and inconsistent with observations from many other
8 earlier studies. However, not including values that are negative or below the detection limit, or
9 assigning these values a fixed number for the statistical analysis is also of concern. To examine
10 and compare the two methods used to analyze data at low levels of bone lead concentration,
11 Kim et al. (1995) performed serial measurements on phantoms containing spiked amounts of
12 lead. The results demonstrated that the use of methodological minimum detection limits to
13 recede low-level observations reduced the efficiency of the analysis and the ability to distinguish
14 between the phantoms. Using the epidemiologic approach of retaining all point estimates of
15 measured bone lead concentrations provided less bias and greater efficiency in comparing the
16 mean or median levels of bone lead of different populations.
17
18 4.3.2.3 Bone Lead as a Biomarker of Lead Body Burden
19 Uptake of Lead in Bone
20 The dominant compartment for lead in the body is in bones. In human adults, more than
21 90% of the total body burden of lead is found in the bones, whereas bone lead accounts for -70%
22 of the body burden in children (Barry, 1975). Bone is comprised of two main types, cortical and
23 trabecular. The tibia consists of more than 95% cortical bone, the calcaneus and patella
24 comprise more than 95% trabecular bone, and finger bone is a mixed cortical and trabecular bone
25 although the second phalanx is dominantly cortical. The cortical and trabecular bones have
26 distinct rates of turnover and lead release, as well as potentially different associated toxicity
27 implications (Hu et al., 1998). For example, adult tibia has a turnover rate of about 2% per year
28 whereas trabecular bone has a turnover rate of more than 8% per year (Rabinowitz, 1991). The
29 proportion of cortical to trabecular bone in the human body varies by age, but on average is
30 about 80 to 20 (International Commission on Radiological Protection, 1973). Although not so
31 important for certain types of measurements, the periosteum is of limited dimension and may
May 2006 4-39 DRAFT-DO NOT QUOTE OR CITE
-------
1 reflect a bone compartment of more rapid deposition and turnover of lead than the other two
2 types (Skerfving et al., 1993), which would also likely have implications for toxicity, especially
3 for chelation therapy.
4 Much of the understanding of bone structure and metal deposition comes from studies of
5 radioactive elements (e.g., International Commission on Radiological Protection, 1996). Durbin
6 (1992, page 823) suggests that there is "an initial deposition of lead on anatomical bone surfaces
7 with some skewing to the well nourished trabecular surfaces in red marrow, intense deposits at
8 bone growth sites, and later on, a nearly diffuse labeling throughout the bone volume. For
9 constant intake of lead during growth, it is expected that lead will be nearly uniformly distributed
10 in the mineralized bone. Single or irregular intakes during growth are expected to result in
11 residual buried lines and hotspots superimposed on a relatively uniform diffuse concentration in
12 bone mineral volume. . . For example, periosteal and subperiosteal lead deposits in the long
13 bones, including those of the hands and feet, are likely to be greater than at many other sites,
14 since bone growth continues at the periosteal surface while the endosteal surface is resorbed."
15 The importance of bone marrow was also stressed by Salmon et al. (1999), with a key
16 factor affecting lead uptake into bone being the fraction of bone surface in trabecular and cortical
17 bone adjacent to active bone marrow. The fraction of total marrow that is red and active
18 decreases from 100% at birth to about 32% in adulthood (Cristy, 1981). Early lead uptake is
19 greater in trabecular bone due to its larger surface area and higher metabolic rate. Of the total
20 bone surface against red marrow, 76% is trabecular and 24% is cortical endosteal (Salmon et al.,
21 1999). Bone marrow has much lower lead concentrations than bone matrix (Skerfving
22 etal., 1983).
23
24 Half-Life of Lead in Bone
25 Estimates of the half-life of lead in trabecular bone are partly dependent on the tissue
26 analyzed and the "purity" of the trabecular component (e.g., patella, calcaneus, and phalanx).
27 Earlier estimates of the half-life of lead in trabecular bone ranged from 12 to 19 years (Bergdahl
28 et al., 1998; Gerhardsson et al., 1993). For cortical bone, estimates for the half-life of lead
29 were on the order of 13 to 27 years (Bergdahl et al., 1998; Gerhardsson et al., 1993;
30 Rabinowitz, 1991).
May 2006 4-40 DRAFT-DO NOT QUOTE OR CITE
-------
1 With respect to half-lives in bone, recent K-shell XRF bone studies have indicated that
2 earlier concepts of a constant rate of removal of lead from bone throughout adulthood assumed
3 in models of human metabolism (Leggett, 1993; O'Flaherty, 1993) may be incorrect. In a study
4 of active and retired smelter workers, Brito et al. (2001) suggested that people less than 40 years:
5 old had a shorter half-life for the release of lead from the tibia than those older than 40 years,
6 4.9 years (95% CI: 3.6, 7.8) compared to 13.8 years (95% CI: 9.7, 23.8), respectively. Also,
7 they suggested that less intensely exposed subjects with a lifetime averaged blood lead of
8 <25 |ig/dL had a shorter half-life in the tibia (6.2 years [95% CI: 4.7, 9.0]) than those with a
9 lifetime averaged blood lead >25 |ig/dL (14.7 years [95% CI: 9.7, 29.9]).
10 Even by the end of the sixth decade, -35 to 40% of skeletal mass consists of
11 unremodelled first generation bone acquired during childhood and adolescence (International
12 Commission on Radiological Protection, 1973). This statement contrasts with that of O'Flaherty
13 (1993) who suggested that because of the relatively short half-life of lead in the bones of children
14 that much of the lead incorporated during active growth would not persist into adulthood. In a
15 comparison of lead in tooth dentine and the tibia from young adults who were followed up after a
16 period of 13 years, Kim et al. (1996) suggested that "pockets" of lead acquired in childhood may
17 persist into adults. Likewise, McNeill et al. (2000) compared tibia lead levels and cumulative
18 blood lead indices in a population of 19 to 29 year olds who had been highly exposed to lead in
19 childhood from the Bunker Hill, Idaho smelter. They concluded that lead from exposure in early
20 childhood had persisted in the bone matrix until adulthood.
21
22 Changes in Bone Lead Concentrations with Age
23 Conventional and XRF analyses of bone have shown significant increases in bone lead
24 with age (Hu et al., 1990, 1996; Kosnett et al., 1994; Morgan et al., 1990). Kosnett et al. (1994)
25 observed no significant change in bone lead concentrations up to age 20 years, but found an
26 increasing trend with the same slope for men and women between the ages of 20 to 55 years and
27 an increase to a faster rate in men older than 55 years. Kosnett et al. reanalyzed earlier cadaver
28 cortical bone data of Drasch et al. (1987) and found that male bone lead values increased
29 significantly after age 40 years, whereas female values slightly declined. A similar analysis of
30 the post-mortem data of Barry (1975) showed an upward inflection for all males after age
31 35 years. Kosnett et al. (1994) found no significant slope to the relationship between age and
May 2006 4-41 DRAFT-DO NOT QUOTE OR CITE
-------
1 bone lead for the 10 to 20 year old subjects, in contrast to Barry (1975) and Drasch et al. (1987).
2 Kosnett et al. (1994) further noted that relatively high environmental lead levels characterized
3 various populations in the past and would have resulted in higher levels of bone lead deposition;
4 a portion of the increase of bone lead with age is thus likely attributable to an exposure cohort
5 effect.
6 Annual increments of lead to bone vary although no attempt has been made to determine
7 whether the differences are significant. For example, the annual increment of 0.46 |ig/g bone
8 mineral/year found by Gordon et al. (1993) was slightly lower than that found by Somervaille
9 et al. (1989), but the difference was not significant. After age 20 years, Kosnett et al. (1994)
10 found the annual increment to be 0.38 jig/g bone mineral/year. Hu et al. (1990) reported a value
11 of 0.31 |ig/g bone mineral/year for subjects ranging in age from 20 to 58 years. Thus,
12 interpreting variations in bone lead as a function of age is complex.
13
14 4.3.2.4 Distribution of Lead from Bone into Blood and Plasma
15 Contribution of Bone Lead to Blood Lead
16 Although the skeleton was recognized as a potentially significant contributor to blood lead
17 in the 1986 Lead AQCD, there have been several investigations using both bone lead XRF and
18 stable lead isotope methods which have helped quantify the contribution. The earlier estimation
19 of skeletal contribution to blood lead was 70% by Manton (1985) and -65% ranging up to 100%
20 by Schiitz et al. (1987b). The more recent isotope studies confirmed these estimates. Using
21 female immigrants to Australia and their children, Gulson et al. (1995, 1997, 1999a) found a
22 mean value of 50% (range 16-73%) deriving from the skeleton. Smith et al. (1996) found a
23 range of 40-70% in five patients who underwent total hip or knee joint replacement. Gwiazda
24 et al. (2005) observed a range of 40-65% in two children and >90% in one child. Studies
25 examining the bone lead contribution to blood lead are presented in Annex Table AX4-2.6.
26 The contribution of skeletal lead to blood lead was further examined in females from
27 varying environments. In middle-aged to elderly subjects (46-74 years), an increase of 19 |ig/g
28 of lead in tibia bone mineral was associated with an increase in blood lead of 1.7 |ig/dL, which
29 corresponds to a 0.09 |ig/dL increase in blood lead per 1 jig/g bone mineral (Korrick et al.,
30 2002). A study of 108 former workers at the Bunker Hill smelter in northern Idaho and
31 99 referents from the Spokane, WA area examined the endogenous bone lead release rate of
May 2006 4-42 DRAFT-DO NOT QUOTE OR CITE
-------
1 postmenopausal and premenopausal women (Popovic et al., 2005). The results indicated that the
2 endogenous release rate in postmenopausal women (0.13 |ig/dL per jig/g bone) was greater than
3 the rate found in premenopausal women (0.07 |ig/dL per |ig/g bone). In a Mexico City study, the
4 endogenous bone lead release rate in postmenopausal women also was observed to be double
5 that in premenopausal women (Garrido-Latorre et al., 2003). A change of 10 |ig/g bone mineral
6 was associated with an increase in blood lead of 1.4 |ig/dL in postmenopausal subjects,
7 compared to an increase of 0.8 |ig/dL in premenopausal women. Lactation was also found to
8 affect the endogenous bone lead release rate. After adjusting for patella lead concentration, an
9 increase in blood lead levels of 12.7% (95% CI: 6.2, 19.6) was observed for women who
10 practiced partial lactation and an increase of 18.6% (95% CI: 7.1, 31.4) for women who
11 practiced exclusive lactation compared to those who stopped lactation (Tellez-Rojo et al., 2002).
12 The mean cortical lead to current blood lead ratios for occupationally-exposed subjects
13 are shown in Figure 4-8. Box plots were calculated using data from the following studies:
14 Bergdahl et al., 1998; Brito et al., 2002; Christoffersson et al., 1984; Erfurth et al., 2001; Erkkila
15 et al., 1992; Fleming et al., 1998; Gerhardsson et al., 1993; Hanninen et al., 1998; Juarez-Perez
16 et al., 2004; Popovic et al., 2005; Roels et al., 1995; Schwartz et al., 2000a,b; Somervaille et al.,
17 1988, 1989; Todd et al., 2001. The mean cortical lead to current blood lead ratio is about 1.2
18 (range 0.4-2.6) for active employees (n = 17). For retired employees (n = 7), the mean is 3.2
19 (range 2.0-5.3), while for environmentally-exposed referent subjects from these industries (n = 7)
20 the mean ratio is about 1.3 (range 1-2.2). The differences in the cortical lead to blood lead ratio
21 between active and retired employees and retired employees and referents are significant
22 (p < 0.01) but not between active employees and referents. Several investigators have pointed
23 out the weak association between bone lead and blood lead in active employees in comparison
24 with the stronger association with retired employees (e.g., Erkkila et al., 1992; Fleming et al.,
25 1997; Gerhardsson et al., 1993). This is likely because circulatory lead of active employees
26 reflects mainly ongoing exposure, whereas that in retired employees is more dependent on lead
27 released from the skeleton.
28 The mean tibia lead to current blood lead ratios for environmentally-exposed subjects is
29 shown in Figure 4-9. The box plot for pregnancy-related subjects was calculated using data from
30 the following studies: Brown et al., 2000; Chuang et al., 2001; Ettinger et al., 2004; Gomaa
31 et al., 2002; Gonzalez-Cossio et al., 1997; Hernandez-Avila et al., 1996, 1998, 2002, 2003;
May 2006 4-43 DRAFT-DO NOT QUOTE OR CITE
-------
6.0
.2
l|3
CO
S 4.0
_i
T3
O
_O
CO
O
+J
T3
ro
03
d 2.0
B3
o
tr
o
o
0.0
I
I
T
T
Active
Retired
Referent
Figure 4-8. Cortical lead to blood leads ratios for occupationally-exposed subjects
(both active and retired) and referents. Data compiled from several studies.
See text for more details.
1 Hu et al., 1996; Moline et al., 2000; Rothenberg et al., 2000; Sanin et al., 2001; Tellez-Rojo
2 et al., 2002, 2004. The box plot for middle-aged and elderly subjects included the following
3 studies: Berkowitz et al., 2004; Cheng et al., 1998; Garrido-Lattore et al., 2003; Hu et al., 1996,
4 2001; Korrick et al., 2002; Kosnett et al., 1994; Oliveira et al., 2002; Schafer et al., 2005; Tsaih
5 et al., 2004; Webber et al., 1995. The box plot for the younger subjects (age range 1-30 years)
6 included Farias et al., 1998; Kim et al., 1996; Rosen et al., 1989; Stokes et al., 1998. The mean
7 tibia lead to blood lead ratio for pregnancy-related subjects (n = 21) is 1.5 (range 1.0-4.2) and is
8 statistically significantly different (p < 0.001) from the mean ratio of 3.4 (range 1.6-5.4) for
9 middle-aged to elderly subjects (n = 27). Similar relationships are observed for the patella lead
10 to blood lead ratios for pregnancy-related subjects and middle-aged to elderly subjects.
May 2006
4-44
DRAFT-DO NOT QUOTE OR CITE
-------
6.0
_o
TS
T3
ro
T3
O
_O
DO
O
O3
lo
4,0
2.0-
T
T
T
o.o
Pregnancy Middle-aged Young
to Elderly
Figure 4-9. Tibia leads to blood lead ratios for environmentally-exposed pregnancy-
related subjects, middle-aged to elderly subjects, and younger subjects.
Data compiled from several studies. See text for more details.
1 In several other studies of environmentally-exposed subjects, there is a stronger
2 relationship between patella lead and blood lead than tibia lead and blood lead (e.g., Hernandez-
3 Avila et al., 1996; Hu et al., 1996, 1998). Hu et al. (1998) suggest that these relationships
4 indicate that trabecular bone is the predominant bone type providing lead back into circulation
5 under steady-state and pathologic conditions. The stronger relationships between blood lead and
6 trabecular lead compared with cortical bone is probably associated with the larger surface area of
7 trabecular bone allowing for more lead to bind via ion exchange mechanisms and more rapid
8 turnover making it more sensitive to changing patterns of exposure.
9
10 Partitioning of Bone Lead into Plasma
11 Although most of the lead in whole blood is associated with erythrocytes (-99%), it has
12 been suggested that the small fraction of lead in plasma (<0.3%) may be the more biologically
13 labile and lexicologically active fraction of the circulating lead. Several authors have proposed
May 2006
4-45
DRAFT-DO NOT QUOTE OR CITE
-------
1 that lead released from the skeleton was preferentially partitioned into serum compared with red
2 cells (Cake et al., 1996; Hernandez-Avila et al., 1998; Tsaih et al., 1999) with one explanation
3 being that the lead from endogenous sources was in a different form to that from exogenous
4 sources. In the latter study, Tsaih et al. (1999) suggested that urine was a satisfactory proxy for
5 serum. However, this concept has been withdrawn by its main proponents. In matched blood and
6 urine samples from 13 migrant subjects to Australia who were monitored prior to and during
7 pregnancy, there was no statistically significant difference in the 206Pb/204Pb and 207Pb/206Pb
8 ratios over pregnancy and the urine results for the postpartum period were in the opposite
9 relationships to those predicted for a preferential partitioning hypothesis (Gulson et al., 2000).
10
11 4.3.2.5 Mobilization of Lead From Bone
12 Although earlier investigators such as Brown and Tompsett (1945), Ahlgren et al. (1976)
13 and Christoffersson et al. (1984) suggested that the skeleton was a potential endogenous source
14 of lead poisoning, the opposing concept of the skeleton as a "safe" repository for lead persisted
15 until the mid-1980s and early 1990s. Potential mobilization of lead from the skeleton could
16 occur at times of physiological stress associated with enhanced bone remodeling such as during
17 pregnancy and lactation (Hertz-Picciotto et al., 2000; Manton, 1985; Silbergeld, 1991),
18 menopause or in the elderly (Silbergeld, 1991; Silbergeld et al., 1988), extended bed rest
19 (Markowitz and Weinberger, 1990), hyperparathyroidism (Kessler et al., 1999), and
20 weightlessness. The lead deposited in the bone of adults can serve to maintain blood lead levels
21 long after exposure has ended (Fleming et al., 1997; Gulson et al., 1995; Inskip et al., 1996;
22 Kehoe, 1987; Manton, 1985; Nilsson et al., 1991; O'Flaherty et al., 1982; Schutz et al., 1987b;
23 Smith etal., 1996).
24 In the 1986 Lead AQCD, there was a comprehensive summary of chelation therapies and
25 the recognition that there was limited release of lead from bones. The potential role of bone lead
26 as an endogenous source of lead in blood, resulting in elevated levels for former lead employees,
27 was mentioned although data to support this hypothesis were limited.
28
29 Mobilization of Lead from Bone during Pregnancy and Lactation
30 Bone lead studies of pregnant and lactating subjects are summarized in Annex Table
31 AX4-2.7. Most of the bone XRF studies on pregnancy and lactation have focused on subjects
May 2006 4-46 DRAFT-DO NOT QUOTE OR CITE
-------
1 from Mexico City and Latin subjects from Los Angeles, California. Relationships and/or health
2 outcomes from these investigations include: patella bone as a significant contributor to blood
3 lead (Brown et al., 2000; Hernandez-Avila et al., 1996); a positive association between plasma
4 lead and bone lead in the highest bone lead group of pregnant women (Tellez-Rojo et al., 2004);
5 a positive association of tibia and calcaneus lead with prenatal lead concentration, and calcaneus
6 lead with postnatal lead (Rothenberg et al., 2000); a positive association of tibia lead and
7 seasonal variations in blood lead (Rothenberg et al., 2001); maternal tibia and patella lead as
8 significant predictors of fetal exposure determined using cord blood (Chuang et al., 2001);
9 a positive association of calcaneus lead and increased systolic and diastolic blood pressure in the
10 third trimester (Rothenberg et al., 2002); an inverse relationship between maternal tibia and
11 patella lead, and birth weight (Gonzalez-Cossio et al., 1997; Sanin et al., 2001); an inverse
12 association between tibia lead and birth length, and patella lead and head circumference
13 (Hernandez-Avila et al., 2002); an inverse association of maternal patella bone and Mental
14 Development Index (Gomaa et al., 2002); increased bone resorption during lactation (Tellez-
15 Rojo et al., 2002); increased lead in breast milk with an increase in patella and tibia lead
16 (Ettinger et al., 2004).
17 Lead isotope studies on immigrant women to Australia (Gulson et al., 1997, 1998a)
18 confirmed the earlier work of Manton (1985) of increased blood lead during pregnancy. Gulson
19 et al. reported that, during pregnancy, blood lead concentrations in the first immigrant cohort
20 (n = 15) increased by an average of about 20% compared to non-pregnant migrant controls
21 (n = 7). The percentage change in blood lead concentration was significantly greater during the
22 postpregnancy period than during the second and third trimesters (p < 0.001). Skeletal
23 contribution to blood lead, based on the isotopic composition for the immigrant subjects,
24 increased in an approximately linear manner during pregnancy. The mean increases for each
25 individual during pregnancy varied from 26% to 99%. Skeletal lead contribution to blood lead
26 was significantly greater during the postpregnancy period than during the second and third
27 trimesters. The contribution of skeletal lead to blood lead during the postpregnancy period
28 remained essentially constant at the increased level of lead mobilization. In a follow-up study
29 using a different immigrant cohort of 12 women with calcium supplementation at the
30 recommended level of approximately 1,000 mg/day (National Institutes of Health, 1994), Gulson
31 et al. (2004) found increased mobilization of lead occurred in the third trimester rather than in
May 2006 4-47 DRAFT-DO NOT QUOTE OR CITE
-------
1 the second trimester as observed with first cohort. In addition, the extra flux released from bone
2 during late pregnancy and postpartum varied from 50 to 380 jig (geometric mean 145 jig)
3 compared with 330 jig in the previous cohort.
4 In an extended monitoring of 7 subjects for up to 22 months postpartum, Gulson et al.
5 (1999a) found that blood lead concentrations in some of the subjects decreased to about half the
6 earlier levels almost immediately after cessation of breastfeeding. However, in 4 of the 7 cases
7 there was a rebound in blood lead concentrations that exceeded the earlier levels in 3 cases. The
8 authors interpreted these results to indicate that there is ongoing increased mobilization of lead
9 from the maternal skeleton for much longer than predicted, probably associated with remodeling
10 processes. Also using lead isotopes, Manton et al. (2003) observed that blood lead
11 concentrations decreased in early pregnancy and rose during late pregnancy. They attributed
12 these results to changes in bone resorption with decoupling of trabecular and cortical bone sites.
13
14 Transplacental Transfer of Lead and Transfer through Breast Milk
15 Transplacental transfer of lead in humans has been suggested in a number of studies based
16 on cord blood to maternal blood lead ratios ranging from about 0.6 to 1.0 at the time of delivery.
17 Maternal-to-fetal transfer of lead appears to be related partly to the mobilization of lead from the
18 maternal skeleton. Evidence for transfer of maternal bone lead to the fetus has been provided
19 from stable lead isotope studies in cynomolgus monkeys (Macacafascicularis). Approximately
20 7 to 39% of the maternal lead burden that is transferred to the fetus appears to derive from the
21 maternal skeleton (Franklin et al., 1997; O'Flaherty et al., 1998). Further evidence for maternal-
22 to-fetal transfer of lead in humans can be gained from stable lead isotope measurements. For
23 example, a 0.99 correlation in lead isotopic ratios for maternal and cord blood (Manton, 1985;
24 Gulson et al., 1998b) and the similarity of isotopic ratios in maternal blood and in blood and
25 urine of newly-born infants provide strong evidence for placental transfer of lead to the fetus
26 (Gulson et al., 1999b).
27 Breast milk can also be a pathway of maternal excretion of lead. However, given the very
28 low lead concentrations and analytical difficulties arising from high fat contents in breast milk,
29 their analyses require careful attention. Selected studies appear to show a linear relationship
30 between breast milk and maternal whole blood with the percentage of lead in breast milk
31 compared with whole blood of <3% in subjects for blood lead concentrations ranging from 2 to
May 2006 4-48 DRAFT-DO NOT QUOTE OR CITE
-------
1 34 |ig/dL. Blood lead concentrations in breastfed newborn infants decreased in spite of the
2 maternal blood lead concentrations having risen or remained elevated postpartum compared to
3 lower levels during prepregnancy or in the first trimester (Gulson et al., 1999b). Similar trends
4 were noted by Manton et al. (2000). However, in a Mexico City study, an association between
5 patella lead and blood lead concentrations was higher for women with partial lactation than for
6 those who stopped lactation, and it was increased among women who breastfed exclusively
7 (Tellez-Rojo et al., 2002). In another Mexico City study, Ettinger et al. (2004) concluded that an
8 interquartile increase in patella lead was associated with a 14% increase in breast milk lead,
9 whereas for tibial lead the increase was -5%.
10 In conclusion, there is evidence that maternal-to-fetal transfer of lead occurs, likely
11 resulting from the mobilization of lead from the maternal skeleton during pregnancy. Breast-fed
12 infants appear to be at greater risk only if the mother is exposed to high lead concentrations
13 either from exogenous sources or endogenous sources such as the skeleton.
14
15 Mobilization of Lead in Bone During Menopause and in the Elderly
16 Increases in blood lead for postmenopausal women have been attributed to release of lead
17 from the skeleton associated with increased bone remodeling during menopause. Many of the
18 studies have been based on blood lead concentration. Bone lead studies of menopausal and
19 middle-aged to elderly subjects are summarized in Annex Table AX4-2.8.
20 Overall, the various studies of bone and blood lead levels, as well as hormone
21 replacement therapy, have provided conflicting outcomes. Hormone replacement therapy alone
22 or combined with calcium supplementation prevents bone resorption and increases the bone
23 mineral density in trabecular and cortical bones of women with or without metabolic bone
24 disease. The effect of hormone replacement therapy may result in a decrease of lead
25 mobilization from bone along with a reduction in blood lead concentration levels. Several
26 studies have found that tibia bone lead levels were higher in women who used hormone
27 replacement therapy (Popovic et al., 2005; Webber et al., 1995). In contrast, other investigators
28 have found no association between bone lead and use of estrogens (Berkowitz et al., 2004;
29 Korrick et al., 2002). In addition, some studies observed a decrease in blood lead concentrations
30 associated with hormone replacement therapy (Garrido-Latorre et al., 2003), whereas others
31 observed no association (Webber et al., 1995).
May 2006 4-49 DRAFT-DO NOT QUOTE OR CITE
-------
1 The endogenous release rate of lead from bone in postmenopausal women was double the
2 rate in premenopausal former smelter employees (Popovic et al., 2005) and environmentally-
3 exposed women from Mexico (Garrido-Latorre et al., 2003). In middle-aged to elderly males
4 from the Normative Aging Study, patella lead accounted for the dominant portion of variance in
5 blood lead (Hu et al., 1996).
6
7 Effect of Nutritional Status on Mobilization of Lead from Bone
8 Most studies that investigated the effect of nutritional status on the mobilization of lead
9 from the skeleton have examined the effects of calcium supplementation. Several studies have
10 suggested that dietary calcium may have a protective role against lead by decreasing absorption
11 of lead in the gastrointestinal tract and by decreasing the mobilization of lead from bone stores to
12 blood, especially during periods of high metabolic activity of the bone such as pregnancy,
13 lactation, and menopause. An inverse association between patella lead and low calcium intake in
14 postpartum women has been found (Hernandez-Avila et al., 1996). In contrast, Rothenberg et al.
15 (2000) observed that dietary calcium intake had no effect on calcaneus lead in women monitored
16 during the third trimester and 1 to 2 months postpartum. Likewise, no effect from calcium
17 supplementation on bone lead was found amongst lactating women from Mexico City (Tellez-
18 Rojo et al., 2002), although in a follow-up study, Hernandez-Avila et al. (2003) reported a 16.4%
19 decrease in blood lead concentration among women with the highest patella bone lead levels who
20 were taking supplements. Gulson et al. (2004) observed that calcium supplementation was found
21 to delay increased mobilization of lead from bone during pregnancy and halved the flux of lead
22 release from bone during late pregnancy and postpartum. In another study, women whose daily
23 calcium intake was 850 mg per day showed lower amounts of bone resorption during late
24 pregnancy and postpartum than those whose intake was 560 mg calcium per day (Manton et al.,
25 2003). Tellez-Rojo et al. (2004) observed that plasma lead levels were inversely related to
26 dietary calcium intake. Results for whole blood lead were similar but less pronounced.
27 Some researchers have noted concerns regarding potential lead toxicity resulting from
28 calcium supplementation. However, Gulson et al. (2001) observed that lead in calcium or
29 vitamin supplements did not appear to increase blood lead concentrations. No information was
30 available on the effects of other nutritional supplements (e.g., iron or zinc) on lead body burden.
31
May 2006 4-50 DRAFT-DO NOT QUOTE OR CITE
-------
1 4.3.2.6 Summary of Bone Lead as a Biomarker of Lead Body Burden and Exposure
2 Bone accounts for more than 90% of the total body burden of lead in adults and 70% in
3 children. In addition, the longer half-life of lead in bone, which largely depends on the bone type
4 but is generally estimated in terms of years compared to days for blood lead, allows a more
5 cumulative measure of lead dose. The more widespread use of in vivo XRF lead measurements
6 in bone and indirect measurements of bone processes with stable lead isotopes since the 1986
7 Lead AQCD have enhanced the use of bone lead as a biomarker of lead body burden.
8 In addition to considering bone lead as an indicator of cumulative lead exposure, lead in
9 the skeleton can also be regarded as a source of lead. Key studies have examined the
10 contribution of bone lead to blood lead; the preferential partitioning of bone lead into plasma;
11 mobilization of lead from bones during pregnancy, lactation, and menopause; and the role of
12 nutritional supplementation in bone mobilization.
13
14 4.3.3 Lead in Teeth
15 4.3.3.1 Summary of Key Findings from the 1986 Lead AQCD
16 The importance of dentine as a potential indicator of lead exposure was noted in the 1986
17 Lead AQCD. There was more emphasis and optimism on using dentine to assess lead exposure
18 in this document as the bone XRF method was in its infancy. The issue of deciduous tooth type
19 was addressed but there was little information on permanent teeth. The portion of the tooth
20 analyzed (i.e., whole tooth or circumpulpal dentine) was also addressed. In the 1990 Addendum,
21 the use of tooth lead as an exposure metric was described in a number of the longitudinal and
22 cross-sectional studies.
23
24 4.3.3.2 Analytical Methods for Measuring Lead in Teeth
25 Analytical methods for tooth analysis vary from the most widely used AAS, to energy-
26 dispersive XRF, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and
27 high precision lead isotopes.
28 As a standard analytical method has yet to be established for tooth lead analysis, some of
29 the discrepancies in findings between studies could arise from several factors, including
30 differences in tooth type, part of the tooth analyzed, and tooth location. Any real differences
31 among populations are unlikely to be the result of physiological factors such as blood supply to
May 2006 4-51 DRAFT-DO NOT QUOTE OR CITE
-------
1 teeth or mineralization rates. As enamel and dentine in different teeth calcify at overlapping but
2 different times (Orban, 1953), they could retain varying amounts of lead.
3 In a systematic evaluation of the magnitude of random errors associated with dentine lead
4 measurements, Fergusson et al. (1989) measured lead concentrations in two samples of dentine
5 from 996 New Zealand children. They estimated that 15 to 20% of the variance was
6 unexplained. Tests of differences of means and variances showed no significant differences
7 between the two samples.
8 Lead measurements in deciduous teeth in individuals from urban and remote
9 environments and from polluted environments are presented in Annex Tables AX4-2.9 and
10 AX4-2.10, respectively. Based on the limited number of studies, it would appear that the range
11 in whole deciduous tooth lead for environmentally exposed subjects is about 1-10 |ig/g, but the
12 most likely levels are <5 jig/g and probably even <2 |ig/g. Studies of whole deciduous teeth
13 from industrial environments, including those in urban settings, are also commonly much less
14 than 10 |ig/g.
15 The utility of circumpulpal dentine (Shapiro et al., 1973) as the metric of lead exposure in
16 deciduous teeth has not been enthusiastically received. This is likely due to the separation
17 difficulties, as well as the limited amount of circumpulpal dentine that may be present when the
18 teeth are resorbed, prior to exfoliation.
19 In another approach to gain more information about exposure during pregnancy and early
20 childhood, the teeth may be sectioned into dominantly enamel or dominantly dentine. These
21 samples can then be analyzed for lead isotopic ratios and lead concentrations (Gulson and
22 Wilson, 1994). Even for children living in lead mining and smelting communities, levels of lead
23 in the enamel are generally low (<5 |ig/g) and are consistent with other studies of whole teeth.
24 However, higher levels are observed in the dentine samples (e.g., 32 |ig/g), which likely reflect
25 the early childhood exposure. Permanent teeth tend to have up to three times the level of lead
26 compared with deciduous teeth, but the number of studies is very limited.
27
28 4.3.3.3 Tooth Lead as a Biomarker of Lead Body Burden
29 Compared with the amount of lead in the skeleton, tooth lead is a minor contributor to the
30 body burden of lead. Most of the tooth lead information is based on analyses of deciduous teeth.
31 There is still controversy over the amounts of lead in different whole teeth but it appears that the
May 2006 4-52 DRAFT-DO NOT QUOTE OR CITE
-------
1 highest concentrations are in central incisors, with decreasing amounts in lateral incisors,
2 canines, first molars, and second molars. Teeth from the upper jaw tend to have higher lead
3 concentrations than those from the lower jaw.
4 As teeth accumulate lead, tooth lead levels are generally considered an estimate of
5 cumulative lead exposure. Rabinowitz et al. (1993) found that tooth lead was a better measure of
6 exposure than current blood lead levels; however, it was not a good measure of the child's
7 cumulative exposure from birth to exfoliation due to the mobilization of lead from dentine.
8 Teeth are composed of several tissues formed over the years. Therefore, if a child's lead
9 exposure during the years of tooth formation varied widely, different amounts of lead would be
10 deposited at different rates (Rabinowitz et al., 1993). This may allow investigators to elucidate
11 the history of lead exposure in a child.
12 Gulson and Wilson (1994) advocated the use of sections of enamel and dentine to obtain
13 additional information compared with analysis of the whole tooth (e.g., Fosse et al., 1995;
14 Tvinnereim et al., 1997). For example, deciduous teeth lead in the enamel provides information
15 about in utero exposure whereas that in dentine from the same tooth provides information about
16 postnatal exposure until the tooth exfoliates at about 6 to 7 years of age.
17
18 4.3.3.4 Relationship between Tooth Lead and Blood Lead
19 As with bone lead-blood lead relationships, there is interest in understanding more about
20 potential relationships between tooth lead and blood lead. The tooth lead-blood lead relationship
21 is more complex than the bone lead-blood lead relationship because of differences in tooth type,
22 location, and analytical method.
23 Rabinowitz (1995) used studies which reported values for dentine, whole shed teeth, or
24 crowns, but discarded those measuring circumpulpal dentine because of the higher values in this
25 medium. The mean tooth lead levels varied from 2.8 to 12.7 jig/g and blood lead levels from
26 6.5 to 17 |ig/dL. In a plot of blood versus tooth lead, Rabinowitz found a good fit (R2 = 0.97;
27 p< 0.0001) with the relationship:
28
29 Tooth Lead (|ig/g) = P x [Blood Lead (jig/dL)], where P = 0.49 (SE 0.04) (4-1)
30
31 In an earlier Boston study, Rabinowitz et al. (1989) found that the association between
32 tooth and blood lead increased with age, first achieving statistical significance at 18 months;
May 2006 4-53 DRAFT-DO NOT QUOTE OR CITE
-------
1 by 57 months, the correlation coefficient was 0.56. A correlation of 0.47 was found between
2 current blood lead and incisors amongst 302 German children (Ewers et al., 1982).
3
4 4.3.3.5 Mobilization of Lead from Teeth
5 Although mobilization of lead from bone appears well established, this is not the case for
6 lead in teeth. Conventional wisdom has lead fixed once it enters the tooth. Although that may
7 be the case for the bulk of enamel, it is not true for the surface of the enamel and dentine.
8 In evaluating deciduous teeth data, Rabinowitz et al. (1993) suggested that their data were
9 compatible with a model that allows lead to be slowly removed from dentine. Such a process
10 may be associated with resorption of the root and dentine that precedes exfoliation, which allows
11 reequilibration of dentine lead with blood lead.
12 In children exposed to lead sources from mining, paint, or petrol in communities such as
13 the Broken Hill lead mining community, Gulson and Wilson (1994) and Gulson (1996) showed
14 that the source of lead from the incisal (enamel) sections was different from the source of lead in
15 the cervical (dentine) sections of deciduous teeth, reflecting the change in lead from in utero
16 exposure to early childhood. Based on changes in the isotopic composition of enamel and
17 dentine in deciduous teeth sections from the Broken Hill mining community children, Gulson
18 (1996) estimated that lead is added to dentine at a rate of approximately 2-3% per year.
19 Stable lead isotopes and lead concentrations were measured in the enamel and dentine of
20 permanent (n = 37) and deciduous teeth (n = 14) from 47 European immigrants to Australia to
21 determine whether lead exchange occurs in teeth and how it relates to lead exchange in bone
22 (Gulson et al., 1997). The authors concluded that enamel exhibited no exchange of its European-
23 origin lead with lead from the Australian environment, whereas dentine lead exchanged with
24 Australian lead to the extent of ~1 ± 0.3% per year.
25
26 4.3.3.6 Summary of Tooth Lead as a Biomarker of Lead Body Burden and Exposure
27 Tooth lead is a minor contributor to the total body burden of lead. Moderate-to-high
28 correlations have been observed between tooth lead levels and blood lead levels. Differences in
29 tooth type, part of the tooth analyzed, and tooth location may contribute to some of the
30 discrepancies in findings between studies of tooth lead. As teeth are composed of several tissues
31 formed over the years, if a child's lead exposure during the years of tooth formation varied
May 2006 4-54 DRAFT-DO NOT QUOTE OR CITE
-------
1 widely, different amounts of lead would be deposited at different rates. Deciduous teeth lead in
2 the enamel provides information about in utero exposure, whereas that in dentine provides
3 information about postnatal exposure until the tooth exfoliates.
4
5 4.3.4 Lead in Urine
6 4.3.4.1 Summary of Key Findings from the 1986 Lead AQCD
7 The 1986 Lead AQCD provided an extensive discussion of the physiological basis for
8 "chelatable" urinary lead. Also discussed was lead excretion provoked by EDTA, including the
9 pools of lead in the body that might be mobilized in the EDTA provocation test, and the
10 relationship between the outcome and blood lead concentration. The 1986 Lead AQCD noted
11 observations that formed the basis for application of the EDTA provocation test for detecting
12 elevated lead body burden.
13
14 4.3.4.2 Analytical Methods for Measuring Lead in Urine
15 Standard methods that have been reported for urine lead analysis are summarized in
16 Annex Table AX4-2.1 and are, in general, the same as those analyses noted for determination of
17 lead in blood. Reported detection limits are approximately 50 |ig/L for AAS, 5-10 |ig/L for
18 ICP AES, and 4 |ig/L for ASV for urine lead analyses. Sample preparation usually consists of
19 wet ashing; however, chelation and solvent extraction has also been reported (National Institute
20 for Occupational Safety and Health, 1994, 1977a).
21
22 4.3.4.3 Levels of Lead in Urine
23 A summary of selected measurements of urine lead levels in humans can be found in
24 Annex Table AX4-2.11. Urine lead concentrations in the U. S. general population have been
25 monitored in NHANES. Data from the most recent survey (NHANES IV, Centers for Disease
26 Control, 2005) for subjects >6 years of age are shown in Table 4-4. The geometric mean for the
27 entire sample (n = 2,689) was 0.64 |ig/g creatinine (95% CI: 0.60, 0.68). The geometric means
28 for males (n = 1,334) and females (n = 1,335) were 0.64 |ig/g creatinine (95% CI: 0.61, 0.67)
29 and 0.64 |ig/g creatinine (95% CI: 0.59, 0.69), respectively. These values correspond to an
30 excretion rate of approximately 1-1.3 jig lead/day for an adult, assuming a daily creatinine
31
May 2006 4-55 DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-4. Urine Lead Concentrations in U.S. by Age, NHANES IV (1999-2002)
Age
Survey Period
N
Urine Lead3
6-11 years
1999-2000
340
1.17
(0.98, 1.41)
2001-2002
368
0.92
(0.84, 1.00)
12-19 years
1999-2000
719
0.50
(0.46, 0.54)
2001-2002
762
0.40
(0.38,0.43)
^20 years
1999-2000
1406
0.72
(0.68, 0.76)
2001-2002
1559
0.66
(0.62, 0.70)
aUrine lead concentrations presented are geometric means (95% CI) of ug-lead/g-creatinine.
1 excretion rate of approximately 1.5 g/day in adult females, a body weight of 70 kg for males and
2 58 kg for females, and a lean body mass fraction of 0.88 for males and 0.85 for females (Forbes
3 and Bruining, 1976; International Commission on Radiological Protection, 1975).
4 Geometric mean urinary lead excretion rates of 7-10 |ig/g creatinine (maximum 43) have
5 been reported in groups of children living in areas impacted by lead smelting operations
6 (Brockhaus et al., 1988). Daily urinary lead excretion can exceed 200 |ig/day in association with
7 occupational exposures (Biagini et al., 1977; Cramer et al., 1974; Lilis et al., 1968; Lin et al.,
8 2001; Wedeenetal., 1975).
9
10 4.3.4.4 Urine Lead as a Biomarker of Lead Body Burden
11 Urine is a major route of excretion of absorbed lead (Chamberlain et al., 1978; Griffin
12 et al., 1975; Kehoe, 1987; Rabinowitz et al., 1976). The kinetics of urinary excretion following a
13 single dose of lead is similar to that of blood (Chamberlain et al., 1978), likely due to the fact
14 that lead in urine derives largely from lead in blood plasma. Evidence for this is the observation
15 that urinary lead excretion is strongly correlated with the rate of glomerular filtration of lead
16 (i.e., glomerular filtration rate x plasma lead concentration; Araki et al., 1986). Estimates of
17 urinary clearance of lead from serum (or plasma) range from 13-22 L/day, with a mean of
18 18 L/day (Araki et al., 1986; Chamberlain et al., 1978; Manton and Cook, 1984; Manton and
19 Malloy, 1983). Estimates of blood-to-urine clearance, on the other hand, range from
20 0.03-0.3 L/day with a mean of 0.12 L/day (Araki et al., 1990; Berger et al., 1990; Chamberlain
21 et al., 1978; Gulson et al., 2000; Koster et al., 1989; Manton and Malloy, 1983; Rabinowitz et al.,
May 2006
4-56
DRAFT-DO NOT QUOTE OR CITE
-------
1 1973, 1976; Ryu et al., 1983; see Diamond, 1992 for an analysis of these data), consistent with a
2 plasma to blood concentration ratio of approximately 0.005-0.01 L/day (U.S. Environmental
3 Protection Agency, 2003). Based on the above, urinary excretion of lead can be expected to
4 reflect the concentration of lead in plasma and variables that affect delivery of lead from plasma
5 to urine (e.g., glomerular filtration and other transfer processes in the kidney).
6 Plasma lead makes a small contribution (<1%) to the blood lead concentration and a
7 negligible contribution to total lead body burden. Furthermore, the kinetics of elimination of
8 lead from plasma is fast, relative to lead in bone, where most of the lead burden resides.
9 Therefore, the basic concepts described for blood as a biomarker for body burden also apply to
10 urine. A single urine lead measurement, or a series of measurements taken over short-time span,
11 is likely a relatively poor index of lead body burden (Figure 4-10). On the other hand, long-term
12 average measurements of urinary excretion can be expected to be a better index of body burden.
13 In the hypothetical simulation shown in Figure 4-10, both the long-term average urinary lead
14 excretion rate and the body burden have approximately doubled.
15 The above considerations do not exclude the potential utility of urine lead as a dose metric
16 in epidemiological studies. Some effect outcomes may be more strongly associated with plasma
17 concentrations of lead (e.g., ferrochelatase inhibition) than lead body burden. Given the
18 technical difficulties in accurately measuring the concentrations of lead in plasma, especially at
19 low blood lead concentrations (e.g., <10 |ig/dL), measurements of urinary lead may serve as a
20 more feasible surrogate for measurements of plasma lead concentration.
21
22 4.3.4.5 Relationship Between Lead in Blood and Urine
23 Assuming first-order kinetics, a plasma-to-urine clearance (UC1P) of 13-22 L/day
24 corresponds to half-time for transfer of lead from plasma to urine of 0.1-0.16 day for a 70 kg
25 adult who has a plasma volume (VP) of approximately 3 L:
26
'»>= <4'2)
28
29 This translates to a very rapid steady-state, much faster than observed for blood lead after
30 a change in exposure level. The kinetics of change in urinary lead excretion in response to a
May 2006 4-57 DRAFT-DO NOT QUOTE OR CITE
-------
30 40
Age (year)
50
30
40
Age (year)
50
Figure 4-10. Simulation of relationship between urinary lead excretion and body burden
in adults. An abrupt change in lead uptake gives rise to a relatively rapid
change in urinary excretion of lead, to a new quasi-steady state, and a
relatively small change in body burden (upper panel). The long-term
average urinary lead excretion more closely tracks the pattern of change
in body burden (lower panel). Simulation based on Leggett (1993) lead
biokinetics model.
May 2006
4-58
DRAFT-DO NOT QUOTE OR CITE
-------
1 change in exposure, therefore, will be determined by variables that affect the plasma lead level,
2 including partitioning of lead into erythrocytes and exchanges with lead in soft tissues and
3 mobile pools within bone (e.g., bone surface). Here again, the basic concepts that apply to blood
4 lead as a biomarker of exposure also apply to urine lead. Urinary lead excretion reflects, mainly,
5 the exposure history of the previous few months; thus, a single urinary lead measurement cannot
6 distinguish between a long-term low level of exposure or a higher acute exposure. The
7 relationship between urinary lead concentration and lead uptake is thought to be linear, unlike
8 that for blood lead concentration, although there are no direct empirical tests of this assumption
9 in humans. This assumption predicts a linear relationship between lead intake (at constant
10 absorption fraction) and urinary lead excretion rate. Figure 4-11 presents a simulated
11 relationship between lead intake and urinary lead excretion in adults and children using both the
12 Leggett (1993) model and O'Flaherty (1993, 1995) model. The major difference between the
13 Leggett model and the O'Flaherty model is in the assignment of the time dependence of bone
14 lead residence. The Leggett model assumes a slow accumulation of a nonexchangable lead pool,
15 whereas the O'Flaherty model assumes a gradual distancing of lead from bone surfaces by
16 diffusion throughout the bone volume (O'Flaherty, 1998).
17 It is important to emphasize that the above concepts apply to urinary lead excretion rate,
18 not to urinary lead concentration. The concentration of lead in urine (Upb) is a function of the
19 urinary lead excretion (UEPb) and the urine flow rate (UFR, L/day):
20
21 UEph=UPh-UFR (4-3)
22
23 Urine flow rate can vary by a factor or more than 10, depending on the state of hydration
24 and other factors that affect glomerular filtration rate and renal tubular reabsorption of the
25 glomerular filtrate. All of these factors can be affected by lead exposure at levels that produce
26 nephrotoxicity (i.e., decreased glomerular filtration rate, impaired renal tubular transport
27 function; see Section 6.4 for discussion of effects of lead on the renal system). Therefore, urine
28 lead concentration measurements provide little reliable information about exposure (or lead body
29 burden), unless they can be adjusted to account for unmeasured variability in urine flow rate
30 (Arakietal., 1990).
31 A determination of urinary lead excretion rate requires measurement of two variables,
32 urine lead concentration, and urine flow rate; the later requires collection of a timed urine
May 2006 4-59 DRAFT-DO NOT QUOTE OR CITE
-------
120
3: 100
I
£
o
X
LJU
"O
re
-------
1 sample, which is often problematic in epidemiologic studies. Collection of un-timed ("spot")
2 urine samples, a common alternative to timed samples, requires adjustment of the lead
3 measurement in urine to account for variation in urine flow (Diamond, 1988). Several
4 approaches to this adjustment have been explored, including adjusting the measured urine lead
5 concentration by the urine creatinine concentration, urine osmolality, or specific gravity (Araki
6 etal., 1990).
7 The measurement of lead excreted in urine following an injection (intravenous or
8 intramuscular) of the chelating agent calcium disodium EDTA (EDTA provocation) has been
9 used to detect elevated body burden of lead in adults (Biagini et al., 1977; Lilis et al., 1968;
10 Wedeen, 1992; Wedeen et al., 1975) and children (Chisolm et al., 1976; Markowitz and Rosen,
11 1981). EDTA-provoked urinary lead excretion has been shown to correlate with tibia bone lead
12 measurements (Wedeen, 1992). Given the difficulties associated with the parenteral
13 administration of EDTA, XRF measurements of bone lead, offer a more feasible alternative to
14 the EDTA provocation test for assessment of bone lead stores in epidemiologic studies. More
15 recently, DMSA (DMSA-provocation) has been used as an orally-effective alternative to EDTA
16 and has been applied to epidemiologic studies as dose metric for lead body burden (e.g., Lee
17 et al., 2001; Schwartz et al., 2001, 2000a,b).
18
19 4.3.4.6 Summary of Urine Lead as a Biomarker of Lead Body Burden and Exposure
20 Similar to blood lead concentration measurements, urinary lead excretion measured in an
21 individual at a single point in time will reflect the recent exposure history of the individual and
22 physiological variables that determine the plasma lead concentration time profile. As a result,
23 measurement of urinary lead may serve as a more feasible surrogate for plasma lead
24 concentration, and may be useful for exploring dose-response relationships for effect outcomes
25 that may be more strongly associated with plasma lead concentration than lead body burden.
26 Longitudinal measurements of urinary lead excretion can be expected to provide a more reliable
27 measure of exposure history of an individual and will more closely parallel body burden than
28 will single measurements; however, the degree to which this will apply will depend on the
29 sampling frequency with respect to the exposure temporal pattern.
30 Although, in general, higher urinary lead excretion can be interpreted as indicating higher
31 exposures (or lead uptakes), it does not necessarily predict appreciably higher body burdens.
May 2006 4-61 DRAFT-DO NOT QUOTE OR CITE
-------
1 Similar urinary lead excretion rates in two individuals (or populations) do not necessarily
2 translate to similar body burdens or similar exposure histories.
3 Measurement of the urinary lead excretion rate requires either a timed urine sample, or an
4 approach to adjusting measured urinary lead concentrations for variability in urine flow rate,
5 which by itself may be affected by lead exposure (i.e., lead-induced nephrotoxicity). Both
6 approaches, timed urine samples or adjustment of concentration, introduce complications into the
7 assessment and uncertainties into the interpretation of urinary lead measurements as biomarkers
8 of lead body burden or exposure. The EDTA-provocation test provides a more reliable indicator
9 of elevated body burden than do measurements of basal lead excretion; however, it is not feasible
10 to apply this test for epidemiologic investigations. The DMSA-provocation test may provide a
11 more feasible alternative.
12
13 4.3.5 Lead in Hair
14 4.3.5.1 Summary of Key Findings from the 1986 Lead AQCD
15 The 1986 Lead AQCD did not discuss applications of hair lead measurements for
16 assessing lead body burden or exposure.
17
18 4.3.5.2 Analytical Methods for Measuring Lead in Hair
19 Methods used for hair lead analysis are summarized in Annex Table AX4-2.1. Wilhelm
20 et al. (1989) reported a detection limit of 0.16 |ig/g for GFAAS; use of GFAAS for hair lead
21 measurements has been reported elsewhere (Annesi-Maesano et al., 2003). Gerhardsson et al.
22 (1995a) reported a detection limit of 0.5 jig/g for XRF of the hair shaft; but Campbell and
23 Toribara (2001) found XRF to be unreliable for hair root lead determinations. Use of other
24 methods has been reported, including ICP (Tuthill, 1996), ET/AAS (Drasch et al., 1997), and
25 AAS (Sharma and Reutergardh, 2000; Esteban et al., 1999).
26
27 4.3.5.3 Levels of Lead in Hair
28 A summary of selected measurements of hair lead levels in humans can be found in
29 Annex Table AX4-2.12. Reported hair lead levels vary considerably. Esteban et al. (1999)
30 reported a geometric mean levels of 5.4 ng/g (range 1-39) for a sample of 189 children (aged
31 1.9 to 10.6 years) residing in Russian towns impacted by smelter and battery plant operations.
May 2006 4-62 DRAFT-DO NOT QUOTE OR CITE
-------
1 By contrast, Tuthill (1996) reported much higher levels in a sample of Boston, MA children
2 (aged 6.5 to 7.5 years, n = 277). Approximately 41% had levels that ranged from 1 to 1.9 |ig/g.
3 DiPietro et al. (1989) reported a geometric mean hair lead level of 2.42 jig/g (10-90th percentile
4 range <1.0-10.8) in a general population sample of U.S. adults (aged 20 to 73 years, n = 270).
5 In a post-mortem sample of the general population from Germany (aged 16 to 93 years, n = 150),
6 the median hair lead level was 0.76 jig/g (range 0.026-20.6) (Drasch et al., 1997). Also,
7 Gerhardsson et al. (1995a) reported median values for postmortem samples of 8.0 jig/g (range
8 1.5-29,000) in active workers (n = 6), 2.6 |ig/g (range 0.6-9.3) in retired workers (n = 23), and
9 2.1 |ig/g (range 0.3-96) in a reference group (n = 10).
10
11 4.3.5.4 Hair Lead as a Biomarker of Lead Body Burden
12 Lead is incorporated into human hair and hair roots (Bos et al., 1985; Rabinowitz et al.,
13 1976) and has been explored as a possibly noninvasive approach for estimating lead body burden
14 (Gerhardsson et al., 1995a; Wilhelm et al., 1989, 2002). Hair lead measurements are subject to
15 error from contamination of the surface with environmental lead and contaminants in artificial
16 hair treatments (i.e., dyeing, bleaching, permanents) and are a relatively poor predictor of blood
17 lead concentrations, particularly at low levels (<12 |ig/dL) (Campbell and Toribara, 2001;
18 Drasch et al., 1997; Esteban et al., 1999). Studies evaluating quantitative relationships between
19 hair lead and lead body burden have not been reported. Nevertheless, hair lead levels have been
20 used as a dose metric in some epidemiologic studies (e.g., Annesi-Maesano et al., 2003; Esteban
21 et al., 1999; Gerhardsson et al., 1995a; Powell et al., 1995; Sharma and Reutergardh, 2000;
22 Tuthill, 1996).
23
24 4.3.5.5 Hair Lead as a Biomarker of Lead Exposure
25 Rabinowitz et al. (1976) measured hair lead levels in two adult males who received
26 a stable lead isotope supplement to their dietary intake for 124-185 days. Approximately 1% of
27 the daily lead intake was recovered in hair. Temporal relationships between exposure levels and
28 kinetics and hair lead levels, and kinetics of deposition and retention of lead in hair have not
29 been evaluated. Higher hair lead levels were observed in lead workers than in reference subjects
30 with lower blood lead levels (Mortada et al., 2001).
31
May 2006 4-63 DRAFT-DO NOT QUOTE OR CITE
-------
1 4.3.5.6 Summary of Hair Lead as a Biomarker of Lead Body Burden and Exposure
2 Although hair lead measurements have been used in some epidemiologic studies, an
3 empirical basis for interpreting hair lead measurements in terms of body burden or exposure has
4 not been firmly established. Hair lead measurements are subject to error from contamination of
5 the surface with environmental lead and contaminants in artificial hair treatments (i.e., dyeing,
6 bleaching, permanents) and, as such, are relatively poor predictor of blood lead concentration,
7 particularly at low levels (<12 |ig/dL).
10 4.4 MODELING LEAD EXPOSURE AND TISSUE DISTRIBUTION
11 OF LEAD
12 4.4.1 Introduction
13 Models are essential for quantifying human health risks that derive from exposures to
14 lead. Models come in various forms. Multivariate regression models, commonly used in
15 epidemiology, provide estimates of the contribution of variance in the internal dose metric to
16 various determinants or control variables (e.g., surface dust lead concentration, air lead
17 concentration). Structural equation modeling links several regression models together to
18 estimate the influence of determinants on the internal dose metric. Regression models can
19 provide estimates of the rate of change of blood or bone lead concentration in response to an
20 incremental change in exposure level (i.e., slope factor). A strength of regression models is that
21 they are empirically verified within the domain of observation and have quantitative estimates of
22 uncertainty imbedded in the model structure. However, regression models are based on (and
23 require) paired predictor-outcome data, and, therefore, the resulting predictions are confined to
24 the domain of observations. Regression models also frequently exclude numerous parameters
25 that are known to influence human lead exposures (e.g., soil and dust ingestion rates) and the
26 relationship between human exposure and tissue lead levels, parameters which are expected to
27 vary spatially and temporally. Thus, extrapolation of regression models to other spatial or
28 temporal contexts, which is often necessary for regulatory applications of the models, can be
29 problematic.
30 An alternative to regression models are mechanistic models, which attempt to specify all
31 parameters needed to describe the mechanisms (or processes) of transfer of lead from the
May 2006 4-64 DRAFT-DO NOT QUOTE OR CITE
-------
1 environment to human tissues. Such mechanistic models more complex than regression models;
2 this added complexity introduces challenges in terms of their mathematical solution and
3 empirical verification. However, by incorporating parameters that can be expected to vary
4 spatially or temporally, or across individuals or populations, mechanistic models can be
5 extrapolated to a wide range of exposure scenarios, including those that may be outside of
6 domain of paired predictor-outcome data used to develop the model. Exposure-intake models, a
7 type of mechanistic models, are highly simplified mathematical representations of relationships
8 between levels of lead in environmental media and human lead intakes (e.g., jig lead ingested per
9 day). These models include parameters representing processes of lead transfer between
10 environmental media (e.g., air to surface dust) and to humans, including rates of human contact
11 with the media and intakes of the media (e.g., g soil ingested per day). Intake-biokinetic models
12 provide the analogous mathematical representation of relationships between lead intakes and
13 levels of lead in body tissues (e.g., blood lead concentration); and they include parameters that
14 represent processes of lead transfer (a) from portals of entry into the body and (b) from blood to
15 tissues and excreta. Linked together, exposure-intake and intake-biokinetics models (i.e.,
16 integrated exposure-intake-biokinetics models) provide an approach for predicting blood lead
17 concentrations (or lead concentrations in other tissues) that corresponds to a specified exposure
18 (medium, level, and duration). Detailed information on exposure and internal dose can be
19 obtained from controlled experiments, but almost never from epidemiological observations or
20 from public health monitoring programs. Exposure intake-biokinetics models can provide these
21 predictions in the absence of complete information on the exposure history and blood lead
22 concentrations for an individual (or population) of interest. Therefore, these models are critical
23 to applying epidemiologically-based information on blood lead-response relationships to the
24 quantification and characterization of human health risk. They are also critical for assessing the
25 potential impacts of public health programs directed at mitigation of lead exposure or of
26 remediation of contaminated sites.
27 Models (both regression models and mechanistic models) also have several other
28 important features that are useful for risk assessment and for improving our basic understanding
29 of lead exposures and biokinetics. They organize complex information on lead exposure and
30 biokinetics into a form that provides predictions that can be quantitatively compared to
31 observations. By analyzing the relationships between model assumptions and predictions (i.e.,
May 2006 4-65 DRAFT-DO NOT QUOTE OR CITE
-------
1 sensitivity analysis), and by comparing predictions to observations (i.e., model evaluation), such
2 models can contribute to the identification of important gaps in our understanding of lead
3 exposure, biokinetics, and risk. Thus, these models provide a consistent method for making,
4 evaluating and improving predictions that support risk assessment and risk management
5 decisions.
6 Modeling of human lead exposures and biokinetics has advanced considerably during the
7 past several decades. Among the most important new advances are development, evaluation, and
8 extensive application of the Integrated Exposure Uptake Biokinetic (IEUBK) Model for Lead in
9 Children (U.S. Environmental Protection Agency, 1994a) and the development of models that
10 simulate lead biokinetics in humans from birth through adulthood (Leggett, 1993; O'Flaherty
11 1993, 1995). While these developments represent important conceptual advances, several
12 challenges remain for further advancements in modeling and applications to risk assessment.
13 The greatest challenge derives from the complexity of the models. Human exposure-biokinetics
14 models include large numbers of parameters, which are required to describe the many processes
15 that contribute to lead intake, absorption, distribution, and excretion. The large number of
16 parameters complicates the assessment of confidence in parameter values, many of which cannot
17 be directly measured. Statistical procedures can be used to evaluate the degree to which model
18 outputs conform to "real-world" observations and values of influential parameters can be
19 statistically estimated to achieve good agreement with observations. Still, large uncertainty can
20 be expected to remain about many, or even most, parameters in complex exposure-biokinetic
21 models such as those described below. Such uncertainties need to be identified and their impacts
22 on model predictions quantified (i.e., through use of sensitivity analysis, probabilistic methods).
23 Given the difficulty in quantitatively assessing uncertainty in values of all of the
24 individual parameters in an exposure-biokinetics model, assurance that the model accurately
25 represents the real-world in all aspects is virtually impossible. As consequence of this, Oreskes
26 (1998) noted, "... the goals of scientists working in a regulatory context should be not validation
27 but evaluation, and where necessary, modification and even rejection. Evaluation implies an
28 assessment in which both positive and negative results are possible, and where the grounds on
29 which a model is declared, good enough are clearly articulated. " In this context, evaluation of
30 confidence in a given exposure-intake or intake-biokinetics model rests largely on assessment of
31 the degree to which model predictions, based on model inputs appropriate for a situation,
May 2006 4-66 DRAFT-DO NOT QUOTE OR CITE
-------
1 conform to observations and/or expectations; and, most importantly, the degree to which this
2 conformity does or does not satisfy requirements of model application to a specific context.
3 Because of limitations in observations of predicted outcomes, it may be possible to evaluate
4 confidence in some uses of a model, but not others. Similarly, it is possible for confidence in a
5 model to be judged acceptable for a given use, but not for others. The concept of validation of
6 highly complex mechanistic models, outside of the context of a specific use of the model, has
7 little meaning.
8 In the ensuing discussion of specific models, reported efforts to evaluate the models are
9 noted. In most cases, however, the relevance of these evaluations to the assessment of
10 confidence in a specific use of that model (e.g., predicting average blood lead concentrations in
11 children who live in areas that have certain cross-sectionally measured environmental lead
12 levels) cannot be ascertained from the reported literature. Nevertheless, as a framework for
13 qualitatively comparing the various evaluative procedures that have been applied, the following
14 general classification of model evaluations has been adopted:
15 • Sensitivity analysis has been conducted and most influential parameters identified and
16 uncertainty characterized.
17 • Model predictions have been compared qualitatively to observations.
18 • Predictions have been compared quantitatively to observations (i.e., a statistical model
19 has been applied for estimation of "goodness of fit" and uncertainty).
20 • Confidence in model predictions for specific uses has been quantitatively evaluated.
21 • Accuracy of model implementation code has been verified.
22 Descriptions of the individual models are intended to provide only brief snapshots of key
23 features of each model, with particular attention to conceptual features that are unique to each
24 model. Key references are cited in which more complete specifications of model parameters can
25 be found.
26
27 4.4.2 Empirical Models of Lead Exposure Blood Lead Relationships
28 The 1986 Lead AQCD described epidemiological studies that explored models of
29 relationships between lead exposures and blood lead concentrations in children. A more recent
30 summary of this literature can be found in Abadin et al. (1997). Key studies reported since the
May 2006 4-67 DRAFT-DO NOT QUOTE OR CITE
-------
1 completion of the 1986 Lead AQCD are summarized here. Although varying widely in exposure
2 scenarios, blood lead concentration ranges, and modeling approaches, most studies have found
3 significant associations between surface dust lead levels (interior and exterior) and blood lead
4 concentrations. These outcomes support the general concept that contact with lead in surface
5 dust (e.g., surface dust-to-hand-to-mouth) is a major contributor to lead intake in children.
6 TerraGraphics (2000) conducted an analysis of data on environmental lead levels and
7 child blood lead concentrations in children, as part of a 5-year review of the clean-up at the
8 Bunker Hill Superfund site, a former lead mining and smelting site. The analysis included
9 -4,000 observations of blood lead concentrations in children between the ages of 9 months and
10 9 years of age, collected over an 11-year period (1988-1999). The number of children for which
11 blood lead concentrations were available each year ranged from 230 in 1988 to 445 in 1993;
12 -54 to 88% of the child population was sampled each year. Blood lead concentrations (annual
13 geometric mean) ranged from 4.4 to 9.9 |ig/dL. Environmental lead levels (e.g., dust, soil, paint
14 lead levels) data were collected at -1300 residences. Interior dust lead concentrations (annual
15 geometric mean) ranged from -400 to 4200 ppm. Yard soil lead concentration (annual
16 geometric mean) ranged from -100 to 2600 ppm. Several multivariate regression models
17 relating environmental lead levels and blood lead concentration were explored; the model having
18 the highest R2 (0.23) is shown in Table 4-5. The model predicts significant associations between
19 blood lead concentration, and the (natural log-transformed) community soil lead concentration (P
20 = 1.76), neighborhood soil lead concentration (P = 0.73; geometric mean soil lead concentration
21 for areas within 200 ft of the residence), or interior dust lead concentration (P = 0.84). The
22 model predicted a 1.2 |ig/dL decrease in blood lead concentration in association with a decrease
23 in community soil lead concentration from 2000 to 1000 ppm. The same decrease in
24 neighborhood soil lead concentration, or interior dust lead concentration, was predicted to result
25 in a 0.5 or 0.6 |ig/dL decrease in blood lead concentration, respectively. Regression models (R2
26 = 0.86 to 0.94), based on repeated blood lead measurements made on the same children from this
27 data set, predicted much stronger associations between current blood lead concentration and the
28 blood lead concentration measured in the previous year (P = 0.62) for the same child; than to the
29 corresponding community soil lead concentration (P = 0.095) or interior dust lead concentration
30 (P = 0.1). Structural equation modeling was applied to the larger data set, utilizing the model
31 structures shown in Figure 4-12. Model 1 included a direct pathway
May 2006 4-68 DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-5. General Linear Model Relating Blood Lead Concentration in Children and
Environmental Lead Levels—Bunker Hill Superfund Site
Parameter
Intercept
Age (years)
/^(interior dust lead) (ppm)
/w(yard soil lead) (ppm)
ln(GM soil lead within 200 ft of
residence) (ppm)
ln(GM community soil lead) (ppm)
Coefficient
-0.22877
-0.44803
0.83723
0.21461
0.73100
1.76000
P>F
0.7947
0.0001
0.0001
0.0080
0.0001
0.0001
Standardized
Coefficient
0.00000
-0.25541
0.15677
0.06466
0.12938
0.19709
R2 = 0.231; p < 0.0001; based on data from Bunker Hill Superfund Site collected over the period 1988-1999
GM, geometric mean; In, natural log
Source: TerraGraphics (2000).
1 connecting community soil lead to blood lead. Both models yielded similar R values (0.89) and
2 predicted a relatively large influence of interior dust lead on blood lead (Tables 4-6 and 4-7).
3 A subsequent analysis was conducted of paired environmental lead and blood lead
4 concentrations in children (n = 126, ages 9 months to 9 years), collected during 1996 to 1998 at
5 various locations in the Coeur d'Alene Basin (outside of the Bunker Hill Site, TerraGraphics,
6 2001). Blood lead concentrations (annual geometric mean) for the study area was approximately
7 4 |ig/dL. The blood lead concentration range of individuals included in the regression analysis
8 was ~1 to 23 |ig/dL, and yard soil lead concentrations ranged from <100 to 7350 ppm. A model
9 that included all significant (p < 0.05) variables is presented in Table 4-8. The model predicted a
10 0.7 |ig/dL decrease in blood lead concentration per 1000 ppm decrease in exterior soil lead, and a
11 0.16 |ig/dL decrease in blood lead concentration per 1 mg/cm2/day decrease in entryway dust
12 lead loading rate. Entryway dust lead loading rate was estimated from measurements of the
13 amount of lead (and dust) recovered from doormats placed at each residence for and known
14 duration. Regression models (general linear model) relating entryway mat lead loading rate,
15 or mat lead concentration, and environmental variables were also developed. The strongest
16 predictor of both outcome variables (natural log-transformed) was soil lead concentration
May 2006
4-69
DRAFT-DO NOT QUOTE OR CITE
-------
Yard
Soil Lead
Neighborhood
Soil Lead
Community
Soil Lead
Age
Figure 4-12. Structural equation model for relationships between dust and soil lead and
blood lead concentration in children, based on data collected at the Bunker
Hill Superfund Site (1988-1999). Neighborhood soil lead is represented in
the model as the mean soil lead within 200 feet of the residence, whereas
community soil lead is the mean for the city. The pathway between
community soil lead and blood lead was included in model 1 and excluded
form model 2. Units: blood lead, ug/dL; dust and soil lead (ug/g); age, years.
See Tables 4-6 and 4-7 for estimated regression coefficients.
Source: TerraGraphics et al. (2000).
1 (natural log-transformed, P: -0.4; R2 = 0.36-0.46). Lanphear et al. (1998) conducted a pooled
2 analysis of data on environmental lead levels and blood lead concentrations in children
3 (n = 1861) collected as part of 12 epidemiologic studies (conducted over a 15-year period, from
4 1982 to 1997). Seven of the studies were of communities near lead mining and/or smelting sites
5 (Bingham Creek, UT; Butte, MT; Leadville, CO; Magna, UT; Midvale, UT; Palmerton, PA;
6 Sandy, UT); and 5 studies were of urban communities (2 in Boston, MA; 2 in Cincinnati, OH;
7 Rochester, NY). The mean age of children included in the analysis was 16 months; the inter-
8 study range was 6 to 24 months. The geometric mean blood lead concentration for the subjects
9 in the pooled analysis was 5.1 |ig/dL; 95% were within the range 1.2 to 26 |ig/dL and 19% were
10 10 |ig/dL. The geometric mean interior dust lead loading was 13.5 jig/ft2 (95% range: 1 to
May 2006
4-70
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-6. Structural Equation Model (1) Relating Blood Lead Concentration in
Children and Environmental Lead Levels—Bunker Hill Superfund Site
1
2
O
4
5
Parameter
Coefficient
Model for ln(blood lead)
Error
Intercept
Age (years)
/^(interior dust lead) (ppm)
/w(yard soil lead) (ppm)
/w(AM soil lead within 200 ft of
residence) (ppm)
/w(AM community soil lead) (ppm)
Model for
Error
Intercept
/w(yard soil lead) (ppm)
/w(AM soil lead within 200 ft of
residence) (ppm)
/w(AM community soil lead) (ppm)
1.000
-0.519
-0.065
0.159
0.051
0.067
0.095
P>F
(Hg/dL): R2 =
-D
0.05
0.05
0.05
0.05
0.05
0.05
In (Interior dust lead) (ppm): R2
1.000
3.237
0.129
0.133
0.235
-D
0.05
0.05
0.05
0.05
Standardized
Coefficient
0.892
0.329
-0.171
-0.210
0.597
0.171
0.267
0.389
= 0.986
0.117
0.487
0.114
0.141
0.256
Contribution
(%)'
-D
-D
-D
42
12
19
27
-D
-D
22
28
50
Based on data from the Bunker Hill Superfund Site collected over the period 1988 to 1999.
Largest standardized residual, 0.183; Chi-Square, 21.309; P, 0.0001; Comparative fit index, 0.9993;
Normed fit index, 0.9993; Non-normed fit index, 0.9863.
GM, geometric mean; In, natural log
aBased on sum of standardized coefficients for dust and soil lead parameters.
Source: TerraGraphics (2000).
4500 |ig/ft2) and geometric mean exterior soil or surface dust lead level was 508 ppm (95%
range: 8 to 10,200 ppm). A regression model was developed relating natural log-transformed
blood lead concentration to log-transformed environmental lead variables, and categorical
demographic or behavioral variables (Table 4-9). The R2 for the final model was 0.53
(uncorrected for measurement error). Measurement error was included in the model as variance
6 estimates for each environmental lead variable as follows (log-transformed values): dust lead
7 loading, 1.00; exterior lead concentration, 1.00; water lead concentration, 0.75; maximum XRF,
May 2006
4-71
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-7. Structural Equation Model (2) Relating Blood Lead Concentration in
Children and Environmental Lead Levels—Bunker Hill Superfund Site
Parameter
Error
Intercept
Age (years)
/^(interior dust lead) (ppm)
/w(yard soil lead) (ppm)
ln(AM soil lead within 200
residence) (ppm)
Coefficient
Model for ln(blood lead)
1.000
-0.206
-0.064
0.165
0.051
ft of 0.115
P>F
(Hg/dL): R2 =
C
0.05
0.05
0.05
0.05
0.05
Model for In (interior dust lead) (ppm): R2
Error
Intercept
/w(yard soil lead) (ppm)
ln(AM soil lead within 200
residence) (ppm)
1.000
3.237
0.129
ft of 0.133
ln(AM community soil lead) (ppm) 0.235
—
0.05
0.05
0.05
0.05
Standardized
Coefficient
0.892
0.329
-0.116
-0.208
0.619
0.171
0.456
= 0.986
0.117
0.487
0.114
0.141
0.256
Contribution
(%)'
C
C
C
53
14
37
—
—
22
28
50
Based on data from the Bunker Hill Superfund Site collected over the period 1988 to 1999.
Largest standardized residual, 0.183; Chi-Square, 21.309; P, 0.0001; Comparative fit index, 0.9993;
Normed fit index, 0.9993; Non-normed fit index, 0.9863.
AM, arithmetic mean; In, natural log.
aBased on sum of standardized coefficients for dust and soil lead parameters.
Source: TerraGraphics (2000).
1 0.75. Of the model variables listed above, significant variables (p < 0.05, after correction for
2 measurement error) were as follows: interior dust lead loading (P = 0.183, p < 0.0001), exterior
3 soil/dust lead (P = 0.02116, p = 0.00025), age (P = 0.02126, p = 0.0044), mouthing behavior
4 (P = -0.0323, p = 0.0004), and race (P = 0.123, p = 0.0079). Significant interactions in the
5 model included: age and dust lead loading, mouthing behavior and exterior soil/dust level, and
6 SES and water lead level. Predicted relationships between interior dust lead loading or exterior
7 lead concentrations and blood lead concentration are shown in Tables 4-10 and 4-11. The model
8 predicted a geometric mean blood lead concentration of 4.0 |ig/dL (4% probability of
May 2006 4-72 DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-8. General Linear Model Relating Blood Lead Concentration in Children and
Environmental Lead Levels—Coeur d'Alene Basin
Parameter
Intercept
Age (years)
Soil lead (ppm)
Entryway (mat) lead loading rate
(mg/cm2/day)
Median exterior paint lead (mg/cm2)
Minimum interior paint condition
(categorical: 1-3)
Coefficient
2.8644
-0.3351
0.0007
0.1638
0.5176
1.9230
P>F
0.0032
0.0007
0.0012
0.0006
0.0005
0.0008
Standardized
Coefficient
0.00000
-0.2056
0.2249
0.3212
0.2742
0.2313
N: 126 (ages 9 mo to 9 years), R2 = 0.597, p < 0.0001; based on data from the Coeur d'Alene Basin collected
over the period 1996 to 1999.
Source: TerraGraphics (2001).
1 exceeding 10 |ig/dL) assuming the study median environmental lead levels to be as follows: dust
2 lead, 5.0 |ig/ft2; soil lead, 72 ppm; maximum interior paint lead, 1.6 mg/cm2; water lead, 1 ppb.
3 Succop et al. (1998) conducted a meta-analysis of relationships between environmental
4 lead levels and blood lead concentrations in children (n = 1855, age <72 months) based on data
5 collected in 11 epidemiologic studies (conducted over a 13-year period, 1981 to 1994). All but
6 2 of the studies (Cincinnati prospective study, 1981 to 1985; Cincinnati soil lead study, 1989 to
7 1991) were of communities near lead mining and/or smelting sites (Bingham Creek, UT; Butte,
8 MT; Leadville, CO; Magna, UT; Midvale, UT; Palmerton, PA; Sandy, UT; Telluride, CO; Trail,
9 B.C.). The inter-study age range was 15 to 39 months, and inter-study range of the geometric
10 mean blood lead concentration was 2.6 to 12.9 |ig/dL; 7.5% of children were > 10 |ig/dL. The
11 inter-study geometric mean ranges were: interior dust lead loading, 31 to 976 |ig/m2; interior
12 dust lead concentration, 110 to 1548 ppm; handwipe lead, 2 to 9 jig; exterior entry dust lead
13 concentration, 72 to 1830 ppm. Structural equation modeling was applied to the data from each
14 study. The same generic model was applied initially to each dataset, followed by backward
15 elimination of pathways and co-variables until a model for each study evolved in which all
16 predictors and co-variables were significant (p < 0.05). The generic model is shown in
17 Figure 4-13 along with the percent of studies in which a given pathway was found to be
May 2006 4-73 DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-9. Multivariate Regression Model Relating Blood Lead Concentration in
Children and Environmental Lead Levels - Multi-Study Pooled Analysis
Parameter
Intercept
Dust lead loading (ug/ft2)
Water lead (ppb)
Soil or exterior dust lead (ppm)
Soil or exterior exposure dust lead * type of
sample
Soil or exterior exposure dust lead*type of
sample*location
Type of exterior exposure sample
Soil or exterior exposure dust location
Paint lead content (mg/cm3)
CLN(MAX XRF) * paint condition
Paint condition
Age
Age 2
Age 3
Study
Race
Level
Boston
Butte
Bingham Creek
Cincinnati Program
Cincinnati Soil
Leadville
Magna
Rochester
Longitudinal
Rochester LID Study
Sandy
Midvale
Palmerton
Other
White
Estimate
1.496
0.183
0.01398
0.02116
0.005787
0.4802
-0.1336
0.5858
-0.02199
0.03811
-0.0808
0.02126
-0.001399
0.00007854
-0.3932
-0.01167
0.2027
0.2392
0.5383
0.05717
0.1761
-0.04209
0.07257
-0.3712
0.1777
0
0.123
0
P-value
0.0001
0.2067
0.0025
0.9247
0.0409
0.2805
0.0455
0.3402
0.3888
0.1685
O.0001
0.0044
0.0022
O.OOOla
0.0079a
May 2006
4-74
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-9. (cont'd). Multivariate Regression Model Relating Blood Lead Concentration
in Children and Environmental Lead Levels - Multi-study Pooled Analysis
Parameter
Socioeconomic status (SES)
Mouthing behavior
Dust lead loading * Age
Dust lead loading * Age 2
Dust lead loading * Age 3
Exterior lead exposure * mouthing behavior
Water lead levels (ppb) * SES
Age * race
Age * SES
Standard deviation of the prediction error
Level
1
2
3
4
5
Often
Rarely
Sometimes
Unknown
Often
Rarely
Sometimes
Unknown
1
2
3
4
5
Other
White
1
2
3
4
5
Estimate
0.3175
0.2138
0.1799
0.1691
0
-0.03233
-0.2454
-0.1397
0
0.002649
-0.0003381
-0.00001281
0.2212
0.07892
0.1663
0
0.5305
-0.0136
0.1033
-0.09098
0
0.01192
0
-0.01023
0.003849
0.00008468
-0.01679
0
0.5425
P-value
O.lOSla
0.0004a
0.1860
0.0573
0.6185
0.0419a
0.0998a
0.0129a
0.0061a
Interactions are indicated by asterisks. Blood lead concentration (ug/dL) and all environmental lead variables
were natural log-transformed. R2 for blood lead concentration was 0.53 (uncorrected for measurement error).
aOverall factor significance.
Source: Lanphearetal. (1998).
May 2006
4-75
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-10. Children's Predicted Blood Lead Levels for Floor Dust Lead Loading
(ug/ft2) and Exterior Lead Exposures (ppm)a
Geometric mean blood lead levels (jig/dL) with 90% Confidence Intervals
Dust lead
loading
(Jig/ft2)
1
5
10
15
20
25
40
55
70
100
a in parentheses
Exterior lead exposure (ppm)
10
2.3
(0.9, 5.7)
3.2
(1.3,8.0)
3.7
(1.5,9.2)
4.0
(1.6,10.0)
4.2
(1.7,10.6)
4.4
(1.8,11.2)
4.9
(1.9,12.3)
5.2
(2.1,13.2)
5.5
(2.2, 13.8)
5.9
(2.3, 14.9)
72"
2.8
(1.1,7.0)
4.0
(1.6,9.8)
4.6
(1.8,11.3)
5.0
(2.0, 12.3)
5.3
(2.1,13.0)
5.5
(2.2, 13.6)
6.1
(2.4, 15.0)
6.5
(2.6, 16.1)
6.8
(2.7, 16.9)
7.3
(2.9, 18.2)
100
2.9
(1.2,7.3)
4.1
(1.7,10.1)
4.7
(1.9,11.7)
5.1
(2.1, 12.7)
5.4
(2.2, 13.5)
5.7
(2.3, 14.1)
6.3
(2.5, 15.6)
6.7
(2.7, 16.6)
7.0
(2.8, 17.5)
7.6
(3.1,18.9)
500
3.5
(1.4,8.7)
4.9
(2.0, 12.0)
5.6
(2.3, 13.9)
6.1
(2.5,15.1)
6.5
(2.6, 16.0)
6.8
(2.8, 16.8)
7.5
(3.0, 18.5)
8.0
(3.2, 19.7)
8.4
(3.4,20.7)
9.0
(3.7,22.3)
1000
3.8
(1.5,9.4)
5.3
(2.1,13.0)
6.1
(2.5, 15.0)
6.6
(2.7, 16.3)
7.0
(2.8, 17.3)
7.3
(3.0,18.1)
8.1
(3.3, 19.9)
8.6
(3.5,21.3)
9.1
(3.7,22.3)
9.7
(3.9,24.1)
1500
4.0
(1.6,9.8)
5.5
(2.2, 13.6)
6.3
(2.6, 15.7)
6.9
(2.8, 17.0)
7.3
(3.0, 18.0)
7.7
(3.1,18.9)
8.4
(3.4,20.8)
9.0
(3.7,22.2)
9.5
(3.8,23.4)
10.2
(4.1,25.2)
2000
4.1
(1.6,10.1)
5.7
(2.3, 14.0)
6.5
(2.7, 16.2)
7.1
(2.9, 17.6)
7.6
(3.1,18.6)
7.9
(3.2, 19.5)
8.7
(3.5,21.5)
9.3
(3.8,22.9)
9.8
(4.0,24.1)
10.5
(4.3,26.0)
4000
4.4
(1.8,11.0)
6.1
(2.5, 15.2)
7.1
(2.9, 17.5)
7.7
(3.1,19.0)
8.1
(3.3,20.1)
8.5
(3.5,21.1)
9.4
(3.8,23.2)
10.0
(4.1,24.8)
10.5
(4.3,26.0)
11.3
(4.6,28.0)
Confidence interval is estimated to cover 90% of the observed blood lead levels with 5% above and 5% below the interval.
bEstimated median levels based on U.S. Housing and Urban Development national survey, 1989-1990
Source: Lanphear et al. (1998).
1 significant. The most common exposure pathway influencing blood lead concentration (i.e.,
2 significant in models of most studies) was exterior soil, operating through its effect on interior
3 dust lead and hand lead. Paint lead was also a significant influential variable on the soil and
4 interior dust-to-blood pathway in -40% of the studies. Significant co-variables varied across
5 studies and included: child age, mouthing frequency, time spent outdoors, SES, house age and
6 condition, home renovation, parental occupation, bare soil in yard, and presence of pets.
7 The relative strength of the influence of various environmental sources of lead in the structural
8 equation model, on blood lead concentration, was evaluated by applying a simple linear
9
May 2006
4-76
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-11. Likelihood of a Child's Blood Lead >10 ug/dL for Floor Dust Lead Loadings
and Exterior Exposure Levels (ppm)a
Probability of blood lead greater than 10 ug/dL
Dust lead
loading
(Jig/ft2)
1
5
10
15
20
25
40
55
70
100
Exterior lead exposure (ppm)
10
0.33%
(0.05,2.24)
1.8%
(0.4, 7.9)
3.3%
(0.8, 12.6)
4.5%
(1.2,16.2)
5.7%
(1.5,19.2)
6.7%
(1.8,21.8)
9.4%
(2.7, 27.8)
12%
(3, 32)
13%
(4, 36)
17%
(5,41)
72"
1.0%
(0.3,3.8)
4.4%
(1.7,11.0)
7.4%
(3.1,16.5)
9.8%
(4.3,20.7)
12%
(5, 24)
14%
(6,27)
18%
(9, 33)
21%
(10,38)
24%
(12,42)
28%
(14,48)
100
1.2%
(0.3,4.2)
5.0%
(2.0,11.8)
8.3%
(3.8, 17.5)
11%
(5,22)
13%
(6,25)
15%
(7,28)
20%
(10,35)
23%
(12,40)
26%
(14,44)
31%
(16,49)
500
2.7%
(0.9, 7.4)
9.3%
(4.7, 17.6)
14%
(8, 24)
18%
(11,29)
21%
(13,33)
24%
(15,36)
30%
(19,43)
34%
(22,48)
37%
(24, 52)
43%
(28, 58)
1000
3.7%
(1.3,9.7)
12%
(6,21)
18%
(10,29)
22%
(14, 34)
26%
(16,38)
28%
(18,41)
35%
(23, 48)
39%
(27, 53)
43%
(29, 57)
48%
(34, 63)
1500
4.4%
(1.6,
11.5)
14%
(7,24)
20%
(12, 32)
25%
(15,37)
28%
(18,41)
31%
(20, 45)
38%
(25, 52)
42%
(29, 57)
46%
(32, 60)
51%
(37, 66)
2000
4.9%
(1.8,
12.8)
15%
(8,26)
22%
(13,35)
27%
(16,40)
30%
(19,44)
33%
(22, 47)
40%
(27, 54)
45%
(31,59)
48%
(34, 63)
54%
(39, 68)
4000
6.5%
(2.3,
16.9)
18%
(9, 32)
26%
(15,41)
31%
(19,47)
35%
(22,51)
38%
(25, 54)
45%
(31,61)
50%
(35,65)
54%
(38, 69)
59%
(43, 73)
aAll other variables held at their national median.
bEstimated median levels based on U.S. Housing and Urban Development national survey, 1989 to 1990.
Source: Lanphear et al. (1998).
1 regression model to the geometric mean values for environmental variables (natural log-
2 transformed) and blood lead concentrations (natural log-transformed), from the individual
3 studies (Table 4-12). The strongest relationships were obtained for interior dust lead loading
4 ([P = 0.474, R2: 0.96] and handwipe lead [P = 1.184, R2 = 0.90]). The models predicted a
5 8.6 |ig/dL decline in blood lead concentration (from -15 |ig/dL) for a 1000 jig/cm2 reduction in
6 interior dust lead loading (from 1100 jig/cm2), and a 14.4 |ig/dL decline in blood lead
7 concentration (from 10 jig) for a 10 jig reduction in handwipe lead.
May 2006 4-77 DRAFT-DO NOT QUOTE OR CITE
-------
Figure 4-13. Structural equation model for relationships between dust and soil lead
and blood lead concentration in children. Numbers are the percentage of
11 studies included meta-analysis for which the pathway was significant
(p = 0.05). Units: blood lead, ug/dL; dust and soil lead, ug/g; handwipe
lead (jig); pant lead, mg/cm2
Source: Succopetal. (1998).
1 Lanphear and Roghmann (1997) collected data on blood lead concentrations in
2 205 children residing in Rochester, NY (1991-1992) paired with their residential environmental
3 lead levels. The mean age of the children was 20 months (range: 12 to 30 months). Mean blood
4 lead concentration was 7.7 |ig/dL (SD: 5.1); 23% of children had a blood lead concentration
5 > 10 |ig/dL. Geometric mean interior dust lead loading was 106 |ig/ft2 (+SD: 10, 1167) and soil
6 lead level was 981 ppm (+SD: 225, 4267). Data on the following variables were used for
7 structural equations modeling: serum ferritin (ng/dL), blood lead concentration (|ig/dL),
8 hand lead (jig), interior dust lead loading (jig/ft2), paint lead loading (XRF, mg/cm2), water lead
9 (ppb),soil lead (ppm), race, parent marital status, household income, maternal cleaning
10 behaviors, and child exposure behaviors (e.g., time spent outside, mouthing, dirt ingestion).
11 A structural equation model, shown in Figure 4-14, yielded an R2 of 0.41 for blood lead
12 concentration. The exposure pathway most influential on blood lead was interior dust lead
13 loading, directly or through its influence on hand lead. Both soil and paint lead influenced
May 2006
4-78
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-12. Meta-Analysis of the Relationship Between Log-Transformed Blood Lead and
Various Environmental Lead Sources3
Independent variable
In(handwipe lead)
In(interior dust lead loading)
In(interior dust lead loading)0
In(interior dust lead
concentration)
In(exterior entry dust lead
concentration)
In(perimeter soil lead
concentration)
In(maximum interior paint
lead loading)
In(maximum exterior paint
lead loading)
Units
ug
ug/m2
ug/m2
ppm
ppm
ppm
mg/cm2
mg/cm2
Intercept
0.009
-0.479
-0.782
-1.502
-1.101
-0.015
1.562
1.502
Slope
Estimate
1.184
0.444
0.474
0.529
0.435
0.233
0.232
0.152
Squared
Correlation
0.90
0.55
0.96
0.58
0.72
0.65
0.07
0.07
No. of
Studies
6
10
8
10
10
6
8
9
Predicted
Decline in
Blood Leadb
14.4
9.1
8.6
6.5
4.5
2.2
2.1
1.3
aThese are simple relationships unadjusted for covariates.
Predicted decline in blood lead for a reduction in hand lead of 10-1 ug; dust lead loading of 1100 to 100 ug/m2;
dust lead or soil lead concentration of 1100-100 ppm; or paint lead loading of 3.0-0.5 mg/cm2 as calculated from
the fitted linear regression equation: In(blood lead) = intercept + slope x In(environmental lead).
Excluding the Trail and Cincinnati soil project studies, which appear to be outliers. The exposure in these two
studies appears to be primarily from exterior dust lead.
Source: Succopetal. (1998).
1 interior dust lead; with the influence of paint lead greater than that of soil lead. Other influential
2 variables were Black race (direct), family income (direct), and outside play (indirect) through
3 dirt ingestion behavior. Simple correlation analysis also revealed relatively strong (significant,
4 p < 0.5) associations between dust lead loading (r = 0.41), soil lead concentration (0.31) and
5 Black race (r = 0.44).
6 Bornschein et al. (1985) applied structural equation modeling to paired environmental
7 lead and blood lead data collected on a subset of children (n = 45) from the Cincinnati
8 Prospective Study (1981-1985). The age range of children included in the study was 9 to
9 24 months. Group statistics for the blood lead concentrations of children included in the analysis
May 2006
4-79
DRAFT-DO NOT QUOTE OR CITE
-------
Interior
Paint Lead
0.414
Interior
Dust Lead
Black Race
Income
Soil
Lead
0.229
0.178
0.229
Handwipe
Dust Lead
0.221
0.319
-0.143
Plays
Outside
0.154
Blood
Lead
0.186
0.152
Eats Soil
Figure 4-14. Structural equation model for relationships between dust and soil lead
and blood lead concentration in children, based on data collected in the
Rochester (NY) Lead in Dust Study. Numbers are model coefficients.
Units: blood lead, ug/dL; dust lead ug/ft2; soil lead, ug/g; handwipe lead
(ug); pant lead, mg/cm2, plays outside, categorical: 0-1; eats soil, categorical:
0-1. R2 values: blood lead, 0.41; hand lead, 0.14; dust lead, 0.25.
Source: Lanphear and Roghmann (1997).
1 were not reported in Bornschein et al. (1985); however, a subsequent analysis of data from the
2 study reported a geometric mean of 12.9 |ig/dL (n = 149; Succop et al. 1998). Similarly, dust
3 and soil lead levels were not reported in Bornschein et al. (1985a), but were reported in Succop
4 et al. (1998) for a larger study group (n = 149) as follows (geometric means): interior dust lead
5 loading, 976 |ig/m2; interior dust lead concentration, 1548 ppm; handwipe lead, 7 jig; and
6 exterior entry dust lead concentration, 1830 ppm. A structural equation model (Bornschein et al.,
7 1985a), shown in Figure 4-15, yielded R2 values that ranged from 0.44 to 0.59 across age groups
8 from 9 (R2 = 0.59) to 24 months (R2 = 0.44). The exposure pathway most influential on blood
9 lead was interior dust lead concentration, directly or through its influence on hand lead (exterior
10 soil lead concentration and internal paint lead was excluded from the model, as was race). Blood
May 2006
4-80
DRAFT-DO NOT QUOTE OR CITE
-------
-1.07
Figure 4-15. Structural equation model for relationships between dust and soil lead and
blood lead concentration in children, based on data collected in the
Cincinnati (OH) Prospective Child Study. Numbers are model coefficients.
Units: blood lead, ug/dL; dust and soil lead, ug/g; handwipe lead (jug);
pant lead, mg/cm2; maternal involvement, categorical: 0-6; responsivity of
mother, categorical: 0-11; variety in daily stimulation, categorical: 0-5;
housing characteristics, categorical: 0-1. R2 values: blood lead, 0.41;
hand lead, 0.14; dust lead, 0.25.
Source: Bornschein et al. (1985a).
4
5
6
7
8
9
10
11
12
lead concentration was also influenced directly by SES. Interior dust lead loading was
influenced by housing condition variables. Hand dust was directly influenced by maternal
involvement with the child. Based on the above model, the relationship between blood lead
concentration, interior dust lead, and hand lead, at 18 months of age, was as follows:
PbB =1.94- 0.02(SES) + 0.\5(PbD) + 0.15(PbH) (4-4)
PbH = 0.52 - Q.36(material involvement) + 0.50(PbD) (4-5)
where PbB, PbD, PbH are the natural log-transformed blood lead concentration (jig/dL), dust
lead concentration (ppm), and hand lead (|ig), respectively. The above relationship predicts a
decline in blood lead concentration ranging from 8 |ig/dL (maternal involvement score, 6)
May 2006
4-81
DRAFT-DO NOT QUOTE OR CITE
-------
1 to 11 |ig/dL (maternal involvement score, 0), for a reduction in interior dust lead concentration
2 from 1100 ppm to 100 ppm (assuming SES score of 17, based on geometric mean reported for
3 the Cincinnati child study in Succop et al. 1998).
4 The Urban Soil Lead Abatement Demonstration Project (USLADP) was a study
5 conducted to determine if urban soil lead abatement would affect the lead exposures and blood
6 lead concentrations of urban children (U.S. EPA, 1996). The study included measurement of
7 blood lead concentrations and environmental lead prior to and following removal of lead-
8 contaminated soils and surface dusts from selected urban neighborhoods in Baltimore (Farrell,
9 1988), Boston (Aschengrau et al., 1994; Weitzman et al., 1993) and Cincinnati (Clark et al.,
10 1988, 1991, 1996). The numbers of children included in each study were -182 in the Baltimore
11 study, 92 in the Boston study, and 169 in the Cincinnati study. Pre-abatement blood lead
12 concentrations (geometric mean) were ~11 |ig/dL in the Baltimore study, 12 |ig/dL in the Boston
13 study, and 10 |ig/dL in the Cincinnati study. Pre-abatement soil and interior floor dust lead
14 concentrations (geometric mean), respectively, were -420 and 1700 ppm in the Baltimore study;
15 2300 and 2200 ppm in the Boston study; and 400 and 300 ppm in the Cincinnati study.
16 Measurements of paired environmental lead levels and blood lead concentrations provided the
17 basis for the development of regression models relating blood lead concentration to lead levels in
18 interior dust and exterior soil. An extensive analysis of the data collected in each study is
19 reported in U.S. EPA (1996), from which selected examples are provided here.
20 Structural equation modeling was applied to the data from the Boston and Cincinnati
21 studies; the generic model applied to these data is shown in Figure 4-16 and parameters for
22 selected models (based on cross-sectional data) are presented in Table 4-13. The model based on
23 the Cincinnati data showed a stronger association between interior dust lead and blood lead
24 concentration, compared to the model based on the data from the Boston study. Soil lead level
25 influenced blood lead concentration directly and secondarily, through its influence on interior
26 dust. Repeated measure models and longitudinal structural equation models were also developed
27 based on these data, and are described in detail in U.S. EPA (1996).
28
29
May 2006 4-82 DRAFT-DO NOT QUOTE OR CITE
-------
Window
Dust Lead
0.0656
Soil Lead
0.0756
0.046C
0.22C
Floor
Dust Lead
0.14B
4.10C
Blood
Lead
0.16B
0.28C
Figure 4-16. Structural equation model for relationships between dust and soil lead and
blood lead concentration in children, based on pre-abatement cross-sectional
data collected in the Urban Soil Lead Abatement Demonstration Project.
Numbers are model coefficients for the Boston study (B) or Cincinnati study
(C). Units: blood, ug/dL; dust, soil lead, ug/g; blood coefficient, ug/dL lead
in blood per 1000 ug/g lead in soil.
Source: U.S. Environmental Protection Agency (1996).
1 4.4.3 Historic Overview of Mechanistic Models of Lead Biokinetics
2 4.4.3.1 Rabinowitz Model
3 Early lead modeling applications presented lead biokinetics in classical pharmacokinetics
4 terms. Compartments represented kinetically homogeneous pools of lead which might be
5 associated with individual organs or groups of organs. Among the first of such models was one
6 proposed by Rabinowitz et al. (1976) based on a study of the kinetics of ingested stable lead
7 isotope tracers and lead mass balance data in five healthy adult males (Figure 4-17). The
8 Rabinowitz model has three compartments: (1) a central compartment representing blood and
9 other tissues and spaces in rapid equilibrium with blood (e.g., interstitial fluid); (2) a shallow
10 tissue compartment, representing soft tissues and rapidly exchanging pools within the skeleton;
11 and (3) a deep tissue compartment, representing, primarily, slowly exchanging pools of lead
12 within bone. Excretion pathways include urinary (from the central compartment) and bile,
13 sweat, hair, and nails (from the shallow tissue compartment). The model predicts pseudo-first
14 order half-times for lead of approximately 25, 28, and 7000 days in the central, shallow tissue,
May 2006
4-83
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-13. Structural Equation Models Relating Blood Lead Concentration in
Children and Pre-abatement Environmental Lead Levels—Lead in Urban Soil
Abatement Demonstration Project
Boston Cincinnati
Parameter Study Study
Model for blood lead (pg/dL)
Intercept 10.97a 7.55a
Floor dust lead (ppm) 0.14 4.1 Od
Soil lead (ppm) 0.16 0.28
Model for floor dust lead (pg/g)
Intercept 1008a 99.9b
Soil lead (ppm) 0.075 0.2247C
Window dust lead (ppm) 0.065 la 0.0458C
N = 126 (ages 9 mo to 9 years), R2 = 0.597, P < 0.0001; based on data from the Urban Soil Lead Abatement
Demonstration Project. Blood coefficients are expressed as ug/dL per ug/g; floor dust lead coefficients are
expressed as ug/g per ug/g.
aP = <0.0001
bP = 0.0002-0.0019
CP = 0.002-0.0099
dP = 0.01-0.0499
Source: U.S. Environmental Protection Agency (1986).
1 and deep compartments, respectively (these values were calculated based on reported residence
2 times, the reciprocal of the sum of the individual elimination rate constants). The slow kinetics
3 of the deep tissue compartment leads to the prediction that it would contain most of the lead
4 burden following chronic exposures (e.g., for years), consistent with lead measurements made in
5 human autopsy samples (Barry, 1975; Gross et al., 1975; Schroeder and Tipton, 1968). Note that
6 this model did not simulate the distribution of lead within blood (e.g., erythrocytes and plasma),
7 nor did it simulate subcompartments within bone or physiological processes of bone turnover
8 that might affect kinetics in the deep tissue compartment.
9
May 2006 4-84 DRAFT-DO NOT QUOTE OR CITE
-------
DIET* AIR
3
DEEP TISSUE
(BONE)
=200 mg
T1/2=7QOO days
=7 |jg/day
1
=48 pg/day
1
BLOOD
1.9mg
Tia=25 days
'
UR
=36 M
NE
3/day
=15 |jg/day
^2 fjg/doy
2
SHALLOW TISSUE
(SOFT TISSUE)
=0,6 mg
Ti/2=28 days
i •
BILE, HAIR,
SWEAT, NAILS,,.
=12 M9/day
Figure 4-17. Lead biokinetics based on Rabinowitz et al. (1976). Half-times are based on
reported mean residence times for compartments 1, 2, and 3: 36, 40, and
104 days, respectively (half-time = 0.693*residence time).
1 4.4.3.2 Marcus Model(s)
2 Marcus (1985a) reanalyzed the data from stable isotope tracer studies of Rabinowitz et al.
3 (1976) and derived an expanded multicompartment kinetic model for lead (Figure 4-18). The
4 model included separate compartments with different lead turnover rates for cortical (slow,
5 tl/2 = 1.2 x 104 to 3.5 x 104 days) and trabecular (fast, tl/2 = 100 to 700 days) bone, an
6 approach subsequently adopted in several other models (O'Flaherty, 1995; U.S. Environmental
7 Protection Agency, 1994a,b; Leggett, 1993; O'Flaherty, 1993; Bert et al., 1989). A more
8 complex representation of the lead disposition in bone included explicit simulation of lead
9 diffusion within the bone volume of the osteon and exchange with blood at the canaliculus
10 (Marcus, 1985b; Figure 4-19). Lead diffusion in bone was based on lead kinetics data from
11 studies conducted in dogs. A similar approach to simulating radial diffusion of lead in bone,
12 expanded to include eight concentric diffusion shells, was implemented by O'Flaherty (1993,
13 1995). Marcus (1985c) also introduced nonlinear kinetics of exchange of lead between plasma
14 and erythrocytes. The blood kinetics included four blood subcompartments: diffusible lead in
15 plasma, protein-bound lead in plasma, a "shallow" erythrocyte pool, and a "deep" erythrocyte
16 pool (see Figure 4-20). The Marcus (1985c) model predicted the curvilinear relationship
May 2006
4-85
DRAFT-DO NOT QUOTE OR CITE
-------
Figure 4-18. Lead biokinectics based on Marcus (1985a). Bone is represented as a slow
turnover (cortical) compartment and a faster (trabecular) compartment.
4
5
6
7
8
9
10
11
12
between plasma and blood lead concentrations that has been observed in humans
(DeSilva, 1981).
4.4.3.3 Bert Model
Bert et al. (1989) adopted the bone model from Marcus (1985a), in which the bone
compartment is subdivided into slow cortical bone and faster trabecular bone compartments
(Figure 4-21). The central compartment (denoted as blood) is assumed to be 1.5 times the
volume of whole blood (Rabinowitz et al., 1976), with the whole blood volume varying in direct
proportion with body weight. The model includes a discrete pathway for excretion of
unabsorbed lead from the gastrointestinal (GI) tract into feces. Secretion of lead in bile, gastric
secretions, and saliva are represented as transfers from the soft tissue compartment to the
GI tract. Compartment transfer coefficients were based on average values estimated for four
May 2006
4-86
DRAFT-DO NOT QUOTE OR CITE
-------
.' FECES,1
\ etc. /
LEAD INPUT
rv¥
BLOOD
Q
BONE
KIDNEY
OTHER
SOFT
TISSUE
URINE,)
etc. /
Figure 4-19. Lead biokinetics based on Marcus (1985b). Bone is represented as an
extended cylindrical canalicular territory. The canalicular territory has
a radius b, and surrounds the canaliculus of radius a. Lead diffuses
across radius library, between the fluid in the canaliculus (which is in
communication with blood in the Haversian canal, not shown) and the
bone volume of the canalicular territory.
1 individuals from the Rabinowitz et al. (1976) study. Initial average values for lead in cortical
2 bone for a given age at the start of a simulation were derived from Barry (1975).
O
4 4.4.3.4 Contemporary Models
5 Additional information on lead biokinetics, bone mineral metabolism, and lead exposures
6 has led to further refinements and expansions of these earlier modeling efforts. In particular,
7 three pharmacokinetic models are currently being used or are being considered for broad
8 application in lead risk assessment: (1) the Integrated Exposure Uptake BioKinetic (IEUBK)
9 model for lead in children developed by EPA (U.S. Environmental Protection Agency, 1994a,b;
10 White et al., 1998); (2) the Leggett model, which simulates lead kinetics from birth through
May 2006
4-87
DRAFT-DO NOT QUOTE OR CITE
-------
Figure 4-20. Lead biokinetics based on Marcus (1985c). Blood is represented with a
plasma (central exchange) compartment and a red blood cell compartment,
the latter having shallow and deep pools.
1 adulthood (Leggett, 1993); and (3) the O'Flaherty model, which simulates lead kinetics from
2 birth through adulthood (O'Flaherty, 1993, 1995). Of the three approaches, the O'Flaherty
3 model has the fewest lead-specific parameters and relies more extensively on physiologically
4 based parameters to describe volumes, flows, composition, and metabolic activity of blood and
5 bone that determine the disposition of lead in the human body. Both the IEUBK model and the
6 Leggett model are more classical multicompartmental models; that is, the values for the
7 age-specific transfer rate constants for lead are based on kinetics data obtained from studies
8 conducted in animals and humans and may not have precise physiological correlates. Thus, the
9 structure and parameterization of the O'Flaherty model is distinct from both the IEUBK model
10 and Leggett model. All three models represent the rate of uptake of lead (i.e., amount of lead
11 absorbed per unit of time) as relatively simple functions (f) of lead intake:
12
May 2006
4-S
DRAFT-DO NOT QUOTE OR CITE
-------
Air Lead
Diet, Other
Gastrointestinal
tract
Figure 4-21. Lead biokinetics based on Bert et al. (1989).
1
2
3
4
5
6
7
8
9
10
11
Uptake = Intake • AF
Uptake = Intake • f(Intai
(Intake)
(4-6)
(4-7)
Values assigned to absorption factor (AF) or other variables in f(intake) are, in general,
age-specific and environmental medium-specific in some models. However, the models do not
modify the representation of uptake as functions of the many other physiologic variables that
may affect lead absorption (e.g., nutritional status). While one can view this approach as a
limitation of the models, it also represents a limitation of the data available to support more
complex representations of lead absorption.
May 2006
4-89
DRAFT-DO NOT QUOTE OR CITE
-------
1 The IEUBK model simulates multimedia exposures, uptake, and kinetics of lead in
2 children ages 0 to 7 years; the model is not intended for use in predicting lead pharmacokinetics
3 in adults. The O'Flaherty and Leggett models are lifetime models, and include parameters that
4 simulate uptake and kinetics of lead during infancy, childhood, adolescence, and adulthood.
5 Lead exposure (e.g., residence-specific environmental lead concentrations, childhood activity
6 patterns) is not simulated by current versions of the O'Flaherty and Leggett models; however,
7 this is not necessarily a limitation since existing exposure models can be used to derive exposure
8 inputs (in terms of lead intakes) for these models. By contrast, the IEUBK model includes
9 parameters for simulating exposures and uptake to estimate daily uptake of lead (jig/day) among
10 populations of children potentially exposed via soil and dust ingestion, air inhalation, lead-based
11 paint chip ingestion, tap water ingestion, and/or diet.
12 The above three models have been individually evaluated, to varying degrees, against
13 empirical physiological data on animals and humans and data on blood lead concentrations in
14 individuals and/or populations (U.S. Environmental Protection Agency, 1994a,b; Leggett, 1993;
15 O'Flaherty, 1993). However, applications in risk assessment typically require that the models
16 accurately predict blood lead distributions in real populations (U.S. EPA, 1994a), in particular
17 those values or percentages falling in the "upper tails" (e.g., >95th percentiles of the
18 distributions, when input to the models consists of data that describe site-specific exposure
19 conditions (e.g., environmental lead concentrations, physicochemical properties of soil and dust)
20 (Beck et al., 2001; Griffin et al., 1999a,b). In evaluating models for use in risk assessment,
21 exposure data collected at hazardous waste sites have been used to drive model simulations
22 (Bowers and Mattuck, 2001; Hogan et al., 1998). The exposure module in the IEUBK model
23 makes this type of evaluation feasible.
24
25 4.4.4 Integrated Exposure Uptake Biokinetic (IEUBK) Model for
26 Lead in Children
27 4.4.4.1 Model Structure
28 • The IEUBK model for lead in children (see Figure 4-22) is a multicompartmental
29 pharmacokinetics model linked to an exposure and probabilistic model of blood lead
30 concentration distributions in children (U.S. Environmental Protection Agency, 1994a,b;
31 White et al., 1998). The model simulates exposure and biokinetics of lead from birth to
May 2006 4-90 DRAFT-DO NOT QUOTE OR CITE
-------
1
Respiratory
tract
Gastrointestinal tract
Plasma extra-cellular fluid
o
Q.
E
o
O
r Plasma extra-cellular fluid
u •
<
Red blood
cells
j
Kidney
V
Other soft
tissues
o
o
Elimination pools of
the body
Intake from
environmental
Media (|jg/lead/day)
Body compartment
Body compartment or
elimination pool required in
more than one component
Figure 4-22. Structure of the integrated exposure uptake biokinetics model for lead
in children (U.S. Environmental Protection Agency, 1994a,b; White
et al., 1998).
May 2006
4-91
DRAFT-DO NOT QUOTE OR CITE
-------
1 age 7 years (84 months) and was developed for predicting average quasi-steady state blood lead
2 concentrations corresponding to daily average exposures, averaged over periods > 1 year.
3 The model has four major components or submodels:
4 • Exposure model, in which average daily intakes of lead (jig/day, averaged over a 1 year
5 time increment) are calculated for each inputted exposure concentration (or rates) of lead
6 in air, diet, dust, soil, and water;
7 • Uptake model, which converts environmental media-specific lead intake rates calculated
8 from the exposure model into a media-specific time-averaged rates of uptake (jig/day)
9 of lead to the central compartment (blood plasma);
10 • Biokinetic model, which simulates the transfer of absorbed lead between blood and
11 other body tissues, elimination of lead from the body (via urine, feces, skin, hair, and
12 nails), and predicts an average blood lead concentration for the exposure time period of
13 interest; and
14 Blood lead probability model, which simply applies a log-normal distribution (with
15 specific geometric mean and geometric standard deviation parameters) to predict probabilities
16 for the occurrence of a specified blood lead concentration in a population of similarly exposed
17 children.
18
19 Exposure Model. The exposure model simulates intake of lead (jig/day) for exposures to
20 lead in air (|ig/m3), drinking water (|ig/L), soil-derived dust (|ig/g), and diet (jig/day). The
21 temporal resolution of the exposure model is 1 year; exposure inputs are intended to represent
22 annual averages for an age-year time step (e.g., ages 1, 2, 3...years). Exposure inputs that
23 represent the average (e.g., arithmetic mean) daily value for an age-year will yield corresponding
24 daily average intakes for the same age-year. The spatial resolution of the exposure model was
25 intended to be a child's residence (e.g., the home and yard). The model accepts inputs for media
26 intake rates (e.g., air volume breathing rates, drinking water consumption rate, soil and dust
27 ingestion rate). The air exposure pathway partitions exposure to outdoor air and indoor air; with
28 age-dependent values for time spent outdoors and indoors (hours/day). Exposure to lead in soil
29 derived dust is also partitioned into outdoor and indoor contributions. The intakes from all
30 ingested exposure media (diet, drinking water, soil-derived dust) are summed to calculate a total
31 intake to the gastrointestinal tract, for estimating capacity-limited absorption (see description of
32 the Uptake Model).
May 2006 4-92 DRAFT-DO NOT QUOTE OR CITE
-------
1 Uptake Model. The uptake model simulates lead absorption in the gastrointestinal tract as
2 the sum of a capacity-limited (represented by a Michaelis-Menten type relationship) and
3 unlimited processes (represented by a first-order, linear relationship). These two terms are
4 intended to represent two different mechanisms of lead absorption, an approach that is in accord
5 with limited available data in humans and animals that suggest a capacity limitation for lead
6 absorption (Mushak, 1991). One of the parameters for the capacity-limited absorption process
7 (that represents that maximum rate of absorption) is age-dependent. The above representation
8 gives rise to a decrease in the fractional absorption of ingested lead as a function of total lead
9 intake as well as age. Absorption fractions are also medium-specific (Figure 4-23).
10 At 30 months of age, at low intakes (<200 jig/day), below the rates at which capacity -
11 limitation has a significant impact on absorption, the fraction of ingested lead in food or drinking
12 water that is absorbed is 0.5 and decreases to approximately 0.11 at high intake (>5000 jig/day).
13 For lead ingested in soil or dust, fractional absorption is 0.35 at low intake (<200 jig/day) and
14 decreases to 0.09 at high intake (>5000 jig/day).
15 The uptake model assumes that 32% of inhaled lead is absorbed. This value was
16 originally assigned based on a scenario of exposure to active smelter emissions, which assumed
17 the particle size distribution in the vicinity of an active lead smelter; size-specific deposition
18 fractions for the nasopharyngeal, tracheobronchial, and alveolar regions of the respiratory tract;
19 and region-specific absorption fractions (Table 4-14). Lead deposited in the alveolar region is
20 assumed to be completely absorbed from the respiratory tract, whereas, lead deposited in the
21 nasopharyngeal and tracheobronchial regions is assumed to be transported to the gastrointestinal
22 tract where absorption (approximately 30%) occurs. These assumptions are simplifications;
23 particle clearance to the gastrointestinal tract occurs in the alveolar region of the respiratory tract
24 (Bailey and Roy, 1994).
25
26 Biokinetics Model. The biokinetics model includes a central compartment, plasma and
27 extracellular fluid combined (plasma-ECF), six peripheral body compartments, and three
28 elimination pathways. The temporal resolution of the biokinetics model is 1 month and, as
29 discussed below, parameter values for bone-plasma-ECF exchanges were assigned with the
30 objective of simulating the quasi-steady state condition of months, rather than short-term kinetics
31 of days. The body compartments include kidney, liver, trabecular bone, cortical bone, and
May 2006 4-93 DRAFT-DO NOT QUOTE OR CITE
-------
0.55
0.50
0.45
0.40
0.35
0.30
10 20 30 40 50 60 70
Food or Water Lead Intake (ug/day)
-•-Age 6m
-B-Age 18m
—+—Age 30m
80
90
100
0.35
0.30
0.25
0.20
0.15
• Age 6m
-B-Age 18m
-4^ Age 30m
—*—Age 42m
—x—Age 54m
^*—Age 66m
0.10
1000 2000 3000 4000 5000 6000 7000
Soil or Dust Lead Concentration (ppm)
8000
9000
10000
Figure 4-23. Age-dependency of absorption fraction for ingested lead in the IEUBK model
for lead in children. Absorption fraction for food and water (top panel); soil
and dust (bottom panel).
May 2006
4-94
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-14. Basis for Absorption Fraction of Inhaled Lead in the IEUBK Model for
Lead in Children
Particle Size
(|im)
<1.0
1-2.5
2.5-15
15-30
>30
Abundance
12.5
12.5
20
40
15
Alveolar
0.15(1.5)
0.25(1.3)
0.20 (0.5)
-D
-D
Deposition Fraction2
Tracheobronchial
0.05(1.5)
0.10(1.7)
0.25(1.4)
0.05 (0.5)
-D
1
Nasopharyngeal
0.003 (1.5)
0.20(1.5)
0.40 (2.0)
0.95(1.0)
0.95 (1.0)
Lead deposited in the tracheobronchial and nasopharyngeal regions (approximately 80% of inhaled)
is assumed to be transported to the gastrointestinal tract.
aAdjustment factor applied to deposition fractions to account for age.
Source: U.S. Environmental Protection Agency (1989).
1 other soft tissue. The model simulates growth of the body and tissues, compartment volumes,
2 and lead masses and concentrations in each compartment. Blood lead concentration at birth
3 (neonatal) is assumed to be 0.85 of the maternal blood lead. Neonatal lead masses and
4 concentrations are assigned to other compartments based on a weighted distribution of the
5 neonatal blood lead concentration. Exchanges between the central compartment and tissue
6 compartments are simulated as first-order processes, which are parameterized with
7 unidirectional, first-order rate coefficients. Rate coefficients are allometrically scaled as a power
8 function of body weight (B W033).
9 Saturable uptake of lead into erythrocytes is simulated, with a maximum erythrocyte lead
10 concentration of 120 |ig/L. Excretory routes simulated include urine, from the central
11 compartment; bile-feces, from the liver; and a lumped excretory pathway representing losses to
12 skin, hair and nails, from the "other soft tissue" compartment.
13 Bone is simulated as a trabecular bone compartment (20% of bone volume) and a cortical
14 bone compartment (80% of bone volume). Rate constants for transfer from plasma to the two
15 bone compartments are assigned values that result in a 4:1 cortical lead:trabecular lead mass ratio
16 within one biokinetic time step (one month). This is achieved by assigning the two bone
May 2006 4-95 DRAFT-DO NOT QUOTE OR CITE
-------
1 compartments identical rate coefficients for transfer of lead from bone to plasma-ECF (half-time
2 8.5 days, at age 2 years), and faster (cortical, half-time 0.0083 days) and slower transfer
3 (trabecular, half-time 0.035 days) from the plasma-ECF (cortical:trabecular rate ratio is
4 approximately 4:1). Note, this approach is different from previous and subsequent modeling
5 approaches, in which cortical bone-to-plasma (or blood) transfer is assumed to occur slowly,
6 relative to trabecular bone-to-plasma transfer (Marcus, 1985a; Bert et al., 1989; Leggett, 1993;
7 O'Flaherty, 1993, 1995). For predictions of quasi-steady state conditions and the intended use of
8 the IEUBK Model, the two general approaches can be expected to yield similar distributions of
9 lead between the cortical and trabecular bone compartments.
10
11 Blood Lead Probability Model. Inputs to the IEUBK model are exposure point estimates
12 that are intended to represent time-averaged central tendency exposures. The output of the
13 model is a central tendency estimate of blood lead concentration for children who might
14 experience the inputted average exposures. However, within a group of similarly exposed
15 children, blood lead concentrations would be expected to vary among children as a result of
16 inter-individual variability in media intakes (e.g., daily average intakes of soil-derived dust,
17 drinking water, or food), absorption, and biokinetics. The model simulates the combined impact
18 of these sources of variability as a lognormal distribution of blood lead concentration for which
19 the geometric mean (GM) is given by the central tendency blood lead concentration outputted
20 from the biokinetics model, and the geometric standard deviation (GSD) is an input parameter.
21 The resulting lognormal distribution also provides the basis for predicting the probability of
22 occurrence of given blood lead concentration within a population of similarly exposed children:
23
24 PX = probability of exceeding a blood lead concentration of X |ig/dL (4.8)
25
26 PIO = probability of exceeding a blood lead concentration of 10 |ig/dL (4-9)
27
28 The model can be iterated for varying exposure concentrations (e.g., a series of increasing
29 soil lead concentration) to predict the media concentration that would be associated with a
30 probability of 0.05 for the occurrence of a blood lead concentration exceeding 10 |ig/dL
31 (Pio=0.05).
32
May 2006 4-96 DRAFT-DO NOT QUOTE OR CITE
-------
1 4.4.4.2 Model Calibration and Evaluation
2 An evaluation of the IEUBK model has been carried out by comparison of model
3 predictions of blood lead concentrations in children with observations from epidemiologic
4 studies of hazardous waste sites (Hogan et al., 1998). Data characterizing residential lead
5 exposures and blood lead concentrations in children living at four Superfund National Priorities
6 List (NPL) sites were collected in a study designed by the Agency for Toxic Substances and
7 Disease Registry (ATSDR) and EPA. The residential exposure data were used as inputs to the
8 IEUBK model and predicted blood lead concentration distributions were compared to the
9 observed distributions in children living at the same residences. The IEUBK model predictions
10 of geometric mean blood lead concentrations for children whose exposures were predominantly
11 from their residence (i.e., no more than 10 hours/week away from home) were within 0.7 |ig/dL
12 of the observed geometric mean at each site (Table 4-15). The prediction of the percentage of
13 children expected to have blood lead concentrations exceeding 10 |ig/dL were within 4% of the
14 observed percentage at each site (Table 4-16). This evaluation supports IEUBK model use for
15 estimating blood lead concentrations in children at sites where their residential exposures can be
16 adequately characterized. Similar empirical comparisons have shown that agreement or disparity
17 between IEUBK model predictions and observed blood lead concentrations at specific locations
18 is influenced by numerous factors, including (a) the extent to which the exposure and blood lead
19 measurements are adequately matched and (b) site-specific factors (e.g., soil characteristics,
20 behavior patterns, bioavailability) that may affect lead intake or uptake in children (Bowers and
21 Mattuck, 2001; TerraGraphics Environmental Engineering, Inc., 2001). In the absence of a
22 suitable dataset of paired environmental lead and blood lead measurements at a given site, it is
23 not possible to ascertain the degree to which the model predictions will represent the exposure-
24 blood lead concentration relationships at that site (Bowers and Mattuck, 2001).
25
26 4.4.4.3 Model Applications
27 Biomarkers Simulated. The IEUBK model computes masses of lead in bone and various
28 soft tissues, and excretion of lead, which are used in the computation of blood lead
29 concentration. However, the model was not developed for the purpose of predicting lead masses
30 in these tissues or excreta. Blood lead concentration is the only lead biomarker output that is
31 accessible to the user.
May 2006 4-97 DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-15. Comparison of Observed and Predicted Geometric Mean Blood Lead for
Three Community Blood Lead Studies
Dataset
Galena, KA
Jasper Co, MP
Madison Co, ILa
Palmerton, PAb
N
111
333
34
Observed Blood Lead
(|ig/dL)
GM
5.2
5.9
6.8
95% CI
4.5-5.9
5.5-6.4
5.6-8.2
Model Predictions
(|ig/dL)
GM
4.6
5.9
7.5
95% CI
4.0-5.3
5.4-6.3
6.6-8.6
CI = confidence interval; GM = geometric means
aChildren away from home < 10 hours/week
bChildren away from home <20 hours/week
Table 4-16. Comparison of Observed and Predicted Probability of Exceeding a Blood
Lead Concentration of 10 ug/dL Lead for Three Community Blood Lead Studies
Dataset
Galena, KA
Jasper Co, MP
Madison Co, ILa
Palmerton, PAb
N
111
333
34
Observed Blood Lead
(|ig/dL)
Percent
20
19
29
95% CI
13-27
15-23
14-44
Model Predictions
(|ig/dL)
Percent
18
23
31
95% CI
11-25
19-28
16-47
CI, confidence interval
aChildren away from home < 10 hours/week
bChildren away from home <20 hours/week
1 Exposure Inputs. The IEUBK model was developed to predict the probability of elevated
2 blood lead concentrations in children exposed to user-specified annual average exposures to lead
3 in air, food, drinking water, soil, and dust. As noted above, the exposure model has an age-year
4 time step (the smallest time interval for a single exposure event) and, therefore, is more suited to
5 applications in which long-term (i.e., > 1 year) average exposures and quasi-steady state blood
May 2006 4-98 DRAFT-DO NOT QUOTE OR CITE
-------
1 lead concentrations are to be simulated. Intermittent exposures occur for brief periods of time
2 (e.g., a weekend at the beach), or in cases where significant seasonal variations are different from
3 the typical residential or occupational exposure. Intermittent exposures can be simulated as
4 time-weighted average exposures (U.S. EPA, 2003a). Shorter-term dynamics of blood lead
5 concentration, that may result from exposures that are highly variable on time scales of days or
6 weeks, will not be captured with this approach (Lorenzana et al., 2005; Khoury and Diamond,
7 2003).
8
9 Modeling Variability and Uncertainty. As noted above, the IEUBK model uses a
10 lognormal probability model to simulate inter-individual variability in blood lead concentrations
11 attributable to variability in media intakes, absorption, and biokinetics. The model uses a generic
12 default value of 1.6 for the geometric standard deviation (GSD;) of blood lead concentrations.
13 This value was derived from an analysis of exposure (soil lead)-stratified variability in blood
14 lead concentrations in various cohorts of children (U.S. Environmental Protection Agency,
15 1994a; White et al., 1998). Griffin et al. (1999b) also explores various statistical methods for
16 estimating an appropriate GSD; (regression, box modeling, structural equation modeling).
17 A Monte Carlo approach has been used to simulate and propagate variability and
18 uncertainty in exposure and absorption through IEUBK model simulation of blood lead
19 concentrations (Goodrum et al., 1996). This extension of the model provides an alternative to
20 the generic blood lead probability approach for incorporating explicit estimates of variability
21 (and uncertainty in variability) in exposure and absorption into predictions of an expected
22 probability distribution of blood lead concentrations. A quantitative uncertainty analysis of
23 IEUBK model-based estimates of the PIO for a smelter site in Utah revealed that parameters
24 specifying soil ingestion rate were a dominant contributor to uncertainty in the PIO; however,
25 the contribution of soil ingestion uncertainty, relative to uncertainty in other model parameters
26 (i.e., mean soil lead concentration, absorption fraction) varied across individual locations (Initial
27 Study Zones) at the site (Griffin et al., 1999a).
28
29 4.4.4.4 Implementation Code
30 The IEUBK model was initially released to the public in 1994 as a compiled DOS-based
31 C program (IEUBK v99d). This version was subjected to an independent code validation and
May 2006 4-99 DRAFT-DO NOT QUOTE OR CITE
-------
1 verification study which verified that the code accurately implement the model (Mickle, 1998;
2 Zaragoza and Hogan, 1998). A 32-bit C++ (IEUBKwin32) version of the model is available for
3 download from an EPA website (http://www.epa.gov/superfund/programs/lead/ieubk.htm).
4
5 4.4.5 Leggett Model
6 4.4.5.1 Model Structure
7 The Leggett model was developed from a biokinetic model originally developed for the
8 International Commission on Radiological Protection (ICRP), for calculating radiation doses
9 from environmentally important bone-seeking radionuclides, including radioisotopes of lead
10 (Leggett, 1985, 1992a,b). The model has been used to develop cancer risk coefficients for
11 internal radiation exposures to lead and other alkaline earth elements that have biokinetics
12 similar to those of calcium (ICRP, 1993; U.S. Environmental Protection Agency, 1997).
13 The model includes a central exchange compartment, 15 peripheral body compartments, and
14 3 elimination pools (Figure 4-24). The central exchange compartment is the diffusible pool of
15 lead in plasma. The model simulates a bound pool in plasma (i.e., lead bound to plasma
16 proteins); that has an equilibrium ratio (bound:free) of approximately 5. Transport of lead from
17 plasma to tissues is assumed to follow first-order kinetics. The temporal resolution of the model
18 is 1 day. Transfer rate constants vary with age and blood lead concentration. The latter
19 adjustment accounts for the limited uptake of plasma lead into red blood cells and the resulting
20 shift in distribution of lead from plasma-ECF to other tissues. Above a nonlinear threshold
21 concentration in red blood cells (assumed to be 60 |ig/dL), the rate constant for transfer to red
22 blood cells declines and constants to all other tissues increase proportionally (Leggett, 1993).
23 This replicates the nonlinear relationship between plasma and red blood observed in humans
24 (Smith et al., 2002; Manton et al., 2001; Bergdahl et al., 1997a, 1998, 1999). The model
25 simulates blood volume as an age-dependent function, which allows simulation of plasma and
26 blood lead concentrations. However, volumes of other tissues are not simulated; therefore, only
27 lead masses in these tissues, and not concentrations are simulated.
28 First-order transfer coefficients (day-1) between compartments were developed for six age
29 groups, and intermediate age-specific values are obtained by linear interpolation (Leggett, 1993).
30 The total transfer rate from diffusible plasma to all destinations (TPALL) combined is assumed
31 to be 2000 day-1, based on isotope tracer studies in humans receiving lead via injection or
May 2006 4-100 DRAFT-DO NOT QUOTE OR CITE
-------
Losses in
Hair, Nails,
Skin
Figure 4-24. Structure of the Leggett Lead Biokinetic Model (Leggett, 1993). The central
exchange compartment is diffusible plasma. Bone is represented as having
surface (which rapidly exchanges with plasma) and volume compartments;
the latter stimulates slow exchange with the surface and slow return of lead
to the plasma from bone resorption.
May 2006
4-101
DRAFT-DO NOT QUOTE OR CITE
-------
1 inhalation. Values for transfer coefficients from plasma to tissues and tissue compartments are
2 based on measured deposition fractions (DF) or instantaneous fractional outflows of lead
3 between tissues compartments (Leggett, 1993), where the transfer coefficient to a specific tissue
4 or compartment (TP;) is given by:
5
6 TP, = DF . • TPALL (4-10)
7
8 This approach establishes mass balance with respect to the transfer rates from plasma:
9
10 ^TP,= TPALL (4-11)
11
12 The model simulates both rapid exchange of lead with plasma via bone surface and slow loss by
13 bone resorption. Cortical bone volume (80% of bone volume) and trabecular bone volume (20%
14 of bone volume) are simulated as bone surface compartments, which rapidly exchanges with lead
15 in plasma, and bone volume, within which are exchangeable and nonexchangeable pools. Lead
16 enters the exchangeable pool of bone volume via the bone surface and can return to the bone
17 surface, or move to the nonexchangeable pool, from where it can return to the plasma only when
18 bone is resorbed. Transfers from plasma to bone surface, return from bone surface to plasma,
19 and bone surface to exchangeable bone volume are assumed to be relatively fast processes (adult
20 ti/2 = 3.85, 1.4, and 1.4 days, respectively). Return of lead from the exchangeable bone volume
21 is slower (adult ti/2 = 30 days); however, the dominant transfer process determining long-term
22 accrual of bone lead burden are slow rate coefficients for transfer of lead from the
23 nonexchangeable pools of trabecular and cortical bone to plasma (adult ti/2 = 3.8 and 23 years,
24 respectively). Bone transfer coefficients vary with age (faster in children) to reflect the age-
25 dependence of bone turnover. The slow, nonexchangeable, bone volume compartment is much
26 more labile in infants and children than in adults (e.g., cortical ti/2 = 68 days at birth and
27 1,354 days at age 15 years; trabecular ti/2 = 68 days at birth and 725 days at age 15 years). Other
28 physiological states (such as pregnancy and menopause) that affect bone turnover and, therefore,
29 bone lead kinetics are not simulated, although such states could conceivably be accommodated
30 with adjustments to tissue (e.g., bone) transfer coefficients.
31 The liver is simulated as two compartments; one compartment has a relatively short
32 removal half-life for transfers to plasma and to the small intestine by biliary secretion (adult
May 2006 4-102 DRAFT-DO NOT QUOTE OR CITE
-------
1 ti/2 =10 days); a second compartment simulates a more gradual transfer to plasma of
2 approximately 10% of lead uptake in liver (adult ti/2 = 365 days). The kidney is simulated as two
3 compartments, one that exchanges slowly with blood plasma and accounts for lead accumulation
4 in kidney tissue (adult ti/2 = 365 days) and a second compartment that receives lead from blood
5 plasma and rapidly transfers lead to urine (adult ti/2 = 5 days), with essentially no accumulation
6 (urinary pathway). Other soft tissues are simulated as three compartments representing rapid,
7 intermediate, and slow turnover rates, without specific physiologic correlates (adult ti/2 = 0.3,
8 100, and 1824 days, respectively). Other excretory pathways (hair, nails, and skin) are
9 represented as a lumped pathway from the intermediate turnover rate of the soft tissue
10 compartment.
11 The Leggett model simulates lead intakes from inhalation, ingestion, or intravenous
12 injection. The latter was included to accommodate model evaluations based on intravenous
13 injection studies in humans and animal models. The respiratory tract is simulated as four
14 compartments into which inhaled lead is deposited and absorbed with half-times of 1, 3, 10,
15 and 48 hours. Four percent of the inhaled lead is assumed to be transferred to the GI tract.
16 These parameter values reflect the data on which the model was based, which were derived from
17 studies in which human subjects inhaled submicron lead-bearing particles (Morrow et al., 1980;
18 Chamberlain et al., 1978; Wells et al., 1977; Hursh and Mercer, 1970; Hursh et al., 1969). These
19 assumptions would not necessarily apply for exposures to larger airborne particles (see Sections
20 2.3.1 for a discussion of atmospheric transport of lead particles). Absorption of ingested lead is
21 simulated as an age-dependent fraction of the ingestion rate, declining from 0.45 at birth to 0.3 at
22 age 1 year (to age 15 years), and to 0.15 after age 25 years (Figure 4-25).
23
24 4.4.5.2 Model Calibration and Evaluation
25 Leggett (1993) and Pounds and Leggett (1998) describe various qualitative empirical
26 comparisons of model predictions against observations made on adults (e.g., Skerfving et al.,
27 1985; Campbell et al., 1984; Manton and Cook, 1984; Barry, 1981; DeSilva, 1981; Chamberlain
28 et al., 1978; Rabinowitz et al., 1976; Barry, 1975; Griffin et al., 1975; Gross et al., 1975; Hursh
29 and Mercer, 1970; Booker et al., 1969; Hursh et al., 1969; Schroeder and Tipton, 1968).
30 Age-specific changes in parameter values that specify the biokinetics of lead in children were
31 assigned values that resulted in agreement between predicted age-specific lead distribution
May 2006 4-103 DRAFT-DO NOT QUOTE OR CITE
-------
60
\ x-IEUBK Food and Drinking Water
50 ^ *. 1
S^ 40
c
.g
^-j
% \ \ Leggett Model
30 . ' \, [
<
-IEUBK Soil and Dust
O
ro 20
Q
O'Flaherty Model
10
o
0 5 10 15 20 25 30
Age (years)
Figure 4-25. Age-dependency of absorption fraction for ingested lead in the Leggett and
O'Flaherty models. The IEUBK model projects absorption only through age
seven (84 mo). At intakes below those which approach the limit on "active"
absorption of lead, absorption is constant with age, with default valves of
50% for diet and drinking water, 30% for soil and dust. Fractional
absorption via the active pathway decreases with age and lead intake
(see Figure 4-23).
1 (fraction of body burden) in blood, bone, brain, kidney, liver, and other tissues, and reported
2 postmortem values (Schroeder and Tipton, 1968; Barry, 1975, Gross et al. 1975; Barry, 1981).
3 Comparisons of model predictions to observed relationships between plasma and red blood cell
4 lead levels are reported in U. S. EPA (2003b).
5
6 4.4.5.3 Model Applications
7 Biomarkers Simulated. The Leggett model simulates the concentrations of lead in blood
8 and plasma, lead masses of lead in bone and various soft tissues, and excretion of lead in urine
9 that correspond to lifetime exposures (in terms of daily lead intakes).
May 2006 4-104 DRAFT-DO NOT QUOTE OR CITE
-------
1 Exposure Inputs. The model does not contain a detailed exposure module (although it can
2 be linked to an exposure model); lead exposure estimates are incorporated into the simulations as
3 age-specific point estimates of daily intake (jig/day) from ingestion, inhalation, or injection. The
4 model operates with a lead intake time step of 1 day, which allows simulation of rapidly
5 changing (i.e., daily) intermittent exposures (Lorenzana et al., 2005; Khoury and Diamond,
6 2003). Assumptions of blood lead concentrations at birth can also be introduced into the
7 simulations, from which levels in other tissue in the first time step after birth are calculated.
8 Dose reconstruction is possible with this model, since intakes, and corresponding tissue
9 lead burdens accrued at any period in the lifetime, prior to an exposure event of interest, can be
10 simulated. Pounds and Leggett (1998) illustrate this in a study of a childhood lead poisoning
11 case, in which the exposure is followed by chelation. Chelation was simulated as a short-
12 duration increase in the plasma lead deposition fraction to urine, with corresponding proportional
13 decreases in deposition fractions to other tissues.
14
15 4.4.5.4 Implementation Code
16 The Leggett model was initially developed as a Fortran code, which can be run, without
17 compiling, from various platforms, including DOS and Windows (see Pounds and Leggett, 1998
18 for a description). A version compiled in Advanced Continuous Simulation Language (ACSL)
19 has also been reported (Lorenzana et al., 2005). Confirmation of the Leggett model code was
20 carried out by a panel of experts (ICRP, 1989, 1993).
21
22 4.4.6 O'Flaherty Model
23 4.4.6.1 Model Structure
24 The O'Flaherty model simulates lead exposure, uptake, and disposition in humans, from
25 birth through adulthood (O'Flaherty, 1993, 1995, 2000). Figure 4-26 shows a conceptualized
26 representation of the model. Important novel features of the O'Flaherty model are the simulation
27 of growth, bone formation, and resorption. A growth curve is simulated with a logistic
28 expression relating body weight to age in males or females. The full expression relating weight
29 to age has five parameters (constants), so that it can readily be adapted to fit a range of
30 standardized growth curves for males and females. Tissue growth and volumes are linked to
31 body weight; this provides explicit modeling of lead concentrations in all tissues simulated.
May 2006 4-105 DRAFT-DO NOT QUOTE OR CITE
-------
Respiratory tract
o
o
Elimination pools of
the body
Intake from environmental
Media ((jg/lead/year)
Body compartment
Blood plasma
Well-perfused tissues
Poorly-perfused tissues
Cortical bone
Trabecular bone
Liver
Kidney
Diet, Dust, \
Paint, Soil, ]
Water J
Gastrointestinal tract
Figure 4-26. Structure of the O'Flaherty Lead Exposure Biokinetics Model (O'Flaherty,
1993,1995, 2000). The central exchanges compartment is diffusible plasma.
Lead distribution is represented by flows from blood plasma to liver,
kidney, richly-perfused tissues, poorly-perfused tissues, and cortical and
trabecular bone. The model simulates tissue growth with age, including
growth and resorption of bone mineral.
May 2006
4-106
DRAFT-DO NOT QUOTE OR CITE
-------
1 Other physiologic functions (e.g., bone formation) are linked to body weight, age, or to both.
2 The model can be implemented with a temporal resolution of 1 day; however, as originally
3 configured, the rate parameters are expressed in time units of years.
4 Rates of bone formation and resorption are simulated as age-dependent functions
5 (Figure 4-27). Uptake and release of lead from trabecular bone and metabolically active cortical
6 bone are functions of bone formation and resorption rates, respectively; this establishes the age-
7 dependence to the lead kinetics in and out of bone. Lead exchange between blood plasma and
8 bone is simulated as parallel processes occurring in cortical (80% of bone volume) and trabecular
9 bone (20% of bone volume). The model simulates an age-related transition from immature bone,
10 for which bone turnover (formation and resorption) rates are relatively high, to mature bone, for
11 which turnover is relatively slow. Changes in bone mineral turnover associated with aging and
12 senescence (e.g., postmenopausal osteoporosis) can be simulated by introducing an age-
13 dependent increase rate of bone resorption (O'Flaherty, 2000). Metabolically active regions of
14 bone, in which lead uptake and loss is dominated by bone formation and loss, a region of slow
15 kinetics in mature cortical bone is also simulated, in which lead uptake and release to blood
16 occur by heteroionic exchange with other minerals (e.g., calcium). Heteroionic exchange is
17 simulated as a radial diffusion in bone volume of the osteon. All three processes are linked to
18 body weight, or the rate of change of weight with age. This approach allows for explicit
19 simulation of the effects of bone formation (e.g., growth) and loss, changes in bone volume, and
20 bone maturation on lead uptake and release from bone. Exchanges of lead between blood plasma
21 and soft tissues (e.g., kidney and liver) are represented as flow-limited processes. The model
22 simulates saturable binding of lead in erythrocytes (maximum capacity is 2.7 mg Pb/L cell
23 volume); this replicates the curvilinear relationship between plasma and erythrocyte lead
24 concentrations observed in humans (Smith et al., 2002; Manton et al., 2001; Bergdahl et al.,
25 1997a, 1998, 1999). Excretory routes include kidney to urine and liver to bile. Total excretion
26 (clearance from plasma attributable to bile and urine) is simulated as a function of age-dependent
27 glomerular filtration rate. Biliary and urinary excretory rates are proportioned as 70 and 30% of
28 the total plasma clearance, respectively.
29 The O'Flaherty model simulates lead intake from inhalation and ingestion. Inhalation
30 rates are age-dependent. Absorption of inhaled lead is simulated as a fraction (0.5) of the
31 amount inhaled and is independent of age. Gastrointestinal absorption of lead in diet and
May 2006 4-107 DRAFT-DO NOT QUOTE OR CITE
-------
2.5
2.0
1.5
1.0
o
DQ
0.5
0.0
Total bone
10
15
Age (yr)
20
25
30
0.6
0.5
0.4
Juvenile cortical
bone
Juvenile trabecular
bone
Figure 4-27. Bone growth as simulated by the O'Flaherty Lead Exposure Biokinetics
Model (O'Flaherty, 1993,1995, 2000). The model simulates an age-related
transition from juvenile bone, in which bone turn-over (formation and
resorption) rates are relatively high, to mature bone, in which turn-over is
relatively slow. Cortical bone comprises approximately 80% of total
bone volume.
May 2006
4-108
DRAFT-DO NOT QUOTE OR CITE
-------
1 drinking water is simulated as an age-dependent fraction, declining from 0.58 of the ingestion
2 rate at birth to 0.08 after age 8 years (Figure 4-25). These values can be factored to account for
3 relative bioavailability when applied to absorption of lead ingested in dust or soil.
4
5 4.4.6.2 Model Calibration and Evaluation
6 The O'Flaherty model was initially calibrated to predict blood, bone, and tissue lead
7 concentrations in rats (O'Flaherty, 1991a,b,c), and subsequently modified to reflect anatomical
8 and physiological characteristics in children (O'Flaherty, 1995), adults (O'Flaherty, 1993), and
9 Cynomolgus monkeys (M. fasicularis) (O'Flaherty et al., 1998). Model parameters were
10 modified to correspond with available information on species- and age-specific anatomy and
11 physiological processes. Empirical comparisons (largely qualitative) of model predictions
12 against observations made in adults (e.g., Van De Vyver et al., 1988; Kehoe, 1987; Marcus,
13 1985c; Manton and Malloy, 1983; Sherlock et al., 1982; DeSilva, 1981; Moore et al., 1977;
14 Cools et al., 1976; Rabinowitz et al., 1976; Azar et al., 1975) are provided in O'Flaherty (1993);
15 and comparisons against observations made in children (e.g., Sherlock and Quinn, 1986;
16 Bornschein et al., 1985b; Chisolm et al., 1985; Lacey et al., 1985) and adults are described in
17 O'Flaherty (1995, 1998, 2000).
18
19 4.4.6.3 Model Applications
20 Biomarkers Simulated. The O'Flaherty model simulates lead concentrations in blood and
21 plasma, bone, and various soft tissues, and excretion of lead in urine that correspond to lifetime
22 exposures (in terms of daily lead intakes). Lead in feces is a mixture of unknown proportions of
23 unabsorbed lead in food, drinking water, ingested dust, a small amount of inhaled lead entering
24 the GI tract by the mucociliary clearance from the respiratory tract, and a small amount of
25 absorbed lead eliminated with the red blood cells passing along the bile duct to the GI tract.
26 In this respect, lead in feces represents a poorly defined measure of lead exposure.
27 Lead in perspiration represents lead in extracellular plasma, but the concentration is low
28 and difficult to measure in a small volume (1 drop = 0.05 mL), and is potentially contaminated
29 with lead in dust on the skin surface.
30 The model predicts blood lead concentrations for a broad age range (infants to adults),
31 which allows for simulated dose reconstruction, since intakes and corresponding tissue lead
May 2006 4-109 DRAFT-DO NOT QUOTE OR CITE
-------
1 burdens accrued at any period in the lifetime, prior to an exposure event of interest can be
2 simulated. Physiological states (such as pregnancy and menopause) that affect bone turnover
3 and, therefore, bone lead kinetics are not simulated, although such states could be accommodated
4 with adjustments to the physiological bone formation and resorption rates.
5
6 Exposure Inputs. The O'Flaherty model simulates lead intake by inhalation and ingestion.
7 The model simulates ingestion exposures from infant formula, soil, dust, and drinking water.
8 Rates of soil and dust ingestion are age-dependent, increasing to approximately 130 mg/day at
9 age 2 years, and declining to <1 mg/day after age 10 years. However, the ACSL implementation
10 code allows constructions of simulations with an exposure time step as small as 1 day, which
11 would allow simulation of rapidly changing intermittent exposures (e.g., an acute exposure
12 event).
13
14 Modeling Variability and Uncertainty. The O'Flaherty model, as described in O'Flaherty
15 (1993, 1995), utilizes point estimates for parameter values and yields point estimates as output;
16 however, a subsequent elaboration of the model has been reported that utilized a Monte Carlo
17 approach to simulate variability in exposure, absorption, and erythrocyte lead binding capacity
18 (Beck et al., 2001). This approach could be used to predict the probability that children exposed
19 to lead in environmental media will have blood lead concentrations exceeding a health-based
20 level of concern (e.g., 10 jig/dL).
21
22 4.4.6.4 Implementation Code
23 The O'Flaherty model was developed in ACSL and published in O'Flaherty (2000).
24 A compiled C program has also been developed (personal communication, E. O'Flaherty). The
25 extent to which code verification and validation studies have been conducted for the O'Flaherty
26 model is unclear at this time. However, analogs of certain components of the O'Flaherty model
27 (e.g., parameters related to bone growth) have been incorporated into the EPA All Ages Lead
28 Model (see Section 4.4.7) as a potential option for evaluation.
29
May 2006 4-110 DRAFT-DO NOT QUOTE OR CITE
-------
1 4.4.7 EPA All Ages Lead Model
2 4.4.7.1 Model Structure
3 The EPA All Ages Lead Model (AALM) (Figure 4-28), currently under development,
4 simulates lifetime lead exposures and biokinetics in humans. The model is expected to simulate
5 exposure and biokinetics of lead from birth to age 90 years and should also incorporate, at some
6 near-future time, a pregnancy module that simulates transplacental transfer of lead from the other
7 to the fetus.
8
9 Exposure Module. The exposure component of the AALM incorporates and extends the
10 exposure component of the IEUBK model. The AALM exposure model defines an individual in
11 terms of age, sex, date of birth, and activity pattern profile. The age specification establishes up
12 to nine age ranges (e.g., infant, child, adolescent, adult, etc.) for which various exposure (and
13 biokinetic) parameter values can be applied. This provides a means for varying parameter values
14 with age. The sex specification links the modeled individual to the appropriate growth algorithm
15 (O'Flaherty 1993, 1995), and the date specification links the individual to historical exposure
16 levels (e.g., air, diet) for the selected age range. The activity pattern specification sets the
17 relative amount of time the individual spends in various exposure settings (e.g., residential,
18 school, recreational, occupational) for which exposure concentrations can be specified.
19 The diet exposure module allows input values (current or historical) for lead levels (|ig/g)
20 in market basket fruits, vegetables, meat and fish; recreational- or subsistence-harvested fish and
21 meat; and corresponding food intakes for each food type (jig food/day). Lead intake from
22 drinking water is calculated from concentrations (|ig/L) in tap water (first draw and/or flushed),
23 fountain water, and/or bottled water; and corresponding source water intake rates (L/day).
24 The dust exposure module accepts input values for dust concentrations (|ig/g) in various
rj
25 settings (e.g., residential, school, recreational, occupational) or dust loadings (|ig/m ) and
26 corresponding dust ingestion rates (jig dust/day) or contact rates (m2/day), the lead ingestion rate
27 for a given loading being calculated as the product of loading and contact rate. Pica ingestion for
28 soil and/or paint chips can be simulated with input values for lead levels in soil (|ig/g) or paint
29 (jig/cm2) and corresponding pica ingestion rates (g soil/day, cm2 paint/day). Dermal exposure to
30 lead in dust can also be simulated with input values for dust lead level (ng/g), dust loading on the
31 skin (mg/cm2), and skin exposure rate (cm2/day).
May 2006 4-111 DRAFT-DO NOT QUOTE OR CITE
-------
Respiratory
tract
Figure 4-28. Structure of the All Ages Lead Model. The AALM adds a comprehensive
exposure component and an uptake component to a revised and receded
version of the Leggett model to produce a model with fully selectable
exposure, uptake, and biokinetic parameters.
May 2006
4-112
DRAFT-DO NOT QUOTE OR CITE
-------
1 Calculated lead intakes for each exposure pathway are summed to calculate total intakes
2 (ng/day) to the respiratory tract, gastrointestinal tract, and dermal pathway, respectively.
3 The exposure model time step is 1 day (the smallest time interval for a single exposure event).
4
5 Biokinetics Module. The biokinetics module of the AALM is based on Leggett (1993)
6 with the following modifications and enhancements:
7
8 1. A simulation of dermal absorption is implemented that calculates transfer
9 of lead from the skin to the central plasma compartment, as a function of
10 rate of dermal contact with lead (jig/day) and a dermal absorption
11 fraction.
12 2. Male and female growth algorithms for body weight, soft tissues, and
13 cortical and trabecular bone are implemented, based on O'Flaherty
14 (1993, 1995). This allows simulation of tissue growth and volumes,
15 as well as lead concentrations in all tissues simulated.
16 3. A simulation of maternal-fetal transfer is implemented that simulates
17 lead levels in fetal tissues, and establishes blood and tissue lead levels
18 for a postnatal simulation. This provides a means for multigeneration
19 simulation of exposure and lead biokinetics.
20 4.4.8 Slope Factor Models
21 Slope factor models have been used as simpler alternatives to compartmental models for
22 predicting blood lead concentrations, or the change in blood lead concentration associated with a
23 change in exposure (Maddaloni et al., 2005; U. S. Environmental Protection Agency, 2003c;
24 Abadin and Wheeler, 1997; Stern, 1996; Bowers et al., 1994; Stern, 1994; Carlisle and Wade,
25 1992). In slope factor models, lead biokinetics are represented as a linear function between the
26 blood lead concentration and either lead uptake (uptake slope factor, USF) or lead intake (intake
27 slope factor, ISF). The models take the general mathematical forms:
28
29 PbB = E-ISF (4-12)
30
31 PbB = E-AF-USF (4-13)
32
33 where PbB is the blood lead concentration, E is an expression for exposure (e.g., soil intake x
34 soil lead concentration) and AF is the absorption fraction for lead in the specific exposure
May 2006 4-113 DRAFT-DO NOT QUOTE OR CITE
-------
1 medium of interest. Intake slope factors are based on ingested rather than absorbed lead and,
2 therefore, integrate both absorption and biokinetics into a single slope factor, whereas models
3 that utilize an uptake slope factor include a separate absorption parameter. In general, slope
4 factor models predict quasi-steady state blood lead concentrations that correspond to time-
5 averaged daily lead intakes (or uptakes) that occur over sufficiently long periods to produce a
6 quasi-steady state (i.e., >75 days, ~3 times the ti/2 for elimination of lead in blood).
7
8 4.4.9 Model Comparisons
9 Table 4-18 summarizes the major features of various models of human exposure that
10 predict tissue lead burdens. The slope factor models give similar predictions of quasi-steady
11 state blood lead concentration when similar inputs and parameter values were applied to each
12 model (Maddaloni et al., 2005). Of the models presented in Table 4-18, Bowers et al. (1994) and
13 U.S. EPA (2003c) implement uptake slope factors. The slope factors used in both models
14 (-0.4 |ig/dL per jig Pb/day) are similar to biokinetic slope factors predicted from the O'Flaherty
15 model (0.65 |ig/dL per jig Pb uptake/day) and Leggett model (0.43 |ig/dL per jig Pb uptake/day)
16 for simulations of adult exposures (Maddaloni et al., 2005). A review of reported intake slope
17 factors relating medium-specific exposures and blood lead concentrations derived from
18 epidemiologic studies can be found in the 1986 AQCD and in Abadin and Wheeler (1997).
19 Lead uptake-blood lead concentration relationships in children, predicted by the IEUBK,
20 Leggett, and O'Flaherty models are shown in Figure 4-29. In the range of uptakes shown (0.1 to
21 100 jig lead absorbed/day), nonlinearity of the relationship is apparent in the Leggett and
22 O'Flaherty models simulations. This reflects assumptions in each model regarding the limited
23 capacity of red blood cells to take up lead, which has also been observed in humans (Bergdahl
24 et al., 1997a, 1998, 1999; Manton et al., 2001; Smith et al., 2002; see Section 4.3.1 for further
25 discussion of curvilinear relationship between lead intake and blood lead concentration
26 relationship). Regression slopes (|ig/dL blood per |ig/day uptake) for the predictions < 10 |ig/dL
27 are: Leggett model, 0.88; IEUBK model, 0.36; O'Flaherty model, 0.29. The models predict an
28 average blood lead concentration of 10 |ig/dL for the age range 2 to 3 years, in association with
29 average lead uptakes (jig/day) for the same period of approximately: Leggett model, 12; IEUBK
30 model, 29; O'Flaherty model, 36.
31
May 2006 4-114 DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-17. Summary of Models of Human Exposure that Predict Tissue Distribution of Lead
to
o
°"
J^.
1
l^ft
u
>
H
6
o
2|
0
H
/O
O
H
W
O
O
HH
H
W
Age
Model Range Exposure Pathways
U.S. Environmental 0-7 yr Air
Protection Agency Diet
IEUBK Model Soil/dust
White etal. (1998) Water
Other
U.S. Environmental 0-90 yr Air
Protection Agency Diet
AALM (2005) Soil/dust
Water
Other
Leggett (1985) 0-Adult Intakes (inhaled,
ingested, injected)
O'Flaherty (1993, 1995) 0-Adult Air
Diet
Soil/dust
Water
Other
Exposure Biomarkers
Time Step Biokinetics Simulation Predicted
1 year Multicompartmental Blood lead
1 day Multicompartmental Blood
Bone
Brain
Fetus
Kidney
Liver
Urine
1 day Multicompartmental Blood
Bone
Brain
Kidney
Liver
Urine
1 year Multicompartmental Blood
(code supports Bone
1 day) Brain
Kidney
Liver
Urine
Variability and
Uncertainty Simulation
Variability: blood lead
GSD,
Variability/uncertainty :
MCA (Griffin et al., 1999b)
Variability and uncertainty
determined by independent
assessment of multiple runs
of the model.
NA
Beck etal. (2001)
-------
Table 4-17 (cont'd). Summary of Models of Human Exposure that Predict Tissue Distribution of Lead
to
o
o
ON
i
ON
Model
U.S. Environmental
Protection Agency ALM
Maddaloni et al. (2005)
California Environmental
Protection Agency,
Carlisle and Wade
(1992)
Bowers et al. (1994)
Stern (1994, 1996)
Age
Range
Adult
Child
Adult
Adult
Child
Adult
Exposure Pathways
Soil (supports
other pathways)
Air
Diet
Soil/dust
Water
Air
Soil/dust
Water
Dust/soil
Exposure Time Step
>3 months
(quasi-steady state)
>3 months
(quasi-steady state)
<3 months
(quasi-steady state)
>3 months
(quasi-steady state)
Biokinetics
Simulation
Uptake slope factor
Intake slope factor
Uptake slope factor
Intake slope factor
Biomarkers
Predicted
Blood
Blood
Blood
Blood
Variability and
Uncertainty Simulation
Variability: blood lead
GSD,
Variability: blood lead
GSD,
Variability: blood lead
GSD
Variability: blood lead
GSD,: MCA
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
-------
60
50
T3
~B>40
A Leggett - Child (2-3yr)
» O'Flaherty - Child (2-3yr)
IEUBK - Child (2-3yr)
0
20 40 60
Lead Uptake (ug/day)
80
100
40
35
30
25
0
A Leggett - Child (2-3yr)
« O'Flaherty - Child (2-3yr)
IEUBK - Child (2-3yr)
10 20 30
Lead Uptake (ug/day)
40
Figure 4-29. Model comparison of predicted lead uptake-blood lead concentration
relationship in children. In the range of uptakes shown, the nonlinearity
of the relationship is apparent in the Leggett and O'Flaherty Models
simulations, reflecting the simulation of the limited capacity of red blood cells
to take up lead. Regression slopes (ug /dL blood per ug/day uptake) for the
predictions ^lOug/dL are: Leggett Model, 0.88; IEUBK Model, 0.36;
O'Flaherty Model, 0.29.
May 2006
4-117
DRAFT-DO NOT QUOTE OR CITE
-------
1 A similar comparison of uptake-blood lead concentration relationships predicted in adults
2 is shown in Figure 4-30. Regression slopes for adults predicted by the Leggett and O'Flaherty
3 models (at blood lead concentrations < 10 |ig/dL) are more similar for adults (Leggett model,
4 0.54; O'Flaherty model, 0.72) than for children (see Figure 4-29 versus Figure 4-30). The
5 models predict an average blood lead concentration of 10 |ig/dL for the age range 31 to 32 years,
6 in association with average lead uptakes, for the same period, of-18 and 13 jig/day, Leggett and
7 O'Flaherty models, respectively. The nonlinearity in both children and adults is due largely to
8 assumptions made in the models about the limited capacity of red blood cells to take up lead at
9 concentrations above 15 to 20 |ig/dL. The IEUBK model (for children) does not include this
10 nonlinearity feature.
11 Comparisons of predicted bone and soft tissue lead burdens are shown in Figure 4-31.
12 Leggett and O'Flaherty models predict bone lead burdens. Both the Leggett and O'Flaherty
13 models predict a bone lead burden in adults of-90 and 98% of total body burden, respectively.
14 Regression slopes (mg lead in bone per jig uptake/day) are 1.2 for the Leggett model and 2.1 for
15 the O'Flaherty model.
16 Figures 4-32 and 4-33 compare model predictions for blood lead concentration for
17 hypothetical childhood or adult lead exposures. The hypothetical child (Figure 4-32) has a
18 blood lead concentration of 2 |ig/dL at age 2 years and then experiences a 1-year exposure to
19 100 jig Pb/day. All three models (Leggett, IEUBK, and O'Flaherty) predict a similar temporal
20 pattern of increase in blood lead concentration at the start of exposure, then attainment of a
21 quasi-steady state, followed by a decrease in blood lead concentration, with fast and slower
22 phases of the decline in blood lead concentration after the exposure ceases. However,
23 differences in the predicted kinetics of the blood lead changes and the predicted quasi-steady
24 state blood lead concentrations are evident. For this hypothetical scenario, the Leggett model
25 predicts the highest blood lead concentrations (23 |ig/dL) compared to the O'Flaherty (12 |ig/dL)
26 and IEUBK (10 |ig/dL) models. These differences are not solely the result of different values for
27 the absorption fraction in 2 to 3 year old children: Leggett model, 30%; O'Flaherty model, 45%
28 (descending from 49% at age 2 years to 39% at age 3 years); IEUBK model, 25% (at a soil lead
29 intake of 100 jig/day). A similar pattern is evident in the simulation of the same exposure
30 (100 |ig/day for 1 year) in an adult (age 30 years; Figure 4-33). The Leggett model predicts
31 a quasi-steady state blood lead concentration of approximately 8.2 |ig/dL and the O'Flaherty
May 2006 4-118 DRAFT-DO NOT QUOTE OR CITE
-------
60
— Leggett - Adult (30-31 yr)
OU
* O'Flaherty - Adult (30-31 yr)
40
20 40 60 80 100
Lead Uptake (tig/day)
Figure 4-30. Model comparison of predicted lead uptake-blood lead concentration
relationships in adults. The nonlinearity of the relationship is apparent in
both the Leggett and O'Flaherty Models. Regression slopes (jig /dL blood
per jig/day uptake) for the predictions ^10ug/dL are: Leggett Model, 0.54;
O'Flaherty Model, 0.72.
1 model predicts 5.4 |ig/dL. However, most of this difference can be attributed to the different
2 absorption fraction values used for adults in the two models; 15% in the Leggett model and 8%
3 in the O'Flaherty model.
4 A comparison of predictions of quasi-steady state blood lead concentrations from various
5 models was reported in Maddaloni et al. (2005). Results of comparisons between the U.S. ALM,
6 Leggett model and O'Flaherty model are presented in Table 4-19. When similar exposure inputs
7 are used in the three models, similar blood lead concentrations are predicted. Much of the
8 difference between the Leggett model and ALM predictions can be ascribed to the differences in
9 assumed bioavailability of lead in soil: 12% in the U.S. EPA ALM, and 15% in the Leggett
10 model.
11
12
May 2006 4-119 DRAFT-DO NOT QUOTE OR CITE
-------
240
200
| 160
1 120
_i
(!)
§ 80
CD
•Leggett-Adult (30-31 yr)
O'Flaherty - Adult (30-31 yr)
0
20 40 60
Lead Uptake (ug/day)
80
100
CO
CD
CO
O
U)
14
12
10
8
6
-Leggett-Adult (30-31 yr)
O'Flaherty - Adult (30-31 yr)
0
20 40 60
Lead Uptake (ug/day)
80
100
Figure 4-31. Model comparison of predicted of lead uptake-bone and soft tissue lead
burden relationship in adults. Both the Leggett and O'Flaherty Models
predict a bone lead burden of approximately 90% and 98% of total body
burden, respectively. Soft tissue burdens shown include blood. Regression
slopes (mg Pb per ug uptake/day) for uptake-bone burden relationship is:
Leggett, 1.2; O'Flaherty Model, 2.1.
May 2006
4-120
DRAFT-DO NOT QUOTE OR CITE
-------
Base
Leggett Model
IEUBK Model
O'Flaherty Model
Figure 4-32. Comparison of model predictions for childhood lead exposure. The
simulations are of a hypothetical child who has a blood lead concentration
of 2 ug/dL at age 2 years, and then experiences a 1-year exposure to 100 ug
Pb/day. Default bioavailability assumptions were applied in all three models.
10
T3
TO
0>
T3
O
_O
DO
0
Leggett Model
O'Flaherty Model
27 28 29
30 31 32
Age (year)
33 34
35
Figure 4-33. Comparison of model predictions for adult lead exposure. The simulations
are a hypothetical adult who has a blood lead concentration of 2 ug/dL at age
30 years and then experiences a 1-year exposure to 100 ug Pb/day. Default
bioavailability assumptions were applied in the Leggett and O'Flaherty
models.
May 2006
4-121
DRAFT-DO NOT QUOTE OR CITE
-------
Table 4-18. Inputs and Results of Simulations Comparing the U.S. EPA Adult Lead Methodology (ALM)
to
o
o
J^.
1
to
to
Parameters
Soil lead concentration
IRs
AF
Baseline blood lead
Exposure frequency
Exposure duration
Predicted quasi-steady state PbB
Soil lead: 1000 ug/g
Soil lead: 10,000 ug/g
ALM
1000 ug/g
0.05 g/day
0.12
2ug/dL
5 days/week
(260 days/year)1
NA
(jug/dL)
3.7
19
Rabinowitz model
1000 ug/ga'b
0.05 g/day a
0.12a
2 ug/dLe
5 days/week
(260 days/year)
365 days
4.1
23
Bert model
1000 ug/g *°
0.05 g/day a
0.12(0.08)d
2 ug/dLf
5 days/week
(260 days/year)
365 days
4.0 (2.6)k
21 (14)k
Leggett model
1000 ug/ga'c
0.05 g/day a
0.12(0.15)d
2 ug/dLg
5 days/week
(260 days/year)
17-45 years
4.1 (4.9)k
23 (29)k
O'Flaherty model
1000 ug/ga'c
0.05 g/day a
0.08
2 ug/dLh
5 days/week
(260 days/year)
17-45 years'
4.6
24
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
aNot a parameter in the model.
bSimulatedas an increment in daily uptake of 6 ng/day (i.e., 1000 x 0.05 x 0.12) above baseline.
°Simulated as an increment in daily intake of 50 ng/day (i.e., 1000 x 0.05) above baseline.
dDefault values are shown in parenthesis.
eA daily uptake of 4.1 ng/day yielded a quasi-steady state PbB of 2 |ig/dL.
fA daily intake of 38.7 ng/day yielded a quasi-steady state PbB of 2 |ig/dL.
gA daily intake that varied from 12 to 25 jig/day yielded pre-adult PbBs within the ranges reported from Phase I of NHANES III (Brody et al. 1994) and an adult PbB
of 2 |ig/dL.
hSetting all lead concentrations and intakes to null and food lead ingestion by adults born in 1980 to 25 ng/day yielded pre-adult PbBs within the ranges reported from
Phase I of NHANES III (Brody et al. 1994) and an adult PbB of 2 |ig/dL.
'The default exposure frequency for the ALM is 219 days/year; however, the assumption of 260 days/year in the simulations would not change the outcome of the
model comparisons.
JAdults born in 1980.
Predictions based on the default value for the AF are shown in parenthesis.
-------
1 4.4.10 Conclusions and Future Directions
2 Modeling of relationships between lead exposures and lead levels in tissues has advanced
3 considerably during the past 25 years or so. Three mechanistic models have been developed and
4 evaluated to varying degrees for predicting associations between exposure and body burden
5 (TEUBK model, Leggett model, O'Flaherty model). A fourth model, the All Ages Lead Model
6 (AALM), is still under development and may resolve some of the issues regarding minor
7 discrepancies between other models, while at the same time adding new features directly
8 applicable to risk assessment.
9 The IEUBK model has had the most extensive application in the regulatory context,
10 as EPA guidance recommends that, where possible, risk estimates for residential exposures to
11 lead at hazardous waste sites be based on IEUBK model predictions of blood lead concentrations
12 in children. Although, these models are constructed very differently (e.g., the O'Flaherty
13 biokinetics model has only 17 lead parameters, compared to 65 in the Leggett biokinetics model,
14 and 47 in the IEUBK biokinetics model), the three models yield remarkably similar predictions
15 of blood lead concentration for similar hypothetical exposure scenarios. The three models
16 predict similar kinetics of change of blood lead concentrations in association with a change in
17 lead exposure (e.g., Figures 4-32 and 4-33). Both the Leggett and O'Flaherty models predict
18 similar rates of lead accumulation in bone, for the same rates of uptake of lead into the body.
19 Predictions of quasi-steady state blood lead concentrations for the scenarios are simulated in
20 Figures 4-32 and 4-33 and differ across models by a factor of approximately 2. This magnitude
21 of difference is substantial in the context of certain regulatory uses of the models (e.g., for
22 establishing cleanup goals at hazardous waste sites); however, it is not surprising given the
23 various approaches taken to reduce the complex biokinetics of lead to tractable, and relatively
24 simple, mathematical expressions.
25 Several major challenges remain to be confronted in further developing our ability to
26 simulate lead exposure-tissue level relationships in real individuals or populations. The three
27 earlier mechanistic models described above do not simulate the kinetics of lead in pregnancy or
28 in senescence (e.g., menopause). Only one of these three earlier models (Leggett) simulates lead
29 levels in brain, a potential target organ for lead toxicity. None of the models have been
30 rigorously evaluated for accuracy of predictions of bone lead levels in humans, for which there is
31 a rapidly expanding set of observations of importance to dose-response assessment. Of great
May 2006 4-123 DRAFT-DO NOT QUOTE OR CITE
-------
1 importance for regulatory uses of the models, for example, is the need for more rigorous
2 quantitative assessment of confidence (i.e., uncertainty) in model predictions. To date, such
3 assessments have not been applied uniformly in a manner that allows cross-model comparisons
4 of confidence for specific regulatory uses.
5 The IEUBK Model has undergone the most extensive and thoroughly reported evaluation
6 of a regulatory use of the model, i.e., (a) quantitative evaluation of predicted distributions of
7 blood lead concentrations in children who live in areas for which cross-sectional measurements
8 of environmental lead levels were available and (b) independent verification of the IEUBK
9 model implementation code (Hogan et al., 1998; Zaragoza and Hogan, 1998). However, a
10 similar level of evaluation of the Leggett and O'Flaherty models has not been reported, although
11 specific predictions of the models have been evaluated against observations (e.g.,
12 experimentally-observed kinetics of change in blood lead following a change in intakes).
13 To a large extent, the important information gap regarding evaluation of model confidence
14 derives from a lack of observational data and/or public access to observational data on which
15 predictions could be evaluated. An additional challenge for applications of the models in a
16 regulatory context relates to uncertainties in exposure data from which exposure model inputs
17 are derived. Model development and uncertainty assessment could be substantively advanced by
18 assembling verified (for accuracy) sets of data on lead biokinetics against which models could be
19 uniformly evaluated. Examples of the types of data that would be valuable include data on the
20 kinetics of change in blood or tissue lead concentrations, or stable lead isotope ratios, in response
21 to a change in exposure. Also, access to large data bases that include reported lead exposure
22 measurements for various media that are paired with blood or tissue lead measurements for
23 individuals affected by pertinent exposure scenarios would also be extremely valuable for cross-
24 model evaluations.
May 2006 4-124 DRAFT-DO NOT QUOTE OR CITE
-------
1 REFERENCES
2 Abadin, H. G.; Wheeler, J. S. (1997) Guidance for risk assessment of exposure to lead: a site-specific, multi-media
3 approach. In: In Hazardous Waste and Public Health: International Congress on the Health Effects of
4 Hazardous Waste, Andrews, J. S.; Frumkin, H.; Johnson, B.L.; Mehlman, M.A.; Xintaras, C.; Bucsela,
5 J.A., eds. Princeton Scientific Publishing Co, Princeton: pp. 477-485.
6 Agency for Toxic Substances and Disease Registry (ATSDR). (2005) Toxicological profile for lead [draft]. Atlanta,
7 GA: U.S. Department of Health and Human Services, Public Health Service.
8 Aguilera de Benzo, Z.; Fraile, R.; Carrion, N.; Loreto, D. (1989) Determination of lead in whole blood by
9 electrothermal atomisation atomic absorption spectrometry using tube and platform atomisers and dilution
10 with triton X-100. J. Anal. At. Spectrom. 4: 397-400.
11 Ahlgren, L.; Liden, K.; Mattsson, S.; Tejning, S. (1976) X-ray fluorescence analysis of lead in human skeleton in
12 vivo. Scand. J. Work Environ. Health 2: 82-86.
13 Ahmed, N.; Fleming, D. E. B.; Wilkie, D.; O'Meara, J. M. (2006) Effects of overlying soft tissue onX-ray
14 fluorescence bone lead measurement uncertainty Radiat. Phys. Chem. 75: 1-6.
15 Al-Modhefer, A. J. A.; Bradbury, M. W. B.; Simons, T. J. B. (1991) Observations on the chemical nature of lead in
16 human blood serum. Clin. Sci. 81: 823-829.
17 Alexander, F. W.; Clayton, B. E.; Delves, H. T. (1974) Mineral and trace-metal balances in children receiving
18 normal and synthetic diets. Q. J. Med. 43:89-111.
19 Annesi-Maesano, L; Pollitt, R.; King, G.; Bousquet, J.; Hellier, G.; Sahuquillo, J.; Huel, G. (2003) In utero exposure
20 to lead and cord blood total IgE. Is there a connection? Allergy 58: 589-594.
21 Araki, S.; Aono, H.; Yokoyama, K.; Murata, K. (1986) Filterable plasma concentration, glomerular filtration,
22 tubular balance, and renal clearance of heavy metals and organic substances in metal workers. Arch.
23 Environ. Health 41: 216-221.
24 Araki, S.; Sata, F.; Murata, K. (1990) Adjustment for urinary flow rate: an improved approach to biological
25 monitoring. Int. Arch. Occup. Environ. Health 62: 471-477.
26 Armstrong, R.; Chettle, D. R.; Scott, M. C.; Somervaille, L. J.; Pendlington, M. (1992) Repeated measurements of
27 tibia lead concentrations by in vivo X-ray fluorescence in occupational exposure. Br. J. Ind. Med.
28 49: 14-16.
29 Aro, A.; Amarasiriwardena, C.; Lee, M.-L.; Kim, R.; Hu, H. (2000) Validation of K x-ray fluorescence bone lead
30 measurements by inductively coupled plasma mass spectrometry in cadaver legs. Med. Phys. 27: 119-123.
31 Aschengrau, A.; Beiser, A.; Bellinger, D.; Copenhafer, D.; Weitzman, M. (1994) The impact of soil lead abatement
32 on urban children's blood lead levels: phase II results from the Boston lead-in-soil demonstration project.
33 Environ. Res. 67: 125-148.
34 Aufderheide, A. C.; Wittmers, L. E., Jr. (1992) Selected aspects of the spatial distribution of lead in bone.
35 Neurotoxicology 13: 809-819.
36 Aungst, B. J.; Fung, H. (1981) Kinetic characterization of in vitro lead transport across the rat small intestine.
37 Toxicol. Appl. Pharmacol. 61: 39-47.
38 Aungst, B. J.; Dolce, J. A.; Fung, H. (1981) The effect of dose on the disposition of lead in rats after intravenous and
39 oral administration. Toxicol. Appl. Pharmacol. 61: 48-57.
40 Azar, A.; Snee, R. D.; Habibi, K. (1975) An epidemiologic approach to community air lead exposure using personal
41 samplers. In: Griffin, T. B.; Knelson, J. H., eds. Lead. Stuttgart, Federal Republic of Germany: Georg
42 Thieme Publishers; pp. 254-290. (Coulston, F.; Korte, F., eds. Environmental quality and safety:
43 supplement v. 2).
44 Bailey, M. R.; Roy, M. (1994) Clearance of particles from the respiratory tract. In: Human respiratory tract model
45 for radiological protection: a report of a task group of the International Commission on Radiological
46 Protection. Ann. ICRP 24(1-3): 301-413. (ICRP publication 66).
47 Bannon, D. I.; Abounader, R.; Lees, P. S. J.; Bressler, J. P. (2003) Effect of DMT1 knockdown on iron, cadmium,
48 and lead uptake in Caco-2 cells. Am. J. Physiol. 284: C44-C50.
49 Barltrop, D.; Meek, F. (1979) Effect of particle size on lead absorption from the gut. Arch. Environ. Health
50 34:280-285.
51 Barregard, L.; Svalander, C.; Schtitz, A.; Westberg, G.; Sallsten, G.; Blohme, I.; Molne, J.; Attman, P.-O.;
52 Haglind, P. (1999) Cadmium, mercury, and lead in kidney cortex of the general Swedish population:
53 a study of biopsies from living kidney donors. Environ. Health Perspect. 107: 867-871.
54 Barry, P. S. I. (1975) A comparison of concentrations of lead in human tissues. Br. J. Ind. Med. 32: 119-139.
55 Barry, P. S. I. (1981) Concentrations of lead in the tissues of children. Br. J. Ind. Med. 38: 61-71.
May 2006 4-125 DRAFT-DO NOT QUOTE OR CITE
-------
1 Barton, J. C. (1984) Active transport of lead-210 by everted segments of rat duodenum. Am. J. Physiol.
2 247: G193 G198.
3 Barton, J. C.; Conrad, M. E.; Nuby, S.; Harrison, L. (1978a) Effects of iron on the absorption and retention of lead.
4 J. Lab. Clin. Med. 92: 536-547.
5 Barton, J. C.; Conrad, M. E.; Harrison, L.; Nuby, S. (1978b) Effects of calcium on the absorption and retention of
6 lead. J. Lab. Clin. Med. 91: 366-376.
7 Beck, B. D.; Mattuck, R. L.; Bowers, T. S.; Cohen, J. T.; O'Flaherty, E. (2001) The development of a stochastic
8 physiologically-based pharmacokinetic model for lead. Sci. Total Environ. 274: 15-19.
9 Bellinger, D.; Hu, H.; Titlebaum, L.; Needleman, H. L. (1994) Attentional correlates of dentin and bone lead levels
10 in adolescents. Arch. Environ. Health 49: 98-105.
11 Bergdahl, I. A.; Schiitz, A.; Grubb, A. (1996) Application of liquid chromatography-inductively coupled plasma
12 mass spectrometry to the study of protein-bond lead in human erythrocytes. J. Anal. Atom. Spectrom.
13 11:735-738.
14 Bergdahl, I. A.; Schiitz, A.; Gerhardsson, L.; Jensen, A.; Skerfving, S. (1997a) Lead concentrations in human
15 plasma, urine and whole blood. Scand. J. Work Environ. Health 23: 359-363.
16 Bergdahl, I. A.; Grubb, A.; Schtitz, A.; Desnick, R. J.; Wetmur, J. G.; Sassa, S.; Skerfving, S. (1997b) Lead binding
17 to 5-aminolevulinic acid dehydratase (ALAD) in human erythrocytes. Pharmacol. Toxicol. 81: 153-158.
18 Bergdahl, I. A.; Sheveleva, M.; Schtitz, A.; Artamonova, V. G.; Skerfving, S. (1998) Plasma and blood lead in
19 humans: capacity-limited binding to "delta"-aminolevulinic acid dehydratase and other lead-binding
20 components. Toxicol. Sci. 46: 247-253.
21 Bergdahl, I. A.; Vahter, M.; Counter, S. A.; Schtitz, A.; Buchanan, L. H.; Ortega, F.; Laurell, G.; Skerfving, S.
22 (1999) Lead in plasma and whole blood from lead-exposed children. Environ. Res. 80: 25-33.
23 Berger, O. G.; Gregg, D. J.; Succop, P. A. (1990) Using unstimulated urinary lead excretion to assess the need for
24 chelation in the treatment of lead poisoning. J. Pediatr. 116: 46-51.
25 Berkowitz, G. S.; Wolff, M. S.; Lapinski, R. H.; Todd, A. C. (2004) Prospective study of blood and tibia lead in
26 women undergoing surgical menopause. Environ. Health Perspect. 112: 1673-1678.
27 Bert, J. L.; van Dusen, L. J.; Grace, J. R. (1989) A generalized model for the prediction lead body burdens. Environ.
28 Res. 48: 117-127.
29 Biagini, G.; Caudarella, R.; Vangelista, A. (1977) Renal morphological and functional modification in chronic lead
30 poisoning. In: Brown, S. S., ed. Clinical chemistry and chemical toxicology of metals. New York, NY:
31 Elsevier/North-Holland Biomedical Press; pp. 123-126.
32 Blake, K. C. H.; Mann, M. (1983) Effect of calcium and phosphorus on the gastrointestinal absorption of 203Pb in
33 man. Environ. Res. 30: 188-194.
34 Blake, K. H. C.; Barbezat, G. O.; Mann, M. (1983) Effect of dietary constituents on the gastrointestinal absorption
35 of 203Pb in man. Environ. Res. 30: 182-187.
36 Bolanowska, W.; Piotrowski, J.; Garczynski, H. (1967) Triethyllead in the biological material in cases of acute
37 tetraethylleadpoisoning. Arch. Toxicol. 22: 278-282.
38 Booker, D. V.; Chamberlain, A. C.; Newton, D.; Stott, A. N. B. (1969) Uptake of radioactive lead following
39 inhalation and injection. Br. J. Radiol. 42: 457-466.
40 Bornschein, R. L.; Succop, P.; Dietrich, K. N.; Clark, C. S.; Que Hee, S. Hammond PB. (1985a) The influence of
41 social and environmental factors on dust lead, hand lead, and blood lead levels in young children. Environ.
42 Res. 38: 108-118.
43 Bornschein, R. L.; Hammond, P. B.; Dietrich, K. N.; Succop, P.; Krafft, K.; Clark, S.; Berger, O.; Pearson, D.;
44 Que Hee, S. (1985b) The Cincinnati prospective study of low-level lead exposure and its effects on child
45 development: protocol and status report. Environ. Res. 38: 4-18.
46 Bos, A. J. J.; Van der Stap, C. C. A. H.; Valkovic, V.; Vis, R. D.; Verheul, H. (1985) Incorporation routes of
47 elements into human hair: implications for hair analysis used for monitoring. Sci.Total Environ.
48 42: 157-169.
49 Bowers, T. S.; Mattuck, R. L. (2001) Further comparisons of empirical and epidemiological data with predictions of
50 the Integrated Exposure Uptake Biokinetic Model for lead in children. Hum. Ecol. Risk Assess.
51 7:1699-1713.
52 Bowers, T. S.; Beck, B. D.; Karam, H. S. (1994) Assessing the relationship between environmental lead
53 concentrations and adult blood lead levels. Risk Anal. 14: 183-189.
54 Bress, W. C.; Bidanset, J. H. (1991) Percutaneous in vivo and in vitro absorption of lead. Vet. Hum. Toxicol.
55 33:212-214.
May 2006 4-126 DRAFT-DO NOT QUOTE OR CITE
-------
1 Brito, J. A. A.; McNeill, F. E.; Webber, C. E.; Wells, S.; Richard, N.; Carvalho, M. L.; Chettle, D. R. (2002)
2 Evaluation of a novel structural model to describe the endogenous release of lead from bone. J. Environ.
3 Monit. 4: 194-201.
4 Brockhaus, A.; Collet, W.; Dolgner, R.; Engelke, R.; Ewers, U.; Freier, L; Jermann, E.; Kramer, U.; Manojlovic, N.;
5 Turfeld, M.; Winneke, G. (1988) Exposure to lead and cadmium of children living in different areas of
6 north-west Germany: results of biological monitoring studies 1982-1986. Int. Arch. Occup. Environ. Health
7 60:211-222.
8 Brody, D. J.; Pirkle, J. L.; Kramer, R. A.; Flegal, K. M.; Matte, T. D.; Gunter, E. W.; Paschal, D. C. (1994) Blood
9 lead levels in the US population: phase 1 of the third National Health and Nutrition Examination Survey
10 (NHANES III, 1988 to 1991). JAMA J. Am. Med. Assoc. 272: 277-283.
11 Brown, A.; Tompsett, S. L. (1945) Poisoning due to mobilization of lead from the skeleton by leukaemic
12 hyperplasia of bone marrow. Br. Med. J. 2: 764-765.
13 Brown, M. J.; Hu, H.; Gonzales-Cossio, T.; Peterson, K. E.; Sanin, L.-H.; de Luz Kageyama, M.; Palazuelos, E.;
14 Aro, A.; Schnaas, L.; Hernandez-Avila, M. (2000) Determinants of bone and blood lead concentrations in
15 the early postpartum period. Occup. Environ. Med. 57: 535-541.
16 Cake, K. M.; Bowins, R. J.; Vaillancourt, C.; Gordon, C. L.; McNutt, R. H.; Laporte, R.; Webber, C. E.; Chettle,
17 D. R. (1996) Partition of circulating lead between serum and red cells is different for internal and external
18 sources of lead. Am. J. Ind. Med. 29: 440-445.
19 Campbell, J. R.; Toribara, T. Y. (2001) Hair-root lead to screen for lead toxicity. J. Trace Elem. Exp. Med.
20 14:69-72.
21 Campbell, B. C.; Meredith, P. A.; Moore, M. R.; Watson, W. S. (1984) Kinetics of lead following intravenous
22 administration in man. Toxicol. Lett. 21: 231-235.
23 Carbone, R.; Laforgia, N.; Crollo, E.; Mautone, A.; lolascon, A. (1998) Maternal and neonatal lead exposure in
24 southern Italy. Biol. Neonate 73: 362-366.
25 Carlisle, J. C.; Wade, M. J. (1992) Predicting blood lead concentrations from environmental concentrations.
26 Regul. Toxicol. Pharmacol. 16: 280-289.
27 Casteel, S. W.; Cowart, R. P.; Weis, C. P.; Henningsen, G. M.; Hoffman, E.; Brattin, W. J.; Guzman, R. E.; Starost,
28 M. F.; Payne, J. T.; Stockham, S. L.; Becker, S. V.; Drexler, J. W.; Turk, J. R. (1997) Bioavailability of
29 lead to juvenile swine dosed with soil from the Smuggler Mountain NPL site of Aspen, Colorado. Fundam.
30 Appl. Toxicol. 36: 177-187.
31 Casteel, S. W.; Weis, C. P.; Henningsen, G. M.; Brattin, W. L. (2006) Estimation of relative bioavailability of lead
32 in soil and soil-like materials using young swine. Environ. Health Perspect.: 10.1289/ehp.8852.
33 Centers for Disease Control and Prevention. (2005) Third national report on human exposure to environmental
34 chemicals. Atlanta, GA: U.S. Department of Health and Human Services, National Center for
3 5 Environmental Health. NCEH Pub. No. 05-0570.
36 Chamberlain, A. C.; Heard, M. J.; Little, P.; Newton, D.; Wells, A. C.; Wiffin, R. D. (1978) Investigations into lead
3 7 from motor vehicles. Harwell, United Kingdom: United Kingdom Atomic Energy Authority; report no.
38 AERE-R9198.
39 Cheng, Y.; Willett, W. C.; Schwartz, J.; Sparrow, D.; Weiss, S.; Hu, H. (1998) Relation of nutrition to bone lead and
40 blood lead levels in middle-aged to elderly men. The Normative Aging Study. Am. J. Epidemiol.
41 147: 1162-1174.
42 Cheng, Y.; Schwartz, J.; Sparrow, D.; Aro, A.; Weiss, S. T.; Hu, H. (2001) Bone lead and blood lead levels in
43 relation to baseline blood pressure and the prospective development of hypertension: the Normative Aging
44 Study. Am. J. Epidemiol. 153: 164-171.
45 Chettle, D. R.; Scott, M. C.; Somervaille, L. J. (1991) Lead in bone: sampling and quantitation using K X-rays
46 excited by 109Cd. Environ. Health Perspect. 91: 49-55.
47 Chettle, D. R.; Arnold, M. L.; Aro, A. C. A.; Fleming, D. E. B.; Kondrashov, V. S.; McNeill, F. E.; Moshier, E. L.;
48 Nie, H.; Rothenberg, S. J.; Stronach, I. M.; Todd, A. C. (2003) An agreed statement on calculating lead
49 concentration and uncertainty in XRF in vivo bone lead analysis. Appl. Radiat. Isot. 58: 603-605.
50 Chisolm, J. J., Jr.; Mellits, E. D.; Barrett, M. B. (1976) Interrelationships among blood lead concentration,
51 quantitative daily ALA-U and urinary lead output following calcium EDTA. In: Nordberg, G. F., ed.
52 Proceedings of third meeting of the subcommittee on the toxicology of metals under the Permanent
53 Commission and International Association on Occupational Health; November 1974; Toyko, Japan.
54 Amsterdam, The Netherlands: Elsevier Publishing Co.; pp. 416-433.
55 Chisolm, J. J., Jr.; Mellits, E. D.; Quaskey, S. A. (1985) The relationship between the level of lead absorption in
56 children and the age, type, and condition of housing. Environ. Res. 38: 31-45.
May 2006 4-127 DRAFT-DO NOT QUOTE OR CITE
-------
1 Christoffersson, J. O.; Schtitz, A.; Ahlgren, L.; Haeger-Aronsen, B.; Mattsson, S.; Skerfving, S. (1984) Lead in
2 finger-bone analysed in vivo in active and retired lead workers. Am. J. Ind. Med. 6: 447-457.
3 Christoffersson, J. O.; Ahlgren, L.; Schwartz, A.; Skerfving, S.; Mattsson, S. (1986) Decrease of skeletal lead levels
4 in man after end of occupational exposure. Arch. Environ. Health41: 312-318.
5 Chuang, H. Y.; Schwartz, J.; Gonzales-Cossio, T.; Lugo, M. C.; Palazuelos, E.; Aro, A.; Hu, H.; Hernandez-Avila,
6 M. (2001) Interrelations of lead levels in bone, venous blood, and umbilical cord blood with exogenous
7 lead exposure through maternal plasma lead in peripartum women. Environ. Health Perspect. 109: 527-532.
8 Clark, S.; Bornschein, R.; Succop, P.; Peace, B.; Ryan, J.; Kochanowski, A. (1988) The Cincinnati soil-lead
9 abatement demonstration project. In: Davies, B. E.; Wixson, B. G., eds. Lead in soil: issues and guidelines.
10 Northwood, England: Science Review Limited; pp. 287-300. Environ. Geochem. Health 9(suppl.).
11 (Monograph series 4).
12 Clark, S.; Bornschein, R.; Succop, P.; Roda, S.; Peace, B. (1991) Urban lead exposures of children in Cincinnati,
13 Ohio. Chem. Speciation Bioavailability 3(3-4): 163-171.
14 Clark, S.; Bornschein, R. L.; Pan, W.; Menrath, W.; Roda, S.; Grote, J. (1996) The relationship between surface dust
15 lead loadings on carpets and the blood lead of young children. Environ. Geochem. Health 18: 143-146.
16 Cools, A.; Salle, H. J. A.; Verberk, M. M.; Zielhuis, R. L. (1976) Biochemical response of male volunteers ingesting
17 inorganic lead for 49 days. Int. Arch. Occup. Environ. Health 38: 129-139.
18 Cramer, K.; Goyer, R. A.; Jagenburg, R.; Wilson, M. H. (1974) Renal ultrastructure, renal function, and parameters
19 of lead toxicity in workers with different periods of lead exposure. Br. J. Ind. Med. 31: 113-127.
20 Cristy, M. (1981) Active bone marrow distribution as a function of age in humans. Phys. Med. Biol. 26: 389-400.
21 Davis, A.; Ruby, M. V.; Bergstrom, P. D. (1994) Factors controlling lead bioavailability intheButte mining district,
22 Montana, USA. Environ. Geochem. Health 16: 147-157.
23 DeSilva, P. E. (1981) Determination of lead in plasma and studies on its relationship to lead in erythrocytes. Br. J.
24 Ind. Med. 38: 209-217.
25 Delves, H. T.; Campbell, M. J. (1988) Measurements of total lead concentrations and of lead isotope ratios in whole
26 blood by use of inductively coupled plasma source mass spectrometry. J. Anal. At. Spectrom. 3: 343-348.
27 DiPietro, E. S.; Philips, D. L.; Paschla, D. C.; Neese, J. W. (1989) Determination of trace elements in human hair.
28 Biol. Trace Elem. Res. 22: 83-100.
29 Diamond, G. L. (1988) Biological monitoring of urine for exposure to toxic metals. In: Clarkson, T. W.; Nordberg,
30 G.; Sager, P., eds. Scientific basis and practical applications of biological monitoring of toxic metals. New
31 York, NY: Plenum Press; pp. 515-529.
32 Diamond, G. L. (1992) Review of default value for lead plasma-to-urine transfer coefficient (TPLUR) in the U.S.
33 EPA uptake/biokinetic model. Syracuse, NY: Syracuse Research Corporation. Prepared for Environmental
34 Criteria and Assessment Office, U.S. Environmental Protection Agency.
35 Dietrich, K. N.; Berger, O. G.; Succop, P. A. (1993) Lead exposure and the motor developmental status of urban
36 six-year-old children in the Cincinnati prospective study. Pediatrics 91: 301-307.
37 Drasch, G. A.; Bohm, J.; Baur, C. (1987) Lead in human bones. Investigations on an occupationally non-exposed
3 8 population in southern Bavaria (F. R. G.). I. Adults. Sci. Total Environ. 64: 303-315.
39 Drasch, G.; Wanghofer, E.; Roider, G. (1997) Are blood, urine, hair, and muscle valid biomonitors for the internal
40 burden of men with the heavy metals mercury, lead and cadmium? Trace Elem. Electrolytes
41 14(3): 116-123.
42 DuVal, G.; Fowler, B. A. (1989) Preliminary purification and characterization studies of a low molecular weight,
43 high affinity cytosolic lead-binding protein in rat brain. Biochem. Biophys. Res. Commun. 159: 177-184.
44 Durbin, P. W. (1992) Distribution of transuranic elements in bone. Neurotoxicology 13: 821-824.
45 Eaton, D. L.; Stacey, N. H.; Wong, K.-L.; Klaassen, C. D. (1980) Dose-response effects of various metal ions on rat
46 liver metallothionein, glutathione, heme oxygenase, and cytochrome P-450. Toxicol. Appl. Pharmacol.
47 55:393-402.
48 Erfurth, E. M.; Gerhardsson, L.; Nilsson, A.; Rylander, L.; Schtitz, A.; Skerfving, S.; Borjesson, J. (2001) Effects of
49 lead on the endocrine system in lead smelter workers. Arch. Environ. Health 56: 449-455.
50 Erkkila, J.; Armstrong, R.; Riihimaki, V.; Chettle, D. R.; Paakkari, A.; Scott, M.; Somervaille, L.; Stark, J.; Kock,
51 B.; Aitio, A. (1992) In vivo measurements of lead in bone at four anatomical sites: long term occcupational
52 and consequent edogenous exposure. Br. J. Ind. Med. 49: 631-644.
53 Esteban, E.; Rubin, C. H.; Jones, R. L.; Noonan, G. (1999) Hair and blood substrates for screening children for lead
54 poisoning. Arch. Environ. Health 54: 436-440.
May 2006 4-128 DRAFT-DO NOT QUOTE OR CITE
-------
1 Ettinger, A. S.; Tellez-Rojo, M. M; Amarasiriwardena, C.; Gonzalez-Cossio, T.; Peterson, K. E.; Aro, A.; Hu, H.;
2 Hernandez-Avila, M. (2004) Levels of lead in breast milk and their relation to maternal blood and bone
3 lead levels at one month postpartum. Environ. Health Perspect. 112: 926-931.
4 Ewers, U.; Stiller-Winkler, R.; Idel, H. (1982) Serum immunoglobulin, complement C3, and salivary IgA levels in
5 lead workers. Environ. Res. 29: 351-357.
6 Farias, P.; Hu, H.; Rubenstein, E.; Meneses-Gonzalez, F.; Fishbein, E.; Palazuelos, E.; Aro, A.; Hernandez-Avila,
7 M. (1998) Determinants of bone and blood lead levels among teenagers living in urban areas with high lead
8 exposure. Environ. Health Perspect. 106: 733-737.
9 Farrell, K. (1988) Baltimore soil-lead abatement demonstration project. In: Davies, B. E.; Wixson, B. G., eds. Lead
10 in soil: issues and guidelines. Northwood, England: Science Review Limited; pp. 281-286. Environ.
11 Geochem. Health 9(suppl.). (Monograph series 4).
12 Fergusson, J. E.; Kinzett, N. G.; Fergusson, D. M.; Horwood, L. J. (1989) A longitudinal study of dentin lead levels
13 and intelligence school performance and behavior the measurement of dentin lead. Sci. Total Environ.
14 80:229-242.
15 Flanagan, P. R.; Hamilton, D. L.; Haist, J.; Valberg, L. S. (1979) Interrelationships between iron and lead absorption
16 in iron -deficient mice. Gastroenterology 77: 1074-1081.
17 Flegal, A. R.; Smith, D. R. (1995) Measurements of environmental lead contamination and human exposure. In:
18 Ware, G. W., ed. Reviews of environmental contamination and toxicology, continuation of residue reviews,
19 v. 143. New York, NY: Springer, pp. 1-45.
20 Fleming, D. E. B.; Boulay, D.; Richard, N. S.; Robin, J.-P.; Gordon, C. L.; Webber, C. E.; Chettle, D. R. (1997)
21 Accumulated body burden and endogenous release of lead in employees of a lead smelter. Environ. Health
22 Perspect. 105: 224-233.
23 Fleming, D. E. B.; Chettle, D. R.; Wetmur, J. G.; Desnick, R. J.; Robin, J.-P.; Boulay, D.; Richard, N. S.; Gordon,
24 C. L.; Webber, C. E. (1998) Effect of the 5-aminolevulinate dehydratase polymorphism on the
25 accumulation of lead in bone and blood in lead smelter workers. Environ. Res. 77: 49-61.
26 Forbes, G. B.; Braining, G. B. (1976) Urinary creatinine excretion and lean body mass. Am. J. Clin. Nutr.
27 29: 1359-1366.
28 Forbes, G. B.; Reina, J. C. (1972) Effect of age on gastrointestinal absorption (Fe, Sr, Pb) in the rat. J. Nutr.
29 102:647-652.
30 Fosse, G.; Wesenberg, G. R.; Tvinnereim, H. M., Eide, R.; Kristoffersen, 0.; Nag, O. H.; Wierzbicka, M.;
31 Banoczy, J.; De Oliveira, A. A.; Srisopak, C.; Zamudio, A. (1995) Lead in deciduous teeth from larger
32 cities of some countries. Int. J. Environ. Stud. 47: 203-210.
33 Fowler, B. A. (1989) Biological roles of high affinity metal-binding proteins in mediating cell injury. Comments
34 Toxicol. 3:27-46.
35 Fowler, B. A.; DuVal, G. (1991) Effects of lead on the kidney: roles of high-affinity lead-binding proteins. Environ.
36 Health Perspect. 91: 77-80.
37 Franklin, C. A.; Inskip, M. J.; Baccanale, C. L.; Edwards, C. M.; Manton, W. I.; Edwards, E.; O'Flaherty, E. J.
3 8 (1997) Use of sequentially administered stable lead isotopes to investigate changes in blood lead during
39 pregnancy in a nonhuman primate (Macacafascicularis). Fundam. Appl. Toxicol. 39: 109-119.
40 Freeman, G. B.; Johnson, J. D.; Killinger, J. M.; Liao, S. C.; Feder, P. I.; Davis, A. O.; Ruby, M. V.; Chaney, R. L.;
41 Lovre, S. C.; Bergstrom, P. D. (1992) Relative bioavailability of lead from mining waste soil in rats.
42 Fundam. Appl. Toxicol. 19: 388-398.
43 Freeman, G. B.; Johnson, J. D.; Liao, S. C.; Feder, P. I.; Davis, A. O.; Ruby, M. V.; Schoof, R. A.; Chaney, R. L.;
44 Bergstrom, P. D. (1994) Absolute bioavailability of lead acetate and mining waste lead in rats. Toxicology
45 91: 151-163.
46 Freeman, G. B.; Dill, J. A.; Johnson, J. D.; Kurtz, P. J.; Parham, F.; Matthews, H. B. (1996) Comparative absorption
47 of lead from contaminated soil and lead salts by weanling Fischer 344 rats. Fundam. Appl. Toxicol.
48 33: 109-119.
49 Garrido Latorre, F.; Hernandez-Avila, M.; Orozco, J. T.; Medina, C. A. A.; Aro, A.; Palazuelos, E.; Hu, H. (2003)
50 Relationship of blood and bone lead to menopause and bone mineral density among middle-age women in
51 Mexico City. Environ. Health Perspect. Ill: 631-636.
52 Gerhardsson, L.; Brane, D.; Nordberg, G. F.; Wester, P. O. (1986) Distribution of cadmium, lead and zinc in lung,
53 liver and kidney in long-term exposed smelter workers. Sci. Total Environ. 50: 65-85.
54 Gerhardsson, L.; Chettle, D. R.; Englyst, V.; Nordberg, G. F.; Nyhlin, H.; Scott, M. C.; Todd, A. C.; Vesterberg, O.
55 (1992) Kidney effects in long term exposed lead smelter workers. Br. J. Ind. Med. 49: 186-192.
May 2006 4-129 DRAFT-DO NOT QUOTE OR CITE
-------
1 Gerhardsson, L.; Attewell, R.; Chettle, D. R.; Englyst, V.; Lundstrom, N.-G.; Nordberg, G. F.; Nyhlin, H.; Scott,
2 M. C.; Todd, A. C. (1993) In vivo measurements of lead in bone in long-term exposed lead smelter
3 workers. Arch. Environ. Health 48: 147-156.
4 Gerhardsson, L.; Hagmar, L.; Rylander, L.; Skerfving, S. (1995a) Mortality and cancer incidence among secondary
5 lead smelter workers. Occup. Environ. Med. 52: 667-672.
6 Gerhardsson, L.; Englyst, V.; Lundstrom, N.G.; Nordberg, G.; Sandberg, S.; Steinvall, F. (1995b) Lead in tissues of
7 deceased lead smelter worker. J. Trace Elem. Med. Biol. 9: 136-143.
8 Gerr, F.; Letz, R.; Stokes, L.; Chettle, D.; McNeill, F.; Kaye, W. (2002) Association between bone lead
9 concentration and blood pressure among young adults. Am. J. Ind. Med. 42: 98-106.
10 Glenn, B. S.; Stewart, W. F.; Links, J. M.; Todd, A. C.; Schwartz, B. S. (2003) The longitudinal association of lead
11 with blood pressure. Epidemiology 14: 30-36.
12 Goering, P. L.; Fowler, B. A. (1987) Metal constitution of metallothionein influences inhibition of delta-
13 aminolaevulinic acid dehydratase (porphobilinogen synthase) by lead. Biochem. J. 245: 339-345.
14 Gomaa, A.; Hu, H.; Bellinger, D.; Schwartz, J.; Tsaih, S.-W.; Gonzalez-Cossio, T.; Schnaas, L.; Peterson, K.;
15 Aro, A.; Hernandez-Avila, M. (2002) Maternal bone lead as an independent risk factor for fetal
16 neurotoxicity: a prospective study. Pediatrics 110: 110-118.
17 Gonzalez-Cossio, T.; Peterson, K. E.; Sanin, L.-H.; Fishbein, E.; Palazuelos, E.; Aro, A.; Hernandez-Avila, M.;
18 Hu, H. (1997) Decrease in birth weight in relation to maternal bone-lead burden. Pediatrics 100: 856-862.
19 Goodrum, P. E.; Diamond, G. L.; Hassett, J. M.; Johnson, D. L. (1996) Monte Carlo modeling of childhood lead
20 exposure: development of a probabilistic methodology for use with the USEPAIEUBK model for lead in
21 children. Hum. Ecol. Risk Assess. 2: 681-708.
22 Gordon, C. L.; Chettle, D. R.; Webber, C. E. (1993) An improved instrument for the in vivo detection of lead in
23 bone. Br. J. Ind. Med. 50: 637-641.
24 Gordon, C. L.; Webber, C. E.; Chettle, D. R. (1994) The reproducibility of 109Cd-based X-ray fluorescence
25 measurements of bone lead. Environ. Health Perspect. 102: 690-694.
26 Goyer, R. A. (1990) Lead toxicity: from overt to subclinical to subtle health effects. Environ. Health Perspect.
27 86: 177-181.
28 Graziano, J. H. (1994) Validity of lead exposure markers in diagnosis and surveillance. Clin. Chem. 40: 1387-1390.
29 Graziano, J. H.; Popovac, D.; Factor-Litvak, P.; Shrout, P.; Kline, J.; Murphy, M. J.; Zhao, Y.-H.; Mehmeti, A.;
30 Ahmedi, X.; Rajovic, B.; Zvicer, Z.; Nenezic, D. U.; Lolacono, N. J.; Stein, Z. (1990) Determinants of
31 elevated blood lead during pregnancy in a population surrounding a lead smelter in Kosovo, Yugoslavia.
32 In: Conference on advances in lead research: implications for environmental health; January 1989;
33 Research Triangle Park, NC. Environ. Health Perspect. 89: 95-100.
34 Griffin, T. B.; Coulston, F.; Wills, H.; Russell, J. C.; Knelson, J. H. (1975) Clinical studies on men continuously
35 exposed to airborne paniculate lead. In: Griffin, T. B.; Knelson, J. H., eds. Lead. Stuttgart, Federal
36 Republic of Germany: Georg Thieme Publishers; pp. 221-240. (Coulston, F.; Korte, F., eds. Environmental
37 quality and safety: supplement v. 2).
38 Griffin, S.; Goodrum, P. E.; Diamond, G. L.; Meylan, W.; Brattin, W. J.; Hassett, J. M. (1999a) Application of a
39 probabilistic risk assessment methodology to a lead smelter site. Hum. Ecol. Risk Assess. 5: 845-868.
40 Griffin, S.; Marcus, A.; Schulz, T.; Walker, S. (1999b) Calculating the interindividual geometric standard deviation
41 for use in the integrated exposure uptake biokinetic model for lead in children. Environ. Health Perspect.
42 107:481-487.
43 Gross, S. B.; Pfitzer, E. A.; Yeager, D. W.; Kehoe, R. A. (1975) Lead in human tissues. Toxicol. Appl. Pharmacol.
44 32:638-651.
45 Gulson, B. L. (1996) Tooth analyses of sources and intensity of lead exposure in children. Environ. Health Perspect.
46 104:306-312.
47 Gulson, B. L. (2000) Revision of estimates of skeletal contribution to blood during pregnancy and postpartum
48 period. J. Lab. Clin. Med. 136: 250-251.
49 Gulson, B.; Wilson, D. (1994) History of lead exposure in children revealed from isotopic analyses of teeth. Arch.
50 Environ. Health 49: 279-283.
51 Gulson, B. L.; Mahaffey, K. R.; Mizon, K. J.; Korsch, M. J.; Cameron, M. A.; Vimpani, G. (1995) Contribution of
52 tissue lead to blood lead in adult female subjects based on stable lead isotope methods. J. Lab. Clin. Med.
53 125:703-712.
54 Gulson, B. L.; Jameson, C. W.; Mahaffey, K. R.; Mizon, K. J.; Korsch, M. J.; Vimpani, G. (1997) Pregnancy
55 increases mobilization of lead from maternal skeleton. J. Lab. Clin. Med. 130: 51-62.
May 2006 4-130 DRAFT-DO NOT QUOTE OR CITE
-------
1 Gulson, B. L.; Mahaffey, K. R.; Jameson, C. W.; Mizon, K. I; Korsch, M. I; Cameron, M. A.; Eisman, J. A.
2 (1998a) Mobilization of lead from the skeleton during the postnatal period is larger than during pregnancy.
3 J. Lab. Clin. Med. 131: 324-329.
4 Gulson, B. L.; Jameson, C. W.; Mahaffey, K. R.; Mizon, K. J.; Patison, N.; Law, A. J.; Korsch, M. J.; Salter, M. A.
5 (1998b) Relationships of lead in breast milk to lead in blood, urine, and diet of the infant and mother.
6 Environ. Health Perspect. 106: 667-674.
7 Gulson, B. L.; Gray, B.; Mahaffey, K. R.; Jameson, C. W.; Mizon, K. J.; Patison, N.; Korsch, M. J. (1999a)
8 Comparison of the rates of exchange of lead in the blood of newly born infants and their mothers with lead
9 from their current environment. J. Lab. Clin. Med. 133: 171-178.
10 Gulson, B. L.; Mahaffey, K. R.; Jameson, C. W.; Patison, N.; Law, A. J.; Mizon, K. J.; Korsch, M. J.; Pederson, D.
11 (1999b) Impact of diet on lead in blood and urine in female adults and relevance to mobilization of lead
12 from bone stores. Environ. Health Perspect. 107: 257-263.
13 Gulson, B. L.; Mizon, K. J.; Palmer, J. M.; Korsch, M. J.; Donnelly, J. B. (2000) Urinary excretion of lead during
14 pregnancy and postpartum. Sci. Total Environ. 262: 49-55.
15 Gulson, B. L.; Mizon, K. J.; Palmer, J. M.; Korsch, M. J.; Taylor, A. J. (2001) Contribution of lead from calcium
16 supplements to blood lead. Environ. Health Perspect. 109: 283-288.
17 Gulson, B.; Mizon, K.; Smith, H.; Eisman, J.; Palmer, J.; Korsch, M.; Donnelly, J.; Waite, K. (2002) Skeletal lead
18 release during bone resorption: effect of bisphosphonate treatment in a pilot study. Environ. Health
19 Perspect. 110: 1017-1023.
20 Gulson, B. L.; Mizon, K. J.; Korsch, M. J.; Palmer, J. M.; Donnelly, J. B. (2003) Mobilization of lead from human
21 bone tissue during pregnancy and lactation~a summary of long-term research. Sci. Total Environ.
22 303:79-104.
23 Gulson, B. L.; Mizon, K. J.; Palmer, J. M.; Korsch, M. J.; Taylor, A. J.; Mahaffey, K. R. (2004) Blood lead
24 changes during pregnancy and postpartum with calcium supplementation. Environ. Health Perspect.
25 112: 1499-1507.
26 Gwiazda, R.; Campbell, C.; Smith, D. (2005) A noninvasive isotopic approach to estimate the bone lead
27 contribution to blood in children: implications for assessing the efficacy of lead abatement. Environ. Health
28 Perspect. 113: 104-110.
29 Hanninen, H.; Aitio, A.; Kovala, T.; Luukkonen, R.; Matikainen, E.; Mannelin, T.; Erkkila, J.; Riihimaki, V. (1998)
30 Occupational exposure to lead and neuropsychological dysfunction. Occup. Environ. Med. 55: 202-209.
31 Healy, M. A.; Harrison, P. G.; Aslam, M.; Davis, S. S.; Wilson, C. G. (1992) Lead sulphide and traditional
32 preparations: routes for ingestion, and solubility and reactions in gastric fluid. J. Clin. Hosp. Pharm.
33 7: 169-173.
34 Heard, M. J.; Chamberlain, A. C. (1982) Effect of minerals and food on uptake of lead from the gastrointestinal tract
35 in humans. Hum. Toxicol. 1:411-415.
36 Heard, M. J.; Chamberlain, A. C. (1983) Uptake of lead by humans and effects of minerals and food. Sci. Total
37 Environ. 30: 245-253.
38 Heard, M. J.; Wells, A. C.; Newton, D.; Chamberlain, A. C. (1979) Human uptake and metabolism of tetra ethyl and
39 tetra methyl lead vapour labelled with 203Pb. In: International conference: management and control of
40 heavy metals in the environment; September; London, United Kingdom. Edinburgh, United Kingdom:
41 CEP Consultants, Ltd.; pp. 103-108.
42 Hernandez-Avila, M.; Gonzalez-Cossio, T.; Palazuelos, E.; Romieu, L; Aro, A.; Fishbein, E.; Peterson, K. E.;
43 Hu, H. (1996) Dietary and environmental determinants of blood and bone lead levels in lactating
44 postpartum women living in Mexico City. Environ. Health Perspect. 104: 1076-1082.
45 Hernandez-Avila, M.; Smith, D.; Meneses, F.; Sanin, L. H.; Hu, H. (1998) The influence of bone and blood lead on
46 plasma lead levels in environmentally exposed adults. Environ. Health Perspect. 106: 473-477.
47 Hernandez-Avila, M.; Villalpano, C. G.; Palazuelos, E.; Villapando, M. E. G. (2000) Determinants of blood lead
48 levels across the menopausal transition. Arch. Environ. Health 53: 355-360.
49 Hernandez-Avila, M.; Peterson, K. E.; Gonzalez-Cossio, T.; Sanin, L. H.; Aro, A.; Schnaas, L.; Hu, H. (2002)
50 Effect of maternal bone lead on length and head circumference of newborns and 1-month-old infants.
51 Arch. Environ. Health 57: 482-488.
52 Hernandez-Avila, M.; Gonzalez-Cossio, T.; Hernandez-Avila, J. E.; Romieu, I.; Peterson, K. E.; Aro, A.;
53 Palazuelos, E.; Hu, H. (2003) Dietary calcium supplements to lower blood lead levels in lactating women:
54 a randomized placebo-controlled trial. Epidemiology 14: 206-212.
55 Hertz-Picciotto, I.; Schramm, M.; Watt-Morse, M.; Chantala, K.; Anderson, J.; Osterloh, J. (2000) Patterns and
56 determinants of blood lead during pregnancy. Am. J. Epidemiol. 152: 829-837.
May 2006 4-131 DRAFT-DO NOT QUOTE OR CITE
-------
1 Hogan, K.; Marcus, A.; Smith, R.; White, P. (1998) Integrated exposure uptake biokinetic model for lead in
2 children: empirical comparisons with epidemiologic data. Environ. Health Perspect. 106(suppl.
3 6): 1557-1567.
4 Hoppin, J. A.; Aro, A.; Hu, H.; Ryan, P. B. (2000) Measurement variability associated with KXRF bone lead
5 measurement in young adults. Environ. Health Perspect. 108: 239-242.
6 Hu, H.; Milder, F. L.; Burger, D. E. (1990) X-ray fluorescence measurements of lead burden in subjects with low-
7 level community lead exposure. Arch. Environ. Health 45: 335-341.
8 Hu, H.; Aro, A.; Rotnitzky, A. (1995) Bone lead measured by X-ray fluorescence: epidemiologic methods. Environ.
9 Health Perspect. 103(suppl. 1): 105-110.
10 Hu, H.; Aro, A.; Payton, M.; Korrick, S.; Sparrow, D.; Weiss, S. T.; Rotnitzky, A. (1996) The relationship of bone
11 and blood lead to hypertension. The Normative Aging Study. JAMA J. Am. Med. Assoc. 275: 1171-1176.
12 Hu, H.; Rabinowitz, M.; Smith, D. (1998) Bone lead as a biological marker in epidemiologic studies of chronic
13 toxicity: conceptual paradigms. Environ. Health Perspect. 106: 1-8.
14 Hu, H.; Wu, M.-T.; Cheng, Y.; Sparrow, D.; Weiss, S.; Kelsey, K. (2001) The 5-aminolevulinic acid dehydratase
15 (ALAD) polymorphism and bone and blood lead levels in community-exposed men: the Normative Aging
16 Study. Environ. Health Perspect. 109: 827-832.
17 Hursh, J. B.; Mercer, T. T. (1970) Measurement of 212Pb loss rate from human lungs. J. Appl. Physiol. 28: 268-274.
18 Hursh, J. B.; Suomela, J. (1968) Absorption of 212Pb from the gastrointestinal tract of man. Acta Radiol. 7: 108-120.
19 Hursh, J. B.; Schraub, A.; Sattler, E. L.; Hofmann, H. P. (1969) Fate of 212Pb inhaled by human subjects. Health
20 Phys. 16: 257-267.
21 Hursh, J. B.; Clarkson, T. W.; Miles, E. F.; Goldsmith, L. A. (1989) Percutaneous absorption of mercury vapor by
22 man. Arch. Environ. Health 44: 120-127.
23 Inskip, M. J.; Franklin, C. A.; Baccanale, C. L.; Manton, W. L; O'Flaherty, E. J.; Edwards, C. M. H.; Blenkinsop,
24 J. B.; Edwards, E. B. (1996) Measurement of the flux of lead from bone to blood in a nonhuman primate
25 (Macaca fascicularis) by sequential administration of stable lead isotopes. Fundam. Appl. Toxicol.
26 33:235-245.
27 International Commission on Radiological Protection. (1973) Alkaline earth metabolism in adult man. Oxford,
28 United Kingdom: Pergamon Press; ICRP publication 20. (Health Phys. 24: 125-221).
29 International Commission on Radiological Protection. (1975) Report of the task group on reference man: a report
3 0 prepared by a task group of committee 2 of the International Commission on Radiological Protection.
31 Oxford, United Kingdom: Pergamon Press. (International Commission on Radiological Protection no. 23).
32 International Commission on Radiological Protection. (1989) Age-dependent doses to members of the public from
33 intake of radionuclides: part 1. New York, NY: Pergamon Press. (ICRP publication 56; Annals of the
34 ICRP: v. 20, no. 2).
3 5 International Commission on Radiological Protection. (1993) Age-specific biokinetics for the alkalille earth
36 elements. In: Age-dependent doses to members of the public from intake of radionuclides: part 2. Ingestion
37 dose coefficients. New York, NY: Elsevier Science, Inc.; pp. 95-120. (ICRP publication no. 67, appendix
38 A).
39 International Commission on Radiological Protection. (1996) Basic anatomical & physiological data for use in
40 radiological protection: the skeleton. Oxford, United Kingdom: Elsevier Science Publishers; ICRP
41 publication 70; Annals of the ICRP, v. 25, no. 2.
42 James, H. M.; Hilburn, M. E.; Blair, J. A. (1985) Effects of meals and meal times on uptake of lead from the
43 gastrointestinal tract of humans. Hum. Toxicol. 4: 401-407.
44 James, A. C.; Stahlhofen, W.; Rudolf, G.; Kobrich, R.; Briant, J. K.; Egan, M. J.; Nixon, W.; Birchall, A. (1994)
45 Deposition of inhaled particles. In: Human respiratory tract model for radiological protection: a report of a
46 task group of the International Commission on Radiological Protection. Ann. ICRP 24(1-3): 231-299.
47 (ICRP publication 66).
48 Juarez-Perez, C. A.; Aguilar-Madrid, G.; Smith, D. R.; Lacasana-Navarro, M.; Tellez-Rojo, M. M.; Piacitteli, G.;
49 Hu, H.; Hernandez-Avila, M. (2004) Predictors of plasma lead among lithographic print shop workers in
50 Mexico City. Am. J. Ind. Med. 46: 245-252.
51 Kehoe, R. A. (1987) Studies of lead administration and elimination in adult volunteers under natural and
52 experimentally induced conditions over extended periods of time. Food Chem. Toxicol. 25: 425-493.
53 Kehoe, R. A.; Thamann, F. (1931) The behavior of lead in the animal organism. II. Tetraethyl lead. Am. J. Hyg.
54 13:478-498.
May 2006 4-132 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kessler, M; Durand, P. Y.; Huu, T. C.; Royer-Morot, M. I; Chanliau, J.; Netter, P.; Due, M. (1999) Mobilization of
2 lead from bone in end-stage renal failure patients with secondary hyperparathyroidism. Nephrol. Dial.
3 Transplant. 14:2731-2733.
4 Khoury, G. A.; Diamond, G. L. (2003) Risks to children from exposure to lead in air during remedial or removal
5 activities at Superfund sites: a case study of the RSR lead smelter superfund site. J. Exposure Anal.
6 Environ. Epidemiol. 13: 51-65.
7 Kim, R.; Aro, A.; Rotnitzky, A.; Amarasiriwardena, C.; Hu, H. (1995) K x-ray fluorescence measurements of bone
8 lead concentration: the analysis of low-level data. Phys. Med. Biol. 40: 1475-1485.
9 Kim, R.; Hu, H.; Rotnitzky, A.; Bellinger, D.; Needleman, H. (1996) Longitudinal relationship between dentin lead
10 levels in childhood and bone lead levels in young adulthood. Arch. Environ. Health 51: 375-382.
11 Kondrashov, V. S.; Rothenberg, S. J. (2001a) How to calculate lead concentration and concentration uncertainty in
12 XRF in vivo bone lead analysis. Appl. Radiat. Isot. 55: 799-803.
13 Kondrashov, V. S.; Rothenberg, S. J. (200 Ib) One approach for doublet deconvolution to improve reliability in
14 spectra analysis for in vivo lead measurement. Appl. Radiat. Isot. 54: 691-694.
15 Korrick, S. A.; Hunter, D. J.; Rotnitzky, A.; Hu, H.; Speizer, F. E. (1999) Lead and hypertension in a sample of
16 middle-aged women. Am. J. Public Health 89: 330-335.
17 Korrick, S. A.; Schwartz, J.; Tsaih, S.-W.; Hunter, D. J.; Aro, A.;Rosner, B.; Speizer, F. E.; Hu, H. (2002) Correlates
18 of bone and blood lead levels among middle-aged and elderly women. Am. J. Epidemiol. 156: 335-343.
19 Kosnett, M. J.; Becker, C. E.; Osterloh, J. D.; Kelly, T. J.; Pasta, D. J. (1994) Factors influencing bone lead
20 concentration in a suburban community assessed by noninvasive K x-ray fluorescence. JAMA J. Am. Med.
21 Assoc. 271: 197-203.
22 Koster, J.; Erhardt, A.; Stoeppler, M.; Mohl, C.; Ritz, E. (1989) Mobilizable lead in patients with chronic renal
23 failure. Eur. J. Clin. Invest. 19: 228-233.
24 Kostial, K.; Kello, D.; Jugo, S.; Rabar, I.; Maljkovic, T. (1978) Influence of age on metal metabolism and toxicity.
25 Environ. Health Perspect. 25: 81-86.
26 Lacey, R. F.; Moore, M. R.; Richards, W. N. (1985) Lead in water, infant diet and blood: the Glasgow Duplicate
27 Diet Study. Sci. Total Environ. 41: 235-257.
28 Lagerkvist, B. J.; Ekesrydh, S.; Englyst, V.; Nordberg, G. F.; Soderberg, H.-A.; Wiklund, D.-E. (1996) Increased
29 blood lead and decreased calcium levels during pregnancy: a prospective study of Swedish women living
30 near a smelter. Am. J. Public Health 86: 1247-1252.
31 Lanphear, B. P.; Roghmann, K. J. (1997) Pathways of lead exposure in urban children. Environ. Res. 74: 67-73.
32 Lanphear, B. P.; Burgoon, D. A.; Rust, S. W.; Eberly, S.; Galke, W. (1998) Environmental exposures to lead and
33 urban children's blood lead levels. Environ. Res. 76: 120-130.
34 Laug, E. P.; Kunze, F. M. (1948) The penetration of lead through the skin. J. Ind. Hyg. Toxicol. 30: 256-259.
35 Laxen, D. P. H.; Raab, G. M.; Fulton, M. (1987) Children's blood lead and exposure to lead in household dust and
36 water — a basis for an environmental standard for lead in dust. Sci. Total Environ. 66: 235-244.
37 Lee, B.-K.; Lee, G.-S.; Stewart, W. F.; Ahn, K.-D.; Simon, D.; Kelsey, K. T.; Todd, A. C.; Schwartz, B. S. (2001)
3 8 Associations of blood pressure and hypertension with lead dose measures and polymorphisms in the
39 vitamin D receptor and 5-aminolevulinic acid dehydratase genes. Environ. Health Perspect. 109: 383-389.
40 Leggett, R. W. (1985) A model of the retention, translocation and excretion of systemic Pu. Health Phys.
41 49: 1115-1137.
42 Leggett, R. W. (1992a) A retention-excretion model for americium in humans. Health Phys. 62: 288-310.
43 Leggett, R. W. (1992b) A generic age-specific biokinetic model for calcium-like elements. Radiat. Prot. Dosim.
44 41: 183-198.
45 Leggett, R. W. (1993) An age-specific kinetic model of lead metabolism in humans. Environ. Health Perspect.
46 101:598-616.
47 Lilis, R.; Gavrilescu, N.; Nestorescu, B.; Dumitriu, C.; Roventa, A. (1968) Nephropathy in chronic lead poisoning.
48 Br. J. Ind. Med. 25: 196-202.
49 Lin, J.-L.; Yu, C.-C.; Lin-Tan, D.-T.; Ho, H.-H. (2001) Lead chelation therapy and urate excretion in patients with
50 chronic renal diseases and gout. Kidney Int. 60: 266-271.
51 Lorenzana, R. M.; Troast, R.; Klotzbach, J. M.; Follansbee, M. H.; Diamond, G. L. (2005) Issues related to time
52 averaging of exposure in modeling risks associated with intermittent exposures to lead. Risk Anal.
53 25: 169-178.
54 Maddaloni, M.; Lolacono, N.; Manton, W.; Blum, C.; Drexler, J.; Graziano, J. (1998) Bioavailability of soilborne
55 lead in adults, by stable isotope dilution. Environ. Health Perspect. 106: 1589-1594.
May 2006 4-133 DRAFT-DO NOT QUOTE OR CITE
-------
1 Maddaloni, M; Ballew, M.; Diamond, G.; Follansbee, M.; Gefell, D.; Goodram, P.; Johnson, M.; Koporec, K.;
2 Khoury, G.; Luey, I; Odin, M.; Troast, R.; Van Leeuwen, P.; Zaragoza, L. (2005) Assessing lead risks at
3 non-residential hazardous waste sites. Hum. Ecol. Risk Assess. 11: 967-1003.
4 Mahaffey, K. R.; Annest, J. L. (1986) Association of erythrocyte protoporphyrin with blood lead level and iron
5 status in the second national health and nutrition examination survey, 1976-1980. Environ. Res.
6 41:327-338.
7 Mahaffey, K. R.; Gartside, P. S.; Glueck, C. J. (1986) Blood lead levels and dietary calcium intake in 1-11 year-old
8 children: the second national health and nutrition examination survey, 1976-1980. Pediatrics 78: 257-262.
9 Maldonado-Vega, M.; Cerbon-Solorzano, J.; Albores-Medina, A.; Hernandez-Luna, C.; Calderon-Salinas, J. V.
10 (1996) Lead: intestinal absorption and bone mobilization during lactation. Hum. Exp. Toxicol. 15: 872-877.
11 Manton, W. I. (1985) Total contribution of airborne lead to blood lead. Br. J. Ind. Med. 42: 168-172.
12 Manton, W. I.; Malloy, C. R. (1983) Distribution of lead in body fluids after ingestion of soft solder. Br. J. Ind. Med.
13 40:51-57.
14 Manton, W. I.; Cook, J. D. (1984) High accuracy (stable isotope dilution) measurements of lead in serum and
15 cerebrospinal fluid. Br. J. Ind. Med. 41: 313-319.
16 Manton, W. I.; Angle, C. R.; Stanek, K. L.; Reese, Y. R.; Kuehnemann, T. J. (2000) Acquisition and retention of
17 lead by young children. Environ. Res. 82: 60-80.
18 Manton, W. I.; Rothenberg, S. J.; Manalo, M. (2001) The lead content of blood serum. Environ. Res. 86: 263-273.
19 Manton, W. I.; Angle, C. R.; Stanek, K. L.; Kuntzelman, D.; Reese, Y. R.; Kuehnemann, T. J. (2003) Release of
20 lead from bone in pregnancy and lactation. Environ. Res. 92: 139-151.
21 Marcus, A. H. (1985a) Multicompartment kinetic models for lead. II. Linear kinetics and variable absorption in
22 humans without excessive lead exposures. Environ. Res. 36: 459-472.
23 Marcus, A. H. (1985b) Multicompartment kinetic models for lead. I. Bone diffusion models for long-term retention.
24 Environ. Res. 36: 441-458.
25 Marcus, A. H. (1985c) Multicompartment kinetic model for lead. III. Lead in blood plasma and erythrocytes.
26 Environ. Res. 36: 473-489.
27 Marcus, A. H.; Schwartz, J. (1987) Dose-response curves for erythrocyte protoporphyrin vs blood lead: effects of
28 iron status. Environ. Res. 44: 221-227.
29 Markowitz, M. E.; Rosen, J. F. (1981) Zinc (Zn) and copper (Cu) metabolism in CaNa2 EDTA-treated children with
30 plumbism. Pediatr. Res. 15: 635.
31 Markowitz, M. E.; Weinberger, H. L. (1990) Immobilization-related lead toxicity in previously lead-poisoned
32 children. Pediatrics 86: 455-457.
33 McMichael, A. J.; Baghurst, P. A.; Wigg, N. R.; Vimpani, G. V.; Robertson, E. F.; Roberts, R. J. (1988) Port Pirie
34 cohort study: environmental exposure to lead and children's abilities at the age of four years. N. Engl. J.
35 Med. 319:468-475.
36 McNeill, F. E.; Stokes, L.; Chettle, D. R.; Kaye, W. E. (1999) Factors affecting in vivo measurement precision and
37 accuracy of 109Cd K x-ray fluorescence measurements. Phys. Med. Biol. 44(9): 2263-2273.
38 McNeill, F. E.; Stokes, L.; Brito, J. A.; Chettle, D. R.; Kaye, W. E. (2000) 109Cd K x-ray fluorescence
3 9 measurements of tibial lead content in young adults exposed to lead in early childhood. Occup. Environ.
40 Med. 57: 465-471.
41 Mickle, M. H. (1998) Structure, use, and validation of the IEUBK model. Environ. Health Perspect.
42 106(suppl. 6): 1531-1534.
43 Moline, J.; Carrillo, L. L.; Sanchez, L. T.; Godbold, J.; Todd, A. (2000) Lactation and lead body burden turnover:
44 a pilot study in Mexico. J. Occup. Environ. Med. 42: 1070-1075.
45 Moore, M. R.; Meredith, P. A.; Campbell, B. C.; Goldberg, A.; Pocock, S. 1. (1977) Contribution of lead in drinking
46 water to blood-lead. Lancet 2(8039): 66 Iff.
47 Moore, M. R.; Meredith, P. A.; Watson, W. S.; Sumner, D. J.; Taylor, M. K.; Goldberg, A. (1980) The percutaneous
48 absorption of lead-203 in humans from cosmetic preparations containing lead acetate, as assessed by
49 whole-body counting and other techniques. Food Cosmet. Toxicol. 18: 399-405.
50 Morgan, W. D.; Ryde, S. J.; Jones, S. J.; Wyatt, R. M.; Hainsworth, I. R.; Cobbold, S. S.; Evans, C. J.; Braithwaite,
51 R. A. (1990) In vivo measurements of cadmium and lead in occupationally-exposed workers and an urban
52 population. Biol. Trace Elem. Res. 26-27: 407-414.
53 Morrison, J. N.; Quarterman, J. (1987) The relationship between iron status and lead absorption in rats. Biol. Trace
54 Elem. Res. 14: 115-126.
55 Morrow, P. E.; Beiter, H.; Amato, F.; Gibb, F. R. (1980) Pulmonary retention of lead: an experimental study in man.
56 Environ. Res. 21: 373-384.
May 2006 4-134 DRAFT-DO NOT QUOTE OR CITE
-------
1 Mortada, W. I.; Sobh, M. A.; El-Defrawy, M. M; Farahat, S. E. (2001) Study of lead exposure from automobile
2 exhaust as a risk for nephrotoxicity among traffic policemen. Am. J. Nephrol. 21: 274-279.
3 Mushak, P. (1989) Biological monitoring of lead exposure in children: overview of selected biokinetic and
4 lexicological issues. In: Smith, M. A.; Grant, L. D.; Sors, A. I., eds. Lead exposure and child development:
5 an international assessment [workshop organized by the Commission of the European Communities and the
6 U.S. Environmental Protection Agency]; September 1986; Edinburgh, United Kingdom. Dordrecht, The
7 Netherlands: Kluwer Academic Publishers BV; pp. 129-145.
8 Mushak, P. (1991) Gastro-intestinal absorption of lead in children and adults: overview of biological and
9 biophysico-chemical aspects. Chem. Speciation Bioavailability 3(3/4): 87-104.
10 Mushak, P. (1993) New directions in the toxicokinetics of human lead exposure. Neurotoxicology 14: 29-42.
11 Mushak, P. (1998) Uses and limits of empirical data in measuring and modeling human lead exposure. Environ.
12 Health Perspect. Suppl. 106(6): 1467-1484.
13 Mykkanen, H. M.; Wasserman, R. H. (1981) Gastrointestinal absorption of lead (203Pb) in chicks: influence of lead,
14 calcium, and age. J. Nutr. Ill: 1757-1765.
15 Mykkanen, H. M.; Wasserman, R. H. (1982) Effect of vitamin D on the intestinal absorption of 203pb and 47ca in
16 chicks. J. Nutr. 112: 520-527.
17 Nash, D.; Magder, L. S.; Sherwin, R.; Rubin, R. J.; Silbergeld, E. K. (2004) Bone density-related predictors of blood
18 lead level among peri- and postmenopausal women in the United States: the Third National Health and
19 Nutrition Examination Survey, 1988-1994. Am. J. Epidemiol. 160: 901-911.
20 National Institute for Occupational Safety and Health. (1977a) Manual of analytical methods. 2nd ed. Cincinnati,
21 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
22 Control, National Institute for Occupational Safety and Health. DHEW (NIOSH) publication no. 77/157-A.
23 Method No. P&CAM 102. V. 1.
24 National Institute for Occupational Safety and Health. (1977b) Manual of analytical methods. 2nd ed. Cincinnati,
25 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
26 Control, National Institute for Occupational Safety and Health. DHEW (NIOSH) publication no. 77/157-A.
27 Method No. P&CW 195. V. 1.
28 National Institute for Occupational Safety and Health. (1977c) Manual of analytical methods. 2nd ed. Cincinnati,
29 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
30 Control, National Institute for Occupational Safety and Health, 200-1 to 200-8. Method No. P&CAM 200.
31 Vol.1.
32 National Institute for Occupational Safety and Health. (1977d) Manual of analytical methods. 2nd ed. Cincinnati,
33 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
34 Control. National Institute for Occupational Safety and Health. 214-1 to 214-6. Method No. P&CAM 214.
35 Vol. 1.
36 National Institute for Occupational Safety and Health. (1977e) Manual of analytical methods. 2nd ed. Cincinnati,
37 OH: U.S. Department of Health, Education and Welfare. Public Health Service, Centers for Disease
3 8 Control, National Institute for Occupational Safety and Health. Method No. P&CAM 262. Vol. 1.
39 National Institute for Occupational Safety and Health. (1977f) Manual of analytical methods. 2nd ed. Cincinnati,
40 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
41 Control, National Institute for Occupational Safety and Health. Method No. P&CAM 208. Vol. 1.
42 National Institute for Occupational Safety and Health. (1984) Manual of analytical methods. 3rd ed. Cincinnati, OH:
43 U.S. Department of Health and Human Services, Centers for Disease Control, National Institute for
44 Occupational Safety and Health. Method No. 7300, 8003, and 8310. Vol. 1.
45 National Institute for Occupational Safety and Health. (1994) Manual of analytical methods. 4rd ed. Cincinnati, OH:
46 U.S. Department of Health and Human Services, Centers for Disease Control, National Institute for
47 Occupational Safety and Health; DHHS (NIOSH) publication 94-113; method no. 7105.
48 National Institutes of Health (NIH) Consensus Development Panel on Optimal Calcium Intake. (1994) Optimal
49 calcium uptake. JAMA J. Am. Med. Assoc. 272: 1942-1948.
50 Nielsen, T.; Jensen, K. A.; Grandjean, P. (1978) Organic lead in normal human brains. Nature (London)
51 274:602-603.
52 Nielson, K. B.; Atkin, C. L.; Winge, D. R. (1985) Distinct metal-binding configurations in metallothionein. J. Biol.
53 Chem. 260: 5342-5350.
54 Nilsson, U.; Attewell, R.; Christoffersson, J.-O.; Schutz, A.; Ahlgren, L.; Skerfving, S.; Mattsson, S. (1991)
5 5 Kinetics of lead in bone and blood after end of occupational exposure. Pharmacol. Toxicol. (Copenhagen)
56 68:477-484.
May 2006 4-135 DRAFT-DO NOT QUOTE OR CITE
-------
1 O'Flaherty, E. J. (1991a) Physiologically based models for bone-seeking elements. I. Rat skeletal and bone growth.
2 Toxicol. Appl. Pharmacol. Ill: 299-312.
3 O'Flaherty, E. J. (1991b) Physiologically based models for bone-seeking elements: II. kinetics of lead disposition in
4 rats. Toxicol. Appl. Pharmacol. Ill: 313-331.
5 O'Flaherty, E. J. (1991c) Physiologically based models for bone-seeking elements. III. Human skeletal and bone
6 growths. Toxicol. Appl. Pharmacol. Ill: 332-341.
7 O'Flaherty, E. J. (1993) Physiologically based models for bone-seeking elements. IV. Kinetics of lead disposition in
8 humans. Toxicol. Appl. Pharmacol. 118: 16-29.
9 O'Flaherty, E. J. (1995) Physiologically based models for bone-seeking elements: V. Lead absorption and
10 disposition in childhood. Toxicol. Appl. Pharmacol. 131: 297-308.
11 O'Flaherty, E. J. (1998) A physiologically based kinetic model for lead in children and adults. Environ. Health
12 Perspect. 106(supp. 6): 1495-1503.
13 O'Flaherty, E. J. (2000) Modeling normal aging bone loss, with consideration of bone loss in osteoporosis. Toxicol.
14 Sci. 55: 171-188.
15 O'Flaherty, E. J.; Hammond, P. B.; Lerner, S. I. (1982) Dependence of apparent blood lead half-life on the length of
16 previous lead exposure in humans. Fundam. Appl. Toxicol. 2: 49-54.
17 O'Flaherty, E. J.; Inskip, M. J.; Franklin, C. A.; Durbin, P. W.; Manton, W. I.; Baccanale, C. L. (1998) Evaluation
18 and modification of a physiologically based model of lead kinetics using data from a sequential isotope
19 study in cynomolgus monkeys. Toxicol. Appl. Pharmacol. 149: 1-16.
20 Oldereid, N. B.; Thomassen, Y.; Attramadal, A.; Olaisen, B.; Purvis, K. (1993) Concentrations of lead, cadmium
21 and zinc in the tissues of reproductive organs of men. J. Reprod. Fertil. 99: 421-425.
22 Oliveira, S.; Aro, A.; Sparrow, D.; Hu, H. (2002) Season modifies the relationship between bone and blood lead
23 levels: the Normative Aging Study. Arch. Environ. Health 57: 466-472.
24 Ong, C. N.; Lee, W. R. (1980) Distribution of lead-203 in human peripheral blood in vitro. Br. J. Ind. Med.
25 37:78-84.
26 Orban, B. (1953) Oral histology and embryology. 3rd ed. St. Louis, MO: Mosby Year Book Publishers.
27 Oreskes, N. (1998) Evaluation (not validation) of quantitative models. Environ. Health Perspect.
28 106(suppl. 6): 1453-1460.
29 Otto, D.; Robinson, G.; Baumann, S.; Schroeder, S.; Mushak, P.; Kleinbaum, D.; Boone, L. (1985) Five-year
3 0 follow-up study of children with low-to-moderate lead absorption: electrophy siological evaluation.
31 Environ. Res. 38: 168-186.
32 Pirkle, J. L.; Brody, D. J.; Gunter, E. W.; Kramer, R. A.; Paschal, D. C.; Flegal, K. M.; Matte, T. D. (1994) The
3 3 decline in blood lead levels in the United States: the National Health and Nutrition Examination Surveys
34 (NHANES). JAMA J. Am. Med. Assoc. 272: 284-291.
35 Pirkle, J. L.; Kaufmann, R. B.; Brody, D. J.; Hickman, T.; Gunter, E. W.; Paschal, D. C. (1998) Exposure of the U.S.
36 population to lead, 1991-1994. Environ. Health Perspect. 106: 745-750.
37 Pocock, S. J.; Shaper, A. G.; Walker, M.; Wale, C. J.; Clayton, B.; Delves, T.; Lacey, R. F.; Packham, R. F.;
38 Powell, P. (1983) The effects of tap water lead, water hardness, alcohol, and cigarettes on blood lead
39 concentrations. J. Epidemiol. Community Health 37: 1-7.
40 Popovic, M.; McNeill, F. E.; Chettle, D. R.; Webber, C. E.; Lee, C. V.; Kaye, W. E. (2005) Impact of occupational
41 exposure on lead levels in women. Environ. Health Perspect. 113: 478-484.
42 Pounds, J. G.; Leggett, R. W. (1998) The ICRP age-specific biokinetic model for lead: validations, empirical
43 comparisons, and explorations. Environ. Health Perspect. 106(suppl. 6): 1505-1511.
44 Pounds, J. G.; Marlar, R. J.; Allen, J. R. (1978) Metabolism of lead-210 in juvenile and adult rhesus monkeys
45 (Macaca mulatto). Bull. Environ. Contam. Toxicol. 19: 684-691.
46 Powell, J. J.; Greenfield, S. M.; Thompson, R. P. H.; Cargnello, J. A.; Kendall, M. D.; Landsberg, J. P.; Watt, F.;
47 Delves, H. T.; House, I. (1995) Assessment of toxic metal exposure following the Camelford water
48 pollution incident: evidence of acute mobilization of lead into drinking water. Analyst (Cambridge, U. K.)
49 120:793-798.
50 Que Hee, S. S.; MacDonald, T. J.; Bornschein, R. L. (1985) Blood lead by furnace-Zeeman atomic absorption
51 spectrophotometry. Microchem. J. 32: 55-63.
52 Rabinowitz, M. B. (1991) Toxicokinetics of bone lead. Environ. Health Perspect. 91: 33-37.
53 Rabinowitz, M. B. (1995) Relating tooth and blood lead levels in children. Bull. Environ. Contam. Toxicol.
54 55: 853-857.
55 Rabinowitz, M. B.; Wetherill, G. W.; Kopple, J. D. (1973) Lead metabolism in the normal human: stable isotope
56 studies. Science (Washington, DC) 182: 725-727.
May 2006 4-136 DRAFT-DO NOT QUOTE OR CITE
-------
1 Rabinowitz, M. B.; Wetherill, G. W.; Kopple, J. D. (1976) Kinetic analysis of lead metabolism in healthy humans.
2 J. Clin. Invest. 58: 260-270.
3 Rabinowitz, M. B.; Wetherill, G. W.; Kopple, J. D. (1977) Magnitude of lead intake from respiration by normal
4 man. J. Lab. Clin. Med. 90: 238-248.
5 Rabinowitz, M. B.; Kopple, J. D.; Wetherill, G. W. (1980) Effect of food intake and fasting on gastrointestinal lead
6 absorption in humans. Am. J. Clin. Nutr. 33: 1784-1788.
7 Rabinowitz, M.; Needleman, H.; Burley, M.; Finch, H.; Rees, J. (1984) Lead in umbilical blood, indoor air, tap
8 water, and gasoline in Boston. Arch. Environ. Health 39: 299-301.
9 Rabinowitz, M. B.; Leviton, A.; Bellinger, D. C. (1989) Blood lead—tooth lead relationship among Boston children.
10 Bull. Environ. Contam. Toxicol. 43: 485-492.
11 Rabinowitz, M. B.; Leviton, A.; Bellinger, D. (1993) Relationships between serial blood lead levels and exfoliated
12 tooth dentin lead levels: models of tooth lead kinetics. Calcif. Tissue Int. 53: 338-341.
13 Roels, H.; Konings, J.; Green, S.; Bradley, D.; Chettle, D.; Lauwerys, R. (1995) Time-integrated blood lead
14 concentration is a valid surrogate for estimating the cumulative lead dose assessed by tibial lead
15 measurement. Environ. Res. 69: 75-82.
16 Rosen, J. F.; Pounds, J. G. (1998) "Severe chronic lead insult that maintains body burdens of lead related to those in
17 the skeleton": observations by Dr. Clair Patterson conclusively demonstrated. Environ. Res.78: 140-151.
18 Rosen, J. F.; Markowitz, M. E.; Bijur, P. E.; Jenks, S. T.; Wielopolski, L.; Kalef-Ezra, J. A.; Slatkin, D. N. (1989)
19 L-line x-ray fluorescence of cortical bone lead compared with the CaNa2EDTA test in lead-toxic children:
20 public health implications. Proc. Natl. Acad. Sci. U. S. A. 86: 685-689,
21 Rothenberg, S. J.; Karchmer, S.; Schnaas, L.; Perroni, E.; Zea, F.; Alba, J. F. (1994) Changes in serial blood lead
22 levels during pregnancy. Environ. Health Perspect. 102: 876-880.
23 Rothenberg, S. J.; Khan, F.; Manalo, M.; Jian, J.; Cuellar, R.; Reyes, S.; Acosta, S.; Jauregui, M.; Diaz, M.;
24 Sanchez, M.; Todd, A. C.; Johnson, C. (2000) Maternal bone lead contribution to blood lead during and
25 after pregnancy. Environ. Res. 82: 81-90.
26 Rothenberg, S. J.; Kondrashov, V.; Manalo, M.; Manton, W. I.; Khan, F.; Todd, A. C.; Johnson, C. (2001) Seasonal
27 variation in bone lead contribution to blood lead during pregnancy. Environ. Res. 85: 191-194.
28 Rothenberg, S. J.; Kondrashov, V.; Manalo, M.; Jiang, J.; Cuellar, R.; Garcia, M.; Reynoso, B.; Reyes, S.; Diaz, M.;
29 Todd, A. C. (2002) Increases in hypertension and blood pressure during pregnancy with increased bone
30 lead levels. Am. J. Epidemiol. 156: 1079-1087.
31 Ruby, M. V.; Schoof, R.; Brattin, W.; Goldade, M.; Post, G.; Harnois, M.; Mosby, D. E.; Casteel, S. W.; Berti, W.;
32 Carpenter, M.; Edwards, D.; Cragin, D.; Chappell, W. (1999) Advances in evaluating the oral
33 bioavailability of inorganics in soil for use in human health risk assessment. Environ. Sci. Technol.
34 33: 3697-3705.
35 Ryu, J. E.; Ziegler, E. E.; Nelson, S. E.; Fomon, S. J. (1983) Dietary intake of lead and blood lead concentration in
36 early infancy. Am. J. Dis. Child. 137: 886-891.
37 Sakai, T.; Yanagihara, S.; Kunugi, Y.; Ushio, K. (1982) Relationships between distribution of lead in erythrocytes in
3 8 vivo and in vitro and inhibition of ALA-D. Br. J. Ind. Med. 39: 382-387.
39 Salmon, P. L.; Bondarenko, O. A.; Henshaw, D. L. (1999) DOSE210, a semi-empirical model for prediction of
40 organ distribution and radiation doses from long term exposure to 210Pb and 210Po. Radiat. Prot. Dosim.
41 82: 175-192.
42 Sanin, L. H.; Gonzalez-Cossio, T.; Romieu, I.; Peterson, K. E.; Ruiz, S.; Palazuelos, E.; Hernandez-Avila, M.;
43 Hu, H. (2001) Effect of maternal lead burden on infant weight and weight gain at one month of age among
44 breastfed infants. Pediatrics 107: 1016-1023.
45 Schafer, J. H.; Glass, T. A.; Bressler, J.; Todd, A. C.; Schwartz, B. S. (2005) Blood lead in a predictor of
46 homocysteine levels in a population-based study of older adults. Environ. Health Perspect. 113:31-35.
47 Schnaas, L.; Rothenberg, S. J.; Perroni, E.; Martinez, S.; Hernandez, C.; Hernandez, R. M. (2000) Temporal pattern
48 in the effect of postnatal blood lead level on intellectual development of young children. Neurotoxicol.
49 Teratol. 22: 805-810.
50 Schroeder, H. A.; Tipton, I. H. (1968) The human body burden of lead. Arch. Environ. Health 17: 965-978.
51 Schuhmacher, M.; Hernandez, M.; Domingo, J. L.; Fernandez-Ballart, J. D.; Llobet, J. M.; Corbella, J. (1996)
52 A longitudinal study of lead mobilization during pregnancy: concentrations in maternal and umbilical cord
53 blood. Trace Elem. Electrol. 13: 177-181.
54 Schtitz, A.; Skerfving, S.; Christoffersson, J. O.; Ahlgren, L.; Mattson, S. (1987a) Lead in vertebral bone biopsies
55 from active and retired lead workers. Arch. Environ. Health 42: 340-346.
May 2006 4-137 DRAFT-DO NOT QUOTE OR CITE
-------
1 Schiitz, A.; Skerfving, S.; Ranstam, J.; Christoffersson, J.-O. (1987b) Kinetics of lead in blood after the end of
2 occupational exposure. Scand. J. Work Environ. Health 13: 221 231.
3 Schiitz, A.; Bergdahl, I. A.; Ekholm, A.; Skerfving, S. (1996) Measurement by ICP-MS of lead in plasma and whole
4 blood of lead workers and controls. Occup. Environ. Med. 53: 736-740.
5 Schwartz, B. S.; Lee, B.-K.; Lee, G.-S.; Stewart, W. F.; Simon, D.; Kelsey, K.; Todd, A. C. (2000a) Associations of
6 blood lead, dimercaptosuccinic acid-chelatable lead, and tibia lead with polymorphisms in the vitamin D
7 receptor and "delta"-aminolevulinic acid dehydratase genes. Environ. Health Perspect. 108: 949-954.
8 Schwartz, B. S.; Stewart, W. F.; Todd, A. C.; Simon, D.; Links, J. M. (2000b) Different associations of blood lead,
9 meso 2,3-dimercaptosuccinic acid (DMSA)-chelatable lead, and tibial lead levels with blood pressure in
10 543 former organolead manufacturing workers. Arch. Environ. Health. 55: 85-92.
11 Schwartz, B. S.; Lee, B. K.; Lee, G. S.; Stewart, W. F.; Lee, S. S.; Hwang, K. Y.; Ahn, K.-D.; Kim, Y.-B.; Bolla,
12 K. I.; Simon, D.; Parsons, P. J.; Todd, A. C. (2001) Associations of blood lead, dimercaptosuccinic acid-
13 chelatable lead, and tibia lead with neurobehavioral test scores in South Korean lead workers. Am. J.
14 Epidemiol. 153:453-464.
15 Shapiro, I. M.; Dobkin, B.; Tuncay, O. C.; Needleman, H. L. (1973) Lead levels in dentine and circumpulpal dentine
16 of deciduous teeth of normal and lead poisoned children. Clin. Chim. Acta46: 119-123.
17 Sharma, K.; Reutergardh, L. B. (2000) Exposure of preschoolers to lead in the Makati area of Metro Manila, the
18 Philippines. Environ. Res. A 83: 322-332.
19 Sherlock, J. C.; Quinn, M. J. (1986) Relationship between blood and lead concentrations and dietary lead intake in
20 infants: the Glasgow Duplicate Diet Study 1979-1980. Food Addit. Contam. 3: 167-176.
21 Sherlock, J.; Smart, G.; Forbes, G. I.; Moore, M. R.; Patterson, W. J.; Richards, W. N.; Wilson, T. S. (1982)
22 Assessment of lead intakes and dose-response for a population in Ayr exposed to a plumbosolvent water
23 supply. Hum. Toxicol. 1: 115-122.
24 Sherlock, J. C.; Ashby, D.; Delves, H. T.; Forbes, G. I.; Moore, M. R.; Patterson, W. J.; Pocock, S. J.; Quinn, M. J.;
25 Richards, W. N.; Wilson, T. S. (1984) Reduction in exposure to lead from drinking water and its effect on
26 blood lead concentrations. Hum. Toxicol. 3: 383-392.
27 Silbergeld, E. K. (1991) Lead in bone: implications for toxicology during pregnancy and lactation. Environ. Health
28 Perspect. 91:63-70.
29 Silbergeld, E. K.; Schwartz, J.; Mahaffey, K. (1988) Lead and osteoporosis: mobilization of lead from bone in
30 postmenopausal women. Environ. Res. 47: 79-94.
31 Skerfving, S. (1988) Biological monitoring of exposure to inorganic lead. In: Clarkson, T. W.; Friberg, L.;
32 Nordberg, G. F.; Sager, R. P., eds. Biological monitoring of toxic metals. New York, NY: Plenum Press;
33 pp. 169-197.
34 Skerfving, S.; Ahlgren, L.; Christoffersson, J.-O.; Haeger-Aronsen, B.; Mattsson, S.; Schtitz, A. (1983) Metabolism
35 of inorganic lead in occupationally exposed humans. Arh. Hig. Rada Toksikol. 34: 341-350.
36 Skerfving, S.; Ahlgren, L.; Christoffersson, J -O.; Haeger-Aronson, B.; Mattsson, S.; Schtitz, A; Lindberg, G. (1985)
37 Metabolism of inorganic lead in man. Nutr. Res. (Suppl. 1): 601.
38 Skerfving, S.; Nilsson, U.; Schtitz, A.; Gerhardsson, L. (1993) Biological monitoring of inorganic lead. Scand. J.
39 Work Environ. Health 19(suppl. 1): 59-64.
40 Smith, D. R.; Osterloh, J. D.; Flegal, A. R. (1996) Use of endogenous, stable lead isotopes to determine release of
41 lead from the skeleton. Environ. Health Perspect. 104: 60-66.
42 Smith, D. R.; Ilustre, R. P.; Osterloh, J. D. (1998) Methodological considerations for the accurate determination of
43 lead in human plasma and serum. Am. J. Ind. Med. 33: 430-438.
44 Smith, D. R.; Kahng, M. W.; Quintanilla-Vega, B.; Fowler, B. A. (1998) High-affinity renal lead-binding proteins
45 ini environmentally-exposed humans. Chem. Biol. Interact. 115: 39-52.
46 Smith, D.; Hernandez-Avila, M.; Tellez-Rojo, M.M.; Mercado, A.; Hu, H. (2002) The relationship between lead in
47 plasma and whole blood in women. Environ. Health Perspect. 110: 263-268.
48 Somervaille, L. J.; Chettle, D. R.; Scott, M. C.; Aufderheide, A. C.; Wallgren, J. E.; Wittmers, L. E., Jr.; Rapp,
49 G. R., Jr. (1986) Comparison of two in vitro methods of bone lead analysis and the implications for in vivo
50 measurements. Phys. Med. Biol. 31: 1267-1274.
51 Somervaille, L. J.; Chettle, D. R.; Scott, M. C.; Tennant, D. R.; McKiernan, M. J.; Skilbeck, A.; Trethowan, W. N.
52 (1988) In vivo tibia lead measurements as an index of cumulative exposure in occupationally exposed
53 subjects. Br. J. Ind. Med. 45: 174-181.
54 Somervaille, L. J.; Nilsson, U.; Chettle, D. R.; Tell, L; Scott, M. C.; Schtitz, A.; Mattsson, S.; Skerfving, S. (1989)
55 In vivo measurements of bone lead~a comparison of two x-ray fluorescence techniques used at three
56 different bone sites. Phys. Med. Biol. 34: 1833-1845.
May 2006 4-138 DRAFT-DO NOT QUOTE OR CITE
-------
1 Stauber, J. L.; Florence, T. M; Gulson, B. L.; Dale, L. S. (1994) Percutaneous absorption of inorganic lead
2 compounds. Sci. Total Environ. 145: 55-70.
3 Stern, A. H. (1994) Derivation of a target level of lead in soil at residential sites corresponding to a de minimis
4 contribution to blood lead concentration. Risk Anal. 14: 1049-1056.
5 Stern, A. H. (1996) Derivation of a target concentration of Pb in soil based on elevation of adult blood pressure.
6 Risk Anal. 16:201-210.
7 Stokes, L.; Letz, R.; Gerr, F.; Kolczak, M.; McNeill, F. E.; Chettle, D. R.; Kaye, W. E. (1998) Neurotoxicity in
8 young adults 20 years after childhood exposure to lead: the Bunker Hill experience. Occup. Environ. Med.
9 55:507-516.
10 Succop, P.; Bornschein, R.; Brown, K.; Tseng, C.-Y. (1998) An empirical comparison of lead exposure pathway
11 models. Environ. Health Perspect. Suppl. 106(6): 1577-1583.
12 Sun, C. C.; Wong, T. T.; Hwang, Y. H.; Chao, K. Y.; Jee, S. H.; Wang, J. D. (2002) Percutaneous absorption of
13 inorganic lead compounds. AIHA J. 63: 641-646.
14 Symanski, E.; Hertz-Picciotto, I. (1995) Blood lead levels in relation to menopause, smoking, and pregnancy
15 history. Am. J. Epidemiol. 141: 1047-1058.
16 Tellez-Rojo, M. M.; Hernandez-Avila, M.; Gonzalez-Cossio, T.; Romieu, L; Aro, A.; Palazuelos, E.; Schwartz, J.;
17 Hu, H. (2002) Impact of breastfeeding on the mobilization of lead from bone. Am. J. Epidemiol.
18 155:420-428.
19 Tellez-Rojo, M. M.; Hernandez-Avila, M.; Lamadrid-Figueroa, H.; Smith, D.; Hernandez-Cadena, L.; Mercado, A.;
20 Aro, A.; Schwartz, J.; Hu, H. (2004) Impact of bone lead and bone resorption on plasma and whole blood
21 lead levels during pregnancy. Am. J. Epidemiol. 160: 668-678.
22 TerraGraphics Environmental Engineering, Inc. (2000) 1999 five year review report: Bunker Hill Superfund site.
23 [Final]. Available: http://yosemite.epa.gov/rlO/cleanup.nsf/webpage/Idaho+Cleanup+Sites [1 May, 2006].
24 TerraGraphics Environmental Engineering, Inc. (2001) Human health risk assessment for the Coeur d'Alene Basin
25 extending from Harrison to Mullan on the Coeur d'Alene River and tributaries remedial
26 investigation/feasibility study. [Final]. Washington, DC: U.S. Environmental Protection Agency, prepared
27 for the Idaho Department of Health and Welfare, Idaho Department of Environmental Quality.
28 Todd, A. C. (2000) Coherent scattering and matrix correction in bone-lead measurements. Phys. Med. Biol.
29 45: 1953-1963.
30 Todd, A. C.; Chettle, D. R. (2003) Calculating the uncertainty in lead concentration for in vivo bone lead x-ray
31 fluorescence. Phys Med Biol. 48: 2033-2039.
32 Todd, A. C.; Carroll, S.; Godbold, J. H.; Moshier, E. L.; Khan, F. A. (2000) Variability in XRF-measured tibia lead
33 levels. Phys. Med. Biol. 45: 3737-3748.
34 Todd, A. C.; Buchanan, R.; Carroll, S.; Moshier, E. L.; Popovac, D.; Slavkovich, V.; Graziano, J. H. (2001) Tibia
35 lead levels and methodological uncertainty in 12-year-old children. Environ. Res. 86: 60-65.
36 Todd, A. C.; Carroll, S.; Geraghty, C.; Khan, F. A.; Moshier, E. L.; Tang, S.; Parsons, P. J. (2002a) L-shell x-ray
37 fluorescence measurements of lead in bone: accuracy and precision. Phys. Med. Biol. 47: 1399-1419.
38 Todd, A. C.; Parsons, P. J.; Carroll, S.; Geraghty, C.; Khan, F. A.; Tang, S.; Moshier, E. L. (2002b) Measurements
39 of lead in human tibiae. A comparison between K-shell x-ray fluorescence and electrothermal atomic
40 absorption spectrometry. Phys. Med. Biol. 47: 673-687.
41 Treble, R. G.; Thompson, T. S. (1997) Preliminary results of a survey of lead levels in human liver tissue. Bull.
42 Environ. Contam. Toxicol. 59: 688-695.
43 Tsaih, S.-W.; Schwartz, I; Lee, M.-L. T.; Amarasiriwardena, C.; Aro, A.; Sparrow, D.; Hu, H. (1999) The
44 independent contribution of bone and erythrocyte lead to urinary lead among middle-aged and elderly men:
45 the normative aging study. Environ. Health Perspect. 107: 391-396.
46 Tsaih, S.-W.; Korrick, S.; Schwartz, J.; Amarasiriwardena, C.; Aro, A.; Sparrow, D; Hu, H. (2004) Lead, diabetes,
47 hypertension, and renal function: the Normative Aging Study. Environ. Health Perspect. 112:1178-1182.
48 Turlakiewicz, Z.; Chmielnicka, J. (1985) Diethyllead as a specific indicator of occupational exposure to
49 tetraethyllead. Br. J. Ind. Med. 42: 682-685.
50 Tuthill, R. W. (1996) Hair lead levels related to children's classroom attention-deficit behavior. Arch. Environ.
51 Health 51: 214-220.
52 Tvinnereim, H. M.; Eide, R.; Riise, T.; Wesenberg, G. R.; Fosse, G.; Steinnes, E. (1997) Lead in primary teeth from
53 Norway: changes in lead levels from the 1970s to the 1990s. Sci. Total Environ. 207: 165-177.
54 U.S. Environmental Protection Agency. (1986) Air quality criteria for lead. Research Triangle Park, NC: Office of
55 Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no.
56 EPA-600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
May 2006 4-139 DRAFT-DO NOT QUOTE OR CITE
-------
1 U.S. Environmental Protection Agency. (1989) Review of the national ambient air quality standards for lead:
2 exposure analysis methodology and validation. OAQPS staff report. Research Triangle Park, NC: Office of
3 Air Quality Planning and Standards; report no. EPA-450/2-89-011. Available from: NTIS, Springfield, VA;
4 PB89-207914.
5 U.S. Environmental Protection Agency. (1994a) Guidance manual for the integrated exposure uptake biokinetic
6 model for lead in children. Washington, DC: Office of Emergency and Remedial Response; report no.
7 EPA/540/R-93/081. Available from: NTIS, Springfield, VA; PB93-963510.
8 U.S. Environmental Protection Agency. (1994b) Technical support document: parameters and equations used in
9 integrated exposure uptake biokinetic model for lead in children (v 0.99d). Washington, DC: Office of
10 Solid Waste and Emergency Response; report no. EPA/540/R-94/040. Available from: NTIS, Springfield,
11 VA; PB94-963505.
12 U.S. Environmental Protection Agency. (1996) Urban soil lead abatement demonstration project. Volume I: EPA
13 integrated report. Research Triangle Park, NC: Office of Research and Development, National Center for
14 Environmental Assessment; report no. EPA/600/P-93/001aF. Available from: NTIS, Springfield, VA;
15 PB96-168356.
16 U.S. Environmental Protection Agency. (1996) Recommendations of the Technical Review Workgroup for Lead for
17 an interim approach to assessing risks associated with adult exposures to lead in soil. Draft report.
18 Washington, DC: Technical Review Workgroup for Lead. Available:
19 www.epa.gov/superfund/programs/lead/products/adultpb.pdf [1999, November 23].
20 U.S. Environmental Protection Agency. (1997) Health risks from low level environmental exposures to
21 radionuclides. Washington, DC: U.S. Environmental Protection Agency. Federal Guidance Report No. 13.
22 EPA402-R-97-014.
23 U.S. Environmental Protection Agency. (2001) Final human health risk assessment for the Coeur d'Alene Basin
24 extending from Harrison to Mullan on the Coeur d'Alene River and Tributaries remedial
25 investigation/feasibility study. Washington, DC: Idaho Department of Environmental Quality.
26 U.S. Environmental Protection Agency (2003a) Assessing intermittent or variable exposures at lead sites.
27 Washington, DC: Office of Solid Waste and Emergency Response; report no. EPA-540-R-03-008;
28 OSWER# 9285.7-76. Available: http://www.epa.gov/superfund/lead/products/twa-fmal-nov2003.pdf
29 [10 March, 2006].
30 U.S. Environmental Protection Agency. (2003b) Evaluation of the ICRP Lead Biokinetics Model: empirical
31 comparisons with observations of plasma-blood lead concentration relationships in humans. Washington,
32 DC: Office of Emergency and Remedial Response; FEDSDVI order no. DABT; Syracuse Research
33 Corporation; contract no. GS-10F-0137K.
34 U.S. Environmental Protection Agency. (2003c) Recommendations of the Technical Review Workgroup for lead for
35 an approach to assessing risks associated with adult exposures to lead in soil. Washington, DC: Technical
3 6 Review Workgroup for Lead; EPA-540-R-03 -001. Available:
37 http://www.epa.gov/superfund/lead/products/adultpb.pdf [11 May, 2006].
38 U. S. Environmental Protection Agency. (2005) All ages lead model [draft version 1.05]. Research Triangle Park,
3 9 NC: National Center for Environmental Assessment.
40 Ulmer, D. D.; Vallee, B. L. (1969) Effects of lead on biochemical systems. Trace Subst. Environ. Health pp. 7-27.
41 VanDe Vyver, F. L.; D'Haese, P. C.; Visser, W. I; Elseviers, M. M.; Knippenberg, L. I; Lamberts, L. V.; Wedeen,
42 R. P.; De Broe, M. E. (1988) Bone lead in dialysis patients. Kidney Int. 33: 601-607.
43 Vural, N.; Duydu, Y. (1995) Biological monitoring of lead in workers exposed to tetraethyllead. Sci. Total Environ.
44 171: 183-187.
45 Waalkes, M. P.; Klaassen, C. D. (1985) Concentration of metallothionein in major organs of rats after administration
46 of various metals. Fundam. Appl. Toxicol. 5: 473-477.
47 Waalkes, M. P.; Harvey, M. I; Klaassen, C. D. (1984) Relative in vitro affinity of hepatic metallothionein for
48 metals. Toxicol. Lett. 20: 33-39.
49 Wasserman, G. A.; Graziano, J. H.; Factor-Litvak, P.; Popovac, D.; Morina, N.; Musabegovic, A.; Vrenezi, N.;
50 Capuni-Paracka, S.; Lekic, V.; Preteni-Redjepi, E.; Hadzialjevic, S.; Slavkovich, V.; Kline, J.; Shrout, P.;
51 Stein, Z. (1994) Consequences of lead exposure and iron supplementation on childhood development at age
52 4 years. Neurotoxicol. Teratol. 16: 233-240.
53 Watson, W. S.; Morrison, J.; Bethel, M. I. F.; Baldwin, N. M.; Lyon, D. T. B.; Dobson, H.; Moore, M. R.; Hume, R.
54 (1986) Food iron and lead absorption in humans. Am. J. Clin. Nutr. 44: 248-256.
May 2006 4-140 DRAFT-DO NOT QUOTE OR CITE
-------
1 Webber, C. E.; Chettle, D. R.; Bowins, R. J.; Beaumont, L. F.; Gordon, C. L.; Song, X.; Blake, J. M; McNutt, R. H.
2 (1995) Hormone replacement therapy may reduce the return of endogenous lead from bone to the
3 circulation. Environ. HealthPerspect. 103: 1150-1153.
4 Wedeen, R. P. (1992) Removing lead from bone: clinical implications of bone lead stores. Neurotoxicology
5 13:843-852.
6 Wedeen, R. P.; Maesaka, J. K.; Weiner, B.; Lipat, G. A.; Lyons, M. M.; Vitale, L. F.; Joselow, M. M. (1975)
7 Occupational lead nephropathy. Am. J. Med. 59: 630-641.
8 Weis, C. P.; Lavelle, J. M. (1991) Characteristics to consider when choosing an animal model for the study of lead
9 bioavailability. Chem. SpeciationBioavailability 3: 113-119.
10 Weitzman, M.; Aschengrau, A.; Bellinger, D.; Jones, R.; Hamlin, J. S. (1993) Lead-contaminated soil abatement and
11 urban children's blood lead levels. JAMA J. Am. Med. Assoc. 269: 1647-1654.
12 Wells, A. C.; Venn, J. B.; Heard, M. J. (1977) Deposition in the lung and uptake to blood of motor exhaust labelled
13 with203Pb. In: Walton, W. H.; McGovern, B., eds. Inhaled particles IV: proceedings of an international
14 symposium, part 1; September 1975; Edinburgh, United Kingdom. Oxford, United Kingdom: Pergamon
15 Press, Ltd.; pp. 175-189.
16 White, P. D.; VanLeeuwan, P.; Davis, B. D.; Maddaloni, M.; Hogan, K. A.; Marcus, A. H.; Elias, R. W. (1998)
17 The conceptual structure of the integrated exposure uptake biokinetic model for lead in children. Environ.
18 Health Perspect. 106(suppl. 6): 1513-1530.
19 Wilhelm, M.; Lombeck, I.; Hafner, D.; Ohnesorge, F. K. (1989) Hair lead levels in young children from the F.R.G.
20 J. Trace Elem. Electrolytes Health Dis. 3: 165-170.
21 Wilhelm, M.; Pesch, A.; Rostek, U.; Begerow, J.; Schmitz, N.; Idel, H.; Ranft, U. (2002) Concentrations of lead in
22 blood, hair and saliva of German children living in three different areas of traffic density. Sci. Total
23 Environ. 297: 109-118.
24 Wittmers, L. E.; Aufderheide, A. C.; Wallgren, J.; Rapp, G.; Alich, A. (1988) Lead in bone. IV. Distribution of lead
25 in the human skeleton. Arch. Environ. Health 43: 381-391.
26 Xie, Y.; Chiba, M.; Shinohara, A.; Watanabe, H.; Inaba, Y. (1998) Studies on lead-binding protein and interaction
27 between lead and selenium in the human erythrocytes. Ind. Health 36: 234-239.
28 Xu, G. B.; Yu, C. P. (1986) Effects of age on deposition of inhaled aerosols in the human lung. Aerosol Sci.
29 Technol. 5: 349-357.
30 Yassin, A. S.; Martonik, J. F.; Davidson, J. L. (2004) Blood lead levels in U.S. workers, 1988-1994. J. Occup.
31 Environ. Med. 46: 720-728.
32 Zaragoza, L.; Hogan, K. (1998) The integrated exposure uptake biokinetic model for lead in children: independent
33 validation and verification. Environ. Health Perspect. 106(suppl. 6): 1551-1556.
34 Zhang, W.; Zhang, G. G., He, H. Z.; Bolt, H. M. (1994) Early health effects and biological monitoring in persons
35 occupationally exposed to tetraethyllead. Int. Arch. Occup. Environ. Health 65: 395-399.
36 Zhang, Z.-W.; Shimbo, S.; Ochi, N.; Eguchi, M.; Watanabe, T.; Moon, C.-S.; Ikeda, M. (1997) Determination of
37 lead and cadmium in food and blood inductively coupled plasma mass spectrometry: a comparison with
38 graphite furnace atomic adsorption spectrometry. Sci. Total Environ. 205: 179-187.
39 Ziegler, E. E.; Edwards, B. B.; Jensen, R. L.; Mahaffey, K. R.; Fomon, S. J. (1978) Absorption and retention of lead
40 by infants. Pediatr. Res. 12: 29-34.
41
May 2006 4-141 DRAFT-DO NOT QUOTE OR CITE
-------
i 5. TOXICOLOGICAL EFFECTS OF LEAD IN
2 LABORATORY ANIMALS, HUMANS, AND IN VITRO
3 TEST SYSTEMS
4
5 5.1 INTRODUCTION
6 As noted in Chapter 1, air quality criteria documents evaluate scientific knowledge of
7 relationships between pollutant concentrations and their effects on the environment and public
8 health. Chapters 2 and 3 of this document discussed the chemistry and physical properties of
9 lead (Pb); sources, emissions, transport, and deposition of Pb; and environmental concentrations
10 and pathways to human exposure. Chapter 4 discussed models of human exposure that predict
11 tissue distribution of lead. This chapter (Chapter 5) assesses information regarding the
12 toxicological effects of Pb in laboratory animals, humans, and in vitro test systems. Emphasis is
13 placed here on qualitative characterization of various Pb-induced effects, with attempts to define
14 dose-effect relationships for the key health effects that are thought to occur at ambient exposure
15 levels encountered by the general population of the United States. Chapter 6 follows with a
16 discussion of epidemiologic studies of ambient Pb-exposure effects. Chapter 7 provides an
17 integrative synthesis of information on Pb exposures and health effects. The environmental
18 effects of Pb are discussed in Chapter 8.
19 The framework used here for presenting the toxicologic effects of Pb is subdivided mainly
20 according to organ systems. As noted in the 1986 Pb AQCD, this facilitates presentation of the
21 information, but it must be stressed that all systems are interdependent, functioning in delicate
22 concert to preserve the physiological integrity of the whole organism.
23 The information discussed in this chapter is derived from a very wide body of literature on
24 studies in humans, laboratory animals, and in vitro test systems of animal cell lines and organ
25 systems that may mimic responses in intact animals. This chapter is not intended to be a
26 compendium of all that is known about lead; rather, it is an update of the reported biological
27 effects from the last previous Pb AQCD (U.S. Environmental Protection Agency, 1986a), the
28 Addendum to that document (Lead Effects on Cardiovascular Function, Early Development, and
29 Stature) (U.S. Environmental Protection Agency, 1986b), and the Supplement to the 1986
30 Addendum (U.S. Environmental Protection Agency, 1990). The historical Pb literature is briefly
May 2006 5-1 DRAFT-DO NOT QUOTE OR CITE
-------
1 summarized at the opening of each section or subsection and is intended as a very concise
2 overview of previous work The reader should refer to the previous documents listed above for
3 more detailed discussion of the literature prior to the late 1980s. Each section then continues
4 with brief discussions of key studies published since 1986. Longer discussions of the newly
5 available studies are included where warranted. Sections are ended with comparisons of data
6 from the 1986 AQCD with new data, and basic conclusions are drawn. More detailed summaries
7 of newly available studies and results are provided in tables in Annex AX5.
8
9
10 5.2 EFFECTS OF LEAD ON HEME SYNTHESIS
11 5.2.1 Effects of Lead on Erythrocyte Biology and Function
12 Lead poisoning is one of the most common acquired environmental diseases, because of
13 physical properties of the metal and its widespread distribution in the environment. It is a
14 complex disorder affecting several organs in the body, including developing erythrocytes (red
15 blood cells [RBCs]). Anemia is frequently observed with Pb poisoning and is thought to result
16 from the shortening of erythrocyte life span and is also due to the effects of Pb on hemoglobin
17 synthesis. However, the exact mechanisms by which Pb affects the red blood cell (RBC) life
18 span and heme synthesis are not clear. It is postulated that the mechanisms may be due to the
19 effects of Pb on iron uptake; Pb poisoning also causes an increased urinary excretion of
20 porphyrins and 5-aminolevulinic acid (ALA), the first precursor for heme synthesis. In addition,
21 the striking similarities between Pb poisoning and acute intermittent porphyria (the disease
22 associated with lesions in the heme biosynthetic enzyme, porphobilinogen deaminase) strongly
23 suggests that one of the major sites of Pb intoxication is the heme biosynthetic pathway.
24 The 1986 Pb AQCD presented a concise summary of literature available at that time from
25 both animal and human studies indicating potential effects of Pb intoxication on enzymes and
26 precursors involved in heme synthesis, erythrocyte morphology and function as well as the
27 influence of these perturbations on the nervous system and vitamin D metabolism and associated
28 physiological process. In summary, these studies reported an association between increased Pb
29 exposure and increased ALAS activity (which is increased in kidney with acute exposure and in
30 spleen with chronic exposure, while it decreased in liver tissue in both the exposure scenarios).
31 The activity of ALAD appeared to be inversely correlated to blood Pb values and was found to
May 2006 5-2 DRAFT-DO NOT QUOTE OR CITE
-------
1 be inhibited in several tissues. It was also inferred from several animal studies that the effect of
2 Pb on heme formation involved both ferrochelatase inhibition and impaired mitochondrial
3 transport of iron. Human studies indicated that occupational exposure to Pb results in decreased
4 erythrocyte cell survival and alterations in erythrocyte membrane integrity and energetics. The
5 vast scientific literature on the effects of Pb on various aspects of heme metabolism in diverse
6 organ systems both in human and animals has accumulated over the past two decades.
7 Recognizing the magnitude of this literature, this chapter is primarily concerned with discussions
8 of data from animal and in vitro studies, while the human studies are dealt with in Chapter 6.
9
10 5.2.2 Effects of Lead on Erythrocyte Functions
11 The cellular membrane is one of the main targets for toxic effects of heavy metals,
12 including Pb. Anemia, one of the clinical symptoms of Pb intoxication, can develop because of
13 impairment of hemoglobin synthesis and damage of erythrocyte membranes by Pb ions.
14 Although, erythrocyte membrane is not as specialized as other cell membranes are, it carries out
15 important functions common to other cell membranes, such as active and passive transport and
16 the production of ionic and electric gradients. Changes in erythrocyte membrane lipid and
17 protein profiles can alter the membrane fluidity, potentially affecting enzymatic activity and the
18 functionality of receptors and ion channels present on the plasma membrane and also can
19 influence the ionic and molecular composition of intracellular spaces.
20
21 Lead Uptake. Binding, and Transport
22 Studies by Simons (1986a) indicated that the uptake of Pb into human RBCs is a passive
23 process, i.e., it does not require the use of energy in the form of ATP. In addition, Pb may be
24 able to cross the membrane passively in either direction. This process involves anion transport
25 mechanisms, as the characteristic anion exchange inhibitors have been found to inhibit the
26 passive uptake of Pb by RBCs (Simons, 1986a,b). It has also been demonstrated that the
27 transport of Pb across the membrane depends on the presence of another anion, the bicarbonate
28 ion, and is transported as Pb-carbonate (Simons, 1986a). When Pb enters the cell, it binds
29 mainly to hemoglobin, and the ratio of bound to free Pb in cytoplasm has been estimated to be
30 6000:1. Simons (1986a,b) carried out studies using citrate buffers, which may cause hemolysis
31 of RBCs. To avoid the influence of a citrate buffer, Sugawara et al. (1990) measured the uptake
May 2006 5-3 DRAFT-DO NOT QUOTE OR CITE
-------
1 of Pb into human RBCs by adding Pb directly into plasma. These investigators also found that
2 the transport of Pb across the erythrocyte membrane is energy-independent (passive) and carrier
3 mediated. Little release of Pb from the cells was observed, suggesting absence of any hemolysis
4 of the cells in this protocol. Furthermore, the progressive accumulation of Pb was not observed.
5 More than 98% of the Pb was found accumulated in the cytoplasm in protein-bound form, while
6 only 2% was found in the membrane fraction. Sugawara et al. (1990) also reported finding
7 45 Pb-binding sites on human hemoglobin. On the other hand, studies reported by Bergdahl
8 et al. (1997) using liquid chromatography coupled with inductive plasma mass spectrometry
9 analysis suggested aminolevulinic acid dehydratase (ALAD), the enzyme involved in the heme
10 synthesis pathway, to be the principle Pb-binding protein, not hemoglobin, as previously thought.
11 Additional studies carried out by Simons (1993a) evaluated the transport of Pb into RBCs
12 for cell Pb contents in the range of 1 to 10 jiM and reported that 203Pb uptake was mediated by an
13 anion exchanger and the efflux was mediated through a vanadate-sensitive pathway identified
14 with the calcium pump (Simons, 1988). He further concluded that the high ratio of RBC to
15 plasma Pb observed in vivo was due to a labile Pb-binding component within the cytoplasm.
16 Simons (1993a) also observed that exit of Pb ions from the RBC was much lower than expected
17 based on his earlier work with erythrocyte ghosts. Utilizing a group of drugs that modify anion
18 exchange and thiol groups in the cytoplasm, Lai et al. (1996) showed that anion exchange
19 mechanisms and thiol groups were critical factors in how Pb stimulates calcium-dependent
20 processes in erythrocytes. Once the role of anion exchanger proteins had been implicated in Pb
21 transport in erythrocytes, Bannon et al. (2000) investigated whether similar anion exchange
22 processes are involved in the uptake and transport of Pb in other cells, such as Madin-Darby
23 canine kidney epithelial cells. Based on a comparative in vitro study using human erythrocytes
24 and canine kidney epithelial cells, these authors reported transport of Pb in kidney epithelial
25 cells, suggesting similar anion exchange involvement.
26
27 Erythrocyte Survival, Mobility, and Membrane Integrity
28 It is well recognized that Pb intoxication interferes with RBC survival by shortening the
29 life span and altering the mobility of the erythrocytes; however, the molecular mechanisms
30 behind these effects of Pb on erythrocyte functions are not well understood. The shape and
31 deformability of the human erythrocyte, or RBC is maintained by several factors including low
May 2006 5-4 DRAFT-DO NOT QUOTE OR CITE
-------
1 concentration of free intracellular Ca2+ (<0.1 jiM) and a replenished ATP level. An elevated
2 interfacial Ca2+ concentration inside the RBC activates the passive ion efflux via a K+ selective
3 (voltage independent) channel and a concomitant water transport (Gordos effect). Low
4 concentrations of Pb ions can mimic Ca2+ and activate the same channel in the RBC.
5 Intraperitonially injected Pb significantly decreases rat erythrocyte membrane mobility
6 (Terayama et al., 1986), an effect evident to some extent even below blood Pb concentration of
7 100 jig/100 ml. This decrease in rat erythrocyte mobility was found simultaneous or prior to
8 changes in hematological parameters such as hemoglobin (Hb) levels and hematocrits (Hct). The
9 same group (Terayama and Muratsugu, 1988) also reported a significant decrease in erythrocyte
10 membrane sialic acid content at the same levels of blood Pb with exposure to Pb (20 mM
11 Pb-acetate once a week for 5 weeks). Additional studies by the same group reported that other
12 hematological parameters, such as mean corpuscular volume (MCV), mean corpuscular
13 hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC), were also
14 significantly decreased upon Pb exposure, along with decreased mobility, sialic acid content, and
15 deformability of rat RBCs. However, the blood lead levels reported in these studies range from
16 100 to 800 |ig/dL and, at best, point out newer mechanistic details of erythrocyte membrane
17 alterations to their survival and mobility. However, it has to be noted that these changes were
18 observed to a minor extent even at blood lead levels under 100 |ig/dL. It was speculated that Pb-
19 induced decreases in sialic acid content and deformability of RBCs shorten RBC survival time
20 and may lead to anemia in Pb poisoning. Jehan and Motlag (1995) reported Pb exposure caused
21 significant change in RBC membrane cholesterol and phospholipid contents along with sialic
22 acid. Coexposure to Zn was found to reduce these alterations.
23 Pb-induced morphological changes in human RBC were studied by Eriksson and Bering
24 (1993) using electron paramagnetic resonance imaging. These authors reported that Pb ions
25 (a) induced time-dependent changes in MCV and cell shrinkage and (b) inhibited the Gardos
26 effect. Trialkyl-Pb compounds have also been reported to induce hemolytic activity in
27 erythrocytes, with intensity increasing with hydrophobicity of the compounds (Kleszcyriska
28 et al., 1997). Serrani et al. (1997) reported that Pb ions confer protection against RBC lysis in
29 hypotonic low ionic strength media, presumably due to interaction of Pb with certain constituents
30 in the cell membrane. This resistance to erythrocyte lysis was found to significantly increase
31 with Pb (20 to 25 jiM) compared to other metals such as Al, Cd, and Zn (Corchs et al., 2001).
May 2006 5-5 DRAFT-DO NOT QUOTE OR CITE
-------
1 The Pb-induced reduction in MCV (RBCs derived from umbilical cord) was found to be reversed
2 when the cells were treated with quinidine, an inhibitor of a potassium channel activator, without
3 any effect on resistance to cell lysis, suggesting changes in cell membrane structure. This effect
4 may also be involved in membrane deformability (Mojzis and Nistiar, 2001).
5 Heavy metals, including Cd, Zn, and Pb, have been found to alter RBC membrane
6 microviscosity and fluidity (Amoruso et al., 1987). These authors labeled RBC membranes with
7 fluorescent lipid probe all trans 1, 6-diphenyl-l,3,5-hexatriene (DPH) and demonstrated
8 increased polarization with increased membrane lipid viscosity on exposure to heavy metals.
9 They also postulated that such alterations in cell membrane lipid and possibly also protein
10 fluidity may contribute to abnormal cellular function. Similar changes in RBC fluidity were
11 observed in the RBC collected from workers exposed to Pb (Cook et al., 1987). The RBC ghost
12 membranes isolated from Pb-exposed workers exhibited a significant increase in
13 phosphotidylcholine to phosphotidylethanolamine ratio (an established correlate of membrane
14 fluidity) along with an increase in RBC cholesterol levels, as also reported by Jehan and Motlag
15 (1995) discussed above. These authors predict that such alterations in phospholipid composition
16 of the membrane are responsible for biochemical instability of RBC in Pb-exposed workers.
17 Zimmermann et al. (1993) investigated the potential of such membrane lipid alterations to cause
18 resistance to oxidation. These investigators induced hyperlipidemia by treating Pb-exposed
19 Wistar rats with triton and observed an increase in erythrocyte choline phospholipid levels,
20 together with a significant decrease in membrane lipid resistance to oxidation. They postulated
21 that such a decrease in resistance might cause RBC fragility, and ultimate destruction, leading to
22 anemic conditions. It has been also reported that exposure to Pb may also increase the levels of
23 fatty acids, e.g., arachidonic acid, in the RBC membrane in humans exposed to Pb (Osterode and
24 Ulberth, 2000). Based on the negative correlation between serum calcium and increased
25 arachidonic acid content, these authors postulated that Pb ions might have substituted for calcium
26 in the activation of phospholipase enzymes, leading to increased synthesis of arachidonic acid.
27 The fact that these biochemical and molecular changes were reported at somewhat higher blood
28 lead levels (70 |ig/dL) probably does not undermine these observations made from the RBCs of
29 humans exposed to lead over a period of time and enhances our understanding of the several
30 molecular facets that may play a role in the altered erythrocyte mobility. Suwalsky et al. (2003)
31 investigated the interaction of Pb with the RBC membrane, utilizing intact as well as isolated
May 2006 5-6 DRAFT-DO NOT QUOTE OR CITE
-------
1 unsealed RBC membrane models (representing phospholipids present in the inner and outer
2 layers of the membrane). Electron microscopy, fluorescence spectroscopy, and X-ray diffraction
3 analyses of these models by Suwalsky et al. (2003) indicated that Pb particles adhere to both
4 external and internal surfaces of the membrane. Pb ions also have been found to disturb the
5 lamellar organization by causing considerable molecular disorder within lipid layers.
6 Recently, it has been shown that osmotic shock, oxidative stress, and/or energy depletion
7 activate Ca2+-sensitive erythrocyte scramblase, leading to the exposure of phosphotidylserine at
8 the cell surface. This exposure of phosphotidylserine had been implicated in the phagocytosis of
9 RBC by macrophages that can be measured by annexin binding, as determined by fluorescence
10 activated cell sorting analysis. Kempe et al. (2005) carried out experiments to investigate
11 whether anemic conditions reported in Pb intoxication are the result of the decreased life span of
12 RBCs due to the above-mentioned mechanisms. These investigators reported that when human
13 RBCs were exposed to Pb-nitrate (above 0.3 |iM), it caused a significant increase in Pb annexin
14 binding, indicative of phosphotidylserine exposure. Using inhibitors for Ca2+- sensitive
15 potassium channels and whole cell patch clamp experiments, they concluded that Pb exposure
16 increased activation of potassium channels, leading to shrinkage of cells and also activation of
17 scramblase, resulting in the exposure of phosphotidylserine on the cell membrane surface. These
18 authors further postulated that this exposure of phosphotidylserine on the membrane might have
19 led to them being engulfed by macrophages and the ultimately decreased life span of RBCs in Pb
20 intoxication.
21
22 Membrane Proteins
23 Earlier studies by Fukumoto et al. (1983) reported the differential profile for
24 RBC-membrane polypeptides determined by SDS-PAGE analysis. These investigators found
25 decreased levels of polypeptides in band 3 and increases in the levels of four other bands (i.e.,
26 bands 2, 4, 6, and 7) in the RBCs of human workers exposed to Pb. From these observations,
27 they postulated that such Pb-induced alteration in RBC membrane proteins may lead to
28 membrane permeability changes. Apostoli et al. (1988) also observed similar changes in RBC
29 membrane polypeptides in Pb-exposed workers and suggested that band 3 may represent an
30 anion channel protein; they also found that these changes occurred at blood Pb levels of
31 >50 |ig/100 ml.
May 2006 5-7 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead exposure has been known to increase the amount of membrane-bound protein
2 kinase C in rat brain, endothelial, and glial cells. Belloni-Olivi et al. (1996) reported an
3 increased phosphorylation of RBC membrane proteins on Pb exposure. When human RBCs
4 were incubated with Pb-acetate (>100 nM) for 60 min, it was found to increase phosphorylation
5 of membrane cytoskeletal proteins (120, 80, 52 and 45 kDa). This increase was accompanied by
6 increase in protein kinase C activity. Membrane proteins were not phosphorylated when treated
7 with protein kinase C inhibitors. Calcium and diacylglycerol were found not to be involved in
8 this process. The authors suggested that this activation of protein kinase was a direct interaction
9 of the enzyme protein with Pb. Slobozhanina et al. (2005) reported that incubation of human
10 RBCs with Pb-acetate (1 to 10 jiM for 3 h) caused differential binding of fluorescent probes to
11 the membrane, suggesting alterations in the physicochemical state of the membrane proteins and
12 lipids. Based on these observations, the authors postulated that such alterations in membrane
13 molecular composition may influence the activity of membrane enzymes and the functioning of
14 receptors and channels present on the membrane. These and other related studies are
15 summarized in Annex Table AX5-2.1.
16
17 5.2.3 Effect of Lead on Erythrocyte Heme Metabolism
18 Enzyme studies of the heme pathway have shown that Pb is an inhibitor of several
19 enzymes involved in heme synthesis, including 5-aminolevulinic acid dehydratase (ALAD),
20 coproporphyrinogen oxidase, and ferro chelatase (see Figure 5-2.1 for a schematic representation
21 of heme biosynthesis). ALAD is a cytoplasmic enzyme that catalyzes the second, rate-limiting
22 step of the heme biosynthesis pathway; that is, ALAD catalyzes formation of porphobilinogen
23 through the conjugation of two molecules of 5-aminolevulinic acid. ALAD is a Zn-dependent
24 enzyme, and thiol groups are essential for its activity (Bernard and Lauwerys, 1987). Decreased
25 erythrocyte ALAD is the most sensitive indicator of human Pb exposure, to the extent that
26 measurement of ALAD activity reflects well Pb levels in the blood. Similarly, erythrocyte
27 ALAD activity measurements have been used to assess Pb toxicity in other species.
28
29 Ervthrocvte ALAD
30 Terayama et al. (1986) reported decreased ALAD activity in rat RBCs at blood Pb
31 levels of 10 |ig/dL. Scheuhammer (1987) studied the usefulness of the ALAD ratio
May 2006 5-8 DRAFT-DO NOT QUOTE OR CITE
-------
Zn protoporphyrin
7 Ferrochelatase
Protoporphyrin IX f Pb
Succinyl CoA+ Glycine
1 11 ALA synthatase 11 ALA-S
Protoporphynnogen Ix oxidase
6-aminolevulinic acid
Protoporphynnogen IX
A
Coporphyrinogen
oxidase
Coporphyrinogen
5-aminolevulinic acid
ALA dehydratase
Uroporphyrinogen
cosynthase
Uroporphyrinogen I
Cytoplasm
Uroporphyrinogen I
synthetase
Porphobilinogen i ^"^. Uroporphyrinogen I
Coproporphyrinogen I
Coporphyrinogen I
Figure 5-2.1. Schematic presentation of heme synthesis pathway. Potential lead (Pb)
interacting sites are indicated by curved arrows ( "(increased, JJecreased)
1 (activated/nonactivated enzyme activity) to study Pb effects in avian RBCs. The ALAD activity
2 ratio is a sensitive, dose responsive measure of Pb exposure regardless of the mode of Pb
3 administration. For example, dietary Pb concentrations as low as 5 ppm (dry weight) can be
4 estimated through the use of the ALAD enzyme activity ratio method. A highly significant
5 positive correlation was observed between dietary Pb concentration over the 5 to 100 ppm range
6 and the ALAD activity ratio. The author concluded that RBC ALAD ratio may be a useful
7 method for estimating average dietary concentrations of Pb over an environmentally relevant
8 range, in situations where diet is the major source of exposure to Pb or where accurate
9 estimations of dietary Pb are not possible. Redig et al. (1991) reported heme synthetic pathway
10 alterations upon chronic exposure (3 or 11 weeks) to Pb in red-tailed hawks. This treatment
11 resulted in a severe decrease in RBC ALAD activity, which did not return to normal levels until
May 2006
5-9
DRAFT-DO NOT QUOTE OR CITE
-------
1 5 weeks after termination of Pb treatment. Lead exposure also decreased ALAD activity in the
2 bone marrow and in the liver but did not alter aminolevulinic acid synthase activity. Dorward
3 and Yagminas (1994), using comparative enzyme kinetic analysis of ALAD in Pb-exposed
4 female cynomolgus monkeys and human erythrocyte ALAD, found similar inhibition profiles
5 and concluded that ALAD could be a useful model for measuring the biological response in
6 monkeys. Santos et al. (1999) reported that rat RBC heme biosynthesis was affected by either Pb
7 treatment alone or Pb in combination with ethanol, due to the inhibition of ALAD activity.
8 Analysis of blood ALAD activity had been used as a powerful clinical biomarker in
9 evaluating Pb toxicity in occupational exposure. Fontanellas et al. (2002) further suggested that
10 this enzyme assay be used in identifying even subclinical Pb poisoning in chronic renal failure
11 (see Section 5.7 for details).
12
13 Other Heme Metabolism Enzymes
14 Taketani et al. (1985) studied the heme synthesizing activity of ferric ion using purified
15 ferrochelatase from rat liver mitochondria and reported that Pb reduced NAD(P)H-dependent
16 heme synthesis by 50% at 10~5 M, but that it had no effect when ferrous ion was used as the
17 substrate. Based on these results, the authors concluded that heme synthesis from ferric ion was
18 more susceptible to Pb than the ferrous ion. These studies also revealed that the NAD(P)H
19 oxidizing system reduces ferric ion to ferrous ion, which in turn was used for heme synthesis by
20 ferrochelatase.
21 The effect of various metals, including Pb, on RBC porphobilinogen synthase (PBG-S)
22 was studied using human RBC hemolysate. Farant and Wigfield (1987) reported that the effect
23 on the enzyme depends on the affinity of the metal for thiol groups at its active sites. Additional
24 studies carried out by the same group utilizing rabbit erythrocyte PBG-S indicated that Pb acts as
25 a potent effector of this enzyme both in vitro and in vivo (Farant and Wigfield, 1990). Human
26 RBC porphobilinogen synthetase activity was found to be inhibited by Pb, while Zn ions
27 activated this enzyme (Simons, 1995). Another enzyme involved in the heme synthetic pathway,
28 porphobilinogen deaminase, was inhibited in human RBC by Pb-nitrate (100 mM) in in vitro
29 studies, but had no effect in vivo (Tomokuni and Ichiba, 1990). Rossi et al. (1992) reported no
30 inhibition of coproporphyrinogen oxidase activity in human lymphocytes on exposure to Pb.
31 Heme synthesis can also be affected in Pb intoxication by interference with Fe transport into
May 2006 5-10 DRAFT-DO NOT QUOTE OR CITE
-------
1 reticulocytes. Using a rabbit reticulocyte model, Qian and Morgan (1990) reported that
2 inhibitory effects of Pb on transferrin endocytosis and iron transport across the membrane may
3 also contribute to altered heme metabolism in RBCs. These and other related studies are
4 summarized in Annex Tables AX5-2.2 and 5-2.3.
5
6 5.2.4 Effect of Lead on Other Hematological Parameters
7 The RBC pyrimidine 5-nucleotidase (P5N) catalysis of the hydrolytic dephosphorylation
8 of pyrimidine 5-monophosphates is sensitive to inhibition by Pb. Tomokuni et al. (1989)
9 evaluated the activity of RBC and bone marrow 5-nucleotidase (P5N) and RBC ALAD in mice
10 exposed to drinking water Pb (200 to 500 ppm) for 14 or 30 days. These authors reported that Pb
11 exposure decreased both P5N and ALAD activities in erythrocytes. Additional studies from this
12 group, using a similar exposure regimen, indicated no change in levels of urinary coporphyrins.
13 Lead exposure (4 mg/kg and 6 mg/Kg body wt/30 days) in splenectomized rats was found
14 to cause depletion of RBC Hb content, to increase numbers of reticulocytes in peripheral blood,
15 and to increase urinary delta aminolevulinic acid excretion (Gautam and Chowdhury, 1987).
16 These authors further reported that the increased number of reticulocytes found in the blood may
17 be due to induced acceleration of the erythropoeitic cell series. Redig et al. (1991) reported
18 biphasic effects of Pb on hematological parameters from their chronic exposure studies in red-
19 tailed hawks over 3 or 11 weeks. These authors observed a rapid and relatively brief increase in
20 RBC free protoporphyrin and a slower, but more prolonged, increase in its Zn complex with
21 3-week exposure to Pb (0.82 mg/kg body wt). On the other hand, exposure to a higher dose of
22 Pb (1.64 mg/kg body wt) for a longer duration (11 weeks) resulted in a decrease in the Hct and
23 Hb. Panemangalore and Bebe (1996) reported that Zn deficiency increased the Pb-induced
24 accumulation of porphyrin in RBCs to a lesser extent compared to its accumulation in the liver in
25 weaning rats.
26 The effects of Pb on RBC number and other Hct parameters appear to be dose dependent.
27 lavicoli et al. (2003) investigated these effects by feeding mice with eight different doses of Pb
28 below (0.6 to <2.0 |ig/dL) and above (>2.0 to!3 |ig/dL) normal background levels. These
29 authors reported that mice receiving below normal background levels of dietary Pb displayed
30 enhanced RBC counts and increased Hb and Hct values, whereas a marked decrease in RBC
31 number occurred when blood Pb levels approached 10 |ig/dL. Sivaprasad et al. (2003) also
May 2006 5-11 DRAFT-DO NOT QUOTE OR CITE
-------
1 reported significant reductions in RBC Hb content and Hct on Pb exposure (0.02% Pb-acetate in
2 drinking water for 5 weeks). Toplan et al. (2004) observed significant decreases in RBC Hb
3 content and Hct and increases in blood viscosity in Wistar rats after 5-week exposure to Pb.
4 Studies cited above are summarized in Annex Table AX5-2.4.
5
6 5.2.5 Effects of Lead on Erythrocyte Enzymes
7 The toxic effects of Pb on RBCs result from its complexation with the sulfhydryl,
8 carboxyl, and imidazole groups of proteins, particularly enzymes, by competitive binding of Pb2+
9 with Zn2+ or Mg2+ in metalloenzymes. This binding of Pb to enzyme proteins can inhibit
10 enzymes involved in the glycolytic and pentose phosphate pathway, both of which are sources of
11 energy compounds and intermediates of purine conversion, thus causing a disruption of energy
12 metabolism. Along with these changes, Pb-induced changes in the membrane integrity, as
13 discussed earlier (Section 5.2.1), may also affect the enzymes' associated ion channels and other
14 transport mechanisms.
15
16 Energy Metabolism
17 Erythrocytes generate high-energy ATP by anerobic glycolysis and cycle oxidized and
18 reduced nicotinamide adenine dinucleotide phosphate (NADP) by the aerobic pentose phosphate
19 pathway. Anemic conditions associated with Pb poisoning, along with the inhibitory effects of
20 Pb on heme synthesis, may result in increased RBC destruction due to the inhibitory effects of
21 Pb on the activities of the enzyme, pyramidine 5-nucleotidase (P5N). Deficiency of this enzyme
22 is characterized by intracellular accumulation of pyramidine-containing nucleotides, leading to
23 hemolysis. Inhibition of this enzyme along with the perturbations in heme metabolism creates
24 imbalances in the energy currency of the erythrocyte. Perturbations in energy metabolism can be
25 followed by changes in the concentration of purine nucleotides. In erythrocytes, these
26 compounds cannot be synthesized de novo; they can only be reconstructed from preexisting free
27 purine bases on nucleosides through salvage type reactions. The cell energy content can be
28 measured by adenylate (ATP + ADP + AMP) and guanylate (GTP + GDP + GMP) nucleotides,
29 and by their sum total. The concentrations of nucleoside monophosphates increase in cases of
30 cell energy deficit, but they quickly degrade to nucleosides and bases.
May 2006 5-12 DRAFT-DO NOT QUOTE OR CITE
-------
1 Cook et al. (1987) compared P5N and deoxypyramidine-5-nucleotidase levels in the RBC
2 of Pb-exposed workers and matched controls and reported significantly lower levels of P5N in
3 Pb-exposed workers. Konantakieti et al. (1986) reported similar observations in neonatal rat
4 RBCs. These authors further indicated that the low levels of nucleotides were due to inhibition
5 of P5N activity by Pb, as the depression in enzyme activity was correlated with blood Pb levels.
6 This was further validated by in vitro inhibition of P5N in a dose-dependent manner. Tomokuni
7 and Ichiba (1988) found similar results with human RBCs both in vitro and in vivo. They
8 reported activation of Pb-exposed human RBCs. Antonowicz et al. (1990) observed significantly
9 higher levels of glycolytic enzymes and increased production of lactic acid and 2,3-diphospho
10 glycerol, when human RBCs were incubated with Pb. Based on their observations, these authors
11 suggested that Pb exposure may result in anaerobic glycolysis activation in human RBCs.
12 In contrast, Grabowska and Guminska (1996) reported that Pb exposure diminished the ATP
13 levels in human RBCs by inhibiting aerobic glycolysis.
14 Erythrocyte energy metabolism in workers exposed to heavy metals, but without clinical
15 manifestations of toxicity, was found to intensify and become more pronounced when they were
16 occupationally exposed to Pb. Nikolova and Kavaldzhieva (1991) measured the exposed
17 workers and reported higher ratios of ATP/ADP in Pb-exposed workers. Because the RBC
18 energy pool is perturbed due to Pb exposure, Morita et al. (1997) evaluated the effect of Pb on
19 NAD synthetase and reported an apparent dose-dependent decrease in NAD synthetase activity
20 in the erythrocytes of Pb exposed workers.
21 Baranowska-Bosiacka and Hlynczak (2003) evaluated Pb effects on distribution profiles
22 of adenine, guanine nucleotide pools, and their degradation products in human umbilical cord
23 RBCs. In vitro exposure equivalent (Pb-acetate; 100 to 200 |ig/dL) to Pb exposure for 20 h were
24 found to significantly lower the levels of nucleotide pools, including NAD and NADP,
25 accompanied by a significant increase in purine degradation products (adenosine, guanosine,
26 inosine, and hypoxanthine). Associated morphological RBC alterations were also observed, with
27 marked significant increases in stomatocytes, spherocytes, and echinocytes. These investigators
28 also observed similar alterations in the nucleotide pools in Wistar rat RBCs with short-term
29 exposure to Pb (Baranowska-Bosiacka and Hlynczak, 2004). Based on these observations, the
30 authors postulated that decreases in NAD and NADP concentrations in RBCs may be a good
31 indicator of Pb-induced disturbance in the energy process and can serve as a useful marker for
May 2006 5-13 DRAFT-DO NOT QUOTE OR CITE
-------
1 chronic Pb exposure. If NAD synthetase activity had been measured in these studies, it might
2 have provided experimental support for the observation of inhibition of NAD synthetase reported
3 by Morita et al. (1997).
4
5 Other Enzymes
6 Lead-induced efflux of K+ from human RBCs had been recognized as being due to the
7 ability of Pb to selectively increase the membrane permeability for this cation. Studying the
8 efflux of 86Rb using inside-out RBC vesicles, Alvarez et al. (1986) demonstrated that Pb
9 promoted the selective efflux of K+ ions by altering the sensitivity of Ca2+ binding site on the
10 membrane either by direct binding or by altering Mg2+-mediated modulation. Fehlau et al.
11 (1989) indicated that this modulation of the Ca2+-activated K+ channel in human RBCs coincides
12 with the activation of RBC membrane-bound oxidoreductase. These authors suggested that,
13 even though these two are independent events, the oxidoreductase enzyme activity may influence
14 K channel gating.
15 Earlier studies by Mas-Oliva (1989) on the potential effects of Pb on the RBC membrane
16 (using RBC ghosts) indicated that Pb has inhibitory effects on Ca2+-Mg2+-ATPase. Further
17 investigations on the role of calmodulin in the inhibition of Ca2+-Mg2+-ATPase indicated that the
18 inhibitory activity on the enzyme may be due either to the effect of Pb on sulfhydryl groups on
19 the enzyme or by direct binding to calmodulin.
20 Jehan and Motlag (1995) reported that when albino rats were administered Pb i.p (5 or
21 20 mg/kg body wt) for 14 consecutive days either alone or in combination with Cu (2 mg/kg
22 body wt) or zinc (5 mg/kg body wt), there were severe decreases in RBC membrane enzyme,
23 acetylcholine esterase (AChE), NADH dehydrogenase, and Na+-K+ ATPase levels along with
24 decreases in phospholipid content, hexose, and hexosamine. Of the combined metal treatment
25 exposure regimens, Zn was found to considerably reduce such changes. Grabowska and
26 Guminska (1996) assayed three ATPase activities (i.e., Na+-K+ ATPase, Mg2+-ATPase, and
27 Ca2+-ATPase) in human RBC in vitro and reported RBC Na+-K+ ATPase to be the only enzyme
28 inhibited by Pb, while Ca2+ or Mg 2+ATPases were not sensitive to Pb. On the other hand,
29 Sivaprasad et al. (2003) observed Pb-induced reductions in RBC activities for all three of those
30 types of ATPase activities.
May 2006 5-14 DRAFT-DO NOT QUOTE OR CITE
-------
1 Two reports by Calderon-Salinas et al. (1999a,b) indicated Pb effects on calcium transport
2 in human RBC. Initial studies by this group indicated that Pb and Ca are capable of inhibiting
3 the passive transport of other metals in a noncompetitive way. Inhibition studies using N-ethyl-
4 maleimide indicated that Pb and Ca share the same permeability pathway in human RBCs and
5 that this transport system is electrogenic (Calderon-Salinas et al., 1999a). Additional studies by
6 the same group reported that Pb is capable of inhibiting Ca efflux by inhibiting Ca-ATPase
7 (Calderon-Salinas et al., 1999b). These authors further suggested that under physiological
8 conditions, Pb, via Ca2+-ATPase, alters Ca influx, while chronic Pb intoxication inhibits Ca
9 efflux by altering RBC calcium homeostasis. Silkin et al. (2001) reported Pb-induced activation
10 of K channels in the RBCs of the teleost fish S. porcus. Exposure of teleost fish RBCs to 1 to
11 2 |iM Pb led to a minor loss in cellular K+; but, at 20 to 50 |iM Pb, about 70% of cellular K+ was
12 lost. Based on their observations of Pb-induced K+ efflux from RBCs under competitive and
13 inhibitory regimens, these authors suggested that Pb activates RBC K+ channels.
14 Eder et al. (1990) and Loipfiihrer et al. (1993) investigated activity levels of Ca2+-ATPase
15 and calcium accumulation, respectively, in Pb-depleted rat RBCs. No alteration in Ca2+-ATPase
16 activity or Ca accumulation was observed in the PO generation (Eder et al., 1990). On the other
17 hand, significant reduction in Ca-ATPase activity was observed in the Fl generation. It was
18 suggested that Pb-induced alterations in the metabolism of phosphoproteins and glycoproteins
19 result from Pb depletion and may be responsible for the reduced enzyme activity. Both of the
20 groups postulated that the decreased MCV observed in Pb depleted rat RBCs could be due to
21 reduced Ca2+-ATPase activity in the RBCs. These and other related studies are summarized in
22 Annex Tables AX5-2.5 and 5-2.6.
23
24 5.2.6 Erythrocyte Lipid Peroxidation and Antioxidant Defense
25 Although several mechanisms have been proposed to explain Pb toxicity, no mechanisms
26 have been defined explicitly. Recent literature on Pb toxicity suggests oxidative stress as one of
27 the important mechanisms for toxic effects of Pb in various organs. Because RBCs accumulate
28 major amounts of Pb compared to other tissues, oxidative stress may also result in the
29 accentuation of lipid peroxidation with concomitant inhibition of antioxidant enzymes, such as
30 superoxide dismutase (SOD), catalase, GSH peroxidase, GSH reductase, and simultaneous
31 increases in oxidized GSH (GSSG) and reduced GSH/GSSG ratios. Pb-induced lipid
May 2006 5-15 DRAFT-DO NOT QUOTE OR CITE
-------
1 peroxidation and the mitigating effects of experimental chelation therapy are discussed with
2 relevance to each tissue or organ within this chapter. The discussion focuses on the available
3 literature with reference to studies on erythrocytes.
4 Patra and Swarup (2000) reported significant changes in RBC lipid peroxide levels and
5 anti oxidant defense (SOD and catalase) levels in RBC hemolysates from male calves exposed to
6 Pb (7.5 mg/kg body wt for 28 days). These authors suggested the potential role for increased
7 peroxide levels in Pb-induced alterations in RBCs. Mousa et al. (2002) investigated the levels of
8 various antioxidant enzymes, thiols, lipid peroxide in erythrocytes, and total thiol status of
9 plasma in goats exposed to Pb (Pb-acetate, 5.46 mg/kg body wt for 2 weeks). These authors
10 reported that all the parameters referred above were significantly increased in RBCs by day 7
11 and receded to normal levels by day 14, while peroxides remained significantly increased even
12 by day 14. Based on these observations, it was suggested that Pb-induced lipid peroxide
13 generation in RBCs appears to be a continuous process and can lead to persistent oxidative stress
14 in RBCs with chronic exposure.
15 The effects of chelative agents on RBC lipid peroxidation are summarized in
16 Annex Table AX5-2.7.
17
18 Summary
19 • The 1986 Pb AQCD reported that the activity of ALAD appeared to be inversely
20 correlated to blood Pb values and was found inhibited in several tissues. Human studies
21 reviewed in 1986 Pb AQCD also indicated that occupational exposure to Pb results in
22 decreased RBC survival along with alterations in RBC membrane integrity and energetics.
23 • More recent studies reviewed in this AQCD indicate that the transport of Pb across the
24 RBC membrane is energy-independent, carrier-mediated, and that the uptake of Pb is
25 mediated by an anion exchanger through a vanadate-sensitive pathway.
26 • Lead intoxication interferes with RBC survival and alters RBC mobility. Hematological
27 parameters, such as mean corpuscular volume (MCV), mean corpuscular hemoglobin
28 (MCH), and mean corpuscular hemoglobin concentration (MCHC), are also significantly
29 decreased upon exposure to Pb. These changes are accompanied by decreased membrane
30 sialic acid content.
31 • Morphological analyses using electron paramagnetic resonance imaging and spin labeling
32 techniques indicate that changes occur in RBC morphology upon Pb exposure.
May 2006 5-16 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Lead-induced RBC membrane lamellar organization and decreases in membrane lipid
2 resistance to oxidation in rats appear to be mediated by perturbations in RBC membrane
3 lipid profiles. Similarly, Pb-induced altered phosphorylation profiles of RBC membrane
4 proteins have been reported.
5 • Erythrocyte ALAD activity ratio (ratio of activated/non activated enzyme activity) has
6 been shown to be a sensitive, dose-responsive measure of Pb exposure, regardless of the
7 mode of administration of Pb. Competitive enzyme kinetic analyses in RBCs from both
8 human and Cynomolgus monkeys indicated similar inhibition profiles by Pb.
9 • Consistent observation of Pb-mediated inhibition of pyramidine 5'-nucleotidase (P5N)
10 suggests this enzyme as a potential biomarker for Pb exposure.
11 • Significant reductions in levels of nucleotide pools (e.g., NAD and NADP) accompanied
12 by significant increase in purine degradation products have been implicated in the Pb-
13 induced altered energetics of RBCs.
14 • Lead-induced increased permeability for K+ in RBCs appears to be due to the selective
15 efflux of K+ ions on the RBC membrane due to altered sensitivity of the Ca2+-binding site
16 on the membrane. Erythrocyte Na+-K+ ATPase appears to be more sensitive to Pb-induced
17 inhibition than Ca2+-Mg2+ ATPase.
18 The newly available (since 1986) scientific evidence presented in this section clearly
19 demonstrates deleterious Pb effects on erythrocyte cell morphology, function, Pb uptake and
20 alterations in certain enzymes involved in heme synthetic pathways. However, some of the
21 interesting and important conclusions are derived mainly from in vitro studies, often using short
22 time incubations. It would be useful to substantiate such findings further by more systematic
23 studies employing meaningful experimental designs for in vivo evaluation of laboratory animal
24 models.
25
26
27 5.3 NEUROLOGIC/NEUROBEHAVIORAL EFFECTS OF LEAD
28 5.3.1 Neurotoxicologic/Neurobehavioral Effects of Lead in Animals
29 5.3.1.1 Introduction
30 Since the initial description of Pb encephalopathy in the developing rat in the mid-1960s
31 (Pentschew and Garro, 1966), a continuing research focus has been on defining the extent of
32 CNS involvement at subencephalopathic, environmentally relevant levels of exposure. These
33 efforts have primarily addressed the developing animal, consistent with the primary public health
May 2006 5-17 DRAFT-DO NOT QUOTE OR CITE
-------
1 concerns for neurotoxicity from Pb during this period. While significant research advances have
2 been made in animal studies over the last four decades, relating these findings to neurotoxicity in
3 children has been challenging and difficult. The barriers to greater progress have primarily been
4 due to Pb's multiple toxic mechanisms of action in brain tissue, which encompass variable,
5 overlapping, and, at times, opposing dose-effect relationships. The goal of this section is to
6 bring greater clarity to the current state of knowledge.
7 Discussions of the biologic effects of lead in the 1986 Pb AQCD focused on general
8 questions relating to (1) the internal exposure levels, as measured by blood lead concentrations
9 (PbB), at which neurotoxic effects occur; (2) the persistence or reversibility of these effects; and
10 (3) the populations that are especially sensitive to the neurotoxic effects of lead. The state of
11 knowledge at publication of the 1986 AQCD provided answers for these questions as follows.
12 At very high levels of exposure producing PbB of 100 to 120 |ig/dL in adults and 80 to
13 100 |ig/dL in children, serious neurotoxic effects occur including acute encephalopathy that can
14 progress to convulsions, coma, and sudden death. Less severe exposures creating PbB of 40 to
15 60 |ig/dL produce both central and peripheral nerve dysfunction including slowed nerve
16 conduction velocity and overt signs and symptoms of neurotoxicity. Decrements in IQ are
17 observed in children with PbB of 30 to 50 |ig/dL, with some studies showing effects at lower
18 PbB. Neurobehavioral effects are observed in rats and monkeys at levels <20 |ig/dL.
19 (1) Human studies provide little information on the persistence of effects. Animal studies
20 show that alterations in neurobehavioral function can persist long after lead exposure
21 has stopped and PbB levels have returned to normal. Persistent learning deficits occur
22 in both rats and monkeys, consistent with morphologic, electrophysiologic, and
23 biochemical endpoints that indicate lasting changes in synaptogenesis, dendritic
24 development, myelin and fiber track formation, ionic mechanisms of
25 neurotransmission, and energy metabolism.
26 (2) Animal studies show that the order of susceptibility of neurotoxic effects of lead is
27 young > adults and female > male.
28 At the time of publication of the 1986 AQCD, one line of evidence concerned the effects
29 of acute exposure to Pb2+ in vitro on voltage-sensitive Ca2+ channel function in the nerve cell
30 membrane, developed to a great extent by Cooper and co-workers (Kober and Cooper, 1976;
31 Cooper and Manalis, 1984; Suszkiw et al., 1984). Using neuromuscular endplate or
32 synaptosomal preparations, these studies demonstrated that Pb2+ interfered with Ca2+ influx
33 through voltage-sensitive channels. Subsequent work has replicated and extended these findings
May 2006 5-18 DRAFT-DO NOT QUOTE OR CITE
-------
1 (e.g., Tomsig and Suszkiw, 1993; Westerink and Vijverberg, 2002), and has demonstrated that
2 Pb2+ exhibits Ca2+-mimetic properties in stimulating transmitter exocytosis. While acute
3 exposure in vitro has been assumed to bear little resemblance to environmentally relevant routes,
4 durations, and magnitudes of exposure, recent findings nonetheless suggest that inhibition of
5 Ca2+ influx through voltage-sensitive Ca2+ channels and the Ca2+-mimetic properties of Pb2+ are
6 important neurotoxic mechanisms in intact animals across a range of chronic exposure levels
7 (Lasley and Gilbert, 2002).
8 In the ensuing two decades, the Pb neurotoxicity literature has reflected an increased
9 focus on cognitive-related mechanisms and the refinement of approaches and methodologies.
10 Exposure-induced alterations at glutamatergic synapses have received considerable attention.
11 Synaptic plasticity models (e.g., long-term potentiation [LTP]) came into use in the 1990s for Pb
12 studies in laboratories around the world. Behavioral paradigms, refined to more consistently
13 discriminate Pb effects, aided in identifying optimal testing conditions and developmental
14 periods for exposure. These advances have lead to clearer understanding of the likely
15 mechanisms underlying Pb-induced cognitive impairments in exposed children.
16 The evidence for Pb neurotoxicity reviewed in this section is organized largely according
17 to scientific discipline: neurochemical alterations involving glutamatergic, cholinergic, and
18 dopaminergic function; mechanisms defined by neurophysiologic approaches; changes in
19 auditory and visual function; identification of altered components of behavioral function;
20 induced alterations in cellular morphology; and findings on cellular disposition of Pb. This type
21 of organization permits a more focused analysis of an extensive and broad literature. In each
22 section below, a brief description of work previously described in the 1986 AQCD introduces
23 each section. An integrative synthesis of the health effects of Pb exposure based on toxicologic
24 and epidemiologic findings is presented in Chapter 7.
25
26 5.3.1.2 Neurochemical Alterations Resulting from Lead Exposure
27 Earlier work demonstrated that lead interfered with chemically mediated synaptic
28 transmission, probably due to its resemblance to endogenous divalent cations. At that time, a
29 selective vulnerability of any particular neurotransmitter system to the effects of the metal was
30 not apparent. Some generalizations made in the 1986 AQCD regarding neurochemical effects at
31 blood levels of -50 to -90 |ig/dL were as follows.
May 2006 5-19 DRAFT-DO NOT QUOTE OR CITE
-------
1 (1) Synthesis, turnover, and uptake of dopamine and norepinephrine are depressed in the
2 striatum and elevated in the midbrain, frontal cortex, and nucleus accumbens. These
3 changes were paralleled by concomitant increases in dopamine receptor binding in the
4 striatum and decreases in dopamine receptor binding in the nucleus accumbens, possibly
5 involving a specific subset (D2) of dopamine receptors.
6 (2) The findings for pathways utilizing y-aminobutyric acid (GABA) showed similar
7 parallels. Increases in GABA synthesis in the striatum are coupled with decreases in
8 GABA receptor binding in that region, while the converse holds true for the cerebellum.
9 In these cases, cyclic GMP activity mirrors the apparent changes in receptor function.
10 The following areas of investigation discussed below have been accorded notable
11 attention in the Pb neurotoxicity field over the last 20 years, as reflected by the number of papers
12 published and number of investigators with these research foci.
13
14 Lead and Neurotransmitter Release Processes
15 By the mid-1980s, it was evident that acute exposure to Pb2+ in vitro reduced the
16 magnitude of depolarization-induced transmitter release, apparently by inhibiting Ca2+ influx
17 into the nerve ending through voltage-sensitive Ca2+ channels (Kober and Cooper, 1976; Cooper
18 and Manalis, 1984; Suszkiw et al., 1984). Since then, several investigators utilizing various
19 preparations (Shao and Suszkiw, 1991 [cortical synaptosomes]; Tomsig and Suszkiw, 1993
20 [bovine chromaffin cells]; Braga et al., 1999a,b [cultured hippocampal cells]; Westerink and
21 Vijverberg, 2002 [PC12 cells]) have demonstrated that in the absence of Ca2+, Pb2+ exhibits
22 Ca2+-mimetic properties in stimulating exocytosis and is substantially more potent in doing so.
23 That is, in the absence of Ca2+ and depolarization, nanomolar concentrations of Pb2+ alone
24 stimulate transmitter release. Many investigators have proposed that this action, in conjunction
25 with the ability of Pb2+ to suppress evoked release of neurotransmitters, produces a higher noise
26 level in synaptic transmission in Pb-exposed animals.
27 Lead has been demonstrated to diminish stimulated transmitter release in intact
28 chronically exposed animals with blood lead values in the range of -20 to 40 |ig/dL via
29 intracerebral microdialysis (Kala and Jadhav, 1995; Lasley and Gilbert, 1996; Lasley et al.,
30 1999). More recently, Lasley and Gilbert (2002) used Ca2+-free perfusate containing a Ca2+
31 channel antagonist for microdialysis to identify the Ca2+-independent component of
32 neurotransmitter release. Under these conditions, high K+-stimulated release of glutamate and
33 GABA was elevated in chronic Pb-exposed animals, suggesting a Pb2+-induced enhancement of
34 evoked release at higher exposure levels. It was concluded that this pattern of results indicated
May 2006 5-20 DRAFT-DO NOT QUOTE OR CITE
-------
1 the presence of two actions of Pb on transmitter release in vivo: (1) a more potent suppression of
2 stimulated release seen at lower exposure levels (associated with PbB values of 27 to 62 |ig/dL)
3 combined with (2) Ca2+-mimetic actions that independently induce the exocytosis seen at higher
4 exposure levels (associated with PbB values of >62 jig/dL). Together, these two actions produce
5 a biphasic dose-effect relationship (see Figure 5-3.1). Thus, there is good correspondence
6 between findings of in vitro and in vivo studies with respect to the actions of Pb on transmitter
7 release.
8
9 Lead and Glutamatergic NMDA Receptors
10 Because of the established importance of the jV-methyl-D-aspartate (NMDA) subtype of
11 glutamate receptor in synaptic plasticity and learning, these receptors have been a focus of
12 intense interest in Pb neurotoxicity for the last 15 years. Using whole cell and single channel
13 patch clamp methodologies, Alkondon et al. (1990) were the first to report that Pb2+ inhibited the
14 function of the NMDA receptor channel complex. Guilarte and Miceli (1992) reported similar
15 findings using nominal Pb2+ concentrations and receptor binding techniques and drew parallels
16 between Zn2+-, Ca2+-, and Pb2+-induced inhibition of the channel. However, Lasley and Gilbert
17 (1999), using free Pb2+ ion concentrations and radioligand binding, demonstrated that despite
18 similarities to the actions of Zn2+, Pb2+ did not inhibit the NMDA receptor channel complex by
19 binding to the Zn2+ allosteric site. Furthermore, these workers indicated that the Pb2+ ICso of
20 0.55 jiM for inhibition of the channel complex was likely about two orders of magnitude greater
21 than the extracellular fluid concentrations of Pb2+ associated with environmentally relevant
22 exposure. This does not imply that NMDA receptor function does not change after Pb exposure,
23 but it strongly suggests that the alterations are not based on a direct Pb2+ action.
24 Unfortunately, a consensus on the effects of chronic Pb exposure on NMDA receptor
25 expression and function has not been achieved. Extensive effort has been invested to assess
26 NMDA receptor subunit mRNA and protein expression in exposed animals with blood lead
27 values in the range of 25 to 45 ng/dL (Guilarte and McGlothan, 1998; Nihei and Guilarte, 1999;
28 Guilarte et al., 2000; Nihei et al., 2000; Toscano et al., 2002; Guilarte and McGlothan, 2003),
29 but consistent findings have not emerged. A possible exception was the work of Nihei et al.
May 2006 5-21 DRAFT-DO NOT QUOTE OR CITE
-------
5.0
4.5
4.0
3.5
3,0
2.5
2.0
1.5
1.0
0.5
0.0
150 mM K+
Total Release
-O— Control
•- - • 0.2% Pb
l I
-120 -90 -60 -30 0 20 40 60 80
Time, min
110 140
tf)
m
•0
9
.*:
O
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
*
*
T
*
*
#
J_
#
Control
0.1%
0.2%
0.5%
1.0%
Figure 5-3.1. Time course and magnitude of response of extracellular GLU
concentration as a result of chronic lead exposure.
*** p < 0.001; ** p < 0.01 relative to the GLU concentration in control animals;
*p < 0.0001 relative to the GLU concentration in the 0.2% Pb group.
Source: Lasley and Gilbert (2002).
May 2006
5-22
DRAFT-DO NOT QUOTE OR CITE
-------
1 (2000, 25 to 32 |ig/dL) who found decreases in hippocampal NR1 subunit mRNA and protein
2 expression associated with animals that exhibited deficits in LTP and spatial learning after
3 chronic exposure. Correlations of this type with functional measures are valuable in validating
4 biochemical observations. However, it should also be noted that such correlations do not
5 confirm a direct relationship between LTP or the behavior and the NMDA receptor subunit
6 changes.
7 While exposure-induced alterations of NMDA receptor binding have been observed in
8 multiple laboratories, there has been no uniform agreement as to the direction of change.
9 Upregulation of NMDA receptor density has been observed in rats continuously exposed
10 throughout development with blood leads in the range of 39 to 62 |ig/dL (Ma et al., 1997; Lasley
11 et al., 2001), but receptor downregulation has also been reported when exposure was begun
12 immediately postweaning and PbB levels achieved 16 to 28 |ig/dL (Cory-Slechta et al., 1997a).
13 The results of behavioral investigations are most parsimoniously explained by increases in
14 NMDA receptor density. Cohn and Cory-Slechta (1993, 1994a), using a repeated learning
15 component of a multiple reinforcement schedule, observed enhanced performance sensitivity to
16 exogenous NMDA administration and diminished sensitivity to MK-801, an NMDA receptor
17 antagonist, in exposed animals with PbB values of 25 to 74 |ig/dL. The same findings resulted
18 when a drug discrimination paradigm was utilized (Cory-Slechta, 1995; Cory-Slechta et al.,
19 1996b): enhanced sensitivity to NMDA and reduced sensitivity to MK-801 in Pb-exposed
20 groups in the presence of PbB values in the range of 13 to 36 |ig/dL. A decreased sensitivity to
21 MK-801 can result from either increased numbers of NMDA receptors or a diminished access of
22 he antagonist to its binding site in the ion channel. Thus, all these behavioral observations may
23 be accounted for by Pb-induced increases in NMDA receptor density resulting in increased
24 sensitivity to agonists coupled with decreased sensitivity to antagonists. That is, the functional
25 measures suggest that an NMDA receptor upregulation occurs. Nonetheless, this interpretation
26 should not preclude the possibility that experimental outcomes can change significantly in the
27 presence of apparently small modifications in exposure parameters.
28
29 Pb2+-Ca2+ Interactions
30 At the time of publication of the 1986AQCD/Addendum, one of the most reproducible
31 lines of evidence concerned the effects of acute exposure to Pb2+ in vitro on voltage-sensitive
May 2006 5-23 DRAFT-DO NOT QUOTE OR CITE
-------
1 Ca2+ channel function in the nerve cell membrane, developed to a great extent by Cooper and
2 co-workers (Kober and Cooper, 1976; Cooper and Manalis, 1984; Suszkiw et al., 1984). Using
3 neuromuscular endplate or synaptosomal preparations, these studies demonstrated that Pb2+
4 interfered with Ca2+ influx through voltage-sensitive channels. Subsequent work has replicated
5 and extended these findings (e.g., Tomsig and Suszkiw, 1993; Westerink and Vijverberg, 2002),
6 and has demonstrated that Pb2+ exhibits Ca2+-mimetic properties in stimulating transmitter
7 exocytosis. While acute exposure in vitro has been assumed to bear little resemblance to
8 environmentally relevant routes and magnitudes of exposure, recent findings nonetheless suggest
9 that inhibition of Ca2+ influx through voltage-sensitive Ca2+ channels and the Ca2+-mimetic
10 properties of Pb2+ are important neurotoxic mechanisms in intact animals across a range of
11 chronic exposure levels (Lasley and Gilbert, 2002).
12 Simons (1993b) has reviewed the ability of Pb2+ to disturb intracellular Ca2+ homeostasis,
13 and has emphasized the importance of utilizing free Pb2+ concentrations to define Pb2+-Ca2+
14 interactions clearly. Multiple laboratories have investigated the inhibition of depolarization-
15 induced Ca2+ currents produced by acute exposure of cultured cells using this approach, resulting
16 in free Pb2+ ICso values in the range of 0.3 to 1.3 jiM (e.g., Audesirk and Audesirk, 1991; Sun
17 and Suszkiw, 1995). Other workers examined the stimulation of spontaneous transmitter release
18 by acute exposure of permeabilized synaptosomes or cultured cells (Shao and Suszkiw, 1991;
19 Tomsig and Suszkiw, 1996) and reported a free Pb2+ ECso of 4 nM. Westerink and Vijverberg
20 (2002) addressed this same question using fluorescent dyes and confocal laser scanning
21 microscopy of permeabilized PC12 cells, an independent approach also based on determination
22 of free Pb2+ concentrations. They observed a threshold for acute Pb2+ to induce exocytosis of
23 between 10 and 20 nM. Suszkiw (2004) has reviewed this literature and has suggested that
24 Pb2+-induced augmentation of spontaneous release may involve stimulation of vesicle
25 mobilization consequent to Pb2+ activation of CaMKII-dependent phosphorylation of synapsin I
26 and/or stimulation of asynchronous exocytosis via direct Pb2+ activation of the putative
27 exocytotic Ca2+-sensor protein synaptotagmin I. Other Ca2+-dependent proteins whose actions
28 are stimulated by Pb2+ include calmodulin and calmodulin-dependent phosphodiesterase
29 (reviewed by Goldstein, 1993), calcineurin (Kern and Audesirk, 2000), and Ca2+-ATPase
30 (Ferguson et al., 2000). These actions of Pb2+, shown in Figure 5-3.2, are proposed to be the
31 points of initiation of much of the metal's cellular toxicity.
May 2006 5-24 DRAFT-DO NOT QUOTE OR CITE
-------
Presynaptic Terminal
Post Synaptic Dendritic Spine
Figure 5-3.2. Simplified diagram showing the actions of Pb at a synapse. Pb decreases
release of GABA, dopamine, and glutamate and also decreases Ca2+
movement through voltage-sensitive Ca2+ channels. Low levels of Pb
increase PKC, while higher concentrations inhibit the enzyme. GABA,
y-aminobutyric acid; ER, endoplasmic reticulum; DA, dopamine; Glu,
glutamate; PKC, protein kinase C; NMD A, N-methyl-D-aspartate.
1
2
3
4
5
6
7
1.2+
Pb and Protein Kinase C
As mentioned above, another intriguing focus area for Pb neurotoxicity research has been
the interactions of Pb2+ with protein kinases. Protein kinase (PKC), a family of serine/threonine
protein kinases, has been shown to be targets of Pb2+ neurotoxicity. Markovac and Goldstein
(1988a) were the first to report that Pb2+ directly stimulated PKC activity at picomolar
concentrations, thereby exhibiting greater potency for this action than Ca2+ by 4 to 5 orders of
magnitude. Long et al. (1994) made similar observations using free Pb2+ and Ca2+ ion
concentrations and nuclear magnetic resonance spectroscopy, finding an ECso of 55 pM for
May 2006
5-25
DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb2+ stimulation of PKC. These workers also presented evidence suggesting that the maximal
2 efficacy of Pb2+ was less than that of Ca2+, despite its greater potency. Tomsig and Suszkiw
3 (1995) further elucidated multiple interactions of Pb2+ with PKC, identifying both stimulatory
4 (affinity in the picomolar range) and inhibitory (affinities in the nanomolar and micromolar
5 range) binding sites on the kinase. They also showed that on the basis of these interactions, Pb2+
6 induced a peak efficacy for stimulation of PKC that was only -40% of the maximal efficacy
7 produced by Ca2+, leading them to refer to Pb2+ as a partial agonist of the kinase as reflected in
8 Figure 5-3.3.
>s 1.5
1 1.0
0
°~ 0.5
n r\
9 Lead
— O— Calcium
-
_
~ ^^**"^
14 13 12 11 10 9 8 7 6 5 4
-log [free metal]
Figure 5-3.3. PKC activity as a function of Ca2+ and Pb2+ concentrations.
Source: Tomsig and Suszkiw (1995).
9
10
11
12
13
14
The effects of chronic Pb exposure on PKC signaling have been more difficult to evaluate.
Most investigators have utilized broken cell preparations and measures of either kinase
translocation or enzyme activity; however, the broken cell preparation has not been shown to
simulate the intracellular milieu of a chronically exposed intact animal. In the preparation of;
tissue extract for determination of kinase activity, the unbound Pb2+ is removed or greatly
diluted, so that the resulting activity measure largely reflects changes in total PKC expression
L of a
May 2006
5-26
DRAFT-DO NOT QUOTE OR CITE
-------
1 resulting from the exposure. That is, this measure does not identify a synaptic pool of PKC or
2 necessarily represent the pool of kinase involved in signal transduction. Alternatively, the
3 translocation of kinase from a cytosolic to membrane cellular fraction is a somewhat nonspecific
4 measure, and observed changes should be independently confirmed. From the effects of acute
5 Pb2+ exposure in vitro, it seems clear that PKC is a lexicologically significant intracellular target
6 for Pb2+.However, various investigators have been unable to define how this acute effect
7 translates, if at all, to chronic exposure in the intact animal. Neither is it evident how one could
8 discriminate inhibition of PKC activity (due to decreased efficacy relative to that associated with
9 Ca2+, for example) from downregulation of the enzyme due to prolonged stimulation. Resolution
10 of these issues awaits the development of more specific methodologies.
11
12 Lead Exposure and Cholinergic Neuronal Systems
13 The actions of chronic Pb exposure have also been studied with respect to changes in CNS
14 cholinergic systems as another substrate thought to underlie cognitive function. Bielarczyk et al.
15 (1996) reported (1) decreased functional cholinergic innervation in the hippocampus and
16 (2) depression of choline acetyltransferase activity in the hippocampus and cortex of young adult
17 rats exposed to Pb only during early development. This model produced a PbB of 22 |ig/dL at
18 the end of exposure. Similar changes were reported by Bourjeily and Suszkiw (1997) in which
19 PbB levels were -20 |ig/dL, leading to the conclusion that perinatal Pb exposure results in a loss
20 of septohippocampal cholinergic projection neurons that persists until testing in young
21 adulthood. Tian et al. (2000) exposed PC12 cells to Pb2+ for <48 h and found that the
22 downregulation of choline acetyltransferase activity reflected the effects of the metal at the level
23 of gene expression. Consistent with these findings, Jett et al. (2002) employed a similar perinatal
24 exposure protocol, producing a PbB of 47 |ig/dL at the end of exposure. They observed
25 increased nicotinic receptor binding in multiple brain regions. Zhou and Suszkiw (2004) found
26 that acute systemic nicotine reversed a deficit in spatial learning observed in the offspring of
27 maternally Pb-exposed rats, presumably by compensating for deficient nicotinic function.
28 However, PbB levels in the Pb-exposed animals were not reported. These reports reinforce the
29 belief that Pb exposure during early development impacts cholinergic function and suggest that
30 these actions may comprise a component of the cognitive impairment resulting from exposure to
31 the metal.
May 2006 5-27 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.3.1.3 Actions of Lead Exposure Defined by Neurophysiologic Approaches
2 An important advance in Pb neurotoxicity research over the last two decades is the
3 widespread application of synaptic plasticity models to study of the effects of exposure. These
4 plasticity models have served as an intermediate link between biochemical and behavioral
5 assessments in that they demonstrate the functional importance of underlying neurochemical
6 mechanisms. Moreover, these models are thought to involve the same physiological substrates
7 as do behavioral paradigms examining cognitive function. Key studies are listed in
8 Table AX5-3.1.
9
10 Chronic Lead and Models of Synaptic Plasticity
11 About 1990, the LTP model of synaptic plasticity began to be used to study Pb
12 neurotoxicity to evaluate the synaptic processes involved in learning and cognitive function.
13 These investigations have characterized the actions of chronic exposure across several
14 experimental parameters (see Table 5-3.1). Furthermore, there was uniform agreement as to the
15 alterations that resulted in the hippocampal CA1 and dentate gyrus subregions.
16 Chronic developmental Pb exposure decreased the magnitude of LTP and increased the threshold
17 for LTP induction (Altmann et al., 1993; Gilbert et al., 1996; Gutowski et al., 1998; Ruan et al.,
18 1998). Simultaneous assessments of paired-pulse functions also uncovered reductions in paired-
19 pulse facilitation, indicating reduced glutamate release (Lasley and Gilbert, 1996;Ruan et al.,
20 1998). It was also shown that the potentiation produced in Pb-exposed animals decayed more
21 rapidly than in controls (Gilbert and Mack, 1998). Blood and brain Pb values reported in these
22 studies are shown in Table 5-3.1; Lasley and Gilbert (1996) reported the same values as shown
23 for Gilbert etal. (1996).
24 Gilbert et al. (1999a) compared the effects on LTP when exposure occurred during
25 different developmental periods (see Table 5-3.1 for blood and brain Pb levels). These workers
26 found that animals whose exposure began shortly after weaning exhibited the same impairments
27 in LTP as animals continuously exposed from late gestation when testing in both groups
28 occurred well into adulthood. A smaller effect on potentiation was observed when exposure was
29 restricted to the period from late gestation to weaning.
30 Gilbert et al. (1999b) also examined the effects of Pb on LTP as a function of chronic
31 exposure level, using a range of 0.1 to 1.0% Pb in the drinking water (corresponding to PbB
May 2006 5-28 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-3.1. Chronic Lead Exposure and LTP
Exposure Effect of Exposure on
Recording Site Period1 Blood Pb2 Brain Pb3 Preparation LTP
Hippocampal Dentate Gyrus
Gilbert et al. (1996) PO - P90-120
Ruanetal. (1998) PO-P90-115
Gilbertetal. (1999a) G16-P130-210
P30-P130-210
Gilbert etal. (1999b) G16-P120-180
Gilbert and Mack
(1998)
Hippocampal CA1
Altmannetal. (1993)
Gl 6-P210-540
GO-P70-210
Gutowski et al. (1998) GO - P90-130
Hippocampal CAS
Gutowski et al. (1997) GO - PI 3-140
Gutowski et al. (1998) GO - P90-130
37.2
30.1
40.2
38.7
26.84
40.2
61.8
ND
14.3
16.0
28.5
16.0
ND In vivo Elevated induction threshold
180 In vivo Diminished magnitude
378 In vivo Elevated induction threshold
350 and diminished magnitude
220 In vivo Elevated induction threshold
378 and diminished magnitude
670
ND In vivo Accelerated decay
160 slices Blocked, required exposure
during early development
135 Slices Diminished magnitude
180 Slices No effect across 4 ages
135 Slices No effect
'Exposure duration in terms of gestational (G) or postnatal (P) days of age; PO = day of birth.
2Values expressed as ug/100 mL.
3Values expressed as ng/g tissue.
4Different blood Pb values generated by differing levels of exposure.
ND = Not determined
4
5
6
values of 27 to 118 |ig/dL; brain Pb measures are shown in Table 5-3.1). A reduced capacity for
LTP was found at all exposure levels except in the 1.0% group, indicating a biphasic dose-effect
relationship (Figure 5-3.4). The 1.0% Pb-exposure level was clearly less effective than the lower
exposure groups in reducing LTP magnitude and did not differ significantly from control values.
Blood Pb values were elevated as a function of increasing exposure and could not account for the
lack of effect in the 1.0% exposure group.
May 2006
5-29
DRAFT-DO NOT QUOTE OR CITE
-------
600 H
I
0 0.1 0.2 0.5 1.0
Pb Concentration (%)
Figure 5-3.4. Difference score measure of population spike amplitude.
Source: Gilbert et al. (1999b).
1 Zhao et al. (1999) utilized low frequency electrical stimulation in the paradigm of long-
2 term depression (LTD) and found that chronic Pb exposure, producing PbB of 30 |ig/dL,
3 depressed the magnitude of this form of synaptic plasticity in both hippocampal CA1 and dentate
4 gyrus subregions. The authors also concluded that in combination with the reduced magnitude
5 of LTP as reported by other workers, the decrease in LTD magnitude results in a reduced range
6 of synaptic plasticity in chronically exposed subjects.
7 While the effects of Pb on synaptic plasticity are quite similar in the CA1 and dentate
8 gyrus, they are not uniformly present throughout this region of the hippocampus. Gutowski et al.
9 (1997, 1998) were unable to find any effect of chronic Pb exposure on LTP in hippocampal CA3
10 (i.e., mossy fiber LTP), even when the investigation was extended across multiple ages (see
11 Table 5-3.1 for blood and brain Pb values). The bases for this regional distinction await future
12 investigation.
13
14 Lead Exposure, Glutamatergic Transmission, and Synaptic Plasticity
15 Investigation of the synaptic processes underlying LTP has provided insight into the bases
16 for Pb exposure-induced impairment of potentiation and cognitive ability (reviewed by Lasley
May 2006
5-30
DRAFT-DO NOT QUOTE OR CITE
-------
1 and Gilbert, 2000). Biochemical and neurophysiologic approaches (Lasley and Gilbert, 1996;
2 Gilbert et al., 1996; Ruan et al., 1998) have found stimulated glutamate release to be diminished
3 in the hippocampus at PbB values where deficits in LTP have been observed. Multiple actions
4 of Pb may be involved at this exposure level, because animals exposed postweaning exhibited
5 similar decrements in evoked glutamate release to those exposed continuously from conception
6 (Lasley et al., 1999; adult PbB values of 39 to 45 jig/dL), similar to the observations for
7 measures of LTP (Gilbert et al., 1999a). A biphasic dose-effect relationship was also found in
8 which stimulated glutamate release in the hippocampus was decreased at intermediate exposures
9 (PbB of 27 to 40 (ig/dL), but not at higher levels (PbB of 62 to 117 (ig/dL) (Lasley and Gilbert,
10 2002). On the basis of these observations, it appears that decreases in stimulated glutamate
11 release may contribute to the biphasic dose-effect relationship in LTP.
12 In comparison to the high concordance across laboratories with regard to the effects of
13 chronic Pb exposure on LTP and the notable similarities to its actions on glutamate release, there
14 is no general agreement as to the exposure-induced changes in the NMDA receptor. Alterations
15 in receptor function occur readily in response to externally applied treatments and might be
16 expected to vary in a dynamic fashion as a function of exposure parameters, e.g., Lasley et al.
17 (2001) reported receptor upregulation at PbB levels in the range of 39 to 62 |ig/dL. However,
18 most studies have involved measures of NMDA receptor expression binding in adult animals
19 exposed to constant levels of Pb for at least 3, and more commonly for 6 to 15 months, so that
20 receptor-mediated effects should have stabilized. Consequently, the following alternative
21 conclusions could be proposed regarding the actions of Pb exposure on the NMDA receptor that
22 are related to its effects on LTP. First, changes in NMDA receptor function may depend on
23 specific Pb exposure conditions. For example, a postweaning exposure protocol may not
24 necessarily produce similar effects to an exposure protocol initiated during earlier development.
25 Alternatively, effects on LTP may be produced at signal transduction or other cellular loci that
26 exert regulatory influences on the NMDA receptor. This latter conclusion implies that changes
27 in the NMDA receptor do not mediate the primary action of Pb on LTP. Furthermore, this
28 suggests that identification of some site of direct Pb effect that has regulatory influence on the
29 receptor would produce more consistently observable findings.
30
May 2006 5-31 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead and Electrophysiologic Changes in Dopaminergic/Cholinergic Systems
2 Electrophysiologic approaches have been employed to delineate other interesting findings
3 in Pb-exposed animals not directly related to synaptic plasticity. Using standard extracellular
4 recording methods, Tavakoli-Nezhad et al. (2001) identified an exposure-dependent decrease in
5 the number of spontaneously active dopamine cells in the substantia nigra and ventral tegmental
6 area in the presence of PbB levels of 29 to 54 |ig/dL, but they found no evidence that this
7 decrease was related to a physical loss of cells. In subsequent work, Tavakoli-Nezhad and Pitts
8 (2005) determined that the decrease in the number of active dopamine cells in the presence of
9 PbB values of 31 |ig/dL was not based on depolarization inactivation. However, they discerned
10 a reduced impulse flow in dopamine neurons and a diminished sensitivity of DI receptors in the
11 nucleus accumbens. The functional importance of these observations remains to be determined.
12 The actions of Pb2+ on cholinergic nicotinic receptors have been investigated in acutely
13 dissociated or cultured hippocampal cells using the patch clamp technique in whole cell mode
14 (Ishihara et al., 1995). These workers found that Pb2+potently inhibits activation of
15 fast-desensitizing nicotinic currents in a noncompetitive and voltage-dependent manner. The
16 nicotinic receptors affected (methyllycaconitine-sensitive) were more sensitive to Pb2+ than other
17 nicotinic subtypes and are known to be highly permeable to Ca2+. This latter observation likely
18 explains the potency for their inhibition by Pb2+.
19
20 5.3.1.4 Lead Exposure and Sensory Organ Function
21 Research presented in the 1986 AQCD demonstrated that the visual system is especially
22 sensitive to perturbation by neonatal lead exposure. Suckling rats exposed through dams' milk
23 creating PbB values of 65 |ig/dL at postnatal day (PND) 21 had significant alterations in their
24 visual-evoked responses and decreased visual acuity, indicating depressed conduction velocities
25 in visual pathways. It was hypothesized that neonatal lead exposure increases the ratio of
26 excitatory to inhibitory systems in the developing cerebrospinal axis and decreases the number of
27 cholinergic receptors, leading to lasting decreases in visual acuity and spatial resolution.
28 Sensory organ function has continued to be a productive focus area for Pb neurotoxicity
29 research, generating important scientific findings. Visual and auditory systems have received the
30 most attention, have generated results closely resembling clinical observations, and have been
May 2006 5-32 DRAFT-DO NOT QUOTE OR CITE
-------
1 successful in defining some of the mechanisms underlying the exposure-induced alterations.
2 These studies are summarized in Table AX5-3.3.
3
4 Sensory Organ Assessments in Nonhuman Primates
5 Lilienthal and Winneke (1996) tested monkeys continuously exposed to Pb from gestation
6 through 8 to 9 years of age, producing PbB of 33 to 56 |ig/dL before termination of exposure.
7 They found increased latencies for waves I, II, and IV in brainstem auditory evoked potentials.
8 These effects persisted for at least 18 months after exposure was terminated and PbB values had
9 declined nearly to control levels, leading to the conclusion that these actions of Pb were not
10 dependent on current exposure. Rice (1997) determined pure tone detection thresholds in
11 monkeys exposed continually from birth to 13 years of age, resulting in PbB of 30 |ig/dL from
12 3 to 9 years of age and 109 |ig/dL around the time of testing. Half of the subjects exhibited
13 thresholds outside of the control range at some frequencies. These findings are consistent with
14 reported alterations in auditory function in humans developmentally exposed to Pb (reviewed by
15 Otto and Fox, 1993). Moreover, these authors concluded that evidence from human and animal
16 studies indicate that Pb exposure impairs auditory function. In both developing and mature
17 humans and experimental animals, the cochlear nerve and more central structures appear to be
18 preferentially sensitive. At low to moderate levels of Pb exposure, consistent findings include
19 elevations in hearing thresholds and increased latencies in brainstem auditory evoked potentials.
20 Thus, there is good correspondence between human and animal studies in the effects of chronic
21 Pb on auditory function.
22 Visual pathology was assessed by Reuhl et al. (1989) in monkeys by exposing low- and
23 high-dose groups from birth to 6 years of age. PbB values were 10 and 50 |ig/dL, respectively,
24 except for a 3- to 4-month period when values rose to 20 and 220 |ig/dL. This investigation
25 uncovered a decrease in neuronal volume density in cortical areas VI and V2 in the
26 high-exposure compared to the low-exposure group, and also a decrease in dendritic arborization
27 in pyramidal neurons in these brain areas. These authors concluded that chronic developmental
28 Pb exposure produces changes in cytoarchitecture in visual projection areas. Lilienthal et al.
29 (1988) continuously exposed monkeys to 350- or 600-ppm Pb acetate beginning prenatally,
30 producing PbB values of-40 and 50 |ig/dL, respectively. Visual evoked potentials and
31 electroretinograms (ERG) were recorded at ~7 years of age. Exposure-related decreases in
May 2006 5-33 DRAFT-DO NOT QUOTE OR CITE
-------
1 amplitudes and increases in latencies were observed. In Pb-exposed monkeys, the effects on
2 amplitude were greater in dark conditions, and the effects on latencies were greater in bright
3 conditions. Electroretinograms, studied during dark adaptation, showed greater increases in
4 amplitude of the b-wave in exposed animals. Thus, visual function in primates is also impaired
5 as a result of exposure.
6
7 Retinal Function in Rodents
8 The actions of Pb on retinal cells have been a focus of research for more than two
9 decades. It has long been recognized that Pb2+ exhibits a selective effect on rod cells (Fox and
10 Sillman, 1979) and, more recently, that the associated loss of rod and bipolar cells was due to
11 exposure-induced apoptotic changes (e.g., Fox et al., 1997, in the presence of PbB values of
12 19 to 59 |ig/dL at the termination of exposure). These observations have been linked with
13 exposure-related alterations in rod-mediated visual function. In vitro studies using free Pb2+ ion
14 concentrations have done much to elucidate the mechanistic bases of these observations.
15 These latter efforts have established the concentration-dependent inhibition of cyclic
16 GMP (cGMP) hydrolysis by free Pb2+, in addition to increases in retinal cGMP and rod Ca2+
17 levels (e.g., Srivastava et al., 1995). Kinetic studies have shown that picomolar Pb2+
18 concentrations competitively inhibit rod cGMP phosphodiesterase relative to the millimolar
19 concentrations that are required for Mg2+ cofactor activity, thus binding with 104- to 106-fold
20 higher affinity than Mg2+ and preventing cGMP hydrolysis (Srivastava et al., 1995). When
21 retinas are incubated in Ca2+ and/or Pb2+ in vitro, the rods selectively die by apoptosis associated
22 with mitochondrial depolarization, release of mitochondrial cytochrome c, and increased caspase
23 activity (He et al., 2000). He et al. (2003) have proposed that apoptosis is triggered by Ca2+ and
24 Pb2+ overload resulting from translocation of cytosolic Bax to the mitochondria, which likely
25 sensitized the overloaded mitochondria to release cytochrome c. This effect occurred at a PbB
26 level of 26 |ig/dL at the end of exposure. Subsequent work found the elevations in free Ca2+ and
27 Pb2+ to be localized to photoreceptors and determined that the effects of the two ions were
28 additive and blocked by a mitochondrial permeability transition pore inhibitor (He et al., 2000).
29 This suggested that the two ions bind to the internal metal binding site of this pore and, thereby,
30 initiate the apoptosis cascade.
May 2006 5-34 DRAFT-DO NOT QUOTE OR CITE
-------
1 These mechanisms are consistent with ERG changes observed in animals chronically
2 exposed during early development: decreases in maximal ERG amplitude, decreases in absolute
3 ERG sensitivity, and increases in mean ERG latency that were selective for rod photoreceptors in
4 the presence of PbB values of 59 |ig/dL at the termination of exposure (Fox and Farber, 1988).
5 Also in agreement with these mechanisms were observed elevations in retinal cGMP levels and
6 reductions in light-activated cGMP phosphodiesterase activity. Moreover, the degenerating rod
7 and bipolar cells exhibited the classical morphological features of apoptotic cell death (Fox et al.,
8 1997). Other measures of visual function in chronically exposed animals also have been found
9 to be consistent with the mechanistic data. Long-term dose-dependent elevations in response
10 thresholds were observed only at scotopic (i.e., rod-mediated) levels of illumination, and dark
11 adaptation was delayed (Fox et al., 1994; in the presence of PbB values of 19 to 59 |ig/dL at the
12 termination of exposure). In addition, exposure-induced decreases in rhodopsin content that
13 were proportional to the loss of rod cells have been reported (Fox et al., 1997) as well as
14 dose-dependent decreases in retinal Na, K- ATPase activity (Fox et al., 1991a; PbB levels as
15 above in Fox et al., 1994).
16 The studies investigating rod photoreceptors are perhaps the best examples of the ability
17 to correlate data obtained in vitro with findings derived from in vivo exposure and with changes
18 in visual physiology. In multiple instances, the same cellular mechanisms were affected with
19 each approach and are consistent with ERG and rod-mediated functional measures. These
20 relationships are summarized in Table 5-3.2.
21
22 5.3.1.5 Neurobehavioral Toxicity Resulting from Pb Exposure
23 As discussed elsewhere in this chapter, the young are vulnerable to the effects of Pb
24 exposure due to their greater absorption and retention of Pb. The developing state of the nervous
25 system makes the perinatal period a particularly critical time for the initiation of neurobehavioral
26 perturbations by exposure to Pb. Work reviewed in the 1986 Pb AQCD demonstrated that
27 behavioral effects in animals are found with both perinatal exposures and with exposures after
28 weaning or during adulthood.
29 Very early research on the effects of Pb on learning ability failed to adequately report
30 exposure regimen or the resulting body burden. Studies reviewed in the 1986 AQCD were more
31 useful; they reported this information and further attempted to control for the confounding
May 2006 5-35 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-3.2. Mechanisms of Pb-Induced Impairment of Retinal Function
In Vitro Evidence
In Vivo Evidence
Physiologic Changes
Competitive inhibition of
cGMP PDE
Increased retinal cGMP
Increased rod [Ca2+]
Apoptosis from increased
photoreceptor Ca2+/Pb2+ via
binding to mitochondrial
permeability transition pore
Decreased retinal Na
K+-ATPase activity
Decreased stimulated cGMP PDE
activity
Increased retinal cGMP
Decreased maximal ERG amplitude
Decreased absolute ERG sensitivity
Increased mean ERG latency
Morphological features of apoptotic rod, Increased response thresholds at
bipolar cell death scotopic backgrounds
Decreased rhodopsin proportional to Delayed dark adaptation
cell loss
Translocated cytosolic Bax to the
mitochondria, cytochrome c released
Decreased retinal Na+,K+-ATPase
activity
Abbreviations: PDE, phosphodiesterase; ERG, electroretinogram.
1 factors of litter size and undernutrition. Thirty-four rat studies were evaluated, from which it
2 was possible to ascertain that learning was altered at PbB levels of 15 to 30 |ig/dL. Test methods
3 that revealed learning deficits in rats included radial arm maze testing and fixed-interval (FI)
4 operant conditioning. Rats in these studies tended to respond more rapidly (i.e., higher response
5 rates, shorter interresponse times, or shorter response latencies) or to respond even when
6 inappropriate (i.e., when no reward is provided for responses or when reward is specifically
7 withheld for responding). Impaired acquisition of discrimination and performance in other tests
8 has been demonstrated with similar blood Pb levels in rats.
9 Thirteen nonhuman primate studies previously reviewed showed that exposures from birth
10 impaired learning ability, even after current PbB levels had dropped to control values. Studies
11 using operant conditioning tasks demonstrated that learning ability was impaired when monkeys'
12 PbB levels reached 5 |ig/dL and steady state levels were 11 |ig/dL. In both the Pb-treated rats
13 and monkeys, a high degree of response variability occurred. Other significant findings in these
14 studies, consistent with the rat findings mentioned above, were the tendency for Pb-induced
May 2006
5-36
DRAFT-DO NOT QUOTE OR CITE
-------
1 excessive or inappropriate responses in the monkeys and higher response rates and shorter
2 interresponse times on FI operant schedules. The neural mechanisms responsible for this
3 "hyperreactive" behavior were thought to originate in the hippocampus, as similar behaviors
4 have been shown in animals with lesions of that brain region. These increased response
5 tendencies were shown to change to decreased responding with sufficiently high exposure levels.
6 An explanation of this curvilinear dose-response was that there are differences in the time
7 required for response rates to reach their maximum as a function of different exposure levels.
8 At sufficiently toxic Pb concentrations, responding declines due to the inability to perform the
9 necessary motor responses.
10 A survey of the major animal studies published since the 1986 AQCD that characterized
11 Pb-induced neurobehavioral deficits that may correlate with behavioral deficits observed in
12 humans are presented below, organized by endpoint, test method, and species. Summaries of
13 key animal neurobehavioral studies are presented in AX5-3.4.
14
15 Effects ofPb on Learning Ability
16 In the past 20 years, major advances have occurred in the understanding of the effects of
17 Pb on learning ability, which is impacted throughout the life cycle. Assessments of Pb-induced
18 deficits in learning ability in both rats and primates are discussed below.
19
20 Schedule-Controlled Behavior
21 Schedule-controlled behavior studies, such as FI and fixed ratio (FR) operant
22 conditioning, have been used with both rats and monkeys to assess cognitive ability (integrated
23 with sensory and motor abilities). The effects of prolonged Pb exposure on FR performance was
24 evaluated in Long Evans (LE) rats exposed throughout the study to 50 or 500 ppm from
25 weaning, producing PbB levels of 30.3 and 58 to 94 |ig/dL, respectively (Cory-Slechta, 1986).
26 At PND 55, assessment of FR performance was started using increasing ratio values. No effects
27 were seen in the 50-ppm group. In the 500-ppm group, response rates initially decreased, then
28 reached control levels, primarily because of longer interresponse times (IRTs). In comparing
29 these data to earlier studies with similar Pb exposures, the author concluded that FI response
30 rates are more sensitive to perturbation by Pb than FR response rates.
May 2006 5-37 DRAFT-DO NOT QUOTE OR CITE
-------
1 To evaluate the effects of exposure duration on FI performance, PND 21 LE rats were
2 exposed to 50 ppm Pb for 8 to 11 months, then tested using an FI 1-min schedule of food
3 reinforcement (Cory-Slechta, 1990a). These rats demonstrated decreased FI response rates (i.e.,
4 longer IRTs and lower running rates) compared to controls. The author suggested that this
5 suppression of FI response rates, which contrasted with earlier studies showing increased
6 response rates with shorter exposures but similar PbB levels (-20 jig/dL), was due to the greater
7 body and brain burdens of Pb. Following changes in schedule parameters, Pb-treated rats
8 demonstrated a delay in acquisition. In the same study, adult rats (6 to 8.5 months at exposure)
9 were trained on FI schedules and then exposed to 50 or 500 ppm Pb for 3 to 5 months. These
10 animals demonstrated no consistent changes in FI performance, suggesting that once a behavior
11 has been acquired, it may be resistant to disruption by subsequent Pb exposure.
12 To examine old age as a possible vulnerable period for Pb exposure, Cory-Slechta and
13 Pokora (1991) dosed Fischer 344 (F344) rats at PND 21, 8-months of age (adult), and 16-months
14 of age (old) with 2 or 10 ml/kg/day Pb acetate for 9.5 months. Training began 2.5 months after
15 the start of exposure. Steady state PbB levels of 13 to 18 |ig/dL were obtained. Young and old
16 rats demonstrated increased variable-interval (VI) and FI response rates, while adult rats showed
17 decreased response rates on both schedules. Effects on FI responding were seen with the 2 mg
18 dose and on VI with only the 10 mg dose. Additionally, these data suggest that F344 rats are less
19 sensitive to Pb effects than the LE rats used in most of the previous schedule-controlled behavior
20 studies.
21 To characterize neurotransmitter system involvement in Pb-induced changes in FI
22 performance, rats were exposed from weaning to 0, 50, or 150 ppm Pb acetate, resulting in PbB
23 levels of ~<5, 15 to 25, and 30 to 50 |ig/dL, respectively (Cory-Slechta et al., 1996b). Behavior
24 was shaped at PND 40 to 45 days, followed by imposition a FI 2-min schedule of reinforcement.
25 Dopaminergic (DA) agonists quinpirole (D2), SKF38393 (Di), and SKF82958 (Di); |i-opioid
26 agonist morphine; muscarinic cholinergic agonist arecoline; glutamate agonist NMD A; and
27 NMDA antagonist MK801 were administered after 50 FI sessions. FI performance was altered
28 by all drugs tested except NMDA. Pb exposures attenuated the decrements in rates produced by
29 the two DI agonists and, at 150 ppm Pb exposure, altered the rate change associated with the low
30 dose (0.033 mg/kg) of quinpirole. The effects of the DA agonists were not
31 concentration-dependent. These data suggest that Pb-induced changes in behavior were
May 2006 5-38 DRAFT-DO NOT QUOTE OR CITE
-------
1 mediated by DI receptors. Additional evidence suggesting Pb's attenuation of DA activity was
2 obtained using the D2 agonist quinpirole and the D2 antagonist eticlopride (Areola and Jadhav,
3 2001). Post-weaning, rats that had been exposed to 50-ppm lead acetate, producing a PbB level
4 of 15.1 |ig/dL, were tested on an FI 1-min schedule. Quinpirole at 0.05 mg/kg reversed the
5 effects of Pb, while eticlopride (0.01 and 0.05 mg/kg) had no effect on response rates in Pb-
6 treated animals.
7 To test the hypothesis that elevated nucleus accumbens (NAC) DA is a mechanism of
8 Pb-induced changes in FI performance, NAC DA activity was evaluated using the DA antagonist
9 N-ethoxycarbonyl-2-ethoxy-l,2-dihydroquinone(EEDQ)(Cory-Slechtaetal., 1998). LE rats
10 were exposed to 0, 50, or 500 ppm Pb acetate continuously from weaning, creating PbB levels of
11 2.1/0.5, 7.2/9.6, and 49.1/49.4 |ig/dL (~3 months of exposure/end of experiment). After shaping
12 (lever press), rats performed an FI 1-min schedule of reinforcement for at least 50 sessions.
13 DA increased FI rates in the 0 and 50 ppm groups and decreased rates in the 500-ppm group.
14 Intra-NAC administration of EEDQ suppressed FI response rates. At the highest EEDQ dose,
15 Pb at 500 ppm delayed recovery of response rates to control level rates, suggesting that NAC DA
16 activity may be one mechanism mediating FI response rates. Using a similar exposure paradigm,
17 Cory Slechta et al. (2002a) examined the involvement of the dorsomedial striatum in Pb-induced
18 increases in FI response rates. Both DA and EEDQ, microinjected into the dorsomedial striatum,
19 increased or decreased FI response rates, which depended on baseline FI overall rates. DA
20 mimicked the effects of Pb in this region. At this point, it is unclear whether this area of the
21 striatum modulates Pb-induced changes in FI performance. Changes in FI performance were
22 also used to characterize interactions between chronic Pb exposure and intermittent stress
23 (Virgolini et al., 2005), discussed below.
24 Rice (1988a) orally dosed cynomolgus monkeys from birth with 2 mg/kg/day of Pb
25 acetate continuously throughout the study. At PND 100, PbB levels peaked at 115 |ig/dL and
26 declined to 33 |ig/dL by PND 270. At PND 60, the monkeys were tested on an FR schedule,
27 learning to respond by pushing a button to receive a reinforcement. The Pb-treated monkeys at
28 2.5 to 5.0 months of age demonstrated increased mean FR pause times compared to controls. In
29 later, but not earlier sessions, FI pause was decreased in Pb-treated monkeys. Following FR
30 training, the monkeys were tested on a discrimination reversal, then a chain FR Imin-FI 2 min
31 operant schedule, which required the monkeys to complete the FR, followed by the FI to receive
May 2006 5-39 DRAFT-DO NOT QUOTE OR CITE
-------
1 one reinforcer (chain FI-FR). The monkeys were then tested as juveniles (3 years of age) on a
2 multiple FI-FR schedule of reinforcement. Pb-treated juvenile monkeys demonstrated increased
3 FI run rate, pause time, and index of curvature. At both ages, the treated monkeys showed
4 increased variability of performance (both within and between sessions, and between subjects)
5 compared to controls.
6 To evaluate the effect of Pb exposure during different developmental periods, Rice
7 (1992a) exposed cynomolgus monkeys to 1.5 mg/kg/day Pb acetate either continuously from
8 birth, from birth to PND 400, or from PND 300 onward. These exposures resulted in a steady
9 state PbB level of 20 to 35 |ig/dL during dosing. Tested at 3 years of age on a multi FI-FR, the
10 Pb-treated monkeys showed no effects on FI rate. Tested at 7-8 years of age, all three groups of
11 treated monkeys demonstrated increased run rates and decreased interresponse times on the FI.
12 To explain the negative results in the juveniles and the positive results in the adults, the author
13 postulated a possible interaction of Pb with the behavioral history. The monkeys had been tested
14 first with a multi FI-FR, then a differential reinforcement of low rate (DRL) schedule, a series of
15 nonspatial discrimination reversal tasks, a delayed spatial alternation (DSA) task, and then a
16 second multi FI-FR at 7 to 8 years of age. Additionally, the author stated that FI performance
17 can be affected even without exposure to Pb during infancy and that exposure only during
18 infancy is sufficient to affect responses.
19 A concurrent schedule of reinforcement was used to test squirrel monkeys exposed
20 gestationally to Pb (Newland et al., 1994). Maternal PbB levels ranged from 21 to 79 |ig/dL.
21 At 5 to 6 years of age, the monkeys were tested using a concurrent reinforcement with VI
22 schedules. The monkeys were allowed to respond on either of two levers, one of which had a
23 greater density of reinforcement than the other. The ratio of reinforcement density was changed
24 within the test session trial. Control monkeys learned to follow the reinforcement density by
25 responding to a greater degree to the lever associated with the richer density. Monkeys whose
26 PbB level in utero had been >40 |ig/dL changed their responses more slowly or in the wrong
27 direction to the changing reinforcement, suggesting to the authors that this faulty response to
28 changes in reinforcement may be one mechanism of learning impairment.
29 Schedule-controlled behavior in squirrel monkeys was assessed at ages 3 to 7 years
30 following in utero-only exposure to Pb acetate (Newland et al., 1996). Doses were adjusted
31 individually to provide a maternal PbB level of 21 to 70 |ig/dL. The monkeys were trained to
May 2006 5-40 DRAFT-DO NOT QUOTE OR CITE
-------
1 pull a 1-kg weighted bar during acquisition of FR and FI schedules of reinforcement and during
2 steady state. Pb-treated monkeys demonstrated an increase in the number of responses that
3 failed to adequately displace the bar. This increase in incomplete responses occurred in the
4 acquisition and steady state FR schedules, but not in the FI schedule. Because the monkeys had
5 to use greater physical force to complete the response than the monkeys in the studies discussed
6 above, this study identified a deficit in the physical execution of the response. The lack of
7 increased response rate could also be related to the physical effort required. These data
8 suggested to the authors that gestational exposure to Pb can produce motor impairments long
9 after exposure has ended and that these motor impairments accompany deficits in acquisition
10 behavior.
11 In both rats and monkeys, an increased rate of FI responding has been seen with Pb
12 exposures producing PbB levels as low as 11 |ig/dL. Figure 5-3.5 shows a graph summarizing
13 studies examining Pb-induced changes in FI response rates (Cory-Slechta, 1994). This figure
14 summarizes the dose effect function for Pb-induced changes in FI performance for several
15 species. Low-level Pb exposures increase FI response rates and high-level Pb exposures
16 decrease FI response rates. These data extend earlier findings of a curvilinear dose-response
17 relationship for this endpoint.
18
19 Differential Reinforcement of Low Rates
20 On the basis of the results of the FI testing done on monkeys described above, Rice
21 (1992b) used a DRL to assess whether the monkeys could learn to inhibit inappropriate
22 responding. Monkeys were exposed to 2 mg/kg/day Pb acetate, creating a steady state PbB level
23 of 33 |ig/dL after withdrawal of infant formula. Compared to controls, the Pb-treated monkeys
24 demonstrated greater non-reinforced responding, less reinforced responding, and had a shorter
25 average time between responses. These results suggested to the author that Pb exposure may
26 cause a failure to inhibit inappropriate responding and a poorer ability to use internal cues for
27 timing.
28
29 Radial Arm Maze and Passive Avoidance
30 The radial arm maze evaluates spatial acquisition and retention by measuring animals'
31 retrieval of food from the arms of the maze. A study was done to determine if Pb-induced
May 2006 5-41 DRAFT-DO NOT QUOTE OR CITE
-------
300
1.0 10.0 100.0
Pb DOSE (mg/kg)
1000
Figure 5-3.5. Dose-effect function for lead-induced changes in fixed-interval
performance. The lead effect (response rate, interresponse time, or
percentage of reinforcement) was plotted as a percentage of the control
group value for sessions in which peak effects were observed. Different
symbols represent different experimental species: circles, rats; triangles,
monkeys; squares, sheep; diamonds, pigeons. Numbers next to curves or
selected points represent data from the following studies: (1) Cory-Slechta
et al., 1983; (2) Cory-Slechta and Thompson, 1979; (3) Van Gelder et al.,
1973; (4) Barthalmus et al., 1977;(5) Zenick et al., 1979; (6) Rice et al., 1979;
(7) Angell and Weiss, 1982; (8) Cory-Slechta and Pokora, 1991; (9) Cory-
Slechta et al., 1985; (10), Cory-Slechta and Weiss, 1989; (11) Nation et al,
1989; (12) Rice 1992a; (13) Rice, 1988b.
Source: Copyright 1994 from Principles ofNeurotoxicology by Louis W. Chang, Ed. Reproduced by permission
of Routledge/Taylor & Francis Group, LLC.
May 2006
5-42
DRAFT-DO NOT QUOTE OR CITE
-------
1 behavioral deficits in this learning endpoint are related to injury of hippocampal neurons (Munoz
2 et al., 1988). Female Wistar rats were fed 750-ppm lead acetate in their diet and then bred after
3 50 days. Pups were either continued on the same Pb diet for permanent exposure or fed control
4 chow for maternal-only exposure. PbB values at PND 16 were 17.3 |ig/dL in Pb-exposed rats
5 and ranged from 32-39 |ig/dL in continuously dosed animals. Brain Pb levels were 7.3 |ig/g at
6 PND 16 in Pb-exposed animals. Hippocampal lesions consisting of complete bilateral depletion
7 of granular and pyramidal cells in dorsal hippocampus were induced in other rats by stereotaxic
8 injection of ibotenic acid. The lesioned animals showed no effects on acquisition of learning in
9 the radial arm maze, while the Pb-exposed animals did. Tested 4 weeks later, both lesioned and
10 Pb-treated animals showed impaired retention, suggesting to the authors that lead may damage
11 the dorsal region of the hippocampus and may be associated with the retention component of
12 learning. A subsequent study by the same group (Munoz et al., 1989), using a similar Pb
13 exposure protocol and ibotenic acid lesions to the amygdala, was done to determine if that brain
14 region was involved in Pb-induced learning deficits. Both treatments impaired both acquisition
15 of food-retrieval behavior in the maze and passive avoidance behavior, but neither treatment
16 affected locomotor activity. The permanently exposed rats showed greater deficits, indicating
17 possible reversibility of Pb-induced effects in prenatal-only exposures or the cumulative effects
18 of the chronic exposure creating a greater body burden of Pb. Further, these data point to the
19 amygdala as another target of lead.
20
21 Discrimination
22 Early studies demonstrated Pb-induced impairments in tests of discrimination of relevant
23 environmental stimuli. To study the effects of chronic Pb exposure on discrimination, Morgan
24 et al. (2000) exposed LE rats continuously from the beginning of gestation. Lead acetate at 0,
25 75, or 300 ppm in drinking water produced adult PbB levels of <5, 20, and 36 |ig/dL. At ages
26 7 to 9 weeks, an automated, three-choice visual discrimination task revealed a dose-dependent
27 slowing of learning and an increased incidence of "impaired" animals. The authors concluded
28 that chronic developmental Pb exposure results in associative deficits and an increased tendency
29 to respond rapidly. In another study, Morgan et al. (2001) evaluated Pb-induced alterations in
30 visual discrimination in LE rats exposed only during early development. One group received Pb
31 acetate in drinking water throughout gestation and lactation (GL300), other groups received
May 2006 5-43 DRAFT-DO NOT QUOTE OR CITE
-------
1 300 or 600 ppm Pb during lactation only (L300 and L600). PbB levels were <5 (controls), 36-3
2 at PND 8, 27-34 at PND24, 131-158 at PND 53, and 16-18 jig/dL at PND 53 (treated animals).
3 Pb-treated animals showed no differences in learning rate, motivation, or response latency for
4 correct or incorrect responses.
5
6 Discrimination Reversal
1 Discrimination reversal studies examine the ability to alter behavior in response to a
8 change in reinforcement contingencies. Earlier studies showed that chronic low-level exposures
9 in monkeys, creating a steady state PbB level of 11 to 15 |ig/dL, produced deficits in nonspatial
10 discrimination reversal tests, with and without irrelevant cues. Reversal of previous learning
11 appears to be consistently affected by Pb exposure, often resulting in perseverative behavior.
12 Additionally, in early cynomolgus monkey studies, the Pb-treated monkeys were found to be
13 more distracted by irrelevant cues than control monkeys.
14 Using this same cohort of cynomolgus monkeys, Gilbert and Rice (1987) examined
15 spatial discrimination reversal at 9 to 10 years of age. The monkeys had been exposed to 50 or
16 100 jig/kg/day Pb acetate, resulting in PbB peaks of 15.4 and 25.4 |ig/dL, respectively. Steady
17 state PbB levels were 10.9 and 13.1 |ig/dL, respectively. Compared to controls, the treated
18 monkeys were impaired in the presence, but not the absence, of irrelevant cues. In the lower-
19 dose group monkeys (PbB 10.9 |ig/dL), impairment ended when the irrelevant stimuli became
20 familiar.
21 To evaluate the effects of timing of exposure on this learning task, monkeys were exposed
22 to one of three protocols: (1) 1.5 mg/kg/day Pb acetate continuously from birth; (2) during
23 infancy only (birth to PND 400); or (3) beginning after infancy (Pb from PND 300 and
24 thereafter) (Rice and Gilbert, 1990a). These exposures resulted in PbB levels of 32 to 36 |ig/dL
25 during dosing and given infant formula and levels of 19 to 26 |ig/dL during Pb exposure in the
26 post-infancy group. At age 5 to 6 years, the monkeys were tested on a nonspatial discrimination
27 reversal task. Monkeys exposed continuously and those exposed beginning after infancy
28 demonstrated a dose-dependent impairment of learning. The monkeys exposed only during
29 infancy showed no impaired learning of the task. At 7 to 8 years of age (adults), the monkeys
30 were tested on spatial discrimination tasks (Rice, 1990). Using no irrelevant cues or irrelevant
31 form and color cues, results showed that the continuously exposed monkeys were impaired in the
May 2006 5-44 DRAFT-DO NOT QUOTE OR CITE
-------
1 absence of irrelevant cues. All three treatment groups were impaired when irrelevant cues were
2 present. These results are in contrast to the results on the nonspatial tasks described by Rice and
3 Gilbert (1990a) and suggested to the author that the developmental period of exposure may
4 differentially affect spatial and nonspatial tasks.
5 The effects of Pb on olfactory reversal discrimination have been examined in two rodent
6 studies. Hilson and Strupp (1997) exposed LE rats chronically from conception to 0, 75, or
7 300 ppm Pb acetate in water. PbB levels were, respectively, <5, 26, and 51 |ig/dL on PND 1;
8 <5, 22, and 37.5 jig/dL on PND 17; and <5, 27.5, and 51 jig/dL in adulthood. At 20, 14, and
9 22 weeks of age for the three replicates, testing consisted of acquisition of the original
10 discrimination (i.e., learning to respond to an odor), then reversal learning in which the other
11 odor became correct. Pb treatment did not affect learning the original discrimination; however, it
12 did impair learning the reversals in the high dose group by prolonging the postperseverative
13 phase, which the authors note is similar to the effects seen with lesions of the amygdala. Both
14 groups of Pb-treated rats also showed impairment during an extradimensional shift in which the
15 rats had to learn the correct spatial location of the odor for reward. Garavan et al. (2000) further
16 investigated these responses in LE rats exposed to: (1)0 ppm Pb; (2) 300 ppm Pb acetate during
17 both gestation and lactation (GL300); (3) 300 ppm during lactation (L300); or (4) 600 ppm
18 during lactation to (L600). At testing on PND 53, PbB levels were <5, 16, 12, and 18 |ig/dL,
19 respectively. Compared to controls in a two-choice olfactory serial reversal task, all Pb-treated
20 groups needed more trials to reach the point at which perseverative responding to the previously
21 correct cue ended. The authors hypothesized that this deficit was not due to perseverative
22 responding, but rather to a Pb-related spatial response bias and a concurrent, but independent,
23 associative impairment.
24
25 Learning Set Formation
26 Learning set formation tasks evaluate an animal's ability to "learn to learn"
27 discriminations by presenting a series of visual discrimination problems and quantifying the rate
28 at which each successive problem is learned. To ascertain Pb's effects on this learning endpoint,
29 Lilienthal et al. (1986) exposed rhesus monkeys to either 0 (control), 350 (low,) or 600 ppm
30 (high) Pb in utero, resulting in PbB levels of 50 and 110 |ig/dL, respectively. At age 12 to
31 15 months, only the high-dose group exhibited deficits in simple discrimination learning, which
May 2006 5-45 DRAFT-DO NOT QUOTE OR CITE
-------
1 the authors attributed to possible Pb-induced reduced attention, higher frustration levels, and
2 lowered adaptability. Both groups showed impairments in forming a learning set, which the
3 authors hypothesize was due to Pb-induced cognitive deficits.
4
5 Concurrent Discrimination
6 Concurrent discrimination tests an animal's ability to learn a number of visual
7 discrimination problems at the same time. Rice (1992c) further evaluated the monkeys used in
8 the discrimination reversal studies described by Rice and Gilbert (1990a). At 8 to 9 years old,
9 the monkeys were tested on two sets of concurrent discrimination tasks. Pb-treated monkeys in
10 all three exposure groups learned more slowly, although there was less impairment in the
11 monkeys exposed only during infancy. Perseverative behavior was also demonstrated in the
12 treated monkeys. These data are consistent with the other discrimination studies.
13
14 Repeated Acquisition and Performance Schedule
15 Another test method effectively utilized to distinguish changes in chronically Pb-exposed
16 animals is the repeated acquisition and performance schedule (Cohn et al., 1993). The purpose
17 of this test is to determine the selectivity of Pb-induced changes in learning, as distinct from
18 nonspecific or performance effects, and to explore the nature of the underlying error patterns
19 contributing to any learning deficits. This schedule required completion of a sequence of three
20 responses for reinforcement, with the correct sequence for the learning component changing with
21 each successive experimental session (i.e., repeated acquisition). In contrast, the correct
22 sequence remained constant across sessions in the performance component; thus, once learned,
23 this component did not require further learning to complete successfully.
24 This schedule was used in animals chronically exposed from weaning to Pb acetate at
25 0, 50, or 250 ppm in drinking water, producing PbB levels of 2.8, 25.1, and 73.5 |ig/dL,
26 respectively. Pb treatment caused significant decrements in accuracy on the learning component,
27 but not on the performance component, compared to controls (Cohn et al., 1993). A detailed
28 analysis of the subjects' behavior indicated that Pb exposure impaired learning by increasing
29 perseverative responding on a single lever, even though such repetitive responding was not
30 directly reinforced. In a subsequent study using the same exposures, dose-effect curves for the
31 NMDA receptor antagonist MK-801 were determined in controls and animals in which chronic
May 2006 5-46 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb exposure began at weaning (Cohn and Cory-Slechta, 1993). The decline in learning accuracy
2 and the increases in perseverative responding produced by MK-801 were attenuated by Pb
3 exposure, and dose-effect curves relating MK-801 dose to changes in rates of responding were
4 shifted to the right in Pb-exposed rats compared to control animals. These observations
5 demonstrate a sub sensitivity of Pb-exposed animals to both the accuracy-impairing and response
6 rate-altering properties of the antagonist. An additional investigation used the same Pb exposure
7 protocol and administration of doses of NMD A as a receptor agonist to rats performing this test
8 (Cohn and Cory-Slechta, 1994a). In control animals, NMDA was found to decrease accuracy of
9 response in both the repeated acquisition and performance components of this multiple schedule
10 and to suppress response rates as well. Pb exposure potentiated the accuracy-impairing effects of
11 NMDA by further increasing the frequencies of errors and likewise potentiated the drug's
12 rate-suppressing effects. Thus, as stated earlier in this section, the Pb-induced potentiation of the
13 agonist effects and reduced sensitivity to the antagonist effects in this test are consistent with a
14 functional upregulation of NMDA receptors in Pb-exposed brain. In other work, Cohn and
15 Cory-Slechta (1994b) were unable to distinguish any evidence of dopaminergic modulation of
16 responding in this behavioral paradigm. Thus, the repeated acquisition and performance
17 schedule proved valuable not only in providing a finer dissection of the animal's behavior, but
18 also in elucidating important mechanistic aspects of Pb neurotoxicity. It also provides an
19 unambiguous indication of an adverse effect (learning impairment) in the absence of sensory and
20 motor deficits.
21
22 Avoidance Learning
23 Altmann et al. (1993) examined the effects of Pb on active avoidance learning (AAL) in
24 the offspring of Wistar rats fed 750-ppm Pb acetate for 50 days prior to mating. Deficits in AAL
25 were demonstrated in rats exposed to Pb either during pre-weaning or pre- and postweaning,
26 creating a PbB level of 15 jig/dL and a brain Pb level of 0.09 to 0.16 jig/g wet weight. Rats that
27 received only postweaning exposure (PbB of 16 |ig/dL and brain level of 0.09 |ig/g) had reduced
28 deficits in AAL. Another study of AAL (Chen et al., 1997a) used SD rats exposed to 0.2% Pb
29 acetate either during gestation and lactation (gestation day to until PND 21), during postweaning
30 only (PND 21 until testing at PND 56), or continuously. PbB levels at PND 56 were <2, 3.8,
31 25.3, and 29.9 |ig/dL, respectively. No Pb-associated effects in learning were seen with just
May 2006 5-47 DRAFT-DO NOT QUOTE OR CITE
-------
1 maternal or postweaning exposure. Compared to controls, continuously exposed rats showed a
2 tendency of lower avoidance and higher no response levels in the two-way active avoidance
3 tasks. Chen et al. (2001) tested step-down passive avoidance learning in SD rats similarly
4 exposed. All three Pb-treated groups tested at PND 55 to 56 demonstrated impaired learning but
5 unimpaired retention. Results of parallel autoradiographic analyses suggested that the Pb-
6 induced deficits in acquisition were associated with alterations in AMPA receptor binding.
7
8 Open Field Performance
9 Salinas and Huff (2002) compared learning in Pb-exposed spatially trained and cue-
10 trained F344 rats using an open field arena. The chronically exposed rats were tested at
11 -29 weeks of age when PbB levels were -42 |ig/dL. The Pb-treated rats trained to find food
12 using extra-maze spatial cues demonstrated better performance than either controls or the
13 Pb-exposed rats trained using intra-maze discrete cues. Additionally, by the seventh day of
14 testing, both groups of Pb-treated rats spent less time on the periphery of the maze. The authors
15 hypothesized that "a Pb-induced overflow of mesolimbic DA may have facilitated the expression
16 of rearing behaviors," which assisted in the spatial learning. Further, they suggested that this
17 overflow may cause "impulsivity" that results in less time spent by the Pb-treated rats on the
18 periphery.
19
20 Effects ofPb on Memory
21 Studies reported in the 1986 AQCD showed that monkeys with steady state PbB levels of
22 33 |ig/dL and tested at 3 to 4 years of age had impaired delayed matching-to-sample in both
23 spatial- and nonspatial-based paradigms. However, Cory-Slechta (2003) pointed out that much
24 of this work was done with animals that had previous behavior testing done with them and that
25 may have altered results. New studies characterizing Pb-induced deficits in matching-to-sample
26 tests have not been found. Other studies evaluating Pb-induced deficits in memory are described
27 below.
28 Morris Water Maze
29 The Morris water maze tests both learning and memory by requiring rats to learn and
30 remember the position of a platform hidden in opaque water. The effect of chronic
May 2006 5-48 DRAFT-DO NOT QUOTE OR CITE
-------
1 developmental Pb exposure on water maze performance was tested in LE rats (Jett et al., 1997).
2 Dams were dosed with 250-ppm Pb acetate in feed from 10 days before breeding through
3 lactation. Offspring continued on the same Pb-dosed chow through testing. PbB levels were not
4 reported. Hippocampal Pb levels were 1.73 (PND 21), 1.02 ( PND 56), and 0.91 |ig/g (PND 91).
5 Reference (long-term) memory and working (short-term) memory were tested on PND 21, 56,
6 and 91, with different rats in each test. Pb-exposure had no effect on working memory at any
7 age tested, but did affect reference memory (significant in females and nearly significant in
8 males) in the PND 21 rats. This group (Jett et al., 1997) also demonstrated an increase in escape
9 latency in adult LE rats injected with Pb acetate directly into the dorsal hippocampus. A study
10 examined the effects of timing of Pb exposure (Kuhlmann et al., 1997) in which rats were
11 exposed to 750 ppm Pb acetate in diet either maternally (gestation and lactation), permanently
12 (gestation onward), or postweaning (at 750 or 100 ppm). PbB levels at PND 100 were 1.8, 21.3,
13 22.8, and 26.3 |ig/dL, respectively. Compared to controls, maternal and permanent exposure
14 groups were impaired in water maze performance, with maternal exposure producing both the
15 greatest escape latency and longest escape path length. There were no effects on performance in
16 the postweaning exposure groups. This study provides additional evidence of a window of
17 vulnerability to Pb exposure and that early exposure can produce long-term deficits in learning
18 and memory.
19 Yang et al. (2003) exposed Wistar rats gestationally to 0.03% (low), 0.09% (middle), or
20 0.27% (high) lead acetate in food. Pups were fostered by control dams. PbB levels were-30,
21 -33, and -42 |ig/dL, respectively at PND 0 and -2 |ig/dL in all treatment groups at testing
22 (PND 49). By measuring swim path and time spent in target quadrants, it was shown that Pb
23 exposure at all three doses impaired memory retrieval in males. In female offspring, only the
24 low dose affected memory retrieval, suggesting a greater impact of low level Pb exposure on
25 females. Results on the fixed location/visible platform tasks showed that motor performance and
26 vision were not affected by Pb treatment and suggested to the authors that gestational exposure is
27 sufficient to cause memory deficits in young adults.
28 Results from recent studies have provided evidence that environmental enrichment during
29 development may protect against lead-induced effects on learning and memory deficits.
30 Schneider et al. (2001) exposed male LE rats to 0 or 0.2% Pb acetate from PND 25 until testing
31 at PND 100. At PND 25, some of the rats were raised in isolation with no access to any stimulus
May 2006 5-49 DRAFT-DO NOT QUOTE OR CITE
-------
1 objects, while the "enriched" rats were raised in groups of 8 with stimulus objects or toys.
2 PbB levels were ~5 |ig/dL in controls and -30 in Pb-treated animals. Pb-exposed rats raised in
3 isolation demonstrated spatial learning deficits in the Morris water maze, whereas the
4 Pb-exposed rats raised in the enriched environment performed better than the isolated Pb group.
5 Additionally, Pb-exposed rats had diminished hippocampal levels of the neurotrophic factors
6 brain-derived neurotrophic growth factor (BDNF), nerve growth factor-p, neurotrophin-3, and
7 basic fibroblast growth factor. This suggested to the authors a possible relationship between Pb
8 levels, neurotrophic factor levels, and diminished hippocampal development and function.
9 Earlier exposures to Pb showed some similar effects of environmental enrichment (Guilarte
10 et al., 2003) LE rats were exposed during gestation and lactation to 0- or 1500-ppm Pb acetate.
11 Pb exposure was stopped at PND 21 and rats were placed in isolation or in an enriched
12 environment. At PND 50 when PbB levels were 0.25 and 3.9 |ig/dL, respectively, testing in a
13 water maze showed enhanced performance of the Pb-treated rats raised in the enriched
14 environment. The environmental enrichment was accompanied by increased gene expression in
15 the hippocampus of NMD A receptor subunit 1 and BDNF. These results demonstrate that
16 Pb-induced learning impairments and molecular changes in hippocampus can be reversed by
17 environmental enrichment, even after the exposure has occurred.
18
19 Delayed A Iternation
20 Delayed alternation trials assess both memory and attention by requiring the animal to
21 alter a previous response following a delay period. Typically, the longer the delay between
22 choices, the greater the inaccuracy of the choice. A number of studies have examined Pb's
23 effects on delayed alternation tasks in rodents. To compare the effects of Pb exposure on
24 memory during different stages of life, rodent studies of this endpoint were completed (Cory-
25 Slechta et al., 1991). PND 21 (young), 8-month-old (adult), and 16-month-old (old) F344 rats
26 were exposed to 0, 2, or 10 mg/kg Pb acetate, resulting in PbB levels of-23 at the 2 mg dose and
27 of-42 (adult), -48 (old), and- 58 |ig/dL (young) at the 10 mg dose. Training began after
28 4 months of exposure and testing continued until 8.5 months of exposure. Rats were trained with
29 many sessions using a cue light alternating between two positions and tested after 4 months of
30 exposure. Aging itself caused impaired accuracy. In both young and old rats, Pb exposure
31 increased accuracy, at the longest delay periods (12 sec) in young rats, and at the short delay
May 2006 5-50 DRAFT-DO NOT QUOTE OR CITE
-------
1 periods in old rats. In adult rats, performance was not affected by Pb exposure. The authors
2 hypothesized that the improved performance was due to perseveration of alternation behavior
3 learned during the training and that both young and old animals may have enhanced vulnerability
4 to Pb. The effect of chronic postweaning Pb exposure (0, 75, or 300 ppm in drinking water
5 starting at PND 25) on DSA was evaluated in LE rats (Alber and Strupp, 1996). PbB levels were
6 19 and 39 |ig/dL. At 22 weeks of age, nose poke training was followed by cued alternation,
7 spatial, and DSA training. Learning the alternation rule was not affected by Pb treatment.
8 Across all delay periods, the treated rats performed more poorly than controls, suggesting that
9 memory was not affected by Pb exposure. An additional finding was Pb-induced side bias, a
10 strategy commonly adopted by rats in response to an insoluble problem.
11 Nonhuman primate DSA studies have also been completed. Levin and Bowman (1986)
12 evaluated DSA in 5- to 6-year-old rhesus monkeys exposed to two early pulses of 10 mg/kg Pb
13 acetate and a chronic exposure of 0.7 mg/kg/day for the first year. The pulses of Pb were done to
14 simulate brief periods of higher-level exposure that can occur in children with Pb pica. Peak
15 PbB levels were 250 to 300 |ig/dL, which decreased to 80 |ig/dL for the remainder of the first
16 year. Deficits occurred most commonly with short inter-trial delays, suggesting that memory
17 was not affected by Pb, but that deficits in attention or strategy may have been present. Most
18 Pb-induced deficits were accounted for by lose-shift errors, possibly due to perseveration on the
19 alternation strategy despite loss of reinforcement. The authors hypothesized a "window of
20 sensitivity" to Pb, wherein exposures during the first year of life can create long-term cognitive
21 deficits. Another cohort of rhesus monkeys was dosed with 1.0 mg/kg/day Pb acetate for the
22 first year of life, producing a PbB level of 70 |ig/dL (Levin and Bowman, 1989). They were
23 tested on DSA at 4 years of age, by which time PbB levels had returned to control levels. The
24 monkeys performed better than controls on choice accuracy, which suggested to the authors that
25 a Pb-induced decrease in attentiveness may make the monkeys less susceptible to irrelevant
26 stimuli and thus able to perform better.
27 Rice and Karpinski (1988) evaluated the effects of low-level lifetime exposure on delayed
28 alternation tasks. Cynomolgus monkeys were dosed with 0, 50, or 100 jig/kg/day Pb acetate
29 from PND 1 through the completion of the study. PbB levels peaked at PND 100 (~3, 15.4,
30 and 25.4 |ig/dL, respectively) and reached steady state by PND 300 (3, 10.9, and 13.1 |ig/dL).
31 Tested at 7 to 8 years of age using delay values that increased over the course of the trial,
May 2006 5-51 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb-induced impairment of initial acquisition of tasks was observed. Longer delays between
2 alternations resulted in poorer performance by the Pb-treated monkeys and perseverative
3 behavior, sometimes lasting for hours. Further, the treated monkeys repeatedly pounded buttons
4 indiscriminately, suggesting to the authors a failure to inhibit inappropriate responding. Rice and
5 Gilbert (1990b) attempted to evaluate the effect of timing of exposure on this endpoint. The
6 cynomolgus monkeys described above (Rice and Gilbert, 1990a) exposed to Pb either
7 continuously from birth, during infancy only, or beginning after infancy were given a set of DSA
8 tasks at 7 to 8 years of age. Monkeys had to push two buttons alternately with delays increasing
9 from 0.1 to 15 sec. All Pb-treated groups had the same impairments of initial acquisition,
10 indiscriminate responding, greater impairment with longer delays, and perseverative responses.
11 All three exposure groups had similar degrees of impairment, indicating to the authors a possible
12 lack of sensitive period for Pb's affects on this endpoint.
13 Levin et al. (1987) examined the involvement of cholinergic (ACh) and DA
14 neurotransmitter systems in Pb-induced impairments of DSA performance. Rhesus monkeys
15 were exposed during the first year of life to daily doses of 0.7 mg/kg/day plus two early high
16 pulses (10 mg/kg/day during the second and fourth weeks of life). PbB levels were 63 at weeks
17 1 to 4, 174 at weeks 5 to 10, 68 at weeks 11 to 52, 4 at 6 years of age, and 2 |ig/dL by the time of
18 testing (7 to 9 years of age). Thirty min prior to testing, one of the following drugs was
19 administered: the DA receptor blockers, haloperidol and sulpiride; the muscarinic ACh receptor
20 blocker, scopolamine; or the DA agonist, amphetamine. In addition, amphetamine and L-dopa
21 were injected for 2 weeks for chronic testing. In both controls and Pb-treated monkeys,
22 scopolamine caused a dose-related decline in performance. Chronic L-dopa ameliorated the
23 Pb-induced DSA deficits, which returned following cessation of L-dopa administration. These
24 data again show long-term cognitive impairments resulting from early Pb exposures and
25 implicate DA mechanisms as a causal factor in these impairments.
26
27 Avoidance
28 A shuttle avoidance task evaluated retention in rats exposed during gestation and lactation
29 to 0.5, 2.0, or 4.0 mM lead acetate in drinking water (Rodrigues et al., 1996a). PbB levels
30 ranged from 11 to 50 |ig/dL. The Pb-treated rats demonstrated no increases in avoidance
31 response between sessions, suggesting less retention in the treated animals compared to controls.
May 2006 5-52 DRAFT-DO NOT QUOTE OR CITE
-------
1 Murphy and Regan (1999) exposed Wistar rats from PND 1 to PND 30 to 400 mg of Pb
2 chloride/L drinking water, producing PbB of 10 to 15 |ig/dL by PND 8, -45 |ig/dL by weaning,
3 and 2 to 4 ng/dL by PND 80. At PND 80, the rats were trained on a 1-trial, step-through, light-
4 dark passive avoidance test. At 48 h postexposure, the rats showed no Pb-induced changes in
5 recall; but at 5 days postexposure, the rats exhibited a decline in recall. The authors
6 hypothesized that the Pb exposure affected long-term memory storage.
7
8 Discrimination Retention
9 Munoz et al. (1986) used visual discrimination learning and spatial learning in a retesting
10 approach to evaluate changes in long-term memory storage in Wistar rats. The rats were
11 exposed to 750-ppm Pb acetate either through PND 16 (maternal exposure) or chronically
12 through testing. PbB in males tested at PND 110 was <1 |ig/dL in controls and maternally
13 exposed rats and 34 |ig/dL in chronically exposed rats. Males were tested at PND 100 in visual
14 discrimination and then retested 42 days later. Both Pb-treated groups learned the original
15 discrimination comparably to controls, but both groups showed a deficit in retention of the
16 discrimination. Females were tested at PND 180 in spatial discrimination, then retested 4 weeks
17 later. The Pb-treated female rats took longer to reach criterion in the acquisition learning and
18 longer to eat the pellets in the retention phase. These data suggest that early gestational Pb
19 exposure can cause long-lasing retention deficits and that subsequent direct dietary exposure
20 does not potentiate these effects.
21
22 Effects ofPb on Attention
23 Human studies have suggested that Pb exposure is associated with deficits in attention
24 (e.g., inattentiveness, impulsivity, distractibility, attention deficit disorder); however, only scant
25 evidence from early animal studies pointed to attention deficits as a causal factor in
26 neurocognitive dysfunction. Related to deficits in attention are increased response rates and
27 response perseveration, both of which are associated with Pb exposure as discussed above.
28 Several laboratories have examined the effect of Pb on attention specifically. Brockel and
29 Cory-Slechta (1998) exposed male LE rats to 0-, 50-, or 150-ppm Pb acetate in water from
30 weaning. After 3 months of exposure, PbB levels were <5, 10.8, and 28.5 |ig/dL, respectively.
31 After 40 days of exposure, the rats were trained on a FR/waiting-for-reward behavioral baseline,
May 2006 5-53 DRAFT-DO NOT QUOTE OR CITE
-------
1 learning to produce food delivery by pressing a lever 50 times. Additional food could be earned
2 by withholding lever presses (i.e., by waiting); free food was given at increasing time intervals
3 after completion of the FR. In the FR component of the study, the high-dose animals had
4 significantly higher response rates and more frequent resets of the waiting period than the low
5 dose group and controls. Wait time was significantly lower in both treated groups compared to
6 controls in the waiting behavior component. The high-dose animals also had an increased
7 number of reinforcers and a higher response to reinforcement ratio than low dose and controls.
8 These data suggest that PbB levels as low as 11 |ig/dL are associated with inefficient response
9 patterns and an inability to manage delays of reinforcement. The authors hypothesized that this
10 pattern of behavior in humans could have the consequence of eventual dissipation of effort or
11 lack of motivation.
12 Involvement of dopamine-like receptors in the Pb-induced decrements in waiting behavior
13 was tested using this FR/waiting-for-reward schedule (Brockel and Cory-Slechta, 1999a). The
14 same 0, 50, and 150 Pb dosing was done, resulting in PbB levels of <5, 9.7, and 26.2 |ig/dL after
15 both 3 and 7 months of exposure. Following performance stabilization, drugs were administered
16 IP 30 min prior to behavioral testing: the D2 agonist quinpirole, the DI agonist SKF 82958, the
17 D2 antagonist eticlopride, or the DI antagonist SCH 23390. The drugs administered to control
18 rats did not cause Pb-like effects. All the drugs decreased FR response rates, but only quinpirole
19 reversed the Pb-induced effects on FR response rate, FR resets, wait reinforcers, and wait time.
20 This suggested to the authors a role for D2 receptors in Pb's effects, a dissociation of Pb's effects
21 on FR and waiting time, and a possibility that decreased waiting behavior is a direct effect of
22 Pb exposure.
23 A similar postweaning Pb exposure resulting in PbB levels of <5, 16.0, and 28.0 |ig/dL
24 was used to evaluate sustained attention (Brockel and Cory-Slechta, 1999b). Food rewards were
25 obtained by the rats for discriminating correctly between a target and distracter light. A 13-sec
26 time-out was given for incorrect responses. Pb produced no effects on sustained attention in this
27 study, suggesting to the authors that Pb affects other aspects of attention and that Pb-induced
28 attention deficits are modified by time-out contingencies and reinforcement. Morgan et al.
29 (2001) evaluated changes in attention in a study with LE rats exposed to Pb acetate in drinking
30 water. One group (GL300) received Pb throughout gestation and lactation (GL), other groups
31 received 300 or 600 ppm Pb during lactation only (L300 and L600). PbB levels were <5 for
May 2006 5-54 DRAFT-DO NOT QUOTE OR CITE
-------
1 controls, 36 to 43 at PND 8, 27 to 34 at PND 24, 131 to 158 at PND 53, and 16 to 18 jig/dL at
2 PND 53 (treated animals). Pb-exposed animals (both GL and L) committed more errors of
3 omission when a delay was imposed prior to cue presentation and in trials that followed an
4 incorrect response. Response initiation was also impaired in Pb-treated animals in a sustained
5 attention task in which the onset and duration of the visual cue varied randomly across trials.
6 These data suggested to the authors that early Pb exposure caused long-lasting increased
7 reactivity to errors and impairment of sustained attention. Inconsistencies in these results
8 compared to those of Brockel and Cory-Slechta (1998,1999b) may be accounted for by the
9 differences in exposure period and the higher PbB and the small percentage change in endpoints
10 in the later study. In a review of the attention literature, Cory-Slecta (2003) stated that
11 impulsivity and waiting-for-reward behavior may be more strongly affected by Pb than are
12 sustained attention and hyperkinesis. Further, the Pb-induced impulsivity as a behavioral
13 dysfunction may lead to cognitive impairments.
14
15 Effects ofPb on Motor Function, Locomotor Activity, and Vocalization
16 Evaluations of the effects of Pb on development of motor function and reflexes discussed
17 in the 1986 AQCD showed that Pb affects the air righting reflex in rat pups with PbB levels of
18 35 |ig/dL and rotarod performance at 175 |ig/dL. Developmental lags in gross activity were
19 produced in rat pups with PbB as low as 14 |ig/dL. Studies ruled out the possible contribution of
20 Pb-exposed dams to their offspring's slowed development. In the early evaluations of
21 spontaneous activity, numerous issues were apparent, including a lack of consensus for the
22 definition of "activity" and activity being affected by confounding variables such as age, sex,
23 estrous cycle, time of day, novelty of environment, and food deprivation. Discrepant findings
24 summarized in the 1986 Pb AQCD included 11 studies showing increased activity with Pb
25 exposure, 6 studies showing decreased activity, and 28 studies showing age-dependent,
26 qualitative, mixed or no changes. Thus, no conclusions were reached regarding Pb's affect on
27 these endpoints.
28 Lilienthal et al. (1986) evaluated activity in the rhesus monkeys exposed prenatally to Pb
29 as discussed above. Activity, measured in unfamiliar environments at age 12-15 months,
30 showed no Pb-related effects in these monkeys. In the study of schedule-controlled behavior
31 discussed above, Newland et al. (1996) identified a deficit in the physical execution of pulling a
May 2006 5-55 DRAFT-DO NOT QUOTE OR CITE
-------
1 weighted bar in Pb-treated monkeys, suggesting a motor impairment occurring long after the
2 exposure period. Open field behavior was assessed in rhesus monkeys exposed to a "pulse-
3 chronic" dosing paradigm (two pulses of 10 mg/kg the first month of life and chronic level of
4 0.7 mg/kg/day for the rest of the first year of life) (Ferguson and Bowman, 1990). PbB peaked at
5 5 weeks of age (55 jig/dL), averaged 36 |ig/dL for the remainder of the first year, and was
6 < 5 |ig/dL for at least 1.5 years prior to testing at 4 years of age. The Pb-treated monkeys
7 demonstrated a longer latency to enter the open area, increased durations of environmental
8 exploration and activity, and a failure to habituate.
9 Laughlin et al. (1999) evaluated the effects of Pb on behavior of neonatal rhesus monkeys
10 using the Schneider Neonatal Assessment for Primates (SNAP). Monkeys were dosed orally
11 with Pb acetate daily to eventually achieve a target PbB level of 35 |ig/dL. PbB levels for
12 controls was <5 |ig/dL, and for treated animals was 15-20 |ig/dL during week 3 and
13 22 to 28 |ig/dL during week 4. Testing was done during the first four weeks of life, at which
14 time few differences between control and lead exposed monkeys were seen. The authors
15 reported less stability in SNAP performance in the Pb-exposed monkeys compared to controls,
16 which they suggested may be caused by a disruption of continuity of development by Pb. The
17 same animals were evaluated for exploration behavior starting at the second postnatal week
18 (Lasky and Laughlin, 2001). The Pb-exposed monkeys demonstrated more agitation, climbing,
19 fear, and exploration of the periphery than controls.
20 In the Rodrigues et al. (1996a) study cited above, rats were also subjected to open-field
21 testing, where a Pb-associated increase in locomotor activity was observed. To assess the effects
22 of developmental exposure on a number of neurobehavioral endpoints, Wistar rats were exposed
23 during gestation and lactation to 500-ppm Pb acetate (Moreira et al., 2001). PbB levels were
24 41 |ig/dL (dams), 21 |ig/dL (PND 23 pups), and <0.1 |ig/dL (PND 70). The PND 23 pups
25 exhibited a Pb-induced increased ambulation in the open-field tests, decreased exploratory
26 behavior in the holeboard tests, and no differences from control in the elevated maze tests. The
27 PND 70 rats showed a Pb-induced increase in head dipping in the holeboard test. No differences
28 were noted in the rotarod tests. Ferguson et al. (1998) evaluated activity in SD rats exposed to
29 350-ppm Pb acetate (through dams' drinking water) from birth until weaning . PbB was
30 46 |ig/dL in pups at weaning. No Pb-related effects were seen in the following behavioral
31 assessments: play (PND 38 and 45), burrowing (PND 49-54), dominance (PND 58 and 65),
May 2006 5-56 DRAFT-DO NOT QUOTE OR CITE
-------
1 residential running wheel (PND 67-80), residential figure 8 maze (PND 70-84), complex maze
2 (PND 83-94), acoustic startle (PND 98), emergence (PND 121 or 128), and prepulse inhibition
3 (PND 177). The authors suggested that at these Pb exposure levels, the development of Pb-
4 induced functional changes may require substantial demands on the system for detection.
5 To evaluate the effects of early Pb exposure on activity and vocalization, De Marco et al.
6 (2005) exposed female Wistar rats to 8, 16, or 24 mg/ml lead acetate in water, allowed them to
7 breed, and then crossfostered pups to them to allow exposure during pregnancy, during
8 pregnancy and lactation, or during lactation. In the treated rats, PbB levels ranged from
9 5.7 to 36.6 |ig/dL, with levels dropping to 0.5 |ig/dL in adults. In all three exposure groups, the
10 PND 7 pups showed a dose-dependent decrease in ultrasonic vocalization, whereas the PND 14
11 pups showed an increase compared to controls. These results contrast with the normal
12 developmental pattern of vocalization and suggested to the authors a Pb-induced alteration in the
13 maturation pattern of this behavior. Additionally, the PND 14 pups showed higher activity levels
14 than controls.
15 One animal study has shown behavioral deficits in offspring resulting from paternal
16 exposure to Pb (Nelson et al., 1997). Male Dutch Belted rabbits were dosed with Pb acetate for
17 15 weeks to produce PbB levels of <5 (control), 20, 40 and 80 |ig/dL. They were then mated
18 with nonexposed females and the offspring were tested for exploratory behavior at PND 15, 20,
19 25, and 30 in a figure-eight activity monitor. For those F2 offspring of male rats that had
20 paternal PbB >40 |ig/dL, exploratory behavior was affected at PND 25, the time of peak activity
21 in rabbits. This is the only animal study available showing these effects. Another study
22 demonstrated that behavioral effects of Pb can extend to a second generation (Trombini et al.,
23 2001). First, Pb-induced behavioral effects were assessed in Wistar rats exposed during
24 gestation and lactation. Pregnant rats were dosed with 750 ppm lead acetate in drinking water.
25 PbB levels in offspring were 25 |ig/dL at PND 30 and 0.1 |ig/dL at PND 90. No Pb-associated
26 changes in elevated maze behavior were noted in 30- and 90-day-old rats. In open-field behavior
27 studies, PND 30 Pb-treated rats showed decreased freezing, increased ambulation, and increased
28 grooming. PND 90 Pb-treated rats showed decreased freezing and increased ambulation.
29 Offspring of Pb-treated females were mated with nonexposed males and evaluated at PND 30
30 and 90. At both ages, the F2 generation rats demonstrated increased ambulation and decreased
31 grooming, suggesting evidence of intergenerational effects of Pb.
May 2006 5-57 DRAFT-DO NOT QUOTE OR CITE
-------
1 In an attempt to discern the mechanism of motor deficits resulting from Pb exposure,
2 Morley et al. (2003) exposed Drosophila instar larvae to 100 jiM lead acetate and examined the
3 neuromuscular junction. They observed nonuniform matching between the size of the motor
4 terminal and the muscle area, suggesting a possible mechanism of Pb's neurobehavioral effects.
5
6 Effects ofPb on Social Behavior
1 Early work evaluating Pb-induced alterations in social behavior or behavioral interactions
8 showed inconsistent results. In both rats and monkeys, Pb tended to reduce aggressive behavior.
9 Pb-treated mice demonstrated gender differences in sexual interaction and social investigation,
10 which could have been attributed to differences in brain Pb concentrations. Interactions between
11 mothers and offspring were shown to be affected by Pb exposure. These included increased
12 clinging by infants, less food-seeking activity by pups, suppressed play behavior, increased time
13 spent in the nest by dams, and increased retrieval of pups to the nest by dams.
14 Studies published since the 1986 Pb AQCD have examined the effects of Pb on social
15 behavior in greater detail. Donald et al. (1986) exposed male and female BK:W mice to
16 0.13% Pb acetate before breeding. At weaning, the pups were continued on the 0.13% Pb
17 chronically. At 18 weeks, brain and femur Pb concentrations in males were 27.6 ash and
18 998 jiM Pb/g, respectively (controls were 7.5 and 78). At 34 weeks, brain and femur
19 concentrations in males were 445 and 5364 (controls 40 and 100). At 34 weeks, brain and femur
20 concentrations in females were 787 and 4026 (controls 88 and 334). PbB was not reported.
21 Young Pb-exposed female mice habituated more slowly to the environment, while young
22 Pb-exposed males habituated more rapidly. In general, in adults, Pb caused an enhancement of
23 social and sexual investigation. The same laboratory (Donald et al., 1987) evaluated activity
24 resulting from a higher Pb exposure (0.25% chronically from conception). Exploratory behavior
25 and social investigation were increased in both sexes of Pb-treated mice at age 3-4 weeks
26 compared to controls. At age 7 to 8 weeks, social investigation was increased, but exploratory
27 behavior was decreased in Pb-treated mice. At age 15 to 16 weeks, nonsocial activity was
28 decreased in females, but increased in males. At age 17 to 18 weeks, Pb-treated males
29 demonstrated shorter latencies to aggression than controls.
30 Holloway and Thor (1987) tested social behavior in LE rats exposed to 500-ppm Pb
31 chloride during lactation. They estimated PbB to be 42 |ig/dL on PND 20 based on similar
May 2006 5-58 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposures. AT PND 11, they found that Pb induced no sex differences, no effects on pup
2 activity, and no differences in pup retrieval by dams. At PND 26, Pb treatment influenced all
3 social behavior tested (i.e., investigation duration and frequency, crossover frequency, pinning)
4 but did not change activity levels compared to controls. At PND 36, Pb-treated pups
5 demonstrated increased crossover frequencies but no change in activity levels compared to
6 controls. The authors hypothesized that low-level Pb exposure increases social investigation and
7 "rough and tumble" play behaviors, due to increased behavioral reactivity to stimuli, and does
8 not increase aggression. Pb-induced changes in aggression were assessed in golden hamsters
9 exposed to 100 ppm lead acetate from gestational day 8 until PND 42 (Delville, 1999). PbB at
10 PND 42 was 10 to 15 |ig/dL. At PND 19 to 20, the Pb-exposed hamsters were significantly
11 smaller than controls and exhibited less play fighting. At PND 45, the treated and control
12 animals' weights were not significantly different, and the treated animals displayed more
13 aggression as measured by attacking and biting an intruder put in the cage. In the assessment of
14 developmental Pb exposure discussed above (Moreira et al., 2001), the early Pb exposure
15 resulted in a decrease in social interaction time in the PND 70 rats.
16 Levin et al. (1988) exposed rhesus monkeys to a pulse-chronic Pb exposure protocol as
17 described above (Levin and Bowman, 1986) resulting in a PbB level of 56 during week 5 and
18 33-43 |ig/dL for the remainder of the first 6 months of life. During the first 6 weeks after birth,
19 results of the Early Infant Behavioral Scale showed Pb-induced lowered muscle tonus and
20 greater agitation, but no effects on sensorimotor measures. Beginning at PND 14, monkeys were
21 tested on a Piagetian object permanence task, which revealed no Pb-related effects. Starting at
22 2 months of age, monkeys were tested on a visual exploration task, which showed decreased
23 visual attentiveness in Pb-treated monkeys. Laughlin et al. (1991) evaluated the effects of Pb
24 exposure and diet in rhesus monkeys exposed to 1 mg/kg/day Pb acetate from PND 5 until
25 PND 365. Monkeys were given either low-milk or high-milk diets because of milk's ability to
26 enhance tissue levels of Pb. PbB levels reached a plateau of-70 |ig/dL during the first year
27 when initial testing occurred and then decreased to ~ 35 |ig/dL at 16 months postexposure.
28 During the first year of life, Pb-induced disruption of social play and increases in both self-
29 stimulation and fearful behavior were observed. At 16 months of age, these changes were still
30 present. Differences in milk intake had little effect on behavior in this study.
May 2006 5-59 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb Exposure and the Stimulus Properties of Neuropharmacologic Agents
2 The drug discrimination paradigm has been utilized to characterize postsynaptic receptor
3 status for multiple neurotransmitter systems. Rats chronically exposed to Pb beginning at
4 weaning and tested as adults were trained to discriminate either a systemically administered DI
5 or D2 receptor agonist (Cory-Slechta and Widzowski, 1991). Exposed rats learned the
6 discrimination task more rapidly than controls and exhibited greater levels of responding to
7 lower doses of the training drugs and less blockade by a D2 receptor antagonist, consistent with
8 generalized dopaminergic receptor supersensitivity. In groups of animals exposed only from
9 birth to weaning and trained to discriminate the same drugs, the D2-D3 subtype receptor
10 supersensitivity in exposed animals was again present, but no changes in responding to the DI
11 agonist were apparent (Cory-Slechta et al., 1992). Further work with this test employing the
12 postweaning exposure protocol failed to demonstrate any Di-D2 receptor interactions in the
13 supersensitivity displayed by Pb-exposed animals (Cory-Slechta et al., 1996a).
14 To test cholinergic sensitivity in animals chronically exposed after weaning, rats were
15 trained to discriminate a muscarinic agonist (Cory-Slechta and Pokora, 1995) and were tested in
16 the added presence of a muscarinic antagonist. The results suggest an increased sensitivity to at
17 least one subtype of muscarinic receptor in lead-exposed rats.
18 Glutamatergic functioning also has been assessed by use of the drug discrimination
19 paradigm. Rats chronically exposed beginning at weaning and tested as adults exhibited
20 diminished responsiveness to an NMDA subtype receptor antagonist (Cory-Slechta, 1995), but
21 enhanced responding to lower doses of NMDA (Cory-Slechta et al., 1996a). When exposure
22 was limited to the period between birth and weaning, the diminished sensitivity to the NMDA
23 receptor antagonist was less evident but still present (Cory-Slechta, 1997).
24 Thus, the drug discrimination method appears to have provided useful insights into the
25 status of some neurotransmitter systems in chronically exposed animals. The reports cited above
26 indicate an upregulation of dopaminergic, cholinergic, and glutamatergic receptors that are
27 generally consistent with findings of diminished presynaptic function described earlier in this
28 section. Nonetheless, this paradigm has some limitations. As all drugs in the cited studies were
29 administered systemically, the results provide no evidence on brain regional sites of action. In
30 addition, the chronic intermittent administration of the training drug has the potential to induce
31 compensatory neuronal changes by itself, and thus may mask or otherwise alter the manifestation
May 2006 5-60 DRAFT-DO NOT QUOTE OR CITE
-------
1 of the effects of lead exposure. Future use of this method in lead neurotoxicity studies must
2 acknowledge this latter consideration.
3
4 5.3.1.6 Lead-Induced Changes in Cellular Development and Disposition of the Metal
5 Alterations in cellular differentiation and morphology can be important structural
6 components of the manifestations of Pb neurotoxicity in neurons and glia. While these issues
7 have not been thoroughly addressed by research investigations, important observations have
8 nonetheless been made, as discussed below in the following subsections.
9
10 Lead Exposure and Neural/Glial Progenitor Cells
11 Recent Pb neurotoxicity studies have evaluated the effects of Pb exposure on neural and
12 glial progenitor cells. Chronic Pb exposure of rats beginning at PND 25 and producing PbB
13 levels of 20 |ig/dL at the termination of exposure, was found to significantly decrease
14 proliferation of new cells in the dentate gyrus compared to control animals (Schneider et al.,
15 2005). Other workers determined that continuous exposure from birth to adulthood producing
16 PbB levels of 35 to 40 |ig/dL reduced the total number of labeled cells in the hippocampal
17 dentate gyrus at 28 days after the last administration of a DNA synthesis marker (Gilbert et al.,
18 2005). Rats whose exposure was terminated at weaning showed no changes in cellular labeling
19 or survival, indicating that chronic exposure reduces the capacity for hippocampal neurogenesis.
20 Studies have also been conducted to investigate the effects of Pb exposure on glial
21 progenitor cells. Deng et al. (2001) examined cultured oligodendrocytes and their progenitor
22 cells acutely exposed to Pb2+ in vitro; they observed an exposure-induced delay in the
23 differentiation of the progenitors and that the progenitor cultures were more sensitive to Pb2+
24 than the mature oligodendrocytes. These findings suggested interference with the timely
25 developmental maturation of the progenitor cells. A subsequent study found that a low
26 concentration of Pb2+ in vitro inhibited proliferation and differentiation of these progenitors
27 without affecting cell viability (Deng and Poretz, 2002). Proliferative capability was decreased
28 and cell-intrinsic lineage progression was inhibited at a late progenitor stage. Thus, acute Pb2+
29 exposure suppresses both the proliferation and differentiation of progenitor cells.
30
May 2006 5-61 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead Exposure andNeurite Outgrowth
2 Neurite initiation is highly sensitive to neurotoxic compounds and has been the focus of
3 studies examining morphological alterations caused by in vitro exposure to Pb2+. Kern and
4 Audesirk (1995) found that 100 nM Pb2+ inhibited neurite initiation in cultured rat hippocampal
5 neurons and, on the basis of results with kinase inhibitors, concluded that this occurred by
6 inappropriate stimulation of protein phosphorylation by Ca2+-calmodulin-dependent or cyclic
7 AMP-dependent protein kinases, possibly through stimulation of calmodulin. Intracellular free
8 Ca2+ concentrations were not altered by up to 48 h exposure to nominal 100 nM Pb2+, suggesting
9 that the stimulation of the above kinases or calmodulin were not via increased Ca2+, but instead
10 were attributable to intracellular Pb2+ concentrations. Evidence of Pb2+-induced inhibition of
11 neurite outgrowth is in general agreement with results seen after chronic exposure to Pb
12 employing in vivo models. Cline et al. (1996) employed an exposure protocol of
13 0.1 nM to 100 jiM nominal Pb2+ for 6 weeks localized to the retinotectal system of frog tadpoles;
14 they observed that the area and number of retinal ganglion cell axon arborizations within the
15 optic tectum was reduced at nanomolar Pb2+ concentrations. As discussed in Section 5.3.1.4,
16 Reuhl et al. (1989) exposed primates to 2 mg Pb/kg/day from infancy to 6 years of age and found
17 that neuronal volume density was reduced in primary visual area VI and in visual projection area
18 V2, compared to a group exposed to 25 jig Pb/kg/day. Moreover, a relative decrease in the
19 number of arborizations among pyramidal neurons in both areas VI and V2 was observed in the
20 higher-dose group. Thus, there was good correspondence between reports that acute Pb2+
21 exposure in vitro and extended exposure in animal models in vivo results in diminished neuronal
22 growth and differentiation at Pb levels of apparent environmental relevance. Studies employing
23 intact animals have not investigated specific cellular mechanisms underlying these effects.
24
2 5 Lead Exposure and Neural Stem Cells
26 Given considerable contemporary interest in the use of neural stem cells to treat various
27 neurological diseases, the efforts of Huang and Schneider (2004) to examine the actions of
28 exposure to Pb2+ in vitro on these cells is noteworthy. Pb exposure produced no effect on
29 neurosphere viability, but caused a significant dose-dependent inhibition of proliferation. In
30 addition, the number of neurons differentiated from Pb2+-exposed neurospheres was significantly
31 decreased versus control, as were the number of oligodendrocytes obtained. However, Pb
May 2006 5-62 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposure increased the number of astrocytes obtained. These observations suggest an important
2 Pb2+-induced influence on stem cell proliferation and differentiation.
3
4 Lead and the Blood-Brain Barrier
5 Early work demonstrated that the capillary epithelium in the brain is a target for Pb and
6 that Pb intoxication can disrupt the blood-brain barrier (BBB). Pb-exposed capillary endothelial
7 cells isolated from rat cerebral cortex showed deposits of Pb preferentially sequestered in
8 mitochondria, suggesting Pb-induced disruption of transepithelial transport of Ca2+ and other
9 ions. Furthermore, the developing CNS is especially sensitive to Pb-induced vascular damage.
10 Cerebral endothelial cells are known to accumulate Pb much more than other cell types and the
11 choroid plexus in both humans and animals accumulates much higher Pb concentrations than
12 other brain regions. However, these studies employed high exposure levels and, thus, are of
13 limited utility in evaluating the effects of environmentally relevant exposures.
14 Bradbury and Deane (1986) examined the rate of uptake of 203Pb into brain and other soft
15 tissues of the rat at constant radiotracer levels in plasma. Uptake of 203Pb in the brain was linear
16 up to 4 h, and the authors hypothesized that the capillary endothelium was the rate-limiting
17 component of Pb transport into the brain because of its relatively small area. The rate of uptake
18 in the brain contrasted with that into cisternal cerebrospinal fluid, which plateaued at -5% of that
19 of plasma at 1 to 2 h, and into the choroid plexus, in which Pb accumulated to -350% of plasma
20 levels at 4 h suggesting a 10-fold greater uptake. Bradbury et al. (1991) found that albumin
21 rarely enters the brain from blood, suggesting that Pb transport into brain is likely as free Pb2+ or
22 Pb in the form of inorganic complexes (e.g., PbOH+, PbHCC>3+, or PbCl+) or Pb bound to a low
23 molecular weight organic ligand (e.g., cysteine). Further work (Bradbury and Deane, 1993)
24 using short vascular perfusion of a cerebral hemisphere determined that 203Pb enters the brain
25 very quickly in the absence of an organic ligand but that transport is abolished in the presence of
26 albumin, L-cysteine, or EDTA. It was proposed that PbOH+ or some other simple organic Pb2+
27 complex passively enters the endothelium, and that the entry is mitigated by active back
28 transport of Pb2+ into blood by Ca-ATPase pumps.
29 To evaluate mechanisms by which Pb increases the permeability of the BBB, Dyatlov
30 et al. (1998a) dosed BALB/cByJ suckling male mice with 2.5 jig/g body weight of Pb acetate,
31 LPS (100 ng/g body weight), recombinant IL-6 (5 ng/ body weight), Pb + IL-6, or sodium
May 2006 5-63 DRAFT-DO NOT QUOTE OR CITE
-------
1 acetate + LPS. Following five injections over 10 days, they measured the transendothelial
2 electrical resistance across the BBB. Pb at this level alone had no effect, but did potentiate the
3 increases due to LPS. Pb plus IL-6 also caused a delay in the increase in arteriole resistance.
4 Thus, Pb potentiates the actions of both IL-6 and LPS. Glutamate topically applied to the
5 cerebrum caused a reversible decrease in resistance, whereas Pb caused this decrease to be
6 irreversible. The authors hypothesize that this disruption of the BBB allows glutamate to enter
7 the brain, further disrupting the BBB and irreversibly potentiating brain injury.
8 Pb also compromises the function of the barrier between the cerebrospinal fluid and
9 systemic circulation, allowing transfer between tight junctions of the choroid plexus. Zheng
10 et al. (1996) demonstrated that chronic Pb exposure (50 or 250 mg/ml in drinking water for 30,
11 60, or 90 days) reduced transthyretin levels in cerebrospinal fluid of male weanling rats in the
12 presence of PbB levels of 18.2 and 48.9 |ig/dL, respectively. Transthyretin, which is expressed
13 in early fetal development, is produced in the choroid plexus and is the major thyroid hormone
14 binding protein, allowing transfer of thyroxine from choroid plexus into cerebrospinal fluid. The
15 authors proposed that this Pb-induced reduction in transthyretin may be a factor in Pb-induced
16 alterations in brain development.
17 Thus, the BBB allows significant entry of Pb into both the adult and developing brain.
18 This transport is dependent on the chemical form of Pb, interactions of Pb with proteins and
19 other components of the blood, and other biochemical and physiologic factors that are not fully
20 defined.
21
22 Pb Binding Proteins and Tissue Uptake
23 Pb2+ appears to be taken up into cultured cells by multiple ion channel-based mechanisms,
24 including influx through channels activated by depletion of intracellular Ca2+ stores, non-L-type
25 Ca2+ channels, and NMDA receptor-associated channels (Kerper and Hinkle, 1997; Mazzolini
26 et al., 2001). Astroglia are well-known to act as Pb sinks and in culture and can accumulate up
27 to 24 times more of the metal than neuronal cells (Lindahl et al., 1999). There is also evidence
28 that glutathione may regulate Pb uptake into astroglia.
29 Histologic studies (e.g., Struzyriska et al., 1997) have demonstrated the transport of Pb
30 into the brains of chronically exposed adult animals. Weanling rats were dosed with 2 g/L lead
31 acetate in water for 3 months, creating PbB levels of 39 |ig/dL. Using horseradish peroxidase as
May 2006 5-64 DRAFT-DO NOT QUOTE OR CITE
-------
1 a tracer of vascular permeability, leaky microvessels were demonstrated by both light and
2 electron microscopy. Focal leakage of tracer was observed in the short segment wall of
3 microvessels, the surrounding neuropil, and regions of parenchyma near microvessels. Staining
4 was also evident in the cytoplasm of pericytes and on the basement membrane of endothelial
5 cells.
6 A few Pb-binding proteins have been identified in brain tissue. Generally, these are low
7 molecular weight, high binding affinity proteins rich in aspartic and glutamic dicarboxyl amino
8 acid residues and distinct from analogous proteins found in the kidney (Fowler, 1998). The
9 existence of a lead-binding protein in brain cytosol was reported by Goering et al. (1986) and
10 was invoked to explain the relatively weak inhibition by Pb2+ of brain AD AD activity. Two
11 cytosolic Pb-binding proteins were found in human brain tissue by Quintanilla-Vega et al.
12 (1995), one identified to be thymosin beta 4. Pb2+ also has been reported to bind to p32/6.3, a
13 low-abundance, highly conserved nuclear matrix protein that becomes a prominent component of
14 Pb-induced intranuclear inclusion bodies (Klann and Shelton, 1989). Expression of this protein
15 increases significantly during ontogeny and was proposed to be useful as an indicator of neuronal
16 maturation (Klann and Shelton, 1990). Expression also increases markedly in the presence of
17 acute Pb2+ exposure in vitro, suggesting that Pb2+ either structurally alters the protein or inhibits
18 a protease for which p32/6.3 is a substrate (Shelton et al., 1993).
19 Recently an astroglial glucose-regulated protein (GRP78) has been identified that acts as a
20 molecular chaperone in endoplasmic reticulum (Qian et al., 2000, 2005a). Intracellular levels of
21 this protein are increased in cultured astroglia during a 1-week exposure to Pb2+. GRP78
22 depletion significantly increased the sensitivity of cultured glioma cells to Pb2+, as indicated by
23 the generation of reactive oxygen species. This suggests that GRP78 is a component of the
24 intracellular tolerance mechanism that handles high intracellular Pb accumulation through a
25 direct interaction Thus, it appears that Pb2+ directly targets the protein and induces its
26 compartmentalized redistribution, enabling it to play a protective role in Pb neurotoxicity.
27 The generation of reactive oxygen species also has been reported to occur via Pb2+ binding to
28 astroglial copper-transporting ATPase, resulting in disruption of copper homeostasis (Qian et al.,
29 2005b).
May 2006 5-65 DRAFT-DO NOT QUOTE OR CITE
-------
1 Accumulation ofPb in Blood and Brain
2 Early animal studies often neglected to include blood Pb and concomitant tissue levels
3 achieved by the exposure protocols. The 1986 Pb AQCD was able to draw some limited
4 conclusions about the relationship of exposure levels to blood and brain Pb concentrations.
5 In general, at exposure concentrations of >0.2% Pb in drinking water and for exposure durations
6 extending beyond the birth to weaning period, the ratio of blood to brain Pb concentration is <1,
7 suggesting that even as blood Pb peaks and then falls due to excretion or removal, the high-
8 affinity binding of the metal to brain proteins promotes further accumulation in the brain.
9 The decline in blood Pb after exposure is terminated has been shown to depend on the
10 level and duration of exposure (O'Flaherty et al., 1982; Hryhorczuk et al., 1985). Widzowski
11 and Cory-Slechta (1994) exposed rat pups to various concentrations of Pb in the drinking water
12 from birth to weaning, and they found that PbB declined rapidly with a half-life of <20 days.
13 Wedeen (1992) reported a half-life of ~1 month in children, but Manton et al. (2000) found
14 half-lives of 10 to 38 months in young children, depending somewhat on duration of Pb exposure
15 from home remodeling. Because of the dependence of decreases in blood Pb concentrations on
16 exposure level and duration, estimates of half-life vary significantly from one exposure scenario
17 to another.
18 Using the same exposure protocol, Widzowski and Cory-Slechta (1994) measured brain
19 regional half-lives for Pb and found that these values averaged -20 days and did not vary
20 between brain regions. Because of binding to brain tissue proteins, Pb concentrations in brain
21 decline or respond to chelation more slowly than do blood Pb levels (Stangle et al., 2004).
22 Other studies describing chelation of Pb are included in Table AX5-3.5.
23
24 5.3.1.7 Susceptibility and Vulnerability Factors Modifying Pb Exposure and Thresholds
25 for CNS Effects
26 The effects of chronic Pb exposure may be modified by a number of physiologic variables
27 and exposure parameters that can significantly enhance or diminish the toxic response. These
28 susceptibility factors impact the toxic manifestations observed in the organism. A few of these
29 factors are considered below.
30
May 2006 5-66 DRAFT-DO NOT QUOTE OR CITE
-------
1 Aging
2 The neurotoxic effect of chronic exposure to low level Pb with advancing age is becoming
3 an important public health social issue (Yun et al., 2000a). Physiologic conditions associated
4 with bone resorption, e.g., pregnancy, lactation, and aging, can potentiate the CNS effects of Pb
5 and enhance exposure of adults. Such demineralization conditions can also add to the in utero
6 exposure of the fetus, and postmenopausal resorption can increase PbB levels in women by 25%
7 (Silbergeld, 1990).
8 Bone Pb levels serve as a marker of the burden of Pb in middle-aged and elderly men.
9 During the demineralization that occurs during aging, PbB levels increase and may lead to
10 declines in cognitive function (Weisskopf et al., 2004a,b; Payton et al., 1998). Supporting data
11 have been obtained from animal studies. Cory-Slechta (1990b) administered various amounts of
12 Pb for a constant duration beginning in young, adult, or old rats. An increased vulnerability to
13 Pb was observed in older animals due to increased exposure from an elevated resorption from
14 bone and an apparently greater sensitivity to the biochemical effects of the metal. Yun et al.
15 (2000b) have presented evidence suggesting that this increased vulnerability may also be due to
16 cerebral energy depletion in exposed animals. However, such findings have not been uniformly
17 observed. Rice and Hayward (1999) exposed monkeys to Pb chronically and tested temporal
18 visual function and contrast sensitivity at two different ages. Pb-exposed subjects exhibited
19 differences in temporal function at the first, but no the second assessment, and there was no sign
20 of accelerated decline in contrast sensitivity at either testing period. Thus, the deleterious
21 Pb-aging interactions would appear to be dependent on the CNS function under study.
22 Recent studies in rats have demonstrated the importance of Pb exposure during early
23 development in promoting the emergence of Alzheimer's-like changes in old age. Basha et al.
24 (2005) exposed rat offspring to Pb through the dam during the lactational period and monitored
25 gene expression of beta-amyloid precursor protein (APP). APP mRNA was induced in neonates,
26 and exhibited a delayed overexpression 20 months after exposure was terminated. At this point,
27 APP protein and its beta-amyloidogenic product were increased, and a rise in the activity of the
28 transcription factor Spl, one of the regulators of the APP gene, was also present. The changes
29 induced by early exposure to Pb could not be reproduced by exposure to the metal during
30 senescence. It was concluded that environmental influences occurring during brain development
31 predetermined the expression and regulation of APP later in life. Subsequent work observed the
May 2006 5-67 DRAFT-DO NOT QUOTE OR CITE
-------
1 same responses in monkeys who had been exposed to Pb as infants (Zawia and Basha, 2005),
2 arguing for both an environmental trigger and a developmental origin of Alzheimer's disease.
3
4 Gender
5 Relatively few animal studies have attempted a clear demonstration of gender differences
6 for toxic responses to chronic Pb exposure. For example, Donald et al. (1986) reported enhanced
7 social investigatory behavior in exposed mice that differed in time course between males and
8 females. A subsequent report (Donald et al., 1987) showed Pb-induced nonsocial activity
9 decreased in females, but increased in males and also caused shorter latencies to aggression in
10 males. Also, Yang et al. (2003) found a gender difference in rats in memory retrieval, wherein
11 higher doses of Pb affected memory in males than in females.
12 A significant functional impact of such gender differences has recently emerged. Cory-
13 Slechta et al. (2004) evaluated the effects of interactions of chronic Pb exposure and maternal
14 restraint stress on offspring. Corticosterone levels, neurotransmitter changes, and FI operant
15 behavior were measured in animals exposed only during gestational and lactational periods,
16 creating PbB levels of 30 to 40 |ig/dL. These workers found that synergistic effects of Pb and
17 stress were observed more frequently in female offspring, and that Pb with (in females) or
18 without (in males) stress permanently elevated corticosterone levels. It was proposed that these
19 findings uncovered a new mechanism by which exposure could enhance susceptibility to
20 diseases. Virgolini et al. (2005) used continuous Pb exposure in the drinking water to males
21 beginning at weaning, creating a maximal PbB of 27 |ig/dL, in combination with variable
22 intermittent stress challenges and found that Pb alone decreased basal plasma corticosterone
23 levels and glucocorticoid receptor binding. Novelty stress in combination with exposure was
24 found to modify FI behavior. These findings support the results of Cory-Slechta et al. (2004) in
25 suggesting the potential for hypothalamic-pituitary-adrenal axis-mediated effects of Pb on CNS
26 function.
27 Virgolini et al. (2006) extended this line of investigation by exposing rats to Pb prior to
28 breeding and continuing throughout gestation and lactation. The exposure created maximal PbB
29 levels of 33-43 |ig/dL at termination of exposure at weaning. Maternal restraint stress was
30 applied on gestational days 16 and 17 in some of the animals. Female offspring were then tested
31 for responsiveness to various stressors (i.e., restraint, novelty, cold) as measured by FI operant
May 2006 5-68 DRAFT-DO NOT QUOTE OR CITE
-------
1 performance. The combination of exposure and maternal stress produced more changes in
2 responsiveness than either factor alone: operant behavior was altered following both restraint and
3 cold, and the corticosterone response was modified by cold. It thusly appears that maternal Pb
4 exposure can permanently alter stress responsivity and does so with a profile of effects that differ
5 from those produced by exposure and maternal stress. These studies are also among the first to
6 make clear delineations of the effects of exposure across gender.
7
8 Developmental Period of Exposure
9 While early development is well-known to represent a period of particular sensitivity to
10 the neurotoxic effects of Pb, several studies have made comparisons to the CNS effects produced
11 by exposure encompassing later periods of development. There has been some consistency
12 across these behavioral, neurophysiologic, and neurochemical observations.
13 As discussed in Section 5.3.1.5, Rice and Gilbert (1990a) employed a nonspatial
14 discrimination reversal task in monkeys using form and colors as cues. The group continuously
15 exposed to Pb from birth exhibited the most impairment on this task, whereas the group exposed
16 continuously beginning at 300 days of age displayed impairment, but not as great as that of the
17 preceding group. Another group exposed to Pb from birth but discontinued at 400 days of age
18 did not exhibit an effect when tested as adults, suggesting that beginning Pb exposure after
19 infancy results in altered performance, while exposure also during infancy exacerbates the effect.
20 Rice (1990) later tested these same monkeys on a spatial discrimination reversal task and again
21 found that the group continuously exposed from birth exhibited the most impairment.
22 Rice (1992a) utilized the same exposure protocols, with PbB levels of 20 to 35 |ig/dL, and
23 tested monkeys on a multi FI-FR schedule of reinforcement at two different ages. Few effects
24 were seen during the first testing period at 3 years of age, but at 7 to 8 years of age increased
25 response run rates and decreased interresponse times in FI responding were evident in all three
26 exposed groups. These results indicated that exposure during infancy was not required for a Pb
27 effect on this task, and that exposure only during infancy was sufficient to produce alterations.
28 Gilbert et al. (1999b) used a model of synaptic plasticity, i.e., LTP in the hippocampal
29 dentate gyrus, to examine the effects of Pb exposure encompassing various developmental
30 periods in intact animals with maximal PbB levels of 35 to 40 |ig/d. Similar effects were seen in
31 groups continuously exposed from birth or continuously exposed from PND 30: the magnitude
May 2006 5-69 DRAFT-DO NOT QUOTE OR CITE
-------
1 of population spike LTP was diminished and the threshold for induction of the phenomenon was
2 elevated. A group exposed only during the lactational period displayed a diminished magnitude
3 of excitatory postsynaptic potential (EPSP) LTP also, but the threshold for EPSP slope LTP
4 induction was higher only in the group continuously exposed from birth. Thus, exposure
5 restricted to the lactational period was less disruptive to LTP in adult animals than exposure
6 beginning around birth or weaning.
7 Lasley et al. (1999) examined stimulated release of glutamate and GABA in the
8 hippocampus to evaluate the effects of developmental Pb exposure in intact animals with
9 maximal PbB levels of 39 to 45 |ig/dL. Similar decreases in Ca2+-dependent depolarization-
10 induced glutamate and GABA release were observed in groups continuously exposed from
11 conception or continuously exposed from PND 35. The pattern of changes induced in the group
12 continuously exposed from the beginning of gestation was similar to that observed previously in
13 a group continuously exposed from birth (Lasley and Gilbert, 1996), indicating that gestational
14 exposure did not further enhance the impact of Pb beginning at birth when exposure in both
15 groups extended into adulthood. The changes found in the group continuously exposed
16 beginning in the early postweaning period demonstrated that exposure during early development
17 is not required to produce changes in glutamate and GABA release. Reductions in stimulated
18 release were also observed in a group exposed only during the gestational and lactational
19 periods, indicating that Pb limited to early development is also sufficient to produce deficits in
20 evoked transmitter release.
21 Altmann et al. (1993) also examined synaptic plasticity and learning in rats chronically
22 exposed during early development, producing maximal PbB levels of 14 to 16 |ig/dL, but the
23 results were in contrast to the others cited in this section. These workers found impaired LTP
24 and AAL in groups continually exposed from the beginning of gestation, even if Pb was
25 terminated in the early developmental period. Another group whose exposure began just prior to
26 weaning did not display any Pb-related differences from controls.
27 These studies indicate that continuous exposure begun pre- or perinatally consistently
28 results in a Pb effect as great as or greater than that produced by exposure over any other
29 developmental period. Continuous exposure begun postweaning also is consistently potent in
30 producing alterations, but whether the magnitude of the effect is similar to that of the preceding
May 2006 5-70 DRAFT-DO NOT QUOTE OR CITE
-------
1 group, and whether exposure limited to the gestational and/or lactational period elicits an effect,
2 appear to be task- or process-dependent.
3
4 Nutrition
5 It has long been known that diets sufficiently high in minerals such as zinc, iron, and
6 calcium offer some protection from Pb exposure by competing with Pb2+ for absorption from the
7 gastrointestinal tract. A full discussion of gastrointestinal absorption in humans is found in
8 Chapter 4, and information on absorption in animals is contained in Section 5.10.2. In fact, this
9 dietary influence may comprise one component of the socioeconomic status (SES) factor
10 repeatedly identified as important in studies of Pb neurotoxicity in children, as maternal dietary
11 habits influence risk of exposure in infants. More recent studies have shown that vitamin D
12 administration can reduce blood and bone Pb values (Cheng et al., 1998; Cortina-Ramirez et al.,
13 2006), but whether this occurs as a result of increased Ca2+ uptake has not been determined.
14 Diets designed to reduce caloric intake and increase weight loss have also been associated with
15 increases in blood Pb values (Han et al., 1999).
16
17 Thresholds for CNS Effects
18 There is no evidence in the animal Pb neurotoxicity literature reflecting well- defined
19 thresholds for any of the toxic mechanisms of the metal. Most studies performed with in vivo
20 models report PbB values in the range of 15 to 35-40 |ig/dL or higher. Moreover, in view of the
21 complex and undefined speciation equilibria and distribution of Pb2+ in physiological milieus,
22 there is no way to directly relate a blood Pb value to the levels of free Pb2+ ion or to any other
23 complexed active form of the metal, either in extracellular or intracellular fluids. Generally
24 accepted estimates of the free Pb2+ ion concentrations produced in brain extracellular fluid by
25 environmentally relevant exposures fall in the low nanomolar range.
26 Nonetheless, changes induced by chronic Pb exposure have been reported on
27 neurochemical (e.g., Cory-Slechta et al., 1997b) and neurophysiologic (e.g., Altmann et al.,
28 1993) measures at blood Pb values of-15 |ig/dL. Recent studies have reported behavioral
29 changes at blood Pb concentrations of-10 |ig/dL (Brockel and Cory-Slechta, 1998; 1999a,b),
30 and the results on measures of attention have closely paralleled those observed in children at the
May 2006 5-71 DRAFT-DO NOT QUOTE OR CITE
-------
1 same blood Pb levels. These observations serve to validate the accuracy and usefulness of the
2 animal exposure models.
3
4 5.3.1.8 Summary
5 • Pb2+-Ca2+ interactions resulting from exposure; e.g., the Ca 2+-mimetic properties of Pb2+
6 are important components of the cellular toxicity of the metal, and are closely related to the
7 dose-dependent effects of exposure on neurotransmitter release. Some of these actions of
8 Pb2+are shown in Figure 5-3.3.
9 • Exposure-induced decreases in glutamatergic, cholinergic, and dopaminergic transmission
10 are important because of the purported role of these neuronal systems in brain development
11 and cognitive function.
12 • The majority of the data suggests an upregulation of NMD A receptors resulting from chronic
13 exposure, but a consensus on the effects of Pb on NMD A receptor subunit expression and
14 function remains to be attained. It is increasingly apparent that this glutamate receptor
15 subtype may not be a direct primary target of chronic exposure in the intact animal.
16 • In vitro interactions of Pb2+ and PKC have been carefully described and are broadly relevant
17 to cellular signaling pathways, but functional effects of these interactions in intact animals
18 have not been achieved.
19 • Using hippocampal models of synaptic plasticity, it has been demonstrated that Pb exposure
20 decreases the magnitude of LTP and increases the threshold for induction with a biphasic
21 dose-effect relationship, another indication of the nonlinear effects of Pb.
22 • Decreases in stimulated glutamate release are a significant factor contributing to Pb-induced
23 changes in LTP.
24 • Lead induces decreased activity of dopaminergic cells in substantia nigra and ventral
25 tegmental area and inhibits activation of nicotinic currents in cultured hippocampal cells.
26 • Evidence from nonhuman primate studies demonstrates convincingly that Pb exposure
27 producing PbB values as low as 33 |ig/dL impairs auditory function by increasing latencies
28 in brainstem auditory evoked potentials and elevating hearing thresholds.
29 • It has been shown that Pb exhibits selective effects on rod and bipolar cells in rats at a PbB of
30 19 |ig/dL, causing decreases in maximal ERG amplitude, decreases in ERG sensitivity, and
31 increases in mean ERG latency.
32 • Mechanisms for Pb-induced deficits in visual function include concentration-dependent
33 inhibition of cGMP phosphodiesterase, increased rod Ca2+ levels, decreased retinal Na-
34 K-ATPase activity, and apoptotic death of rod cells.
May 2006 5-72 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Developmental exposure to Pb, creating steady state PbB levels of-10 |ig/dL, results in
2 behavioral impairments that persist into adulthood in monkeys. There is no evidence of a
3 threshold and Pb-induced deficits are, for the most part, irreversible.
4 • In monkeys, permanent neurobehavioral deficits are observed both with in utero-only
5 exposure and with early postnatal-only exposure when peak PbB levels did not exceed
6 15 |ig/dL and steady state levels were ~1 l|ig/dL. Exposure started at -300 of age creates
7 deficits similar to those created with exposure from birth onward. In rats, permanent deficits
8 are observed with prenatal, preweaning, and postweaning exposure.
9 • The developmental period of exposure is critical to the type of behavioral deficit produced.
10 • Lead affects the performance on a number of neurobehavioral tasks by inducing (1) reduced
11 ability to inhibit inappropriate responding, (2) distractibility, (3) reduced ability to adapt to
12 changes in behavioral contingencies and, (4) perseveration.
13 • Response perseveration, insensitivity to changes in reinforcement density or contingencies,
14 and deficits in attention appear to be important mechanisms of Pb-induced learning deficits.
15 Impulsivity and waiting-for-reward behavior may be more strongly affected by Pb than are
16 sustained attention and hyperkinesis. Pb-induced impulsivity may be factor in cognitive
17 impairments.
18 • Pb impairs learning at PbB levels as low as 11 |ig/dL as tested in FI tasks. Performance on
19 spatial and nonspatial discrimination reversal tasks is affected following developmental
20 exposures in nonhuman primates. Distracting irrelevant stimuli potentiate these impairments.
21 Pb also impairs performance on olfactory reversal tasks in rats. Discrimination reversal
22 appears to be a more sensitive indicator of Pb-induced learning impairment than simple
23 discrimination. Repeated-acquisition tests show that these deficits are unlikely to be caused
24 by sensory or motor impairment.
25 • The effects of lead on memory are not as clear-cut: in some cases, the animals showed
26 impairment of memory at PbB levels of as low as 10 |ig/dL while in other studies animals
27 demonstrated improved memory following Pb exposure. Short-term memory does not
28 appear to be affected by low level Pb exposure. Some behavioral deficits in tests of working
29 memory (e.g., DSA) appear to result from impaired attention rather than memory.
30 • Lead has been demonstrated to affect reactivity to environment and social behavior in both
31 rodents and nonhuman primates at exposure levels of 15-40 |ig/dL.
32 • Other test paradigms such as drug discrimination and repeated acquisition/performance tasks
33 have provided useful assessments of the integrity of CNS neurotransmitter systems in Pb
34 exposed animals. Evidence from both methods has been in general agreement in indicating
35 upregulated neurotransmitter receptor systems.
36 • Pb has been shown to decrease cell proliferation in vivo at 20 |ig/dL and to decrease
37 proliferation, differentiation, and neurite outgrowth in vitro.
May 2006 5-73 DRAFT-DO NOT QUOTE OR CITE
-------
1 • In both the adult and developing brain, the BBB allows entry of Pb into the brain. Entry is
2 dependent upon the chemical form of the Pb and interactions with proteins and other
3 components of blood.
4 • Pb-binding proteins, including the recently identified glucose-regulated protein, modulate the
5 effects of Pb in brain and can exert a protective effect by sequestering Pb.
6 • The rate at which Pb accumulates in the brain depends upon the level and duration of
7 exposure. The half-life of Pb in brain tissue is-20 days in rats.
8 • Susceptibility and vulnerability factors that modify responses to lead include (1) age,
9 (2) gender, (3) socioeconomic status, (4) period of exposure, and (5) nutrition.
10 • A well-defined threshold for any toxic effects in animals has not been identified.
11 Neurochemical and neurophysiologic effects have been seen at PbB values of-15 |ig/dL and
12 neurocognitive effects have been observed at -10 |ig/dL.
13
14 5.3.2 Neurotoxicological/Neurobehavioral Effects of Lead in Humans
15 This section is divided into three subsections, based upon age and exposure scenarios.
16 The subsections include (1) children with blood lead levels above and below 10 |ig/dL, (2) adult
17 manifestations of neurotoxicity and other disease states as a result of excessive exposure to lead
18 as children, (3) adults who were exposed to ambient levels of lead. Discussions of biomarkers of
19 Pb exposure in these groups are presented in Chapter 4 and discussions of the epidemiology
20 studies of these groups are presented in Chapter 6.
21 In each of these subsections, the neurotoxic effects are discussed as an introduction to the
22 epidemiology studies in the following chapter. For children and adults, other aspects of
23 vulnerability are considered, such as SES, nutrition, and genetic polymorphisms. Based this
24 information, conclusions are drawn in Chapter 7 relating to dose-response paradigms and clinical
25 extensions of epidemiologic data to individual children and groups of children exposed to point
26 sources of lead.
27 5.3.2.1 Effects of Lead in Young Children to Mid-Adolescence
28 Since EPA's publication of the Pb AQCD in 1986 and Supplement in 1990, major studies
29 with new and critical information have substantially extended previous hypotheses expressed by
30 the EPA. These new data are the primary and major departure from EPA's earlier lead criteria
31 reviews. It is now recognized that lead has adverse effects on the developing central nervous
May 2006 5-74 DRAFT-DO NOT QUOTE OR CITE
-------
1 system of young children at blood lead levels below and above 10 |ig/dL and that these effects
2 on cognition and behavior persist (at least) into the school-aged years and beyond into
3 mid-adolescence. This new information causally links detrimental effects of lead to behavior
4 and cognition at PbB levels both above and below 10 |ig/dL. Compared to the earlier EPA
5 documents, there is solid evidence, presented in Chapter 6, for detrimental effects of lead on
6 neuropsychologic functions such as fine motor skills, visual-spatial-constructional skills,
7 executive functioning, and attention in large groups of children. Apparently, there is no
8 threshold below which lead is without adverse effects on the CNS of young children to
9 mid-adolescence.
10
11 Vulnerability and Susceptibility
12 The unique susceptibility of children to the adverse health effects of lead was recognized
13 previously by EPA in 1986-1990. Some of these aspects included the specific behaviors of
14 children (including their metabolism of lead), physiologic considerations that separate children
15 from adults, greater potential absorption of lead per square meter of body surface, hand-to-mouth
16 activity, and prevalence of nutritional factors that can enhance the absorption of lead from the
17 GI tract.
18 Since 1986-1990, an enlarged database is now available to construct a somewhat wider
19 approach to understanding not only new information relating to children's susceptibility, but also
20 further characterizing interindividual variability as related to manifestations of lead's adverse
21 health effects in children. This section includes topics of developmental toxicology, growth and
22 development, economic status, nutritional aspects of lead and children, and, finally, genetic
23 considerations of children with the possibility of biologically based genetic polymorphisms
24 interacting with environmental lead exposures. Considerations in this section also delve into risk
25 assessment focused on some child-specific factors related to health outcomes in specific
26 populations of children as well as individual children.
27 Moreover, as a general principle of toxicology and neurotoxicology, it is recognized that a
28 variety of factors can either enhance or decrease the sensitivity of individuals or populations to
29 toxic exposures of lead. Besides individual children, there are factors that modify the selective
30 neurotoxic responses of subgroups of children. Some of these variables that increase a child's
31 vulnerability are discussed below.
May 2006 5-75 DRAFT-DO NOT QUOTE OR CITE
-------
1 Developmental Toxicology
2 In addition to child-specific factors detailed above, it was concluded previously that the
3 critical window of adverse health effects of lead in children was at less than 3 years of age
4 (Bellinger et al., 1991, 1992). Blood lead levels at 2 years of age were correlated with cognitive
5 impairments at 57 months and 10 years of age. However, as discussed in Section 6.2, the age
6 range for time windows for lead's adverse effects on the CNS has been significantly extended to
7 school-aged children, into adolescence, and into adulthood (Dietrich et al., 1993; long et al.,
8 1996; Wasserman et al., 2000; Canfield et al., 2003, 2004; Chen et al., 2005; Lanphear et al.,
9 2000, 2005; Ris et al., 2004; Dietrich et al., 2004; Rice and Barone, 2000).
10 Developmental exposures to toxicants can result in adverse health effects prenatally,
11 postnatally, in childhood, into school-aged years, and into adult age groups to the elderly
12 (Selevan et al, 2000; Weiss, 2000; Rice and Barone, 2000). An important concept in risk
13 management is to identify, whenever possible, developmental windows for evaluating dose-
14 response relationships. Moreover, in risk management, identification of critical windows is
15 aimed at recognizing especially susceptible subgroups within the general population to provide
16 specific interventions (Selevan et al., 2000). Information on critical windows of development is
17 needed to assess real and potential environmental health risks (Weiss, 2000).
18 In development of the CNS, unidirectional inhibition at one developmental stage can
19 cause substantial alterations in subsequent processes. In addition, stages of development occur
20 in temporally distinct time frames across regions of the brain (Rice and Barone, 2000; Weiss,
21 2000). As a result, the CNS has a very limited capability to compensate for cell loss or other
22 injury (Rice and Barone, 2000). Thus, exposure criteria should be based on information relevant
23 to predicting risks and to accounting for toxicokinetic differences that occur during different
24 stages of development (Faustman et al., 2000).
25 Recapitulation of synaptogenesis in the form of synaptic plasticity is modified by
26 experience and the environment as children become adults and age into the elderly life phase
27 (Rice and Barone, 2000). This concept provides a toxicological framework for identifying latent
28 or persistent expressions of childhood lead exposure in adults as "growing into a lesion" (Ris
29 et al., 2004) or magnification of an earlier insult with aging (Rice and Barone, 2000). This
30 toxicological recognition of latent or persistent expressions of childhood exposure in adults
31 forms the basis of Section 5.3.2.2, discussed below. Additional areas of concern for children
May 2006 5-76 DRAFT-DO NOT QUOTE OR CITE
-------
1 related to risk assessment include consideration of lead's deleterious effects on somatic growth,
2 SES, nutritional correlates of lead exposure and interactions between biologically inherent
3 genetic polymorphisms and the external environment (discussed below).
4
5 Growth and Development
6 In the Supplement to the 1986 Addendum, early results from prospective studies in
7 Cincinnati, Boston, Port Pirie, and Yugoslavia were noted in terms of lead's effects on perinatal
8 and postnatal growth and development. However, evidence regarding physical growth effects
9 related to prenatal or early postnatal exposure was inconsistent. Limitations in these early data
10 from prospective studies included definitions of the length of gestation, racial makeup, maternal
11 age, sample sizes, and levels of lead exposure. It appeared likely that prenatal lead exposure did
12 pose a potential hazard to the developing fetus as related to reduced gestational length and
13 possibly other aspects of fetal growth. It proved difficult, however, to define a definite dose-
14 response relationship for fetal outcomes, although there were some indications that pointed to
15 adverse effects on the fetus at PbB levels of 10 to 15 |ig/dL.
16 More recently reported data presented in Chapter 6 have extended assessments of impacts
17 of lead on early postnatal outcomes (birth weight, early weight gain to 1-month of age, birth
18 length and head circumference) to measurements of maternal bone lead post-delivery by K-XRF.
19
20 Socioeconomic Status (Including Demographic Considerations)
21 In the U.S. EPA's Supplement to the 1986 addendum, very little information was
22 discussed relating to socioeconomic status (SES) and the vulnerability of children to lead
23 exposure and resulting deficits in cognitive skills. Primarily as a result of analyses of NHANES
24 III, the importance of SES has reached its appropriate focus and attention. Additional peer-
25 reviewed articles have also contributed to now well-documented interactions between SES and
26 children's vulnerabilities to the neurotoxic effects of lead.
27 A child's SES clearly has an important influence on the possibility of lead exposure in
28 young children. Disadvantaged children may have an already compromised neuropsychological
29 status that is further impaired by the toxic effects of lead. Although the exact mechanisms of the
30 impact of SES on lead's neurotoxic effects on the CNS are unknown, poverty, pre-1960 housing
31 in segregated communities, ethnicity, and nutritional deficiencies, collectively, can contribute
May 2006 5-77 DRAFT-DO NOT QUOTE OR CITE
-------
1 substantially to increased vulnerability of individual children and subgroups of children. The
2 peer-reviewed literature, discussed in Chapter 6, provides support for these conditions
3 contributing to children's susceptibility to the toxic effects of lead. Based upon the studies
4 discussed above, there is conclusive evidence that SES has a profound influence on children's
5 vulnerability and susceptibility to the neurotoxic effects of lead exposure.
6
7 Nutrition
8 There was little discussion of nutritional factors and their impacts on children's
9 vulnerability to lead in earlier EPA documents, because very little, if any, information was
10 available at that time. It has become evident that the dangers of lead exposure in children are
11 substantially enhanced by diet deficient in calcium, iron, zinc and other essential nutrients;
12 specific dietary deficiencies are not infrequently coupled to increased susceptibility to lead in
13 low SES children.
14
15 Genetic Polymorphisms
16 A paucity of information was previously available regarding genetic polymorphisms and
17 lead toxicity in EPA's documents in the time frame of 1986 to 1990. Since that time, at least
18 three genes have been identified that may affect the accumulation and toxicokinetics of lead in
19 children and adults. The three genes are aminolevulinic acid dehydratase (ALAD) , the vitamin
20 D receptor gene (VDR), and the hemochromatosis gene (HFE). Relatively few studies relating
21 to genetic polymorphisms have been reported in children compared to a substantial body of
22 clinical research studies reported especially in excessively exposed adults. ALAD, VDR, and
23 HFE are discussed here in detail to serve as an introduction for clinical research reports in adults.
24 The primary importance of incorporating a discussion of genetic polymorphisms in the
25 field of environmental health is their usefulness in detecting differences in levels of risk within
26 specific populations (Kelada et al, 2003). The range of responses to toxic environmental
27 exposures can vary, and population attributable risk may be substantial. Furthermore,
28 understanding the possible role of genetic polymorphisms in risk assessment can lead to an
29 enhanced delineation of mechanisms underlying toxic exposures.
30 The ALAD gene (chromosome 9q34) encodes for ALAD, which catalyzes the second step
31 of heme synthesis and is polymorphic (the heme synthesis pathway is discussed in detail in
May 2006 5-78 DRAFT-DO NOT QUOTE OR CITE
-------
1 Section 5.2). This polymorphism yields two codominant alleles, ALAD-1 and ALAD-2, and
2 these have been differentially implicated in some clinical research studies to lead toxicity
3 (Kelada et al., 2001). It is evident that genotypic frequencies differ by ethnicity and geography;
4 and these considerations require careful assessment in the interpretation of research results.
5 It has been suggested in some studies that ALAD-2 may possibly offer some level of
6 "resistance" to the toxic effects of lead by generating a protein that avidly binds to lead, perhaps
7 sequestering lead from its toxic expressions at various tissue sites. Other studies suggest that the
8 rarer ALAD-2 allele has been associated with higher blood lead levels and may, thereby increase
9 the risk of lead toxicity by producing a protein that binds more tightly than the ALAD-1 protein.
10 Some recent studies in adults, discussed in Chapter 6, have reported that individuals homozygous
11 for the ALAD-1 allele have higher cortical bone lead concentrations and may be at higher risk
12 for long-term adverse effects of lead. Occupationally exposed adults have been most frequently
13 studied in terms of the possible interaction of ALAD polymorphism and adverse health
14 outcomes. Reports in children concerning ALAD polymorphism and risk assessment are limited.
15 A group of 142 lead-poisoned children (mean PbB: 27.1 |ig/dL; SD: 15.2) were studied
16 in New York City. Children who expressed the 2-2 or 1-2 isozyme phenotype were reported to
17 have blood lead levels 9 to 11 |ig/dL higher than children who were homozygous for the
18 ALAD-1 allele (Wetmur et al., 1991). These authors suggested the possibility that, because the
19 ALAD-2 polypeptide binds lead more effectively, these individuals may be more susceptible to
20 lead poisoning. At the time of publication, the lead binding properties of purified ALADl-1 and
21 2-2 proteins and tissue distribution of these alleles were unknown.
22 The relationship was investigated between ALAD isozymes and blood lead levels in
23 229 Chinese children within the age range of 6 to 10 years old (Shen et al., 2001). The mean
24 blood lead value was 10.3 |ig/dL (SD: 3.3) and for the 92% of children homozygous for
25 ALAD-1, the mean blood lead was 9.7 |ig/dL compared with the 8% of children who were
26 heterozygous (ALAD-1-2) and who had a mean blood lead level of 11.7 |ig/dL (p < 0.05). Using
27 step-wise multiple regression, children who had the ALAD-2 allele were shown to be more
28 likely to have higher blood lead concentrations compared to children who had the ALAD-1
29 allele.
30 As discussed in Chapter 6, in the only published article to date, environmental samples,
31 blood lead levels, and nutritional factors were assessed together with determinations of
May 2006 5-79 DRAFT-DO NOT QUOTE OR CITE
-------
1 VDR-Fokl genotype (Haynes et al., 2003). A significant interaction was found between dust
2 lead, such that at a 1 |ig/ft2 increase in floor dust lead, in children with VDR-FF genotype, led to
3 a 1.1% increase in blood lead; VDR-Ff, a 0.53% increase; and VDR-ff; a 3.8% increase.
4 At floor dust levels less than 10 |ig/ft2, children with VDR-ff had the lowest blood lead
5 concentrations. It is noteworthy that only 17 children in this study were homozygous for the ff
6 allele. Nonetheless, the authors suggested that VDR-Fokl is an effect modifier for the
7 relationship of floor dust lead exposure and blood lead concentrations. The implications for risk
8 assessment and health significance in these three pediatric studies are limited. Far more detailed
9 studies in this area of investigation are needed before any firm conclusions can be reached.
10 The vitamin D receptor (VDR) is a ligand-activated transcription factor that modulates the
11 genomic effects of the vitamin D hormone, 1,25-dihydroxyvitamin D, in a wide variety of
12 tissues. The gene encoding for VDR is on chromosome 12q and has common allelic variants
13 (Zmuda et al., 2000). The allelic variants and their haplotypes have been extensively studied
14 with regard to osteoporosis susceptibility. Studies involving other disease states, such as breast
15 and prostate cancer, diabetes, coronary artery disease, and primary hyperparathyroidism, have
16 also focused on the role(s) of VDR gene variants. Consideration of VDR gene variants have also
17 been extended to populations with increased lead exposure, particularly within an occupational
18 setting. Very little information is available on these gene variants and lead exposure in the
19 pediatric age group.
20 Hereditary hemochromatosis (HHC) is an autosomal recessive disorder of iron
21 metabolism characterized by an increase in iron absorption and deposition in the liver, heart,
22 pancreas, joints, and pituitary gland. FIFE, the gene for HHC, has been mapped to the short arm
23 of chromosome 6 (Hanson et al., 2001). Two of the 37 allelic variants of HFE described to date,
24 C282Y and H63D, have been significantly correlated with HHC. Homozygosity for the C282Y
25 mutation has been found in the majority of patients and their probands diagnosed with HHC.
26 Implications of HFE polymorphism have been proposed in studies of adults excessively exposed
27 to lead, particularly in occupational settings. No studies of HFE have been reported in children
28 with varying blood lead concentrations.
29 As yet, studies have failed to evaluate arylsulfatase (ASA) polymorphisms in lead
30 exposed children and adults. ASA is recognized as playing a significant role in regions of the
31 brain known to be affected by lead, and it has been established in experimental studies that lead
May 2006 5-80 DRAFT-DO NOT QUOTE OR CITE
-------
1 produces low levels of ASA at sensitive stages of nervous system development (Poretz et al.,
2 2000). Studies of ASA in children and adults may yield important information that may explain
3 some of the neurocognitve effects of lead in pediatric and adult populations. As yet, no studies
4 of this nature are available.
5
6 5.3.2.2 Clinical Manifestations in Adults with Childhood Lead Poisoning
7 It is reasonable to conclude from the studies discussed in Chapter 6 that clinical
8 manifestations become manifest in adults as persistent or latent consequences of earlier
9 childhood lead poisoning. Specific effects include impairments in cognitive abilities that directly
10 involve the central nervous system (White et al., 1993). These data have been applied to
11 cognitive outcomes (White et al., 1993) and mortality rates in adults following severe childhood
12 lead poisoning (McDonald and Potter, 1996). Data from these analyses also indicate the
13 presence of long-term latent and/or persistent effects on blood pressure in adults several decades
14 after severe childhood lead poisoning (Hu, 1991). These data have been extended to more recent
15 studies of lead's impacts on adults from early excessive childhood exposure, in terms of adverse
16 health impacts on the central and peripheral nervous systems. With current analytical
17 techniques, these data have been applied and connected to bone lead concentrations, as well as to
18 the development of hypertension (Stokes et al., 1998; Gerr et al., 2002).
19 Based on studies presented in the following chapter, it is reasonable to conclude that
20 excessive accumulation of lead in childhood has latent and/or persistent adverse health effects on
21 both the peripheral and central nervous systems of adults assessed 19 to 29 years later.
22 Information is needed in less severely exposed children followed longitudinally into adolescence
23 and the adult age group.
24
25 5.3.2.3 Adults with Ambient Exposures to Lead
26 In the previous 1986 AQCD/Addendum, the focus was on adverse health effects in adults
27 at PbB levels in the range of 30 to 50 |ig/dL. The studies reviewed focused on slowed nerve
28 conduction velocities, altered testicular function, reduced Hg production, and other signs of
29 impaired heme synthesis evident at somewhat lower blood lead levels. These effects pointed to a
30 generalized impairment of normal physiologic functioning as adult PbB levels exceeded 30 to
31 40 |ig/dL. The lowest observed effect levels of 15 to 30 |ig/dL were related to impairments in
May 2006 5-81 DRAFT-DO NOT QUOTE OR CITE
-------
1 heme synthesis. In contrast, in the 1990 Supplement to the 1986 Addendum, it was concluded
2 that the relationship between lead and blood pressure held across a wide range of blood lead
3 values, possibly extending down to 7 |ig/dL for middle-aged men. In brief, except for effects of
4 lead on heme synthesis down to adult blood lead values of about 15 |ig/dL, the emphasis was on
5 adverse health effects in the 30- to 40- to 50-jig/dL blood lead range.
6 Since that time, studies have shown lead's effects in terms of biomarkers and indices of
7 vulnerability and susceptibility in adult populations with blood lead concentrations, on average,
8 less than 10 |ig/dL. These studies are discussed in Chapter 6.
9
10 Summary
11 • Pb has adverse effects on the developing CNS of young children at PbB levels below
12 -10 |ig/dL. These effects on cognition and behavior persist (at least) into the school-aged
13 years and beyond into mid-adolescence.
14 • The unique susceptibility of children to the adverse health effects of lead were recognized
15 previously and include their metabolism of lead, physiological considerations that separate
16 children from adults, greater potential absorption of lead per square meter of body surface,
17 hand-to-mouth activity, and prevalence of nutritional factors that can enhance the absorption
18 of lead from the GI tract.
19 • There are well-documented interactions between SES and children's vulnerability to the
20 neurotoxic effects of lead. Low-income families are found to be at substantially elevated risk
21 for having children with PbB levels above 5 |ig/dL, and the odds ratios in these families were
22 the highest when comparing the 10 to 20 |ig/dL group to those children with blood leads
23 <5 |ig/dL.
24
25
26 5.4 REPRODUCTIVE AND DEVELOPMENTAL EFFECTS OF LEAD
27 5.4.1 Summary of Key Findings on the Developmental and Reproductive
28 Effects of Lead in Animals from the 1986 Lead AQCD
29 The 1986 Pb AQCD presented unequivocal evidence for effects of Pb on reproduction and
30 development in laboratory animals, derived principally from studies of rodents. Fetotoxic effects
31 (spontaneous abortion and fetal death) were reported following chronic exposures to relatively
32 high doses (600 to 800 ppm) of inorganic lead in the diet, and more subtle effects (such as
33 changes in ALAD activity or hematocrit in offspring) at lower doses (5 to 10 ppm in drinking
May 2006 5-82 DRAFT-DO NOT QUOTE OR CITE
-------
1 water and 10 |ig/m3 in air). The 1986 Pb AQCD reported that the lowest observed adverse effect
2 level (LOAEL) for reproductive and developmental effects was 64 ng/kg per day (multiple
3 exposures by gavage).
4 The 1986 Pb AQCD also reported evidence for a variety of sublethal effects on
5 reproduction and development in experimental laboratory animals following Pb exposure.
6 Sublethal effects included changes in levels or function of reproductive hormones as well as
7 effects on the gonads (both male and female) and conception. The animal data also suggested
8 more subtle effects on hormone metabolism and reproductive cell structure. Stowe and Goyer
9 (1971) classified the reproductive effects of Pb as gametotoxic, whether intrauterine or
10 extrauterine.
11 The data reported in the 1986 Pb AQCD, and more recent studies conducted in
12 experimental animal models, provide convincing evidence that Pb induces temporary and long-
13 lasting effects on male and female reproductive and developmental function. The newer
14 literature supports the earlier conclusions presented in the 1986 Pb AQCD that Pb disrupts
15 endocrine function at multiple points along the hypothalamic-pituitary-gonad axis (Sokol et al.,
16 1985; Stowe and Goyer, 1971; Vermande-Van Eck and Meigs, 1960; Junaid et al., 1997;
17 McGivern at al., 1991; Ronis et al., 1996, 1998b,c; Sokol, 1987; Sokol et al., 1985, 1994, 1998;
18 Sokol and Berman, 1991; Kempinas at al., 1988, 1990, 1994; Tchernitchin et al., 1998b; Sant'
19 Ana et al., 2001; Srivastava et al., 2004). A schematic representation of the hypothalamic-
20 pituitary-gonadal (HPG) axis is shown in Figure 5-4.1.
21 The majority of the experimental animal studies on developmental and reproductive
22 effects of Pb examined effects due to inorganic forms of lead; very little is known about the
23 reproductive and developmental effects due to organic forms. In general, the few available
24 studies suggest that effects of organic forms of Pb are similar to those produced by inorganic
25 forms. Administration of triethyl-Pb-chloride during early gestation reduces pregnancy rates in
26 mice (Odenbro and Kihlstrom, 1977). Growth retardation following organolead exposure has
27 been reported (Kennedy et al., 1975; McClain and Becker, 1972). More recent studies have
28 demonstrated that exposure of mice to triethyl-Pb-chloride during late gestation reduces perinatal
29 growth rate (Odenbro et al., 1988).
30 This section summarizes the evidence for effects of Pb exposure in developing organisms
31 exposed during the period from conception to maturity that has been reported since 1986.
May 2006 5-83 DRAFT-DO NOT QUOTE OR CITE
-------
Testosterone or
Estradiol
Figure 5-4.1. Data from male and female experimental animals suggests that Pb
has multiple targets in the hypothalmic-pituitary-gonadal axis.
1 Effects on neurological, immunological, or renal endpoints in developing organisms are
2 discussed in Sections 5.3, 5.9 and 5.7, respectively.
3
4 5.4.2 Effects on Male Reproductive Function
5 The 1986 Pb AQCD reported convincing evidence based on experimental animal studies
6 that Pb acts as an endocrine disrupter in males. Those studies demonstrated an association
7 between reduced male fertility and repeat-dose Pb exposure. Lead exposure had been reported to
8 alter sperm development and function; however, the mechanism underlying these effects was not
9 completely understood. These effects were attributed to either alterations in testicular enzymes
10 important for hormone production or to changes in the hormone receptors. More recent research
11 supports the conclusion that mechanisms for endocrine disruption in males involve lead acting at
12 multiple sites along the hypothalamic-pituitary-gonadal axis (see Figure 5-4.1).
13 Reported effects of Pb on male reproduction differ substantially across studies, with some
14 studies finding severe adverse effects and other studies finding no or minimal effects. The
15 variable findings have been attributed to the complex mechanisms involved in hormone
16 regulation and the multiple sites of action for lead. Sokol et al. (2002) suggested that differences
May 2006
5-84
DRAFT-DO NOT QUOTE OR CITE
-------
1 in results among studies may be, in part, attributed to an adaptive mechanism in the
2 hypothalamic-pituitary-gonadal axis that may render the expression of some toxic effects
3 dependent on dose and exposure duration. The mechanisms underlying this possible adaptation
4 have not been completely elucidated. Lead exposure produces, a dose (PbB)-related suppression
5 of serum testosterone levels and spermatogenesis, with an increase in GnRH mRNA in
6 hypothalamus (at PbB<50). The latter effect is attenuated at higher exposures (>50 |ig/dL) and
7 with increasing exposure duration (Sokol et al., 2002). Sokol and Berman (1991) found that
8 timing of exposure was critical to Pb-induced male reproductive toxicity in rats. Studies
9 conducted in nonhuman primates supported the importance of timing, found that the adverse
10 effects of Pb on male reproduction are dependent upon age (i.e., developmental stage at time of
11 exposure) and duration of exposure (Foster et al., 1993; Singh et al., 1993a). It is currently
12 unclear whether these effects reflect a physiological adaptation to the stress of lead exposure, or
13 reflect the combined outcome of distinct dose-duration-response relationships for multiple
14 effects on the HPG axis.
15 The adverse effects of Pb on male reproduction may be expressed as perturbations in
16 sexual development and maturation, changes in fertility, endocrine disruption, and alterations in
17 structure of reproductive cells or tissue. Each of these effects is discussed in greater detail in the
18 sections that follow.
19
20 5.4.2.1 Effects on Male Sexual Development and Maturation
21 The 1986 Pb AQCD reported adverse effects of Pb on male sexual development and
22 maturation. Experimental studies conducted in animals demonstrated that high-dose (e.g.,
23 dietary exposure to 0.08 to 1.0% (800-1000 ppm) lead acetate in mice and to 100 ppm in dogs)
24 preadolescent Pb exposure can produce long-lasting detrimental effects on male sexual
25 development. Numerous more recent studies conducted in experimental animals support the
26 earlier findings that Pb exposure during early development can delay the onset of male puberty
27 and alter reproductive function later in life (McGivern et al., 1991; Al-Hakkak et al., 1988;
28 Chowdhuri et al., 2001; Dearth et al., 2002, 2004; Gandley et al., 1999; McGivern et al., 1991;
29 Ronis et al., 1998a,c; Sokol et al., 1994; Yu et al., 1996). Studies that provide the strongest
30 evidence for the dose-response range for typical effects in rodents are discussed below
31 (Table 5-4.1).
May 2006 5-85 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-4.1. Selected Studies Showing the Effects of Lead on Reproductive Function in Males
to
o
o
Citation
Species/
Strain
Dose/Route/Form/Duration/Group Size Endpoint/Magnitude of Effect/p-value Blood Lead Concentration (PbB)
oo
Oi
Foster etal. Monkey/ 0-1500 jig Pb-acetate/kg-d in gelatin capsules
(1993) Cynomolgus p.o. for various durations: 9 control monkeys,
4 monkeys in lifetime group (birth to 9 years),
4 in infancy group (first 400 days of life), 4 in
post-infancy exposure (from 300 days to 9 years)
Foster etal. Monkey/ 0-1500 jig Pb-acetate/kg-d in gelatin capsules
(1996a) Cynomolgus p.o. from birth until 9 years of age
8 control monkeys, 4 monkeys in low group
(6-20 ng/dL), 7 monkeys in high group
(22-148 (ig/dL)
Foster etal. Monkey/ 0-1500 |ig Pb-acetate/kg-d in gelatin capsules
(1998) Cynomolgus p.o. for various durations: birth to 10 years
(lifetime); PND 300 to 10 years (post-infancy);
birth to 300 days (infancy);
3 control monkeys, 4 lifetime, 4 infancy,
5 post-infancy
Suppressed LH response to GnRH stimulation in
the lifetime group (p = 0.0370); Sertoli cell
function (reduction in the inhibin to FSH ratio)
(p = 0.0286) in lifetime and post-infancy groups.
Mean PbB of 56 ng/dL showed no significant
alterations in parameters of semen quality
(count, viability, motility, or morphology).
Circulating concentrations of FSH, LH, and
testosterone were not altered by treatment;
semen characteristics (count, motility,
morphology) were not affected by treatment
possibly because not all Sertoli cells were
injured; degeneration of seminiferous epithelium
in infancy and lifetime groups (no difference in
severity between these groups); ultrastructural
alterations in seminal vesicles, most prominent
in infancy and post-infancy groups.
Lifetime group 3-26 ng/dL at 4-5
years
Infancy group 5-36 ng/dL at 100-300
days, 3-3 ng/dL at 4-5 years
Post-infancy group 20-35 ng/dL
PbB10±3or56±49|ig/dL
PbB -35 ng/dL
H
6
o
o
H
O
O
H
W
O
O
HH
H
W
McGivern Rat/Sprague- 0.1% Pb-acetate in drinking water from GD 14 to
et al. Dawley parturition; 8 control litters; 6 Pb-acetate litters
(1991) (5 males per litter)
Ronis et al. Rat/Sprague- 0.6% Pb-acetate in drinking water for various
(1996) Dawley durations: PND 24-74 (pubertal exposure); PND
60-74 (post pubertal exposure); 11 males and
females in pubertal exposure group (10 each in
control pubertal group); 6 males and females
post-pubertal exposure and control groups
Decreased sperm count (21% at 70 days and
24% at 165 days, p < 0.05); reduced male
behavior (p < 0.05); enlarged prostate (25%
increase in weight; p < 0.07); irregular release
patterns of both FSH and LH (p < 0.05).
PbB >250 ng/dL reduced circulating
testosterone levels in male rats 40-50%
(p < 0.05); reduction in male secondary sex
organ weight (p < 0.005); delayed vaginal
opening (p < 0.0001); disrupted estrous cycle in
females (50% of rats); increased incidence of
stillbirth (2% control vs. 19% Pb) (p < 0.005).
Control PbB <5 ng/dL at birth
Maternal PbB 73 ng/dL at birth
Pup PbB 64 ng/dL at birth
Pubertal PbB 30-60 ng/dL
Post-pubertal PbB 30-60 ng/dL
Mean PbBs in male rats 30-60 ng/dL,
respectively
-------
Table 5-4.1 (cont'd). Selected Studies Showing the Effects of Lead on Reproductive Function in Males
to
o
o
Species/
Citation Strain Dose/Route/Form/Duration/Group Size Endpoint/Magnitude of Effect/p-value Blood Lead Concentration (PbB)
fj\
oo
H
6
O
o
H
O
o
H
W
O
O
HH
H
W
Ronis et al. Rat/Sprague- 0.6% Pb-acetate in drinking water ad libitum for
(1998a) Dawley various durations as follows: GD 5 to PND 1;
GD 5 to weaning; PND 1 to weaning; 3 control
litters, 2 gestation exposure litters, 2 lactation
exposure litters, 2 gestation and lactation
exposure litters, 2 postnatal exposure litters,
2 chronic exposure litters; 4 male and 4 female
pups per litter
Suppression of adult mean serum testosterone
levels was only observed in male pups exposed
to Pb continuously from GD 5 throughout life
(p<0.05).
Group
Naive
Control
Gest
Lact
Gest+Lact
Postnatal
Chronic
Male PbB
5. 5 ±2.0 ug/dL
1.9 ±0.2 ug/dL
9.1 ±0.7 ug/dL
3.3 ±0.4 ug/dL
16.1 ±2.3 ug/dL
226.0 ± 29 ug/dL
316.0 ±53 ug/dL
Ronis et al. Rat/Sprague- Lead acetate in drinking water (0.05% to 0.45%
(1998b) Dawley w/v); dams exposed until weaning; exposure of
pups which continued until PND 21, 35, 55, or
85; 5 control litters (0%), 10 low-dose litters
(0.05%), 8 mid-dose litters (0.15%), 9 high-dose
litters (0.45%); 4 male and 4 female pups per
litter
Ronis et al. Rat/Sprague- Lead acetate 0.05, 0.15, or 0.45% in drinking
(1998c) Dawley water beginning GD 5 continuing until PND 21,
35, 55, or 85; 5 control litters (0%), 10 low-dose
litters (0.05%), 8 mid-dose litters (0.15%), 9
high-dose litters (0.45%); 4 male and 4 female
pups per litter
Dose-response reduction in birth weight
(p < 0.05), more pronounced in male pups;
decreased growth rates in both sexes (p < 0.05)
were accompanied by a statistically significant
decrease in plasma concentrations of IGF 1
through puberty PND 35 and 55 (p < 0.05);
increase in pituitary growth hormone during
puberty (p < 0.05).
Dose-responsive decrease in birth weight
(p < 0.05); dose-responsive decrease in crown-
to-rump length (p < 0.05); dose-dependent delay
in sexual maturity (p < 0.05); decrease in
prostate weight (p < 0.05); decrease in plasma
concentration of testosterone during puberty
(p < 0.05); decrease in plasma LH (p < 0.05);
elevated pituitary LH content (p < 0.05);
decrease in plasma testosterone/LH ratio at high
dose (p < 0.05).
Mean PbB in offspring at 0.05% (w/v)
49 ± 6 ug/dL
Mean PbB in offspring at 0.15% (w/v)
126 ±16 ug/dL
Mean PbB in offspring at 0.45% (w/v)
263 ± 28 ug/dL
Dams: 0, 48, 88, or 181 ug/dL
Pups PND 1: <1, 40, 83, or 120 ug/dL
Pups PND 21: <1,46, 196, or
236 ug/dL
Pups PND 35: <1,20, 70, or
278 ug/dL
Pups PND 55: <1,68, 137, or
379 ug/dL
Pups PND 85: <1,59, 129, or
214 ug/dL
-------
Table 5-4.1 (cont'd). Selected Studies Showing the Effects of Lead on Reproductive Function in Males
to
o
o
oo
oo
H
6
o
o
H
O
O
H
W
O
O
HH
H
W
Citation
Singh et al.
(1993a)
Sokol and
Berman
(1991)
Species/
Strain Dose/Route/Form/Duration/Group Size
Monkey/ 0-1500 |ig Pb-acetate/kg-d in gelatin capsules for
Cynomolgus various durations: 3 control monkeys, 4 monkeys
in infancy group (exposure first 400 days), 5 in
post-infancy group (exposure 300 days to 9 years
of age), 4 in lifetime group (exposure from birth
until 9 years)
Rat/Wistar 0, 0. 1, or 0.3% Pb-acetate in drinking water for
30 days beginning at 42, 52, or 70 days old; 8-11
control rats for each age, 8-1 1 rats for each age in
0.1% group, 8-11 rats for each age in 0.3% group
Endpoint/Magnitude of Effect/p-value Blood Lead Concentration (PbB)
Degeneration of seminiferous epithelium in all Chronic PbB
exposed groups (frequency not specified); <40-50 |ig/dL
ultrastructural alterations in seminal vesicles,
most prominent in infancy and post-infancy
groups (frequency not specified).
Dose-related suppression of spermatogenesis Group
(decreased sperm count and sperm production
rate) in the exposed rats of the two highest age 0%
groups (p < 0.05); dose-related suppression of
serum testosterone in 52-day old rats (p = 0.04)
and in 70-day old rats (p < 0.003).
0.1%
0.3%
Age
All
42 d
52 d
70 d
42 d
52 d
70 d
PbB
<7 ng/dL
25 |ig/dL
35 |ig/dL
37 ng/dL
36 ng/dL
60 ng/dL
42 ng/dL
FSH, follicle stimulating hormone; GD, gestational day; GnRH, gonadotropin releasing hormone; IGF], insulin-like growth factor 1; LH, luteinizing hormone; PbB, blood Pb
concentration; PND, post-natal day
-------
1 McGivern et al. (1991) found that male rats born to dams that received Pb-acetate in
2 drinking water beginning on gestation day 14 and through parturition (PbB 73 |ig/dL) exhibited
3 reduced sperm counts, altered male reproductive behavior, and enlarged prostates later in life.
4 Prepubertal exposure of male Sprague-Dawley rats (age 24 to 74 days) to Pb-acetate in drinking
5 water (PbB 30 to 60 |ig/dL) resulted in significant reduction in testis weight and in the weight of
6 secondary sex organs; however, these effects were not observed in rats exposed postpubertally
7 (day 60 to 74; Ronis et al., 1996). A dose-dependent delay in sexual maturation was found in
8 male rats, following prenatal Pb exposure that continued until adulthood (age 85 days) (Ronis
9 et al., 1998a,b,c). In these studies, PbBs in the pups between the ages of 21 and 85 days were
10 >100 |ig/dL. Additional details concerning these studies are provided in Table 5-4.1.
11 One possible explanation for the persistent effects of Pb exposure on the male
12 reproductive system is a disruption in pulsatile release of sex hormones during early
13 development (Ronis et al., 1998c). Lead effects on sex hormones are discussed in
14 Section 5.4.2.3
15
16 5.4.2.2 Effects on Male Fertility: Effects on Sperm Production and Function
17 The 1986 Pb AQCD presented evidence that Pb exposure affects male fertility in various
18 animal species, including rabbits (Cole and Bachhuber, 1915), guinea pigs (Weller, 1915), rats
19 (Ivanova-Chemishanska et al., 1980), and mice (Schroeder and Mitchener, 1971).
20 Several more recent studies, conducted in various animal species, have demonstrated
21 Pb-induced alterations of sperm parameters (e.g., count, motility, number of abnormal) (Sokol
22 et al., 1985; and eight other studies). These effects, however, have not been reproduced in all
23 studies. For example, Foster et al. (1996a) reported that 15- to 20-year-old cynomolgus monkeys
24 receiving Pb-acetate for their lifetime (mean PbB 56 |ig/dL) showed no significant alterations in
25 sperm parameters (i.e., sperm count, viability, motility, and morphology) or circulating levels of
26 testosterone (see Section 5.4.2.3 for discussion of lead-induced changes in testosterone levels).
27 Adaptive (Sokol et al., 2002) or multiple effects on the UPG axis having different dose-duration-
28 response relationships may explain the apparent inconsistency in reported effects on circulating
29 testosterone levels, sperm count, and sperm production following lead exposure. As a result,
30 changes in testosterone levels and certain sperm parameters may not always serve as reliable
May 2006 5-89 DRAFT-DO NOT QUOTE OR CITE
-------
1 endpoints for assessing the effects of lead on male fertility and reproductive function for all
2 exposure durations.
3 Although gross changes in sperm parameters were not observed in monkeys in which
4 chronic PbB was approximately 56 |ig/dL, Foster et al. (1996a) reported that monkey sperm
5 exhibited a statistically significant, dose-related reduction in chromatin structure (as determined
6 by susceptibility to weak acid denaturation). These changes may have adverse impacts on
7 fertility, and they are thought to be related to dominant lethal effects of Pb (similar to the effects
8 reported by al-Hakkak et al. [1988] in mice). Additional details concerning Foster et al. (1996a)
9 are provided in Table 5-4.1.
10 The data from Foster et al. (1996a), demonstrating a change in monkey sperm chromatin
11 suggestive of a subtle lead-induced reduction in male fertility (in the absence of gross changes in
12 sperm parameters), are consistent with observations of reduced in vitro fertilization capacity of
13 sperm collected from other mammalian species. Sokol et al. (1994) reported that exposure of
14 adult male rats to Pb-acetate in drinking water for 14 to 60 days (PbB 33 to 46 |ig/dL) resulted in
15 reduced in vitro fertilization of eggs harvested from unexposed females. No differences were
16 observed in sperm ultrastructure or in the DNA histogram of sperm obtained from lead-exposed
17 rats compared to controls. Consistent with this finding are reports of reduced fertilization
18 capacity of rabbit sperm exposed to high concentrations (25 jiM) of Pb chloride in vitro (Foote,
19 1999) and reduced in vitro fertilization capacity of sperm from mice exposed to Pb in drinking
20 water at 1 g/L for 4 months (PbB not reported) (Johansson et al., 1987).
21 Two modes of action have been proposed for lead-induced alterations in sperm capacity
22 for fertilization. The affinity of Pb for sulfhydryl groups may explain some of the lead-induced
23 alterations in sperm structure and function. Mammalian sperm possess high concentrations of
24 sulfhydryl groups, including chromatin stabilizing protamines, which are critical for maintenance
25 of normal function (Johansson and Pellicciari, 1988; Quintanilla-Vega et al., 2000). Reyes et al.
26 (1976) demonstrated that binding of Pb to membrane thiols inhibits sperm maturation.
27 In addition, recent experimental data also suggest that lead-induced generation of reactive
28 oxygen species (ROS) may contribute to the injury of tissues responsible for sperm formation
29 (see Section 5.4.2.4).
May 2006 5-90 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.4.2.3 Effects on Male Sex Endocrine System
2 The 1986 Pb AQCD reported that, although the mode of action for the adverse effects of
3 Pb on the male reproductive system was not understood, effects on hormone production or
4 hormone receptors were likely contributors. More recent studies provide convincing evidence
5 that Pb acts as an endocrine disrupter in males at various points along the hypothalamic-
6 pituitary-gonadal axis (Figure 5-4.1). In rats, Pb exposures that decreased serum testosterone
7 levels increased mRNA levels of GnRH and LH in the hypothalamus and pituitary, respectively,
8 and increased levels of LH in pituitary; these changes can occur in the absence of a change in
9 serum gonadotropin levels (Klein et al., 1994; Ronis et al., 1998c; Sokol et al., 2002).
10 In monkeys, chronic Pb exposures (PbB 20 to 35 |ig/dL) suppressed GnRH-induced secretion of
11 LH and decreased serum testosterone:LH and inhibin:FSH ratios (Foster et al., 1993). The
12 mechanisms underlying the effects on the hypothalamic-pituitary-gonadal axis have not been
13 elucidated but may involve a suppression of GnRH secretion (Bratton et al., 1994; Sokol, 1987;
14 Sokol etal., 1998).
15 Although there is evidence for a common mode of action, consistent effects on circulating
16 testosterone levels are not always observed in lead-exposed animals. Rodamilans et al. (1988)
17 and Kempinas et al. (1994) attributed these inconsistencies to the normal biological variation
18 (circannual and seasonal) of testosterone secretion in rats and monkeys. Observations of
19 lead-induced reductions in testosterone levels in some studies, but not others, may be due to
20 enhanced sensitivity to inhibition of the testosterone secretory system during certain periods of
21 development. In addition, compensatory mechanisms in the hypothalamic-pituitary-gonad axis
22 may attenuate some effects of lead during prolonged Pb exposure (Sokol et al., 2002). Taken
23 together, the sensitivity of testosterone secretion during certain periods and potential for
24 modulation of the effects during long-term exposures studies, may explain some of the apparent
25 inconsistencies in the reported effects of Pb exposure on circulating testosterone levels.
26
27 5.4.2.4 Effects on Morphology and Histology of Male Sex Organs
28 The 1986 Pb AQCD reported evidence for histological changes in the testes or prostate in
29 rats, in association with relatively high doses of Pb (Chowdhury et al., 1984; Hilderbrand et al.,
30 1973; Golubovich et al., 1968). More recent studies conducted in animal models provide
31 persuasive support for testicular damage, i.e., ultrastructural changes in testes and cytotoxicity in
May 2006 5-91 DRAFT-DO NOT QUOTE OR CITE
-------
1 Sertoli cells (Foster et al., 1998; Singh et al., 1993a; Batra et al., 2001; Chowdhury et al., 1986,
2 1987; Corpas et al., 1995; Pinon-Lataillade et al., 1993; Saxena et al., 1990). Studies conducted
3 in nonhuman primates warrant particular attention. These studies found ultrastructural changes
4 in the testes (Sertoli and other spermatogenic cells) of monkeys at PbB 35 to 40 |ig/dL (Foster
5 et al., 1998; Singh et al., 1993a).
6 Foster et al. (1998) reported that chronic Pb exposure (PbB -35 |ig/dL), beginning in
7 infancy, resulted in persistent ultrastructural changes in the testes of cynomolgus monkeys.
8 Electron microscopy showed disruption of the general structure of the seminiferous epithelium
9 involving Sertoli cells, basal lamina, and spermatids in the groups exposed for lifetime and
10 during infancy only (no duration difference in severity). Chronic exposures to Pb beginning
11 after infancy, that achieved similar PbBs, did not produce these effects.
12 Similarly, Singh et al. (1993a) demonstrated ultrastructural changes in testicular basement
13 membrane and Sertoli cell morphology (seminiferous tubules) in cynomolgus monkeys exposed
14 chronically to Pb (PbB <40 to 50 |ig/dL); the effects were most prominent when dosing began in
15 infancy or post-infancy. These results suggest that, in monkeys, Pb exposure during certain
16 periods of development produces persistent testicular alterations. Additional details concerning
17 Foster et al. (1998) and Singh et al. (1993a) are provided in Table 5-4.1.
18 A possible mode of action for lead-induced testicular injury is oxidative stress. Foster
19 et al. (1998) suggested that lead-induced oxygen free radical generation was a plausible
20 mechanism of testicular injury in primates. This oxygen radical hypothesis is supported by
21 studies conducted in rodents (Chowdhury et al., 1984; Acharya et al., 2003; Adhikari et al.,
22 2001; Batra et al., 2001; Bizarro et al., 2003; Chowdhury et al., 1984; Gorbel et al., 2002; Mishra
23 and Acharya, 2004). Also supporting the oxidative stress hypothesis are observations of
24 increases in the percentage of apoptotic cells in the testes of rodents in response to Pb exposure
25 (Pace et al., 2005; Gorbel et al., 2002; Adhikari et al., 2001).
26 Studies in experimental animals (presented in the 1986 Pb AQCD and others published
27 subsequent to the 1986 Pb AQCD) provide convincing evidence that Pb acts as an endocrine
28 disrupter in males. The majority of present studies support the conclusion that endocrine
29 disruption in males involves Pb acting at multiple sites along the hypothalamic-pituitary-gonadal
30 axis. The adverse effects of Pb on male reproduction include perturbations in sexual
May 2006 5-92 DRAFT-DO NOT QUOTE OR CITE
-------
1 development and maturation, changes in fertility, changes in male sex hormone levels, and
2 alterations in gonad tissues and cell structure.
3
4 5.4.3 Effects on Female Reproductive Function
5 Lead has been shown to disrupt the hypothalamic-pituitary-gonadal axis and to produce
6 ovarian atrophy and reproductive dysfunction in females (Figure 5-4.1). The 1986 Pb AQCD
7 reported that Pb exposure was associated with inhibition of menstruation, ovulation, and
8 follicular growth in monkeys (Vermande-Van Eck and Meigs, 1960), and, in rodents, Pb
9 exposure delayed vaginal opening, decreased frequency of implantation, and reduced rates of
10 pregnancy (Kimmel et al., 1980; Odenbro and Kihlstrom, 1977, respectively).
11 Data from more recent experimental animal studies support these findings. Lead effects
12 on female reproduction may be classified as alterations in female sexual maturation, effects on
13 fertility and menstrual cycle, endocrine disruption, and changes in morphology or histology or
14 female reproductive organs as well as the placenta. Recent literature concerning each of these
15 effects is summarized below.
16
17 5.4.3.1 Effects on Female Sexual Development and Maturation
18 The 1986 Pb AQCD reported that Pb exposure in rodents produced delays in sexual
19 maturation. Grant et al. (1980) reported delayed vaginal opening in female rats exposed in utero
20 and during lactation and maturation (PbB -20 to 40 |ig/dL). More recent studies in experimental
21 animals (primarily rodent studies) provide convincing evidence that Pb exposure before puberty
22 (particularly prenatal and early postnatal exposure) delays the maturation of the female
23 reproductive system (Dearth et al., 2002, 2004; Ronis et al., 1996, 1998b,c).
24 The study of Dearth et al. (2002) is of particular interest, because it employed a cross-
25 fostering design (to allow comparison of pups exposed during gestation only, lactation only, or
26 both) and because maternal and offspring PbBs were monitored throughout gestation and
27 lactation. Fisher 344 dams were exposed to Pb by gavage beginning 30 days before mating until
28 weaning of the pups at 21 days of age (gavage exposure removes possible confounding of
29 exposure by consumption of Pb in drinking water by pups in those studies where drinking water
30 is the route of exposure for dams). Mean maternal PbB was approximately 40 |ig/dL. Pups
31 exposed during gestation and lactation had the highest PbB (38.5 |ig/dL) on day 10; at this time,
May 2006 5-93 DRAFT-DO NOT QUOTE OR CITE
-------
1 the PbBs in pups exposed during gestation only or lactation only were 13.7 and 27.6 |ig/dL,
2 respectively. By postnatal day (PND) 30, all three groups had PbB <3 |ig/dL. Dearth et al.
3 (2002) reported a statistically significant delay in the onset of puberty (vaginal opening and days
4 at first diestrus) in rats exposed during lactation, gestation, or during lactation and gestation (with
5 no differences among the groups). In addition, a statistically significant reduction in the
6 circulating levels of insulin-like growth factor 1 (IGFi), LH, and estradiol (£2) were reported on
7 PND 30 in all three treatment groups (with no differences among treatment groups). Additional
8 details concerning Dearth et al. (2002) are provided in Table 5-4.2.
9 A subsequent study in both Sprague-Dawley and F344 rats (Dearth et al., 2004) showed
10 that the F344 strain is more sensitive to maternal Pb exposure than Sprague-Dawley rats to lead-
11 induced delayed puberty, which could, in part, explain the inconsistencies with effect levels
12 observed in Sprague Dawley rats (e.g., Ronis et al., 1998a,b,c; McGivern et al., 1991). Ronis
13 et al. (1998c) suggested that the delayed onset of puberty may arise from a lead-induced
14 disruption of pulsatile release of sex hormones (see Section 5.4.3.3).
15
16 5.4.3.2 Effects on Female Fertility
17 The 1986 Pb AQCD reported convincing evidence from experimental animal studies for
18 lead-induced alterations in female fertility, including interference with implantation and
19 pregnancy (Odenbro and Kihlstrom, 1977; Wide and Nilsson, 1977). More recent studies have
20 confirmed these effects. In general, Pb exposure does not produce total sterility, although Pb
21 exposure clearly disturbs female fertility (Taupeau et al., 2001). Studies in nonhuman primates
22 and rodents have shown that exposure of gravid females to Pb produces implantation dysfunction
23 and reduces litter size and newborn survival (Logdberg et al., 1987; Flora and Tandon, 1987;
24 Johansson and Wide, 1986; Pinon-Lataillade et al., 1995; Piasek and Kostial, 1991; Ronis et al.,
25 1996). See Section 5.4.4.1 for details.
26
27 5.4.3.3 Effects on the Female Sex Endocrine System and Menstrual Cycle
28 The 1986 Pb AQCD described numerous studies that found effects of Pb on the female
29 endocrine system and menstrual cycle in various species, including nonhuman primates, and that
30 supported the conclusion that Pb was an endocrine disrupter in females (Grant et al., 1980;
31 Maker et al., 1975; Vermande-Van Eck and Meigs, 1960). Observations of delayed vaginal
May 2006 5-94 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-4.2. Selected Studies Showing the Effects of Lead on Reproductive Function in Females
to
o
o
Species/ Dose/Route/Form/Duration/
Citation Strain Group Size
Endpoint/Magnitude of Effect
(% or incidence) /p-value
Blood Lead Concentration
(PbB)
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Dearth
etal.
(2002)
Foster
(1992)
Foster et al.
(1992)
Foster et al.
(1996b)
Rat/Fisher
344
Monkey/
Cynomolgus
Monkey/
Cynomolgus
Monkey/
Cynomolgus
12 mg/mL Pb-acetate gavage from
30 days prior breeding until pups were
weaned 21 day afterbirth; 10-32 litters
per group, control group, gestation and
lactation exposure, gestation only
exposure, lactation only exposure
Daily dosing for up to 10 years with
gelatin capsules containing Pb-acetate
(1.5 mg/kg); 8 control group monkeys,
8 lifetime exposure (birth-10 years),
8 childhood exposure (birth-400 days),
and 8 adolescent exposure
(PND 300-10 years of age)
Daily dosing for up to 10 years with
gelatin capsules containing Pb-acetate
(1.5 mg/kg); 8 control group monkeys,
8 childhood (birth-400 days),
7 adolescent (PND 300-10 years),
7 lifetime (birth-10 years)
Chronic exposure to Pb-acetate 50 to
2000 ug/kg-day p.o. beginning at birth
for 15-20 years; 20 control monkeys,
4 monkeys in 50 ug/kg-d group,
3 monkeys in 100 ug/kg-d, 2 monkeys
in 500 ug/kg-d group, and 3 monkeys in
2000 ug/kg-d group
Delay in onset of puberty (p < 0.05); reduced
serum levels of IGFj (p < 0.001), LH
(p< 0.001), and E2 (p < 0.001).
Statistically significant reductions in circulating
levels of LH, (p < 0.042), FSH (p < 0.041), and
E2 (p < 0.0001) during menstrual cycle;
progesterone concentrations were unchanged and
menstrual cycle was not significantly affected.
No effect on endometrial response to gonadal
steroids as determined by ultrasound.
Reduced corpora luteal production of
progesterone (p = 0.04), without alterations in
E2, 20-alpha-hydroxyprogesterone, or menstrual
cyclicity.
Maternal PbB -40 ug/dL
Pups PbB as follows:
Gest+lact -38 ug/dL PND 10
Gest+lact -15 ug/dL PND 21
Gest+lact -3 ug/dL PND 30
Gest -14 ug/dL PND 10
Gest~3 ug/dL PND 21
Gest~l ug/dL PND 30
Lact-28 ug/dL PND 10
Lact-15 ug/dL PND 21
Lact-3 ug/dL PND 30
PbB <40 ug/dL
PbB <40 ug/dL
PbB 10-15 ug/dL in low group
(50 or 100 ug/kg-day)
PbB 25-30 ug/dL in moderate
group (500 or 2000 ug/kg-day)
-------
Table 5-4.2 (cont'd). Selected Studies Showing the Effects of Lead on Reproductive Function in Females
to
o
o
Species/ Dose/Route/Form/Duration/
Citation Strain Group Size
Endpoint/Magnitude of Effect
(% or incidence)/p-value
Blood Lead Concentration
(PbB)
Oi
Franks Monkey/ Lead acetate in drinking water (2-8
etal. Rhesus mg/kg-d) for33 months; 7 control
(1989) and 10 Pb monkeys
Laughlin
etal.
(1987)
Logdberg
etal.
(1988)
Monkey/ Lead acetate in drinking water at 3.6,
Rhesus 5.9, or 8.1 mg/kg-day for 1-2 years
7 control and 10 experimental monkeys
per group
Monkey/ Lead acetate (varying concentrations
Squirrel <0.1% in diet) maternal dosing from
5-8.5 weeks pregnant to PND 1
11 control monkeys, 3 low Pb exposure
group (PbB 24 ug/dL), 7 medium Pb
group (PbB 40 ug/dL, 5 high Pb group
(PbB 56 ug/dL)
Reduced circulating concentration of
progesterone (p < 0.05); treatment with Pb did
not prevent ovulation, but produced longer and
more variable menstrual cycles and shorter
menstrual flow.
Reductions in cycle frequency (pO.Ol); fewer
days of flow (p<0.01); longer and more variable
cycle intervals (p<0.025).
Dose-dependent reduction in placental weight
(p<0.0007); various pathological lesions were
seen in the placentas (n = 4), including
hemorrhages, hyalinization of the parenchyma
with destruction of the villi and massive
vacuolization of chorion epithelium.
PbB 68.9 ± 6.54 ug/dL
PbB 44-89 ug/dL
51.2 ug/dL (low dose)
80.7 ug/dL (mid dose)
88.4 ug/dL (high dose)
Mean maternal PbB 37 ug/dL
(22-82 ug/dL)
24 (22-26) ug/dL (low dose)
40 (35-46) ug/dL (mid dose)
56 (43-82) ug/dL (high dose)
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
E2, estradiol; FSH, follicle stimulating hormone; GD, gestational day; IGF!, insulin-like growth factor 1; LH, luteinizing hormone; PbB, blood Pb
concentration; PND, post-natal day
-------
1 opening (see Section 5.4.3.1) were attributed to the endocrine disruption effects of Pb on the
2 hypothalamic-pituitary-gonadal axis (Stowe and Goyer, 1971; Vermande Van Eck and Meigs,
3 1960).
4 More recent studies have provided convincing support for endocrine-mediated alterations
5 of the female reproductive system in rats (Srivastava et al., 2004; Dearth et al., 2002; Ronis
6 et al., 1998a,b,c; Junaid et al., 1997; Ronis et al., 1996), guinea pigs (Sierra and Tiffany-
7 Castiglioni, 1992), and nonhuman primates (Foster et al., 1992, 1996b; Foster, 1992; Franks
8 et al., 1989; Laughlin et al., 1987). The nonhuman primate studies are particularly relevant to
9 extrapolations to humans and provide dose-response information for effects of Pb on female sex
10 hormones and menstrual cycle.
11 Laughlin et al. (1987) found that exposure to Pb (PbB 44 to 89 |ig/dL) alters menstrual
12 cycles (specifically, causing reductions in cycle frequency, fewer days of menstrual flow, and
13 longer and more variable cycle intervals) in female rhesus monkeys. Consistent with these
14 observations, Franks et al. (1989) found that chronic exposure to Pb in the drinking water
15 (PbB 70 |ig/dL) reduced circulating concentrations of progesterone (suggesting impaired luteal
16 function), produced longer and more variable menstrual cycles and temporally shorter menstrual
17 flow in female rhesus monkeys. Additional details concerning these studies are provided in
18 Table 5-4.2.
19 At lower blood Pb levels (PbB <40 jig/dL), female cynomolgus monkeys exhibited
20 statistically significant reductions in circulating levels of LH, FSH, and £2 during the menstrual
21 cycle; however, serum progesterone concentrations were unchanged and menstrual cycle was not
22 significantly affected (Foster, 1992). Similar exposures and PbB were shown to have no effect
23 on endometrial response to gonadal steroids in cynomolgus monkeys as determined by
24 ultrasound analysis (Foster et al., 1992). At lower blood lead concentrations (25 to 30 |ig/dL),
25 reduced corpora luteal production of progesterone occurred in the absence of alterations in E2,
26 20-alpha-hydroxyprogesterone, or menstrual cyclicity (Foster et al., 1996b). In contrast to Foster
27 et al. (1992), this study (Foster et al., 1996b) found no statistically significant effect of Pb on
28 serum progesterone levels in cynomolgus monkeys that had lower PbB (10 to 15 |ig/dL).
29 Additional details concerning these studies are provided in Table 5-4.2.
30 Several modes of action for lead-induced, endocrine disruption-mediated alterations in
31 female reproduction have been proposed, including changes in hormone synthesis or metabolism
May 2006 5-97 DRAFT-DO NOT QUOTE OR CITE
-------
1 at the enzyme level (Wiebe and Barr, 1988; Wiebe et al., 1988) and changes in hormone receptor
2 levels (Wiebe et al., 1988; Wide and D'Argy, 1986). In addition, Pb may alter sex hormone
3 release and imprinting during early development (Ronis et al., 1998c; Tchernitchin et al.,
4 1998a,b). The latter effects would be consistent with observations of persistent changes in
5 estrogen receptor levels in the uterus (Wiebe and Barr, 1988) and LH function in the ovary
6 (Srivastava et al., 2004) in lead-exposed animals.
7
8 5.4.3.4 Effects on Morphology and Histology of Female Sex Organs and the Placenta
9 Lead-induced changes in morphology or histology in female sex organs and the placenta
10 may explain reduced fertility and impaired female reproductive success (see Sections 5.4.3.2 and
11 5.4.4.1.). Logdberg et al. (1988) reported a dose-dependent reduction in placental weight and an
12 increase in pathological lesions of the placenta in squirrel monkeys that received oral doses of
13 Pb-acetate (0.001 to 0.1% in diet) during the last three-fourths or two-thirds of pregnancy (mean
14 maternal PbB 37 |ig/dL; range: 22 to 82 |ig/dL). These effects occurred without overt toxicity in
15 the mothers. Additional details concerning Logdberg et al. (1988) are provided in Table 5-4.2.
16 Similar effects on placental weight and histology were observed in mice (Fuentes et al.,
17 1996; Nayak et al., 1989a). These effects on the placenta may explain the reduced birth weight
18 that has been associated with prenatal Pb exposure (see Section 5.4.5). Exposure to Pb in early
19 pregnancy also produces structural changes in the epithelium of the uterus of mice (Nilsson
20 et al., 1991; Wide and Nilsson, 1979). These changes in uterine tissue may impair successful
21 implantation of the blastocysts (see Section 5.4.4.1).
22 The 1986 Pb AQCD reported that Pb exposure (PbB 20 to 40 (ig/dL) in rodents produced
23 delays in sexual maturation. More recent studies in experimental animals (primarily rodent
24 studies) provide convincing evidence that Pb exposure before puberty (prenatal and early
25 postnatal PbB -40 |ig/dL) delays maturation of the female reproductive system (Dearth et al.,
26 2002, 2004; lavicoli et al., 2004; McGivern et al., 1991; Ronis et al., 1998a,b,c,). Ronis et al.
27 (1998c) suggested that lead-induced disruption of pulsatile release of sex hormones may result in
28 delayed onset of puberty.
29
30
May 2006 5-98 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.4.4 Effects on Embryogenesis
2 Lead exposure can increase fetal mortality, produce a variety of sublethal effects, and
3 disrupt the growth and development of the offspring. Many of the lead-induced sublethal
4 developmental effects occur at maternal PbB levels that do not result in clinical toxicity in the
5 mothers.
6
7 5.4.4.1 Embryo/Fetal Mortality
8 The 1986 Pb AQCD concluded that that acute exposure to high doses of Pb interfered
9 with implantation and pregnancy (Wide, 1985; Odenbro and Kihlstrom, 1977; Wide and Nilsson,
10 1977; Vermande-Van Eck and Meigs, 1960). This conclusion is supported by results of more
11 recent studies (Logdberg et al., 1987; Giavini et al., 1980; Jacquet, 1976, 1977; Jacquet et al.,
12 1975, 1976; Johansson and Wide 1986; Johansson et al., 1987; Johansson, 1989; Maisin et al.,
13 1978; Pinon-Lataillade et al., 1995; Wide and Nilsson, 1977, 1979).
14 Logdberg et al. (1987) reported an increase in pre- and perinatal mortality in squirrel
15 monkeys that received Pb-acetate orally during the last two-thirds of pregnancy (45% versus
16 7 to 8% among controls). Mean maternal PbB was 54 |ig/dL (39 to 82 |ig/dL). These fetotoxic
17 effects occurred without overt toxicity in the mothers. Additional details concerning Logdberg
18 et al. (1987) are provided in Table 5-4.3. These effects are consistent with data from rodent
19 studies, wherein gestational exposure to Pb (PbB 32 to >70 |ig/dL) resulted in smaller litters and
20 fewer implantation sites (e.g., Pinon-Lataillade et al., 1995; Singh et al., 1993b; Piasek and
21 Kostial, 1991). Numerous studies have been performed to elucidate possible mechanisms by
22 which Pb causes prenatal death (Maisin at al., 1978; Jacquet, 1977, 1976; Jacquet et al., 1976,
23 1975). The available data suggest that Pb may alter blastocyst development and impair
24 implantation. Hanna et al. (1997) demonstrated that in vitro exposure of 2- and 4-cell mouse
25 embryos to 200 jiM Pb-acetate resulted in reduced cell proliferation and blastocyst formation.
26 Additional evidence for an effect on blastocysts is provided by data from in vitro fertilization
27 studies (Chowdhuri et al., 2001; Johansson, 1989; Johansson et al., 1987). Johansson and co-
28 workers (1989, 1987) reported that Pb delayed the timing of escape of spermatozoa from the
29 zona pellucida and induced a premature acrosome reaction. These effects could disrupt
30 attachment and implantation of the blastocyst if they were to occur in vivo.
31
May 2006 5-99 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-4.3. Selected Studies Showing the Effects of Lead on Mammalian Embryogenesis and Development
to
o
o
Citation
Species/
Strain
Dose/Route/Form/Duration/Group size Endpoint/Magnitude of Effect/p-value
Blood Lead Concentration
(PbB)
o
o
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Cory-Slechta
et al. (2004)
Rat/Long-
Evans
Dearth et al. Rat/Fisher
(2002) 344
Flora and
Tandon
(1987)
Fox et al.
(1991a)
Rat/Albino
(NOS)
Rat/Long-
Evans
hooded
Lead acetate in drinking water (150 ppm);
2 months before breeding until the end of
lactation; 14 rats no maternal stress with Pb
exposure, 15 rats no maternal stress with Pb
exposure, 18 rats maternal stress without Pb
exposure, 23 rats maternal stress and Pb
exposure
12 mg/mL Pb-acetate gavage during gestation
and lactation exposure
4 groups: control group, gestation and
lactation exposure, gestation only exposure,
lactation only exposure
10-32 litters per group (NOS)
Lead nitrate dissolved in water 2-20 mg/kg-d
i.v. on day 9, 10, 11 of gestation; 6 rats in
each group (0, 5, 10 , 20, 40 mg/kg lead)
Lactation exposure via dams exposed to
0.02 or 0.2% Pb in drinking water from PND
1 through weaning (PND 21); 8 female pups
per litter (number of litter unspecified) control
pups, 8 pups for litter (number of litter
unspecified) low-level exposure pups, 8 pups
per litter (number of litter unspecified)
moderate level exposure pups
Pb alone (in male) (p < 0.05) and Pb plus stress
(in females) (p < 0.05) permanently elevated
corticosterene levels in offspring
Delayed onset of puberty (p < 0.05); suppressed
serum levels of IGFb LH, and E2 (p < 0.001);
Pb altered translation and/or secretion of IGF!
(p< 0.001).
Dose-dependant increase in external malformations
at all doses (p < 0.001), particularly tail defects;
dose-dependant decrease in number of live births
at 20 and 400 mg/kg (p < 0.001); dose-dependent
increase in number of resorptions per dam at
< 10 mg/kg (p< 0.01).
Long-term, dose-dependent decreases retinal Na/K
ATPase activity in the female offspring (only
female pups were used) (-11%; -26%) (p < 0.05).
PbB 30^10 ng/dL
Maternal PbB -40 ng/dL
Pups PbB as follows:
Gest+lact~38 ng/dL PND 10
Gest+lact -15 ng/dL PND 21
Gest+lact ~3 ng/ PND 30
Gest~14|ig/dLPND10
Gest~3|ig/dLPND21
Gest ~1 ng/dL PND 30
Lact~28|ig/dLPND10
Lact~15|ig/dLPND21
Lact ~3 ng/dL PND 30
PbB 4.13 ± 0.61 ng/dL 0 mg/kg
PbB 10.21 ± 0.61 ng/dL 5 mg/kg
PbB 13.13 ± 0.27 ng/dL 10 mg/kg
PbB 29.41 ± 0.41 ng/dL 20 mg/kg
PbB 45.03 ± 0.31 ng/dL 40 mg/kg
PbB 18.8 ng/dL (0.02%) or
59.4 ng/dL (0.2%) at weaning
-------
Table 5-4.3 (cont'd). Selected Studies Showing the Effects of Lead on Mammalian Embryogenesis and Development
to
o
o
Citation
Species/
Strain
Dose/Route/Form/Duration/Group Size Endpoint/Magnitude of Effect/p-value
Blood Lead Concentration
(PbB)
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Fox et al.
(1997)
Rat/Long-
Evans
hooded
0.02 or 0.2% Pb-acetate in drinking water
from PND 0-PND 21; 8 female pups per litter
control pups; 8 pups per litter low-level
exposure; 8 pups per litter moderate level
exposure (number of litters per dose
unspecified)
lavicoli et al.
(2003)
Mouse/Swiss
Lead acetate in food (0.02, 0.06, 0.11, 0.2, 2,
4, 20, 40 ppm); exposure began 1 day after
mating until litter was 90 days old; one litter
of mice exposed to each dietary concentration
Developmental and adult Pb exposure for 6 weeks
produced age and dose-dependent retinal
degeneration such that rods and bipolar cells were
selectively lost; at the ultrastructural level, all
dying cells exhibit the classical morphological
features of apoptotic cell death; decrease in the
number of rods was correlated with the loss of
rhodopsin content per eye confirming that rods
were directly affected by Pb (p < 0.05); single-
flash rod ERGs and cone ERGs obtained from
lead-exposed rats demonstrated that there were
age- and dose-dependent decreases in the rod a-
wave and b-wave sensitivity and maximum
amplitudes without any effect on cones; in adult
rats exposed to Pb for three weeks, qualitatively
similar ERG changes occurred in the absence of
cell loss or decrease in rhodopsin content
(p < 0.05); developmental and adult Pb exposure
for three and six weeks produced age- and dose-
dependent decreases in retinal cGMP
phosphodiesterase (PDE) activity resulting in
increased cGMP levels (p < 0.05); retinas of
developing and adult rats exposed to Pb exhibit
qualitatively similar rod mediated ERG alterations
as well as rod and bipolar apoptotic cell death
(p<0.05).
Similar biochemical mechanism such as the
inhibition of rod and bipolar cell cGMP PDE,
varying only in degree and duration, underlies both
the lead-induced ERG rod-mediated deficits and
the rod and bipolar apoptotic cell death (p<0.05).
Low-level Pb exposure (PbB 2-13 ug/dL) reduced
red cell synthesis (p<0.05); high-level exposure
(PbB 0.6-2 ug/dL) enhanced red cell synthesis
(p<0.05).
PbB weanlings 19 ± 3 (low exposure)
or 59 ± 8 ug/dL (moderate exposure),
adult 7 ± 2 ug/dL (at PND 90)
PbB 0.6 to <2.0 ug/dL or
>2.0-13 ug/dL
-------
Table 5-4.3 (cont'd). Selected Studies Showing the Effects of Lead on Mammalian Embryogenesis and Development
to Dose/Route/Form/Duration/Group
o Citation Species/ Strain size
Endpoint/Magnitude of effect/p-value
Blood Lead Concentration
(PbB)
o
to
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Logdberg Monkey/ Squirrel Lead acetate (5-20 mg/kg daily to maintain
et al. PbB) maternal dosing from 5-8.5 weeks
(1987) pregnant to PND1 20 control; 11 lead-
exposed monkeys
Ronis Rat/Sprague- 0.6% Pb-acetate in drinking water for
et al. Dawley various durations: PND 24-74 (pubertal
(1996) exposure); PND 60-74 (post pubertal
exposure); 11 males and females in pubertal
exposure group (10 each in control pubertal
group)
6 males and females post-pubertal exposure
and control groups
Ronis Rat/Sprague- 0.6% Pb-acetate in drinking water ad libitum
et al. Dawley for various durations; GD 5 to PND 1; GD 5
(1998a) to weaning; PND 1 to weaning; 3 control
litters, 2 gestation exposure litters, 2
lactation exposure litters, 2 gestation and
lactation exposure litters, 2 postnatal litters,
2 chronic litters (4 male and 4 female pups
Increase in pre- and perinatal mortality among
squirrel monkeys receiving Pb-acetate p.o. during
the last two-thirds of pregnancy (45% vs. 7-8%
among controls). Statistically significant
reductions in mean birth weight (p<0.05) were
observed in Pb exposed monkeys as compared to
controls. Effects occurred without clinical
manifestation of toxic effects in the mothers.
Reduction in serum testosterone levels in male, not
female; in female suppression of circulating E2
(p<0.05) and LH (p<0.05); reduction in male
secondary sex organ weight (p<0.0005); delayed
vaginal opening and disrupted diestrous in females
(p<0.005); increased incidence of stillbirth (2%
control vs. 19% Pb) (p<0.005).
Dose-dependent delay in sexual maturation
(delayed vaginal opening) (p < 0.0002) following
prenatal Pb exposure that continued until
adulthood (85 days old); reduced birth weight
(p < 0.05), more pronounced among male pups.
PbB 54 ng/dL (39-
82
In utero PbB 250-
300 ng/dL
pre-pubertal PbB
30-60 ng/dL
post pubertal PbB
30-60 ng/dL
PbBs in the dams
and offspring in this
experiment were
>200 ng/dL
Naive
Control
PCI IHICIJ La(;
Gest+Lac
Postnatal
Chronic
-3 ng/dL
-13 ng/dL
-260 ng/dL
-287 ng/dL
-------
Table 5-4.3 (cont'd). Selected Studies Showing the Effects of Lead on Mammalian Embryogenesis and Development
g Species/
o Citation Strain
Dose/Route/Form/Duration/Group Size Endpoint/Magnitude of Effect/p-value
Blood Lead Concentration
(PbB)
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Ronis
etal.
(1998b)
Rat/Sprague-
Dawley
Ronis
etal.
(1998c)
Rat/Sprague-
Dawley
Ronis
etal.
(2001)
Rat/Sprague-
Dawley
Lead acetate in drinking water (0.05% to
0.45% w/v); dams exposed until weaning;
exposure of pups which continued until PND
21,35, 55, or 85
5 control litters (0%), 10 low-dose litters
(0.05%), 8 mid-dose litters (0.15%), 9 high-
dose litters (0.45%)
(4 male and 4 female pups per litter)
Lead acetate 0.05, 0.15, or 0.45% in drinking
water beginning GD 5 continuing until PND
21, 35, 55, or 85; 5 control litters (0%),
10 low-dose litters (0.05%), 8 mid-dose litters
(0.15%), 9 high-dose litters (0.45%)
(4 male and 4 female pups per litter)
Lead acetate in drinking water to 825 or
2475 ppm ad libitum from GD 4 to GD 55
postpartum; 1 male and female pup/litter
(5 litters per group) control group, 1 male and
female pup/litter (5 litters per group) 825 ppm
Pb-acetate group, 1 male and female pup/litter
(5 litters per group) 2475 ppm Pb-acetate
group
Prenatal Pb exposure that continues until adulthood
(85 days old) delays sexual maturation in female pups
in a dose-related manner (p < 0.05); birth weight
reduced (p < 0.05), more pronounced among male
pups; decreased growth rates (p < 0.05) in both sexes
accompanied by decrease in plasma concentrations of
IGF] through puberty (p < 0.05) and a significant
increase in pituitary growth hormone during puberty
(p<0.05).
Dose-responsive decrease in birth weight (p < 0.05),
and crown-to-rump length (p < 0.05); dose-responsive
delay in sexual maturity in male (p < 0.05) and female
(p < 0.05); neonatal decrease in sex steroids
(p < 0.05); pubertal decrease in testosterone (male)
(p < 0.05), and E2 (female) (p < 0.05); decrease estrous
cyclicity at high dose (p < 0.05).
Dose-dependent decrease of the load of failure in male
(p < 0.05); no difference in plasma levels of vitamin D
metabolites; reduced somatic growth (p < 0.05),
longitudinal bone growth (p < 0.05, and bone strength
during the pubertal period (p < 0.05); sex steroid
replacement did not restore skeletal parameters in Pb
exposed rats; L-Dopa increased plasma IGF]
concentrations, rates of bone growth, and bone
strength measures in controls while having no effect in
Pb exposed groups; DO gap x-ray density and
proximal new endostreal bone formation were
decreased in the distration gaps of the lead-treated
animals (p < 0.01); distraction initiated at 0.2 mm
30 to 60 days of age.
PbBs in the pups between the ages of
21 and 85 days were >100 ug/dL and
reached up to 388 ug/dL
Dams: 0, 48, 88, or 181 ug/dL
Pups PND 1: <1, -40, -70, or
>120 ug/dL
Pups PND 21: <1, >50, >160, or
-237 ug/dL
Pups PND 35: <1, -22, >70, or
>278 ug/dL
Pups PND 55: <1, >68, >137, or
-380 ug/dL
Pups PND 85: <1, >43, >122, or
>214 ug/dL
PbB at 825 ppm was 67-192 ug/dL
PbB at 2475 ppm was 120-388 ug/dL
-------
to
o
o
Table 5-4.3 (cont'd). Selected Studies Showing the Effects of Lead on Mammalian Embryogenesis and Development
Species/
Citation Strain
Dose/Route/Form/Duration/Group Size Endpoint/Magnitude of Effect/p-value
Blood Lead Concentration
(PbB)
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Rat/Sprague- Lead in drinking water at 34 ppm from
Dawley weaning of mothers through gestation and
weaning of offspring until birth; 6 pups
control group, 6 pups experimental group
Reduced body weight (p = 0.04); parotid function was
decreased by nearly 30% (p = 0.30); higher mean
caries scores than the control pups (p = 0.005); pre-
and perinatal Pb exposure had significantly increased
susceptibility to dental caries (p = 0.015).
PbB48±13|ig/dL
GMP, cyclic guanosine—3',5'-monophosphate; DO, distraction osteogenesis; E2, estradiol; ERG, electroretinographic; GD, gestational day; IGF!, insulin-like growth factor 1;
LH, luteinizing hormone; NOS, not otherwise specified; PbB, blood Pb concentration; PDE, phosphodiesterase; PND, post-natal day
-------
1 Observations from more recent experimental animal studies support these findings. The
2 effects of Pb on female reproduction may be classified as alterations in female sexual maturation,
3 effects on fertility and menstrual cycle, alterations in levels of female sex hormones, and changes
4 in morphology or histology of female reproductive organs as well as the placenta.
5
6 5.4.4.2 Effects on embryo/fetal morphology
7 The 1986 Pb AQCD summarized numerous reports that found associations between
8 prenatal exposure to high doses of Pb and increased incidences of teratogenic effects
9 (particularly tail stunting) in rodents (Ferm and Carpenter, 1967, Wide, 1985). More recent
10 studies provide additional support for the teratogenic effects of lead in experimental animals
11 (Dey et al., 2001; Flora and Tandon, 1987; Ronis et al., 1996). However, the few studies
12 (including those described in the 1986 Pb AQCD and more recent reports) that have
13 demonstrated teratogenic effects of Pb exposure are confounded by maternal toxicity.
14
15 5.4.5 Effects on Growth and Endocrine Regulation of Growth
16 Studies conducted in rodents provide convincing evidence for an association between
17 gestational Pb exposure and reduced birth weight and postnatal growth at doses that produce no
18 clinical toxicity in the mothers (Dearth et al., 2002; Hamilton et al., 1994; Logdberg et al., 1987;
19 Piasek and Kostial, 1991; Pinon-Lataillade et al., 1995; Ronis et al., 1998a,b,c; Singh et al.,
20 1993b; Watson et al., 1997). In squirrel monkeys, Logdberg et al. (1987) reported a statistically
21 significant reduction in mean birth weight following oral exposure to Pb-acetate during the latter
22 trimesters of pregnancy (mean maternal PbB 54 |ig/dL [39 to 82 |ig/dL]). Additional details
23 concerning Logdberg et al. (1987) are provided in Table AX5-4.3.
24 In addition, the literature provides convincing support for lead-induced impairment of
25 postnatal growth. Although some early studies (Minnema and Hammond, 1994; Hammond
26 et al., 1993, 1990) ascribed the reduction in postnatal growth to reduced food consumption
27 (suggesting an effect of Pb on the satiety endpoint), more recent studies report impaired growth
28 unrelated to changes in food consumption. Ronis et al. (1996, 1998a,b,c) reported lead-induced
29 reductions in birth weight and postnatal growth that occurred in the absence of a significant
30 alteration in food consumption. Han et al. (2000) found a reduction in the birth length of pups
31 (pup PbB -16 |ig/dL on PND 1) whose mothers had been exposed to Pb up to 1 month before
May 2006 5-105 DRAFT-DO NOT QUOTE OR CITE
-------
1 mating (maternal PbB on GD 9, 16, and 21 <40 ng/dL). Berry et al. (2002) reported depressed
2 growth in rats exposed to lead for six weeks beginning at weaning, even though food
3 consumption was higher in the lead-exposed rats.
4 Ronis et al. (2001) showed that in rats, pre- and postnatal (through PND 55) exposure to
5 Pb reduced somatic longitudinal bone growth and bone strength during the pubertal period
6 (PbB >67 jig/dL). These effects could not be reversed by stimulation of the growth hormone
7 axis by supplemental sex hormone. These results suggest that Pb exposure may impair growth
8 through a mechanism that involves a suppressed pituitary response to hypothalamic stimulation.
9 The mechanism may be related to a reduction in plasma concentrations of IGFi following Pb
10 exposure (Dearth et al., 2002; Ronis et al., 1998b). Dearth et al. (2002) exposed F344 rats to Pb
11 by gavage beginning 30 days before mating and continuing until weaning of the pups at 21 days
12 of age. By PND 30, all three groups had PbB <3 |ig/dL and all lead-exposed groups exhibited
13 decreased serum levels of IGFi, LH, and £2. Since liver IGFi mRNA was not affected, it
14 appeared that Pb altered the translation and/or secretion of IGFi, which in turn decreased
15 LH-releasing hormone at the hypothalamic level. Additional details concerning Dearth et al.
16 (2002) are provided in Table AX5-4.3. An effect on IGFi also been demonstrated by Ronis et al.
17 (1998b).
18
19 5.4.6 Effects on Other Endocrine Systems during Development
20 Recent experimental animal studies provide evidence for an interaction between Pb
21 exposure and stress hormones, including glucocorticoids and catecholamines (Cory-Slechta
22 et al., 2004; Yu et al., 1996; Vyskocil et al., 1991; Saxena et al., 1990). Lead has been reported
23 to increase stress hormone levels (Vyskocil et al., 1991).
24 Cory-Slechta et al. (2004) reported a persistent effect of maternal lead exposure
25 (PbB 30-40 |ig/dL) on corticosteroid levels in adult offspring. Both male and female offspring
26 born to dams exposed to lead exhibited elevated corticosteroid levels as adults. In female
27 offspring, the lead effect was potentiated when maternal lead exposure occurred in combination
28 with environmental stress (administered as restraint). These data suggest that brief exposures to
29 lead during development may result in persistent changes in the hypothalamic-pituitary-adrenal
30 axis (e.g., fetal glucocorticoid programming). Additional details concerning Cory-Slechta et al.
31 (2004) are provided in Table AX5-4.3.
May 2006 5-106 DRAFT-DO NOT QUOTE OR CITE
-------
1 The interplay between Pb and stress hormones is consistent with the findings of Yu et al.
2 (1996) wherein neonatal exposure to Pb (PbB 70 |ig/dL) decreased cold-water swimming
3 endurance (a standard test for stress endurance). The enhancement of lead-induced toxicity by
4 stress was also reported by Saxena et al. (1990) in adult male rats. Saxena et al. (1990) reported
5 enhanced testicular injury when rats were exposed to immobilization stress in combination with
6 Pb exposure (PbB >200 (ig/dL).
7
8 5.4.7 Effects on Other Organ Systems during Development
9 5.4.7.1 Developmental Effects on Blood and Liver
10 Recent data provide evidence for lead-induced alterations in developing hematopoietic
11 and hepatic system. The data concerning the effect of Pb exposure on the developing
12 hematopoietic system are limited. The 1986 Pb AQCD proposed that alterations in blood ALAD
13 activity and erythrocyte protoporphyrin were possible biomarkers for subtle, prenatal effects of
14 Pb on heme synthesis (Hayashi 1983a,b; Jacquet et al., 1977; Prigge and Greve, 1977;
15 Hubermont et al., 1976). A more recent study (lavicoli et al., 2003) of Pb effects on RBC
16 production, Hb concentration, and Hct was not able to clearly establish a dose-response
17 relationship for these endpoints. Although limited by small group size (one litter per dose),
18 dietary exposure during conception, lactation, and through weaning to 90 days of age increased
19 red blood cell synthesis, blood hemoglobin concentration, and hematocrit in offspring in
20 offspring that had blood lead concentrations in the range 0.6-2 |ig/dL; and decreased red cell
21 blood cell synthesis, blood hemoglobin concentration, and hematocrit in offspring in that had
22 blood lead concentrations in the range 2-13 |ig/dL. More data are needed to clarify the effect of
23 low-dose Pb exposure on blood endpoints.
24 Two rodent studies provide limited suggestive evidence that Pb exposure during
25 development produces changes in hepatic enzymes and other biomarkers of hepatic function.
26 Pillai and Gupta (2005) reported that long-term exposure of rats (pre-mating, gestation, and
27 lactation) to lead acetate (subcutaneous injections of 0.05 mg/kg-day; PbB not reported) resulted
28 in reduced activities of maternal hepatic steroid (£2) metabolizing enzymes (17-B-hydroxy
29 steroid oxidoreductase and UDP glucuronyl transferase) and decreased hepatic CYP450 content.
30 Corpas (2002) reported that exposure to Pb in drinking water exposure during gestation and
31 lactation (pup PbB -22 |ig/dL at PND 12 and PND 21) resulted in alterations in the hepatic
May 2006 5-107 DRAFT-DO NOT QUOTE OR CITE
-------
1 systems of neonates (PND 12) and pups (PND 21). The effects manifested as alterations in
2 several biochemical indicators of hepatic toxicity: reductions in Hb, iron, alkaline and acid
3 phosphatase levels, and hepatic glycogen, and elevated blood glucose. These data suggest that
4 Pb may alter hepatic function during development; however, more data are needed to determine
5 whether these effects are persistent.
6 5.4.7.2 Developmental Effects on Skin
7 Recent data provide limited evidence of altered soft tissue development resulting from Pb
8 exposure. The literature includes one report of lead-induced abnormalities in skin development.
9 Dey et al. (2001) reported that the pups of mice exposed orally to Pb citrate (5 jig/kg-day)
10 throughout gestation exhibited a variety of skin anomalies, including perforations, cell deformity,
11 and disordered collagen bundles. The PbB levels for mothers and pups were not provided.
12 Although detailed biochemical studies are required to elucidate the mechanism for structural
13 abnormalities, it appears that covalent binding of Pb ions to the sulfate group of
14 glycosaminoglycans may be involved.
15
16 5.4.7.3 Developmental Effects on the Retina
17 Several studies have found that Pb exposure during early postnatal development impairs
18 retinal development in female Long-Evans hooded rats (Fox et al., 1997, 1991a,b; Fox and
19 Rubenstein, 1989; Fox and Chu, 1988). Of these, two studies are particularly important.
20 Fox et al. (199la) demonstrated that lactation exposure to Long-Evans hooded rats (PbB 18.8
21 or 59.4 |ig/dL) resulted in long-term, dose-dependent decreases retinal Na/K ATPase activity in
22 the female offspring (only female pups were used). Fox et al. (1997) subsequently demonstrated
23 that lactation exposure to female Long-Evans hooded rats (PbB 19 ± 3 or 59 ± 8 |ig/dL) or
24 drinking water exposure to adult females (PbB 56 ± 9 |ig/dL) resulted in differential age- and
25 dose-dependent alterations in retinal structure and function following low (PbB <20 |ig/dL) and
26 moderate (PbB <60 |ig/dL) exposures during lactation or long-term (-60 days) exposure during
27 adulthood. The mode of action for the effects of Pb on retinal development may be related to
28 impaired Na/K ATPase activity (Fox et al., 1991a). The observation of reduced enzyme activity
29 in the retina, but not in the kidney, suggests specificity for the retinal alpha-3 isozyme of Na/K
May 2006 5-108 DRAFT-DO NOT QUOTE OR CITE
-------
1 ATPase, rather than the renal alpha-1 isozyme of Na/K ATPase. The authors suggested that this
2 specificity may play a role in the target organ-specific toxicity of Pb (Fox et al., 1991a).
3
4 Summary
5 The 1986 Pb AQCD presented unequivocal evidence (derived principally from studies of
6 rodents) for effects of Pb on reproduction and development in laboratory animals. This included
7 evidence for lethal effects in developing organisms exposed to Pb during gestation and in the
8 neonatal period, as well as a variety of sublethal effects on reproduction and development.
9 Sublethal effects included changes in levels or function of reproductive hormones, effects on
10 maturation of reproductive systems, persistent toxic effects on the gonads (both male and
11 female), and adverse effects on the conceptus. More subtle effects on hormone metabolism and
12 reproductive cell structure of developing organisms were also documented.
13 • More recent studies support earlier conclusions, presented in the 1986 Pb AQCD, that Pb
14 can produce temporary and persistent effects on male and female reproductive function and
15 development and that Pb disrupts endocrine function at multiple points along the
16 hypothalamic-pituitary-gonadal axis.
17 • Studies conducted in male experimental animals unequivocally demonstrate that Pb exposure
18 during early development (PbB >30 |ig/dL) can delay the onset of puberty and alter
19 reproductive function later in life.
20 • Persistent effects of Pb exposure on the male reproductive system may derive from
21 disruption in pulsatile release of sex hormones during early development (Ronis et al.,
22 1998c).
23 • Experimental animal studies provide convincing evidence that Pb acts as an endocrine
24 disrupter in males at various points along the hypothalamic-pituitary-gonadal axis. Although
25 there is evidence for a common mode of action, consistent effects on circulating testosterone
26 levels are not always observed in lead-exposed animals. The inconsistency in the reports of
27 circulating testosterone levels complicates the derivation of a dose-response relationship for
28 this endpoint.
29 • More recent studies in animals provide additional support for testicular damage (i.e.,
30 ultrastructural changes in testes and cytotoxicity in Sertoli cells) following exposure to Pb
31 and demonstrated ultrastructural changes in testes of monkeys at PbB 35 to 40 |ig/dL.
32 Lead-induced oxygen free radical generation is the plausible mechanism of testicular injury
33 in primates and rodents.
34 • Recent studies in various mammalian species provide convincing support for endocrine-
35 mediated alterations of the female reproductive system. The nonhuman primate studies
May 2006 5-109 DRAFT-DO NOT QUOTE OR CITE
-------
1 provide dose-response information concerning the effects of Pb on female sex hormones and
2 menstrual cycle.
3 • Exposures of monkeys to Pb resulting in chronic PbB <20 |ig/dL produce few effects on
4 circulating hormone levels and do not alter the menstrual cycle. Higher exposures of
5 monkeys to Pb (PbB >40 |ig/dL) alter circulating hormone levels and the menstrual cycle,
6 with more marked changes in these endpoints occurring at higher PbB levels.
7 • Several modes of action for lead-induced alterations in female reproduction have been
8 proposed, including changes in hormone synthesis or metabolism and changes in hormone
9 receptor levels. In addition, Pb may alter sex hormone release and imprinting during early
10 development.
11 • More recent studies have confirmed that Pb exposure disturbs female fertility; however, Pb
12 exposure does not generally produce total sterility.
13 • Studies in nonhuman primates and rodents have also demonstrated reductions in litter size,
14 implantation dysfunction, and decreased postnatal survival following Pb exposure of gravid
15 female experimental animals (PbB >30 jig/dL).
16 • Lead-induced changes in morphology or histology in female sex organs and placenta may
17 explain reduced fertility and impaired female reproductive success.
18 • Exposure to Pb in early pregnancy also produces structural changes in the epithelium of the
19 uterus of mice. These changes in uterine tissue may impair successful implantation of the
20 blastocysts.
21 • Histological and morphological effects on the uterus and placenta may explain the reduced
22 birth weight that has been associated with prenatal Pb exposure (possibly due to placental
23 insufficiency).
24 • Pre- and postnatal exposure to Pb has been demonstrated to result in fetal mortality and
25 produce a variety of sublethal effects in the offspring. Many of these lead-induced sublethal
26 developmental effects occur at maternal PbB that do not result in clinical (overt) toxicity in
27 the mothers. The few studies that have reported teratogenic effects resulting from Pb
28 exposure are confounded by maternal toxicity.
29 • Studies conducted in rodents and primates provide convincing evidence for an association
30 between Pb exposure and reduced birth weight and postnatal growth at doses that produce no
31 clinical toxicity in the mothers (maternal PbB >40 |ig/dL).
32 • Recent experimental animal studies provide evidence for an interaction between Pb exposure
33 during development (PbB 30 to 40 |ig/dL) and stress hormones, including glucocorticoids
34 and catecholamines.
35 • Lead exposure during early postnatal development (PbB -20 |ig/dL) impairs retinal
36 development in female Long-Evans hooded rats.
May 2006 5-110 DRAFT-DO NOT QUOTE OR CITE
-------
1 • In addition, recent studies provide limited evidence for lead-induced alterations in developing
2 skin, and hematopoietic and hepatic systems.
3
4
5 5.5 CARDIOVASCULAR EFFECTS OF LEAD
6 5.5.1 Introduction
7 Numerous large and small epidemiological studies have attempted to examine the link
8 between Pb exposure and development of hypertension (HTN) in the general population and
9 occupationally exposed individuals. In addition, a number of studies have reported on other
10 cardiovascular effects of Pb in Pb-exposed humans (U.S. Environmental Protection Agency,
11 1990). While several studies have demonstrated a positive correlation between blood pressure
12 and blood Pb concentration, others have failed to show such association when controlling for
13 confounding factors such as tobacco smoking, exercise, body weight, alcohol consumption, and
14 socioeconomic status. Thus, the studies that have employed blood Pb level as an index of
15 exposure have shown a relatively weak association with blood pressure. In contrast, the majority
16 of the more recent studies employing bone Pb level have found a strong association between
17 long-term Pb exposure and arterial pressure (Chapter 6). Since the residence time of Pb in the
18 blood is relatively short but very long in the bone, the latter observations have provided
19 compelling evidence for the positive relationship between Pb exposure and a subsequent rise in
20 arterial pressure. This section reviews the published studies pertaining to the cardiovascular
21 effects of Pb exposure in experimental animals, isolated vascular tissues, and cultured vascular
22 cells.
23
24 5.5.2 Lead Exposure and Arterial Pressure in Experimental Animals
25 Numerous studies have shown that exposure to low levels of Pb for extended periods
26 results in a delayed onset of arterial HTN that persists long after the cessation of Pb exposure in
27 genetically normal animals (see Tables AX5-5.1 to AX5-5.5). In addition, Pb exposure during
28 gestation has been reported to significantly raise arterial pressure in the third trimester of
29 pregnancy in SD rats given a low calcium diet (Bogden et al., 1995). Taken together, these
30 observations provide irrefutable evidence that extended exposure to low levels of Pb can result in
31 the subsequent onset of HTN in experimental animals.
May 2006 5-111 DRAFT-DO NOT QUOTE OR CITE
-------
1 Many studies have been conducted to explore the mechanisms by which chronic Pb
2 exposure may cause HTN. Most of these studies have examined various blood-pressure
3 regulatory and vasoactive systems in animal models of Pb-induced HTN. In addition, several
4 studies have investigated the direct effect of Pb on vascular tone or the ability of Pb to modify
5 the response to vasoconstrictor/vasodilator agents in isolated vascular tissues. Finally, a number
6 of studies have explored the effect of Pb on cultured endothelial and vascular smooth muscle
7 cells. An overview of the findings of these studies is provided below:
8
9 5.5.2.1 Effect of Lead on Production of Reactive Oxygen Species and Nitric
10 Oxide Metabolism
11 Reactive oxygen species (ROS), such as, superoxide (02), hydroxyl radical (OH) and
12 hydrogen peroxide (H2O2) are normally produced in the course of metabolism and are safely
13 contained by the natural antioxidant defense system. Excess production and/or diminished
14 containment of ROS can lead to oxidative stress in which uncontained ROS can attack and
15 denature functional/structural molecules and, thereby, promote tissue damage, cytotoxicity, and
16 dysfunction. In fact, oxidative stress has been implicated in the pathogenesis of HTN,
17 atherosclerosis, neurodegenerative disorders, aging, and neoplasm among other afflictions.
18 During the past decade, several studies have demonstrated that Pb exposure causes oxidative
19 stress, particularly in the kidney and cardiovascular tissues, as well as in cultured endothelial and
20 vascular smooth muscle cells (VSMC). The in vivo studies have further shown that Pb-induced
21 oxidative stress is, at least in part, responsible for the associated HTN in experimental animals.
22 Relevant published studies pertaining to this issue are summarized below and listed in Annex
23 Table AX5-5.1.
24 Khalil-Manesh et al. (1994) were among the first to suggest that oxidative stress may be
25 involved in the pathogenesis of Pb-induced HTN. This assumption was based on the observation
26 that chelation therapy with dimethyl succinic acid (DMSA) rapidly ameliorated HTN and raised
27 plasma cGMP level in rats with Pb-induced HTN. They further demonstrated that DMSA
28 possesses strong antioxidant properties in vitro. Accordingly, they theorized (a) that Pb exposure
29 may increase the generation of ROS, which, in turn, elevate arterial pressure by reacting with and
30 inactivating endothelium-derived-relaxing factor (EDRF), and (b) that by scavenging ROS,
31 DMSA rapidly lowers blood pressure prior to significantly affecting body Pb burden.
May 2006 5-112 DRAFT-DO NOT QUOTE OR CITE
-------
1 In a subsequent study, Gonick et al. (1997) showed a marked increase in renal tissue
2 content of lipid peroxidation product malondialdehyde (MDA) coupled with significant
3 upregulations of endothelial (eNOS) and inducible (iNOS) nitric oxide synthases. Thus, the
4 study provided evidence for the occurrence of oxidative stress and compensatory upregulation of
5 NOS isotypes in the kidney of animals with Pb-induced HTN.
6 In another study, Ding et al. (1998) showed that infusion of NOS substrate, L-Arginine,
7 lowers blood pressure to a much greater extent in rats with Pb-induced HTN than that seen in
8 either control animals or DMSA-treated Pb-exposed animals. The data, therefore, provided
9 indirect evidence for the role of depressed NO availability in the pathogenesis of Pb-induced
10 HTN. The study further suggested that oxidative stress may be responsible for diminished NO
11 availability in this model. It should be noted that administrating cell-impermeable native SOD
12 did not lead to a further reduction of blood pressure beyond that seen with L-Arginine alone.
13 As with the previous study (Khalil-Manesh 1994), oral DMSA therapy for 2 weeks significantly
14 lowered blood pressure in the Pb-exposed animals. This was accompanied by a significant
15 reduction of blood Pb concentration. In an attempt to explore whether the observed amelioration
16 of Pb-induced HTN was due to the reduction of Pb burden or alleviation of oxidative stress by
17 DMSA, Vaziri et al. (1997) carried out a study in which rats with Pb-induced HTN were treated
18 with a lazaroid compound, a potent, non-chelating antioxidant. The study revealed marked
19 elevation of blood pressure and oxidative stress (increased lipid peroxidation) and reduced NO
20 availability (depressed urinary NO2 + NO3 excretion) in the untreated rats with Pb-induced HTN.
21 Antioxidant therapy with the lazaroid compound resulted in a significant alleviation of oxidative
22 stress, improved NO availability, and a marked attenuation of HTN without affecting blood Pb
23 concentration. Thus, the latter study provided convincing evidence for the role of oxidative
24 stress as a major mediator of Pb-induced HTN. The study further demonstrated that Pb-induced
25 HTN is associated with diminished NO availability and that the latter was mediated by oxidative
26 stress. The reduction in NO availability observed in rats with Pb-induced HTN (Pb-acetate,
27 100 ppm in drinking water for 12 weeks) was recently confirmed by Dursun et al. (2005) in rats
28 treated with daily IP injection of Pb-acetate (8 mg/Kg) for 2 weeks. The authors showed that the
29 rise in arterial pressure was accompanied by a significant reduction of urinary NO2 + NOs
30 excretion and a significant fall in renal blood flow (indicating increased renal vascular
31 resistance), mimicking the effect of the NOS inhibitor LNAME.
May 2006 5-113 DRAFT-DO NOT QUOTE OR CITE
-------
1 To further explore the cause for the observed reduction of NO availability, Vaziri et al.
2 (1999a) subsequently studied the expression of eNOS and iNOS in the kidney and cardiovascular
3 tissues of rats with Pb-induced HTN. The study showed that the reduction in NO availability is
4 paradoxically associated with a significant upregulation of NOS isotypes. Moreover, in vitro
5 incubation experiments revealed no significant change in NOS activity in the presence of lead.
6 Interestingly, antioxidant therapy with pharmacological doses of vitamin E and ascorbic acid
7 reversed the upregulation of NOS isotypes and paradoxically raised NO availability in the
8 subgroup of rats with Pb-induced HTN (Vaziri et al., 1999a). These observations were
9 subsequently confirmed by Vaziri and Ding (2001) who showed marked reduction of NO
10 availability despite significant upregulations of eNOS, nNOS, and iNOS in the aorta, heart,
11 kidney, and brain of rats with Pb-induced HTN and their normalization with the administration
12 of superoxide-scavenger tempol (15 mg/Kg IP/day) for 2 weeks. It is noteworthy that tempol
13 administration had no effect on the measured parameters in the control animals. Taken together,
14 these observations indicated that ROS-mediated NO inactivation and, hence, depressed NO
15 availability, results in a compensatory upregulation of NOS isotypes in animals with Pb-induced
16 HTN. This phenomenon is consistent with other studies from this group, which have
17 demonstrated the presence of a negative-feedback regulation of eNOS by NO (Vaziri and Wang,
18 1999; Vaziri etal., 2005).
19 The occurrence of compensatory upregulation of NOS by oxidative stress in Pb-exposed
20 intact animals described above was subsequently replicated by Vaziri and Ding (2001) in
21 cultured human endothelial cells incubated in media containing different concentrations of
22 Pb-acetate (versus control media containing sodium acetate). Once again, co-incubation with
23 tempol prevented this phenomenon. This study confirmed the ability of Pb to affect endothelium
24 independently of its effects on humoral or hemodynamic factors, which are operative in vivo.
25 Taken together, these observations suggest that Pb-induced reduction of biologically active NO
26 is not due to the reduction of NO-production capacity. Instead, it is linked to oxidative stress.
27 In an attempt to explore this supposition, in a separate study, Vaziri et al. (1999b), tested the
28 hypothesis that avid inactivation and sequestration of NO by ROS may be, in part, responsible
29 for the reduction of NO availability in animals with Pb-induced HTN. To this end, they tested
30 for the presence of immunodetectable nitrotyrosine in kidney, brain, and cardiovascular tissues
31 harvested from untreated and antioxidant-treated (vitamin E + vitamin C) rats with Pb-induced
May 2006 5-114 DRAFT-DO NOT QUOTE OR CITE
-------
1 HTN and normal control rats. Nitrotyrosine was used as a marker of NO oxidation by ROS
2 (NO + O2 -»• ONOO , ONOO + tyrosine -»• nitrotyrosine). The study showed an
3 overabundance of nitrotyrosine in all plasma and tested tissues in the untreated rats with
4 Pb-induced HTN. Antioxidant therapy reduced nitrotyrosine abundance, attenuated HTN, and
5 simultaneously raised NO availability in the subgroup of rats with Pb-induced HTN but had no
6 effect on the normal control group. These observations provided compelling evidence that
7 Pb-induced HTN causes oxidative stress, which, in turn, promotes functional NO deficiency via
8 ROS-mediated NO inactivation. The latter, in turn, participates in the development and
9 maintenance of HTN and cardiovascular abnormalities. In addition, the formation of the highly
10 cytotoxic reactive nitrogen species, peroxynitrite (ONOO ), from the NO-ROS interaction and
11 the associated nitrosative stress could potentially contribute to the long-term cardiovascular,
12 renal, and neurological consequences of Pb exposure.
13 In a series of subsequent studies, Vaziri et al. (2003) explored the expression of
14 NAD(P)H oxidase (which is a well-recognized source of ROS in, not only, the immune cells but
15 also in renal, cardiovascular, and neuronal tissues) in animals with Pb-induced HTN.
16 In addition, expression of the main antioxidant enzymes, namely Mn and CuZn-superoxide
17 dismutases (SOD), catalase and glutathione peroxidase were investigated. The study revealed
18 significant upregulation the gp91phox subunit of NAD(P)H oxidase in the brain as well as a trend
19 for higher levels in the renal cortex and left ventricle of rats with Pb-induced HTN. This was
20 accompanied by a significant compensatory upregulation of CuZn SOD in the kidney and brain,
21 and of Mn SOD in the heart, of rats with Pb-induced HTN. In contrast, despite the presence of
22 oxidative stress, catalase and glutathione peroxidase activity levels were unchanged. In a more
23 recent study, Farmand et al. (2005) showed a significant increase in CuZn SOD activity with no
24 change in either catalase or glutathione peroxidase activity in the aorta of rats with Pb-induced
25 HTN compared with control animals. Since the latter enzymes are responsible for the reduction
26 of H2O2 and lipoperoxides, the lack of an appropriate rise in their tissue levels may contribute to
27 the severity of oxidative stress in Pb-exposed animals.
28 The contribution of oxidative stress in the pathogenesis of HTN in this model was
29 confirmed by experiments that demonstrated normalization of arterial pressure with the infusion
30 of superoxide-scavenger, tempol, in rats with Pb-induced HTN (but no change was observed in
31 the blood pressure in the control rats) (Vaziri et al., 2003). As noted above, the relative
May 2006 5-115 DRAFT-DO NOT QUOTE OR CITE
-------
1 reduction of tissue catalase and glutathione peroxidase, which are responsible for the reduction
2 of H2O2 to water and molecular oxygen (2H2O2 — CAT > 2H2O + O2) , can result in accumulation of
3 H2O2. H2C>2 serves as a cellular growth signal, as well as a substrate for hydroxyl radical (-OH)
4 generation. The former action can potentially contribute to cardiovascular remodeling, whereas
5 the latter can promote oxidative injury. In a recent study, Ni et al. (2004) demonstrated a
6 transient rise in O2 production followed by a sustained rise in H2O2 production by human
7 coronary endothelial and vascular smooth muscle cells cultured in media containing Pb-acetate
8 versus the control media containing Na-acetate. This was accompanied by, and primarily due to,
9 upregulation of NAD(P)H oxidase and SOD together with reduced or unchanged catalase and
10 glutathione peroxidase levels. Accordingly, the results of this in vitro study confirmed the
1 1 findings of the in vivo studies and validated the anticipated accumulation of H2O2.
12 As noted above, H2O2 is the substrate for the Fenton and Haber-Weiss reactions, which
13 culminate in formation of the highly cytotoxic-OH (H2O2 + e~ — >• OH + OH ). Thus,
14 accumulation of H2O2 in animals with Pb-induced HTN can facilitate-OH production and,
15 thereby, promote oxidative stress and tissue injury. This supposition was confirmed in a series
16 of studies by Ding et al. (2001), who showed increased hydroxyl radical production in rats with
17 Pb-induced HTN. Oxidative stress, HTN, and excess hydroxyl radical production were all
18 reversed with IV infusion of the reputed hydroxyl radical scavenger, DMTU, in the Pb-exposed
19 animals. Increased hydroxyl radical production observed in intact animals with Pb-induced HTN
20 was confirmed in lead-treated cultured endothelial cells (Ding et al., 2000). The role of oxidative
21 stress in the pathogenesis of HTN and endothelial dysfunction (depressed NO availability) has
22 been substantiated by a number of other investigators. For instance, Attri et al. (2003),
23 demonstrated that exposure to Pb for up to 3 months resulted in a significant rise in arterial
24 pressure, which was substantially ameliorated by coadministration of the antioxidant vitamin
25 ascorbic acid (20 mg/rat) in Wistar-Kyoto rats. The rise in arterial pressure in lead-treated rats
26 was accompanied by diminished NO availability (low plasma NO2 + NOs) and biochemical
27 evidence of oxidative stress, i.e., elevations of plasma MDA, a DNA oxidation product
28 (8-hydroxyguanosine), and diminished ferric-reducing antioxidant power, as well as
29 electrophoretic evidence of DNA damage. Amelioration of HTN by antioxidant therapy was
30 accompanied by improved NO availability (plasma NO2 + NOs), marked attenuation of oxidative
May 2006 5-116 DRAFT-DO NOT QUOTE OR CITE
-------
1 stress, and partial reduction of DNA damage in this model. In another study, Malvezzi et al.
2 (2001) showed partial amelioration of HTN in Pb-exposed rats with the administration of either
3 DMSA or L-arginine and showed a much greater response with the combination thereof. These
4 observations support the role of interaction of ROS and NO in the pathogenesis of Pb-induced
5 HTN in the rat.
6 As cited above, Pb-induced HTN is associated with and is, at least in part, due to
7 ROS-mediated inactivation and hence, reduced availability of biologically active NO. Many of
8 the biological actions of NO are mediated by cGMP, which is produced from the substrate GTP
9 by the cytosolic enzyme soluble guanylate cyclase (sGC). sGC is expressed in VSMC and
10 several other cell types. The enzyme is activated by NO to produce cGMP, which, in turn,
11 promotes vasorelaxation by lowering cytosolic Ca2+ concentrations. In an earlier study, Khalil-
12 Manesh et al. (1993a) demonstrated a significant reduction of plasma and urinary cGMP in rats
13 with Pb-induced HTN. These observations prompted a number of studies to evaluate the effect
14 of Pb on sGC expression and cGMP production in vascular tissues obtained from rats with
15 Pb-induced HTN or in normal vascular tissues incubated in Pb-containing media. For instance,
16 Marques et al. (2001) found significant reductions of acetylcholine- and Na-nitroprusside-
17 induced vasorelaxation, despite upregulation of eNOS, in the aorta of rats with Pb-induced HTN.
18 This was associated with marked downregulation of sGC abundance and diminished cGMP
19 production in the aorta. In an attempt to explore the possible role of oxidative stress in
20 Pb-induced downregulation of sGC, they included a group of rats that were co-treated with Pb
21 and the antioxidant vitamin ascorbic acid. Antioxidant therapy ameliorated HTN, restored
22 vasorelaxation response to acetylcholine and Na-nitroprusside, and normalized sGC expression
23 and cGMP production. The authors, therefore, identified diminished sGC as another mechanism
24 by which Pb exposure can promote endothelial dysfunction and HTN. They further showed that
25 Pb-induced downregulation of sGC is mediated by oxidative stress, as evidenced by its
26 prevention with antioxidant therapy. Downregulation of sGC protein abundance in the aorta of
27 Wistar rats with Pb-induced HTN was recently confirmed by Farmand et al. (2005) in the
28 Pb-exposed Sprague-Dawley rats. In another study, Courtois et al. (2003) showed that 24-h
29 incubation of normal rat aorta in the lead-containing media resulted in a concentration-dependent
30 downregulation of sGC (beta subunit), with the maximum effect observed at 1 ppm
31 concentration. This was associated with increased Q^ production and upregulation of
May 2006 5-117 DRAFT-DO NOT QUOTE OR CITE
-------
1 cyclooxygenase-2 (COX-2) expression. Co-incubation with ascorbic acid reduced COX-2
2 expression and C>2 production and attenuated, but did not fully prevent, the Pb-induced
3 downregulation of sGC. Similarly, addition of COX-2 inhibitor Rofecoxib or of protein kinase
4 A inhibitor (H-89) partially mitigated the Pb-induced downregulation of sGC in vitro. However,
5 the COX-2 inhibitor failed to reduce Q^ production in Pb-exposed vascular tissues. Based on
6 these observations, the authors concluded that Pb exposure downregulates vascular tissue sGC
7 abundance via induction of oxidative stress and upregulation of COX-2.
8 Oxidative stress and altered NO metabolism can potentially trigger a cascade of events
9 that work in concert to promote HTN and cardiovascular disease in Pb-exposed organisms.
10 Some of these potential links are illustrated in Figure 5-5.1.
11
12 5.5.2.2 Protein Kinase C, Inflammation, NFidJ Activation and Apoptosis
13 Protein kinase C (PKC) isoforms belong to a family of serine-threonine kinases, which
14 serve numerous diverse cellular functions. For instance, PKC is involved in regulating vascular
15 contractility, blood flow, permeability, and cell growth. In this regard, the activation of PKC has
16 been shown to cause vascular contraction and Pb exposure has been found to raise PKC activity.
17 For example, Hwang et al. (2002) found increased PKC activity in the erythrocytes of a
18 group of Pb-exposed Korean workers, and Markovac and Goldstein (1988b) showed a significant
19 increase in PKC activity in rat brain micro vessels following exposure to micromolar Pb
20 concentrations. Also, Watts et al. (1995) demonstrated that Pb-acetate (10~10 to 10~3 M) caused
21 contraction in an isolated rabbit mesenteric artery preparation. This Pb-induced vasoconstriction
22 was unaffected by denudation of endothelium, while it was significantly potentiated by PKC
23 agonists and attenuated by a PKC inhibitor. Calcium channel blockade with verapamil
24 attenuated, but did not abolish, Pb-induced vasoconstriction. These findings were considered to
25 indicate that activation of PKC is, in part, responsible for Pb-induced vasoconstriction,
26 independently of endothelium or extracellular influx of calcium. Taken together, these
27 observations suggest that the activation of PKC in the vascular smooth muscle cells may, in part,
28 contribute to the pathogenesis of Pb-induced HTN by enhancing vascular contractility. It should
29 be noted, however, that Pb-induced contraction has been shown to be unaffected by a PKC
30 inhibitor in rat aorta rings (Valencia 2001). Thus, the contribution of PKC activation to the
31 Pb-induced alteration of vascular contractility appears to be both vessel- and species-specific.
May 2006 5-118 DRAFT-DO NOT QUOTE OR CITE
-------
Chronic Lead Exposure
Oxidative Stress
NO inactivation
I NO production
(eNOS uncoupling,
BH4 depletion)
.[ NO bioavailability
Inflammation
Oxidation of
arachidonic acid
Vasoconsfriction,
Renal Na retention
+
[ Sympathetic activity
Isoprostanes
Vasoconstriction,
Renal Na retention
RAS
Activation
Endothelial dysfunction
Cardiovascular
remodeling,
Platelet
activation
Hypertension
Arteriosclerosis,
Thrombosis
Figure 5-5.1. This illustration depicts some of the potential mechanisms by which
oxidative stress may participate in the pathogenesis of Pb-induced HTN
and cardiovascular complications. In the presence of oxidative stress,
uncontained reactive oxygen species (ROS) inactivate nitric oxide (NO),
deplete NO synthase cofactor (tetrahydrobiopterin), uncouple eNOS,
promote generation of isoprostanes by oxidizing aracidonic acid, and activate
the redox-sensitive transcription factor NFidJ. Together, these events can
cause vasoconstriction, salt retention, sympathetic system activation, renin-
angiotensin system stimulation, platelet adhesion, and, thereby, endothelial
dysfunction, hypertension (HTN), inflammation, arteriosclerosis, and
thrombosis.
May 2006
5-119
DRAFT-DO NOT QUOTE OR CITE
-------
1 It is of note, that at high concentrations, Pb can reduce PKC activity in certain cell types,
2 including mouse macrophages and rat brain cortex (reviewed by Watts et al. [1995]).
3 As noted earlier, Pb exposure results in oxidative stress in cultured VSMC and endothelial
4 cells, as well as in intact animals. Oxidative stress can promote the activation of the nuclear
5 transcription factor kappa B (NFicB) and, thereby, trigger inflammation and apoptosis. In this
6 context, Ramesh et al. (2001) showed that exposure to low Pb levels (50 ppm in drinking water)
7 for 90 days activates NFicB and capsases in the rat brain. It is of note that several studies have
8 revealed the presence of renal tubulointerstitial infiltration of activated T cells, macrophages, and
9 angiotensin II (Ang-II) producing cells in various forms of genetic and acquired HTN in
10 experimental animals. Moreover, the associated tubulointerstitial inflammation has been shown
11 to contribute to the pathogenesis of HTN in these disorders (Rodriguez-Iturbe, 2004). These
12 abnormalities are accompanied by activation of the redox-sensitive NFicB, which can account for
13 the associated inflammation (reviewed by Rodriguez-Iturbe et al. [2004]). The NFicB activation,
14 the accompanying inflammation, and HTN are ameliorated by antioxidant therapy in these
15 models, pointing to the role of oxidative stress in this process. In a recent study, Rodriguez-
16 Iturbe, et al. (2005) observed marked activation of NFicB coupled with tubulointerstitial
17 accumulation of activated T-cells, macrophages, and Ang-II-producing cells, as well as increased
18 apoptotic cells in the kidneys of Pb-exposed rats (100 ppm Pb-acetate in water for 3 months).
19 This was associated with increased nitrotyrosine staining (a marker of NO/ROS interaction) in
20 the kidney tissue. Since tubulointerstitial inflammation plays a crucial role in the pathogenesis
21 of HTN in various other models of HTN, its presence in the Pb-exposed animals may contribute
22 to the associated HTN. Inflammation in Pb-induced HTN is not limited to the kidney. In fact,
23 lymphocyte infiltration is reported in the periaortic tissues in rats with Pb-induced HTN
24 (Carmignani et al., 2000). The inflammatory response to Pb exposure in the renal and vascular
25 tissues outlined above parallels observations reported for the immune system in Section 5.9 of
26 this chapter.
27
28 5.5.2.3 Effect of Lead Exposure on the Adrenergic System
29 The adrenergic system plays an important role in regulating arterial pressure, renal and
30 systemic hemodynamics, and cardiac function in health and disease. For this reason, a number
31 of clinical and animal studies have focused on the sympathetic system as a possible mediator of
May 2006 5-120 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb-induced HTN and cardiovascular abnormalities. For instance, in a study of a group of
2 Pb-exposed workers, Chang et al. (1996), found elevated plasma norepinephrine (NE), but
3 normal plasma dopamine and epinephrine, levels. The constellation of these biochemical
4 abnormalities points to increased sympathetic nervous system activity in Pb-exposed humans.
5 The impact of Pb exposure on the sympathetic nervous system activity has been substantiated in
6 experimental animals. For example, Chang et al. (1997) showed that administration of Pb
7 (Pb-acetate 0.5% in drinking H2O) for 2 months resulted in significant rises in arterial pressure
8 and plasma NE (but not epinephrine) in Wistar rats. This was coupled with significant
9 reductions of the aorta P adrenergic receptor density and isoproterenol (P agonist)-stimulated
10 cAMP production. In a subsequent study, Tsao et al. (2000) reported a significant rise in plasma
11 NE coupled with marked reductions of P receptor density as well as diminished basal and
12 isoproterenol-stimulated cAMP productions in the aorta and heart of Wistar rats with Pb-induced
13 HTN. In contrast to the heart and aorta, P receptor density as well as basal and
14 P agonist-stimulated cAMP production were increased in the kidneys of Pb-exposed animals.
15 In another study, Carmignani et al. (2000) found significant elevations of blood pressure,
16 plasma catecholamines, and cardiac contractility (dP/dt), together with reduced carotid blood
17 flow in rats with Pb-induced HTN. The effect of Pb on the sympathetic nervous system activity
18 was examined by Lai et al. (2002) who tested the rapid response to intrathecal (IT) injection of
19 PbCb in vivo and its addition to the thoracic cord slices in vitro in the rats. They found
20 significant rises in arterial pressure and heart rate with IT injection of Pb-chloride. These effects
21 of Pb were abrogated by the administration of ganglionic blockade using hexomethonium. The
22 in vitro studies revealed a significant rise in excitatory and significant fall in inhibitory
23 post-synaptic potentials with the addition of Pb to the bathing medium and their reversal with
24 saline washout.
25 In a recent study, Chang et al. (2005) showed a gradual decline in blood, kidney, heart,
26 and aorta Pb contents toward the control values within 7 months following cessation of exposure
27 in rats with Pb-induced HTN. This was coupled with a parallel declines in arterial pressure,
28 plasma NE and renal tissue P receptor density as well as parallel rises in the aorta and heart
29 P receptors densities during the 7-month period following cessation of Pb exposure. However,
30 while HTN and P receptor abnormalities were significantly improved, they were not completely
31 reversed. It should be noted that bone Pb contents were not measured in this study and were
May 2006 5-121 DRAFT-DO NOT QUOTE OR CITE
-------
1 most likely elevated despite normalization of blood and soft tissue levels. These findings
2 provided evidence for the stimulatory effect of Pb on the sympathetic nervous system and for its
3 contribution to the cardiovascular effects of Pb exposure.
4
5 5.5.2.4 Effects of Lead on the Renin-Angiotensin-Aldosterone (RAAS) and
6 Kininergic Systems
7 The available data on the effects of Pb exposure on the RAAS are contradictory. This
8 appears to be primarily due to variability in the dosage and duration of Pb exposure, as well as
9 the age at which exposure is initiated or the animals studied. In addition, when present,
10 nephropathy can potentially affect the RAAS profile of Pb-exposed animals or humans. The
11 majority of animal studies of the effects of Pb on RAAS were conducted and published in the
12 late 1970s and 1980s. In a meta-analysis of the studies published in that period, Vander (1988)
13 found increased plasma renin activity and renal tissue renin content in young rats after several
14 weeks of Pb exposure sufficient to achieve blood Pb concentrations in the range of 30 to
15 40 |ig/dL. Similar results were found in rats exposed to Pb in utero and for 1 month after birth.
16 In contrast, plasma renin activity and renal renin contents were generally unchanged or even
17 reduced in older rats whose Pb exposure had commenced in utero.
18 In a more recent study, Carmignani et al. (1999) showed a significant increase in plasma
19 angiotensin converting enzyme (ACE) activity in the rats exposed to Pb (60 ppm Pb-acetate in
20 water) for 10 months beginning at an early age (weaning). This was accompanied by a
21 significant increase in plasma kininase II, kininase I, and kallikrein activities. In a subsequent
22 study, Sharifi et al. (2004) examined plasma and tissue ACE activity in young adult rats
23 (weighing 200 g) exposed to Pb (100 ppm Pb-acetate) for 2 to 8 weeks. They found significant
24 rises in plasma, aorta, heart, and kidney ACE activities, peaking at 2 to 4 weeks. This was
25 followed by a decline in plasma and tissue ACE activity to subnormal values by 8 weeks, at
26 which point arterial pressure was markedly elevated. The authors concluded that the elevated
27 ACE activity is involved in the induction of HTN but may not be necessary for maintaining
28 HTN in Pb-exposed animals. Finally, in a recent study, Rodriguez-Iturbe et al. (2005)
29 demonstrated a marked increase in the number of Ang-II positive cells in the kidneys of rats
30 treated with lead acetate (100 ppm in water) for 3 months. This observation points to heightened
31 intra-renal Ang-II generation in rats with Pb-induced HTN.
May 2006 5-122 DRAFT-DO NOT QUOTE OR CITE
-------
1 Taken together, the data point to activation of the RAAS at some point in the course of
2 Pb-induced HTN. Further studies are needed to fully elucidate the effects of Pb exposure on
3 various other RAAS components.
4
5 5.5.3 Effects of Lead Exposure on Vasomodulators
6 In a study of a group of Pb workers with elevated blood Pb concentration, Cardenas et al.
7 (1993) found a significant increase in urinary excretion of the metabolite of vasoconstrictive
8 prostaglandin, thromboxan (TXB2), and significant reduction of the vasodilatory prostaglandin,
9 6-keto-PGFl, when compared with the control workers. Subsequently, Hotter et al. (1995)
10 confirmed the elevation of urinary TXB2 in another group of Pb-exposed workers. Based on
11 these observations, the authors suggested that Pb can alter the balance between vasoconstrictive
12 and vasodilatory prostaglandins in a way that may contribute to HTN and cardiovascular disease.
13 In an attempt to examine such possible effects of Pb exposure in experimental animals, Gonick
14 et al. (1998) measured urinary excretion of the above metabolites in the rat model of Pb-induced
15 HTN. The study showed no significant difference in urinary excretion of the given prostaglandin
16 metabolites between the Pb-exposed and control rats. However, in a recent in vitro study,
17 Dorman and Freeman (2002) demonstrated that Pb promotes the release of arachidonic acid by
18 vascular smooth cells via activation of phospholipase A2. They further showed that, at low
19 concentrations, Pb augments Ang-II-induced VSMC proliferation, whereas at a high
20 concentration it reduces viability and cell count in unstimulated cells and reduces DNA
21 synthases in Ang-II and fetal calf serum (FCS)-stimulated VSMC. Thus, Pb can increase the
22 release of arachidonic acid (the substrate for prostaglandins) via activation of phospholipase A2.
23 Given the limited and contradictory nature of the published data, further in-depth studies
24 are needed to clarify the effects of Pb on regulation of arachidonic acid metabolism and the
25 synthesis of various classes of prostaglandins.
26 Endothelin
27 Endothelins (ET) represent a family of potent vasoconstrictive peptides that are produced
28 by endothelium and a number of other cell types. Excess production or increased sensitivity to
29 ET can raise arterial pressure. In an attempt to explore the possible contribution of ET to the
30 pathogenesis of Pb-induced HTN, Khalil-Manesh et al. (1993a) studied the effects of exposure to
May 2006 5-123 DRAFT-DO NOT QUOTE OR CITE
-------
1 low and high levels of Pb (100 ppm versus 5000 ppm) in the drinking water for 1 to 12 months in
2 rats. Rats exposed to low (but not high) levels of Pb exhibited HTN and a significant increase in
3 plasma ET-3 concentration. These findings were confirmed by these investigators in a
4 subsequent study of rats with Pb-induced HTN (Khalil-Manesh et al., 1994). Similarly, Gonick
5 et al. (1997) demonstrated a significant elevation of plasma concentration and urinary excretion
6 of ET-3 in rats with Pb-induced HTN. In a recent study, Martin et al. (2005) showed that
7 incubation in the lead-containing media resulted in the downregulation of soluble guanylate
8 cyclase and cGMP production in the isolated artery segment of normal rats. They further found
9 that co-incubation with an ET-A receptor antagonist can partially reverse this effect of lead.
10 These findings suggest that the adverse effect of Pb exposure on cGMP production in the
11 vascular tissue is, in part, mediated by its ability to raise ET activity. It, thus, appears that
12 exposure to low-levels of Pb can raise activity or production of ET, which can, in turn, play a
13 part in the pathogenesis of Pb-induced HTN in the rat. Further studies are required to carefully
14 explore the effects of Pb on various components of the ET system.
15
16 Atrial Natriuretic Factor
17 Atrial natriuretic factor (ANF) is produced and secreted by cardiac myocytes. Plasma
18 concentration of ANF rises with volume expansion and declines with volume contraction. ANF
19 serves as a vasodilator and a natriuretic agent and, as such, plays a role in regulating blood
20 volume, vascular resistance, and, hence, arterial pressure. Giridhar and Isom (1990) measured
21 ANF in rats treated with IP injection of Pb-acetate (0.0 to 1.0 mg/kg/twice weekly for 30 days).
22 The Pb-exposed animals exhibited fluid retention, which was coupled with a paradoxical dose-
23 dependent decline in plasma ANF concentration. Based on these findings, they suggested that
24 Pb may interfere with the hormonal regulation of cardiovascular system, which may, in turn,
25 relate to the cardiovascular toxicity of this metal.
26 5.5.4 Effects of Lead on Vascular Reactivity
27 Addition of Pb-acetate to the bathing medium has been shown to elicit a cumulative
28 concentration-dependent vasoconstriction in isolated rabbit mesenteric artery (Watts et al.,
29 1995). This effect was reported to be partly mediated by activation of PKC. In a more recent
30 study, Valencia et al. (2001) found a concentration-dependent vasoconstrictive response to
May 2006 5-124 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb-acetate (0.1 to 3.1 mM) in Wistar rat thoracic aorta rings. The contractile response was
2 observed in both intact and endothelium-denuded rings. Likewise, Pb-induced vasoconstriction
3 was preserved in calcium-free medium and was unaffected by either a-1 blockade (prazosin),
4 PKC inhibition (Calphostin) or L-type calcium channel blockade (verapamil). However,
5 Pb-induced vasoconstriction was inhibited by lanthanum, which is a general calcium-channel
6 blocker. These observations suggest that Pb can promote an endothelium-independent
7 vasoconstriction by a direct effect on the vascular smooth muscle cells. The data further
8 suggests that the effect of Pb is Ca-independent and may depend on the entry of Pb to the cell via
9 a lanthanum-blockable channel. In contrast to the latter studies, addition of Pb-acetate did not
10 cause vasoconstriction in the rat aorta rings used in a study reported by Shelkovnikov and
11 Gonick (2001). Moreover, Pb-acetate at either high (10~4m) or low (10~8m) concentrations did
12 not modify the response to NE, phorbol ester, or isoproterenol. However, at 10~4M, Pb-acetate
13 augmented the contractile response to submaximal concentrations of calcium. Thus, the rapid
14 action of Pb on vascular reactivity in vitro seems to vary depending on the type of the vessel
15 used, the Pb concentration employed, and the animal species being studied.
16 A number of studies have endeavored to discern possible differences in vascular reactivity
17 to various agonists between animals with Pb-induced HTN and control animals. For instance,
18 Purdy et al. (1997) found no significant difference in vasoconstrictive response to NE and
19 phenylephrine or vasodilatory response to acetylcholine or nitroprusside in the aorta rings
20 obtained from Sprague-Dawley rats with Pb-induced HTN. In contrast, Marques et al. (2001)
21 showed a significant reduction of vasodilatory response to both acetylcholine and nitroprusside
22 in Wistar rats with Pb-induced HTN. It should be noted that the Wistar rats employed in the
23 latter study had been treated with 5 ppm Pb-acetate in the drinking water for 1 month, whereas
24 those reported by Purdy et al. (1997) had been given a higher dosage (100 ppm) for a longer
25 period (3 months). Therefore, the magnitude and duration of exposure may account for the
26 differences observed between the two reports. Also, the effect of Pb on vascular reactivity may
27 vary from one tissue to the next, as clearly exemplified by studies (Oishi et al., 1996) that
28 showed significant endothelium-dependent vasorelaxation of mesenteric artery response to
29 acetylcholine in the presence of the NOS inhibitor L-NAME in tissues from rats exposed to
30 Pb-acetate for 3 months. These observations suggest that chronic Pb exposure may impair
May 2006 5-125 DRAFT-DO NOT QUOTE OR CITE
-------
1 endothelium-dependent hyperpolarization in the rat mesenteric artery. However, no such effect
2 was noted in the aorta obtained from the same animals.
3
4 5.5.5 Lead-Calcium Interactions in Vascular Tissue
5 Changes in cytosolic Ca2+ concentrations are intimately involved in regulating vascular
6 tone and vascular smooth muscle contraction. Consequently, several studies have focused on the
7 interaction of Pb with cellular Ca2+ and Ca2+-dependent signaling pathways as a means to gain
8 insight into the pathogenesis of Pb-induced HTN (Piccini et al., 1977; Favalli et al., 1977; Webb
9 et al., 1981; Goldstein, 1993; Watts et al., 1995). Lead can potentially compete with Ca2+ in
10 transport systems (i.e., channels and pumps) involved in physiological movements of ions,
11 particularly Ca2+, into and out of the cell (Simons, 1993a,b). Moreover, Pb can alter the
12 intracellular distribution of Ca2+ between cytoplasm, endoplasmic reticulum, and mitochondria,
13 which normally regulates cytosolic Ca2+ concentration, (Simons 1993a,b). In addition, Pb can
14 serve as a substitute for calcium in Ca2+-dependent signaling pathways by interacting with
15 calmodulin, PKC, and calcium-dependent potassium channels (Haberman, 1983; Richardt et al.,
16 1986; Chai and Webb, 1988; Simons, 1993a,b; Watts et al., 1995). Thus, interactions of Pb with
17 cellular Ca2+ via these complex mechanisms in the vascular cells may contribute to alterations of
18 vascular resistance and HTN. For example, Piccini et al. (1977) and Favalli et al. (1977) showed
19 that Pb exposure increases calcium content in the tail artery in rats. The authors attributed this
20 phenomenon to a possible Pb-induced inhibition of Ca2+ extrusion from the vascular cells. Using
21 rabbit mesenteric artery preparations, Watts et al. (1995), showed that blockade of either PKC or
22 voltage-gated Ca channels by verapamil substantially attenuated Pb-induced vasoconstriction in
23 both intact and endothelium-denuded preparations. Based on these observations, the authors
24 suggested that Pb promotes a vasoconstrictive response in rabbit mesenteric artery via a
25 Ca2+-dependent activation of PKC. In contrast, Valencia et al. (2001) using rat aorta rings
26 reported a vasoconstrictive response to Pb-acetate in rat aorta rings bathed in either Ca2+-free or
27 Ca2+-containing media and in the presence or absence of the L-type calcium-channel blocker
28 verapamil or of the PKC inhibitor calphostin. Moreover, depletion of intracellular Ca2+ stores by
29 preincubation of rings in EGTA, while diminishing the intensity, did not abrogate Pb-induced
30 vasoconstriction in this system. In contrast, Pb-induced vasoconstriction was prevented by
31 lanthanum (a general blocker of calcium channels) in both Ca2+-containing and Ca2+-free media.
May 2006 5-126 DRAFT-DO NOT QUOTE OR CITE
-------
1 Based on these observations, the authors concluded that Pb can elicit a PKC-independent
2 contractile response in the rat aorta by entering VSMC via a non-voltage-gated Ca2+ channel and
3 mimicking the action of Ca2+. It, thus, appears that Pb exerts its effect by mechanisms that are
4 species- and vessel-specific.
5
6 5.5.6 Cardiotoxicity and Atherogenesis
7 Acute Pb exposure has been reported to affect cardiac function, and chronic exposure has
8 been linked to atherosclerosis and increased cardiovascular mortality by some, but not by all
9 investigators, in humans (See Chapter 6). In an attempt to assess the cardiotoxicity of lead,
10 Prentice and Kopp (1985) carried out the in vitro perfusion of isolated rat heart preparations with
11 a perfusate containing 0.3 and 30 jiM Pb-acetate for up to 60 min. At 30 jiM concentration, Pb
12 prolonged the AV node and His bundle conduction times, reduced coronary blood flow and heart
13 rate, and altered cardiac energy metabolism. Milder, and statistically insignificant, changes were
14 also observed at 0.3 jiM Pb concentration in this model. These observations illustrate the direct
15 cardiotoxicity of Pb independently of its systemic and neuroendocrine actions in acute
16 intoxication. In an attempt to determine whether chronic exposure to Pb or cadmium can cause
17 atherosclerosis, Revis et al. (1981), studied male white pigeons that were exposed to Pb (0.8 ppm
18 in drinking water) for extended periods. Long-term low-level Pb exposure in this model resulted
19 in a significant rise in arterial pressure and a near doubling of the number of atheromatous
20 plaques in the aorta. These observations demonstrate the proatherogenic effects of chronic
21 exposure to low levels of Pb in pigeons.
22
23 5.5.7 Effects of Lead on Endothelial Cells
24 Endothelium is an important constituent of the blood vessel wall and regulates
25 macromolecular permeability, vascular smooth muscle tone, tissue perfusion, and blood fluidity.
26 Endothelial damage or dysfunction results in atherosclerosis, thrombosis, and tissue injury.
27 Chronic Pb exposure has been shown to promote atherosclerosis in experimental animals (Revis
28 et al., 1981). Given the central role of endothelial injury/dysfunction in the pathogenesis of
29 atherosclerosis, numerous studies have explored the effect of Pb on cultured endothelial cells.
30 These studies have searched for evidence of Pb-mediated endothelial cell injury and the effects
31 of Pb on endothelial cell proliferation, tube formation (angiogenesis), monolayer wound repair,
May 2006 5-127 DRAFT-DO NOT QUOTE OR CITE
-------
1 and production of heparansulfate proteoglycans, plasminogen activator (tPA), and plasminogen
2 activator inhibitor-1 (PAI-1).
3 Using cultured bovine aorta endothelial cells, Kaji et al. (1995a) showed that incubation
4 with Pb-nitrate at concentrations equal to or below 50 jiM for 24 h, results in mild
5 de-endothelialization of endothelial monolayers in vitro. They further showed that adding Pb at
6 10 jiM concentration markedly increased cadmium-induced endothelial injury.
7 Proliferation of endothelial cells is a critical step for the repair of injured endothelium.
8 Failure of the repair process can result in thrombosis, VSM cell migration and proliferation, and
9 atherosclerosis. In this regard, Pb (Pb-nitrate 0.5 to 5 jiM) has been shown to significantly
10 reduce DNA synthesis and cell proliferation in growing cultured bovine aorta endothelial cells
11 (Kaji, 1995a). Similarly, the proliferative response to PFGF and aFGF is significantly attenuated
12 by Pb in this system (Kaji, 1995b). The reported inhibition of endothelial cell proliferation by Pb
13 can potentially diminish the repair process in response to endothelial injury. This supposition
14 has been confirmed by Fujiwara et al. (1998) who showed that at 5 to 10 jiM concentrations, Pb
15 markedly inhibited the repair of the wounded endothelial monolayer in vitro. Moreover, Pb
16 severely mitigated the zinc-stimulated endothelial cell proliferation and repopulation of the
17 denuded sections in this system.
18 Endothelial cell proliferation is the primary step in angiogenesis, a phenomenon that is
19 essential for numerous physiological functions such as growth, development, wound repair, and
20 menstrual cycle as well as certain pathological events including diabetic retinopathy and tumor
21 growth. In view of the demonstrated inhibition of endothelial cell growth by lead, it has been
22 postulated that Pb may impair angiogenesis. This assumption has been confirmed by a number
23 of studies testing the effect of Pb by angiogenesis assay (tube formation) in endothelial cells
24 cultured on matrigel (a laminin-rich basement membrane product) matrix in vitro. For instance,
25 Ueda et al. (1997) and Kishimoto et al. (1995) have shown that Pb-acetate (1 to 100 |iM) results
26 in a concentration- and time-dependent inhibition of tube formation by human umbilical vein
27 endothelial cells cultured on a matrigel matrix.
28 Endothelial cell migration and proliferation are critical for angiogenesis and repair of the
29 damaged endothelium. PFGF is a powerful mitogen for endothelial cells as well as several other
30 cell types. Endothelial cells synthesize PFGF, which is released following injury or spontaneous
31 death of endothelial cells and acts in an autocrine fashion to facilitate the repair process by
May 2006 5-128 DRAFT-DO NOT QUOTE OR CITE
-------
1 promoting endothelial cell migration and proliferation. Binding of PFGF to its receptor on the
2 endothelial cell is facilitated by heparan sulfate proteoglycans (HSPGs) that are normally
3 produced and released by the endothelial cells for attachment to the cell surface as well as
4 incorporation in the extracellular matrix. As noted above, Pb significantly attenuates PFGF and
5 oFGF-mediated DNA synthesis and proliferation in cultured endothelial cells (Kaji et al.,
6 1995b). In this regard, Pb has been shown to reduce PFGF binding to the cell surface HSPGs
7 without changing the biosynthesis or intracellular abundance of PFGF in cultured bovine
8 endothelial cells (Fujiwara and Kaji, 1999). Moreover, Pb has been shown to significantly
9 reduce the synthesis of glycosamino-glycans (GAG, measured by sulfate incorporation into
10 heparan sulfate) in the growing endothelial cells.
11 The above observations suggest that Pb-induced reduction of pFGF-mediated proliferative
12 response in cultured endothelial cells is largely due to impaired production of HSPGs. This
13 supposition is further supported by observations that DNA synthesis can be restored by adding
14 heparin in lead-treated growing endothelial cells (Fujiwara et al., 1995). The reduction in the
15 production of GAGs by Pb in the growing endothelial cells (Fujiwara et al., 1995) is also seen in
16 confluent (quiescent) cells. For instance, Kaji et al. (1991) demonstrated a marked reduction of
17 GAG production following incubation with 10 jiM Pb nitrate in confluent endothelial cells in
18 vitro. The Pb-induced reduction of heparan sulfate production was more severe than that of the
19 other GAGs. Moreover, the reduction in the cell surface-associated GAGs was more severe than
20 that of the newly synthesized GAG found in the incubation media. GAGs combine with a series
21 of specific core proteins to form anionic macromolecular complexes known as proteoglycans,
22 which are widely distributed in the extracellular matrix of the mammalian tissues. Endothelial
23 cells produce two types of HSPGs, i.e., the high-molecular weight and low-molecular weight
24 classes. Perlecan is a high-molecular weight heparan-sulfate proteoglycan that is a component of
25 the basement membrane. Syndecan, glypican, ryudocan, and fibroglygan are among the
26 low-molecular weight subclass and are primarily associated with the cell surface. Proteoglycans
27 play an important role in regulating vascular function and structure. For instance, by providing a
28 negative electrostatic charge, these molecules constitute a major barrier against extravasations of
29 negatively charged plasma proteins. In addition, by interacting with antihthrombin-III and tPA,
30 these molecules serve as important endogenous anticoagulants. Moreover, perlecans facilitate
31 PFGF binding to its receptor on endothelial cells and, thus, contributes to the endothelial growth
May 2006 5-129 DRAFT-DO NOT QUOTE OR CITE
-------
1 and repair processes. In contrast, these molecules tend to inhibit migration and growth of
2 vascular smooth muscle cells and, thereby, help to prevent athero- and arteriosclerosis. Another
3 important function of HSPGs is their role in stabilizing and anchoring lipoprotein lipase and
4 VLDL receptors on the endothelial surface. Consequently, they play an important indirect part
5 in the clearance of VLDL and chylomicrons from the circulation, a process that has major
6 implications for energy metabolism and cardiovascular protection.
7 In a study of cultured bovine endothelial cells, Kaji et al. (1997) found that Pb-chloride, at
8 10 jiM concentration, markedly lowers incorporation of precursors (glycosamine and sulfate)
9 into HSPG in confluent bovine aorta endothelial cells. The effect of Pb was more severe on
10 low-molecular than high-molecular weight HSPGs. However, Pb did not change the length of
11 heparan sulfate chains. It is of note that Pb slightly increased the abundance of the HSPG core
12 proteins. This observation excluded a reduction in core protein synthesis as a cause of
13 diminished HSPGs in the lead-treated confluent endothelial cells. In a subsequent study,
14 Fujiwara and Kaji (1999) investigated the effect of Pb-nitrate on production of high- and
15 low-molecular weight subclasses of HSPGs in growing bovine aorta endothelial cells. In
16 contrast to the quiescent cells, lead-treated growing cells exhibited a marked reduction in the
17 high-molecular weight with no change in production of low molecular weight (-50KD) HSPGs.
18 They further showed a significant reduction of the core protein of perlecan, which is a high-
19 molecular weight (400 KD) HSPG. Thus, Pb appears to affect productions of subclasses of
20 HSPGs differently depending on the cells' growth cycle. Accordingly, in the growing
21 endothelial cells (a condition that simulates the response to injury), Pb downregulates perlecan,
22 which is involved in pFGF-mediated migration and proliferation of endothelial cells and
23 inhibition of migration and proliferation of VSMC. This phenomenon may adversely affect
24 endothelial repair and promote athero- and arteriosclerosis. On the other hand, Pb-induced
25 reduction of the cell surface-associated low-molecular weight HSPGs (which are predominantly
26 involved with lipolytic, anticoagulant, and other functions of confluent endothelial cells
27 (simulating intact endothelium) can contribute to hyperlipidemia and thromboembolism, among
28 other disorders.
29 One of the major properties of normal endothelium is its ability to prevent coagulation.
30 Several factors contribute to the thromboresistance of the endothelial lining. These include the
31 surface coating of HSPG (which confers heparin-like properties), nitric oxide (which inhibits
May 2006 5-130 DRAFT-DO NOT QUOTE OR CITE
-------
1 platelet adhesion and activation), and tPA (which promotes thrombolysis), thrombomodulin, and
2 prostacycline. As noted earlier, Pb exposure reduces HSPG-production (Kaji et al., 1995b, 1997)
3 and diminishes nitric oxide availability via ROS-mediated NO inactivation (Vaziri et al., 1999b).
4 In addition, Kaji et al. (1992) showed that incubation of confluent human umbilical vein
5 endothelial cells with Pb nitrate, at 0.01 to 1.0 jiM concentrations, significantly reduced basal
6 and thrombin-stimulated tPA release. It thus, appears that Pb exposure may confer a
7 thrombophilic diathesis.
8
9 5.5.8 Effects of Lead on Vascular Smooth Muscle Cells
10 Lead has been shown to stimulate proliferation of bovine aorta VSMCs in a
11 concentration-dependent manner (Fujiwara et al., 1995). Moreover, the combination of Pb and
12 PPGF results in an additive effect on VSMC proliferation. As with bovine aorta VSMCs,
13 cultured rat aorta VSMCs exhibit hyperplasia in response to a low concentration of (100 |ig/L) of
14 Pb-citrate (Carsia et al., 1995). The reported hyperplasia is accompanied by phenotypical
15 transformation of cells from the spindle or ribbon shape to cobblestone shape, simulating the
16 neointimal cell morphology. This was accompanied by a significant reduction in Ang-II receptor
17 but no change in a, P, or ANP receptor densities. It is of note that, in contrast to the low
18 concentration, a high concentration (500 |iM/L) of Pb resulted in growth arrest in this system.
19 Thus, the effect of low concentration of Pb on VSMC proliferation is opposite of its action on the
20 endothelial cells.
21 Under normal conditions, intact endothelial lining shields the cells residing in the
22 subendothelial tissue, i.e., fibroblasts and VSMCs, from coming into contact with the circulating
23 blood. However, this barrier is lost when the endothelium is injured, an event which can lead to
24 platelet adhesion and fibrin thrombosis formation. Propagation of fibrin thrombus is limited by
25 activation of the fibrinolytic system, which, in turn, depends on the balance between tPA and
26 plasminogen activator inhibitor-1 (PAI-1). In addition to endothelial cells, VSMCs and
27 fibroblasts express tPA and PAI-1. Using cultured human aorta VSMCs and fetal lung
28 fibroblasts, Yamamoto et al. (1997) investigated the effect of Pb chloride on the release of tPA
29 and PAI-1 in vitro. The authors found that Pb causes a significant inhibition of tPA release and a
30 significant increase in PAI-1 release in cultured fibroblasts in a dose-dependent manner. The
31 lead-treated VSMC exhibited a significant dose-dependent decline in tPA release and to a lesser
May 2006 5-131 DRAFT-DO NOT QUOTE OR CITE
-------
1 extent of PAI-1 release. Taken together, exposure to Pb appears to evoke a negative effect on
2 fibrinolytic process by the cellular constituents of the subendothelial tissue.
3
4 Summary
5 • In vivo and in vitro studies published during the past 15 years have considerably expanded
6 our knowledge of the effects of Pb exposure on the cardiovascular system. However,
7 many questions remain unanswered and await further investigation.
8 • A number of in vivo and in vitro studies conducted during the review period have provided
9 compelling evidence for the role of oxidative stress in the pathogenesis of Pb-induced
10 HTN. Moreover, the effect of oxidative stress on blood pressure has been shown to be, in
11 part, mediated by avid inactivation of NO and downregulation of sGC. In addition, a
12 limited number of in vitro studies have provided indirect evidence that, via activations of
13 PKC and NFicB, Pb may raise vascular tone and promote inflammation.
14 • Based on several studies that evaluated the role of adrenergic system on Pb-toxicity,
15 chronic low-level lead exposure appears to increase central sympathetic activity, reduce
16 cardiac and vascular and raise kidney P adrenergic receptor density. These events can, in
17 turn, increase peripheral vascular resistance and renal renin release/production and,
18 thereby, arterial pressure. Since sympathetic outflow is inhibited by NO, inactivation of
19 NO by oxidative stress may be, in part, responsible for the increased sympathetic activity
20 in Pb-exposed animals.
21 • The renin-angiotensin-aldosterone system (RAAS) plays an important role in regulating
22 blood pressure and cardiovascular function and structure. The available new data suggest
23 that Pb exposure can raise plasma ACE and kininase activities at different points in the
24 course of Pb-induced HTN in experimental animals. This can, in turn, contribute to the
25 genesis and/or maintenance of HTN. Since renin release (which is responsible for
26 production of ACE substrate, i.e., Ang-1) is, in part, driven by P adrenergic activation,
27 upregulation of renal P adrenergic activity may, in part, account for increased RAAS
28 activity in the Pb-exposed animals.
29 • The balance in production of vasodilator and vasoconstrictor prostaglandins plays an
30 important role in regulation of blood pressure and cardiovascular function. Studies of the
31 Pb exposed humans have revealed an imbalance in production of prostaglandins favoring a
32 rise in arterial pressure. However, the animal and in vitro studies published during the
33 review period have been limited and inconsistent. Further studies are needed to address
34 this issue.
35 • Based on the available studies, Pb exposure appears to increase endothelin production in
36 experimental animals. This phenomenon can, in part, contribute to the rise in blood
37 pressure in the Pb-exposed animals. For instance, Pb has been shown to cause
38 vasoconstriction and to attenuate acetylcholine- and NO-mediated vasodilatation in some,
39 but not all vascular tissues and in some, but not all, studies. These effects have been
40 variably attributed to lead-mediated activation of PKC and Ca2+-mimetic action of Pb,
41 among other possibilities.
May 2006 5-132 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Finally, a number of studies have explored the effects of endothelial and vascular smooth
2 muscle cells to explore the possible atherogenic effect of Pb exposure. In this context, Pb
3 has been found to inhibit proliferation of the growing (non-confluent) endothelial cells
4 (mimicking in vivo response to injury), impair tube formation (angiogenesis), and the
5 repair of wounded endothelial monolayer in vitro. Likewise, Pb exposure was shown to
6 reduce production of HSPGs and tPA by confluent endothelial monolayers, events that
7 may favor thrombosis and hyperlipidemia. Lead exposure has been also shown to promote
8 vascular smooth muscle cell and fibroblast proliferation and phenotypic transformation in
9 ways that seem to favor arteriosclerosis and vascular remodeling.
10 • Among many questions awaiting clarification, a few are of particular interest. For
11 instance, it is not clear as to why low, but not high, levels of Pb exposure cause HTN in
12 experimental animals. Similarly, it is uncertain as to why HTN occurs long after the onset
13 of Pb exposure in the intact animals, whereas the effects on cultured cells and isolated
14 tissues are manifested within short periods of time.
15
16
17 5.6 GENOTOXIC AND CARCINOGENIC EFFECTS OF LEAD
18 5.6.1 Introduction
19 The 1986 Pb AQCD (U.S. Environmental Protection Agency, 1986) and its 1990
20 Supplement (U.S. Environmental Protection Agency, 1990) concluded that, at relatively high
21 concentrations, Pb may be carcinogenic to laboratory animals, particularly the rat. Cell culture
22 studies were considered to be supportive of these observations, but also indicated that Pb was not
23 particularly potent. Human data were considered to be of concern, but not definitive, and given
24 the animal data, the prudent choice was to consider Pb to be a possible human carcinogen.
25 This section reviews reports of Pb-induced carcinogenesis and DNA damage published
26 since 1986. More than 200 publications were read and considered and those that reported any
27 effect related to carcinogenesis or genotoxicity that was attributable to Pb are presented below.
28 This report follows the same format as the previous one (1986) and the explanations for
29 the relative importance of the various types of studies (e.g. epidemiology, animal and cell
30 culture) can be found in the original report and are not repeated here. Carcinogenesis studies are
31 presented first, followed by genotoxicity studies. Each of these sections is further subdivided
32 into human studies (considering adults and then children), animal studies, and then cell culture
33 studies (considering human, mammalian, and then nonmammalian). When appropriate, these
34 sections are followed by a section describing acellular (cell-free) model studies.
May 2006 5-133 DRAFT-DO NOT QUOTE OR CITE
-------
1 There are some differences with this new report. For one, each section is more distinctly
2 broken out. The epidemiology has been reviewed in more detail in Chapter 6 (Section 6.7) in
3 this document and, so, only a brief summary is presented here. Because of more recent concerns
4 about effects on childhood development, this issue was specifically considered in a separate
5 section. Following advances in hypotheses and technology, much more specific sections about
6 the possible epigenetic effects of Pb have also been added.
7
8 5.6.2 Carcinogenesis Studies
9 5.6.2.1 Human Studies
10 The human carcinogenesis studies are only briefly reviewed in this section; for a more
11 detailed review, see Chapter 6 (Section 6.7) in this document.
12
13 Adults
14 The assessment of the carcinogenicity of Pb through human epidemiological studies
15 remains ambiguous. Several reports state that occupational exposure to Pb increases the risk of
16 lung, kidney, brain, stomach, and liver cancer (Fu and Boffetta, 1995; Kauppinen et al., 1992;
17 Gerhardsson et al., 1995; Ades and Kazantzis, 1988; Wicklund et al., 1988; Steenland et al.,
18 1992; Englyst et al., 2001; Gerhardsson et al., 1986; Anttila et al., 1995, 1996; Cocco et al.,
19 1998; Shukla et al., 1998). However, a full interpretation of the data in these studies is
20 complicated by the fact that the study participants also incurred coexposure to other known
21 carcinogens, such as arsenic, cadmium, and hexavalent chromium. Thus, it is difficult to
22 determine if the excess cancers observed were due to exposure to Pb, one of these other
23 carcinogens, or some combination of the various chemicals. In addition, other reports indicate
24 that occupational or environmental exposure to Pb did not alter cancer risk (Cocco et al., 1996;
25 Fanning, 1988; Jemal et al., 2002). Consequently, a definitive assessment of the carcinogenicity
26 of Pb from human studies cannot be made at this time.
27
28 Children
29 There have been no recent studies of Pb-induced cancers in children. This lack of data is
30 not unexpected and is largely because Pb has not been considered a likely cause of childhood
31 cancers. There have, however, been studies of cancers in children resulting from paternal
May 2006 5-134 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposure. Here again, the same confounding problems encountered are as seen in the adult
2 population studies, and it is difficult to draw any definitive conclusions. For example, two
3 studies reported elevated childhood tumors (Wilm's tumor and acute nonlymphocytic leukemia)
4 in children whose fathers worked in Pb-related industries, such as welding, painting, and auto
5 repair (Buckley et al, 1989; Olshan et al., 1990). However, workers in these occupations also
6 experienced coexposure to arsenic, cadmium, and hexavalent chromium, and so the cancers
7 observed cannot be solely linked to Pb exposure. In addition, a report from the printing industry
8 in Norway found no link between paternal exposure and childhood cancers and, perhaps, even
9 found a possible reduction in the incidence of childhood cancers with paternal Pb exposure
10 (Kristensen and Andersen, 1992).
11 The possible interaction of paternal occupation and childhood cancer is an important area
12 of concern. However, a definitive assessment of paternal exposure to Pb cannot be made at this
13 time and more research is needed.
14
15 5.6.2.2 Laboratory Animal Studies
16 Lead is a well-established animal carcinogen, as noted in the 1986 Lead AQCD.
17 Consequently, limited tumorigenesis studies have been conducted in animal models and the
18 focus has been more on the mechanism of neoplasia (e.g., the roles of calcium and
19 metallothionein) and possible immunomodulatory effects of Pb in the promotion of cancer.
20 These studies are summarized in Table AX5-6.1.
21 All of the studies exposed animals to Pb-acetate except one, which focused on
22 Pb-chromate. One study investigated the carcinogen!city of a series of chromate compounds,
23 i.e., Pb-chromate and several Pb-chromate-based compounds were included as part of the group
24 of chromate compounds. The Pb-chromate was administered by implantation into the lung after
25 being embedded within a cholesterol pellet. The authors indicated that in this design,
26 Pb-chromate was not carcinogenic, but that 4 of the Pb chromate compounds did induce a very
27 rare tumor in the mice. Thus, there is some ambiguity about the carcinogenicity of Pb-chromate
28 in the study, as the statistics calculated an expected tumor level based on any tumor and were not
29 based on the occurrence of this very rare (for rats) tumor. It is likely that had the expected value
30 been adjusted for the rare tumor, a conclusion would have been reached that either Pb-chromate
31 was tumorigenic or that the study lacked the power to make any determination. The previous
May 2006 5-135 DRAFT-DO NOT QUOTE OR CITE
-------
1 EPA report had concluded that Pb-chromate is tumorigenic. Thus, it is difficult to draw a firm
2 conclusion from this study.
3 The remaining five studies focused on Pb-acetate (Schrauzer, 1987; Blakley, 1987; Teraki
4 and Uchiumi, 1990; Bogden et al., 1991; Waalkes et al., 2004). In most studies, this compound
5 was administered in drinking water at concentrations from 0.5 to 4000 ppm, but one study
6 considered effects from a subcutaneous (SC) injection both in mice and in rats. Consistent with
7 the findings in the 1986 Pb AQCD, Pb not only induced renal tumors, but also induced other
8 tumors, although the possible effect on mammary tumors is difficult to interpret, as important
9 study details were omitted, as discussed below. In a surprising development, during one lifetime
10 exposure study, Pb suppressed liver tumors (Waalkes et al., 2004).
11 The key study in this group of studies was a lifetime exposure study that investigated
12 mice exposed to drinking water concentrations of 1,000 to 4,000 ppm Pb and also considered the
13 role of metallothionein. In wild-type mice, Pb-acetate induced a low frequency of renal tumors,
14 but hyperplasia was common and exhibited overexpression of cyclin Dl. Lead inclusion bodies
15 were also common. Lead also suppressed liver tumors in this study.
16 By contrast, in metallothionein-deficient mice, Pb-acetate induced a high frequency of
17 kidney tumors and severe inflammation. Both the tumors and the regions of inflammation
18 exhibited cyclin Dl overexpression. Lead also suppressed liver tumors in these animals.
19 In contrast to the wild-type mice, Pb inclusion bodies were not seen in these animals.
20 Another study focused on the ability of Pb to induce tumors in rats after SC injection of
21 Pb-acetate (Teraki and Uchiumi, 1990). Tumors formed at the site of injection, and Pb
22 accumulated in the tumors, indicating that Pb is tumorigenic. However, full interpretation of the
23 data is complicated by the absence of data on control animals and the fact that only a single dose
24 was considered.
25 Three studies investigated compounds that might reduce or prevent Pb-induced cancers,
26 specifically selenium and calcium compounds (Schrauzer, 1987; Bogden et al., 1991). The first
27 study used a rather complex approach to study the possibly protective effects of selenium
28 (Shrauzer, 1987). In this study, mice were infected with the murine mammary tumor virus,
29 because they are known to develop mammary adenocarcinomas when maintained on a
30 low-selenium diet. The data indicated that Pb can induce tumors in these mice even when they
31 are maintained on a high-selenium diet. However, the data are difficult to interpret and the
May 2006 5-136 DRAFT-DO NOT QUOTE OR CITE
-------
1 impact of the study is uncertain, as the methods are incomplete, the data on control animals are
2 not provided, and the experimental results are stated but not presented in tables or figures.
3 The second study investigated the effect of calcium (Bogden et al., 1991). The main
4 focus of this study appeared to be blood pressure, but tumorigenesis was also considered.
5 It might be anticipated that calcium might reduce Pb tumorigenesis by competing for its binding
6 sites or blocking its uptake. However, in this study, calcium did not affect Pb levels in tissue and
7 actually exacerbated Pb-induced carcinogenesis. The full impact of this study is also difficult to
8 assess, as the calcium-treated animals incurred profound nephrocalcinosis.
9 The remaining study considered Pb-induced immunosuppression as a possible factor
10 contributing to the tumorigenesis induced by other agents, including viruses or chemicals
11 (Blakley, 1987). The results indicated that Pb may suppress humoral immunity but not cellular
12 immunity. However, this is the only study of its kind and the results need to be repeated in other
13 settings. In addition, it is difficult to determine if these data are specific to the agents used (e.g.,
14 murine lymphocytic leukemia virus) or if they represent a class of agents (e.g., viruses in
15 general).
16 Overall, the above studies confirm that Pb is an animal carcinogen and extends our
17 understanding of mechanisms involved to include a role for metallothionein. Specifically, the
18 recent data show that metallothionein may participate in Pb inclusion bodies and, thus, serves to
19 prevent or reduce Pb-induced tumorigenesis. Much more work is needed to determine the
20 potential exacerbating or ameliorating roles of calcium and selenium and to determine what role
21 Pb-induced immunomodulation may play in the promotion of tumors.
22
23 5.6.2.3 Cell Culture Studies
24 Carcinogenesis is measured in cell culture systems through studies of neoplastic
25 transformation, where morphologically transformed cells are injected into athymic mice to see if
26 the cells can form a tumor in the host animal. Morphological transformation refers to cells that
27 incur a change in morphology, such as formation of a focus (or foci) of cell growth. In addition,
28 for faster study results and as a screening tool, the ability of cells to grow in agar without a
29 surface to attach to (anchorage independence) is often used as a short-term substitute measure for
30 transformation.
May 2006 5-137 DRAFT-DO NOT QUOTE OR CITE
-------
1 Human Cell Cultures
2 Since the 1986 Pb AQCD, only four studies have used human cell culture systems to
3 study the carcinogenesis of Pb compounds. One found that Pb-acetate induced anchorage
4 independence in primary human foreskin fibroblasts (HFF) (Hwua and Yang, 1998). The full
5 impact of these data is uncertain, as previous studies of known metal carcinogens in primary
6 HFF found that these carcinogens induced anchorage independence, but those anchorage-
7 independent cells ultimately senesced. These studies are summarized in Table AX-6.2. Further
8 study is needed to confirm that Pb can induce anchorage independence and to see if these cells
9 can progress to full neoplastic transformation.
10 In an effort to explore the importance of oxidative metabolism in inducing anchorage
11 independence, Hwua and Yang (1998) also co-treated some cells with 3-aminotriazole, a known
12 catalase inhibitor. This co-treatment had no effect on Pb-acetate-induced anchorage
13 independence, suggesting that catalase was not involved in this effect. It would be premature to
14 conclude that oxidative metabolism is not involved in anchorage independence, as these are the
15 only data available and are limited to catalase only. More data are needed to elucidate whether
16 oxidative metabolism is involved in this lead effect.
17 The remaining three studies focused on Pb-chromate (Beiderman and Landolph, 1987,
18 1990; Sidhu et al., 1991). Two used similar HFF cells and found that Pb-chromate-induced
19 anchorage independence (Beiderman and Landolph, 1987, 1990). However, these
20 anchorage-independent cells ultimately underwent senescence, suggesting that anchorage
21 independence may not be a suitable short-term marker for neoplastic transformation in primary
22 HFF. It should be noted that these studies were focused on the chromate component of this
23 compound and the potential contribution of Pb was not investigated or discussed. By contrast,
24 Sidhu et al. (1991) found that Pb-chromate did not induce anchorage independence in a human
25 osteosarcoma cell line, while it did induce full neoplastic transformation of these cells and the
26 transformed cells did grow in agar. It should be noted that this study was also focused on the
27 chromate component of this compound and that the potential contribution of Pb was not
28 investigated or discussed.
29 The 1986 Pb AQCD did not include any studies of transformation in human cells. Given
30 that other chromate compounds have been shown to induce anchorage independence, it seems
31 quite possible that the data from Pb-chromate exposures may represent effects from chromate
May 2006 5-138 DRAFT-DO NOT QUOTE OR CITE
-------
1 and not from Pb. Thus, the data currently seem to indicate that Pb can induce anchorage
2 independence in human cells, but its ability to induce neoplastic transformation of human cells is
3 uncertain. Further study of different Pb compounds and the full assessment of their neoplastic
4 potential (i.e., including studies of the ability of treated cells to form tumors in experimental
5 animal models) are needed before definitive conclusions can be drawn.
6
7 Animal Cell Cultures
8 The 1986 Pb AQCD presented several studies demonstrating that Pb compounds could
9 induce anchorage independence and morphological and neoplastic transformation in rodent cell
10 culture systems. Since that report, six studies have further considered the ability of Pb
11 compounds to induce these effects. Three focused on Pb-chromate and three on Pb compounds
12 without the confounding factor of chromate; and these studies are summarized in Table AX5-6.3.
13 Four studies considered Pb-acetate, Pb-chloride, or Pb-nitrate in Syrian hamster embryo
14 and C3H10T1/2 mouse embryo cells (Zelikoff et al., 1988; Patierno et al., 1988; Patierno and
15 Landolph, 1989; Elias et al., 1991). Three found that Pb compounds did not induce
16 transformation (Patierno et al., 1988; Patierno and Landolph, 1989; Elias et al., 1991); but the
17 third study (Zelikoff et al., 1988) indicated that Pb was weakly positive, though no statistics were
18 performed to validate this conclusion. Zelikoff et al. (1988) indicated that the observations were
19 repeated several times, but only showed data from one experimental run. It is unclear why the
20 studies were not averaged together, as multiple repeats would likely have provided the power to
21 detect whether the observed weak increase was significant.
22 Five studies considered Pb-chromate, which induced neoplastic and morphological
23 transformation of Syrian hamster and mouse C3H10T1/2 embryo cells, as well as enhancing
24 viral transformation (Patierno et al., 1988; Patierno and Landolph, 1989; Schectman et al., 1986;
25 Elias et al., 1989, 1991). The focus on Pb-chromate was based largely on concern about
26 chromate; but these studies found that Pb-chromate was more potent than other chromate
27 compounds, suggesting that Pb may enhance or contribute to the carcinogenicity. Indeed, one
28 study found that combining Pb-nitrate with soluble chromate was as potent as Pb-chromate and
29 greater than soluble chromate alone (Elias et al., 1991).
30 Thus, all together, these studies suggest that Pb ions alone cannot transform rodent cells;
31 however, they may be co-carcinogenic or promote the carcinogenicity of other compounds.
May 2006 5-139 DRAFT-DO NOT QUOTE OR CITE
-------
1 These data are in contrast to findings described in the 1986 Pb AQCD that included a positive
2 study. One possible factor may be exposure duration; the study in question indicated that the
3 Pb-transformed cells were exposed for 9 days. The studies discussed here all exposed cells for
4 7 days or less. Further careful study of a time course of exposure is necessary to determine
5 whether Pb actually induces transformation in cultured rodent cells.
6
7 Nonmammalian Cell Cultures
8 No carcinogenesis studies were located that used nonmammalian cell culture models.
9
10 5.6.2.4 Organ-Specific Studies
11 No organ-specific or organ culture studies concerning Pb carcinogenesis were located.
12
13 5.6.2.5 Carcinogenesis Summary
14 It remains difficult to conclude whether Pb is a human carcinogen. The assessment of the
15 carcinogenicity of Pb through human epidemiological studies remains ambiguous. By contrast,
16 the studies confirm that Pb is an animal carcinogen and further extend our understanding of the
17 mechanism to include a role for metallothionein. The cell culture data suggest that Pb can
18 induce anchorage independence, but whether it can induce full neoplastic transformation of
19 human cells is uncertain.
20 To conclude, animal tumorigenicity studies clearly implicate lead (primarily tested as lead
21 acetate) as being carcinogenic, although i.v. administration has been the main route of exposure
22 employed in such studies. Based on neoplastic transformation in animal cell culture studies, lead
23 has also been implicated as a carcinogen with chromate.
24
25 5.6.3 Genotoxicity Studies
26 The human genotoxicity studies are only briefly reviewed in this section. For a more
27 detailed review, see Chapter 6 (Section 6.7) in this document.
28
29
May 2006 5-140 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.6.3.1 Human Studies
2 Adults
3 A number of studies investigating the potential genotoxicity of Pb have been conducted in
4 human populations. Endpoints considered include chromosome aberrations, sister chromatid
5 exchanges (SCE), micronuclei formation, DNA strand breaks, and hypoxanthine guanine
6 phosphoribosyl transferase (HPRT) mutations. In general, these studies were much more
7 specific than the carcinogenesis studies, as correlations with blood-Pb levels could be made,
8 other confounders could be ruled out, and the endpoints were more short-term.
9 The chromosome damage studies are ambiguous and contained some methodological
10 flaws. Four studies were positive (Huang et al., 1988; De at al., 1995; Bilban, 1998; Pinto et al.,
11 2000), while two were negative (Anwar and Kamal, 1988; Rajah and Ahuja, 1996). Moreover,
12 the four positive studies included two that could not rule out potential contributions from other
13 genotoxic metals and one that found a correlation only at very high blood Pb levels (>52 |ig/dL).
14 By contrast, the studies of micronucleus formation (Bilban, 1998; Vaglenov et al., 1998;
15 Pinto et al., 2000; Palus et al., 2003; Minozzo et al., 2004), SCE (Huang et al., 1988; Bilban,
16 1998; Pinto et al., 2000; Duydu et al., 2001; Palus et al., 2003), DNA strand breaks (Restrepo
17 et al., 2000; Fracasso et al., 2002; Hengstler et al., 2003; Danadevi et al., 2003; Palus et al.,
18 2003) all consistently found clear correlations between Pb and genotoxicity. It should be noted
19 that there were two negative studies for SCE (Rajah and Ahuja, 1995, 1996), but both were by
20 the same group and considered the same very small population of workers (only 5 Pb-exposed
21 workers) and, thus, may not have had enough power to detect potential differences.
22 It is notable that one study found an interesting correlation of HPRT mutation rates and
23 blood Pb levels from environmental Pb exposure in Belgian women (Van Larebeke et al., 2004).
24 This study is the first and only one to consider Pb-induced mutations. Further research is needed
25 to assess the validity of these data.
26 Thus, it appears from these studies that Pb is genotoxic to humans, although it may not
27 induce substantial amounts of chromosome damage. This conclusion is consistent with the
28 laboratory studies discussed below. For more in-depth consideration of the epidemiology
29 studies, see Chapter 6, Section 6.7.
30
May 2006 5-141 DRAFT-DO NOT QUOTE OR CITE
-------
1 Children
2 Two recent studies of Pb-induced genotoxicity in children have been published. One
3 study of children living in a high Pb contamination area of Czechoslovakia found no increase in
4 chromosome damage in white blood cells compared with children living in an area with lower Pb
5 contamination (Smejkalova, 1990). Comparisons were not done with children living in an area
6 with little or no Pb contamination. Measurements of blood Pb levels indicated a statistical
7 difference in blood levels between the two groups but not necessarily a substantial, or
8 biologically significant, difference between them. (Typically, the control group levels were in
9 the high 20s compared to the low 30s |ig/dL in the exposed group). Thus, the possibility that
10 each group was exposed to a Pb level that could induce a baseline level of damage cannot be
11 ruled out and, thus, it cannot be conclusively stated that Pb was not clastogenic in this study.
12 The other study found an increase in Pb-induced strand breaks in white blood cells from
13 children living in an area of Mexico with high Pb contamination compared to children living in
14 an area with lower Pb contamination (Yanez et al., 2003). Blood Pb levels confirmed a
15 difference in exposure to Pb, but urinary arsenic levels confirmed that these children were
16 exposed to higher levels of arsenic, too; and, thus, it cannot be determined which chemical was
17 responsible for the damage.
18 The possible genotoxicity of Pb for children is an important concern. However, there are
19 simply too few data to draw definitive conclusions, and more research is needed. See Chapter 6
20 (Section 6.7) for more in-depth discussion of the epidemiology of Pb in human populations.
21
22 5.6.3.2 Laboratory Animal Studies
23 Fourteen studies evaluated the genotoxicity of Pb compounds in animal models. The
24 majority of these studies focused on mice, and the Pb was administered by intraperitoneal (IP) or
25 intravenous (IV) injection. Several endpoints were considered including chromosome
26 aberrations, SCE, micronucleus formation, and DNA strand breaks. Overall, the results are
27 ambiguous, due in part to study design and the various endpoints considered. These studies are
28 summarized in Table AX5-6.4.
29 Lead compounds appear to be able to damage chromosomes, if only weakly. Two studies
30 with well-performed analyses were positive (Fahmy, 1999; Aboul-Ela, 2002). The other positive
31 studies observed that Pb could induce karyotypic arrangements, indicating a possible clastogenic
May 2006 5-142 DRAFT-DO NOT QUOTE OR CITE
-------
1 response; however, these studies did not analyze very many cells (Chakraborty et al., 1987;
2 Nayak et al., 1989a,b; Dhir et al., 1990, 1992a,b; Nehez et al., 2000). Some found chromosome
3 damage, but it did not increase with dose (Chakraborty et al., 1987; Nayak et al., 1989a,b; Dhir
4 et al., 1990). Altogether, the data do suggest some role for Pb in inducing chromosome damage,
5 but it may be a weak effect.
6 Similarly, the data for micronuclei and DNA damage are ambiguous. One study found
7 that Pb induced micronucleus formation in a dose-associated manner, but only considered two
8 doses (Roy et al., 1992). The other study found that Pb induced micronucleus formation but not
9 in a dose-dependent manner (Jagetia and Aruna, 1998). This difference may reflect the
10 somewhat shorter exposure time in the second study.
11 One DNA damage study found that Pb nitrate could induce DNA strand breaks in the
12 white blood cells of mice (Devi et al., 2000); however, the damage was not dose-dependent.
13 Another found DNA damage in a number of organs, but only one dose was considered and the
14 authors described the effect as weak (Valverde et al., 2002). In both studies, the highest doses
15 caused less damage than the moderate- to low-doses. These data again suggest that Pb is only
16 weakly causing damage.
17 By contrast, the results for SCE are consistently positive. The three studies that were
18 positive found that SCEs were induced in a dose-dependent manner (Fahmy, 1999; Nayak et al.,
19 1989a; Dhir etal., 1993).
20 The route of administration complicates the interpretation of all of these genetic studies.
21 All of the studies, except for three chromosome damage studies, used injection-based exposures.
22 It is unknown if exposures that reflect more realistic scenarios (e.g., from drinking water) would
23 cause any of these effects. Only one study of DNA strand breaks used a physiologically relevant
24 exposure (inhalation).
25 Four studies exposed animals by gavage, which is still a somewhat artificial exposure.
26 One was a DNA damage study that found weak activity (Devi et al., 2000). The other three
27 considered chromosome damage (Aboul-Ela, 2002; Dhir et al., 1992b; Nehez et al., 2000).
28 Two found a dose-response for a 24 h-exposure to Pb nitrate-induced chromosome aberrations in
29 mice (Aboul-Ela, 2002; Dhir et al., 1992b). The other found that a 4-week exposure to
30 Pb-acetate induced aneuploidy, but not chromosome aberrations, in rats (Nehez et al., 2000).
31 It is difficult to reconcile these two studies, as they use different exposure times, chemicals, and
May 2006 5-143 DRAFT-DO NOT QUOTE OR CITE
-------
1 species. More work is needed using relevant doses and exposure conditions to Pb compounds in
2 multiple species to determine if Pb induces chromosome aberrations.
3 Some studies also tried to offset the effects of Pb with a variety of compounds. Potential
4 modulators included fruit extract from Phyllanthus emblica, ascorbic acid, calcium, and iron
5 (Aboul-Ela, 2002; Dhir et al., 1990, 1992a, 1993; Roy et al., 1992). Other studies sought to
6 determine if coexposure to other toxicants would potentiate the effects of Pb (Dhir et al., 1992b;
7 Nehez et al., 2000) and considered both zirconium and cypermethrin. The data indicated that the
8 fruit extract could block the toxic effects of Pb, an effect that may, in part, be attributable to
9 ascorbic acid, but that other components must also be involved, because ascorbic acid alone
10 produced variable results. Iron also had an effect, but only if given just before, or with, the Pb
11 compound; post treatments with iron had no effect. Calcium had a strong effect.
12 The effects with zirconium and cypermethrin are less clear. Both were reported to
13 exacerbate the effects of Pb, but the effects for both are complicated by experimental design
14 problems. For example, zirconium only exacerbated Pb's effects when given simultaneously and
15 not when given 2 h before, or after, Pb. This seems rather unusual as the total exposure to each
16 was 24 h and, thus, simultaneous exposure occurred in every circumstance. Thus, the data would
17 seem to suggest that a 22-h coexposure had no effect, but that a 24-h exposure did.
18 Alternatively, there may have been some interaction of the two chemicals in the gut during
19 coexposure, creating a more toxic species.
20 Interpretation of the cypermethrin study is complicated by its design and the results. Only
21 20 metaphases were analyzed for each animal, instead of the recommended 100. In addition, the
22 statistical analyses were done relative to untreated controls and not to animals treated with Pb or
23 cypermethrin alone. Careful inspection of the tables reveals that actual exposure to Pb plus
24 cypermethrin induced less damage than that induced by Pb alone. Thus, the effects of them
25 together appear to be less than additive. More work is needed to explore the meaning of these
26 data and the importance of Pb mixtures.
27 The previous report found a similar amount of ambiguity; some animal studies were
28 positive for chromosome damage and others were negative. Other endpoints were not described
29 after Pb exposure in experimental animals. These data suggest that Pb can induce SCE but that it
30 can induce chromosome damage, DNA damage, or micronuclei either weakly or not at all.
31
May 2006 5-144 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.6.3.3 Cell Culture Studies
2 Few cell culture studies were reported in the 1986 Pb AQCD. Since 1986, a great deal of
3 theoretical and technological progress has allowed for a large number of cell culture studies to be
4 performed, as discussed below.
5
6 Human Cell Culture
1 Mutagenicity
8 Two studies considered Pb-acetate-induced mutagenesis in human cells. Both considered
9 mutations at the HPRT locus, with one using keratinocytes and the other skin fibroblasts (Ye,
10 1993; Hwua and Yang, 1998). These studies are summarized in Table AX5-6.5.
11 One study reported no lead-induced mutagenesis (Hwua and Yang, 1998) but sought to
12 explore the importance of oxidative metabolism in lead-induced mutagenesis by co-treatment
13 with 3-aminotriazole, a known catalase inhibitor. This co-treatment did not increase Pb-acetate-
14 induced mutagenesis, suggesting that either catalase was not involved in this effect or that Pb is
15 truly not mutagenic. It would be premature to conclude that oxidative metabolism is not
16 involved in anchorage independence, as these are the only data and are limited to catalase.
17 Further data is needed to elucidate whether oxidative metabolism is involved in this effect of Pb
18 as well as further studies of lead-induced mutagenesis.
19 The other study reported that Pb-acetate induced mutagenesis (Ye, 1993). However,
20 interpretation of this study is hampered by its methodology. The study did not actually measure
21 HPRT mutations or colony formation, but rather it attempted a quicker methodology that
22 measured tritium incorporation. Although a shorter assay is highly desirable, the study did not
23 verify the observed effects with standard methods, and, thus, it is uncertain if the tritium
24 incorporation actually reflected lead-induced mutations.
25 One study considered Pb-chromate and found that it was not mutagenic (Biedermann and
26 Landolph, 1990).
27 There are insufficient data at this point to conclude whether Pb is mutagenic in human
28 cells, although the few data that exist are largely negative.
29
30
May 2006 5-145 DRAFT-DO NOT QUOTE OR CITE
-------
1 Clastogenicity
2 Ten studies investigated the ability of Pb compounds to induce chromosome damage in
3 cultured human cells. All but one were essentially from the same research group, and all but two
4 considered Pb-chromate. All were done using normal, or nearly normal, human cells. These
5 studies are summarized in Table AX5-6.6.
6 Only two of those studies focused on the clastogenicity of Pb itself (Wise et al., 2004b,
7 2005), the remainder used Pb compounds but focused on either chromate or radioactive particles
8 as the clastogenic species. These studies found that Pb-glutamate was not clastogenic.
9 All of the Pb-chromate studies found that Pb-chromate induced chromosome damage in a
10 concentration-dependent manner. However, the effects were either attributed or demonstrated to
11 be caused by chromate ions. Lead ions were produced by Pb-chromate, but they were not
12 clastogenic.
13 There was one study of radioactive Pb (Martins et al., 1993). The focus was on the
14 clastogenic activity of alpha particles, and the identity of the specific Pb salt was not provided.
15 The alpha particles were able to induce chromosome damage.
16 Overall, the data appear to indicate that Pb does not induce chromosome damage in
17 human cells, although more investigation of different compounds is needed.
18
19 DNA Damage
20 Studies of DNA damage in cultured human cells have considered DNA strand breaks,
21 Pb-DNA adducts, and DNA-protein crosslinks for a variety of Pb compounds. The only clear
22 positive damage induced by Pb was Pb-DNA adducts following Pb-chromate exposure, although
23 the authors referred to them as Pb associated with DNA (Singh et al., 1999). It is uncertain if
24 these represent actual adducts or some weaker association. Two studies found no DNA strand
25 breaks induced by Pb (Hartwig et al., 1990; Snyder and Lachmann, 1989), and one study
26 involving several laboratories found no DNA-protein crosslinks after Pb exposure (Costa et al.,
27 1996). The other study found DNA double-strand breaks, but these were attributed to chromate
28 and not Pb (Xie et al., 2005). These studies are summarized in Table AX5-6.7.
29 One other study was positive (Wozniak and Blasiak, 2003), but the results were unusual
30 and their impact uncertain. Specifically, this study found that Pb-acetate induced DNA single-
31 strand breaks but that the amount of damage decreased with concentration, and ultimately the
May 2006 5-146 DRAFT-DO NOT QUOTE OR CITE
-------
1 highest concentration had less damage than the control. DNA double-strand breaks were
2 observed, but were lowest at the highest concentration. DNA-protein crosslinks were seen only
3 at the highest concentration, and the authors attempted to explain the decrease in strand breaks
4 with this effect. This explanation may partially correct, but it does not entirely explain the
5 decreased amount of damage at the middle concentration. These data need to be repeated by an
6 independent group before they can be fully assessed.
7 Together, these data suggest that Pb likely does not induce DNA damage; however, the
8 data are still too limited to allow any definitive conclusions.
9
10 Human Cell Genotoxicity Summary
11 The cumulative data suggest that Pb is not mutagenic and does not induce chromosome
12 aberrations or DNA damage in cultured human cells. It is interesting to note that Pb-induced
13 SCEs have not been considered in human cells.
14
15 5.6.3.4 Animal Cell Cultures
16 Mutagenicity
17 The potential mutagenicity of Pb compounds in rodent cells was considered in six studies.
18 In particular, three mutagenesis systems were considered: mutagenesis at the HPRT locus, the
19 gpt locus, and mutations in sodium-potassium ATPase. The results are highly variable and may
20 be specific to the Pb compound considered in each case. In particular, Pb-chromate and
21 Pb-acetate appear to be nonmutagenic. Lead acetate was positive but only at highly cytotoxic
22 concentrations. By contrast, Pb-chloride and Pb-sulfate appeared to be mutagenic at relatively
23 nontoxic concentrations. These studies are summarized in Table AX5-6.8.
24 Insufficient data exist at this point to conclude whether or not Pb is mutagenic in animal
25 cells.
26
27 Clastogenicity
28 Seven studies investigated the ability of Pb compounds to induce chromosome aberrations
29 in cultured mammalian cells (Table AX5-6.9). Four of these studies considered Pb-chromate
30 and further investigation revealed that chromate was responsible for the clastogenic effect (Wise
31 et al., 1992, 1993; Blankenship et al., 1997). Three of these studies considered other
May 2006 5-147 DRAFT-DO NOT QUOTE OR CITE
-------
1 lead-containing compounds (Wise et al., 1994; Lin et al., 1994; Cai and Arenaz, 1998). All but
2 one were negative and that one only found a small response at a single high dose (Wise et al.,
3 1994). Lower doses had no effect. Considered together, the studies indicate that Pb does not
4 induce chromosomal aberrations in cultured mammalian cells.
5 Only two studies considered Pb-induced micronuclei in cultured mammalian cells. One
6 was negative (Lin et al., 1994) and the other positive (Bonacker et al., 2005).
7 Four studies considered Pb-induced SCE in cultured mammalian cells. The results were
8 predominately negative (three studies [Hartwig et al, 1990; Lin et al., 1994; Zelikoff et al.,
9 1988]). Interpreting these studies, however, is complicated by the fact that too few metaphase
10 cells (less than 30 per concentration) were analyzed in each study. The one positive study
11 considered 100 metaphases per concentration, making those data more reliable (Cai and Arenaz,
12 1998).
13
14 DNA Damage
15 Several measures of DNA damage in cultured human cells have been investigated,
16 including DNA single-strand breaks and DNA-protein crosslinks. Most Pb compounds did not
17 induce DNA single-strand breaks. The exception was Pb-chromate, which did induce DNA
18 strand breaks, but this effect was likely a result of the chromate ion. These studies are
19 summarized in Table AX5-6.10.
20 Both Pb-chromate and Pb-nitrate induced DNA-protein crosslinks in cultured mammalian
21 cells. These data suggest that Pb is genotoxic in this manner; however, it is thought that the
22 Pb-chromate-induced DNA-protein crosslinks result from the chromate and that the method used
23 for Pb-nitrate is not sufficiently rigorous. Thus, while the data are certainly suggestive, they are
24 insufficient to make any definitive conclusion.
25
26 Nonmammalian Cell Cultures
27 Only one study was located considering Pb in a nonmammalian model (Table AX5-6.11).
28 This study found that Pb-chromate was not mutagenic in a bacterial assay. The compound was
29 studied because of its chromate content and, given that it is the lone study, no definitive
30 conclusions can be reached.
May 2006 5-148 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.6.3.5 Cell-Free Studies
2 No cell-free studies concerning Pb carcinogenesis or genotoxicity were located.
O
4 5.6.3.6 Organ-Specific Studies
5 One study (Valverde et al., 2002) considered organ-specific effects (see Table AX5-6.4).
6 That study found a different pattern of DNA strand breaks in mice after inhalational exposure to
7 Pb-acetate. DNA in the brain and lung were damaged the most, kidney and liver next, then nasal
8 epithelia and leukocytes, with no damage in testicle DNA. These data are intriguing, as they
9 suggest organ-specific responses after a physiologically relevant exposure (inhalation). More
10 research is needed, however, to fully assess the impact of these findings. Moreover, while the
11 damage was statistically significant, the authors described the effects as weak.
12
13 5.6.3.7 Genotoxicity Section Summary
14 There is some ambiguity in the genotoxicity results, as some endpoints were positive
15 while most were negative. Consistent with the animal study data, Pb can induce SCE in rodent
16 cells, but it is unknown if it can do so in human cells because this has not been tested. Lead also
17 seems to induce DNA-protein crosslinks in rodent cells.
18
19 5.6.4 Genotoxicity as it Pertains to Potential Developmental Effects
20 The human genotoxicity studies are only briefly reviewed in this section. For a more
21 detailed review, see Chapter 6 (Section 6.7). Only limited animal data and no cell culture studies
22 focused on this issue as a concern. The available data are described below.
23
24 Adults
25 One study was located that considered the effects of Pb on sperm quality and quantity.
26 This study considered Pb, cadmium, and selenium levels in 56 nonsmoking volunteers (Xu et al.,
27 2003). No effects on sperm quality were correlated with Pb exposure up to 10 |ig/L. Two other
28 studies were located on the effects of Pb on sperm morphology in animals (Fahmy, 1999; Aboul-
29 Ela, 2002). Both were positive, indicating that Pb may have an effect on sperm. They also
30 found that Pb induced DNA damage in the sperm (See Table AX5-6.4). These studies are
31 summarized in Table AX5-6.12.
May 2006 5-149 DRAFT-DO NOT QUOTE OR CITE
-------
1 Children
2 No studies were analyzed that considered the genotoxic effects of Pb in children as a
3 developmental hazard. There are two studies that considered the genotoxic effects of Pb in
4 children. They were discussed in Section 5.6.3.1.
5 Three studies were located on the fetal effects of Pb-nitrate on the fetus (Kristensen et al.,
6 1993; Nayak et al., 1989a,b). Lead induced an increase in resorptions and there were hints of
7 possible fetal chromosome damage, but the methods were poorly described and much more work
8 is needed before conclusions can be drawn. These studies are summarized in Table AX5-6.13.
9
10 5.6.5 Epigenetic Effects and Mixture Interactions
11 Lead has been proposed to be a co-mutagen or possibly a promoter. Thus, a number of
12 epigenetic mechanisms have been proposed. Epigenetic effects occur when a compound such as
13 Pb induces changes in cellular processes that do not result from changes in DNA sequence.
14 In other words, Pb has been proposed to alter cells in ways that may change the cell without
15 breaking or mutating DNA. There are three possible mechanisms: (1) alterations of gene
16 expression that can stimulate cells to grow (mitogenesis) and/or can interfere with DNA repair;
17 (this possibility has been investigated in several studies); (2) interaction with other metals; and
18 (3) alteration of oxidative metabolism. Neither of the latter two have been extensively
19 investigated.
20
21 5.6.5.1 Gene Expression
22 It has been argued that Pb may induce or co-induce carcinogenesis by altering cellular
23 metabolism or by altering the metabolism of another chemical. Both whole animal and cell
24 culture studies have been conducted to address this question and are described below.
25
26 Animal
27 Animal studies indicate that Pb can induce the expression of some phase I metabolizing
28 enzymes, such as cytochrome P4501 Al, and phase II metabolizing enzymes, such as glutathione
29 and glutathione-S-transferase. These studies are summarized in Table AX5-6.14.
30 Thus, it is plausible that through this mechanism, Pb may act as a co-carcinogen by
31 affecting the metabolism of other chemicals or possibly as a direct carcinogen by enhancing
May 2006 5-150 DRAFT-DO NOT QUOTE OR CITE
-------
1 endogenously induced damage. However, no studies have directly shown that such Pb effects
2 are linked to cancer or alter the potency of another chemical; and, thus, it remains only a
3 plausible hypothesis.
4
5 Human Cell Culture Studies
6 A few human cell culture studies have been done, and these generally confirm the animal
7 studies. These studies are summarized in Table AX5-6.15.
8 Lead has been shown to affect the induction of some phase I metabolizing enzymes (such
9 as cytochrome P4501A1) and phase II metabolizing enzymes (such as glutathione and
10 glutathione-S-transferase and NAPDH oxidase). These experiments also indicate that Pb can
11 affect the metabolism of other carcinogenic compounds, although they do not show that the
12 genotoxic or carcinogenic effects change as a result of these effects; and, thus, more work
13 remains to make this more than just a plausible explanation.
14
15 Animal Cell Culture Studies
16 No animal cell culture studies concerning the effects of Pb on the expression of metabolic
17 genes were located.
18
19 5.6.5.2 DNA Repair
20 It has been argued that Pb may induce or co-induce carcinogenesis by altering the repair
21 of DNA lesions induced by another agent. The greatest focus has been on damage induced by
22 ultraviolet (UV) light. Only cell culture and cell-free studies have been conducted to address this
23 question and are described below.
24
25 Human
26 Only one study considered Pb-induced effects on DNA repair in cultured human cells (see
27 Table AX5-6.16). This study found that coexposure to Pb caused persistence of strand breaks
28 induced by UV light. This persistence suggests that Pb interfered with the repair of these lesions,
29 but direct evidence of that interference was not provided. These are the only data in human cells
30 and, thus, it cannot be determined if Pb inhibits DNA repair in human cells.
May 2006 5-151 DRAFT-DO NOT QUOTE OR CITE
-------
1 Mammalian Cell Culture Models
2 Two studies considered Pb-induced effects on DNA repair in cultured mammalian cells.
3 These studies are summarized in Table AX5-6.17. Both found that Pb-acetate increased
4 UV-induced DNA damage including SCE, mutagenesis, and cytotoxicity. Lead did not affect
5 strand breaks induced by UV. These data suggest that Pb may indeed inhibit repair, although
6 direct interactions with repair proteins were not demonstrated.
7
8 Cell Free Systems
9 One study considered the effects of Pb on DNA repair proteins (McNeill et al., 2004).
10 That study found that Pb can inhibit APE nuclease in cell-free systems.
11
12 5.6.5.3 Mitogenesis
13 It has been argued that Pb may induce or co-induce carcinogenesis by inducing cells to
14 grow when they should not. Both animal and cell culture studies have been conducted to address
15 this question and are described below.
16
17 5.6.5.3.1 Animal
18 Several studies have considered Pb-induced mitogenesis in animal models. These studies
19 are summarized in Table AX5-6.18. These studies found that Pb can stimulate cell growth, but
20 primarily in the liver. One study did consider TNF-a expression in brain cells, but it was not
21 demonstrated whether these effects were mitogenic. The interpretation of many of the studies is
22 complicated by the exposure method (IV injection), which does not reflect human exposure.
23 In general, the data indicate that Pb is mitogenic to the liver.
24
25 Human Cell Culture Studies
26 A number of studies have considered the potential growth-stimulatory effects of Pb in
27 cultured human cells (Table AX5-6.19). These studies all found that Pb did not stimulate cell
28 growth. Thus, mitogenesis is not a likely epigenetic effect for Pb in human cells.
29
30
May 2006 5-152 DRAFT-DO NOT QUOTE OR CITE
-------
1 Mammalian Cell Culture Studies
2 A number of studies have considered the potential growth-stimulatory effects of Pb in
3 cultured mammalian cells other than the kidney. These studies all found that Pb did not
4 stimulate cell growth. Thus, mitogenesis is not a likely epigenetic effect of Pb in human cells.
5 One study found an increased mitotic index; however, it did not consider possible cell cycle
6 arrest (Lin et al., 1994). Indeed, another study found that Pb increased the mitotic index, because
7 it induced M-phase arrest (Wise et al., 2005).
8
9 Other
10 Lead-induced oxidative damage has been investigated as a potential cause of genotoxic or
11 carcinogenic effects. Generally, the results suggest that Pb only produces low levels of reactive
12 oxygen species, but that it may inhibit some enzymes involved in oxidative metabolism
13 (Table AX5-6.20). Thus, Pb may affect oxidative metabolism, but more work is needed to draw
14 meaningful conclusions.
15
16 5.6.5.4 Epigenetic Mechanisms Summary
17 The collective data support the hypothesis that Pb can induce an epigenetic effect. Lead
18 can alter the expression of metabolic genes in cultured cells and may alter DNA repair, although
19 much more study is needed. Lead may also affect oxidative metabolism or interact with other
20 metals, but again more study is needed. By contrast, it is unclear if Pb is mitogenic. It is
21 mitogenic to the liver in animals, but it is not mitogenic in cultured cells. More study is needed
22 to determine if this difference reflects differences between in vivo and cell culture models or if
23 this property is specific to only certain organs, e.g., the liver.
24
25 Summary
26 • Overall, the above studies confirm that Pb is an animal carcinogen and extends our
27 understanding of mechanisms involved to include a role for metallothionein. Specifically,
28 the recent data show that metallothionein may participate in Pb inclusion bodies and, thus,
29 serves to prevent or reduce Pb-induced tumorigenesis.
30 • Much more work is needed to determine the potential exacerbating or ameliorating roles of
31 calcium and selenium and to determine what role Pb-induced immunomodulation may
32 play in the promotion of tumors.
May 2006 5-153 DRAFT-DO NOT QUOTE OR CITE
-------
1 • All together, these studies suggest that Pb ions alone cannot transform rodent cells;
2 however, they may be co-carcinogenic or promote the carcinogen!city of other
3 compounds. These data are in contrast to findings described in the 1986 Pb AQCD that
4 included a positive study. One possible factor may be exposure duration; the study in
5 question indicated that the Pb-transformed cells were exposed for 9 days. The studies
6 discussed here all exposed cells for 7 days or less. Further careful study of a time course
7 of exposure is necessary to determine whether Pb actually induces transformation in
8 cultured rodent cells.
9 • The previous report found a similar amount of ambiguity; some animal studies were
10 positive for chromosome damage and others were negative. Other endpoints were not
11 described after Pb exposure in experimental animals.
12 • These data suggest that Pb can induce SCE but that it can induce chromosome damage,
13 DNA damage, or micronuclei either weakly or not at all.
14 • Overall, the data appear to indicate that Pb does not induce chromosome damage in human
15 cells, although more investigation of different compounds is needed.
16 • Together, these data suggest that Pb likely does not induce DNA damage; however, the
17 data are still too limited to allow any definitive conclusions.
18 • There is some ambiguity in the genotoxicity results, as some endpoints were positive while
19 most were negative. Consistent with the animal study data, Pb can induce SCE in rodent
20 cells, but it is unknown if it can do so in human cells because this has not been tested.
21 Lead also seems to induce DNA-protein crosslinks in rodent cells.
22 • The collective data support the hypothesis that Pb can induce an epigenetic effect.
23 • Lead can alter the expression of metabolic genes in cultured cells and may alter DNA
24 repair, although much more study is needed.
25 • Lead may also affect oxidative metabolism or interact with other metals, but again more
26 study is needed.
27 • It is unclear if Pb is mitogenic. It is mitogenic to the liver in animals, but it is not
28 mitogenic in cultured cells. More study is needed to determine if this difference reflects
29 differences between in vivo and cell culture models or if this property is specific to only
30 certain organs, e.g., the liver.
31 • The overall conclusions have not changed much from the 1986 Pb AQCD. Lead remains
32 an ambiguous carcinogen in humans and a clear carcinogen in animals.
33 • Cell culture studies support these conclusions, as effects in rodent cells were not seen in
34 human cells.
35 • Lead does appear to be genotoxic in human epidemiology studies.
May 2006 5-154 DRAFT-DO NOT QUOTE OR CITE
-------
1 • By contrast, the laboratory studies are more ambiguous in both animal and cell culture
2 studies. In these systems, the genotoxicity in culture is limited to SCE and, perhaps, to
3 DNA-protein crosslinks. For other endpoints, it is only weakly active, if at all.
4 • Lead has not been evaluated sufficiently as a potential genotoxic hazard, but this probably
5 stems from the fact it appears to be weakly genotoxic.
6 • The available data suggest that Pb can damage sperm and affect fetuses. More work is
7 urgently needed on this topic.
8 • Cell culture studies do support a possible epigenetic mechanism or co-mutagenic effects.
9
10
11 5.7 LEAD AND THE KIDNEY
12 5.7.1 Review of Earlier Work
13 This section summarizes key finding from the 1986 Pb AQCD on the effects of Pb on the
14 kidney in animals. Human studies published since 1986 are then reviewed in Section 6.4.
15 Both in vivo and in vitro studies on several different animal species revealed that renal
16 accumulation of Pb is an efficient process that occurs in both proximal and distal portions of the
17 nephron and at both luminal and basolateral membranes (Victery et al., 1979a; Vander et al.,
18 1977). The transmembrane movement of Pb appears to be mediated by an uptake process that is
19 subject to inhibition by several metabolic inhibitors and the acid-base status of the organism.
20 Alkalosis increases Pb entry into tubule cells via both the luminal and basolateral membranes
21 (Victery et al., 1979b).
22 Goyer et al. (1970a) were principally responsible for defining the role of renal proximal
23 tubular nuclear inclusion bodies in the response to Pb intoxication. In addition to the early
24 reports of nuclear inclusion bodies appearing in the proximal tubule following Pb exposure
25 (Goyer et al., 1970b), biochemical studies on the protein components of isolated rat kidney
26 intranuclear inclusion bodies have shown that the main component has an approximate molecular
27 weight of 27 kDa (Moore et al., 1973) or 32 kDa (Shelton and Egle, 1982) and is rich in
28 glutamate and aspartate. Goyer et al. (1970c) suggested that the intranuclear inclusion body
29 sequesters Pb, to some degree, away from sensitive renal organelles and metabolic pathways.
30 Goyer and Wilson (1975) and Goyer et al. (1978) also showed that single or repeated
31 administration of CaNa2EDTA leads to the disruption of the nuclear inclusion bodies and their
May 2006 5-155 DRAFT-DO NOT QUOTE OR CITE
-------
1 removal from the nuclei. Rats treated for 24 weeks with both Pb and CaNa2EDTA had no
2 inclusion bodies, but showed early interstitial nephropathy. As an extension of this study,
3 Cramer et al. (1974) examined renal biopsies from 5 Pb workers with 0.5 to 20 years of
4 exposure. The two workers with normal GFRs, and shortest exposure duration, showed
5 intranuclear inclusion bodies, whereas the remaining three workers had no intranuclear
6 inclusions but showed peritubular fibrosis.
7 Formation of intranuclear inclusion bodies was a common pathognomic feature for all
8 species examined. In addition, proximal tubular cytomegaly and swollen mitochondria with
9 increased numbers of cytosomes were also observed (Fowler et al., 1980; Spit et al., 1981). The
10 morphological changes were principally localized in the straight (S3) segments of the proximal
11 tubule. Goyer (1968) and Goyer et al. (1968) had demonstrated earlier that, after lead exposure,
12 mitochondria were not only swollen but had decreased respiratory control ratios (RCRs) and
13 inhibited state-3 respiration.
14 Aminoaciduria has been reported in several studies (Studnitz and Haeger-Aronson, 1962;
15 Goyer et al., 1970b; Wapnir et al., 1979). Other studies have reported increased urinary
16 excretion of electrolytes (e.g., sodium, potassium, calcium, water) following Pb administration
17 (Mouw et al., 1978). Victery et al. (1981, 1982a,b, 1983) found that zinc excretion was
18 increased following inj ection of lead.
19 Wapnir et al. (1979) observed that Pb-acetate administration caused a reduction in renal
20 alkaline phosphatase activity and an increase in Mg-ATPase activity, but no significant changes
21 in NaK-ATPase activity. On the other hand, Suketa et al. (1979) found marked a decrease in
22 renal NaK-ATPase activity following a single oral administration of Pb-acetate at a dose of
23 200 mg/kg, but no change in Mg-ATPase.
24 Renal ALAD was found to be inhibited by Pb in both acute and chronic experiments
25 (Silbergeld et al., 1982). Renal ALAD was similar to control levels when GSH was present but
26 was significantly reduced in the absence of GSH (Gibson and Goldberg, 1970). Accumulation of
27 both ALA and porphobilinogen was also observed in kidney tissue of Pb-treated rabbits,
28 compared to controls. Other studies have not shown a reduction in renal ALAD following Pb
29 exposure (e.g., Fowler et al., 1980). Higher levels of Pb may be required to cause the reduction
30 in ALAD reported by Silbergeld et al. (1982), and it may possibly involve Pb-binding proteins in
31 the kidney.
May 2006 5-156 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.7.2 Markers of Renal Toxicity
2 The establishment and validation of new screening tests for nephrotoxic effects have been
3 principally due to the efforts of the Belgian group (Price et al., 1996; Price, 2000; Lauwerys
4 et al., 1992). They proposed the following battery of tests be used to screen both
5 environmentally exposed and occupationally exposed individuals: (1) measures of glomerular
6 integrity, i.e., urinary high-molecular weight proteins (albumin, IgG, transferring (2) measures
7 of tubular absorption and secretion, i.e., low-molecular weight proteins (retinol binding protein,
8 a-1-microglobulin; (3) measures of tubular integrity, i.e., enzymes, lysosomal N-acetyl
9 p-D-glucosaminidase (NAG), brush border alanine aminopeptidase, brush border intestinal
10 alkaline phosphatase, nonspecific alkaline phosphatase, a-glutathione-S-transferase (GST), and
11 brush border antigens (BB50, BBA, HF5); (4) measures of glomerular and distal tubular
12 function, i.e., prostanoids (thromboxane B2, prostaglandin F2 alpha, 6-keto prostaglandin
13 Fl alpha); (5) measures of glomerular structural proteins (fibronectin and laminin fragments); and
14 (6) measures of distal tubular function, i.e., Tamm-Horsfall protein and u-GST. Other useful
15 markers include urinary p2-microglobulin, as a marker of proximal tubular integrity; PGE2 and
16 PGF2, distal nephron markers; kallikrein, a marker of the distal tubule; lysozyme, ribonuclease,
17 and y-glutamyl transferrase, enzymes reflecting proximal tubule integrity; and sialic acid, an
18 extracellular matrix marker (Pels et al., 1994; Pergande et al., 1994; Taylor et al., 1997). One or
19 several of these urinary markers have been used in screening tests for human Pb workers and in
20 animal studies of renal nephrotoxicity, although none has proved to be specific for lead.
21 Questions have been raised about the usefulness of urinary NAG as a nephrotoxic marker
22 due to the absence of light or electron microscopic changes in low-dose Pb-treated animals that
23 showed substantial increases in NAG (vide infra) (Khalil-Maesh et al., 1993). Furthermore, Chia
24 et al. (1994) found that urinary NAG in workers exposed to Pb correlated best with recent blood
25 lead changes, suggesting that the increased urinary NAG activity reflected an acute response to a
26 sharp increase in the renal Pb burden rather than to exocytosis. Questions have also been raised
27 about the value of measuring the vasoconstricting prostariod cytokine thromboxane B2 (TXB2)
28 and the vasodilating prostanoid 6-keto prostaglandin Fl alpha (PGF1 alpha). Conflicting results
29 have been reported in human Pb-exposed workers. Cardenas et al. (1993) reported an elevation
30 in TXB2 and a diminution in PGF1 alpha in 41 Pb-exposed workers in contrast to 41 controls.
31 Hotter et al. (1995), on the other hand, reported that both substances were increased in
May 2006 5-157 DRAFT-DO NOT QUOTE OR CITE
-------
1 69 Pb-exposed workers in contrast to 62 controls. Blood Pb levels in the two worker groups
2 were comparable, i.e., 48 |ig/dL in the first group and 43 |ig/dL in the second. In animal
3 experiments (Gonick et al., 1998), the excretion of both prostanoids was equal in low-Pb
4 (100 ppm)-fed rats as contrasted to normal controls after 3 months, despite an elevation in blood
5 pressure in the Pb-fed rats. Blood Pb in the Pb-fed rats averaged 12.4 |ig/dL compared to
6 1 jig/dL in the controls. Thus, measurements of these prostanoids remain of questionable value.
7 Attempts to validate nephrotoxic markers were conducted by Pergande et al. (1994),
8 utilizing Pb-exposed workers as contrasted to normal controls. They found that about 30% of the
9 Pb workers showed an increased excretion of ai-microglobulin, NAG, ribonuclease, and/or
10 Tamm-Horsfall protein, with positive correlations between these tubular indicators and blood Pb
11 concentration.
12
13 5.7.3 Biochemical Mechanisms of Lead Toxicity
14 Nolan and Shaikh (1992) summarized what was known about biochemical mechanisms
15 underlying Pb-induced toxicity at that time. A more detailed description based on recent animal
16 studies follows in the next section.
17 The initial accumulation of absorbed Pb occurs primarily in the kidneys. This takes place
18 mainly through glomerular filtration and subsequent reabsorption, and, to a small extent, through
19 direct absorption from the blood. Lead may be taken up by the renal tubular epithelial cells from
20 the basolateral side by active transport of the free ion. Smaller amounts can also cotransport
21 with low molecular weight organic anions. The uptake of Pb through the renal brush border does
22 not appear to occur via any specific carriers. Instead, the process may involve binding of Pb to
23 nonspecific surface sites on the brush border membrane, followed by internalization via
24 endocytosis. Acute kidney damage due to Pb manifests primarily in the proximal tubules. The
25 ultrastructural changes observed in acute experimental Pb nephropathy include both specific and
26 nonspecific effects on the proximal tubular epithelium, e.g., dilation of the endoplasmic
27 epithelium, blebbing of the nuclear membrane, enlargement of the autophagosomes, changes in
28 mitochondrial structure, formation of inclusion bodies. Chronic exposure to Pb affects
29 glomerular filtration, renal clearance, and tubular reabsorption and can lead to renal failure from
30 interstitial nephritis.
May 2006 5-158 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kidneys of chronically exposed individuals often show fewer or no nuclear inclusion
2 bodies compared to kidneys of acutely exposed individuals. The specific ultrastructural changes
3 associated with Pb nephropathy are the formation of cytoplasmic and nuclear Pb inclusion bodies
4 (discussed at greater length in Section 5.11). These inclusion bodies are not limited to the
5 proximal tubular epithelium, and have also been observed in peritoneum, astrocytes,
6 neuroblastoma cells, lung cells, and osteoclasts upon Pb exposure. The inclusion bodies are
7 roughly spherical and typically consist of an electron-dense core, with a fibrillary network at the
8 periphery. Research has revealed that the formation of the nuclear inclusion bodies is preceded
9 by the synthesis of cytoplasmic inclusion bodies with a very similar structure. A protein unique
10 to these structures is rich in acidic amino acids and has an isoelectric point of 6.3 and a
11 molecular weight of 32 kDa. Two additional proteins with apparent molecular weights of
12 11.5 kDa and 63 kDa have been identified in kidney extracts. Both of these proteins have a high
13 affinity, but little capacity, for binding lead. A Pb-binding protein of 12 kDa molecular weight
14 was identified in the supernatant of brain homogenate from Pb-treated rats. A Pb binding protein
15 of 10 kDa has also been isolated from the erythrocytes of Pb-exposed workers.
16 Mitochondrial function, in addition to structure, is very sensitive to lead. Changes include
17 the uncoupling of oxidative phosphorylation, decreased substrate oxidation, and modification of
18 ion transport processes. Other effects of Pb on cellular energetics include chelation of ATP and
19 inhibition of microsomal NaK-ATPase. These changes may account for the proximal tubular
20 dysfunction seen with acute Pb poisoning in children.
21 A new area of investigation of the mechanism of Pb toxicity was initially proposed by
22 Quinlan et al. (1988) and Hermes-Lima et al. (1991). Both investigators proposed that free
23 radicals, or ROS, stimulated by lead, may accelerate iron-dependent lipid peroxidation, causing
24 tissue injury. Hermes-Lima et al. (1991) stated further that ALA, which is formed in large
25 amounts in Pb toxicity, may undergo enolization and autoxidation, yielding ROS. Autoxidation
26 of ALA, in the presence or absence of iron complexes, yields superoxide, peroxide, and hydroxyl
27 radicals. Gurer and Ercal (2000), based on several animal studies to be discussed below, have
28 proposed that antioxidant supplementation following Pb exposure may provide a partial remedy
29 by restoring the cell's antioxidant capacity.
30
31
May 2006 5-159 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.7.4 Animal Studies
2 Two excellent review articles have been written about the effects of heavy metals on, and
3 their handling by, the kidney (Barbier et al., 2005) as well as the mechanisms of kidney cell
4 injury from metals (Fowler, 1992). The interested reader is directed to these reviews, although
5 individual effects and mechanisms will be discussed subsequently.
6
7 5.7.4.1 Lead Toxicokinetics
8 DeVries et al. (1998) published a model for Pb toxicokinetics to be used in planning
9 treatment. The model is a four-compartment model with first-order kinetics. The four
10 compartments of this model are blood, bone, liver, and kidney. Soft tissues are represented by
11 the kidney and liver compartments. In addition, intake and excretion are included in the model.
12 Excretion of Pb is mainly via the kidneys (70 to 80%), via bile and feces (15%), via nails, hair,
13 and sweat (8%). The blood makes up the central compartment from which Pb is distributed after
14 uptake in the body. The blood compartment contains about 4% of the total body burden of lead,
15 and within this compartment, the Pb is mainly taken up by erythrocytes. The half-life of Pb in
16 blood is about 30 days. From the blood, Pb is distributed relatively quickly to the soft tissues
17 and bone. The distribution constant from blood to bone is much higher than the one from bone
18 to blood, resulting in the accumulation of Pb in bone. The half-life in the soft tissues is about
19 30 to 40 days. Most of the body burden of Pb can be found in the bone compartment (-94%),
20 where the half-life of Pb is several decades. Because of the vast amount of Pb in bone, a
21 rebound in blood Pb usually occurs after chelation therapy. This model can be compared with a
22 toxicokinetic model developed by Marcus (1985a,b,c) and further explored by Hogan et al.
23 (1998), as discussed in Chapter 4 of this document.
24 Dieter et al. (1993) examined the effect of the nature of the Pb salt on the oral intake of Pb
25 in male F344 rats. For 30 days, they administered doses of 0, 10, 30, and 100 ppm Pb in the
26 form of soluble Pb-oxide, Pb-acetate, Pb-sulfide, and Pb-ore. At 100 ppm of Pb-acetate or
27 soluble Pb-oxide, the rats developed -80 |ig/dL of blood and -200 jig/g of bone Pb levels,
28 whereas rats fed Pb-sulfide or Pb ore developed -10 |ig/dL of blood Pb and 10 jig/g of bone
29 lead. In rats fed Pb-acetate or soluble Pb-oxide, blood Pb progressively increased with
30 increasing dose, while in the other two groups measurable levels of Pb were observed only at the
31 highest dose (100 ppm).
May 2006 5-160 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.7.4.2 Pathology, Ultrastructural, and Functional Studies
2 Two important series of studies contrast the pathological and functional changes in the
3 kidney after prolonged exposure to lead, with and without chelation therapy (i.e., DMSA or
4 CaNa2EDTA). In the first series of 3 long-term studies, Khalil-Manesh et al. (1992a,b, 1993b)
5 described the effects of Pb-acetate on renal function and morphology in male Sprague-Dawley
6 rats fed a low-calcium diet. Lead acetate was used in concentrations of 0.5% (high dose) and
7 0.01% (low dose) in drinking water for periods from 1 to 12 months, and then Pb-exposed
8 animals were compared to pair-fed controls (12 rats in each group). In all studies, GFR was
9 measured as 125I-iothalamate clearance by a single injection technique. Urinary markers
10 included NAG, GST, and brush border antigens (BB50, HF5, and CG9) and were expressed as
11 units/g creatinine. Blood and urine Pb were measured prior to sacrifice in each group of animals.
12 Wet and dry weights of kidneys were determined, then the kidneys were processed for light,
13 electron, and immunofluorescent microscopy.
14 In the first study (Khalil-Manesh et al., 1992a), animals treated with continuous high-dose
15 Pb for 12 months reached a maximum blood Pb of 125.4 ± 10.1 |ig/dL after 6 months, at which
16 time the dose of Pb was reduced from 0.5% to 0.1%. Blood Pb at the end of 12 months averaged
17 55 |ig/dL. Urine Pb remained above 100 jig/g creatinine at all times, but it was highest at
18 3 months, averaging 340 jig/g creatinine. In the Pb-treated animals, GFR was increased above
19 controls at 3 months (1.00 ± 0.14 vs. 0.83 ± 0.26 mL/min/ 100 g body wt, p = 0.05), then
20 declined after 6 months to 0.78 ±0.16 vs. 0.96 ± 0.08 mL/min/100 g body wt in controls
21 (Figures 5-7.1 and 5-7.2).
22 As indicated by the ratio of kidney dry/wet weight, increased kidney tissue mass was
23 observed during the first 3 months of Pb exposure, but decreased tissue mass was observed by 12
24 months. With regard to urinary markers, NAG was elevated above control levels at 3, 6, and
25 9 months of Pb exposure; GST was elevated at 3, 6, and 12 months of Pb exposure; and no
26 significant differences were observed in the brush border antigens. Proximal tubular nuclear
27 inclusion bodies were present at all time periods in Pb-treated animals. Enlargement of proximal
28 tubular cells and nuclei were seen beginning at 3 months. At 6 months, focal tubular atrophy and
29 interstitial fibrosis appeared, increasing in extent up to 12 months. Mitochondrial alterations,
30 consisting of rounding and elongation, appeared by 1 month and were persistent. Glomeruli
31 were normal through 9 months, but, at 12 months, they showed focal and segmental sclerosis.
May 2006 5-161 DRAFT-DO NOT QUOTE OR CITE
-------
P<0.05
P<0.05
O)
O
0.0
1 3 6 9 12
Duration of exposure, months
Figure 5-7.1. Changes in GFR of experimental high-dose lead and control animals with
duration of exposure to lead. Open and closed bars represent GFR in
experimental and control rats, respectively.
Source: Khalil-Manesh et al. (1992a), with permission.
1.50
•g 1.00 •
I
0.50
0.00
r = 0.703
0 15 30 45 60 75 90 105 120 135 150
Blood lead, fj.g/dl
Figure 5-7.2. Correlation between GFR and blood lead during the first 6 months of
high-dose lead exposure.
Source: Khalil-Manesh et al. (1992a), with permission.
May 2006
5-162
DRAFT-DO NOT QUOTE OR CITE
-------
1 There were no electron-dense deposits and immunofluorescent studies were negative. Renal
2 arteries and arterioles were normal at all time point examined.
3 The second study (Khalil-Manesh et al., 1992b) consisted of the discontinuation of both
4 the high- and low-dose Pb exposure after 6 months, then treatment with three courses of DMSA
5 or discontinuation of high-dose Pb alone after 1, 6, and 9 months of Pb feeding. Controls were
6 pair-fed, exposed to Pb for 6 months, then removed from exposure for 6 months without
7 receiving DMSA. Low-dose Pb-treated rats showed no significant pathologically with or
8 without DMSA treatment but exhibited a significant increase in GFR after DMSA treatment
9 (1.09 ± 0.19 vs. 0.88 ± 0.22 mL/min/100 g body weight; P < 0.03) (Figure 5-7.3). Urinary
10 markers remained unchanged, and there were no structural alterations by light or electron
11 microscopy. High-dose Pb-treated animals showed no functional or pathologic changes when Pb
12 exposure was discontinued after 1 month. However, when the duration of exposure was 6 or
13 9 months, GFR was decreased and serum creatinine and urea nitrogen were increased compared
14 to controls. Tubulointerstitial disease was severe. Administration of DMSA resulted in an
15 improvement in GFR (Figure 5-7.3) and a decrease in albuminuria, together with a reduction in
16 size and number of nuclear inclusion bodies in proximal tubules.
17 However, tubulointerstitial scarring was only minimally reduced. In conclusion, except
18 for a brief initial exposure, discontinuation of high-dose Pb exposure failed to reverse Pb-
19 induced renal damage. Treatment with the chelator, DMSA, improved renal function but had
20 less effect on pathologic alterations. Because GFR improved after DMSA treatment in both low-
21 and high-dose Pb-treated animals, irrespective of the degree of pathologic alterations, it may be
22 concluded that the DMSA effect is most likely mediated by hemodynamic changes.
23 The third study (Khalil-Manesh et al., 1993b) examined the course of events over
24 12 months in continuous low-level Pb-exposed animals. Maximum blood Pb levels in
25 experimental animals were reached at 3 months, averaging 29.4 ±4.1 |ig/dL. GFR was found
26 to be significantly increased above pair-fed controls at 1 and 3 months, but it was normal at
27 other time periods (1 month experimental, 1.18 ± 0.12 vs. control, 0.76 ± 0.15mL/min/100 g;
28 p < 0.001; 3 month experimental, 1.12 ± 0.16 , vs. control, 0.86 ± 0.10 mL/min/100 g; p < 0.001)
29 (Figure 5-7.4).
30 Levels of urinary NAG in Pb-exposed rats exceeded control levels at all time periods,
31 except at 12 months, when the normal increase with aging obscured differences between
May 2006 5-163 DRAFT-DO NOT QUOTE OR CITE
-------
1.50
High Lead
I. 1.00-
o
0.50
Low Lead
ED6 C12 DMSA E06
GROUPS
C12 DMSA
Figure 5-7.3. GFR in high-lead and low-lead experimental discontinuous (ED6)
and DMSA-treated rats (DMSA) as compared to controls (C12).
All rats were studied at 12 months.
*p < 0.01 when compared to ED6 and C12.
**p < 0.05 when compared to ED6.
Source: Khalil-Manesh et al. (1992b), with permission.
o
o
2.00
1.50
jl 1 oo
1
tr
U-
O
0.50
0.00
p<0 001
p<0 001
1
3612
Duration of Exposure (Months)
Figure 5-7.4. Changes in GFR in experimental and control rats, at various time periods.
Source: Khalil-Manesh et al. (1993b).
May 2006
5-164
DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
experimental animals and controls (Figure 5-7.5). In contrast, urinary GST, a more specific
marker of metal-associated proximal tubular injury, was normal at all time periods. Proximal
tubular nuclear inclusion bodies were sparse and were observed only at 1 and 3 months.
600
500
300
O
<
200
100
p<0 001
p<0 001
p<0 05
p<0,001
369
Duration of Exposure (Months)
Figure 5-7.5. Urinary NAG concentration in experimental and control rats at various
time periods.
Source: Khalil-Manesh et al. (1993b).
5 No other pathologic alterations were found in the kidneys until 12 months of exposure,
6 when mild tubular atrophy and interstitial fibrosis were seen. The absence of changes in urinary
7 GST accorded with the relative absence of morphologic changes, whereas the observed increases
8 in urinary NAG suggest that this enzyme may be an overly sensitive indicator of tubular injury,
9 more probably reflecting upregulation of the enzyme even in the absence of tubular injury.
10 It should be noted that both low-dose Pb-treated animals and high-dose Pb-treated animals
11 showed a "hyperfiltration" phenomenon during the first 3 months of Pb exposure. This
12 observation could be invoked as a partial explanation for the late changes of glomerulosclerosis
13 in the high-dose animals, but it cannot explain the lack of glomerular changes in the low-dose
14 animals. Thus, these studies join those of Roels et al. (1994) and Hu (1991) in humans that
May 2006
5-165
DRAFT-DO NOT QUOTE OR CITE
-------
4
5
6
7
10
11
indicate that Pb nephropathy should be added to diabetic nephropathy as diseases that lead to
early hyperfiltration.
The second series of studies were performed by Sanchez-Fructuoso et al. (2002a,b).
Sanchez-Fructuoso et al. (2002a,b) evaluated the effect of CaNa2EDTA on tissue mobilization of
Pb in six-month-old Wistar rats initially treated with 500 ppm Pb-acetate for 90 days, followed
by treatment with three courses of CaNa2EDTA 50 mg/kg/day for 5 days, separated by 9 days, or
placebo. Lead levels were measured in blood, urine, kidney, liver, brain, and femur. There was
no change in bone Pb after CaNa2EDTA compared to placebo, but Pb levels were significantly
reduced in all other tissues (Figure 5-7.6).
I
I
I
109
80
40
20
IE
12
111 125 1S9
60 50 111 125 1J9 days
10
S
1
e
CO
60
111
125 130 days
60
i
20
~T~ End «»*xpotut»
60
90
111
125 139
(lays
Figure 5-7.6. Kidney, liver, brain, and bone Pb levels in 56 Pb-exposed rats. After 90 days
of poisoning, animals were administered serum saline (solid line) or calcium
disodium EDTA (broken line).
Source: Sanchez-Fructuoso et al. (2002a), with permission.
May 2006
5-166
DRAFT-DO NOT QUOTE OR CITE
-------
1 The authors emphasized that there was no redistribution to brain. Cory-Slechta et al.
2 (1987) had originally reported that with one day of CaNa2EDTA chelation in Pb-exposed rats,
3 Pb is preferentially mobilized from bone and then redistributed to other organs, including brain,
4 but with further CaNa2EDTA treatment, brain levels return to baseline. The Sanchez-Fructuoso
5 et al. (2002a,b) findings stand in contrast, explained by the authors as due to a 3-fold higher level
6 of CaNa2EDTA used by Cory-Slechta et al. (1987).
7 Sanchez-Fructuoso et al. (2002b) also evaluated pathologic changes, as well as the
8 response of ALAD activity before and after CaNa2EDTA treatment in the same rats. In the
9 90-day Pb-treated animals, the main findings were hypertrophy and vacuolization of medium and
10 small arteries (Figure 5-7.7); mucoid edema and muscular hypertrophy in arterioles; loss of cell
11 brush borders, cell loss, and intranuclear inclusion bodies in the proximal tubule; and fibrosis and
12 the presence of infiltrates in the interstitial component. Treatment with CaNa2EDTA slowed the
13 progression of most alterations (Figure 5-7.8) and resulted in a diminution in nuclear inclusion
14 bodies. ALAD activity was reduced from 3.18 ± 0.52 U/mL in controls, to 0.82 ± 0.16 U/mL in
15 the Pb-exposed rats. In the rats treated with CaNa2EDTA, ALAD returned to near control levels
16 (2.98 ± 0.41 U/mL) at 137 days. It is surprising that such remarkable vascular changes were
17 noted in this study, while none were noted in Khalil-Manesh et al. (1992a), even with high-dose
18 Pb for longer periods of time. The kidney content of Pb (mean 74.6 |ig/g) was also lower than
19 the mean kidney content at 12 months (294 |ig/g) in the Khalil-Manesh et al. (1992a) study.
20 The only explanation for these striking differences that can be offered is that different strains of
21 rats were employed, i.e., Wistar in the Sanchez-Fructuoso (2002b) study and Sprague-Dawley in
22 the Khalil-Manesh et al. (1992a) study. The presence or absence of hypertension cannot be
23 invoked as an explanation, because in another Khalil-Manesh et al. (1993a) study the low-dose
24 Pb animals became hypertensive while the high-dose animals did not. These and other related
25 studies are summarized in Table AX5-7.1.
26
27 5.7.4.3 Biochemical Mechanisms of Lead Toxicity
28 Role of Free Radicals (Reactive Oxygen Species)
29 Since the early 1990s, it has been appreciated that free radicals, now known as reactive
30 oxygen species (ROS), are involved in the manifestations of Pb poisoning, presumably via their
31 adverse effects on tissue integrity and/or their vasoconstrictive effects on vascular endothelium.
May 2006 5-167 DRAFT-DO NOT QUOTE OR CITE
-------
100
111 125 139" 111 125 139 Days
No treatment EDTA
Figure 5-1.1. Percentage of moderate and severe hypertrophy and vacuolization lesions in
small and medium sized arteries in the kidney of lead-exposed rats.
Source: Sanchez-Fructuoso et al. (2002b), with permission.
100 jj
801
60-
40
20
60 90 111 125 139 111 125 139 Days
No treatment EDTA
Figure 5-7.8. Percentage of moderate and severe muscular hypertrophy lesions in
arterioles of the kidney in lead-exposed rats.
Source: Sanchez-Fructuoso et al. (2002b), with permission.
1 Wolin (2000) produced an extensive review of individual ROS, and their interactions with
2 NO, the major endogenous vasodilator, which acts via a second messenger, cGMP. The
3 production of ROS often begins with a one-electron reduction of molecular oxygen to superoxide
May 2006
5-168
DRAFT-DO NOT QUOTE OR CITE
-------
1 anion (O2 ) by various oxidases. NAD(P)H oxidases are the principal enzymes involved.
2 Superoxide anion is a negatively charged free radical that can be broken down to hydrogen
3 peroxide (H2O2) by superoxide dismutase (SOD) or can interact with NO to form the highly
4 reactive peroxynitrite ion (ONOO ), which, because of its extremely short half-life, is measured
5 as its reaction product, tissue nitrotyrosine. Catalase and glutathione peroxidase (GSHPx)
6 metabolize H2O2 to Compound I and oxidized glutathione (GSSG), respectively, while
7 myeloperoxidase metabolizes H2O2 to hypochlorous acid (HOC1). The reaction of H2O2 with
8 ferrous ion results in the formation of hydroxyl ion (*OH). ROS can be scavenged by
9 endogenous thiols (e.g., GSH) or exogenous thiol, e.g., N-acetylcysteine (NAC). ROS can be
10 measured as the concentration of the lipid peroxidation product, malondialdehyde-thiobarbituric
11 acid (MDA-TBA) or by the more recently introduced F-2 isoprostanes.
12 Kumar and Das (1993) explored the involvement of ROS in the pathobiology of human
13 essential hypertension. They found that plasma levels of lipid peroxides were higher in subjects
14 with uncontrolled essential hypertension compared to normal controls. Angiotensin II, a potent
15 vasoconstrictor, was found to stimulate free radical generation in normal leukocytes, which was
16 thought to inactivate NO, and possibly prostacyclin, which can lead to increased peripheral
17 vascular resistance and hypertension.
18 Hermes-Lima et al. (1991) also explored the involvement of ROS in Pb poisoning. They
19 described the process of autoxidation of ALA in the presence or absence of iron complexes,
20 which yields free radicals. Free radicals are also produced by Pb-stimulated iron-dependent lipid
21 peroxidation, as determined by quantification of thiobarbituric acid-reactive species (TEARS).
22 Pereira et al. (1992) demonstrated that chronically ALA-treated rats (40 mg/kg body weight
23 every 2 days for 15 days) under swimming training reached fatigue significantly earlier than the
24 control group, as well as demonstrating decreased mitochondrial enzymatic activities. In vivo
25 prooxidant properties of ALA were also suggested by the observed increase of CuZnSOD in
26 brain, muscle, and liver of untrained rats submitted to chronic treatment with ALA.
27 Ercal et al. (1996) contrasted the effects of treatment with DMSA or NAC in Pb-exposed
28 C57BL/6 mice. Five weeks of Pb exposure was found to deplete GSH levels, increase GSSG,
29 and promote MDA production in both liver and brain samples. Glutathione levels increased and
30 GSSG and MDA levels decreased in groups of Pb-exposed mice that received 1 mmol/kg DMSA
31 or 5.5 mM/kg NAC for 7 days prior to sacrifice. Treatment with DMSA caused reduction in
May 2006 5-169 DRAFT-DO NOT QUOTE OR CITE
-------
1 blood, liver, and brain Pb levels consistent with its function as a chelating agent, while treatment
2 with NAC did not reduce these Pb levels. However, NAC treatment reduced indices of oxidative
3 stress in both brain and liver samples. Concentrations of blood Pb in controls were
4 0.5 ± 0.5 |ig/dL; in Pb-treated mice, were 36.5 ± 2.4 |ig/dL; in Pb + DMSA-treated mice, were
5 13.7 ± 1.3 |ig/dL; and in Pb + NAC-treated mice, were 36.0 ±3.5 |ig/dL. Thus, both DMSA and
6 NAC acted as antioxidants, presumably via their thiol groups, but only DMSA reduced the
7 concentrati on of 1 ead.
8 Daggett et al. (1998) and Fowler et al. (2004) have explored the effects of lead and lead
9 mixed with cadmium and arsenic on oxidative stress in the rat kidney. Daggett et al. (1998)
10 found that a single injection of lead failed to deplete GSH or alter MDA levels in the kidney
11 within 24 hours. All subunits of glutathione-S-transferase (GST), however, were increased,
12 apparently not the result of oxidative stress. Fowler et al. (2004) reported preliminary studies of
13 oxidative stress produced at 30, 90, and 180 days by mixtures of lead (lead acetate at 25 ppm),
14 cadmium (cadmium chloride at 10 ppm), and arsenic (sodium arsenite at 5 ppm). These dosages
15 were at the lowest observed adverse effect levels (LOAEL). Kidney carbonyls (a marker of
16 protein oxidation) were increased at all time points in the combination group, but decreased at
17 90 days in individually administered metal groups. Kidney non-protein thiols (representing
18 glutathione) increased in all groups at 180 days, suggesting that the induction of glutathione or
19 metallothionine attenuated increases in oxidative stress.
20 Vaziri and co-workers (Gonick et al., 1997; Ding et al., 1998, 2000, 2001; Vaziri and
21 Ding, 2001; Vaziri et al., 1997, 1999a,b, 2000, 2001a,b, 2003; Zhou et al., 2002; Ni et al., 2004)
22 have published a number of articles relating to the production of ROS and alterations in
23 enzymatic activities in Pb-induced hypertension. These were discussed in detail in Section 5.5
24 but are described briefly here. In the majority of studies, Pb-induced hypertension was produced
25 by the administration of Pb-acetate, 100 ppm in drinking water, for 3 months to male Sprague-
26 Dawley rats. Early studies (Gonick et al., 1997) revealed that hypertension could occur in the
27 absence of changes in NO or cGMP but with an attendant rise in plasma and kidney MDA-TEA,
28 indicating an increase in ROS. In a second study, Ding et al. (1998) showed that infusion of
29 arginine, the precursor of NO, or DMSA, a thiol Pb chelator and antioxidant, reduced blood
30 pressure to or towards normal, while simultaneously increasing depressed urinary NO and
31 decreasing an elevated MDA-TBA. Ding et al. (2000, 2001) further showed that the ROS
May 2006 5-170 DRAFT-DO NOT QUOTE OR CITE
-------
1 species, *OH, measured as salicylate-trapped 2,3 dihydroxybutyric acid, was increased in plasma
2 and cultured rat aortic endothelial cells after exposure to lead, and that dimethylthiourea, a
3 reputed scavenger of 'OH, returned blood pressure, MDA-TBA, *OH, and nitrotyrosine to or
4 towards normal. Ni et al., in 2004, demonstrated in both human coronary endothelial (EC) and
5 vascular smooth muscle cells (VSMC) that Pb-acetate also increased superoxide (demonstrated
6 by flow cytometry using hydroethidine) and H2O2 (demonstrated with dihydrorhodamine)
7 production. After long-term (60-h) exposure, detectable superoxide levels fell to near normal
8 while H2O2 production remained high.
9 Vaziri et al. (1997) showed that lazaroids, a class of non-thiol antioxidant, also restored
10 blood pressure, NO, and MDA-TBA to normal. Vaziri et al. (1999a) studied rats treated for
11 12 weeks with either Pb-acetate alone or Pb-acetate + vitamin E-fortified food (5000 units/kg rat
12 chow). They measured urinary excretions of stable NO metabolites (NOX) and plasma and tissue
13 abundance of nitrotyrosine, the footprint of NO oxidation by ROS. The Pb-treated group showed
14 a marked rise in blood pressure; a significant increase in plasma and kidney, heart, liver, and
15 brain nitrotyrosine abundance; and a substantial fall in urinary NOX excretion. Concomitant
16 administration of high-dose vitamin E ameliorated hypertension and normalized both urinary
17 NOX excretion and tissue nitrotyrosine without altering tissue Pb content. Vaziri et al. (1999b)
18 also measured eNOS and iNOS in the aorta and kidney of Pb-treated and Pb + vitamin E-treated
19 rats. Lead treatment increased both isotypes in aorta and kidney, signifying increased NO
20 production, while Pb + vitamin E lowered aortic, but not kidney, expression of eNOS and iNOS.
21 Vaziri and Ding (2001) tested the effect of lead, 1 ppm, on cultured human EC cells. Lead was
22 tested alone or with either the SOD-mimetic agent, tempol, or a potent antioxidant lazaroid
23 compound (both at 10"8 or 10"7mol/L) on eNOS expression and NO production. Lead-treated
24 cells showed a significant upregulation of endothelial eNOS, increase in protein abundance, and
25 increase in the production of NO metabolites. Treatment with either tempol or lazaroids
26 abrogated the Pb-induced upregulation of eNOS protein and NOX production. Vaziri et al.
27 (2001) also studied increases in NOS isoforms in vivo in Pb-induced hypertension and reversal
28 by tempol. Both eNOS and iNOS were increased in kidney, aorta, and heart, while NOS was
29 increased in cerebral cortex and brain stem, of Pb-treated rats; blood pressure and NOS isoforms
30 were returned to normal by tempol. Vaziri et al. (2003) determined whether the oxidative stress
31 in animals with Pb-induced hypertension is associated with dysregulation of the main antioxidant
May 2006 5-171 DRAFT-DO NOT QUOTE OR CITE
-------
1 enzymes (i.e., SOD, catalase, and GSHPx), or increases in the superoxide-producing enzyme
2 NAD(P)H oxidase. At the conclusion of the experiment, immunodetectable CuZnSOD,
3 MnSOD, catalase, GSHPx, and the gp91phox subunit of NAD(P)H oxidase were measured by
4 Western analysis in the kidney, brain, and left ventricle of control and Pb-exposed rats. Lead
5 exposure resulted in a significant increase in kidney and brain CuZnSOD with a significant
6 increase in brain, and insignificant increase in kidney and heart, gp91phox. In contrast, MnSOD,
7 catalase, and GSHPx in the kidney, brain, and left ventricle were unchanged. Incubation with
8 Pb-acetate did not alter SOD activity in vitro. Thus, animals with Pb-induced hypertension
9 exhibited oxidative stress, which was associated with mild upregulation of the superoxide-
10 generating enzyme NAD(P)H oxidase, with no evidence of quantitative SOD, catalase, or
11 GSHPx deficiencies.
12 Vaziri et al. (2000) demonstrated that induction of oxidative stress in normal animals
13 (by feeding the GSH synthase inhibitor, buthionine sulfoximine, 30 mmol/L in drinking water
14 for 2 weeks) led to an increase in blood pressure, a reduction of urinary NOX, a 3-fold decrease in
15 liver GSH, and an increase in nitrotyrosine in kidney, aorta, heart, liver and plasma.
16 Administration of vitamin E + ascorbic acid ameliorated hypertension and mitigated
17 nitrotyrosine accumulation despite persistent GSH depletion. This experiment demonstrated the
18 importance of GSH in protecting against the adverse effects of ROS accumulation in normal
19 animals. The majority of the studies reported by Vaziri and co-workers indicated that low Pb
20 exposure induced hypertension to be primarily mediated by ROS-induced depletion of NO.
21 NO production, on the other hand, is stimulated, as shown by the increase in eNOS and iNOS.
22 Enzymatic control of ROS levels by low Pb is achieved by upregulation of NAD(P)H oxidase
23 with no decrease in SOD, catalase, or GSHPx, i.e., the enzymes that breakdown ROS.
24 Scavengers of ROS ameliorate the elevated blood pressure, while the depletion of the
25 endogenous methyl scavenger, GSH, increases blood pressure in normal animals. No studies
26 have been done to date to address the question of why high-dose Pb administration does not lead
27 to hypertension.
28 Farmand et al. (2005) pursued enzymatic studies by activity measurements and measures
29 of protein abundance in the rat kidney and aorta when rats are fed Pb-acetate 100 ppm for
30 12 weeks. They demonstrated that the activities of CuZnSOD and catalase were increased by Pb
31 administration in renal cortex and medulla, whereas GSHPx was unchanged. In the thoracic
May 2006 5-172 DRAFT-DO NOT QUOTE OR CITE
-------
1 aorta, Pb exposure resulted in significant upregulation of CuZnSOD activity, while catalase and
2 GSHPx activities were unchanged, CuZnSOD, MnSOD, and catalase protein abundance were
3 likewise unchanged. However, guanylate cyclase protein abundance in the thoracic aorta was
4 decreased. The authors suggested that the Pb-induced compensatory upregulation of CuZnSOD
5 and catalase and the decrease in aortic guanylate cyclase may be related to Pb-induced
6 hypertension.
7 Gurer et al. (1999a) evaluated whether captopril, an ACE inhibitor, acted as an
8 antioxidant in Pb-exposed F344 rats. Lead acetate was given in drinking water for 6 weeks.
9 Group I were the controls; group II received 1100 ppm Pb for 5 weeks and plain water during the
10 week 6; group III received 1100 ppm Pb for 5 weeks and, during the week 6, received water
11 containing captopril (10 mg/day). Blood Pb concentrations in the control group measured
12 0.8 ng/dL; in the Pb treated group, 24.6 ± 20 ng/dL; and in the Pb + captopril group, 23.8 ±
13 1.6 |ig/dL. MDA concentrations in liver, brain, and kidney were increased by Pb administration
14 and reduced to or towards normal by the Pb + captopril treatment. GSH concentrations were
15 decreased by Pb administration and restored by Pb + captopril treatment, whereas GSSG
16 concentrations were increased by Pb administration and reduced by Pb + captopril treatment.
17 Thus, this study showed that captopril was capable of augmenting the reducing capacity of the
18 cells by increasing GSH/GSSG ratios without affecting blood Pb concentrations.
19 McGowan and Donaldson (1987) examined total nonprotein sulfhydryl and GSH
20 concentrations in liver and kidney as well as GSH-related free amino acid concentrations in liver,
21 kidney, and plasma in 3-week-old Pb-treated (2000 ppm dietary lead) chicks. Cysteine,
22 converted from methionine, is the rate-limiting amino acid in GSH formation. The availability
23 of glutamate, cysteine, and glycine becomes important in the restoration of depleted GSH.
24 GSH, nonprotein sulfhydryl groups, glycine, and methionine were increased versus controls in
25 the liver, but only nonprotein sulfhydryl, glycine, cysteine, and cystathionine increased in the
26 kidney. Plasma levels of cysteine, taurine, and cystathione were reduced. Thus, Pb, for short
27 periods of time, increases GSH turnover. These and other studies are summarized in
28 Table AX5-7.2.
29
May 2006 5-173 DRAFT-DO NOT QUOTE OR CITE
-------
1 Effect of Lead on Selective Renal Enzyme Levels
2 Effects of Lead on Renal NAG
3 Dehpour et al. (1999) studied NAG release by the rat kidney perfused with Pb-acetate at
4 10, 20, and 50 ng/dL for 120 min, or Pb + arginine (the substrate for NO), or Pb + L-NAME
5 (an inhibitor of NOS). Lead acetate caused a time and concentration-dependent increase in
6 enzymuria. Addition of arginine decreased, while addition of L-NAME increased, Pb-induced
7 NAG release. Histologic studies showed damage to some of the proximal tubule epithelial cells
8 in rats treated with 50 |ig/dL Pb-acetate, damage that which was increased further by the addition
9 of L-NAME.
10
11 Effect of Lead on Renal GST
12 Two studies (Moser et al., 1995; Oberley et al., 1995) reported the effects of Pb
13 administration on GST isoforms in developing rat kidney. In the first study (Moser et al., 1995),
14 rats were treated either acutely (14- and 50-day old rats given three daily injections of Pb-acetate,
15 114mg/kg) or chronically (Pb levels of 0, 50, 250, and 500 ppm in drinking water for 1, 2, 3, 4,
16 and 7 weeks postnatal). Chronic treatment rats were also given a 0.66% low calcium diet or
17 standard rat chow. Essentially all kidney cytosolic GSTs (Ybl, Yb2, Yp, Ycl, Yl, Yb3, Yal,
18 Ya2, Yk) increased in the acute experiment (1.1- to 6.0-fold). In the chronic experiment, all but
19 one isoform (Yb3) increased, and these results were markedly exacerbated by placing the rats on
20 a low-calcium diet (Ybl and Yp increased >25-fold). In the second study (Oberley et al., 1995),
21 pregnant rats were given 250 ppm Pb from conception until weaning, then pups received
22 500 ppm from weaning until termination at either 3 or 7 weeks of age. By 7 weeks, proximal
23 tubular cells showed intranuclear inclusions, tubular injury, and interstitial fibrosis. Creatinine
24 clearances were reduced (0.55 + 0.05 versus 1.05 + 0.07 mL/min/lOOg; P< 0.001). Treatment
25 with Pb also caused large increases in the immunoreactive protein of Yc, Yk, Ybl, and Yp GST
26 subunits in proximal tubules but did not increase in the antioxidant enzymes CuZnSOD, catalase,
27 and GSHPx.
28 Another experiment that examined the effect of an acute dose of Pb as Pb-nitrate
29 (100 |imol/kg IV) on GST levels in rat liver and kidney was reported by Planas-Bohne and
30 Elizade (1992). Seventy hours after injection, there was a marked increase in GST activity in
31 both organs, accompanied by induction of the isoenzyme GST 7-7 in the liver.
May 2006 5-174 DRAFT-DO NOT QUOTE OR CITE
-------
1 The relationship between GST induction by acute exposure to Pb-acetate and oxidative
2 stress was explored by Daggett et al. (1998). Rats in the 72-h and 7-day experimental groups
3 received three consecutive daily injections of 114 mg/kg body weight of Pb-acetate. The level of
4 kidney GST was increased at 3, 6, 12, and 24 h after injection, but MDA levels remained
5 unchanged. Immunohistochemical markers of oxidative stress and NO production (MnSOD,
6 eNOS, iNOS, and 4-hydroxy-2-nonenal) also did not change. The authors concluded that the
7 GST changes were not the result of oxidative stress.
8 Witzman et al. (1998) and Kanitz et al. (1999) utilized two-dimensional (2-D) gel
9 electrophoresis to explore protein markers of Pb exposure. Witzman et al. (1998) gave three
10 consecutive IP injections of Pb-acetate (114 mg/kg) to Sprague-Dawley rats, sacrificed them on
11 the fourth day, and subjected the cytosolic fraction of kidney homogenate to 2-D gel
12 electrophoresis. Lead exposure caused detectable inductions in both GSTP1 and GSTM1 and
13 caused quantifiable charge modifications in GSTP1. Kanitz et al. (1999) examined kidney
14 protein expression in male rabbits injected with Pb-acetate (260, 360, or 100 |ig/kg) designed to
15 produce blood levels of 20, 40, or 80 |ig/dL. Injections were given during weeks 6 to 10,
16 followed by maintenance doses during study weeks 11 to 20. Kidney homogenates were
17 subjected to 2-D electrophoresis. Significant quantitative changes occurred in 12 proteins in a
18 dose-related manner. Four proteins cross-reacted with anti-rat GSTpl (rc-GST). Thus, both
19 studies confirmed GST induction by lead.
20 Daggett et al. (1997) examined the effects of triethyl Pb administration on the expression
21 on GST isoenzymes and quinone reductase in rat kidney and liver. Fischer 344 rats were given
22 one IP injection of triethyl Pb chloride (10 mg/kg body weight) and subsequent changes in
23 enzyme expression were measured. There was a significant increase in GST activity in kidney;
24 all GST subunits were significantly elevated, the largest increase being a 3.2-fold increase in
25 GST Ybl. In the liver, injection of triethyl Pb-chloride resulted in decreased GST activity.
26 The largest decrease in subunits was a 40% reduction in GST Yal. The activity of quinone
27 reductase was elevated 1.5-fold in kidney and 2.7-fold in liver within 14 days after the injection
28 of triethyl Pb chloride.
29
May 2006 5-175 DRAFT-DO NOT QUOTE OR CITE
-------
1 Effects of Lead on Renal Heme Enzymes
2 Vij et al. (1998) explored Pb-induced alterations in male rats in the heme synthesizing
3 enzymes, ALAD, and uroporphyrinogen I synthetase, and the effect of ascorbic acid
4 supplementation in reversing these alterations. Lead-treated rats were injected IP with 20 mg/kg
5 of Pb-acetate for 3 consecutive days and sacrificed 4 days later. A separate group of animals was
6 administered 100 mg/kg ascorbic acid PO for 3 days following Pb administration. Blood Pb
7 concentration was 4.7 ±1.5 |ig/dL in control rats, 16.6 ± 4.7 |ig/dL in Pb-treated rats, and
8 7.8 ± 2.0 |ig/dL in the Pb + ascorbic acid treated rats. Lead content of liver and kidney followed
9 the same pattern. Blood ALAD activity was diminished in the Pb-treated rats but was restored in
10 the Pb + ascorbic acid-treated rats. Uroporphyrinogen I synthetase activity followed the same
11 pattern in blood but was not restored by ascorbic acid in liver. Total and nonprotein sulfhydryl
12 concentrations in blood were depressed by Pb administration and were not restored by ascorbic
13 acid. However, levels in liver and kidney were restored by ascorbic acid.
14 ALAD levels following administration of Pb were also investigated by Rodrigues et al.
15 (1996a) and Peixoto et al. (2004). The study by Rodrigues et al. (1996a) examined rats from
16 Pb-exposed mothers that were maintained after weaning on either 0.5 or 4.0 mM Pb-acetate in
17 drinking water for 21 days or 6 months. At sacrifice, ALAD activity was measured in kidney,
18 forebrain, and cerebellum. Both 6-month-old Pb-exposed groups showed an increase in the
19 kidney-to-body weight ratio, suggesting Pb-induced cell proliferation in the kidney. Blood Pb
20 increased from 6.5 to 7.6 |ig/dL in the 21-day-old exposed rats compared to 6-month-old
21 controls. In the 0.5 mM Pb-treated group, blood Pb was 9.8 |ig/dL in the 21-day-old and
22 41.6 |ig/dL in 6-month-old rats, while in the 4.0 mM group, blood Pb was 44.4 |ig/dL in the
23 21-day-old and 116.9 |ig/dL in the 6-month-old group. ALAD activity was reduced at 6 months
24 in the forebrain of the 4.0 mM Pb-treated group, and in the kidneys at 6 months in both the
25 0.5 mM and 4.0 mM Pb-treated groups. The study by Peixoto et al. (2004) examined the in vitro
26 sensitivity (ICso) to Pb of ALAD activity of brain, kidneys, and liver from suckling rats aged
27 between 1 and 5, 8 and 13, or 17 and 21 days. The metal concentrations ranged from 0 to 50 jiM
28 for Pb-acetate. Rats in the first age group showed the greatest sensitivity in all three organs.
29 Liver was the least sensitive to ALAD inhibition by lead, while brain was the most sensitive.
30
May 2006 5-176 DRAFT-DO NOT QUOTE OR CITE
-------
1 Effects of Lead on NaK-A TPase
2 Fox et al. (1991b) explored the effect of in vivo Pb exposure on adult rat retinal and
3 kidney NaK-ATPase. Pups, exposed to Pb through the milk of dams consuming 0, 0.02, or
4 0.2% Pb solutions, had mean blood Pb concentrations of 1.2, 18.8, and 59.4 |ig/dL at weaning,
5 respectively, and 5 to 7 |ig/dL as 90 to 100-day-old adults. Prior Pb exposure produced
6 significant dose-dependent decreases in isolated retinal NaK-ATPase activity (-11%; -26%),
7 whereas activity in the kidney was unchanged. In contrast, NaK-ATPase from both isolated
8 control tissues was inhibited by Pb in vitro. The half-maximal inhibitory dose of Pb for retinal
9 and renal NaK-ATPase was 5.2 x 10~7 and 1.3 x 10~5 M, respectively. Retinal and renal
10 NaK-ATPase were 20-fold and 1.1-fold more sensitive to inhibition by Pb than calcium. The
11 increased sensitivity of retinal, compared to renal, NaK-ATPase to inhibition following in vivo
12 or in vitro Pb exposure may be related to their different a subunit composition.
13 Kramer et al. (1986) had also explored the half-maximal inhibitory dose for Pb-chloride
14 on renal cortical homogenate NaK-ATPase, and found it to be 7 x 10~5 M. There was a
15 competitive inhibition with regard to the substrate, ATP. Of several metals tested, Pb was
16 second only to Hg in potency as a NaK-ATPase inhibitor.
17 Weiler et al. (1990) studied the effect of Pb on the kinetics of purified (from hog cerebral
18 cortex) NaK-ATPase and potassium-stimulated p-nitrophenylphosphatase (K-pNPPase), which is
19 referred to as the E2 configuration of the NaK-ATPase system. ICso for Pb was found to be
20 8.0 x 10~5 M for NaK-ATPase and 5.0 x 10~6 M for K-pNPPase. Inhibition of NaK-ATPase by
21 Pb was found to be noncompetitive with respect to K, but competitive with respect to Na and
22 MgATP. Inhibition of K-pNPPase by Pb was competitive with respect to K.
23
24 Effects of Lead on Cardiovascular Hormones
25 Effects of Lead on Endothelin
26 Khalil-Manesh et al. (1993a) examined the role of endothelial factors in Pb-induced
27 hypertension. They found that low Pb administration (0.01%), but not high Pb administration,
28 (0.5%) resulted in increased blood pressure in rats treated for 12 months. In the low-Pb-treated
29 rats, measurement of plasma endothelins-1 and -3 revealed that endothelin-3 concentration
30 increased significantly after both 3 months (lead, 92.1 ± 9.7 vs. control, 46.7 ± 12.0 pmol/ml;
31 p < 0.001) and 12 months (lead, 105.0 ± 9.3 vs. control, 94.1 ± 5.0 pmol/ml; p < 0.01), while
May 2006 5-177 DRAFT-DO NOT QUOTE OR CITE
-------
1 endothelin-1 was unaffected. Plasma and urinary cyclic GMP concentrations, as a reflection of
2 endothelium-derived relaxing factor (EDRF), decreased significantly at 3 months (plasma lead,
3 1.8 ± 0.9 vs. control, 4.2 ± 1.6 pmol/ml; p < 0.001) and 12 months (plasma Pb 2.2 ± 0.7 vs.
4 control, 4.2 ± 0.9 pmol/ml; p < 0.001). High levels of Pb exposure did not result in hypertension,
5 perhaps related to the fact that plasma concentrations of endothelin-1, endothelin-3, and cyclic
6 GMP were unaltered at 3 months, while their concentrations were significantly decreased at 12
7 months (plasma cyclic GMP at 12 months, 2.2 ± 0.7, lead, vs. 4.2 ± 0.9 pmol/ml, control; p
8 < 0.001). Thus, the path to development of hypertension in low-Pb rats was thought to be
9 through an increase in the concentration of the vasoconstrictor, endothelin-3, and a decrease in
10 the vasodilator hormone, endothelium-derived relaxing factor or NO.
11 Novak and Banks (1995) studied the effects of Pb on the actions of endothelin. They
12 measured renal clearances and mean arterial pressure in rats in which endothelin-1 was infused at
13 110 ng/kg/min for 30 min. Lead was infused as Pb-acetate throughout the experiment at 0.48,
14 4.8, and 24 nmoles/min. At the two higher doses, Pb significantly attenuated the endothelin-
15 induced increase in mean arterial pressure; Pb infused as 0.48 nmoles/min had no effect.
16 An endothelin-induced decrease in GFR in control rats was completely blocked at the higher
17 doses of lead. In additional experiments, calcium chloride was infused at 500 nmoles/min for
18 105 min, and then calcium + Pb (4.8 nmoles/min) were infused for another 105 min. In these
19 experiments, there was no Pb-induced inhibition of the mean arterial pressure response to
20 endothelin. However, the GFR response to the peptide remained blocked. These data illustrate
21 that Pb inhibits the cardiorenal actions of endothelin and that a calcium-related process is
22 involved in the systemic, but not the renal, component of this inhibition.
23
24 Effects of Lead on the Catecholamine System
25 Carmignani et al. (2000) studied the effects of 10 months of low Pb exposure (60 ppm of
26 Pb-acetate), on catecholamine and monoaminoxidase (MAO) levels. Plasma catecholamines
27 were measured by HPLC and MAO in aorta, liver, heart, kidney, and brain by a histochemical
28 technique. Plasma norepinephrine (NE) increased by 104% and adrenaline by 81%, with no
29 changes noted in L-DOPA and dopamine levels. MAO activity was increased in all organs.
30 These workers ascribed the low Pb-induced hypertension in part to raised catecholamines levels.
May 2006 5-178 DRAFT-DO NOT QUOTE OR CITE
-------
1 Tsao et al. (2000) and Chang et al. (2005) measured changes in the P-adrenergic system in
2 Wistar rats during and following Pb exposure. In Tsao et al. (2000), rats were chronically fed
3 with 0.01, 0.05, 0.1, 0.5, 1.0, and 2.0% Pb-acetate for 2 months. Plasma catecholamine levels
4 were measured by HPLC; cAMP levels in heart, kidney, and aorta by radioimmunoassay; and
5 P-adrenergic receptors in heart, kidney, and aorta membranes by a radio ligand binding assay.
6 Blood Pb increased from 0.05 ± 0.05 |ig/dL in controls to 85.8 ± 4.1 |ig/dL in the
7 2.0% Pb-treated group. Plasma NE, but not E, levels increased with increasing Pb dosage.
8 p-adrenoreceptor density of heart and kidney decreased progressively with increasing Pb dosage,
9 whereas kidney P-adrenoreceptor density increased up to the 0.5% Pb group and then remained
10 constant. Unstimulated cAMP was constant in all tissues, but cAMP stimulated by isoprotorenol
11 was lowered progressively in aorta and heart and increased in kidney. Chang et al. (2005)
12 continued these measurements in rats fed 2% Pb-acetate for 2 months then withdrawn from Pb
13 for periods of 1, 2, 3, 4, 5, 6, and 7 months. Blood Pb levels, systolic and diastolic blood
14 pressure levels, and plasma NE were reduced after cessation of Pb exposure. This occurred in
15 conjunction with an increase in P-adrenoreceptor density in heart and aorta and a decrease in
16 P-adrenoreceptor density in kidney. (See Table AX5-5.5 for experimental details on these
17 studies).
18
19 Effects ofChelators (Single or Combined) on Lead Mobilization
20 These studies are summarized in Tables AX5.7-3 and AX5.7-4. For the sake of brevity,
21 they will not be discussed further here.
22
23 Effects of Other Metals on Lead Distribution
24 Lead and Calcium
25 Fullmer (1992) published a review of intestinal interactions of Pb and calcium. High
26 affinity Pb binding to intracellular calcium receptors and transport proteins, as well as the
27 involvement of Pb in calcium-activated and calcium-regulating processes, are thought to provide
28 a partial molecular basis for the cellular and systemic effects of lead.
29 Maidonado-Vega et al. (1996) examined the intestinal absorption of Pb and bone
30 mobilization during lactation. All experiments were started with 3-week-old female Wistar rats.
31 Rats were impregnated at 16 weeks and were fed a 100 ppm solution of Pb-acetate for 158 or
May 2006 5-179 DRAFT-DO NOT QUOTE OR CITE
-------
1 144 days (mid-lactation or before lactation). Rats were also exposed for only 14 days, from 144
2 to 158 days (i.e., only during lactation). Nonpregnant rats from the same litter were exposed to
3 Pb for periods equivalent to each of these groups. In the nonpregnant rats, blood Pb increased to
4 27.3 |ig/dL from 5.2 |ig/dL in controls. Similarly, kidney Pb increased to 13.2 nmol/g from
5 0.5 nmol/g, and bone Pb increased to 88.9 nmol/g from 0.9 nmol/g. ALAD activity decreased to
6 410 nmol/h/ml from 1004 nmol/h/ml. Compared to nonpregnant rats, there was a moderate
7 increase in blood Pb in the lactating animals whether the Pb was given to mid-lactation or up to
8 the period before lactation. Similarly, when Pb was administered only during lactation, there
9 was a much higher increase in blood Pb in the pregnant rats than in the nonpregnant rats. Bone
10 Pb concentration increased when Pb was given only during lactation, whereas bone Pb decreased
11 (compared to Pb-treated nonpregnant rats) when the Pb was given either before lactation or
12 before and during lactation. The authors considered that resorption of Pb from bone was the
13 main additional source of Pb during lactation. The data indicate that Pb stored in bone as a result
14 of prior maternal exposure should be considered as a major source of self intoxication and of Pb
15 in milk available to suckling pups.
16
17 Lead and Cadmium
18 Skoczyriska et al. (1994) compared the effects of the combined exposure to Pb and
19 cadmium to each metal singly on tissue composition of trace metals. Experiments were
20 performed on 5- to 6-week-old male Buffalo rats given Pb-acetate (70 mg lead/kg body weight
21 twice a week) and cadmium chlorate (20 mg Cd/kg body weight once a week) intragastrically for
22 7 weeks either singly or in combination. Blood Pb in the control group was 5.1 |ig/dL, compared
23 to 29.6 |ig/dL in the Pb-treated group. In contrast, the Pb + cadmium group showed a blood Pb
24 of 37.4 |ig/dL. After combined exposure to Pb and cadmium, the level of these metals in the
25 liver and kidney was lower than after the single administration of Pb or cadmium. Exposure of
26 the rats to cadmium resulted in an increase of kidney zinc and copper and liver zinc
27 concentrations; combined exposure to Pb + cadmium did not produce more extensive changes in
28 tissue zinc and copper concentrations.
29 Lead and Selenium
30 Othman and El Missiry (1998) examined the effect of selenium against Pb toxicity in
31 male rats. Male albino rats were given a single dose of Pb-acetate (100 jimol/kg body weight)
May 2006 5-180 DRAFT-DO NOT QUOTE OR CITE
-------
1 and sacrificed 3 or 24 h later. Another group of animals was pretreated with sodium selenite
2 (10 jimol/kg body weight) 2 h before receiving Pb-acetate and sacrificed 24 h later. Selenium is
3 well known as an antioxidant and cofactor for GSHPx. In this experiment, GSH content,
4 GSHPx, SOD activities, and the products of lipid peroxidation (i.e., TEARS) were determined.
5 It was found that lipid peroxidation was prevented and the reduction in GSH caused by Pb in
6 liver and kidney was diminished by selenium. Lead-induced diminution in SOD activity and
7 GSHPx activity was also returned to normal by selenium.
8 Tandon et al. (1992) studied the effect of selenium supplementation during chelation of
9 Pb with CaNa2EDTA. Rats were given Pb-acetate 10 mg/kg/day by gastric gavage for 6 weeks.
10 This was followed by a 5-day treatment course of CaNa2EDTA, 0.3 mmol/kg IP or of
11 CaNa2EDTA + sodium selenite, 0.5 mg/kg PO. Selenium had marginal effects on Pb removal
12 by CaNa2EDTA in blood, liver, and kidney and similar effects on ALAD activity.
13
14 Lead and Zinc
15 Flora et al. (1989) examined the role of thiamine, zinc, or their combination in the
16 prevention or therapy of Pb intoxication. Albino rats received the following treatments daily
17 through gastric gavage for 6 days each week over a six-week period, 10 mg/kg of Pb as
18 Pb-acetate; or the same dose of Pb-acetate + thiamine (25 mg/kg) zinc sulfate (25 mg/kg) or
19 Pb + thiamine and zinc. Rats that had been exposed to Pb only were additionally divided into
20 four groups treated by gastric gavage daily for 6 days as follows: group I, water only; group II,
21 thiamine only; group III, zinc only; and group IV, combined zinc + thiamine. The activities of
22 blood ALAD, blood ZPP, blood lead, and urine ALA were determined. Blood Pb concentrations
23 increased from 6.2 to 120.9 |ig/dL, contrasting normal controls with Pb-treated animals. There
24 was a slight reduction in blood Pb in animals treated with either thiamine or zinc and a greater
25 reduction in animals treated with thiamine + zinc. In the post-Pb-exposure treatment group,
26 thiamine + zinc was also the most effective treatment. Liver and kidney Pb levels followed the
27 same course but brain Pb was not reduced by treatment. Blood ALAD activity was decreased
28 from a normal level of 7.63 (imol ALA/min/L to 0.69 in Pb-treated animals and restored to 7.52
29 in Pb + thiamine + zinc-treated rats. ZPP was increased from 1.78 |ig/g hemoglobin to 4.22 in
30 Pb-treated animals and reduced to 2.50 in Pb + thiamine + zinc-treated animals. Urine ALA was
31 increased from 0.07 to 0.24 mg/dL in Pb-treated animals and decreased to 0.17 in
May 2006 5-181 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb + thiamine + zinc-treated rats. Prevention was more effective than post-Pb-exposure
2 treatment. This was thought to be due mainly to the decrease in the absorption of Pb in the GI
3 tract in the presence of thiamine and/or zinc.
4 Flora et al. (1994) explored the dose-dependent effects of zinc supplementation during
5 chelation of Pb in rats. The chelator employed was CaNa2EDTA, whose toxic effects are known
6 to be mainly due to the depletion of endogenous zinc and, possibly, copper and manganese.
7 In this experiment, male Wistar rats were started on exposure to Pb-acetate, 10 mg/kg,
8 administered through gastric gavage once daily for 56 days. Twenty-four hours later, the
9 Pb-exposed animals were treated daily for 5 days as indicated: group I, saline ; group II,
10 CaNa2EDTA 0.3 mmol/kg, IP, once daily for 5 days; group III, CaNa2EDTA + zinc sulfate,
11 10 mg/kg, PO once daily for 5 days; and group IV, CaNa2EDTA + zinc sulfate, 50 mg/kg,
12 PO once daily for 5 days. Blood ALAD decreased from 6.30 to 1.44 nmol/min/mL erythrocyte
13 in Pb-exposed animals, with no change after CaNa2EDTA treatment and partial restoration after
14 the CaNa2EDTA + zinc, 10 mg/kg treatment. There was no improvement following zinc,
15 50 mg/kg. Lead concentration in blood increased from 4.6 |ig/dL to 43.0 |ig/dL in Pb exposed
16 animals, decreasing to 22.5 |ig/dL in CaNa2EDTA-treated animals and decreasing further to
17 16.5 |ig/dL in CaNa2EDTA plus zinc-treated animals. Zinc at 50 mg/kg led to an increase in
18 blood Pb to 56.1 |ig/dL. Changes in the liver follow the same pattern, while in the kidney, zinc
19 increased the Pb levels further, and in the femur, zinc had no influence on Pb content. Blood
20 zinc decreased from 6.1 to 5.7 |ig/ml in Pb-exposed rats and further to 5.0 |ig/ml in
21 CaNa2EDTA-treated animals. There was an increase to levels of 6.6 |ig/ml on the 10 mg/kg
22 supplement of zinc and a further increase to 8.1 |ig/ml on the 50 mg/kg zinc supplement.
23
24 Lead and Iron
25 Hashmi et al. (1989) examined the influence of dietary iron deficiency, Pb exposure, or
26 the combination of the two on the accumulation of Pb in vital organs of rats. Animals fed an iron
27 deficient diet for 2 weeks were also subjected to orbital plexus puncturing twice a week to allow
28 a Hb levels to decrease to 7 to 8 g/dL. Animals were thereafter treated for the next 6 weeks with
29 iron deficient diets or iron-deficient diets + 0.1% Pb-acetate in drinking water. At the end of
30 3 and 6 weeks, animals from each group were sacrificed. Feeding of an iron-deficient diet
31 during Pb exposure enhanced the accumulation of Pb in soft tissues and flat bones. For example,
May 2006 5-182 DRAFT-DO NOT QUOTE OR CITE
-------
1 liver Pb content was 0.75 |ig/g in control animals, 8.43 in Pb treated animals, and 12.93 in iron-
2 deficient and Pb-treated animals. The sequence of events was similar in kidney, spleen, and
3 femur except that the Pb content in femur was reduced in the iron deficient and Pb-treated group.
4 Singh et al. (1991) conducted a study to ascertain the role of iron deficiency during
5 pregnancy in inducing fetal nephrotoxicity in mothers exposed to lead. Rats were fed either a
6 normal iron diet or an iron free synthetic diet for 15 days, followed by a diet containing half of
7 the daily required iron (47 mg/100 g ferrous ammonium sulfate) for a further 15 days. Female
8 animals were mated with healthy adult males. Lead doses of 250, 500, 1000, and 2000 ppm
9 were given in drinking water during pregnancy and lactation. Fetuses were removed by
10 Caesarean section on the 21st day. Maternal blood Pb levels in rats on an iron deficient diet
11 were higher than those in rats on a normal iron diet at all levels of Pb dosing. Similarly,
12 placental Pb levels were higher in animals on an iron-deficient diet as compared to a normal diet.
13 Lead content in the fetuses were higher on the iron-deficient diet. Lead administration resulted
14 in dose-dependent hydropic degeneration of renal proximal tubular cells in the fetuses. At a dose
15 of 2000 ppm Pb with iron deficiency, more Pb accumulated in maternal blood, placenta, and
16 fetuses and maximum pathological changes were seen in the fetal kidney as compared to other
17 doses.
18
19 Lead and Aluminum
20 Shakoor et al. (2000) reported beneficial effects of aluminum on the progression of
21 Pb-induced nephropathy in rats. Male albino rats were treated with water only or Pb-acetate
22 (125 mg/kg) and/or aluminum chloride (50 mg/kg or 100 mg/kg) for a period of 90 days.
23 Aluminum was found to prevent the Pb-induced increase in relative kidney weight in a dose-
24 dependent manner. Aluminum also prevented Pb-induced increases in plasma creatinine levels
25 of Pb-treated animals. The net deposition of Pb in kidneys was lower in animals that were given
26 both Pb-acetate and aluminum chloride simultaneously. By day 90, plasma creatinine was
27 1.26 mg/dL in control animals, 1.88 mg/dL in Pb-treated animals, and 1.34 and 1.44 mg/dL in
28 Pb- and aluminum-treated animals. Similarly, kidney Pb increased from 5.4 |ig/g in control
29 animals to 220.0 jig/g in Pb-treated animals and decreased to 138.5 and 98.9 jig/g in Pb- and
30 aluminum-treated animals. These and other studies are summarized in Table AX5-7.5.
31
May 2006 5-183 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead, Cadmium, and Arsenic
2 In their review of mechanisms of nephrotoxicity from metal combinations, Madden and
3 Fowler (2000) discuss the effects of lead, cadmium, and arsenic combinations, as such
4 combinations may be found in the industrial setting or at toxic dump sites. Cadmium has been
5 shown to interact with lead, minimizing the kidney effects of lead by lowering the renal lead
6 burden and preventing the appearance of lead inclusion bodies (Mahaffey et al., 1981).
7 Cadmium may therefore affect the binding of lead to lead-binding protein (Mistry et al., 1985).
8 Lead, cadmium, and arsenic combinations also increase the degree of porphyrinuria beyond that
9 produced by lead alone (Fowler and Mahaffey, 1978).
10
11 5.7.4.4 Effect of Age on Lead Toxicity
12 Han et al. (1997) examined the hypothesis that the high rate of bone remodeling during
13 childhood and the consequent high calcium and Pb turnover would result in a substantial
14 reduction in bone Pb stores, so that much of the Pb incorporated in bone during childhood does
15 not persist into adulthood. They treated female Sprague-Dawley rats with 250 ppm of Pb in
16 drinking water for 5 weeks beginning at 5, 10, or 15 weeks of age. Organ harvesting occurred
17 4 weeks after the end of Pb exposure for all groups, as well as 8 and 20 weeks after cessation of
18 Pb ingestion in the rats exposed beginning at 5 weeks of age. Organs examined were brain,
19 kidney, liver, femur, and spinal column bone. Blood and organ Pb concentrations were
20 significantly higher in the rats exposed beginning at 5 weeks of age than in those exposed
21 beginning at 10 or 15 weeks of age. The results of this experiment rejected the hypothesis and
22 suggested instead that a younger age at Pb exposure is associated with greater Pb retention and
23 toxicity, even in the absence of continued Pb exposure.
24 Garcia and Corredor (2004) examined biochemical changes in the kidneys after perinatal
25 intoxication with Pb and/or cadmium. Lead acetate (300 ppm) and/or cadmium acetate (10 ppm)
26 were administered in drinking water to pregnant Wistar rats from day 1 of pregnancy to
27 parturition (day 0) or until weaning (day 21). The following kidney enzyme activities were
28 determined: alkaline and acid phosphatases, Mg-ATPase, and NaK-ATPase. Blood Pb was
29 measured in control pups as well as in pups exposed to lead at parturition and at weaning.
30 Control pups showed 1.43 |ig/dL of blood Pb compared to 31.5 |ig/dL at day 0 and 22.8 |ig/dL
31 at day 21 in pups exposed to lead. In those rats receiving both cadmium and Pb, the blood Pb
May 2006 5-184 DRAFT-DO NOT QUOTE OR CITE
-------
1 concentration was 23.2 |ig/dL at day 0 and 13.2 |ig/dL at day 21. Lead caused a significant
2 inhibition of kidney alkaline phosphatase and kidney acid phosphatase. At parturition, Pb
3 intoxication produced a strong inhibition of NaK-ATPase (-80%) as well as of Mg-ATPase
4 activities (-24%); whereas, when Pb was given in combination with cadmium, these inhibitory
5 effects were attenuated. At weaning, Pb continued to produce a significant inhibition of
6 Mg-ATPase but had no effect on NaK-ATPase. Thus, simultaneous perinatal administration of
7 both Pb and cadmium seemed to protect against the toxicity produced by Pb separately.
8 Cory-Slechta (1990b,c) published two articles on the effects of old age on the disposition
9 of lead. In the study (1990c) male F344 rats, at the ages of 8 months (adult) and 16 months (old)
10 were exposed to concentrations of 0, 250, or 500 ppm Pb-acetate in drinking water for 7 months.
11 At these Pb doses, prior studies had indicated that blood Pb levels ranged from 60 to 90 |ig/dL.
12 Blood lead, ZPP, and urinary ALA levels were determined after both 3 and 7 months of
13 exposure. Organ weights, tissue Pb concentrations, and urinary excretion of lead, calcium,
14 copper, and zinc were examined after 7 months of exposure. Tissue Pb distribution was
15 markedly altered in old rats: in bone and kidney, Pb levels were reduced while liver Pb was
16 substantially increased. Blood Pb levels in adult and old rats were comparable at both
17 measurement intervals, as was urinary Pb excretion at 7 months. Lead-induced elevation of ZPP
18 exhibited differential changes between 3 and 7 months; values in adults declined while levels in
19 old rats increased or remained unchanged. In the adult group, Pb exposure increased calcium
20 excretion primarily at the 500 ppm exposure level. In contrast, Pb exposure decreased urinary
21 calcium excretion in old animals at the higher exposure level. No effects of either age or Pb
22 exposure were detected in the comparison of adult versus old urinary excretion of zinc or copper.
23 In the second study, Cory-Slechta (1990b), young (21 days old), adult (8 months old), and
24 (16 months old) rats exposed to 0, 2, or 10 mg of Pb-acetate/kg per day for a period of
25 9.5 months were evaluated. Differences in the tissue distribution of Pb with age included lower
26 bone levels, but increased concentrations in brain, liver, and kidney. Differences in blood Pb
27 levels over the course of exposure were not remarkable. Thus, these effects did not appear to
28 reflect an enhanced Pb absorption from the GI tract with age. Instead, the bone changes may
29 reflect enhanced bone resorption with a concurrent decline in bone apposition with age,
30 combined with altered patterns of urinary Pb excretion over time, i.e., elevated urinary Pb at 3
31 and 6 months, but comparable Pb excretion at 9.5 months, as compared to young and adult rats.
May 2006 5-185 DRAFT-DO NOT QUOTE OR CITE
-------
1 Summary
2 Highlights of the previous 1986 Pb AQCD and of studies done between 1986 and the
3 present are outlined in this section.
4
5 1986 Document
6 • In animal studies, nuclear inclusion bodies were found in proximal tubules, identified as
7 27 kDa or 32 kDa proteins in combination with lead. Subsequently, a 63 kDa Pb-binding
8 cytosolic protein was described in kidney.
9 • Swollen mitochondria, with diminished mitochondrial function, were found in the
10 proximal tubules.
11 • Renal ALAD was the same in Pb-treated animals as in controls when GSH was present,
12 but was reduced when GSH was absent.
13
14 Newer studies
15 • Experimental studies have shown that early effects of lead on tubular cells are generally
16 reversible, but with continued exposure, a chronic irreversible nephropathy is likely to
17 ensue.
18 • Hyperfiltration, when compared to age- and sex-matched normal controls, was found in
19 adults who had suffered from childhood Pb poisoning, in young occupationally exposed
20 Pb workers in Korea, and in both low-Pb-treated rats and high-Pb-treated rats up to
21 3 months of exposure. This is paralleled in animal experiments by an increase in
22 kidney weight.
23 • Various new urinary markers for Pb toxicity have been described. These include NAG,
24 p2-microglobulin, al-microglobulin, retinol binding protein, GST, lysozyme, y-glutamyl
25 transferase, alanine aminopeptidase, prostanoids, and brush border antigens. The
26 literature on these markers is voluminous, but, on review, only GST and
27 al-microglobulin seemed to be appropriate urinary markers. NAG, which has been most
28 extensively investigated, appears in detailed-animal studies to be overly sensitive,
29 increasing in low-Pb-treated animals, despite an absence of pathological changes on
30 ultrastructural study. p2-Microglobulin, and possibly retinol binding protein, which are
31 low-molecular weight proteins reabsorbed by the proximal tubule, appeared to be
32 elevated only with high levels of blood Pb (>80 jig/dL).
33 • Animal studies have implicated free radicals in the pathogenesis of Pb-induced
34 hypertension and renal disease. A sequence of free radicals can be demonstrated in
35 Pb-induced disease, as evidenced by an increase in superoxide radicals, hydroxyl
36 radicals, hydrogen peroxide, and peroxynitrite, together with a diminution in GSH in
37 liver, brain, and aorta. Nitric oxide is most commonly decreased (by free radicals) as is
May 2006 5-186 DRAFT-DO NOT QUOTE OR CITE
-------
1 urinary cyclic GMP. Aortic guanylate cyclase is decreased. The enzyme responsible for
2 an increase in the production of free radicals, NAD(P)H oxidase, is increased by Pb,
3 whereas eNOS and iNOS, the enzymes involved in the production of nitric oxide, are also
4 increased, attesting to the importance of free radical destruction of nitric oxide.
5 Antioxidants reverse these changes and diminish blood pressure.
6 • Norepinephrine and epinephrine are increased by Pb administration, whereas
7 p-adrenoreceptor density of heart and kidney are decreased. In a second study,
8 norepinephrine, but not epinephrine, was increased by Pb.
9 • Various antioxidants have been used in conjunction with chelators, to both remove Pb
10 from tissue and to diminish free radicals. Taurine, lipoic acid, arginine, ascorbic acid,
11 vitamin E, thiamine, tempol, and lazaroids have been used in conjunction with DMSA,
12 all improving free radical diminution.
13 • Metal combinations have also been employed to reduce tissue Pb and/or affect free
14 radicals. Cadmium increases Pb in blood when both are given, but diminishes Pb in liver
15 and kidney. Selenium, an antioxidant, improves both parameters, as does thiamine or
16 L-lysine plus zinc. Iron deficiency increases intestinal absorption of Pb and the Pb
17 content of soft tissues and bone. Aluminum decreases kidney Pb content and serum
18 creatinine in Pb-intoxicated animals.
19 • Age also has an effect on Pb retention. There is higher Pb retention at a very young age
20 and lower bone and kidney Pb at old age, attributed in part to increased bone resorption
21 and decreased bone accretion.
22
23
24 5.8 EFFECTS ON BONE AND TEETH
25 5.8.1 Biology of Bone and Bone Cells
26 By weight, bone is composed of 28% collagen fibers (predominantly type I collagen) and
27 5% noncollagenous proteins (osteocalcin, osteonectin, and other proteoglycans), with crystals of
28 hydroxyapatite [Caio(PO4)e(OH)2] making up the remaining 67%. In addition to providing
29 mechanical support for the body and protection of vital organs, the skeletal system also functions
30 in a metabolic capacity. Historically, bones have been classified as either long or flat based on
31 their appearance, with long bones including limb bones, e.g., the femur and humerus, and flat
32 bones including the bones of the skull, sternum, pelvis, and scapula. Long and flat bones
33 originate by distinct methods of formation, endochondral and intramembranous, respectively,
34 with long bones eventually using both processes. In endochondral bone formation, a
35 mineralized, cartilaginous matrix precedes the transition into true bone, while in
May 2006 5-187 DRAFT-DO NOT QUOTE OR CITE
-------
1 intramembranous formation, the bone forming cells create bone directly without the cartilaginous
2 template.
3 Bone cells responsible for producing the bone matrix of collagen and ground substance
4 are called osteoblasts. Several signaling factors including growth factors and hormones
5 influence pre-osteoblastic cells to differentiate into mature osteoblasts and subsequently
6 synthesize and mineralize the extracellular matrix to form mature bone. It is during the process
7 of bone mineralization that the Pb ion (Pb2+) can become incorporated by substituting for the
8 calcium ion (Ca2+). The bone cells responsible for bone resorption are the osteoclasts.
9 Osteoclasts, which are large and multicellular (4 to 20 cells), dissolve bone matrix and
10 hydroxyapatite by synthesizing and releasing lysosomal enzymes and acidifying the extracellular
11 surroundings. It is during the process of dissolving bone, or demineralization that Pb stored in
12 bone can be released locally and into the general system.
13 Bone cell function may be compromised both directly and indirectly by exposure to Pb.
14 Regulation of bone cells occurs by numerous local and systemic factors, including growth
15 hormone (GH), epidermal growth factor (EGF), transforming growth factor-beta I(TGF-PI), and
16 parathyroid hormone-related protein (PTHrP). As discussed further below in this section, the
17 presence of lead can potentially interfere with each of these factors. The bones of the skeleton
18 serve as the primary reservoir for calcium and phosphate in the body and help to maintain
19 homeostasis of these ions in the serum through bone turnover or remodeling. Vitamin D
20 [1,25-(OH2)D3] maintains the normal range of calcium in the serum by increasing the efficiency
21 of calcium absorption in the intestines and facilitating differentiation of stem cells into
22 osteoclasts, which break down bone and mobilize calcium (and lead) stores. Parathyroid
23 hormone (PTH), in turn, regulates the production of vitamin D in the kidney. Lead has been
24 shown to interfere with the action of both of these hormones. Other substances influenced by
25 lead and discussed in this section are alkaline phosphatase, an enzyme necessary for
26 mineralization of bones and teeth, and osteocalcin, a noncollagenous protein whose spatial and
27 temporal pattern of expression suggests a role in bone mineralization. Both substances are also
28 markers for osteoblast activity and, by default, bone formation. Alkaline phosphatase is a
29 potential carrier of ionic calcium and is capable of hydrolyzing inhibitors of mineral deposition
30 such as pyrophosphates.
31
May 2006 5-188 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.8.2 Summary of Information Presented in the 1986 Lead AQCD
2 Lead has been shown to become localized and accumulate in bones and teeth, with
3 accumulation beginning as early as fetal development. Lead administered to rats as a single dose
4 results in blood lead concentrations that are initially elevated, but rapidly fall as Pb is transferred
5 to bone or excreted. The dose of Pb administered does not apparently affect distribution to the
6 various body compartments; however, the rate-limiting step in the clearance of Pb from rats and
7 mice involves absorption into/clearance from the skeletal system. The loss of Pb from various
8 organs and tissues follows first-order kinetics, except from bone. More absorbed Pb is retained
9 by young animals compared with adult animals, leading to higher tissue levels. Moreover, once
10 Pb is incorporated into the young animal's body, the long-term rate of retention is greater than
11 that of adults. In Pb-exposed animals, Pb is distributed subcellularly, preferentially to the
12 nucleus and mitochondrial fractions.
13 During lactation in mice, a redistribution of tissue Pb occurs (mobilization), resulting in
14 the transfer of Pb and calcium from mother to pups via the milk and subsequent overall loss of
15 Pb in the mothers. Lead transfer to suckling rats via mother's milk has been reported to be
16 approximately 3% of the maternal body burden or more, if Pb exposure continues during
17 lactation. Eight days after a single injection of Pb, the content of Pb in rabbit's milk was 8-fold
18 higher than the maternal blood level, suggesting Pb transfer can occur against a concentration
19 gradient. Transplacental transfer of Pb from mother to fetus also occurs in various animals.
20 In rats, a significant reduction of calcium in the diet leads to enhanced uptake of lead into
21 the bones and other tissues. In general, an enhanced uptake of Pb into tissues is also seen in rats
22 fed diets deficient in iron, zinc, copper, or phosphorus, and in the presence of low or excess
23 vitamin D.
24
25 5.8.3 Bone Growth in Lead-Exposed Animals
26 Lead is readily taken up and stored in the bone of experimental animals, where it can
27 potentially manifest toxic effects that result in stunted skeletal growth. In experiments reported
28 since the 1986 Pb AQCD, Hac and Krechniak (1996) determined uptake and retention of Pb in
29 bone from rats exposed to plain water or water containing Pb-acetate (41.7 to 166.6 mg/L) for
30 12 to 16 weeks. After 4 weeks, the skeletal Pb in animals receiving the lowest dose was almost
31 5 times higher than control animals (5.9 versus 1.2 jig Pb/g bone, respectively). Lead levels in
May 2006 5-189 DRAFT-DO NOT QUOTE OR CITE
-------
1 bones from animals receiving 83.3 mg/L and 166.6 mg/L were dose-dependently higher at 11.7
2 and 17.0 jig Pb/g bone, respectively, after 4 weeks of exposure. All bone Pb levels were
3 maintained essentially in a steady state until the completion of exposure, when all animals were
4 placed on control water. Approximately 64% of Pb remained in the bones of rats in the
5 83.3 mg/L exposed group at 64 days postexposure. No blood levels of Pb were reported.
6 Similarly, airborne Pb can be inhaled and subsequently incorporated into bone. Grobler and co-
7 workers (1991) exposed 6-week-old rats to either "clean air" (0.05 jig Pb/m3) or air containing
8 77 jig Pb/m3 and found significant differences in the amount of Pb incorporated into the alveolar
9 bones of the animals. After 70 days, a mean of only 0.2 jig Pb/g of bone dry mass was found in
10 bone from control animals, while 16.9 jig Pb/g was present in bone from the 77 jig Pb/m3
11 exposure group. Exposure to air containing 249 jig Pb/m3 for 28 days or 1,546 jig Pb/m3 for
12 50 days, resulted in mean values of 15.9 and 158 jig Pb/g dry weight of Pb incorporation into the
13 bone, respectively, highlighting the fact that dose and length of exposure are determinates of
14 amount of Pb contained in the bones of these animals. Blood Pb levels were 2.6 |ig/dL in control
15 animals and ranged from 11.5 |ig/dL to 61.2 |ig/dL in the experimental groups. The uptake of Pb
16 by bone has the potential for immediate toxic effects on the cellular processes occurring during
17 bone growth, development, and maintenance, with the additional potential for delayed toxicity
18 from release of stored Pb during periods of normal or accelerated bone remodeling.
19 Numerous studies have examined growth suppression associated with developmental Pb
20 exposure. Hamilton and O'Flaherty (1994) examined the effects of Pb on growth in female rats,
21 and subsequently, on growth and skeletal development in their offspring. Administration of
22 drinking water containing either 250 or 1,000 ppm lead to weaning female rats for 49 days
23 produced no alteration in growth rate in these future dams. Blood Pb levels prior to mating were
24 2.7 ± 0.6 |ig/dL (control), 39.9 ± 3.5 |ig/dL (250 ppm group), and 73.5 ± 9.3 |ig/dL (1000 ppm
25 group). The rats were then bred, with Pb exposure continuing through parturition and lactation.
26 Lead did not affect gestation time nor Day 1 suckling body weight, however, pup body weight
27 and tail length were subsequently decreased in both exposure groups. A 10% increase in tibial
28 growth plate width and disruption of chondrocyte organization were observed in offspring from
29 the high exposure group.
30 In male rats exposed to 100 ppm Pb in drinking water and a low calcium diet for up to one
31 year, bone density was significantly decreased after 12 months, while rats exposed to 5,000 ppm
May 2006 5-190 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb had significantly decreased bone density after 3 months (Gruber et al., 1997). Pb content of
2 femurs was significantly elevated over the content of control rats at all time points (1, 3, 6, 9,
3 12 months). Blood Pb levels ranged from 1 to 4 |ig/dL in control animals, 17 to 29 |ig/dL in low
4 dose animals, and 45 to 126 |ig/dL in high dose animals. Trabecular bone from the low dose
5 animals was significantly decreased from 3 months forward. Young female rats exposed to
6 17 mg of Pb-acetate per kg of feed for 50 days showed no differences in the length of the femurs,
7 but the mean length of the 5th lumbar vertebra was significantly decreased (Gonzalez-Riola
8 et al., 1997; Escribano et al., 1997). The mean length of the femur growth plate cartilage was
9 also significantly decreased in Pb-exposed animals. Blood Pb levels were not reported.
10 In a dose-response study, Ronis et al. (1998a, 1998b) exposed pregnant rats to Pb-acetate
11 in drinking water (0.05% up to 0.45% w/v) beginning at gestation Day 5 and continuing through
12 weaning of offspring at Day 21. Early bone growth was significantly depressed in a
13 dose-dependent fashion in pups of all Pb-exposed groups, with growth suppression in male
14 offspring considerably greater than in females. Significant decreases in plasma insulin-like
15 growth factor and plasma sex steroids and increased pituitary growth hormone were also
16 observed. Blood Pb levels in offspring ranged from 49 ± 6 |ig/dL (0.05% group) to
17 263 ± 28 |ig/dL (0.45% group). This is somewhat in contrast to the findings of Camoratto and
18 co-workers (1993), who reported low exposure to 0.02% Pb nitrate (125 ppm Pb) did not
19 significantly affect growth, though males weighed significantly less than females. Note however
20 that the blood Pb levels in the rat pups were less (43.3 ± 2.7 |ig/dL at 5d and 18.9 ± 0.7 |ig/dL
21 at 49d) than in the Camorrato study. Between age 57 and 85 days, Ronis et al. (1998b) noted
22 that growth rates were similar in control and Pb-exposed pups, suggesting exposure at critical
23 growth periods such as puberty and gender may account for differences in growth reported by
24 various investigators. In a series of follow-up experiments (Ronis et al., 2001) reported a dose-
25 dependent decrease in load to failure in tibia from Pb-exposed (0.15% and 0.45% Pb-acetate in
26 drinking water) male pups only. Hormone treatments (estradiol in females or L-dopa,
27 testosterone or dihydrotestosterone in males) failed to attenuate Pb deficits during the pubertal
28 period. Distraction osteogenesis experiments performed after stabilization of endocrine
29 parameters (at 100 days of age) found decreased new endosteal bone formation and gap x-ray
30 density in the distraction gaps of Pb-exposed animals (Ronis et al., 2001). Again blood Pb levels
31 were high, ranging from 67 to 388 |ig/dL in the offspring.
May 2006 5-191 DRAFT-DO NOT QUOTE OR CITE
-------
1 Hamilton and O'Flaherty (1995) found Pb disrupted mineralization during growth when
2 they implanted demineralized bone matrix subcutaneously into male rats. In the matrix that
3 contained 200 jig Pb/g of plaque tissue, alkaline phosphatase activity and cartilage
4 mineralization were absent, though calcium deposition was enhanced. Separate experiments
5 found enhanced calcification and decreased alkaline phosphatase activity in rats implanted with a
6 control (no Pb) matrix and given 1,000 ppm Pb in drinking water for 26 days (blood Pb 96.4 to
7 129.8 |ig/dL).
8 In summary, results from animal studies suggest Pb exposure is capable of adversely
9 affecting bone growth and density, potentially manifesting its action through interference with
10 growth and hormonal factors as well as toxic effects directly on bone.
11
12 5.8.4 Regulation of Bone Cell Function in Animals - Systemic Effects
13 of Lead
14 Lead may exhibit multiple complex systemic effects that ultimately could influence bone
15 cell function. As discussed in the animal studies below, Pb can modulate alterations in calcium
16 binding proteins and in calcium and phosphorus concentration in the blood stream, in addition to
17 potentially altering bone cell differentiation and function by altering plasma levels of growth
18 hormone and calciotropic hormones such as vitamin D3 [1,25-(OH2)D3] and parathyroid
19 hormone.
20
21 5.8.4.1 Hypercalcemia/Hyperphosphatemia
22 Intravenous injection of Pb has been shown to produce both an acute hypercalcemia and
23 hyperphosphatemia in rats (Kato et al., 1977). Injection of a relatively high dose of 30 mg/kg Pb
24 resulted in maximum values of calcium (17 mg%) after one hour and maximum values of
25 phosphorus (13.5 mg%) after 30 minutes. After 12 hours, the levels of both calcium and
26 phosphorus had returned to baseline levels. Histochemical examination demonstrated deposition
27 of Pb into bone and dentin in the rats, suggesting a direct action of Pb on bone and/or teeth,
28 ultimately displacing calcium and phosphorus and thereby producing hypercalcemia and
29 hyperphosphatemia. Blood Pb levels were not reported.
30
May 2006 5-192 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.8.4.2 Vitamin D [1,25-(OH2)D3]
2 As discussed above, vitamin D [1,25-(OH2)D3] modulates the normal range of calcium in
3 serum. In rats fed a low calcium or low phosphorus diet, ingestion of 0.82% Pb in the diet
4 reduced plasma levels of 1,25-(OH2)D3; however, this effect is lost when a high calcium or
5 normal phosphorus diet is given (Smith et al., 1981), suggesting a high calcium/phosphorus diet
6 reduces the susceptibility of vitamin D system to the effect of Pb. No mobilization of calcium
7 from bone or elevation of inorganic phosphorus was seen. Ronis et al. (2001) also reported no
8 effects of Pb on plasma concentrations of vitamin D metabolites, 25-OH D3 or 1,25-(OH2)D3, in
9 pubertal male rats exposed to either 0.15% or 0.45% Pb acetate in drinking water and maintained
10 on an adequate diet. High blood Pb levels (over 350 |ig/dL) were reported in some animals in
11 both of these studies. Fullmer (1995) found vitamin D function was severely compromised in
12 young growing chicks given a diet low in calcium (0.1% calcium) for two weeks and then
13 exposed to 0.2% or 0.8% Pb in their diet for an additional one or two weeks. In chicks
14 maintained on an adequate diet (1.2% calcium), exposure to 0.2% or 0.8% Pb in the diet resulted
15 in increased plasma levels of 1,25-(OH2)D3 as well as significantly increased intestinal
16 Calbindin-D protein [a calcium binding protein induced by 1,25-(OH2)D3] and its associated
17 mRNA, when compared with unexposed control chicks. Levels of intestinal Calbindin-D mRNA
18 and protein and plasma levels of 1,25-(OH2)D3 were elevated during the first week of Pb
19 exposure to chicks fed a diet deficient in calcium, but were significantly decreased by the second
20 week of Pb exposure. The study suggested Pb was mediating its effect through 1,25-(OH2)D3,
21 rather than via a direct action on the Calbindin-D protein. Follow up studies by Fullmer et al.
22 (1996) confirmed dose dependent increases in serum 1,25-(OH2)D3 levels (and Calbindin-D
23 protein and mRNA) with increasing dietary Pb exposure (0.1% to 0.8%) in similar experiments
24 performed on Leghorn cockerel chicks fed an adequate calcium diet. No blood Pb levels were
25 reported in either study.
26 5.8.4.3 Parathyroid Hormone
27 At least one animal study has associated experimental Pb exposure with secondary
28 hyperparathyroidism. Szabo et al. (1991) exposed Wistar Kyoto rats to either 1% Pb acetate in
29 water for a short term (10 weeks) or varying concentrations (0.001 to 1% Pb acetate) for a longer
30 term (24 weeks) to assess the influence of Pb on the interaction of the parathyroids with
May 2006 5-193 DRAFT-DO NOT QUOTE OR CITE
-------
1 1,25-(OH2)D3. Blood Pb levels in the short term experiment were reported simply as less than
2 0.2 |ig/dL in control animals and greater than 50 |ig/dL in the lead-exposed animals. No levels
3 were reported for the longer term experiment. Short term administration of 1% Pb resulted in
4 significant increases in bone Pb; however, total serum calcium and ionized serum calcium were
5 significantly decreased, as compared to controls. Circulating levels of 1,25-(OH2)D3 were also
6 decreased, though the rats were maintained on a normal calcium diet (0.95%). Parathyroid
7 glands from rats exposed short term to Pb were significantly increased in size over those in
8 control animals (178 jig per gland versus 96 jig per gland) and specific binding of 1,25-(OH2)D3
9 to parathyroid and intestinal tissue was increased. Likewise, long term administration of 1% Pb
10 resulted in significant increases in bone Pb and normalized parathyroid gland weights, and a
11 significant decrease in the level of 1,25-(OH2)D3. In the long term study, a dose-dependent
12 increase in parathyroid weight occurred with increasing exposure to Pb in drinking water.
13 The authors concluded the secondary hyperparathyroidism was associated with, and/or a result
14 of, the hypocalcemia and decreased 1,25-(OH2)D3 levels secondary to Pb exposure.
15
16 5.8.4.4 Growth Hormone
17 As discussed in Section 5.8.3, exposure to Pb has been associated with altered bone
18 metabolism and decreased growth and skeletal development (Hamilton and O'Flaherty, 1994,
19 1995; Gruber et al., 1997; Gonzalez-Riola et al., 1997; Escribano et al., 1997; Ronis et al.,
20 1998a,b, 2001; Camoratto et al., 1993), suggesting perturbation of one or more endocrine factors
21 such as growth hormone. To examine the effect of exposure to low-level Pb on pituitary growth
22 hormone release, Camoratto et al. (1993) exposed pregnant female rats to 0.02% Pb nitrate
23 (125 ppm Pb) beginning on gestational day 5 and continuing in pups through postnatal day 48.
24 Basal release of growth hormone from control and Pb-exposed pups at age 49 days was not
25 significantly different. Growth hormone releasing factor-stimulated release of growth hormone
26 from pituitaries of Pb-exposed pups was smaller than the stimulated release of growth hormone
27 from pituitaries of control animals (75% increase over baseline vs. 171% increase, respectively),
28 but the difference did not achieve significance (p = 0.08). Growth hormone content of the
29 pituitary glands was also not influenced by Pb exposure. Ronis et al. (1998b) reported similar
30 findings in rat pups exposed to 0.05%, 0.15%, or 0.45% Pb acetate in drinking water from
31 gestation day 5 through postnatal day 85, with the exception being significantly elevated
May 2006 5-194 DRAFT-DO NOT QUOTE OR CITE
-------
1 pituitary growth hormone levels at postnatal day 55. Blood Pb levels for both of these studies
2 were reported above in Section 5.8.3. Taken together, these rat studies suggest that differences
3 in growth seen with Pb exposure may not necessarily be the result of alterations in secretion of
4 growth hormone.
5
6 5.8.5 Bone Cell Cultures Utilized to Test the Effects of Lead
7 5.8.5.1 Bone Organ Culture
8 In an early bone organ culture study utilizing incorporated radioactive Pb into fetal radii
9 and ulnae, Rosen and Wexler (1977) reported release of Pb as the concentration of calcium in the
10 media was reduced or with addition of parathyroid hormone, but that calcitonin inhibited the
11 release of Pb as expected, verifying the capacity of this model system. The bone organ system
12 was subsequently used to evaluate the efficacy of Pb chelating agents, such as D-Penicillamine
13 and CaNa2EDTA (Rosen and Markokwitz, 1980; Rosen et al., 1982).
14
15 5.8.5.2 Primary Cultures of Osteoclasts and Osteoblasts
16 The ability to isolate primary cultures of osteoclasts and osteoblasts from mouse calvaria
17 provided an additional experimental model system to study the effects of Pb on specific bone
18 cells. Using isolated osteoclasts and osteoblasts, Rosen (1983) reported that uptake of
19 radioactive Pb by osteoclasts was rapid, almost linear, while osteoblasts showed very little
20 increase in uptake of Pb at increasing media concentrations. Physiological concentrations of
21 parathyroid hormone markedly increased uptake of Pb and calcium by osteoclast cells and, once
22 loaded with Pb, osteoclasts were capable of releasing Pb slowly into the media. Further kinetic
23 analysis of cultured osteoclastic bone cells indicated that cellular Pb is primarily associated with
24 the mitochondrial fraction (-78%) and that this Pb is readily exchangeable with the outside
25 media (Pounds and Rosen, 1986; Rosen and Pounds, 1988). Experiments conducted to
26 characterize the steady-state kinetic distribution and metabolism of calcium and Pb supported the
27 concept that the two elements are metabolized similarly in the osteoclast cells (Rosen and
28 Pounds, 1989).
29
May 2006 5-195 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.8.5.3 Rat Osteosarcoma Cell Line (ROS 17/2.8)
2 In recent years, the rat osteosarcoma cell line ROS 17/2.8 has been used extensively to
3 investigate the influence of Pb on various cellular processes and kinetics within these
4 osteoblast-like cells. The ROS 17/2.8 cell model is useful in that the cells are capable of
5 producing osteocalcin (a bone protein important for proper bone mineralization), have high
6 alkaline phosphatase activity (an enzyme normally associated with mineralization of cartilage),
7 possess vitamin D receptors, and respond to parathyroid hormone. In comparisons of cellular
8 lead toxicity and metabolism between primary cell culture from mouse calvaria and the rat
9 osteosarcoma cell line, Long and co-workers (1990) reported remarkable similarities in the
10 profile of radiolabeled Pb kinetics and intracellular Pb distribution. Using this cell line, Schanne
11 and co-workers (1989) simultaneously measured intracellular Pb and calcium concentrations and
12 found 5 and 25 micromolar Pb produced sustained 50% and 120% (respectively) increases in
13 intracellular calcium over a 5 hour period, and that measurable entry of Pb into the cells could be
14 demonstrated at the higher concentration. These findings advanced the hypothesis that
15 perturbation of intracellular calcium concentration may be the mechanism of Pb bone toxicity.
16 Schirrmacher and co-workers (1998) reported that calcium homeostasis is upset within
17 20 minutes of its addition to calvarial bone cell culture. Their results suggested that the calcium -
18 ATPases of intracellular stores were potentially poisoned by Pb entering the cells. Wiemann
19 et al. (1999) demonstrated that Pb was also capable of interfering with the calcium release
20 activated calcium influx (CRAC) in calvarial bone cell cultures. Pb was found to partially inhibit
21 the influx of calcium into the bone cells, plus influx of Pb into the cells was greatly enhanced
22 (2.7 fold) after CRAC had been induced. These effects of Pb were found to be independent of
23 any inhibitory effect on calcium-ATPase.
24 Miyahara et al. (1995) performed a series of experiments in 45Ca-labeled bone organ
25 culture to determine whether the Pb-induced hypercalcemia was the result of the active process
26 of biological bone resorption or simply physiochemical mineral dissolution. Lead introduced
27 into the culture at concentrations of 50 jiM and above stimulated the release of calcium and
28 hydroxyproline into the medium, however no release was elicited from bones inactivated by
29 freezing and thawing. Pb-stimulated 45Ca release was inhibited by eel calcitonin,
30 bafilomycin AI, and scopadulcic acid B, suggesting the release was secondary to osteoclastic
31 bone resorption. Further evidence to support this conclusion came from experiments examining
May 2006 5-196 DRAFT-DO NOT QUOTE OR CITE
-------
1 the influence of two inhibitors of cyclooxygenase on Pb-induced bone resorption. Lead was
2 found to stimulate prostaglandin E2 release and in cultures, there was a high correlation between
3 prostaglandin E2 released into the media and 45Ca release. In the presence of cyclooxygenase
4 inhibitors (blocking prostaglandin synthesis), Pb-stimulated 45Ca release was inhibited
5 suggesting the mechanism of bone resorption in this instance was via a prostaglandin
6 E2-mediated mechanism.
7 Lead has been demonstrated to directly impair production of osteocalcin by ROS 17/2.8
8 cells by 70% after 24 hours of exposure to 25 micromolar Pb (Long et al., 1990). The resulting
9 decrease in cell proliferation is in agreement with similar studies by Sauk et al., 1992).
10 Interestingly, exposure of dental pulp cells, which also produce osteocalcin, to a similar
11 concentration of Pb reduced osteocalcin production by 55% after 12 hours of exposure
12 (Thaweboon et al., 2002). Vitamin D has been shown to increase osteocalcin production in
13 ROS 17/2.8 cells; however, Pb inhibited the vitamin D-stimulated osteocalcin production
14 in a dose-dependent manner from 0 up to 25 micromolar concentrations, plus was shown to be
15 capable of attenuating basal (non-vitamin D-stimulated) osteocalcin production (Long et al.,
16 1990). Lead (5 to 20 micromolar) inhibition of vitamin D stimulation of osteocalcin in ROS
17 cells was also reported by Guity and co-workers (2002). Later studies suggested that Pb acts by
18 inhibiting vitamin D activation of calcium channels and interferes with regulation of calcium
19 metabolism (Schanne et al., 1992), though apparently this effect is not mediated via PKC (Guity
20 et al., 2002). Angle and co-workers (1990) reported that 24 hours of incubation with vitamin D
21 (10 nM) was capable of evoking a 4 to 5 fold increase in osteocalcin production and a
22 100% increase in cellular alkaline phosphatase activity in ROS cells. Osteocalcin production and
23 cellular DNA contents were increased 100% and 20% respectively by addition of insulin-like
24 growth factor (92.5 ng/mL). Consistent with a toxic effect of Pb on osteoblast function, the
25 addition of 1 to 10 jiM Pb to the system inhibited both basal and stimulated osteocalcin
26 secretion, alkaline phosphatase activity and DNA contents (Angle et al., 1990). Dose- and time-
27 dependent reduction in alkaline phosphatase activity with Pb exposure (2 to 200 micromolar) has
28 also been reported in osteosarcoma cells, along with parallel reductions in steady state levels of
29 alkaline phosphatase mRNA levels (Klein and Wiren, 1993). No effect on cell number or DNA
30 and protein synthesis was seen at these levels of Pb exposure.
May 2006 5-197 DRAFT-DO NOT QUOTE OR CITE
-------
1 Though the exact mechanism of Pb toxicity on osteocalcin was unclear, Pb was known to
2 inhibit some of the functional properties of osteocalcin including inhibition of osteocalcin
3 adsorption to hydroxyapatite. An investigation by Dowd and co-workers (1994) utilized the
4 ability of osteocalcin added to a solution of 43CaCl2 to broaden 43Ca resonance, as a method to
5 examine binding of calcium to osteocalcin and the influence of Pb on calcium binding. It was
6 determined that the dissociation constant of calcium for osteocalcin was 7 micromolar, while the
7 dissociation constant for Pb was determined by competitive displacement to be 2 nM, indicating
8 more than three orders of magnitude tighter binding of Pb than calcium to osteocalcin and the
9 likelihood that even submicromolar levels of free Pb would significantly inactivate osteocalcin.
10 Circular dichroism indicated that upon binding, Pb induces a similar structural change in
11 osteocalcin to that found with calcium binding, but the binding with Pb occurs at 2 orders of
12 magnitude lower than with calcium (Dowd et al., 2001). Similarly, hydroxyapatite binding
13 assays indicated Pb causes an increased absorption to hydroxyapatite that is similar to calcium,
14 but again at 2 to 3 orders of magnitude lower concentration, potentially leading to low bone
15 formation rates and/or density (Dowd et al., 2001).
16 Besides perturbation of calcium metabolism, Pb has been shown to reduce intracellular
17 free magnesium concentrations by 21% in osteosarcoma cells incubated in 10 micromolar Pb for
18 2 hours (Dowd et al., 1990). Under these same conditions, the unidirectional rate of ATP
19 synthesis (i.e. P; to ATP) was reduced by a factor greater than 6 over control cultures.
20 Impairment of both of these processes by Pb could ultimately influence bone growth and
21 development.
22 Lead has also been show to perturb Epidermal Growth Factor's (EGF) control of
23 intracellular calcium metabolism and collagen production in ROS cells (Long and Rosen, 1992).
24 EGF is known to activate protein kinase C (PKC), resulting in increased calcium influx and
25 through this mechanism, decreased collagen synthesis. Incubation of ROS cells with
26 5 micromolar Pb and 50 ng/mL EGF for 20 hours resulted in a 50% increase in total cell calcium
27 versus the calcium increase seen in cells treated with EGF alone, suggesting more than one site
28 of action is involved in calcium messenger perturbation. A similar finding was reported by Long
29 and co-workers (1992) who found that treatment of Pb (25 micromolar) intoxicated
30 osteosarcoma cells with parathyroid hormone (PTH, 400 mg/mL) resulted in a greater increase in
31 cell calcium than with either treatment alone. Supplementary inhibition of collagen synthesis has
May 2006 5-198 DRAFT-DO NOT QUOTE OR CITE
-------
1 also been reported with the addition of 25 micromolar Pb plus 50 ng/mL EOF, suggesting more
2 than one site of action for the effect of Pb on collagen synthesis (Long and Rosen, 1992).
3 Additional study has since suggested that Pb activates PKC in ROS cells and that PKC mediates
4 the rise in intracellular calcium (Schanne et al., 1997). The observation that calphostin C, an
5 inhibitor of PKC, prevented the Pb-induced elevation of intracellular calcium supported this
6 hypothesis, as did the fact that free Pb at concentrations of 10"11 to 10"7 M directly activated PKC
7 in the absence of activating concentrations of calcium. This would suggest Pb is capable of
8 activating PKC at concentrations approximately 3,000 times lower than calcium.
9 Finally, Pb has been shown to be capable of inhibiting secretion of osteonectin, a bone
10 related protein found in areas of active morphogenesis (Sauk et al., 1992). Treatment of
11 ROS 17/2.8 cells with lead (4.5 X 10"6 M to 4.5 10"7 M) demonstrated that intracellular
12 osteonectin levels were actually enhanced; however, the secretion of osteonectin into the media
13 was delayed or inhibited. Protein production of collagen and the endoplasmic reticulum protein,
14 Hsp47, were relatively unaffected by Pb at these concentrations. The intracellular retention of
15 osteonectin coincided with a decrease in levels of osteonectin mRNA, suggesting the processes
16 associated with translation and secretion of osteonectin are sensitive to Pb.
17
18 5.8.5.4 Human Osteosarcoma Cells (HOS TE 85)
19 Evidence exists that Pb is directly osteotoxic to bone cells in culture. Studies examining
20 the sensitivity of human osteosarcoma cells (HOS TE 85) to Pb found proliferation of the cells
21 was inhibited at Pb concentrations of 4 |imol/l, while cytotoxicity occurred at the 20 |imol/l Pb
22 concentration (Angle et al., 1993). In parallel experiments, rat osteosarcoma cells (ROS 17/2.8)
23 were found to be somewhat less sensitive to the effects of Pb with inhibition of proliferation
24 occurring at 6 |imol/l Pb concentration and cytotoxicity at Pb concentrations over 20 |imol/l.
25
26 5.8.5.5 Chick Chondrocytes
27 The effects of Pb on cartilage biology have been examined in isolated avian chondrocytes
28 obtained from 3 to 5 week old chicks (Hicks et al., 1996). Exposure to media containing 0.1 to
29 200 jiM Pb acetate or chloride were found to decrease thymidine incorporation, suppress alkaline
30 phosphatase, and suppress both type II and type X collagen expression at the mRNA and protein
31 levels. Cytotoxicity of the cultures from Pb exposure was dismissed as proteoglycan synthesis
May 2006 5-199 DRAFT-DO NOT QUOTE OR CITE
-------
1 was found to be augmented, suggested Pb selectively inhibits specific aspects of the chondrocyte
2 growth plate. Using the avian chondrocyte model, Zuscik et al. (2002) similarly reported Pb
3 exposure (1 to 30 jiM) causing a dose-dependent inhibition of thymidine incorporation into the
4 growth plate, with a 60% reduction in proliferation at the highest concentration. Addition of
5 TGF-P1 and PTHrP, regulators of growth plate, both separately stimulated thymidine
6 incorporation, an effect that was dose-dependently blunted in the presence of Pb. At the highest
7 Pb concentration (30 |iM), inhibition was significantly less in the chondrocytes treated with
8 Pb + TGF-P1 (24%) and Pb + PTHrP (19%) than for Pb alone (60%), suggesting the interaction
9 of Pb with these growth factors may be independent of its primary action on the chondrocyte
10 cells. Support for a direct action of Pb on these growth regulators is supported by the finding
11 that normal TGF-pl and PTHrP suppression of type X collagen expression is significantly
12 reversed in a dose-dependent fashion in the presence of Pb. This effect evidently was not
13 mediated by BMP-6 (Bone Morphogenic Protein), an inducer of terminal differentiation known
14 to partially reverse the inhibitory effect of PTHrP, because in the presence of Pb, PTHrP
15 significantly suppressed BMP expression, while combined exposure to Pb and TGF-pl increased
16 BMP expression approximately 3-fold. Further experiments performed on chick sternal
17 chondrocyte cultures, utilized PTHrP responsive (AP-1) and non-responsive (NF-KB) reporter
18 constructs to examine potential effects of Pb on signaling. While having no effect on the basal
19 activity of the AP-1 reporter, Pb dose-dependently enhanced PTHrP induction of the responsive
20 AP-1 reporter. Lead dose-dependently inhibited the basal activity of the non-PTHrP responsive,
21 NF-KB reporter. Taken together, these studies demonstrate that Pb has an inhibitory effect on the
22 process of endochondral bone formation and that the effects of Pb are likely from its modulation
23 of growth factors and second messengers involved in cell signaling responses.
24
25 5.8.6 Bone Lead as a Potential Source of Toxicity in Altered
26 Metabolic Conditions
27 Lead is avidly taken up by bone and incorporated into bone matrix, where a substantial
28 amount can remain over the lifetime of an organism. The uptake and incorporation of Pb into
29 bone during acute exogenous exposures may be of short term benefit by limiting the exposure of
30 other, more sensitive tissues; however, this does not eliminate Pb from the system. Subsequent
31 release of Pb from this endogenous storage can produce a lifetime of steady, low level Pb
May 2006 5-200 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposure during periods of normal bone remodeling, while elevated Pb release during times of
2 increased bone metabolism and turnover (i.e., pregnancy, lactation, menopause, and
3 osteoporosis) can elevate blood levels of Pb significantly, potentially to toxic concentrations.
4 This is especially relevant when there is concurrent exogenous exposure to Pb, as current blood
5 Pb levels are a composite of current and past Pb exposure. Of greater concern is the mobilization
6 of Pb during pregnancy and subsequent transfer to the developing brain of the fetus across the
7 poorly developed blood:brain barrier. Maternal Pb also appears in breast milk, providing further
8 exposure of the infant to Pb during lactation. Currently, the majority of animal studies
9 examining mobilization of Pb from bone stores have focused principally on elevation of Pb
10 levels or transfer of Pb, rather than reporting toxic effects associated with these exposures. Note
11 that in most instances the mobilization and elimination of Pb is much faster in laboratory animals
12 than in humans. For example, as discussed in Section 5.8.3, Hac and Kruchniak (1996) reported
13 approximately 64% of Pb given over a 12 week period remained in the bones of rats 64 days post
14 exposure. Therefore, the caveats of experiments performed in small animals, especially when
15 examining mobilization of Pb stores, must be taken into consideration.
16
17 5.8.6.1 Pregnancy and Lactation
18 Pregnancy, and to a much greater extent, lactation, place significant calcium demands on
19 the mother as she provides all the necessary calcium requirements of the developing fetus/infant.
20 During these times of metabolic stress, increased demineralization of maternal bone occurs to
21 supplement demand, unfortunately accompanied by the concurrent mobilization and release of
22 Pb stored in the maternal skeleton from past exposure. Studies in several animal models have
23 shown that maternal bone Pb can be mobilized during pregnancy and lactation, ultimately being
24 transferred to the fetus during gestation and breast feeding. Keller and Doherty (1980)
25 administered radiolabeled Pb drinking water (200|ig/mL) to female mice for 105 days prior to
26 mating or 105 days prior to mating and during periods of gestation and lactation (total 160 days
27 of exposure). The results suggested very little Pb was transferred from mother to fetus during
28 gestation, however, Pb transferred in milk and retained by the pups accounted for 3% of the
29 maternal body burden of those mice exposed to Pb prior to mating only. No blood Pb levels
30 were reported for any of the animals. The amount of Pb retained in these pups exceeded that
31 retained in the mothers, suggesting lactation effectively transfers Pb burden from mother to
May 2006 5-201 DRAFT-DO NOT QUOTE OR CITE
-------
1 suckling offspring. Transfer of Pb from mothers was significantly higher when Pb was supplied
2 continuously in drinking water, rather than terminated prior to mating. Considerably higher
3 lactational transfer of Pb from rat dams compared to placental transfer has also been reported
4 (Palminger Hallen et al., 1996). Continuous exposure of rat dams to Pb until day 15 of lactation
5 resulted in milk Pb levels 2.5 times higher than in whole blood, while termination of maternal Pb
6 exposure at parturition yielded equivalent blood and milk levels of Pb, principally from Pb
7 mobilized from maternal bone. Blood Pb concentrations at day 15 of lactation were
8 1.4 ± 0.4 |ig/dL (control), 32.0 ± 5.5 |ig/dL (lead-exposed until parturition), and
9 126.0 ± 17.1 |ig/dL (lead-exposed until day 15 of lactation).
10 Using rats chronically exposed to Pb in drinking water, Maidonado-Vega et al. (1996)
11 studied intestinal absorption of Pb, its mobilization, and redistribution during lactation. In rats
12 exposed to Pb 144 days prior to lactation, the process of lactation itself elevated blood Pb and
13 decreased bone Pb, indicating mobilization of Pb from bone as there was no external source of
14 Pb during the lactation process. Rats exposed to Pb for 158 days (144 days prior to lactation and
15 14 days during lactation) also experienced elevated BLLs and loss of Pb from bone. Lead
16 exposure only during the 14 days of lactation was found to significantly increase intestinal
17 absorption and deposition (17 fold increase) of Pb into bone compared to non-pregnant rats,
18 suggesting enhanced absorption of Pb takes place during lactation. As in other previous studies,
19 the highest concentration of Pb in bone was found in non-pregnant non-lactating control animals,
20 with significantly decreased bone Pb in lactating rats secondary to bone mobilization and transfer
21 via milk to suckling offspring. Blood Pb levels at day 14 of lactation or equivalent ranged from
22 24.7 to 31.2 |ig/dL. Follow-up studies examining the influence of dietary calcium found when
23 calcium was altered from the normal 1% to 0.05%, bone calcium concentration decreased by
24 15% and bone Pb concentration decreased by 30% during the first 14 days of lactation
25 (Maldonado-Vega et al., 2002). In non-lactating rats on the 0.05% calcium diet, there were also
26 decreases in bone calcium, but neither incremental bone resorption nor Pb efflux from bone,
27 suggesting the efflux from bone during lactation was related to bone resorption. Of interest,
28 enhancement of calcium (2.5%) in the diet of lactating rats increased calcium concentration in
29 bone by 21%, but did not decrease bone resorption, resulting in a 28% decrease in bone Pb
30 concentration and concomitant rise in systemic toxicity. Blood Pb levels were similar to those
May 2006 5-202 DRAFT-DO NOT QUOTE OR CITE
-------
1 reported in the prior study above. In both studies, the authors concluded that Pb stored in bone
2 should be considered a major source of self-intoxication and of exposure to suckling offspring.
3 In one of few studies showing a toxic effect, Han et al. (2000) demonstrated adverse
4 effects in rat offspring born to females whose exposure to Pb ended well before pregnancy. Five
5 week-old-female rats had been given Pb-acetate in drinking water (250 mg/mL) for five weeks,
6 followed by a one month period without Pb exposure before mating. To test the influence of
7 dietary calcium on Pb absorption and accumulation, some pregnant rats were fed diets deficient
8 in calcium (0.1%) while others were maintained on a normal calcium (0.5%) diet. As expected,
9 all Pb-exposed dams and pups had elevated blood Pb levels; however, pups born to dams fed the
10 diet deficient in calcium during pregnancy had higher blood (up to 24 |ig/dL) and organ Pb
11 concentrations compared to pups from dams fed the normal diet. Significantly, pups born to
12 Pb-exposed dams had lower mean birth weights and birth lengths than pups born to non-
13 Pb-exposed control dams (p < 0.0001), even after confounders such as litter size, pup sex, and
14 dam weight gain were taken into account. The authors concluded that while increases in dietary
15 calcium during pregnancy are capable of reducing Pb accumulation in the fetus, they cannot
16 prevent the decreases in birth weight and length associated with pre-maternal Pb exposure and
17 subsequent mobilization. This has relevance in human pregnancy, as many women experience
18 exposure to Pb during their lifetimes (especially during childhood) and mobilization of the Pb
19 from bone stores during pregnancy could present toxic complications.
20 Within the last decade, an invaluable method to explore the kinetics of Pb transfer from
21 bone to blood has been developed and evaluated (Inskip et al., 1996; O'Flaherty et al., 1998).
22 The method utilizes recent administration of sequential doses of Pb mixes enriched in stable
23 isotopes ( 204Pb, 206Pb, and 207Pb) to female cynomolgus monkeys (Macaca fascicularis) that
24 have been chronically (1,300 to 1,500 jig Pb/kg body weight per day for ten years or greater)
25 administered a common Pb isotope mix. The stable isotope mixes serve as a marker of recent,
26 exogenous Pb exposure, while the chronically administered common Pb serves as a marker of
27 endogenous (principally bone) Pb. From thermal ionization mass spectrometry analysis of the
28 Pb isotopic ratios of blood and bone biopsies collected at each isotope change, and using end-
29 member unmixing equations, it was determined that administration of the first isotope label
30 allows measurement of the contribution of historic bone stores to blood Pb. Exposure to
31 subsequent isotopic labels allowed measurements of the contribution from historic bone Pb
May 2006 5-203 DRAFT-DO NOT QUOTE OR CITE
-------
1 stores and the recently administered enriched isotopes that incorporated into bone (Inskip et al.,
2 1996). In general the contribution from the historic bone Pb (common Pb) to blood lead level
3 was constant (-20%), accentuated with spikes in total blood Pb due to the current administration
4 of the stable isotopes. Blood Pb ranged from 31.2 to 62.3 jig/100 g in the animals. After
5 cessation of each sequential administration, the concentration of the signature dose rapidly
6 decreased. Initial attempts to apply a single-bone physiologically based model of Pb kinetics
7 were unsuccessful until adequate explanation of these rapid drops in stable isotopes in the blood
8 were incorporated (O'Flaherty et al., 1998). Once revisions were added to account for rapid
9 turnover of the trabecular bone compartment and slower turnover rates of cortical bone
10 compartment, an acceptable model evolved. From this model it was reported that historic bone
11 Pb from 11 years of continuous exposure contributes approximately 17% of the blood Pb
12 concentration at Pb concentration over 50 |ig/dL, reinforcing the concept that the length of Pb
13 exposure and the rates of past and current Pb exposures help determine the fractional
14 contribution of bone Pb to total blood Pb levels (O'Flaherty et al., 1998). The turnover rate for
15 cortical (-88% of total bone by volume) bone in the adult cynomolgus monkey was estimated by
16 the model to be -4.5% per year, while the turnover rate for trabecular bone was estimated to be
17 33% per year.
18 Using the method of sequential stable isotope administration, Franklin et al. (1997)
19 examined flux of Pb from maternal bone during pregnancy of 5 female cynomolgus monkeys
20 who had been previously exposed to common Pb (approximately 1,100 tol,300 jig Pb/kg body
21 weight) for about 14 years. In general, lead levels in maternal blood (as high as 65 jig/100 g)
22 attributable to Pb from mobilized bone were reported to drop 29 to 56% below prepregnancy
23 baseline levels during the first trimester of pregnancy. This was ascribed to the known increase
24 in maternal fluid volume, specific organ enlargement (e.g., mammary glands, uterus, placenta),
25 and increased metabolic activity that occurs during pregnancy. During the second and third
26 trimesters, when there is a rapid growth in the fetal skeleton and compensatory demand for
27 calcium from the maternal blood, the Pb levels increased up to 44% over pre-pregnancy levels.
28 With the exception of one monkey, blood Pb concentrations in the fetus corresponded to those
29 found in the mothers, both in total Pb concentration and proportion of Pb attributable to each
30 isotopic signature dose (common = 22.1% vs. 23.7%, 204Pb = 6.9% vs. 7.4%, and 206Pb = 71.0%
31 vs. 68.9%, respectively). From 7 to 25% of the Pb found in fetal bone originated from maternal
May 2006 5-204 DRAFT-DO NOT QUOTE OR CITE
-------
1 bone, with the balance derived from oral dosing of the mothers with isotope during pregnancy.
2 Of interest, in offspring from a low Pb exposure control monkey (blood Pb <5 jig/100 g) -39%
3 of Pb found in fetal bone was of maternal origin, suggesting enhanced transfer and retention of
4 Pb under low Pb conditions.
5 Clearly, the results of these studies show that Pb stored in bone is mobilized during
6 pregnancy and lactation, exposing both mother and fetus/nursing infant to blood/milk Pb levels
7 of potential toxicity. Of equal concern, a significant proportion of Pb transferred from the
8 mother is incorporated into the developing skeletal system of the offspring, where it can serve as
9 a continuing source of toxic exposure. The above study by Franklin et al. (1997) illustrates the
10 utility of sequentially administered stable isotopes in pregnancy; however, its use may also be
11 applicable in studies of lactation, menopause, osteoporosis, and other disease states where
12 mobilization of bone and release of Pb stores occurs. Furthermore, given that isotopic ratios of
13 common Pbs vary by location and source of exposure, when humans migrate from one area and
14 source of exposure to another, it is possible to document changes in mobilized Pb, especially
15 during times of metabolic stress.
16
17 5.8.6.2 Age/Osteoporosis
18 The age of an animal at the time of exposure to Pb has been shown to influence the uptake
19 and retention of Pb by bone. In experiments to determine the influence of age on this process,
20 Han et al. (1997) exposed rats for five weeks to 250 mg/L Pb-acetate in drinking water beginning
21 at 5 weeks of age (young child), 10 weeks of age (mid-adolescence), or 15 weeks of age (young
22 adult), followed by a 4 week period of without Pb exposure. An additional group of rats were
23 exposed to Pb beginning at 5 weeks, but examined following an 8 or 20 week period after
24 cessation of Pb. Significantly lower blood and bone Pb concentrations were associated with
25 greater age at the start of Pb exposure and increased interval since the end of exposure.
26 No blood Pb levels were greater than approximately 30 |ig/dL. However, young rats beginning
27 exposure to Pb at 5 weeks and examined 20 weeks after cessation of exposure, still had bone Pb
28 concentrations higher than those found in older rats only 4 weeks after cessation of exposure.
29 This demonstrated that exposure to Pb at a young age leads to significant skeletal Pb
30 accumulation and retention, despite the high rate of bone remodeling that occurs during growth
31 and development at that time.
May 2006 5-205 DRAFT-DO NOT QUOTE OR CITE
-------
1 At the opposite end of the spectrum, Cory-Slechta et al. (1989) studied differences in
2 tissue distribution of Pb in adult and old rats. Adult (8 months old) and old (16 months old) rats
3 were exposed to 50 ppm Pb-acetate in drinking water for 11 months, at which time the
4 experiment was completed. Bone (femur) Pb levels in older rats were found to be less than those
5 in younger rats; however, blood lead levels were higher in the older rats. All levels of Pb in the
6 blood were reported to be 31 |ig/dL or less. Of interest, brain Pb concentrations in the older rats
7 exposed to Pb were significantly higher, and brain weights were significantly less than the brain
8 Pb concentration and weights of unexposed older control rats or adult rats exposed to Pb,
9 suggesting a potential detrimental effect. The authors suggested that a possibility for the
10 observed differences in tissue concentrations of Pb was due to changes in the capacity of bone to
11 store Pb with advanced age. In a subsequent study, Cory-Slechta (1990b) examined kinetic and
12 biochemical responses of young (21 day old), adult (8 months old), and old (16 months old) rats
13 exposed to Pb at 0, 2, or 10 mg Pb acetate/kg/day over a 9.5 month experimental period (blood
14 Pb as high as 45 jig/dL). Results suggested that older rats may have increased vulnerability to
15 Pb due to increased exposure of tissues to Pb and greater sensitivity of the tissues to the effects
16 of Pb. As in the previous study (Cory-Slechta et al., 1989), lower bone levels of Pb were present
17 in older rats with concomitant elevated levels of Pb in brain and other tissues, supporting the
18 hypothesis that exposure to Pb over a lifetime may contribute to deterioration of health in old
19 age, potentially during times of heightened bone remodeling such as occurs during osteoporosis.
20 In studies of bone Pb metabolism in a geriatric, female nonhuman primates exposed to Pb
21 approximately 10 years previously (historic blood Pb concentration of 44 to 89 |ig/dL), McNeill
22 et al. (1997) reported no significant changes in bone Pb level over a 10 month observation period
23 as measured by 109Cd K X-ray fluorescence. The mean half-life of Pb in bone of these animals
24 was found to be 3.0 ± 1.0 years, consistent with data found in humans, while the endogenous
25 exposure level due to mobilized Pb was 0.09 ± 0.02 |ig/dL blood. Results examining Pb
26 accumulation in the bones of aging male mice suggest low levels of bone Pb contributing to the
27 osteopenia observed normally in C57BL/6J mice (Massie and Aiello, 1992). The mice were
28 maintained on regular diet (0.258 ppm Pb) and water (5.45 ppb Pb) from 76 to 958 days of age.
29 While the Pb content of femurs increased by 83%, no significant relationship was found between
30 Pb and bone density, bone collagen, or loss of calcium from bone. Blood Pb levels were not
31 reported.
May 2006 5-206 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.8.6.3 Weight Loss
2 The relationship between body mass and bone mass is highly correlated and during times
3 of loss of body weight, such as dietary restriction, a concomitant loss of bone mass also occurs.
4 It is therefore possible that Pb stored in bone from prior exposures could be released into the
5 system as skeletal bone is mobilized and result in Pb toxicity. To examine the influence of
6 weight loss on release of stored Pb, Han et al. (1996) first exposed rats to Pb in drinking water
7 (250 mg/1 of Pb as acetate) for 5 weeks, followed by a 4 week washout period without Pb to
8 allow primarily accumulation in the skeleton. Rats were then randomly assigned to a weight
9 maintenance group, a moderate weight loss group (70% of maintenance diet), or a substantial
10 weight loss group (40% of maintenance diet) for a four week period. At the end of this
11 experimental period the blood (24 to 28 |ig/dL) and bone levels of Pb did not differ between
12 groups, however, the amount and concentration of Pb in the liver increased significantly. A
13 follow up study in rats previous exposed to Pb for two weeks was undertaken to determine the
14 effect of weight loss and exercise on the distribution of Pb (Han et al., 1999). They found weight
15 loss secondary to dietary restriction to be the critical factor elevating organ Pb levels and,
16 contrary to their first study, elevated blood levels of Pb (as high as 42 |ig/dL). No significant
17 difference in organ or blood Pb concentrations was reported between the exercise vs. no exercise
18 groups. These studies suggest Pb toxicity could occur in those previously exposed to Pb during
19 times of dietary restriction.
20
21 Summary
22 • Pb substitutes for calcium and is readily taken up and stored in the bone of experimental
23 animals, potentially allowing bone cell function to be compromised both directly and
24 indirectly by exposure.
25 • Relatively short term exposure of mature animals to Pb does not result in significant
26 growth suppression, however, chronic Pb exposure to exposure during times of inadequate
27 nutrition have been shown to adversely influence bone growth, including decreased bone
28 density, decreased trabecular bone, and growth plates.
29 • Exposure of developing animals to Pb during gestation and the immediate postnatal period
30 has clearly been shown to significantly depress early bone growth in a dose-dependent
31 fashion, though this effect is not manifest below a certain threshold.
32 • Systemically, Pb has been shown to disrupt mineralization of bone during growth, to alter
33 calcium binding proteins, and to increase calcium and phosphorus concentration in the
May 2006 5-207 DRAFT-DO NOT QUOTE OR CITE
-------
1 blood stream, in addition to potentially altering bone cell differentiation and function by
2 altering plasma levels of growth hormone and calciotropic hormones such as vitamin D3
3 [1,25-(OH2)D3].
4 • Bone cell culture studies have indicated that Pb is primarily taken up by osteoclasts and
5 likely perturbs intracellular calcium homeostasis secondary to osteoclastic bone resorption.
6 • Exposure of bone cell cultures to Pb has been shown to impair vitamin D-stimulated
7 production of osteocalcin, inhibit secretion of bone-related proteins such as osteonectin
8 and collagen, and suppress bone cell proliferation, potentially by interference with such
9 factors as Growth Hormone (GH), Epidermal Growth Factor (EGF), Transforming Growth
10 Factor-Beta I(TGF-PI), and Parathyroid Hormone-related Protein (PTHrP).
11 • Periods of extensive bone remodeling, such as occur during weight loss, advanced age,
12 altered metabolic state, and pregnancy and lactation are all associated with mobilization of
13 Pb stores from bone of animals.
14 • Several animal studies have suggested Pb stored in bone can serve as a continuous,
15 endogenous source of exposure for an individual or can be transferred from mother to
16 offspring during pregnancy and/or lactation, with potentially toxic consequences.
17 • During pregnancy, transfer of Pb from mother to offspring has been documented, however,
18 available evidence suggests a more significant transfer from mother to offspring occurs
19 during lactation when the concentration of Pb in mother's milk can be several times higher
20 than corresponding blood levels.
21 • Despite the extensive remodeling of bone that occurs during growth and development of
22 young animals, a significant amount of Pb can be accumulated and retained during times
23 of exposure.
24
25 5.8.7 Teeth - Introduction
26 There was little information in the prior 1986 Pb AQCD relating lead exposure to adverse
27 outcomes in the teeth of animals. At that time, the incorporation of Pb into teeth was recognized,
28 as was the fact that tooth Pb increased with age, proportional to the rate of exposure and roughly
29 proportional to the blood Pb concentration.
30 Teeth consist of a hard outer layer of enamel, supported by an underlying layer of dentin,
31 which itself is supported by a connective tissue known as the dental pulp. Enamel is the hardest
32 substance in the body and the most highly mineralized, consisting of-96% mineral (calcium
33 hydroxyapatite substituted with carbonate ions) and 4% other organic materials, while dentin is
34 only -70% mineral. The formation of enamel (amelogenesis) occurs as a two stage process of
35 organic matrix production with -30% mineralization, followed by removal of water and proteins
May 2006 5-208 DRAFT-DO NOT QUOTE OR CITE
-------
1 from the matrix with concurrent further mineralization. As in bone, Pb ions are apparently
2 capable of substituting for calcium ions in the mineralizing tooth, becoming essentially trapped.
3 However, unlike bone, the tooth, with subtle exceptions, does not undergo a remodeling process.
4 Dentin formation (dentinogenesis) can be likened to endochondral bone formation, in that an
5 unmineralized matrix (predentin, rather than cartilage) is laid down first, followed by
6 mineralization to mature dentin. The cells responsible for amelogenesis and dentinogenesis,
7 called ameloblasts and odontoblasts respectively, are similar to osteoblasts in that they respond
8 to various signaling factors, secrete matrix proteins, and create an environment favorable to
9 deposition of minerals. After enamel formation on a specific tooth is completed, ameloblasts are
10 lost and no additional enamel is laid down with the exception of certain teeth in rodents. These
11 teeth, typically incisors on rats, mice, and most other rodents, continuously erupt to offset the
12 attrition that occurs with daily use. Therefore, the process of amelogenesis is ongoing, albeit
13 confined to a localized area, throughout the life of the animals. For this reason, rodents have
14 been utilized extensively to examine the processes of amelogenesis and the influence of various
15 toxic agents, such as Pb, on tooth development. Ameloblasts are especially sensitive to toxins
16 and altered metabolic conditions and respond to such insults with disruption of enamel
17 formation. When disruption occurs, defects in the enamel can occur, typically as a band of
18 malformed or altered enamel. As described below, exposure of animals to various
19 concentrations of Pb during tooth development is not only capable of creating distinctive
20 marking of enamel ("Pb lines"), but may influence the resistance of the enamel to dental decay.
21 Within the dental pulp, a layer of odontoblasts continues to reside against the inner layer of the
22 primary dentin for the life of the tooth. During this time, the odontoblasts are systematically
23 slowly putting down thin layers of secondary dentin, slowly decreasing the size of the pulp
24 chamber with age. Lead present during this process has been shown to be readily taken up by
25 this dentin layer, providing a potential marker of historic Pb exposure. Though the enamel is a
26 non-living substance, it is not entirely inert. The external surface of enamel is more or less in a
27 continuous state of flux or turnover as it chemically demineralizes from acids consumed or
28 produced in the mouth by bacteria, followed by remineralization of demineralized enamel when
29 contact with saliva supersaturated with calcium and phosphate ions occurs. Lead present during
30 this process can easily be released from enamel and/or incorporated initially or back into it
31 depending on the circumstances.
May 2006 5-209 DRAFT-DO NOT QUOTE OR CITE
-------
1 In summary, Pb has the potential to disrupt the various processes associated with
2 formation of teeth, plus incorporate itself into all mineralized tooth tissues during formation.
3 Posteruptively, Pb can become incorporated into the secondary dentin, and can be taken up or
4 released from the outer surface layer of enamel during times of remineralization or
5 demineralization. As described below, exposure of animals to Pb has been associated with
6 adverse dental outcomes.
7
8 5.8.8 Uptake of Lead by Teeth
9 As seen with bone, uptake of Pb into the teeth of animals has been demonstrated in a
10 number of studies and by multiple routes of administration. Twenty four hours after a single
11 intraperitoneal injection of radioactive Pb-203 (203Pb, 1 |ig/kg) to young (15 day suckling rats)
12 and old (120 day) female rats, 0.7% of the injected dose was present in the four incisor teeth of
13 the younger animals and 0.6% was present in the same teeth of the older animals (Momcilovic
14 and Kostial, 1974). These percentages jumped to 1.43% and 0.88%, respectively, 192 hours
15 after the injection, suggesting incorporation and retention of Pb by teeth is greater in younger
16 animals than in adults, as found in bone. Lead has also been shown to be incorporated into
17 incisors of rats exposed to airborne Pb. Grobler and co-workers (1991) exposed 6 week old rats
18 to either "Clean Air" (0.05 jig Pb/m3) or air containing 77 jig Pb/m3 and found significant
19 differences in the amount of Pb incorporated into the incisors of the animals. After 70 days, a
20 mean of only 0.8 jig Pb/g of incisor dry mass was found in incisors from control animals, while
21 11.0 jig Pb/g was present in incisors from the 77 jig Pb/m3 group. Exposure to air containing
22 249 jig Pb/m3 for 28 days or to 1,546 jig Pb/m3 for 50 days resulted in mean values of 13.8 and
23 153 jig Pb/g incisor dry weight of Pb incorporation, respectively, highlighting the fact that dose
24 and length of exposure are determinates of amount of Pb contained in the teeth of these animals.
25 Blood Pb levels were 2.6 |ig/dL (control), 11.5 |ig/dL (low exposure), 24.1 |ig/dL (middle
26 exposure), and 61.2 |ig/dL (high exposure). Lead has also been shown to be taken up into the
27 teeth of weanling rats whose mothers were exposed to Pb in drinking water. The offspring of
28 pregnant rats exposed during gestation and lactation until 21 days post partum to water
29 containing 0, 3, or 10 ppm Pb showed dose-dependent, significant increases in the Pb content of
30 incisors, first molars, and second molars (Grobler et al., 1985). No blood Pb levels were
31 reported. Taken together, these studies confirm the uptake of Pb into teeth as delivered by
May 2006 5-210 DRAFT-DO NOT QUOTE OR CITE
-------
1 various means and suggest that maternal exposure can result in uptake in offspring, during
2 gestation and/or lactation.
3
4 5.8.9 Effects of Lead on Enamel and Dentine Formation
5 Early microscopic studies by Eisenmann and Yaeger (1969) confirmed alterations in rat
6 incisor enamel formation 7 days after a single SC dose of Pb (0.15 or 1.5 mM/lOOg animal
7 weight); however, no effect was seen at the 0.075 mM/lOOg dose. Lead was found to have
8 inhibited mineralization of both enamel and dentin, but only to a "mild to moderate" extent with
9 the mineralization of dentin more affected. It was speculated at the time that Pb could affect the
10 production of normal, mineralizable organic matrix; affect enzymes specific to enamel or dentin
11 formation; affect crystal structure and/or growth; or affect a combination of these factors. In
12 studies of dentinogenesis, incubation of fixed rat molar germs with Pb-pyrophosphate has shown
13 localization of Pb to the mineralization front of dentin (i.e., the area of recently formed dentin),
14 to the stratum intermedium, and to subodontoblastic cells, suggesting Pb may react with mineral
15 components located in the mineralization zone or have a high affinity for these incompletely
16 mineralized areas (Larsson and Helander, 1974). Localization of Pb was also seen at the area of
17 the dentino-enamel junction. Similar examination of first molar germs from 3-day-old rats
18 showed that Pb also localized to the periphery of dentinal globules (Larsson, 1974). A single,
19 high-dose injection of Pb-acetate (30 mg/kg body weight) produces an immediate (within 6 h)
20 response in the growing dentin of the rat incisor, leading to the formation of a so-called "Pb line"
21 (Appleton, 1991). A transient rise in serum calcium and phosphorus accompanied the injection,
22 leading to speculation that lead may have been replacing these minerals in the apatite structure.
23 However, backscattered electron imaging of the Pb line showed it to be composed of continuous
24 hypomineralized interglobular dentin with some incomplete fusion of calcospherites resulting in
25 uneven mineralization, but no localized concentration of Pb was detectable. This is consistent
26 with Featherstone and co-workers (1981) who reported that Pb incorporation during apatite
27 synthesis was widely dispersed, rather than concentrated in areas of calcium deficiency. Once
28 synthesis is complete, however, Pb is capable of entering calcium deficient areas in enamel,
29 substituting for calcium (Featherstone et al., 1979). This is essentially the process that occurs
30 during demineralization/remineralization of enamel. Appleton (1991, 1992) suggested that Pb
31 has a direct effect on odontoblasts, creating a local disturbance of calcium metabolism, a process
May 2006 5-211 DRAFT-DO NOT QUOTE OR CITE
-------
1 similar to that described in bone (Pounds et al., 1991). Interestingly, no ultrastructural changes
2 in ameloblasts from rat pups whose mothers had been drinking water containing Pb was
3 observed.
4 During the normal process of amelogenesis, water and proteins contained within the
5 organic matrix are lost, leaving densely mineralized enamel. The removal of enamel proteins
6 during this phase is facilitated by enamel proteinases, which are believed to degrade the proteins
7 into smaller units capable of diffusing from the matrix. Using crude extracts from scrapings of
8 rat incisor teeth, Gerlach and co-workers (2000a) demonstrated that Pb inhibited these
9 proteinases in vitro at micromolar concentrations. In rats given drinking water containing Pb at
10 either 0, 34, or 170 mg/L as Pb-acetate for 70 days, increased amounts of proteins were found in
11 enamel matrix from animals exposed to Pb (Gerlach et al., 2002). Moreover, enamel
12 microhardness analysis of upper incisors revealed a significant decrease in microhardness in
13 regions of enamel maturation, but not in areas of fully mature enamel, suggesting Pb exposure
14 mediates a delay in enamel mineralization. In adult rats with incisors trimmed to remove
15 occlusal (biting) contact, a single IP dose of Pb-acetate (40 mg/kg) significantly delayed the
16 continuous eruption of the incisor at all time points between 8 and 28 days after dosing,
17 compared with controls (Gerlach et al., 2000b). Blood Pb levels were approximately 48 |ig/dL
18 immediately after injection and 16 |ig/dL 30d after injection. It is of interest that delayed
19 eruption of teeth in children living in areas of heavy metal contamination (Pb and zinc) has been
20 reported previously (Curzon and Bibby, 1970).
21
22 5.8.10 Effects of Lead on Dental Pulp Cells
23 Hampered by a general lack of cell cultures specifically for teeth, there remains a paucity
24 of information regarding both the cultures themselves and the effect of Pb upon such cultures. In
25 a single in vitro study using a human dental pulp cell culture obtained from teeth extracted for
26 orthodontic purposes, Thaweboon and co-workers (2002) examined the effects of three
27 concentrations (4.5 x 10"5 M, 4.5 x 10"6 M, 4.5 x 10"7 M) of Pb-glutamate on cell proliferation,
28 protein production, and osteocalcin secretion. Under serum free conditions (DMEM only) all
29 concentrations of Pb significantly increased cell proliferation on day 1, day 3 and day 5 of
30 exposure, as measured indirectly by mitochondrial dehydrogenase enzyme assay. In the
31 presence of 2% fetal bovine serum only, the higher concentration of Pb significantly increased
May 2006 5-212 DRAFT-DO NOT QUOTE OR CITE
-------
1 protein production, suggesting an influence of serum constituents on cell growth or binding of
2 free Pb in the medium. Similar results were reported when rat osteosarcoma cells (ROS 17/2.8)
3 were exposed to identical concentrations of Pb over 2-, 4-, and 6-day time points (Sauk et al.,
4 1992). Concentrations of Pb less than 4.5 x 10"5 M concentration did not affect osteosarcoma
5 cell proliferation in the presence of serum, but in the absence of serum 4.5 x 10"7 M Pb increased
6 cell proliferation at day 4, while at day 6, 4.5 x 10"6 M Pb inhibited proliferation. Further testing
7 of human dental pulp cells in serum-free conditions showed that Pb exposure caused dose-
8 dependent decreases in intracellular protein and procollagen type I production over the 5-day
9 period experimental period (Thaweboon et al., 2002). Short-term exposure of the cells to Pb
10 significantly decreased osteocalcin production in a dose-dependent manner at 8- and 12-h
11 exposure time points. These results suggest that Pb is capable of exerting multiple toxic effects
12 on cells derived from human dental pulp.
13
14 5.8.11 Adverse Effects of Lead on Teeth—Dental Caries
15 In a recent review, Bowen (2001) highlighted 12 epidemiological studies that examined
16 the association between Pb exposure and dental caries (decay), reporting that 8 studies supported
17 the concept that Pb is a caries-promoting element. Unfortunately, the source and actual exposure
18 to Pb and measurement of prevalence of caries varied greatly, providing less than completely
19 satisfactory evidence in the opinion of the author. There is also a paucity of well-controlled
20 animal studies examining this issue.
21 In an early study examining the effect of drinking solutions containing various metallic
22 ions on dental caries in hamsters, Wisotzky and Hein (1958) reported post-eruptive ingestion of
23 drinking water containing 0.5 mEq of Pb significantly increased caries scores in molar teeth of
24 males after 84 days, but, perplexingly, not in females after 98 days of exposure. It should be
25 noted that in animal studies such as these it is routine to maintain the animals on cariogenic or
26 caries-promoting diets high in fermentable sugars. Clear evidence supporting Pb's role in
27 enhancing susceptibility to dental caries was reported by Watson and co-workers in 1997.
28 In their study, female rats were exposed to Pb in drinking water (34 ppm as Pb-acetate) as young
29 adults, during pregnancy, and during lactation. Lead exposure of the subsequent offspring from
30 the dams was, therefore, from transfer of endogenous Pb from dam to pup during gestation and
31 lactation, with no further exposure after weaning. This pre- and perinatal exposure to Pb resulted
May 2006 5-213 DRAFT-DO NOT QUOTE OR CITE
-------
1 in a significant, almost 40%, increase in the prevalence of dental caries over control animals.
2 The study was significant for other reasons, as it mimicked the conditions found in many inner
3 cities where young females are exposed to Pb in their environment and later transfer this Pb to
4 their own fetuses during the extensive bone remodeling that occurs during pregnancy and
5 lactation. The mean blood Pb level in the dams upon weaning was 48 |ig/dL, which is not unlike
6 upper levels reported in humans.
7 The mechanisms by which Pb enhances susceptibility to caries remain uncertain, though
8 clearly altered mineralization and/or incorporation of Pb into enamel as described above could
9 enhance its solubility in acid. Lead also appears in the saliva of rats at about 5% of the whole
10 blood level and at about 61% of the plasma filtrate Pb level (Mobarak and P'an, 1984), providing
11 an avenue for post-eruptive interaction with the exposed enamel in the oral cavity. Notably,
12 decreased salivary flow has been reported in rats exposed to Pb, and decreased salivary function
13 is known to increase caries risk. Stimulated parotid function was decreased by nearly 30% in the
14 Pb-exposed offspring in the study by Watson and co-workers (1997), an effect that could have
15 been mediated by the salivary gland requirement of intact parasympathetic and sympathetic
16 nervous systems for normal development (Schneyer and Hall, 1970) and Pb's known adverse
17 effect on neurotransmitters (Bressler and Goldstein, 1991). Acute infusion of 4 jig of Pb per min
18 has been reported to significantly reduce pilocarpine-stimulated salivary secretion in rats over a
19 50-min period (Craan et al., 1984), while 24-day administration of 0.05% Pb-acetate
20 significantly reduced the concentration of protein and calcium in pilocarpine-stimulated rat
21 submandibular saliva (Abdollahi et al., 1997). Of potential interest, postnatal exposure of rats to
22 Pb (10 or 25 ppm in drinking water) and a caries-enhancing diet containing fluoride (sucrose
23 containing 15 ppm fluoride) was not associated with an increased risk of dental caries,
24 suggesting that Pb does not interfere with the protective effect of fluoride (Tabchoury et al.,
25 1999). Clearly though, the effect of Pb exposure on salivary gland function and the mechanism
26 by which Pb exposure enhances caries risk needs to be further explored.
27 5.8.12 Lead from Teeth as a Potential Source of Toxicity
28 Although no studies currently document the contribution of Pb incorporated into teeth as a
29 source of endogenous Pb exposure, the potential exists during the process of exfoliation of the
30 primary dentition. As described above (Section 5.8.9) Pb is avidly incorporated into the
May 2006 5-214 DRAFT-DO NOT QUOTE OR CITE
-------
1 developing dentin and enamel components of teeth. Like bone, the uptake and incorporation of
2 Pb into teeth during acute exogenous exposures may be of short-term benefit by limiting the
3 exposure of other, more sensitive tissues, but, unlike bone, teeth do not undergo a gross
4 remodeling process (the continuous, superficial demineralization/remineralization of the exposed
5 tooth surfaces, principally enamel, are assumed here to be insignificant). However, during the
6 exfoliative process, the erupting secondary tooth erodes away the root (composed of cementum
7 and dentin) of the overlying primary tooth along with some surrounding alveolar bone. Any Pb
8 incorporated into these portions of bone and primary tooth would be released by the erosive
9 process, with the potential to produce highly elevated local concentrations of Pb in the proximity
10 of remodeling alveolar bone and developing secondary teeth. A more modest contribution to
11 circulating blood Pb would be predicted. Animal research in this area has been hampered, as
12 most common rodents (i.e., rats, mice) are monophyodonts (have only one set of teeth).
13 Although monkeys are an acceptable model, it is problematic as to how release of Pb stored in
14 teeth could be differentiated from that of remodeling skeletal bones formed at a similar time
15 point, plus the disproportionate size of the skeletal mass compared to the dentition may mask any
16 contribution of Pb mobilized by exfoliation.
17
18 Summary
19 • Pb substitutes for calcium and is readily taken up and incorporated into the developing
20 teeth of experimental animals.
21 • Unlike bone, teeth do not undergo remodeling per se and, with few exceptions, most Pb
22 incorporated into tooth structure remains essentially in a state of permanent storage.
23 • Administration of high doses of Pb to animals has demonstrated the formation of a "lead
24 line," visible in both the enamel and dentin and localized to areas of recently formed tooth
25 structure. Within this lead line, areas of inhibition of mineralization are evident in enamel
26 and dentin.
27 • Pb has been shown to decrease cell proliferation, intracellular protein, procollagen type I
28 production, and osteocalcin in human dental pulp cells in culture.
29 • Studies of Pb exposure in adult rats have reported inhibition of post-eruptive enamel
30 proteinases, delayed teeth eruption times, and decreased microhardness of surface enamel.
31 • During the process of enamel formation, Pb is apparently widely dispersed when first
32 incorporated into the developing apatite crystal; however, post-formation, Pb is capable of
33 entering and concentrating in areas of calcium deficiency within the enamel.
May 2006 5-215 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Numerous epidemiologic studies and, separately, animal studies (both post-eruptive Pb
2 exposure and pre- and perinatal Pb exposure studies) have suggested Pb is a caries-
3 promoting element; however, whether Pb incorporation into the enamel surface
4 compromises the integrity and resistance of the surface to dissolution and, ultimately
5 increases risk of dental decay, is unclear.
6 • No animal studies have examined the role exfoliation of the primary dentition in release of
7 Pb previously stored in tooth structure, though it is likely this process could serve as an
8 additional source of Pb exposure in childhood.
9
10
11 5.9 EFFECTS OF LEAD ON THE IMMUNE SYSTEM
12 5.9.1 Introduction
13 The immune system, along with the neurological system, has emerged as one of the more
14 sensitive targets of Pb-induced toxicity. However, because Pb exposure at low to moderate
15 levels does not produce overt cytotoxicity of immune cells, immune-associated health effects
16 result from misregulation and shifts in functional capacity rather than profound lymphoid
17 deficiencies. As a result, the most sensitive biomarkers of Pb-induced immunotoxicity are those
18 associated with specific functional capacities as opposed to measures of cell enumeration and/or
19 lymphoid organ pathology. This distinguishes Pb from some other types of immunotoxicants.
20 The following sections provide a survey of the reported immune effects resulting from exposure
21 to Pb in humans and animal models. In general, the focus is on those studies that have been
22 reported since the 1986 Pb AQCD (U.S. Environmental Protection Agency, 1986) was prepared
23 and have altered our understanding of lead-induced immunotoxicity and associated immune-
24 related health risks.
25
26 5.9.2 Host Resistance
27 Host resistance to disease has been used as an effective measure of the impact of
28 environmental toxicants on immune function. Because different diseases require different
29 combinations of immune effector functions for host protection, analysis of environmental
30 modulation of host resistance across a spectrum of diseases can help identify clinically relevant
31 immunotoxicity.
32 The 1986 AQCD presented a range of studies in which exposure to Pb inhibited host
33 resistance to disease. Since the time of that report, few new infectious diseases have been added
May 2006 5-216 DRAFT-DO NOT QUOTE OR CITE
-------
1 to the list of those that Pb is known to influence. Instead, a much broader understanding of the
2 likely basis for the increased disease susceptibility to these pathogens has become evident.
3 Additionally, recognition of an increased risk for some atopic and autoimmune diseases arising
4 from lead-induced immunotoxicity has occurred in recent years. This is discussed under
5 Section 5.9.8. Lead-induced alterations of host resistance against infectious and neoplastic
6 diseases are considered in the following sections.
7 To date, there has been either no effect or an increased susceptibility to disease resulting
8 from exposure to lead for virtually every infectious agent examined. Given the capacity of Pb to
9 shift immune responses toward Th2, one might expect that enhanced resistance might occur for
10 diseases where robust Th2 responses were required. For example, an increased resistance
11 against helminth parasitic disease might be hypothesized. However, this possible association has
12 not been widely examined to date.
13
14 5.9.2.1 Viral Diseases
15 In general, exposure to Pb increases the susceptibility to viral infections. Studies include
16 host resistance directed against the encephalomyocarditis virus (Gainer, 1977; Exon et al, 1979),
17 Langat virus (Thind and Khan, 1978), and Semliki Forrest virus (Gupta et al., 2002). In the last
18 example, oral dosing of Swiss mice with Pb-acetate (250 mg/kg for 28 days) significantly
19 increased mortality to sublethal doses of the virus. Ewers et al. (1982) reported that occupational
20 exposure to Pb resulted in an increased incidence of influenza cases among workers. In chickens
21 administered Pb-acetate orally (20 and 40 mg/lOOg body weight) for 56 days, antibody
22 production against Newcastle virus vaccine was reduced, while mortality against viral challenge
23 was increased (Youssef, 1996). It seems likely that the reduced Thl capacity (including
24 effective CTL generation) combined with increased TNF-a, ROI, and prostaglandin £2 (PGE2)
25 production by responding macrophages would contribute to increased tissue pathology but
26 reduce viral clearance for many infections.
27
28 5.9.2.2 Bacterial Diseases
29 Most of the lead-associated host resistance research has been conducted on bacterial
30 diseases. Hemphill et al. (1971) first described the increased susceptibility of mice exposed to
31 Pb (250 jig given i.p. for 30 days) to Samonella typhimurium, while Selye et al. (1966) reported
May 2006 5-217 DRAFT-DO NOT QUOTE OR CITE
-------
1 increased susceptibility of rats to bacteria endotoxins. Cook et al. (1975) found increased
2 susceptibility of lead-exposed rats (2 mg/lOOg body weight given i.v. once) to both Eschrichia
3 coli and Staphylococcus epidermidis.
4 The vast majority of studies have been conducted using the intracellular bacterium,
5 Listeria monocytogenes, in mice. Listeria infection and host resistance to the disease have been
6 well characterized. Essentially, this infection requires an effective antigen presentation
7 (probably involving toll-like receptor 2 involvement), a robust response by activated
8 macrophages leading to interlukin-12 (IL-12) and interferon-y (IFN-y) production and robust Thl
9 driven host protection (Torres et al., 2004; Lara-Tejero and Pamer, 2004). Ideally, activated
10 macrophages would produce NO in an effective response against Listeria (Ito et al., 2005).
11 In the case of lead-induced immunotoxicity, everything works against this type of response.
12 First, macrophages have severely suppressed NO production. Yet, overproduction of
13 TNF-a, ROIs and PGE2 leads to tissue inflammation and damage. The skewing of the response
14 toward Th2 means that both IL-12 and IFN-y are lacking. Excessive production of IL-6 and
15 other pro-inflammatory cytokines results in what has been termed "sickness behavior" which
16 involves both the immune and central nervous systems (Dantzer et al., 1998; Dyatlov et al.,
17 1998a,b; Lawrence and Kim, 2000; Dyatlov and Lawrence, 2002). Lead-induced impairment in
18 host resistance to listeria was reported by Lawrence (1981). CBA/J mice exposed orally to
19 80 ppm or greater of Pb-acetate for 4 weeks had 100% mortality (after 10 days) compared with
20 no mortality for mice exposed to 0 or 16 ppm lead.
21 In an important study concerning individual variation to lead-induced immunotoxicity and
22 host resistance, Kim and Lawrence (2000) demonstrated that neurological circuitry as it pertains
23 to brain lateralized behavior could impact the effect of Pb on immune responses and host
24 resistance to Listeria. Not surprisingly, this suggests that host genotype and epigenetic factors
25 can be influenced by Pb exposure to the individual. Using female BALB/c mice, Kishikawa
26 et al., (1997) demonstrated that exogenously administered recombinant IL-12 (1 jig each for
27 three days i.p.) could enhance production of IFN-y as well as host resistance to Listeria in lead-
28 exposed (2 mM in water for 3 weeks) mice. However, lead-exposed mice continued to have
29 excess IL-6 production (part of the sickness behavior phenotype). The result with IL-12
30 validates the importance of the Th skewing and macrophage impairment induced by Pb on host
31 resistance to certain diseases.
May 2006 5-218 DRAFT-DO NOT QUOTE OR CITE
-------
1 Additional bacterial infections in which Pb exposure has been reported to reduce host
2 resistance include Serratia marcesem (Schlipkopter and Frieler, 1979) and Pasteurella
3 multocida (Bouley et al., 1977).
4
5 5.9.2.3 Parasitic Diseases
6 Few studies have been conducted to date regarding the effects of Pb on host resistance to
7 parasitic diseases. This is unfortunate as some parasitic disease challenges require effective Th2
8 responses for optimal resistance. Hence, it is not clear that Pb exposure would depress host
9 resistance in every case (e.g., for helminth parasites). Since the 1986 Pb AQCD, one study was
10 conducted examining the effect of Pb on the killing ability ofLeishmania enriettii parasites in
11 vitro by mouse macrophages (Maue'l et al., 1989). The authors found that 30-100 mM
12 Pb-acetate interfered with the killing ability of macrophages without producing macrophage
13 cytotoxicity.
14
15 5.9.2.4 Tumors
16 The primary study concerning tumor immunity/turn or growth and Pb was already known
17 at the time of the 1986 AQCD. In this study, male C57B1/6 mice were exposed to Pb-acetate in
18 the drinking water at concentrations of 0, 13, 130, or 1300 ppm. Moloney sarcoma virus
19 (MSV)-induced tumor formation and growth were compared following the exposure of mice to
20 Pb for 10-12 weeks. MSV-induced transplantable tumors were also used in this study. Primary
21 tumor growth was enhanced in animals that received 130 and 1300 ppm of Pb vs. the control.
22 Still, all tumors regressed eventually. Most other studies involving Pb exposure and tumors
23 describe the fact that Pb can exacerbate the ability of other toxins to promote tumor formation
24 (Kobayashi and Okamoto, 1974; Hinton et al., 1979). Much of the tumor-promoting activity of
25 Pb would seem to involve depressed Thl and macrophage function, as well as the promotion of
26 excessive ROI release into tissues.
27
28 5.9.3 Humoral Immunity
29 The irony of Pb as an immunotoxicant is that the overall effects on humoral immunity are
30 reasonably modest compared to those reported for macrophages and T lymphocytes (McCabe
31 1994). McCabe et al. (1991) discussed the fact that Pb is not profoundly cytotoxic for most
May 2006 5-219 DRAFT-DO NOT QUOTE OR CITE
-------
1 immune cells yet can cause major functional shifts within the immune system as well as
2 decreased host resistance to disease. In many cases, antibody production can remain robust in
3 lead-exposed animals and humans. However, the nature and spectrum of the antibodies
4 produced is the more significant cause for concern. Lead appears to alter the course of T
5 lymphocyte-driven B cell maturation such that class switching may be skewed in lead-exposed
6 animals and humans. If Pb dosage and duration of exposure is sufficient, antibody production
7 may be depressed overall. However, with low-level Pb exposure, skewed isotype production is
8 the greater health risk.
9
10 5.9.3.1 General Effects on B lymphocytes and Iniiminoglobulins
11 Despite the fact that T lymphocytes and macrophages appear to be the more sensitive
12 targets of lead, the metal can alter B lymphocyte maturation and shift immunoglobulin
13 production. The 1986 AQCD describes the fact that some early studies reported no effect of Pb
14 on antibody production (Reigart and Graber, 1976; Ewers et al., 1982), while others reported a
15 significant decrease in the humoral immune response (Roller, 1973; Roller and Rovaic, 1974;
16 Blakley et al., 1980). In retrospect, this apparent discrepancy may have been caused by the
17 various concentrations of Pb administered as well as variations in the duration of exposure.
18 Additionally, as mentioned in the 1986 AQCD, the temporal relationship of Pb exposure to
19 antigen challenge may be important.
20 In studies measuring generation of plaque forming cells (PFCs) against sheep red blood
21 cells (SRBCs), Pb incubation with lymphocytes in vitro caused an increased response (Lawrence,
22 1981). In a comprehensive study using several strains of mice, Mudzinski et al. (1986) reported
23 that Pb-acetate administered in the drinking water (10 mM for 8 weeks) elevated the response in
24 the one strain (BALB/c mice) but failed to alter the humoral response to SRBCs (either PFCs or
25 antibody liters) in all other strains. McCabe and Lawrence (1990) reported that Pb caused an
26 elevation in B cell expression of Class II molecules, thereby influencing B cell differentiation.
27 Lead seemed to impact Class II molecule density at the cell surface via the levels of mRNA
28 translational and/or the posttranslational stages of cell surface protein synthesis (McCabe et al.,
29 1991).
30 Some human epidemiological and occupational studies have reported lead-associated
31 differences in levels of circulating immunoglobulins. However, Tryphonas (2001) discussed the
May 2006 5-220 DRAFT-DO NOT QUOTE OR CITE
-------
1 pitfalls of relying on total serum immunoglobulin in assessing immunotoxic effects in humans.
2 Sun et al. (2003) reported that immunoglobulin M (IgM) and immunoglobulin G (IgG) were
3 lower but that IgE was higher among females within their high-Pb group. Basaran and Undeger
4 (2000) found that IgM, IgG, and some complement proteins were reduced among battery
5 workers with high Pb exposure. Results of Undeger et al. (1996) were similar as well.
6 In contrast, Sarasua et al. (2000) reported an elevation in immunoglobulin A (IgA), IgG, and
7 IgM associated with environmental Pb exposure. Pinkerton et al. (1998) found no major effects
8 but reported a significant lead-associated decline in serum IgG and an elevation in B cell
9 percentage. In a human in vitro study, Borella and Giardino (1991) showed that Pb exposure
10 caused an increased IgG production following stimulation of cells with pokeweed mitogen.
11 In more recent animal studies, Miller et al. (1998) and Chen et al. (1999) reported no
12 effect on antigen-specific IgG liters against keyhole limpet hemocyanin (KLH) protein in F344
13 strain rats that had been exposed in utero to Pb (0-500 ppm Pb-acetate in drinking water).
14 It seems likely that Pb exposure may be capable of reducing serum immunoglobulin levels
15 given sufficient dose and duration of exposure. However, the more critical issue pertains to the
16 distribution of class and subclass of immunoglobulins produced after exposure to lead. Because
17 Pb can alter the development of T cells involved in specific antigen responses, this can impact
18 the spectrum of immunoglobulins produced in response to T-dependent antigens. As discussed
19 in the following section, production of IgE (a class of immunoglobulin that is poorly represented
20 in serum but of great clinical significance) is a central issue for lead-induced immunotoxicity.
21 One additional health concern is the potential for Pb to enhance the likelihood of autoantibody
22 production (Lawrence and McCabe, 2002; Hudson et al., 2003). This latter concern is discussed
23 under Section 5.9.8.
24
25 5.9.3.2 IgE Alterations
26 One of the three predominant hallmarks of lead-induced immunotoxicity is an increase in
27 IgE production. This can occur in the context of antigen-specific responses or as measured by
28 total serum IgE. For this endpoint, the human and animal findings are very similar. Virtually all
29 of the information concerning the capacity of Pb to elevate IgE production in humans and
30 animals has been obtained since the 1986 AQCD. As a result, this represents a relatively new
May 2006 5-221 DRAFT-DO NOT QUOTE OR CITE
-------
1 biomarker for lead-induced immunomodulation, and one not included in most animal or human
2 studies conducted prior to 1990 (e.g., Wagerova et al., 1986).
3 Table 5-9.1 lists the studies reporting lead-induced elevation of IgE. The disease
4 implications of lead-induced increases in IgE production are potentially significant and may help
5 to address, in part, the allergy epidemic that has occurred in the last several decades (Isolauri
6 et al., 2004). A relationship has been established between relative Th2 cytokine levels, serum
7 IgE levels, and the risk of allergic airway inflammation (Maezawa et al., 2004; Cardinale et al.,
8 2005). In fact, attempts to manage allergic inflammation use IgE as one of the major targets
9 (Stokes and Casale, 2004). IgE levels are directly related to the production of Th2 cytokines
10 such as interlukin-4 (IL-4), among others (Tepper et al., 1990; Burstein et al., 1991; Carballido
11 et al., 1995; Takeno et al., 2004; Wood et al., 2004). The relationship between Th2 cytokines
12 (e.g., IL-4), IgE levels, and allergic airway disease is supported through various pharmacological
13 interventions in both animals and humans that either induce Th2 cytokine and promote allergic
14 airway disease (Wu et al., 2004) or interfere with Th2 cytokine-driven IgE production and inhibit
15 allergic inflammation (Holgate et al., 2005; Ban and Hettich, 2005). The production of IgE is of
16 importance in terms of potential inflammation. Not only is the level of IgE a consideration, but
17 also the expression of the Fc receptor for the epsilon (e) chain of IgE on mast cells and basophils.
18 In humans, Karmaus et al. (2005) reported a positive association of blood Pb levels with
19 serum IgE concentration among second grade children living near a waste incinerator or other
20 lead-emitting industries. Sun et al. (2003) also found a positive association of blood lead and
21 serum IgE levels among children in Taiwan. Lutz et al. (1999) reported a correlation of blood
22 lead levels and serum IgE levels in children in Missouri from 9 months-6 years of age. This
23 association appears to hold not only for children but also for adults. Heo et al. (2004) recently
24 showed that battery workers with blood leads > 30 |ig/dL differed significantly in serum IgE
25 levels from those with blood leads < 30 |ig/dL. Additionally, serum IgE concentration correlated
26 with blood lead among the populations examined (r = 0.0872).
27 Animal data support this relationship between blood lead concentration and IgE level and
28 further suggest that even very low-level Pb exposure early in development may produce elevated
29 IgE production in the juvenile offspring. Miller et al. (1998) found that gestational exposure of
30 rats to 100 ppm Pb-acetate in the drinking water could produce elevated IgE in the adult
31 offspring. Snyder et al. (2000) showed that gestational and/or neonatal exposure of mice to
May 2006 5-222 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-9.1. Recent Studies Reporting Lead-Induced Increase in IgE
Species
Human
Human
Human
Mouse
Human
Rat
Mouse
Human
Strain/Gender
Both genders
Both genders,
91% males
Females
Balb/c males
and females
Both genders,
56% male
F344 females
Balb/c females
Males
Age
Children
Adult
Children
Fetal
Juvenile
Embryo -
fetal
Adult
Adult
In vivo
Ex vivo
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Lowest
Effective Dose
Not available
Not Available
Not Available
0.1 mM
Not Available
100 ppm
50 |j£ 3x per
week s.c.
Not Available
Exposure
Duration
Not Available
Not Available
Not Available
3 days
Not Available
5 weeks to dam (2
and 3 gestational)
3 weeks
Not Available
Reference
Karmous
et al. (2005)
Heo et al.
(2004)
Sun et al.
(2003)
Snyder et al.
(2000)
Lutz et al.
(1999)
Miller et al.
(1998)
Heo et al.
(1996)
Horiguchi
etal. (1992)
1 Pb-acetate produced neonatal blood lead levels not above background (5.0 |ig/dL), but
2 nevertheless, could result in elevated IgE production in the juvenile mouse. In most cases, Pb
3 exposures associated with elevated IgE were also associated with increases in IL-4 production by
4 T cells (Chen et al., 1999; Snyder et al., 2000). This is consistent with the fact that high IL-4
5 production can predispose B lymphocytes to undergo a specific class switch for the production of
6 IgE.
7 For NK cells, activation can occur through various pathogenic components such as double
8 stranded RNA. However, recently Borg et al. (2004) showed that mature dendritic cells
9 produced a Thl-promoting cytokine, IL-12, and this in turn activates NK cells to produce the
10 further Thl-promoting cytokine, IFN-y. Interleukin-18 (IL-18) produced by macrophages is also
11 an activator of NK cells, facilitating Thl-promoting cytokine release while interleukin-2 and
12 interleukin-15 (IL-2, IL-15) are growth factors for NK cells. NK cells would appear to be
13 relatively resistant to the effects of Pb compared to some T lymphocytes and macrophages.
14 For a detailed consideration of the effects of Pb on NK cells, see Section 5.9.7.
May 2006
5-223
DRAFT-DO NOT QUOTE OR CITE
-------
1 Cytotoxic T lymphocytes are generated in response to antigen presentation delivered with
2 Thl cytokines. These cells are capable of mediating antigen specific destruction of neoplastic
3 and virally infected cells via binding and release of cytolytic proteins into the intracellular space.
4 Frequently, the most effective antigen targets of CTLs are the early viral proteins produced in the
5 first phase of host cell infection by viruses. IL-12, produced largely by dendritic cells, appears to
6 be important in the generation of antigen CTL cells and IFN-y produced by Thl lymphocytes.
7 NK cells are a potent regulator of CTL activity. Cell signaling via certain toll-like receptors on
8 antigen presenting cells seems to have a role in determining the nature of the Th activation (Thl
9 vs. Th2) and can, therefore, influence the extent of CTL production.
10 Because T lymphocytes and their regulator and effector functions are so critical in CMI,
11 the maturation of thymocytes within the thymus microenvironment and the selection of
12 repertoire among the maturing T lymphocytes are crucial issues for potential developmental
13 immunotoxicants. In fact, lead seems to be capable of disrupting several aspects of T cell
14 maturation, activation, and repertoire usage (McCabe and Lawrence, 1991; Heo et al., 1998;
15 Miller et al., 1998; McCabe et al., 2001, Lee and Dietert, 2003).
16
17 5.9.4 General Effects on Thymocytes and T lymphocytes
18 In general, cells of the T cell lineage appear to be relatively sensitive to the toxic effects
19 of Pb compared to other lymphoid populations. At the time of the 1986 AQCD, there was some
20 understanding of this sensitivity. However, there appear to be considerable differences in
21 sensitivity across various T cell subpopulations (McCabe and Lawrence, 1991; Heo et al., 1996;
22 1997; 1998). This was largely unknown when the prior AQCD was prepared, as the partitioning
23 of T helper cells into functionally distinct subpopulations (e.g., ThO, Thl, and Th2) was not
24 known until the latter part of the 1980s. The differential impact of Pb on T helper cell
25 populations and on immune balance was established during the 1990s. This has become one of
26 the four hallmarks of lead-induced immunotoxicity.
27 Original observations of both in vivo and in vitro T-dependent immune responses in the
28 presence of Pb suggest that T helper function, as well as the spectrum of cytokines produced, are
29 skewed toward the Th2. The cytokine skewing is discussed as well in Section 5.9.5.3. Smith
30 and Lawrence (1988) have shown that Pb can inhibit antigen presentation and stimulation of a
31 T cell clone of the Thl phenotype. McCabe and Lawrence (1991) were the first to show that this
May 2006 5-224 DRAFT-DO NOT QUOTE OR CITE
-------
1 was caused by the novel capacity of Pb to inhibit Thl stimulation while promoting presentation
2 to Th2 clones. Heo et al. (1996) provided both in vitro and in vivo results supporting this
3 immunomodulation of lead. Cytokine skewing accompanied the differential stimulation of
4 Th cells.
5 Using naive splenic CD4+ T cells derived from Dl 1.10 ovalbumin-transgenic mice, Heo
6 et al. (1998) developed T cell clones in vitro in the presence of lead. The authors found the
7 T cells that developed from the naive precursors were significantly skewed toward the Th2
8 helper phenotype and away from the Thl phenotype. If IL-4 was inhibited with the addition of
9 anti-IL-4 to the cultures or if the Thl- promoting cytokine IL-12 was added exogenously to the
10 culture, the effects of Pb could be largely overcome. This study provided firm evidence that Pb
11 can directly promote Th2 development among precursor Th(0) cells and impair development of
12 Thl cells. Among its effects, Pb enhanced adenyl cyclase activity and increased the levels of
13 cAMP. The authors suggested that Pb may influence cell signaling in such as manner as to
14 promote the Th2 pathway.
15 Beyond the biasing of immune responses at the level of the T lymphocyte based on
16 Thl/Th2 balance, Pb has the capacity to bias usage of certain VP genes (VP5, VP?, and VP13)
17 among T lymphocyte clones in mice (Heo et al., 1997). This is of concern, as it suggests that
18 exposure to Pb may alter the T cell repertoire and skew its representation. Heo et al. (1997)
19 discussed the fact that many autoimmune diseases are characterized by a disproportionate usage
20 of certain VP genes. Different autoimmune conditions are associated with the differential
21 overabundant usage of a specific VP gene. They suggest that this feature of lead-induced
22 T lymphocyte immunotoxicity may contribute to and enhance the risk of autoimmunity.
23 Lee and Dietert (2003) exposed the developing thymus of embryonic day 12 (E12)
24 chickens to Pb-acetate (single injection of 400 jig) and evaluated the capacity of thymocytes
25 (ex vivo) from juvenile chickens to produce IFN-y. They found that embryonic exposure at
26 doses that impair juvenile delayed type hypersensitivity (DTK) also inhibit IFN-y production.
27 Similarly, IFN-y production was decreased when thymocytes from juvenile chickens were
28 exposed to Pb in vitro (0.45 |iM). However, in vitro exposure of thymic stroma to Pb did not
29 result in suppression of control thymocyte IFN-y production in co-cultures. There is a suggestion
30 that the balance of reproductive hormones in early life may influence the impact of Pb on
31 developing thymocytes (Hussain et al., 2005).
May 2006 5-225 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.9.4.1 Delayed Type Hypersensitivity
2 The DTH assay is an in vivo assay requiring antigen-specific T lymphocytes to be primed,
3 expanded, and then recruited to a local site of antigen deposition. The most common application
4 of the DTH is the tuberculin assay for TB in humans. The assay has a long history of application
5 in immunotoxicology, and its utility within the national toxicology program assessment in the
6 mouse has been previously reported (Luster et al., 1992). The assay is known to depend largely
7 on Thl participation and is, therefore, an effective measure of Thl-dependent function.
8 However, there are at least two different portions of the response that are under somewhat
9 separate control. Priming and expansion of the antigen-specific T lymphocytes is largely Thl
10 dependent. However, recruitment of T lymphocytes to the periphery involves a variety of locally
11 produced chemotactic signals that may not be under the same regulation. In fact, Chen et al.
12 (1999) showed that a commonly used chelator for Pb poisoning (succimer, meso-2,
13 3-dimercaptosuccinic acid [DMSA]) fails to restore lead-induced suppression of DTH in rats,
14 because the chelator itself somehow interferes with the production of chemotactic factors
15 necessary for T lymphocyte recruitment. The DTH assay is also generally useful in questions of
16 possible developmental immunotoxicity, because of the natural skewing toward Th2 that occurs
17 during gestation through birth and the issue of effective Thl functional acquisition in the
18 newborn.
19 Lead-induced suppression of the DTH response is one of the four hallmarks of lead-
20 induced immunotoxicity. At the time of the 1986 AQCD, the capacity of Pb to suppress DTH
21 function was already known from two studies conducted during the late 1970s. However, the
22 association of the function with Thl help had not been established. Muller et al. (1977) were
23 among the first to demonstrate lead-induced suppression of DTH. Using mice, these
24 investigators administered Pb-acetate i.p. for 30 days prior to assessment of primary and
25 secondary DTH responses against SRBCs. Both primary and secondary responses were severely
26 depressed following exposure to Pb, even at the lowest dose tested (0.025 mg). Faith et al.
27 (1979) exposed developing Sprague-Dawley rats to Pb-acetate in the drinking water (lowest dose
28 at 25 ppm) first via the dams during gestation and through weaning and then with direct exposure
29 of the offspring until 6 weeks of age. In this case, the purified protein derivative (PPD) of
30 tuberculin was used as the antigen compared against the saline injection control. Rats
31 administered the lowest dose of Pb evaluated (producing a BLL of 29.3 |ig/dL) had a
May 2006 5-226 DRAFT-DO NOT QUOTE OR CITE
-------
1 significantly reduced DTK response. Laschi-Loquerie et al. (1984) measured the contact
2 hypersensitivity reaction against picryl chloride in mice that had received 0.5 mg/Kg Pb via s.c.
3 administration. Lead administration was given from 3-6 days in duration at varying times
4 relative to the sensitization period. These investigators reported that Pb suppressed the DTH
5 type of response regardless of the window (before or during sensitization) in which it had been
6 administered.
7 More recently, Miller et al. (1998) found that female F344 rats gestationally exposed to
8 250 ppm of Pb-acetate in drinking water had a persistently reduced DTH reaction against KLH
9 protein. Chen et al. (1999), Bunn et al. (2001a,b,c) and Chen et al. (2004) had similar findings in
10 studies that included both the F344 and CD strains of rats. In the last study conducted in F344
11 rats, a BLL of 6.75 |ig/dL at 4 weeks of age, postgestational exposure to Pb-acetate (250 ppm in
12 drinking water) was associated with depressed DTH against KLH in the 13-week-old adult
13 female offspring (Chen et al., 2004). McCabe et al. (1999) were among the first to draw
14 attention to the relationship between lead-induced suppression of DTH and the prior observations
15 of lead-induced Th skewing. These authors gave varying doses of Pb-acetate in drinking water
16 (32,128, 512, 2048 ppm) to female BALB/c mice for 3 weeks prior to measuring the DTH
17 against SRBCs. They found that the 512-ppm dose producing a BLL of 87 |ig/dL significantly
18 impaired the DTH response. Antigen routes proved to be important as Pb depressed DTH when
19 an i.v. primed with SRBCs was used, but not when SRBCs were administered i.p. Timing of Pb
20 administration was found to be important relative to the capacity to depress the DTH response.
21 Lee et al. (2001) showed that Pb-acetate (200 jig) administered in ovo to chicken embryos at
22 9 days of incubation failed to depress juvenile DTH against bovine serum albumin (BSA), but
23 when the same dose of Pb was administered 3 days later producing the same BLL, juvenile DTH
24 was severely reduced. Using the latter model, embryonic administration of exogenous thymulin
25 was found to partially restore juvenile DTH function following embryonic exposure to Pb (Lee
26 and Dietert, 2003).
27 Regarding developmental sensitivity of the DTH response to lead-induced
28 immunosuppression, parallel findings were obtained in the developing rat (CD strain females)
29 (Bunn et al., 2001c) in agreement with those found in the chicken. Administration of 500 ppm
30 Pb-acetate during gestational days 3 to 9 or 15 to 21 produced no DTH effect compared with
May 2006 5-227 DRAFT-DO NOT QUOTE OR CITE
-------
1 DTH suppression in the corresponding adult offspring. As shown in Figure 5-9.1, the sensitivity
2 of the DTH response to Pb appears to develop sometime between days 9 and 15 of rat embryonic
3 development. Apparently, the status of the developing thymus may be a consideration in the
4 capacity of Pb to impact the subsequent DTH response. This is discussed further in
5 Section 5.9.10.
Rat
Conception
0 3
1 1
Chicken
Start of
incubation
0 3
1 1
6 9
1 1
f 1
12 15 18
1 1 1
13-14 17
t |
Migration of
T precursors
to thymus
\
Appearance
of double
positives
12 15 18
1
Birth
21
1
20 1 post
W birth
— •
Appearance
..f hilly 1
mature |
Irymocytes ^V
Emigration to
periphery
Hatch
21
1
Day of Embryonic Development
First wave T
precursors to
thymus
Sec end wave T
precursors to
thymus
Third wave
precursors t
thymus
T
0
Figure 5-9.1. Windows during prenatal development (days postconception for rat) or
embryonic development (days postincubation initiation for chicken)
during which sensitivity of DTH to lead emerges.
6
7
8
9
10
1 1
12
It should be noted that in several studies, lead-induced suppression of the DTH response
was associated with reduced capacity to produce the Thl cytokine, IFN-y (Chen et al., 1999;
Lee etal., 2001).
5.9.4.2 Other T-Dependent Cell-Mediated Immune Changes
The in vitro response of T lymphocyte populations to various mitogens (e.g.,
Concavavalin A [ConA], Phytohemagglutinin A [PHA]) has been used as a surrogate measure of
May 2006
5-228
DRAFT-DO NOT QUOTE OR CITE
-------
1 antigen-driven T lymphocyte stimulation. The impact of Pb on these parameters is presented in
2 Section 5.9.5. Another T cell response altered by exposure to Pb is the mixed lymphocyte
3 response (MLR). This in vitro assay is a measure for the responsiveness of T cells to the
4 presentation of allogeneic major histocompatibility complex (MHC) molecules by antigen
5 presenting cells. The in vivo correlate of the MLR is usually considered to be the graft vs. host
6 (GvH) reaction. Several investigators have reported Pb alteration of the MLR as summarized in
7 Table AX5-9.4.
8 McCabe et al. (2001) demonstrated that Pb at very low physiological concentrations
9 (0.1 jiM or approximately the equivalent of 10 |ig/dL) in vitro significantly enhanced the
10 proliferation and expansion of murine alloreactive CD4+ T lymphocytes in the MLR reaction.
11 In fact, the resulting population was found to have a high density of CD4 molecules on
12 the cell surface, making them phenotypically similar to memory T lymphocytes. The authors
13 hypothesized that lead-induced creation of an exaggerated pool of memory-type T lymphocytes
14 (possessing a lower threshold required for subsequent activation) would be problematic for the
15 host. In a study using Lewis strain rats, Razani-Boroujerdi et al. (1999) also found evidence for
16 lead-induced stimulation of the in vitro MLR response. In this case, both the alloreactive
17 mixtures of cells as well as syngeneic mixtures were elevated in proliferation when cultured in
18 the presence of Pb-acetate (e.g., 50 ppm or approximately 131 jiM). When concentrations of Pb
19 were significantly higher (200 ppm or greater), proliferation was inhibited in these cultures.
20 Figure 5-9.1 illustrates the developmental appearance of initial sensitivity for Pb-induced
21 suppression of the DTH function. The mid-embryonic developmental window is the time during
22 which the capacity of Pb to impair later-life DTH responses first emerges. Earlier pulsed
23 exposure to Pb fails to impair juvenile and/or adult DTH despite the continuing of presence of Pb
24 in the embryo. However, during the second half of embryonic development the embryo becomes
25 remarkably sensitive to lead-induced suppression of DTH. Both the rat and chicken are similar
26 in this window of emerging Thl-dependent functional sensitivity. Thymus-related
27 developmental events are indicated along with the emergence of DTH functional sensitivity to
28 lead. Information was derived from Gobel (1996), Vicente et al. (1998), Dunon et al. (1998),
29 Dietert et al., (2000), Bunn et al. (2001c), Lee et al. (2001) and Holsapple et al. (2003).
30
May 2006 5-229 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.9.5 Lymphocyte Activation and Responses
2 Many of the broader functional ramifications of Pb exposure on lymphocytes are
3 discussed under Sections 5-9.3 and 5-9.4. However, the capacity of Pb to directly alter lymphoid
4 responses is a significant component of lead-induced immunotoxicity and is summarized within
5 the present section. Lymphoid responses are usually assessed in terms of proliferation and
6 activation (functional changes). One of the recent endpoints reflecting functional status is the
7 production of cytokines. These both autoregulate the producing cells and significantly impact
8 the activity of other immune and nonimmune cells carrying the appropriate receptors. The
9 spectrum and levels of cytokines produced by a population of immune cells tends to reflect their
10 capacity to regulate the host immune response.
11
12 5.9.5.1 Activation by Mitogens
13 The capacity of certain plant- and bacterially derived products to stimulate lymphoid
14 populations to enter the cell cycle and undergo mitogenesis has been used for decades to assess
15 the potential capacity of lymphocytes to receive proliferation signals and expand their
16 population. Among the mitogens employed within the Pb exposure studies are the T lymphocyte
17 subpopulation mitogens, PHA and Con A; the dual T and B cell mitogen, pokeweed mitogen
18 (PWM); the B lymphocyte mitogen derived from gram-negative bacteria, lipopolysaccharide
19 (LPS), and the B cell mitogen, Staphylococcus aureus enterotoxin (SE). It should be noted that
20 these mitogens do not necessarily stimulate all T lymphocytes or all lymphocytes but, instead,
21 stimulate selected populations of the cells. The mitogens react with a large array of cell surface
22 molecules producing cross-linking and appropriate signal transduction to initiate mitogenesis.
23 In the case of the plant-derived mitogens, lectins, numerous glycoproteins and glycolipids
24 carrying the correct carbohydrate residues serve as the cell surface binding sites for cross-
25 linking. Mitogen stimulation in vitro has been used as a surrogate for antigen-driven stimulation
26 and proliferation of antigen-specific T and B cell clones. However, it should be noted that while
27 the assays have been used for decades, there are now more specific assays utilizing more
28 functionally relevant cell surface receptors to assess lymphoid activation potential.
29 The 1986 AQCD has an extensive review of mitogenic responses of lymphocytes
30 following both in vivo and in vitro treatment by lead. The results at that time showed no clear
31 pattern. At low to moderate levels, Pb was potentially co-mitogenic for some cells and at very
May 2006 5-230 DRAFT-DO NOT QUOTE OR CITE
-------
1 high concentrations could suppress proliferation. Little has changed in conclusions for this
2 assessment measure since the 1986 report. The most significant findings from the mitogenic
3 studies are that at doses encountered physiologically Pb is not a potent cytotoxic agent for most
4 immune cells. At low concentrations, it can marginally stimulate lymphoid mitogenesis.
5 However, as one examines more refined subpopulations of lymphocytes than what were able to
6 be identified prior to 1986 (e.g., Thl vs. Th2 clone of T lymphocytes), it becomes clear that Pb
7 can promote expansion of some lymphoid populations while suppressing others.
8 Annex Table AX5-9.5 for this section summarizes results of Pb effects on mitogen-
9 stimulated proliferation of lymphoid populations.
10
11 5.9.5.2 Activation via Other Receptors
12 In recent years, lymphoid activation and population expansion has been measured using
13 the triggering of specific T and B cell surface receptors (e.g., CD3 on T cells) as well as antigen-
14 driven proliferation of T cell clones known to be specific for the antigen in question. The latter
15 has provided the opportunity to simulate in vivo lymphoid activation and antigen-driven
16 proliferation by using receptors in vitro, which are more physiologically relevant than those
17 activated by plant lectins. Because Pb does not cause profound population loss across the entire
18 population of T or B lymphocytes, these more refined and functionally-relevant assay systems
19 have enabled a much clearer picture to emerge concerning lead-induced changes in lymphoid
20 population than was available for the 1986 AQCD report.
21 Smith and Lawrence (1988) and McCabe and Lawrence (1991) utilized antigen-specific
22 mouse T clones. They found that Pb directly promoted antigen presentation and stimulation of
23 the T cell clones when these clones were Th2 cells. However, when the Thl clones were used,
24 Pb suppressed the antigen-specific presentation signal. In the McCabe and Lawrence study,
25 direct comparisons were made between Thl and Th2 clones specific for mouse allogeneic MHC
26 molecules. These studies provided the first clear picture of the differential effects of Pb on Thl
27 vs. Th2 cells. Several studies since these have verified this major effect of Pb (Heo et al., 1996;
28 1997, 1998). Many of these later studies utilized the transgenic mouse strain (DO 11.10 OVA-tg)
29 that carries T cells specific for a peptide fragment of ovalbumin. These enabled the same
30 comparisons to be made with the presentation of a soluble protein antigen as the stimulating
31 signal. Heo et al. (1998) showed that Pb not only selectively stimulates Th2 cells and suppresses
May 2006 5-231 DRAFT-DO NOT QUOTE OR CITE
-------
1 Thl cells but that it preferentially causes precursor ThO cells to mature into Th2, rather Thl cells,
2 as well. Additionally, the T cell clones in the presence of Pb are skewed in terms of their usage
3 of VP genes (as reflected in their cell surface receptors) (Heo et al., 1997). This is of particular
4 concern relative to the risk of autoimmunity. More recently, McCabe et al. (2001) examined Pb
5 exposure in the context of the allogeneic MLR against allogeneic MHC molecules. In vitro
6 exposure to Pb (as low as 1.0 jiM) enhanced the primary MLR response, but not the secondary
7 MLR response and not the mitogenic response using PHA. Significantly, the T cell clones that
8 emerged from the primary MLR were in greater proportion than normal and were of the
9 specialized phenotype CD4-plus high density (CD4+hlgh). Because these fit the phenotype of
10 memory cells, it is likely that an overabundance of memory cells was produced during the
11 primary response, where the antigen may be of lesser biological significance than in a secondary
12 response. The authors discussed the fact that Pb may cause T cells to respond under conditions
13 of low antigen concentration, which could waste valuable and limited resources by generating
14 T memory cell clones when they are not needed (against unimportant antigens) or even increase
15 the risk of autoimmune responses by altering the threshold requirements for stimulation.
16 The putative mechanisms suggested for the differential effects of Pb on Th cells are presented in
17 Section 5.9.9.
18
19 5.9.5.3 Cytokine Production
20 At the time of the 1986 AQCD, immune cytokines were essentially absent from the
21 information available for consideration. Only the antiviral interferons (a,P) had been examined
22 among studies available for that report. Therefore, one of the most important effects of Pb on the
23 immune system, i.e., Pb-induced cytokine production was not known at that time.
24 Most studies since 1986 have shown that Pb exposure at low to moderate levels causes a
25 significant shift in the production of Thl vs. Th2 cytokines with the bias toward the latter.
26 Hence, production of IFN is decreased and IL-12 is inadequate for effective host resistance.
27 In contrast, production of IL-4, IL-6, and, frequently, interlukin-10 (IL-10) is elevated.
28 Table 5-9.2 illustrates the studies reporting shifts in cytokine production induced by lead.
29 (Please note that TNF-a production is considered in the macrophage section, Section 5.9.6).
30 These shifts in cytokine production are remarkably consistent, occur even at low levels of
May 2006 5-232 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-9.2. Studies Reporting Lead-Induced Shifts in Thl vs. Th2 Cytokines
to
o
o
ON
i
i
to
OJ
OJ
o
r™
n
H
O
o
^^
H
O
O
H
W
O
^
O
HH
H
in
Species
Rat
Human
Chicken
Mouse
Rat
Chicken
Mouse
Mouse
Mouse
Rat
Strain/ Gender
F344 Females
Males
Cornell K females
Balb/c
CD females
Cornell K females
Balb/c male
NOD
Autoimmune strain
adult
C51 Bl/6 females
NOD autoimmune
strain females
F344 females
Age
Embryo-fetal
Adults
Embryonic
Neonatal/
Juvenile
Fetal
Embryonic
Adults
Adult
Adult
Embryo-
fetal
In vivo/
Cytokine Alterations Ex vivo
tIL-4 Yes
4 IFN-y splenic lymphocytes
t IFN-y Yes
PHA stimulated peripheral
blood lymphocytes
4IFN-y Yes
stimulated thymocytes
tJL-6 Yes
serum during infection
tIL-10 Yes
4IFN-y Yes
tIL-6 Yes
serum during infection in
certain groups
4 IFN-y, no change long Yes
term
4TGF-P intestinal levels
No effect on gut balance in Yes
normal mice
4TGF-P in autoimmune mice
4IFN-y Yes
tIL-10
Lead Dose/
Concentration
250 ppm in water
to dams
Not available
400 \ig
0.5 mM in water to
dams and their
pups
550ppminwaterto
dams
50 ng
2mM
Oral 10 mM and
ovalbumin antigen
0.5 mg/kg injection
and oral ovalbumin
250 ppm to dams
Duration of
Exposure
2 weeks prior and 3rd
week of gestation for
dam
Not available
Single injection E12
4 weeks (3 via dams)
6 days via gestation
of dam
Single injection
8 weeks
10 days
6 injections over
2 weeks
2 weeks before and
3rd week of gestation
References
Chen et al.
(2004)
Mishra et al.
(2003)
Lee and
Dietert (2003)
Dyatlov and
Lawrence
(2002)
Bunn et al.
(200 Ic)
Lee et al.
(2001)
Kim and
Lawrence
(2000)
Goebel et al.
(2000)
Goebel et al.
(1999)
Chen et al.
(1999)
-------
Table 5-9.2 (cont'd). Studies Reporting Lead-Induced Shifts in Thl vs. Th2 Cytokines
^H
to
o
o
ON
i
i
to
OJ
•^
o
H
1
O
o
0
H
O
o
H
W
O
O
H
W
Species Strain/ Gender Age
Mouse DOll.lOova-tg, Adult
ova mice and RAG
knockouts
Rat F344 females Embryo-
fetal
Mouse Balb/c ByJ females Adult
Mouse Balb/c and Adult
DOll.lOova-tg
mice
Mouse Balb/c ByJ female Adult
or male
Mouse Balb/c ByJ female Adult
or male
Cytokine Alterations
4IFN-Y
4IFN-Y
4IFN-Y
tIL-6
4IFN-Y
4IFN-Y/IL-4
ratio
4IFN-Y
tIL-4
4IFN-Y
tIL-4
In vivo/ Lead Dose/
Ex vivo Concentration
No 25 |jM
Yes 500 ppm to dams
Yes 2mM
Yes 50 pg each
injection (s.c.)
3 per week
Yes 50 ng each
injection (s.c.)
3 per week
No 10 |jM - 50 |jM
Duration of
Exposure References
3 days Heo et al.
(1998)
2 weeks before and Miller et al.
3rd week of gestation (1998)
3 weeks Kishikawa
etal. (1997)
2 weeks Heo et al.
(1997)
2 weeks Heo et al.
(1996)
2 days Heo et al.
(1996)
-------
1 exposure, and are reported following both in vivo and in vitro exposure to lead. Furthermore, the
2 effects are persistent even when exposure to Pb was restricted to early development and cytokine
3 assessment was performed in the subsequent juvenile or adult (Miller et al., 1998; Bunn et al.,
4 200Ic; Lee et al., 2001; Chen et al., 2004).
5 The only exceptions to lead-induced biasing in favor of Th2 occur in the reports by
6 Goebel et al. (2000) and Mishra et al. (2003). In the latter case, the authors attributed this
7 difference (in humans) to the very high Pb levels considered in the study. In the prior case,
8 Goebel et al. (2000) saw a local bias to Thl in the intestinal tract of a specialized autoimmune
9 diabetes-prone strain of mice (NOD) but not in normal mice. Initially, the Pb-induced cytokine
10 skewing favored Th2 (after 1 day), but this shifted to Thl with more prolonged Pb exposure
11 (after 10 days). Loss of oral tolerance accompanied this long-term shift. These results suggest
12 that in most cases, lead-induced skewing would favor Th2. But with some genotypes or
13 additional disease conditions, an imbalance may occur in the direction of a gut-associated Thl
14 environment, increasing risk for loss of oral tolerance and the potential for increased food
15 allergies.
16 One ramification for the capacity of Pb to promote Th2 cells is the impact of elevated
17 IL-4 on IgE. It seems clear that lead-induced overproduction of IgE (seen in virtually all animal
18 models examined as well as humans) is directly linked with the overproduction of IL-4.
19 Excessive IL-4 and the resulting IgE production increase the risk for IgE-mediated atopy and
20 asthma.
21 Additionally, Kishikawa et al. (1997) demonstrated that administration of the potent
22 Thl-promoting cytokine, IL-12, to lead-exposed mice can restore the balance of Thl (IFN-y) vs.
23 Th2 cytokines (e.g., IL-6), reduce corticosterone levels, and enhance host resistance in Listeria-
24 infected mice. This observation supports the critical role of Thl/Th2 balance in overall risk to
25 host resistance against disease presented by Pb disruption of that balance
26
27 5.9.6 Macrophage Function
28 Macrophages represent a diverse population of cells that play critical roles in both host
29 defense and tissue homeostasis. Macrophage subpopulations provide a front line of defense
30 against bacteria, parasites, viruses, and tumors via the innate immune response. Additionally,
31 they are important in tissue repair and remodeling as well as in the removal of senescent cells.
May 2006 5-235 DRAFT-DO NOT QUOTE OR CITE
-------
1 Some forms of macrophages are efficient in the processing of antigens and the presentation of
2 antigen fragments to T lymphocytes. Additionally, macrophages can regulate lymphoid activity
3 through the secretion of a variety of cytokines and through the production of various
4 immunomodulatory metabolites (e.g., NO, ROIs) and the products of the cyclooxygenase and
5 lipoxygenase pathways.
6 Because macrophages can be found residing in most tissues, lead-induced modulation of
7 macrophage functional capacity has the potential to alter overall organ function. Macrophages
8 originate in the bone marrow from pluripotent stem cells that give rise to both the monocyte-
9 macrophage lineage as well as polymorphonuclear leukocyte populations. Bone marrow-derived
10 macrophages mature under the influence of various cytokine growth factors to become the full
11 array of mature cell subpopulations. Various investigators have examined the effects of lead on
12 the maturation of macrophages in vitro as well as on the functional capacity on fully mature cells
13 both in vitro and in vivo. Blood monocytes represent a functional, yet not fully specialized, form
14 of macrophage. As a result, the influence of environmental toxicants on monocytes may not be
15 fully predictive of the effects of the same toxicants on splenic or alveolar macrophages, glial
16 cells, or Kupffer cells.
17 Because macrophages give rise to several specialized populations, e.g. Kupffer cells in the
18 liver, glial cells in the brain, and various skin macrophage populations, it is important to realize
19 that different specialized macrophage populations are likely to have somewhat different
20 sensitivities to lead, as well as potentially different responses following exposure. Not
21 surprisingly, blood monocytes may not always be an appropriate model to accurately predict the
22 outcome of lead-induced immunotoxicity for alveolar macrophages following an inhalation
23 exposure.
24 The 1986 Pb AQCD identified macrophages as a significant target for lead-induced
25 immunotoxicity. Research since the mid-1980s has served to underscore this point. The
26 understanding of lead-induced alterations in macrophage function has increased significantly
27 since the prior AQCD report. The following sections describe the reported immunotoxic effects
28 of lead on macrophages. It should be noted that for a number of endpoints, such as lead-induced
29 alterations in the production of NO, ROIs and TNF-a, there is a general consensus among a
30 majority of immunotoxicology studies and agreement with the effects described for the
31 cardiovascular system (see Chapter 5.5).
May 2006 5-236 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.9.6.1 Nitric Oxide (NO) Production
2 Nitric oxide is a short-lived metabolite produced in large quantities by macrophages
3 during cellular activation. The enzyme responsible is an inducible form of nitric oxide synthase
4 (iNOS), which, utilizing a bioptrin cofactor, converts the amino acid arginine into NO and
5 citrulline. A competing alternative pathway utilizing arginine leads to the production of
6 polyamines, which themselves are immunomodulatory for lymphocytes. Nitric oxide is critical
7 in the defense against certain infectious agents, including various bacteria.
8 Among the most sensitive immunomodulatory effects of Pb exposure is the capacity to
9 impair NO production by macrophages (Table AX5-9.6). Several research groups have shown
10 that in vitro as well as in vivo exposure to Pb results in significantly reduced production of NO
11 (Tian and Lawrence, 1995, 1996; Chen et al., 1997b; Lee et al., 2001; Pineda-Z aval eta et al.,
12 2004 [also reviewed in Singh et al., 2003]). Similar results were obtained in human, mouse, rat
13 and chicken. Depression of NO production capacity usually occurs shortly after exposure to
14 lead. However, the long-term effects of Pb on NO production following very early life exposure
15 are less clear (Miller et al., 1998; Chen et al., 1999; Bunn et al., 2001a).
16 Tian and Lawrence (1996) have hypothesized that because very low Pb concentrations
17 (in vitro equivalents to 10 |ig/dL) can impair NO production, impaired NO production may be
18 responsible for reduced host resistance to Listeria seen among lead-exposed rodents as well as
19 for lead-induced hypertension among humans (Pirkle et al., 1985). Indeed, impaired NO
20 production by macrophages seems to be one of the more sensitive endpoints for immediate lead-
21 induced immunotoxicity.
22
23 Other Functional Alterations
24 TNF-a Production
25 Early studies identified the fact that Pb exposure could predispose animals for a
26 dramatically increased sensitivity to bacterially derived endotoxin (Trejo et al., 1972; Filkins and
27 Buchanan, 1973; Schlick and Friedberg, 1981).
28 It is now known that the increased sensitivity to endotoxin is linked to the capacity of Pb
29 to increase production of TNF-a among macrophages (Dentener et al., 1989; Zelikoff et al.,
30 1993; Guo et al., 1996; Miller et al., 1998; Chen et al., 1999; Krocova et al., 2000; Flohe et al.,
31 2002). Studies in mouse, rat, rabbit, and human provide a clear indication that one effect of Pb
May 2006 5-237 DRAFT-DO NOT QUOTE OR CITE
-------
1 on macrophages is to boost production of the proinflammatory cytokine TNF-a. While most
2 studies examined the immediate effects of Pb exposure on TNF-a production, studies by Miller
3 et al. (1998) and Chen et al. (1999, (2004) showed that the effects of early gestational exposure
4 to Pb on macrophages could persist well into later life, including adulthood. Additionally, Chen
5 et al. (1999) showed that chelation of Pb with succimer in developing female rats in utero could
6 eliminate the persistent effect of elevated TNF-a production in the adult offspring. Flohe et al.
7 (2002) found evidence that lead-induced elevation in TNF-a production is sensitive to both PKC
8 signaling as well as to protein production. While the production of TNF-a can be elevated
9 following exposure to lead, the expression of the receptor for TNF-a (TNF-R) was also increased
10 during the in vitro exposure of human blood monocytes to Pb-chloride (Guo et al., 1996).
11 Therefore, the combined effect of elevated cytokine production by macrophages as well as
12 increased receptor expression would be expected to contribute to problematic inflammatory
13 responses.
14
15 Production of Other Proinflammatory Cytokines
16 Several studies have indicated that macrophage production of cytokines (or that levels of
17 cytokines known to be produced primarily by macrophage populations) is altered after exposure
18 to lead. These vary somewhat, depending upon the exposure protocol and the source of
19 macrophages examined. In addition to the previously discussed elevation of TNF-a by lead, the
20 most significant and consistent lead-induced effects seem to involve elevated production of the
21 other major proinflammatory cytokines, interleukin-lp (IL-1(3) and IL-6. Increased production
22 of IL-6 following exposure to Pb has been reported by Dyatlov and Lawrence (2002), Flohe et al.
23 (2002), Kim and Lawrence (2000), Krocova et al. (2000), Kishikawa and Lawrence (1998) and
24 Kishikawa et al. (1997). Because IL-6 is a proinflammatory cytokine, its increased production
25 following Pb exposure has the potential to influence many different tissues. Dyatlov et al.
26 (1998a,b) provided evidence that lead, IL-6 and LPS can combine to exert a significant impact
27 on the permeability of the blood brain barrier as well as the properties of brain neurons and
28 endothelial cells. Lead-induced elevation of IL-1(3 production has been reported by Dyatlov and
29 Lawrence (2002). It is probable that enhanced co-production of IL-1P and IL-6 would increase
30 the likelihood of local tissue inflammation.
31
May 2006 5-238 DRAFT-DO NOT QUOTE OR CITE
-------
1 Production of Reactive Oxygen Intermediates (ROIs)
2 Reactive oxygen intermediates (ROIs) are important metabolites in the capacity of
3 macrophages and other inflammatory cells to kill invading bacteria and to attack cancer cells.
4 However, increased overall production or inappropriate triggering of ROI release by
5 macrophages can be a major contributor to tissue damage and the oxidation of cell surface lipids
6 as well as DNA. The latter is one mechanism through which improperly regulated macrophages
7 can actually increase the incidence of cancer. Results from many studies suggest that lead-
8 exposure of macrophages can increase the release of superoxide anion and/or hydrogen peroxide
9 at least shortly after exposure. Key studies are summarized in Table AX5-9.6.
10 In a recent study on environmentally exposed children in Mexico, Pineada-Zavaleta et al.
11 (2004) reported that production of superoxide anion by directly activated (interferon-
12 gamma + LPS) monocytes was directly correlated with blood Pb level. This was in contrast with
13 the effect of arsenic, which had a negative association. In other studies involving low levels of
14 exposures, Zelikoff et al. (1993) demonstrated that rabbits exposed to Pb via inhalation had
15 pulmonary macrophages that produced elevated levels of both H2O2 and superoxide anion upon
16 stimulation in vitro. In an in vitro study, Shabani and Rabani (2000) reported that Pb nitrate
17 exposure produced a dose dependent increase in superoxide anion by rat alveolar macrophages.
18 Baykov et al. (1996) fed BALB/c mice dietary Pb and found that peritoneal macrophages had an
19 increased spontaneous release of H2O2.
20 Other studies have reported no effects of Pb on superoxide anion production when a long
21 recovery period was included following in vivo exposure (Miller et al., 1998) as well as negative
22 effects of Pb on oxidative metabolism by certain macrophages or macrophage cell lines
23 (Castranova et al., 1980; Hilbertz et al., 1986; Chen et al., 1997b). These somewhat different
24 results suggest that the subpopulations of macrophages examined (e.g., alveolar vs. splenic vs.
25 peritoneal) and the timeframe of assessment relative to exposure may be important factors in the
26 effect of Pb on ROI production.
27 The biological importance of increased ROI production by lead-exposed macrophages
28 should not be underestimated. Fernandez-Cabezudo et al. (2003) demonstrated that the potent
29 antioxidant, vitamin E could protect TO strain mice against some lead-induced
30 immunosuppressive alterations. Hence, macrophage-associated oxidative damage following
31 exposure to Pb may be a mitigating factor in nonlymphoid organ lead-induced pathologies.
May 2006 5-239 DRAFT-DO NOT QUOTE OR CITE
-------
1 Arachidonic Acid Content and Prostaglandin Production
2 Archidonic acid (AA) is a major surface component of many cells, including
3 macrophages, and is the precursor of cyclooxygenase and lipoxygenase metabolites. As a result,
4 the specific AA content of membranes and the capacity of macrophages to produce
5 immunomodulatory metabolites from AA are important to overall health of the individual. One
6 of the findings since 1986 concerning lead-induced modulation of macrophage function is the
7 impact of Pb on PGE2 production. One study (Knowles and Donaldson, 1990) reported that diets
8 supplemented with Pb at 500 ppm and fed to chicks produced an increase in the percentage of
9 AA included in cell membranes. Such an increase would be expected to raise the risk of overall
10 inflammation.
11 Several groups have reported that Pb exposure increases macrophage production of the
12 immunosuppressive metabolite PGE2. Lee and Battles (1994) reported that mouse macrophages
13 exposed to Pb (10 jiM) in vitro had elevated basal PGE2 production, but under some stimulatory
14 conditions, had decreased production of PGE2. When Knowles and Donaldson (1997) fed Pb to
15 turkey poults in the diet at a level of 100 ppm, macrophage production of prostaglandin F2
16 (PGF2), PGE2 and thromboxane production were all significantly elevated vs. the control. Flohe
17 et al. (2002) showed that exposure of mouse bone marrow-derived macrophages to Pb-chloride
18 resulted in increased production of PGE2 that correlated with increased mRNA production for the
19 necessary enzyme, prostaglandin H synthase type-2.
20
21 Tissue Homeostasis
22 In an important observation reflecting the impact of lead-induced immunotoxicity on
23 nonlymphoid tissues, Pace et al. (2005) showed that neonatal exposure of mice to Pb-acetate via
24 drinking water (0.1 ppm for 6 weeks, both through maternal nursing and direct) produced a
25 significant reduction in the testicular macrophage population. This correlated with increased
26 estradiol levels in the testis and reduced male reproductive performance. The authors
27 hypothesized that lead-induced alteration among testicular macrophages is linked to an impaired
28 tissue environment that likely includes increased oxidative stress, apoptotic somatic cells, and
29 reduced fertility of males.
30
May 2006 5-240 DRAFT-DO NOT QUOTE OR CITE
-------
1 Colony Formation and Population Distribution
2 The ability of bone marrow-derived macrophages (BMDM) to form colonies in response
3 to certain growth factors (e.g., colony stimulating factor-1 [CSF-1]) is a property related to the
4 growth and differentiation of subsequent macrophage populations. Kowolenko et al. (1991)
5 found that exposure to CBA/J female mice to Pb-acetate (0.4 mM in drinking water for 2 weeks)
6 reduced colony formation of macrophages in response to CSF-1. Infection of the mice with
7 Listeria only exacerbated this effect of lead. The same authors (Kowolenko et al., 1989) had
8 previously demonstrated that when BMDM were cultured in vitro with Pb-chloride (0.1 |iM),
9 colony formation was significantly impaired. These combined results suggest that exposure to
10 Pb can impair the generation of macrophage populations as well as modulate the functional
11 spectrum of fully matured macrophages. Bunn et al. (200la) reported that gestational exposure
12 of CD rats to 50 ppm Pb-acetate via the drinking water of the dams resulted in female adult
13 offspring with a significantly decreased percentage (58% reduced) of circulating monocytes.
14 A 100-ppm dose of Pb-acetate produced a significant reduction (74% reduced) in the absolute
15 numbers of monocytes as well. The blood lead level at birth associated with the decreased
16 percentage of macrophages in the adult offspring was 8.2 |ig/dL. In general agreement, Lee
17 et al. (2002) reported a significant decrease in the absolute numbers of circulating monocytes and
18 polymorphonuclear leukocytes (PMNs) in juvenile female chickens exposed in ovo on
19 embryonic day (E) 12 to 200 jig Pb-acetate. The corresponding blood lead level at hatching was
20 11.0 |ig/dL. However, in this case, the lead-induced reduction in monocytes and PMNs was only
21 seen in concert with an airway viral infection (viral stressor) and not in the resting uninfected
22 animal.
23
24 Antigen Presentation and Lymphoid Stimulation
25 Exposure to Pb influences the interaction between macrophages and T lymphocytes, and
26 as a result, the capacity of macrophages to support T lymphocyte proliferation and activation can
27 be altered as well. Kowolenko et al. (1988) found that mouse macrophages exposed to Pb
28 (both in vivo and in vitro) can induce an increased proliferative response of T lymphocytes in co-
29 culture but that antigen-specific stimulation of primed T cells is significantly reduced. Lead-
30 suppressed antigen presentation capabilities of mouse macrophages were also reported by both
31 Smith and Lawrence (1988) and Blakley and Archer (1981).
May 2006 5-241 DRAFT-DO NOT QUOTE OR CITE
-------
1 Chemotaxis
2 Chemotactic activity of macrophages is an important function required for the directed
3 migration of macrophages to sites of infection and tumor growth. However, it is a functional
4 capacity that has not been systematically examined within the lead-immune literature. Using
5 female Moen-Chase guinea pigs, Kiremidjian-Schumacher et al. (1981) showed that Pb chloride
6 exposure of peritoneal macrophages in vitro (10-6 jiM) inhibited the electrophoretic mobility of
7 the cells.
8
9 Phagocytosis and Clearance of Particles
10 Phagocytosis of targets and removal/clearance of dead cells and particles are major
11 functions of macrophages. However, phagocytosis can involve a variety of different cell surface
12 receptors on macrophages, depending upon both the nature of the target encountered and the
13 subpopulation of macrophages examined. In general, phagocytic capacity of macrophages seems
14 to be relatively insensitive to lead-induced immunomodulation compared with the effects on NO
15 and TNF-a production.
16 However, differences in outcome in phagocytosis evaluations are likely to be based on the
17 differences in the source of macrophages used and their relative activation state at the time of
18 assessment. A few studies have described significant effects on phagocytosis, but these have
19 usually relied upon phagocytosis mediated through the Fc receptor on macrophages. Because
20 cell adherence to surfaces may be influenced negatively by Pb (Sengupta and Bishali, 2002),
21 impairment of phagocytosis may also involve some lack in efficiency with macrophage
22 anchoring to substrates. De Guise et al. (2000) reported no effect on bovine macrophage
23 phagocytosis of latex beads by Pb at in vitro treatment concentration of 104 M. This was in
24 contrast with suppressive effects of both cadmium and mercury. Using Sephadex-elicited
25 peritoneal macrophages derived from young turkeys fed 100 ppm Pb in the diet, Knowles and
26 Donaldson (1997) found a 50% reduction in the percentage of phagocytic macrophages using
27 SRBC targets. The activity per phagocytic macrophage was also reduced.
28 Kowolenko et al. (1988) studied the effect of Pb-acetate at 10 mM in the drinking water of
29 CBA/J mice. They reported no effect on phagocytosis ofListeria monocytogenes targets, yet
30 they found an overall decreased resistance to Listeria. When the same investigators exposed
31 peritoneal and splenic macrophages to Pb in vitro (100 |iM), they also found no significant effect
May 2006 5-242 DRAFT-DO NOT QUOTE OR CITE
-------
1 of Pb on phagocytic activity. Jian et al. (1985) reported that New Zealand white rabbit-derived
2 alveolar macrophages exposed to Pb in vitro at 10"5 M concentration were significantly impaired
3 in the phagocytosis of opsonized chicken erythrocytes (Fc receptor-mediated phagocytosis).
4 Trejo et al. (1972) reported that a single i.v. injection of Pb (5 mg/rat) into male Sprague Dawley
5 (SD) strain rats produced an inhibition in the phagocytic capacity of Kupffer cells.
6 Several studies have reported a decreased clearance capacity of the reticuloendothelial
7 system following in vivo exposure to lead. Filkins and Buchanan (1973) found that injection of
8 5 mg of Pb-acetate i.v. into male Holtzman strain rats produced reduced carbon clearance.
9 Similarly, Trejo et al. (1972) reported that a single i.v. injection of Pb (2.5 mg) into male SD
10 strain rats significantly reduced clearance of colloidal carbon.
11 In contrast, Schlick and Friedberg (1981) found that 20 |ig/kg Pb-acetate in a single i.p.
12 injection of NMRI strain mice significantly increased the clearance of India ink. Ironically, oral
13 administration of Pb for 10, but not 30, days of 10 |ig/kg resulted in an increase in clearance
14 activity. Difference in route of Pb administration may be a factor in the different results
15 obtained.
16
17 Induction of Heat Shock Proteins
18 One study (Miller and Qureshi, 1992), using a macrophage cell line, reported that
19 exposure of macrophages (MQ-NCSU) in culture to Pb-acetate (1000 jiM) induced the same set
20 of four heat shock proteins as when the macrophages were subjected to thermal stress. This
21 result fits the hypothesis that Pb produces a profound immunomodulatory effect in macrophages
22 that has similarities with the exposure of macrophages to certain pathogens.
23
24 Apoptosis
25 Significant differences exist in the literature concerning the potential role of Pb in the
26 apoptosis of macrophages. The difference may be based on the exposure methodologies (in vivo
27 vs. in vitro) as well as the source of macrophages utilized. De la Fuente et al. (2002) found that
28 human monocytes exposed to Pb in vitro at high concentrations did not undergo apoptosis. This
29 was in direct contrast with the apoptosis-promoting effects of cadmium in the same assessment
30 protocol. In contrast, Shabani and Rabibani (2000) exposed rat alveolar macrophage to Pb
May 2006 5-243 DRAFT-DO NOT QUOTE OR CITE
-------
1 nitrate in vitro and found that 60 jiM concentration produced a significant increase (2x) in DNA
2 fragmentation after 3 to 24 h in culture.
3
4 5.9.7 Granulocytes and Natural Killer (NK) Cells
5 Other cell types important in innate immunity, as well as in immunoregulation, are the
6 lymphoid population of natural killer cells and granulocytes, including PMNs (i.e., neutrophils).
7 Neither population appears to be a major target for lead-induced immunotoxicity, although both
8 may be influenced indirectly via immune cell-cell interactions as well as by changes in cytokine
9 production. Among the two, neutrophils may be the more sensitive cell type based on assays
10 conducted to date. For neutrophils, several groups have reported alteration in chemotactic
11 activity following exposure to lead. Queiroz et al. (1993) found impaired migration ability of
12 neutrophils from battery workers occupationally exposed to lead. Likewise, Valentino et al.
13 (1991) had a similar observation among male occupationally exposed workers. Lead exposure of
14 young SD strain rats can increase the population of neutrophils (Villagra et al., 1997), although,
15 as the authors indicated, this does not necessarily afford enhanced host protection against
16 disease. Baginski and Grube (1991) reported that human neutrophils exposed to Pb had
17 increased killing capacity, probably via increased release of ROIs despite having reduced
18 phagocytic capacity. This would fit the same general profile as the effects of Pb on
19 macrophages. Therefore, neutrophils may contribute to lead-induced tissue inflammation and
20 damage via increased ROI release. Yet, their effectiveness in protection against disease
21 challenge may be no greater following exposure to Pb, because some impairment in chemotaxis
22 and phagocytosis has been reported as well.
23 Yucesoy et al. (1997) reported that either Pb exposure or simultaneous exposure to Pb and
24 cadmium in human workers did not impair NK cytotoxicity activity. This finding was supported
25 by studies using in vivo exposure to Pb in rats (Kimber et al., 1986) and mice (Neilan et al.,
26 1983). Therefore, it would appear that NK cells are not a prime target associated with lead-
27 induced immunotoxicity, although more subtle effects may certainly exist within the cell type.
28 Eosinophils represent an important granulocytic cell type in type 2 associated
29 inflammatory and allergic reactions. However, few studies have examined Pb exposure and
30 eosinophil activity. Villagra et al. (1997) reported that exposure of female juvenile SD rats to Pb
31 [four alternate-day s.c. injections of 172 mg/g body wt Pb-acetate] increased the degranulation of
May 2006 5-244 DRAFT-DO NOT QUOTE OR CITE
-------
1 eosinophils (in animals given estrogen 1 day later). Such a response would be expected to
2 contribute to increased inflammation.
3
4 5.9.8 Hypersensitivity and Autoimmunity
5 At the time of preparation of the 1986 AQCD, little was known about the potential for Pb
6 to influence the risk of allergic and autoimmune diseases. However, since the early 1990s, a
7 significant number of studies have all pointed toward the fact that Pb causes a profound
8 dysregulation of the immune system. It skews the balance of responses in directions that reduce
9 certain host defenses against infectious diseases while enhancing the risk of allergic and
10 autoimmune disease. Lead exposure at low to moderate levels appears to alter T lymphocyte
11 responses in such a way as to increase the risk of atopy, asthma, and some forms of
12 autoimmunity. Increased IgE production following exposure to Pb is among the most frequently
13 reported immune alterations. Elevated IgE levels would be an associated risk factor for atopy
14 and allergic disease. Several investigators have discussed the fact that Pb is a likely risk factor
15 associated with the increased incidence of childhood allergic asthma (Miller et al., 1998; Heo
16 et al., 1998; Snyder et al., 2000; McCabe et al., 2001; Dietert et al., 2004; Trasande and
17 Thurston, 2005) as well as later life allergic disease (Heo et al., 2004; Carey et al., 2006). Joseph
18 et al. (2005) observed no association for childhood BLL and risk of asthma among an African-
19 American population. However, results on other populations from this study, including those
20 involving Caucasian children with BLLs above 5 |ig/dL, led the authors to call for further studies
21 into the possible linkage of early life lead exposure and risk of asthma (Joseph et al., 2005).
22 As described by McCabe et al. (1991) and discussed by Dietert et al. (2004), lead-induced
23 immunotoxicity is novel in that profound cellular toxicity is not evident following exposure at
24 low to moderate exposure concentrations. In fact, antibody responses overall are usually
25 unaffected or may be increased depending upon the class/isotype measured. However, the
26 functional responses mounted following Pb exposure do not reflect the normal immune balance
27 that would otherwise occur. This dysregulation can alter the risk of certain autoimmune diseases
28 based on several observations. Holladay (1999) has considered the importance of the timing of
29 exposure and the fact that early life exposure may establish the immune profile that then
30 contributes to later disease including autoimmunity.
May 2006 5-245 DRAFT-DO NOT QUOTE OR CITE
-------
1 Hudson et al. (2003) reported that exposure to Pb can exacerbate systemic lupus
2 erythmatosus (SLE) in lupus-prone strains of mice. In contrast with the effect of mercury, these
3 authors found that for lupus, Pb exposure would not induce this autoimmune condition in
4 genetically resistant mice but would increase severity of the disease in genetically prone animals.
5 The authors noted some gender effects within certain strains (e.g., NZM88). Using early in ovo
6 exposure to Pb (10 jig/egg), Bunn et al. (2000) found that Pb-acetate-exposed male chicks could
7 be induced to produce autoantibodies against thyroglobulin, which were not present in acetate-
8 exposed controls. No lead-induced alteration was observed in females that were predisposed to
9 mount anti-thyroglobulin responses. The gender effect is intriguing in that autoimmune
10 thyroiditis in genetically predisposed strains is always more severe in females than in males.
11 Two lines of evidence suggest that the capacity of Pb to influence the risk of
12 autoimmunity is not always associated with simply a strict shift from Thl to Th2 responses.
13 Hudson et al. (2003) discussed the fact that lupus is not purely a Th2-mediated disease, but rather
14 seems to occur under conditions associated with skewing in either direction. McCabe et al.
15 (2001) found that Pb can increase the stimulation of alloantigen reactive T cells (where
16 macrophage processing of antigen is required) but not enhancement of T cell clonotypic
17 responses against either mitogens or superantigens (where processing is not required). This
18 suggests that the role of Pb in influencing risk of autoimmune disease goes beyond a simple
19 consideration of Thl/Th2 balance. In fact, Goebel et al. (2000), studying mucosal immunity,
20 reported that administration of Pb-chloride to NOD strain mice produced a gut cytokine
21 microenvironment that was skewed toward Th2 over the short run, but later was shifted toward
22 Thl with increased production of IFN-y. This shift to Thl was accompanied by a loss of
23 tolerance and capacity to mount an immune response against a diet-associated protein (chicken
24 ovalbumin). The authors proposed that reduction of the capacity for oral tolerance would
25 predispose an individual toward autoimmune disease. The findings of Carey et al. (2006) had
26 similar implications. These authors reported that exposure of mice to Pb chloride increased
27 activation of neo-antigen-specific T cells, thereby increasing the risk of autoimmunity.
28 Finally, Waterman et al. (1994) and El-Fawal et al. (1999) have described the production
29 of autoantibodies against neural proteins in both battery workers and rats exposed to low levels
30 of Pb via drinking water. These authors have suggested that exposure to Pb may precipitate the
31 autoimmunity by altering antigen immunogenicity and/or the capacity of the immune system to
May 2006 5-246 DRAFT-DO NOT QUOTE OR CITE
-------
1 respond to certain antigens. This, in turn, may contribute to the eventual lead-associated
2 neurological disease.
3
4 5.9.9 Mechanism of Lead-Based Immunomodulation
5 In the 1986 AQCD, there was little direct information available about the immune system
6 regarding the molecular mechanism(s) of lead-induced immunotoxicity. Binding to thiol groups
7 and altering cell surface receptors were indicated as possible factors in altered immune function.
8 Since that time, some additional information has been generated through a variety of studies on
9 human and animal immune cells. However, a clear or simple explanation remains to be
10 determined. Table 5-9.3 lists studies on the immune system that have contributed to a better
11 understanding of potential mechanisms or have forwarded potential hypotheses with some
12 supporting data.
13 At the level of cell-cell interactions, it seems clear that Pb alters metabolism and cytokine
14 production by macrophages and antigen presenting cells. It also reduces their capacity to
15 respond to growth factors such as CSF-1 (Kowolenko et al., 1989). Pace et al. (2005) discussed
16 the hypothesis that reduced populations of functionally altered macrophages (because of lead-
17 induced unresponsiveness to CSF-1 and over production of ROIs) in tissues can produce
18 nonimmune problems. The model they used is the homeostatic presence of testicular
19 macrophages and the likelihood that lead-induced macrophage immunotoxicity contributes
20 directly to lead-associated reduction in male fertility.
21 Additionally, Pb is known to selectively alter cell signaling to CD4+ T cell
22 subpopulations, promoting proliferation in some but not others. The outcome is enhanced tissue
23 inflammation, reduced CMI, and increased production of atopy-inducing antibodies. Risk of
24 autoimmune reactions is increased in some models of lead-induced immunotoxicity. For
25 example, Heo et al. (1997) reported that lead-exposed murine T lymphocytes are biased in
26 expression of VP genes. This is potentially problematic as this phenotype is common among a
27 variety of human and animal model autoimmune conditions. A variety of exogenous factors has
28 been reported to partially ameliorate the immunotoxic effects of lead. Chelation of Pb in lead-
29 exposed dams corrected some lead-induced immunotoxic problems in the rat female offspring,
30 but it left the animals with some DMSA-induced immune alterations (Chen et al., 1999). Other
31 exogenously administered factors that have been reported to partially restore lead-suppressed
May 2006 5-247 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-9.3. Suggested Mechanisms of Lead-Induced Immunotoxicity
Species
Mouse
Mouse
Chicken
Mouse
Mouse
Rat
Mouse
Mouse
Human
Mouse
Mouse
Strain/Gender
Balb/c
TO strain males
Cornell K Strain
Balb/c females
C57 Bl/6
females
C 57B1/6
PC-12 cells
DO11. 10 ova-
mice
DOll.lOova-tg
mice
-
CBA/J females
Swiss Females
Suggested
Endpoints
CSF-1
Responsiveness of
Macrophages
Vitamin E
protection against
lead-induced
splenomegaly
Thymulin partial
reversal of Th
skewing
Lead disruption of
antigen
processing and
presentation
signals
PKC activation
NF-KB activation
AP-1 induction
C-Jun kinase
induction
Adenylcyclase
activation with
elevated cAMP
levels
V(3 gene usage
NF-KB activation
in CD4+ cells
t Immunogenicity
of neural proteins
tTNF-a
production
Associated
Functional
Alteration
ITesticular
macrophages
^Fertility
tPutative ROI
associated
splenomegaly
ILead-induced
DTH
suppression
tAlloreactive
CD4+ hlgh cells
tRisk of
autoimmunity
tTNF-a, tIL-6
tPGE2
tROI
tTh skewing
tRisk of
autoimmunity
tRisk of
autoimmunity
and
hypersensitivity
t Autoimmune
mediated
neurological
damage
t Sensitivity to
endotoxin
Lowest
Effective
Dose
0.1 ppm
Img/kg
400 jig
0.5 |jM in
vitro
20|jM in
vitro
1 |jMin
vitro
2.5 |jM in
vitro
50 ng
2x/week
s.c.
IpM
Lead-
altered
proteins
used as
antigens
5mg
Duration
6 weeks
2 weeks
Single in
ovo
injection
4 days
4.5 hrs
5-120 min
15 mins-
6 hrs
8 weeks
30 min
3 injections
of lead-
modified
neural
proteins
Single i.p.
injection
References
Pace et al.
(2005)
Fernandez-
Cabezudo
et al. (2003)
Lee and
Dietert,
(2003)
McCabe
etal. (2001)
Flohe et al.
(2002)
Ramesh
etal. (1999)
Heo et al.
(1998)
Heo et al.
(1997)
Pyatt et al.
(1996)
Waterman,
etal. (1994)
Dentener
etal. (1989)
May 2006
5-248
DRAFT-DO NOT QUOTE OR CITE
-------
1 immune function are vitamin E (Fernandez-Carbezudo et al., 2003) and thymulin (Lee and
2 Dietert, 2003).
3 At the subcellular level, the bases for immunotoxic changes remain speculative. McCabe
4 et al. (2001) suggested that altered antigen processing and subsequent cell signaling to T cells
5 may be an explanation for the capacity of Pb to selectively increase CD4+ (high density) cells.
6 Certainly, Pb appears to alter signal transduction. It appears to elevate expression of the nuclear
7 transcription factor NF-KB (Pyatt et al., 1996; Ramesh et al., 1999) as well as increase
8 expression of AP-1 and cJun (Ramesh et al., 1999). Flohe et al. (2002) found evidence that Pb
9 can elevate the activation of PKC. The authors speculated that this might be involved in lead-
10 induced increases in TNF-a production. Additionally, Heo et al. (1998) reported that Pb
11 increases adenyl cyclase activity among T lymphocytes, generating elevated cAMP levels.
12 The authors hypothesized that this effect, in conjunction with differences in cell signaling
13 pathways for promoting Thl vs. Th2 cells, may be involved in the capacity of Pb to skew
14 ThO helper cell s toward Th2.
15
16 5.9.10 Age-Based Differences in Sensitivity
17 With the literature available at the time of the 1986 AQCD, it was virtually impossible to
18 evaluate age-based differences in susceptibility to lead-induced immunotoxicity. However, in
19 recent years, this has become a major topic of study for many toxicants including lead (Dietert
20 and Piependrink, 2006). Several studies have added to the available data assessing the
21 developmental immunotoxicity of Pb (reviewed in Barnett [1996], Dietert et al. [2000, 2004],
22 Lee and Dietert [2003]). Several patterns have emerged from exposure data using animals of
23 different ages.
24 First, it seems clear that blood Pb levels at or near birth of below 10 |ig/dL can be
25 associated with juvenile and/or adult immunotoxicity. Several studies reported effects in the
26 range of 5-8 |ig/dL. These low levels would seem to place the immune system on par with the
27 neurological system in terms of potential sensitivity to lead. Table 5-9.4 shows examples of
28 studies in which low blood lead levels were linked with immunotoxicity.
29 A second finding is that the immunotoxic effects induced by Pb are persistent long after
30 blood levels and potential body burdens of Pb are significantly reduced. Miller et al. (1998),
31 Chen et al. (1999), Snyder et al. (2000), and Lee et al. (2001) all emphasize this latter point.
May 2006 5-249 DRAFT-DO NOT QUOTE OR CITE
-------
Table 5-9.4. Immunomodulation Associated with Low Blood Lead Levels
in Animals
Species
Mouse
Rat
Rat
Rat
Chicken
Chicken
Chicken
Blood lead
Oig/dL)
-5.0
8.2
6.75
8.0
8.2
11.0
7.0
Age at
Measurement
1 week
1 day
4 weeks
4 weeks
1 day
1 day
1 day
Immune Parameter(s)
tlgE,
4 Splenic
T Cell Populations
Imonocytes
4DTH,
lIFN-y,
tIL-4
tTNF-a
tRel. Spleen weight
^circulating lymphocytes post
infection
4DTH and 4TLC, monocytes,
PMNs post infection
tautoantibody production
Age at
Assessment
2 weeks
13 weeks
13 weeks
13 weeks
5 weeks
5 weeks
10 weeks
Reference
Snyder et al.
(2000)
Bunn et al.
(200 la)
Chen et al. (2004)
Lee et al. (2002)
Lee et al. (2002)
Lee etal. (2001)
Bunn et al. (2000)
1 In fact, in most of these studies immunotoxic alterations were present when Pb levels in exposed
2 animals were not distinguishable from control levels. This should provide a cautionary note
3 regarding studies in humans. Data from adult exposures provides little insight into the potential
4 persistence following adult exposure to lead. However, rather than the developing immune
5 system being more regenerative postexposure and able to withstand immunotoxic insult, it
6 appears that the non-dispersed developing immune system is a particularly susceptible target to
7 many immunotoxicants (Dietert et al., 2002).
8 A third, and somewhat surprising, finding concerning early exposure to Pb is that
9 qualitative differences in the spectrum of immune alterations can exist, depending upon the
10 developmental window of exposure. Figure 5-9.1 illustrates this point. Early embryonic
11 exposure of rats and chickens to Pb failed to alter juvenile DTK responses, despite significant
12 effects on macrophage function. However, exposure to Pb after the mid-embryonic point of
13 embryonic development readily suppressed subsequent DTH. As shown in Figure 5-9.1, the
14 development window in which sensitivity to DTH suppression emerges is quite similar in the
15 two species. This observation suggests that both quantitative (LOAELs) and qualitative (range
16 of immune alterations) differences in sensitivity to Pb can exist across different age groups.
May 2006
5-250
DRAFT-DO NOT QUOTE OR CITE
-------
1 Additionally, some studies in animals have noted gender differences in the effects of Pb
2 following exposure (Bunn et al., 2000, 2001a,b, c; Hudson et al., 2003). Gender differences
3 have also extended to results in humans as per lead-induced immune and inflammatory
4 alterations (Karmaus et al., 2005; Fortoul et al., 2005). It seems feasible that, even in the
5 embryo, hormonal differences among females and males may impact some outcomes of low-
6 level Pb exposure.
7 Table 5-9.5 shows comparisons of the lowest reported blood Pb levels at different ages
8 associated with the same immunotoxic endpoint. From these limited comparisons, it would
9 appear that different ages of rodents (e.g., embryonic vs. adult) differ in dose sensitivity for lead-
10 induced immunotoxicity somewhere in the range of 3 to 12-fold. Clearly, additional direct
11 comparisons would help to refine this estimate.
Table 5-9.5. Comparisons of Age-Based Sensitivity to Lead-Induced Immunotoxicity
Species Altered Endpoint
Embryo - fetal* Neonatal* Adult*
References
Mouse tlgE
Rat 4DTH
(persistent effect assessed
13 weeks post-exposure)
Mouse 4DTH
Rat tTNF - a
(persistent effect assessed
13 weeks post-exposure)
12
38
34 |^g/dL
Snyder et al.
(2000)
Heo etal. (1996)
Miller et al.
(1998)
(measured at birth
for persistent Bunn et al
effect)
29 ng/dL 87 ng/dL
8 ng/dL
(200 Ib)
Faith etal. (1979)
McCabe et al.
(1999)
Miller et al.
J , . , (1998)
(measured at birth
for persistent Chen et al. (2004)
effect)
*Lowest blood lead concentration reported with effect.
12 A fourth observation from the early exposure studies is that exposure to even very low
13 levels of Pb can predispose the immune system for unanticipated postnatal responses when the
14 system is stressed. This general phenomenon is called latency. Lee et al. (2002) provided an
May 2006
5-251
DRAFT-DO NOT QUOTE OR CITE
-------
1 example of this following the single in ovo exposure of embryonic day 5 chick embryos to low
2 levels of Pb (10 jig; blood lead level 1 day post hatch of 8.2 |ig/dL). The leukocyte profiles of
3 the animals appeared to be completely normal. However, when these animals were exposed to a
4 respiratory virus, their pattern of leukocyte mobilization was completely aberrant from controls.
5 Therefore, some immunotoxic alterations following early exposure to low levels of Pb may only
6 be evident during periods of postnatal stress.
7 Several studies have reported the positive association of blood Pb levels in children
8 with elevated serum IgE (Karmaus et al., 2005; Sun et al., 2003; Lutz et al., 1999). These
9 observations are supported by the animal data in rats and mice (Miller et al., 1998; Snyder et al.,
10 2000) and suggest that lead-induced risk of atopy and asthma may be a particular health issue.
11 Trasande et al. (2005) recently discussed the fact that, despite progress in reducing the
12 deposition of Pb in the environment, Pb continues to be a concern relative to asthma and
13 children's health.
14
15 Summary
16 The immune system appears to be one of the more sensitive systems to the toxic effects of
17 lead. The 1986 AQCD provided an excellent summary of the studies that had been conducted
18 prior to that date. But knowledge of fundamental immunology has progressed greatly during the
19 past 20 years. Not surprisingly, the large number of studies conducted since the mid-1980s
20 provided a much clearer understanding of the immune-associated problems that can arise from
21 problematic exposure to lead. Studies across humans and a variety of animal models are in
22 general agreement concerning both the nature of the immunotoxicity induced by Pb as well as
23 the exposure conditions that are required to produce immunomodulation. Figure 5-9.2
24 summarizes the basic immunotoxic changes induced by Pb that result in Th skewing, impaired
25 macrophage function, and increased risk of inflammation-associated tissue damage.
26 Lead is unlike many immunotoxicants in that, at low to moderate levels of exposure, it
27 does not produce overt cellular cytotoxicity or lymphoid organ pathology. However, it can
28 induce profound functional alterations that influence risk of disease. Lead preferentially targets
29 macrophages and T lymphocytes, although effects have been reported in B cells and neutrophils
30 as well. There are three major hallmarks of lead-induced immunotoxicity. First, Pb can
May 2006 5-252 DRAFT-DO NOT QUOTE OR CITE
-------
Key Effects of Lead on the Immune System
Inflammatory Tissue
Macrophages, Macrophages and Antigen
Presenting Cells
Membrane
Arachidonic
Acid
Ac tn? ab on
Effects on Anfagen
Processing
Presentation
T cells
Thl
INF-?
Reduced Cell -
mediated
Immunity
B cells
Cell Surface
Q ass II
Host Proteins
I
Modified Neural Antigens
Auto-antibodies and
Possible Tissue
Damage
Inert asedTissue Inflammation
Reduced Cell-mediated Immunity
!gE | & Increased Risk of
Atopy and Asthma
Figure 5-9.2. This figure shows the fundamental alterations to the immune system and to
immunological response and recognition induced by exposure to lead. The
functional shifts are disproportionate compared to the relatively modest
changes among leukocytes with low to moderate exposure to lead.
1 dramatically suppress the Thl-dependent DTK response, as well as production of associated
2 Thl cytokines. Second, Pb can dramatically elevate production of IgE while increasing
3 production of Th2 cytokines, such as IL-4. Third, and perhaps most sensitive, is the modulation
4 of macrophages by Pb into a hyperinflammatory phenotype. After exposure to lead,
5 macrophages significantly increase production of the proinflammatory cytokines TNF-a and
6 IL-6 (and in some studies IL-1). Many studies also reported elevated release of ROIs and
7 prostaglandins. Ironically, production of one of the most important host defense factors, NO,
May 2006
5-253
DRAFT-DO NOT QUOTE OR CITE
-------
1 is consistently and severely suppressed by exposure to lead. This package of lead-induced
2 changes among macrophages makes them more prone to promote tissue destruction but actually
3 less capable of killing bacteria or possibly presenting antigens to T lymphocytes. The
4 Pb-induced shift in phenotype explains the capacity of inhaled Pb to promote bronchial
5 inflammation while bacterial resistance is severely depressed.
6 Lead-induced skewing of Th activity (biasing responses toward Th2) across a population
7 argues for the expectation of a greater risk of atopy, asthma, and some forms of autoimmunity.
8 Concomitantly, resistance to some infectious diseases could be reduced. This predicted change
9 of risk might help explain some recent trends in the incidence of diseases, such as the epidemic
10 rise in allergy and some forms of asthma in the United States.
11 Sensitivity of the immune system to Pb appears to differ across life stages. Studies in rats
12 and mice suggest that the gestation period is the most sensitive life stage followed by the early
13 neonatal stage. But even during embryonic, fetal, and early neonatal development, critical
14 windows of vulnerability are likely to exist. Compared to adults, the increased dose sensitivity
15 of the embryo-fetus would appear to fall in the range of 3-1 Ox depending upon the immune
16 endpoint considered. Some studies have found evidence for gender differences in the impact of
17 Pb on the immune system particularly with early life exposures. Potential gender differences in
18 immunotoxic outcome may be important in the evaluation of those populations at greatest risk.
19 Recent studies have suggested that exposure of embryos to Pb producing neonatal blood
20 lead concentrations below 10 |ig/dL can also produce later-life immunotoxicity (see
21 Table 5-9.4). Furthermore, immunotoxicity persists long after any evidence of prior embryonic
22 Pb exposure. This latter observation from several laboratories may have implications for the
23 design of human epidemiological studies.
24
25
26 5.10 EFFECTS OF LEAD ON OTHER ORGAN SYSTEMS
27 In the 1986 Pb AQCD, the discussion of other organ systems included cardiovascular,
28 hepatic, gastrointestinal (GI), and endocrine systems. Due to our increased understanding on the
29 effects of Pb on cardiovascular and renal systems and their contribution to potential health
30 effects of Pb, separate sections (5.5, 5.7) were dedicated earlier in this chapter to detailed
31 discussions on these aspects. Similarly, with our increased understanding on the effects of Pb on
May 2006 5-254 DRAFT-DO NOT QUOTE OR CITE
-------
1 endocrine functions and its inherent role with respect to neurotoxicological, reproductive, and
2 developmental effects, literature reviewed for Pb effects on the endocrine system is discussed in
3 the respective sections. This section focuses on the discussion of Pb effects on the hepatic and
4 GI systems.
5
6 5.10.1 Effects of Lead on the Hepatic System
7 The liver is a highly active metabolic tissue. Apart from its roles in fatty acid metabolism
8 and limited heme synthesis function, the liver also has a major role in guarding other systems
9 from the toxic effects of xenobiotic compounds using a huge complement of detoxification
10 machinery referred to as phase I and phase II enzyme systems. Limited studies on experimental
11 animals reported in the 1986 Pb AQCD indicated that Pb induced effects in the hepatic system.
12 Laboratory animals, especially rats, exposed to Pb-nitrate have exhibited increased liver cell
13 proliferation, DNA synthesis, cholesterol synthesis, and glucose -6-phosphate dehydrogenase
14 (G6PD) activity indicative of Pb-induced hyperplasia. Further, the literature reviewed in the
15 1986 Pb AQCD reported alterations in the levels of drug metabolizing enzymes in experimental
16 animals given large doses of Pb. The evidence for such effects in humans was less consistent.
17 The 1986 document also concluded that the effects on the liver occurred only at high exposure
18 levels. The majority of studies on the effects of Pb on the hepatic system in experimental
19 animals that are reviewed in this document report functional and biochemical changes in the
20 liver, clearly pointing to metabolic perturbations in liver. For ease in understanding and
21 integration of these functional changes, the discussion is divided into the following four
22 subsections: hepatic drug metabolism, lipid and glycogen metabolism and lipid peroxidation, and
23 heme synthesis.
24 5.10.1.1 Hepatic Drug Metabolism
25 Approximately 75% of the hepatic blood comes directly from the gastrointestinal viscera,
26 with the majority of drugs or xenobiotics absorbed coming directly to the liver in concentrated
27 form. The liver is equipped with a huge complement of drug metabolizing enzymes that detoxify
28 many of the xenobiotics but also activate the toxicity of others. Oxidation and conjugation of
29 xenobiotics have historically been referred to as phase I and phase II reactions. The phase I
30 enzymes include cytochrome P450 (CYP450) heme-containing monoxygenases, flavin-
May 2006 5-255 DRAFT-DO NOT QUOTE OR CITE
-------
1 containing monoxygenases, and epoxide hydrolases. The phase II enzymes include glutathione
2 (GSH) S-transferases (GST), UDP-glucuronyl transferases (UGT), N-acetyltransferases (NAT),
3 and sulfotransferases (SULT). Xenobiotic metabolism by these two complements of enzyme
4 systems are essential for catabolizing and eliminating of drugs; however, this process can also
5 produce activated toxicants and carcinogens. A limited number of these CYP450s are involved
6 in the biosynthetic pathways of steroid and bile acid production. It has been increasingly
7 recognized that, under certain circumstances, CYP P450s can produce ROS that result in
8 oxidative stress and cell death.
9 Liver is an active tissue. In addition to xenobiotic metabolism, it also participates in
10 gluconeogenesis, fatty acid metabolism, and cholesterol biosynthesis. Research concerning the
11 effects of Pb on the hepatic system in the past 15 years has provided some preliminary
12 indications of Pb-induced alterations in many of the hepatic functions described above. The
13 following discussion presents, as much as possible, the effects of Pb on individual enzymes, but
14 due to the multifarious interactions of many of these metabolic enzymes, there may be places
15 such separation was not possible.
16
17 Phase I Enzyme
18 Earlier studies on the toxic effects of Pb on hepatic drug metabolizing enzymes
19 demonstrated that acute exposure to Pb-acetate decreased rat hepatic CYP450s with increased
20 levels of urinary 5-aminolevulinic acid (ALA). Co-treatment with phenobarbitol, a CYP450
21 inducer, was shown to reverse the decrease CYP450 levels, suggesting a Pb-acetate-mediated
22 inhibition of heme synthetic enzymes. Decreased activities of estradiol-17 beta enzyme
23 observed in rat liver treated with triethyl Pb-chloride (Odenbro and Arhenius, 1984) suggest that
24 both Pb and organo-Pb compounds are capable of inhibiting CYP450 activities. Roomi et al.
25 (1986) also observed decreased levels of hepatic microsomal CYP450s and decreased
26 aminopyrene-N-demethylase activity on exposure to a single dose of Pb-nitrate (5-10 mmol/kg
27 body wt). This decrease in phase I enzymes was followed by increased levels of phase II
28 components such as GSH, GST, and DT diaphorase, suggesting that Pb-nitrate and Pb
29 compounds can induce biochemical properties characteristic of hepatocyte nodules. Subchronic
30 (2-3 months) exposure to Pb-acetate (5-50 mg/kg body wt) had been found to induce CYP450s
May 2006 5-256 DRAFT-DO NOT QUOTE OR CITE
-------
1 and cytochrome b5 in rat liver and kidney (Nehru and Kaushal, 1992). As described earlier,
2 multiple isoforms of CYP450s exist in the liver.
3 To identify the inhibitory effect of acute Pb exposure on specific isoform(s), Degawa
4 et al. (1994) exposed male F344 rats to Pb nitrate (20,100 jimol/kg body wt) and evaluated liver
5 CYP450s 24 h postexposure. Lead-nitrate exposure preferentially inhibited cytochrome
6 P4501A2 enzyme activity in liver microsomal preparations as assayed for mutagenic conversion
7 of substrates 2-amino-6-methyl-dipyridol [1,2-a; 3',2-d] imidazole and 3-amino-l-methyl-5H-
8 pyridol [4,3,-b] indole. Lead-nitrate exposure also inhibited the induction of cytochrome
9 P4501A2 by the inducers 3-methylcholanthrene and 2-methoxy-4-aminoazobenzene at both the
10 protein and mRNA levels. The authors further concluded that the specific inhibition of P4501A2
11 by Pb-nitrate observed may have been due to inhibition of heme synthesis, as Pb-nitrate was not
12 found to inhibit P4501A2 activity in vitro. Additional studies carried out by the same group
13 using various metal ions (e.g., Pb, Ni, Co, and Cd) found that the specific inhibition of P4501A2
14 was unique to Pb-nitrate (Degawa et al., 1994, 1995). Degawa et al. (1996) also investigated the
15 effect of Pb-nitrate-mediated inhibition of CYP1A gene activity in rat liver by specific inducers
16 and reported that Pb-nitrate inhibited the induction of CYP1A mRNA by aromatic amines, but
17 not by aryl hydrocarbons, suggesting the role of other cellular factors in the transcriptional
18 activation of CYP1A genes. Lead-nitrate has been reported to induce the production of TNF-a
19 in rat liver (Shinozuka et al., 1994), a cytokine implicated in the suppression of constitutive
20 expression of CYP1A2 mRNA in rat hepatocytes. Based on these findings, Degawa et al. (1996)
21 concluded that the inhibition of constitutive and aromatic amine-induced expression of CYP1A2
22 in rat liver caused by Pb-nitrate may occur at least in part by TNF-a-associated mechanisms.
23 Lead-nitrate (0.33 mg/kg body wt) pretreatment-mediated protection conferred against carbon
24 tetrachloride (0.3 mL/kg)-induced hepatotoxicity as reported by Calabrese et al. (1995) may be
25 due to the inhibition of CYP450 activities in liver by Pb.
26 Jover et al. (1996) investigated the effect of heme deficiency on Pb-induced hepatic P450
27 function and transcription. These authors concluded that the decrease in hepatic P450 resulting
28 from Pb intoxication was mediated by two different mechanisms. One mechanism is involved
29 inhibitory effects on P450 by Pb at the transcriptional level; the second was heme- dependent, as
30 Pb-mediated inhibition of heme synthesis decreased the heme saturation of P450 and the
31 apo-P450 ratio.
May 2006 5-257 DRAFT-DO NOT QUOTE OR CITE
-------
1 The effect of heavy metals (Cd, Co, Cu, Ni, Pb, and Zn) on 3-methylcholanthrene-
2 induction of cytochrome P4501A and the activity of ethoxyresorufin-O-deethylase (EROD) were
3 investigated in fish hepatoma cells (PLHC-1) by Briischweiler et al. (1996). The authors
4 reported that all the heavy metals tested had more pronounced effects on EROD activity
5 compared to controls. The inhibitory potency of Pb was reported to be very low compared to
6 cadmium or cobalt. A single treatment of Pb-acetate induced hepatic DT diaphorase activity
7 (Sugiura et al., 1993). This induction of hepatic DT diaphorase by Pb-acetate has been reported
8 to be decreased with concomitant administration of Dil, a calcium antagonist. Based on these
9 observations, Arizono et al. (1996) suggested that DT diaphorase induction by Pb-acetate may
10 occur de novo via protein synthesis mediated by increased cellular calcium. The potential
11 interaction of metals, including Pb, on the induction of CYP1A1 and CYP1A2 by polycyclic
12 aromatic hydrocarbons (PAHs) in human hepatocyte cultures was investigated by Vakharia et al.
13 (2001). Lead-nitrate, like other metals such as Cd, Hg, and As, decreased the extent of CYP1A1
14 and CYP1A2 induction by five different PAHs. The authors concluded from these studies that
15 Pb (5 jiM) diminished the induction of CYP1A1 and CYP1A2 in human hepatocytes by
16 ultimately decreasing the levels of CYP1 Al protein that was normally attainable through PAH
17 induction. Korashy and El-Kadi (2004) also investigated similar interactions of metals with
18 aryl hydrocarbon receptor (AHR)-regulated gene expression and enzyme activities in wild-type
19 murine hepatoma cells (Hepa Iclc7) and AHR-deficient cells (C12). These studies indicated
20 that metals alone (including Pb) did not significantly alter CYP1 Al proteins or activity, or
21 change AHR ligand-induced enzyme activity. There was no change in mRNA levels. Lead, in
22 the presence or absence of AHR ligand, increased the activity of NAD(P)H:quinone
23 oxidoreductase and its mRNA levels.
24 Phase II Enzymes
25 A single injection of Pb-nitrate (5-10 jiM/100 g body wt) was found to increase GST
26 activity levels (Roomi et al., 1986). Additional studies by the same group identified induction of
27 a specific form GST-P by Pb-nitrate in rat liver (Roomi et al., 1987). Because a single injection
28 of Pb-nitrate decreased phase I and increased phase II hepatic enzymes, these investigators
29 concluded that Pb-nitrate treatment initiated a biochemical phenotype similar to carcinogen-
30 induced hepatocyte nodules. Immunohistochemical analysis by the same group reported that
May 2006 5-258 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pb-nitrate administration resulted in the appearance of GST-P in most of the hepatocytes, an
2 enzyme that is otherwise undetectable in normal rat liver (Columbano et al., 1988; Roomi et al.,
3 1987). On the other hand, Nakagawa (1991) reported inhibition of GST on acute exposure to Pb
4 and that the inhibition of GST followed a reduction in liver GSH levels. Nakagawa (1991)
5 concluded that the depletion of GSH was not necessarily a critical factor in inhibiting GST.
6 Planas-Bohne and Elizdale (1992) reported that acute exposure to Pb-nitrate
7 (100 |imol/kg) caused a significant increase in liver and kidney GST activity. Gel
8 electrophoresis analysis to evaluate the contribution of various GST isoforms indicated that
9 enhancement of liver GST activity was predominantly due to induction of GST isoform 7-7 in
10 liver compared to all isoforms in kidney. Liver GST-P isoform was reported to be induced by
11 both Pb-acetate and Pb-nitrate (Boyce and Mantle, 1993; Koo et al., 1994). This transient
12 induction of GST-P has been regulated at transcription, post-transcription, and post-translational
13 levels. Suzuki et al. (1996) utilized a transgenic approach to investigate the transcriptional
14 regulation of GST-P induced by Pb and identified glutathione S-transferase P enhancer I (GPEI),
15 an enhancer (whose core consists of two AP-1 site-like sequences) located at the 5' flanking
16 region of this gene. The authors demonstrated that GPEI is an essential element in the activation
17 of the GST-P by Pb and that the trans activating factor AP-1 is likely to be involved, at least in
18 part, in the transcriptional activation of the GST-P gene by Pb via the GPEI sequence.
19 Daggett et al. (1997, 1998) investigated the effect of inorganic and organic Pb on liver
20 GST expression and other phase II detoxifying enzymes in rat liver and kidney. Triethyl Pb
21 chloride (TEL) injection (10 mg/kg body wt) decreased liver GST activity, as well as levels of
22 various other GST isoforms (Daggett et al., 1997), in contrast to significant induction of kidney
23 GST activity, suggesting that a single compound, TEL, had opposite effects on the expression of
24 GST isozymes and indicated the complexity of GST regulation. Similarly, this group also
25 reported that a single injection of Pb-acetate (114 mg/kg body wt) reduced GSH levels, increased
26 production of malondialdehyde (MDA), and did not change the expression of various GST
27 isoforms analyzed, except GST-pl on repeated injection (Daggett et al., 1998). Similar to
28 studies with TEL, Pb-acetate also increased the expression of GST enzyme activity and
29 expression of various isoforms without changing GSH and MDA levels, suggesting that
30 oxidative stress may not be mediating the toxicity in kidney. On the other hand, TEL exposure
31 was found to decrease microsomal estradiol metabolism (Odenbro and Rafter, 1988).
May 2006 5-259 DRAFT-DO NOT QUOTE OR CITE
-------
1 The suppression of GST expression reported by Daggett et al. (1997, 1998) is in contrast to the
2 induction of GST reported by various other groups discussed earlier. Other GSH-dependent
3 enzymes (i.e., GSH peroxidase, GSH reductase) have been found to be suppressed with a
4 simultaneous increase in oxidized GSH (GSSG) and a reduction in GSH/GSSG ratio (Sandhir
5 and Gill, 1995). More detailed information on these and related studies is summarized in
6 Table AX5-10.1.
7
8 5.10.1.2 Biochemical and Molecular Perturbations in Lead-Induced Liver Tissue Injury
9 Oskarsson and Hellstrom-Lindahl et al. (1989) studied the cellular transport of Pb (203Pb),
10 in rat hepatocytes using dithiocarbamate (DTC). Cells treated with Pb-acetate and Pb-DTC
11 lipophylic complex demonstrated increased cytosolic Pb levels compared to Pb alone. This was
12 further evaluated by measuring levels of ALAD. Cells treated with Pb-DTC complex showed
13 rapid and stronger inhibition of ALAD compared to Pb-acetate, suggesting that this inhibition
14 was due to increased mobilization of Pb into cells treated with Pb-DTC complex. Another report
15 by the same group, Hellstrom-Lindahl and Oskarsson (1990), suggested that the increased
16 inhibition of ALAD was due to the release of Pb from the Pb-DTC complex by decomposition.
17 Using the mouse strain with a duplication of the ALAD gene (DBA), Claudio et al. (1997)
18 reported increased accumulation of Pb in this strain by many fold as compared to mice with a
19 single copy of the ALAD gene (C57).
20 A single injection of Pb-nitrate was reported to cause hepatic hyperplasia correlating with
21 hepatic de novo synthesis of cholesterol along with alterations in glucose and lipid metabolism
22 leading to altered serum lipid profiles (Dessi et al., 1984; Pani et al., 1984). Mobilization of
23 hepatic glycogen and altered gluconeogenic enzymes, including differential expression of G6PD,
24 has been reported following Pb exposure (Batetta et al., 1990; Hacker et al., 1990). Chronic Pb
25 intoxication has also been reported to inhibit gluconeogenic enzymes, alterations that were
26 implicated in Pb bio-transformation rather than liver cell proliferation in Wistar rats (Calabrese
27 and Baldwin, 1992). Although these studies point out to newer directions on the lead effects on
28 hepatic carbohydrate metabolism, due to lack of information on blood lead levels, have limited
29 value for extrapolation to human exposure scenarios and associated health effect assessment.
30 Increased levels of serum lipid peroxide (LPO) were also observed in rats given SC injection of
31 Pb-acetate, supporting similar increased levels of serum LPO in humans exposed to Pb (Ito et al.,
May 2006 5-260 DRAFT-DO NOT QUOTE OR CITE
-------
1 1985). These initial studies suggest that alterations in liver intermediary metabolism occur on
2 exposure to Pb with a role for Pb-induced LPO in hepatotoxicity and potential involvement of
3 oxidative stress in Pb toxicity. Limited studies on the hepatic lipid provide peroxidation blood
4 lead levels in the range of 18 to 35 |ig/dL.
5 Dessi et al. (1990 ) investigated the role of fasting on Pb-induced hepatic hyperplasia by
6 monitoring the activities of enzymes involved in cholesterol synthesis and the hexose
7 monophosphate shunt and reported that stimulation of these enzymes, even in Pb-acetate-treated
8 fasting rats, supported the role of new endogenous synthesis of cholesterol and gluconeogenic
9 mechanisms in Pb-induced hepatic cell proliferation. Chronic exposure to Pb was found to
10 increase the arachidonate/linoleic acid ratio in liver and serum (Donaldson and Leeming, 1984;
11 Donaldson et al., 1985) along with the GSG concentration (McGowan and Donaldson, 1987).
12 As GSH and arachidonate are precursors for peptido-leukotrienes, Donaldson's group
13 investigated the potential effects of dietary Pb on levels of fatty acids, peptido-leukotrienes, and
14 arachidonate/linoleic ratios in chicken fed with diets low in calcium and methionine. These
15 investigations found similar increases in arachidonate/linoelic acid ratio and in GSH levels
16 without bearing on peptido-leukotriene levels. The authors also found the influence of a low
17 calcium and methionine diet on Pb-induced serum fatty acid profiles (Knowles and Donaldson,
18 1990).
19 Chronic sublethal exposure (5 ppm Pb-nitrate for 30 days) has been found to alter liver
20 lipid profiles in blood and liver tissue of the fresh water fish Anabas testudineus (Tulasi et al.,
21 1992). These authors reported significant increases in liver total lipids, cholesterol, and free fatty
22 acids. Tandon et al. (1994b) reported that iron deficiency enhanced the accumulation of Pb in
23 liver and kidney and also increased liver calcium levels. Induced expression of metallothionein
24 (MT) in renal and intestine was also observed in iron deficiency. Han et al. (1996) investigated
25 the effect of Pb burden on weight loss using an energy restriction diet regimen on rats with prior
26 Pb exposure. The authors reported that rats on a substantial weight loss regimen (40% of normal
27 calories) exhibited a significant increase in the quantity and concentration of liver Pb and a
28 decrease in the concentration of other metals (e.g., Ca, Cu, Mg, Zn). The authors concluded that
29 weight loss can increase the liver concentration of Pb, even in the absence of continued
30 exposure. Combined exposure to Pb (70 mg/kg) and Cd (20 mg/kg) in Buffalo rats for 7 weeks
31 was found to alter liver levels of Zn and Cu, with less accumulation of Pb and Cd, compared to
May 2006 5-261 DRAFT-DO NOT QUOTE OR CITE
-------
1 individuals exposure to either Pb or Cd alone (Skoczyriska et al., 1993). These authors also
2 reported that a combined exposure regimen interfered with serum lipid profiles (Skoczyriska and
3 Smolik, 1994).
4 Liu et al. (1997) utilized rat primary hepatocyte cultures to explore the protective effect of
5 Zn-induced expression of metallothionein (MT) in Pb toxicity. These authors found that, in the
6 control cells without prior Zn exposure, most of the Pb was found bound to high-molecular
7 weight proteins in the cytosol, while in the Zn pretreated cells, a majority of Pb bound to MT,
8 indicating a MT-mediated protection against Pb toxicity to hepatocytes. More details about these
9 and related studies are summarized in Table AX5-10.2.
10
11 5.10.1.3 Effects of Lead Exposure on Hepatic Cholesterol Metabolism
12 Lead-nitrate-induced hyperplasia or liver cell proliferation involves simultaneous increase
13 in both liver and serum total cholesterol levels. Recent studies have reported various molecular
14 events associated with this process. Induction of gene expression for CYP51 (Lanosterol
15 14a-demethylase), an essential enzyme for cholesterol biosynthesis, was reported in Pb-nitrate-
16 induced liver hyperplasia, although other cytochrome P450 enzymes involved in drug
17 metabolism have been reported as being suppressed, as discussed in earlier sections. This gene
18 has various regulatory elements and its constitutive expression in liver is mediated by sterol
19 regulatory element (SRE) and by the SRE binding proteins-la, 2, and Ic. Kojima et al. (2002)
20 reported that Pb-nitrate induced the expression of CYP51 in the livers of both immature (4-week-
21 old) and mature (7-week-old) rats and that this induction appeared to be mediated by the
22 upregulation of SRE binding protein-2. However, this increased synthesis of cholesterol
23 observed in rat liver was not mediated by endogenous feedback regulation by sterols, as no
24 decrease in serum total cholesterol was observed. To understand the molecular mechanisms
25 involved in the Pb-nitrate-mediated development of hepatic hypercholesterolemia, Kojima et al.
26 (2004) investigated the expression of various enzymes involved in cholesterol homeostasis,
27 including some of the associated transcription factors in male rats exposed to Pb-nitrate
28 (100 jimol/kg body wt). The authors reported that Pb-nitrate exposure caused a significant
29 increase in liver and serum total cholesterol levels at 3 to 72 h and 12 to 72 h, respectively. The
30 enzymes involved in cholesterol biosynthesis viz. (i.e., 3-hydroxy-3methyglutaryl-CoA
31 reductase, farnesyl diphosphate synthase, squalene synthase, CYP51) were all activated (3-24 h),
May 2006 5-262 DRAFT-DO NOT QUOTE OR CITE
-------
1 while the enzymes involved in cholesterol catabolism such as 7a-hydroxylase were remarkably
2 suppressed 3 to 72 h. Figure 5-10.1 shows the involvement of Pb at various stages of the
3 cholesterol synthesis pathway. The induction of the cytokines interleukin-loc and TNF-a in rat
4 liver prior to the induction of the genes for these synthesis enzymes suggested that Pb-nitrate-
5 induced cholesterol synthesis is independent of sterol homeostasis regulation. Following
6 gestational and lactational exposure to Pb-acetate (0.05 mg/kg body wt), Pillai and Gupta (2005)
7 reported that the activities of the hepatic steroid metabolizing enzyme 17-p-hydroxy steroid
8 reductase, UDP glucouronyl transferase, and CYP450 levels decreased in rat pups on PND21.
9 Alterations in the hepatic system of neonates and pups (at PND12 and PND21) after
10 gestational and lactational exposure to Pb-acetate (300 mg/L) have been reported by Corpas et al.
11 (2002). The authors found significant reductions in the liver weight of pups and in hepatic
12 glycogen that correlated with increased blood glucose levels. The authors also reported
13 reductions in liver protein, lipid levels, and alkaline and acid phosphatase activities but did not
14 find any gross structural alterations in liver tissue. These and other studies are summarized in
15 Table AX5-10.3.
16
17 5.10.1.4 Effect of Lead on Hepatic Oxidative Stress
18 Although several mechanisms have been proposed to explain Pb toxicity, no mechanism
19 has been defined explicitly. Recent literature on Pb toxicity suggests oxidative stress as one of
20 the important mechanisms of toxic effects of Pb in liver, kidneys, brain, and other organs.
21 Schematic representation of the various mechanisms by which Pb induces lipid peroxidation is
22 shown Figure 5-10.2. Lead toxicity to the liver has been found to be associated with significant
23 accumulation of Pb in the liver. This results in the accentuation of lipid peroxidation with
24 concomitant inhibition of antioxidant enzymes (i.e., SOD, catalase, GSH peroxidase, GSH
25 reductase) and a simultaneous increase in GSSG with a reduction in GSH/GSSG ratio (Sandhir
26 and Gill, 1995; Aykin-Burns et al., 2003). However, Furono et al. (1996) studied the potential of
27 various redox-active metals to induce LPO in normal and alpha-linolenic acid-loaded rat
28 hepatocytes and suggested that Pb ions were not capable of inducing lipid peroxidation in such
29 hepatocytes.
30
May 2006 5-263 DRAFT-DO NOT QUOTE OR CITE
-------
Acetyl-CoA
HMG-CoA
j~| HMGR HMGR-3-hydroxy-3 methyl glutaryl- T Pb
"^ CoA Reductase
Mevalonate
J I FPPS Farnesyl pyrophosphate synthase I Pb
Farnesyl pyrophosphate
4J- SQS Squalene synthase \ Pb
Squalene
J I Squaline oxidosterol
Lanosterol
J I cyp51 Lanosterol 14-a-demethylase [ Pb
Cholesterol
J I cyp7A1 Cholesterol 7-a-hydroxylase + Pb
Bile acids
Figure 5-10.1. Flow diagram indicating the Pb effects on the cholesterol synthesis
pathway.
Pb-lnduced Oxidative Stress
I J I
Cell membrane: Genome: Antioxidant system:
• Interaction with PUFA • Accumulated ALA acts as • Inhibition of functional
• FA chain elongation alkylating agent and forms sulfhydryl groups on enzymes:
• Altered membrane enzymes DNA adducts SOD, GSH peroxidase,
• Altered solute transport • Interference with Zn-binding GSH reductase
• Altered signal transduction proteins in transcription • Depletion of GSH
complex
Figure 5-10.2. Schematic diagram illustrating the mode of Pb-induced lipid peroxidation.
1 The currently approved clinical intervention method is to give chelating agents that form a
2 soluble complex with Pb and remove the same from Pb-burdened tissues. The details of these
3 studies are provided in Annex Table AX5-10.4.
May 2006 5-264 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.10.1.5 Lead-Induced Liver Hyperplasia: Mediators and Molecular Mechanisms
2 The biochemical and molecular events associated with Pb-induced hyperplasia has been
3 accumulating in the scientific literature. Lead-nitrate, a known mitogen, is also considered to be
4 a carcinogen that induces liver cell proliferation in rats without any accompanying liver cell
5 necrosis. It has been recognized that this proliferation is a transient process and that apoptosis
6 plays a major role in the regression of Pb-nitrate-induced hepatic hyperplasia (Nakajima et al.,
7 1995). Columbano et al. (1996) studied the cell proliferation and regression phases by apoptosis
8 in Wistar male rat liver by monitoring the incorporation of tritiated thymidine as a marker for
9 increased DNA synthesis. These studies demonstrated the production of Pb-induced
10 proliferation 3 days after a single injection of Pb-nitrate with complete regression of hyperplasia
11 seen after 15 days. The authors suggested that the apoptosis process observed in the regression
12 phase also involved newly initiated hepatocytes. On the other hand, Dini et al. (1999) reported
13 the regressive or involutive phase as beginning 5 days post single injection of Pb-nitrate.
14 Apostoli et al. (2000) evaluated the proliferative effects of various Pb salts (i.e., Pb-acetate,
15 Pb-chloride, Pb-monoxide, Pb-sulfate) using liver-derived REL cells. These authors reported
16 that all the Pb compounds tested showed dose- and time-dependent effects on the proliferation of
17 REL cells. Unlike other tumor promoters, Pb compounds did not exhibit effects on cell
18 junctional coupling. Liver hyperplasia induced by Pb-nitrate has been shown to demonstrate
19 sexual dimorphism in all phases of the proliferation as well as in apoptosis (Tessitore et al.,
20 1995). Biochemical changes associated with liver hyperplasia in the intermediary metabolic
21 pathways were discussed in earlier sections of this chapter; the present discussion focuses on
22 other molecular characteristics of this process. As the numerous molecular networks involved in
23 both the proliferation and apoptosis processes have many common mediators and pathways, it is
24 very difficult to provide a discussion without an overlap.
25 DNA hypomethylation has been recognized to play a major role in the proliferation of
26 cells in regenerating and in hepatic pre-malignant lesions when compared to normal non-dividing
27 liver cells. A single dose of Pb-nitrate (75 |iM/kg body wt) has been found to cause extensive
28 hypomethylation in rat liver (Kanduc et al., 1991). Additional investigations from the same
29 group reported that this hypomethylation status of liver DNA by Pb-nitrate changed significantly
30 with age and exhibited liver cell specificity (Kanduc and Frisco, 1992).
May 2006 5-265 DRAFT-DO NOT QUOTE OR CITE
-------
1 Investigations of cell cycle-dependent expression of proto-oncogenes in Pb-nitrate
2 (10 jiM/100 g body wt)-induced liver cell proliferation by Coni et al. (1989) showed that peak
3 DNA synthesis occurred at 36 h after a single injection of Pb-nitrate. In addition to DNA
4 synthesis, induced expression of c-fos, c-myc, and c-Ha-ras oncogenes was also observed in rat
5 liver tissue. Additional studies by the same group reported that Pb-nitrate-induced liver
6 hyperplasia involved an increased expression of c-jun in the absence of c-fos expression (Coni
7 et al., 1993). The induced expression of c-myc persisted up to 40 h post Pb-nitrate exposure.
8 Pb-nitrate-induced liver proliferation and DNA synthesis, as monitored by 5-bromo-
9 2-deoxyuridine immunohistochemistry, lead to DNA labeling in a few hepatocytes (Rijhsinghani
10 et al., 1993). The observed DNA synthesis appeared to be due to the increased activity and
11 expression of DNA polymerase-a observed at 8 h postexposure to a single injection of Pb-nitrate
12 (Menegazzi et al., 1992). Along with DNA synthesis, poly (ADP-ribose) polymerase was also
13 induced by Pb-nitrate (Menegazzi et al., 1990). Differential activation of various PKC isoforms,
14 downregulation of PKC-a, and marked activation of PKC-e in Pb-nitrate-mediated liver
15 hyperplasia suggested the involvement of these PKC enzymes in DNA synthesis and related
16 signal transduction pathways (Tessitore et al., 1994; Liu et al., 1997).
17 Coni et al. (1992) reported the proliferation of normal and pre-neoplastic hepatic cells
18 treated with the plasma derived from male Wistar rats treated with a single injection of
19 Pb-nitrate; this was the first report on the secretion of biological cell proliferation signals in the
20 liver after Pb-nitrate treatment. These authors reported that DNA synthesis was detected as early
21 as 30 min and persisted up to 5 days after Pb-nitrate exposure. This observation has opened up
22 the inquiry into the involvement of various growth factors and other biological mediators in
23 hepatic hyperplasia. Shinozuka et al. (1994) investigated the expression of various growth
24 factors (i.e., hepatocyte growth factor, TGF-a, TGF-P) in rat liver after a single injection of
25 Pb-nitrate (100 |iM/kg body wt) and reported the involvement of these growth factors in liver
26 cell proliferation. Additional studies by this group to observe LPS sensitivity in rats given
27 Pb-nitrate reported that animals given a single injection of LPS up to 100 jig survived, whereas
28 in the presence of Pb-nitrate, they tolerated only 6 jig of LPS, indicating that Pb-nitrate may
29 sensitize the animals for LPS toxicity.
30 Earlier studies by Honchel et al. (1991) reported that coexposure of rats to Pb-acetate
31 (15 mg/kg) and LPS or TNF showed markedly increased serum levels for various liver injury
May 2006 5-266 DRAFT-DO NOT QUOTE OR CITE
-------
1 parameters. They concluded that Pb may potentiate liver toxicity by LPS via a TNF-mediated
2 pathway. The role of TNF-a in Pb-nitrate-induced liver cell proliferation was further
3 investigated by (Ledda-Columbano et al., 1994) who demonstrated the inhibition of Pb-nitrate-
4 induced cell proliferation by pretreatment with dexamethasone, an inhibitor of TNF-a
5 expression. Additional studies by the same group evaluated the liver cell specificity in
6 Pb-nitrate-induced cell proliferation (Shinozuka et al., 1996). They monitored the incorporation
7 of 5-bromo-2-deoxyuridine by immunohistochemical analysis on rat liver as induced by
8 Pb-nitrate and TNF-a and observed 5-bromo-2-deoxyuridine incorporation in hepatocytes and
9 non-parenchymal cells (i.e., Kupffer cells, endothelial cells, periportal nondescript cells),
10 confirming that Pb-induced liver cell proliferation was mediated by TNF-a. Kubo et al. (1996)
11 used various TNF-a inhibitors to further confirm the role of TNF-a in Pb-nitrate-induced
12 hepatocyte proliferation. Menegazzi et al. (1997) reported that Pb-nitrate induced proliferation
13 involved the induction of iNOS along with TNF-a and that appeared to be mediated by a strong,
14 prolonged activation of NFtcB but not activator protein-1 (AP-1). Nemoto et al. (2000)
15 investigated the potential role of neurotrophins and their receptors in Pb-nitrate-induced hepatic
16 hyperplasia. The expression profile of TNF-a, neurotrophins (i.e., nerve growth factor, brain-
17 derived neurotrophic factor neurotrophin-3 and (their receptors), tyrosine kinase receptor (Trk)
18 and neurotrophin receptor (p75NTR) were investigated in liver tissue after a single injection of
19 Pb-nitrate (100 |iM/kg body wt). The Pb-nitrate induced increased expression of TNF-a
20 preceded the expression of the neurotrophins and their receptors. Based on these results, the
21 author's suggested that neurotrophins and neurotrophin receptors are involved in mediating
22 mitogenic signals related to hepatic hyperplasia.
23 The regression phase of Pb-induced liver hyperplasia appears to be mediated by OS.
24 As discussed earlier, this process involves LPO and other cytokine mediators, including TNF-a.
25 Sieg and Billings (1997) reported that Pb potentiated cytokine-induced OS, producing a
26 significant decline in intracellular ATP concentration in mouse hepatocyte culture studies. The
27 authors suggested that cytotoxic interaction between Pb and cytokines (e.g., TNF-a and IFN)
28 may be mediated by oxidative DNA damage resulting from OS. The potential role OS along
29 with TNF-a has been implicated in the apoptosis of hepatocytes by Milosevic and Maier (2000).
30 Using freshly isolated cultures of hepatocytes and Kupffer cells and their co-culture system
31 exposed to Pb-acetate (2-50 |iM) and LPS (0.1-1000 ng/mL), the authors reported that, in the
May 2006 5-267 DRAFT-DO NOT QUOTE OR CITE
-------
1 co-culture system, the Pb-LPS-induced release of TNF-a from the Kupffer cells, increased nitric
2 oxide levels by 6-fold and downregulated the acute phase protein, albumin, in hepatocytes.
3 From these observations the authors concluded that Pb-induced Kupffer cell-derived signals
4 promoted the toxicity of Pb in hepatocytes, resulting in hepatocyte death by proteolysis. The
5 importance of the Kupffer cells role in Pb-nitrate-induced heptatocyte apoptosis was further
6 demonstrated (Pagliara et al., 2003a,b). These authors reported that in vivo hepatic apoptosis
7 including oxidative response induced by Pb-nitrate, was prevented by pretreatment with
8 gadolinium chloride, a Kupffer cell toxicant that specifically suppresses Kupffer cell activity.
9 When treated hepatocytes were exposed in vitro to Pb-nitrate, hepatocyte apoptosis was not
10 observed. On the other hand, hepatocyte apoptosis was evident when the hepatocytes were
11 incubated with culture medium derived from Kupffer cells that had been exposed to Pb-nitrate.
12 Based on these studies, the authors concluded that heptocyte apoptosis was potentiated by
13 soluble factors secreted by Pb-exposed Kupffer cells. The role of activated Kupffer cells,
14 macrophages, and TNF-a in chemical-induced hepatotoxicity is presented schematically in
15 Figure 5-10.3.
16 Dini et al. (1993) investigated the expression of asialoglycoprotein receptors on the
17 surface of hepatocytes and galactose-specific receptors of non-parenchymal cells during the
18 apoptic phase of Pb-induced hepatic hyperplasia.
19 A significant increase in asialoglycoprotein receptor expression in hepatocytes coincided with
20 massive apoptosis. Later studies from this group demonstrated that sinusoidal liver cells
21 predominantly phagocytosed the Pb-nitrate-induced apoptic hepatic cells and concluded that this
22 process appeared to be mediated by the cell surface carbohydrate receptors (i.e., mannose and
23 galactose receptors) (Ruzittu et al., 1999). Pretreatment of rats with gadolinium chloride,
24 a kupffer cell toxicant, was also found to abolish the altered expression of galactose receptors
25 (Pagliara et al., 2003b).
26 The role of glucocorticoid-mediated signal transduction in the hepatotoxicity of Pb was
27 evaluated by Heiman and Tonner (1995), using H4-IIE-C3 hepatoma cells (HTC). Acute
28 exposure of cells to Pb (300 nMT1 or 10 jiM) was found to inhibit processes involved
29 inglucocorticoid-mediated enzyme induction (e.g., tyrosine aminotransferase activity) in a dose-
30 dependent manner both at the transcriptional and translational level, without altering
31 glucocorticoid receptor binding characteristics. Tonner and Heiman (1997) also reported
May 2006 5-268 DRAFT-DO NOT QUOTE OR CITE
-------
Chemical Exposure
c
Tissue Necrosis
C
Macrophage Activation
Secretion of Proinflammatory
Cytokines
"N k TNF-a
J IL"1
( Apoptosis J ( Inflammation J f Proliferation J
Reactive Oxygen Species
Nitric Oxide
Generalized Liver
Damage
Figure 5-10.3. Hypothesis of chemical-induced liver injury generated primarily on the
basis of different types of inhibitors.
4
5
6
7
8
9
10
Pb-induced hepatotoxicity by glucocorticoid-mediated signaling and its involvement in the
interference with calcium-mediated events as well as the differential modulation and
translocation of protein kinase isoforms a and P into the nucleus. More information on these and
other related studies is summarized in Table AX5-10.5.
5.10.1.6 Effects of Lead on Liver Heme Synthesis
Effects of Pb on heme metabolism have been extensively investigated in major target
tissues such as liver and erythrocytes. Section 5.2 described Pb effects on heme synthesis, with
particular relevance to erythrocytes. The effects of Pb on heme synthesis in the liver and the role
of chelation therapy in this process are discussed in this section.
May 2006
5-269
DRAFT-DO NOT QUOTE OR CITE
-------
1 Fifteen percent of heme is produced in the liver. Heme metabolism in the liver is an
2 essential component of various cytochrome P450s that participate in cellular redox reactions and
3 xenobiotic detoxification pathways in the liver tissue and, hence, heme plays a vital role in liver
4 function (Jover et al., 1996). Due to the important and critical role of heme in liver function,
5 Pb-induced effects on hepatic heme metabolism are discussed below.
6 Initial studies on the effects of Pb-nitrate on hepatic heme biosynthesis were reported by
7 Lake and Gerschenson (1978) using the rat liver cell line (RLC-GAI). The effects of various
8 organic metal compounds on ALAD activity have been studied by Bondy (1986). The authors
9 reported that triethyl Pb-chloride has the same potency as Pb-nitrate in inhibiting ALAD both
10 in vitro and in vivo, with liver and blood ALAD exhibiting similar sensitivities to Pb
11 compounds. By measuring the conversion of ALA into heme, these authors showed that heme
12 biosynthesis was inhibited by Pb in a dose dependent manner. Using a lipophilic complex of Pb-
13 acetate + DTC to increase the cellular uptake of Pb, Osksarsson et al. (1989) demonstrated the
14 inhibition of ALAD activity in primary rat hepatocytes cultures. Lead-acetate has been reported
15 to inhibit ALAD activity in rabbit liver tissue without any effect on delta-aminolevulinic acid
16 synthase (ALAS) activity (Zareba and Chemielnicka, 1992). Exposure to Pb (500 ppm) in
17 drinking water did not inhibit hepatic ALAS, but did inhibit ALAD activity in mice (Tomokuni
18 et al., 1991). Exposure to Pb-acetate (20 mg/kg body wt for 3 days) has been reported to
19 decrease hepatic ALAD and uroporphyrinogen activity (Satija and Vij, 1995). These authors
20 also reported that IP injection of zinc (5 mg/kg body wt for 3 days) conferred protection against
21 Pb-acetate effects in liver tissue.
22 Effects of Pb on hepatic porphyrins, intermediate metabolites of heme metabolism, were
23 investigated by few researchers. Quintanilla-Vega et al. (1995) reported that 3T3-hepatocyte
24 cultures, when incubated with a micromolar concentration of Pb-acetate increased cellular
25 porphyrin content and excretion. This increased porphyrin production may have been due to an
26 accumulation of protoporphyrin and coproporphyrin, as in coproporphyrinuria, a well-
27 characterized sign of Pb intoxication (Ichiba and Tomokuni, 1987; Zareba and Chemielnicka,
28 1992). Dietary supplementation of selenium and monensin increased Pb-induced accumulation
29 of prophyrins in chicken liver (Khan and Szarek, 1994). Species-specific differences in the
30 effects of Pb on protoporphyrins were reported by Jacobs et al. (1998). These authors
31 investigated the effect of Pb on zinc protoporphyrin synthesis in cultured chick and rat
May 2006 5-270 DRAFT-DO NOT QUOTE OR CITE
-------
1 hepatocytes and observed decreased levels of protoporphyrin in rat hepatocytes, but no effect on
2 chick hepatocytes. Santos et al. (1999) also reported Pb-induced derangements (including
3 porphyrin metabolism) in rat liver heme metabolism, but these effects were far less severe than
4 those observed in erythrocytes. Their investigations on the effect of chronic alcoholism on Pb
5 effects in hepatic heme metabolism suggested no potentiation by alcohol.
6 Transferrin (TF) is the major iron-transport protein in serum and other biological fluids.
7 Transferrin can also has the capacity to transport other metals. Lead was found to inhibit TF
8 endocytosis and transport of iron across the cell membrane of rabbit reticulocytes (Qian and
9 Morgan, 1990). The effect of Pb on TF gene expression was investigated by Adrian et al. (1993)
10 using a transgenic mouse with the human TF gene. They found that Pb suppressed the
11 expression of TF transgene in mouse liver at the transcriptional level; however, the same dose of
12 Pb did not inhibit mouse endogenous hepatic TF gene expression. Lead exposure was also found
13 to inhibit recombinant TF expression in human hepatoma hepG2 cells. Other studies by the
14 same group found that Pb exposure suppressed the expression of endogenous TF in HepG2 cells
15 (Barnum-Huckins et al., 1997). These authors further suggested that Pb effects on hepatic TF
16 levels may also interfere with iron metabolism in humans. (See Annex Table AX5-10.6 for more
17 information on these and related studies.)
18
19 Summary
20 Extensive in vivo and in vitro experimental evidence has accumulated over the past
21 20 years and increased our understanding of the potential toxic effects of Pb in the hepatic
22 system. These studies ranged from simple biochemical studies to molecular characterizations of
23 the induction of drug-metabolizing enzymes, liver hyperplasia, and the protective effects of
24 chelation therapy.
25 • Rat liver microsomal cytochrome P-450 levels were found to decrease with a single dose
26 exposure of Pb nitrate. Inhibition of both constitutive and induced expression of
27 microsomal P450 Al and A2 activity occurred. Simultaneous induction of the activities
28 of phase II drug metabolizing enzymes with decreased phase I enzymes with single
29 exposure to Pb nitrate suggests biochemical properties similar to hepatic nodules.
30 • Newer studies examined the induction of GST-P at both transcriptional and translational
31 levels using in vitro systems and indicated a role for Pb-nitrate and Pb-acetate in the
32 induction process. On the other hand, triethyl Pb compounds have been found to
33 suppress the activity of various GST isoforms.
May 2006 5-271 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Studies on Pb-induced liver hyperplasia demonstrated de novo synthesis of cholesterol,
2 alterations in the gluconeogenic mechanism, as well as DNA hypomethylation and
3 subsequent changes in the expression of protooncogenes.
4 • Lead-induced alterations in cholesterol metabolism appear to be mediated by the
5 induction of several enzymes related to cholesterol metabolism and the decrease of
6 7 a-hydroxylase, a cholesterol catabolizing enzyme. This regulation of cholesterol
7 homeostasis is modulated by changes in cytokine expression and related signaling.
8 • Studies using an inhibitor to block TNF-a have clearly demonstrated TNF-a as one of the
9 major mitogenic signals that mediate Pb-nitrate-induced liver hyperplasia. Lead-induced
10 hyperplasia also appears to be modulated by neurotrophins and their receptors.
11 • In vitro co-culture systems with Kupffer cells and hepatocytes suggested liver cell
12 apoptosis is mediated by Kupffer cell-derived signals and Pb-induced oxidative stress.
13 • Newer experimental evidence suggests that Pb-induced alterations in liver heme
14 metabolism involves perturbations in ALAD activity, and porphyrin metabolism,
15 alterations in Transferrin gene expression, and associated changes in iron metabolism.
16 • Limited experimental evidence on the role of weight loss on liver Pb burden in exposed
17 animals indicate that liver Pb content increases even in the absence of prolonged
18 continued exposure.
19
20 5.10.2 Gastrointestinal System and Lead Absorption
21 Lead enters the body by many routes, but primarily via the GI tract. The intestinal
22 epithelium serves as one of the body's primary interfaces with the outside world. The
23 transporting epithelia in the small intestine are characterized by layers of anatomically and
24 biochemically polarized cells that are connected to each other by tight junctions and resting on a
25 basement membrane. Classically, the intestinal epithelium is thought of primarily as a barrier,
26 but it also is a highly reactive barrier. Even modest perturbations in its functions may lead to
27 diarrhea, constipation, malnutrition, dehydration, and infectious diseases (i.e., ulcerative colitis,
28 collectively referred as chronic intestinal inflammatory diseases) (Gewirtz et al., 2002).
29 Abdominal colic and constipation are symptoms of Pb poisoning, but its mechanism is not fully
30 understood. Studies have been carried out in the past decade to increase our understanding of the
31 fundamental mechanism(s) in order to extrapolate the experimental observations to human
32 health effects.
33 One of the key factors required to access the risk is an understanding and quantification of
34 bioavailability. Detailed discussions on the bioavailability of lead, methodologies in
35 bioavailability measurements, bioavailability and speciation, etc. are discussed in detail in
May 2006 5-272 DRAFT-DO NOT QUOTE OR CITE
-------
1 Section 8.1.3.1. This section is primarily focused on the gastrointestinal absorption of lead with
2 relevance to animal studies and in vitro test systems of intestinal origin.
3 The intestinal absorption of Pb is influenced by a variety of factors, including the
4 chemical and physical forms of the element, age at intake, and various nutritional factors.
5 Gastrointestinal absorption of Pb is thought to occur primarily in the duodenum. In the isolated
6 rat intestine, absorption, and, in particular, serosal Pb transfer activity (net transfer of Pb from
7 the small intestine lumen across the epithelium and into the serosal space) is highest in the
8 duodenum. The mechanisms of absorption may involve active transport and/or diffusion through
9 the intestinal epithelial cells. Both saturable and non-saturable pathways of absorption have been
10 inferred from the studies in different animal models, although the understanding of the former is
11 slightly more robust (Diamond et al., 1998).
12 Transport of Pb as a complex with proteins via endocytosis or as a complex with amino
13 acids are postulated as possible mechanisms. Direct evidence for transport of an organic Pb
14 complex has not been provided, but it seems possible.
15 In the cell, Pb interacts with a variety of intracellular ligands, including calcium-binding
16 proteins and high-affinity Pb-binding proteins. Transfer across the cell or basolateral membrane
17 (or both) involves a mechanism(s) that may be sensitive to vitamin D and iron status. Alternate
18 transport mechanisms via a Ca2+-Na+ exchanger, independent of regulation by vitamin D, are
19 also possible.
20
21 5.10.2.1 Lead and In vitro Cytotoxicity in Intestinal Cells
22 In vitro cytotoxicity of metal salts for 48 h was determined in the intestinal epithelial cell
23 line 1-407 by Keogh et al. (1994). The investigations identified rank order cytotoxicity in terms
24 of LC50 values: HgCl2 (32 |iM)>Cdd2 (53 |iM) > CuCl2 (156 |iM) > Ti2SO4 (377 |iM) > Pb
25 (NO3)2 (1.99 mM). Further studies using a noncytotoxic concentration of butathione
26 sulphoxamine pretreatment for GSH depletion revealed that the cytotoxicity of Pb was
27 unaffected by GSH depletion (see Table AX5-10.7).
28
29 5.10.2.2 Alterations in Intestinal Physiology and Ultrastructure
30 Karmakar et al. (1986) investigated the pathologic alterations that occur in the intestine,
31 liver, and kidney of Pb-intoxicated rats upon short-term exposure to sublethal doses of Pb
May 2006 5-273 DRAFT-DO NOT QUOTE OR CITE
-------
1 (44 mg/Kg body wt) and reported degeneration of intestinal mucosal epithelium leading to
2 potential malabsorption.
3 The effect of low-concentration Pb-acetate (0.1%) on the jejunal ultrastructure was
4 studied by Tomczok et al. (1988) in young male rats. The studies revealed that the villi of
5 jejunum of rats exposed to Pb for 30 days had a rough appearance on the surface, which could be
6 associated with a distortion of glycocalyx layer. Areas of extensive degenerative lesions were
7 also observed on the surface of most villi on the 60th day of exposure. All intestinal epithelial
8 cells exhibited various degrees of glycocalyx disturbance, indicating that pronounced toxic
9 effects of Pb were related to modifications of the biochemical properties of the surface coat of
10 the cells. These authors also reported the appearance of goblet cells and of Pb deposition along
11 the goblet cell membrane in blocks of tissue along the border between duodenum and jejunum.
12 Continued treatment up to 60 days resulted in mucus droplets in the cytoplasm of goblet cells,
13 along with deposition of silver salts indicative of Pb in these cells. These results demonstrated
14 the significance of goblet cells in Pb detoxification.
15 In another study on the ultrastructure of rat jejunum exposed to Pb-acetate (100 mg/kg
16 body wt/day), Tomczok et al. (1991) found that 30-day treatment resulted in numerous small,
17 rough-membraned vesicles and dilated golgi complexes in the cytoplasm. Continued treatment
18 for 60 days resulted in vacuolated cytoplasm associated with the golgi complexes, rough-
19 membraned vesicles, and dilated cisternae. Also, the surface of the intestinal epithelial cell
20 microvilli showed evidence of Pb deposition, as evidenced by Timm sulfide silver reaction sites.
21
22 5.10.2.3 Intestinal Uptake and Transport
23 Infants are a particularly susceptible population for Pb toxicity, possibly due to the
24 immaturity of the digestive tract, feeding pattern, or source of Pb. To investigate these aspects,
25 Henning's group (Beach and Henning, 1988; Henning and Cooper, 1988) carried out a series of
26 experiments using suckling rat pups and reported that Pb in rat and bovine milk and infant milk
27 formula was primarily associated with casein micelles. Casein-bound Pb may be the most
28 common form of Pb presented to the small intestine (Beach and Henning, 1988). Other studies
29 by this group investigated potential differences in the mechanisms when Pb was presented in
30 ionic or milk-bound form, using 203Pb as a tracer. These studies clearly showed that when 203Pb
31 was administered intragastrically as a soluble salt, it was primarily accumulated in the
May 2006 5-274 DRAFT-DO NOT QUOTE OR CITE
-------
1 duodenum, regardless of dose or vehicle used. In contrast, substantial accumulation of 203Pb
2 was found in the ileal tissue following Pb administration in milk. These studies clearly indicated
3 strikingly different patterns in the intestinal accumulation of ionic and milk-bound Pb and
4 suggest a greater toxicity for Pb in drinking water compared to Pb ingestion via milk (Henning
5 and Cooper, 1988).
6 Dekaney et al. (1997) investigated the uptake and transport of Pb using intestinal
7 epithelial cells (IEC-6). The authors observed that Pb accumulation in Pb-exposed (5-10 jiM)
8 IEC-6 cells was time- and dose-dependent up to 1 h and that reduction of the incubation
9 temperature significantly reduced the total cellular Pb content of IEC-6 cells. Simultaneous
10 exposure to Zn resulted in decreased cellular Pb content compared to cells exposed to Pb only.
11 Exposure of cells to ouabin or sodium azide has been found to increase Pb accumulation in the
12 cells compared to cells treated with Pb (5 jiM) alone. These studies clearly demonstrate that Pb
13 transport in IEC-6 cells is time- and temperature-dependent, involves the presence of sulfydryl
14 groups, and competes with the uptake of Zn.
15 Lead speciation and transport across intestinal epithelium in artificial human digestive
16 fluid (chyme), both in vivo and in vitro, in Caco-2 cells were evaluated by Oomen et al. (2003).
17 In vivo studies indicated that in chyme, Pb-phosphate and Pb-bile complexes are important
18 fractions. The metal ions dissociated from these complexes can subsequently be transported
19 across the intestinal epithelium or they may traverse the intestinal membrane. In vitro studies, on
20 the transport of bioaccessible Pb across the intestinal epithelium in Caco-2 cells exposed to
21 diluted artificial chyme for 24 h, indicated that 3% of the Pb was transported across the cell
22 monolayer. Lead associated with cells in a linear relationship to the total amount of Pb in the
23 system. Bile levels were not found to affect the fraction of Pb associated with the cells. The free
24 Pb2+ concentration in chyme was negligible. Extrapolating these results to the in vivo situation,
25 the authors concluded that Pb species other than the free metal ion may have contributed to the
26 Pb flux towards the cells, possibly involving the dissociation of labile Pb species, such as
27 Pb-phosphate and Pb-labile complexes and the subsequent transport of the released free metal
28 ions toward the intestinal membrane.
29
May 2006 5-275 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.10.2.4 Alterations in Gastrointestinal Motility/Gastrointestinal Transit and Function
2 The effect of Pb on contractility of rat duodenum was determined in vivo in rats given an
3 oral dose of Pb-acetate (44 mg/kg per day, Pb as 53 mM/L for 4 weeks) to investigate the
4 possible mechanisms associated with Pb-induced abdominal colic and constipation (Karmakar
5 and Anand, 1989). Deodenal motility and the amplitude of contractility of rat duodenum were
6 decreased significantly in the Pb-exposed rats, leading the authors to conclude that there was a
7 fundamental change in the contractility of the intestinal tract due to Pb intoxication.
8 Chronic Pb ingestion through drinking water (2-5 mg/mL, Pb-acetate for 55 days) caused
9 a 20-fold increase in urinary excretion of D-ALA and an increase in blood Pb level (80 |ig/dL),
10 without any perturbations in propulsive motility of guinea pig colon (Rizzi et al., 1989). On the
11 other hand, Lawler et al. (1991) observed no changes in gastric contractions during ingestion in
12 red-tailed hawks exposed to Pb-acetate (0.82 or 1.64 mg/kg body wt for 3 weeks). This low
13 level of exposure has also been found to have no bearing on the regular passing of pellets of
14 undigested material. Shraideh (1999) studied the effect of triethyl Pb-chloride on the rhythmic
15 and peristalitic contractile activity of ileum isolated from Swiss mice. These authors observed
16 no significant effect below 40 jiM of TEL, while higher concentrations (40-120 jiM) caused
17 changes in contraction rhythm. These studies also reported that TEL above 120 jiM induced
18 irreversible changes in the ileal contractile activity. These and related studies are summarized in
19 Table AX5-10.8.
20
21 5.10.2.5 Lead, Calcium, and Vitamin D Interactions in the Intestine
22 The complex biological interactions between Pb and calcium have been recognized and
23 demonstrated in virtually every type of tissue. Studies of high-affinity Pb binding to intracellular
24 calcium receptors and transport proteins, as well as the involvement of Pb in calcium-activated
25 and calcium-regulated processes, have added to our understanding of the effects of Pb on
26 biological processes at the cellular level. The intestinal absorption of Pb is influenced by a
27 variety of factors, including chemical and physical forms of the element, age at intake, and
28 various nutritional factors. Work dating back to the 1940s established that the deposition of Pb
29 in bone and soft tissue significantly increases under conditions of dietary calcium and
30 phosphorus deprivation or by the administration of vitamin D to rachitic animals. Later, in the
May 2006 5-276 DRAFT-DO NOT QUOTE OR CITE
-------
1 1970s, it was demonstrated that dietary calcium status was a major contributing factor
2 determining relative susceptibility to Pb intoxication.
3 Fullmer's group (Fullmer and Rosen, 1990; Fullmer, 1991, 1992, 1997) carried out a
4 series of studies to investigate the potential interaction between calcium and Pb in the ingestion
5 and intestinal absorption of Pb. Various parameters, such as absorption kinetics for Ca and Pb,
6 activity of alkaline phosphatase, expression of the clabindin D gene, and the potential role of
7 endocrine function in this interaction (as assessed by cholecalciferol and its active hormonal
8 form, 1,25-dihydroxycholecalciferol levels) were investigated. Fullmer and Rosen (1990)
9 observed that chicks fed with low (0.5%) and adequate (1.2%) dietary calcium and exposed to Pb
10 (0-0.8%) exhibited differential effects on intestinal Ca absorption depending on their dietary Ca
11 status. In the chicks fed a low-calcium diet, Pb inhibited intestinal Ca absorption and calbindin
12 D and alkaline phosphatase synthesis in a dose-dependent fashion. On the other hand, chicks fed
13 the normal diet, showed no inhibition of Ca absorption. Based on these results, the authors
14 postulated that Pb-induced alterations in intestinal Ca absorption may involve cholecalciferol and
15 the endocrine system. In an extension of this study using young growing chicks, Fullmer (1991)
16 observed similar results in 2-week Pb-exposed, but not in 1-week exposed, chicks.
17 As dietary Ca deficiency is associated with a marked increase in the body burden of Pb
18 and in the susceptibility to Pb toxicity during chronic ingestion, Fullmer (1992) examined the
19 effects of vitamin D supplementation on intestinal Pb and Ca absorption. When vitamin D-
90^
20 deficient chicks received physiologic amounts of vitamin D (O.lmg/day), intestinal Pb and
21 47Ca absorption rates were elevated by 4- and 8-fold, respectively. Along with this, calbindin D
22 and alkaline phosphatase activities were also found to be significantly elevated. Ingestion of
23 even the highest level of Pb (0.8 %) during the repletion phase had no effect on intestinal Ca
24 absorption. To further understand the Pb-Ca interactions and the potential involvement of
25 vitamin D on intestinal absorption, Fullmer (1997) evaluated serum levels of
26 1,25-dihydroxyvitamin D. Lead ingestion and Ca deficiency alone, or in combination, generally
27 increased serum 1,25-dihydroxyvitamin D levels over most of the ranges of Pb or Ca studied.
28 However, in severe Ca deficiency, Pb ingestion resulted in marked decreases in serum
29 1,25-dihydroxyvitamin D, intestinal Ca absorption, and calbindin D mRNA. From these studies
30 using response surface models, Fullmer (1997) concluded that the interactions between Pb and
May 2006 5-277 DRAFT-DO NOT QUOTE OR CITE
-------
1 Ca were mediated via changes in circulating 1,25-dihydroxy vitamin D hormone, rather than via
2 direct effects on the intestine.
3 Similar to Ca deficiency, iron deficiency has also been found to increase intestinal
4 absorption of Pb, as indicated by increased blood and kidney Pb levels in iron-deficient rats
5 exposed to dietary Pb; but the mechanistic details are not known (Crowe and Morgan, 1996).
6 These and other related studies are summarized in Table AX5-10.9.
7
8 5.10.2.6 Lead and Intestinal Enzymes
9 Differential effects of Pb on intestinal brush border enzyme activity profiles were reported
10 by Gupta et al. (1994). Across a concentration range of 0.5-6.0 mM, Pb-acetate was found to
11 significantly inhibit Ca-Mg-ATpase, g-glutamyl transpeptidase, and acetylcholineesterase
12 activities in a dose-dependent manner without effects on alkaline phosphatase.
13 Cremin et al. (2001) investigated the effects of oral succimer on the intestinal absorption
14 of Pb in infant rhesus monkeys. These studies indicated that chelation therapy with DMSA for
15 two successive 19-day periods significantly decreased GI absorption of Pb and increased urinary
16 excretion of endogenous lead (see Table AX5-10.9).
17
18 Summary
19 • Gastrointestinal absorption of Pb is influenced by a variety of factors, including chemical
20 and physical forms of the element, age at intake, and various nutritional factors. The
21 degeneration of intestinal mucosal epithelium leading to potential malabsorption and
22 alterations in the jejunal ultrastructure (possibly associated with distortion of glycocalyx
23 layer) have been reported in the intestine of Pb-exposed rats.
24 • Lead in rat and bovine milk and, also, infant milk formula was demonstrated to be
25 primarily associated with caseine micelles.
26 • Tracer studies using 203Pb indicated that intragastric administration of Pb as a soluble salt
27 resulted in Pb primarily accumulating in the deuodenum, regardless of dose or vehicle
28 used, whereas Pb from milk was found to be taken up by ileal tissue. Studies also
29 suggested Pb ingestion through water was more toxic than ingestion through milk.
30 • Lead induced decreases in duodenal motility and amplitude of contractility of the
31 intestinal tract has been reported for rats.
32 • Nutritional studies using various levels of Pb, Ca, and vitamin D in the diet indicate
33 competition of Pb with Ca absorption. Supplementation with vitamin D has been
34 reported to enhance intestinal absorption of Ca and lead. Physiological amounts of
35 vitamin D administered to vitamin D-deficient rats resulted in elevated Pb and Ca levels.
May 2006 5-278 DRAFT-DO NOT QUOTE OR CITE
-------
1 In the case of severe Ca deficiency, Pb ingestion results in a marked decrease in serum
2 1,25-dihydroxy vitamin D.
3 Overall, our understanding of Pb effects on hepatic and gastro intestinal systems using in
4 vitro cell culture models and in vivo animal models has increased greatly compared to the 1986
5 AQCD. Significant insights have emerged regarding the role of Pb in hepatic cholesterol
6 synthesis, the role of inflammation in Pb-induced hepatotoxicity, and the contribution of newer
7 chelation therapy in the amelioration of Pb-induced oxidative burden. Similarly, our knowledge
8 has greatly enhanced as to the absorption, transport, and toxicity of Pb in the gastrointestinal
9 tract.
10
11
12 5.11 LEAD-BINDING PROTEINS
13 Lead-binding proteins that are constitutively expressed within the cells and bind Pb can be
14 classified into two types of protein. The first type of Pb-binding proteins are inducible, i.e., their
15 concentration increases after exposure to Pb. The second type of Pb-binding proteins have
16 binding sites that are saturable by Pb, but no discernible increase in protein content occurs after
17 exposure to Pb. The second type is, perhaps, most pertinent to enzymes that can be inhibited
18 byPb.
19 The history of research on Pb-binding proteins dates back to 1936, when the presence of
20 intranuclear inclusion bodies in the liver and kidney as manifestations of Pb poisoning was first
21 described (Blackman, 1936). Later, detailed studies of the composition of renal tubular
22 intranuclear Pb inclusion bodies and consequent alterations in mitochondrial structure and
23 function followed.
24
25 5.11.1 Lead-Binding Proteins within Intranuclear Inclusion Bodies
26 in Kidney
27 Goyer (1968) examined the renal tubules of rats fed 1% Pb-acetate for up to 20 weeks,
28 and found that dense, deeply staining intranuclear inclusions were located in the straight portion
29 of the proximal tubules, accompanied by swollen, globular or ovoid, closely packed
30 mitochondria with many marginated, irregular, or vesicular cristae. Accompanying these
31 mitochondrial changes was the presence of generalized aminoaciduria. Goyer et al. (1968) also
May 2006 5-279 DRAFT-DO NOT QUOTE OR CITE
-------
1 isolated mitochondria from Pb-exposed and control rats and demonstrated that mitochondria
2 from the Pb-exposed rats showed reduced rates of respiration and oxidative phosphorylation.
3 Lead within the kidneys in Pb-poisoned rats was found to be concentrated in the nuclei
4 and, within nuclei, in the nuclear inclusion body (Goyer et al., 1970a,b). Choie and Richter
5 (1972) showed that rapid induction of inclusion bodies by injections of Pb salts in the rat resulted
6 in cytoplasmic inclusions, suggesting that they were precursors to the intranuclear inclusions.
7 This was further confirmed by McLachlin et al. (1980) who showed in tissue culture studies of
8 rat kidney cells incubated with lead that the cytoplasmic inclusion bodies preceded and
9 disappeared shortly after the appearance of nuclear inclusion bodies.
10 Lead-containing nuclear inclusions were also found in organs other than the kidney,
11 including liver and glial cells of the central nervous system (Goyer and Rhyne, 1973). Moore
12 et al. (1973) dissolved the rat renal intranuclear inclusions in strong denaturing agents and found
13 that the protein in the inclusions is acidic, with high levels of aspartic acid, glutamic acid,
14 glycine, and cystine. Moore and Goyer (1974) later characterized the protein as a 27.5 kDa
15 protein, which migrates as a single band on acrylamide gel electrophoresis. Repeated
16 intraperitoneal injections of CaNa2EDTA resulted in the disappearance of the inclusion bodies in
17 Pb-exposed rats, together with a marked decrease in kidney Pb levels (Goyer et al., 1978).
18 Shelton and co-workers have also explored the composition of Pb-binding proteins in the
19 nuclear inclusion proteins of Pb-exposed rat kidneys. Shelton and Egle (1982) first described a
20 32 kDa protein with an isoelectric point of 6.3, which was isolated from the kidneys of rats
21 treated with 1% Pb-acetate in rat chow or 0.75% Pb-acetate in drinking water for 13-17 weeks.
22 In contrast to Goyer and co-workers, they used two-dimensional gel electrophoresis to isolate the
23 protein from the nuclear inclusion bodies and demonstrated that it was present in Pb-exposed,
24 but not control, kidneys (hence, inducible). This protein has been termed p32/6.3. Inhibitor
25 studies with cycloheximide and actinomycin D (McLachlin et al., 1980; Choie et al., 1975) had
26 indicated earlier that protein synthesis was required for induction of the nuclear and cytoplasmic
27 inclusion bodies.
28 Egle and Shelton (1986) unexpectedly found that p32/6.3, now characterized by a
29 monoclonal antibody, was constitutively present in the cerebral cortex, both in neurons and
30 astrocytes. The protein was concentrated in the insoluble nuclear protein, findings similar to the
31 Pb-exposed kidney. Brain p32/6.3 was detected in rat, mouse, dog, man, and chicken. In rat
May 2006 5-280 DRAFT-DO NOT QUOTE OR CITE
-------
1 brain, adult levels were achieved in 1 to 2 weeks after birth, whereas only trace amounts were
2 found at 3 days. Brain p32/6.3 increased between postnatal days 10 to 12 in the guinea pig and
3 days 15 to 21 in the rat, suggesting that the increase may be related in part to exposure to the
4 external environment (Shelton et al., 1993). When neuroblastoma cells were cultured after 1-day
5 and 3-day exposure to Pb, the abundance of p32/6.3 increased. Simultaneous incubation with Pb
6 and cycloheximide or actinomycin D showed an increase in p32/6.3, suggesting that Pb
7 selectively retards the degradation of the brain protein (Klann and Shelton, 1989). The amino
8 acid composition of partially purified p32/6.3 revealed a high percentage of glycine, aspartic and
9 glutamic acid (Shelton et al., 1990). Thus, the inducible protein, p32/6.3, can be extracted from
10 nuclear inclusion bodies from the Pb-exposed rat kidney, and a similar or identical protein from
11 adult rat brain. Whether the brain protein is constitutive or inducible by exposure to
12 environmental Pb has yet to be determined. Selvin-Testa et al. (1991) and Harry et al. (1996)
13 reported that developing rat brain astrocytes exposed to lead developed an elevation in glial
14 fibrillary acidic protein (GFAP), a developmentally-regulated protein. Harry et al. (1996)
15 consider that the elevated levels of GFAP mRNA during the second postnatal week after lead
16 exposure may reflect the demand on astrocytes to sequester lead.
17 Oskarsson and Fowler (1985) examined the influence of pretreatment with Pb by a single
18 IP injection of Pb-acetate (50 mg Pb per kg) 1, 3, and 6 days before injecting 203Pb. Rats were
19 sacrificed 24 h later and the kidneys were examined both microscopically and for the distribution
20 of 203Pb. At 3 days, rat kidneys displayed fibrillar cytoplasmic inclusions, but at 6 days, these
21 inclusions were less prominent and intranuclear inclusions were observed. 203Pb uptake at 6 days
22 was maximal in the purified nuclear fraction and in the nuclear inclusion bodies (7 x and 20 x
23 control, respectively).
24
25 5.11.2 Cytoplasmic Lead-Binding Proteins in Kidney and Brain
26 The remaining studies of non-Pb-stimulated cytoplasmic kidney and brain Pb-binding
27 proteins have been provided by Fowler and associates.
28 The first study (Oskarsson et al., 1982) reported on the Pb-binding proteins in kidney
29 postmitochondrial cytosolic fractions. Binding of 203Pb was found in two protein fractions of
30 control kidneys with molecular weights of 11.5 and 63 kDa. Binding was markedly decreased
31 after Pb pretreatment. The use of cadmium to stimulate metallothionein synthesis did not
May 2006 5-281 DRAFT-DO NOT QUOTE OR CITE
-------
1 increase 203Pb binding to the 11.5 kDa protein. The two binding proteins were also present in
2 brain, but not in liver or lung. Subsequently, Mistry et al. (1985) demonstrated three Pb-binding
3 proteins (11.5, 63, and >200 kDa) in rat kidney cytosol, which had binding characteristics of
4 high affinity, low capacity with respective Kd values of 13, 40, and 123 nM. The 11.5 kDa and,
5 possibly, the 63 kDa proteins were capable of translocating Pb into the nucleus as shown by
6 uptake of 203Pb into nuclei incubated with tagged cytosolic proteins. Goering and Fowler (1984)
7 showed that the 11.5 kDa protein, but not the 63 kDa protein was capable of reversing
8 Pb-induced ALAD inhibition in liver homogenates. This effect was mediated both by chelation
9 of Pb by the Pb-binding protein and by donation of zinc to ALAD (Goering and Fowler, 1985).
10 Various divalent metal ions influence the binding of Pb to the rat kidney cytosolic binding
11 proteins, with an order of displacement of Cd2+>Zn2+>Pb2+. Ca2+ had no effect, while Fe2+ had a
12 cooperative effect (Mistry et al., 1986). These observations may account for the previously
13 demonstrated effect of concomitant Pb and cadmium administration in reducing total kidney Pb
14 (Mahaffey et al., 1981) and preventing the development of intranuclear inclusion bodies
15 (Mahaffey and Fowler, 1977).
16 Later studies by Fowler and Duval (1991) identified the rat renal Pb-binding protein as a
17 cleavage product of oc2-microglobulin, with a Kd of 10"8 M Pb. There are two forms of the
18 protein in the kidney, differentiated by the cleavage of the first 9-N terminal residues from the
19 higher-molecular weight form. Other studies by Smith et al. (1998) found two Pb-binding
20 proteins in environmentally exposed human kidneys, identified as acyl-CoA binding protein
21 (ACBP) or diazepam binding inhibitor (molecular weight 9 kDa) and thymosin (34 (molecular
22 weight 5 kDa). These polypeptides have a high affinity for Pb (Kd~14 nM).
23 In rat brain, Goering et al. (1986) and DuVal and Fowler (1989) explored the effects of
24 environmental Pb on Pb-binding proteins and the ability of rat brain Pb-binding proteins to
25 diminish the inhibition of hepatic ALAD by Pb (liver does not contain the Pb-binding protein).
26 In the first study, a brain protein of 12 kDa was described, in comparison to the kidney
27 Pb-binding protein of 9 kDa. Both competition of Pb binding between the brain Pb-binding
28 protein and ALAD and donation of zinc by the brain protein (shown by 65Zn uptake) were found
29 to account for the decreased ALAD inhibition. In the second study the rat brain Pb-binding
30 protein was described as having a molecular weight of 23 kDa, with significant levels of
31 glutamic acid, aspartic acid, and cysteine. Polyclonal antibody to rat renal Pb-binding proteins
May 2006 5-282 DRAFT-DO NOT QUOTE OR CITE
-------
1 showed a lack of reactivity with the brain protein, indicating that the proteins are
2 immunologically distinct.
3 Fowler et al. (1993) examined monkey kidney and brain from non-Pb-treated animals and
4 isolated Pb-binding proteins that also had a relatively high content of aspartic and glutamic
5 amino acid residues and were similar in size to the rat Pb-binding proteins. Polyclonal
6 antibodies to oc-2 microglobulin and metallothionein did not cross-react with either monkey
7 kidney or brain proteins. Quintanilla-Vega et al. (1995) isolated a thymosin 04 and a second, as
8 yet unidentified, protein with a molecular weight of 20 kDa and a pi of 5.9 from brains of
9 environmentally Pb-exposed humans.
10
11 5.11.3 Lead-Binding Proteins in Erythrocytes
12 Intra-erythrocytic Pb-binding was initially attributed primarily to hemoglobin, molecular
13 weight 64 kDa (Barltrop and Smith, 1972; Raghavan and Gonick, 1977; Ong and Lee, 1980;
14 Lolin and O'Gorman, 1988), but more recent studies have ascribed the major Pb binding to
15 ALAD, molecular weight 240-280 kDa. In contrast to this protein, several studies have focused
16 on an inducible low molecular weight protein in workers chronically exposed to Pb and which
17 seems to have a protective effect. The first recognition of this protein was by Raghavan and
18 Gonick (1977) who found an approximately 10 kDa protein in Pb workers but not in controls,
19 following Sephadex G-75 fractionation (Figure 5-11.1). Upon subsequent SDS-polyacrylamide
20 gel electrophoresis, the protein split into two bands, only the uppermost of which contained Pb
21 (Figure 5-11.2).
22 Raghavan et al. (1980) then went on to fractionate the erythrocyte Pb into a hemoglobin
23 fraction, a 10 kDa fraction, free Pb, and a "residual Pb" fraction thought to be composed of
24 membrane Pb and a high-molecular weight fraction. Lead workers manifesting toxicity at both
25 high blood Pb and relatively low blood Pb levels showed high levels of residual Pb, attributed in
26 the workers with toxicity at low blood leads to a very low quantity of the 10 kDa fraction. In a
27 follow-up study, Raghavan et al. (1981) reported elevated levels of Pb in the high molecular
28 weight fraction (pre-hemoglobin) and in the membrane fraction in workers with toxicity at both
29 high and low BLLs. Again, those with toxicity at low blood Pb had low levels of the Pb bound
30 to the 10 kDa protein. Membrane Pb was found to correlate inversely with membrane
31 NaK-ATPase; no correlation was seen with total blood Pb.
May 2006 5-283 DRAFT-DO NOT QUOTE OR CITE
-------
20r
MW
H300
UW
-1*00
- 200
HlOO
(cpm/mt)
80 100 120 140
ELUTION VOLUME (mi)
160
Figure 5-11.1. Sephadex G-75 gel filtration of RBC hemolysate from lead-exposed
individual. Ultraviolet absorption and radioactivity of 210Pb are plotted
against elution volume. The column was calibrated with ovalbumin (mol
wt 45,000) and ribonuclease (mol wt 13,700). Also indicated is the locus of
hemoglobin (Hb). Hemolysates from normal control individuals showed
no UV absorption or radioactivity in the volume eluting between 130 and
155 mL.
Source: Raghavan and Gonick (1977) with permission.
1 Gonick et al. (1985) partially purified the 10 kDa protein by HPLC using a protein 1-125
2 column followed by isoelectric focusing on a sucrose gradient column. Three protein peaks
3 resulted: one of 30 kDa, and two of 10 kDa. Only one of the latter peaks contained Pb. This
4 peak had a pi of 5.3 and a molecular weight, determined by SDS-PAGE, of 12 kDa.
5 The majority of Pb was found in this peak, which also contained calcium, zinc, and
6 cadmium. Amino acid analysis showed a very high percentage of glycine (44%) and lower
7 quantities of histidine, aspartic acid, and leucine.
8 Ong and Lee (1980) studied the distribution of 203Pb in components of normal human
9 blood. Ninety-four percent of 203Pb was incorporated into the erythrocyte and 6% remained in
10 the plasma. SDS-PAGE of plasma showed that 90% was present in the albumin fraction. Within
11 the erythrocyte membrane, the most important binding site was the high molecular weight
May 2006
5-284
DRAFT-DO NOT QUOTE OR CITE
-------
I
t
B
Apparent
Molecular
Weight
+A 0,000
Figure 5-11.2. SDS-polyacrylamide gel electrophoresis of RBC hemolysates from normal
control (A) and lead-exposed individuals (B), and of low-mol-wt. lead-
binding protein (C) stained with coomassie blue.
Source: Raghavan and Gonick (1977) with permission.
1 fraction, about 130-230 kDa. Within the erythrocytic cytoplasm, the protein band associated
2 with 203Pb had a molecular weight of 67 kDa as shown by the elution characteristics on G-75
3 chromatography. This was thought to be hemoglobin.
4 Lolin and O'Gorman (1988) and Church et al. (1993 a,b), following the same procedure
5 as Raghavan and Gonick (1977), confirmed the findings of a low molecular weight protein in the
6 erythrocytes of Pb workers, but not found in control patients. Lolin and O'Gorman (1988)
7 quantitated the protein, which ranged from 8.2 to 52.2 mg/L RBC in Pb workers but found none
8 in controls, again implying it to be an inducible protein. They found that the low molecular
9 weight protein first appeared when the blood Pb concentration exceeded 39 |ig/dL. A positive
10 correlation was seen between the amount of the intra-erythocytic low molecular weight protein
11 and dithiothreitol-activated ALAD activity but not the non-activated activity. Church et al.
May 2006
5-285
DRAFT-DO NOT QUOTE OR CITE
-------
1 (1993a,b) also confirmed the findings of Raghavan and Gonick (1977). In 1993a, they described
2 two patients with high blood Pb levels: an asymptomatic worker with a blood Pb of 180 |ig/dL,
3 and a symptomatic worker with a blood Pb of 161 |ig/dL. In the first patient, approximately 67%
4 of the erythrocyte Pb was bound to a low molecular weight protein of approximately 6-7 kDa.
5 In the second patient, the protein only contained 22% of the total erythrocytic Pb. Church et al.
6 (1993b) found that a sample of the low molecular weight protein purified from Pb workers,
7 which they termed protein M, had characteristics of metallothionein, such as a molecular weight
8 of 6.5 kDa, a pi between 4.7 and 4.9, and a greater UV absorbance at 254 nm than at 280 nm.
9 Amino acid composition showed 33% cysteine but no aromatic amino acids. This composition
10 differed from that of the low molecular weight protein described by Gonick et al. (1985), which
11 had a molecule weight of 12 kDa, a pi of 5.3, and amino acid analysis that showed no cysteine.
12 This discrepancy might be explained by a combined Pb and cadmium exposure in the Church
13 et al. (1993b) study, which may have produced a Pb-thionein.
14 Xie et al. (1998) used a Biogel A column instead of Sephadex G-75 to separate
15 Pb-binding proteins from erythrocyte hemolysates from a control patient and from Pb-exposed
16 workers. They clearly showed that the major Pb-binding was associated with a large molecular
17 weight protein, consistent with ALAD, in both the controls and Pb workers. When they added
18 increasing amounts of Pb to the blood of the control patient, a second low molecular weight
19 protein peak occurred, in which Pb binding was larger than the ALAD peak (Figure 5-11.3).
20 This second peak was also seen in a chronically Pb-exposed worker (Figure 5-11.4) and was
21 estimated to be less than 30 kDa in molecular weight. Thus these results are consistent with the
22 aforementioned studies.
23
24 5.11.4 Lead-Binding Proteins in Rat Liver
25 Sabbioni and Marafante (1976) explored the distribution of 203Pb in rat whole tissue as well as in
26 subcellular liver fractions. By far the largest quantity of Pb recovered was in the kidney, with
27 lesser amounts in liver, spleen, and blood. Upon subcellular fractionation of the liver, the
28 majority of 203Pb was found in the nuclei, and most of the Pb was detected in the nuclear
29 membrane fraction, bound exclusively to membrane proteins. The intranuclear Pb was
30 associated with histone fractions. As reported by Oskarsson et al. (1982), Pb binding proteins
31 were not found in the cytoplasm of the liver.
May 2006 5-286 DRAFT-DO NOT QUOTE OR CITE
-------
Pb Cone.
ALAD Activity
Se Cone.
Protein
11
16
21
26
31
36
0.8
0.6
(0
«
D
O
0.4 -f
0.2
30
S 25
O
•§ 20
. 15
s>
I 10
I
o 5
0
11 16 21 26
Fraction number
31
36
0.8
Of,
.6
®-
8
O
0.4
0.2
Figure 5-11.3. Chromatographic profiles of protein, ALAD activity and Pb in human
erythrocytes incubated with 5% glucose solution containing Pb acetate.
Blood was incubated (a) without Pb (b) 10 uM Pb (final concentrations).
Source: Adapted from Xie et al. (1998).
1 5.11.5 Lead-Binding Proteins in Intestine
2 Fullmer et al. (1985) showed in the chick and cow that although Pb does not directly
3 stimulate Pb-binding proteins in the intestine, Pb can displace calcium from calcium-binding
4 proteins; and, thus, calcium-binding proteins may play a role in intestinal Pb transport. Purified
5 calcium-binding protein from chick and cow, as well as calmodulin, troponin C, and
May 2006
5-287
DRAFT-DO NOT QUOTE OR CITE
-------
20
O 15
10
20
8 15
10
-Q
Q.
20
O
00
I
O 15
c
a
•-^
Dl 10
I
Pb Cone.
ALAD Cone.
Se Cone.
Protein
11
11
16
21
16
21
26
31
11 16 21 26 31
Fraction number
36
36
36
to
in
D
0.6 O
2-
0.4 1
0.2 <
ID
10
D
0.6 O
£•
0.4 1
0.2
0.8 5T
in
in
O
0.6 Q.
0.2 <
Figure 5-11.4. Chromatic profiles of protein, ALAD activity, Pb, and Se in the
erythrocytes of lead-exposed workers, (a) control, (b) subacute
exposure, (c) chronic exposure.
Source: Xie et al. (1998) with permission.
May 2006
5-288
DRAFT-DO NOT QUOTE OR CITE
-------
1 oncomodulin were dialyzed against added labeled and unlabeled Pb or calcium. Results
2 disclosed high affinity binding sites, with greater affinity for Pb than for calcium. Similar results
3 were obtained with calmodulin, troponin C, and oncomodulin, all members of the troponin C
4 superfamily of calcium-binding proteins.
5
6 5.11.6 Lead-binding Protein in Lung
7 Singh et al. (1999) described intracellular lead-inclusion bodies in normal human lung
8 small airway epithelial cells cultured with either lead chromate particles or sodium chromate.
9 Cells exposed to both forms of chromate underwent dose-dependent apoptosis. Lead-inclusion
10 bodies were found in nucleus and cytoplasm of lead chromate, but not sodiumchromate, treated
11 cells. Lead, but not chromium, was detected in the inclusion bodies by energy-dispersive X-ray
12 analysis. The protein within the inclusion bodies has not been analyzed.
13
14 5.11.7 Relationship of Lead-Binding Protein to Metallothionein
15 Similarities of Pb-binding protein to metallothionein have been discussed earlier. Maitani
16 et al. (1986) commented that hepatic zinc-metallothionein could be induced by intravenous and
17 intraperitoneal injections of Pb into mice, but not by subcutaneous injection. Ikebuchi et al.
18 (1986) found that a sublethal dose of Pb-acetate injected intraperitoneally into rats induced the
19 synthesis of a Pb-metallothionein in addition to zinc-metallothionein. The Pb-metallothionein
20 contained 28% half-cysteine and cross-reacted with an antibody against rat zinc-thionein II.
21 Goering and Fowler (1987 a,b) demonstrated that pretreatment of rats with zinc 48 and
22 24 h prior to injection of 203Pb resulted in both zinc and Pb co-eluting with a zinc-thionein
23 fraction on Sephadex G-75 filtration. In addition, both purified zinc-thionein-I and II bound
24 203Pb in vitro. Gel filtration of incubates containing liver ALAD and 203Pb demonstrated that the
25 presence of zinc-thionein alters the cytosolic binding pattern of Pb, with less binding to ALAD.
26 Zinc-thionein also donates zinc to activate ALAD. Goering and Fowler (1987b) found that
27 pretreatment of rats with either cadmium or zinc affected liver ALAD activity when incubated
28 with Pb. Liver and kidney zinc-thioneins, and to a lesser extent, cadmium, zinc-thionein
29 decreased the free pool of Pb available to interact with ALAD, resulting in attenuated ALAD
30 inhibition. Liu et al. (1991) further showed that zinc-induced metallothionein in primary
May 2006 5-289 DRAFT-DO NOT QUOTE OR CITE
-------
1 hepatocyte cultures protects against Pb-induced cytotoxicity, as assessed by enzyme leakage and
2 loss of intracellular potassium.
3 Qu et al. (2002) and Waalkes et al. (2004) have shown that metallothionein-null
4 phenotypic mice are more susceptible to Pb injury over a 20-week period than wild type mice.
5 Unlike the wild type mice, Pb-treated metallothionein-null mice showed nephromegaly and
6 significantly decreased renal function after exposure to Pb. The metallothionein-null mice
7 accumulated less renal Pb than wild type and formed no inclusion bodies. When the
8 observations were extended to 104 weeks, renal proliferative lesions (adenoma and cystic tubular
9 atypical hyperplasia) were more common and severe in metallothionein-null than in wild type
10 mice. A metastatic renal cell carcinoma occurred in a metallothionein-null mouse, whereas none
11 occurred in wild type mice. Such studies lend credence to the view that metallothinein, or a
12 closely related gene, is involved in the formation of Pb-binding proteins in the kidney.
13
14 5.11.8 Is ALAD an Inducible Enzyme and Is It the Principal Lead-Binding
15 Protein in the Erythrocyte?
16 The enzyme ALAD has been found to be the most sensitive indicator of Pb exposure and
17 toxicity (Granick et al., 1973, Buchet et al., 1976). In the 1980s, two articles were presented
18 appearing to show that ALAD is inducible after Pb exposure in humans. By comparing a
19 nonexposed control population of Pb workers and assaying ALAD by means of immunoassay or
20 as "restored" ALAD activity (i.e., incubation with heat, zinc and dithiothreitol) both articles
21 indicated that the amount of ALAD, as contrasted to ALAD activity, was increased by Pb
22 exposure (Fujita et al., 1982; Boudene et al., 1984). Similar findings were reported for the rat
23 (Fujita et al., 1981). Subsequent studies have focused on the effect of ALAD polymorphism on
24 the susceptibility to Pb intoxication. ALAD is a zinc-containing enzyme, which catalyzes the
25 second step of heme synthesis, i.e., catalyzes the condensation of two delta-aminolevulinic acid
26 molecules into one molecule of porphobilinogen (Boudene et al., 1984). It is a polymorphic
27 protein with three isoforms: ALAD-1, ALAD 1-2, and ALAD 2-2. Several studies have shown
28 that, with the same exposure to Pb, individuals with the ALAD-2 gene have higher blood Pb
29 levels (Astrin et al., 1987; Wetmur, 1994; Wetmur et al., 1991; Smith et al., 1995a; Bergdahl
30 et al., 1997; Perez-Bravo et al., 2004; Kim et al., 2004). Initially it was thought that these
31 individuals might be more susceptible to Pb poisoning (Wetmur et al., 1991), but it is now
May 2006 5-290 DRAFT-DO NOT QUOTE OR CITE
-------
1 appreciated that the ALAD-2 gene offers protection against Pb poisoning by binding Pb more
2 securely (Kelada et al., 2001). In support of this statement, it can be cited that individuals with
3 the ALAD 1-2/2-2 genotypes, in comparison to those with the ALAD 1-1 genotype, have not
4 only higher blood Pb but also decreased plasma levulinic acid (Schwartz et al., 1997), lower zinc
5 protopophyrin (Kim et al., 2004), lower cortical bone Pb (Smith et al., 1995b), and lower
6 amounts of DMSA-chelatable Pb (Schwartz et al., 1997, 2000).
7 The significance of erythrocyte ALAD binding to Pb was initially confirmed by a study
8 by Bergdahl et al. (1997) in which the authors used a FPLC Superdex 200 HR 10/30
9 chromatographic column coupled to ICP-MS (for determination of Pb) to examine erythrocytes
10 from Pb workers and controls. They found the principal Pb-binding protein peak to be 240 kDa
11 (rather than the presumed hemoglobin peak reported by Barltrop and Smith (1972) and
12 Raghavan and Gonick (1977), using Sephadex G-75 chromatography). This was shown to be
13 ALAD by binding to specific ALAD antibodies. Two additional smaller Pb-binding peaks of
14 45 kDA and 10 kDa were also seen, but not identified. Bergdahl et al. (1997) attributed the
15 discrepancies in the studies to the fact that Sephadex G-75 separates proteins in the range of 3 to
16 80 kDa, making the separation of hemoglobin (molecular weight 64 kDa) from ALAD
17 (molecular weight 240-280 kDa) very difficult. In addition, the earlier studies had utilized
18 binding of 203Pb or 210Pb to identify the binding proteins, a technique which may have skewed
19 the findings if ALAD were already saturated. ALAD binding capacity for Pb has been measured
20 at 85 |ig/dL in erythrocytes or 40 |ig/dL in whole blood (Bergdahl et al., 1998), which would
21 permit a greater degree of binding to the low molecular weight component when blood Pb
22 exceeded 40 |ig/dL. Bergdahl et al. (1998) have speculated that the low molecular weight
23 component might be acyl-CoA-binding protein, identical to the kidney Pb-binding protein
24 described by Smith et al. (1995b). Goering and Fowler (1987) had reported earlier that the
25 presence of low molecular weight high affinity (Kd 10"8M) Pb-binding proteins in kidney and
26 brain served as protection against ALAD inhibition in those organs, whereas the absence of the
27 low molecular weight proteins in liver contributed to the greater sensitivity to ALAD inhibition
28 in that organ.
29 A summary of the findings on Pb-binding protein can be found in Table AX5-11.1.
30
May 2006 5-291 DRAFT-DO NOT QUOTE OR CITE
-------
1 Summary
2 • Nuclear inclusion bodies stimulated by lead have been extensively investigated. The
3 nuclear inclusion body within the kidney and brain of rats contains a relatively insoluble
4 protein, tentatively identified as a 32 kDa protein with an isoelectric point of 6.3. The
5 nuclear inclusion body is preceded by the development and subsequent disappearance of a
6 cytoplasmic inclusion body. Whether the proteins within these two inclusion bodies are
7 similar or the same remains to be determined.
8 • There appears to be a consensus that the enzyme, ALAD, a 280 kDa protein, is inducible
9 and is the major Pb-binding protein within the erythrocyte. ALAD polymorphism
10 influences the degree of Pb-binding as the ALAD-2 phenotype binds more Pb in a
11 nontoxic fashion than ALAD-1. What is more confusing is the nature and importance of
12 the low molecular weight erythrocytic Pb-binding protein. There is no doubt that it
13 appears in Pb-exposed workers but not in controls and that its molecular weight is
14 approximately 10 kDa. The in vitro addition of Pb to erythrocytes of controls results in
15 progressively increasing Pb binding to a low molecular weight protein peak migrating in
16 the same position as the low molecular weight protein from Pb workers. This confirms
17 the fact that once the binding capacity of ALAD is saturated, Pb shifts to the low
18 molecular weight protein. The nature of the low-molecular weight protein is also
19 questionable; it has been variously identified as a 12 kDa protein with a high percentage of
20 glycine plus histidine, aspartic acid, and leucine and as a 6.5 kDa molecule with a large
21 percentage of cysteine and a greater UV absorbance at 254 than 280 nm. The latter
22 findings suggest that the protein might be a metallothionein.
23 • Metallothionein is a protein that is mildly inducible by Pb but to a much greater degree by
24 zinc and cadmium. What is more significant is that Pb binds to pre-formed
25 metallothionein, stimulated by zinc or cadmium, so that under these conditions a
26 Pb-thionein forms. Thus, if concomitant Pb and cadmium exposure occurred in Pb
27 workers that could account for the finding of a metallothionein-like protein in those
28 workers.
29 • The possible role of metallothionein as a renal Pb-binding protein assumes greater
30 importance because of the work showing that metallothionein-null mice failed to respond
31 to Pb exposure by developing intranuclear Pb inclusion bodies or greatly increased Pb
3 2 content of the ki dney s.
33 • Extensive studies of cytoplasmic Pb-binding proteins in non-Pb-treated rats, human, and
34 monkeys have been reported. The Pb-binding protein in rat kidney has been identified as
35 a cleavage product of a-2 microglobulin. The low molecular weight Pb-binding proteins
36 in human kidney have been identified as thymosin 04 (molecular weight 5 kDa) and acyl-
37 CoA binding protein (molecular weight 9 kDa). In human brain the Pb-binding proteins
38 were thymosin 04 and an unidentified protein of 23 kDa. Antibodies to a-2 microglobulin
39 and metallothionein did not cross-react with monkey kidney or brain Pb-binding proteins,
40 suggesting species differences. Whether the low molecular weight human kidney and
41 brain Pb-binding proteins are similar or identical to the low molecular weight Pb-binding
42 proteins in erythrocytes is at present unknown. Perhaps some clarification would be
43 provided were subsequent investigators to contrast normal with Pb-exposed rats and to
May 2006 5-292 DRAFT-DO NOT QUOTE OR CITE
-------
1 measure the resting and inducible Pb-binding protein levels in kidney, brain, and
2 erythrocyte.
May 2006 5-293 DRAFT-DO NOT QUOTE OR CITE
-------
1 REFERENCES
2 Abdollahi, M; Dehpour, A. R.; Fooladgar, M. (1997) Alteration of rat submandibulary gland secretion of protein,
3 calcium and 7V-acetyl-p-D-glucosaminidase activity by lead. Gen. Pharmacol. 29: 675-680.
4 Aboul-Ela, E. I. (2002) The protective effect of calcium against genotoxicity of lead acetate administration on bone
5 marrow and spermatocyte cells of mice in vivo. Mutat. Res. 516: 1-9.
6 Acharya, U. R.; Acharya, S.; Mishra, M. (2003) Lead acetate induced cytotoxicity in male germinal cells of Swiss
7 mice. Ind. Health 41: 291-294.
8 Ades, A. E.; Kazantzis, G. (1988) Lung cancer in a non-ferrous smelter: the role of cadmium. Br. J. Ind. Med.
9 45; 435-442.
10 Adhikari, N.; Sinha, N.; Saxena, D. K. (2000) Effect of lead on Sertoli-germ cell coculture of rat. Toxicol. Lett.
11 116:45-49.
12 Adhikari, N.; Sinha, N.; Narayan, R.; Saxena, D. K. (2001) Lead-induced cell death in testes of young rats. J. Appl.
13 Toxicol. 21:275-277.
14 Adrian, G. S.; Rivera, E. V.; Adrian, E. K.; Lu, Y.; Buchanan, J.; Herbert, D. C.; Weaker, F. J.; Walter, C. A.;
15 Bowman, B. H. (1993) Lead suppresses chimeric human transferrin gene expression in transgenic mouse
16 liver. Neurotoxicology 14: 273-282.
17 Alber, S. A.; Strupp, B. J. (1996) An in-depth analysis of lead effects in a delayed spatial alternation task:
18 assessment of mnemonic effects, side bias, and proactive interference. Neurotoxicol. Teratol. 18:3-15.
19 Al-Hakkak, Z. S.; Zahid, Z. R.; Ibrahim, D. K.; Al-Jumaily, I. S.; Bazzaz, A. A. (1988) Effects of ingestion of lead
20 monoxide alloy on male mouse reproduction. Arch. Toxicol. 62: 97-100.
21 Alkondon, M.; Costa, A. C. S.; Radhakrishnan, V.; Aronstam, R. S.; Albuquerque, E. X. (1990) Selective blockade
22 of NMDA-activated channel currents may be implicated in learning deficits caused by lead. FEES Lett.
23 261: 124-130.
24 Alomran, A. H.; Shleamoon, M. N. (1988) The influence of chronic lead exposure on lymphocyte proliferative
25 response and immunoglobulin levels in storage battery workers. J. Biol. Sci. Res. 19: 575-585.
26 Altmann, L.; Weinsberg, F.; Sveinsson, K.; Lilienthal, H.; Wiegand, H.; Winneke, G. (1993) Impairment of long-
27 term potentiation and learning following chronic lead exposure. Toxicol. Lett. 66: 105-112.
28 Alvarez, J.; Garcia-Sancho, J.; Herreros, B. (1986) Inhibition of Ca2+-dependent K+ channels by lead in one-step
29 inside-out vesicles from human red cell membranes. Biochim. Biophys. Acta 857: 291-294.
30 Amoruso, M. A.; Witz, G.; Goldstein, B. D. (1987) Alteration of erythrocyte membrane fluidity by heavy metal
31 cations. Toxicol. Ind. Health 3: 135-144.
32 Angell, N. F.; Weiss, B. (1982) Operant behavior of rats exposed to lead before or after weaning. Toxicol. Appl.
33 Pharmacol. 63:62-71.
34 Angle, C. R.; Thomas, D. J.; Swanson, S. A. (1990) Lead inhibits the basal and stimulated responses of a rat
35 osteoblast-like cell line ROS 17/2.8 to la, 25-dihydroxyvitaminD3 and IGF-I. Toxicol Appl. Pharmacol.
36 103:281-287.
37 Angle, C. R.; Thomas, D. J.; Swanson, S. A. (1993) Osteotoxicity of cadmium and lead inHOS TE 85 and ROS
3 8 17/2.8 cells: relation to metallothionein induction and mitochondrial binding. BioMetals 6: 179-184.
39 Antonowicz, J.; Andrzejak, R.; Smolik, R. (1990) Influence of heavy metal mixtures on erythrocyte metabolism. Int.
40 Arch. Occup. Environ. Health 62: 195-198.
41 Anttila, A.; Heikkila, P.; Pukkala, E.; Nykyri, E.; Kauppinen, T.; Hernberg, S; Hemminki, K. (1995) Excess lung
42 cancer among workers exposed to lead. Scand. J. Work Environ. Health. 21: 460-469.
43 Anttila, A.; Heikkila, P.; Nykyri, E.; Kauppinen, T.; Pukkala, E.; Hernberg, S.; Hemminki, K. (1996) Risk of
44 nervous system cancer among workers exposed to lead. J. Occup. Environ. Med. 38: 131-136.
45 Anwar, W. A.; Kamal, A. A. M. (1988) Cytogenetic effects in a group of traffic policemen in Cairo. Mutat Res.
46 208:225-231.
47 Apostoli, P.; Romeo, L.; De Matteis, M. C.; Menegazzi, M.; Faggionato, G.; Vettore, L. (1988) Effects of lead on
48 red blood cell membrane proteins. Int. Arch. Occup. Environ. Health 61: 71-75.
49 Apostoli, P.; Huard, C.; Chaumontet, C.; Mattel, P.; Allesio, L.; Mazzoleni, G. (2000) Effects of four inorganic lead
50 compounds on the proliferation and junctional coupling of cultured REL liver cells. Am. J. Ind. Med.
51 38:340-348.
52 Appleton, J. (1991) The effect of lead acetate on dentine formation in the rat. Arch. Oral Biol. 36: 377-382.
53 Appleton, J. (1992) Dentinogenesis and the calciotraumatic response to the injection of lead or fluoride ions.
54 Scanning Microsc. 6: 1073-1081.
May 2006 5-294 DRAFT-DO NOT QUOTE OR CITE
-------
1 Areola, O. O.; Jadhav, A. L. (2001) Low-level lead exposure modulates effects of quinpirole and eticlopride on
2 response rates in a fixed-interval schedule. Pharmacol. Biochem. Behav. 69: 151-156.
3 Ariza, M. E.; Williams, M. V. (1996) Mutagenesis of AS52 cells by low concentrations of lead(II) and mercury(II).
4 Environ. Mol. Mutagen. 27: 30-33.
5 Ariza, M. E.; Bijur, G. N.; Williams, M. V. (1998) Lead and mercury mutagenesis: role of H2O2, superoxide
6 dismutase, and xanthine oxidase. Environ. Mol. Mutagen. 31: 352-361.
7 Arizono, K.; Sugiura, S.; Miyazato, S.; Takiguchi, M.; Ariyoshi, T. (1996) DT-diaphorase induction by lead acetate
8 in the liver of rats. Bull. Environ. Contam. Toxicol. 57: 41-46.
9 Astrin, K. H.; Bishop, D. F.; Wetmur, J. G.; Kaul, B.; Davidow, B.; Desnick, R. J. (1987) 5-aminolevulinic acid
10 dehydratase isozymes and lead toxicity. In: Silbergeld, E. K.; Fowler, B. A., eds. Mechanisms of chemical-
11 induced porphyrinopathies. New York, NY: New York Academy of Sciences; pp. 23-29. (Annals of the
12 New Yord Academy of Sciences: v. 514).
13 Attri, J.; Dhawan, V.; Mahmood, S.; Pandhi, P.; Parwana, H. K.; Nath, R. (2003) Effect of vitamin C
14 supplementation on oxidative DNA damage in an experimental model of lead-induced hypertension. Ann.
15 Nutr. Metab. 47: 294-301.
16 Aykin-Burns, N.; Laegeler, A.; Kellogg, G.; Ercal, N. (2003) Oxidative effects of lead in young and adult Fisher 344
17 rats. Arch. Environ. Contam. Toxicol. 44: 417-420.
18 Baginski, B.; Grube, B. (1991) EinfluB vonblei, zink, und cadmium auf die zelltoxische wirkung humaner
19 polymorphkerniger leukozyten am beispiel von hefzellen. Zentralbl. Hyg. Umweltmed. 191:28-35.
20 Ban, M.; Hettich, D. (2005) Effect of Th2 cytokine antagonist treatments on chemical-induced allergic response in
21 mice. J. Appl. Toxicol. 25: 239-247.
22 Bannon, D. I.; Olivi, L.; Bressler, J. (2000) The role of anion exchange in the uptake of Pb by human erythrocytes
23 and Madin-Darby canine kidney cells. Toxicology 147: 101-107.
24 Baranowska-Bosiacka, I.; Hlynczak, A. J. (2003) The effect of lead ions on the energy metabolism of human
25 erythrocytes in vitro. Comp. Biochem. Physiol. Part C: Toxicol. Pharmacol. 134: 403-416.
26 Baranowska-Bosiacka, I.; Hlynczak, A. J. (2004) Effect of lead ions on rat erythrocyte purine content. Biol. Trace
27 Elem. Res. 100: 259-273.
28 Barbier, O.; Jacquillet, G.; Tauc, M.; Cougnon, M.; Poujeol, P. (2005) Effect of heavy metals on, and handling by,
29 the kidney. Nephron. Physiol. 99: 105-110.
30 Barltrop, D.; Smith, A. (1972) Lead binding to human haemoglobin. Experientia 28:16-11.
31 Barnett, J. B. (1996) Developmental immunotoxicology. In. Smialowicz, R. J.; Holsapple, M. P., eds. Experimental
32 immunotoxicology. Boca Raton, FL: CRC Press, Inc.; 47-62.
33 Barnum-Huckins, K. M.; Martinez, A. O.; Rivera, E. V.; Adrian, E. K., Jr.; Herbert, D. C.; Weaker, F. J.; Walter, C.
34 A.; Adrian, G. S. (1997) A comparison of the suppression of human transferrin synthesis by lead and
35 lipopolysaccharide. Toxicology 118: 11-22.
36 Barthalmus, G. T.; Leander, J. D.; McMillan, D. E.; Mushak, P.; Krigman, M. R. (1977) Chronic effects of lead on
37 schedule-controlled pigeon behavior. Toxicol. Appl. Pharmacol. 42: 271-284.
38 Basaran, N.; Undeger, U. (2000) Effects of lead on immune parameters in occupationally exposed workers. Am. J.
39 Ind. Med. 38: 349-354.
40 Basha, M. R.; Wei, W.; Bakheet, S. A.; Benitez, N.; Siddiqi, H. K.; Ge, Y.-W.; Lahiri, D. K.; Zawia, N. H. (2005)
41 The fetal basis of amyloidogenesis: exposure to lead and latent overexpresson of amyloid precursor protein
42 and p-amyloid in the aging brain. J. Neurosci. 25: 823-829.
43 Bataineh, H.; Al-Hamood, M. H.; Elbetieha, A. M. (1998) Assessment of aggression, sexual behavior and fertility in
44 adult male rat following long-term ingestion of four industrial metals salts. Human Exp. Toxicol.
45 17:570-576.
46 Batetta, B.; Dessi, S.; Pulisci, D.; Carrucciu, A.; Pani, P. (1990) Multiple molecular forms of rat liver glucose-6-
47 phosphate dehydrogenase during liver hyperplasia induced by lead nitrate. Res. Commun. Chem. Pathol.
48 Pharmacol. 67: 279-288.
49 Batra, N.; Nehru, B.; Bansal, M. P. (2001) Influence of lead and zinc on rat male reproduction at 'biochemical and
50 histopathological levels'. J. Appl. Toxicol. 21: 507-512.
51 Baykov, B.; Gunova, M.; Stoyanov, M.; Neychev, H.; Stefanova, T.; Nicolova, N. (1996) Designing an artificial
52 ecological mesocosm for the study of Cd and Pb impact on the immune system of experimental animals.
53 Toxicol Lett. 89:5-10.
54 Beach, J. R.;Henning, S. J. (1988) The distribution of lead in milk and the fate of milk lead in the gastrointestinal
55 tract of suckling rats. Pediatr. Res. 23: 58-62.
May 2006 5-295 DRAFT-DO NOT QUOTE OR CITE
-------
1 Bellinger, D. C. (2004) What is an adverse effect? A possible resolution of clinical and epidemiological
2 perspectives on neurobehavioral toxicity. Environ. Res. 95: 394-405.
3 Bellinger, D.; Sloman, I; Leviton, A.; Rabinowitz, M; Needleman, H. L.; Waternaux, C. (1991) Low-level lead
4 exposure and children's cognitive function in the preschool years. Pediatrics 87: 219-227.
5 Bellinger, D. C.; Stiles, K. M.; Needleman, H. L. (1992) Low-level lead exposure, intelligence and academic
6 achievement: a long-term follow-up study. Pediatrics 90: 855-861.
7 Bellinger, D.; Hu, H.; Titlebaum, L.; Needleman, H. L. (1994) Attentional correlates of dentin and bone lead levels
8 in adolescents. Arch. Environ. Health 49: 98-105.
9 Belloni-Olivi, L.; Annadata, M.; Goldstein, G. W.; Bressler, J. P. (1996) Phosphorylation of membrane proteins in
10 erythrocytes treated with lead. Biochem. J. 315: 401-406.
11 Bendich, A.; Belisle, E. H.; Strausser, H. R. (1981) Immune responses of rats chronically fed subclinical doses of
12 lead. Clin. Exp. Immunol. 43: 189-194.
13 Bergdahl, I. A.; Grubb, A.; Schtitz, A.; Desnick, R. J.; Wetmur, J. G.; Sassa, S.; Skerfving, S. (1997) Lead binding
14 to 5-aminolevulinic acid dehydratase (ALAD) in human erythrocytes. Pharmacol. Toxicol. 81: 153-158.
15 Bergdahl, I. A.; Sheveleva, M.; Schtitz, A.; Artamonova, V. G.; Skerfving, S. (1998) Plasma and blood lead in
16 humans: capacity-limited binding to 5-aminolevulinic acid dehydratase and other lead-binding components.
17 Toxicol. Sci. 46: 247-253.
18 Bernard, A.; Lauwerys, R. (1987) Metal-induced alterations of 5-aminolevulinic acid dehydratase. In: Silbergeld,
19 E. K.; Fowler, B. A., eds. Mechanisms of chemical-induced porphyrinopathies. New York, NY: New York
20 Academy of Sciences; pp. 41-47. [Annals of the New York Academy of Sciences: v. 514].
21 Bernard, S. M.; McGeehin, M. A. (2003) Prevalence of blood lead levels > 5 ug/dL among US children 1 to 5 years
22 of age and socioeconomic and demographic factors associated with blood of lead levels 5 to 10 ug/dL,
23 Third National Health and Nutrition Examination Survey, 1988-1994. Pediatrics 112: 1308-1313.
24 Berry, W. D., Jr.; Moriarty, C. M.; Lau, Y. S. (2002) Lead attenuation of episodic growth hormone secretion in male
25 rats. Int. J. Toxicol. 21: 93-98.
26 Bhattacharya, A.; Shukla, R.; Dietrich, K. N.; Miller, J.; Bagchee, A.; Bornschein, R. L.; Cox, C.; Mitchell, T.
27 (1993) Functional implications of postural disequilibrium due to lead exposure. Neurotoxicology
28 14: 179-189.
29 Biedermann, K. A.; Landolph, J. R. (1987) Induction of anchorage independence in human diploid foreskin
30 fibroblasts by carcinogenic metal salts. Cancer Res. 47: 3815-3823.
31 Biedermann, K. A.; Landolph, J. R. (1990) Role of valence state and solubility of chromium compounds on
32 induction of cytotoxicity, mutagenesis, and anchorage independence in diploid human fibroblasts.
33 Cancer Res. 50: 7835-7842.
34 Bielarczyk, H.; Tian, X.; Suszkiw, J. B. (1996) Cholinergic denervation-like changes in rat hippocampus following
3 5 developmental lead exposure. Brain Res. 708: 108-115.
3 6 Bilban, M. (1998) Influence of the work environment in a Pb-Zn mine on the incidence of cytogenetic damage in
37 miners. Am. J. Ind. Med. 34: 455-463.
38 Bizarro, P.; Acevedok, S.; Nino-Cabrera, G.; Mussali-Galante, P.; Pasos, F.; Avila-Costa, M. R.; Fortoul, T. I.
3 9 (2003) Ultrastructural modifications in the mitochondrion of mouse Sertoli cells after inhalation of lead,
40 cadmium or lead-cadmium mixture. Reprod. Toxicol. 17: 561-566.
41 Blackman, S. S., Jr. (1936) Intranuclear inclusion bodies in the kidney and liver caused by lead poisoning.
42 Bull. Johns Hopkins Hosp. 58: 384-402.
43 Blakley, B. R. (1987) The effect of lead on chemical- and viral-induced tumor production in mice. J. Appl. Toxicol.
44 7: 167-172.
45 Blakley, B. R.; Archer, D. L. (1981) The effect of lead acetate on the immune response in mice. Toxicol. Appl.
46 Pharmacol. 61: 18-26.
47 Blakley, B. R.; Sisodia, C. S.; Mukkur, T. K. (1980) The effect of methylmercury, tetraethyl lead, and sodium
48 arsenite on the humoral immune response in mice. Toxicol. Appl. Pharmacol. 52: 245-254.
49 Blankenship, L. J.; Carlisle, D. L.; Wise, J. P., Sr; Orenstein, J. M.; Dye, L. E., Ill; Patierno, S. R. (1997) Induction
50 of apoptotic cell death by paniculate lead chromate: differential effects of vitamins C and E on genotoxicity
51 and survival. Toxicol. Appl. Pharmacol. 146: 270-280.
52 Blanusa, M.; Kostial, K.; Piasek, M.; Jones, M. M.; Singh, P. K. (1995) Reduction of lead retention by mono-3-
53 methylbutan-1-yl 7weso-2,3-dimercaptosuccinate in suckling rats. Analyst (Cambridge, U. K.)
54 120:951953.
55 Blazka, M. E.; Harry, G. J.; Luster, M. I. (1994) Effect of lead acetate on nitrite production by murine brain
56 endothelial cell cultures. Toxicol. Appl. Pharmacol. 126: 191-194.
May 2006 5-296 DRAFT-DO NOT QUOTE OR CITE
-------
1 Bogden, J. D.; Gertner, S. B.; Kemp, F. W.; McLeod, R.; Braening, K. S.; Chung, H. R. (1991) Dietary lead and
2 calcium: effects on blood pressure and renal neoplasia in Wistar rats. J. Nutr. 121: 718-728.
3 Bogden, J. D.; Kemp, F. W.; Han, S.; Murphy, M; Fraiman, M; Czerniach, D.; Flynn, C. J.; Banua, M. L.;
4 Scimone, A.; Castrovilly, L.; Gertner, S. B. (1995) Dietary calcium and lead interact to modify maternal
5 blood pressure, erythropoiesis, and fetal and neonatal growth in rats during pregnancy and lactation.
6 J. Nutr. 125: 990-1002.
7 Bonacker, D.; Stoiber, T.; Bohm, K. J.; Prots, L; Wang, M.; Unger E.; Thier, R.; Bolt, H. M.; Degen, G. H. (2005)
8 Genotoxicity of inorganic lead salts and disturbance of microtubule function. Environ. Mol. Mutagen.
9 45: 346-353.
10 Bondy, S. C. (1986) Effect of triethyl lead chloride on 5-aminolevulinic acid dehydratase. J. Toxicol. Environ.
11 Health 18: 639-649.
12 Bondy, S. C. Guo, S. X. (1996) Lead potentiates iron-induced formation of reactive oxygen species. Toxicol. Lett.
13 87: 109-112.
14 Borella, P.; Giardino, A. (1991) Lead and cadmium at very low doses affect in vitro immune response of human
15 lymphocytes. Environ. Res. 55: 165-177.
16 Borg, C.; Abdelali, J.; Laderach, D.; Maruyama, K.; Wakasugi, H.; Charrier, S.; Ryffel, B.; Vainchenker, W.;
17 Galy, A.; Caignard, A.; Zitvogel, L.; Cambi, A.; Figdor, C. (2004) NK cell activation by dendritic cells
18 (DC) require the formation of a synapse leading to IL-12 polarization in DC. Blood 104: 3267-3275.
19 Boudene, C.; Despaux-Pages, N.; Comoy, E.; Bohuon, C. (1984) Immunological and enzymatic studies of
20 erythrocytic 5-aminolevulinate dehydratase [Comparison of results obtained in normal and lead-exposed
21 subjects]. Int. Arch. Occup. Environ. Health 55: 87-96.
22 Bouley, G.; Dubreuil, A.; Arsac, F.; Boudene, C. (1977) Effet du plomb microparticulaire, introduit dans 1'appareil
23 respiratoire, sur la sensibilite de la souris a 1'infection par aerosol de Pasteurella multocida [Effect of
24 microparticulate lead, introduced through respiratory apparatus, on the resistance of mice to infection by
25 aerosolized Pasteurella multocida]. C. R. Hebd. Seances Acad. Sci. Ser. D 285: 1553-1556.
26 Bourjeily, N.; Suszkiw, J. B. (1997) Developmental cholinotoxicity of lead: loss of septal cholinergic neurons and
27 long-term changes in cholinergic innervation of the hippocampus in perinatally lead-exposed rats. Brain
28 Res. 771:319-328.
29 Bowen, W. H. (2001) Exposure to metal ions and susceptibility to dental caries. J. Dent. Ed. 65: 1046-1053.
3 0 Boyce, S. J.; Mantle, T.J.(1993) Effect of lead acetate and carbon particles on the expression of glutathione
31 S-transferase YfYf in rat liver. Biochem. J. 294: 301-304.
32 Bradbury, M. W.; Deane, R. (1986) Rate of uptake of lead-203 into brain and other soft tissues of the rat at constant
33 radiotracer levels in plasma. Ann. N. Y. Acad. Sci. 481: 142-160.
34 Bradbury, M. W. B.; Deane, R. (1993) Permeability of the blood-brain barrier to lead. Neurotoxicology 14: 131-136.
35 Bradbury, M. W.; Lightman, S. L.; Yuen, L.; Pinter, G. G. (1991) Permeability of blood-brain and blood-nerve
36 barriers in experimental diabetes mellitus in the anaesthetized rat. Exp. Physiol. 76: 887-898.
37 Bradman, A.; Eskenazi, B.; Sutton, P.; Athanasoulis, M.; Goldman, L. R. (2001) Iron deficiency associated with
3 8 higher blood lead in children living in contaminated environments. Environ. Health Perspect.
39 109: 1079-1084.
40 Braga, M. F. M; Pereira, E. F. R.; Albuquerque, E. X. (1999a) Nanomolar concentrations of lead inhibit
41 glutamatergic and GABAergic transmission in hippocampal neurons. Brain Res. 826: 22-34.
42 Braga, M. F. M.; Pereira, E. F. R.; Marchioro, M.; Albuquerque, E. X. (1999b) Lead increases tetrodotoxin-
43 insensitive spontaneous release of glutamate and GABA from hippocampal neurons. Brain Res. 826: 10-21.
44 Braga, M. F.; Pereira, E. F.; Mike, A.; Albuquerque, E. X. (2004) Pb2+ via protein kinase C inhibits nicotinic
45 cholinergic modulation of synaptic transmission in the hippocampus. J. Pharmacol. Exp. Ther.
46 311:700-710.
47 Bratton, G. R.; Hiney, J. K.; Dees, W. L. (1994) Lead (Pb) alters the norepinephrine-induced secretion of luteinizing
48 hormone releasing hormone from the medium eminence of adult male rats in vitro. Life Sci. 55: 563-571.
49 Breen, K. C.; Regan, C. M. (1988) Lead stimulates Golgi sialyltransferase at times coincident with the embryonic to
50 adult conversion of the neural cell adhesion molecule (N-CAM). Toxicology 49: 71-76.
51 Breslau, N.; Chilcoat, H. D.; Susser, E. S.; Matte, T.; Liang, K.-Y.; Peterson, E. L. (2001) Stability and change in
52 children's intelligence quotient scores: a comparison of two socioeconomically disparate communities.
53 Am. J. Epidemiol. 154: 711-717.
54 Bressler, J. P.; Goldstein, G. W. (1991) Mechanisms of lead neurotoxicity. Biochem. Pharmacol. 41: 479-484.
55 Bressler, J.; Kim, K.-A.; Chakraborti, T.; Goldstein, G. (1999) Molecular mechanisms of lead neurotoxicity.
56 Neurochem. Res. 24: 595-600.
May 2006 5-297 DRAFT-DO NOT QUOTE OR CITE
-------
1 Brockel, B. J.; Cory-Slechta, D. A. (1998) Lead, attention, and impulsive behavior: changes in a fixed-ratio waiting-
2 for-reward paradigm. Pharmacol. Biochem. Behav. 60: 545-552.
3 Brockel, B. J.; Cory-Slechta, D. A. (1999a) Lead-induced decrements in waiting behavior: involvement of D2-like
4 dopamine receptors. Pharmacol. Biochem. Behav. 63: 423-434.
5 Brockel, B. J.; Cory-Slechta, D. A. (1999b) The effects of postweaning low-level Pb exposure on sustained
6 attention: a study of target densities, stimulus presentation rate, and stimulus predictability.
7 Neurotoxicology 20: 921-933.
8 Brody, D. J.; Pirkle, J. L.; Kramer, R. A.; Flegal, K. M; Matte, T. D.; Gunter, E. W.; Paschal, D. C. (1994) Blood
9 lead levels in the US population: phase 1 of the third National Health and Nutrition Examination Survey
10 (NHANES III, 1988 to 1991). JAMA J. Am. Med. Assoc. 272: 277-283.
11 Briischweiler, B. J.; Wtirgler, F. E.; Pent, K. (1996) Inhibitory effects of heavy metals on cytochrome P4501A
12 induction in permanent fish hepatoma cells. Arch. Environ. Contam. Toxicol. 31: 475-482.
13 Buchet, J.-P.; Roels, H. E.; Hubermont, G.; Lauwerys, R. (1976) Effect of lead on some parameters of the heme
14 biosynthetic pathway in rat tissues in vivo. Toxicology 6: 21-34.
15 Buckley, J. D.; Robison, L. L.; Swotinsky, R.; Garabrant, D. H.; LeBeau, M.; Manchester, P.; Nesbit, M. E.; Odom,
16 L.; Peters, J. M.; Woods, W. G.; Hammond, G. D. (1989) Occupational exposures of parents of children
17 with acute nonlymphocytic leukemia: a report from the children's cancer study group. Cancer Res. 49:
18 4030-4037.
19 Bunn, T. L.; Marsh, J. A.; Dietert, R. R. (2000) Gender differences in developmental immunotoxicity to lead in a
20 chicken: analysis following a single early low-level exposure in ovo. J. Toxicol. Environ. Health A
21 61:677-693.
22 Bunn, T. L.; Parsons, P. J.; Kao, E.; Dietert, R. R. (2001a) Gender-based profiles of developmental immunotoxicity
23 to lead in the rat: assessment in juveniles and adults. J. Toxicol. Environ. Health A 64: 223-240.
24 Bunn, T. L.; Ladies, G. S.; Holsapple, M. P.; Dietert, R. R. (200Ib) Developmental immunotoxicology assessment
25 in the rat: age, gender and strain comparisons after exposure to Pb. Toxicol. Methods 11: 41-58.
26 Bunn, T. L.; Parsons, P. J.; Kao, E.; Dietert, R. R. (2001c) Exposure to lead during critical windows of embryonic
27 development: differential immunotoxic outcome based on stage of exposure and gender. Toxicol. Sci.
28 64:57-66.
29 Burchfiel, J. L.; Durry, F. H.; Bartels, P. H.; Needleman, H. L. (1992) Low-level lead exposure: effect on
30 quantitative electroencephalography and correlation with neuropsychologic measures. In: Needleman,
31 H. L., ed. Human lead exposure. Boca Raton, FL: CRC Press; pp. 209-222.
32 Burkey, R. T.; Nation, J. R. (1994) Brain stimulation reward following chronic lead exposure in rats. Behav.
33 Neurosci. 108: 532-536.
34 Burstein, H. J.; Tepper, R. I.; Leder, P.; Abbas, A. K. (1991) Humoral immune functions in IL-4 transgenic mice.
35 J. Immunol. 147: 2950-2956.
36 Cai, M. Y.; Arenaz, P. (1998) Antimutagenic effect of crown ethers on heavy metal-induced sister chromatid
37 exchanges. Mutagenesis 13: 27-32.
38 Calabrese, E. J.; Baldwin, L. A. (1992) Lead-induced cell proliferation and organ-specific tumorigenicity. Drug
39 Metab. Rev. 24:409-416.
40 Calabrese, E. J.; Baldwin, L. A.; Leonard, D. A.; Zhao, X. Q. (1995) Decrease in hepatotoxicity by lead exposure is
41 not explained by its mitogenic response. J. Appl. Toxicol. 15: 129-132.
42 Calderon-Salinas, J. V.; Quintanar-Escorza, M. A.; Hernandez-Luna, C. E.; Gonzalez-Martinez, M. T. (1999a)
43 Effect of lead on the calcium transport in human erythrocyte. Hum. Exp. Toxicol. 18: 146-153.
44 Calderon-Salinas, J. V.; Quintanar-Escorcia, M. A.; Gonzalez-Martinez, M. T.; Hernandez-Luna, C. E. (1999b)
45 Lead and calcium transport in human erythrocyte. Hum. Exp. Toxicol. 18: 327-332.
46 Camoratto, A. M.; White, L. M.; Lau, Y.-S.; Ware, G. O.; Berry, W. D.; Moriarty, C. M. (1993) Effect of exposure
47 to low level lead on growth and growth hormone release in rats. Toxicology 83: 101-114.
48 Campbell, T. F.; Needleman, H. L.; Riess, J. A.; Tobin, M. J. (2000) Bone lead levels and language processing
49 performance. Dev. Neuropsychol. 18: 171-186.
50 Canfield, R. L.; Henderson, C. R., Jr.; Cory-Slechta, D. A.; Cox, C.; Jusko, T. A.; Lanphear, B. P. (2003)
51 Intellectual impairment in children with blood lead concentrations below 10 ugrams per deciliter. N. Engl.
52 J. Med. 348: 1517-1526.
53 Canfield, R. L.; Gendle, M. H.; Cory-Slechta, D. A. (2004) Impaired neuropsychological functioning in lead-
54 exposed children. Dev. Neuropsychol. 26: 513-540.
May 2006 5-298 DRAFT-DO NOT QUOTE OR CITE
-------
1 Carballido, J. M; Schols, D.; Namikawa, R.; Zurawski, S.; Zurawski, Z.; Roncarolo, M. G.; de Vries, J. E. (1995)
2 IL-4 induces human B cell maturation and IgE synthesis in SCID-hu mice. Inhibition of ongoing IgE
3 production by in vivo treatment with an IL-4/IL-13 receptor antagonist. J. Immunol. 155: 4162-4170.
4 Cardenas, A.; Roels, H.; Bernard, A. M.; Barbon, R.; Buchet, J. P.; Lauwerys, R. R.; Rosello, J.; Ramis, I.; Mutti,
5 A.; Franchini, I.; Pels, L. M.; Stolte, H.; De Broe, M. E.; Nuyts, G. D.; Taylor, S. A.; Price, R. G. (1993).
6 Markers of early renal changes induced by industrial pollutants. II. Application to workers exposed to lead.
7 Br. J. Ind. Med. 50: 28-36.
8 Cardinale, F.; de Benedictis, F. M.; Muggeo, V.; Giordana, P.; Loffredo, M. S.; lacoviello, G.; Armenio, L. (2005)
9 Exhaled nitric oxide, total serum IgE and allergic sensitization in childhood asthma and allergic rhinitis.
10 Pediatr. Allergy Immunol. 16: 236-242.
11 Carey, J. B.; Allshire, A.; Van Pelt, F. N. (2006) Immune modulation by cadmium and lead in the acute reporter
12 antigen-popliteal lymph node assay. Toxicol. Sci. 91: 113-122.
13 Carmignani, M.; Boscolo, P.; Poma, A.; Volpe, A. R. (1999) Kininergic system and arterial hypertension following
14 chronic exposure to inorganic lead. Immunopharmacology 44: 105-110.
15 Carmignani, M.; Volpe, A. R.; Boscolo, P.; Qiao, N.; Gioacchino, M. Di; Grilli, A.; Felaco, M. (2000) Catcholamine
16 and nitric oxide systems as targets of chronic lead exposure in inducing selective functional impairment.
17 Life Sci. 68: 401-415.
18 Carsia, R. V.; Forman, D.; Hock, C. E.; Nagele, R. G.; Mcllroy, P. J. (1995) Lead alters growth and reduces
19 angiotensin II receptor density of rat aortic smooth muscle cells. Proc. Soc. Exp. Biol. Med. 210: 180-190.
20 Castranova, V.; Bowman, L.; Reasor, M. J.; Miles, P. R. (1980) Effects of heavy metal ions on selected oxidative
21 metabolic processes in rat alveolar macrophages. Toxicol. Appl. Pharmacol. 53: 14-23.
22 Celotti, L.; Furlan, D.; Seccati, L.; Levis, A. G. (1987) Interactions of nitrilotriacetic acid (NTA) with Cr(VI)
23 compounds in the induction of gene mutations in cultured mammalian cells. Mutat. Res. 190: 35-39.
24 Chai, S.; Webb, R. C. (1988) Effects of lead on vascular reactivity. Environ. Health Perspect. 78: 85-89.
25 Chakraborty, I.; Sharma, A.; Talukder, G. (1987) Antagonistic and synergistic effects of lead and selenium inRattus
26 norvegicus. Toxicol. Lett. 37: 21-26.
27 Chalkley, S. R.; Richmond, J.; Barltrop, D. (1998) Measurement of vitamin D3 metabolites in smelter workers
28 exposed to lead and cadmium. Occup. Environ. Med. 55: 446-452.
29 Chang, H.-R.; Chen, S.-S.; Chen, T.-J.; Ho, C.-K.; Chiang, H.-C; Yu, H.-S. (1996) Lymphocyte (32-adrenergic
30 receptors and plasma catecholamine levels in lead-exposed workers. Toxicol. Appl. Pharmacol. 139: 1-5.
31 Chang, H.-R.; Chen, S.-S.; Tsao, D.-A.; Cheng, J.-T.; Ho, C.-K.; Yu, H.-S. (1997) Change of cardiac (3-
32 adrenoceptors in lead-exposed rats. Toxicology 123: 27-32.
33 Chang, H.-R.; Tsao, D.-A.; Yu, H.-S.; Ho, C.-K. (2005) The change of (3-adrenergic system after cessation of lead
34 exposure. Toxicology 207: 73-80.
3 5 Chaurasia, S. S.; Kar, A. (1997) Protective effects of vitamin E against lead-induced deterioration of membrane
36 associated type-I iodothyronine 5'-monodeiodinase (5'D-I) activity in male mice. Toxicology 124: 203-209.
37 Chaurasia, S. S.; Gupta, P.; Maiti, P. K.; Kar, A. (1998) Possible involvement of lipid peroxidation in the inhibition
38 of type I iodothyronine 5'-monodeiodinase activity by lead in chicken liver. Toxicol. Appl. Pharmacol.
39 18:299-300.
40 Chavez, E.; Jay, D.; Bravo, C. (1987) The mechanism of lead-induced mitochondrial Ca2+ efflux. J. Bioenerg.
41 Biomembrane 19: 285-295.
42 Chen, H.-H.; Ma, T.; Paul, I. A.; Spencer, J. L.; Ho, I. K. (1997a) Developmental lead exposure and two-way active
43 avoidance training alter the distribution of protein kinase C activity in the rat hippocampus. Neurochem.
44 Res. 22: 1119-1125.
45 Chen, S.; Miller, T. E.; Golemboski, K. A.; Dietert, R. R. (1997b) Suppression of macrophage metabolite production
46 by lead glutamate in vitro is reversed by meso-2,3-dimercaptosuccinic acid (DMSA). In Vitro Toxicol.
47 10:351-358.
48 Chen, S.; Golemboski, K. A.; Sanders, F. S.; Dietert, R. R. (1999) Persistent effect of in utero meso-2,3-
49 dimercaptosuccinic acid (DMSA) on immune function and lead-induced immunotoxicity. Toxicology
50 132:67-79.
51 Chen, H.; Ma, T.; Ho, I. K. (2001) Effects of developmental lead exposure on inhibitory avoidance learning and
52 glutamate receptors in rats. Environ. Toxicol. Pharmacol. 9: 185-191.
53 Chen, S. C.; Golemboski, K. A.; Piepenbrink, M.; Dietert, R. R. (2004) Developmental immunotoxicity of lead in
54 the rat: influence of maternal diet. J. Toxicol. Environ. Health Part A 67: 495-511.
May 2006 5-299 DRAFT-DO NOT QUOTE OR CITE
-------
1 Chen, A.; Dietrich, K. N.; Ware, J. H.; Radcliffe, I; Rogan, W. J. (2005) IQ and blood lead from 2 to 7 years of age:
2 are the effects in older children the residual of high blood lead concentrations in 2-year-olds? Environ.
3 HealthPerspect. 113: 597-601.
4 Cheng, Y.; Willett, W. C.; Schwartz, J.; Sparrow, D.; Weiss, S.; Hu, H. (1998) Relation of nutrition to bone lead and
5 blood lead levels in middle-aged to elderly men. The Normative Aging Study. Am. J. Epidemiol. 147:
6 1162-1174.
7 Chia, K. S.; Mutti, A.; Tan, C.; Ong, H. Y.; Jeyaratnam, J.; Ong, C. N.; Lee, E. (1994) Urinary N-acetyl-(3-D-
8 glucosaminidase activity in workers exposed to inorganic lead. Occup. Environ. Med. 51: 125-129.
9 Chisolm, J. J., Jr. (1990) Evaluation of the potential role of chelation therapy in treatment of low to moderate lead
10 exposures. Environ. Health Perspect. 89: 67-74.
11 Choie, D. D.; Richter, G. W. (1972) Lead poisoning: rapid formation of intranuclear inclusions. Science
12 (Washington, DC) 177: 1194-1195.
13 Choie, D. D.; Richter, G. W.; Young, L. B. (1975) Biogenesis of intranuclear lead-protein inclusions in mouse
14 kidney. Beitr. Pathol. 155: 197-203.
15 Chowdhuri, O.K.; Narayan, R.; Saxena, D. K. (2001) Effect of lead and chromium on nucleic acid and protein
16 synthesis during sperm-zona binding in mice. Toxicol. In Vitro 15: 605-613.
17 Chowdhury, A. R.; Dewan, A.; Gandhi, D. N. (1984) Toxic effect of lead on the testes of rat. Biomed. Biochim.
18 Acta 43: 95-100.
19 Chowdhury, A. R.; Rao, R. V.; Gautam, A. K. (1986) Histochemical changes in the testes of lead induced
20 experimental rats. Folia Histochem. Cytobiol. 24: 233-237.
21 Chowdhury, A. R.; Rao, R. V.; Gautam, A. K.; Kashyap, S. K. (1987) Functional changes of testes in lead
22 intoxicated rats. Ind. Health 25: 55-62.
23 Church, H. J.; Day, J. P.; Braithwaite, R. A.; Brown, S. S. (1993a) Binding of lead to a metallothionein-like protein
24 in human erythrocytes. J. Inorg. Biochem. 49: 55-68.
25 Church, H. J.; Day, J. P.; Braithwaite, R. A.; Brown, S. S. (1993b) The speciation of lead in erythrocytes in relation
26 to lead toxicity: case studies of two lead-exposed workers. Neurotoxicology 14: 359-364.
27 Claudio, L.; Lee, T.; Wolff, M. S.; Wetmur, J. G. (1997) A murine model of genetic susceptibility to lead
28 bioaccumulation. Fundam. Appl. Toxicol. 35: 84-90.
29 Cline, H. T.; Witte, S.; Jones, K. W. (1996) Low lead levels stunt neuronal growth in a reversible manner. Proc.
30 Natl. Acad. Sci. U. S. A. 93: 9915-9920.
31 Cocco, P.; Carta, P.; Flore, C.; Congia, P.; Manca, M. B.; Saba, G.; Salis, S. (1996) Mortality of lead smelter
32 workers with the glucose-6-phosphate dehydrogenase-deficient phenotype. Cancer Epidemiol. Biomarkers
33 Prev. 5: 223-225.
34 Cocco, P.; Dosemeci, M.; Heineman, E. F. (1998) Brain cancer and occupational exposure to lead. J. Occup.
35 Environ. Med. 40: 937-942.
36 Cohn, J.; Cory-Slechta, D. A. (1993) Subsensitivity of lead-exposed rats to the accuracy-impairing and rate-altering
37 effects of MK-801 on a multiple schedule of repeated learning and performance. Brain Res. 600: 208-218.
38 Cohn, J.; Cory-Slechta, D. A. (1994a) Assessment of the role of dopaminergic systems in lead-induced learning
39 impairments using a repeated acquisition and performance baseline. Neurotoxicology 15: 913-926.
40 Cohn, J.; Cory-Slechta, D. A. (1994b) Lead exposure potentiates the effects of NMD A on repeated learning.
41 Neurotoxicol. Teratol. 16: 455-465.
42 Cohn, J.; Cox, C.; Cory-Slechta, D. A. (1993) The effects of lead exposure on learning in a multiple repeated
43 acquisition and performance schedule. Presented at: Ninth international neurotoxicology conference;
44 October 1991; Little Rock, AR. Neurotoxicology 14(2-3): 329-346.
45 Cole, L. J.; Bachhuber, L. J. (1915) The effect of lead on the germ cells of the male rabbit and fowl as indicated by
46 their progeny. Proc. Soc. Exp. Biol. Med. 12: 24-29.
47 Columbano, A.; Ledda-Columbano, G. M.; Ennas, M. G.; Curto, M.; de Montis, M. G.; Roomi, M. W.; Pani, P.;
48 Sarma, D. S. R. (1988) Modulation of the activity of hepatic gamma-glutamyl transpeptidase, adenosine
49 triphosphatase, placental glutathione S-transferase and adenylate cyclase by acute administration of lead
50 nitrate. Basic Appl. Histochem. 32: 501-510.
51 Columbano, A.; Endoh, T.; Denda, A.; Noguchi, O.; Nakae, D.; Hasegawa, K.; Ledda-Columbano, G. M.; Zedda,
52 A. I.; Konishi, Y. (1996) Effects of cell proliferation and cell death (apoptosis and necrosis) on the early
53 stages of rat hepatocarcinogenesis. Carcinogenesis 17: 395-400.
54 Commissaris, R. L.; Tavakoli-Nezhad, M.; Barren, A. J.; Pitts, D. K. (2000) Effects of chronic low-level oral lead
55 exposure on prepulse inhibition of acoustic startle in the rat. Neurotoxicol. Teratol. 22: 55-60.
May 2006 5-300 DRAFT-DO NOT QUOTE OR CITE
-------
1 Coni, P.; Bignone, F. A.; Pichiri, G.; Ledda-Columbano, G. M; Columbano, A.; Rao, P. M; Rajalakhmi, S.; Sarma,
2 D. S. (1989) Studies on the kinetics of expression of cell cycle dependent proto-oncogenes during mitogen-
3 induced liver cell proliferation. Cancer Lett. (Shannon, Irel.) 47: 115-119.
4 Coni, P.; Pichiri-Coni, G.; Ledda-Columbano, G. M.; Semple, E.; Rajalakshmi, S.; Rao, P. M.; Sarma, D. S. R.;
5 Columbano, A. (1992) Stimulation of DNA synthesis by rat plasma following in vivo treatment with three
6 liver mitogens. Cancer Lett. 61: 233-238.
7 Coni, P.; Simbula, G.; De Prati, A. C.; Menegazzi, M.; Suzuki, H.; Sarma, D. S. R.; Ledda-Columbano, G. M.;
8 Columbano, A. (1993) Differences in the steady-state levels of c-fos, c-jun and c-myc messenger RNA
9 during mitogen-induced liver growth and compensatory regeneration. Hepatology (Baltimore)
10 17: 1109-1116.
11 Connor, T. H.; Pier, S. M. (1990) Reduction of the mutagenicity of lead chromate-based pigments by encapsulation
12 with silica. Mutat. Res. 245: 129-133.
13 Cook, J. A.; Hoffmann, E. O.; Di Luzio, N. R. (1975) Influence of lead and cadmium on the susceptibility of rats to
14 bacterial challenge. Proc. Soc. Exp. Biol. Med. 150: 741-747.
15 Cook, L. R.; Stohs, S. J.; Angle, C. R.; Hickman, T. I.; Maxell, R. C. (1987) Erythrocyte membrane microviscosity
16 and phospholipid composition in lead workers. Br. J. Ind. Med. 44: 841-844.
17 Cooper, G. P.; Manalis, R. S. (1984) Interactions of lead and cadmium on acetylcholine release at the frog
18 neuromuscular junction. Toxicol. Appl. Pharmacol. 74: 411-416.
19 Corchs, J.; Gioia, I. A.; Serrani, R. E.; Taborda, D. (2001) Lead ions but not other metallic ions increase resistance
20 to hypotonic lysis in prenatal hemopoiesis red blood cells. Biocell 25: 287-289.
21 Corpas, I.; Caspar, I.; Martinez, S.; Codesal, J.; Candelas, S.; Antonio, M. T. (1995) Testicular alterations in rats due
22 to gestational and early lactational administration of lead. Reprod. Toxicol. 9: 307-313.
23 Corpas, I.; Benito, M. J.; Marquina, D.; Castillo, M.; Lopez, N.; Antonio, M. T. (2002) Gestational and lactational
24 lead intoxication produces alterations in the hepatic system of rat pups. Ecotoxicol. Environ. Saf. 51: 35-43.
25 Cortina-Ramirez, G. E.; Cerbon-Solorzano, J.; Calderon-Salinas, J. V. (2006) Effects of 1,25-
26 dihydroxicolecalciferol and dietary calcium—phosphate on distribution of lead to tissues during growth.
27 Toxicol. Appl. Pharmacol. 210: 123-127.
28 Cory-Slechta, D. A. (1986) Prolonged lead exposure and fixed ratio performance. Neurobehav. Toxicol. Teratol.
29 8:237-244.
30 Cory-Slechta, D. A. (1988) Mobilization of lead over the course of DMSA chelation therapy and long-term efficacy.
31 J. Pharmacol. Exp. Ther. 246: 84-91.
32 Cory-Slechta, D. A. (1990a) Exposure duration modifies the effects of low level lead on fixed-interval performance.
33 Neurotoxicology 11: 427-441.
34 Cory-Slechta, D. A. (1990b) Lead exposure during advanced age: alterations in kinetics and biochemical effects.
35 Toxicol. Appl. Pharmacol. 104: 67-78.
36 Cory-Slechta, D. A. (1990c) Alterations in tissue Pb distribution and hematopoietic indices during advanced age.
37 Arch. Toxicol. 64:31-37.
38 Cory-Slechta, D. A. (1994) Neurotoxicant-induced changes in schedule-controlled behavior. In: Chang, L. W., ed.
39 Principles of neurotoxicology. New York, NY: Marcel Dekker, Inc.; pp. 313-344. (Neurological disease
40 and therapy: v. 26).
41 Cory-Slechta, D. A. (1995) MK-801 subsensitivity following postweaning lead exposure. Neurotoxicology
42 16:83-95.
43 Cory-Slechta, D. A. (1997) Postnatal lead exposure and MK-801 sensitivity. Neurotoxicology 18: 209-220.
44 Cory-Slechta, D. A. (2003) Lead-induced impairments in complex cognitive function: offerings from experimental
45 studies. Child Neuropsychol. 9: 54-75.
46 Cory-Slechta, D. A.; Pokora, M. J. (1991) Behavioral manifestations of prolonged lead exposure initiated at
47 different stages of the life cycle. 1. Schedule-controlled responding. Neurotoxicology 12: 745-760.
48 Cory-Slechta, D. A.; Pokora, M. J. (1995) Lead-induced changes in muscarinic cholinergic sensitivity.
49 Neurotoxicology 16: 337-347.
50 Cory-Slechta, D. A.; Thompson, T. (1979) Behavioral toxicity of chronic postweaning lead exposure in the rat.
51 Toxicol. Appl. Pharmacol. 47: 151-159.
52 Cory-Slechta, D. A.; Weiss, B. (1989) Efficacy of the chelating agent CaEDTA in reversing lead-induced changes in
53 behavior. Neurotoxicology 10: 685-697.
54 Cory-Slechta, D. A.; Widzowski, D. V. (1991) Low level lead exposure increases sensitivity to the stimulus
5 5 properties of dopamine Dj and D2 agonists. Brain Res. 553: 65-74.
May 2006 5-301 DRAFT-DO NOT QUOTE OR CITE
-------
1 Cory-Slechta, D. A.; Weiss, B.; Cox, C. (1983) Delayed behavioral toxicity of lead with increasing exposure
2 concentration. Toxicol. Appl. Pharmacol. 71: 342-352.
3 Cory-Slechta, D. A.; Weiss, B.; Cox, C. (1985) Performance and exposure indices of rats exposed to low
4 concentrations of lead. Toxicol. Appl. Pharmacol.78: 291-299.
5 Cory-Slechta, D. A.; Weiss, B.; Cox, C. (1987) Mobilization and redistribution of lead over the course of calcium
6 disodium ethylenediamine tetraacetate chelation therapy. J. Pharmacol. Exp. Ther. 243: 804-813.
7 Cory-Slechta, D. A.; Weiss, B.; Cox, C. (1989) Tissue distribution of Pb in adult vs. old rats: a pilot study.
8 Toxicology 59: 139-149.
9 Cory-Slechta, D. A.; Pokora, M. J.; Widzowski, D. V. (1991) Behavioral manifestations of prolonged lead exposure
10 initiated at different stages of the life cycle. II. Delayed spatial alternation. Neurotoxicology 12: 761-776.
11 Cory-Slechta, D. A.; Pokora, M. J.; Widzowski, D. V. (1992) Postnatal lead exposure induces supersensitivity to the
12 stimulus properties of D2-D3 agonist. Brain Res. 598: 162-172.
13 Cory-Slechta, D. A.; Pokora, M. J.; Johnson, J. L. (1996a) Postweaning lead exposure enhances the stimulus
14 properties of N-methyl-D-aspartate: possible dopaminergic involvement? Neurotoxicology 17: 509-521.
15 Cory-Slechta, D. A.; Pokora, M. J.; Preston, R. A. (1996b) The effects of dopamine agonists on fixed interval
16 schedule-controlled behavior are selectively altered by low-level lead exposure. Neurotoxicol. Teratol.
17 18:565-575.
18 Cory-Slechta, D. A.; Pokora, M. J.; Fox, R. A. V.; O'Mara, D. J. (1996c) Lead-induced changes in dopamine
19 D! sensitivity: modulation by drug discrimination training. Neurotoxicology. 17: 445-457.
20 Cory-Slechta, D. A.; McCoy, L.; Richfield, E. K. (1997a) Time course and regional basis of Pb-induced changes in
21 MK-801 binding: reversal by chronic treatment with the dopamine agonist apomorphine but not the Dj
22 agonist SKF-82958. J. Neurochem. 68: 2012-2023.
23 Cory-Slechta, D. A.; Garcia-Osuna, M.; Greenamyre, J. T. (1997b) Lead-induced changes inNMDA receptor
24 complex binding: correlations with learning accuracy and with sensitivity to learning impairments caused
25 by MK-801 and NMDA administration. Behav. Brain Res. 85: 161-174.
26 Cory-Slechta, D. A.; Brockel, B. J.; O'Mara, D. J. (2002) Lead exposure and dorsomedial striatum mediation of
27 fixed interval schedule-controlled behavior. Neurotoxicology 23: 313-327.
28 Cory-Slechta, D. A.; Virgolini, M. B.; Thiruchelvam, M.; Weston, D. D.; Bauter, M. R. (2004) Maternal stress
29 modulates the effects of developmental lead exposure. Environ. Health Perspect. 112: 717-730.
30 Costa, M.; Zhitkovich, A.; Gargas, M.; Paustenbach, D.; Finley, B.; Kuykendall, J.; Billings, R.; Carlson, T. J.;
31 Wetterhahn, K.; Xu, J.; Patierno, S.; Bogdanffy, M. (1996) Interlaboratory validation of a new assay for
32 DNA-protein crosslinks. Mutat. Res. 369: 13-21.
33 Courtois, E.; Marques, M.; Barrientos, A.; Casado, S.; Lopez-Farre, A. (2003) Lead-induced downregulation of
34 soluble guanylage cyclase in isolated rat aortic segments mediated by reactive oxygen species and
35 cyclooxygenase-2. J. Am. Soc. Nephrol. 14: 1464-1470.
36 Craan, A. G.; Nadon, G.; P'an, A. Y. (1984) Lead flux through the kidney and salivary glands of rats. Am. J.
37 Physiol. 247: F773-F783.
38 Cramer, K.; Goyer, R. A.; Jagenburg, R.; Wilson, M. H. (1974) Renal ultrastructure, renal function, and parameters
39 of lead toxicity in workers with different periods of lead exposure. Br. J. Ind. Med. 31: 113-127.
40 Cremin, J. D., Jr.; Luck, M. L.; Laughlin, N. K.; Smith, D. R. (1999) Efficacy of succimer chelation for reducing
41 brain lead in a primate model of human lead exposure. Toxicol. Appl. Pharmacol. 161: 283-293.
42 Cremin, J. D., Jr.; Luck, M. L.; Laughlin, N. K.; Smith, D. R. (2001) Oral succimer decreases the gastrointestinal
43 absorption of lead in juvenile monkeys. Environ. Health Perspect. 109: 613-619.
44 Crowe, A.; Morgan, E. H. (1996) Interactions between tissue uptake of lead and iron in normal and iron-deficient
45 rats during development. Biol. Trace Elem. Res. 52: 249-261.
46 Curzon, M. E. J.; Bibby, B. G. (1970) Effect of heavy metals on dental caries and tooth eruption. J. Dent. Child.
47 37:463-465.
48 Daggett, D. A.; Nuwaysir, E. F.; Nelson, S. A.; Wright, L. S.; Kornguth, S. E.; Siegel, F. L. (1997) Effects of
49 triethyl lead administration on the expression of glutathione S-transferase isoenzymes and quinone
5 0 reductase in rat kidney and liver. Toxicology 117:61-71.
51 Daggett, D. A.; Oberley, T. D.; Nelson, S. A.; Wright, L. S.; Kornguth, S. E.; Siegel, F. L. (1998) Effects of lead on
52 rat kidney and liver: GST expression and oxidative stress. Toxicology 128: 191-206.
53 Danadevi, K.; Rozati, R.; Saleha Banu, B.; Hanumanth R. P.; Grover, P. (2003) DNA damage in workers exposed to
54 lead using comet assay. Toxicology 187: 183-193.
55 Dantzer, R.; Bluthe, R. M.; Gheusi, G.; Cremona, S.; Laye, S.; Parnet, P.; Kelley, K. W. (1998) Molecular basis of
56 sickness behavior. Ann. N.Y. Acad. Sci. 856: 132-138.
May 2006 5-302 DRAFT-DO NOT QUOTE OR CITE
-------
1 Davis, S. F.; Nation, J. R.; Mayleben, M. A. (1993) The effects of chronic lead exposure on reactivity to frustrative
2 nonreward in rats. Toxicol. Lett. 66: 237-246.
3 De, M.; Ghosh, S.; Palit, S.; Ghosh, A.; Talukder, G.; Sharma, A. (1995) Clastogenic effects in human samples
4 following prolonged exposure in metal industry. Bull. Environ. Contam. Toxicol. 54: 357-362.
5 De Guise, S.; Bernier, J.; Lapierre, P.; Dufresne, M. M.; Dubreuil, P.; Fornier, M. (2000) Immune function of bovine
6 leukocytes after in vitro exposure to selected heavy metals. Am. J. Vet. Res. 61: 339-344.
7 De la Fuente, H.; Portales-Perez, D.; Baranda, L.; Diaz-Barriga, F.; Saavedra-Alanis, V.; Layseca, E.; Gonzalez-
8 Amaro, R. (2002) Effect of arsenic, cadmium and lead on the induction of apoptosis of normal human
9 mononuclear cells. Clin. Exp. Immunol. 129: 69-77.
10 De Marco, M.; Halpern, R.; Barros, H. M. T. (2005) Early behavioral effects of lead perinatal exposure in rat pups.
11 Toxicology 211:49-58.
12 De Vries, L; Spaans, E.; VanDijk, A.; Meulenbelt, J. (1998) Lead toxicokinetics. Development of a biokinetic
13 model to understand and predict the outcome of treatment. Przegl. Lek. 55: 500-504.
14 Dearth, R. K.; Hiney, J. K.; Srivastava, V.; Burdick, S. B.; Bratton, G. R.; Dees, W. L. (2002) Effects of lead (Pb)
15 exposure during gestation and lactation on female pubertal development in the rat. Reprod. Toxicol.
16 16:343-352.
17 Dearth, R. K.; Hiney, J. K.; Srivastava, V.; Les Dees, W.; Bratton, G. R. (2004) Low level lead (Pb) exposure during
18 gestation and lactation: assessment of effects on pubertal development in Fisher 344 and Sprague-Dawley
19 female rats. Life Sci. 74: 1139-1148.
20 Degawa, M.; Arai, H.; Miura, S.; Hashimoto, Y. (1993) Preferential inhibitions of hepatic P450IA2 expression and
21 induction by lead nitrate in the rat. Carcinogenesis (London) 14: 1091-1094.
22 Degawa, M.; Arai, H.; Kubota, M.; Hashimoto, Y. (1994) Ionic lead, a unique metal ion as an inhibitor for
23 cytochrome P450IA2 (CYP1A2) expression in the rat liver. Biochem. Biophys. Res. Commun.
24 200: 1086-1092.
25 Degawa, M.; Arai, H.; Kubota, M.; Hashimoto, Y. (1995) Ionic lead, but not other ionic metals (Ni2+, Co2+ and
26 Cd2+), suppresses 2-methoxy-4-aminoazobenzene-mediated cytochrome P450IA2 (CYP1A2) induction in
27 rat liver. Biol. Pharm. Bull. 18: 1215-1218.
28 Degawa, M.; Matsuda, K.; Arai, H.; Hashimoto, Y. (1996) Lead nitrate inhibits the induction of CYP1A mRNAs by
29 aromatic amines but not by aryl hydrocarbons in the rat liver. J. Biochem. (Tokyo, Jpn.) 120: 547-551.
30 Dehpour, A. R.; Essalat, M.; Ala, S.; Ghazi-Khansari, M.; Ghafourifar, P. (1999) Increase by NO synthase inhibitor
31 of lead-induced release of 7V-acetyl-p-D-glucosaminidase from perfused rat kidney. Toxicology
32 132: 119-125.
33 Dekaney, C. M.; Harris, E. D.; Bratton, G. R.; Jaeger, L. A. (1997) Lead transport in IEC-6 intestinal epithelial cells.
34 Biol. Trace Elem. Res. 58: 13-24.
3 5 Delville, Y. (1999) Exposure to lead during development alters aggressive behavior in golden hamsters.
36 Neurotoxicol. Teratol. 21: 445-449.
37 Deng, W.; Poretz, R. D. (2002) Protein kinase C activation is required for the lead-induced inhibition of
3 8 proliferation and differentiation of cultured oligodendroglial progenitor cells. Brain Res. 929: 87-95.
39 Deng, W.; McKinnon, R. D.; Poretz, R. D. (2001) Lead exposure delays the differentiation of oligodendroglial
40 progenitors in vitro. Toxicol. Appl. Pharmacol. 174: 235-244.
41 Dentener, M. A.; Greve, J. W.; Maessen, J. G.; Buurman, W. A. (1989) Role of tumour necrosis factor in the
42 enhanced sensitivity of mice to endotoxin after exposure to lead. Immunopharmacol. Immunotoxicol.
43 11:321-334.
44 Dessi, S.; Batetta, B.; Laconi, E.; Ennas, C.; Pani, P. (1984) Hepatic cholesterol in lead nitrate induced liver
45 hyperplasia. Chem. Biol. Interact. 48: 271-279.
46 Dessi, S.; Batetta, B.; Pulisci, D.; Carrucciu, A.; Mura, E.; Ferreli, A.; Pani, P. (1990) Modifying influence of fasting
47 on liver hyperplasia induced by lead nitrate. Res. Commun. Chem. Pathol. Pharmacol. 68: 103-116.
48 Devi, K. D.; Banu, B. S.; Grover, P.; Jamil, K. (2000) Genotoxic effect of lead nitrate on mice using SCGE (comet
49 assay). Toxicology 145: 195-201.
50 Dey, S.; Arjun, J.; Das, M.; Bhattacharjee, C. R.; Dkhar, P. S. (2001) Effect of prenatal lead toxicity on surface
51 ultrastructural features, elemental composition and infrared absorption characteristics of the skin of albino
52 mice. Cytobios 106(suppl. 2): 245-254.
53 Dhir, H.; Roy, A. K.; Sharma, A.; Talukder, G. (1990) Modification of clastogenicity of lead and aluminium in
54 mouse bone marrow cells by dietary ingestion of Phyllanthus emblica fruit extract. Mutat. Res.
55 241:305-312.
May 2006 5-303 DRAFT-DO NOT QUOTE OR CITE
-------
1 Dhir, H.; Ghosh, S.; Sharma, A.; Talukder, G. (1992a) Interaction between two group IV metals: - lead and
2 zirconium - in bone marrow cells of Mus musculus in vivo. Biometals 5: 81-86.
3 Dhir, H.; Sharma, A.; Talukder, G. (1992b) Modifying effect of iron on lead-induced clastogenicity in mouse bone
4 marrow cells. Biol. Trace Elem. Res. 34: 279-286.
5 Dhir, H.; Roy, A. K.; Sharma, A. (1993) Relative efficiency of Phyllanthus emblica fruit extract and ascorbic acid in
6 modifying lead and aluminium-induced sister-chromatid exchanges in mouse bone marrow. Environ. Mol.
7 Mutagen. 21:229-236.
8 Diamond, G. L.; Goodrum, P. E.; Felter, S. P.; Ruoff, W. L. (1998) Gastrointestinal absorption of metals. Drug
9 Chem. Toxicol. 21: 223 -251.
10 Dieter, M. P.; Matthews, H. B.; Jeffcoat, R. A.; Moseman, R. F. (1993) Comparison of lead bioavailability inF344
11 rats fed lead acetate, lead oxide, lead sulfide, or lead ore concentrate from Skagway, Alaska. J. Toxicol.
12 Environ. Health 39: 79-93.
13 Dietert, R. R.; Lee, J.-E. (2005) Toxicity of lead to the developing immune system. In: Holladay, S. D., ed.
14 Developmental immunotoxicology. Boca Raton, FL: CRC Press, Inc.; pp. 169-177.
15 Dietert, R. R.; Piepenbrink, M. S. (2006) Perinatal immunotoxicity: why adult exposure assessment fails to predict
16 risk. Environ. Health Perspect. 114: 477-483.
17 Dietert, R. R.; Etzel, R. A.; Chen, D.; Halonen, M.; Holladay, S. D.; Jarabek, A. M.; Landreth, K.; Peden, D. B.;
18 Pinkerton, K.; Smialowicz, R. J.; Zoetis, T. (2000) Workshop to identify critical window of exposure for
19 children's health: immune and respiratory systems work group summary. Environ. Health Perspect.
20 Suppl. 108(3): 483-490.
21 Dietert, R. R.; Lee, J.-E.; Bunn, T. L. (2002) Developmental immunotoxicology: emerging issues. Hum. Exp.
22 Toxicol. 21:479-485.
23 Dietert, R. R.; Lee, J.-E.; Hussain, L; Piepenbrink, M. (2004) Developmental immunotoxicology of lead. Toxicol.
24 Appl. Pharmacol. 86-94.
25 Dietrich, K. N.; Succop, P. A.; Berger, O. G.; Keith, R. W. (1992) Lead exposure and the central auditory processing
26 abilities and cognitive development of urban children: the Cincinnati lead study cohort at age 5 years.
27 Neurotoxicol. Teratol. 14: 51-56.
28 Dietrich, K. N.; Berger, O. G.; Succop, P. A.; Hammond, P. B.; Bornschein, R. L. (1993) The developmental
29 consequences of low to moderate prenatal and postnatal lead exposure: intellectual attainment in the
30 Cincinnati Lead Study Cohort following school entry. Neurotoxicol. Teratol. 15: 37-44.
31 Dietrich, K. N.; Ris, M. D.; Succop, P. A.; Berger, O. G.; Bornschein, R. L. (2001) Early exposure to lead and
32 juvenile delinquency. Neurotoxicol. Teratol. 23: 511-518.
33 Dietrich, K. N.; Ware, J. H.; Salganik, M.; Radcliffe, J.; Rogan, W. J.; Rhoads, G. G.; Fay, M. E.; Davoli, C. T.;
34 Denckla, M. B.; Bornschein, R. L.; Schwarz, D.; Dockery, D. W.; Adubato, S.; Jones, R. L.; for the
3 5 Treatment of Lead-Exposed Children Clinical Trial Group. (2004) Effect of chelation therapy on the
3 6 neuropsychological and behavioral development of lead-exposed children after school entry. Pediatrics
37 114: 19-26.
38 Ding, Y.; Vaziri, N. D.; Gonick, H. C. (1998) Lead-induced hypertension. II. Response to sequential infusions of
39 L-arginine, superoxide dismutase, and nitroprusside. Environ. Res. 76: 107-113.
40 Ding, Y.; Gonick, H. C.; Vaziri, N. D. (2000) Lead promotes hydroxyl radical generation and lipid peroxidation in
41 cultured aortic endothelial cells. Am. J. Hypertens. 13: 552-555.
42 Ding, Y.; Gonick, H. C.; Vaziri, N. D.; Liang, K.; Wei, L. (2001) Lead-induced hypertension. III. Increased
43 hydroxyl radical production. Am. J. Hypertens. 14: 169-173.
44 Dini, L.; Falasca, L.; Lentini, A.; Mattioli, P.; Piacentini, M.; Piredda, L.; Autuori, F. (1993) Galactose-specific
45 receptor modulation related to the onset of apoptosis in rat liver. Eur. J. Cell. Biol. 61: 329-337.
46 Dini, L.; Giudetti, A. M.; Ruzittu, M.; Gnoni, G. V.; Zara, V. (1999) Citrate carrier and lipogenic enzyme activities
47 in lead nitrate-induced proliferative and apoptotic phase in rat liver. Biochem. Mol. Biol. Int. 47: 607-614.
48 Dock, L. (1989) Induction of rat liver glutathione transferase isoenzyme 7-7 by lead nitrate. Biol. Trace Elem. Res.
49 21:283-288.
5 0 Donald, J. M.; Cutler, M. G.; Moore, M. R.; Bardley, M. (1986) Effects of lead in the laboratory mouse - 2:
51 development and social behaviour after lifelong administration of a small dose of lead acetate in drinking
52 fluid. Neuropharmacology 25: 151-160.
53 Donald, J. M.; Cutler, M. G.; Moore, M. R. (1987) Effects of lead in the laboratory mouse. Development and social
54 behaviour after lifelong exposure to 12 uM lead in drinking fluid. Neuropharmacology 26: 391-399.
55 Donaldson, W. E.; Leeming, T. K. (1984) Dietary lead: effects on hepatic fatty acid composition in chicks. Toxicol.
56 Appl. Pharmacol. 73: 119-123.
May 2006 5-304 DRAFT-DO NOT QUOTE OR CITE
-------
1 Donaldson, I; Hemming, R.; LaBella, F. (1985) Vanadium exposure enhances lipid peroxidation in the kidney of
2 rats and mice. Can. J. Physiol. Pharmacol. 63: 196-199.
3 Dorman, R. V.; Freeman, E. J. (2002) Lead-dependent effects on arachidonic acid accumulation and the
4 proliferation of vascular smooth muscle. J. Biochem. Mol. Toxicol. 16: 245-253.
5 Dorward, A.; Yagminas, A. P. (1994) Activity of erythrocyte 5-aminolevulinic acid dehydratase in the female
6 cynomolgus monkey (Macaca fascicularis): kinetic analysis in control and lead-exposed animals. Comp.
7 Biochem. Physiol. B: Biochem. Mol. Biol. 108: 241-252.
8 Dowd, T. L.; Rosen, J. F.; Gupta, R. K. (1990) 31P NMR and saturation transfer studies of the effect of PB2+ on
9 cultured osteoblastic bone cells. J. Biol. Chem. 265: 20833-20838.
10 Dowd, T. L.; Rosen, J. F.; Gundberg, C. M; Gupta, R. K. (1994) The displacement of calcium from osteocalcin at
11 submicromolar concentrations of free lead. Biochim. Biophys. Acta 1226: 131-137.
12 Dowd, T. L.; Rosen, J. F.; Mints, L.; Gundberg, C. M. (2001) The effect of Pb2+ on the structure and
13 hydroxyapatite binding properties of osteocalcin. Biochim. Biophys. Acta 1535: 153-163.
14 Driscoll, K. E. (2000) TNF a and MIP-2: Role in particle induced inflammation and regulation by oxidative stress.
15 Toxicol. Lett. 112-113: 177-183.
16 Dunon, D.; Allioli, N.; Vainio, O.; Ody, C.; Imhof, B. A. (1998) Renewal of thymocyte progenitors and emigration
17 of thymocytes during avian development. Dev. Comp. Immunol. 22: 279-287.
18 Dursun, N.; Arifoglu, C.; Siier, C.; Keskinol, L. (2005) Blood pressure relationship to nitric oxide, lipid
19 peroxidation, renal function, and renal blood flow in rats exposed to low lead levels. Biol. Trace Elem. Res.
20 104: 141-150.
21 DuVal, G.; Fowler, B. A. (1989) Preliminary purification and characterization studies of a low molecular weight,
22 high affinity cytosolic lead-binding protein in rat brain. Biochem. Biophys. Res. Commun. 159: 177-184.
23 Duydu, Y.; Siizen, H. S.; Aydin, A.; Gander, O.; Uysal, H.; Isimer, A.; Vural, N. (2001) Correlation between lead
24 exposure indicators and sister chromatid exchange (SCE) frequencies in lymphocytes from inorganic lead
25 exposed workers. Arch. Environ. Contam. Toxicol. 41: 241-246.
26 Dyatlov, V. A.; Lawrence, D. A. (2002) Neonatal lead exposure potentiates sickness behavior induced by Listeria
27 monocytogenes infection of mice. Brain Behav. Immun. 16: 477-492.
28 Dyatlov, V. A.; Platoshin, A. V.; Lawrence, D. A.; Carpenter, D. O. (1998a) Lead potentiates cytokine- and
29 glutamate-mediated increases in permeability of the blood-brain barrier. Neurotoxicology 19: 283-292.
30 Dyatlov, V. A.; Dyatlova, O. M.; Parsons, P. J.; Lawrence, D. A.; Carpenter, D. O. (1998b) Lipopolysaccharide and
31 interleukin-6 enhance lead entry into cerebellar neurons: application of a new and sensitive flow cytometric
32 technique to measure intracellular lead and calcium concentrations. Neurotoxicology 19: 293-302.
33 Eder, K.; Reichlmayr-Lais, A. M.; KirchgeBner, M. (1990) Activity of Na-K-ATPase and Ca-Mg-ATPase in red
34 blood cell membranes of lead-depleted rats. J. Trace Elem. Electrolytes Health Dis. 4: 21-24.
3 5 Egle, P.M.; Shelton, K. R. (1986) Chronic lead intoxication causes a brain-specific nuclear protein to accumulate in
36 the nuclei of cells lining kidney tubules. J. Biol. Chem. 261: 2294-2298.
37 Eisenmann, D. R.; Yaeger, J. A. (1969) Alterations in the formation of rat dentine and enamel induced by various
38 ions. Arch. Oral Biol. 14: 1045-1064.
39 El-Fawal, H. A. N.; Waterman, S. J.; De Feo, A.; Shamy, M. Y. (1999) Neuroimmunotoxicology: humoral
40 assessment of neurotoxicity and autoimmune mechanisms. Environ. Health Perspect.
41 107(suppl. 5): 767-775.
42 Elias, Z.; Poirot, O.; Pezerat, H.; Suquet, H.; Schneider, O.; Daniere, M. C.; Terzetti, F.; Baruthio, F.; Fournier, M.;
43 Cavelier, C. (1989) Cytotoxic and neoplastic transforming effects of industrial hexavalent chromium
44 pigments in Syrian hamster embryo cells. Carcinogenesis 10: 2043-2052.
45 Elias, Z.; Poirot, O.; Baruthio, F.; Daniere, M. C. (1991) Role of solubilized chromium in the induction of
46 morphological transformation of Syrian hamster embryo (SHE) cells by paniculate chromium(VI)
47 compounds. Carcinogenesis 12: 1811-1816.
48 El-Missiry, M. A. (2000) Prophylactic effect of melatonin on lead-induced inhibition of heme biosynthesis and
49 deterioration of antioxidant systems in male rats. J. Biochem. Mol. Toxicol. 14: 57-62.
50 Elreedy, S.; Krieger, N.; Ryan, P. B.; Sparrow, D.; Weiss, S. T.; Hu, H. (1999) Relations between individual and
51 neighborhood-based measures of socioeconomic position and bone lead concentrations among community -
52 exposed men: the Normative Aging Study. Am. J. Epidemiol. 150: 129-141.
53 Engellenner, W. J.; Burright, R. G.; Donovick, P. J. (1986) Lead, age and aggression in male mice. Physiol. Behav.
54 36: 823-828.
55 Englyst, V.; Lundstrom, N. G.; Gerhardsson, L.; Rylander, L.; Nordberg, G. (2001) Lung cancer risks among lead
56 smelter workers also exposed to arsenic. Sci. Total Environ. 273: 77-82.
May 2006 5-305 DRAFT-DO NOT QUOTE OR CITE
-------
1 Ercal, N.; Treeratphan, P.; Hammond, T. C.; Matthews, R. H.; Grannemann, N. H.; Spitz, D. R. (1996) In vivo
2 indices of oxidative stress in lead-exposed C57BL/6 mice are reduced by treatment with meso-2,3-
3 dimercaptosuccinic acid or 7V-acetylcysteine. Free Radical Biol. Med. 21: 157-161.
4 Eriksson, L. E. G.; Beving, H. (1993) Calcium- and lead-activated morphological changes in human erythrocytes:
5 a spin label study of the cytoplasm. Arch. Biochem. Biophys. 303: 296-301.
6 Escribano, A.; Revilla, M; Hernandez, E. R.; Seco, C.; Gonzalez-Riola, I; Villa, L. F.; Rico, H. (1997) Effect of
7 lead on bone development and bone mass: a morphometric, densitometric, and histomorphometric study in
8 growing rats. Calcif. Tiss. Int. 60: 200-203.
9 Ewers, U.; Stiller-Winkler, R.; Idel, H. (1982) Serum immunoglobulin, complement C3, and salivary IgA levels in
10 lead workers. Environ. Res. 29: 351-357.
11 Exon, J. H.; Koller, L. D.; Kerkvliet, N. I. (1979) Lead-cadmium interaction: effects on viral-induced mortality and
12 tissue residues in mice. Arch. Environ. Health 34: 469-475.
13 Fahmy, M. A. (1999) Lead acetate genotoxicity in mice. Cytologia 64: 357-365.
14 Faith, R. E.; Luster, M. I.; Kimmel, C. A. (1979) Effect of chronic developmental lead exposure on cell-mediated
15 immune functions. Clin. Exp. Immunol. 35: 413-420.
16 Fanning, D. (1988) A mortality study of lead workers, 1926-1985. Arch. Environ. Health 43: 247-251.
17 Farant, J.-P.; Wigfield, D. C. (1987) Interaction of divalent metal ions with normal and lead-inhibited human
18 erythrocytic porphobilinogen synthase in vitro. Toxicol. Appl. Pharmacol. 89: 9-18.
19 Farant, J.-P.; Wigfield, D. C. (1990) The effects of copper, zinc, mercury, and cadmium on rabbit erythrocytic
20 porphobilinogen synthase in vivo. J. Anal. Toxicol. 14: 222-226.
21 Farias, P.; Borja-Aburto, V. H.; Rios, C.; Hertz-Picciotto, I.; Rojas-Lopez, M.; Chavez-Ayala, R. (1996) Blood lead
22 levels in pregnant women of high and low socioeconomic status in Mexico City. Environ. Health Perspect.
23 104: 1070-1074.
24 Farmand, F.; Ehdale, A.; Roberts, C. K.; Sindhu, R. K. (2005) Lead-induced dysregulation of superoxide
25 dismutases, catalase, glutathione peroxidase, and guanylate cyclase. Environ. Res. 98: 33-39.
26 Faust, D.; Brown, J. (1987) Moderately elevated blood lead levels: effects on neuropsychologic functioning in
27 children. Pediatrics 80: 623-629.
28 Faustman, E. M.; Silbernagel, S. M.; Fenske, R. A.; Burbacher, T. M.; Ponce, R. A. (2000) Mechanisms underlying
29 children's susceptibility to environmental toxicants. Environ. Health Perspect. Suppl. 108(1): 13-21.
30 Favalli, L.; Chiari, M. C.; Piccinini, F.; Rozza, A. (1977) Experimental investigations on the contraction induced by
31 lead in arterial smooth muscle. Acta Pharmacol. Toxicol. 41: 412-420.
32 Featherstone, J. D.; Goodman, P.; McLean, J. D. (1979) Electron microscope study of defect zones in dental enamel.
33 J. Ultrastruct. Res. 67: 117-123.
34 Featherstone, J. D. B.; Nelson, D. G. A.; McLean, J. D. (1981) An electron microscope study of modifications to
35 defect regions in dental enamel and synthetic apatites. Caries Res. 15: 278-288.
3 6 Federal Register. (2001) Lead and lead compounds; lowering of reporting thresholds; community right-to-know
37 toxic chemicals release reporting: delay of effective date. F. R. 66 (February 16): 10585-10586.
38 Fehlau, R.; Grygorczyk, R.; Fuhrmann, G. F.; Schwarz, W. (1989) Modulation of the Ca2+- or Pb2+-activated
3 9 K+-selective channels in human red cells. II. Parallelisms to modulation of the activity of a membrane-
40 bound oxidoreductase. Biochim. Biophys. Acta 978: 37-42.
41 Pels, L. M.; Herbert, C.; Pergande, M.; Jung, K.; Hotter, G.; Rosello, J.; Gelpi, E.; Mutti, A.; De Broe, M.; Stolte, H.
42 (1994) Nephron target sites in chronic exposure to lead. Nephrol. Dial. Transplant. 9: 1740-1746.
43 Ferguson, S. A.; Bowman, R. E. (1990) Effects of postnatal lead exposure on open field behavior in monkeys.
44 Neurotoxicology Teratol. 12: 91-97.
45 Ferguson, S. A.; Holson, R. R.; Gazzara, R. A.; Siitonen, P. H. (1998) Minimal behavioral effects from moderate
46 postnatal lead treatment in rats. Neurotoxicol. Teratol. 20: 637-643.
47 Ferguson, C.; Kern, M.; Audesirk, G. (2000) Nanomolar concentrations of inorganic lead increase Ca2+ efflux and
48 decrease intracellular free Ca2+ ion concentrations in cultured rat hippocampal neurons by a calmodulin-
49 dependent mechanism. Neurotoxicology 21: 365-378.
50 Fergusson, D. M.; Horwood, L. J.; Lynskey, M. T. (1997) Early dentine lead levels and educational outcomes at
51 18 years. J. Child Psychol. Psychiatry 38: 471-478.
52 Perm, V. H.; Carpenter, S. J. (1967) Developmental malformations resulting from the administration of lead salts.
53 Exp. Mol. Pathol. 7: 208-213.
54 Fernandez-Cabezudo, M. J.; Hassan, M. Y.; Mustafa, N.; El-Sharkawy, R.; Fahim, M. A.; Al-Ramada, K. (2003)
5 5 Alpha tocopherol protects against immunosuppressive and immunotoxic effects of lead. Free Radical Res.
56 37:437-445.
May 2006 5-306 DRAFT-DO NOT QUOTE OR CITE
-------
1 Filkins, J. P.; Buchanan, B. J. (1973) Effects of lead acetate on sensitivity to shock, intravascular carbon and
2 endotoxin clearances, and hepatic endotoxin detoxification. Proc. Soc. Exp. Biol. Med. 142: 471-475.
3 Finkelstein, Y.; Markowitz, M. E.; Rosen, J. F. (1998) Low-level lead-induced neurotoxicity in children: an update
4 on central nervous system effects. Brain Res. Rev. 27: 168-176.
5 Fleming, D. E. B.; Boulay, D.; Richard, N. S.; Robin, J.-P.; Gordon, C. L.; Webber, C. E.; Chettle, D. R. (1997)
6 Accumulated body burden and endogenous release of lead in employees of a lead smelter. Environ. Health
7 Perspect. 105: 224-233.
8 Fleming, D. E. B.; Chettle, D. R.; Wetmur, J. G.; Desnick, R. J.; Robin, J.-P.; Boulay, D.; Richard, N. S.; Gordon,
9 C. L.; Webber, C. E. (1998) Effect of the 5-aminolevulinate dehydratase polymorphism on the
10 accumulation of lead in bone and blood in lead smelter workers. Environ. Res. 77: 49-61.
11 Flohe, S. B.; Briiggemann, J.; Herder, C.; Goebel, C.; Kolb, H. (2002) Enhanced proinflammatory response to
12 endotoxin after priming of macrophages with lead ions. J. Leukoc. Biol. 71:417-424.
13 Flora, G. J. S.; Seth, P. K. (1999) Beneficial effects of S-adenosyl-L-methionine on aminolevulinic acid dehydratase,
14 glutathione, and lipid peroxidation during acute lead-ethanol administration in mice. Alcohol 18: 103-108.
15 Flora, S. J. S.; Tandon, S. K. (1987) Influence of calcium disodium edetate on the toxic effects of lead
16 administration in pregnant rats. Indian J. Physiol. Pharmacol. 31: 267-272.
17 Flora, S. J. S.; Singh, S.; Tandon, S. K. (1989) Thiamine and zinc in prevention or therapy of lead intoxication.
18 J. Int. Med. Res. 17: 68-75.
19 Flora, S. J. S.; Jeevaratnam, K.; Kumar, D. (1993) Preventive effects of sodium molybdate in lead intoxication in
20 rats. Ecotoxicol. Environ. Saf. 26: 133-137.
21 Flora, S. J. S.; Bhattacharya, R.; Sachan, S. R. S. (1994) Dose-dependent effects of zinc supplementation during
22 chelation of lead in rats. Pharmacol. Toxicol. 74: 330-333.
23 Flora, S. J. S.; Bhattacharya, R.; Vijayaraghavan, R. (1995) Combined therapeutic potential ofmeso-2,3-
24 dimercaptosuccinic acid and calcium disodium edetate on the mobilization and distribution of lead in
25 experimental lead intoxication in rats. Fundam. Appl. Toxicol. 25: 233-240.
26 Flora, S. J. S.; Pande, M.; Mehta, A. (2003) Beneficial effect of combined administration of some naturally
27 occurring antioxidants (vitamins) and thiol chelators in the treatment of chronic lead intoxication. Chem.
28 Biol. Interact. 145: 267-280.
29 Fontanellas, A.; Navarro, S.; Moran-Jimenez, M.-J.; Sanchez-Fructuoso, A. L; Vegh, L; Barrientos, A.; De
30 Salamanca, R. E. (2002) Erythrocyte aminolevulinate dehydratase activity as a lead marker in patients with
31 chronic renal failure. Am. J. Kidney Dis. 40: 43-50.
32 Foote, R. H. (1999) Fertility of rabbit sperm exposed in vitro to cadmium and lead. Reprod. Toxicol. 13: 443-449.
33 Fortoul, T. L; Moncada-Hernandez, S.; Saldivar-Osorio, L.; Espejel-Maya, G.; Mussali-Galante, P.; Del Carmen
34 Avila-Casando, M.; Colin-Barenque, L.; Hernandez-Serrato, M. L; Avila-Costa, M. R. (2005) Sex
3 5 differences in brochiolar epithelium response after the inhalation of lead acetate (Pb). Toxicology
36 207:323-330.
37 Foster, W. G. (1992) Reproductive toxicity of chronic lead exposure in the female cynomolgus monkey. Reprod.
38 Toxicol. 6: 123-131.
39 Foster, W. G.; Stals, S. L; McMahon, A. (1992) An ultrasound study of the effect of chronic lead exposure on
40 endometrial cycle changes in the female cynomolgus monkey. J. Med. Primatol. 21: 353-356.
41 Foster, W. G.; McMahon, A.; YoungLai, E. V.; Hughes, E. G.; Rice, D. C. (1993) Reproductive endocrine effects of
42 chronic lead exposure in the male cynomolgus monkey. Reprod. Toxicol. 7: 203-209.
43 Foster, W. G.; McMahon, A.; Rice, D. C. (1996a) Sperm chromatin structure is altered in cynomolgus monkeys with
44 environmentally relevant blood lead levels. Toxicol. Ind. Health 12: 723-735.
45 Foster, W. G.; McMahon, A.; Rice, D. C. (1996b) Subclinical changes in luteal function in cynomolgus monkeys
46 with moderate blood lead levels. J. Appl. Toxicol. 16: 159-163.
47 Foster, W. G.; Singh, A.; McMahon, A.; Rice, D. C. (1998) Chronic lead exposure effects in the cynomolgus
48 monkey (Macaca fascicularis) testis. Ultrastruct. Pathol. 22: 63-71.
49 Fowler, B. A. (1992) Mechanisms of kidney cell injury from metals. Environ. Health Perspect. 100: 57-63.
50 Fowler, B. A. (1998) Roles of lead-binding proteins in mediating lead bioavailability. Environ. Health Perspect.
51 Suppl. 106(6): 1585-1587.
52 Fowler, B. A.; DuVal, G. (1991) Effects of lead on the kidney: roles of high-affinity lead-binding proteins. Environ.
53 Health Perspect. 91: 77-80.
54 Fowler, B. A.; Mahaffey, K. R. (1978) Interactions among lead, cadmium, and arsenic in relation to porphyrin
55 excretion patterns. Environ. Health Perspect. 25: 87-90.
May 2006 5-307 DRAFT-DO NOT QUOTE OR CITE
-------
1 Fowler, B. A.; Kimmel, C. A.; Woods, J. S.; McConnell, E. E.; Grant, L. D. (1980) Chronic low-level lead toxicity
2 in the rat. III. An integrated assessment of long-term toxicity with special reference to the kidney. Toxicol.
3 Appl. Pharmacol. 56: 59-77.
4 Fowler, B. A.; Kahng, M. W.; Smith, D. R.; Conner, E. A.; Laughlin, N. K. (1993) Implications of lead binding
5 proteins for risk assessment of lead exposure. J. Exposure Anal. Environ. Epidemiol. 3: 441-448.
6 Fowler, B. A.; Whittaker, M. H.; Lipsky, M.; Wang, G.; Chen, X.-Q. (2004) Oxidative stress induced by lead,
7 cadmium and arsenic mixtures: 30-day, 90-day, and 180-day drinking water studies in rats: an overview.
8 Biometals 17: 567-568.
9 Fox, D. A.; Chu, L. W.-F. (1988) Rods are selectively altered by lead: II. ultrastructure and quantitative histology.
10 Exp. Eye Res. 46:613-625.
11 Fox, D. A.; Farber, D. B. (1988) Rods are selectively altered by lead: I. electrophysiology and biochemistry.
12 Exp. Eye Res. 46:597-611.
13 Fox, D. A.; Rubinstein, S. D. (1989) Age-related changes in retinal sensitivity, rhodopsin content and rod outer
14 segment length in hooded rats following low-level lead exposure during development. Exp. Eye Res.
15 48:237-249.
16 Fox, D. A.; Sillman, A. J. (1979) Heavy metals affect rod, but not cone, photoreceptors. Science (Washington, DC)
17 206:78-80.
18 Fox, D. A.; Katz, L. M.; Farber, D. B. (1991a) Low level developmental lead exposure decreases the sensitivity,
19 amplitude and temporal resolution of rods. Neurotoxicology 12: 641-654.
20 Fox, D. A.; Rubinstein, S. D.; Hsu, P. (1991b) Developmental lead exposure inhibits adult rat retinal, but not kidney,
21 Na+,K+-ATPase. Toxicol. Appl. Pharmacol. 109: 482-493.
22 Fox, D. A.; Srivastava, D.; Hurwitz, R. L. (1994) Lead-induced alterations in rod-mediated visual functions and
23 cGMP metabolism: new insights. Neurotoxicology 15: 503-512.
24 Fox, D. A.; Campbell, M. L.; Blocker, Y. S. (1997) Functional alterations and apoptotic cell death in the retina
25 following developmental or adult lead exposure. Neurotoxicology 18: 645-664.
26 Fracasso, M. E.; Perbellini, L.; Solda, S.; Talamini, G.; Franceschetti, P. (2002) Lead induced DNA strand breaks in
27 lymphocytes of exposed workers: role of reactive oxygen species and protein kinase C. Mutat. Res.
28 515: 159-169.
29 Franklin, C. A.; Inskip, M. J.; Baccanale, C. L.; Edwards, C. M.; Manton, W. I.; Edwards, E.; O'Flaherty, E. J.
30 (1997) Use of sequentially administered stable lead isotopes to investigate changes in blood lead during
31 pregnancy in a nonhuman primate (Macacafascicularis). Fundam. Appl. Toxicol. 39: 109-119.
32 Franks, P. A.; Laughlin, N. K.; Dierschke, D. J.; Bowman, R. E.; Meller, P. A. (1989) Effects of lead on luteal
33 function in rhesus monkeys. Biol. Reprod. 41: 1055-1062.
34 Fu, H.; Boffetta, P. (1995) Cancer and occupational exposure to inorganic lead compounds: a meta-analysis of
35 published data. Occup. Environ. Med. 52: 73-81.
36 Fuentes, M.; Torregrosa, A.; Mora, R.; Gotzens, V.; Corbella, J.; Domingo, J. L. (1996) Placenta! effects of lead in
37 mice. Placenta 17: 371-376.
38 Fujita, H.; Orii, Y.; Sano, S. (1981) Evidence of increased synthesis of 5-aminolevulinic acid dehydratase in
39 experimental lead-poisoned rats. Biochim. Biophys. Acta 678: 39-50.
40 Fujita, H.; Sato, K,; Sano, S. (1982) Increase in the amount of Erythrocyte 5-aminolevulinic acid dehydratase in
41 workers with moderate lead exposure. Int. Arch. Occup. Environ. Health 50: 287-297.
42 Fujiwara, Y.; Kaji, T. (1999) Possible mechanism for lead inhibition of vascular endothelial cell proliferation: a
43 lower response to basic fibroblast growth factor through inhibition of heparan sulfate synthesis. Toxicology
44 133: 147-157.
45 Fujiwara, Y.; Kaji, T.; Yamamoto, C.; Sakamoto, M.; Kozuka, H. (1995) Stimulatory effect of lead on the
46 proliferation of cultured vascular smooth-muscle cells. Toxicology 98: 105-110.
47 Fujiwara, Y.; Watanabe, S.; Sakamoto, M.; Kaji, T. (1998) Repair of wounded monolayers of cultured vascular
48 endothelial cells after simultaneous exposure to lead and zinc. Toxicol. Lett. 94: 181-188.
49 Fukumoto, K.; Karai, I.; Horiguchi, S. (1983) Effect of lead on erythrocyte membranes. Br. J. Ind. Med.
50 40:220-223.
51 Fullmer, C. S. (1991) Intestinal calcium and lead absorption: effects of dietary lead and calcium. Environ. Res.
52 54: 159-169.
53 Fullmer, C. S. (1992) Intestinal interactions of lead and calcium. Neurotoxicology 13: 799-807.
54 Fullmer, C. S. (1995) Dietary calcium levels and treatment interval determine the effects of lead ingestion on plasma
55 1,25-dihydroxyvitaminD concentration in chicks. J. Nutr. 125: 1328-1333.
May 2006 5-308 DRAFT-DO NOT QUOTE OR CITE
-------
1 Fullmer, C. S. (1997) Lead—calcium interactions: involvement of 1,25-dihydroxyvitamin D. Environ. Res.
2 72:45-55.
3 Fullmer, C. S.; Rosen, J. F. (1990) Effect of dietary calcium and lead status on intestinal calcium absorption.
4 Environ. Res. 51: 91-99.
5 Fullmer, C. S.; Edelstein, S.; Wasserman, R. H. (1985) Lead-binding properties of intestinal calcium-binding
6 proteins. J. Biol. Chem. 260: 6816-6819.
7 Fullmer, C. S.; Chandra, S.; Smith, C. A.; Morrison, G. H.; Wasserman, R. H. (1996) Ion microscopic imaging of
8 calcium during 1,25-dihydroxyvitamin D-mediated intestinal absorption. Histochem. Cell Biol.
9 106:215-222.
10 Furono, K.; Suetsugu, T.; Sugihara, N. (1996) Effects of metal ions on lipid peroxidation in cultured rat hepatocytes
11 loaded with a-linolenic acid. J. Toxicol. Environ. Health 48: 121-129.
12 Gainer, J. H. (1977) Effects of heavy metals and of deficiency of zinc on mortality rates in mice infected with
13 encephalomyocarditis virus. Am. J. Vet. Res. 38: 869-872.
14 Gallagher, K.; Matarazzo, W. J.; Gray, I. (1979) Trace metal modification of immunocompetence. II. Effect of
15 Pb2+, Cd2+, and Cr3+ on RNA turnover, hexokinase activity, and blastogenesis during B-lymphocyte
16 transformation in vitro. Clin. Immunol. Immunopathol. 13: 369-377.
17 Gallicchio, L.; Scherer, R. W.; Sexton, M. (2002) Influence of nutrient intake on blood lead levels of young children
18 at risk for lead poisoning. Environ. Health Perspect. 110: hi 61-All 2.
19 Gandley, R.; Anderson, L.; Silbergeld, E. K. (1999) Lead: male-mediated effects on reproduction and development
20 in the rat. Environ. Res. A 89: 355-363.
21 Caravan, H.; Morgan, R. E.; Levitsky, D. A.; Hermer-Vazquez, L.; Strupp, B. J. (2000) Enduring effects of early
22 lead exposure: evidence for a specific deficit in associative ability. Neurotoxicol. Teratol. 22: 151-164.
23 Garcia, T. A.; Corredor, L. (2004) Biochemical changes in the kidneys after perinatal intoxication with lead and/or
24 cadmium and their antagonistic effects when coadministered. Ecotoxicol. Environ. Saf. 57: 184-189.
25 Gautam, A. K.; Chowdhury, A. R. (1987) Effect of lead on erythropoietic system of intact and splenectomized rats.
26 Indian J. Physiol. Pharmacol. 31:117-124.
27 Gaworski, C. L.; Sharma, R. P. (1978) The effects of heavy metals on [3H]thymidine uptake in lymphocytes.
28 Toxicol. Appl. Pharmacol. 46: 305-313.
29 Gerhardsson, L.; Brune, D.; Nordberg, G. F.; Wester, P. O. (1986) Distribution of cadmium, lead and zinc in lung,
30 liver and kidney in long-term exposed smelter workers. Sci. Total Environ. 50: 65-85.
31 Gerhardsson, L.; Hagmar, L.; Rylander, L.; Skerfving, S. (1995) Mortality and cancer incidence among secondary
32 lead smelter workers. Occup. Environ. Med. 52: 667-672.
33 Gerlach, R. F.; Souza, A. P.; Cury, J. A.; Line, S. R. P. (2000a) Effect of lead, cadmium and zinc on the activity of
34 enamel matrix proteinases in vitro. Eur. J. Oral Sci. 108: 327-334.
35 Gerlach, R. F.; Toledo, D. B.; Novaes, P. D.; Merzel, J.; Line, S. R. P. (2000b) The effect of lead on the eruption
36 rates of incisor teeth in rats. Arch. Oral Biol. 45: 951-955.
37 Gerlach, R. F.; Cury, J. A.; Krug, F. J.; Line, S. R. P. (2002) Effect of lead on dental enamel formation. Toxicology
38 175:27-34.
39 Gerr, F.; Letz, R.; Stokes, L.; Chettle, D.; McNeill, F.; Kaye, W. (2002) Association between bone lead
40 concentration and blood pressure among young adults. Am. J. Ind. Med. 42: 98-106.
41 Gewirtz, A. T.; Liu, Y.; Sitaraman, S. V.; Madara, J. L. (2002) Intestinal epithelial pathobiology: past, present and
42 future. Best Pract. Res. Clin. Gastroenterol. 16: 851-867.
43 Giavini, E.; Prati, M.; Vismara, C. (1980) Effects of cadmium, lead and copper on rat preimplantation embryos.
44 Bull. Environ. Contam. Toxicol. 25: 702-705.
45 Gibson, S. L. M.; Goldberg, A. (1970) Defects in haem synthesis in mammalian tissues in experimental lead
46 poisoning and experimental porphyria. Clin. Sci. 38: 63-72.
47 Gilbert, M. E.; Mack, C. M. (1998) Chronic lead exposure accelerates decay of long-term potentiation in rat dentate
48 gyms in vivo. Brain Res. 789: 139-149.
49 Gilbert, S. G.; Rice, D. C. (1987) Low-level lifetime lead exposure produces behavioral toxicity (spatial
50 discrimination reversal) in adult monkeys. Toxicol. Appl. Pharmacol. 91: 484-490.
51 Gilbert, M. E.; Mack, C. M.; Lasley, S. M. (1996) Chronic developmental lead exposure increases the threshold for
52 long-term potentiation in rat dentate gyrus in vivo. Brain Res. 736: 118-124.
53 Gilbert, M. E.; Mack, C. M.; Lasley, S. M. (1999a) The influence of developmental period of lead exposure on long-
54 term potentiation in the adult rat dentate gyrus in vivo. Neurotoxicology 20: 57-69.
55 Gilbert, M. E.; Mack, C. M.; Lasley, S. M. (1999b) Chronic developmental lead exposure and hippocampal long-
56 term potentiation: biphasic dose-response relationship. Neurotoxicology 20: 71-82.
May 2006 5-309 DRAFT-DO NOT QUOTE OR CITE
-------
1 Gilbert, M. E.; Kelly, M. E.; Samsam, T. E.; Goodman, J. H. (2005) Chronic developmental lead exposure reduces
2 neurogenesis in adult rat hippocampus but does not impair spatial learning. Toxicol. Sci. 86:
3 Giridhar, J.; Isom, G. E. (1990) Interaction of lead acetate with atrial natriuretic factor in rats. Life Sci. 46: 569-576.
4 Gobel, T. W. F. (1996) The T-dependent immune system. In: Davidson, T. F.; Morris, T. R.; Payne, L. N., eds.
5 Poultry immunology. Abingdon, Oxfordshire, England: Carfax Publishing Co.; pp. 83-114. (Poultry
6 science symposium series, no. 24).
7 Goebel, C.; Kirchhoff, K.; Wasmuth, H.; Flohe, S. B.; Elliott, R. B.; Kolb, H. (1999) The gut cytokine balance as a
8 target of lead toxicity. Life Sci. 64: 2207-2214.
9 Goebel, C.; Flohe, S. B.; Kirchhoff, K.; Herder, C.; Kolb, H. (2000) Orally administered lead chloride induces bias
10 of mucosal immunity. Cytokine 12: 1414-1418.
11 Goering, P. L.; Fowler, B. A. (1984) Regulation of lead inhibition of 5-aminolevulinic acid dehydratase by a low
12 molecular weight, high affinity renal lead-binding protein. J. Pharmacol. Exp. Ther. 231: 66-71.
13 Goering, P. L.; Fowler, B. A. (1985) Mechanism of renal lead-binding protein reversal of 5-aminolevulinic acid
14 dehydratase inhibition by lead. J. Pharmacol. Exp. Ther. 234: 365-371.
15 Goering, P. L.; Fowler, B. A. (1987a) Regulatory roles of high-affinity metal-binding proteins in mediating lead
16 effects on 5-aminolevulinic acid dehydratase. Ann. N. Y. Acad. Sci. 514: 235-247.
17 Goering, P. L.; Fowler, B. A. (1987b) Kidney zinc-thionein regulation of delta-aminolevulinic acid dehydratase
18 inhibition by lead. Arch. Bichem. Biophys. 253: 48-55.
19 Goering, P. L.; Mistry, P.; Fowler, B. A. (1986) A low molecular weight lead-binding protein in brain attenuates
20 lead inhibition of 5-aminolevulinic acid dehydratase: comparison with a renal lead-binding protein. J.
21 Pharmacol. Exp. Ther. 237: 220-225.
22 Goldstein, G. W. (1993) Evidence that lead acts as a calcium substitute in second messenger metabolism. Presented
23 at: Ninth international neurotoxicology conference; October 1991; Little Rock, AR. Neurotoxicology
24 14(2-3): 97-101.
25 Golubovich, E. Ya.; Avkhimenko, M. M.; Chirkova, E. M. (1968) Biochemical and morphological changes in the
26 testicles of rats induced by small doses of lead. Toksikol. Nov. Prom. Khim. Veschestv. 10: 63-73.
27 Gong, Z.; Evans, H. L. (1997) Effect of chelation with Tweso-dimercaptosuccinic acid (DMSA) before and after the
28 appearance of lead-induced neurotoxicity in the rat. Toxicol. Appl. Pharmacol. 144: 205-214.
29 Gonick, H. C.; Khalil-Manesh, F.; Raghavan, S. R. V. (1985) Characterization of human erythrocyte lead-binding
30 protein. In: Lekkas, T. D., ed. International conference: heavy metals in the environment; September;
31 Athens, Greece, v. 1. Edinburgh, United Kingdom: CEP Consultants, Ltd.; pp. 313-316.
32 Gonick, H. C.; Ding, Y.; Bondy, S. C.; Ni, Z.; Vaziri, N. D. (1997) Lead-induced hypertension: interplay of nitric
33 oxide and reactive oxygen species. Hypertension 30: 1487-1492.
34 Gonick, H. C.; Ding, Y.; Vaziri, N. D. (1998) Effect of low lead exposure on eicosanoid excretion in rats.
3 5 Prostaglandins Other Lipid Mediators 55: 77-82.
36 Gonzalez-Cossio, T.; Peterson, K. E.; Sanin, L.-H.; Fishbein, E.; Palazuelos, E.; Aro, A.; Hernandez-Avila, M.;
37 Hu, H. (1997) Decrease in birth weight in relation to maternal bone-lead burden. Pediatrics 100: 856-862.
3 8 Gonzalez-Riola, J.; Hernandez, E. R.; Escribano, A.; Revilla, M.; Villa, C.-S. L. F.; Rico, H. (1997) Effect of lead
39 on bone and cartilage in sexually mature rats: a morphometric and histomorphometry study. Environ. Res.
40 74:91-93.
41 Corbel, F.; Boujelbene, M.; Makni-Ayadi, F.; Guermazi, F.; Croute, F.; Soleilhavoup, J. P.; El Feki, A. (2002)
42 Exploration des effets cytotoxiques du plomb sur la fonction sexuelle endocrine et exocrine chez le rat
43 pubere male et femelle. Mise en evidence d'une action apoptotique [Impact of lead given in drinking water
44 on the endocrine and exocrine sexual activity in pubescent rats. Determination of an apoptotic process].
45 C. R. Biol. 325: 927-940.
46 Goyer, R. A. (1968) The renal tubule in lead poisoning. I. Mitochondrial swelling and aminoaciduria. Lab. Invest.
47 19:71-77.
48 Goyer, R. A.; Rhyne, B. C. (1973) Pathological effects of lead. Int. Rev. Exp. Pathol. 12: 1-77.
49 Goyer, R. A.; Wilson, M. H. (1975) Lead-induced inclusion bodies: results of ethylenediaminetetraacetic acid
50 treatment. Lab. Invest. 32: 149-156.
51 Goyer, R. A.; Krall, A.; Kimball, J. P. (1968) The renal tubule in lead poisoning. II. In vitro studies of mitochondrial
52 structure and function. Lab. Invest. 19: 78-83.
53 Goyer, R. A.; Leonard, D. L.; Bream, P. R.; Irons, T. G. (1970a) Aminoaciduria in experimental lead poisoning.
54 Proc. Soc. Exp. Biol. Med. 135: 767-771.
55 Goyer, R. A.; Leonard, D. L.; Moore, J. F.; Rhyne, B. Krigman, M. R. (1970b) Lead dosage and the role of the
56 intranuclear inclusion body: an experimental study. Arch. Environ. Health 20: 705-711.
May 2006 5-310 DRAFT-DO NOT QUOTE OR CITE
-------
1 Goyer, R. A.; May, P.; Gates, M. M; Krigman, M. R. (1970c) Lead and protein content of isolated intranuclear
2 inclusion bodies from kidneys of lead-poisoned rats. Lab. Invest. 22: 245-251.
3 Goyer, R. A.; Cherian, M. G.; Delaquerriere-Richardson, L. (1978) Renal effects of repeated administration of
4 calcium disodium ethylenediamnetetraacetate during excessive exposure to lead in rats. J. Environ. Pathol.
5 Toxicol. 1:403-410.
6 Grabowska, M.; Guminska, M. (1996) The effect of lead on lactate formation, ATP level and membrane ATPase
7 activities in human erythrocytes in vitro. Int. J. Occup. Med. Environ. Health 9: 265-274.
8 Graca, A.; Ramalho-Santos, J.; De Lourdes Pereira, M. (2004) Effect of lead chloride on spermatogenesis and sperm
9 parameters in mice. Asian J. Androl. 6: 237-241.
10 Granick, J. L.; Sassa, S.; Granick, S.; Levere, R. D.; Kappas, A. (1973) Studies in lead poisoning. II. correlation
11 between the ratio of activated to inactivated 5-aminolevulinic acid dehydratase of whole blood and the
12 blood lead level. Biochem. Med. 8: 149-159.
13 Grant, L. D.; Kimmel, C. A.; West, G. L.; Martinez-Vargas, C. M.; Howard, J. L. (1980) Chronic low-level lead
14 toxicity in the rat. II. Effects on postnatal physical and behavioral development. Toxicol. Appl. Pharmacol.
15 56:42-58.
16 Grobler, S. R.; Rossouw, R. J.;Kotze,D. (1985) Lead in teeth of weanling rats received via the maternal drinking
17 water. Arch. Oral Biol. 30: 509-511.
18 Grobler, S. R.; Rossouw, R. J.; Kotze, T. J. V.; Slander, I. A. (1991) The effect of airborne lead on lead levels of
19 blood, incisors and alveolar bone of rats. Arch. Oral Biol. 36: 357-360.
20 Grover, C. A.; Nation, J. R.; Brattom. G. R. (1993) Chronic exposure to lead attenuates cocaine-induced behavioral
21 activation. Pharmacol. Biochem. Behav. 44: 221-225.
22 Gruber, H. E.; Gonick, H. C.; Khalil-Manesh, F.; Sanchez, T. V.; Motsinger, S.; Meyer, M.; Sharp, C. F. (1997)
23 Osteopenia induced by long-term, low- and high-level exposure of the adult rat to lead. Miner. Electrolyte
24 Metab. 23:65-73.
25 Guilarte T. R.; McGlothan, J. L. (1998) Hippocampal NMDA receptor mRNA undergoes subunit specific changes
26 during developmental lead exposure. Brain Res. 790: 98-107.
27 Guilarte T. R.; McGlothan, J. L. (2003) Selective decrease in NR1 subunit splice variant mRNA in the hippocampus
28 of Pb2+-exposed rats: implications for synaptic targeting and cell surface expression of NMDAR
29 complexes. Mol. Brain Res. 113: 37-43.
3 0 Guilarte, T. R.; Miceli, R. C. (1992) Age-dependent effects of lead on [3H]MK-801 binding to the NMDA receptor-
31 gated ionophore: in vitro and in vivo studies. Neurosci. Lett. 148: 27-30.
32 Guilarte, T. R.; McGlothan, J. L.; Nihei, M. K. (2000) Hippocampal expression of N-methyl-D-aspartate receptor
33 (NMDARl) subunit splice variant mRNA is altered by developmental exposure to Pb2+. Mol. Brain Res.
34 76:299-305.
35 Guilarte, T. R.; Toscano, C. D.; McGlothan, J. L.; Weaver, S. A. (2003) Environmental enrichment reverses
3 6 cognitive and molecular deficits induced by developmental lead exposure. Ann. Neurol. 53: 50-56.
37 Guity, P.; McCabe, M. J.; Pitts, D. K.; Santini, R. P.; Pounds, J. G. (2002) Protein kinase C does not mediate the
3 8 inhibitory action of lead on vitamin D3-dependent production of osteocalcin in osteoblastic bone cells.
39 Toxicol. Appl. Pharmacol. 178: 109-116.
40 Guo, T. L.; Mudzinski, S. P.; Lawrence, D. A. (1996) The heavy metal lead modulates the expression of both TNF-a
41 and TNF-a receptors in lipopolysaccharide-activated human peripheral blood mononuclear cells. J. Leukoc.
42 Biol. 59: 932-939.
43 Gupta, K.; Upreti, R. K.; Kidwai, A. M. (1994) Toxicokinetic study of rat intestinal brush border membrane
44 enzymes following in vitro exposure to lead and vanadium. Bull. Environ. Contam. Toxicol. 52: 919-926.
45 Gupta, P.; Husain, M. M.; Shankar, R.; Seth, P. K.; Maheshwari, R. K. (2002) Lead exposure enhances virus
46 multiplication and pathogenesis in mice. Vet. Hum. Toxicol. 44: 205-210.
47 Gurer, H.; Ercal, N. (2000) Can antioxidants be beneficial in the treatment of lead poisoning? Free Rad. Biol. Med.
48 29: 927-945.
49 Gtirer, H.; Ozgtines, H.; Neal, R.; Spitz, D. R.; Ercal, N. (1998) Antioxidant effects of 7V-acetylcysteine and
50 succimer in red blood cells from lead-exposed rats. Toxicology 128: 181-189.
51 Gurer, H.; Neal, R.; Yang, P.; Oztezcan, S.; Ercal, N. (1999a) Captopril as an antioxidant in lead-exposed Fischer
52 344 rats. Hum. Exp. Toxicol. 18: 27-32.
53 Gurer, H.; Ozgunes, H.; Oztezcan, S.; Ercal, N. (1999b) Antioxidant role of a-lipoic acid in lead toxicity. Free
54 Radical Biol. Med. 27: 75-81.
55 Gtirer, H.; Ozgunes, H.; Saygin, E.; Ercal, N. (2001) Antioxidant effect of taurine against lead-induced oxidative
56 stress. Arch. Environ. Contam. Toxicol. 41: 397-402.
May 2006 5-311 DRAFT-DO NOT QUOTE OR CITE
-------
1 Gutowski, M; Altmann, L.; Sveinsson, K.; Wiegand, H. (1997) Postnatal development of synaptic plasticity in the
2 CAS hippocampal region of control and lead-exposed Wistar rats. Dev. Brain Res. 98: 82-90.
3 Gutowski, M.; Altmann, L.; Sveinsson, K.; Wiegand, H. (1998) Synaptic plasticity in the CA1 and CAS
4 hippocampal region of pre- and postnatally lead-exposed rats. Toxicol. Lett. 95: 195-203.
5 Habermann, E.; Crowell, K.; Janicki, P. (1983) Lead and other metals can substitute for Ca2+ in calmodulin.
6 Arch. Toxicol. 54: 61-70.
7 Hac, E.; Krechniak, J. (1996) Lead levels in bone and hair of rats treated with lead acetate. Biol. Trace Elem. Res.
8 52:293-301.
9 Hacker, H.-J.; Bannasch, P.; Columbano, A. (1990) Effect of lead nitrate on liver carbohydrate enzymes and
10 glycogen content in the rat. Carcinogenesis 11: 2199-2204.
11 Haider, S.; Shameem, S.; Ahmed, S. P.; Perveen, T.; Haleem, D. J. (2005) Repeated administration of lead decreases
12 brain 5-HT metabolism and produces memory deficits in rats. Cell. Mol. Biol. Lett. 10: 669-676.
13 Hamilton, J. D.; O'Flaherty, E. J. (1994) Effects of lead exposure on skeletal development in rats. Fundam. Appl.
14 Toxicol. 22: 594-604.
15 Hamilton, J. D.; O'Flaherty, E. J. (1995) Influence of lead on mineralization during bone growth. Fundam. Appl.
16 Toxicol. 26: 265-271.
17 Hamilton, J. D.; O'Flaherty, E. J.; Ross, R.; Shukla, R.; Gartside, P. S. (1994) Structural equation modeling and
18 nested ANOVA: effects of lead exposure on maternal and fetal growth in rats. Environ. Res. 64: 53-64.
19 Hammad, T. A.; Sexton, M.; Langenberg, P. (1996) Relationship between blood lead and dietary iron intake in
20 preschool children: a cross-sectional study. Ann. Epidemiol. 6: 30-33.
21 Hammond, P. B.; Chernausek, S. D.; Succop, P. A.; Shukla, R.; Bornschein, R. L. (1989) Mechanisms by which
22 lead depresses linear and ponderal growth in weanling rats. Toxicol. Appl. Pharmacol. 99: 474-486.
23 Hammond, P. B.; Minnema, D. J.; Shulka, R. (1990) Lead exposure lowers the set point for food consumption and
24 growth in weanling rats. Toxicol. Appl. Pharmacol. 106: 80-87.
25 Hammond, P. B.; Minnema, D. J.; Succop, P. A. (1993) Reversibility of lead-induced depression of growth. Toxicol.
26 Appl. Pharmacol. 123: 9-15.
27 Han, S.; Qiao, X.; Simpson, S.; Ameri, P.; Kemp, F. W.; Bogden, J. D. (1996) Weight loss alters organ
28 concentrations and contents of lead and some essential divalent metals in rats previously exposed to lead.
29 J. Nutr. 126:317-323.
30 Han, S.; Qiao, X.; Kemp, F. W.; Bogden, J. D. (1997) Lead exposure at an early age substantially increases lead
31 retention in the rat. Environ. Health Perspect. 105: 412-417.
32 Han, S.; Li, W.; Jamil, U.; Dargan, K.; Orefice, M.; Kemp, F. W.; Bogden, J. D. (1999) Effects of weight loss and
3 3 exercise on the distribution of lead and essential trace elements in rats with prior lead exposure. Environ.
34 Health Perspect. 107: 657-662.
35 Han, S.; Pfizenmaier, D. H.; Garcia, E.; Eguez, M. L.; Ling, M.; Kemp, F. W.; Bogden, J. D. (2000) Effects of lead
3 6 exposure before pregnancy and dietary calcium during pregnancy on fetal development and lead
37 accumulation. Environ. Health Perspect. 108: 527-531.
38 Haneef, S. S.; Swamp, D.; Kalicharan; Dwivedi, S. K. (1995) The effect of concurrent lead and cadmium exposure
39 on the cell-mediated immune response in goats. Vet. Hum. Toxicol. 37: 428-429.
40 Hanna, L. A.; Peters, J. M.; Wiley, L. M.; Clegg, M. S.; Keen, C. L. (1997) Comparative effects of essential and
41 non-essential metals on preimplantation mouse embryo development in vitro. Toxicology 116: 123-131.
42 Hanson, E. H.; Imperatore, G.; Burke, W. (2001) HFE gene and hereditary hemochromatosis: a HuGE review.
43 Am. J. Epidemiol. 154: 193-206.
44 Harry, G. J.; Schmitt, T. J.; Gong, A.; Brown, H.; Zawia, N.; Evans, H. L. (1996) Lead-induced alterations of glial
45 fibrillary acidic protein (GFAP) in the developing rat brain. Toxicol. Appl. Pharmacol. 139: 84-93.
46 Hartman, D. E. (1995) Lead. In: Hartman, D. E. Neuropsychological toxicology: identification and assessment of
47 human neurotoxic syndromes. 2nd ed. New York, NY: Plenum Press; pp. 95-125.
48 Hartwig, A.; Schlepegrell, R.; Beyersmann, D. (1990) Indirect mechanism of lead-induced genotoxicity in cultured
49 mammalian cells. Mutat. Res. 241: 75-82.
50 Hashmi, N. S.; Kachru, D. N.; Khandelwal, S.; Tandon, S. K. (1989) Interrelationship between iron deficiency and
51 lead intoxication (part 2). Biol. Trace Elem. Res. 22: 299-307.
52 Hayashi, M. (1983a) Lead toxicity in the pregnant rat. I. the effect of high - level lead on 5-aminolevulinic acid
53 dehydratase activity in maternal and fetal blood or tissues. Environ. Res. 30: 152-160.
54 Hayashi, M. (1983b) Lead toxicity in the pregnant rat. II. Effects of low-level lead on delta-aminolevulinic acid
55 dehydratase activity in maternal and fetal blood or tissue. Ind. Health 21: 127-135.
56 Hayes, R. B. (1997) The carcinogenicity of metals in humans. Cancer Causes Control 8: 371-385.
May 2006 5-312 DRAFT-DO NOT QUOTE OR CITE
-------
1 Haynes, E. N.; Kalkwarf, H. I; Hornung, R.; Wenstrap, R.; Dietrich, K.; Lanphear, B. P. (2003) VitaminD receptor
2 Fokl polymorphism and blood lead concentration in children. Environ. Health Perspect. Ill: 1665-1669.
3 He, L.; Poblenz, A. T.; Medrano, C. J.; Fox, D. A. (2000) Lead and calcium produce rod photoreceptor cell
4 apoptosis by opening the mitrochondrial permeability transition pore. J. Biol. Chem. 275: 12175-12184.
5 He, L.; Perkins, G. A.; Poblenz, A. T.; Harris, J. B.; Hung, M; Ellisman, M. H.; Fox, D. A.. (2003) Bcl-xL
6 overexpression blocks bax-mediated mitochondria! contact site formation and apoptosis in rod
7 photoreceptors of lead-exposed mice. Proc. Natl. Acad. Sci. U. S. A. 100: 1022-1027.
8 Heiman, A. S.; Tonner, L. E. (1995) The acute effect of lead acetate on glucocorticoid regulation of tyrosine
9 aminotransferase in hepatoma cells. Toxicology 100: 57-68.
10 Helleday, T.; Nilsson, R.; Jenssen, D. (2000) Arsenic [III] and heavy metal ions induce intrachromosomal
11 homologous recombination in the hprt gene of V79 Chinese hamster cells. Environ. Mol. Mutagen.
12 35: 114-122.
13 Hellstrom-Lindahl, E.; Oskarsson, A. (1990) Cellular response after mobilization of metals by
14 diethyldithiocarbamate in rat hepatocyte cultures. Toxicology 65: 23-32.
15 Hemphill, F. E.; Kaeberle, M. L.; Buck, W. B. (1971) Lead suppression of mouse resistance to Salmonella
16 typhimurium. Science (Washington, DC) 172: 1031-1032.
17 Hengstler, J. G.; Bolm-Audorff, U.; Faldum, A.; Janssen, K.; Reifenrath, M.; Gotte, W.; Jung, D.; Mayer-Popken,
18 O.; Fuchs, J.; Gebhard, S.; Bienfait, H. G.; Schlink, K.; Dietrich, C.; Faust, D.; Epe, B.; Oesch, F. (2003)
19 Occupational exposure to heavy metals: DNA damage induction and DNA repair inhibition prove co-
20 exposures to cadmium, cobalt and lead as more dangerous than hitherto expected. Carcinogenesis
21 24:63-73.
22 Henning, S. J.; Cooper, L. C. (1988) Intestinal accumulation of lead salts and milk lead by suckling rats (42645).
23 Proc. Soc. Exp. Biol. Med. 187: 110-116.
24 Heo, Y.; Parsons, P. J.; Lawrence, D. A. (1996) Lead differentially modifies cytokine production in vitro and
25 in vivo. Toxicol. Appl. Pharmacol. 138: 149-157.
26 Heo, Y.; Lee, W. T.; Lawrence, D. A. (1997) In vivo the environmental pollutants lead and mercury induce
27 oligoclonal T cell responses skewed toward type-2 reactivities. Cell. Immunol. 179: 185-195.
28 Heo, Y.; Lee, W. T.; Lawrence, D. A. (1998) Differential effects of lead and cAMP on development and activities of
29 Thl- and Th2-lymphocytes. Toxicol. Sci. 43: 172-185.
30 Heo, Y.; Lee, B.-K.; Ahn, K.-D.; Lawrence, D. A. (2004) Serum IgE elevation correlates with blood lead levels in
31 battery manufacturing workers. Hum. Exp. Toxicol. 23: 209-213.
32 Herak-Kramberger, C. M.; Sabolic, I. (2001) The integrity of renal cortical brush-border and basolateral membrane
33 vesicles is damaged in vitro by nephrotoxic heavy metals. Toxicology 156: 139-147.
34 Hermes-Lima, M.; Pereira, B.; Bechara, E. J. H. (1991) Are free radicals involved in lead poisoning? Xenobiotica
35 21: 1085-1090.
36 Hernandez-Avila, M.; Gonzalez-Cossio, T.; Hernandez-Avila, J. E.; Romieu, I.; Peterson, K. E.; Aro, A.;
37 Palazuelos, E.; Hu, H. (2003) Dietary calcium supplements to lower blood lead levels in lactating women:
38 a randomized placebo-controlled trial. Epidemiology 14: 206-212.
39 Hicks, D. G.; O'Keefe, R. J.; Reynolds, K. J.; Cory-Slechta, D. A.; Puzas, J. E.; Judkins, A.; Rosier, R. N. (1996)
40 Effects of lead on growth plate chondrocyte phenotype. Toxicol. Appl. Pharmacol. 140: 164-172.
41 Hilbertz, U.; Kramer, U.; De Ruiter, N.; Baginski, B. (1986) Effects of cadmium and lead on oxidative metabolism
42 and phagocytosis by mouse peritoneal macrophages. Toxicology 39: 47-57.
43 Hilderbrand, D. C.; Der, R.; Griffin, W. T.; Fahim, M. S. (1973) Effect of lead acetate on reproduction. Am. J.
44 Obstet. Gynecol. 115: 1058-1065.
45 Hill, A. B. (1965) The environment and disease: association or causation? Proc. R. Soc. Med. 58: 295-300.
46 Hilson, J. A.; Strupp, B. J. (1997) Analyses of response patterns clarify lead effects in olfactory reversal and
47 extradimensional shift tasks: assessment of inhibitory control, associative ability, and memory. Behav.
48 Neurosci. 111:532-542.
49 Hinton, D. E.; Lipsky, M. M.; Heatfield, B. M.; Trump, B. F. (1979) Opposite effects of lead on chemical
50 carcinogenesis in kidney and liver of rats. Bull. Environ. Contam. Toxicol. 23: 464-469.
51 Hogan, K.; Marcus, A.; Smith, R.; White, P. (1998) Integrated exposure uptake biokinetic model for lead in
52 children: empirical comparisons with epidemiologic data. Environ. Health Perspect. 106(suppl.
53 6): 1557-1567.
54 Holgate, S.; Casale, T.; Webzek, S.; Bousquet, J.; Deniz, Y.; Reisner, C. (2005) The anti-inflammatory effects of
55 omalizumab confirm the central role of IgE in allergic inflammation. J. Allergy Clin. Immunol.
56 115:459-465.
May 2006 5-313 DRAFT-DO NOT QUOTE OR CITE
-------
1 Holian, A.; Uthman, M. O.; Goltsova, T.; Brown, S. D.; Hamilton, R. F., Jr. (1997) Asbestos and silica-induced
2 changes in human alveolar macrophage phenotype. Environ. Health Perspect. Suppl. 105(5): 1139-1142.
3 Holladay, S. D. (1999) Prenatal immunotoxicant exposure and postnatal autoimmune disease. Environ. Health
4 Perspect. Suppl. 107(5): 687-691.
5 Holladay, S. D., ed. (2005) Developmental immunotoxicology. Boca Raton, FL: CRC Press, Inc.
6 Holloway, W. R., Jr.; Thor, D. H. (1987) Low level lead exposure during lactation increases rough and tumble play
7 fighting of juvenile rats. Neurotoxicol. Teratol. 9: 51-57.
8 Holsapple, M. P.; West, L. J.; Landreth, K. S. (2003) Species comparison of anatomical and functional immune
9 system development. Birth Defects Res. B. 68: 321-334.
10 Honchel, R.; Marsano, L.; Cohen, D.; Shedlofsky, S.; McClain, C. J. (1991) Lead enhances lipopolysaccharide and
11 tumor necrosis factor liver injury. J. Lab. Clin. Med. 117: 202-208.
12 Horiguchi, S.; Kiyoya, L; Endo, G.; Teramoto, K.; Shinagawa, K.; Wakitani, F.; Konishi, Y.; Kiyota, A.; Ota, A.;
13 Tanaka, H.; Wang, C.; Fukui, M. (1992) Serum immunoglobulins and complement C3 levels in workers
14 exposed to lead. Osaka City Med. J. 38: 149-153.
15 Hossain, M. A.; Russell, J. C.; Miknyoczki, S.; Ruggeri, B.; Lai, B.; Laterra, J. (2004) Vascular endothelial growth
16 factor mediates vasogenic edema in acute lead encephalopathy. Ann. Neurol. 55: 660-667.
17 Hotter, G.; Pels, L. M.; Closa, D.; Rosello, J.; Stolte, H.; Gelpi, E. (1995) Altered levels of urinary prostanoids in
18 lead-exposed workers. Toxicol. Lett. 77: 309-312.
19 Hryhorczuk, D. O.; Rabinowitz, M. B.; Hessl, S. M.; Hoffman, D.; Hogan, M. M.; Mallin, K.; Finch, H.; Orris, P.;
20 Berman, E. (1985) Elimination kinetics of blood lead in workers with chronic lead intoxication. Am. J. Ind.
21 Med. 8: 33-42.
22 Hu, H. (1991) A 50-year follow-up of childhood plumbism: hypertension, renal function, and hemoglobin levels
23 among survivors. Am. J. Dis. Child. 145: 681-687.
24 Huang, F., Schneider, J. S. (2004) Effects of lead exposure on proliferation and differentiation of neural stem cells
25 derived from different regions of embryonic rat brain. Neurotoxicology.25: 1001-1012.
26 Huang, X. P.; Feng, Z. Y.; Zhai, W. L.; Xu, J. H. (1988) Chromosomal aberrations and sister chromatid exchanges
27 in workers exposed to lead. Biomed. Environ. Sci. 1: 382-387.
28 Hubermont, G.; Buchet, J.-P.; Roels, H.; Lauwerys, R. (1976) Effect of short-term administration of lead to pregnant
29 rats. Toxicology 5: 379-384.
30 Hudson, C. A.; Cao, L.; Kasten-Jolly, J.; Kirkwood, J. N.; Lawrence, D. A. (2003) Susceptibility of lupus-prone
31 NZM mouse strains to lead exacerbation of systemic lupus erythematosus symptoms. J. Toxicol. Environ.
32 Health A 66: 895-918.
33 Hussain, I.; Piepenbrink, M. S.; Dietert, R. R. (2005) Impact of in ovo-administered lead and testosterone on
34 developing female thymocytes. J. Toxicol. Environ. Health A. 68: 1309-1319.
35 Hwang, K.-Y.; Lee, B.-K.; Bressler, J. P.; Bolla, K. I.; Stewart, W. F.; Schwartz, B. S. (2002) Proteinkinase C
3 6 activity and the relations between blood lead and neurobehavioral function in lead workers. Environ.
37 Health Perspect. 110: 133-138.
3 8 Hwua, Y. S.; Yang J. L. (1998) Effect of 3-aminotriazole on anchorage independence and mutagenicity in cadmium-
39 and lead-treated diploid human fibroblasts. Carcinogenesis 19: 881-888.
40 lavicoli, I.; Carelli, G.; Stanek, E. J., Ill; Castellino, N.; Calabrese, E. J. (2003) Effects of low doses of dietary lead
41 on red blood cell production in male and female mice. Toxicol. Lett. 137: 193-199.
42 lavicoli, I.; Carelli, G.; Stanek, E. J., Ill; Castellino, N.; Calabrese, E. J. (2004) Effects of low doses of dietary lead
43 on puberty onset in female mice. Reprod. Toxicol. 19: 35-41.
44 Ichiba, M.; Tomokuni, K. (1987) Urinary excretion of 5-hydroxyindoleacetic acid, 5-aminolevulinic acid and
45 coproporphyrin isomers in rats and men exposed to lead. Toxicol. Lett. 38: 91-96.
46 Ichiba, M.; Tomokuni, K.; Sugimoto, K. (1987) Erythrocyte pyrimidine 5'-nucleotidase test for occupational lead
47 exposure. Ind. Health 25: 195-203.
48 Ikebuchi, H.; Teshima, R.; Suzuki, K.; Terao, T.; Yamane, Y. (1986) Simultaneous induction of Pb-metallothionein-
49 like protein and Zn-thionein in the liver of rats given lead acetate. Biochem. J. 233: 541-546.
50 Inskip, M. J.; Franklin, C. A.; Baccanale, C. L.; Manton, W. I.; O'Flaherty, E. J.; Edwards, C. M. H.; Blenkinsop,
51 J. B.; Edwards, E. B. (1996) Measurement of the flux of lead from bone to blood in a nonhuman primate
52 (Macaca fascicularis) by sequential administration of stable lead isotopes. Fundam. Appl. Toxicol.
53 33:235-245.
54 Ishihara, K.; Alkondon, M.; Monies, J. G.; Albuquerque, E. X. (1995) Nicotinic responses in acutely dissociated rat
55 hippocampal neurons and the selective blockade of fast-desensitizing nicotinic currents by lead. J.
56 Pharmacol. Exp. Ther. 273: 1471-1482.
May 2006 5-314 DRAFT-DO NOT QUOTE OR CITE
-------
1 Isolauri, E.; Huurre, A.; Salminen, S.; Impivaara, O. (2004) The allergy epidemic extends beyond the past few
2 decades. Clin. Exp. Allergy. 34: 1007-1010.
3 Ito, Y.; Niiya, Y.; Kurita, H.; Shima, S.; Sarai, S. (1985) Serum lipid peroxide level and blood superoxide dismutase
4 activity in workers with occupational exposure to lead. Int. Arch. Occup. Environ. Health 56: 119-127.
5 Ito, S.; Ishii, K. I; Ihata, A.; Klinman, D. M. (2005) Contribution of nitric oxide to CPG-mediated protection against
6 Listeriamonocytogenes. Infect. Immun. 73: 3803-3805.
7 Ivanova-Chemishanska, L.; Antonov, G.; Khinkova, L.; Volcheva, VI.; Khristeva, V. (1980) Deistvie na oloviniya
8 atsetat v"rkhu reproduktsiyata na m"zhki beli pl"khove [Effect of lead acetate on reproduction in male
9 white rats]. Khig. Zdraveopaz. 23: 304-308.
10 Jaako-Movits, K.; Zharkovsky, T.; Romantchik, O.; Jurgenson, M.; Merisalu, E.; Heidmets, L. T.; Zharkovsky, A.
11 (2005) Developmental lead exposure impairs contextual fear conditioning and reduces adult hippocampal
12 neurogenesis in the rat brain. Int. J. Dev. Neurosci. 23: 627-635.
13 Jacobs, J. M.; Sinclair, P. R.; Sinclair, J. F.; Gorman, N.; Walton, H. S.; Wood, S. G.; Nichols, C. (1998) Formation
14 of zinc protoporphyrin in cultured hepatocytes: effects of ferrochelatase inhibition, iron chelation or lead.
15 Toxicology 125: 95-105.
16 Jacquet, P. (1976) Effets du plomb administre durant la gestation a des souris C57B1 [Effects of lead administered
17 during the gestation period of mice C57B1]. C. R. Seances Soc. Biol. SesFil. 170: 1319-1322.
18 Jacquet, P. (1977) Early embryonic development in lead-intoxicated mice. Arch. Pathol. Lab. Med. 101: 641-643.
19 Jacquet, P.; Leonard, A.; Gerber, G. B. (1975) Embryonic death in mouse due to lead exposure. Experientia
20 31:24-25.
21 Jacquet, P.; Leonard, A.; Gerber, G. B. (1976) Action of lead on early divisions of the mouse embryo. Toxicology
22 6: 129-132.
23 Jacquet, P.; Gerber, G. B.; Maes, J. (1977) Biochemical studies in embryos after exposure of pregnant mice to
24 dietary lead. Bull. Environ. Contam. Toxicol. 18: 271-277.
25 Jagetia, G. C.; Aruna, R. (1998) Effect of various concentrations of lead nitrate on the induction of micronuclei in
26 mouse bone marrow. Mutat. Res. 415: 131-137.
27 Jehan, Z. S.; Motlag, D. B. (1995) Metal induced changes in the erythrocyte membrane of rats. Toxicol. Lett. 78:
28 127-133.
29 Jemal, A.; Graubard, B. I.; Devesa, S. S.; Flegal, K. M. (2002) The association of blood lead level and cancer
30 mortality among whites in the United States. Environ. Health Perspect. 110: 325-329.
31 Jett, D. A.; Kuhlmann, A. C.; Guilarte, T. R. (1997) Intrahippocampal administration of lead (Pb) impairs
32 performance of rats in the Morris water maze. Pharmacol. Biochem. Behav. 57: 263-269.
33 Jett, D. A.; Beckles, R. A.; Navoa, R. V.; McLemore, G. L. (2002) Increased high-affinity nicotinic receptor-binding
34 in rats exposed to lead during development. Neurotoxicol. Teratol. 24: 805-811.
35 Jian, Z.; Ying-Han, X.; Hog-Fu, C. (1985) The effects of lead ion on immune function of rabbit alveolar
3 6 macrophages: quantification of immune phagocytosis and rosette formation by Pb in vitro. Toxicol. Appl.
37 Pharmacol. 78: 484-487.
3 8 Johansson, L. (1989) Premature acrosome reaction in spermatozoa from lead-exposed mice. Toxicology
39 54: 151-162.
40 Johansson, L.; Pellicciari, C. E. (1988) Lead-induced changes in the stabilization of the mouse sperm chromatin.
41 Toxicology 51: 11-24.
42 Johansson, L.; Wide, M. (1986) Long-term exposure of the male mouse to lead: effects on fertility. Environ. Res.
43 41:481-487.
44 Johansson, L.; Sjoblom, P.; Wide, M. (1987) Effects of lead on the male mouse as investigated by in vitro
45 fertilization and blastocyst culture. Environ. Res. 42: 140-148.
46 Jones, M. M.; Basinger, M. A.; Gale, G. R.; Atkins, L. M.; Smith, A. B.; Stone, A. (1994) Effect of chelate
47 treatments on kidney, bone and brain levels of lead-intoxicated mice. Toxicology 89: 91-100.
48 Joseph, C. L. M.; Havstad, S.; Ownby, D. R.; Peterson, E. L.; Maliarik, M.; McCabe, J., M.J.; Barone, C.; Johnson,
49 C. C. (2005) Blood lead levels and risk of asthma. Environ. Health Perspect. 113: 900-904.
50 Jover, R.; Lindberg, R. L. P.; Meyer, U. A. (1996) Role of heme in cytochrome P450 transcription and function in
51 mice treated with lead acetate. Mol. Pharmacol. 50: 474-481.
52 Junaid, M.; Chowdhuri, D. K.; Narayan, R.; Shanker, R.; Saxena, D. K. (1997) Lead-induced changes in ovarian
53 follicular development and maturation in mice. J. Toxicol. Environ. Health 50: 31-40.
54 Kaji, T.; Yamamoto, C.; Sakamoto, M. (1991) Effect of lead on the glycosaminoglycans metabolism of bovine
55 aortic endothelial cells in culture. Toxicology 68: 249-257.
May 2006 5-315 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kaji, T.; Yamamoto, C.; Sakamoto, M; Kozuka, H. (1992) Inhibitory effect of lead on the release of tissue
2 plasminogen activator from human vascular endothelial cells in culture. Toxicology 73: 219-227.
3 Kaji, T.; Suzuki, M.; Yamamoto, C.; Mishima, A.; Sakamoto, M.; Kozuka, H. (1995a) Severe damage of cultured
4 vascular endothelial cell monolayer after simultaneous exposure to cadmium and lead. Arch. Environ.
5 Contam. Toxicol. 28: 168-172.
6 Kaji, T.; Fujiwara, Y.; Hoshino, M.; Yamamoto, C.; Sakamoto, M.; Kozuka, H. (1995b) Inhibitory effect of lead on
7 the proliferation of cultured vascular endothelial cells. Toxicology 95: 87-92.
8 Kaji, T.; Ohkawara, S.; Nakajima, M.; Yamamoto, C.; Fujiwara, Y.; Miyajima, S.; Koizumi, F. (1997) Lead-induced
9 alteration of heparan sulfate proteoglycans in cultured vascular endothelial cells. Toxicology 118: 1-10.
10 Kala, S. V.; Jadhav, A. L. (1995) Low level lead exposure decreases in vivo release of dopamine in the rat nucleus
11 accumbens: a microdialysis study. J. Neurochem. 65: 1631-1635.
12 Kamel, F.; Umbach, D. M.; Lehman, T. A.; Park, L. P.; Munsat, T. L.; Shefner, J. M.; Sandier, D. P.; Hu, H.;
13 Taylor, J. A. (2003) Amyotrophic lateral sclerosis, lead, and genetic susceptibility: polymorphisms in the
14 5-aminolevulinic acid dehydratase and vitamin D receptor genes. Environ. Health Perspect.
15 111:1335-1339.
16 Kanduc, D.; Frisco, M. (1992) Hepatic DNA methylation in young, middle-aged, and senescent rats: the effect of
17 mitogen-induced cell proliferation. Biochem. Med. Metab. Biol. 48: 286-291.
18 Kanduc, D.; Rossiello, M. R.; Aresta, A.; Cavazza, C.; Quagliariello, E.; Farber, E. (1991) Transitory DNA
19 hypomethylation during liver cell proliferation induced by a single dose of lead nitrate. Arch. Biochem.
20 Biophys. 286: 212-216.
21 Kanitz, M. H.; Witzmann, F. A.; Zhu, H.; Fultz, C. D.; Skaggs, S.; Moorman, W. J.; Savage, R. E., Jr. (1999)
22 Alterations in rabbit kidney protein expression following lead exposure as analyzed by two-dimensional gel
23 electrophoresis. Electrophoresis 20: 2977-2985.
24 Karmakar, N.; Anand, S. (1989) Study of the inhibitory effect of lead acetate on duodenal contractility in rat.
25 Clin. Exp. Pharmacol. Physiol. 16: 745-750.
26 Karmakar, N.; Saxena, R.; Anand, S. (1986) Histopathological changes induced in rat tissues by oral intake of lead
27 acetate. Environ. Res. 41: 23-28.
28 Karmaus, W.; Brooks, K. R.; Nebe, T.; Witten, J.; Obi-Osius, N.; Kruse, H. (2005) Immune functionbiomarkers in
29 children exposed to lead and organochlorine compounds: a cross-sectional study. Environ. Health Glob.
30 Access Sci. 4: 1-10.
31 Kato, Y.; Takimoto, S.; Ogura, H. (1977) Mechanism of induction of hypercalcemia and hyperphosphatemia by lead
32 acetate in the rat. Calcif. Tissue Res. 24: 41-46.
33 Kauppinen, T.; Riala, R.; Seitsamo, J.; Hernberg, S. (1992) Primary liver cancer and occupational exposure. Scand.
34 J. Work Environ. Health. 18: 18-25.
35 Kelada, S. N.; Shelton, E.; Kaufmann, R. B.; Khoury, M. J. (2001) 5-aminolevulinic acid dehydratase genotype and
36 lead toxicity: a HuGE review. Am. J. Epidemiol. 154: 1-13.
37 Kelada, S. N.; Eaton, D. L.; Wang, S. S.; Rothman, N. R.; Khoury, M. J. (2003) The role of genetic polymorphisms
38 in environmental health. Environ. Health Perspect. Ill: 1055-1064.
39 Keller, C. A.; Doherty, R. A. (1980) Bone lead mobilization in lactating mice and lead transfer to suckling offspring.
40 Toxicol. Appl. Pharmacol. 55: 220-228.
41 Kempe, D. A.; Lang, P. A.; Eisele, K.; Klarl, B. A.; Wieder, T.; Huber, S. M.; Duranton, C.; Lang, F. (2005)
42 Stimulation of erythrocyte phosphatidylserine exposure by lead ions. Am. J. Physiol. 288: C396-C402.
43 Kempinas, W. G.; Lamano-Carvalho, T. L.; Petenusci, S. O.; Lopes, R. A.; Azoubel, R. (1988) Morphometric and
44 stereological analysis of rat testis and epididymis in an early phase of saturnism. Exp. Biol. 8: 51-56.
45 Kempinas, W. G.; Melo, V. R.; Oliveira-Filho, R. M.; Santos, A. C.; Favaretto, A. L.; Lamano-Carvalho, T. L.
46 (1990) Saturnism in the male rat: endocrine effects. Braz. J. Med. Biol. Res. 23: 1171-1175.
47 Kempinas, W. G.; Favaretto, A. L. V.; Melo, V. R.; Lamano Carvalho, T. L.; Petenusci, S. O.; Oliveira-Filho, R. M.
48 (1994) Time-dependent effects of lead on rat reproductive functions. J. Appl. Toxicol. 14: 427-433.
49 Kennedy, G. L.; Arnold, D. W.; Calandra, J. C. (1975) Teratogenic evaluation of lead compounds in mice and rats.
50 Food Cosmet. Toxicol. 13: 629-632.
51 Keogh, J. P.; Steffen, B.; Siegers, C.-P. (1994) Cytotoxicity of heavy metals in the human small intestinal epithelial
52 cell line 1-407: the role of glutathione. J. Toxicol. Environ. Health 43: 351-359.
53 Kern, M.; Audesirk, G. (1995) Inorganic lead may inhibit neurite development in cultured rat hippocampal neurons
54 through hyperphosphorylation. Toxicol. Appl. Pharmacol. 134: 111-123.
55 Kern, M.; Audesirk, G. (2000) Stimulatory and inhibitory effects of inorganic lead on calcineurin. Toxicology
56 150: 171-178.
May 2006 5-316 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kerper, L. E.; Hinkle, P.M. (1997) Cellular uptake of lead is activated by depletion of intracellular calcium stores.
2 J. Biol. Chem. 272: 8346-8352.
3 Khalil-Manesh, F.; Gonick, H. C. Cohen, A. H.; Alinovi, R.; Bergamaschi, E.; Mutti, A.; Rosen, V. J. (1992a)
4 Expermiental model of lead nephropathy. I. Continuous high-dose lead administration. Kidney Int.
5 41: 1192-1203.
6 Khalil-Manesh, F.; Gonick, H. C.; Cohen, A.; Bergamaschi, E.; Mutti, A. (1992b) Experimental model of lead
7 nephropathy. II. Effect of removal from lead exposure and chelation treatment with dimercaptosuccinic
8 acid (DMSA). Environ. Res 58: 35-54.
9 Khalil-Manesh, F.; Gonick, H. C.; Weiler, E. W. J.; Prins, B.; Weber, M. A.; Purdy, R. E. (1993a) Lead-induced
10 hypertension: possible role of endothelial factors. Am. J. Hypertens. 6: 723-729.
11 Khalil-Manesh, F.; Gonick, H. C.; Cohen, A. H. (1993b) Experimental model of lead nephropathy. III. Continuous
12 low-level lead administration. Arch. Environ. Health 48: 271-278.
13 Khalil-Manesh, F.; Gonick, H. C.; Weiler, E. W. J.; Prins, B.; Weber, M. A.; Purdy, R.; Ren, Q. (1994) Effect of
14 chelation treatment with dimercaptosuccinic acid (DMSA) on lead-related blood pressure changes.
15 Environ. Res. 65:86-99.
16 Khan, M. Z.; Szarek, J. (1994) Effects of concurrent oral administration of lead, selenium or monensin on hepatic
17 porphyrin levels in broiler chickens during sub-acute toxicosis. J. Vet. Med. B. 41: 77-82.
18 Kim, D.; Lawrence, D. A. (2000) Immunotoxic effects of inorganic lead on host resistance of mice with different
19 circling behavior preferences. Brain Behav. Immun. 14: 305-317.
20 Kim, J. S.; Hamilton, D. L.; Blakley, B. R.; Rousseaux, C. G. (1992) The effects of thiamin on lead metabolism:
21 organ distribution of lead 203. Can. J. Vet. Res. 56: 256-259.
22 Kim, R.; Rotnitsky, A.; Sparrow, D.; Weiss, S. T.; Wager, C.; Hu, H. (1996) A longitudinal study of low-level lead
23 exposure and impairment of renal function. The Normative Aging Study. JAMA J. Am. Med. Assoc.
24 275: 1177-1181.
25 Kim, H.-S.; Lee, S.-S.; Lee, G.-S.; Hwangbo, Y.; Ahn, K.-D.; Lee, B.-K. (2004) The protective effect of 5-
26 aminolevulinic acid dehydratase 1-2 and 2-2 isozymes against blood lead with higher hematologic
27 parameters. Environ. Health Perspect. 112: 538-541.
28 Kimber, I.; Stonard, M. D.; Gidlow, D. A.; Niewola, Z. (1986) Influence of chronic low-level exposure to lead on
29 plasma immunoglobulin concentration and cellular immune function in man. Int. Arch. Occup. Environ.
30 Health 57: 117-125.
31 Kimmel, C. A.; Grant, L. D.; Sloan, C. S.; Gladen, B. C. (1980) Chronic low-level lead toxicity in the rat. I.
32 Maternal toxicity and perinatal effects. Toxicol. Appl. Pharmacol. 56: 28-41.
33 Kiremidjian-Schumacher, L.; Stotzky, G.; Dickstein, R. A.; Schwartz, J. (1981) Influence of cadmium, lead, and
34 zinc on the ability of guinea pig macrophages to interact with macrophage migration inhibitory factor.
35 Environ. Res. 24: 106-116.
36 Kishikawa, H.; Lawrence, D. A. (1998) Differential production of interleukin-6 in the brain and spleen of mice
37 treated with lipopolysaccharide in the presence and absence of lead. J. Toxicol. Environ. Health A
38 53: 357-373.
39 Kishikawa, H.; Song, R.; Lawrence, D. A. (1997) Interleukin-12 promotes enhanced resistance to Listeria
40 monocytogenes infection of lead-exposed mice. Toxicol. Appl. Pharmacol. 147: 180-189.
41 Kishimoto, T.; Oguri, T.; Ueda, D.; Tada, M. (1995) Effect of lead on tube formation by cultured human vascular
42 endothelial cells. Arch. Toxicol. 69:718-721.
43 Klann, E.; Shelton, K. R. (1989) The effect of lead on the metabolism of a nuclear matrix protein which becomes
44 prominent in lead-induced intranuclear inclusion bodies. J. Biol. Chem. 264: 16,969-16,972.
45 Klann, E.; Shelton, K. R. (1990) A lead-associated nuclear protein which increases in maturing brain and in
46 differentiating neuroblastoma 2 A cells exposed to cyclic AMP-elevating agents. Dev. Brain Res. 57: 71-75.
47 Klein, R. F.; Wiren, K. M. (1993) Regulation of osteoblastic gene expression by lead. Endocrinology
48 132:2531-2537.
49 Klein, D.; Wan, Y.-J. Y.; Kamyab, S.; Okuda, H.; Sokol, R. Z. (1994) Effects of toxic levels of lead on gene
50 regulation in the male axis: increase in messenger ribonucleic acids and intracellular stores of gonadotrophs
51 within the central nervous system. Biol. Reprod. 50: 802-811.
52 Kleszcyriska, H.; Hladyszowski, J.; Pruchnik, H.; Przestalski, S. (1997) Erythrocyte hemolysis by organic tin and
53 lead compounds. Z. Naturforsch. C J. Biosci. 52: 65-69.
54 Knowles, S. O.; Donaldson, W. E. (1990) Dietary modification of lead toxicity: effects on fatty acid and eicosanoid
55 metabolism in chicks. Comp. Biochem. Physiol. C 95: 99-104.
May 2006 5-317 DRAFT-DO NOT QUOTE OR CITE
-------
1 Knowles, S. O.; Donaldson, W. E. (1997) Lead disrupts eicosanoid metabolism, macrophage function, and disease
2 resistance in birds. Biol. Trace Elem. Res. 60: 13-26.
3 Kobayashi, N.; Okamoto, T. (1974) Effects of lead oxide on the induction of lung tumors in Syrian hamsters. J. Natl.
4 Cancer Inst. 52: 1605-1610.
5 Kober, T. E.; Cooper, G. P. (1976) Lead competitively inhibits calcium-dependent synaptic transmission in the
6 bullfrog sympathetic ganglion. Nature (London) 262: 704-705.
7 Kohila, T.; Tahti, H. (2004) Effects of aluminium and lead on ATPase activity of knockout +/- mouse cerebral
8 synaptosomes in vitro. Altern. Lab. Anim. 32: 361-367.
9 Kojima, M; Nemoto, K.; Murai, U.; Yoshimura, N.; Ayabe, Y.; Degawa, M. (2002) Altered gene expression of
10 hepatic lanosterol 14x-demethylase (CYP51) in lead nitrate-treated rats. Arch. Toxicol. 76: 398-403.
11 Kojima, M.; Masui, T.; Nemoto, K.; Degawa, M. (2004) Lead nitrate-induced development of hypercholesterolemia
12 in rats: sterol-independent gene regulation of hepatic enzymes responsible for cholesterol homeostasis.
13 Toxicol. Lett. 154: 35-44.
14 Koller, L. D. (1973) Immunosuppression produced by lead, cadmium, and mercury. Am. J. Vet. Res. 34: 1457-1458.
15 Koller, L. D.; Kovacic, S. (1974) Decreased antibody formation in mice exposed to lead. Nature 250: 148-150.
16 Koller, L. D.; Roan, J. G. (1977) Effects of lead and cadmium on mouse peritoneal macrophages. J.
17 Reticuloendothel. Soc. 21: 7-12.
18 Koller, L. D.; Roan, J. G. (1980) Effects of lead, cadmium and methylmercury on immunological memory.
19 J. Environ. Pathol. Toxicol. 4: 47-52.
20 Konantakieti, C.; Beuthin, F. C.; Louis-Ferdinand, R. T. (1986) Erythrocyte pyrimidine 5'-nucleotidase inhibition by
21 acute lead exposure in neonatal rats. J. Biochem. Toxicol. 1: 51-59.
22 Koo, W. W. K.; Succop, P. A.; Bornschein, R. L.; Krugwispe, S. K.; Steinchen, J. J.; Tsang, R. C.; Berger, O.G.
23 (1991) Serum vitamin D metabolites and bone mineralization in young children with chronic low to
24 moderate lead exposure. Pediatrics 87: 680-687.
25 Koo, P.; Nagai, M. K.; Farber, E. (1994) Multiple sites of control of glutathione S-transferase Pl-1 in rat liver.
26 J. Biol. Chem. 269: 14601-14606.
27 Korashy, H. M.; El-Kadi, A. O. S. (2004) Differential effects of mercury, lead and copper on the constitutive and
28 inducible expression of aryl hydrocarbon receptor (AHR)-regulated genes in cultured hepatoma Hepa
29 Iclc7 cells. Toxicology 201: 153-172.
30 Kordas, K.; Lopez, P.; Rosado, J. L.; Vargas, G. G.; Rico, J. A.; Ronquillo, D.; Cebrian, M. E.; Stoltzfus, R. J.
31 (2004) Blood lead, anemia, and short stature are independently associated with cognitive performance in
32 Mexican school children. J. Nutr. 134: 363-371.
33 Korrick, S. A.; Hunter, D. J.; Rotnitzky, A.; Hu, H.; Speizer, F. E. (1999) Lead and hypertension in a sample of
34 middle-aged women. Am. J. Public Health 89: 330-335.
35 Kostial, K.; Blanusa, M.; Piasek, M.; Restek-Samarzija, N.; Jones, M. M.; Singh, P. K. (1999) Combined chelation
36 therapy in reducing tissue lead concentrations in suckling rats. J. Appl. Toxicol. 19: 143-147.
37 Kowolenko, M.; Tracy, L.; Mudzinski, S.; Lawrence, D. A. (1988) Effect of lead on macrophage function. J.
3 8 Leukocyte Biol. 43: 357-364.
39 Kowolenko, M.; Tracy, L.; Lawrence, D. A. (1989) Lead-induced alterations of in vitro bone marrow cell responses
40 to colony stimulating factor-1. J. Leukocyte Biol. 45: 198-206.
41 Kowolenko, M.; Tracy, L.; Lawrence, D. (1991) Early effects of lead on bone marrow cell responsiveness in mice
42 challenged with Listeria monocytogenes. Fundam. Appl. Toxicol. 17: 75-82.
43 Kramer, H. J.; Gonick, H. C.; Lu, E. (1986) In vitro inhibition of Na-K-ATPase by trace metals: relation to renal and
44 cardiovascular damage. Nephron 44: 329-336.
45 Kristensen, P.; Andersen, A. (1992) A cohort study on cancer incidence in offspring of male printing workers.
46 Epidemiology 3: 6-10.
47 Kristensen, P.; Eilertsen, E.; Einarsdottir, E.; 0vrebo, S.; Haugen, A. (1993) Effect modification by inorganic lead in
48 the dominant lethal assay. Mutat. Res. 302: 33-38.
49 Krocova, Z.; Macela, A.; Kroca, M.; Hernychova, L. (2000) The immunomodulatory effect(s) of lead and cadmium
50 on the cells of immune system in vitro. Toxicol. In Vitro. 14: 33-40.
51 Kubo, Y.; Yasunaga, M.; Masuhara, M.; Terai, S.; Nakamura, T.; Okita, K. (1996) Hepatocyte proliferation induced
52 in rats by lead nitrate is suppressed by several tumor necrosis factor a inhibitors. Hepatology 23: 104-114.
53 Kuhlmann, A. C.; McGlothan, J. L.; Guilarte, T. R. (1997) Developmental lead exposure causes spatial learning
54 deficits in adult rats. Neurosci. Lett. 233: 101-104.
55 Kumar, K. V.; Das, U. N. (1993) Are free radicals involved in the pathobiology of human essential hypertension?
56 Free Radical Res. Commun. 19: 59-66.
May 2006 5-318 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kumar, P.; Rai, G. P.; Flora, S. J. S. (1994) Immunomodulation following zinc supplementation during chelation of
2 lead in male rats. Biometals 7: 41-44.
3 Lai, C.-C.; Lin, H. H.; Chen, C. W.; Chen, S.-H.; Chiu, T. H. (2002) Excitatory action of lead on rat sympathetic
4 preganglionic neurons in vitro and in vivo. Life Sci. 71: 1035-1045.
5 Lake, L.; Gerschenson, L. E. (1978) Cellular and molecular toxicology of lead. III. Effect of lead on heme synthesis.
6 J. Toxicol. Environ. Health 4: 527-540.
7 Lai, B.; Goldstein, G.; Bressler, J. P. (1996) Role of anion exchange and thiol groups in the regulation of potassium
8 efflux by lead in human erythrocytes. J. Cell Physiol. 167: 222-228.
9 Langrish, C. L.; Buddie, J. C.; Thrasher, A. J.; Goldblatt, D. (2002) Neonatal dendritic cells are intrinsically biased
10 against Th-1 immune responses. Clin. Exp. Immunol. 128: 118-123.
11 Lanphear, B. P.; Bearer, C. F. (2005) Biomarkers in paediatric research and practice. Arch. Dis. Child. 90: 594-600.
12 Lanphear, B. P.; Dietrich, K.; Auinger, P.; Cox, C. (2000) Cognitive deficits associated with blood lead
13 concentrations < 10 ug/dL inU.S. children and adolescents. Public Health Rep. 115: 521-529.
14 Lanphear, B. P.; Hornung, R.; Khoury, J.; Yolton, K.; Baghurst, P.; Bellinger, D. C.; Canfield, R. L.; Dietrich, K.
15 N.; Bornschein, R.; Greene, T.; Rothenberg, S. J.; Needleman, H. L.; Schnaas, L.; Wasserman, G.;
16 Graziano, J.; Roberts, R. (2005) Low-level environmental lead exposure and children's intellectual
17 function: an international pooled analysis. Environ. Health Perspect. 113: 894-899.
18 Lara-Tejero, M; Pamer, E. G. (2004) T cell responses to Listeria monocytogenes. Curr. Opin. Microbiol. 7: 45-50.
19 Larsson, A. (1974) Studies on dentinogenesis in the rat. The interaction between lead-pyrophosphate solutions and
20 dentinal globules. Calcif. Tiss. Res. 16: 93-107.
21 Larsson, A.; Helander, H. F. (1974) Studies on dentinogenesis in the rat. Light, electron microscopic and
22 histochemical studies on the interaction between lead pyrophosphate solutions and dentin-producing
23 tissues. Calcif. Tiss. Res. 14: 87-104.
24 Laschi-Loquerie, A.; Decotes, J.; Tachon, P.; Evreux, J. C. (1984) Influence of lead acetate on hypersensitivity
25 experimental study. J. Immunopharmacol. 6: 87-93.
26 Lasky, R. E.; Laughlin, N. K. (2001) Exploring a partially enclosed space by lead-exposed female rhesus monkeys.
27 Neurotoxicol. Teratol. 23: 177-183.
28 Lasley, S. M.; Gilbert, M. E. (1996) Presynaptic glutamatergic function in dentate gyrus in vivo is diminished by
29 chronic exposure to inorganic lead. Brain Res. 736: 125-134.
30 Lasley, S. M.; Gilbert, M. E. (1999) Lead inhibits the rat TV-methyl-D-aspartate receptor channel by binding to a site
31 distinct from the zinc allosteric site. Toxicol. Appl. Pharmacol. 159: 224-233.
32 Lasley, S. M.; Gilbert, M. E. (2000) Glutamatergic components underlying lead-induced impairments in
33 hippocampal synaptic plasticity. Neurotoxicology 21: 1057-1067.
34 Lasley, S. M.; Gilbert, M. E. (2002) Rat hippocampal glutamate and GABA release exhibit biphasic effects as a
35 function of chronic lead exposure level. Toxicol. Sci. 66: 139-147.
36 Lasley, S. M.; Green, M. C.; Gilbert, M. E. (1999) Influence of exposure period on in vivo hippocampal glutamate
37 and GABA release in rats chronically exposed to lead. Neurotoxicology 20: 619-629.
38 Lasley, S. M.; Green, M. C.; Gilbert, M. E. (2001) Rat hippocampal NMD A receptor binding as a function of
39 chronic lead exposure level. Neurotoxicol. Teratol. 23: 185-189.
40 Laughlin, N. K.; Bowman, R. E.; Franks, P. A.; Dierschke, D. J. (1987) Altered menstural cycles in rhesus monkeys
41 induced by lead. Fundam. Appl. Toxicol. 9: 722-729.
42 Laughlin, N. K.; Bushnell, P. J.; Bowman, R. E. (1991) Lead exposure and diet: differential effects on social
43 development in the rhesus monkey. Neurotoxicol. Teratol. 13: 429-440.
44 Laughlin, N. K.; Lasky, R. E.; Giles, N. L.; Luck, M. L. (1999) Lead effects on neurobehavioral development inthe
45 neonatal rhesus monkey (Macaca mulatto). Neurotoxicol. Teratol. 21: 627-638.
46 Lauwerys, R.; Bernard, A.; Cardenas, A. (1992) Monitoring of early nephrotoxic effects of industrial chemicals.
47 Toxicol. Lett. 64-65: 33-42.
48 Lawler, E. M.; Duke, G. E.; Redig, P. T. (1991) Effect of sublethal lead exposure on gastric motility of red-tailed
49 hawks. Arch. Environ. Contam. Toxicol. 21: 78-83.
50 Lawrence, D. A. (1981a) Heavy metal modulation of lymphocyte activities. I. In vitro effects of heavy metals on
51 primary humoral immune responses. Toxicol. Appl. Pharmacol. 57: 439-451.
52 Lawrence, D. A. (1981b) Heavy metal modulation of lymphocyte activities - II: lead, an in vitro mediator of B-cell
53 activation. Int. J. Immunopharmacol. 3: 153-161.
5 4 Lawrence, D.A.(1981c)In vivo and in vitro effects of lead on humoral and cell- mediated immunity. Infect.
55 Immun. 31: 136-143.
May 2006 5-319 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lawrence, D. A.; Kim, D. (2000) Central/peripheral nervous system and immune responses. Toxicology
2 142: 189-201.
3 Lawrence, D. A.; McCabe, M. J., Jr. (2002) Immunomodulationby metals. Int. Immunopharmacol. 2: 293-302.
4 Ledda-Columbano, G. M.; Columbano, A.; Cannas, A.; Simbula, G.; Okita, K.; Kayano, K.; Kubo, Y.; Katyal, S. L.;
5 Shinozuka, H. (1994) Dexamethasone inhibits induction of liver tumor necrosis factor-a mRNA and liver
6 growth induced by lead nitrate and ethylene dibromide. Am. J. Pathol. 145: 951-958.
7 Lee, J. J.; Battles, A. H. (1994) Lead toxicity via arachidonate signal transduction to growth responses in the splenic
8 macrophage. Environ Res. 67: 209-219.
9 Lee, J.-E.; Dietert, R. R. (2003) Developmental immunotoxicity of lead: impact on thymic function. Birth Defects
10 Res. A Clin. Mol. Teratol. 67: 861-867.
11 Lee, J.-E.; Chen, S.; Golemboski, K. A.; Parsons, P. J.; Dietert, R. R. (2001) Developmental windows of differential
12 lead-induced immunotoxicity in chickens. Toxicology 156: 161-170.
13 Lee, J.-E.; Naqi, S. A.; Kao, E.; Dietert, R. R. (2002) Embryonic exposure to lead: Comparison of immune and
14 cellular responses in unchallenged and virally stressed chickens. Arch Toxicol. 75: 717-724.
15 Legare, M. E.; Barhoumi, R.; Herbert, E.; Bratton, G. R.; Burghardt, R. C.; Tiffany-Castiglioni E. (1998) Analysis
16 of Pb2+ entry into cultured astroglia. Toxicol. Sci. 46: 90-100.
17 Leggett, R. W. (1993) An age-specific kinetic model of lead metabolism in humans. Environ. Health Perspect.
18 101:598-616.
19 Levin, E. D.; Bowman, R. E. (1986) Long-term lead effects on the Hamiliton Search Task and delayed alternation in
20 monkeys. Neurobehav. Toxicol. Teratol. 8: 219-224.
21 Levin, E. D.; Bowman, R. E. (1989) Long-term effects of chronic postnatal lead exposure on delayed spatial
22 alternation in monkeys. Neurotoxicol. Teratol. 10: 505-510.
23 Levin, E. D.; Bowman, R. E.; Wegert, S.; Vuchetich, J. (1987) Psychopharmacological investigations of a lead-
24 induced long-term cognitive deficit in monkeys. Psychopharmacology 91: 334-341.
25 Levin, E. D.; Schneider, M. L.; Ferguson, S. A.; Schantz, S. L.; Bowman, R. E. (1988) Behavioral effects of
26 developmental lead exposure in rhesus monkeys. Dev. Psychobiol. 21: 371-382.
27 Lezak, M. D. (2004) Neuropsychological assessment. 4th ed. New York, NY: Oxford University Press.
28 Lidsky, T. I.; Schneider, J. S. (2003) Lead neurotoxicity in children: basic mechanisms and clinical correlates.
29 Brain 126: 5-19.
30 Lidsky, T. I.; Schneider, J. S. (2006) Adverse effects of childhood lead poisoning: the clinical neuropsychological
31 perspective. Environ. Res. 100: 284-293.
32 Lilienthal, H.; Winneke, G. (1996) Lead effects on the brain stem auditory evoked potential in monkeys during and
33 after the treatment phase. Neurotoxicol. Teratol. 18:17-32.
34 Lilienthal, H.; Winneke, G.; Brockhaus, A.; Molik, B. (1986) Pre- and postnatal lead-exposure in monkeys: effects
35 on activity and learning set formation. Neurobehav. Toxicol. Teratol. 8: 265-272.
36 Lilienthal, H.; Lenaerts, C.; Winneke, G.; Hennekes, R. (1988) Alteration of the visual evoked potential and the
37 electroretinogram in lead-treated monkeys. Neurotoxicol. Teratol. 10: 417-422.
38 Lin, R. H.; Lee, C. H.; Chen, W. K.; Lin-Shiau, S. Y. (1994) Studies on cytotoxic and genotoxic effects of cadmium
39 nitrate and lead nitrate in Chinese hamster ovary cells. Environ. Mol. Mutagen. 23: 143-149.
40 Lin, C.; Kim, R.; Tsaih, S.-W.; Sparrow, D.; Hu, H. (2004) Determinants of bone and blood lead levels among
41 minorities living in the Boston area. Environ. Health Perspect. 112: 1147-1151.
42 Lindahl, L. S.; Bird, L.; Legare, M. E.; Mikeska, G.; Bratton, G. R.; Tiffany-Castiglioni, E. (1999) Differential
43 ability of astroglia and neuronal cells to accumulate lead: dependence on cell type and on degree of
44 differentiation. Toxicol Sci. 50: 236-243.
45 Liu, J.; Kershaw, W. C.; Klaassen, C. D. (1991) The protective effect of metallothionein on the toxicity of various
46 metals in rat primary hepatocyte culture. Toxicol. Appl. Pharmacol. 107: 27-34.
47 Liu, J.-Y.; Lin, J.-K.; Liu, C.-C; Chen, W.-K.; Liu, C.-P.; Wang, C.-J.; Yen, C.-C; Hsieh, Y.-S. (1997)
48 Augmentation of protein kinase C activity and liver cell proliferation in lead nitrate-treated rats. Biochem.
49 Mol. Biol. Int. 43:355-364.
50 Logdberg, B.; Berlin, M.; Schtitz, A. (1987) Effects of lead exposure on pregnancy outcome and the fetal brain of
51 squirrel monkeys. Scand. J. Work Environ. Health 13: 135-145.
52 Logdberg, B.; Bran, A.; Berlin, M.; Schtitz, A. (1988) Congenital lead encephalopathy in monkeys. Acta
53 Neuropathol. 77: 120-127.
54 Loipfuhrer, A. M.; Reichlmayr-Lais, A. M.; Kirchgessner, M. (1993) Concentration of free calcium in erythrocytes
55 of lead-depleted rats. J. Trace Elem. Electrolytes HealthDis. 7: 37-40.
May 2006 5-320 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lolin, Y.; O'Gorman, P. (1988) An intra-erythrocyctic low molecular weight lead-binding protein in acute and
2 chronic lead exposure and its possible protective role in lead toxicity. Ann. Clin. Biochem. 25: 688-97.
3 Long, G. I; Rosen, J. F. (1992) Lead perturbs epidermal growth factor (EOF) modulation of intracellular calcium
4 metabolism and collagen synthesis in clonal rat osteoblastic (ROS 17/2.8) cells. Toxicol. Appl. Pharmacol.
5 114:63-70.
6 Long, G. J.; Rosen, J. F.; Pounds, J. G. (1990) Lead impairs the production of osteocalcin by rat osteosarcoma
7 (ROS 17/2.8) cells. Toxicol. Appl. Pharmacol. 106: 270-277.
8 Long, G. J.; Pounds, J. G.; Rosen, J. F. (1992) Lead intoxication alters basal and parathyroid hormone-regulated
9 cellular calcium homeostasis in rat osteosarcoma (ROS 17/2.8) cells. Calcif. Tissue Int. 50: 451-458.
10 Long, G. J.; Rosen, J. F.; Schanne, F. A. X. (1994) Lead activation of protein kinase C from rat brain. Determination
11 of free calcium, lead, and zinc by 19F NMR. J. Biol. Chem. 269: 834-837.
12 Lucas, S. R.; Sexton, M; Langenberg, P. (1996) Relationship between blood lead and nutritional factors in
13 preschool children: a cross-sectional study. Pediatrics 97: 74-78.
14 Luebke, R. W.; Chen, D. H.; Dietert, R.; Yang, Y.; King, M.; Luster, M. I. (2006) The comparative immunotoxicity
15 of five selected compounds following developmental or adult exposure. J. Toxicol. Environ. Health Part B
16 9: 1-26.
17 Lundstrom, N.-G.; Nordberg, G.; Englyst, V.; Gerhardsson, L.; Hagmar, L.; Jin, T.; Rylander, L.; Wall, S. (1997)
18 Cumulative lead exposure in relation to mortality and lung cancer morbidity in a cohort of primary smelter
19 workers. Scand. J. Work Environ. Health 23: 24-30.
20 Lustberg, M.; Silbergeld, E. (2002) Blood lead levels and mortality. Arch. Intern. Med. 162: 2443-2449.
21 Luster, M. I.; Faith, R. E.; Kimmel, C. A. (1978) Depression of humoral immunity in rats following chronic
22 developmental lead exposure. J. Environ. Pathol. Toxicol. 1: 397-402.
23 Luster, M. I.; Portier, C.; Pait, D. G.; White, K. L. J.; Gennings, C.; Munson, A. E.; Rosenthal, G. J. (1992) Risk
24 assessment in immunotoxicology. I. Sensitivity and predictability of immune tests. Fund. Appl. Toxicol.
25 18:200-210.
26 Lutz, P. M.; Wilson, T. J.; Ireland, A. L.; Gorman, J. S.; Gale, N. L.; Johnson, J. C.; Hewett, J. E. (1999) Elevated
27 immunoglobulin E (IgE) levels in children with exposure to environmental lead. Toxicology 134: 63-78.
28 Ma, T.; Chen, H. H.; Chang, H. L.; Hume, A. S.; Ho, I. K. (1997) Effects of chronic lead exposure on [3H]MK-801
29 binding in the brain of rat. Toxicol. Lett. 92: 59-66.
30 Madden, E. F.; Fowler, B. A. (2000) Mechanisms of nephrotoxicity from metal combinations: a review. Drug Chem.
31 Toxicol. 23: 1-12.
32 Maezawa, Y.; Nakajima, H.; Seto, Y.; Suto, A.; Kumano, K.; Kubo, S.; Karasuyama, H.; Saito, Y.; Iwamoto, I.
33 (2004) IgE-dependent enhancement of Th2 cell-mediated allergic inflammation in the airways. Clin. Exp.
34 Immunol. 135: 12-18.
3 5 Mahaffey, K. R.; Fowler, B. A. (1977) Effects of concurrent administration of lead, cadmium, and arsenic in the rat.
36 Environ. Health Perspect. 19: 165-171.
37 Mahaffey, K. R.; Capar, S. G.; Gladen, B. C.; Fowler, B. A. (1981) Concurrent exposure to lead, cadmium, and
38 arsenic. J. Lab. Clin. Med. 98: 463-481.
39 Mahaffey, K. R.; Rosen, J. F.; Chesney, R. W.; Peeler, J. T.; Smith, C. M.; De Luca, H. F. (1982) Association
40 between age, blood lead concentration, and serum 1,25-dihydroxycholecalciferol levels in children. Am. J.
41 Clin. Nutr. 35: 1327-1331.
42 Mahaffey, K. R.; Gartside, P. S.; Glueck, C. J. (1986) Blood lead levels and dietary calcium intake in 1-11 year-old
43 children: the second national health and nutrition examination survey, 1976-1980. Pediatrics 78: 257-262.
44 Maisin, J. R.; Lambiet-Collier, M.; De Saint-Georges, L. (1978) Toxicite du plomb pour les embryons de la souris
45 [Lead toxicity for mouse embryos]. C. R. Seances Soc. Biol. Ses. Fil. 172: 1041-1043.
46 Maitani, T.; Watahiki, A.; Suzuki, K. T. (1986) Induction of metallothionein after lead administration by three
47 injection routes in mice. Toxicol. Appl. Pharmacol. 83: 211-217.
48 Maker, H. S.; Lehrer, G. M.; Silides, D. J. (1975) The effect of lead on mouse brain development. Environ. Res.
49 10:76-91.
50 Malamitsi-Puchner, A.; Protonotariou, E.; Boutsikou, T.; Makrakis, E.; Sarandakou, A.; Creatas, G. (2005) The
51 influence of the mode of delivery on circulating cytokine concentrations in the perinatal period. Early Hum.
52 Dev. 81:387-392.
53 Malcoe, L. H.; Lynch, R. A.; Kegler, M. C.; Skaggs, V. J. (2002) Lead sources, behaviors, and socioeconomic
54 factors in relation to blood lead of Native American and white children: a community-based assessment of
55 a former mining area. Environ. Health Perspect. Suppl. 110(2): 221-231.
May 2006 5-321 DRAFT-DO NOT QUOTE OR CITE
-------
1 Maldonado-Vega, M; Cerbon-Solorzano, J.; Albores-Medina, A.; Hernandez-Luna, C.; Calderon-Salinas, J. V.
2 (1996) Lead: intestinal absorption and bone mobilization during lactation. Hum. Exp. Toxicol. 15: 872-877.
3 Maldonado-Vega, M.; Cerbon-Solorzano, J.; Calderon-Salinas, J. V. (2002) The effects of dietary calcium during
4 lactation on lead in bone mobilization: implications for toxicology. Hum. Exp. Toxicol. 21: 409-414.
5 Malvezzi, C. K.; Moreira, E. G.; Vassilieff, I.; Vassilieff, V. S.; Cordellini, S. (2001) Effect of L-arginine,
6 dimercaptosuccinic acid (DMSA) and the association of L-arginine and DMSA on tissue lead mobilization
7 and blood pressure level inplumbism. Braz. J. Med. Biol. Res. 34: 1341-1346.
8 Manton, W. I.; Cook, J. D. (1984) High accuracy (stable isotope dilution) measurements of lead in serum and
9 cerebrospinal fluid. Br. J. Ind. Med. 41: 313-319.
10 Manton, W. I.; Angle, C. R.; Stanek, K. L.; Reese, Y. R.; Kuehnemann, T. J. (2000) Acquisition and retention of
11 lead by young children. Environ. Res. 82: 60-80.
12 Manton, W. I.; Rothenberg, S. J.; Manalo, M. (2001) The lead content of blood serum. Environ. Res. 86: 263-273.
13 Marchlewicz, M.; Protasowicki, M.; Rozewicka, L.; Piasecka, M.; Laszczyriska, M. (1993) Effect of long-term
14 exposure to lead on testis and epididymis in rats. Folia Histochem. Cytobiol. 31: 55-62.
15 Marcus, A. H. (1985a) Multicompartment kinetic models for lead. I. Bone diffusion models for long-term retention.
16 Environ. Res. 36: 441-458.
17 Marcus, A. H. (1985b) Multicompartment kinetic models for lead. II. Linear kinetics and variable absorption in
18 humans without excessive lead exposures. Environ. Res. 36: 459-472.
19 Marcus, A. H. (1985c) Multicompartment kinetic model for lead. III. Lead in blood plasma and erythrocytes.
20 Environ. Res. 36: 473-489.
21 Markovac, J.; Goldstein, G. W. (1988a) Lead activates protein kinase C in immature rat brain microvessels. Toxicol.
22 Appl. Pharmacol. 95: 14-23.
23 Markovac, J.; Goldstein, G. W. (1988b) Picomolar concentrations of lead stimulate brain protein kinase C. Nature
24 (London, U.K.) 334: 71-73.
25 Markowitz, M. E.; Sennett, M.; Rosen, J. F. (2004) A randomized trial of calcium supplementation for childhood
26 lead poisoning. Pediatrics 113: e34-e39.
27 Marques, M.; Millas, I.; Jimenez, A.; Garcia-Colis, E.; Rodriguez-Feo, J. A.; Velasco, S.; Barrientos, A.; Casado, S.;
28 Lopez-Farre, A. (2001) Alteration of the soluble guanylate cyclase system in the vascular wall of lead-
29 induced hypertension in rats. J. Am. Soc. Nephrol. 12: 2594-2600.
30 Martin et al. (2005).
31 Martins, M. B.; Sabatier, L.; Ricoul, M.; Pinton, A.; Dutrillaux, B. (1993) Specific chromosome instability induced
32 by heavy ions: a step towards transformation of human fibroblasts? Mutat. Res. 1285: 229-237.
33 Mas-Oliva, J. (1989) Effect of lead on the erythrocyte (Ca2+,Mg2+)-ATPase activity. Calmodulin involvement.
34 Mol. Cell. Biochem. 89: 87-93.
35 Mason, H. J.; Somervaille, L. J.; Wright, A. L.; Chettle, D. R.; Scott, M. C. (1990) Effect of occupational lead
36 exposure on serum 1,25-dihydroxyvitamin D levels. Hum. Exp. Toxicol. 9: 29-34.
37 Massie, H. R.; Aiello, V. R. (1992) Lead accumulation in the bones of aging male mice. Gerontology 38: 13-17.
38 Maue'l, J.; Ransijn, A.; Buchmuller-Rouiller, Y. (1989) Lead inhibits intracellular killing of Leishmania parasites
39 and extracellular cytolysis of target cells by macrophages exposed to macrophage activating factor. J.
40 Leukoc. Biol. 45: 401-409.
41 Mazzolini, M.; Traverse, S.; Marchetti, C. (2001) Multiple pathways of Pb2+ permeation in rat cerebellar granule
42 neurones. J. Neurochem. 79: 407-416.
43 McCabe, M. J., Jr. (1994) Mechanisms and consequences of immunomodulationby lead. In: Dean, J. H.; Luster,
44 M. I.; Munson, A. E.; Kimber, I., eds. Immunotoxicology and immunopharmacology. 2nd ed. New York,
45 NY: Raven Press, Ltd.; pp. 143-162.
46 McCabe, M. J., Jr.; Lawrence, D. A. (1990) The heavy metal lead exhibits B cell-stimulatory factor activity by
47 enhancing B cell la expression and differentiation. J. Immunol. 145: 671-677.
48 McCabe, M. J.; Lawrence, D. A. (1991) Lead, a major environmental pollutant, is immunomodulatory by its
49 differential effects on CD4+ T cell subsets. Toxicol. Appl. Pharmacol. Ill: 13-23.
50 McCabe, M. J., Jr.; Bias, J. A.; Lawrence, D. A. (1991) Lead influences translational or posttranslational regulation
51 of la expression and increases invariant chain expression in mouse B cells. J. Biochem. Toxicol.
52 6:269-276.
53 McCabe, M. J., Jr.; Singh, K. P.; Reiners, J. J., Jr. (1999) Lead intoxication impairs the generation of a delayed type
54 hypersensitivity response. Toxicology 139: 255-264.
May 2006 5-322 DRAFT-DO NOT QUOTE OR CITE
-------
1 McCabe, M. J., Jr.; Singh, K. P.; Reiners, J. I, Jr. (2001) Low level lead exposure in vitro stimulates the
2 proliferation and expansion of alloantigen-reactive CD4high T cells. Toxicol. Appl. Pharmacol.
3 177:219-231.
4 McClain, R. M.; Becker, B. A. (1972) Effects of organolead compounds on rat embryonic and fetal development.
5 Toxicol. Appl. Pharmacol. 21: 265-274.
6 McDonald, J. A.; Potter, N. U. (1996) Lead's legacy? Early and late mortality of 454 lead-poisoned children.
7 Arch. Environ. Health 51: 116-121.
8 McGivern, R. F.; Sokol, R. Z.; Berman, N. G. (1991) Prenatal lead exposure in the rat during the third week of
9 gestation: long-term behavioral, physiological and anatomical effects associated with reproduction.
10 Toxicol. Appl. Pharmacol. 110: 206-215.
11 McGowan, C.; Donaldson, W. E. (1987) Effect of lead toxicity on the organ concentration of glutathione and
12 glutathione-related free amino acids in the chick. Toxicol. Lett. 38: 265-270.
13 McLachlin, J. R.; Goyer, R. A.; Cherian, M. G. (1980) Formation of lead-induced inclusion bodies in primary rat
14 kidney epithelial cell cultures: effect of actinomycin D and cycloheximide. Toxicol. Appl. Pharmacol.
15 56:418-431.
16 McMurry, S. T.; Lochmiller, R. L.; Chandra, S. A. M.; Quails, C. W., Jr. (1995) Sensitivity of selected
17 immunological, hematological, and reproductive parameters in the cotton rat (Sigmodon hispidus) to
18 subchronic lead exposure. J. Wildl. Dis. 31: 193-204.
19 McNeill, F. E.; Laughlin, N. K.; Todd, A. C.; Sonawane, B. R.; Van de Wai, K. M.; Fowler, B. A. (1997) Geriatric
20 bone lead metabolism in a female nonhuman primate population. Environ. Res. 72: 131-139.
21 McNeill, F. E.; Stokes, L.; Brito, J. A.; Chettle, D. R.; Kaye, W. E. (2000) 109Cd Kx-ray fluorescence
22 measurements of tibial lead content in young adults exposed to lead in early childhood. Occup. Environ.
23 Med. 57: 465-471.
24 McNeill, D. R.; Narayana, A.; Wong, H. K.; Wilson, D. M. III. (2004) Inhibition of Apel nuclease activity by lead,
25 iron, and cadmium. Environ. Health Perspect. 112: 799-804.
26 Melchiorri, C.; Chieco, P.; Zedda, A. I.; Coni, P.; Ledda-Columbano, G. M.; Columbano, A. (1993) Ploidy and
27 nuclearity of rat hepatocytes after compensatory regeneration or mitogen-induced liver growth.
28 Carcinogenesis 14: 1825-1830.
29 Menegazzi, M.; Carcereri De Prati, A.; Ledda-Columbano, G. M.; Columbano, A.; Uchida, K.; Miwa, M.; Suzuki,
30 H. (1990) Regulation of poly(ADP-ribose) polymerase mRNA levels during compensatory and mitogen-
31 induced growth of rat liver. Arch. Biochem. Biophys. 279: 232-236.
32 Menegazzi, M.; Carcereri de Prati, A.; Ogura, T.; Columbano, A.; Ledda-Columbano, G. M.; Libonati, M.;
3 3 Esumi, H.; Suzuki, H. (1992) Involvement of DNA polymerase beta in proliferation of rat liver induced by
34 lead nitrate or partial hepatectomy. Febs. Lett. 310: 135-138.
35 Menegazzi, M.; Carcereri-De Prati, A.; Suzuki, H.; Shinozuka, H.; Pibiri, M.; Piga, R.; Columbano, A.; Ledda-
36 Columbano, G. M. (1997) Liver cell proliferation induced by nafenopin and cyproterone acetate is not
3 7 associated with increases in activation of transcription factors NF-icB and AP-1 or with expression of tumor
38 necrosis factor a. Hepatology 25: 585-592.
39 Meng, X.-M.; Zhu, D.-M.; Ruan, D.-Y.; She, J.-Q.; Luo, L. (2005) Effects of chronic lead exposure on H MRS of
40 hippocampus and frontal lobes in children. Neurology 64: 1644-1647.
41 Miller, L.; Qureshi, M. A. (1992) Heat-shock protein synthesis in chicken macrophages: Influence of in vivo and
42 in vitro heat shock, lead acetate, and lipopolysaccharide. Poul. Sci. 71: 988-998.
43 Miller, T. E.; Golemboski, K. A.; Ha, R. S.; Bunn, T.; Sanders, F. S.; Dietert, R. R. (1998) Developmental exposure
44 to lead causes persistent immunotoxicity in Fischer 344 rats. Toxicol. Sci. 42: 129-135.
45 Miller, D. K.; Nation, J. R.; Bratton, G. R. (2001) The effects of perinatal exposure to lead on the discriminative
46 stimulus properties of cocaine and related drugs in rats. Psychopharmacology (Berl). 158: 165-174.
47 Milosevic, N.; Maier, P. (2000) Lead stimulates intercellular signalling between hepatocytes and Kupffer cells.
48 Eur.J. Pharmacol. 401:317-328.
49 Minnema, D. J.; Hammond, P. B. (1994) Effect of lead exposure on patterns of food intake in weanling rats.
50 Neurotoxicol. Teratol. 16: 623-629.
51 Minozzo, R.; Deimling, L. I.; Gigante, L. P.; Santos-Mello, R. (2004) Micronuclei in peripheral blood lymphocytes
52 of workers exposed to lead. Mutat. Res. 565: 53-60.
53 Mishra, M.; Acharya, U. R. (2004) Protective action of vitamins on the spermatogenesis in lead-treated Swiss mice.
54 J. Trace Elem. Med. Biol. 18: 173-178.
May 2006 5-323 DRAFT-DO NOT QUOTE OR CITE
-------
1 Mishra, K. P.; Singh, V. K.; Rani, R.; Yadav, V. S.; Chandran, V.; Srivastava, S. P.; Seth, P. K. (2003) Effect of
2 lead exposure on the immune response of some occupationally exposed individuals. Toxicology
3 188:251-259.
4 Mistry, P.; Lucier, G. W.; Fowler, B. A. (1985) High-affinity lead binding proteins in rat kidney cytosol mediate
5 cell-free nuclear translocation of lead. J. Pharmacol. Exp. Ther. 232: 462-469.
6 Mistry, P.; Mastri, C.; Fowler, B. A. (1986) Influence of metal ions on renal cytosolic lead-binding proteins and
7 nuclear uptake of lead in the kidney. Biochem. Pharmacol. 35:711-713.
8 Miyahara, T.; Komiyama, H.; Miyanishi, A.; Takata, M; Nagai, M; Kozuka, H.; Hayashi, T.; Yamamoto, M.;
9 Ito, Y.; Odake, H.; Koizumi, F. (1995) Stimulative effects of lead on bone resorption in organ culture.
10 Toxicology 97: 191-197.
11 Mobarak, N.; P'an, A. Y. (1984) Lead distribution in the saliva and blood fractions of rats after intraperitoneal
12 injections. Toxicology 32: 67-74.
13 Mojzis, J.; Nistiar, F. (2001) Lead-induced changes of cation-osmotic hemolysis in rats. Gen. Physiol. Biophys.
14 20:315-319.
15 Molero, L.; Carrasco, C.; Marques, M.; Vaziri, N. D.; Mateos-Caceres, P. J.; Casado, S.; Macaya, C.; Barriento, A.;
16 Lopez-Farre, A. J. (2006) Involvement of endothelium and endothelin-1 in lead-induced smooth muscle
17 cell dysfunction in rats. Kidney Int. 69: 685-690.
18 Molfese, D. L.; Laughlin, N. K.; Morse, P. A.; Linnville, S. E.; Wetzel, W. F.; Erwin, R. J. (1986) Neuroelectrical
19 correlates of categorical perception for place of articulation in normal and lead-treated rhesus monkeys.
20 J. Clin. Exp. Neuropsychol. 8: 680-696.
21 Momcilovic, B.; Kostial, K. (1974) Kinetics of lead retention and distribution in suckling and adult rats. Environ.
22 Res. 8: 214-220.
23 Moore, J. F.; Goyer, R. A. (1974) Lead-induced inclusion bodies: composition and probable role in lead metabolism.
24 Environ. Health Perspect. 7: 121 -127.
25 Moore, J. F.; Goyer, R. A.; Wilson, M. (1973) Lead-induced inclusion bodies: solubility, amino acid content, and
26 relationship to residual acidic nuclear proteins. Lab. Invest. 29: 488-494.
27 Moorman, W. J.; Skaggs, S. R.; Clark, J. C.; Turner, T. W.; Sharpnack, D. D.; Murrell, J. A.; Simon, S. D.; Chapin,
28 R. E.; Schrader, S. M. (1998) Male reproductive effects of lead, including species extrapolation for the
29 rabbit model. Reprod. Toxicol. 12: 333-346.
30 Moreira, E. G.; Vassilieff, I.; Vassilieff, V. S. (2001) Developmental lead exposure: behavioral alterations in the
31 short and long term Neurotoxicol. Teratol. 23: 489-495.
32 Morgan, R. E.; Levitsky, D. A.; Strupp, B. J. (2000) Effects of chronic lead exposure on learning and reaction time
33 in a visual discrimination task. Neurotoxicol Teratol. 22: 337-345.
34 Morgan, R. E.; Caravan, H.; Smith, E. G.; Driscoll, L. L.; Levitsky, D. A.; Strupp, B. J. (2001) Early lead exposure
3 5 produces lasting changes in sustained attention, response initiation, and reactivity to errors. Neurotoxicol.
36 Teratol. 23:519-531.
37 Morita, Y.; Sakai, T.; Araki, S.; Araki, T.; Masuyama, Y. (1997) Nicotinamide adenine dinucleotide synthetase
3 8 activity in erythrocytes as a tool for the biological monitoring of lead exposure. Int. Arch. Occup. Environ.
39 Health 70: 195-198.
40 Morley, E. J.; Hirsch, H. V.; Hollocher, K.; Lnenicka, G. A. (2003) Effects of chronic lead exposure on the
41 neuromuscularjunctioninDmsophila larvae. Neurotoxicology 24: 35-41.
42 Morse, P. A.; Molfese, D.; Laughlin, N. K.; Linnville, S.; Wetzel, F. (1987) Categorical perception for voicing
43 contrasts in normal and lead-treated Rhesus monkeys: electrophysiological indices. Brain Lang. 30: 63-80.
44 Moser, R.; Oberley, T. D.; Daggett, D. A.; Friedman, A. L.; Johnson, J. A.; Siegel, F. L. (1995) Effects of lead
45 administration on developing rat kidney: I. Glutathione S-transferase isoenzymes. Toxicol. Appl.
46 Pharmacol. 131:85-93.
47 Mousa, H. M.; Al-Qarawi, A. A.; Ali, B. H.; Abdel Rahman, H. A.; ElMougy, S. A. (2002) Effect of lead exposure
48 on the erythrocytic antioxidant levels in goats. J. Vet. Med. A Physiol. Pathol. Clin. Med. 49: 531-534.
49 Mouw, D. R.; Vander, A. J.; Cox, J.; Fleischer, N. (1978) Acute effects of lead on renal electrolyte excretion and
50 plasma renin activity. Toxicol. Appl. Pharmacol. 46: 435-447.
51 Mudd, S. H.; Levy, H. L.; Skovby, F. (1995) Disorders of transsulfuration. In: Scriver, C. R.; Beaudet, A. L.; Sly,
52 W. S.; Valle, D., eds. The metabolic and molecular bases of inherited disease. New York, NY:
53 McGraw-Hill Publishing Co.; pp. 1279-1328.
54 Mudzinski, S. P.; Rudofsky, U. H.; Mitchell, D. G.; Lawrence, D. A. (1986) Analysis of lead effects on in vivo
55 antibody-mediated immunity in several mouse strains. Toxicol. Appl. Pharmacol. 83: 321-330.
May 2006 5-324 DRAFT-DO NOT QUOTE OR CITE
-------
1 Muldoon, S. B.; Cauley, J. A.; Kuller, L. H.; Scott, I; Rohay, J. (1994) Lifestyle and sociodemographic factors as
2 determinants of blood lead levels in elderly women. Am. J. Epidemiol. 139: 599-608.
3 Muller, S.; Gillert, K.-E.; Krause, C.; Gross, U.; L'Age-Stehr, J.; Diamantstein, T. (1977) Suppression of delayed
4 type hypersensitivity of mice by lead. Experientia 33: 667-668.
5 Munoz, C.; Garbe, K.; Lilienthal, H.; Winneke, G. (1986) Persistence of retention deficit in rats after neonatal lead
6 exposure. Neurotoxicology 7: 569-580.
7 Munoz, C.; Garbe, K.; Lilienthal, H.; Winneke, G. (1988) Significance of hippocampal dysfunction in low level lead
8 exposure of rats. Neurotoxicol. Teratol. 10: 243-253.
9 Munoz, C.; Garbe, K.; Lilienthal, H.; Winneke, G. (1989) Neuronal depletion of the amygdala resembles the
10 learning deficits induced by low level lead exposure in rats. Neurotoxicol. Teratol. 11: 257-264.
11 Murphy, K. J.; Regan, C. M. (1999) Low-level lead exposure in the early postnatal period results in persisting
12 neuroplastic deficits associated with memory consolidation. J. Neurochem. 72: 2099-2104.
13 Murthy, R. C.; Saxena, D. K.; Gupta, S. K.; Chandra, S. V. (1991) Lead induced ultrastructural changes in the testis
14 ofrats. Exp. Pathol. 42:95-100.
15 Murthy, R. C.; Gupta, S. K.; Saxena, D. K. (1995) Nuclear alterations during acrosomal cap formation in spermatids
16 of lead-treated rats. Reprod. Toxicol. 9: 483-489.
17 Nakagawa, K. (1991) Decreased glutathione S-transferase activity in mice livers by acute treatment with lead,
18 independent of alteration in glutathione content. Toxicol. Lett. 56: 13-17.
19 Nakajima, T.; Deguchi, T.; Kagawa, K.; Hikita, H.; Ueda, K.; Katagishi, T.; Ohkawara, T.; Kakusui, M.;
20 Kimura, H.; Okanoue, T.; Kashima, K.; Ashihara, T. (1995) Identification of apoptotic hepatocytes in situ
21 in rat liver after lead nitrate administration. J. Gastroenterol. 30: 725-730.
22 Nathan, E.; Huang, H. F. S.; Pogach, L.; Giglio, W.; Bogden, J. D.; Seebode, J. (1992) Lead acetate does not impair
23 secretion of Sertoli cell function marker proteins in the adult Sprague Dawley rat. Arch. Environ. Health
24 47:370-375.
25 Nation, J. R.; Frye, G. D.; Von Stultz, J.; Bratton, G. R. (1989) Effects of combined lead and cadmium exposure:
26 changes in schedule-controlled responding and in dopamine, serotonin, and their metabolites. Behav.
27 Neurosci. 103: 1108-1114.
28 Nation, J. R.; Livermore, C. L.; Burkey, R. T. (1996) Chronic lead exposure attenuates sensitization to the
29 locomotor-stimulating effects of cocaine. Drug Alcohol Depend. 41: 143-149.
30 Nation, J. R.; Cardon, A. L.; Heard, H. M.; Valles, R.; Bratton, G. R. (2003) Perinatal lead exposure and relapse to
31 drug-seeking behavior in the rat: a cocaine reinstatement study. Psychopharmacology (Berl). 168:236-243.
32 Nation, J. R.; Smith, K. R.; Bratton, G. R. (2004) Early developmental lead exposure increases sensitivity to cocaine
33 in a self-administration paradigm. Pharmacol. Biochem. Behav. 77: 127-135.
34 National Research Council, Committee on Measuring Lead in Critical Populations. (1993) Measuring lead exposure
35 in infants, children, and other sensitive populations. Washington, DC: National Academy Press. Available:
36 http://www.nap.edu/openbooy030904927X/html/ [21 July, 2005].
37 Nayak, B. N.; Ray, M.; Persaud, T. V. N.; Nigli, M. (1989a) Relationship of embryotoxicity to genotoxicity of lead
38 nitrate in mice. Exp. Pathol. 36: 65-73.
39 Nayak, B. N.; Ray, M.; Persaud, T. V. N. (1989b) Maternal and fetal chromosomal aberrations in mice following
40 prenatal exposure to subembryotoxic doses of lead nitrate. Acta Anat. 135: 185-188.
41 Needleman, H. L.; Gunnoe, C.; Leviton, A.; Reed, R.; Peresie, H.; Maher, C.; Barrett, P. (1979) Deficits in
42 psychologic and classroom performance of children with elevated dentine lead levels. N. Engl. J. Med.
43 300:689-695.
44 Needleman, H. L.; Schell, A.; Bellinger, D.; Leviton, A.; Allred, E. N. (1990) The long-term effects of exposure to
45 low doses of lead in childhood; an 11-year follow-up report. N. Engl. J. Med. 322: 83-88.
46 Needleman, H. L.; Riess, J. A.; Tobin, M. J.; Biesecker, G. E.; Greenhouse, J. B. (1996) Bone lead levels and
47 delinquent behavior. JAMA J. Am. Med. Assoc. 275: 363-369.
48 Needleman, H. L.; McFarland, C.; Ness, R. B.; Fienberg, S. E.; Tobin, M. J. (2002) Bone lead levels in adjudcated
49 delinquents. A case control study. Neurotoxicol. Teratol. 24: 711-717.
50 Nehez, M.; Lorencz, R.; Desi, I. (2000) Simultaneous action of cypermethrin and two environmental pollutant
51 metals, cadmium and lead, on bone marrow cell chromosomes of rats in subchronic administration.
52 Ecotoxicol. Environ. Saf. 45: 55-60.
53 Nehru, B.; Kaushal, S. (1992) Effect of lead on hepatic microsomal enzyme activity. J. Appl. Toxicol. 12: 401-405.
54 Neilan, B. A.; Taddeini, L.; McJilton, C. E.; Handwerger, B. S. (1980) Decreased T cell function in mice exposed to
55 chronic, low levels of lead. Clin. Exp. Immunol. 39: 746-749.
May 2006 5-325 DRAFT-DO NOT QUOTE OR CITE
-------
1 Neilan, B. A.; O'Neill, K.; Handwerger, B. S. (1983) Effect of low-level lead exposure on antibody-dependent and
2 natural killer cell-mediated cytotoxicity. Toxicol. Appl. Pharmacol. 69: 272-275.
3 Nelson, B. K.; Moorman, W. I; Schrader, S. M; Shaw, P. B.; Krieg, E. F., Jr. (1997) Paternal exposure of rabbits to
4 lead: behavioral deficits in offspring. Neurotoxicol. Teratol. 19: 191-198.
5 Nemoto, K.; Miyata, S.; Nemoto, F.; Yasumoto, T.; Murai, U.; Kageyama, H.; Degawa, M. (2000) Gene expression
6 of neutrophins and their receptors in lead nitrate-induced rat liver hyperplasia. Biochem. Biophys. Res.
7 Commun. 275: 472-476.
8 Newland, M. C.; Yezhou, S.; Logdberg, B.; Berlin, M. (1994) Prolonged behavioral effects of in utero exposure to
9 lead or methyl mercury: reduced sensitivity to changes in reinforcement contingencies during behavioral
10 transitions and in steady state. Toxicol. Appl. Pharmacol. 126: 6-15.
11 Newland, M. C.; Yezhou, S.; Lodgberg, B.; Berlin, M. (1996) In utero lead exposure in squirrel monkeys: motor
12 effects seen with schedule-controlled behavior. Neurotoxicol. Teratol. 18: 33-40.
13 Ni, Z.; Hou, S.; Barton, C. H.; Vaziri, N. D. (2004) Lead exposure raises superoxide and hydrogen peroxide in
14 human endothelial and vascular smooth muscle cells. Kidney Int. 66: 2329-2336.
15 Nihei, M. K.; Guilarte, T. R. (1999) NMDAR-2A subunit protein expression is reduced in the hippocampus of rats
16 exposed to Pb2+ during development. Mol. Brain Res. 66: 42-49.
17 Nihei, M. K.; Desmond, N. L.; McGlothan, J. L.; Kuhlmann, A. C.; Guilarte, T. R. (2000) A^-methyl-D-aspartate
18 receptor subunit changes are associated with lead-induced deficits of long-term potentiation and spatial
19 learning. Neuroscience 99: 233-242.
20 Nikolova, P.; Kavaldzhieva, B. (1991) The effect of certain heavy metals (Mn and Pb) on parameters of erythrocyte
21 energy metabolism. J. Hyg. Epidemiol. Microbiol. Immunol. 35: 361-365.
22 Nilsson, B. O.; Ljung, L.; Wide, M. (1991) Electron microscopy and X-ray microanalyses of uterine epithelium
23 from lead-injected mice in an experimental delay of implantation. Arch. Toxicol. 65: 239-243.
24 Nolan, C. V.; Shaikh, Z. A. (1992) Lead nephrotoxicity and associated disorders: biochemical mechanisms.
25 Toxicology 73: 127-146.
26 Novak, J.; Banks, R. O. (1995) Lead and nickel alter the cardiorenal actions of endothelin in the rat. Proc. Soc. Exp.
27 Biol. Med. 208: 191-198.
28 Oberley, T. D.; Friedman, A. L.; Moser, R.; Siegel, F. L. (1995) Effects of lead administration on developing rat
29 kidney. II. functional, morphologic, and immunohistochemical studies. Toxicol. Appl. Pharmacol.
30 131:94-107.
31 Odenbro, A.; Arrhenius, E. (1984) Effects of triethyllead chloride on hepatic microsomal N- and C-oxygenation of
32 7V,7V-dimethylaniline in rats. Toxicol. Appl. Pharmacol. 74: 357-363.
33 Odenbro, A.; Kihlstrom, J. E. (1977) Frequency of pregnancy and ova implantation in triethyl lead-treated mice.
34 Toxicol. Appl. Pharmacol. 39: 359-363.
35 Odenbro, A.; Rafter, J. (1988) Effects of triethyl lead chloride on oestradiol metabolism in the female rat liver
36 microsomal fraction. Pharmacol. Toxicol. (Copenhagen) 63: 248-52.
37 Odenbro, A.; Kihlstrom, I.; Kihlstrom, J. E. (1988) Perinatal growth retardation caused by triethyl lead chloride
38 treatment of mice during late gestation. Pharmacol. Toxicol. (Copenhagen) 63: 253-256.
39 O'Flaherty, E. J.; Hammond, P. B.; Lerner, S. I. (1982) Dependence of apparent blood lead half-life on the length of
40 previous lead exposure in humans. Fundam. Appl. Toxicol. 2: 49-54.
41 O'Flaherty, E. J.; Inskip, M. J.; Franklin, C. A.; Durbin, P. W.; Manton, W. I.; Baccanale, C. L. (1998) Evaluation
42 and modification of a physiologically based model of lead kinetics using data from a sequential isotope
43 study in cynomolgus monkeys. Toxicol. Appl. Pharmacol. 149: 1-16.
44 Oishi, H.; Nakashima, M.; Totoki, T.; Tomokuni, K. (1996) Chronic lead exposure may inhibit endothelium-
45 dependent hyperpolarizing factor in rats. J. Cardiovasc. Pharmacol. 28: 558-563.
46 Olshan, A. F.; Breslow, N. E.; Daling, J. R.; Falletta, J. M.; Grufferman, S.; Robison, L. L.; Waskerwitz, M.,
47 Hammond, G. D. (1990) Wilms' tumor and paternal occupation. Cancer Res. 50: 3212-3217.
48 Ong, C. N.; Lee, W. R. (1980) Distribution of lead-203 in human peripheral blood in vitro. Br. J. Ind. Med.
49 37:78-84.
50 Oomen, A. G.; Tolls, J.; Sips, A. J.; Groten, J. P. (2003) In vitro intestinal lead uptake and transport in relation to
51 speciation. Arch. Environ. Contam. Toxicol. 44: 116-124.
52 Oskarsson, A.; Fowler, B. A. (1985) Effects of lead inclusion bodies on subcellular distribution of lead in rat kidney:
53 the relationship to mitochondria! function. Exp. Mol. Pathol. 43: 397-408.
54 Oskarsson, A.; Squibb, K. S.; Fowler, B. A. (1982) Intracellular binding of lead in the kidney: the partial isolation
5 5 and characterization of postmitochondrial lead binding components. Biochem. Biophys. Res. Commun.
56 104:290-298.
May 2006 5-326 DRAFT-DO NOT QUOTE OR CITE
-------
1 Oskarsson, A.; Hellstrom-Lindahl, E. (1989) Lead-dithiocarbamate interaction. Effect on ALAD activity in isolated
2 rat hepatocytes. Biol. Trace Elem. Res. 21: 325-330.
3 Osterode, W.; Ulberth, F. (2000) Increased concentration of arachidonic acid in erythrocyte membranes in
4 chronically lead-exposed men. J. Toxicol. Environ. Health A 59: 87-95.
5 Othman, A. I.; El Missiry, M. A. (1998) Role of selenium against lead toxicity in male rats. J. Biochem. Mol.
6 Toxicol. 12: 345-349.
7 Otto, D. A.; Fox, D. A. (1993) Auditory and visual dysfunction following lead exposure. Neurotoxicology
8 14: 191-207.
9 Pace, B. M.; Lawrence, D. A.; Behr, M. J.; Parsons, P. J.; Bias, J. A. (2005) Neonatal lead exposure changes quality
10 of sperm and number of macrophages in testes of BALB/c mice. Toxicology 210: 247-256.
11 Pagliara, P.; Carla, E. C.; Caforio, S.; Chionna, A.; Massa, S.; Abbro, L.; Dini, L. (2003a) Kupffer cells promote
12 lead nitrate-induced hepatocyte apoptosis via oxidative stress. Comp. Hepatol. 2:8-21.
13 Pagliara, P.; Chionna, A.; Carla, E. C.; Caforio, S.; Dini, L. (2003b) Lead nitrate and gadolinium chloride
14 administration modify hepatocyte cell surfaces. Cell Tissue Res. 312: 41-48.
15 Palminger Hallen, I.; Jonsson, S.; Karlsson, M. O.; Oskarsson, A. (1996) Kinetic observations in neonatal mice
16 exposed to lead via milk. Toxicol. Appl. Pharmacol. 140: 13-18.
17 Palus, J.; Rydzynski, K.; Dziubaltowska, E.; Wyszynska, K.; Natarajan, A. T.; Nilsson, R. (2003) Genotoxic effects
18 of occupational exposure to lead and cadmium. Mutat. Res. 540: 19-28.
19 P'an, A. Y. S.; Kennedy, C. (1989) Lead distribution in rats repeatedly treated with low doses of lead acetate.
20 Environ. Res. 48: 238-247.
21 Pande, M.; Flora, S. J. (2002) Lead induced oxidative damage and its response to combined administration of
22 a-lipoic acid and succimers in rats. Toxicology 177: 187-196.
23 Pande, M.; Mehta, A.; Pant, B. P.; Flora, S. J. S. (2001) Combined administration of a chelating agent and an
24 antioxidant in the prevention and treatment of acute lead intoxication in rats. Environ. Toxicol. Pharmacol.
25 9: 173-184.
26 Panemangalore, M.; Bebe, F. N. (1996) Effects of low oral lead and cadmium exposure and zinc status on heme
27 metabolites in weanling rats. Int. J. Occup. Med. Environ. Health 9: 141-151.
28 Pani, P.; Dessi, S.; Rao, K. N.; Batetta, B.; Laconi, E. (1984) Changes in serum and hepatic cholesterol in lead-
29 induced liver hyperplasia. Toxicol. Pathol. 12: 162-167.
30 Papaioannou, N.; Vlemmas, I.; Balaskas, N.; Tsangaris, T. (1998) Histopathological lesions in lead intoxicated dogs.
31 Vet. Hum. Toxicol. 40: 203-207.
32 Pappas, J. B.; Ahlquist, J. T.; Allen, E. M.; Banner, W., Jr. (1995) Oral dimercaptosuccinic acid and ongoing
33 exposure to lead: effects on heme synthesis and lead distribution in a rat model. Toxicol. Appl. Pharmacol.
34 133: 121-129.
35 Patierno, S. R.; Landolph, J. R. (1989) Soluble vs insoluble hexavalent chromate. Relationship of mutation to in
36 vitro transformation and particle uptake. Biol. Trace Elem. Res. 21: 469-474.
37 Patierno, S. R.; Banh, D.; Landolph, J. R. (1988) Transformation of C3H/10T1/2 mouse embryo cells to focus
3 8 formation and anchorage independence by insoluble lead chromate but not soluble calcium chromate:
39 relationship to mutagenesis and internalization of lead chromate particles. Cancer Res. 48: 5280-5288.
40 Patra, R. C.; Swamp, D. (2000) Effect of lead on erythrocytic antioxidant defence, lipid peroxide level and thiol
41 groups in calves. Res. Vet. Sci. 68: 71-74.
42 Patra, R. C.; Swamp, D.; Dwivedi, S. K. (2001) Antioxidant effects of a tocopherol, ascorbic acid and L-thenionine
43 on lead induced oxidative stress to the liver, kidney and brain in rats. Toxicology 162: 81-88.
44 Payne, K. J.; Crooks, G. M. (2002) Human hematopoietic lineage commitment. Immunol. Rev. 187: 48-64.
45 Payton, M.; Riggs, K. M.; Spiro, A., Ill; Weiss, S. T.; Hu, H. (1998) Relations of bone and blood lead to cognitive
46 function: the VA Normative Aging Study. Neurotoxicol. Teratol. 20: 19-27.
47 Peixoto, N. C.; Roza, T.; Pereira, M. E. (2004) Sensitivity of 5-ALA-D (B.C. 4.2.1.24) of rats to metals in vitro
48 depends on the stage of postnatal growth and tissue. Toxicol. in Vitro 18: 805-809.
49 Pentschew, A.; Garro, F. (1966) Lead encephalo-myelopathy of the suckling rat and its implications on the
50 porphyrinopathic nervous diseases, with special reference to the permeability disorders of the nervous
51 system's capillaries. Acta Neuropathol. 6: 266-278.
52 Pereira, B.; Curi, R.; Kokubun, E.; Bechara, E. J. H. (1992) 5-aminolevulinic acid-induced alterations of oxidative
53 metabolism in sedentary and exercise-trained rats. J. Appl. Physiol. 72: 226-230.
May 2006 5-327 DRAFT-DO NOT QUOTE OR CITE
-------
1 Perez-Bravo, F.; Ruz, M; Moran-Jimenez, M. I; Olivares, M; Rebolledo, A.; Codoceo, J.; Sepulveda, J.; Jenkin, A.;
2 Santos, J. L.; Fontanellas, A. (2004) Association between aminolevulinate dehydrase genotypes and blood
3 lead levels in children from a lead-contaminated area in Antofagasta, Chile. Arch. Environ. Contam.
4 Toxicol. 47(2): 276-280.
5 Pergande, M.; Jung, K.; Precht, S.; Pels, L. M.; Herbert, C.; Stolte, H. (1994) Changed excretion of urinary proteins
6 and enzymes by chronic exposure to lead. Nephrol. Dial. Transplant. 9: 613-618.
7 Piasecka, M.; Rozewicka, L.; Laszczynska, M.; Marchlewicz, M. (1995) Electron-dense deposits in epididymal cells
8 of rats chronically treated with lead acetate [Pb(II)]. Folia Histochem. Cytobiol. 33: 89-94.
9 Piasek, M.; Kostial, K. (1991) Reversibility of the effects of lead on the reproductive performance of female rats.
10 Reprod. Toxicol. 5:45-51.
11 Piccinini, F.; Favalli, L.; Chiari, M. C. (1977) Experimental investigations on the conctraction induced by lead in
12 arterial smooth muscle. Toxicology 8: 43-51.
13 Pillai, A.; Gupta, S. (2005) Effect of gestational and lactational exposure to lead and/or cadmium on reproductive
14 performance and hepatic oestradiol metabolising enzymes. Toxicol. Lett. 155: 179-186.
15 Pineda-Zavaleta, A. P.; Garcia-Vargas, G.; Borja-Aburto, V. H.; Acosta-Saavedea, L. C.; Vera Aguilar, E.;
16 Gomez-Munoz, A.; Cebrian, M. E. Calderon-Aranda, E. S. (2004) Nitric oxide and superoxide anion
17 production in monocytes from children exposed to arsenic and lead in region Lagunera, Mexico. Toxicol.
18 Appl. Pharmacol. 198: 283-290.
19 Pinkerton, L. E.; Biagini, R. E.; Ward, E. M.; Hull, R. D.; Deddens, J. A.; Boeniger, M. F.; Schnorr, T. M.;
20 MacKenzie, B. A.; Luster, M. I. (1998) Immunologic findings among lead-exposed workers. Am. J. Ind.
21 Med. 33:400-408.
22 Pinon-Lataillade, G.; Thoreux-Manlay, A.; Coffigny, H.; Monchaux, G.; Masse, R.; Soufir, J.-C. (1993) Effect of
23 ingestion and inhalation of lead on the reproductive system and fertility of adult male rats and their
24 progeny. Hum. Exp. Toxicol. 12: 165-172.
25 Pinon-Lataillade, G.; Thoreux-Manlay, A.; Coffigny, H.; Masse, R.; Soufir, J. C. (1995) Reproductive toxicity of
26 chronic lead exposure in male and female mice. Hum. Exp. Toxicol. 14: 872-878.
27 Pinto, D.; Ceballos, J. M.; Garcia, G.; Guzman, P.; Del Razo, L. M.; Vera, E.; Gomez, H.; Garcia, A.; Gonsebatt,
28 M. E. (2000) Increased cytogenetic damage in outdoor painters. Mutat. Res. 467: 105-111.
29 Pires, J. B.; Bezerra, F. F.; Laboissiere, F. P.; Miekeley, N.; Donangelo, C. M. (2001) Lead levels in erythrocytes
3 0 and biomarkers of bone turnover in pregnant and lactating women with marginal calcium intakes. Nutr.
31 Res. 21:831-841.
32 Pirkle, J. L.; Schwartz, J.; Landis, J. R.; Harlan, W. R. (1985) The relationship between blood lead levels and blood
33 pressure and its cardiovascular risk implications. Am. J. Epidemiol. 121: 246-258.
34 Pirkle, J. L.; Brody, D. J.; Gunter, E. W.; Kramer, R. A.; Paschal, D. C.; Flegal, K. M.; Matte, T. D. (1994) The
3 5 decline in blood lead levels in the United States: the National Health and Nutrition Examination Surveys
36 (NHANES). JAMA J. Am. Med. Assoc. 272: 284-291.
37 Pirkle, J. L.; Kaufmann, R. B.; Brody, D. J.; Hickman, T.; Gunter, E. W.; Paschal, D. C. (1998) Exposure of the U.S.
38 population to lead, 1991-1994. Environ. Health Perspect. 106: 745-750.
39 Planas-Bohne, F.; Elizalde, M. (1992) Activity of glutathione-S-transferase in rat liver and kidneys after
40 administration of lead or cadmium. Arch. Toxicol. 66: 365-367.
41 Poblano, A.; Rothenberg, S. J.; Schnaas, L.; Elias, Y.; Cruz, M. L. (2001) Spatial distribution of EEC theta activity
42 as a function of lifetime lead exposure in 9-year-old children. Neurotoxicology 22: 439-446.
43 Popovic, M.; McNeill, F. E.; Chettle, D. R.; Webber, C. E.; Lee, C. V; Kaye, W. E. (2005) Impact of occupational
44 exposure on lead levels in women. Environ. Health Perspect. 113: 478-484.
45 Poretz, R. D.; Yang, A.; Deng, W.; Manowitz, P. (2000) The interaction of lead exposure and arylsulfatase A
46 genotype affects sulfatide catabolism in human fibroblasts. Neurotoxicology 21: 379-387.
47 Pounds, J. G.; Rosen, J. F. (1986) Cellular metabolism of lead: a kinetic analysis in cultured osteoclastic bone cells.
48 Toxicol. Appl. Pharmacol. 83: 531-545.
49 Pounds, J. G.; Long, G. J.; Rosen, J. F. (1991) Cellular and molecular toxicity of lead in bone. Environ. Health
50 Perspect. 91: 17-32.
51 Prentice, R. C.; Kopp, S. J. (1985) Cardiotoxicity of lead at various perfusate calcium concentrations: functional and
52 metabolic responses of the perfused rat heart. Toxicol. Appl. Pharmacol. 81: 491-501.
53 Price, R. G. (2000) Urinalysis to exclude and monitor nephrotoxicity. Clin. Chim. Acta 297: 173-182.
May 2006 5-328 DRAFT-DO NOT QUOTE OR CITE
-------
1 Price, R. G.; Taylor, S. A.; Olivers, I.; Arce-Tomas, M; Crutcher, E.; Franchini, I.; Slinovi, R.; Cavazzini, S.;
2 Bergamaschi, E.; Mutti, A.; Vettori, M. V.; Lauwerys, R.; Bernard, A.; Kabanda, A.; Roels, H.;
3 Thielemans, N.; Hotz, P.; De Broe, M. E.; Elseviers, M. M.; Nuyts, G. D.; Gelpi, E.; Hotter, G.; Rosello, I;
4 Ramis, I.; Stolte, H.; Pels, L. M.; Eisenberger, U. (1996) Development and validation of new screening
5 tests for nephrotoxic effects. Hum. Exp. Toxicol. 15(suppl. 1): S10-S19.
6 Prigge, E.; Greve, J. (1977) Effekte einer Bleiinhalation alleinund inKombination mit Kohlenmonoxidbei
7 nichttragenden und tragenden Ratten und deren Feten. II. Effekte auf die Aktivitat der 5-
8 Aminolavulinsaure-Dehydratase, den Hematokrit und das Korpergewicht [Effects of lead inhaltion
9 exposures alone and in combination with carbon monoxide in nonpregnant and pregnant rats and fetuses. II.
10 Effects on 5-aminolevulinic acid dehydratase activity, hematocrit and body weight. Zentralbl. Bakteriol.
11 Parasitenkd. Infektionskrankh. Hyg. 16: 294-304.
12 Purdy, R. E.; Smith, J. R.; Ding, Y.; Oveisi, F.; Varizi, N. D.; Gonick, H. C. (1997) Lead-induced hypertension is
13 not associated with altered vascular reactivity in vitro. Am. J. Hypertens. 10: 997-1003.
14 Pyatt, D. W.; Zheng, J.-H.; Stillman, W. S.; Irons, R. D. (1996) Inorganic lead activates NF-kB in primary human
15 CD4+ T lymphocytes. Biochem. Biophys. Res. Commun. 227: 380-385.
16 Qian, Z. M.; Morgan, E. H. (1990) Effect of lead on the transport of transferrin-free and transferrin-bound iron into
17 rabbit reticulocytes. Biochem. Pharmacol. 40: 1049-1054.
18 Qian, Y.; Harris, E. D.; Zheng, Y.; Tiffany-Castiglioni, E. (2000) Lead targets GRP78, a molecular chaperone, in C6
19 rat glioma cells. Toxicol. Appl. Pharmacol. 163: 260-266.
20 Qian, Y., Zheng, Y., Ramos, K. S.; Tiffany-Castiglioni, E. (2005a) GRP78 compartmentalized redistribution in Pb-
21 treated glia: role of GRP78 in lead-induced oxidative stress. Neurotoxicology. 26: 267-275.
22 Qian, Y.; Zheng, Y.; Ramos, K. S.; Tiffany-Castiglioni, E. (2005b) The involvement of copper transporter in lead-
23 induced oxidative stress in astroglia. Neurochem. Res. 30: 429-438.
24 Qu, W.; Diwan, B. A.; Liu, J.; Goyer, R. A.; Dawson, T.; Horton, J. L.; Cherian, M. G.; Waalkes, M. P. (2002)
25 The metallothionein-null phenotype is associated with heightened sensitivity to lead toxicity and an
26 inability to form inclusion bodies. Am. J. Pathol. 160: 1047-1056.
27 Queiroz, M. L. S.; Almeida, M.; Gallao, M. I.; Hoehr, N. F. (1993) Defective neutrophil function in workers
28 occupationally exposed to lead. Pharmacol. Toxicol. 72: 73-77.
29 Quinlan, G. J.; Halliwell, B.; Moorhouse, C. P.; Gutteridge, J. M. (1988) Action of lead(II) and aluminium(III) ions
30 on iron-stimulated lipid peroxidation in liposomes, erythrocytes and rat liver microsomal fractions.
31 Biochim. Biophys. Acta. 962: 196-200.
32 Quinn, M. R.; Harris, C. L. (1995) Lead inhibits Ca2+-stimulated nitric oxide synthase activity from rat cerebellum.
33 Neurosci. Lett. 196: 65-68.
34 Quintanilla-Vega, B.; Smith, D. R.; Kahng, M. W.; Hernandez, J. M.; Albores, A.; Fowler, B. A. (1995) Lead-
3 5 binding proteins in brain tissue of environmentally lead-exposed humans. Chem. Biol. Interact.
36 98: 193-209.
37 Quintanilla-Vega, B.; Hoover, D. J.; Bal, W.; Sibergeld, E. K., Waalkes, M. P., Anderson, L. D. (2000) Lead
3 8 interaction with human protamine (HP2) as a mechanism of male reproductive toxicity. Chem. Res.
39 Toxicol. 13: 594-600.
40 Raghavan, S. R. V.; Gonick, H. C. (1977) Isolation of low-molecular-weight lead-binding protein from human
41 erythrocytes. Proc. Soc. Exp. Biol. Med. 155: 164-167.
42 Raghavan, S. R. V.; Culver, B. D.; Gonick, H. C. (1980) Erythrocyte lead-binding protein after occupational
43 exposure. I. Relationship to lead toxicity. Environ. Res. 22: 264-270.
44 Raghavan, S. R. V.; Culver, B. D.; Gonick, H. C. (1981) Erythrocyte lead-binding protein after occupational
45 exposure. II. influence on lead inhibition of membrane Na+, K+ - adenosinetriphosphatase. J. Toxicol.
46 Environ. Health 7: 561-568.
47 Rajah, T. T.; Ahuja, Y. R. (1995) In vivo genotoxic effects of smoking and occupational lead exposure in printing
48 press workers. Toxicol. Lett. 76: 71-75.
49 Rajah, T. T.; Ahuja, Y. R. (1996) In vivo genotoxicity of alcohol consumption and lead exposure in printing press
50 workers. Alcohol 13:65-68.
51 Ramesh, G. T.; Manna, S. K.; Aggarwal, B. B.; Jadhav, A. L. (1999) Lead activates nuclear transcription factor -kB,
52 activator protein-1, and amino-terminal c-Jun kinase in pheochromocytoma cells. Toxicol. Appl.
53 Pharmacol. 155: 280-286.
54 Ramesh, G. T.; Manna, S. K.; Aggarwal, B. B.; Jadhav, A. L. (2001) Lead exposure activates nuclear factor kappa
55 B, activator protein-1, c-Jun N-terminal kinase and caspases in the rat brain. Toxicol. Lett. 123: 195-207.
May 2006 5-329 DRAFT-DO NOT QUOTE OR CITE
-------
1 Razani-Boroujerdi, S.; Edwards, B.; Sopori, M. L. (1999) Lead stimulates lymphocyte proliferation through
2 enhanced T cell-B cell interaction. J. Pharmacol. Exp. Therap. 288: 714-719.
3 Redig, P. T.; Lawler, E. M.; Schwartz, S.; Dunnette, J. L.; Stephenson, B.; Duke, G. E. (1991) Effects of chronic
4 exposure to sublethal concentrations of lead acetate on herne synthesis and immune function in red-tailed
5 hawks. Arch. Environ. Contam. Toxicol. 21:12-11.
6 Reigart, J. R.; Graber, C. D. (1976) Evaluation of the humoral immune response of children with low level lead
7 exposure. Bull. Environ. Contam. Toxicol. 16: 112-117.
8 Restrepo, H. G.; Sicard, D.; Torres, M. M. (2000) DNA damage and repair in cells of lead exposed people. Am. J.
9 Ind. Med. 38: 330-334.
10 Reuhl, K. R.; Rice, D. C.; Gilbert, S. G.; Mallett, J. (1989) Effects of chronic developmental lead exposure on
11 monkey neuroanatomy: visual system. Toxicol. Appl. Pharmacol. 99: 501-509.
12 Revis, N. W.; Zinsmeister, A. R.; Bull, R. (1981) Atherosclerosis and hypertension induction by lead and cadmium
13 ions: an effect prevented by calcium ion. Proc. Natl. Acad. Sci. U. S. A. 78: 6494-6498.
14 Reyes, A.; Mercado, E.; Goicoechea, B.; Rosado, A. (1976) Participation of membrane sulfhydryl groups in the
15 epididymal maturation of human and rabbit spermatozoa. Fertil. Steril. 27: 1452-1458.
16 Rice, D. C. (1988a) Chronic low-level exposure in monkeys does not affect simple reaction time. Neurotoxicology
17 9: 105-108.
18 Rice, D. C. (1988b) Schedule-controlled behavior in infant and juvenile monkeys exposed to lead from birth.
19 Neurotoxicology 9: 75-88.
20 Rice, D. C. (1990) Lead-induced behavioral impairment on a spatial discrimination reversal task in monkeys
21 exposed during different periods of development. Toxicol. Appl. Pharmacol. 106: 327-333.
22 Rice, D. C. (1992a) Lead exposure during different developmental periods produces different effects on FI
23 performance in monkeys tested as juveniles and adults. Neurotoxicology 13: 757-770.
24 Rice, D. C. (1992b) Behavioral effects of lead in monkeys tested during infancy and adulthood. Neurotoxicol.
25 Teratol. 14: 235-245.
26 Rice, D. C. (1992c) Effect of lead during different developmental periods in the monkey on concurrent
27 discrimination performance. Neurotoxicology 13: 583-592.
28 Rice, D. C. (1997) Effects of lifetime lead exposure in monkeys on detection of pure tones. Fundam. Appl. Toxicol.
29 36: 112-118.
30 Rice, D.; Barone, S., Jr. (2000) Critical periods of vulnerability for the developing nervous system: evidence from
31 humans and animal models. Environ. Health Perspect. Suppl. 108(3): 511-533.
32 Rice, D. C.; Gilbert, S. G. (1990a) Lack of sensitive period for lead-induced behavioral impairment on a spatial
33 delayed alternation task in monkeys. Toxicol. Appl. Pharmacol. 103: 364-373.
34 Rice, D. C.; Gilbert, S. G. (1990b) Sensitive periods for lead-induced behavioral impairment (nonspatial
35 discrimination reversal) in monkeys. Toxicol. Appl. Pharmacol. 102: 101-109.
36 Rice, D. C.; Hay ward, S. (1999) Comparison of visual function at adulthood and during aging in monkeys exposed
37 to lead or methylmercury. Neurotoxicology 20: 767-784.
38 Rice, D. C.; Karpinski, K. F. (1988) Lifetime low-level lead exposure produces deficits in delayed alternation in
39 adult monkeys. Neurotoxicol. Teratol. 10: 207-214.
40 Rice, D. C.; Gilbert, S. G.; Willes, R. F. (1979) Neonatal low-level lead exposure in monkeys: locomotor activity,
41 schedule-controlled behavior, and the effects of amphetamine. Toxicol. Appl. Pharmacol. 51: 503-513.
42 Richardt, G.; Federolf, G.; Habermann, E. (1986) Affinity of heavy metal ions to intracellular Ca2+-binding
43 proteins. Biochem. Pharmacol. 35: 1331-1335.
44 Rico, J. A.; Kordas, K.; Lopez, P.; Rosado, J. L.; Vargas, G. G.; Ronquillo, D.; Stoltzfus, R. J. (2006) The efficacy
45 of iron and/or zinc supplementation on cognitive performance of lead-exposed Mexican school children:
46 a randomized, placebo-controlled trial. Pediatrics 117: e518-e527.
47 Rijhsinghani, K.; Choi, H.-S. H.; Burton, L. A.; Paronetto, F.; Tavoloni, N. (1993) Immunoelectron microscopy
48 identification of early proliferating cells in rat liver tissue during hyperplasia induced by lead nitrate.
49 Hepatology (Baltimore) 17: 685-692.
50 Ris, M. D.; Dietrich, K. N.; Succop, P. A.; Berger, O. G.; Bornschein, R. L. (2004) Early exposure to lead and
51 neuropsychological outcome in adolescence. J. Int. Neuropsychol. Soc. 10: 261-270.
52 Rizzi, C. A.; Manzo, L.; Tonini, M.; Minoia, C.; Crema, A. (1989) Propulsive motility of the guinea-pig colon after
53 chronic lead treatment. Pharmacol. Res. 21: 127-128.
54 Roberts, J. R.; Reigart, J. R.; Ebeling, M.; Hulsey, T. C. (2001) Time required for blood lead levels to decline in
5 5 nonchelated children. Clin. Toxicol. 39:153-160.
May 2006 5-330 DRAFT-DO NOT QUOTE OR CITE
-------
1 Rocha, A.; Valles, R.; Cardon, A. L.; Bratton, G. R.; Nation, J. R. (2005) Enhanced acquisition of cocaine self-
2 administration in rats developmentally exposed to lead. Neuropsychopharmacology 30: 2058-2064.
3 Rodamilans, M.; Mtz.-Osaba, M. J.; To-Figueras, J.; Rivera-Fillat, F.; Torra, M.; Perez, P.; Corbella, J. (1988)
4 Inhibition of intratesticular testosterone synthesis by inorganic lead. Toxicol. Lett. 42: 285-290.
5 Rodrigues, A. L.; Rocha, J. B.; Mello, C. F.; Souza, D. O. (1996a) Effect of perinatal lead exposure on rat behaviour
6 in open-field and two-way avoidance tasks. Pharmacol. Toxicol. 79: 150-156.
7 Rodrigues, A. L.; Rocha, J. B.; Pereira, M. E.; Souza, D. O. (1996b) 5-aminolevulinic acid dehydratase activity in
8 weanling and adult rats exposed to lead acetate. Bull. Environ. Contam. Toxicol. 57: 47-53.
9 Rodriguez-Iturbe, B.; Vaziri, N. D.; Herrera-Acosta, J.; Johnson, R. J. (2004) Oxidative stress, renal infiltration of
10 immune cells, and salt-sensitive hypertension: all for one and one for all. Am. J. Physiol. 286: F606-F616.
11 Rodriguez-Iturbe, B.; Sindhu, R. K.; Quiroz, Y.; Vaziri, N. D. (2005) Chronic exposure to low doses of lead results
12 in renal infiltration of immune cells, NF-KB activation, and overexpression of tubulointerstitial angiotensin
13 II. Antioxid. Redox Signaling 7: 1269-1274.
14 Roels, H.; Lauwerys, R.; Konings, J.; Buchet, J.-P.; Bernard, A.; Green, S.; Bradley, D.; Morgan, W.; Chettle, D.
15 (1994) Renal function and hyperfiltration capacity in lead smelter workers with high bone lead. Occup.
16 Environ. Med. 51: 505-512
17 Rogan, W. J.; Dietrich, K. N.; Ware, J. H.; Dockery, D. W.; Salganik, M.; Radcliffe, J.; Jones, R. L.; Ragan, N. B.;
18 Chisolm, J. J., Jr.; Rhoads, G. G. (2001) The effect of chelation therapy with succimer on
19 neuropsychological development in children exposed to lead. New Engl. J. Med. 344: 1421-1426.
20 Ronis, M. J. J.; Badger, T. M.; Shema, S. J.; Roberson, P. K.; Shaikh, F. (1996) Reproductive toxicity and growth
21 effects in rats exposed to lead at different periods during development. Toxicol. Appl. Pharmacol.
22 136:361-371.
23 Ronis, M. J.; Badger, T. M.; Shema, S. J.; Roberson, P. K.; Shaikh, F. (1998a) Effects on pubertal growth and
24 reproduction in rats exposed to lead perinatally or continuously throughout development. J. Toxicol.
25 Environ. Health A 53: 327-341.
26 Ronis, M. J. J.; Gandy, J.; Badger, T. (1998b) Endocrine mechanisms underlying reproductive toxicity in the
27 developing rat chronically exposed to dietary lead. J. Toxicol. Environ. Health Part A 54: 77-99.
28 Ronis, M. J. J.; Badger, T. M.; Shema, S. J.; Roberson, P. K.; Templer, L.; Ringer, D.; Thomas, P. E. (1998c)
29 Endocrine mechanisms underlying the growth effects of developmental lead exposure in the rat. J. Toxicol.
30 Environ. Health Part A 54: 101-120.
31 Ronis, M. J. J.; Aronson, J.; Gao, G. G.; Hogue, W.; Skinner, R. A.; Badger, T. M.; Lumpkin, C. K., Jr. (2001)
32 Skeletal effects of developmental lead exposure in rats. Toxicol. Sci. 62: 321-329.
33 Roomi, M. W.; Columbano, A.; Ledda-Columbano, G. M.; Sarma, D. S. R. (1986) Lead nitrate induces certain
34 biochemical properties characteristic of hepatocyte nodules. Carcinogenesis 7: 1643-1646.
35 Roomi, M. W.; Columbano, A.; Ledda-Columbano, G. M.; Sarma, D. S. R. (1987) Induction of the placenta! form
36 of glutathione S-transferase by lead nitrate administration in rat liver. Toxicol. Pathol. 15: 202-205.
37 Rosen, J. F. (1983) The metabolism of lead in isolated bone cell populations: interactions between lead and calcium.
38 Toxicol. Appl. Pharmacol. 71: 101-112.
39 Rosen, J. F.; Markowitz, M. E. (1980) D-Penicillamine: its actions on lead transport in bone organ culture. Pediatr.
40 Res. 14: 330-335.
41 Rosen, J. F.; Mushak, P. (2001) Primary prevention of childhood lead poisoning ~ the only solution [comment].
42 N. Engl. J. Med. 344: 1470-1471.
43 Rosen, J. F.; Pounds, J. G. (1988) The cellular metabolism of lead and calcium: a kinetic analysis in cultured
44 osteoclastic bone cells. In: De Broe, M. E.; Van de Vyver, F. L., eds. Bone and renal failure: international
45 symposium; November 1986; Antwerp, Belgium. Basel, Switzerland: S. Karger; pp. 74-82. (Contributions
46 to nephrology: v. 64.)
47 Rosen, J. F.; Pounds, J. G. (1989) Quantitative interactions between Pb2+ and Ca2+ homeostasis in cultured
48 osteoclastic bone cells. Toxicol. Appl. Pharmacol. 98: 530-543.
49 Rosen, J. F.; Wexler, E. E. (1977) Studies of lead transport in bone organ culture. Biochem. Pharmacol.
50 26:650-652.
51 Rosen, J. F.; Chesney, R. W.; Hamstra, A.; DeLuca, H. F.; Mahaffey, K. R. (1980) Reduction in 1,25-
52 dihydroxyvitamin D in children with increased lead absorption. N. Engl. J. Med. 302: 1128-1131.
53 Rosen, J. F.; Kraner, H. W.; Jones, K. W. (1982) Effects of CaNa2EDTA on lead and trace metal metabolism in
54 bone organ culture. Toxicol. Appl. Pharmacol. 64: 230-235.
55 Rossi, E.; Attwood, P. V.; Garcia-Webb, P. (1992) Inhibition of human lymphocyte coproporphyrinogen oxidase
56 activity by metals, bilirubin and haemin. Biochim. Biophys. Acta 1135: 262-268.
May 2006 5-331 DRAFT-DO NOT QUOTE OR CITE
-------
1 Rothenberg, S. I; Cansino, S.; Sepkoski, C.; Torres, L. M; Medina, S.; Schnaas, L.; Poblano, A.; Karchmer, S.
2 (1995) Prenatal and perinatal lead exposures alter acoustic cry parameters of neonate. Neurotoxicol.
3 Teratol. 17: 151-160.
4 Rothenberg, S. I; Poblano, A.; Schnaas, L. (2000) Brainstem auditory evoked response at five years and prenatal
5 and postnatal blood lead. Neurotoxicol. Teratol. 22: 503-510.
6 Roy, A. K.; Dhir, H.; Sharma, A. (1992) Modification of metal-induced micronuclei formation in mouse bone
7 marrow erythrocytes by Phyllanthus fruit extract and ascorbic acid. Toxicol. Lett. 62: 9-17.
8 Ruan, D. Y.; Tang, L. X.; Zhao, C.; Guo, Y. J. (1994) Effects of low-level lead on retinal ganglion sustained and
9 transient cells in developing rats. Neurotoxicol. Teratol. 16: 47-53.
10 Ruan, D.-Y.; Chen, J.-T.; Zhao, C.; Xu, Y.-Z.; Wang, M.; Zhao, W.-F. (1998) Impairment of long-term potentiation
11 and paired-pulse facilitation in rat hippocampal dentate gyrus following developmental lead exposure in
12 vivo. Brain Res. 806: 196-201.
13 Ruzittu, M.; Carla, E. C.; Montinari, M. R.; Maietta, G.; Dini, L. (1999) Modulation of cell surface expression of
14 liver carbohydrate receptors during in vivo induction of apoptosis with lead nitrate. Cell Tissue Res.
15 298: 105-112.
16 Sabbioni, E.; Marafante, E. (1976) Identification of lead-binding components in rat liver: in vivo study. Chem. Biol.
17 Interact. 15: 1-20.
18 Salinas, J. A.; Huff, N. C. (2002) Lead and spatial vs. cued open field performance. Neurotoxicol. Teratol.
19 24:551-557.
20 Sanchez-Fructuoso, A. I.; Blanco, J.; Cano, M.; Ortega, L.; Arroyo, M.; Fernandez, C.; Prats, D.; Barrientos, A.
21 (2002a) Experimental lead nephropathy: treatment with calcium disodium ethylenediaminetetraacetate.
22 Am. J. Kidney Dis. 40: 59-67.
23 Sanchez-Fructuoso, A. I.; Cano, M.; Arroyo, M.; Fernandez, C.; Prats, D.; Barrientos, A. (2002b) Lead mobilization
24 during calcium disodium ethylenediaminetetraacetate chelation therapy in treatment of chronic lead
25 poisoning. Am. J. Kidney Dis. 40: 51-58.
26 Sandhir, R.; Gill, K. D. (1995) Effect of lead on lipid peroxidation in liver of rats. Biol. Trace Elem. Res. 48: 91-97.
27 Sanin, L. H.; Gonzalez-Cossio, T.; Romieu, I.; Peterson, K. E.; Ruiz, S.; Palazuelos, E.; Hernandez-Avila, M.; Hu,
28 H. (2001) Effect of maternal lead burden on infant weight and weight gain at one month of age among
29 breastfed infants. Pediatrics 107: 1016-1023.
30 Sant'Ana, M. G.; Spinosa, H. S.; Florio, J. C.; Bernardi, M. M.; Oliveira, C. A.; Sarkis, J. E.; Kakazu, M. H. (2001)
31 Role of early GnRH administration in sexual behavior disorders of rat pups perinatally exposed to lead.
32 Neurotoxicol. Teratol. 23: 203-212.
33 Santos, J. L.; Fontanellas, A.; Moran, M. J.; Enriquez de Salamanca, R. (1999) Nonsynergic effect of ethanol and
34 lead on heme metabolism in rats. Ecotoxicol. Environ. Saf. 43: 98-102.
35 Sarasua, S. M.; Vogt, R. F.; Henderson, L. O.; Jones, P. A.; Lybarger, J. A. (2000) Serumimmunoglobulins and
3 6 lymphocyte subset distributions in children and adults living in communities assessed for lead and
37 cadmium exposure. J. Toxicol. Environ. Health A. 60: 1-15.
38 Sargent, J. D.; Dalton, M. A.; O'Connor, G. T.; Olmstead, E. M.; Klein, R. Z. (1999) Randomized trial of calcium
39 glycerophosphate-supplemented infant formula to prevent lead absorption. Am. J. Clin. Nutr.
40 69: 1224-1230.
41 Satija, N. K.; Vij, A. G. (1995) Preventive action of zinc against lead toxicity. Indian J. Physiol. Pharmacol.
42 39: 377-382.
43 Sauk, J. J.; Smith, T.; Silbergeld, E. K.; Fowler, B. A.; Somerman, M. J. (1992) Lead inhibits secretion of
44 osteonectin/SPARC without significantly altering collagen or Hsp47 production in osteoblast-like ROS
45 17/2.8 cells. Toxicol. Appl. Pharmacol. 116: 240-247.
46 Saxena, D. K.; Lai, B.; Srivastava, R. S.; Chandra, S. V. (1990) Lead induced testicular hypersensitivity in stressed
47 rats. Exp. Pathol. 39: 103-109.
48 Schafer, J. H.; Glass, T. A.; Bressler, J.; Todd, A. C.; Schwartz, B. S. (2005) Blood lead in a predictor of
49 homocysteine levels in a population-based study of older adults. Environ. Health Perspect. 113:31-35.
50 Schanne, F. A. X.; Dowd, T. L.; Gupta, R. K.; Rosen, J. F. (1989) Lead increases free Ca2+ concentration in
51 cultured osteoblastic bone cells: simultaneous detection of intracellular free Pb2+ by 19F NMR. Proc. Natl.
52 Acad. Sci.U. S. A. 86:5133-5135.
53 Schanne, F. A. X.; Gupta, R. K.; Rosen, J. F. (1992) Lead inhibits 1,25-dihydroxyvitamin D-3 regulation of calcium
54 metabolism in osteoblastic osteosarcoma cells (ROS 17/2.8). Biochim. Biophys. Acta 1180: 187-194.
55 Schanne, F. A. X.; Long, G. J.; Rosen, J. F. (1997) Lead induced rise in intracellular free calcium is mediated
56 through activation of protein kinase C in osteoblastic bone cells. Biochim. Biophys. Acta 1360: 247-254.
May 2006 5-332 DRAFT-DO NOT QUOTE OR CITE
-------
1 Schantz, S. L.; Laughlin, N. K.; Van Valkenberg, H. C.; Bowman, R. E. (1986) Maternal care by rhesus monkeys of
2 infant monkeys exposed to either lead or 2,3,7,8-tetrachlorodibenzo-P-dioxin. Neurotoxicology 7: 637-650.
3 Schechtman, L. M; Hatch, G. G.; Anderson, T. M; Putman, D. L.; Kouri, R. E.; Cameron, J. W.; Nims, R. W.;
4 Spalding, J. W.; Tennant, R. W.; Lubet, R. A. (1986) Analysis of the interlaboratory and intralaboratory
5 reproducibility of the enhancement of simian adenovirus S A7 transformation of Syrian hamster embryo
6 cells by model carcinogenic and noncarcinogenic compounds. Environ. Mutagen. 8: 495-514.
7 Schell, L. M.; Denham, M.; Stark, A. D.; Ravenscroft, J.; Parsons, P.; Schulte, E. (2004) Relationship between blood
8 lead concentration and dietary intakes of infants from 3 to 12 months of age. Environ. Res. 96: 264-273.
9 Scheuhammer, A. M. (1987) Erythrocyte 5-aminolevulinic acid dehydratase in birds. II. The effects of lead exposure
10 in vivo. Toxicology 45: 165-175.
11 Schirrmacher, K.; Wiemann, M.; Bingmann, D.; Btisselberg, D. (1998) Effects of lead, mercury, and methyl
12 mercury on gap junctions and [CA2+]t in bone cells. Calcified Tiss. Int. 63: 134-139.
13 Schlick, E.; Friedberg, K. D. (1981) The influence of low lead doses on the reticulo-endothelial system and
14 leucocytes of mice. Arch. Toxicol. 47: 197-207.
15 Schlipkoter, H.-W.; Frieler, L. (1979) Der Einfluss kurzzeitiger Bleiexposition auf die Bakterienclearance der Lunge
16 [The influence of short-term lead exposure on the bacterial clearance of the lung]. Zentralbl. Bakteriol.
17 Parasitenkd. Infektionskr. Hyg. Abt. 1: Orig. Reihe B 168: 256-265.
18 Schmitt, C. J.; Caldwell, C. A.; Olsen, B.; Serdar, D.; Coffey, M. (2002) Inhibition of erythrocyte 5-aminolevulinic
19 acid dehydratase (ALAD) activity in fish from waters affected by lead smelters. Environ. Monit. Assess.
20 77:99-119.
21 Schneider, J. S.; Lee, M. H.; Anderson, D. W.; Zuck, L.; Lidsky, T. I. (2001) Enriched environment during
22 development is protective against lead-induced neurotoxicity. Brain Res. 896: 48-55.
23 Schneider, J. S.; Anderson, D. W.; Wade, T. V.; Smith, M. G.; Leibrandt, P.; Zuck, L.; Lidsky, T. I. (2005)
24 Inhibition of progenitor cell proliferation in the dentate gyrus of rats following post-weaning lead exposure.
25 Neurotoxicology 26: 141-145.
26 Schneyer, C. A.; Hall, H. D. (1970) Influence of physiological activity on mitosis in immature rat parotid gland.
27 Proc. Soc. Exp. Biol. Med. 133: 349-352.
28 Schrauzer, G. N. (1987) Effects of selenium antagonists on cancer susceptibility: new aspects of chronic heavy
29 metal toxicity. J. UOEH 9 Suppl: 208-215.
30 Schroeder, H. A.; Mitchener, M. (1971) Toxic effects of trace elements on the reproduction of mice and rats. Arch.
31 Environ. Health 23: 102-106.
32 Schwartz, J. (1994) Low-level lead exposure and children's IQ: a meta-analysis and search for a threshold. Environ.
33 Res. 65: 42-55.
34 Schwartz, J.; Angle, C.; Pitcher, H. (1986) Relationship between childhood blood lead and stature. Pediatrics
35 77:281-288.
36 Schwartz, B. S.; Lee, B.-K.; Stewart, W.; Ahn, K.-D.; Springer, K.; Kelsey, K. (1995) Associations of 5-
37 aminolevulinic acid dehydratase genotype with plant, exposure duration, and blood lead and zinc
3 8 protoporphyrin levels in Korean lead workers. Am. J. Epidemiol. 142: 738-745.
39 Schwartz, B. S.; Lee, B.-K.; Stewart, W.; Sithisarankul, P.; Strickland, P. T.; Ahn, K.-D.; Kelsey, K. (1997) 5-
40 Aminolevulinic acid dehydratase genotype modifies four hour urinary lead excretion after oral
41 administration of dimercaptosuccinic acid. Occup. Environ. Med. 54: 241-246.
42 Schwartz, B. S.; Lee, B.-K.; Stewart, W.; Ahn, K.-D.; Kelsey, K.; Bresssler, J. (1997) Associations of subtypes of
43 hemoglobin with delta-aminolevulinic acid dehydratase genotype and dimercaptosuccinic acid-chelatable
44 lead levels. Arch. Environ. Health 52: 97-103.
45 Schwartz, B. S.; Stewart, W. F.; Bolla, K. I.; Simon, M. S.; Bandeen-Roche, K.; Gordon, B.; Links, J. M.; Todd,
46 A. C. (2000) Past adult lead exposure is associated with longitudinal decline in cognitive function.
47 Neurology 55: 1144-1150.
48 Schwartz, B. S.; Lee, B.-K.; Lee, G.-S.; Stewart, W. F.; Simon, D.; Kelsey, K.; Todd, A. C. (2000) Associations of
49 blood lead, dimercaptosuccinic acid-chelatable lead, and tibia lead with polymorphisms in the vitamin D
50 receptor and 5-aminolevulinic acid dehydratase genes. Environ. Health Perspect. 108: 949-954.
51 Schwartz, B. S.; Lee, B. K.; Lee, G. S.; Stewart, W. F.; Lee, S. S.; Hwang, K. Y.; Ahn, K.-D.; Kim, Y.-B.; Bolla,
52 K. I.; Simon, D.; Parsons, P. J.; Todd, A. C. (2001) Associations of blood lead, dimercaptosuccinic acid-
53 chelatable lead, and tibia lead with neurobehavioral test scores in South Korean lead workers. Am. J.
54 Epidemiol. 153:453-464.
May 2006 5-333 DRAFT-DO NOT QUOTE OR CITE
-------
1 Schwartz, B. S.; Lee, B.-K.; Bandeen-Roche, K.; Stewart, W.; Bolla, K.; Links, J.; Weaver, V.; Todd, A. (2005)
2 Occupational lead exposure and longitudinal decline in neurobehavioral test scores. Epidemiology
3 16: 106-113.
4 Seaton, C. L.; Lasman, J.; Smith, D. R. (1999) The effects of CaNa2EDTA on brain lead mobilization in rodents
5 determined using a stable lead isotope tracer. Toxicol. Appl. Pharmacol. 159: 153-160.
6 Selevan, S. G.; Kimmel, C. A.; Mendola, P. (2000) Identifying critical windows of exposure for children's health.
7 Environ. Health Perspect. Suppl. 108(3): 451-455.
8 Selevan, S. G.; Rice, D. C.; Hogan, K. A.; Euling, S. Y.; Pfahles-Hutchens, A.; Bethel, J. (2003) Blood lead
9 concentration and delayed puberty in girls. N. Engl. J. Med. 348: 1527-1536.
10 Selvin-Testa, A.; Lopez-Costa, J. J.; Nessi-de Avinon, A. C.; Saavedra, J. P. (1991) Astroglial alterations in rat
11 hippocampus during chronic lead exposure. Glia 4: 384-392.
12 Selye, H.; Tuchweber, B.; Bertok, L. (1966) Effect of lead acetate on the susceptibility of rats to bacterial
13 endotoxins. J. Bacteriol. 91: 884-890.
14 Senapati, S. K.; Dey, S.; Dwivedi, S. K.; Patra, R. C.; Swamp, D. (2000) Effect of thiamine hydrochloride on lead
15 induced lipid peroxidation in rat liver and kidney. Vet. Hum. Toxicol. 42: 236-237.
16 Sengupta, M; Bishayi, B. (2002) Effect of lead and arsenic on murine macrophage response. Drug Chem. Toxicol.
17 25:459-472.
18 Serrani, R. E.; Gioia, I. A.; Corchs, J. L. (1997) Lead effects on structural and functional cellular parameters in
19 human red cells from a prenatal hematopoiesis stage. Biometals 10:331-335.
20 Shabani, A.; Rabbani, A. (2000) Lead nitrate induced apoptosis in alveolar macrophages from rat lung. Toxicology
21 149: 109-114.
22 Shakoor, A.; Gupta, P. K.; Singh, Y. P.; Kataria, M. (2000) Beneficial effects of aluminum on the progression of
23 lead-induced nephropathy in rats. Pharmacol. Toxicol. 87: 258-260.
24 Shalan, M. G.; Mostafa, M. S.; Hassouna, M. M.; El-Nabi, S. E.; El-Refaie, A. (2005) Amelioration of lead toxicity
25 on rat liver with vitamin C and silymarin supplements. Toxicology 206: 1-15.
26 Shao, Z.; Suszkiw, J. B. (1991) Ca2+-surrogate action of Pb2+ on acetylcholine release from rat brain
27 synaptosomes. J. Neurochem. 56: 568-574.
28 Sharifi, A. M.; Darabi, R.; Akbarloo, N.; Larijani, B.; Khoshbaten, A. (2004) Investigation of circulatory and tissue
29 ACE activity during development of lead-induced hypertension. Toxicol. Lett. 153: 233-238.
30 Shelkovnikov, S. A.; Gonick, H. C. (2001) Influence of lead on rat thoracic aorta contraction and relaxation. Am. J.
31 Hypertens. 14: 873-878.
32 Shelton, K. R.; Egle, P. M. (1982) The proteins of lead-induced intranuclear inclusion bodies. J. Biol. Chem.
33 257:-l 1802-11807.
34 Shelton, K. R.; Cunningham, J. G.; Klann, E.; Merchant, R. E.; Egle, P. M.; Bigbee, J. W. (1990) Low-abundance
3 5 32-kilodalton nuclear protein specifically enriched in the central nervous system. J. Neurosci. Res.
36 25:287-294.
37 Shelton, K. R.; Egle, P. M.; Bigbee, J. W.; Klann, E. (1993) A nuclear matrix protein stabilized by lead exposure:
3 8 current knowledge and future prospects. Presented at: Ninth international neurotoxicology conference;
39 October 1991; Little Rock, AR. Neurotoxicology 14(2-3): 61-67.
40 Shen, X.-M; Wu, S.-H.; Yan, C.-H.; Zhao, W.; Ao, L.-M; Zhang, Y.-W.; He, J.-M; Ying, J.-M; Li, R.-Q.;
41 Wu, S.-M; Guo, D. (2001) Delta-aminolevulinate dehydratase polymorphism and blood lead levels in
42 Chinese children. Environ. Res. 85: 185-190.
43 Shenker, B. J.; Matarazzo, W. J.; Hirsch, R. L.; Gray, I. (1977) Trace metal modification of immunocompetence. 1.
44 Effect of trace metals in the cultures on in vitro transformation of B lymphocytes. Cell. Immunol.
45 34: 19-24.
46 Shinozuka, H.; Kubo, Y.; Katyal, S. L.; Coni, P.; Ledda-Columbano, G. M.; Columbano, A.; Nakamura, T. (1994)
47 Roles of growth factors and of tumor necrosis factor-a on liver cell proliferation induced in rats by lead
48 nitrate. Lab. Invest. 71: 35-41.
49 Shinozuka, H.; Ohmura, T.; Katyal, S. L.; Zedda, A. I.; Ledda-Columbano, G. M.; Columbano, A. (1996) Possible
50 roles of nonparenchymal cells in hepatocyte proliferation induced by lead nitrate and by tumor necrosis
51 factor a . Hepatology 23: 1572-1577.
52 Shraideh, Z. (1999) Effect of triethyl lead on peristaltic contractile activity of the ileurn of mice. Cytobios
53 99:97-104.
54 Shukla, V. K.; Prakash, A.; Tripathi, B. D.; Reddy, D. C.; Singh, S. (1998) Biliary heavy metal concentrations in
55 carcinoma of the gall bladder: case-control study. BMJ 317: 1288-1289.
May 2006 5-334 DRAFT-DO NOT QUOTE OR CITE
-------
1 Sidhu, M. K.; Fernandez, C.; Khan, M. Y.; Kumar, S. (1991) Induction of morphological transformation, anchorage-
2 independent growth and plasminogen activators in non-tumorigenic human osteosarcoma cells by lead
3 chromate. AnticancerRes. 11: 1045-1053.
4 Sieg, D. I; Billings, R. E. (1997) Lead/cytokine-mediated oxidative DNA damage in cultured mouse hepatocytes.
5 Toxicol. Appl. Pharmacol. 142: 106-115.
6 Sierra, E. M.; Tiffany-Castiglioni, E. (1992) Effects of low-level lead exposure on hypothalamic hormones and
7 serum progesterone levels in pregnant guinea pigs. Toxicology 72: 89-97.
8 Silbergeld, E. K. (1990) Toward the 21st century: lessons from lead and lessons yet to learn. Environ. Health
9 Perspect. 86: 191-196.
10 Silbergeld, E. K.; Hruska, R. E.; Bradley, D. (1982) Neurotoxic aspects of porphyrinopathies: lead and
11 succinylacetone. Environ. Res. 29: 459-471.
12 Silkin, Y. A.; Silkina, E. N.; Sherstobitov, A. O.; Gusev, G. P. (2001) Activation of potassium channels in
13 erythrocytes of marine teleost Scorpaena porcus. Membr. CellBiol. 14: 773-782.
14 Simons, T. J. B. (1986a) Passive transport and binding of lead by human red blood cells. J. Physiol. 378: 267-286.
15 Simons, T. J. B. (1986b) The role of anion transport in the passive movement of lead across the human red cell
16 membrane. J. Physiol. 378: 287-312.
17 Simons, T. J. B. (1988) Active transport of lead by the calcium pump in human red cell ghosts. J. Physiol. (London)
18 405: 105-13.
19 Simons, T. J. B. (1993a) Lead transport and binding by human erythrocytes in vitro. Pflugers Arch. 423: 307-313.
20 Simons, T. J. B. (1993b) Lead-calcium interactions in cellular lead toxicity. Presented at: Ninth international
21 neurotoxicology conference; October 1991; Little Rock, AR. Neurotoxicology 14(2-3): 77-86.
22 Simons, T. J. B. (1995) The affinity of human erythrocyte porphobilinogen synthase for Zn2+ and Pb2+. Eur. J.
23 Biochem. 234: 178-183.
24 Singh, U. S.; Saxena, O.K.; Singh, C.; Murthy, R. C.; Chandra, S. V. (1991) Lead-induced fetal nephrotoxicity in
25 iron-deficient rats. Reprod. Toxicol. 5: 211-217.
26 Singh, A.; Cullen, C.; Dykeman, A.; Rice, D.; Foster, W. (1993a) Chronic lead exposure induces ultrastructural
27 alterations in the monkey testis. J. Submicrosc. Cytol. Pathol. 25: 479-486.
28 Singh, C.; Saxena, D. K.; Murthy, R. C.; Chandra, S. V. (1993b) Embryo-fetal development influenced by lead
29 exposure in iron-deficient rats. Hum. Exp. Toxicol. 12: 25-28.
30 Singh, J.; Pritchard, D. E.; Carlisle, D. L.; Mclean, J. A.; Montaser, A.; Orenstein, J. M.; Patierno, S. R. (1999)
31 Internalization of carcinogenic lead chromate particles by cultured normal human lung epithelial cells:
32 formation of intracellular lead-inclusion bodies and induction of apoptosis. Toxicol. Appl. Pharmacol.
33 161:240-248.
34 Singh, V. K.; Mishra, K. P.; Rani, R.; Yadav, V. S.; Awasthi, S. K.; Garg, S. K. (2003) Immunomodulationby lead.
35 Immunol. Res. 28: 151-165.
36 Sivaprasad, R.; Nagaraj, M.; Varalakshmi, P. (2002) Lipoic acid in combination with a chelator ameliorates lead-
37 induced peroxidative damages in rat kidney. Arch. Toxicol. 76: 437-441.
38 Sivaprasad, R.; Nagaraj, M.; Varalakshmi, P. (2003) Combined efficacies of lipoic acid and meso-2,3-
39 dimercaptosuccinic acid on lead-induced erythrocyte membrane lipid peroxidation and antioxidant status in
40 rats. Hum. Exp. Toxicol. 22: 183-192.
41 Sivaprasad, R.; Nagaraj, M.; Varalakshmi, P. (2004) Combined efficacies of lipoic acid and 2,3-dimercaptosuccinic
42 acid against lead-induced lipid peroxidation in rat liver. J. Nutr. Biochem. 15: 18-23
43 Skoczyriska, A.; Smolik, R. (1994) The effect of combined exposure to lead and cadmium on serum lipids and lipid
44 peroxides level in rats. Int. J. Occup. Med. Environ. Health 7: 263-271.
45 Skoczynska, A.; Smolik, R.; Men, M. (1993) Lipid abnormalities in rats given small doses of lead. Arch. Toxicol.
46 67:200-204.
47 Skoczynska, A.; Smolik, R.; Milian, A. (1994) The effect of combined exposure to lead and cadmium on the
48 concentration of zinc and copper in rat tissues. Int. J. Occup. Med. Environ. Health 7: 41-49.
49 Slobozhanina, E. I.; Kozlova, N. M.; Lukyanenko, L. M.; Oleksiuk, O. B.; Gabbianelli, R.; Fedeli, D.; Caulini,
50 G. C.; Falcioni, G. (2005) Lead-induced changes in human erythrocytes and lymphocytes. J. Appl. Toxicol.
51 25:109-114.
52 Smejkalova, J. (1990) The chromosomal aberrations investigation in children permanently living in the lead polluted
53 area. Sb. Ved. Pr. Lek. Fak. Karlovy Univerzity Hradci Kralove 33: 539-564.
54 Smith, D. R.; Flegal, A. R. (1992) Stable isotopic tracers of lead mobilized by DMSA chelation in low lead-exposed
55 rats. Toxicol. Appl. Pharmacol. 116: 85-91.
May 2006 5-335 DRAFT-DO NOT QUOTE OR CITE
-------
1 Smith, K. L.; Lawrence, D. A. (1988) Immunomodulation of in vitro antigen presentation by cations. Toxicol. Appl.
2 Pharmacol. 96: 476-484.
3 Smith, C. M; DeLuca, H. F.; Tanaka, Y.; Mahaffey, K. R. (1981) Effect of lead ingestion on functions of vitamin D
4 and its metabolites. J. Nutr. Ill: 1321-1329.
5 Smith, C. M.; Hu, H.; Wang, X.; Kelsey, K. T. (1995a) ALA-D genotype is not associated with HT or HB levels
6 among workers exposed to low levels of lead. Med. Lav. 86: 229-235.
7 Smith, C. M.; Wang, X.; Hu, H.; Kelsey, K. T. (1995b) A polymorphism in the 5-aminolevulinic acid dehydratase
8 gene may modify the pharmacokinetics and toxicity of lead. Environ. Health Perspect. 103: 248-253.
9 Smith, D.; Bayer, L.; Strupp, B. J. (1998) Efficacy of succimer chelation for reducing brain Pb levels in a rodent
10 model. Environ. Res. 78: 168-176.
11 Smith, D. R.; Kahng, M. W.; Quintanilla-Vega, B.; Fowler, B. A. (1998) High-affinity renal lead-binding proteins
12 ini environmentally-exposed humans. Chem. Biol. Interact. 115: 39-52.
13 Smith, D. R.; Woolard, D.; Luck, M. L.; Laughlin, N. K. (2000) Succimer and the reduction of tissue lead in
14 juvenile monkeys. Toxicol. Appl. Pharmacol. 166: 230-240.
15 Smith, D.; Hernandez-Avila, M.; Tellez-Rojo, M.M.; Mercado, A.; Hu, H. (2002) The relationship between lead in
16 plasma and whole blood in women. Environ. Health Perspect. 110: 263-268.
17 Snyder, R. D.; Lachmann, P. J. (1989) Thiol involvement in the inhibition of DNA repair by metals in mammalian
18 cells. J. Mol. Toxicol. 2: 117-128.
19 Snyder, J. E.; Filipov, N. M.; Parsons, P. J.; Lawrence, D. A. (2000) The efficiency of maternal transfer of lead and
20 its influence on plasma IgE and splenic cellularity of mice. Toxicol. Sci. 57: 87-94.
21 Sokol, R. Z. (1987) Hormonal effects of lead acetate in the male rat: mechanism of action. Biol. Reprod.
22 37: 1135-1138.
23 Sokol, R. Z.; Berman, N. (1991) The effect of age of exposure on lead-induced testicular toxicity. Toxicology
24 69:269-278.
25 Sokol, R. Z.; Madding, C. E.; Swerdloff, R. S. (1985) Lead toxicity and the hypothalamic-pituitary-testicular axis.
26 Biol. Reprod. 33:722-728.
27 Sokol, R. Z.; Okuda, H.; Nagler, H. M.; Berman, N. (1994) Lead exposure in vivo alters the fertility potential of
28 sperm in vitro. Toxicol. Appl. Pharmacol. 124: 310-316.
29 Sokol, R. Z.; Berman, N.; Okuda, H.; Raum, W. (1998) Effects of lead exposure on GnRH and LH secretion in male
30 rats: response to castration and a-methyl-p-tyrosine (AMPT) challenge. Reprod. Toxicol. 12: 347-355.
31 Sokol, R. Z.; Wang, S.; Wan, Y.-J. Y.; Stanczyk, F. Z.; Gentzschein, E.; Chapin, R. E. (2002) Long-term, low-dose
32 lead exposure alters the gonadotropin-releasing hormone system int he male rat. Environ. Health Perspect.
33 110:871-874.
34 Somashekaraiah, B. V.; Padmaja, K.; Prasad, A. R. K. (1992) Lead-induced lipid peroxidation and antioxidant
35 defense components of developing chick embryos. Free Radic. Biol. Med. 13: 107-114.
36 Spit, B. J.; Wibowo, A. A. E.; Feron, V. J.; Zielhuis, R. L. (1981) Ultrastructural changes in the kidneys of rabbits
37 treated with lead acetate. Arch. Toxicol. 49: 85-91.
38 Srivastava, D.; Hurwitz, R. L.; Fox, D. A. (1995) Lead- and calcium-mediated inhibition of bovine rod cGMP
39 phosphodiesterase: interactions with magnesium. Toxicol. Appl. Pharmacol. 134: 43-52.
40 Srivastava, V.; Dearth, R. K.; Hiney, J. K.; Ramirez, L. M.; Bratton, G. R.; Dees, W. (2004) The effects of low-level
41 Pb on steroidogenic acute regulatory protein (StAR) in the prepubertal rat ovary. Toxicol. Sci. 77: 35-40.
42 Stangle, D. E.; Strawderman, M. S.; Smith, D.; Kuypers, M.; Strupp, B. J. (2004) Reductions in blood lead
43 overestimate reductions in brain lead following repeated succimer regimens in a rodent model of childhood
44 lead exposure. Environ. Health Perspect. 112: 302-308.
45 Steenland, K.; Selevan, S.; Landrigan, P. (1992) The mortality of lead smelter workers: an update. Am. J. Public
46 Health 82: 1641-1644.
47 Stiles, K. M.; Bellinger, D. C. (1993) Neuropsychological correlates of low-level lead exposure in school-age
48 children: a prospective study. Neurotoxicol. Teratol. 15: 27-35.
49 Stokes, J.; Casale, T. B. (2004) Rationale for new treatments aimed at IgE immunomodulation. Ann. Allergy
50 Asthma Immunol. 93: Ill-Ill.
51 Stokes, L.; Letz, R.; Gerr, F.; Kolczak, M.; McNeill, F. E.; Chettle, D. R.; Kaye, W. E. (1998) Neurotoxicity in
52 young adults 20 years after childhood exposure to lead: the Bunker Hill experience. Occup. Environ. Med.
53 55:507-516.
54 Stowe, H. D.; Goyer, R. A. (1971) The reproductive ability and progeny of Fj lead-toxic rats. Fertil. Steril.
55 22:755-760.
May 2006 5-336 DRAFT-DO NOT QUOTE OR CITE
-------
1 Struzyriska, L.; Walski, M.; Gadamski, R.; Dabrowska-Bouta, B.; Rafalowska, U. (1997) Lead-induced
2 abnormalities in blood-brain barrier permeability in experimental chronic toxicity. Mol. Chem.
3 Neuropathol. 31: 207-224.
4 Studnitz, W. von; Haeger-Aronsen, B. (1962) Urinary excretion of amino acids in lead-poisoned rabbits. Acta
5 Pharmacol. Toxicol. 19: 36-42.
6 Sugawara, E.; Nakamura, K.; Fukumura, A.; Seki, Y. (1990) Uptake of lead by human red blood cells and
7 intracellular distribution. Kitasato Arch. Exp. Med. 63: 15-23.
8 Sugiura, S.; Dhar, S. K.; Arizono, K.; Ariyoshi, T. (1993) Induction of DT-diaphorase in the liver of rats treated
9 with various metals. Jpn. J. Toxicol. Environ. Health 39: 7.
10 Suketa, Y.; Hasegawa, S.; Yamamoto, T. (1979) Changes in sodium and potassium in urine and serum of lead-
11 intoxicated rats. Toxicol. Appl. Pharmacol. 47: 203-207.
12 Sun, X.; Tian, X.; Tomsig, J. L.; Suszkiw, J. B. (1999) Analysis of differential effects of Pb2+ on protein kinase C
13 isozymes. Toxicol. Appl. Pharmacol. 156: 40-45.
14 Sun, L.; Hu, J.; Zhao, Z.; Li, L.; Cheng, H. (2003) Influence of exposure to environmental lead on serum
15 immunoglobulin in preschool children. Environ. Res. 92: 124-128.
16 Suszkiw, J.; Toth, G.; Murawsky, M.; Cooper, G. P. (1984) Effects of Pb2+ and Cd2+ on acetylcholine release and
17 Ca2+ movements in synaptosomes and subcellular fractions from rat brain and Torpedo electric organ.
18 Brain Res. 323:31-46.
19 Suwalsky, M.; Villena, F.; Norris, B.; Cuevas, F.; Sotomayor, C. P.; Zatta, P. (2003) Effects of lead on the human
20 erythrocyte membrane and molecular models. J. Inorg. Biochem. 97: 308-313.
21 Suzuki, T.; Morimura, S.; Diccianni, M. B.; Yamada, R.; Hochi, S.-L; Hirabayashi, M.; Yuki, A.; Nomura. K.;
22 Kitagawa, T.; Imagawa, M.; Muramatsu, M. (1996) Activation of glutathione transferase P gene by lead
23 requires glutathione transferase P enhancer I. J. Biol. Chem. 271: 1626-1632.
24 Symanski, E.; Hertz-Picciotto, I. (1995) Blood lead levels in relation to menopause, smoking, and pregnancy
25 history. Am. J. Epidemiol. 141: 1047-1058.
26 Szabo, A.; Merke, J.; Htigel, U.; Mall, G.; Stoeppler, M.; Ritz, E. (1991) Hyperparathyroidism and abnormal
27 l,25(OH)2vitaminD3 metabolism in experimental lead intoxication. Eur. J. Clin. Invest. 21: 512-520.
28 Tabchoury, C. M.; Pearson, S. K.; Bowen, W. H. (1999) Influence of lead on the cariostatic effect of fluoride
29 co-crystallized with sucrose in desalivated rats. Oral Dis. 5: 100-103.
30 Takeno, M.; Yoshikawa, H.; Kurokawa, M.; Takeba, Y.; Kashoiwakura, J. L; Sakaguchi, M.; Yasueda, H.; Suzuki,
31 N. (2004) Thl-dominant shift of T cell cytokine production and subsequent reduction of serum
3 2 immunoglobulin E response by administration in vivo of plasmid expressing Txk/Rlk, a member of Tec
33 family tyrosine kinases, in a mouse model. Clin. Exp. Immunol. 34: 965-970.
34 Taketani, S.; Tanaka, A.; Tokunaga, R. (1985) Reconstitution of heme-synthesizing activity from ferric ion and
35 porphyrins, and the effect of lead on the activity. Arch. Biochem. Biophys. 242: 291-296.
36 Tandon, S. K.; Dhawan, M.; Kumar, A.; Flora, S. J. S. (1992) Influence of selenium supplementation during
37 chelation of lead in rats. Indian J. Physiol. Pharmacol. 36: 201-204.
38 Tandon, S. K.; Singh, S.; Jain, V. K. (1994a) Efficacy of combined chelation in lead intoxication. Chem. Res.
39 Toxicol. 7: 585-589.
40 Tandon, S. K.; Khandelwal, S.; Jain, V. K.; Mathur, N. (1994b) Influence of dietary iron deficiency on nickel, lead
41 and cadmium intoxication. Sci. Total Environ. 148: 167-173.
42 Tandon, S. K.; Singh, S.; Prasad, S.; Mathur, N. (1997) Influence of L-lysine and zinc administration during
43 exposure to lead or lead and ethanol in rats. Biol. Trace Elem. Res. 57: 51-58.
44 Tang, H.-W.; Huel, G.; Campagna, D.; Hellier, G.; Boissinot, C.; Blot, P. (1999) Neurodevelopmental evaluation of
45 9-month-old infants exposed to low levels of lead in utero: involvement of monoamine neurotransmitters.
46 J. Appl. Toxicol. 19: 167-172.
47 Taupeau, C.; Poupon, J.; Nome, F.; Lefevre, B. (2001) Lead accumulation in the mouse ovary after treatment-
48 induced follicular atresia. Reprod. Toxicol. 15: 385-391.
49 Tavakoli-Nezhad, M.; Pitts, D. K. (2005) Postnatal inorganic lead exposure reduces midbrain dopaminergic impulse
50 flow and decreases dopamine Dl receptor sensitivity in nucleus accumbens neurons. J. Pharmacol.
51 Exp. Ther. 312: 1280-1288.
52 Tavakoli-Nezhad, M.; Barren, A. J.; Pitts, D. K. (2001) Postnatal inorganic lead exposure decreases the number of
53 spontaneously active midbrain dopamine neurons in the rat. Neurotoxicology 22: 259-269.
May 2006 5-337 DRAFT-DO NOT QUOTE OR CITE
-------
1 Taylor, S. A.; Olivers, I. D.; Price, R. G.; Arce-Thomas, M.; Milligan, P.; Francini, I.; Alinovi, R.; Cavazzini, S.;
2 Bergamaschi, E.; Vittori, M.; Mutti, A.; Lauwerys, R. R.; Bernard, A. M.; Roels, H. A.; De Broe, M. E.;
3 Nuyts, G. D.; Elseviers, M. M.; Hotter, G.; Ramis, I.; Rosello, I; Gelpi, E.; Stolte, H.; Eisenberger, U.;
4 Pels, L. M. (1997) The assessment of biomarkers to detect nephrotoxicity using an integrated database.
5 Environ. Res. 75:23-33.
6 Tchernitchin, N. N.; Tchernitchin, A. N.; Mena, M. A.; Villarroel, L.; Guzman, C.; Poloni, P. (1998a) Effect of
7 subacute exposure to lead on responses to estrogen in the immature rat uterus. Bull. Environ. Contam.
8 Toxicol. 60: 759-765.
9 Tchernitchin, N. N.; Villagra, A.; Tchernitchin, A. N. (1998b) Antiestrogenic activity of lead. Environ. Toxicol.
10 Water Qual. 13:43-53.
11 Tepper, R. L; Levinson, D. A.; Stanger, B. Z.; Campos-Torres, I; Abbas, A. K.; Leder, P. (1990) IL-4 induces
12 allergic-like inflammatory disease and alters T cell development in transgenic mice. Cell 62: 457-467.
13 Teraki, Y.; Uchiumi, A. (1990) Inorganic elements in the tooth and bone tissues of rats bearing nickel acetate- and
14 lead acetate-induced tumors. Shigaku. 78: 269-273.
15 Terayama, K. (1993) Effects of lead on electrophoretic mobility, membrane sialic acid, deformability and survival of
16 rat erythrocytes. Ind. Health 31:113-126.
17 Terayama, K.; Muratsugu, M. (1988) Effects of lead on sialic acid content and survival of rat erythrocytes.
18 Toxicology 53: 269-276.
19 Terayama, K.; Maehara, N.; Muratsugu, M.; Makino, M.; Yamamura, K. (1986) Effect of lead on electrophoretic
20 mobility of rat erythrocytes. Toxicology 40: 259-265.
21 Tessitore, L.; Perletti, G. P.; Sesca, E.; Pani, P.; Dianzani, M. U.; Piccinini, F. (1994) Proteinkinase C isozyme
22 pattern in liver hyperplasia. Biochem. Biophys. Res. Commun. 205: 208-214.
23 Tessitore, L.; Sesca, E.; Pani, P.; Dianzani, M. U. (1995) Sexual dimorphism in the regulation of cell turnover
24 during liver hyperplasia. Chem. Biol. Interact. 97: 1-10.
25 Thaweboon, S.; Chunhabundit, P.; Surarit, R.; Swasdison, S.; Suppukpatana, P. (2002) Effects of lead on the
26 proliferation, protein production, and osteocalcin secretion of human dental pulp cells in vitro. Southeast
27 Asian J. Trap. Med. Public Health 33: 654-661.
28 Theppeang, K.; Schwartz, B. S.; Lee, B.-K.; Lustberg, M. E.; Silbergeld, E. K.; Kelsey, K. T.; Parsons, P. J.; Todd,
29 A. C. (2004) Associations of patella lead with polymorphisms in the vitamin D receptor, 5-aminolevulinic
30 acid dehydratase and endothelial nitric oxide synthase genes. J. Occup. Environ. Med. 46: 528-537.
31 Thind, I. S.; Khan, M. Y. (1978)Potentiationof the neurovirulence of Langat virus infection by lead intoxication in
32 mice. Exp. Mol. Pathol. 29: 342-347.
33 Thoreux-Manlay, A.; Le Goascogne, C.; Segretain, D.; Jegou, B.; Pinon-Lataillade, G. (1995a) Lead affects
34 steroidogenesis in rat Leydig cells in vivo and in vitro. Toxicology 103: 53-62.
35 Thoreux-Manlay, A.; Velez de la Calle, J. F.; Olivier, M. F.; Soufir, J. C.; Masse, R.; Pinon-Lataillade, G. (1995b)
3 6 Impairment of testicular endocrine function after lead intoxication in the adult rat. Toxicology
37 100: 101-109.
38 Tian, L.; Lawrence, D. A. (1995) Lead inhibits nitric oxide production in vitro by murine splenic macrophages.
39 Toxicol. Appl. Pharmacol. 132: 156-163.
40 Tian, L.; Lawrence, D. A. (1996) Metal-induced modulation of nitric oxide production in vitro by murine
41 macrophages: Lead, nickel, and cobalt utilize different mechanisms. Toxicol. Appl. Pharmacol.
42 141:540-547.
43 Tian, X.; Sun, X.; Suszkiw, J. B. (2000) Upregulation of tyrosine hydroxylase and downregulation of choline
44 acetyltransferase in lead-exposed PC12 cells: the role of PKC activation. Toxicol. Appl. Pharmacol.
45 167:246-252.
46 Tomczok, J.; Grzybek, H.; Sliwa, W.; Panz, B. (1988) Ultrastructural aspects of the small intestinal lead toxicology.
47 Part II. The small intestine goblet cells of rats during lead poisoning. Exp. Pathol. 35: 93-100.
48 Tomczok, J.; Sliwa-Tomczok, W.; Grzybek, H. (1991) The small intestinal enterocytes of rats during lead
49 poisoning: the application of the Timm sulphide silver method and an ultrastructural study. Exp. Pathol.
50 42: 107-113.
51 Tomokuni, K.; Ichiba, M. (1988) Comparison of inhibition of erythrocyte pyrimidine 5'-nucleotidase and delta-
52 aminolevulinic acid dehydratase by lead. Toxicol. Lett. 40: 159-163.
5 3 Tomokuni, K.; Ichiba, M. (1990) Effect of lead on the activity of erythrocyte porphobilinogen deaminase in-vivo
54 and in-vitro. Toxicol. Lett. 50: 137-142.
May 2006 5-338 DRAFT-DO NOT QUOTE OR CITE
-------
1 Tomokuni, K.; Ichiba, M.; Hirai, Y. (1989) Effect of lead exposure on some biological indices related to porphyrin
2 metabolism and the activity of erythrocyte pyrimidine 5'-nucleotidase in the mice. Arch. Toxicol.
3 63:23-28.
4 Tomokuni, K.; Ichiba, M.; Hirai, Y. (1991) Elevated urinary excretion of p-aminoisobutyric acid and
5 5-aminolevulinic acid (ALA) and the inhibition of ALA-synthase and ALA-dehydratase activities in both
6 liver and kidney in mice exposed to lead. Toxicol. Lett. 59: 169-173.
7 Tomsig, J. L.; Suszkiw, J. B. (1993) Intracellular mechanism of Pb2+-induced norepinephrine release from bovine
8 chromaffin cells. Am. J. Physiol. 265: C1630-C1636.
9 Tomsig, J. L.; Suszkiw, J. B. (1995) Multisite interactions between Pb2+ and protein kinase C and its role in
10 norepinephrine release from bovine adrenal chromaffin cells. J. Neurochem. 64: 2667-2673.
11 Tong, S.; Baghurst, P.; McMichael, A.; Sawyer, M.; Mudge, J. (1996) Lifetime exposure to environmental lead and
12 children's intelligence at 11-13 years: the Port Pirie cohort study. Br. Med. J. 312: 1569-1575.
13 Tong, S.; McMichael, A. J.; Baghurst, P. A. (2000) Interactions between environmental lead exposure and
14 sociodemographic factors on cognitive development. Arch. Environ. Health 55: 330-335.
15 Tonner, L. E.; Heiman, A. S. (1997) Lead may affect glucocorticoid signal transduction in cultured hepatoma cells
16 through inhibition of protein kinase C. Toxicology 119: 155-166.
17 Toplan, S.; Ozcelik, D.; Gulyasar, T.; Akyoleu, M. C. (2004) Changes in hemorheological parameters due to lead
18 exposure in female rats. J. Trace Elem. Med. Biol. 18: 179-182.
19 Torres, D.; Barrier, M.; Bihl, F.; Quesniaux, V. J.; Maillet, L; Akira, S.; Ryffel, B.; Erard, F. (2004) Toll-like
20 receptor 2 is required for optimal control of Listeria monocytogenes infection. Infect. Immun.
21 72:2131-2139.
22 Toscano, C. D.; Guilarte, T. R. (2005) Lead neurotoxicity: from exposure to molecular effects. Brain Res. Rev.
23 49: 529-554.
24 Toscano, C. D.; Hashemzadeh-Gargari, H.; McGlothan, J. L.; Guilarte, T. R. (2002) Developmental Pb2+ exposure
25 alters NMDAR subtypes and reduces CREB phosphorylation in the rat brain. Dev. Brain Res.
26 139:217-226.
27 Trasande, L.; Thurston, G. D. (2005) The role of air pollution in asthma and other pediatric morbidities. J.
28 Allergy Clin. Immunol. 115: 689-699.
29 Trejo, R. A.; Di Luzio, N. R.; Loose, L. D.; Hoffman, E. (1972) Reticuloendothelial and hepatic functional
30 alterations following lead acetate administration. Exp. Mol. Pathol. 17: 145-158.
31 Trombini, T. V.; Pedroso, C. G.; Ponce, D.; Almeida, A. A.; Godinho, A. F. (2001) Developmental lead exposure in
32 rats: is abehavioral sequel extended at F2 generation? Pharmacol. Biochem. Behav. 68: 743-751.
33 Trope, L; Lopez-Villegas, D.; Cecil, K. M.; Lenkinski, R. E. (2001) Exposure to lead appears to selectively alter
34 metabolism of cortical gray matter. Pediatrics 107: 1437-1443.
3 5 Tryphonas, H. (2001) Approaches to detecting immunotoxic effects of environmental contaminants in humans.
36 Environ. Health Perspect. Suppl. 109(6): 877-884.
37 Tsaih, S.-W.; Korrick, S.; Schwartz, J.; Lee, M.-L. T.; Amarasiriwardena, C.; Aro, A.; Sparrow, D.; Hu, H. (2001)
3 8 Influence of bone resorption on the mobilization of lead from bone among middle-aged and elderly men:
39 the Normative Aging Study. Environ. Health Perspect. 109: 995-999.
40 Tsao, D.-A.; Yu, H.-S.; Cheng, J.-T.; Ho, C.-K.; Chang, H.-R. (2000) The change of (3-adrenergic system in lead-
41 induced hypertension. Toxicol. Appl. Pharmacol. 164: 127-133.
42 Tulasi, S. J.; Reddy, P. U. M.; Ramana Rao, J. V. (1992) Accumulation of lead and effects on total lipids and lipid
43 derivatives in the freshwater fish Anabas testudineus (Bloch). Ecotoxicol. Environ. Saf. 23: 33-38.
44 U.S. Environmental Protection Agency. (1986a) Air quality criteria for lead. Research Triangle Park, NC: Office of
45 Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no.
46 EPA-600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
47 U.S. Environmental Protection Agency. (1986b) Lead effects on cardiovascular function, early development, and
48 stature: an addendum to U.S. EPA Air Quality Criteria for Lead (1986). In: Air quality criteria for lead, v.
49 1. Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria
50 and Assessment Office; pp. A1-A67; EPA report no. EPA-600/8-83/028aF. Available from: NTIS,
51 Springfield, VA; PB87-142378.
52 U.S. Environmental Protection Agency. (1990) Air quality criteria for lead: supplement to the 1986 addendum.
53 Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and
54 Assessment Office; report no. EPA/600/8-89/049F. Available from: NTIS, Springfield, VA; PB91-138420.
55 Ueda, D.;Kishimoto, T.; Dekio, S.; Tada, M. (1997) Inhibitory effect of lead on tube formation by cultured human
56 vascular endothelial cells. Hum. Cell 10: 283-291.
May 2006 5-339 DRAFT-DO NOT QUOTE OR CITE
-------
1 Undeger, U.; Bas.aran, N.; Canpinar, H.; Kansu, E. (1996) Immune alterations in lead-exposed workers. Toxicology
2 109: 167-172.
3 Upasani, C. D.; Khera, A.; Balaraman, R. (2001) Effect of lead with vitamin E, C, or Spimlina on malondialdehyde,
4 conjugated dienes and hydroperoxides in rats. Indian J. Exp. Biol. 39: 70-74.
5 Vaglenov, A.; Carbonell, E.; Marcos, R. (1998) Biomonitoring of workers exposed to lead. Genotoxic effects, its
6 modulation by polyvitamin treatment and evaluation of the induced radioresistance. Mutat. Res.
7 418:79-92.
8 Vakharia, D. D.; Liu, N.; Pause, R.; Fasco, M; Bessette, E.; Zhang, Q.-Y.; Kaminsky, L. S. (2001) Effect of metals
9 on polycyclic aromatic hydrocarbon induction of CYP1 Al and CYP1A2 in human hepatocyte cultures.
10 Toxicol. Appl. Pharmacol. 170: 93-103.
11 Valencia, L; Castillo, E. E.; Chamorro, G.; Bobadilla, R. A.; Castillo, C. (2001) Lead induces endothelium- and
12 Ca2+-independent contraction in rat aortic rings. Pharmacol. Toxicol. (Oxford, UK) 89: 177-182.
13 Valentino, M.; Governa, M.; Marchiseppe, I.; Visona, I. (1991) Effects of lead on polymorphonuclear leukocyte
14 (PMN) functions in occupationally exposed workers. Arch. Toxicol. 65: 685-688.
15 Valverde, M.; Fortoul, T. I.; Diaz-Barriga, F.; Majia, J.; Del Castillo, E. R. (2002) Genotoxicity induced in CD-I
16 mice by inhaled lead: differential organ response. Mutagenesis 17: 55-61.
17 Van Gelder, G. A.; Carson, T.; Smith, R. M.; Buck, W. B. (1973) Behavioral toxicologic assessment of the
18 neurologic effect of lead in sheep. Clin. Toxicol. 6: 405-418.
19 VanLarebeke, N.; Koppen, G.; Nelen, V; Schoeters, G.; VanLoonH, AlberingH, RigaL, Vlietinck, R.; Kleinjans,
20 J.; Flemish Environment and Health Study Group. (2004) Differences in HPRT mutant frequency among
21 middle-aged Flemish women in association with area of residence and blood lead levels. Biomarkers
22 9:71-84.
23 Vander, A. J. (1988) Chronic effects of lead on the renin-angiotensin system. In: Victery, W., ed. Symposium on
24 lead-blood pressure relationships; April 1987; Chapel Hill, NC. Environ. Health Perspect. 78: 77-83.
25 Vander, A. J.; Taylor, D. L.; Kalitis, K.; Mouw, D. R.; Victery, W. (1977) Renal handling of lead in dogs: clearance
26 studies. Am. J. Physiol. 2: F532-F538.
27 Varnai, V. M.; Piasek, M.; Blanusa, M.; Juresa, D.; Saric, M.; Kostial, K. (2003) Ascorbic acid supplementation
28 does not improve efficacy of meso-dimercaptosuccinic acid treatment in lead-exposed suckling rats.
29 Pharmacol. Toxicol. (Oxford, UK) 93: 180-185.
30 Varnai, V. M.; Piasek, M.; Blanusa, M.; Saric, M. M.; Kostial, K. (2001) Succimer treatment during ongoing lead
31 exposure reduces tissue lead in suckling rats. J. Appl. Toxicol. 21: 415-416.
32 Vaziri, N.; Ding, Y. (2001) Effect of lead on nitric oxide synthase expression in coronary endothelial cells: role of
33 superoxide. Hypertension 37: 223-226.
34 Vaziri, N. D.; Wang, X. Q. (1999) cGMP-mediated negative-feedback regulation of endothelial nitric oxide synthase
35 expression by nitric oxide. Hypertension 34: 1237-1241.
36 Vaziri, N. D.; Ding, Y.; Ni, Z.; Gonick, H. C. (1997) Altered nitric oxide metabolism and increased oxygen free
37 radical activity in lead-induced hypertension: effect of lazaroid therapy. Kidney Int. 52: 1042-1046.
38 Vaziri, N. D.; Ding, Y.; Ni, Z. (1999a) Nitric oxide synthase expression in the course of lead-induced hypertension.
39 Hypertension 34: 558-562.
40 Vaziri, N. D.; Liang, K.; Ding, Y. (1999b) Increased nitric oxide inactivationby reactive oxygen species in lead-
41 induced hypertension. Kidney Int. 56: 1492-1498.
42 Vaziri, N. D.; Wang, X. Q.; Oveisi, F.; Rad, B. (2000) Induction of oxidative stress by glutathione depletion causes
43 severe hypertension in normal rats. Hypertension 36: 142-146.
44 Vaziri, N. D.; Ding, Y.; Ni, Z. (2001) Compensatory up-regulation of nitric-oxide synthase isoforms in lead-induced
45 hypertension; reversal by a superoxide dismutase-mimetic drug. J. Pharmacol. Exp. Ther. 298: 679-685.
46 Vaziri, N. D.; Lin, C.-Y.; Farmand, F.; Sindhu, R. K. (2003) Superoxide dismutase, catalase, glutathione peroxidase
47 and NADPH oxidase in lead-induced hypertension. Kidney Int. 63: 186-194.
48 Vaziri, N. D.; Ding, Y.; Ni, Z.; Barton, C. H. (2005) Bradykinin down-regulates, whereas arginine analogs up-
49 regulates, endothelial nitric-oxide synthase expression in coronary endothelial cells. J. Pharmacol. Exp.
50 Ther. 313: 121-126.
51 Vermande-van Eck, G. J.; Meigs, J. W. (1960) Changes in the ovary of the rhesus monkey after chronic lead
52 intoxication. Fertil. Steril. 11: 223-234.
53 Vicente, A.; Varas, A.; Acedon, R. S.; Jimenez, E.; Munoz, J. J.; Zapata, A. G. (1998) Appearance and maturation
54 of T-cell subsets during rat thymus development. Dev. Cornp. Immunol. 5: 319-331.
5 5 Vickers, C.; Paterson, A. T. (1986) Two types of chronic lead treatment in C57BL/6 mice: interaction with
56 behavioural determinants of pain. Life Sci. 39: 47-53.
May 2006 5-340 DRAFT-DO NOT QUOTE OR CITE
-------
1 Victery, W.; Vander, A. I; Mouw, D. R. (1979a) Effect of acid-base status on renal excretion and accumulation of
2 lead in dogs and rats. Am. J. Physiol. 237: F398-F407.
3 Victery, W.; Vander, A. J.; Mouw, D. R. (1979b) Renal handling of lead in dogs: stop-flow analysis. Am. J. Physiol.
4 237: F408-F414.
5 Victery, W.; Soifer, N. E.; Weiss, J. S.; Vander, A. J. (1981) Acute effects of lead on the renal handling of zinc in
6 dogs. Toxicol. Appl. Pharmacol. 61: 358-367.
7 Victery, W.; Vander, A. J.; Markel, H.; Katzman, L.; Shulak, J. M; Germain, C. (1982a) Lead exposure, begun
8 in utero, decreases renin and angiotensin II in adult rats. Proc. Soc. Exp. Biol. Med. 170: 63-67.
9 Victery, W.; Vander, A. J.; Shulak, J. M.; Schoeps, P.; Julius, S. (1982b) Lead, hypertension, and the renin-
10 angiotensin system in rats. J. Lab. Clin. Med. 99: 354-362.
11 Victery, W.; Vander, A. J.; Schoeps, P.; Germain, C. (1983) Plasma renin is increased in young rats exposed to lead
12 in utero and during nursing. Proc. Soc. Exp. Biol. Med. 172: 1-7.
13 Vij, A. G.; Satija, N. K.; Flora, S. J. (1998) Lead induced disorders in hematopoietic and drug metabolizing enzyme
14 system and their protection by ascorbic acid supplementation. Biomed. Environ. Sci. 11: 7-14.
15 Villagra, R.; Tchernitchin, N. N.; Tchernitchin, A. N. (1997) Effect of subacute exposure to lead and estrogen on
16 immature pre-weaning rat leukocytes. Bull. Environ. Contam. Toxicol. 58: 190-197.
17 Virgolini, M. B.; Chen, K.; Weston, D. D.; Bauter, M. R.; Cory-Slechta, D. A. (2005) Interactions of chronic lead
18 exposure and intermittent stress: consequences for brain catecholamine systems and associated behaviors
19 and HPA axis function. Toxicol. Sci. 87: 469-482.
20 Virgolini, M. B.; Bauter, M. R.; Weston, D. D.; Cory-Slechta, D. A. (2006) Permanent alterations in stress
21 responsivity in female offspring subjected to combined maternal lead exposure and/or stress.
22 Neurotoxicology 27: 11-21.
23 Virgolini, M. B.; Chen, K.; Weston, D. D.; Bauter, M. R.; Cory-Slechta, D. A. (2006) Interactions of chronic lead
24 exposure and intermittent stress: consequences for brain catecholamine systems and associated behaviors
25 and HPA axis function. Toxicol. Sci. 87: 469-482.
26 Vyskocil, A.; Fiala, Z.; Salandova, J.; Popler, A.; Ettlerova, E.; Emminger, S. (1991) The urinary excretion of
27 specific proteins in workers exposed to lead. Arch. Toxicol. Suppl. 14: 218-221.
28 Waalkes, M. P.; Liu, J.; Goyer, R. A.; Diwan, B. A. (2004) Metallothionein-I/II double knockout mice are
29 hypersensitive to lead-induced kidney carcinogenesis: role of inclusion body formation. Cancer Res.
30 64:7766-7772.
31 Wadi, S. A.; Ahmad, G. (1999) Effects of lead on the male reproductive system in mice. J. Toxicol. Environ. Health
32 Part A 56: 513-521.
33 Wagerova, M.; Wagner, V.; Madlo, Z.; Zavazal, V.; Wokounva, D.; Kfiz, J.; Mohyla, O. (1986) Seasonal variations
34 in the level of immunoglobulins and serum proteins of children differing by exposure to air-borne lead.
35 J. Hyg. Epidem. Microbiol. 30: 127-138.
3 6 Walkowiak, J.; Altmann, L.; Kramer, U.; Sveinsson, K.; Turfeld, M.; Weishoff-Houben, M.; Winneke, G. (1998)
3 7 Cognitive and sensorimotor functions in 6-year-old children in relation to lead and mercury levels:
3 8 adjustment for intelligence and contrast sensitivity in computerized testing. Neurotoxicol. Teratol.
39 20:511-521.
40 Wang, J.; Huff, A. M.; Spence, J. D.; Hegele, R. A. (2004) Single nucleotide polymorphism in CTH associated with
41 variation in plasma homocysteine concentration. Clin. Genet. 65: 483-486.
42 Wapnir, R. A.; Moak, S. A.; Lifshitz, F.; Teichberg, S. (1979) Alterations of intestinal and renal functions in rats
43 after intraperitoneal injections of lead acetate. J. Lab. Clin. Med. 94: 144-151.
44 Warner, G. L.; Lawrence, D. A. (1986) Stimulation of murine lymphocyte responses by cations. Cell. Immunol.
45 101:425-439.
46 Wasserman, G. A.; Musabegovic, A.; Liu, X.; Kline, J.; Factor-Litvak, P.; Graziano, J. H. (2000) Lead exposure and
47 motor functioning in 4 1/2-year-old children: the Yugoslavia prospective study. J. Pediatr. 137: 555-561.
48 Waterman, S. J.; El-Fawal, H. A. N.; Snyder, C. A. (1994) Lead alters the immunogenicity of two neural proteins:
49 A potential mechanism for the progression of lead-induced neurotoxicity. Environ. Health Perspect.
50 102: 1052-1056.
51 Watson, G. E.; Davis, B. A.; Raubertas, R. F.; Pearson, S. K.; Bowen, W. H. (1997) Influence of maternal lead
52 ingestion on caries in rat pups. Nature Med. 3: 1024-1025.
53 Watts, S. W.; Chai, S.; Webb, R. C. (1995) Lead acetate-induced contraction in rabbit mesenteric artery: interaction
54 with calcium and protein kinase C. Toxicology 99: 55-65.
May 2006 5-341 DRAFT-DO NOT QUOTE OR CITE
-------
1 Weaver, V. M; Schwartz, B. S.; Ahn, K.-D.; Stewart, W. F.; Kelsey, K. T.; Todd, A. C.; Wen, J.; Simon, D. I;
2 Lustberg, M. E.; Parsons, P. J.; Silbergeld, E. K.; Lee, B.-K. (2003) Associations of renal function with
3 polymorphisms in the 5-aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide synthase
4 genes in Korean lead workers. Environ. Health Perspect. Ill: 1613-1619.
5 Weaver, V. M.; Schwartz, B. S.; Jaar, B. G.; Ahn, K.-D.; Todd, A. C.; Lee, S.-S.; Kelsey, K. T.; Silbergeld, E. K.;
6 Lustberg, M. E.; Parsons, P. J.; Wen, J.; Lee-B.-K. (2005) Associations of uric acid with polymorphisms in
7 the 5-aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide synthase genes in Korean lead
8 workers. Environ. Health Perspect. 113: 1509-1515.
9 Webb, R. C.; Winquist, R. J.; Victery, W.; Vander, A. J. (1981) In vivo and in vitro effects of lead on vascular
10 reactivity in rats. Am. J. Physiol. 241: H211-H216.
11 Wedeen, R. P. (1992) Removing lead from bone: clinical implications of bone lead stores. Neurotoxicology
12 13:843-852.
13 Wedrychowski, A.; Schmidt, W. N.; Hnilica, L. S. (1986) The in vivo cross-linking of proteins and DNAby heavy
14 metals. J. Biol. Chem. 261: 3370-3376.
15 Weiler, E.; Khalil-Manesh, F.; Gonick, H. C. (1990) Effects of lead and a low-molecular-weight endogenous plasma
16 inhibitor on the kinetics of sodium - potassium-activated adenosine triphosphatase and potassium-activated
17 para-nitrophenylphosphatase. Clin. Sci. 79: 185-192.
18 Weisberg, I. S.; Park, E.; Ballman, K. V.; Berger, P.; Nunn, M.; Suh, D. S.; Breksa, A. P., Ill; Garrow, T. A.;
19 Rozen, R. (2003) Investigations of a common genetic variant in betaine—homocysteine methyltransferase
20 (BHMT) in coronary artery disease. Atherosclerosis 167: 205-214.
21 Weiss, B. (2000) Vulnerability of children and the developing brain to neurotoxic hazards. Environ. Health Perspect.
22 Suppl. 108(3): 375-381.
23 Weiss, B.; Landrigan, P. J. (2000) The developing brain and the environment: an introduction. Environ. Health
24 Perspect. 108(Suppl. 3): 373-374.
25 Weisskopf, M. G.; Hu, H.; Mulkern, R. V.; White, R.; Aro, A.; Oliveira, S.; Wright, R. O. (2004a) Cognitive deficits
26 and magnetic resonance spectroscopy in adult monozygotic twins with lead poisoning. Environ. Health
27 Perspect. 112:620-625.
28 Weisskopf, M. G.; Wright, R. O.; Schwartz, J.; Spiro, A., Ill; Sparrow, D.; Aro, A.; Hu, H. (2004b) Cumulative lead
29 exposure and prospective change in cognition among elderly men. The VA Normative Aging Study. Am. J.
30 Epidemiol. 160: 1184-1193.
31 Weiler, C. V. (1915) The blastophthoric effect of chronic lead poisoning. J. Med. Res. 33: 271-293.
32 Wenda-Rozewicka, L.; Marchlewicz, M.; Barcew-Wiszniewska, B.; Piasecka, M. (1996) The ultrastructure of the
33 testis in rats after long-term treatment with lead acetate. Andrologia 28: 97-102.
34 Westerink, R. H.; Vijverberg, H. P. (2002) Ca2+-independent vesicular catecholamine release in PC12 cells by
35 nanomolar concentrations of Pb2+. J. Neurochem. 80: 861-867.
36 Wetmur, J. G. (1994) Influence of the common human delta-aminolevulinate dehydratase polymorphism on lead
37 body burden. Environ. Health Perspect. 102(suppl. 3): 215-219.
38 Wetmur, J. G.; Lehnert, G.; Desnick, R. J. (1991) The 5-aminolevulinate dehydratase polymorphism: higher blood
39 lead levels in lead workers and environmentally exposed children with the 1-2 and 2-2 isozymes. Environ.
40 Res. 56: 109-119.
41 White, R. F.; Diamond, R.; Proctor, S.; Morey, C.; Hu, H. (1993) Residual cognitive deficits 50 years after lead
42 poisoning during childhood. Br. J. Ind. Med. 50: 613-622.
43 Wicklund, K. G.; Daling, J. R.; Allard, J.; Weiss, N. S. (1988) Respiratory cancer among orchardists in Washington
44 State, 1968-1980. J. Occup. Med. 30: 561-564.
45 Wide, M. (1985) Lead exposure on critical days of fetal life affects fertility in the female mouse. Teratology
46 32:375-380.
47 Wide, M.; D'Argy, R. (1986) Effect of inorganic lead on the primordial germ cells in the mouse embryo. Teratology
48 34:207-212.
49 Wide, M.; Nilsson, O. (1977) Differential susceptibility of the embryo to inorganic lead during periimplantation in
50 the mouse. Teratology 16: 273-276.
51 Wide, M.; Nilsson, B. O. (1979) Interference of lead with implantation in the mouse: a study of the surface
52 ultrastructure of blastocysts and endometrium. Teratology 20: 101-113.
53 Widzowski, D. V.; Cory-Slechta, D. A. (1994) Homogeneity of regional brain lead concentrations.
54 Neurotoxicology 15: 295-308.
55 Wiebe, J. P.; Barr, K. J. (1988) Effect of prenatal and neonatal exposure to lead on the affinity and number of
56 estradiol receptors in the uterus. J. Toxicol. Environ. Health 24: 451-460.
May 2006 5-342 DRAFT-DO NOT QUOTE OR CITE
-------
1 Wiebe, J. P.; Barr, K. I; Buckingham, K. D. (1988) Effect of prenatal and neonatal exposure to lead on
2 gonadotropin receptors and steroidogenesis in rat ovaries. J. Toxicol. Environ. Health 24: 461-476.
3 Wiemann, M; Schirrmacher, K.; Btisselberg, D. (1999) Interference of lead with the calcium release activated
4 calcium flux of osteoblast-like cells. Calcif. Tissue Int. 65: 479-485.
5 Winneke, G.; Kramer, U. (1997) Neurobehavioral aspects of lead neurotoxicity in children. Cent. Eur. J. Public
6 Health 5: 65-69.
7 Wise, J. P.; Leonard, J. C.; Patierno, S. R. (1992) Clastogenicity of lead chromate particles in hamster and human
8 cells. Mutat. Res. 278: 69-79.
9 Wise, J. P.; Orenstein, J. M.; Patierno, S. R. (1993) Inhibition of lead chromate clastogenesis by ascorbate:
10 relationship to particle dissolution and uptake. Carcinogenesis (London) 14: 429-434.
11 Wise, J. P., Sr; Stearns, D. M.; Wetterhahn, K. E.; Patierno, S. R. (1994) Cell-enhanced dissolution of carcinogenic
12 lead chromate particles: the role of individual dissolution products in clastogenesis. Carcinogenesis 15:
13 2249-2254.
14 Wise, S. S.; Schuler, J. H.; Holmes, A. L.; Katsifis, S. P.; Ketterer, M. E.; Hartsock, W. J.; Zheng, T.; Wise, J. P., Sr.
15 (2004a) Comparison of two paniculate hexavalent chromium compounds: Barium chromate is more
16 genotoxic than lead chromate in human lung cells. Environ. Mol. Mutagen. 44: 156-162.
17 Wise S. S.; Holmes A. L.; Ketterer, M. E.; Hartsock, W. J.; Fomchenko, E.; Katsifis, S.; Thompson, W. D.; Wise,
18 J. P. Sr. (2004b) Chromium is the proximate clastogenic species for lead chromate-induced clastogenicity
19 in human bronchial cells. Mutat. Res. 560: 79-89.
20 Wise, S. S.; Holmes, A. L.; Moreland, J. A.; Xie, H .; Sandwick, S. J.; Stackpole, M. M.; Fomchenko, E.;
21 Teufack, S.; May, A. J., Jr.; Katsfis, S. P.; Wise, J. P., Sr. (2005) Human lung cell growth is not stimulated
22 by lead ions after lead chromate-induced genotoxicity. Mol. Cell. Biochem. 279: 75-84.
23 Wisotzky, J.; Hein, J. W. (1958) Effects of drinking solutions containing metallic ions above and below hydrogen in
24 the electromotive series on dental caries in the Syrian hamster. J. Am. Dent. Assoc. 57: 796-800.
25 Witzmann, F. A.; Daggett, D. A.; Fultz, C. D.; Nelson, S. A.; Wright, L. S.; Kornguth, S. E.; Siegel, F. L. (1998)
26 Glutathione S-transferases: two-dimensional electrophoretic protein markers of lead exposure.
27 Electrophoresis 19: 1332-1335.
28 Wolf, A. W.; Jimenez, E.; Lozoff, B. (2003) Effects of iron therapy on infant blood lead levels. J. Pediatr.
29 143:789-795.
30 Wolin, M. S. (2000) Interactions of oxidants with vascular signaling systems. Arterioscler. Thromb. Vase. Biol.
31 20:1430-1442.
32 Wong, O.; Harris, F. (2000) Cancer mortality study of employees at lead battery plants and lead smelters,
33 1947-1995. Am. J. Ind. Med. 38: 255-270.
34 Wood, N.; Bourque, K.; Donaldson, D. D.; Collins, M.; Vercelli, D.; Goldman, S. J.; Kasaian, M. T. (2004) IL-21
35 effects on human IgE production in response to IL-4 or IL-13. Cell. Immunol. 231: 133-145.
36 Wozniak, K.; Blasiak, J. (2003) In vitro genotoxicity of lead acetate: induction of single and double DNA strand
37 breaks and DNA-protein cross-links. Mutat. Res. 535: 127-139.
38 Wright, R. O.; Shannon, M. W.; Wright, R. J.; Hu, H. (1999) Association between iron deficiency and low-level
39 lead poisoning in an urban primary care clinic. Am. J. Public Health 89: 1049-1053.
40 Wright, R. O.; Silverman, E. K.; Schwartz, J.; Tsaih, S.-W.; Senter, J.; Sparrow, D.; Weiss, S. T.; Aro, A.; Hu, H.
41 (2004) Association between hemochromatosis genotype and lead exposure among elderly men: the
42 Normative Aging Study. Environ. Health Perspect. 112: 746-750.
43 Wu, T.; Buck, G. M.; Mendola, P. (2003) Blood lead levels and sexual maturation in U.S. girls: the Third National
44 Health and Nutrition Examination Survey, 1988-1994. Environ. Health Perspect. Ill: 737-741.
45 Wu, W.; Rinaldi, L.; Fortner, K. A.; Russell, J. Q.; Tschoop, J.; Irvin, C.; Budd, R. C. (2004) Cellular FLIP long
46 form-transgenic mice manifest a Th2 cytokine bias and enhanced allergic airway inflammation. J.
47 Immunol. 172: 4724-4732.
48 Xie, Y.; Chiba, M.; Shinohara, A.; Watanabe, H.; Inaba, Y. (1998) Studies on lead-binding protein and interaction
49 between lead and selenium in the human erythrocytes. Ind. Health 36: 234-239.
50 Xie, L.; Gao, Q.; Xu, H. (2003) Ameliorative effect of L-methionine on Pb-exposed mice. Biol. Trace Elem. Res.
51 93:227-236.
52 Xie, H.; Wise, S. S.; Holmes, A. L.; Xu, B, Wakeman, T. P.; Pelsue, S. C.; Singh, N. P.; Wise, J. P., Sr. (2005)
53 Carcinogenic lead chromate induces DNA double-strand breaks in human lung cells. Mutat. Res.
54 586: 160-172.
May 2006 5-343 DRAFT-DO NOT QUOTE OR CITE
-------
1 Xu, D. X.; Shen, H. M; Zhu, Q. X.; Chua, L.;, Wang, Q. N.; Chia, S. E.; Ong, C. N. (2003) The associations among
2 semen quality, oxidative DNA damage in human spermatozoa and concentrations of cadmium, lead and
3 selenium in seminal plasma. Mutat. Res. 534: 155-163.
4 Yamamoto, C.; Miyamoto, A.; Sakamoto, M.; Kaji, T.; Kozuka, H. (1997) Lead perturbs the regulation of
5 spontaneous release of tissue plasminogen activator and plasminogen activator inhibitor-1 from vascular
6 smooth muscle cells and fibroblasts in culture. Toxicology 117: 153-161.
7 Yanez, L.; Garcia-Nieto, E.; Rojas, E.; Carrizales, L.; Mejia, I; Calderon, I; Razo, L; Diaz-Barriga, F. (2003) DNA
8 damage in blood cells from children exposed to arsenic and lead in a mining area. Environ. Res.
9 93:231-240.
10 Yang, Y.; Ma, Y.; Ni, L.; Zhao, S.; Li, L.; Zhang, I; Fan, M.; Liang, C.; Cao, I; Xu, L. (2003) Lead exposure
11 through gestation-only caused long-term learning/memory deficits in young adult offspring. Exp. Neurol.
12 184:489-495.
13 Ye, S.-H. (1993) Hypoxanthine phosphoribosyl transferase assay of lead mutagenicity on keratinocytes. Zhongguo
14 YaoliXuebao 14: 145-147.
15 Youssef, S. A. H. (1996) Effect of subclinical lead toxicity on the immune response of chickens to Newcastle's
16 disease virus vaccine. Res. Vet. Sci. 60: 13-16.
17 Yu, S. Y.; Mizinga, K. M.; Nonavinakere, V. K.; Soliman, K. F. (1996) Decreased endurance to cold water
18 swimming and delayed sexual maturity in the rat following neonatal lead exposure. Toxicol. Lett.
19 85: 135-141.
20 Yticesoy, B.; Turhan, A.; tire, M.; imir, T.; Karakaya, A. (1997) Simultaneous effects of lead and cadmium on NK
21 cell activity and some phenotypic parameters. Immunopharmacol. Immunotoxicol. 19: 339-348.
22 Yun, S.-W.; Lannert, H.; Hoyer, S. (2000a) Chronic exposure to low-level lead impairs learning ability during aging
23 and energy metabolism in aged rat brain. Arch. Gerontol. Geriatr. 30: 199-213.
24 Yun, S. W.; Gartner, U.; Arendt, T.; Hoyer, S. (2000b) Increase invulnerability of middle-aged rat brain to lead by
25 cerebral energy depletion. Brain Res. Bull. 52: 371-378.
26 Zareba, G.; Chmielnicka, J. (1992) Disturbances in heme biosynthesis in rabbits after administration per os of low
27 doses of tin or lead. Biol. Trace Elem. Res. 34: 115-122.
28 Zawia, N. H.; Basha, M. R. (2005) Environmental risk factors and the developmental basis for Alzheimer's disease.
29 Rev. Neurosci. 16: 325-337.
30 Zelikoff, J. T.; Li, J. H.; Hartwig, A.; Wang, X. W.; Costa, M.; Rossman, T. G. (1988) Genetic toxicology of lead
31 compounds. Carcinogenesis 9: 1727-1732.
32 Zelikoff, J. T.; Parsons, E.; Schlesinger, R. B. (1993) Inhalation of paniculate lead oxide disrupts pulmonary
3 3 macrophage-mediated functions important for host defense and tumor surveillance in the lung. Environ.
34 Res. 62: 207-222.
35 Zenick, H.; Rodriquez, W.; Ward, J.; Elkington, B. (1979) Deficits in fixed-interval performance following prenatal
36 and postnatal lead exposure. Dev. Psychobiol. 12: 509-514.
37 Zhao, W.-F.; Ruan, D.-Y.; Xy, Y.-Z.; Chen, J.-T.; Wang, M.; Ge, S.-Y. (1999) The effects of chronic lead exposure
38 on long-term depression in area CA1 and dentate gyrus of rat hippocampus in vitro. Brain Res.
39 818: 153-159.
40 Zheng, W.; Shen, H.; Blaner, W. S.; Zhao, Q.; Ren, X.; Graziano, J. H. (1996) Chronic lead exposure alters
41 transthyretin concentration in rat cerebrospinal fluid: the role of the choroid plexus. Toxicol. Appl.
42 Pharmacol. 139: 445-450.
43 Zhou, M.; Suszkiw, J. B. (2004) Nicotine attenuates spatial learning deficits induced in the rat by perinatal lead
44 exposure. Brain Res. 999: 142-147.
45 Zhou, J.; Xu, Y.-H.; Chang, H.-F. (1985) The effects of lead ion on immune function of rabbit alveolar
46 macrophages: quantitation of immune phagocytosis and rosette formation by 51Cr in vitro. Toxicol. Appl.
47 Pharmacol. 78: 484-487.
48 Zhou, X. J.; Vaziri, N. D.; Wang, X. Q.; Silva, F. G.; Laszik, Z. (2002) Nitric oxide synthase expression in
49 hypertension induced by inhibition of glutathione synthase. J. Pharmacol. Exp. Ther. 300: 762-767'.
50 Zierold, K. M.; Anderson, H. (2004) Trends in blood lead levels among children enrolled in the Special
51 Supplemental Nutrition Program for Women, Infants and Children from 1996 to 2000. Am. J. Public
52 Health 94: 1513-1515.
53 Zimmermann, L.; Pages, N.; Antebi, H.; Hafi, A.; Boudene, C.; Alcindor, L. G. (1993) Lead effect on the oxidation
54 resistance of erythrocyte membrane in rat triton-induced hyperlipidemia. Biol. Trace Elem. Res.
55 38:311-318.
May 2006 5-344 DRAFT-DO NOT QUOTE OR CITE
-------
1 Zmuda, J. M; Cauley, J. A.; Ferrell, R. E. (2000) Molecular epidemiology of vitamin D receptor gene variants.
2 Epidemiol. Rev. 22: 203-217.
3 Zuscik, M. J.; Pateder, D. B.; Puzas, J. E.; Schwarz, E. M.; Rosier, R. N.; O'Keefe, R. J. (2002) Lead alters
4 parathyroid hormone-related peptide and transforming growth factor-pi effects and AP-1 and NF-KB
5 signaling in chondrocytes. J. Orthop. Res. 20: 811-818.
6
May 2006 5-345 DRAFT-DO NOT QUOTE OR CITE
-------
i 6. EPIDEMIOLOGIC STUDIES OF HUMAN HEALTH
2 EFFECTS ASSOCIATED WITH LEAD EXPOSURE
3
4
5 6.1 INTRODUCTION
6 This chapter assesses information regarding the biological effects of lead exposure,
7 with emphasis on (1) qualitative characterization of lead-induced effects and (2) delineation of
8 concentration-response relationships for key health effects of most concern. Epidemiologic
9 studies linking lead exposure to health effects were assessed in the 1986 Air Quality Criteria for
10 Lead (U.S. Environmental Protection Agency, 1986a), an associated addendum (U.S.
11 Environmental Protection Agency, 1986b), and a 1990 Supplement (U.S. Environmental
12 Protection Agency, 1990). Environmental exposures to lead result from human contact with
13 multimedia exposure pathways (e.g., air, food, water, surface dust), as discussed extensively in
14 Chapters 3 and 4 of this document. In this chapter, while recognizing the multimedia nature of
15 lead exposure of the general population, exposure to lead is generally represented by tissue lead
16 concentration measured in biomarkers such as blood and bone. Many earlier studies reported
17 lead effects on child development (psychometric intelligence), blood pressure and related
18 cardiovascular endpoints, heme biosynthesis, kidney, and reproduction and development.
19 Numerous more recent epidemiologic studies discussed in this chapter have further evaluated
20 these relationships to lead exposure, thereby providing an expanded basis for assessment of
21 health effects associated with exposure to lead at concentrations currently encountered by the
22 general U.S. population.
23 Special emphasis is placed here on discussion of the effects of lead exposure in children.
24 Children are particularly at risk due to sources of exposure, mode of entry, rate of absorption and
25 retention, and partitioning of lead in soft and hard tissues. The greater sensitivity of children to
26 lead toxicity, their inability to recognize symptoms, and their dependence on parents and
27 healthcare professionals make them an especially vulnerable population requiring special
28 consideration in developing criteria and standards for lead.
29 As discussed elsewhere in this document (Chapter 5), extensive experimental evidence
30 also links lead exposure with health effects in laboratory animals. Thus, many of the reported
31 epidemiologic associations of lead health effects have considerable biological credibility.
May 2006 6-1 DRAFT-DO NOT QUOTE OR CITE
-------
1 Accordingly, the new epidemiologic studies of lead assessed here are best considered in
2 combination with information from the other chapters on lead exposure and on toxicological
3 effects of lead in animals. The epidemiologic studies constitute important information on
4 associations between health effects and exposures of human populations to "real world" lead
5 concentrations and also help to identify susceptible subgroups and associated risk factors.
6
7 6.1.1 Approach to Identifying Lead Epidemiologic Studies
8 Numerous lead epidemiologic papers have been published since completion of the 1986
9 Lead AQCD/Addendum, and 1990 Supplement. A systematic approach has been employed to
10 identify relevant new epidemiologic studies for consideration in this chapter. In general, an
11 ongoing literature search has been used in conjunction with other strategies to identify lead
12 epidemiologic literature pertinent to developing criteria for the National Ambient Air Quality
13 Standards (NAAQS) for lead. A publication base was established using Medline, Pascal,
14 BIOSIS, and Embase, and a set of search terms aimed at identifying pertinent literature.
15 While the above search regime accessed much of the pertinent literature, additional
16 approaches augmented such traditional search methods. For example, a Federal Register Notice
17 was issued requesting information and published papers from the public at large. Also, non-EPA
18 chapter authors, expert in this field, identified literature on their own; and EPA staff also
19 identified publications as part of their assessment and interpretation of the literature. Lastly,
20 additional potentially relevant publications have been identified and included as a result of
21 external review of this draft document by the public and CAS AC. The principal criteria used for
22 selecting literature for the present assessment is to focus mainly on those identified studies that
23 evaluate relationships between health outcome and lead exposure at concentrations in the range
24 of those currently encountered in the United States. New studies published or accepted for
25 publication through December 2005, as identified using the approaches above, have been
26 included in this draft Lead Air Quality Criteria Document (Lead AQCD), and additional efforts
27 are being made to identify and assess more recent studies.
28
29 6.1.2 Approach to Assessing Epidemiologic Evidence
30 Epidemiologic studies have evaluated lead effects on a wide range of health endpoints that
31 include, but are not limited to: neurotoxic effects (e.g., psychometric intelligence, behavioral
May 2006 6-2 DRAFT-DO NOT QUOTE OR CITE
-------
1 disturbances, and neurodevelopmental deficits), renal effects, cardiovascular effects,
2 reproductive and developmental effects, genotoxic and carcinogenic effects, and immune effects.
3 The epidemiologic strategies most commonly used in lead health studies are: (1) cross-sectional
4 studies that examine the exposure and health outcome at a single point in time; and/or
5 (2) prospective longitudinal cohort studies that follow a group of individuals over time.
6 Both of these are types of observational, rather than experimental, studies.
7 An overall approach useful for assessing epidemiologic evidence was stated in the 2004
8 PM AQCD (U.S. Environmental Protection Agency, 2004), as summarized here. That is, the
9 critical assessment of epidemiologic evidence presented in this chapter is conceptually based
10 upon consideration of salient aspects of the evidence of associations so as to reach fundamental
11 judgments as to the likely causal significance of the observed associations (see Hill, 1965). The
12 general evaluation of the strength of the epidemiologic evidence reflects consideration not only
13 of the magnitude and precision of reported lead effect estimates and their statistical significance,
14 but also of the robustness of the effects associations. Statistical significance corresponds to the
15 allowable rate of error (Type I error) in the decision framework constructed from assuming that a
16 simple null hypothesis of no association is true. It is a conditional probability; for statistical
17 significance, typically there is a less than 0.05 chance of rejecting the null hypothesis given that
18 it is true. Robustness of the associations is defined as stability in the effect estimates after
19 considering a number of factors, including alternative models and model specifications, potential
20 confounding by copollutants, as well as issues related to the consequences of measurement error.
21 Consideration of the consistency of the effects associations, as discussed in the following
22 sections, involves looking across the results obtained by various investigators in different
23 populations, locations, and times. Relevant factors are known to exhibit much variation across
24 studies, e.g., (1) presence and levels of other toxicants or pollutants of concern and (2) relevant
25 demographic factors related to sensitive subpopulations. Thus, consideration of consistency is
26 appropriately understood as an evaluation of the similarity or general concordance of results,
27 rather than an expectation of finding quantitative results within a very narrow range.
28 Looking beyond the epidemiologic evidence, evaluation of the biological plausibility of
29 the lead-health effects associations observed in epidemiologic studies reflects consideration of
30 both exposure-related factors and dosimetric/toxicologic evidence relevant to identification of
31 potential biological mechanisms underlying the various health outcomes. These broader aspects
May 2006 6-3 DRAFT-DO NOT QUOTE OR CITE
-------
1 of the assessment are only touched upon in this chapter but are more fully addressed and
2 integrated in Chapter 7 (Integrative Synthesis) discussions.
3 In assessing the relative scientific quality of epidemiologic studies reviewed here and to
4 assist in interpreting their findings, the following considerations were taken into account:
5 (1) To what extent are the biological markers used of adequate quality and sufficiently
6 representative to serve as credible exposure indicators, well-reflecting interpersonal
7 differences in exposure for specified averaging times?
8 (2) Were the study populations well defined and adequately selected so as to allow
9 for meaningful comparisons between study groups or meaningful temporal analyses
10 of health effects results?
11 (3) Were the health endpoint measurements meaningful and reliable, including clear
12 definition of diagnostic criteria utilized and consistency in obtaining dependent
13 variable measurements?
14 (4) Were the statistical analyses used appropriate, as well as being properly performed
15 and interpreted?
16 (5) Were likely important covariates (e.g., potential confounders or effect modifiers)
17 adequately controlled for or taken into account in the study design and statistical
18 analyses?
19 (6) Were the reported findings internally consistent, biologically plausible, and coherent
20 in terms of consistency with other known facts?
21 These guidelines provide benchmarks for judging the relative quality of various studies
22 and in assessing the overall body of epidemiologic evidence. Detailed critical analysis of all
23 epidemiologic studies on lead health effects, especially in relation to all of the above questions,
24 is beyond the scope of this document.
25
26 6.1.3 Considerations in the Interpretation of Epidemiologic Studies of
27 Lead Health Effects
28 Prior to assessing results from recent lead epidemiologic studies, issues and questions
29 arising from study designs and analysis methods used in the evaluation of lead health effects are
30 first briefly discussed here. Study design can restrict the health effect parameters that can be
31 estimated. Separate considerations need to be made for acute versus chronic effect studies, as
32 well as individual versus aggregate-level analyses. Issues include measurement error, the
33 functional form of relationships (especially at low exposure levels) and the potential for
May 2006 6-4 DRAFT-DO NOT QUOTE OR CITE
-------
1 confounding. Aspects of these issues are briefly noted below, then are considered as various
2 studies are reviewed in the following sections on specific health effect endpoints. Finally, they
3 are further examined as part of the interpretive assessment (Section 6.10) at the end of this
4 chapter.
5 Measurement error is an important factor to consider, both for measurement of the health
6 effect outcome and the representativeness of the biomarkers of exposure (principally blood and
7 bone lead) used in most key epidemiologic studies. For health outcome measures, the reliability
8 and validity of the measurements need to be assessed. In addition, the appropriateness of the
9 outcome measure for studying the hypothesis of interest needs to be determined. The critical
10 issues of outcome measurement and classification are, to some extent, endpoint-specific, and are
11 therefore discussed further in ensuing individual sections.
12 Exposure misclassification can result in a notable reduction of statistical power in studies,
13 especially in those that focus on the lower end of the exposure range. Limitations of blood lead
14 as an exposure index include the use of a single blood lead concentration to represent lead body
15 burden. Also of concern is the most relevant blood sample collection time point for to use in
16 evaluating possible associations with health outcomes (e.g., at 2 years of age when peak lead
17 exposure is expected versus concurrent blood lead samples). Another consideration is that
18 similar blood lead concentrations in two individuals do not necessarily reflect similar body
19 burdens. An added complication is that the relationship between lead intake and blood lead
20 concentration appears to be curvilinear. Bone lead determinations are typically considered a
21 measure of longer-term lead exposure; but, the X-ray fluorescence (XRF) method typically used
22 to assess lead levels in bone also has limitations, including the relatively high minimum
23 detection limit. The type of bone measured to determine lead exposure is another important
24 aspect.
25 The relationship between a measurement of a health outcome endpoint and an estimate of
26 lead exposure based on a biomarker is an important concept. Modeling this relationship provides
27 a numerical slope that quantifies the relationship between lead exposure and health outcome.
28 These models must address differences in the relationship at different concentration ranges of
29 exposure and present the functional form that best describes such data. Various models, both
30 linear and nonlinear, have been considered to examine lead exposure-health effect relationships.
May 2006 6-5 DRAFT-DO NOT QUOTE OR CITE
-------
1 This is especially important at low lead exposures. For example, a curvilinear relationship has
2 been reported for neurodevelopmental and cardiovascular outcomes at low lead exposure levels.
3 Depending on the subjects being examined for lead exposure effects, various other factors
4 can lead to confounding of the relationship being considered. Potential confounding factors
5 largely depend on the health outcome of interest and the study population. Some potential
6 confounding factors in children, for whom the major health concerns include neurological and
7 developmental deficiencies, include: socioeconomic status (SES); nutritional status; quality of
8 home environment (e.g., HOME score); parental education; parental IQ; and birth weight, as a
9 few examples. For adults, factors that may confound the association between lead and
10 cardiovascular health outcomes include: age; diet; alcohol use; smoking; and potential for
11 copollutant exposures, such as cadmium. For adult neurotoxic effects, potential confounders
12 include age, education, depressive symptoms, medications, alcohol use and smoking. Also,
13 given that lead-related cognitive deficits in adults tend to be specific, not generalized, vocabulary
14 and reading ability, which correlate highly with year of education and are predictors of
15 performance on other specific cognitive tests, also may serve as confounders or modifiers of lead
16 effects on adult cognitive function. Control for potential confounding factors can be attempted at
17 the study design phase and/or during statistical analysis. Confounding is discussed in the text
18 throughout the chapter when appropriate and also in Section 6.10.6.
19
20 6.1.4 Approach to Presenting Lead Epidemiologic Evidence
21 In the main body of this chapter, each section starts by concisely highlighting important
22 points derived from the 1986 Lead AQCD/Addendum and the 1990 Supplement. Particular
23 emphasis is focused on studies and analyses that provide pertinent information of importance for
24 the critical assessment of health risks from lead exposure. Not all studies are accorded equal
25 weight in the overall interpretive assessment of evidence regarding lead-associated health effects.
26 Among well-conducted studies with adequate control for confounding, increasing scientific
27 weight is accorded in proportion to the precision of their effect estimates. To ensure a thorough
28 appraisal of the evidence, more detailed information on key features (including study design,
29 analysis, lead biomarkers of exposure, and health outcome results) of important new studies are
30 summarized in tables in the Annex for this Chapter 6 (Annex AX6).
May 2006 6-6 DRAFT-DO NOT QUOTE OR CITE
-------
1 In the main body text discussion, emphasis is placed on (1) new studies employing
2 standardized methodological analyses for evaluating lead effects across different study
3 populations and providing overall effect estimates based on combined analyses of information
4 pooled across different cohort groups; (2) meta-analyses of individual studies conducted in
5 various study populations; (3) studies assessing lead health effects at current relevant levels of
6 exposure (e.g., blood lead levels <10 |ig/dL); and (4) studies conducted in the U.S. Multiple
7 cohort studies are of particular interest and value due to their evaluation of a wider range of lead
8 exposures and large numbers of observations, thus generally providing more precise effect
9 estimates than most smaller scale studies of single cohorts. Furthermore, multiple cohort studies
10 have the potential to provide especially valuable evidence regarding relative homogeneity and/or
11 heterogeneity of lead health effects relationships between different study populations. Also of
12 particular interest in recent years are those health effects observed at the lower range of lead
13 exposure, as typically assessed using blood lead levels. The potential impacts of the underlying
14 health status of populations and cultural differences in the case of intelligence testing (one of the
15 major health outcomes in children) also need to be accounted for in the assessment; thus, U.S.
16 studies are emphasized over non-U.S. studies. In accordance with the emphasis placed on the
17 lead epidemiologic studies in this chapter, Chapter 6 Annex tables are organized by emphasis on
18 multiple cohort studies and U.S. studies.
19 In the ensuing sections, epidemiological studies of the neurotoxic effects of lead exposure
20 in children are discussed first, in Section 6.2. The neurotoxic effects of lead on adults are
21 discussed next in Section 6.3, followed by discussion of the renal and cardiovascular effects of
22 lead in Sections 6.4 and 6.5. Section 6.6 then discusses reproductive and developmental effects
23 of lead, Section 6.7 discusses genotoxic and carcinogenic effects of lead, and Section 6.8
24 discusses lead effects on the immune system. Lead effects on other organ systems (including the
25 hematopoietic, endocrine, hepatic, gastrointestinal, and respiratory systems) are assessed in
26 Section 6.9. Lead effects on bone and teeth, as well as on ocular health, are also discussed in
27 Section 6.9. Finally, Section 6.10 provides an interpretative assessment of the overall
28 epidemiologic evidence for lead health effects.
29
30
May 2006 6-7 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.2 NEUROTOXIC EFFECTS OF LEAD IN CHILDREN
2 This section assesses epidemiologic evidence for neurotoxic effects of lead exposure in
3 children. First presented are studies of the neurotoxic effects of lead on children, with a focus on
4 several prospective studies examining neurocognitive ability. Other topics include measures of
5 academic achievement, cognitive abilities, disturbances in behavior, mood, and social conduct,
6 measures of brain anatomical development and activity, gene-environmental interaction, and
7 reversibility of neurodevelopmental deficits. The neurotoxic effects of environmental and
8 occupational lead exposure of adults are then discussed in Section 6.3.
9
10 6.2.1 Summary of Key Findings on Neurotoxic Effects of Lead in Children
11 from 1986 Lead AQCD/Addendum and 1990 Supplement
12 The 1986 Lead AQCD stated that children were particularly susceptible to lead-induced
13 neural damage. In particular, human infants and toddlers below 3 years of age were considered
14 to be at special risk due to possible in utero exposure, increased opportunity for exposure
15 because of normal mouthing behavior of lead-containing obj ects, and increased rates of lead
16 absorption due to factors such as iron and calcium deficiencies.
17 Effective blood lead levels for producing encephalopathy or death in children were noted
18 in the 1986 Lead AQCD as starting at 80-100 |ig/dL. Various types of neural dysfunction were
19 stated as being evident at lower blood lead levels. Behavioral (e.g., reaction time, psychomotor
20 performance) and electrophysiological (e.g., altered electrophysiological patterns, evoked
21 potential measures, and peripheral nerve conduction velocities) effects were observed at blood
22 levels as low as 15-30 |ig/dL and possibly lower. A concentration-response relationship between
23 blood lead levels and IQ also was observed; a 1-2 point difference in IQ was generally seen with
24 blood lead levels in the 15-30 |ig/dL range. However, Schroeder and Hawk (1987) found a
25 highly significant linear relationship between a measure of IQ and blood lead levels over the
26 range of 6 to 47 |ig/dL among a cohort of all African-American children of low SES, suggesting
27 that IQ effects might be detected even at blood lead levels below 15 to 30 |ig/dL.
28 The 1986 Addendum also discussed the newly published results of several prospective
29 cohort studies on the developmental effects of lead in children. These studies improved upon
30 previous studies by utilizing longitudinal study design that followed children from the prenatal
31 stage, larger numbers of subjects, and better analytic techniques to more accurately measure
May 2006 6-8 DRAFT-DO NOT QUOTE OR CITE
-------
1 blood lead levels. The four prospective studies (conducted in Boston, MA; Cincinnati, OH;
2 Cleveland, OH; and Port Pirie, Australia) reported significant associations between prenatal and
3 postnatal blood lead levels and neurobehavioral deficits, after adjusting for various potential
4 confounding factors such as maternal IQ and HOME (Home Observation for Measurement of
5 Environment) scores (Bellinger et al., 1984; Dietrich et al., 1986; Ernhart et al., 1985, 1986;
6 McMichael et al., 1986; Vimpani et al., 1985; Wolf et al., 1985). In these studies, the observed
7 maternal and cord blood lead levels were fairly low, with mean levels of approximately
8 10 |ig/dL. These results led the 1986 Addendum to conclude that neurobehavioral deficits,
9 including declines in Bayley Mental Development Index (MDI) scores and other assessments of
10 neurobehavioral function, are associated with prenatal blood lead exposure levels on the order of
11 10 to 15 |ig/dL and possibly even lower, as indexed by maternal or cord blood lead
12 concentrations.
13 The 1990 Supplement updated evidence from the above-mentioned longitudinal cohort
14 studies and summarized results from other more recent prospective cohort studies conducted in
15 Glasgow, Scotland; Kosovo, Yugoslavia; Mexico City; and Sydney, Australia. Results from
16 several other international cross-sectional studies also were discussed. The collective evidence
17 from the various prospective cohort and cross-sectional studies reaffirmed the conclusions from
18 the 1986 Addendum that neurobehavioral effects were related to blood lead levels of 10 to
19 15 |ig/dL and possibly lower. Further analyses of the Boston data indicated that deficits in MDI
20 could be detected in relation to cord blood lead levels of 6-7 |ig/dL in children within the lower
21 strata for SES (Bellinger et al., 1988). In the Port Pirie study, the relationship between postnatal
22 blood lead levels and MDI at two years of age provided little evidence of a threshold effect
23 (Wigg et al., 1988). Restricting the analysis to children with blood lead levels below 25 |ig/dL
24 yielded an even stronger association between integrated postnatal blood lead and McCarthy
25 General Cognitive Index (GCI) scores in the Port Pirie study (McMichael et al., 1988).
26 Impaired neurobehavioral development was associated with blood lead measures in
27 pregnant women, umbilical cords, and infants up to at least 2 years of age; thus, no distinction
28 could be made as to whether this level of concern applied to only fetuses or infants or preschool-
29 age children. The issue of the persistence of the neurobehavioral effects from low-level lead
30 exposure also was considered. Although the Boston and Cincinnati studies provided limited
May 2006 6-9 DRAFT-DO NOT QUOTE OR CITE
-------
1 evidence suggesting that the effects of prenatal lead exposure on neurobehavioral development
2 were not permanent, the evidence available to support this conclusion was inadequate.
3
4 6.2.2 Introduction to Neurotoxic Effects of Lead in Children
5 Several major developments have occurred in lead research on child neurodevelopment
6 following the 1986 Lead AQCD/Addendum and the 1990 Supplement. First, there has been an
7 attempt to broaden outcome assessments beyond neurocognitive deficits. The earlier emphasis
8 on neurocognitive measures (e.g., MDI, GCI, IQ) in previous studies is understandable from the
9 perspectives of the strong psychometric properties of most of these rigorously standardized
10 measures as well as the immediate pubic health concerns. Examples of other outcomes used to
11 assess neurodevelopment include the number of errors on tests of visual-motor integration, the
12 time required to complete a task assessing manual dexterity, the number of errors and false
13 alarms on a continuous performance test, and the efficiency of short term memory. Additional
14 neurodevelopment outcomes include those which elucidate brain-behavior relationships or the
15 potential real life consequences of early exposure to lead, such as academic and vocational
16 failure and maladjustment to the daily demands of living in a complex society. Thus,
17 epidemiologic studies of lead neurotoxicity have been expanded to adopt measures of academic
18 achievement, specific cognitive abilities, behavior and mood, sensory acuities, neuromotor
19 function, and direct measures of brain anatomical development and activity. Another
20 development has been the initiation of nutritional and pharmacological intervention studies to
21 assess the impact of treatment on reducing blood lead levels and preventing or moderating the
22 degree of harm to the central nervous systems of young children. Also, in addition to blood and
23 tooth lead, bone lead has emerged as a reliable biomarker of lead exposure. The technology for
24 the assessment of lead in cortical (tibial) and trabecular (patellar) bone using K-shell X-ray
25 fluorescence (XRF) has advanced to the point where it could be applied as a reliable and valid
26 index of cumulative lead dose in neuroepidemiologic studies (Aro et al., 1994).
27 In recent years, more studies have investigated the impact of blood lead levels below
28 10 |ig/dL on the developing brain. Average blood lead levels in U.S. children ages one to five
29 years decreased from 15 |ig/dL to approximately 3 |ig/dL between 1976-1980 and 1991-1994,
30 allowing newer studies to examine the effects of low level lead on the neurodevelopment of
31 children (Centers for Disease Control, 2000; Pirkle et al., 1998).
May 2006 6-10 DRAFT-DO NOT QUOTE OR CITE
-------
1 At the time of the last previous criteria review, it was recognized that estimating a
2 threshold for toxic effects of lead on the central nervous system entailed a number of difficulties.
3 As discussed in the 1990 Supplement, insults to the human brain may be irreversible, making it
4 difficult to determine whether any measured insult is the result of current or past exposures.
5 An observed effect concurrent with a measured blood lead concentration may be the result of
6 exposure in the child's earlier life in the womb or infancy. There is also the critical question of
7 reversibility or the persistence of lead effects identified in infants and preschoolers into school
8 age and later. A given effect observed at younger ages may not persist due to functional
9 compensation or a return to a normal neuromaturational trajectory (Dietrich et al., 1990).
10 Another problem is that it is sometimes difficult to distinguish between neurobehavioral effects
11 due to lead and effects owing to the many social, economic, urban-ecological, nutritional, and
12 other medical factors that are known to have important effects on neurobehavioral development.
13 Equally important is the high probability that the concentration-response relationship and even
14 the neurobehavioral lesion associated with childhood lead exposure may vary as a function of
15 these cofactors (Bellinger, 1995).
16 In the following sections, prospective cohort studies and cross-sectional studies of
17 neurocognitive ability published since the 1990 Supplement are first discussed. Then, studies
18 examining the effect of lead on a variety of neurodevelopmental outcomes, including academic
19 achievement; specific cognitive abilities; disturbances in behavior, mood, and social conduct;
20 sensory acuities; neuromotor function; and brain anatomical development and acuity, are
21 discussed. This is followed by discussion of several issues involved in understanding lead
22 neurotoxicity in children, including gene-environment interactions, reversibility of lead effects,
23 times of vulnerability, and potential threshold levels for effects.
24
25 6.2.3 Neurocognitive Ability
26 6.2.3.1 Prospective Longitudinal Cohort Studies of Neurocognitive Ability
27 Several prospective longitudinal cohort studies were initiated in the 1980s because it
28 became widely recognized that the cross-sectional study design was inadequate to address a
29 number of research issues (U.S. Environmental Protection Agency, 1986a; World Health
30 Organization, 1977). These longitudinal studies were characterized by serial measures of dose
31 (blood lead levels) spanning (in most cases) the prenatal and postnatal periods of central nervous
May 2006 6-11 DRAFT-DO NOT QUOTE OR CITE
-------
1 system development, thus helping to clarify the temporal association between exposure and
2 insult. Also, developmental assessments that extended into the school-age period were planned
3 to determine if early lead associated neurobehavioral impairments were permanent or reversible
4 in the fullness of time. It was also determined that assessment of potential confounding factors
5 should be comprehensive and include measures of perinatal health, nutrition, maternal
6 consumption of other neurotoxicants during pregnancy, parental intelligence, and direct
7 observations of parenting behavior. These studies were also characterized by very careful
8 attention to biostatistical issues and strategies (Bellinger, 1995; Ernhart, 1995).
9 At the time of the 1990 Supplement, studies were underway or planned in the United
10 States, Australia, Scotland, the former Yugoslavia, and Mexico. These cohorts differed in the
11 source and degree of lead exposure and in other important aspects, notably ethnicity and SES.
12 Nevertheless, the early results from several of these studies have been largely responsible for the
13 emergence of the current perspective that blood lead concentrations as low as 10 |ig/dL, or
14 perhaps even lower, may pose a risk for neurodevelopmental toxicity (Davis and Svendsgaard,
15 1987; U.S. Environmental Protection Agency, 1990). Most of the prospective studies underway
16 in 1990 continued to follow their subjects into the later preschool and school age years with age-
17 appropriate measures of intelligence. Continued follow-up of these cohorts was important due to
18 the following: (1) greater reliability and precision of measurements attained with assessments of
19 older children; (2) high predictability of adult intellectual functioning from measures of IQ in the
20 older child; and (3) examination of potential effects of lead on important abilities that cannot be
21 easily tapped during infancy such as executive functions and higher order reasoning (McCall,
22 1979).
23 A unique aspect of this research was that most investigators agreed during the formative
24 stages of their projects to develop somewhat similar assessment protocols (Bornschein and
25 Rabinowitz, 1985). This has facilitated comparison of results across studies and allowed for
26 sophisticated meta- and pooled-analyses of these data (e.g., Pocock et al., 1994; Schwartz, 1994;
27 World Health Organization, 1995; Lanphear et al., 2005; Rothenberg and Rothenberg, 2005).
28 In the following sections, further updates on the individual prospective cohort studies are
29 presented in chronological order of study initiation. The prospective cohort studies reviewed are
30 summarized in Annex Table AX6-2.1. Results of the meta- and pooled-analyses are presented
31 later in this section.
May 2006 6-12 DRAFT-DO NOT QUOTE OR CITE
-------
1 Boston Study
2 In the 1986 Addendum, the most advanced investigation at that time was the Boston
3 Prospective Study (Bellinger et al., 1984). The subjects were 216 middle-to upper-middle-class
4 Boston children, 90% of whom had cord blood lead levels below 16 |ig/dL (maximum
5 25 |ig/dL). (The children in this cohort were generally of high SES standing. While this might
6 limit generalization of results to a wide population, this study enhanced the ability to isolate the
7 effect of low level lead exposure on cognitive function, as there were no associations between
8 cord blood lead level and several indicators of social disadvantage (e.g., receipt of public
9 assistance, lower educational achievement, unmarried) in this highly selected subsample.
10 Cord-blood lead levels in the "high" group (mean 14.6 |ig/dL) were associated with lower
11 covariate-adjusted scores on the Mental Development Index (MDI) of the Bayley Scales of
12 Infant Development (BSID) at 6 months of age. It was concluded that although lower level lead
13 exposure in utero may result in delays in early sensorimotor development, the Boston results
14 did not allow estimation of the persistence of these effects nor the public health significance of
15 the findings.
16 In the 1990 Supplement, particular attention was focused on the Boston study, which was
17 among the more mature in terms of follow-up (Bellinger et al., 1987, 1991). With respect to the
18 effects of cord blood lead concentrations on MDI assessed longitudinally from 6 to 24 months,
19 the lead-associated deficits were evident across the entire range of blood lead levels starting at
20 10 |ig/dL, which reinforced the previous designation of 10-15 |ig/dL as a blood level of concern
21 for early neurodevelopmental deficits. At ~5 years of age, significant associations of McCarthy
22 GCI with the cord blood lead level (effect estimates not provided) and concurrent blood lead
23 level (-2.26 points [95% CI: -6.0, 1.4] per one unit increase in In blood lead) were not
24 observed, but the blood lead level at 2 years of age (mean 6.8 |ig/dL [SD 6.3]) was significantly
25 associated with lower scores (-2.95 points [95% CI: -5.7,-0.2]). Boston investigators also
26 examined the relationship between lead measured in shed deciduous teeth obtained from
27 102 children in their cohort (mean 2.8 ppm [SD 1.7]) and GCI at 5 years of age. Prior to
28 covariate-adjustment, there was a very strong and significant relationship amounting to a
29 decrement of 10.04 points (95% CI: 2.6, 17.4) in GCI for each unit increase in In dentine lead.
30 However, in the multivariable analysis the tooth lead coefficient, the effect estimate decreased to
31 -2.51 points (95% CI: -10.2, 5.2) per unit increase in In dentine lead.
May 2006 6-13 DRAFT-DO NOT QUOTE OR CITE
-------
1 Since the 1990 Supplement, the Boston investigators reexamined 148 of their subjects at
2 10 years of age with the Wechsler Intelligence Scale for Children-Revised (WISC-R) and other
3 neurobehavioral assessments (Bellinger et al., 1992). They examined the association of WISC-R
4 scores at 10 years of age with blood lead concentrations in the cord blood and at 6 months,
5 12 months, 18 months, 24 months, 57 months, and 10 years. Only blood lead levels at
6 24 months were significantly associated with full scale and verbal IQ and marginally associated
7 with performance IQ, after adjusting for HOME score, maternal age, birth weight, and maternal
8 IQ. The integrated average blood lead level in this cohort over the first 2 years was 7.0 |ig/dL
9 (range 4-14 |ig/dL). An increase of 10 |ig/dL in blood lead level at age 2 was associated with a
10 decrement of 5.8 points (95% CI: 1.8, 9.9) in full scale IQ. These findings indicated that
11 children's performance was much more strongly associated with blood lead levels at age 2 than
12 with blood lead levels at other ages. It is unclear whether this reflects (1) a special vulnerability
13 of the nervous system during this period; (2) the typical peaking of blood lead levels in the
14 second year; or (3) random chance.
15 A reanalysis involving the total Boston cohort that employed nonparametric smoothing
16 revealed that the inverse association persisted at blood lead levels below 5 |ig/dL (Schwartz,
17 1994). Bellinger and Needleman (2003) reanalyzed data on 48 children whose measured blood
18 lead concentrations never exceeded 10 |ig/dL. Reduction in full scale IQ at 10 years was
19 significantly associated with blood lead levels at 2 years of age following covariate adjustment.
20 A larger deficit of 15.6 points (95% CI not presented) per 10 |ig/dL increase in blood lead levels
21 was observed in this cohort, compared to the 5.8 point deficit observed in the entire cohort.
22 These findings indicated that the inverse slope might be steeper at blood lead levels below
23 10 |ig/dL.
24
25 Cincinnati Study
26 Interim results on a partial sample of 185 subjects from a cohort of 305 were available
27 from the Cincinnati prospective study in the 1986 Addendum and the 1990 Supplement (Dietrich
28 et al., 1986, 1987a). The Cincinnati study investigators reported an inverse relationship between
29 prenatal maternal blood lead levels (mean 8.3 |ig/dL) and 6 month Bayley MDI. This effect was
30 mediated, in part, through lead-associated reductions in birth weight and gestational maturity.
May 2006 6-14 DRAFT-DO NOT QUOTE OR CITE
-------
1 A more complete analysis of the full Cincinnati cohort confirmed these interim findings
2 (Dietrich et al., 1987b).
3 Further updates of the Cincinnati study appeared after the 1990 Supplement. The
4 Kaufman Assessment Battery for Children (KABC) was administered to approximately
5 260 children at 4 and 5 years of age (Dietrich et al., 1991; 1992). The principal findings at
6 4 years were that higher neonatal blood lead concentrations were associated with poorer
7 performance on all KABC subscales. However, this relationship was confined to children from
8 the poorer families. Following full covariate adjustment, few statistically significant
9 relationships remained. At 5 years of age, postnatal blood lead levels were associated with
10 performance on all subscales of the KABC; however, few statistically significant relationships
11 remained after adjustment for covariates. Nevertheless, it is of interest that at both 4 and 5 years
12 the KABC subscale that assessed visual-spatial skills was among those that remained the most
13 highly associated with various indices of postnatal exposure following covariate adjustment.
14 At ~7 years, 253 children in the Cincinnati cohort were administered the WISC-R
15 (Dietrich et al., 1993a). In this cohort, approximately 35% had at least one blood lead
16 concentration >25 |ig/dL, whereas 95% exceeded 10 |ig/dL sometime during the first 5 years
17 of life. Postnatal blood lead concentrations were inversely associated with full scale and
18 performance IQ, after adjusting for HOME score, maternal IQ, birth weight, birth length, child
19 gender, and cigarette consumption during pregnancy. Figure 6-2.1 presents the unadjusted and
20 adjusted concentration-response relationship between lifetime average blood lead concentrations
21 and performance IQ. Following covariate adjustment, a statistically significant relationship was
22 observed between postnatal blood lead levels at 5 and 6 years of age and full scale IQ. Postnatal
23 blood lead levels at nearly all ages (including the integrated average blood lead level) were
24 inversely associated with performance IQ. Due to the high intercorrelation among blood lead
25 measures taken at different time points, it was not practical to examine exposures during any
26 given year for evidence of a sensitive neurodevelopmental period. Concurrent blood lead levels
27 were strongly associated with full scale IQ (-3.3 points [95% CI: -6.0, -0.6] for each 10 |ig/dL
28 increase in blood lead level) and performance IQ (-5.2 points [95% CI: -8.1, -2.3]).
29 A 10 |ig/dL increase in lifetime average blood lead concentration was associated with a 2.6 point
30 (95% CI: 0.2, 5.0) decline in performance IQ.
May 2006 6-15 DRAFT-DO NOT QUOTE OR CITE
-------
100
g
0)
(o
E
I
0)
CL
(0
o
95
90
« 85
o
I
80
O Unadjusted p < 0.004
• Adjusted p < 0.05
JL
1234
0-10 >10-15 >15-20 >20
Average Lifetime Blood Lead (ng/dL)
Figure 6-2.1. Unadjusted and adjusted relationships between average lifetime blood lead
concentrations and Wechsler Scale performance IQ. Mean + SD lifetime
average blood lead concentrations within each category were as follows:
0-10 ug/dL, 7.7 ± 1.4 ug/dL (n = 68); >10-15 ug/dL, 12.3 ± 1.4 ug/dL (n = 89);
>15-20 ug/dL, 17.1 ± 1.2 ug/dL (n = 53); and >20 ug/dL, 26.3 ± 5.0 ug/dL
(n =
Source: Dietrich et al. (1993a).
1 At 15 to 17 years of age, the Cincinnati subjects were administered a comprehensive
2 neuropsychological battery (Ris et al., 2004). Variables derived from the Cincinnati
3 neuropsychological battery were subjected to a principal components factor analysis that yielded
4 five factors, including a learning/IQ factor that had high loadings for the Vocabulary and Block
5 Design subtests from the WISC-III as well as the Reading, Spelling, and Arithmetic subscales of
6 the Wide Range Achievement Test-Revised (WRAT-R). Prenatal, Average Childhood, and
7 78 month blood lead levels were used in a series of multiple regression analyses. Following
8 covariate-adjustment, there was a trend towards significance for higher blood lead concentrations
9 in later childhood (e.g., 78 months) to be associated with lower learning/IQ factor scores, but this
May 2006
6-16
DRAFT-DO NOT QUOTE OR CITE
-------
1 was largely observed in subjects from the lower end of the SES scale in the sample. This finding
2 is consistent with previous reports that children in the lower social strata may be more vulnerable
3 to general effects on cognitive development and learning (Bellinger, 2000; Winneke and
4 Kraemer, 1984).
5
6 Cleveland Study
1 Early results of the Cleveland prospective study also were reviewed in the 1986
8 Addendum and 1990 Supplement. By selection, about half of the mothers had histories of
9 alcohol abuse as measured by the Michigan Alcoholism Screening Test. The other women were
10 matched controls. Through repeated interviews during pregnancy, detailed information
11 regarding maternal alcohol use, smoking, and the use of marijuana and other illicit drugs was
12 obtained. While alcohol use was correlated with maternal blood lead levels, and smoking was
13 correlated with both cord and maternal blood lead levels, no correlations were observed between
14 use of marijuana or other illicit drugs and any blood lead marker. The initial cohort included
15 389 infants with a mean cord blood lead level of 5.8 |ig/dL (maximum 14.7). In addition to size,
16 minor morphological anomalies, and 1- and 5-minute Apgar performances, infants were
17 evaluated on the Brazelton Neonatal Behavioral Assessment Scale (NBAS) and part of the
18 Graham-Rosenblith Behavioral Examination for Newborns (G-R). Of the 17 neonatal outcomes
19 examined, the neurological soft signs assessed by G-R were associated with cord blood lead
20 levels in the range of 3 to 15 |ig/dL following covariate adjustment (Ernhart et al., 1986).
21 A follow-up study observed a significant effect for the neurological soft signs measure on Bayley
22 MDI scores at 12 months (Wolf et al., 1985).
23 In 285 children from the original cohort, maternal and cord blood lead levels, as well as
24 postnatal blood lead levels at 6 months, 2 years, and 3 years were examined in relation to Bayley
25 MDI, Psychomotor Index (PDI), and Kent Infant Development Scale (KID) at 6 months, MDI at
26 1 year and 2 years, and Standford-Binet IQ (S-B IQ) at 3 years of age (Ernhart et al., 1987,
27 1988). The increment in variance of the IQ that can be attributed to the blood lead level was
28 presented as the effect estimate. Most blood lead indices (maternal, cord, and postnatal up to
29 3 years) were negatively correlated with the various neurodevelopmental outcomes. However,
30 only maternal blood lead level at delivery (mean 6.5 |ig/dL [maximum 11.8]) was found to
31 contribute to the variance of MDI, PDI, and KID scores at 6 months after adjustment for various
May 2006 6-17 DRAFT-DO NOT QUOTE OR CITE
-------
1 covariates, including HOME score, maternal IQ, parent education, race, medical problems,
2 maternal alcohol use in pregnancy, Michigan Alcoholism Screening Test score, maternal use of
3 marijuana, and several categories of psychosocial trauma scale. Language development also was
4 assessed in the Cleveland cohort at 1,2, and 3 years of age.
5 Once again, correlations between blood lead measures and speech/language outcomes
6 were generally negative, but none of the relationships remained significant after covariate
7 adjustment (Ernhart and Greene, 1990).
8 The relationship between blood lead levels at 2 years of age with the MDI at 2 years, S-B
9 IQ at 3 years, and Wechsler Preschool and Primary Scale of Intelligence (WPPSI) test at 4 years
10 and 10 months of age was further examined (Greene et al., 1992). The effect estimates ranged
11 from -11.2 to -14.6 point declines (95% CI not provided) in IQ scores for the three tests with an
12 increase in 2-year blood lead from 10 to 25 |ig/dL. After adjusting for the various covariates,
13 effect estimates decreased to -0.36 to -1.79 point declines for the same incremental change in
14 blood lead levels.
15 The association between dentine lead and IQ scores were also examined in this cohort
16 (Greene and Ernhart, 1993). In 164 children, shed deciduous incisors were collected between
17 ages 5 and 7 years. Circumpulpal dentine lead levels were found to be significantly associated
18 with full scale, verbal and performance IQ, assessed using the WPPSI test, at 4 years and 10
19 months, after adjustment for various covariates except for HOME score. After additional
20 adjusting for HOME score, the effect estimates for all three IQ measures diminished, but
21 remained statistically significant for verbal IQ (p = 0.01) and marginally significant for full scale
22 IQ (p = 0.06). An increase in dentine lead from the 10th percentile to the 90th percentile level
23 (13.5 |ig/g to 129.4 |ig/g) was associated with a 6.0 point (95% CI: 1.4, 10.6) decrease in verbal
24 IQ and a 4.5 point (95% CI: -0.2, 9.2) decrease in full scale IQ. Sensitivity analyses indicated
25 that the estimated lead effect was smaller in magnitude when measurement error was ignored.
26 These findings using dentine lead provide stronger evidence of inverse associations between lead
27 exposure and IQ scores compared to the previous analyses of this cohort which indicated that
28 blood lead levels were, generally, not associated with cognitive outcomes after covariate
29 adjustment.
30
May 2006 6-18 DRAFT-DO NOT QUOTE OR CITE
-------
1 Port Pirie, Australia Study
2 Preliminary results from the Port Pirie, Australia study also were described in the 1986
3 Addendum (Vimpani et al., 1985). Lower Bayley MDI scores at 2 years from 592 children were
4 significantly associated with higher integrated postnatal blood lead levels (approximately 20% of
5 the sample had blood lead levels >30 |ig/dL at the time of assessment), but not with maternal
6 prenatal, delivery, or cord blood lead levels. Results of this interim analysis were interpreted
7 with caution since important covariates such as maternal IQ and HOME scores were not
8 available for the entire cohort at the time of the analyses.
9 The Port Pirie cohort study had reported results out to 4 years when the 1990 Supplement
10 was released (McMichael et al., 1988). Following adjustment for covariates, lead concentrations
11 at most postnatal sampling points as well as an integrated average for the 4-year postnatal period
12 were significantly and inversely associated with scores on the McCarthy Scales of Children's
13 Abilities. The GCI scores declined by approximately 4.5 points (95% CI: 0.2, 8.8) for a
14 doubling in blood lead levels. Similar deficits occurred in the perceptual-performance and
15 memory scores. The integrated postnatal blood lead levels among the 537 children in this cohort
16 were among the highest of the prospective studies (geometric mean 19 jig/dL). However, further
17 analyses indicated that the effects observed did not depend on children with the more extreme
18 levels of exposure. The concentration-response relationship between blood lead and GCI was
19 stronger among children with blood lead levels below 25 |ig/dL than it was overall.
20 Of all of the prospective studies of lead and child development, the Port Pirie cohort study
21 was probably among the best positioned to reliably detect effects of low level lead exposure into
22 later childhood owing to its wide range of exposure, large sample size, and lack of extremes in
23 terms of sample social advantage or disadvantage. The WISC-R IQ test was administered to
24 494 children between 7 and 8 years of age (Baghurst et al., 1992). IQ scores were examined in
25 relation to In-transformed blood lead concentration. Following adjustment for covariates there
26 was little association with pre- and perinatal lead exposure assessments. However, significant
27 decrements in full scale and verbal IQ were found to be associated with postnatal blood lead
28 levels. The estimated effect size was a loss of 3.3 points (95% CI: 0.2, 6.5) in full scale IQ and
29 4.0 points (95% CI: 0.7, 7.2) in verbal IQ in association with a doubling of the integrated
30 postnatal blood lead concentration up to three years. In light of the Cincinnati findings, it is of
31 interest that the Block Design subtest of the WISC-R (a measure of visual-spatial abilities),
May 2006 6-19 DRAFT-DO NOT QUOTE OR CITE
-------
1 exhibited the strongest association with lead exposure. Port Pirie investigators also collected
2 deciduous central upper incisors from 262 children in their cohort (McMichael et al., 1994).
3 After covariate adjustment, a significant inverse association was observed between tooth lead
4 concentration and WISC-R full scale IQ at 7 years of age. The adjusted estimated decline in full
5 scale IQ across the tooth lead range from 3 to 22 jig/g (range for 90% of population) was
6 5.1 points (90% CI: 0.2, 10.0). Once again, the Block Design subtest was among the most
7 highly sensitive.
8 Port Pirie children were assessed again at 11 to 13 years of age to examine the persistence
9 of relationships between environmental lead exposure and impacts on intelligence (long et al.,
10 1996). At that age, Port Pirie investigators were able to recall 375 children for IQ assessments.
11 At 11 to 13 years of age, the geometric mean lifetime average blood lead concentration was
12 14.1 |ig/dL. WISC-R scores were significantly and inversely associated with integrated lifetime
13 average blood lead concentrations out to 11 to 13 years. Later blood lead concentrations after
14 3 years of age were more predictive of lower IQ. Mean full scale IQ declined by 3.0 points (95%
15 CI: 0.1, 5.9) for a doubling of lifetime average blood lead concentrations. The authors could
16 find no clear evidence of a threshold level in their data.
17
18 Sydney, Australia Study
19 Unlike Port Pirie, the reports on the Sydney cohort study were consistently negative with
20 respect to the effects of exposure on neurodevelopment (Cooney et al., 1989a,b; McBride et al.,
21 1989). In the 298 mothers and infants sampled, geometric mean blood lead levels at delivery
22 were 9.1 |ig/dL and 8.1 |ig/dL, respectively, with less than 2% in excess of 15 |ig/dL. Mean
23 postnatal blood lead levels peaked at 16.4 |ig/dL when children reached 18 months and then
24 declined to 10.1 |ig/dL at 48 months. No significant, inverse relationships were reported
25 between prenatal or postnatal blood lead concentrations and neurodevelopmental assessments
26 conducted from 6 months through 4 years of age. The McCarthy Scales of Children's Abilities
27 was administered to 207 children at 4 years of age, but no associations with blood lead levels
28 were observed prior to or following covariate-adjustment. As in the case of the Cleveland study,
29 the authors noted that the HOME score was a strong contributor to the neurodevelopmental
30 assessments at all ages. As stated in the 1990 Supplement, this raises the questions of whether
31 lead exposure might have covaried with HOME scores. If so, adjusting for HOME scores would
May 2006 6-20 DRAFT-DO NOT QUOTE OR CITE
-------
1 reduce the statistical power by which to detect postnatal blood lead effects on the neurocognitive
2 measures. It is also noteworthy that the interpretation of the Sydney findings has been
3 complicated by concerns about possible contamination of capillary blood lead samples collected
4 during the early phases of the investigation (Cooney et al., 1989b).
5 The Sydney prospective study further assessed 175 subjects that remained in the study at
6 7 years of age (Cooney et al., 1991). Geometric mean blood lead concentrations peaked at
7 2 years of age (15.2 jig/dL). The geometric mean blood lead level at 7 years of age was
8 7.7 jig/dL. The WISC-R and other neurobehavioral assessments were administered. The
9 adjusted correlations between postnatal blood lead levels and WISC-R scores were consistently
10 negative but nonsignificant at the p < 0.05 level. The r value (units = SD of IQ per SD of blood
11 lead) for the correlation between full scale IQ and concurrent blood lead at age 7 years was
12 -0.06 (95% CI: -0.20,0.09). Sufficient data are not presented in this study to convert the
13 correlation coefficients to a slope estimate. The correlation coefficient is not significantly
14 different from that found by Bellinger et al. (1992) for 57-month-old children (-0.07 [95% CI:
15 -0.23, 0.08]), or by Lanphear et al. (2005) for children aged 4.8 to 10 years (-0.20 [95% CI:
16 -0.28, -0.12]). All correlation coefficients are for full scale IQ and concurrent blood lead
17 concentrations.
18 Results from this follow-up study were consistent with the investigators earlier reports of
19 no association between blood lead levels <15 |ig/dL and developmental deficits among the
20 Sydney cohort children. However, the authors noted that their study was not designed to
21 examine small deficits associated with blood lead levels at this magnitude. They reported that
22 the size of their cohort did not provide sufficient power to detect effects less than 5%. Cooney
23 et al. concluded that results from their study indicate that if developmental deficits do occur at
24 blood lead levels below 25 |ig/dL, the effect size is likely to be less than 5%.
25
26 Mexico City Study (A)
27 Preliminary results of the Mexico City cohort prospective study were presented in the
28 1990 Supplement (Rothenberg et al., 1989). Blood lead levels from 42 mother-infant pairs were
29 measured at 36 weeks of pregnancy (mean 15.0 |ig/dL) and delivery (mean 15.4 |ig/dL), and
30 in the cord blood (mean 13.8 |ig/dL). The Brazelton NBAS was administered to infants at
31 48 hours, 15 days, and 30 days after birth. None of the lead measures were associated with the
May 2006 6-21 DRAFT-DO NOT QUOTE OR CITE
-------
1 NBAS outcomes; however, several differential lead measures (i.e., maternal blood lead at
2 36 weeks of pregnancy minus cord blood lead) were found to be associated with several outcome
3 variables. Increases in the blood lead of the mother during the last month of pregnancy or a cord
4 blood lead level higher than the mother's blood lead level were associated with adverse changes
5 in Regulation of States, Autonomic Regulation, and Gestation Age.
6 Schnaas et al. (2000) further examined the effect of postnatal blood lead level on
7 cognitive development in 112 children with complete data from the Mexico City study. Lead
8 was measured in blood every 6 months from 6 to 54 months. Intellectual status was assessed
9 with the McCarthy GCI. The purpose of the study was to estimate the magnitude of the effect of
10 postnatal blood lead level on the GCI and to determine how the effect varies with the time
11 between blood lead measurements and the neurocognitive assessments. The geometric mean
12 blood lead level between 24 to 36 months was 9.7 |ig/dL (range 3.0 to 42.7). A number of
13 significant interactions were observed between blood lead levels and age of assessment. The
14 greatest effect was found at 48 months, with a decrease of 4.0 points (95% CI not presented) in
15 adjusted GCI score being observed for a doubling of the 24 to 36 month blood lead level. The
16 authors concluded that 4 to 5 years of age (when children are entering school) appears to be a
17 critical period for the manifestation of earlier postnatal blood lead level effects.
18
19 Kosovo, Yugoslavia Study
20 The neurodevelopment results of a large birth cohort study of 577 children in two towns
21 in Kosovo Province, Yugoslavia, were not available at the time of the 1990 Supplement. The
22 study took place in Titova Mitrovica, near the site of a longstanding lead smelter, refinery, and
23 battery plant, and in Pristina, a less exposed community 25 miles to the south. A unique
24 characteristic of this cohort was the high prevalence of anemia secondary to iron deficiency
25 (34% with hemoglobin concentrations <10.5 |ig/dL at 2 years of age). The investigators began
26 providing iron-fortified multivitamin supplements to the entire cohort when the children were
27 between 18 to 38 months of age (Wasserman et al., 1994).
28 Like Port Pirie, this was one of the more highly exposed cohorts. Blood lead levels were
29 obtained during the second trimester, from the umbilical cord at delivery, and postnatally at
30 6-month intervals to 90 months. At birth, geometric mean cord blood lead levels were nearly
31 21 |ig/dL in the smelter area (Wasserman et al., 1992). At age 2 years, geometric mean blood
May 2006 6-22 DRAFT-DO NOT QUOTE OR CITE
-------
1 lead concentrations were 35.5 |ig/dL and 8.4 |ig/dL among infants from Titova Mitrovica and
2 Pristina, respectively.
3 Neurocognitive measures of mental abilities were administered at 2, 4, 7, and 10 to 13
4 years of age. Relationships between these neurocognitive outcomes and log-transformed blood
5 lead levels were assessed. A doubling of blood lead levels at 2 years of age was associated with
6 a covariate-adjusted decline of 1.6 points (95% CI: 0.2, 3.0) in Bayley MDI. Statistically
7 nonsignificant decrements in MDI were associated with blood lead levels measured at all other
8 time points. Iron deficiency anemia also was an independent predictor of lower MDI
9 (Wasserman et al., 1992). When examined at 4 years of age, the geometric mean blood lead
10 concentration of children from the smelter area was 39.9 |ig/dL, whereas the geometric mean for
11 children in the "unexposed" area was 9.6 |ig/dL (Wasserman et al., 1994). Children were
12 administered the McCarthy Scales of Children's Abilities. Higher prenatal and cord blood lead
13 concentrations were associated with lower GCI scores. Following covariate-adjustment, children
14 of mothers with prenatal blood lead levels greater than 20 |ig/dL scored a full standard deviation
15 below children in the lowest exposure group (<5 |ig/dL prenatal blood lead). A statistically
16 significant association also was observed between nearly every blood lead measurement
17 (at 6-month intervals since birth) and GCI. At 4 years of age, a doubling of blood lead levels
18 was associated with a reduction of 2.8 points (95% CI: 1.4, 4.3) on the GCI. The Perceptual-
19 Performance subscale of the McCarthy was found to be most sensitive to lead exposure.
20 When 301 children were examined at 7 years of age with the WISC-III, significant
21 associations were observed between postnatal blood lead concentrations and IQ, with
22 consistently stronger associations between performance IQ and later blood lead measures
23 (Factor-Litvak, 1999). The adjusted intellectual loss associated with a doubling in lifetime
24 average blood lead was 2.7 points (95% CI: 1.7, 3.7) in full scale IQ, 2.8 points (95% CI: 1.7,
25 4.0) in performance IQ, and 2.1 points (95% CI: 1.1, 3.2) in verbal IQ. By 7 years, measures of
26 iron status were no longer significantly associated with IQ.
27 At age 10 to 12 years, 290 subjects with complete data on exposure and covariate factors
28 were again assessed with the WISC-III (Wasserman et al., 2003). However, in addition to well-
29 characterized exposure histories based on serial blood lead assessments, tibial bone lead was also
30 measured using 109Cd based K-shell XRF (Todd et al., 2001) on a representative subsample of
31 167 subjects from both communities. Blood lead and bone lead measurements were highly
May 2006 6-23 DRAFT-DO NOT QUOTE OR CITE
-------
1 correlated in Titova Mitrovica, but not in Pristina. Following covariate-adjustment, average
2 lifetime blood lead level was significantly and negatively related to all components of WISC-III
3 IQ. A doubling of average blood lead concentration was associated with a decrease in full scale,
4 performance, and verbal IQ of 1.6 points (95% CI: 0.4, 2.8), 1.5 points (95% CI: 0.3, 2.8), and
5 1.5 points (95% CI: 0.3, 2.6), respectively. The relationships between bone lead and IQ scores
6 were stronger than those for blood lead, at least in the more highly exposed smelter community.
7 For each doubling of tibial bone lead concentrations, full scale, performance, and verbal IQ
8 decreased by an estimated 5.5, 6.2, and 4.1 points, respectively. The authors also reported that
9 significant associations between tibial lead concentrations and IQ scores persisted despite
10 inclusion of blood lead into the model. The inference drawn from these findings was that
11 associations between bone lead and IQ outcomes may be stronger than those between blood lead
12 measures and IQ.
13
14 Shanghai, China Study
15 A prospective study of low-level prenatal and postnatal exposure was initiated in 1993 by
16 Shen et al. (1998) in Shanghia, China. Pregnant women were recruited from a maternal and
17 child health care facility in the community. Lead levels were determined on 348 cord blood
18 samples. The geometric mean cord blood lead level was 9.2 |ig/dL (range 1.6-17.5); 40.8% of
19 the infants had cord blood lead levels > 10 |ig/dL. Infants were further selected for study on the
20 basis of their cord blood lead concentrations - the low lead group (n = 64) had levels <30th
21 percentile while the high lead group (n = 69) had levels >70th percentile. Mean cord blood lead
22 concentrations in the high lead group and low lead group were 13.4 |ig/dL (SD 2.0) and
23 5.3 |ig/dL (SD 1.4), respectively. At 3, 6, and 12 months, infants were administered the Chinese
24 version of the BSID. Capillary blood samples were collected at each visit to ascertain levels of
25 postnatal exposure. Mean blood lead at 1 year of age was 14.9 |ig/dL (SD 8.7) in the high lead
26 group and 14.4 |ig/dL (SD 7.7) in the low lead group. Postnatal blood lead levels were not
27 significantly different in the high and low lead groups.
28 At all three ages, the Bayley MDI, but not PDI, was associated with cord blood lead
29 groupings following adjustment for covariates, which included a wide range of perinatal,
30 demographic, social, and environmental factors. Postnatal blood lead concentrations were not
31 associated with any Bayley measures. Differences in mean MDI between cord blood lead groups
May 2006 6-24 DRAFT-DO NOT QUOTE OR CITE
-------
1 were 3.4 points at 3 months (p = 0.02), 6.3 points at 6 months (p = 0.03), and 5.2 points at
2 12 months (p = 0.03). The early results of this prospective study are generally in accord with
3 similar investigations in Boston, Cincinnati, and Cleveland. The authors concluded that the
4 adverse effects of prenatal lead exposure on early neurobehavioral development are readily
5 discernible and stable over the first year of life.
6
7 Rochester Study
8 The Rochester prospective study, initiated in 1994, examined the relationship between
9 blood lead levels and IQ at 3 and 5 years of age in 172, predominantly African-American, lower
10 SES children (Canfield et al., 2003a). Participants were enrolled when children were 5 to
11 7 months of age in what was originally a study of lead dust control methods (Lanphear et al.,
12 1999). Blood lead concentrations were assessed at 6-month intervals until 2 years and annually
13 thereafter. No data were available on prenatal exposure. The measure of IQ was the abbreviated
14 Stanford-Binet Intelligence Scale-4th Edition (SBIS-4). Potential confounders assessed included
15 gender, birth weight, iron status, HOME scores, maternal IQ, SES, and tobacco use during
16 pregnancy.
17 Blood lead concentrations in the Rochester cohort were quite low for an urban population,
18 as this study was conducted after public health measures to reduce blood lead levels in children
19 were already having a dramatic impact in the U.S. population. Blood lead levels peaked at
20 2 years of age (mean 9.7 |ig/dL). The mean lifetime average blood lead concentration was
21 7.7 |ig/dL at the age of 3 years and 7.4 |ig/dL at the age of 5 years. At 5 years of age, 56% of the
22 children had a peak blood lead concentration below 10 |ig/dL. Following adjustment for
23 covariates, there were significant inverse associations with full scale IQ at both 3 and 5 years of
24 age for all blood lead variables, including lifetime average up to age of behavioral assessment.
25 The effect of lead on IQ was estimated in all children using lifetime average, peak,
26 concurrent, and average in infancy (6-24 months) blood lead levels. Lead effects on IQ for the
27 subgroup of children whose peak lead concentration never exceeded 10 |ig/dL also was
28 estimated. Table 6-2.1 shows the covariate-adjusted changes in IQ for each 1 |ig/dL increase in
29 blood lead concentration for all children and children with peak blood lead concentrations below
30 10 |ig/dL. In all cases, the effect estimates were larger in the subsample of children with peak
31 blood lead concentrations below 10 |ig/dL. For example, the overall estimate including all
May 2006 6-25 DRAFT-DO NOT QUOTE OR CITE
-------
S Table 6-2.1. Covariate-Adjusted Changes in IQ per 1 ug/dL Increase in Blood Lead Concentration3
to
o
o
ON
to
ON
O
s
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Type of Blood
Lead Measurement
All Children
Lifetime average
Peak
Concurrent
Average in infancy
(6-24 mo)
At 3 Years of Age
n
172
172
171
172
P (95% CI)
-0.35
(-0.69,0.00)
-0.19
(-0.39,0.01)
-0.31
(-0.60, -0.01)
-0.32
(-0.71,0.07)
P
0.05
0.06
0.04
0.10
Children with Peak Blood Lead Concentrations below 10 /ug/dLb
Lifetime average 101 -1.22 0.07
(-2.53,0.09)
Peak
Concurrent
Average in infancy
(6-24 mo)
a Estimates were adjusted
weight, and iron status.
101
101
105
for maternal IQ,
-1.36
(-2.46, -0.27)
-1.36
(-2.37, -0.35)
-0.58
(-1.75,0.59)
0.002
0.009
0.32
race, level of education, use of tobacco
At 5 Years
P (95% CI)
-0.
(-0.93,
-0.
(-0.47,
-0.
(-0.99,
-0.
(-0.93,
-1.
(-2.94,
-1.
(-2.55,
-1.
(-3.00,
57
-0.20)
26
-0.05)
61
-0.24)
53
-0.13)
52
-0.09)
44
- 0.33)
79
-0.60)
-0.92
(-2.09,0.25)
during pregnancy,
of Age
P
0.003
0.02
0.001
0.01
0.04
0.01
0.004
0.12
household income
Overall
B (95% CI)
-0
(-0.76,
-0
(-0.40,
-0
(-0.74,
-0
(-0.77,
-1
(-2.56,
-1
(-2.37,
-1
(-2.50,
-0
(-1.78
.46
-0.15)
.23
-0.05)
.46
-0.18)
.43
-0.09)
.37
-0.17)
.40
-0.44)
.58
-0.65)
.75
, 0.28)
, HOME score, child's
0.
0
0.
0
0
0.
0.
0
gender,
P
004
.01
002
.02
.03
005
001
.15
birth
A total of 71 children were found to have a peak blood lead concentration below 10 ug/dL at both ages; an additional 15 children had a peak concentration
below 10 ug/dL at 3 years of age but at 5 years of age had a higher concentration or were not tested, and another 15 children had a peak concentration below
10 ug/dL at 5 years but were not tested at 3 years. The total number of children in the analysis of the average concentration in infancy is 105, because in 4
children the peak blood lead concentration occurred after the age of 24 months.
Source: Canfield et al. (2003a).
-------
1 children indicated that an increase in the lifetime average blood lead concentration of 1 |ig/dL
2 was associated with a decrease of 0.46 points (95% CI: 0.15, 0.76) in IQ. In comparison, a
3 1 |ig/dL increase in lifetime average lead concentration was associated with a decline of
4 1.37 points (95% CI: 0.17, 2.56) in children with peak blood lead concentrations below
5 10 |ig/dL. In an accompanying editorial on the Canfield et al. (2003a) study, Rogan and Ware
6 (2003) noted that the steepness in the concentration-response relationship below 10 |ig/dL might
7 have been influenced by 10 children with blood lead concentrations at or below 5 |ig/dL and IQs
8 above 115. However, they added that it was unlikely that the associations reported by Canfield
9 et al. were solely due to these values. Regression diagnostics performed by Canfield et al.
10 identified only one potential outlier (a child who had a low IQ and low lead concentration);
11 however, this value was retained in all analyses as it did not pass the discordancy test.
12 In the Rochester study, the relationship between children's IQ score and their blood lead
13 level was found to be nonlinear. A semiparametric analysis indicated a decline of IQ of
14 7.4 points for a lifetime average blood lead concentration of up to 10 |ig/dL, while for levels
15 between 10 to 30 |ig/dL a more gradual decrease of approximately 2.5 points IQ was estimated.
16 The authors concluded that the most important aspect of their findings was that effects below
17 10 |ig/dL that have been observed in previous cross-sectional studies (e.g., Chiodo et al., 2004;
18 Fulton et al., 1987; Lanphear et al., 2000; see Section 6.3.2.1.2) have been confirmed in this
19 rigorous prospective longitudinal investigation.
20
21 Mexico City Study (B)
22 In another prospective cohort study conducted in Mexico City, Gomaa et al. (2002)
23 examined prenatal and postnatal lead exposure effects on the neurodevelopment of 197 children
24 aged 2 years. The study cohort was recruited from 3 maternity hospitals in Mexico City that
25 served a low- to moderate-income population. Lead was measured in the umbilical cord and
26 maternal venous blood samples at the time of delivery. Maternal body burden was measured by
27 obtaining cortical (tibial) and trabecular (patellar) bone lead measurements using K-shell XRF
28 within 4 weeks of delivery. At 2 years of age, the Bayley MDI and PDI were administered. The
29 major objective of this study was to compare lead levels in umbilical cord blood and maternal
30 bone as independent predictors of infant mental development. Mean blood lead concentrations
31 in the cord blood, at 12 months of age, and at 24 months at age were 6.7 |ig/dL (SD 3.4),
May 2006 6-27 DRAFT-DO NOT QUOTE OR CITE
-------
1 7.2 |ig/dL (SD 2.8), and 8.4 |ig/dL (SD 4.6), respectively. Mean maternal patella and tibia bone
2 lead levels were 17.8 jig/g (range 10 |ig/dL, the coefficients of
25 concurrent blood lead for both the 24-month MDI and PDI were significantly steeper for children
26 who never exceeded blood lead levels of 10 |ig/dL (p = 0.01). In children with blood lead levels
27 <10 |ig/dL, a statistically significant decrement of 1.04 points (p < 0.01) was observed per
28 1 |ig/dL increase in 24-month blood lead compared to a 0.07 point increase (p = 0.84) in children
29 with blood lead levels > 10 |ig/dL. In addition, a steeper inverse slope was observed over the
30 blood lead range up to 5 |ig/dL (-1.71 points per 1 |ig/dL increase in blood lead, p = 0.01)
31 compared to the range between 5 and 10 |ig/dL (-0.94 points, p = 0.12); however, these slopes
May 2006 6-28 DRAFT-DO NOT QUOTE OR CITE
-------
1 were not significantly different (p = 0.34). In conclusion, a major finding of this prospective
2 study was that a significant inverse relationship between blood lead concentration and
3 neurodevelopment was observed among children whose blood lead levels did not exceed
4 10 |ig/dL at any age.
5
6 Pooled-Analyses of Prospective Longitudinal Cohort Studies
1 Investigators have collectively analyzed the results of multiple independent studies using
8 the methods of meta- and pooled data analyses. A powerful approach involves pooling the raw
9 data from several high quality studies to examine concentration-response relationships in a large
10 sample of children with diverse sociodemographic backgrounds and levels of exposure. The
11 studies reviewed here are summarized in Annex Table AX6-2.2.
12 Lanphear et al. (2005) reported on a pooled analysis of seven prospective studies that
13 were initiated prior to 1995. The analysis involved 1,333 children with complete data on
14 confounding factors that were essential in the multivariable analyses. The participating sites
15 included Boston, MA; Cincinnati, OH; Cleveland, OH; Rochester, NY; Mexico City; Port Pirie,
16 Australia; and Kosovo, Yugoslavia. A prospective cohort study conducted in Sydney, Australia
17 was not included because the authors were unable to contact the investigators (Cooney et al.,
18 1989b, 1991). The sample size of 175 for children at age 7 years in the Sydney cohort and the
19 wide confidence intervals of the effect estimates, as implied by the lack of significant
20 associations, indicate that the nonavailability of this study is unlikely to influence the results of
21 the pooled analysis by Lanphear et al.
22 The primary outcome measure was full scale IQ measured at school age (mean age at IQ
23 testing was 6.9 years). All children were assessed with an age-appropriate version of the
24 Wechsler scales. Four measures of lead exposure were examined: concurrent blood lead (blood
25 lead level closest in time to the IQ test), maximum blood lead level (peak blood lead measured at
26 any time prior to the IQ test), average lifetime blood lead (mean blood lead from 6 months to the
27 concurrent blood lead test), and early childhood blood lead (defined as the mean blood lead from
28 6 to 24 months). A pooled analysis of the relationship between cord blood lead levels and IQ
29 also was conducted in the subsample for which cord blood lead tests were available.
30 Multivariate regression models were developed adjusting the effect of blood lead for site
31 as well as assessing ten common covariates potentially acting as confounders of the relationship
May 2006 6-29 DRAFT-DO NOT QUOTE OR CITE
-------
1 between lead and cognitive development, including HOME scores, birth weight, maternal
2 education and IQ, and prenatal substance abuse. A thorough statistical analytic strategy was
3 employed to determine the linearity or nonlinearity of the relationship between blood lead levels
4 and full-scale IQ. Regression diagnostics also were performed to ascertain whether lead
5 coefficients were affected by collinearity or influential observations. The fit of all four measures
6 of postnatal blood lead levels was compared using the magnitude of the model R2. The blood
7 lead measure with the largest R2 (adjusted for the same covariates) was nominated a priori as the
8 preferred blood lead index relating lead exposure to IQ in subsequent inspections of the
9 relationships. The primary analysis was done using a fixed-effects model, although a mixed
10 model treating sites as random effects was also examined.
11 The median lifetime average blood lead concentration was 12.4 |ig/dL (5th-95th
12 percentile 4.1-34.8) with about 18% of the children having peak blood lead levels below
13 10 |ig/dL. The 5th to 95th percentile concurrent blood lead levels ranged from 2.4 to 30 |ig/dL.
14 The mean IQ of all children was 93.2 (SD 19.2) but this varied greatly between studies. All four
15 measures of postnatal lead exposure were highly correlated. However, the concurrent blood lead
16 level exhibited the strongest relationship with IQ, as assessed by R2. Nevertheless, the results of
17 the regression analyses for all blood lead measures were very similar. Multivariable analysis
18 resulted in a six-term model including log of concurrent blood lead, study site, maternal IQ,
19 HOME Inventory, birth weight, and maternal education.
20 Various models, including the linear model, cubic spline function, the log-linear model,
21 and the piece-wise linear model, were investigated in this analysis. The shape of the dose-
22 response relationship was determined to be non-linear; the log-linear model was found to be a
23 better fit for the data. Using the log-linear models, the authors estimated a decrement of
24 1.9 points (95% CI: 1.2, 2.6) in full scale IQ for a doubling of concurrent blood lead. However,
25 the IQ point decrements associated with an increase in blood lead from <1 to 10 |ig/dL compared
26 to 10 to 20 |ig/dL were 6.2 points (95% CI: 3.8, 8.6) versus 1.9 points (95% CI: 1.2,2.6).
27 As shown in Figure 6-2.2, the individual effect estimates for the seven studies used in the
28 pooled analysis also generally indicate steeper slopes in studies with lower blood lead levels
29 compared to those with higher blood lead. The issue of greater effects observed at lower blood
30 lead levels will be discussed in detail in Section 6.2.13.
31
May 2006 6-30 DRAFT-DO NOT QUOTE OR CITE
-------
120
110
g
« 100
RJ
u
CO
^ 90
80
70
Boston
Mexico
Port Pirie
^Cleveland
Cincinnati
Rochester
Yugoslavia
10 20 30 40 50
Concurrent Blood Lead (|jg/dl_)
60
Figure 6-2.2 Linear models for the 7 cohort studies in the pooled analysis, adjusted for
maternal IQ, HOME score, maternal education, and birth weight. The
range of data shown for each study represents the 5th to 95th percentile of
the concurrent blood lead level at the time of IQ testing.
Source: Lanphear et al. (2005).
1 Ernhart (2006) expressed the concern that one study site was driving the results and that the
2 HOME score was not always measured with the IQ test. Other limitations were also mentioned,
3 such as the use of capillary finger stick for the early blood lead tests rather than venous blood
4 lead samples. Lanphear et al. (2006) noted that though they agree that using an early measure of
5 the HOME inventory in the Rochester cohort was a potential limitation, excluding this cohort
6 from the pooled analysis changed the coefficient by <3%. Sensitivity analyses reported in
7 Lanphear et al. (2005) indicated that no single study was responsible for the estimated
8 relationship of lead and deficits in IQ; thus, diminishing concerns about unique attributes or
9 potential limitations for any specific sites.
10 In summary, the log-linear model in Lanphear et al. estimated a decline of 6.2 points in
11 full scale IQ for an increase in concurrent blood lead levels from <1 to 10 |ig/dL. This effect
12 estimate was comparable to the 7.4 point decrement in IQ for an increase in lifetime mean blood
May 2006
6-31
DRAFT-DO NOT QUOTE OR CITE
-------
1 lead levels up to 10 |ig/dL observed in the Rochester study (Canfield et al., 2003a), as well as
2 other studies reviewed above.
O
4 6.2.3.2 Cross-Sectional Studies of Neurocognitive Ability
5 Among the cross-sectional studies reviewed in the 1986 Lead AQCD and the 1990
6 Supplement, the most thorough and methodologically rigorous were those of Needleman et al.
7 (1979) and Fulton et al. (1987). Needleman et al. (1979) measured lead in the dentin of
8 deciduous teeth in elementary school children from two Boston area communities. After
9 statistical adjustment for a number of potential confounding factors, children in the higher tooth
10 lead group performed significantly less well on full scale and verbal IQ. Differences in full scale
11 IQ between the high and low tooth lead groups was on the order of 4.5 points.
12 The general population study by Fulton et al. (1987) studied 501 children aged 6 to 9
13 years in Edinburgh, Scotland who were at risk for lead exposure owing to a plumbosolvent water
14 supply and a large number of houses with lead plumbing. Blood lead levels averaged 11.5 |ig/dL
15 (range 3 to 34 |ig/dL). Following covariate adjustment, there were statistically significant
16 relationships between concurrent blood lead levels and total scores on the British Ability Scale
17 and the Quantitative and Reading subscales. Data showed a clear concentration-response
18 relationship with no evidence of a threshold.
19 Recent cross-sectional studies of neurocognitive ability are summarized in Annex
20 Table AX6-2.3. Key studies are further discussed in this section. Lanphear et al. (2000)
21 examined the relationship between blood lead concentrations and cognitive deficits in a
22 nationally representative sample of 4,853 children aged 6 to 16 years children who participated
23 in the third National Health and Nutrition Examination Survey (NHANES III). The purpose of
24 the study was to examine the relationship between low blood lead concentrations (especially
25 those below 10 |ig/dL) and two subtests of the WISC-R, Block Design (a measure of visual-
26 spatial skills) and Digit Span (a measure of short-term and working memory). Academic
27 achievement tests also were administered but are discussed in a later section. A number of
28 potential confounders were assessed and included in multivariable analyses including gender,
29 racial/ethnic background, child's serum ferritin level, serum cotinine level, region of country,
30 marital status and education level of primary caregiver, and a poverty index ratio (the ratio of
31 total family income, as reported by the adult informant, to the federal poverty level for the year
May 2006 6-32 DRAFT-DO NOT QUOTE OR CITE
-------
1 of the interview). Other potential confounders such as in utero and postnatal exposure to tobacco
2 smoke, birth weight, and admission to the neonatal intensive care unit were only available for
3 children between 6 and 11 years of age. Therefore, the authors conducted a secondary analysis
4 of the data on these children to verify that inclusion of these potentially important variables did
5 not alter the findings of the main analysis using the larger sample.
6 The geometric mean blood lead concentration for children in the study sample was
7 1.9 |ig/dL (SE 0.1). Only 2.1% of the NHANES III sample in this analysis had blood lead
8 concentrations > 10 |ig/dL. In multivariate analyses, a significant covariate-adjusted relationship
9 was found between blood lead level and scores on both WISC-R subtest for all children as well
10 as among those children with blood lead levels <10 |ig/dL. Blood lead concentration also was
11 significantly associated with Block Design when the multivariate analysis was restricted to
12 children with blood lead levels <7.5 |ig/dL. For a 1 |ig/dL increase in blood lead level, Block
13 Design scores declined by 0.10 points (SE 0.04) for all children, 0.13 points (SE 0.06) for
14 children with blood lead levels <10 |ig/dL, and 0.11 points (SE 0.06) for children with blood lead
15 levels <7.5 |ig/dL. The authors concluded that deficits in intellectual functioning were
16 associated with blood lead levels <10 |ig/dL; however, it is not clear whether the cognitive
17 deficits observed were due to lead exposure that occurred during early childhood or a function of
18 concurrent exposure. Nevertheless, concurrent blood lead levels likely reflected both ongoing
19 exposure and preexisting body burden. It should be noted that while a large number of potential
20 confounding factors were controlled in these analyses, no data on maternal IQ or direct
21 observations of caretaking quality in the home were available. The study did, however, control
22 for the poverty index ratio and education level of the primary caregiver which may have served
23 as surrogates for maternal IQ or the HOME score.
24 Chiodo et al. (2004) studied the relationship between blood lead concentrations and IQ,
25 assessed using WISC-III at 7.5 years of age in a sample of 237 African-American inner-city
26 children from Detroit, MI. This cohort was derived from a larger study of the effects of prenatal
27 alcohol exposure on child development. However, approximately 83% of children for whom
28 blood lead levels were obtained had either low or no gestational exposure to alcohol. Blood lead
29 levels were low, with a mean of 5.4 |ig/dL (SD 3.3, range 1-25). Following adjustment for a
30 wide range of covariates (including drug and alcohol exposure, HOME scores, SES status, and
31 perinatal health among others), there was a statistically significant association between blood
May 2006 6-33 DRAFT-DO NOT QUOTE OR CITE
-------
1 lead concentrations and full scale, verbal and performance IQ, with the strongest relationship
2 observed for performance IQ. Significant effects of lead on full scale and performance IQ were
3 still evident at blood lead concentrations below 7.5 |ig/dL. Nonparametric smoothing analyses
4 confirmed that these effects were linear in nature.
5 Walkowiak et al. (1998) conducted a cross-sectional study examining relationships
6 between low-level lead and mercury exposure and various measures of neurocognitive and
7 neuromotor functioning in 384 children aged 6 years in three German cities. Blood lead was
8 measured at the time of testing and mercury burden was estimated from urine samples. As their
9 measure of IQ, two subtests of the German WISC, Vocabulary and Block Design were
10 administered. These subtests were treated separately as well as a summed index, which served
11 as a surrogate for full scale IQ. Blood lead concentrations were low (geometric mean 4.3 |ig/dL
12 [95th percentile 8.9]). Following covariate-adjustment, Vocabulary and the combined index, but
13 not Block Design, exhibited negative associations with blood lead of statistical or borderline
14 statistical significance; but no associations were observed for mercury. The authors concluded
15 that these findings roughly correspond with those of other studies that find effects of lead
16 exposure on measures of intelligence at blood lead concentrations below 10 |ig/dL. However,
17 they also cautioned that some important covariates and potential confounding variables were not
18 measured, including parental IQ and home environment (e.g., HOME score).
19 The cross-sectional studies examining the effect of lead on neurocognitive abilities varied
20 widely in study location, population, age of testing, and outcomes measured. Collectively, they
21 generally found that blood or tooth lead levels were significantly associated with declines in
22 intelligence and other neurocognitive outcomes. In addition, these associations were consistently
23 observed in studies with mean blood lead levels <10 |ig/dL.
24
25 6.2.3.3 Meta-Analyses of Studies of Neurocognitive Abilities
26 Several meta-analyses of studies investigating associations between lead exposure and
27 neurocognitive abilities included results from both prospective cohort studies and cross-sectional
28 studies. The studies reviewed here are summarized in Annex Table AX6-2.2. Needleman and
29 Gatsonis (1990) conducted a meta-analysis of 12 studies that used multiple regression techniques
30 to assess the relationship between lead levels in tissues (blood or teeth) while adjusting for
31 potentially confounding variables. Studies were weighted based on sample sizes, which ranged
May 2006 6-34 DRAFT-DO NOT QUOTE OR CITE
-------
1 from 75 to 724 children. The authors divided studies into two groups according to the type of
2 tissue analyzed for lead (blood or teeth). Joint p-values and average effect sizes as measured by
3 partial correlation coefficients were calculated using two different methods by Fisher and by
4 Mosteller and Bush (Rosenthal, 1984). The joint p-values for the blood lead studies were
5 <0.0001 for both methods, whereas joint p-values of <0.0006 and <0.004 were obtained for tooth
6 lead studies. The partial correlations ranged from -0.27 to -0.0003. Sensitivity analyses
7 revealed that no single study was responsible for the significance of the final findings. The
8 authors concluded that the hypothesis that lead lowers children's IQ at relatively low dose was
9 strongly supported by their quantitative analysis.
10 Another meta-analysis conducted by Schwartz (1994) took a different approach. Only
11 studies relating blood lead to IQ were chosen for quantitative review, since the concentration of
12 lead in the bloodstream is the main index of lead exposure typically used as the basis for public
13 health policy. Three longitudinal and four cross-sectional studies relating blood lead to IQ were
14 examined. Furthermore, while the work of Needleman and Gatsonis (1990) essentially involved
15 combining partial correlations, the measure of effect used in the Schwartz analysis was the
16 predicted change in full scale IQ as blood lead increased from 10 to 20 |ig/dL. For the
17 prospective longitudinal studies, blood lead levels at 2 years of age or average blood lead levels
18 up to 3 years of age were used in the analysis. This approach by Schwartz may be related to the
19 belief at the time of the analysis that blood lead levels during the first 3 years of life were the
20 most critical in determining the severity of neurodevelopmental toxicity. The exclusion of blood
21 lead levels from other time points may be of issue, as it appears that later blood lead levels may
22 be more predictive of mental deficits (Baghurst et al., 1992; Canfield et al., 2003a; Chen et al.,
23 2005; Dietrich et al., 1993a; Factor-Litvak et al., 1993). Studies were weighted by the inverse of
24 the variances using a random-effects modeling procedure. The estimated decrease in IQ for an
25 increase in blood lead from 10 to 20 |ig/dL was 2.6 points (95% CI: 1.8,3.4). Sensitivity
26 analyses indicated that the results were not determined by any individual study. Effect estimates
27 were similar for longitudinal and cross-sectional studies. In another analysis, studies with mean
28 blood lead concentrations below 15 |ig/dL and above 15 |ig/dL had estimated effect sizes of
29 -3.23 points (95% CI: -5.70, -0.76) and -2.32 points (95% CI: -3.10, -1.54), respectively.
30 When the study with the lowest mean blood lead level was examined in greater detail using
May 2006 6-3 5 DRAFT-DO NOT QUOTE OR CITE
-------
1 nonparametric smoothing, no evidence of a threshold was found down to a blood lead of
2 1 |ig/dL.
3 Pocock et al. (1994) conducted a review of the epidemiologic evidence for lead effects on
4 IQ that included a meta-analysis. For the meta-analysis, the fixed-effect method described by
5 Thompson and Pocock (1992) was used. Five prospective and 14 cross-sectional studies (with
6 both tooth and blood lead measures) were included. For consistency, only blood lead levels at or
7 around 2 years of age were considered for the prospective studies. Their overall conclusion was
8 that a doubling of blood lead levels from 10 to 20 |ig/dL or of tooth lead from 5 to 10 jig/g was
9 associated with an average estimated IQ deficit of about 1 to 2 points.
10 Other earlier meta-analyses of lead-IQ studies have been published but are not reviewed
11 here, because later work greatly extended these efforts and included more studies, rendering
12 those analyses outdated (Needleman and Bellinger, 1988; Schwartz, 1985; Thacker et al., 1992).
13 The meta-analyses of studies investigating the effect of lead on neurocognitive ability all
14 consistently observed significant associations between blood or tooth lead levels and decrements
15 in IQ. Also, the Schwartz (1994) analysis found no evidence of a threshold at blood lead levels
16 below 10 |ig/dL.
17
18 6.2.4 Measures of Academic Achievement
19 Relatively little data are avalable on the relationship between lead exposure and objective
20 measures of academic achievement. A few earlier studies reported an inverse relationship
21 between lead exposure and reading skills (Fergusson et al., 1988a; Fulton et al., 1987; Yule et al.,
22 1981). Since the 1990 Supplement, more studies have focused on the practical consequences of
23 childhood lead exposure by including measures of academic performance in their batteries.
24 Studies reviewed in this section are summarized in Annex Table AX6-2.4.
25 Using NHANES III data, Lanphear et al. (2000) examined the relationship between blood
26 lead levels and a standardized measure of academic achievement in 4,853 children aged 6 to
27 16 years. This cohort was previously described in Section 6.2.3.2. Subjects were administered
28 the Arithmetic and Reading subtests of the Wide Range Achievement Test-Revised (WRAT-R).
29 The WRAT-R Arithmetic subtest includes oral and written problems ranging in level from
30 simple addition to calculus, while the Reading subtest assesses letter recognition and word
31 reading skills. The geometric mean blood lead concentration was 1.9 |ig/dL. Only 2.1% of the
May 2006 6-36 DRAFT-DO NOT QUOTE OR CITE
-------
1 subjects had blood lead levels > 10 |ig/dL. Multiple linear regression revealed a 0.70 point (95%
2 CI: 0.37, 1.03) decrement in arithmetic scores and a 0.99 point (95% CI: 0.62, 1.36) decrement
3 in Reading scores for each 1 |ig/dL increase in blood lead concentration (p < 0.001). In the next
4 phase of the analysis, the adjusted relationship between performance on WRAT subtests and
5 blood lead concentration for children with blood lead concentrations <10 |ig/dL, <7.5 |ig/dL,
6 <5 |ig/dL, or <2.5 |ig/dL were carried out. Statistically significant inverse relationships between
7 blood lead levels and performance for both Reading and Arithmetic subtests were found for
8 children with blood lead concentrations below 5 |ig/dL. Secondary analysis limited to younger
9 children with data on all covariates did not alter findings from the main analysis. The authors
10 concluded that results of these analyses suggest that deficits in academic skills are associated
11 with blood lead concentrations <5 |ig/dL. For potential limitations of this study, see the
12 discussion in Section 6.2.3.2.
13 Needleman et al. (1990) reexamined the Chelsea and Somerville, MA cohort of first and
14 second graders recruited in the 1970s (Needleman et al., 1979). Of the original 270 children,
15 132 were recalled. Relationships between concentration of lead in shed deciduous teeth and
16 neurobehavioral deficits had persisted into late adolescence. Subjects with dentin lead levels
17 >20 ppm were at higher risk of dropping out of high school (adjusted odds ratio of 7.4, [95% CI:
18 1.4, 40.7]) and of having a reading disability (adjusted odds ratio of 5.8 [95% CI: 1.7, 19.7]).
19 Higher dentin lead levels were also significantly associated with lower class standing, increased
20 absenteeism, and lower vocabulary and grammatical reasoning scores on the Neurobehavioral
21 Evaluation System (NES). The authors concluded that undue exposure to lead had enduring and
22 important effects on objective parameters of success in real life.
23 Bellinger et al. (1992) administered a battery of neuropsychological tests to 148 Boston
24 Lead Study cohort children at age 10 years. The short-form of the Kaufman Test of Educational
25 Achievement (KTEA) was administered in addition to IQ studies. The KTEA assesses
26 reading, math, and spelling skills. The primary outcome was the Battery Composite Score.
27 As previously indicated, exposures in this cohort were low (with a peak mean blood lead at
28 18 months of only 7.8 |ig/dL [SD 5.7]), and the cohort consisted of high-SES white children
29 from intact families with college-educated parents. Average KTEA scores in this cohort were
30 about one standard deviation above the population mean. Nevertheless, postnatal blood lead
31 levels measured at virtually all ages were significantly associated with lower KTEA Battery
May 2006 6-37 DRAFT-DO NOT QUOTE OR CITE
-------
1 Composite Scores. However, after covariate-adjustment, including full scale IQ in the model,
2 only blood lead levels at 24 months of age were significantly predictive of lower academic
3 achievement. Over the range of ~0 to 25 |ig/dL, Battery Composite scores declined by
4 -8.9 points (95% CI: 4.2, 13.6) for each 10 ng/dL increase in 24-month blood lead. The
5 specific subscales of the KTEA that were most significantly associated with lead were Spelling
6 and Math. Within the Math subscale, lead appeared to be more strongly associated with
7 performance on the advanced quantitative Concepts/Applications items than on computation.
8 The associations between these early measures of low level exposure to lead and achievement
9 were significant even after adjustment for IQ, suggesting that lead-sensitive neuropsychological
10 processing and learning factors not reflected in indices of global intelligence may contribute to
11 reduced performance on academic tasks.
12 Leviton et al. (1993) reported on the relationship between pre- and postnatal lead
13 exposure and academic problems in -2,000 children born in one Boston hospital between 1979
14 and 1980 using the Boston Teacher Questionnaire (BTQ). A teacher provided an assessment of
15 each child's academic functioning when the child reached the age of 8 years. Mean umbilical
16 cord blood lead was 6.8 |ig/dL and mean tooth (dentin) lead concentration was 2.8 jig/g. There
17 was limited information on covariate factors. Still, following adjustment for potential
18 confounding variables, elevated dentin lead levels were associated with statistically significant
19 reading and spelling difficulties as assessed by the BTQ among girls. The authors concluded that
20 their findings supported the case for lead-associated learning problems at levels prevalent in the
21 general population. However, they added that the inability to assess child-rearing quality in this
22 questionnaire study conducted by mail limits the inferences that can be drawn from the findings.
23 Rabinowitz et al. (1992) examined the relationship between tooth lead concentrations and
24 scores on BTQ clusters in 493 Taiwanese children in first through third grade. Mean lead levels
25 in incisors were 4.6 jig/g (SD 3.5). Factors associated with lead and BTQ scores included
26 13 variables measuring perinatal, familial, and economic parameters. Prior to adjustment for
27 covariates, girls in this sample with higher exposures to lead showed a borderline significant
28 trend for reading difficulties, whereas boys displayed significantly increased difficulties with
29 respect to activity levels and task attentiveness. In multiple logistic regression models, tooth lead
30 terms failed to achieve statistical significance. The authors concluded that lead levels found in
May 2006 6-3 8 DRAFT-DO NOT QUOTE OR CITE
-------
1 the teeth of children in their Taiwanese sample were not associated with learning problems or
2 syndromes as assessed by the BTQ.
3 Fergusson et al. (1993) examined the relationship between dentin lead levels in shed
4 deciduous teeth at 6 to 8 years and measures of academic attainment and classroom performance
5 in a birth cohort of over 1,200 New Zealand children enrolled in the Christchurch Health and
6 Development Study when they reached 12 to 13 years of age. This study was an extension of
7 earlier work in these children indicating a relationship between low lead levels and deficits in
8 academic skills around the age of 8 years (Fergusson et al., 1988a). Average dentine lead levels
9 in the cohort were 6.2 jig/g (SD 6.2). Measures of academic performance included word
10 recognition from the Burt Reading Test, reading comprehension from the Progressive
11 Achievement Test, a general measure of scholastic skills based on children's scores on the Test
12 of Scholastic Abilities, and teacher ratings of classroom performance in reading, written
13 expression, and mathematics. Following adjustment for a wide range of covariates (including
14 residence in potentially lead-hazardous housing), dentin lead levels were significantly associated
15 with virtually every formal index of academic skills and teacher ratings of classroom
16 performance. Statistical evaluations included a multivariate analysis of all 12 regression
17 equations simultaneously using LISREL modeling methods. This conservative analysis clearly
18 showed that the probability of observing these results under the null hypotheses that lead was
19 unrelated to all covariate-adjusted test outcomes was extremely small. In an adjunct analysis,
20 Fergusson and Horwood (1993) examined low-level lead exposure effects on the growth of word
21 recognition in this cohort from 8 to 12 years of age, using growth curve modeling methods.
22 After adjustment for potential confounding variables, children with dentin lead levels >8 |ig/g
23 displayed significantly slower growth in word recognition abilities with no evidence of catch up.
24 The authors concluded that these results were consistent with their earlier analyses and suggest
25 that early exposure to very low levels of lead result in small but detectable and enduring deficits
26 in children's cognitive abilities.
27 Academic achievement in relationship to lead was reexamined in the New Zealand cohort
28 when subjects reached 18 years of age (Fergusson et al., 1997). The sample at 18 years consisted
29 of 881 subjects, or-70% of the original cohort. Measures of educational achievement included
30 the Burt Reading Test, number of years of secondary education, mean number of School
31 Certificate passes (based on results of national examinations), and leaving school without formal
May 2006 6-39 DRAFT-DO NOT QUOTE OR CITE
-------
1 qualifications (analogous to failure to graduate from high school in the United States). As in
2 previous analyses, a wide range of potentially confounding sociohereditary factors were
3 measured and controlled for in multivariable analyses, which included both linear and logistic
4 regressions. Prior to and following covariate adjustment, there were statistically significant
5 concentration-response relationships between dentin lead concentrations and lower reading test
6 scores, having a reading level of less than 12 years, failing to complete 3 years of high school,
7 leaving school without qualifications, and mean number of School Certificates subjects passed.
8 The authors concluded that their results are consistent with the view that there is a relationship
9 between early low-level lead exposure and later educational outcomes. The late results of the
10 New Zealand studies confirm the Needleman et al. (1990) findings in a cohort with lower levels
11 of environmental lead exposure.
12 Wang et al. (2002a) examined the relationship between blood lead levels and class
13 ranking in 934 third graders living in an urban industrial area of Taiwan. The outcome variables
14 were grades for Chinese (reading and writing), Mathematics, History and Society, and Natural
15 Science. To avoid the impact of teacher's bias in grading criteria, the authors converted the
16 children's grades into class rankings. A limited number of potentially confounding factors were
17 measured, including maternal education and father's SES. Mean blood lead level was 5.5 |ig/dL
18 (SD 1.89). In multiple regression analyses adjusting for gender, maternal education, and father's
19 SES, blood lead was significantly associated with lower class ranking in all academic subjects.
20 The major shortcoming of this cross-sectional study is the lack of control for potentially
21 important confounding factors such as parental intelligence. However, the strength and
22 consistency of the reported relationships suggest that relatively low levels of lead may play a role
23 in lowering academic performance.
24 Al-Saleh et al. (2001) studied the association between blood lead levels and academic
25 achievement in 533 girls aged 6 to 12 years in Riyadh, Saudi Arabia. At the time of this study
26 leaded gasoline was still in wide use. The measure of academic achievement was based on the
27 class ranking of each student as assessed by the teacher. A large number of confounding
28 variables were considered, including growth parameters and various assessments of
29 socioeconomic status, health status, geographical location and family structure. The mean blood
30 level in the cohort was 8.11 |ig/dL (SD 3.5). Following covariate adjustment, there was a
31 statistically significant relationship between higher blood lead levels and lower class rank
May 2006 6-40 DRAFT-DO NOT QUOTE OR CITE
-------
1 percentile subscales. When multiple regression models were fitted to a subset of students with
2 blood lead levels below 10 |ig/dL, class rank percentile continued to show a statistically
3 significant association with blood lead levels.
4 Kordas et al. (2006) examined the relationship between blood lead levels at 7 years of age,
5 and math achievement and vocabulary in 594 second graders living near a metal foundry in
6 Torreon, Mexico. The mean blood lead level was 11.4 |ig/dL (SD 6.1). Following adjustment
7 for covariates measuring other well-documented predictors of cognitive functioning as well as
8 concurrent arsenic exposure, blood lead concentrations were statistically significantly related to
9 poorer math and vocabulary scores. Furthermore, in segmented regression analyses, the slopes
10 for the association of blood lead with vocabulary and math scores were both significantly steeper
11 below 10 |ig/dL than above.
12 The results of these studies strongly suggest that lead exposure can affect the academic
13 performance of children, including children with blood lead levels below 10 |ig/dL.
14
15 6.2.5 Measures of Specific Cognitive Abilities
16 Outcomes of specific cognitive abilities, in particular, the domains of Attention and
17 Executive Functions, Language, Memory and Learning, and Visuospatial Processing have
18 been examined in some detail in recent studies. These studies are summarized in Annex
19 TableAX6-2.5.
20 In the aggregate, studies suggest that lead exposure impairs a child's ability to regulate
21 attention and to engage several related higher-order cognitive processes that have come to be
22 termed "executive functions." Executive functions refer to strategic planning, control of
23 impulses, organized search, flexibility of thought and action, and self-monitoring of one's own
24 behavior—activities that help the subject maintain an appropriate mental set in order to achieve
25 an immediate or future goal (Spreen et al., 1995). In some earlier studies, increased lead
26 exposure was found to be associated with a higher frequency of negative ratings by teachers
27 and/or parents on behaviors such as inattentiveness, impulsivity, distractibility, and less
28 persistence in assigned tasks, as well as slow psychomotor responses and more errors on simple,
29 serial, and choice reaction time tasks (e.g., Hatzakis et al., 1989; Hunter et al., 1985; Needleman
30 et al., 1979; Raab et al., 1990; Winneke et al., 1990). The concept that lead may impact
31 executive functions in particular is biologically plausible. The prefrontal cortex is highly
May 2006 6-41 DRAFT-DO NOT QUOTE OR CITE
-------
1 innervated by projections of neurons from the midbrain and has the highest concentration of
2 dopamine of all cortical areas. Dopamine plays a key role in cognitive abilities mediated by the
3 prefrontal cortex. It has been known for some time that the dopamine system is particularly
4 sensitive to lead based upon data from studies of rodents and nonhuman primates (Cory-Slechta,
5 1995).
6 Bellinger et al. (1994a) examined a portion of the original Chelsea and Somerville cohorts
7 at 19 to 20 years of age. The principal neurobehavioral outcomes used scores on a battery of
8 attentional measures assembled by Mirsky (1987). Higher tooth lead concentrations were
9 significantly associated with poorer scores on the Focus-Execute and Shift factors of the battery,
10 leading the authors to conclude that early lead exposure may be associated with poorer
11 performance on executive/regulatory functions that are thought to depend on frontal or prefrontal
12 brain regions.
13 Stiles and Bellinger (1993) administered a neuropsychological battery of tests to 10-year-
14 old children in the Boston Lead Study cohort. A large number of assessments were made and, as
15 the authors acknowledge, the number of significant associations was about equal to those that
16 would be expected by chance. However, as in previous studies, tasks that assess attentional
17 behaviors and executive functions tended to be among those for which lead was a significant
18 predictor of performance. For example, higher blood lead concentrations at 2 years were
19 significantly associated with (a) lower scores on the Freedom from Distractibility factor of the
20 Wechsler scales and (b) an increase in the percentage of preservative errors on the Wisconsin
21 Card Sorting Test and the California Verbal Learning Test. At 2 years of age, 90% of the
22 children had blood lead levels below 13 |ig/dL.
23 Canfield et al. (2003b) conducted a comprehensive examination of the relationship
24 between low-level lead exposure, executive functioning, and learning in children from the
25 Rochester Lead Study cohort at 48 and 54 months of age. The mean blood lead level at
26 48 months was 6.49 |ig/dL (range 1.7-20.8), with 80% of the children having a blood lead level
27 below 10 |ig/dL. The authors used the Shape School Task (Espy, 1997), which requires only
28 knowing simple shape and primary color names. However, embedded in the tasks are protocols
29 requiring inhibition, attention switching, and a combination of inhibition and switching mental
30 sets. Following covariate-adjustment, blood lead level at 48 months was negatively associated
31 with children's focused attention while performing the tasks, efficiency at naming colors, and
May 2006 6-42 DRAFT-DO NOT QUOTE OR CITE
-------
1 inhibition of automatic responding. Children with higher blood lead concentrations also
2 completed fewer phases of the task and knew fewer color and shape names.
3 Canfield et al. (2004) also administered portions of the Cambridge Neuropsychological
4 Testing Automated Battery (CANTAB) to 174 Rochester cohort children at approximately
5 66 months of age. Children were tested with the Working Memory and Planning CANTAB
6 assessment protocols to assess mnemonic and executive functions. Blood lead levels ranged
7 from 0 to 20 |ig/dL in this cohort. Following covariate adjustment, children with higher blood
8 lead levels showed impaired performance on tests of spatial working memory, spatial memory
9 span, cognitive and cognitive flexibility, and planning as indexed by tests of intradimensional
10 and extradimensional shifts and an analog of the Tower of London task.
11 Ris et al. (2004) administered an extensive neuropsychological battery to 15-17 year old
12 subjects from the Cincinnati Lead Study cohort. In addition to executive functions as assessed
13 by the Wisconsin Card Sorting Test and the Rey-Osterrieth Complex Figure, other domains
14 examined included attention, memory, achievement, verbal abilities, visuoconstructional skills,
15 and fine-motor coordination. About 30% of the subjects had blood lead concentrations
16 >25 |ig/dL during the first 5 years of life; and 80% of the cohort had at least one blood lead
17 concentration > 15 |ig/dL. A factor analysis of scores selected a priori revealed five factors that
18 included Attention. A strong "executive functions" factor did not emerge. Following covariate-
19 adjustment, the strongest associations between lead exposure and performance were observed for
20 factor scores derived from the Attention component, which included high loadings on variables
21 from the Conners Continuous Performance Test. However, this relationship was restricted to
22 males as indicated by a strong lead-by-gender interaction. This obtained gender interaction
23 suggests that neuromechanisms sub-serving attention were affected by lead in this cohort for
24 boys but not for girls. This is not surprising given the heightened vulnerability of males for a
25 wide range of developmental perturbations. A substantial gender difference in the incidence of
26 Attention Deficit/Hyperactivity Disorder (ADHD) is well established, and one could speculate
27 that early exposure to lead exacerbates a latent potential for such problems.
28 Visual-spatial skills have also been also been explored in some depth by a few studies.
29 When investigations of lead-exposed children have used global IQ measures and conducted
30 subscale analyses, it has been observed that Performance IQ or subtests contributing to the
31 performance IQ (i.e., Block Design) are frequently among the most strongly associated with
May 2006 6-43 DRAFT-DO NOT QUOTE OR CITE
-------
1 biological indices of lead exposure (Baghurst et al., 1992; Chiodo et al., 2004; Dietrich et al.,
2 1993a; McMichael et al., 1988; Wasserman et al., 1994). Dietrich et al. (1991, 1992) have also
3 observed that integrated measures of lead exposure over a child's lifetime are most consistently
4 associated with simultaneous processing abilities, cognitive functions closely associated with
5 visual-spatial integration skills and right cerebral functioning (Kaufman and Kaufman, 1983).
6 In addition, studies employing specific measures of visual-motor integration skills, such as the
7 Developmental Test of Visual Motor Integration (VMI), the Bender Visual-Motor Gestalt Test,
8 and others, have found them to be among the most consistently associated with early lead
9 exposure (Al-Saleh et al., 2001; Baghurst et al., 1995; Dietrich et al., 1993b; Wasserman et al.,
10 2000a; Winneke et al., 1990). In a follow-up of Cincinnati Lead Study cohort subjects at age
11 16 years, Ris et al. (2004) observed a significant association between prenatal maternal blood
12 lead levels and deficits in visual-spatial and constructional skills as indexed by Visual-
13 Constructional factor scores. Variables with high loadings on this factor included scores on the
14 WISC-III Block Design subtests and selected variables from the Rey Osterrieth Complex Figure.
15 Kordas et al. (2006) administered an extensive battery of tests assessing specific abilities
16 to 594 first graders (mean blood lead of 11.4 |ig/dL ) in Torreon, Mexico, the site of a metal
17 foundry. The battery included well validated assessments of mental distractibility, sequencing
18 skills, memory, visual spatial skills and stimulus discrimination. Following adjustment for
19 covariates in linear regression analyses, blood lead remained significantly associated with
20 performance on the Sternberg Memory test. For the various tests, steeper slopes were generally
21 observed for blood lead levels below 10 |ig/dL than above.
22 It is still unclear whether the domains of attention/executive functions or visual-motor
23 integration per se are specifically sensitive to lead. This is because there is rarely a one-to-one
24 correspondence between performance on a focused neuropsychological test and an underlying
25 neuropsychological process. Thus, for example, a low score on the Berry VMI may reflect
26 singular or multiple neurobehavioral deficits, including difficulties with graphomotor control,
27 visual perception, behavioral monitoring (impulsivity), or planning (executive functions).
28
29 6.2.6 Disturbances in Behavior, Mood, and Social Conduct
30 The effects of lead on behavior and mood of children has been an area of recent research.
31 Studies conducted prior to 1990 clearly pointed to behavioral problems as potential sequelae of
May 2006 6-44 DRAFT-DO NOT QUOTE OR CITE
-------
1 lower level lead toxicity in children. Several early case control studies have linked lead to
2 hyperactivity (David et al., 1972, 1976, 1979). Low levels of lead in blood and/or teeth have
3 been associated with teacher ratings of hyperactive behavior, aggression, and attention problems
4 (e.g., Fergusson et al., 1988b; Hatzakis et al., 1985; Silva et al., 1988; Thomson et al., 1989;
5 Yule et al., 1984). In the seminal study by Needleman et al. (1979), children with higher
6 concentrations of lead in dentin were more likely to be rated unfavorably by teachers on the
7 dimensions of hyperactivity, impulsivity, and frustration tolerance. New studies reviewed in this
8 section are summarized in Annex Table AX6-2.6.
9 While there is no compelling evidence that lead is directly related to ADHD, elevated
10 blood or tooth lead levels have been linked to behavioral features of ADHD, including
11 distractibility, poor organization, lacking persistence in completing tasks, and daydreaming
12 (Bellinger and Rappaport, 2002). Bellinger et al. (1994b) studied the relationship between early
13 exposure to lead and problem behaviors in the classroom in a cohort of 1,782 children born at
14 one hospital in Boston. Umbilical cord blood lead levels were low (mean 6.8 |ig/dL [SD 3.1])
15 as were tooth lead levels (mean 3.4 jig/g [SD 2.4]). Teachers filled out the Achenbach Child
16 Behavior Profile (ACBP), which yields both broad and narrow band scales indexing
17 externalizing and internalizing problems. Cord blood lead levels were not associated with the
18 prevalence or nature of behavioral problems reported by teachers. However, tooth lead level was
19 significantly associated with ACBP Total Problem Behavior Scores (TPBS). TPBS scores
20 increased by ~2 points for each log unit increase in tooth lead. Statistically significant tooth
21 lead-associated increases in both externalizing and internalizing scores were also noted. Each
22 log unit increase in tooth lead was associated with a 1.5 point increase in scores for these
23 broadband scales assessing under- and overcontrol of behavior. Only weak associations were
24 seen between tooth lead concentrations and the tendency to score in the clinically significant
25 range on these scales. As the authors noted, it was somewhat surprising that lead exposure was
26 not more strongly related to externalizing behavior problems than with internalizing behavior
27 problems. This contradicted several earlier investigations, including one by Sciarillo et al.
28 (1992) (see Annex Table AX6-2.6). It may be that more attention has been accorded
29 undercontrolled behaviors, because they are more readily visible and disruptive in settings such
30 as the classroom. Therefore, internalizing problems may be part of the full spectrum of
31 behaviors in which lead's developmental neurotoxicity is expressed in children. The authors also
May 2006 6-45 DRAFT-DO NOT QUOTE OR CITE
-------
1 cautioned that residual confounding could not be ruled out, because of the lack of covariate
2 information on parental psychopathology or direct observations of the family environment—a
3 problem not unique to this particular study. Nevertheless, these findings are in accord with other
4 studies which suggest that social and emotional dysfunction may be another expression of
5 increased lead exposure during the early postnatal period.
6 Fergusson et al. (1993) examined relationships of tooth lead levels to inattention/
7 restlessness in the large national New Zealand study of over 1,000 children at 12 and 13 years of
8 age. Mothers and teachers were asked to respond to a series of items derived from the Rutter and
9 Conners parental and teacher questionnaires. The selected items related to the degree to which
10 the child was restless, inattentive, easily distracted, and lacking in concentration. At each age, an
11 index of the subject's propensity to inattentive and restless behavior was obtained by summing
12 the total reports of attention deficit behaviors made by both teacher and parent respondents.
13 Following adjustment for a wide range of sociodemographic and other covariate factors, a
14 statistically significant, concentration-response relationship was observed between tooth lead
15 concentrations (range 1 to 12+ |ig/g) and the inattention/restlessness variable. The authors
16 concluded that their results were consistent with the view that early mildly elevated lead levels
17 were associated with small but long-term deficits in attentional behaviors.
18 Two prospective studies have also examined measures of early lead exposure and
19 behavioral problems as assessed by the Achenbach system. Wasserman et al. (1998) studied the
20 relationship between lead exposure and behavior in the Yugoslavian prospective study. The
21 study surveyed 379 children at 3 years of age with the parent report form of the Achenbach
22 CBCL. Following covariate adjustment, concurrent blood lead levels were significantly
23 associated with scores on the Destructive Behaviors CBCL subscale, although the variance
24 accounted for by lead was small compared to sociodemographic factors. As blood lead increased
25 from 10 to 20 |ig/dL, CBCL subscale scores increased by -0.5 points. The authors concluded
26 that while statistically significant, the contribution of lead to social behavioral problems in this
27 cohort was small compared to the effects of correlated social factors. Burns et al. (1999)
28 examined the relationship between lead exposure and children's emotional and behavioral
29 problems at ages 11 to 13 years in the Port Pirie, Australia, cohort study. After adjusting for
30 many confounding variables, including HOME scores, maternal psychopathology and the child's
31 IQ, regression models showed that, for an increase in average lifetime blood lead concentrations
May 2006 6-46 DRAFT-DO NOT QUOTE OR CITE
-------
1 from 10 to 30 |ig/dL, the externalizing behavior problem score increased by 3.5 points (95% CI:
2 1.6, 5.4) in boys but only by 1.8 points (95% CI: -0.1, 11.1) in girls. In contrast, internalizing
3 behavior problems were predicted to increase by 2.1 points (95% CI: 0.0, 4.2) in girls, but by
4 only 0.8 points (95% CI: -0.9, 2.4) in boys.
5 Recently, the question of lead's role in delinquent and criminal behavior has been
6 addressed in several investigations. Previous studies linking attention deficits, aggressive and
7 disruptive behaviors, and poor self-regulation with lead have raised the prospect that early
8 exposure may result in an increased likelihood of engaging in antisocial behaviors in later life.
9 Denno (1990) surveyed 987 Philadelphia African American youths enrolled in the
10 Collaborative Perinatal Project. Data were available from birth through 22 years of age. The
11 analysis initially considered over 100 predictors of violent and chronic delinquent behavior.
12 Repeat offenders presented consistent features such as low maternal education, prolonged male-
13 provider unemployment, frequent moves, and higher lead intoxication (although the level of lead
14 intoxication was not indicated in Denno's report). In male subjects, a history of lead poisoning
15 was among the most significant predictors of delinquency and adult criminality.
16 Needleman et al. (1996) examined the relationship between lead exposure and several
17 measures of behavioral disturbance and delinquent behavior in subjects from the Pittsburgh
18 Youth Study. The Pittsburgh Youth Study is a prospective study of the developmental course of
19 delinquency (Loeber et al., 1991). The population consisted of 850 boys who were prescreened
20 with an instrument that measured serious and potentially indictable behaviors extracted from the
21 teachers' and parents' CBCL. Subjects who scored above the 30th percentile on the risk score
22 and an approximately equal number of subjects randomly selected from the remainder of the
23 distribution formed the sample (n = 503). Body burden of lead was measured in the tibia by
24 K-shell XRF. Measures of antisocial behavior were administered at 7 and 11 years of age and
25 included the Self Reported Antisocial Behavior scale (SRA), the Self Report of Delinquent
26 Behavior (SRD), and the parents' and teachers' versions of the CBCL. Outcome data were
27 adjusted for a number of covariates including mother's IQ, SES, childhood medical problems,
28 and quality of child rearing. Parents of subjects with higher lead levels in bone reported
29 significantly more somatic complaints, more delinquent and aggressive behavior, and higher
30 internalizing and externalizing scores. Teachers reported significant increases in scores on
31 somatic complaints, anxious/depressed, social problems, attention problems, delinquent
May 2006 6-47 DRAFT-DO NOT QUOTE OR CITE
-------
1 behavior, aggressive behavior, and internalizing and externalizing problems in the higher lead
2 subjects. At 11 years, subjects SRD scores also were significantly related to bone lead levels.
3 More of the high lead subjects had CBCL scores in the clinical range for the CBCL subscales
4 assessing attention problems, aggression, and delinquency. Odds ratios for these outcomes
5 ranged from 1.5 (95% CI: 0.45, 4.9) for parental reports of aggression to 19.5 (95% CI: 8.9,
6 41.6) for attention problems. The authors concluded that lead exposure was associated with an
7 increased risk for antisocial and delinquent behavior.
8 Dietrich et al. (2001) reported on the relationship between early exposure to lead and
9 juvenile delinquency in 195 subjects from the Cincinnati Lead Study. Subjects were between
10 16 and 17 years of age when examined. As previously described, this is an inner-city cohort of
11 urban children exposed to relatively high levels of lead by virtue of their residence in older,
12 deteriorated housing units. Relationships between prenatal (maternal) and postnatal exposure to
13 lead (through serial blood lead determinations) and antisocial and delinquent behaviors (self- and
14 parental reports) were examined. Parents were administered a questionnaire developed
15 specifically for the study while the subjects were given the SRD. A wide range of candidate
16 covariates and confounders were examined, but the only ones predicting antisocial or delinquent
17 behavior were birth weight, HOME scores, SES, and parental IQ. In multiple linear regression
18 analyses, prenatal exposure was significantly associated with a covariate-adjusted increase in the
19 frequency of parent-reported delinquent and antisocial acts, whereas prenatal and postnatal lead
20 exposure was significantly associated with a covariate-adjusted increase in frequency of self-
21 reported delinquent and antisocial behaviors, including marijuana use. To clarify the
22 concentration-response relationships, blood lead indices were transformed to categorical
23 variables and least-square means were calculated from an analysis of covariance procedure.
24 Subjects in the highest prenatal blood lead category (>10 |ig/dL) engaged in 2.3 more delinquent
25 acts over the preceding 12 months than subjects in the lowest category (<5 |ig/dL). Using
26 average childhood blood lead levels, subjects in the medium (16-20 |ig/dL) and highest
27 (>20 |ig/dL) category engaged in -1.5 more delinquent acts compared to the lowest category
28 (< 10 |ig/dL). Subjects in the highest 78-month blood lead category (>15 |ig/dL) engaged in
29 4.5 more delinquent acts than subjects in the lowest category (<5 |ig/dL). The authors concluded
30 that lead might play a measurable role in the epigenesis of behavioral problems in inner-city
31 children independent of other social and biomedical cofactors assessed in the study.
May 2006 6-48 DRAFT-DO NOT QUOTE OR CITE
-------
1 Needleman et al. (2002) conducted a case-control study where they examined the levels of
2 lead in bone of 194 adjudicated delinquents and 146 non-delinquent community controls. The
3 subjects were recruited from high schools in the city of Pittsburgh and environs of Allegheny
4 County, PA. Since many delinquents are not arrested or adjudicated, care was taken to ensure
5 that unidentified delinquents did not populate the control group. Potential control subjects were
6 excluded from the analyses if they were found to have a Juvenile Court record or an SRD score
7 above the 90th percentile. Tibial bone lead was measured by K-shell XRF. Covariates included
8 race, parental education and occupation, presence of two parental figures in the home, number of
9 children in the home, and neighborhood crime rate. Logistic regression analyses were used to
10 model the association between bone lead concentration and delinquent status. Cases had
11 significantly higher average concentrations of lead in tibia than controls (11.0 |ig/g [SD 32.7]
12 versus 1.5 |ig/g [SD 32.1]). Stratified analyses showed this for both white and African-American
13 subjects. Following adjustment for covariates, adjudicated delinquents were four times more
14 likely to have bone lead concentration >25 |ig/g than controls (odds ratio of 4.0 [95% CI: 1.4,
15 11.1]). The effect of lead on delinquency was found to be substantial in this study. Bone lead
16 level was the second strongest factor in the logistic regression models, exceeded only by race.
17 In models stratified by race, bone lead was exceeded as a risk factor only by single parent status.
18 The authors concluded that elevated body lead burdens were associated with elevated risk for
19 adjudicated delinquency.
20 The extension of lead effects into delinquent and criminal behavior is significant for both
21 the individual and society as a whole. The particular biological mechanisms that may underlie
22 lead's effects on aggression, impulsivity, and poor self-regulation are not clearly understood.
23 However, lead impacts a large number of sites and processes in the brain that are involved in
24 impulse control (Lidsky and Schneider, 2003). Needleman et al. (2002) proposed another
25 pathway. In addition to lead's direct impact on brain development and neuronal function, lead
26 exposure may increase risk of delinquency through a separate, indirect route: impaired cognitive
27 abilities and academic performance. That is, students who have difficulties in school and fail to
28 achieve academic goals are more likely to become lawbreakers.
29
May 2006 6-49 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.2.7 Sensory Acuities
2 In comparison to cognitive outcomes, there has been relatively less interest in the effects
3 of lead on sensory functions. However, there are clear indications that lead exposure during the
4 developmental period has an impact on complex aspects of visual and auditory acuities. Much of
5 this work has been carried out in animal models (Otto and Fox, 1993). Epidemiologic studies
6 have typically assessed hearing thresholds and features of auditory processing in lead-exposed
7 children. Studies reviewed in this section are summarized in Annex Table AX6-2.7.
8 Schwartz and Otto (1987) observed significant lead-associated elevations in pure-tone
9 hearing thresholds at various frequencies within the range of human speech among over 4,500
10 4 to 19-year-old subjects in NHANES II. In a later study, this finding was replicated in a sample
11 of over 3,000 subjects aged 6 to 19 years in the Hispanic Health and Nutrition Examination
12 Survey (HHANES) (Schwartz and Otto, 1991). An increase in blood lead from 6 to 18 ng/dL
13 was associated with a 2 db loss in hearing at all frequencies, and an additional 15% of children
14 had hearing thresholds that were below the standard at 2,000 Hz. These relationships continued
15 at blood lead levels below 10 |ig/dL.
16 Dietrich et al. (1992) assessed the relationship between scores on a test of central auditory
17 processing (SCAN) and prenatal/postnatal blood lead concentrations in 215 children 5 years of
18 age drawn from the Cincinnati Lead Study. Higher prenatal, neonatal, and postnatal (up to
19 concurrent) blood lead concentrations were associated with more incorrect identification of
20 common monosyllabic words presented under conditions of filtering (muffling). Other variables
21 associated with impaired central auditory processing included the results of pure-tone
22 audiometry testing, social class, HOME scores, birth weight, gestational age, a measure of
23 obstetrical complications, and consumption of alcohol during pregnancy. Following adjustment
24 for these covariates, neonatal and postnatal blood lead levels remained significantly associated
25 with impaired performance on the Filtered Word subtest, more prominently in the right ear.
26 In the right ear, the Filtered Word subtest score decreased by 0.7 points (p < 0.05; 95% CI not
27 presented) for a 10 |ig/dL increase in lifetime average blood lead levels.
28 Osman et al. (1999) examined the relationship between concurrent blood lead levels and
29 hearing loss in 155 children 4 to 14 years of age living in an industrial region of Poland. Blood
30 lead levels ranged from 1.9 to 28 |ig/dL (median 7.2 jig/dL). Hearing thresholds increased
31 significantly with higher blood lead levels at all frequencies (500-8,000 Hz). This relationship
May 2006 6-50 DRAFT-DO NOT QUOTE OR CITE
-------
1 remained statistically significant when restricted to children with blood lead levels below
2 10 |ig/dL.
3 A limited number of epidemiologic studies provide supportive evidence of a relationship
4 between lead exposure and auditory processing. Lead-related deficits in hearing and auditory
5 processing may be one plausible mechanism by which an increased lead burden might impede a
6 child's learning (Bellinger, 1995).
7
8 6.2.8 Neuromotor Function
9 Relatively few studies have focused on neuromotor deficits as an outcome of early lead
10 exposure. However, those that have examined motor functions in lead-exposed children often
11 report positive findings. Studies reviewed here are summarized in Annex Table AX6-2.8.
12 In an early study, unsteadiness, clumsiness, and fine-motor dysfunctions were noted in a
13 group of mildly symptomatic lead-poisoned children in Boston, with such effects persisting long
14 after medical treatment (Pueschel et al., 1972). A study of moderately exposed children living in
15 the vicinity of a longstanding lead smelter in Greece found that children with blood lead levels of
16 35 to 60 |ig/dL had significantly lower scores on both the Gross and Fine Motor Composite
17 scores from the Oseretsky scales when compared to controls (Benetou-Marantidou et al., 1988).
18 Only two modern prospective studies of lead have assessed motor development in a
19 comprehensive manner. Dietrich et al. (1993b) investigated the association between lead
20 exposure and motor developmental status in 245 children 6 years of age in the Cincinnati Lead
21 Study cohort. Following covariate adjustment, they found that postnatal lead exposure was
22 significantly associated with poorer scores on measures of bilateral coordination, visual-motor
23 control, upper-limb speed and dexterity, and the fine motor composite from the Bruininks-
24 Oseretsky scales. Neonatal, but not prenatal, blood lead concentrations also were significantly
25 associated with poorer scores on upper-limb speed and dexterity and the fine motor composite.
26 The strongest and most consistent relationships were observed with concurrent blood lead levels
27 (mean 10.1 |ig/dL [SD 5.6]). A 10 |ig/dL increase in concurrent blood lead levels was associated
28 with a 4.6 point (95% CI: 2.1, 7.1) decline in the fine motor composite score. In the same
29 Cincinnati cohort, postnatal lead exposure was associated with greater postural instability as
30 assessed by a microprocessor-based strain gauge platform system (Bhattacharya et al., 1995).
31 When assessed at 16 years of age, 78-month postnatal blood lead levels were significantly
May 2006 6-51 DRAFT-DO NOT QUOTE OR CITE
-------
1 associated with poorer fine-motor skills as indexed by covariate-adjusted factor scores derived
2 from a factor analysis of a comprehensive neuropsychological battery (Ris et al., 2004). The
3 variables loading highly on the fine-motor component came from the grooved pegboard and
4 finger tapping tasks.
5 Some results of the Cincinnati Lead Study were replicated by Wasserman et al. (2000a)
6 in the Yugoslavian Prospective Study. The Bruininks-Oseretsky Test of Motor Proficiency was
7 adapted for use in their population residing in two towns in the province of Kosovo.
8 The measure of exposure was the log of the lifetime average blood lead concentration through
9 54 months of age. Following covariate-adjustment, average childhood blood lead concentrations
10 were associated with poorer fine motor and visual motor function, but were unrelated to gross
11 motor function.
12 A recent study by Despres et al. (2005) of multiple exposures including lead, mercury,
13 and poly chlorinated biphenyls found that only blood lead concentrations measured at the time of
14 assessment were associated with neuromotor functions in 110 preschool Inuit children residing in
15 Canada. The mean blood lead level was 5.0 |ig/dL (range 0.8-27.1). Blood lead levels were
16 significantly associated with increased reaction time, sway oscillations, alternating arm
17 movements, and action tremor. Ten percent of the children had blood lead levels greater than
18 10 |ig/dL. After eliminating these children from the analyses, results remained significant for
19 reaction time, sway oscillations, and alternating arm movements. These findings indicated that
20 neuromotor effects of lead occurred at blood lead concentrations below 10 |ig/dL.
21
22 6.2.9 Brain Anatomical Development and Activity
23 Electrophysiological evaluations have been conducted on lead-exposed children in
24 attempts to obtain a more direct measure of the toxicant's impact on the nervous system. Much
25 of this work was conducted by Otto and colleagues during the 1980s (e.g., Otto et al., 1985).
26 Studies reviewed in this section are summarized in Annex Table AX6-2.9. These studies have
27 demonstrated effects of lead on neurosensory functioning (auditory and visual evoked potentials)
28 within a broad range of exposures (Otto and Fox, 1993).
29 Rothenberg et al. (1994) reported that higher maternal blood lead levels at 20 weeks of
30 pregnancy were associated with increased I-V and III-V interpeak intervals in the brainstem
31 auditory evoked response recorded in 1-month-old infants. Mean maternal blood lead level at
May 2006 6-52 DRAFT-DO NOT QUOTE OR CITE
-------
1 20 weeks in this subsample from the Mexico City Prospective Study was only 7.7 |ig/dL, with a
2 range of 1 to 30.5 |ig/dL. Rothenberg et al. (2000) repeated these measurements with a larger
3 group of 5 to to 7-year-old children (n = 133). In contrast to their previous findings, prenatal
4 blood lead levels at 20 weeks were associated with decreased interpeak intervals. However, after
5 fitting a nonlinear model to their data, they observed that I-V and III-V interpeak intervals
6 decreased as blood lead rose from 1 to 8 |ig/dL and increased as blood lead rose from 8 to
7 30 |ig/dL. The biphasic effect was only observed with maternal blood leads at 20 weeks of
8 pregnancy. Increasing postnatal blood lead at 12 and 48 months was related to decreased
9 conduction intervals for I-V and III-V interpeak intervals across the entire blood lead range.
10 The methods of Magnetic Resonance Imaging (MRI) and Magnetic Resonance
11 Spectroscopy (MRS) have recently been applied in studies of lead-exposed children. Trope and
12 Lopez-Villegas (1998) were the first to apply MRI and MRS in an evaluation of a lead-exposed
13 subject (see Annex Table AX6-2.9 for a description of the case study). Trope et al. (2001)
14 performed identical MRI and MRS studies on a sample of 16 subjects with a history of elevated
15 blood lead levels (23 to 65 |ig/dL) before five years of age. Average age at time of evaluation
16 was 8 years. These subjects were compared to age-matched controls composed of siblings or
17 cousins. Control subjects had blood lead levels that never exceeded 10 |ig/dL. Although all of
18 the participants had normal MRI examinations, the lead-exposed subjects exhibited a significant
19 reduction in 7V-acetylaspartate: creatine and phosphocreatine ratios in frontal gray matter
20 compared to controls.
21 Meng et al. (2005) performed MRI and MRS studies on children with blood lead
22 concentrations >27 |ig/dL (n = 6) and age- and gender-matched controls with blood lead
23 concentrations <10 |ig/dL (n = 6). The average age at time of evaluation was approximately
24 11 years. Subjects came from the Anhui province in China. Lead-exposed children had an
25 average blood concentration of 37.7 |ig/dL (SD 5.7), while controls averaged 5.4 |ig/dL
26 (SD 1.5). MRS was used to measure 7V-acetylaspartate, choline-containing compounds, and total
27 creatine in the frontal lobes and hippocampus in cases and controls. All children presented
28 with normal MRI with no evidence of structural abnormalities. However, peak values of
29 7V-acetylaspartate, choline, and creatine in all four brain regions were reduced in lead-exposed
30 children relative to controls. The authors concluded that the reduced brain 7V-acetylaspartate
31 levels they observed in cases may be related to decreased neuronal density or neuronal loss.
May 2006 6-53 DRAFT-DO NOT QUOTE OR CITE
-------
1 Furthermore, reduced choline signal may indicate decreased cell membrane turnover or myelin
2 alterations that can lead to central nervous system hypertrophy, while lower creatine may
3 indicate reduced neuronal cell viability.
4 Using functional MRI (fMRI), the influence of childhood lead exposure on language
5 function was examined in a subsample of 48 young adults from the Cincinnati Lead Study
6 (Cecil et al. 2005; Yuan et al., 2006). At age 20-23 years, subjects performed an integrated verb
7 generation/finger tapping paradigm. Higher childhood average blood lead levels were
8 significantly associated with reduced activation in Broca's area, a recognized region of speech
9 production in the left hemisphere. This association remained statistically significant after
10 adjustment for the subject's latest IQ assessment. Higher childhood blood lead levels also were
11 associated with increased activation in the right temporal lobe, the homologue of Wernicke's
12 area (an area associated with speech production) in the left hemisphere. The results of this study
13 suggest elevated childhood lead exposure strongly influences neural substrates of semantic
14 language function on normal language areas with concomitant recruitment of contra-lateral
15 regions resulting in a striking, dose-dependent atypical organization of language function.
16
17 6.2.10 Gene-Environment Interactions in the Expression of Lead-Associated
18 Neurodevelopmental Deficits
19 The discussion of gene-environment interactions with respect to lead exposure
20 encompasses differential susceptibilities with respect to race, gender, and genetic polymorphisms
21 associated with lead metabolism, and neurotransmitter metabolism and function. While the
22 differential effects of lead on neurodevelopment have been studied to some extent with respect to
23 race and gender, very little work has been accomplished with respect to specific genetic
24 polymorphisms.
25 In the U.S., African-American children are at increased risk for having an elevated blood
26 lead level compared with white children. For example, in the last two NHANES surveys,
27 African-American children were found to have significantly higher blood lead levels than whites,
28 even after adjusting for urban residential status and family income (Brody et al., 1994; Mahaffey
29 et al., 1982). However, reliable differences with respect to lead's effects on neurodevelopmental
30 morbidity as a function of race have not been reported with consistency.
31 Most surveys find that boys have higher blood lead levels than girls. The data are less
32 clear with respect to gender-related differences in lead-associated neurodevelopmental
May 2006 6-54 DRAFT-DO NOT QUOTE OR CITE
-------
1 morbidities. At various assessments from birth to adolescence, a greater male vulnerability has
2 been noted in the Cincinnati Lead Study (e.g., Dietrich et al., 1987b; Ris et al., 2004). Data from
3 a cross-sectional study in England showed that the lead-IQ deficit association was more
4 pronounced in boys at 6 years of age (Pocock et al., 1987). However, in a study of 764 children
5 in Taiwan, it was found that the relationship between lead exposure and IQ scores was
6 substantially stronger in girls (Rabinowitz et al., 1991). In the Port Pirie cohort study, lead
7 effects on cognition were significantly stronger in girls at ages 2, 4, 7, and 11-13 years
8 (Baghurst et al., 1992; McMichael et al., 1992; long et al., 2000).
9 At least two genetic polymorphisms have been identified that can influence the
10 absorption, retention and toxicokinetics of lead in humans (Onalaja and Claudio, 2000). The
11 ALAD gene has been the most studied but, as yet, the consequences of the different alleles for
12 susceptibility to the neurodevelopmental consequences of lead exposure are unclear. Individuals
13 with the ALAD12 or ALAD22 polymorphism tend to have higher blood lead levels than those
14 with ALAD11. ALAD2 could increase vulnerability by raising blood lead levels or decrease it
15 by maintaining lead in a sequestered state in the bloodstream. Only one pediatric study has
16 examined this directly. Bellinger et al. (1994a) found that subjects with the ALAD2
17 polymorphism tended to have lower dentin levels than those with ALADl. This is consistent
18 with the concept that increased affinity of the ALAD2 polymorphism inhibits entry of lead from
19 the blood stream into other tissues. After adjustment for exposure level, Bellinger et al. found
20 that adolescents with the ALAD2 polymorphism performed better in the areas of attention and
21 executive functioning assessed in their study when compared to subjects with the ALADl
22 polymorphism. However, as there were only 5 subjects with the ALAD2 form, meaningful
23 statistical comparisons could not be made.
24 The other gene that has been studied is the vitamin D receptor or VDR gene. This gene is
25 involved in calcium absorption through the gut. Research on lead workers has shown that
26 variant VDR alleles modify lead concentrations in bone, and the rate of resorption and excretion
27 of lead over time (Schwartz et al., 2000a). Haynes et al. (2003) examined the relationship
28 between the VDR Fokl polymorphism and blood lead concentrations in 275 children enrolled in
29 the Rochester Longitudinal Study. It was hypothesized that children homozygous for the
30 F allele—a marker for increased calcium absorption—would have higher blood lead
31 concentrations than heterozygotes and children homozygous for the/allele, after adjusting for
May 2006 6-55 DRAFT-DO NOT QUOTE OR CITE
-------
1 environmental sources of lead (floor dust lead). A statistically significant interaction was found
2 between floor dust lead loading and VDR-Fokl genotypes on blood lead concentration, with the
3 FF genotypes having the highest adjusted mean blood lead concentrations at 2 years of age.
4 Consistent with other reports, Haynes et al. (2003) also found that African American children
5 were significantly more likely to have the VDR-FFthan were non-African American children.
6 The ability of African American children to have increased calcium absorption may partially
7 explain the higher blood lead concentrations observed in African American children.
8 Unfortunately, there have been no studies to indicate which, if any, of the VDR polymorphisms
9 are associated with increased vulnerability to the neurodevelopmental toxicity of lead.
10
11 6.2.11 Reversibility of Lead-Related Neurodevelopmental Deficits
12 Associated with Prenatal and Postnatal Exposure
13 The apparent persistence of the neurodevelopmental effects of lead observed into later
14 childhood and adolescence has resulted in a widely held view that the damage to the central
15 nervous system and resulting deficits in neurobehavior are irreversible. The ramifications of the
16 effects of lead on neurodevelopment depend not only on the extent of the initially observable
17 effects in early childhood, but also on their enduring consequences for cognition, attainment, and
18 behavior over the lifetime of the individual. Recent studies examining the reversibility of lead-
19 related neurodevelopmental deficits are summarized in Annex Table AX6-2.10. Key studies are
20 further discussed in this section.
21 Since 1990, several studies attempted to eliminate or at least reduce lead-associated
22 neurodevelopmental damage through nutritional and/or pharmacological interventions.
23 Optimism that such interventions might be effective was raised by a New York study published
24 in the early 1990s. Ruff et al. (1993) observed that among children 13 to 87 months old (blood
25 lead levels 25-55 |ig/dL) who were given chelation with EDTA and therapeutic iron, those with
26 the greatest decline in blood lead levels had improved cognitive test scores, independent of
27 whether they had been given iron or chelation therapy.
28 The Treatment of Lead-Exposed Children (TLC) study was originally designed to test the
29 hypothesis that children with moderate blood lead levels who were given an oral chelating drug
30 (dimercaptosuccinic acid or "succimer") would have better scores than children given placebo on
31 a wide range of tests measuring cognition, neuropsychological functions, and behavior at 36
May 2006 6-56 DRAFT-DO NOT QUOTE OR CITE
-------
1 months of follow-up (Rogan et al., 2001). TLC enrolled 780 children from four clinical sites
2 into a randomized, placebo-controlled, double-blind trial of up to three 26-day courses of
3 treatment with succimer. Most children lived in deteriorating inner-city housing. Seventy-seven
4 percent of the subjects were African American. Succimer was effective in lowering the blood
5 lead levels of subjects on active drug during the first 6 months of the trial. However, after
6 1 year, differences in the blood lead levels of succimer and placebo groups had virtually
7 disappeared. All data analyses were conducted on an intent-to-treat basis. At 36 months of
8 follow-up, the mean IQ score on the WPPSI-R of children given active drug was 1 point lower
9 than that of children administered placebo, and children given succimer evinced more behavioral
10 problems as rated by the primary caregiver on the Conners Parent Rating Scale. Children given
11 succimer scored marginally better on the Developmental Neuropsychological Assessment
12 (NEPSY), a battery of tests designed to measure neuropsychological deficits that can interfere
13 with learning. However, all of these differences were statistically nonsignificant.
14 Although results for the first wave of follow-up for TLC were consistently negative for
15 drug effects on cognition and behavior, they were not necessarily conclusive. Lead may affect
16 higher-level neurocognitive processes that are inaccessible, difficult to assess, or absent in the
17 preschool age child. In older children, scores on psychometric measures are more precise and
18 reliable, a wider and more differentiated range of abilities can be examined, and early academic
19 performance and social functioning outside the home environment can be evaluated. Therefore,
20 TLC followed the cohort into the first years of elementary education to determine whether these
21 later emerging neurodevelopmental functions were spared the effects of lead in treated children
22 compared to placebo controls (Dietrich et al., 2004). While remaining within the limits of
23 hypothesis driven inference, a comprehensive battery of tests were administered to TLC subjects
24 at 7 and 7.5 years of age. These included assessments of cognition, learning, memory, global
25 intellectual attainment, attention/executive functions, psychiatric status, behavioral and academic
26 conduct, neurological functioning, and motor speed. However, treatment with succimer resulted
27 in no benefit in cognitive, behavioral, neurological, and neuromotor endpoints. Indeed, children
28 treated with succimer fared worse than children in the placebo group in several areas, including
29 linear growth, hospitalized and outpatient injury events in the first 3 years of follow-up, and
30 neuropsychological deficits as assessed by the Attention and Executive Functions core domain
31 score from the NEPSY. The authors concluded that these latest follow-up data confirmed their
May 2006 6-57 DRAFT-DO NOT QUOTE OR CITE
-------
1 previous finding that the TLC regimen of chelation therapy is not associated with
2 neurodevelopmental benefits in children with blood lead levels between 20 and 44 |ig/dL.
3 Furthermore, these results emphasize the importance of taking environmental measures to
4 prevent exposure to lead in light of the apparent irreversibility of lead-associated
5 neurodevelopmental deficits.
6 Liu et al. (2002) used the TLC succimer trial data set (Rogan et al., 2001) to examine the
7 question of reversibility. As reviewed above, intent-to-treat analyses revealed no benefits of
8 chelation on neurodevelopmental indices beyond 6 months of treatment. Thus, the scores on the
9 cognitive tests from the two treatment groups could be analyzed either within the treatment
10 groups or as a whole. Data from 741 children were available for analyses. Mean blood lead
11 levels in TLC subjects were 26.2 |ig/dL at baseline, 20.2 |ig/dL at the 6-month follow up, and
12 12.2 |ig/dL at the 36-month follow-up. Mean declines in blood lead levels were 6.0 |ig/dL from
13 baseline to 6-month follow-up, 14.1 |ig/dL from baseline to 36-month follow-up, and 8.0 |ig/dL
14 from 6- to 36-month follow-ups. Blood lead levels declined more quickly in the first 6 months in
15 the succimer group than in the placebo group, but the mean blood lead levels were very similar at
16 baseline and at the 36-month follow-up. Prior to examining changes in blood lead levels in
17 relationship to changes in cognitive test scores, it was verified that baseline and later blood lead
18 levels were indeed significantly associated with deficits on measures administered at specific
19 points in the study after adjustment for sociohereditary factors surveyed in the study including
20 maternal IQ. Unlike in the New York study by Ruff et al. (1993), Liu et al. (2002) found no
21 overall effect of changing blood lead level on changes in cognitive test score from baseline to
22 6 months. However, during the follow-up from baseline to 36 months and from 6 to 36 months,
23 falling blood lead levels were significantly associated with increased cognitive test scores, but
24 only because of an association in the placebo group. Cognitive test scores increased by 2 points
25 overall and 4 points in the placebo group when blood lead levels declined by 10 |ig/dL from
26 baseline to 36 months. There is a possibility that the succimer drug regimen blunted the
27 beneficial effect. Due to the inconsistency in the results, the data do not provide strong
28 supportive evidence that lead-induced cognitive impairments are reversible.
29 In addition to pharmacological interventions, a few studies have attempted to remediate or
30 prevent lead-associated neurodevelopmental deficits through nutritional supplementation.
31 Recent studies attempting to reduce lead absorption through mineral hypersupplementation have
May 2006 6-58 DRAFT-DO NOT QUOTE OR CITE
-------
1 been disappointing (Sargent et al., 1999). However, to date there has been only one controlled
2 clinical trial involving lead-exposed children where central nervous system outcomes have been
3 the focus of study. Kordas et al. (2005) and Rico et al. (2006) conducted a double-blind
4 nutritional supplementation trial among 602 first grade children in the city of Torreon in northern
5 Mexico. The city is located near a metal foundry that has been a source of lead contamination in
6 the community. The average blood lead concentration at baseline was 11.5 |ig/dL (SD 6.1).
7 About half of the children had blood lead concentrations in excess of 10 |ig/dL. Subjects
8 received 30 mg ferrous fumarate, 30 mg zinc oxide, both, or placebo daily for 6 months. In their
9 first report, the principal outcome assessment taken at baseline and at follow-up was the parent
10 and teacher forms of the Conners Rating Scales. There were no consistently significant
11 treatment effects and the authors concluded that this regimen of supplementation did not result in
12 improvements in ratings of behavior in lead-exposed children over 6 months. In addition to
13 behavior, the authors assessed cognitive functioning with 11 tests of memory, attention, visual -
14 spatial abilities, and learning. There were no consistent or lasting differences in cognitive
15 performance among treatment groups confirming the earlier conclusion that nutritional
16 supplementation alone is not effective in eliminating or reducing the impact of early lead
17 exposure on functional neurodevelopment.
18 Children's blood lead levels generally decline after they peak at somewhere around
19 2 years of age. However, the degree of decline is a function of a number of factors including
20 previously acquired body burden and sources of continuing exposure. Some observational
21 studies have examined the extent to which the rate of decline in blood lead levels is associated
22 with improvements in neurocognitive status. Tong et al. (1998) assessed the reversibility of the
23 cognitive effects of lead in early childhood in the Port Pirie, Australia cohort study. A total of
24 375 children were followed to the age of 11-13 years. Average blood lead concentrations
25 decreased from 21.2 |ig/dL at 2 years to 7.9 |ig/dL at 11-13 years. However, scores on
26 standardized measures of intellectual attainment administered at 2, 4, 7, and 11-13 years of age
27 in children whose blood lead levels declined the most were not significantly improved over those
28 obtained by children with a more shallow decline in body burden.
29 Collectively, these studies indicate that primary prevention and preventing additional
30 increases in blood lead levels among children whose blood lead levels are high remain the only
31 effective means of dealing with lead toxicity.
May 2006 6-59 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.2.12 Periods of Enhanced Developmental Susceptibility to Central Nervous
2 System Effects of Environmental Lead
3 It has been difficult to identify discrete periods of development when the fetus or child is
4 particularly susceptible to lead's effects on neurodevelopment. When the prospective studies of
5 lead and child development were underway, it was hoped that this methodological approach
6 would be revealing. However, these studies observed that age strongly predicted the period of
7 peak exposure (around 18-27 months when there is maximum hand-to-mouth activity), making it
8 difficult to distinguish whether greater neurotoxic effects resulted from increased exposure or
9 enhanced susceptibility at a particular age. Furthermore, children with the highest blood lead
10 levels tended to maintain their rank order relative to their lower exposed peers throughout these
11 studies (e.g., Dietrich et al., 1993a; McMichael et al., 1988), limiting the degree to which
12 investigators could identify any particular period of development as critical.
13 From the perspective of human neurodevelopmental biology, one could argue that the first
14 3 years of life should represent a particularly vulnerable period. Maximal ingestion of lead
15 coincides with the same period of time when major events are occurring in the development of
16 the central nervous system including some neurogenesis, rapid dendritic and axonal outgrowth,
17 synaptogenesis, synaptic pruning, and programmed apoptosis (see Figure 6-2.3).
18 This belief that the first 3 years represents a critical window of vulnerability is evident in
19 the lead literature (Chen et al., 2005). Two major meta-analyses of the relationships between
20 childhood lead exposure and IQ focused primarily on the strength of the association between IQ
21 at school age and blood lead concentrations at 2 years of age or average blood lead levels up to
22 3 years of age (Pocock et al, 1994; Schwartz, 1994). Neither meta-analysis considered the
23 importance of concurrent blood lead associations in older children. The focus on these particular
24 age groups implied that the interpretation most consistent with the overall results was that peak
25 blood lead concentration, achieved somewhere between 1 and 3 years of age, was most likely
26 responsible for the cognitive effects observed years later. These meta-analyses were highly
27 influenced by findings from the Boston prospective study where blood lead concentrations at
28 2 years of age have been exclusively and consistently associated with lower IQ and academic
29 achievement (Bellinger et al., 1992).
30 This particular interpretation of the lead literature has also influenced screening programs
31 (which focus on 1 and 2 year olds), clinical trials that recruit children during the first 3 years of
May 2006 6-60 DRAFT-DO NOT QUOTE OR CITE
-------
,
' '
M IJl,
(I : i,
• 1
i -4
- A
,«
Newborn
v
1 month
6 months
Figure 6-2.3. Golgi-stained section of human cerebral cortex taken from equivalent
areas of the anterior portion of the middle frontal gyrus at different ages.
Although the packing density of cortical neurons does not appear to change,
there is a tremendous increase in the complexity of dendritic arborizations
with increasing age with maximal density occurring between two and three
years of age.
Source: Nolle (1993).
1 life, and current interpretation of the cross-sectional literature. For example, the report by
2 Lanphear et al. (2000) that school-age children enrolled in the NHANES III survey displayed a
3 significant inverse relationship between concurrent blood lead concentrations and measures of
4 IQ and academic achievement at blood lead concentrations below 10 |ig/dL was interpreted by
5 some to reflect the effects of the children's higher blood lead concentrations when they were
6 between 1-3 years of age.
7 However, it is not clear that only the period of peak blood lead concentration matters in
8 terms of the risks for neurodevelopmental morbidity. Other prospective studies of children with
9 both high and low lead exposures found concurrent or lifetime average blood lead levels to be
10 more strongly associated with school age IQ and other measures of neurodevelopment (Canfield
11 et al., 2003a; Dietrich et al., 1993a,b; long et al., 1996; Wasserman et al., 2000b). One study
May 2006
6-61
DRAFT-DO NOT QUOTE OR CITE
-------
1 has recently attempted to address this question directly. Chen et al. (2005) sought to clarify the
2 strength of the association between IQ and blood lead at various time points, to examine whether
3 the cross-sectional associations observed in school age children 84-90 months of age represented
4 residual effects from 2 years of age or "new" effects emerging among these children, and how
5 the change in blood lead over time is related to IQ at later ages. Chen et al. (2005) used data on
6 780 children from the previously described TLC multicenter clinical trial (Dietrich et al., 2004;
7 Rogan et al., 2001) to examine these relationships. Homogeneity between the two treatment
8 groups was verified. There were no statistical differences between succimer and placebo groups
9 in either blood lead concentrations or cognitive scores at the time points under consideration.
10 At baseline, children were given the Bayley Scales of Infant Development. The children's full
11 scale IQ at the 36-month follow-up was measured with the WPPSI-R. At the 60 month follow-
12 up, IQ was assessed with the WISC-III. All neurodevelopmental outcomes were adjusted for
13 clinical center, race, gender, language, parent's education, parent's employment, single parent
14 family, age at blood lead concentration, and caregiver's IQ.
15 Figure 6-2.4 displays the mean IQ at current and subsequent ages by quartiles of blood
16 lead measured at 2, 5, and 7 years of age. The concurrent blood lead concentration always had
17 the strongest association with IQ. As the children aged, the relationship grew stronger. The
18 peak blood lead concentration from baseline to 7 years of age was not associated with IQ at
19 7 years of age. Furthermore, in models including both prior and concurrent blood lead
20 concentrations, concurrent blood lead was always more predictive of IQ. Adjustment for prior
21 IQ did not fundamentally change the strength of the association with concurrent blood lead
22 concentration. Chen et al. (2005) found a stronger relationship between IQ at 7 years of age and
23 blood lead concentration at 7 years compared with blood lead at 2 years of age. A similar
24 relationship was observed between IQ and blood lead at 5 years of age. The strength of the
25 cross-sectional associations increase over time, despite lower blood lead concentrations in older
26 children. These data support the idea that lead exposure continues to be toxic to children as they
27 reach school age, and does not lend support to the interpretation that all of the damage is done by
28 the time the child reaches 2 to 3 years of age. These findings also imply that cross-sectional
29 associations observed in children, such as the study recently conducted by Lanphear et al. (2000)
30 using data from NHANES III should not be dismissed. Chen et al. (2005) concluded that if
May 2006 6-62 DRAFT-DO NOT QUOTE OR CITE
-------
95 -i
90 -
3
£
5 85 -I
80 -
75
I
10
I
15
\
20
5 10 15 20 25 30
Blood Lead Concentration ((jg/dL)
35
~
40
-O- MDI at baseline by baseline blood lead concentration
-Q- IQ at age 5 by baseline blood lead concentration
-A" IQ at age 7 by baseline blood lead concentration
-X- IQ at age 5 by blood lead concentration at age 5
-#- IQ at age 7 by blood lead concentration at age 5
-O~ IQ at age 7 by blood lead concentration at age 7
Figure 6-2.4. Full scale IQ test scores by previous or concurrent blood lead concentration.
Each data point shows the mean IQ test scores of children measured at
baseline or at two follow-ups, grouped by quartiles of blood lead
concentration. The abscissa of each point is the middle value of each
blood lead concentration category.
Source: Chen et al. (2005).
1 concurrent blood lead remains important until school age for optimum cognitive development,
2 and if 6 and 7 year olds are as or more sensitive to lead effects as 2 year olds, then the difficulties
3 in preventing lead exposure are magnified but the potential benefits of prevention are greater.
May 2006
6-63
DRAFT-DO NOT QUOTE OR CITE
-------
1 6.2.13 Effect of Environmental Lead Exposure on Neurodevelopment at the
2 Lower Concentration Range
3 Over the last three decades, epidemiologic studies of lead and child development have
4 demonstrated inverse associations between blood lead concentrations and children's IQ and other
5 outcomes at successively lower levels. The 1986 Addendum and 1990 Supplement concluded
6 that neurobehavioral effects were related to blood lead levels of 10 to 15 |ig/dL and possibly
7 lower. In response to these data, agencies such as the U.S. Centers for Disease Control and
8 Prevention and the World Health Organization have repeatedly lowered the definition of an
9 elevated blood lead concentration, which now stands at 10 ng/dL (CDC, 1991; WHO, 1995).
10 At the time when these policies were put in place, there were too few studies of children with
11 blood lead levels consistently below 10 |ig/dL on which to base an opinion as to effects at lower
12 levels of exposure. Since the removal of lead from gasoline, the median blood lead
13 concentration has dropped dramatically in U.S. children, permitting more studies of this nature to
14 be done in recent years. Furthermore, the use of meta- and pooled analytic strategies has
15 permitted investigators to get a clearer picture of effects below 10 |ig/dL.
16 Table 6-2.2 Examines the relationships between IQ and blood lead level for patients with
17 a blood lead level less than 10 |ig/dL. The first group includes studies where all or nearly all of
18 the subjects in the study had blood lead levels less than 10 |ig/dL. The second group includes
19 studies where an analysis was done on the subset of patients whose blood lead levels were less
20 that 10 |ig/dL. The third group of studies are based on models fitted to the entire range of blood
21 lead levels but the model was evaluated over the range of blood lead levels less than 10 |ig/dL
22 Because this involves several parameters (except for linear models), no standard errors could be
23 calculated.
24 The Rochester Prospective Study (n = 172) by Canfield et al. (2003a) is illustrative. This
25 study extended the relationship between blood lead concentrations and deficits in IQ to levels
26 well below 10 |ig/dL. Over half of the children in this study did not have a recorded blood lead
27 concentration above 10 |ig/dL. Nonlinear semiparametric smoothing revealed a covariate-
28 adjusted decline of more than 7 points up to 10 |ig/dL of childhood average blood lead and a
29 further decline of 2 points associated with an increase from 10 to 20 |ig/dL. In response to the
30 Rochester findings, Bellinger and Needleman (2003) reanalyzed data from the Boston
31 Prospective Study focusing on children whose blood lead levels never exceeded 10 |ig/dL
May 2006 6-64 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-2.2. Summary of Studies with Quantitative Relationships of
IQ and Blood Lead for Blood Lead Levels Less than 10 ug/dL
Estimated Slope
(IQ points/jig/dL) for
Blood Lead Under
Reference Study Location n Model Used 10 jig/dL
Studies of Populations with Blood Leads Less than 10 jig/dL
Tellez-Rojo et al. (in press) Mexico City, Mexico 566 Log-linear -1.0
Al-Saleh et al. (2001) Riyadh, Saudia Arabia 532 Log-linear -0.6
Studies of Populations Restricted to Those Subjects with Blood Leads Less than 10 jig/dL
Bellinger etal. (1992) Boston, Massachusetts 116 Linear -1.6
Kordas et al. (2006) Torreon, Mexico 589 Linear -1.1
Canfield et al. (2003a) Rochester, New York 182 Quadratic -0.8
Lanphear et al. (2005) International Pooled Analysis 1,333 Linear -0.8
Studies of Populations with 15 Percent or More of the Population having Blood Leads Levels
Less than 10 jig/dL
Results Based on Models for the Entire Population Evaluated for Blood Lead Levels Less than 10 jig/dL
Dietrich et al. (1993a) Cincinnati, Ohio 221 Linear -0.3
Baghurst etal. (1992) Port Pirie, South Australia 324 Log-linear -0.4
Silva etal. (1988) Dunedin, New Zealand 579 Linear -0.3
1 (n = 48). In their analyses, 10 year IQ was inversely related to blood lead levels at 24 months
2 following adjustment for covariates. Nonparametric smoothing analyses indicated that the
3 inverse association persisted at blood lead levels below 5 |ig/dL.
4 Other recent studies demonstrating effects below 10 |ig/dL include a prospective study
5 conducted in Mexico City by Tellez-Rojo et al. (2006). In a cohort of 294 children with blood
6 lead levels never exceeding 10 |ig/dL, a statistically significant relationship was observed
7 between blood lead concentrations and MDI assessed concurrently at 24 months of age.
8 Furthermore, a stronger effect of lead on MDI was observed among infants with blood lead
9 concentrations below 5 |ig/dL.
May 2006 6-65 DRAFT-DO NOT QUOTE OR CITE
-------
1 The most compelling evidence for effects below 10 |ig/dL comes from an international
2 pooled analysis of seven prospective cohort studies (n = 1,333) by Lanphear et al. (2005)
3 described earlier. Although exposures in some cohorts were high, by pooling data from these
4 studies a substantial number (n = 244) of children with blood lead levels that never exceeded
5 10 |ig/dL were included in the analyses.
6 The slope of the lead effects on IQ was steeper at lower blood lead levels as indicated by
7 the cubic spline function, the log-linear model, and the piece-wise linear model. Initially, the
8 authors attempted to fit a linear model, but the shape of the dose-response relationship was
9 determined to be non-linear insofar as the quadratic and cubic terms for concurrent blood lead
10 were statistically significant (p < 0.001, p = 0.003, respectively). As illustrated in Figure 6-2.5,
11 the shape of the spline function indicated that the steepest declines in IQ were at blood lead
12 concentrations below 10 |ig/dL. Additional support for the notion of steeper slopes at lower
13 blood lead levels was given in Figure 6-2.2 (Section 6.2.3.1), which presented the individual
14 effect estimates for the seven studies used in the pooled analysis. The studies with the lowest
15 mean blood lead concentrations had a steeper slope compared with the studies with higher mean
16 blood lead concentration.
17 The cubic spline regression is a descriptive tool; it is not used for inference. Thus, the
18 agreement of the log-linear with the spline function was tested. Because the restrictive cubic
19 spline indicated that a log-linear model provided a good fit of the data, the log of concurrent
20 blood lead was used in all subsequent analyses of the pooled data. Using a log-linear model, the
21 authors estimated a decrement of 1.9 points (95% CI: 1.2, 2.6) in full scale IQ for a doubling of
22 concurrent blood lead. However, the IQ point decrements associated with an increase in blood
23 lead from <1 to 10 |ig/dL compared to 10 to 20 |ig/dL were 6.2 points (95%CI: 3.8, 8.6) versus
24 1.9 points (95% CI: 1.2,2.6). Figure 6-2.6 illustrates the log-linear model and adjusted mean IQ
25 for the intervals < 5, 5-10, 10-15, 15-20, and >20 |ig/dL. All of these means are within the
26 confidence band for the log linear model. These data support the conclusion that the observed
27 steeper slopes at lower blood lead levels in the pooled analysis were not due to the use of a
28 log-linear model.
29 To further investigate whether the lead-associated decrement was greater at lower blood
30 lead concentrations, the investigators divided the data at two cutpoints a priori, a maximal blood
31 lead of 7.5 and 10 |ig/dL. Separate linear models were then fit to the data above and below the
May 2006 6-66 DRAFT-DO NOT QUOTE OR CITE
-------
03
CO
"5
105
100
90
85
Log-linear Model
5 Knot Spline
95% Cl
0 5 10 15 20 25 30 35 40
Concurrent Blood Lead (|jg/dL)
Figure 6-2.5 Restricted cubic splines and log-linear model for concurrent blood lead
concentration. The dotted lines are the 95% confidence intervals for the
restricted cubic splines.
Source: Lanphear et al. (2005).
1 outpoints and the concurrent blood lead coefficients were compared (see Figure 6-2.7 for the
2 analysis using the cutpoint of 10 |ig/dL). The coefficient for the 103 children with maximal
3 blood lead levels <7.5 |ig/dL was significantly greater (p = 0.015) than the coefficient for the
4 1,230 children with a maximal blood lead >7.5 jig/dL (-2.94 points [95% CI: -5.16, -0.71] per
5 1 |ig/dL increase in blood lead versus -0.16 points [95% CI: -2.4, -0.08]). The coefficient for
6 the 244 children who had a maximal blood lead <10 |ig/dL also was greater than that for the
7 1,089 children who had a maximal blood lead >10 ng/dL (-0.80 points [95% CI: -1.74, -0.14]
8 versus -0.13 points [95% CI: -2.3, -0.03]), although the difference was not statistically
9 significant (p = 0.10). Thus, while the pooled analysis used a log-linear model to quantify the
10 lead-associated decrements, the nonlinear relationship observed in the analysis was clearly not
11 due to the influence of the log-linear model itself.
May 2006
6-67
DRAFT-DO NOT QUOTE OR CITE
-------
105
100
g
"ro
CO
"5
**c
95
90
85
10 20 30
Concurrent Blood Lead (pg/dL)
40
Figure 6-2.6 Log-linear model (95% CI shaded) for concurrent blood lead concentration
adjusted for HOME score, maternal education, maternal IQ, and birth
weight. The mean IQ (95% CI) for the intervals <5, 5-10,10-15,15-20, and
>20 ug/dL are shown.
Source: Lanphear et al. (2005).
105
100
8 95
U.
90
85
Log-linear Model
Peak Blood Lead <10 pg/dL
Peak Blood Lead ^10 pg/dL
10 20 30
Concurrent Blood Lead (ug/dL)
40
Figure 6-2.7. Log-linear model for concurrent blood lead concentration along with linear
models for concurrent blood lead levels among children with peak blood
lead levels above and below 10 ug/dL.
Source: Lanphear et al. (2005).
May 2006
6-68
DRAFT-DO NOT QUOTE OR CITE
-------
1 Rothenberg and Rothenberg (2005) reanalyzed the Lanphear et al. (2005) pooled study to
2 examine the form of the concentration-response function for the lead exposure effect on child IQ.
3 This further analysis also focused on concurrent blood lead levels. Rothenberg and Rothenberg
4 reported that a log-linear relationship between blood lead and IQ was a significantly better fit
5 within the ranges of the blood lead levels than was a linear relationship (p = 0.009), with little
6 evidence of residual confounding from included model variables. Once again, this is consistent
7 with a steeper slope at lower compared to higher levels of lead.
8 For the entire pooled data set, the observed decline of 6.2 points in IQ for an increase in
9 blood lead levels from 1-10 |ig/dL was comparable to the decrements for an increase in lifetime
10 mean blood lead levels from <1 to 10 |ig/dL observed in the Rochester Longitudinal Study
11 (Canfield et al., 2003a). The pooled analysis of Lanphear et al. also demonstrated that deficits in
12 IQ extended to blood lead levels <7.5 |ig/dL. Therefore, recent evidence is suggestive of effects
13 of lead on neurocognitive deficits at blood lead levels below 10 |ig/dL, and possibly below
14 7.5 |ig/dL, in children.
15 A common observation among some of these low blood-lead level studies is the
16 observation of non-linear dose-response relationships between blood lead and
17 neurodevelopmental outcomes. At first this may seem at odds with certain fundamental
18 toxicological concepts. However, there are a number of examples of non-linear or supralinear
19 dose-effect relationships in toxicology (Calabrese and Baldwin, 2001). It is conceivable that the
20 initial neurodevelopmental lesions at lower lead levels may be disrupting very different
21 biological mechanisms than the more severe effects of high exposures that result in symptomatic
22 poisoning or frank mental retardation (Dietrich et al. 2001). As Kordas et al. (2006) states, this
23 might help explain why, within the range of exposures not producing overt clinical effects, an
24 increase in blood lead beyond a certain concentration might cause less additional impairment in
25 children's cognitive functions.
26
27 6.2.14 Selection and Validity of Neuropsychological Outcomes in Children
28 A fair amount of material has been written about methodologies for neurobehavioral
29 evaluation in studies of environmental chemicals and child development (Bellinger, 2002, 2003;
30 Dietrich et al., 2005). Much of the discussion has centered on the ability of neurobehavioral tests
May 2006 6-69 DRAFT-DO NOT QUOTE OR CITE
-------
1 to detect damage to the central nervous system as a result of in utero or early postnatal
2 exposures. In other words, the sensitivity of these tests to toxicity has been in question. The
3 sensitivity of a neuropsychological or any other diagnostic test is defined as the proportion with
4 the abnormality that the test classifies as abnormal (true positives). In the selection of
5 neurodevelopmental measures in studies of lead or any other toxicant, it is clearly advantageous
6 to include tests that have the best prognostic value. This is particularly important in the current
7 context, because the neurobehavioral endpoints reviewed in this document are being
8 incorporated into an assessment of risk (Bellinger, 2002). In addition, it is important to select
9 instruments that tap into neurodevelopmental domains that have shown to be sensitive to
10 particular environmental toxicants. As evident in this review, a large number of
11 neuropsychological instruments, tapping a wide range of domains have proven to be sensitive to
12 lower level lead exposure. Certain domains such as attention, executive functions, visual-spatial
13 skills, fine-motor abilities, academic achievement (reading in particular), and externalizing
14 behaviors appear to be affected by lead with some degree of consistency. However, the
15 identification of behavioral phenotypes for lead has been a largely elusive goal. There are a
16 number of plausible reasons for this. The sample's SES; level, pattern and timing of exposures;
17 nutritional intake; general health; educational opportunities; and the particular instruments that
18 were employed in a given study probably play an important role in between-study differences
19 (Bellinger, 1995; Schantz, 1996). This may be one reason why the broad net provided by global,
20 multiple domain assessments of cognition such as IQ have proven to be the most consistently
21 sensitive across studies of various design and sample characteristics. These measures combine
22 subscales that are representative of a broad number of underlying cognitive functions; thus, they
23 are likely to pick up exposure-related deficits across cohorts that differ in their functional
24 expressions of toxicity (Dietrich et al., 2005).
25 The validity of neuropsychological tests as indices of neurodevelopment in lead studies
26 also is of concern. In psychometrics, there are various types of validity. But the validity lead
27 researchers are usually most concerned about is "construct validity." If a measure has construct
28 validity it measures what it purports to measure. Most lead researchers utilize assessments with
29 proven construct validity. This means that the instruments utilized by the investigator have
30 proven that they possess concurrent and predictive "criterion" validity (i.e., it relates to other
31 manifestations of the construct the instrument is supposed to be measuring and predicts an
May 2006 6-70 DRAFT-DO NOT QUOTE OR CITE
-------
1 individual's performance in the future in specific abilities). It also means that the instrument
2 possesses good "convergent validity." This means that the test returns similar results to other
3 tests that purport to measure the same or related constructs. Finally, the instrument should
4 demonstrate "discriminant validity." That is, the instrument is not measuring a construct that it
5 is not supposed to measure, it discriminates.
6 Bellinger (2003) states that the general literature attests to robust observations between IQ
7 and important measures of life success, such as grades in school, years of education, job success,
8 social status, and income (Neisser et al., 1996; Salkever, 1995). Testing is difficult depending on
9 examined age, especially for infants who are in a period of rapid developmental change. Also,
10 the way an infant's cognitive function can be probed is restricted. The lack of continuity
11 between their response modalities and ones that can be exploited as a child gets older is also a
12 factor. Still neurobehavioral tests scores in infancy do possess strong concurrent validity.
13 There are many potential sources of invalidity which researchers take steps to avoid.
14 These include unreliability (an instrument that, all other things being equal, yields scores that are
15 unrepeatable and inconsistent) and bias (e.g., due to factors such as culture, gender). Most
16 modern standardized measures of development and cognitive attainment have taken steps to
17 reduce these sources of invalidity and must meet certain minimum requirements such as those
18 formulated by the American Educational Research Association, American Psychological
19 Association, and the National Council on Measurement in Education (American Educational
20 Research Association et al., 1999). One reason that global measures of IQ have been used so
21 widely is because of their outstanding psychometric properties. The Wechsler series has
22 excellent reliability and validity (Groth-Marnat, 2003). For example, the average internal
23 consistency for the Wechsler children's scales across all age groups is 0.96. Test-retest
24 reliability is similarly very high. The underlying factor structure of these scales has also been
25 strongly confirmed. The validity of so-called experimental measures of learning and cognition is
26 sometimes less certain.
27 All measurement procedures have the potential for error, so the goal of the researcher is to
28 minimize it. In elementary psychometric theory, any observed test score is made of the "true"
29 score plus measurement error. It is assumed that measurement errors are essentially random (the
30 child's true score may not be reflected in the observed score because of errors of administration,
31 inconsistency of administration across examiners, the child's health, or aspects of the testing
May 2006 6-71 DRAFT-DO NOT QUOTE OR CITE
-------
1 environment that are not conducive to performance). This does not mean that lead researchers
2 cannot take pains to reduce these sources of error. In fact, most modern lead researchers do
3 minimize measurement error through attention to training, establishing inter-examiner reliability,
4 attention to child factors, site factors, and vigilant monitoring of examiner performance
5 throughout the course of a study (Dietrich et al., 2005).
6
7 6.2.15 Confounding, Causal Inference, and Effect Modification of the
8 Neurotoxic Effects of Lead in Children
9 The major challenge to observational studies of lead's impact on parameters of child
10 development has been the assessment and control for confounding factors. By definition, a
11 confounder is associated with both the exposure and the outcome, thus has the potential to
12 influence the association between the exposure and the outcome. Confounding by various
13 factors can be controlled for in the design phase of the study or in the analytical phase. In the
14 realm of lead research, there are a wide range of potential confounders, the foremost of which is
15 SES. Socioeconomic status is measured rather crudely in most studies with such indices as the
16 Hollingshead Four-Factor Index of Social Position that incorporates education and income of
17 both parents. However, even these so-called blunt measures often account for a great deal of the
18 variance in neurodevelopmental outcomes. Given the crude nature of these measures, to control
19 for confounding by SES as well as rearing environment of the child, many recent lead studies
20 have incorporated more direct assessments such as the HOME scale, parental intelligence,
21 parental attitude assessments, and measures of parental substance abuse and psychopathology.
22 Given the relatively high correlation between indices of lead exposure and social environmental
23 factors, the consistency among studies in finding effects following adjustment for these
24 confounding factors is remarkable. In the Boston Prospective Study, confounding by SES was
25 largely controlled for by study design (Bellinger et al., 1984). The study subjects were generally
26 middle- to upper-middle-class children in intact families with college-educated parents.
27 Therefore the potential for confounding by SES in this study was considerably less compared to
28 other lead health effect studies, yet it reported similar and at times even larger effects on
29 neurodevelopmental ouctomes. In addition, it is important to consider the enormous
30 experimental animal evidence not compromised by the possibility of confounding in examining
May 2006 6-72 DRAFT-DO NOT QUOTE OR CITE
-------
1 lead effects on health (Bellinger, 2004; Davis et al., 1990; U.S. Environmental Protection
2 Agency, 1986a, 1990).
3 Another problem in the analyses of data on lead and child development is the lack of
4 critical consideration of which potential confounder in a particular model "owns" the variance in
5 neurodevelopmental performance. Thus, for example, in the case of social class it is assumed
6 that if an effect of lead is reduced to nonsignificance following adjustment for some measure of
7 SES standing, the assumption is that all of the variance belongs to the confounder. However, in
8 some instances this could be seen as an excessively conservative interpretation and raises the
9 specter of Type II error. Social class could be seen as either a confounder or a proxy for
10 exposure. In addition, lead may be on the causal pathway of the association between social class
11 and IQ. Lower social class in urban children is closely linked to residence in older housing in
12 poor condition that, in turn, is associated with higher levels of environmental lead (Clark et al.,
13 1985). If studies adjust for social class in the usual manner, the effects of the toxicant will be
14 underestimated (Bellinger, 2004). One extreme example of overcontrol of this nature can be
15 found in the New Zealand studies where investigators regularly "controlled" for residence in
16 older "weatherboard" housing (e.g., Fergusson et al., 1988a,b). However, it is worth noting that
17 even in the models including this variable lead remained a significant predictor of intellectual
18 and academic under-attainment in the Christchurch Health Study. The proper way to address the
19 possibility that lead may be on the causal pathway of the association between social class and IQ
20 is to use structural equation models, but this has not generally been done.
21 In addition to being a confounder, social class and related variables have been shown to
22 be effect modifiers in many studies of lead and child development (Bellinger, 2000; Tong et al.,
23 2000). Effect modification occurs when the magnitude of an association between an exposure
24 (lead) and an outcome (neurobehavior) varies across strata of some other factor (Last, 2001).
25 The disadvantages that accompany poor education and underemployment have been found to
26 exacerbate the effects of lead when carefully examined (Bellinger et al., 1989). Indeed,
27 evaluating potential effect modifiers should be considered an important part of an overall data
28 analytic plan.
29 Most of the important confounding factors in lead studies have been identified and efforts
30 have been made to control them in studies conducted since the 1990 Supplement. Further
31 discussion on confounding is presented in Section 6.10.6. Invocation of the poorly measured
May 2006 6-73 DRAFT-DO NOT QUOTE OR CITE
-------
1 confounder as an explanation for positive findings is not substantiated in the database as a whole
2 when evaluating the impact of lead on the health of U.S. children (Needleman, 1995). Of course,
3 it is often the case that following adjustment for factors such as social class, parental
4 neurocognitive function, and child rearing environment using covariates such as parental
5 education, income, and occupation, parental IQ, and HOME scores, the lead coefficients are
6 substantially reduced in size and statistical significance (Dietrich et al., 1991). This has
7 sometimes led investigators to be quite cautious in interpreting their study as positive
8 (Wasserman et al., 1997). This is a reasonable way of appraising any single study, and such
9 extreme caution would certainly be warranted if forced to rely on a single study to confirm the
10 lead effects hypothesis. Fortunately, a large database of high quality studies on which to base
11 inferences regarding the relationship between lead exposure and neurodevelopment exists.
12 In addition, lead has been extensively studied in animal models at doses that closely approximate
13 the human situation. Experimental animal studies are not compromised by the possibility of
14 confounding by such factors as social class and correlated environmental factors. The enormous
15 experimental animal literature that proves that lead at low levels causes neurobehavioral deficits
16 and provides insights into mechanisms is to be considered when drawing causal inferences
17 (Bellinger, 2004; Davis et al., 1990; U.S. Environmental Protection Agency, 1986a, 1990).
18
19 6.2.16 Summary of the Epidemiologic Evidence for the Neurotoxic Effects
20 of Lead in Children
21 Effects of lead on neurobehavior have been reported with remarkable consistency across
22 numerous studies of various designs, populations studied, and developmental assessment
23 protocols. The negative impact of lead on IQ and other neurobehavioral outcomes persist in
24 most recent studies following adjustment for numerous confounding factors including social
25 class, quality of caregiving, and parental intelligence. Moreover, these effects appear to be
26 irreversible and persist into adolescence and young adulthood.
27 • An international pooled analysis of seven prospective studies and several meta-analyses
28 provide strong evidence that exposure to lead at low dose has an effect on the intellectual
29 attainment of preschool and school age children. Recent studies examining the
30 association of lead with intellectual attainment and academic performance in children
31 with low lead exposures have consistently observed effects at blood lead concentrations
32 below 10 |ig/dL. The large international pooled analysis of 1,333 children observed a
May 2006 6-74 DRAFT-DO NOT QUOTE OR CITE
-------
1 decline of 6.2 points (95% CI: 3.8, 8.6) in full scale IQ for an increase in concurrent
2 blood lead levels from 1 to 10 |ig/dL.
3 • A common observation among some of these studies of low level lead exposure is the
4 non-linear dose-response relationships between blood lead and neurodevelopmental
5 outcomes. At first this may seem at odds with certain fundamental toxicological
6 concepts. However, there are a number of examples of non- or supralinear dose-response
7 relationships in toxicology (Calabrese and Baldwin, 2001). As previously mentioned, it
8 is conceivable that the initial neurodevelopmental lesions at lower lead levels may be
9 disrupting very different biological mechanisms (e.g., early developmental processes in
10 the central nervous system) than the more severe effects of high exposures that result in
11 symptomatic poisoning and frank mental retardation.
12 • Studies examining aspects of academic achievement related to Pb exposure indicate
13 association of deficits in academic skills and performance which in turn lead to enduring
14 and important effects on objective parameters of success in real life.
15 • The effects of lead on behavior and mood of children has been an important area of
16 recent research. These studies have demonstrated that the impact of lead may extend into
17 increased risk for antisocial and delinquent behavior. This could be a consequence of
18 attentional problems and academic underachievement among children who have suffered
19 higher exposures to lead during their formative years.
20 • Several studies that have used methods of MRI and MRS to assess direct measures of
21 brain damage are also adding important and direct evidence of harm due to lead
22 exposure. Reduced brain N-acetylasparate levels observed may be related to decreased
23 neuronal density or neuronal loss.
24 • It is not clear that only periods of peak blood concentrations matter in terms of risks for
25 neurodevelopmental morbidity. One study attempts to address this question directly and
26 reports that concurrent blood lead concentrations always had the strongest association
27 with IQ as measured at ages 2, 5, and 7 years, with a stronger relationship as the children
28 grow older.
29 • Attempts to reverse or limit lead-associated neurodevelopmental morbidities with
30 pharmacological or nutritional intervention strategies have been ineffective.
31 Epidemiologic studies are reporting effects at blood lead levels for which there is no
32 effective means of medical or secondary environmental interventions to avoid
33 developmental morbidity, thus emphasizing the importance of taking primary protective
34 measures to substantially reduce and ultimately prevent exposure to lead in children.
35
May 2006 6-75 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.3 NEUROTOXIC EFFECTS OF LEAD IN ADULTS
2 6.3.1 Summary of Key Findings on the Neurotoxic Effects of Lead in Adults
3 from the 1986 Lead AQCD
4 Lead intoxication in adults occurred primarily in occupational settings with historically
5 high exposure levels. In more recent times, occupational lead exposure has been reduced to
6 much lower levels and is often associated with no symptoms. The symptom constellation
7 associated with high levels of lead exposure include impaired memory and attention span,
8 irritability, headache, muscular tremors, and hallucinations (Cantarow and Trumper, 1944) that
9 may progress to signs of frank encephalopathy (Smith et al., 1938). Symptoms of lead
10 intoxication begin with blood lead >40 |ig/dL (Baker et al., 1979) accompanied by poorer
11 performance on cognitive and visuomotor tasks, reaction time, verbal learning, and reasoning
12 ability that reflect involvement of both the central nervous system and the peripheral nervous
13 system (Arnvig et al., 1980; Campara et al., 1984; Grandjean et al., 1978; Haenninen et al., 1978,
14 1979; Hogstedt et al., 1983; Mantere et al., 1982; Valciukas et al., 1978; Zimmermann-Tansella
15 et al., 1983). Impaired occulomotor function, measured by saccade accuracy and velocity,
16 depended upon the age group of the lead-exposed worker (Baloh et al., 1979; Glickman et al.,
17 1984; Spiveyetal., 1980).
18 With regard to peripheral nerve function as measured by nerve conduction studies, the
19 28 studies reviewed by the U.S. EPA in the 1986 Lead AQCD found no consistent single nerve
20 involved but, overall, the exposed group had slower conduction velocity at blood lead
21 concentrations as low as 30 |ig/dL.
22 Studies reviewed in 1986 found that amyotrophic lateral sclerosis (ALS) was
23 inconsistently associated with elevated lead levels in the nervous system. Chelation for 1 year
24 did not did not alter elevated lead levels in the tissue of patients with motor neuron disease.
25
26 6.3.2 Overview of Cognitive and Psychomotor Tests Associated with Adult
27 Lead Exposure
28 Examination of lead effects on neurobehavioral performance in adults differs from that in
29 children, since the neurobehavioral tests in adults focus on loss of abilities previously present
30 rather than the lack of attainment of those abilities. Also, there is the contribution of cognitive
31 reserve acquired by years of education, self-education, on-the-job training, avocational, and
May 2006 6-76 DRAFT-DO NOT QUOTE OR CITE
-------
1 non-avocational activities that increases the ability to compensate for the effects of lead exposure
2 on learning new information. The concept of brain reserve capacity has many examples in
3 neurologic disease where neuropathology progresses in the absence of clinical expression -
4 clinical parkinsonism develops once 85% of nigrostriatal cells and dopamine are depleted; multi-
5 infarct dementia is expressed once an aggregate volume of infarction of 50 to 100 cc of the brain;
6 the weakness and atrophy associated with poliomyelitis requires 80% loss of the anterior horn
7 cells; and Alzheimer disease usually requires a frequency for senile plaques and neurofibrillay
8 tangles of >60% in the hippocampus and cerebral cortex (Satz, 1993). Therefore, the goal is to
9 identify these conditions in a preclinical phase. For instance, it is now known that, in individuals
10 diagnosed with Mild Cognitive Impairment, only impairment of recent memory with
11 preservation of other cognitive domains, are at increased risk of developing Alzheimer disease at
12 rates of 12 to 15% per year compared to 1 to 2% in age-matched normal patients. Because of
13 this brain reserve capacity and the decreased exposure to lead both environmentally and
14 occupationally, it is not expected to find clinical disease associated with exposure;however,
15 subclinical effects even if reversible are important to identify as they may be impacting brain
16 reserve capacity. It is known that diminished cognitive reserve increases the risk of decreased
17 cognitive performance associated with lead exposure (Bleecker et al., 2002). Therefore, at this
18 time, it is more critical to study the contribution of lead to performance after adjusting for
19 potential confounders and identify subpopulations that are at increased risk for the
20 neurobehavioral effects of lead. A few studies have stratified outcome using clinical criteria and
21 found higher lead levels associated with more severe clinical abnormalities (Bleecker et al.,
22 2003; Bleecker et al., 2005a).
23 As alterations in mood may influence neuropsychological performance, many
24 neurobehavioral batteries use self-administered questionnaires to screen for mood. The Center
25 for Epidemiologic Studies Depression Scale (CES-D) screens for depression. The Profile of
26 Mood State (POMS) screens for six subscales, namely anger, confusion, depression, fatigue,
27 anxiety/tension, and vigor. The six mood scales of the POMS were originally validated in a
28 clinical psychiatric population; thus, the factor structure needed to be validated in an
29 occupational population. Factor analysis of the POMS in lead smelter workers found only two
30 relevant factors: one composed of five scales (anger, confusion, depression, fatigue, and tension)
May 2006 6-77 DRAFT-DO NOT QUOTE OR CITE
-------
1 and the other contained vigor (Lindgren et al., 1999). This brings into question the use of the six
2 scales as separate outcome variables in the study of lead exposure.
3 Mini-Mental-State Examination (MMSE), a screening tool for cognitive impairment, is a
4 compilation of many cognitive domains, including orientation to time and place, registration, and
5 recall of three words, attention, language, and visual construction, with a total possible score of
6 30 (Folstein et al., 1975). MMSE is sensitive to age and education. In 194 healthy subjects aged
7 40 to 89 years with 7-21 years of education, only 1% of the subjects obtained an MMSE score of
8 24/30 and none below (Bleecker et al., 1988). MMSE errors are sensitive to age effects,
9 including delayed recall, spelling "WORLD" backwards and repetition of "no ifs, ands, or buts."
10 With lead exposure, examination of errors is important to compare with age-related changes and
11 to determine the biological plausibility of the effects of exposure especially when performing
12 repeated measures of the test. This test is sometimes used to describe a population and not as an
13 outcome.
14 When administering a neuropsychological battery, it is necessary to include a test that
15 estimates premorbid ability, such as Vocabulary or a reading test such as the Wide Range
16 Achievement Testing for Reading (WRAT) or the North American Reading Test (NART).
17 These tests are highly correlated with years of education, verbal IQ; and full scale IQ and
18 performance is retained in the presence of cognitive deteriorating conditions, head trauma and
19 polysubstance abuse (Lezak, 2004). Also, these tests are not affected by exposure to
20 neurotoxicants unless severe global brain damage has occurred (e.g., loss of consciousness from
21 huffing toluene) (Weisskopf et al., 2004a). Reading tests are a better measure of educational
22 achievement with lower years of education (Bleecker et al., 2002).
23 "The pattern of cognitive deficits in [adults] reported by Weisskokopf et al., 2004a is
24 generally quite typical of the pattern of deficits reported after high-level lead exposure. This
25 pattern includes predominant impairment in the domains of attention/executive function,
26 visuospatial/visual motor functioning, short-term memory, and confusion and fatigue, whereas
27 verbal language and general intelligence remain relatively unimpaired. Test of single-word
28 reading, basic written arithmetic, and semantic knowledge (e.g., the ability to name common
29 objects) are not generally sensitive to exposure to neurotoxi cants in adults. Disruptions of these
30 types of cognitive functions are usually seen only after widespread brain damage (e.g., frank
31 hypoxia, severe traumatic injury, Alzheimer disease after the initial stages) or focal strokes
May 2006 6-78 DRAFT-DO NOT QUOTE OR CITE
-------
1 involving highly specific brain areas that mediate language and calculations. . . . After exposure
2 to toxicants such as lead in adulthood, cognitive deficits tend to be specific, not generalized and
3 not affecting language centers in the brain." Therefore, in the adult, vocabulary and reading tests
4 correlate highly with years of education and are predictors of performance on other cognitive
5 tests. In the occupational setting, these tests may be confounders when less capable workers are
6 placed in those jobs with the highest lead exposure.
7 Neuropsychological batteries screening for the effects of lead usually include the
8 following domains ( for a more complete description, see Lezak, 2004): attention/concentration
9 (Digit Span); conceptual and executive functioning (Stroop, Trails B); visuoperceptive/
10 visuoconstructive (Block Design); visuomotoric (Reaction Time, Pegboard Test, Digit Symbol
11 Substitution, Trails A); verbal memory (Rey Auditory Verbal Learning Test, Logical Memory,
12 Paired Associated Learning); and nonverbal memory (Rey-Osterreith Complex Figure, Benton
13 Visual Retention). When analyzing the association of lead exposure and test performance,
14 adjusting for potential confounders is critical. Potential confounders are age, education
15 (preferably a measure of verbal intelligence), depressive symptoms, medications, alcohol use,
16 and smoking. In some cases, age and education may serve as effect modifiers; for example the
17 association of lead and poorer neurobehavioral outcome was greater in older workers (Bleecker
18 et al., 1997a) or in those with less cognitive reserve (Bleecker et al., 2002).
19 Adults with medical conditions requiring medications that have nervous system side
20 effects, history of severe head trauma, neurodegenerative disease and other neuropsychiatric
21 conditions that may have a global impact on nervous system performance should be removed
22 from the analysis for the affects of lead.
23
24 6.3.3 Adult Environmental Lead Exposure Effects
25 6.3.3.1 Neurobehavioral Effects Associated with Environmental Lead Exposure
26 Exposure to chronic low levels of environmental lead and its association with effects on
27 the nervous system were examined in several populations originally followed to study conditions
28 associated with aging: the VA Normative Aging Study (NAS) (Payton et al., 1998; Rhodes et al.,
29 2003; Weiskopf et al., 2004b; Wright et al., 2003); the Study of Osteoporotic Fractures
30 (Muldoon et al., 1996); the Kungsholmen Project on aging and dementia (Nordberg et al., 2000)
May 2006 6-79 DRAFT-DO NOT QUOTE OR CITE
-------
1 and the third National Health and Nutrition Evaluation Survey, NHANES III (Krieg et al., 2005).
2 Studies reviewed in this section are summarized in Annex Table AX6-3.1.
3 The VA Normative Aging Study (NAS) conducted at the VA Outpatient Clinic in Boston,
4 MA is a multidisciplinary longitudinal investigation of the aging process established in 1961,
5 consisting of 2,280 men aged 21 to 80 years with no current or past chronic medical conditions.
6 Participants are evaluated every three years with self-administered questionnaires and Brief
7 Symptom Inventory (BSI) for psychiatric symptoms. By evaluating relationships of bone lead
8 (tibia 21.9 jig/g and patella 32.1 |ig/g) and blood lead (6.3 |ig/dL) to psychiatric symptoms in
9 526 men (age 67 years), Rhodes et al. (2003) found mood symptoms for anxiety, depression, and
10 phobic anxiety potentially to be associated with bone lead levels after adjusting for age, age2,
11 alcohol, education and employment variables. Education was inversely related to bone lead;
12 high school graduates had significantly higher general stress that may be related to SES and
13 more people with depression were unemployed or working part time.
14 Neuropsychological testing in NAS found response speed to be sensitive to low levels of
15 lead but it was not a consistent finding in all tests measuring the same domain upon examination
16 of 141 healthy men with a mean age of 67 years, education 14 years. The mean blood lead level
17 was 6 |ig/dL, patella bone lead was 32 jig/g bone mineral, and tibia bone lead was 23 jig/g bone
18 mineral (Payton et al., 1998). Vocabulary, a measure of verbal intelligence, highly correlated
19 with education and a marker of premorbid intelligence, was used as an outcome variable instead
20 of being used as a covariate predictive of performance. Education was negatively correlated
21 with bone lead and blood lead, suggesting other factors bedsides lead exposure may have
22 contributed to neuropsychological performance. The handling of multiple comparisons was not
23 addressed.
24 Another analysis of the NAS (Wright et al., 2003) examined 736 men, mean age 68 years
25 with education level of 54% high school or less. The mean blood lead was 5 |ig/dL, and mean
26 patellar and tibia lead levels were 30 and 22 jig/g bone mineral, respectively. The subjects had a
27 mean MMSE score of 27. Relation of MMSE scores <24 (n = 41) and blood lead by logistic
28 regression estimated an odds ratio of 1.21 (95% CI: 1.07, 1.36). For patella lead and tibia lead,
29 odds ratios of 1.21 (95% CI: 1.00, 1.03) and 1.02 (95% CI: 1.00, 1.04), respectively, were
30 observed. Risk of MMSE <24 (6% of the present population versus 1% of previously described
31 healthy aging study), when comparing the lowest and highest quartiles, was 2.1 (95% CI:
May 2006 6-80 DRAFT-DO NOT QUOTE OR CITE
-------
1 1.1,4.1) for patella lead, 2.2 (95% CI: 1.1, 3.8) for tibia lead, and 3.4 (95% CI: 1.6, 7.2) for
2 blood lead. Interaction of age with patella lead and blood lead in predicting MMSE found
3 steeper decreases in MMSE scores relative to age in the higher quartiles of patella lead and blood
4 lead. Types of errors on the MMSE were not included. Not addressed was the issue of how
5 medical conditions and medications that developed over the duration of the study were handled.
6 Another publication on this population found that blue-collar participants in NAS had
7 significantly more high school graduates, higher blood lead, and bone lead compared to white-
8 collar participants and with non-white blue-collar workers having the highest bone lead levels
9 (Elmarsafawy et al., 2002).
10 Weisskopf et al. (2004b) expanded the MMSE study in NAS by examining 466 men
11 (mean age 70 years), who had completed the MMSE twice with an interval of about 3.5 years.
12 Mean blood lead was 4 |ig/dL, and mean patella and tibia bone lead were 23 and 19 jig/g bone
13 mineral, respectively. A one-interquartile range (20 |ig/g bone mineral) higher patella lead
14 concentration was associated with a MMSE score change of -0.24. This association between
15 patella lead and change in MMSE score had a steeper inverse association at lower lead
16 concentrations. Baseline mean MMSE score was 27 and mean change in MMSE score of
17 -0.24 was equivalent to aging 5 years on baseline MMSE scope. Five years of aging in a
18 healthy population is not associated with any change in MMSE score (Bleecker et al., 1998).
19 Even though MMSE change was significantly associated with bone lead, a change in MMSE
20 score by a fraction of a point does not constitute a meaningful change of cognitive performance.
21 To address the biological plausibility of change in the MMSE over 3.5 years, errors by functional
22 domain need to be identified to rule out the possibility of random errors with repeat performance.
23 Muldoon et al. (1996) studied participants in the Study of Osteoporotic Fractures for any
24 association between nonoccupational lead exposure and cognitive function. The Study of
25 Osteoporotic Fractures began in 1986 and included women over age 65 years living in four
26 different communities - Baltimore, MD; Portland, OR; Minneapolis, MN; and the Monongahela
27 Valley outside of Pittsburgh, PA. A sample of 325 women from rural sites with a mean age of
28 71 years (mean blood lead 4.5 |ig/dL) and 205 women from urban sites with a mean age of 69
29 years (mean blood lead 5.4 |ig/dL) were examined. The urban group was more educated and had
30 higher use of cigarettes and alcohol. Performance examined by blood lead groups adjusting for
31 age, education, smoking, and alcohol use found no significant differences in the urban group.
May 2006 6-81 DRAFT-DO NOT QUOTE OR CITE
-------
1 However, in the rural group, individuals with blood lead >7 |ig/dL had significantly poorer
2 performance when compared to those with blood lead <4 |ig/dL for Trails B, Digit Symbol, and
3 Reaction Time. Response time across blood lead groups increased for the rural group and
4 decreased or remained the same for the urban group. Mean MMSE for the whole population was
5 25, with poorer performance in the rural group. MMSE scores as low as 15 were reported to be
6 compatible with significant cognitive deterioration, as seen in Alzheimer's disease. Even though
7 the neuropsychological battery was simple, 9 participants were unable to perform some of the
8 tests including 3 on the MMSE. Such severe impairments were not found among those with
9 higher occupational lead exposures, which raises the question as to whether other factors not
10 measured accounted for these differences attributed to blood lead.
11 In the Kungsholmen Project on aging and dementia in Stockholm, Sweden, no
12 relationship was found between blood lead and MMSE (Nordberg et al., 2000). The study
13 population included 762 participants with a mean age of 88 years. The mean blood lead in this
14 group was 3.7 |ig/dL and the mean MMSE was 25. In contrast to the other populations
15 examined, this study cohort was more homogenous, comprised entirely of elderly Swedes.
16 Their likelihood of prior exposure to elevated lead levels was low.
17 NHANES III administered 3 computerized neurobehavioral tests (simple reaction time,
18 symbol-digit substitution, and serial digit learning) to 5,662 adults aged 20 to 59 years with a
19 mean blood lead of 3.30 |ig/dL (range 0.7 to 41.8 |ig/dL). No relationship between blood lead
20 and performance was found after adjusting for sex, age, education, family income, race/ethnicity,
21 computer or video game familiarity, alcohol use, test language, and survey phase. Eleven adults
22 with blood lead levels between 25 and 42 |ig/dL were analyzed separately, but no statistically
23 significant relationship was found after adjusting for the covariates (Krieg et al., 2005).
24
25 6.3.3.2 Summary of Adult Environmental Lead Exposure Effects
26 There is no consistent evidence that environmental lead exposure is associated with
27 impaired cognitive performance in the elderly if competing risk factors are considered. It is not
28 expected that environmental lead exposure would result in a pattern of cognitive deficits reported
29 after high lead exposure in adults. Studies with adequate power using tests sensitive to the
30 affects of lead found no association between cognitive performance and environmental lead
31 exposure.
May 2006 6-82 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.3.4 Adult Occupational Lead Exposure Effects
2 6.3.4.1 Neurological Symptoms Associated with Occupational Lead Exposure
3 Studies reviewed in this section are summarized in Annex Table AX6-3.2. Several
4 occupational studies found blood lead levels of 29-43 |ig/dL to be associated with POMS
5 subscales (Hanninen et al., 1998; Maizlish et al., 1995; Niu et al., 2000). However, other studies
6 with blood lead levels of 27-38 |ig/dL found no relationship with POMS (Chia et al., 1997;
7 Lucchini et al., 2000; Osterberg et al., 1997; Stollery et al., 1989). POMS was significantly
8 associated with cumulative blood lead but not current blood lead level of 27 |ig/dL (Lindgren et
9 al., 1999) CES-D was significantly associated with tibia lead (mean 37 jig/g bone mineral), but
10 not with blood lead (mean 32 |ig/dL) (Schwartz et al., 2001a). Physical symptoms were
11 associated with dimercaptosuccinic acid (DMSA)-chelatable lead, ZPP,delta-aminolevulinic acid
12 in urine (mean 3 mg/L) but not blood lead (mean 45 |ig/dL) (Lee et al., 2000).
13 In some studies, difficulty concentrating, irritability, fatigue, muscle pain, and joint pain
14 were more likely in workers with a mean blood lead of 43 |ig/dL (Maizlish et al., 1995) and
15 27 |ig/dL (Lucchini et al., 2000), whereas other studies with mean blood lead >30 |ig/dL found
16 no association with symptoms (Chia et al., 1997; Osterberg et al., 1997). Lucchini et al. (2000)
17 provided an estimated threshold of blood lead 12 |ig/dL for significant increase of neurological
18 symptoms. Increased prolactin levels from modulation of the pituitary dopaminergic system was
19 found at a threshold of a blood lead level of 10 |ig/dL in the same study (Lucchini et al., 2000).
20 In summary, one study suggested a threshold for neurological symptoms at a blood lead
21 of 12 |ig/dL, though many studies with higher blood lead levels found no association with
22 symptoms relating to the nervous system.
23
24 6.3.4.2 Neurobehavioral Effects Associated with Occupational Lead Exposure
25 Occupational studies published since 1990 with a mean blood lead <50 |ig/dL are
26 summarized in Annex Table AX6-3.3. This section highlights some of the findings from these
27 studies.
28 A review of occupational lead exposure in 1995 (Balbus-Kornfeld et al., 1995) concluded
29 that the association of cumulative lead exposure or body burden of lead and neurobehavioral
30 performance in adults was inadequately covered in the literature prior to 1995. Since then,
31 studies have addressed these deficiencies with the use of a working lifetime integrated blood
May 2006 6-83 DRAFT-DO NOT QUOTE OR CITE
-------
1 index and bone lead concentrations. Even though exposure assessment has improved, there is
2 variability based upon differences in past exposure versus present exposure, duration of
3 exposure, frequency of monitoring for blood lead, lead exposure from other occupational sources
4 and non-occupational activities. Bone lead, the largest reservoir for lead stored in the body may
5 not necessarily reflect the dose of lead presented to the nervous system.
6 Table 6-3 . 1 notes the relationship between measures of cumulative lead exposure and/or
7 body burden and three neurobehavioral measures sensitive to lead exposure, Digit Symbol,
8 Trails, and
9
10
Pegboard. Only
studies that used one or all of these measures were included.
Table 6-3.1. Key Neurobehaviorial Effects Studies of Occupational Lead
Study
Lindgren
etal. (1996)
Bleecker
etal. (1997a)
Hanninen
etal. (1998)
Lucchini
et al. (2000)
Schwartz
etal. (200 la)
Earth et al.
(2002)
Schwartz
et al. (2005)
Test
Digit Symbol
Trails
Pegboard
Digit Symbol
Pegboard
Digit Symbol
Pegboard
Symbol Digit
Digit Symbol
Trails
Pegboard
Digit Symbol
Digit Symbol
Trails
Pegboard
Blood Lead Time Weighted Integrated Blood
Level Average Blood Lead Lead Level
ug/dL "g/dL ug-yr/dL
28 (8.4) 40 (4-66) 765 (.6-1625.7)
11 +
- - +
26(7.1) 42 (8.4) 903 (305.9)
27 29 330
- - +
27 (4.5) 32(14.1) 409 (360.8)
32 (4-76) ND ND
+
+
31(11.2) ND 384(0.9-1777.5)
-
31(14.2) ND ND
+
+
Exposures
Bone Lead
fig /g Bone
Mineral
ND
41 (24.4)
20
-
37 (-7-338)
-
-
ND
38 (43)*
+
+
ND = not done
- = no significant association
+ = significant association with lead dose and/or body burden after adjusting for the covairates
Decline in performance over time related to bone lead.
May 2006
6-84
DRAFT-DO NOT QUOTE OR CITE
-------
1 Schwartz et al. (200 la) with use of LOWES S functions suggested a threshold at blood
2 lead of 18 |ig/dL, after which there was a decline of performance in Purdue Pegboard (assembly)
3 and Trails B. Some studies with mean current blood lead levels under 30 |ig/dL had no
4 significant associations with neurobehavioral performance, whereas measures of working
5 lifetime cumulative exposure that incorporated past high lead exposure were related to poorer
6 performance (Lindgren et al., 1996; Bleecker et al., 1997a; Bleecker et al., 2005a). The
7 association of bone lead with neurobehavioral performance occurred when decline in
8 performance over time was the outcome (Schwartz et al., 2005).
9 Significant effect modification occurred for age (Bleecker et al., 1997a), premorbid
10 abilities (Bleecker et al., 2002), and for protein kinase C (PKC) (Hwang et al., 2002). Higher
11 blood lead and poorer neurobehavioral performance occurred only among workers with lower
12 PKC activitythat corresponds to higher in vivo PKC activity. The authors suggest that
13 individuals with high PKC activity may identify a subpopulation at increased risk of
14 neurobehavioral effects of lead.
15 Examination of verbal memory and lead exposure used clinical criteria for part of the
16 analysis with significantly higher IBL and TWA in the group with 'generalized memory
17 impairment' compared to the 'no impaired' group after adjusting for the covariates (Bleecker
18 et al., 2005a).
19
20 Reversibility
21 Twenty-seven workers had three testing sessions with a computerized neurobehavioral
22 battery during four years, while mean blood concentration decreased from 26 |ig/dL to 8 |ig/dL
23 (Chuang et al., 2005). Use of generalized linear mixed models found decreasing blood lead
24 concentrations to be associated with improvement in finger tapping, pattern comparison and
25 pattern memory after adjusting for age and vocabulary. The referent group was only tested in
26 year one and, therefore, no comparison of practice effect across repeated testing with the exposed
27 group could be made. Studies of normal aging have found practice effects with repeated testing
28 at intervals of two years. Therefore, caution is needed when interpreting the etiology of
29 improved testing scores at intervals of one to two years.
30 Winker et al. (2005) studied 48 men formerly exposed to lead (blood lead 5.4 |ig/dL)
31 compared to 48 controls (blood lead 4.7 |ig/dL) matched for age, years of education, verbal
May 2006 6-85 DRAFT-DO NOT QUOTE OR CITE
-------
1 intelligence and alcohol intake and found no difference in cognitive performance on six tests.
2 When the groups were combined, partial correlation adjusting for age found significant negative
3 correlation between blood lead and Block Design, Visual Recognition and Digit Symbol
4 Substitution. Even though the authors conclude that the cognitive deficits associated with low-
5 level lead exposure are reversible, there appears to be a residual effect primarily from those with
6 the highest past lead exposure. Using the same neurobehavioral battery, these formerly exposed
7 workers were compared to currently exposed workers (blood lead 30.8 |ig/dL) with similar age,
8 verbal intelligence, integrated blood level and duration of exposure (Winker et al., 2006). The
9 formerly exposed group performed significantly better on Block Design and Wisconsin Card
10 Sorting Test. To further examine the reduction of cognitive impairment with absence of
11 exposure, workers were stratified by duration of exposure and exposure absence with better
12 performance in the group with shorter exposure and longer absence, again supporting the concept
13 that cognitive deficits from occupational lead exposure are reversible.
14 One difficulty with cumulative lead dose is the inability to separate the effect of past high
15 exposure from a lower proximate exposure. To address this issue, workers with similar past high
16 exposure were grouped by those with proximate exposure above blood lead of 40 |ig/dL and
17 those with proximate exposure below blood lead of 40 |ig/dL and were compared on
18 performance of verbal memory (Lindgren et al., 2003). Use of regression analyses found pattern
19 group contributed significantly to the explanation of variance in verbal memory after adjusting
20 for current blood lead and lifetime integrated blood index measures. The relationship between
21 past high exposure and verbal memory, present in the group with a proximate blood lead above
22 40 |ig/dL, no longer existed in the group that maintained proximate blood lead below 40 |ig/dL
23 suggesting reversibility of the effects of past high lead exposure.
24 In summary, performances on psychomotor, motor speed and dexterity begin to show a
25 decline at a blood lead threshold of 18 |ig/dL. In adults, lead concentrations in bone were a
26 weaker predictor of lead effects on adult brain function. In some studies, cumulative blood lead
27 index reflecting past high exposure was a predictor of neurobehavioral performance at a time
28 when decreased current blood lead levels were not. Improvement in neurobehavioral scores once
29 current blood levels are lowered or occupational exposure has ceased suggests reversibility of the
30 lead effect.
31
May 2006 6-86 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.3.4.3 Neurophysiological Function and Occupational Lead Exposure
2 A meta-analysis including 32 nerve conduction studies with occupational lead exposure
3 found blood lead to be a weak predictor of peripheral nerve impairment (Davis and Svendsgaard,
4 1990). Nerve conduction velocities were reduced in lead-exposed subjects, with the greatest
5 sensitivity observed in the median motor nerve. Decreasing effect sizes were observed with
6 increasing duration of exposure. Meta-analyses of neurobehavioral effects in adults are
7 presented in Annex Table AX6-3.4.
8 Studies reviewed in this section are summarized in Annex Table AX6-3.5. Sensory nerve
9 conduction studies most commonly of the median nerve were related to long-term exposure,
10 lifetime integrated blood index, and duration of exposure or body burden (Yokoyama et al.,
11 1998; Kovala et al., 1997; Chia et al., 1996b).
12 Psychophysical tests, vibration and current perception threshold are used to quantitate
13 sensory impairment in the peripheral nervous system. Vibration threshold examines the integrity
14 of the large myelinated nerve fibers in the extremities and was associated with historical blood
15 lead measures and bone lead (Kovala et al., 1997 and Schwartz et al., 2001a), whereas blood lead
16 was significantly associated with vibration threshold in two other studies (Schwartz et al., 2005;
17 Chuang et al., 2000). Chuang et al. (2000) reported a hockey stick regression with an inflection
18 point around 30 |ig/dL and a positive linear relation above this point, suggesting a potential
19 threshold.
20 Current Perception Threshold (CPT), a neuro-selective test that measures integrity of the
21 large and small myelinated nerve fibers and unmyelinated nerve fibers, detected involvement of
22 the large myelinated fibers with IBL, except for those smelter workers who had periods of time
23 above a blood lead level of 60 |ig/dL (and then small myelinated fibers were involved) (Bleecker
24 et al., 2005b). CPT for large myelinated nerve fibers had a curvilinear relationship with lifetime
25 weighted average blood lead (mean 42 jig/dL), with a curve nadir at 28 |ig/dL. Ergonomic
26 stressors rated by job title were an effect modifier for CPT and IBL above a criterion blood lead
27 of60|ig/dL.
28 In summary, occupational lead exposure studies consistently found peripheral sensory
29 nerve impairment as opposed to the classic motor neuropathy described historically with high
30 lead exposure. A possible threshold for this effect on the sensory nerves was observed at a blood
31 lead of 28-30|ig/dL.
May 2006 6-87 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.3.4.4 Evoked Potentials and Occupational Lead Exposure
2 Visual evoked potentials (VEPs) and brainstem auditory evoked potentials (BAEPs)
3 measure speed of conduction in the visual and auditory pathways. BAEPs have discrete
4 waveforms with wave I arising from the auditory nerve; its latency reflects peripheral
5 transmission time. Wave III is predominantly generated from the caudal pons and wave V from
6 the inferior colliculus. The use of interpeak latencies removes abnormalities in the auditory
7 nerve latency from changes in brainstem transmission along the auditory pathway. Studies
8 reviewed in this section are summarized in Annex Table AX6-3.6.
9 Abbate et al. (1995) performed VEPs on 300 lead-exposed men (aged 30 to 40 years) in
10 good health and with no other neurotoxic exposure. Prolonged VEP began at a blood lead levels
11 of 17-20 |ig/dL. Even though there was no comparison group, careful screening ruled out other
12 medical and eye conditions, and other potential exposures. Detection of subclinical changes in
13 visual function in spite of normal visual acuity is found with measurements of near visual
14 contrast sensitivity threshold. Lucchini et al. (2000) reported significantly decreased sensitivity
15 in lead exposed workers (blood lead level 27.5 |ig/dL).
16 BAEPs recorded in 49 lead-exposed workers and age and sex matched controls (Discalzi
17 et al., 1992; Discalzi et al., 1993) found interpeak latencies, I-V, I-III, and III-V prolonged.
18 Holdstein et al. (1986) examined 20 adults accidentally exposed to lead through food; a
19 concentration-response relationship was observed for the weighted average blood lead
20 (43 |ig/dL) and I-III interpeak interval.
21 BAEPs were performed in 359 currently-employed smelter workers with mean blood lead
22 levels of 28 |ig/dL (SD 8.4), and current and cumulative lead exposure indices were found to be
23 significantly associated with components of BAEPs (Bleecker et al., 2003). When scores were
24 stratified based upon clinical criteria for wave I latency and I-V interpeak interval, blood lead,
25 weighted average blood lead, and lifetime integrated blood index were all significantly higher in
26 the group with prolonged Wave I and I-V interpeak interval compared to the group with normal
27 BAEPs.
28 In summary, one detailed study found blood lead associated with prolonged VEPs with a
29 threshold effect at 17-20 |ig/dL. The four studies examining BAEPs and lead exposure
30 consistently found prolonged interpeak latencies in the brainstem auditory pathway more
31 strongly associated with cumulative or weighted average blood lead levels.
May 2006 6-88 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.3.4.5 Postural Stability, Autonomic Testing, and Electroencephalogram (EEG)
2 and Occupational Lead Exposure
3 Postural sway measures balance or steadiness on a force platform. It is a complex task
4 that requires the integration of visual, vestibular, and peripheral sensory inputs, as well as motor
5 output. Test conditions modify proprioceptive feedback and visual feedback to challenge all
6 afferents responsible for maintaining balance including cerebellar input. No standard protocol
7 was used across studies. Studies reviewed in this section are summarized in Annex Table
8 AX6-3.7.
9 One approach to determine the critical dose of lead affecting postural balance in the
10 occupational setting is the benchmark dose method where a concentration of lead resulted in an
11 increased probability of an abnormal endpoint, a benchmark response, thereby placing exposed
12 subjects at increased risk (Iwata et al., 2005). The benchmark dose level was the 95% lower
13 confidence limit of the benchmark dose. In 121 lead exposed workers, blood lead level
14 40 |ig/dL, almost all sway parameters were significantly larger compared to controls. The mean
15 benchmark dose level of the current blood lead level for postural sway was 14.3 |ig/dL.
16 Postural sway evaluated in 49 chemical workers exposed to lead stearate, with a mean
17 blood lead of 18 |ig/dL and a mean weighted average blood lead of 24 |ig/dL (Yokoyama et al.,
18 1997) found a concentration-response relationship for blood lead and sway in the antedor-
19 posterior direction and for weighted average blood lead with right to left sway. The authors
20 concluded that change in the vestibulocerebellum pathway was affected by blood lead while the
21 anterior cerebellar lobe was affected by average lead exposure.
22 Chia et al. (1994 and 1996c) and Ratzon et al. (2000) used computerized postural sway
23 measurements to observe poorer postural stability that increased with eyes and was associated
24 with integrated blood index. In order to maintain balance, lead-exposed workers required
25 increased oscillations when visual and vestibular inputs were altered (Ratzon et al., 2000). More
26 challenging postural sway conditions such as the one leg condition was associated with a mean
27 blood lead level of 39 |ig/dL but not time-weighted average blood lead level or cumulative blood
28 lead level (Dick et al., 1999).
29 The effects of lead on the cardiac autonomic nervous system, expressed as the decrease of
30 R-R interval variation on an electrocardiogram, was examined (Teruya et al., 1991; Niu et al.,
31 2000). A significant blood lead concentration-related decrease of R-R interval variation during
May 2006 6-89 DRAFT-DO NOT QUOTE OR CITE
-------
1 deep breathing was present. An approximate threshold effect was found at blood lead >20 |ig/dL.
2 Integrity of sympathetic nerve function as reflected by decreased finger blood flow, a measure of
3 sympathetic nerve function was associate with increased blood lead (mean blood lead 13 |ig/dL)
4 (Ishidaetal., 1996).
5 Quantitative electroencephalographs found alpha and beta frequencies more abundant in
6 workers with higher long term lead exposure (Kovala et al., 1997). The finding of slow alpha
7 activity positively correlated with lead exposure may reflect increased episodes of
8 "microdrowsiness" in workers with higher lead exposure. Niu et al. (2000) reported significantly
9 increased beta activity and diminished amplitudes abnormalities in 81% of lead exposed workers
10 (mean blood lead 29 |ig/dL).
11 In summary, the benchmark dose level for blood lead affecting postural sway is 14 |ig/dL.
12 Lead is believed to affect different pathways traveling to the cerebellum. Parasympathetic and
13 sympathetic integrity is compromised in lead-exposed workers beginning at blood lead
14 >20 |ig/dL. Quantitative electroencephalographs found increased beta activity associated with a
15 mean blood lead level of 29 |ig/dL.
16
17 6.3.4.6 Occupational Exposure to Organolead and Inorganic Lead
18 Compared to inorganic lead, organolead exposure has a greater impact on the brain and,
19 therefore, is discussed separately. Direct comparison of trimethyl lead (a metabolite of
20 organolead), tetraethyl lead, and inorganic lead on the in vitro assembly of microtubules from the
21 mammalian brain found no effects with inorganic lead but trimethyl lead produced dramatic
22 impairment of neurotubular structures and functions (Roderer and Doenges, 1983). Another
23 study examining organic and inorganic lead found differential effects on neurite growth in
24 neurons in culture, suggesting that the mechanism of action for organic and inorganic lead was
25 not the same (Audesirk et al., 1989). Studies reviewed in this section are summarized in Annex
26 TableAX6-3.8.
27 Two hundred and twenty-two current employees that manufactured tetraethyl lead had
28 cumulative lead exposure associated with poorer performance in many cognitive domains but
29 most often in manual dexterity and verbal memory/learning (Schwartz et al., 1993). Simple
30 visual reaction time and blood lead had a curvilinear relation with an increase in simple visual
31 reaction time occurring above a blood lead of 30 |ig/dL (Balbus et al., 1997, 1998).
May 2006 6-90 DRAFT-DO NOT QUOTE OR CITE
-------
1 In former organolead workers (n = 543), peak tibial lead was a stronger predictor of
2 poorer cognitive function than current tibial lead (Stewart et al., 1999). Examination of the
3 peripheral nervous system in this population found no strong association between lead
4 biomarkers and measures of sensory and motor function (Tassler et al., 2001). Five hundred and
5 thirty-five of these former organolead workers were re-examined over a 4-year period (Schwartz
6 et al., 2000b, 2001b). Peak tibia lead predicted decline in cognitive tasks and manual dexterity.
7 This relationship of neurobehavioral tests with bone lead levels was influenced by the
8 apolipoprotein E (ApoE) genotype (Stewart et al., 2002). The slope of the relation between tibia
9 lead and neurobehavioral outcome was more negative in those individuals with at least one s4
10 allele than individuals without this allele. It is suggested that the presence of one Apo-e-4 allele
11 increases the risk of persistent central nervous system effects of lead.
12 In summary, those neurobehavioral outcomes related to organolead exposure are
13 compared to the literature reviewed for inorganic lead exposure; and the absence of effects on
14 the peripheral nerves and the global nature of central nervous system impairment suggest that the
15 impact on the brain may be greater with organolead exposure.
16
17 6.3.5 Amyotrophic Lateral Sclerosis and Other Neurological Outcomes
18 Associated with Lead in Adults
19 Studies reviewed in this section are summarized in Annex Table AX6-3.9. The 1986
20 Lead AQCD concluded that the evidence for an association of lead and ALS or motor neuron
21 disease was inconsistent. The subsequent publications remain mixed, but more studies have
22 reported an association. Using 109 cases of ALS and 256 controls matched for age, gender, and
23 region of residence, Kamel et al. (2002) examined the relation of lead and ALS, using blood lead
24 and bone lead levels. Ranges of exposure were <1 to 14 |ig/dL for blood lead, -4 to 107 jig/g
25 for patella lead, and -7 to 61 jig/g for tibia lead. History of occupational lead exposure
26 increased the risk of ALS (adjusted odds ratio of 1.9 [95% CI: 1.1,3.3]). Elevations both in
27 blood lead and in patella and tibia bone lead were found in ALS cases, though the precision of
28 these measurements was questioned. In summary, this study found lead exposure from historical
29 questionnaire data and biological markers to be associated with ALS. The same data was used to
30 determine the associations of ALS with polymorphism in ALAD and VDR and the influence of
May 2006 6-91 DRAFT-DO NOT QUOTE OR CITE
-------
1 genotype in the previously discussed associations of ALS with lead (Kamel et al., 2003). The
2 ALAD2 allele was associated with a 2-fold increased risk of ALS after adjustment for age,
3 gender, region, education, and physical activity. Additionally adjusting for blood lead
4 strengthened the association of ALAD2 and ALS risk. This was not found for bone lead or
5 occupational history of lead exposure. VDR was not associated with lead or ALS risk.
6 A study from the Mayo Clinic examined risk factors for sporadic ALS in 45 male ALS
7 patient-patient control pairs (Armon et al., 1991). When lifetime exposure to lead exceeded
8 200 hours, the relative risk for ALS was 5.5 (95% CI: 1.44, 21.0). Overall, men with ALS had
9 worked more at blue-collar jobs with significantly more time welding or soldering than controls
10 (p < 0.01). The association between lead exposure and development of ALS was supported as
11 these authors had the same findings in a previous pilot study of another patient population
12 (Roelofs-Iverson et al., 1984).
13 Another study of risk factors for ALS in 103 patients found increased odds ratio for
14 manual occupation (2.6 [95% CI: 1.1, 6.3]) and occupational exposure to lead (5.7 [95% CI:
15 1.6, 30]) (Chancellor et al., 1993). A Swedish study of 92 cases of motor neuron disease
16 (includes ALS, progressive bulbar palsy, and progressive muscular atrophy) found a Mantel -
17 Haenszel odds ratio for welding equal to 3.7 (95% CI: 1.1, 13.0) (Gunnarsson et al., 1992).
18 Guidetti et al. (1996) performed a retrospective incidence, prevalence, and mortality
19 survey in northern Italy. The area studied had documented lead pollution for years. Based upon
20 79 cases, incidence and prevalence rates of ALS were comparable to the surrounding area.
21 A subsequent publication by this group found that mean blood lead levels in cases of sporadic
22 ALS and controls were not significantly different (mean blood lead of 13 |ig/dL versus
23 11 |ig/dL) (Vinceti et al., 1997). Blood lead was associated with disability due to ALS but
24 no support was found for involvement of lead in the etiology of sporadic ALS.
25 Louis et al. (2003) examined the relationship between blood lead and essential tremor
26 (ET) in 100 cases with ET (mean blood lead 3 |ig/dL) and 143 controls (mean blood lead
27 2 |ig/dL). Ten cases and 7 controls had bone lead levels measured that were significantly
28 correlated with blood lead suggesting that higher blood lead may have occurred in the past.
29 Logistic regression adjusting for age and current cigarette smoking found an association between
30 blood lead and ET. An odds ratio of 1.19 (95% CI: 1.03, 1.37) was estimated. Blood lead was
May 2006 6-92 DRAFT-DO NOT QUOTE OR CITE
-------
1 higher in the 39 ET cases with no family history. Both current and lifetime prevalence of
2 occupational lead exposure was the same in ET cases and controls. In a second publication
3 (Louis et al., 2005), 63 ET cases (mean blood lead 4 |ig/dL) and 101 controls (mean blood lead
4 3 |ig/dL) who were similar in age, education, gender, and ethnicity were examined for interaction
5 of blood lead and ALAD gene polymorphisms and increased odds of ET. Of the 63 ET cases,
6 18 (29%) had an ALAD2 allele compared to 17 (17%) of the 101 controls (odds ratio of
7 1.98 [95% CI: 0.93, 4.21]). When log blood lead was examined by presence of ALAD2 allele in
8 ET, log blood lead was highest in ET cases with the ALAD2 allele, intermediate in ET cases
9 without an ALAD2 allele, and lowest in controls (test for trend, P = 0.10; p = 0.001). When the
10 ALAD2 allele was present, blood lead was significantly associated with odds of ET (80.29
11 [95% CI: 3.08, 2,096.36]). This increased odds of ET with an ALAD2 allele was 30 times
12 greater than in individuals with only ALAD1 alleles. In the highest log blood lead tertile,
13 ALAD2 allele was present in 22% of ET cases and 5% of controls. It was proposed that
14 increased blood lead along with the ALAD2 allele could affect the cerebellum and, thereby,
15 increase the risk of tremor.
16 Graves et al. (1991) performed a meta-analysis on 11 case-control studies of Alzheimer's
17 disease for occupational exposure to solvents and lead. Four studies had data for lead exposure
18 with a pooled analysis of relative risks for occupational lead of 0.71 (95% CI: 0.36,1.41). The
19 exposure frequencies were 16 of 261 (6%) for the cases and 28 of 337 (8%) for the controls.
20 These nonsignificant results were further confirmed by measuring lead concentration in the brain
21 of cases with diffuse neurofibrillary tangles with calcification (DNTC), Alzheimer's disease, and
22 non-demented controls. The lead concentration was significantly higher in DNTC compared to
23 Alzheimer's disease and non-demented controls (Haraguchi et al., 2001).
24 In summary, more studies are reporting an association with past exposure to lead, usually
25 in the occupational setting, and the motor neuron disease ALS. There appears to be a 2-fold
26 increased risk for ALS when the ALAD2 allele is present. The odds of ET in individuals
27 with the ALAD2 allele were 30 times greater compared to those with only ALAD1 alleles.
28 No increased risk of Alzheimer's disease was related to lead exposure.
29
May 2006 6-93 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.3.6 Summary of the Epidemiologic Evidence for the Neurotoxic Effects
2 of Lead in Adults
3 Neurobehavioral tests in adults focus on loss of abilities previously present. Cognitive
4 reserve acquired by years of education and life activities increases the ability to compensate for
5 the effects of lead exposure on learning new information. Several new publications evaluate
6 effects associated with environmental lead exposure and other information is related to effects
7 associated with occupational exposure.
8 • For environmental lead exposure there appears to be no consistent evidence that is
9 associated with impaired cognitive performance in the elderly if competing risk factors
10 are appropriately considered. It is not expected that environmental lead exposure would
11 result in a pattern of cognitive deficits reported after high lead exposure in adults.
12 Studies with adequate power using tests sensitive to the affects of lead found no
13 association between cognitive performance and environmental lead exposure. In adults,
14 the effect of lead on the nervous system may not be detected through neurobehavioral
15 testing due to cognitive reserve, the ability to compensate for brain impairment.
16 Cognitive reserve is related to pre-morbid cognitive abilities, education, and occupational
17 attainment, and is able to modify the clinical expression of central nervous system insult
18 from lead exposure. Therefore, when chronic lead exposure is the same in two groups of
19 individuals that differ by educational achievement levels, the concentration-response
20 relationship will only be seen in the group with low educational achievement, as
21 cognitive reserve allows the high educational achievement group to compensate for the
22 central nervous system expression of the effects due to lead.
23 • Chronic occupational lead exposure affects the sensory nerve fibers in the extremities
24 with a possible threshold at a weighted average blood lead level of 28 |ig/dL. Intensity of
25 lead exposure appears to be more critical than duration of exposure for this outcome.
26 Slowing in the brainstem auditory pathway in the caudal pons was consistently associated
27 with chronic occupational lead exposure.
28 • Past occupational exposure to lead increased the risk of developing ALS and motor
29 neuron disease in 4 studies. This risk was increased 2-fold by the presence of the
30 ALAD2 allele. Essential tremor in two well-done studies was associated with low blood
31 lead levels (mean 3 jig/dL). The odds of developing ET with the ALAD2 allele increased
32 30-fold compared to those individuals with only an ALAD1 allele.
33 • Numerous studies of occupational lead exposure also found chronic and current blood
34 lead associated with visuomotor and memory impairment with a threshold effect at blood
35 lead 18 |ig/dL. As with ET, postural sway abnormalities associated with blood lead of
36 14 |ig/dL is believed to result from the effects of lead on different parts of the cerebellum.
37
38
May 2006 6-94 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.4 RENAL EFFECTS OF LEAD
2 6.4.1 Summary of Key Findings on the Renal Effects of Lead from the
3 1986 Lead AQCD
4 Chronic lead nephropathy is a disease characterized by tubulointerstitial nephritis, which
5 can ultimately result in small, fibrotic kidneys. It occurs in individuals who sustain chronic high-
6 level lead exposure. In these individuals, lead exposure is the primary cause of renal failure.
7 The pathophysiologic characteristics of lead nephropathy and the populations at increased risk
8 for this diagnosis were the foci of the human research portion of Section 12.5, entitled "Effects
9 of Lead on the Kidney," in the 1986 Lead AQCD. The 1986 document clearly identified several
10 high-risk groups for this diagnosis, including children in the Queensland, Australia lead
11 poisoning epidemic, moonshine alcohol drinkers, and lead workers in poorly controlled settings.
12 The section concluded that data in the latter group indicated an increased risk for lead
13 nephropathy associated with blood lead levels ranging from 40 to >100 |ig/dL, with adverse
14 renal effects possibly occurring at levels as low as 30 |ig/dL.
15 The 1986 Lead AQCD noted that research at that time was not sufficient to address some
16 of the most critical questions relating to the impact of lead exposure on the kidney. The last
17 paragraph of the renal section begins with "Among the questions remaining to be answered more
18 definitively about the effects of lead on the kidneys is the lowest blood lead level at which renal
19 effects occurs." The last sentence reads "Conversely, the most difficult question of all may well
20 be to determine the contribution of low levels of lead exposure to renal disease of non-lead
21 etiologies." Advances in the research conducted since that document was written allow a much
22 more informed discussion of exactly those critical issues. As discussed below, recent research
23 indicates that lead nephropathy is merely the tip of the iceberg in terms of the contribution that
24 lead makes to renal dysfunction overall. Research increasingly indicates that lead, at much lower
25 doses than those causing lead nephropathy, acts as a cofactor with other more established renal
26 risks to increase the risk for renal dysfunction and the rate of subsequent decline. The
27 populations at risk for renal dysfunction (diabetics and hypertensives) are increasing worldwide,
28 particularly in countries where obesity is epidemic. Lead exposure is declining in many
29 industrialized countries, although less so among high-risk minority populations. The extent of
30 the public health impact of lead on the kidney depends on the balance of these two factors.
31
May 2006 6-95 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.4.2 Renal Outcome Definitions
2 The renal literature can be confusing since several of the clinical renal measures are
3 inversely related. Therefore, the pertinent outcomes are briefly reviewed below. The glomerular
4 filtration rate (GFR) is considered to be the best measure of renal function. GFR is assessed by
5 urinary clearance of exogenous (e.g., 125I-iothalamate) or endogenous (e.g., blood urea nitrogen
6 [BUN] and serum creatinine) compounds. Creatinine is used most commonly. Therefore,
7 increases in BUN or serum creatinine or decreases in renal clearance of creatinine or other
8 markers are all consistent with decreased renal function. Serum creatinine and its reciprocal
9 have been the most frequently used measures of renal function in the lead-kidney literature.
10 However, creatinine is not an ideal GFR marker, because it is influenced by factors such as
11 muscle mass, diet, gender, age, and tubular secretion. Measurement or calculation of creatinine
12 clearance takes some of these variables into account. Measured creatinine clearance utilizes
13 timed urine collections, traditionally over a 24-h period, making compliance difficult. Therefore,
14 equations to estimate creatinine clearance have gained popularity. The Cockcroft-Gault equation
15 (Cockcroft and Gault, 1976) has been used most commonly. Recently, several equations to
16 estimate actual GFR were studied in the Modification of Diet in Renal Disease (MDRD) Study
17 (Levey et al., 1999). The abbreviated MDRD equation (GFR in mL/min/1.73m2 = 186 x
18 creatinine L154 x age °'203 x (0.742 if female) x (1.212 if African American); Stevens and Levey
19 [2005a]) estimates GFR more accurately than the Cockcroft-Gault equation in patients with renal
20 insufficiency (Levey et al., 2003). Despite their promise, however, the MDRD equations are
21 relatively new and their use in the literature on the renal effects of lead exposure has been limited
22 to date.
23 Cystatin C is another recent addition to the tools used to assess GFR (Stevens and Levey,
24 2005b). This is a 13,000 Dalton, non-glycosylated basic protein, which is generated by all
25 nucleated cells and filtered, reabsorbed, and catabolized, but not secreted, in the kidney.
26 Very little appears in the urine. The majority of studies done to date indicate that serum cystatin
27 C is a better marker for GFR than serum creatinine (Stevens and Levey, 2005b).
28 Most of the renal outcome measures discussed above were developed for use in the
29 clinical setting. Unfortunately, they are insensitive for early renal damage, as evidenced by the
30 fact that serum creatinine remains normal after kidney donation. Therefore, in the last two
May 2006 6-96 DRAFT-DO NOT QUOTE OR CITE
-------
1 decades, the utility of renal early biological effect (EBE) markers as indicators of preclinical
2 renal damage has been of interest. These can be categorized as markers of function (i.e., low
3 molecular weight proteins that should be reabsorbed in the proximal tubules such as 02-
4 microglobulin and retinol-binding protein [RBP]); biochemical alteration (i.e., urinary
5 eicosanoids such as prostaglandin E2, prostaglandin F2 aipha, 6-keto-prostaglandin FI aipha, and
6 thromboxane B2); and cytotoxicity (e.g., N-acetyl-(3-D-glucosaminidase [NAG]) (Cardenas et al.,
7 1993). Elevated levels may indicate an increased risk for subsequent renal dysfunction.
8 However, with the exception of microalbuminuria in diabetes and (32-microglobulin in cadmium
9 exposure, most are research tools only and their prognostic value remains controversial.
10 European and Asian nephrotoxicant researchers have utilized them more frequently than have
11 renal researchers in the United States. Prospective studies of most of these markers in
12 nephrotoxicant-exposed populations are quite limited to date.
13
14 6.4.3 Lead Exposure Measure Definitions
15 Although these definitions are reviewed in detail elsewhere in this Lead AQCD, a brief
16 discussion is included here due to the number of key studies in this section that measured bone or
17 chelatable lead dose. Inorganic lead is a cumulative toxicant that is stored in bone. Blood lead is
18 a relatively short-term measure (half-life of 30 days [Hu et al., 1998]) that reflects exposure from
19 current exogenous sources and the release of lead from internal lead stores. Bone is a source of
20 lead as well as a repository (Hu et al., 1998). As such, bone lead measures provide information
21 on the potential for ongoing internal exposure as well as cumulative exposure. Lead in
22 trabecular bone (commonly measured in the patella or calcaneus) is more bioavailable than lead
23 in cortical bone (measured in the mid-tibia) and has a shorter half-life (Gerhardsson, et al., 1993;
24 Hu et al., 1998). An additional lead measure, chelatable lead, is thought to represent a
25 bioavailable pool of lead from blood, soft tissue, and bone. Either calcium disodium
26 ethylenediaminetetraacetic acid (EDTA) or dimercaptosuccinic acid (DMSA; succimer) may be
27 used for this purpose although DMSA is newer and, thus, has been used less frequently to date.
28
29
May 2006 6-97 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.4.4 Lead Nephrotoxicity in Adults
2 6.4.4.1 General Population Studies
3 Over the past two decades, several studies have examined the effect of lead exposure on
4 renal function in general populations. This is anew category of lead-renal research. No high
5 quality examples (by current standards) were available for review in the 1986 Lead AQCD. The
6 studies discussed below provide critical evidence that the adverse effects of lead on the kidney
7 occur at much lower doses than previously appreciated. Traditional renal function measures,
8 such as serum creatinine, BUN and creatinine clearance, are emphasized below since much more
9 is known regarding the clinical relevance of these measures than for the renal early biological
10 effect markers. General population studies of the renal effects of lead are further summarized in
11 Annex Table AX6-4.1.
12
13 Cadmibel Study
14 In the first large environmental study that adjusted for multiple renal risk factors, Staessen
15 et al. (1992) evaluated 965 men and 1,016 women in the Belgian Cadmibel study. Lead dose
16 was indexed by blood lead and zinc protoporphyrin. Renal outcome measures included serum
17 creatinine and p2-microglobulin and 24-h measured and calculated (Cockcroft and Gault, 1976)
18 creatinine clearances. Mean blood lead was 11.4 |ig/dL (range 2.3-72.5) and 7.5 |ig/dL (range
19 1.7-60.3) in men and women, respectively. After adjustment, log transformed blood lead and
20 zinc protoporphyrin, in separate models, were negatively associated with measured creatinine
21 clearance (effect estimates are presented in Table 6-4.1). A 10-fold increase in blood lead was
22 associated with a decrease in creatinine clearance of 10 and 13 mL/min in men and women,
23 respectively. Both lead measures were also negatively associated with estimated creatinine
24 clearance. This landmark study raised concern that the lead dose threshold for adverse renal
25 effects in the general population was much lower than previously appreciated based on
26 occupational data.
27
28 Normative Aging Study
29 Research in the Normative Aging Study population reached similar conclusions. Four
30 studies assessing the renal impact of lead exposure in this population have been published to
31 date. Participants in this study were originally recruited in the 1960s in the Greater Boston area.
May 2006 6-98 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-4.1. Summary of Key Studies on the Renal Effects of Environmental Lead Exposure
K> Reference
O Study location
°^ Study population
Sample size
Mean exposure and
outcome measures
Analysis methods
Covariates adjusted for in analysis
Major significant findings
Oi
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Muntner et al. (2003)
NHANES III,
1988-1994
n= 15,211
4,813 hypertensives
Paytonetal. (1994)
Boston, MA
Normative Aging Study,
1988-1991
n=744
Kim etal. (1996)
Boston, MA
Normative Aging Study,
1979-1994
n = 459
Blood lead
4.21 ug/dL (hypertensives)
3.3 ug/dL
(normotensives)
Renal outcomes = elevated
serum creatinine, chronic
kidney disease (GFR
<60mL/min/1.73m2)
Blood lead
8.1 ug/dL
Measured creatinine
clearance
88.2 mL/min
Blood lead at baseline
9.9 ug/dL
Serum creatinine at
baseline
1.2mg/dL
Multiple logistic regression
Age, race, gender, diabetes, systolic blood
pressure, smoking status, history of
cardiovascular disease, body mass index,
alcohol consumption, household income,
marital status, and health insurance
Multiple linear regression
Age, body mass index, analgesic and diuretic
use, alcohol consumption, smoking status,
systolic/ diastolic blood pressure
Cross-sectional and longitudinal analyses
Random-effects modeling
Baseline age, time since initial visit and
between visits, body mass index, smoking
status, alcohol ingestion, education level,
hypertension (defined as blood pressure
> 160 or 95 mm Hg or antihypertensive
medication use), and baseline serum creatinine
Higher odds ratios of both increased serum creatinine and
chronic kidney disease by quartile of blood lead in
hypertensives but not normotensives
Odds ratios for elevated serum creatinine in hypertensives
Blood lead (range, ug/dL) % Odds ratio (95% CI)
Quartile 1 (0.7-2.4)
7.2
1.00
Quartile 2 (2.5-3.5
12.1 1.47(1.03,2.10)
Quartile 3 (3.9-5.9)
12.4 1.80(1.34,2.42)
Quartile 4 (6.0-56.0)
16.3 2.41(1.46,3.97)
p < 0.001 for chi-squared test for trend
Twofold higher blood lead associated with odds ratio of 1.43
(95% CI: 1.20,1.71)
Log blood lead negatively associated with log measured
creatinine clearance
-0.04 (95% CI: -0.079,-0.001)
10 ug/dL higher hi blood lead associated with a 10.4 mL/min
lower In creatinine clearance
In cross-sectional analyses of associations between log
transformed blood lead and concurrent serum creatinine, the
largest (3 was in the 141 participants whose peak blood lead
< 10 ug/dL:
0.06 (95% CI: 0.023, 0.097)
Positive association between log transformed blood lead and
change in serum creatinine over subsequent follow-up period
in participants whose peak blood lead was <25 ug/dL
0.027 (95% CI: 0.0, 0.054)
-------
Table 6-4.1 (cont'd). Summary of Key Studies on the Renal Effects of Environmental Lead Exposure
to
o
o
ON
i
Q
O
O
!>
H-J
o
NW'
o
^^
H
O
O
w
o
o
HH
H
W
Reference
Study location
Study population
Sample size
Wu et al. (2003a)
Boston, MA
Normative Aging Study,
1991-1995
n=709
Tsaih et al. (2004)
Boston, MA
Normative Aging Study
1991—2001
n = 448
Staessen et al. (1992)
Belgium
Cadmibel Study
n= 1,981; 965 males
Mean exposure and
outcome measures
Blood lead
6.2 ug/dL
Patella lead
32.1 ug/g bone
Calculated creatinine
clearance
71.3 mL/min
Blood lead at baseline
6.5 ug/dL
Analysis methods
Covariates adjusted for in analysis
Multiple linear regression
Age, body mass index, hypertension,
smoking status, alcohol ingestion, analgesic
medication use
Longitudinal analysis, mean of 6 years
between evaluations
Major significant findings
Significant association between patella lead and creatinine
clearance
P = -0.069 (SE not provided)
Lead dose not associated with change in creatinine in all
Significant interaction of blood and tibia lead with diabetes in
Tibia lead at baseline
21.5 ug/g bone mineral
Serum Creatinine at
Baseline
1.3mg/dL
Blood lead (geometric
mean)
1 1 .4 ug/dL (males)
7.5 ug/dL (females)
Measured creatinine
clearance
99 mL/min (males)
80 mL/min (females)
Age, body mass index, diabetes, hypertension,
smoking status, alcohol consumption, analgesic
use, baseline serum creatinine and its square
Multiple linear regression
Age, age squared, body mass index, log
transformed gamma-glutamyl transpeptidase,
and diuretic use
predicting annual change in serum creatinine
For natural In baseline blood lead P = 0.076 (95% CI: 0.031,
0.121) compared to P = 0.006 (95% CI: -0.004, 0.016) for
non-diabetics
For natural In baseline tibia lead P = 0.082 (95% CI: 0.029
0.135) compared to P = 0.005 (95% CI: -0.005, 0.015) for
non-diabetics
Log transformed blood lead negatively associated with
measured creatinine clearance
-9.5(95%CI: -18.1, -0.9) males
- 12.6 (95% CI: -20.3, -5.0) females
Tenfold increase in blood lead associated with a decrease in
creatinine clearance of 10 and 13 mL/min in men and women,
respectively
-------
2, Table 6-4.1 (cont'd). Summary of Key Studies on the Renal Effects of Environmental Lead Exposure
to
o
o
ON
Oi
i
O
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Reference
Study location
Study population
Sample size
Akesson et al. (2005)
Women's Health in the
Lund Area Study, Sweden
1999-2000
N=820
Mean exposure and
outcome measures
Blood lead
2.2 ug/dL
Renal outcomes = GFR
(estimated with cystatin
C), estimated creatinine
clearance, urinary NAG
and a{ microglobulin
Analysis methods
Covariates adjusted for in analysis
Multiple linear regression
Age, body mass index, diabetes, hypertension,
and regular use of nephrotoxic drug, blood and
urinary cadmium (in separate models), smoking
status (by stratification)
Major significant findings
Blood lead negatively associated with estimated GFR and
creatinine clearance. No associations with NAG or a!
microglobulin.
Beta coefficient (95% CI) for association between blood lead
(ug/dL) and estimated creatinine clearance (mL/min)
is -1.8 (-3.0, -0.7).
-------
1 Inclusion criteria included male gender, age between 21 and 80 years, and absence of chronic
2 medical conditions. Payton et al. (1994) analyzed data from a periodic follow-up evaluation
3 performed between 1988 and 1991 in 744 participants. Lead dose was assessed with blood lead;
4 renal outcome measures included serum creatinine and 24-h measured and calculated (Cockcroft
5 and Gault, 1976) creatinine clearances. Mean blood lead concentration and measured creatinine
6 clearance were 8.1 |ig/dL (SD 3.9) and 88.2 mL/min (SD 22.0), respectively. After adjustment,
7 In blood lead was negatively associated with In measured creatinine clearance (effect estimates
8 are presented in Table 6-4.1). Borderline statistically significant associations (p < 0.1) between
9 blood lead and serum creatinine and estimated creatinine clearance were also observed. Kim
10 et al. (1996) studied 459 men whose blood lead levels from past periodic examinations,
11 conducted every 3-5 years during 1979-1994, were measured from stored samples. Participants
12 were randomly selected to be representative of the entire Normative Aging Study population in
13 terms of age and follow-up. Renal status was assessed with serum creatinine. Data from 4-5
14 evaluations were available for the majority of participants. Relations were evaluated cross-
15 sectionally (associations between blood lead and concurrent serum creatinine) as well as
16 longitudinally (associations between blood lead and change in serum creatinine over the
17 subsequent follow-up period). Mean age, blood lead level, and serum creatinine, at baseline,
18 were 56.9 years (SD 8.3), 9.9 |ig/dL (SD 6.1), and 1.2 mg/dL (SD 0.2), respectively. With
19 random-effects modeling, a significant positive association between In-transformed blood lead
20 and concurrent serum creatinine was observed. This association was stronger when models were
21 confined to participants with lower peak blood lead levels, i.e., the P coefficient was largest in
22 the 141 participants whose highest blood lead level was < 10 |ig/dL. In longitudinal analysis,
23 In-transformed blood lead was associated (p = 0.05) with change in serum creatinine over the
24 subsequent follow-up period in the 428 participants whose highest blood lead level was
25 <25 |ig/dL. Similar to the cross-sectional analysis, the P coefficient in the participants whose
26 highest blood lead level was < 10 |ig/dL was larger; however, in the longitudinal analysis, the
27 standard error also increased such that the p-value was not significant.
28 Cortical and trabecular bone lead measurements were obtained in evaluations performed
29 between 1991 and 1995 in 709 participants in the Normative Aging Study (Wu et al., 2003a).
30 Lead dose was assessed with blood, tibia, and patella lead concentrations. Renal outcome
31 measures included serum creatinine and estimated creatinine clearance. Mean blood, tibia and
May 2006 6-102 DRAFT-DO NOT QUOTE OR CITE
-------
1 patella lead levels were 6.2 jig/dL (SD 4.1), 22.0 |ig/g bone mineral (SD 13.4), and 32.1 |ig/g
2 bone mineral (SD 19.5), respectively. After adjustment, analyses in the 670 participants from
3 whom these data were available, revealed a significant inverse association between patella lead
4 and creatinine clearance. A borderline significant (p = 0.08) inverse association between tibia
5 lead and creatinine clearance was also observed. None of the lead measures were significantly
6 associated with serum creatinine.
7 Tsaih et al. (2004) reported associations between baseline lead dose and change in serum
8 creatinine in 448 men. Lead dose was assessed with blood, tibia, and patella lead. Serum
9 creatinine was measured at baseline and at follow-up, an average of 6 years later. Six percent
10 and 26% of subjects had diabetes and hypertension, at baseline, respectively. Mean blood lead
11 levels and serum creatinine decreased significantly over the follow-up period in the group. Lead
12 dose was not associated with change in creatinine in all participants. However, the authors found
13 a significant interaction between lead dose (blood and tibia lead) and diabetes on change in
14 serum creatinine. Interaction was also observed between tibia lead and hypertension, although it
15 is possible that many of the 26 diabetics were also included in the hypertensive group and were
16 influential there as well.
17
18 NHANESIII
19 Muntner et al. (2003) analyzed associations between blood lead and renal outcomes in
20 15,211 adult subjects enrolled in the NHANES III study, conducted from 1988 through 1994.
21 Dichotomous renal outcome measures analyzed included elevated serum creatinine and chronic
22 kidney disease (GFR < 60mL/min/l .73 m2). Due to interaction between blood lead and
23 hypertension, the population was stratified. Mean blood lead was 4.21 |ig/dL in the 4,813
24 hypertensives and 3.30 |ig/dL in normotensives. The prevalence of elevated serum creatinine in
25 hypertensives and nonhypertensives was 11.5% and 1.8%, respectively; prevalence of chronic
26 kidney disease was similar. The odds ratios for both renal outcomes increased by quartile of
27 blood lead among the hypertensive subjects but not among those without hypertension. Among
28 those with hypertension, after adjustment for age, race and gender, the odds ratios for elevated
29 creatinine in quartiles 2, 3, and 4 compared to the lowest quartile of blood lead, were 1.56
30 (95% CI: 1.04, 2.35), 1.68 (95% CI: 1.24, 2.26), and 2.07 (95% CI: 1.26, 3.40), respectively.
31 As shown in Table 6-4.1, the odds ratios were the same following additional adjustment. The
May 2006 6-103 DRAFT-DO NOT QUOTE OR CITE
-------
1 authors noted that the "associations were strong, dose-dependent and consistent before and after
2 comprehensive adjustment." They also noted that in nonhypertensives, higher blood lead was
3 associated with a higher prevalence of chronic kidney disease in diabetics. This study is notable
4 for sample size, comprehensive adjustment for other renal risk factors, and the fact that this study
5 population is representative of the U.S. non-institutionalized, civilian population.
6
7 Women's Health in the Lund Area Study
8 In a study of 820 women, ages 53-64 years, in Sweden significant negative associations
9 were observed between blood lead and both GFR (estimated from serum cystatin C) and
10 creatinine clearance (estimated by the Cockcroft-Gault equation [Cockcroft and Gault, 1976])
11 (Akesson et al. 2005). Mean blood lead was only 2.2 |ig/dL; the association was apparent over
12 the entire dose range (Akesson, 2006). This study has the additional advantage of blood and
13 urinary cadmium assessment.
14
15 Summary of Lead-Related Nephrotoxicity in the General Population
16 General populations studies constitute one of the two most important types of research on the
17 adverse renal effects of lead during the past two decades. Overall, a number of strengths are
18 present in this body of literature. These include study design with longitudinal data in some
19 studies; large populations in both Europe and the U.S.; comprehensive assessment of lead dose,
20 including the use of bone lead as a measure of cumulative lead body burden in some studies; and
21 statistical approaches that utilize a range of exposure and outcome measures, while adjusting for
22 numerous renal risk factors. Associations between lead dose and worse renal function were
23 observed in most of the general population studies.
24
25 Threshold for Lead-Related Nephrotoxicity
26 Increased risk for nephrotoxicity has been observed at the lowest lead dose levels studied
27 to date. Specifically, blood lead ranged from 2.5 to 3.8 |ig/dL in the first significant category in
28 Muntner et al. (2003); associations between blood lead as a continuous variable and worse renal
29 function have been reported at a mean of 2.2 |ig/dL (Akesson et al., 2005). An association
30 between cumulative lead dose (mean tibia lead of 21.5 jig/g bone mineral) and longitudinal
31 decline in renal function has been observed as well, although data on any threshold for this effect
May 2006 6-104 DRAFT-DO NOT QUOTE OR CITE
-------
1 were not reported (Tsaih et al., 2004). The data available to date are not sufficient to determine
2 whether nephrotoxicity is related more to current blood lead levels, higher levels from past
3 exposures, or both. However, Kim et al. (1996) noted associations in participants whose peak
4 blood lead levels were < 10 |ig/dL as far back as 1979.
5
6 Alternative Explanations for Observed Associations
1 Residual confounding as an explanation for associations between lead dose and adverse
8 health effects is always a consideration. One general population study provided data useful to
9 address this concern in the lead-renal literature. For both renal outcomes assessed, Muntner et al.
10 (2003) observed that the odds ratios in hypertensives, initially adjusted for age, race and gender,
11 increased following additional adjustment for diabetes, systolic blood pressure, smoking status,
12 history of cardiovascular disease, body mass index, alcohol consumption, household income,
13 education level, marital status, and health insurance. In contrast, after adjustment, regression
14 coefficients decreased in Wu et al. (2003b). However, the analyses were performed in slightly
15 different populations making interpretation of the adjustment differences less certain. Further, as
16 noted in the Agency for Toxic Substances and Disease Registry's Draft Toxicological Profile For
17 Lead ([2005] Atlanta, GA: U.S. Department of Health and Human Services), since increased
18 blood pressure is associated with lead dose in general populations, adjustment for hypertension
19 or blood pressure, although extremely common in lead-renal studies, risks underestimating the
20 actual slope of the association between lead dose and renal dysfunction. Overall, one of the
21 strengths of the lead-renal general population literature is the number of factors adjusted for.
22 Thus, residual confounding is an unlikely explanation for observed associations.
23 Reverse causality has also been considered as an explanation for associations between
24 lower blood lead levels (e.g., <10 |ig/dL) and worse renal function (Staessen et al., 1992).
25 Reverse causality attributes increased lead dose to reduced lead excretion as a consequence of
26 renal insufficiency. The temporal relation between lead dose and renal function decline is a
27 critical factor in determining causality. This can be assessed in longitudinal observations of
28 participants with mean blood lead levels in this lower dose range. Two analyses of longitudinal
29 data from the Normative Aging Study population have been published to date (Kim et al., 1996;
30 Tsaih et al., 2004). Lead dose predicted subsequent decline in renal function over follow-up
31 periods ranging from three to 6 years. This was observed even after adjustment for renal
May 2006 6-105 DRAFT-DO NOT QUOTE OR CITE
-------
1 function at the beginning of the follow-up period. Longitudinal studies in patients with renal
2 insufficiency have reported similar findings. Both blood and EDTA-chelatable lead levels at
3 baseline were significantly associated with decline in estimated GFR over a 4 year follow-up
4 period in 121 patients, even after adjustment for a wide range of co-variates including baseline
5 renal function (Yu et al., 2004) (discussed in Section 6.4.4.3.2). The same was true in a larger
6 study of 202 chronic renal insufficiency patients over a 2-year follow-up period (Lin et al., 2003)
7 (discussed in Section 6.4.4.3.3). Notably, in both studies, EDTA-chelatable lead levels were
8 <600 |ig/72 h in all participants with means well below this traditional cut-point. The Pheecad
9 study (the 1990-95 follow-up to the Cadmibel study) appears to have collected relevant data but
10 the lead data are not reported in the publication (Hotz et al., 1999).
11 Biologically, reverse causality should be most prominent in populations with renal
12 insufficiency for a prolonged period of time. However, as shown graphically in Figure 1 in Kim
13 et al. (1996), blood lead was positively associated over the entire serum creatinine range, most of
14 which was normal in this general population study and where a substantial decrease in lead
15 excretion is unlikely. Further, in reverse causality, urinary excretion of lead should decrease as
16 renal function declines. Urine lead is not a commonly used lead dose biomarker, so data from
17 the lower lead exposure studies are generally not available to assess this. However, higher urine
18 lead was associated with lower estimated creatinine clearance in Swedish women (Akesson,
19 2006). Finally, the positive impact of lead chelation on renal function (discussed in Section
20 6.4.4.3.3) may provide evidence against reverse causality. However, the possibility of a direct
21 beneficial effect of the chelating agent on renal function cannot be excluded as an explanatory
22 factor (Gonick et al., 1996). In summary, several lines of evidence suggest that reverse causality
23 is not likely to be a major explanatory factor for associations between lead dose and renal
24 dysfunction.
25
26 Consistency of the Magnitude of Associations
27 Slopes of the associations between blood lead and creatinine clearance in the general
28 population studies that provided data relevant for such a comparison are displayed in
29 Figure 6.4-1. Since these studies generally had mean blood lead levels less than 10 |ig/dL,
30 slopes of the reported relations were estimated at a blood lead level of 5 |ig/dL. Measured or
31 estimated creatinine clearance data was used from those studies that reported relations for those
May 2006 6-106 DRAFT-DO NOT QUOTE OR CITE
-------
Tsaih et al. (2004), follow-up
Kim etal. (1996)
Tsaih et a!. (2004), baseline
Paytonetal. (1994)
Akesson et al. (2005)
Staessen et al. (1992), men
Staessen et al. (1992), women
-4.0 -2.0 0.0 2.0 4.0
Slope for Creatinine Clearance per Blood Lead (ml_/min)/(fjg/dl_)
Figure 6-4.1. Creatinine Clearance Versus Blood Lead Slope at a Blood Lead of 5 ug/dL.
1 outcomes. For studies that only reported data for serum creatinine, we estimated the slope at a
2 blood lead of 5 |ig/dL and then converted that slope to a creatinine clearance slope using the
3 Cockcroft-Gault equation (Cockcroft and Gault, 1976). Publication bias may impact the data
4 available for this figure. No significant associations between blood lead and renal function were
5 observed in two of the general population studies; beta coefficients were not reported (Wu et al.,
6 2003a; de Burbure at al., 2003). However, since Wu et al. (2003a) observed a significant
7 association between patella lead and creatinine clearance, the study is consistent with results in
8 the majority of the other general population studies. Lastly, a third study reported only that the
9 correlation coefficient between crude blood lead and serum creatinine was 0.0 (Pocock et al.,
10 1984). Furthermore, publications from the Normative Aging population outnumber those from
11 other populations. Slopes ranged from 0.2 to -1.8 mL/min change in creatinine clearance
12 per |ig/dL increase in blood lead.
May 2006
6-107
DRAFT-DO NOT QUOTE OR CITE
-------
1 Clinical Relevance
2 It is now clear that chronic kidney disease (CKD) at earlier stages than those requiring
3 actual renal dialysis or transplantation is a risk factor for cardiac disease and other causes of
4 mortality and morbidity (Levey et al., 2003). The clinical relevance of the lead effect can be
5 estimated from the study by Akesson et al. (2005) in which the 5th and 95th percentile values for
6 blood lead were reported. An increase in blood lead from the 5th to the 95th percentile (3.5
7 Hg/dL) has the same adverse impact on glomerular filtration as an increase of 4.7 years in age or
8 7 kg/m2 in body mass index, both of which are known renal risk factors. In populations at high
9 risk for lead exposure, a 10-fold increase in blood lead (e.g., from 1 to 10 |ig/dL) would result in
10 an 16.2 mL/min decrease in estimated creatinine clearance or a 22.5% decrease from the mean
11 (Akesson et al., 2005). Sixteen and 9% declines from a 10-fold increase in blood lead were
12 predicted based on data in women (Staessen et al., 1992) and men (Payton et al., 1994),
13 respectively. Although lead exposure is higher in rapidly industrializing countries, high risk
14 populations remain in the U.S. In populations with lower blood lead levels, a downward shift in
15 renal function of the entire population due to lead may not result in CKD in identifiable
16 individuals; however, the segment of the population with the lowest renal reserve may be at
17 increased risk for CKD when lead is combined with another renal risk factor.The potential public
18 health importance of population shifts is discussed by the American Thoracic Society (2000) and
19 Rose and Day (1990). Data in both general and patient populations support this concept for lead
20 exposure. Of note, the above estimates are in general populations. Effect estimates in
21 susceptible populations, such as those with diabetes, hypertension, or chronic renal insufficiency
22 from non-lead related causes, are likely to be higher.
23
24 A t-Risk Populations
25 Susceptible populations include those with other risk factors for renal disease, including
26 hypertension, diabetes, and renal disease from other causes. Lead exposed populations who are
27 also at increased risk for obesity, diabetes, and hypertension represent groups likely to be the
28 most impacted by lead exposure. Frequently both risk factors are present in the same lower
29 socioeconomic status groups.
30 In conclusion, the general population literature on the adverse renal effects of lead
31 benefits from a number of strengths. The consistent associations observed in the majority of
May 2006 6-108 DRAFT-DO NOT QUOTE OR CITE
-------
1 these studies provide strong evidence indicating that lead is a contributor to renal dysfunction in
2 susceptible populations at much lower levels than those identified based on data available at the
3 time of the 1986 Lead AQCD.
4
5 6.4.4.2 Occupational Studies
6 The vast majority of studies in the lead-renal literature were conducted in the occupational
7 setting. This was especially true prior to the 1986 Lead AQCD but is still currently the case.
8 Occupational studies of the renal effects of lead are presented in Annex Table AX6-4.2. In
9 contrast to the general population-research discussed above, research on the adverse renal effects
10 of occupational lead exposure is much less consistent. This is puzzling since most dose-response
11 relations are thought to be linear. Therefore, biologically, moderate lead doses (30-50 |ig/dL)
12 should be nephrotoxic if lower doses are. Several explanations for this seeming inconsistency
13 are possible. Some are unique to the occupational literature such as smaller sample sizes. In
14 addition, employed workers are healthier and younger than the general population resulting in
15 the healthy worker bias. This is a particular problem as susceptible risk groups are identified.
16 Survivor bias in cross-sectional studies is also a concern since workers whose renal function has
17 declined will be removed from exposure, particularly if they are followed in a medical
18 surveillance program. Few studies have included former workers. Statistical analyses have been
19 more limited in occupational studies. Analyses for some outcomes were limited to comparisons
20 between exposed workers and controls whose lead levels were in the range associated with
21 adverse renal outcomes in environmental work. Use of multiple linear regression has generally
22 involved more limited adjustment for co-variates than in the environmental studies. Most of
23 these limitations result in bias towards the null which increases the risk that true associations are
24 not detected.
25 Other limitations are pertinent for research on the adverse renal effects of lead exposure in
26 any population. These factors are likely to have a greater impact on the validity of studies in
27 which one or more of the biases discussed above are also present. These include the insensitivity
28 of the clinical renal outcomes and the lack of uniformly accepted early markers of renal damage
29 in lead exposure. Limited lead exposure assessment may also be a factor. Finally, lead appears
30 to be able to induce an element of hyperfiltration in some settings. Hyperfiltration is a process
31 initially observed in diabetes but also implicated in other settings, including hypertension and
May 2006 6-109 DRAFT-DO NOT QUOTE OR CITE
-------
1 obesity (Nenov et al., 2000). In this process, initial supranormal renal function is paradoxically
2 associated with increased risk for subsequent renal dysfunction. Several occupational studies
3 have reported statistically significant higher mean creatinine clearance in lead exposed
4 participants compared to controls and/or positive associations between higher lead dose and
5 lower BUN, serum creatinine and/or higher creatinine clearance (Roels et al., 1994; Weaver
6 et al., 2003a, 2005a; Hsiao et al., 2001). Hu (1991) has also reported increased mean creatinine
7 clearance in 22 adults who were lead poisoned as children compared to matched controls
8 (discussed in Section 6.4.5.1) and a recent study reported higher blood lead associated with
9 lower serum creatinine and cystatin C in a study of 800 European children (discussed in Section
10 6.4.5.3). Longitudinal data for lead-exposed rodents (discussed in Section 5.7.4.2) are critical in
11 relating this process to lead. However, in that work, despite similar initial hyperfiltration,
12 subsequent renal dysfunction was much more severe in the high-dose lead-exposed rodents
13 compared to the low-dose animals. This suggests that hyperfiltration may be one, but not the
14 only, mechanism for the adverse renal effects of lead. Whether hyperfiltration contributes to
15 pathology in humans is unclear; longitudinal studies are needed.
16 Regardless, the issue for risk assessment is that significant findings could be obscured if
17 opposite direction associations are present in different segments of the study population and
18 interaction models to address this are not performed.
19 In the work of Weaver et al. (2003a), in several models, no associations were observed
20 when the entire population was studied; however, when interaction models using age as the
21 effect modifier were evaluated, significant associations in opposite directions were observed.
22 This is illustrated in Figure 6-4.2. This is a valid concern for risk assessment, since the factors
23 involved in these inverse associations in lead exposed populations are not well defined at
24 present. Weaver and colleagues have used age as the effect modifier; however, other factors,
25 such as lead job duration, may be important as well.
26 In conclusion, a number of limiting factors are observed in the body of research on
27 occupational lead exposure and adverse renal outcomes. Most of these factors increase the risk
28 that true associations will be missed (bias towards the null). Moreover, lead appears to have a
29 paradoxical effect on the kidney that further increases this possibility. As a result, the more
30 consistent body of literature in general populations at current Pb exposure conditions provide an
31 appropriate data base for potential renal effects.
May 2006 6-110 DRAFT-DO NOT QUOTE OR CITE
-------
Worse
Renal
Function
Potential
Hyperfiltration
Older
Lead dose
Figure 6-4.2. Effect on associations between lead dose and renal function depending on
whether effect modification (age in this example) is assessed.
1 6.4.4.3 Patient Population Studies
2 Studies in various patient populations have also contributed to the body of knowledge
3 concerning adverse renal impacts of lead exposure (summarized in Annex Table AX6-4.3).
4 Populations studied include those with chronic renal insufficiency (CRT), end-stage renal disease
5 (ESRD), gout, and hypertension since these diseases are thought to be increased by high-level
6 lead exposure, particularly when two or more coexist in the same patient. Early research focused
7 on patients with potential lead nephropathy; and lead body burdens of interest, assessed with
8 EDTA chelation, were above 600 to 650 |ig/72 h.
9 Two issues have been a recurring concern in this work. The first is whether lead body
10 burden is higher in all patients with renal insufficiency or failure due to decreased lead excretion
11 (reverse causality). The second concern is whether EDTA-chelatable lead levels when measured
12 over a 72-h period in patients with CRT can be equated to those in participants with normal renal
13 function measured over 24 h. It is possible that, due to decreased excretion of EDTA in renal
14 insufficiency, more lead per dose is ultimately chelated. These concerns have been addressed in
15 various ways as noted in the research discussed below.
16
17 Lead Body Burden in Chronic Renal Disease
18 Batuman et al. (1983) studied 27 hypertensives with CRT (defined as serum creatinine
19 >1.5 mg/dL) and 21 without associated renal impairment. Despite similar blood lead levels,
May 2006
6-111
DRAFT-DO NOT QUOTE OR CITE
-------
1 mean EDTA-chelatable lead levels were significantly higher in hypertensives with CRI than
2 those without (860 and 340 jig/72 h, respectively). Further, chelatable lead levels in patients
3 with CRI from causes not thought to be related to lead nephropathy and who had no history of
4 lead exposure were similar to patients with hypertension but no CRI.
5 Sanchez-Fructuoso et al. (1996) performed a similar study in a much larger number of
6 patients in Spain, none of whom had a known history of lead exposure. Mean age ranged from
7 53.5 to 61.6 years in different patient subgroups. These authors reported that EDTA-chelatable
8 lead levels >600 jig/72 h were present in none of 30 controls, 16 (15.4%) of 104 patients with
9 essential (primary) hypertension and normal renal function, 74 (56.1%) of 132 patients with CRI
10 of unknown etiology along with hypertension (64 of the 132 also had gout), but none of the
11 30 patients with CRI of known, non-lead related etiology. Mean blood and EDTA-chelatable
12 lead levels in the patients with CRI of known cause were not statistically different from controls
13 with normal renal function. These researchers also reported significant correlations between
14 bone lead levels (assessed by biopsy) and EDTA-chelatable lead level in 12 patients whose
15 chelatable lead levels were >600 jig/72 h, which provides support for the validity of chelatable
16 lead levels in CRI.
17 In contrast, Osterloh et al. (1989) reported no significant difference in EDTA-chelatable
18 lead levels between 40 male subjects with hypertensive nephropathy (hypertension preceded
19 renal insufficiency; serum creatinine 1.8-4 mg/dL) and 24 controls with renal dysfunction from
20 other causes (mean ages of 62 and 52 years, respectively). Lead dose and serum creatinine were
21 not correlated. Chelatable lead levels in this population were much lower than those reported by
22 Wedeen et al. (1983) and Sanchez-Fructuoso et al. (1996). The inconsistent results in these
23 studies may reflect differences in the patients studied. Batuman et al. (1983) studied Veterans
24 Administration patients, Sanchez-Fructuoso et al. (1996) studied patients from a low-medium
25 income area in Madrid, Spain, and Osterloh et al. (1989) recruited patients from the database of a
26 large health maintenance organization in California.
27 Van de Vyver et al. (1988) observed that lead levels in bone biopsies in 8 of 153 dialysis
28 patients were in the range observed in 22 lead workers, suggesting lead as a primary cause of
29 their renal failure. Levels in the 10 patients with analgesic nephropathy were the lowest (all
30 <7 jig/g).
31
May 2006 6-112 DRAFT-DO NOT QUOTE OR CITE
-------
1 Impact of Lead Body Burden on Decline in Renal Function in Patients with CRI
2 Lin and colleagues have addressed the issue of low-level lead as a cofactor with other
3 renal risk factors in susceptible populations, including those with CRI and/or gout. They have
4 approached this work in two ways: prospective follow-up of populations with CRI to determine
5 if renal function decline is greater in those with higher lead body burdens and through
6 randomized trials to determine if chelation therapy changes the rate of renal function decline.
7 Importantly, their work is in an EDTA-chelatable lead range well below that considered
8 abnormal as described in Section 6.4.4.3.1.
9 In their most recent publication, Yu et al. (2004) followed 121 patients over a 4-year
10 period. Eligibility required well-controlled CRI. Importantly, serum creatinine between 1.5 and
11 3.9 mg/dL and EDTA-chelatable lead <600 jig/72 h were required at baseline. Patients with
12 potentially unstable renal disease were excluded (i.e., due to systemic diseases such as diabetes).
13 Mean age was 57 years. Mean blood lead and EDTA-chelatable lead levels were 4.2 jig/dL and
14 99.1 jig/72 h, respectively. Sixty-three patients had "high-normal" EDTA-chelatable lead levels
15 (>80 but <600 jig/72 h); 58 had "low-normal" EDTA-chelatable lead levels (<80 jig lead/72 h).
16 The groups were similar in most other baseline risk factors. Borderline statistically significant
17 (p < 0.1) differences included mean older age in the high chelatable lead group and certain renal
18 diagnoses. Fifteen patients in the "high-normal" group reached the primary endpoint (doubling
19 of serum creatinine over the 4-year study period or need for hemodialysis) compared to only two
20 in the "low-normal" group (p = 0.001).
21 In a Cox multivariate regression analysis, chelatable lead was significantly associated
22 with overall risk for the primary endpoint (hazard ratio for each 1 jig chelatable lead was 1.01
23 [95% CI: 1.00, 1.01; p = 0.002]). The associations between baseline chelatable lead or blood
24 lead level and change in GFR (estimated by an MDRD equation [Levey et al., 1999]) were
25 modeled separately using GEE. Based on these models, a 10 jig higher chelatable lead level or a
26 1 jig/dL higher blood lead level reduced the GFR by 1.3 and 4.0 mL/min, respectively, during
27 the 4-year study period. Similar to the primary outcome analysis, of the many traditional renal
28 risk factors adjusted for in these models, only diagnosis of chronic interstitial nephritis was
29 significantly associated, in this case with an increase in GFR. Of note, chronic interstitial
30 nephritis was also a more frequent diagnosis in the group with the low-normal chelatable lead
31 levels (p = 0.09).
May 2006 6-113 DRAFT-DO NOT QUOTE OR CITE
-------
1 Therapeutic EDTA Chelation in Patients
2 Chelation in lead exposure is controversial due to the potential for it to be used in lieu of
3 exposure reduction. Chelation in lead nephropathy, in particular, is controversial, because cases
4 of acute tubular necrosis were reported following early clinical use of EDTA that involved large
5 doses in the treatment of hypercalcemia and lead poisoning. Adverse renal effects have not been
6 observed in subsequent work using much lower doses (Sanchez-Fructuoso et al., 1996; Wedeen
7 etal., 1983).
8 Work prior to the 1986 Lead AQCD suggested that chelation might be beneficial in lead
9 nephropathy (Morgan, 1975; Wedeen et al., 1979). This issue has been addressed more
10 recently by Lin and colleagues in patients with much lower lead doses. Lin et al. (1999) studied
11 43 patients with serum creatinine and EDTA-chelatable lead levels between 1.5-4 mg/dL and
12 150 and 600 |ig/72 h, respectively. Patients were followed for 12 months to determine their
13 baseline rate of renal function decline. A group of 32 was then randomized; and 16 underwent a
14 2-month treatment period consisting of weekly chelation with 1 g EDTA; whereas the other
15 16 continued their regular care. Traditional renal risk factors, such as blood pressure control,
16 were similar in the two groups. Mean ages were 54.1 and 55.0 years, respectively in treated and
17 control groups. Prior to therapeutic chelation, the rate of progression of renal insufficiency was
18 not statistically different. However, actual improvement in renal function was noted in the
19 treated group during chelation and subsequent renal function decline was slower in this group.
20 The mean difference in the change in the reciprocal of serum creatinine post therapy was
21 0.000042 L/|imol per month (95% CI: 0.00001, 0.00007).
22 In subsequent work, Lin et al. (2003) published results of a randomized chelation trial in a
23 larger group. This work included a 2-year prospective study of renal function decline prior to
24 chelation in 202 patients with CRT and EDTA-chelatable lead <600 |ig/72 h (mean age of
25 56.6 years). Results of the Cox proportional-hazards model were similar to those reported in Yu
26 et al. (2004). Associations between baseline EDTA-chelatable lead level and change in GFR
27 were modeled using GEE. After adjustment, an increase of 10 jig in EDTA-chelatable lead was
28 associated with a GFR decrease of 0.03 mL/min/1.73 m2 of body-surface area during the
29 observation period (p < 0.001). Of note, this effect, although statistically significant, is 40-fold
30 lower than that reported in Yu et al. (2004) over a follow-up period that is only 2-fold shorter.
31 At 24 months, 64 patients whose EDTA-chelatable lead levels were 80-600 |ig/72 h were
May 2006 6-114 DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
7
8
9
10
11
12
13
randomized; half to a 3-month treatment period consisting of weekly chelation with 1 g EDTA
until their excreted lead levels fell below 60 jig/72 h and half to placebo infusion over 5 weeks.
Renal risk factors were similar in the two groups. Mean blood lead levels were 6.1 |ig/dL and
5.9 |ig/dL in treated and control groups, respectively. In the subsequent 24 months, chelation in
19 (59%) participants was repeated due to increases in serum creatinine in association with
rebound increases in EDTA-chelatable lead levels. Each received one additional chelation series
(mean = 4.1 g EDTA) a mean of 13.7 months after the first chelation period. At the end of the
study period, mean estimated GFR increased by 2.1 mL/min/1.73 m2 of body-surface area in the
chelated group compared to a decline of 6.0 mL/min/1.73 m2 of body-surface area in the controls
(p < 0.01) (see Figure 6-4.3). The 95% CI for the difference between the chelated and control
groups was -11.0 to - 5.1 mL/min/1.73 m2 of body-surface area.
CM
«*>
E
E,
o>
*•»
(9
c
.2
**c
ro
JO
3
<5
.2
o
Month
Figure 6-4.3. Estimated mean (+2 SE) glomerular filtration rate according to time in
the chelation group (n = 31) and the control group (n = 30) during the
observation and intervention periods. The patients in the chelation group
received chelation therapy from month 24 to month 51. The asterisks
indicate p < 0.05 by Student's t-test.
Source: Linetal. (2003).
May 2006
6-115
DRAFT-DO NOT QUOTE OR CITE
-------
1 It is also possible that chelation has a direct beneficial effect on kidney function,
2 regardless of lead exposure, since DMSA has been reported to prevent renal damage in a non-
3 lead exposed rat model of nephrosclerosis (Gonick et al., 1996). If so, the benefits of chelation
4 do not appear to occur via reversal of structural damage (Khalil-Manesh et al., 1992); improved
5 hemodynamics from reduction of reactive oxidant species may be a mechanism (Gonick et al.,
6 1996).
7 The key studies in patients followed prospectively with and without chelation constitute
8 the other major advance in research on the adverse renal effects of lead over the past two
9 decades. Strengths of the work of Lin and colleagues include prospective study design, lead
10 dose assessment including bioavailable body burden, randomized chelation, statistical analysis
11 that includes GEE for longitudinal data, and adjustment for more renal risk factors than any of
12 the other key studies discussed in Section 6.4. Limitations include that fact that, to date, this
13 type of research has been conducted in relatively small number of participants and in only one
14 center. As noted above, the two reported lead body burden P coefficients in GEE models of
15 decline in renal function vary widely. Therefore, small study sizes and differences in renal
16 diagnoses between groups may be overly influential in the results. However, this work supports
17 results in general populations by suggesting that lead is nephrotoxic in susceptible populations at
18 lower levels than currently appreciated. If confirmed in large populations, the potential public
19 health benefit could be substantial. Lin et al. (2003) noted that, based on their data, chelation
20 could delay the need for hemodialysis by 3 years. Therefore, this unique line of research is
21 deserving of further study.
22
23 6.4.4.4 Mortality Studies
24 As summarized in Steenland et al. (1992), mortality studies have consistently shown
25 excess mortality from chronic kidney disease in lead workers. This increased risk has been most
26 apparent in workers exposed in earlier time periods, becoming nonsignificant in later calendar
27 time periods in a number of studies. Steenland et al. (1992) reported similar results in a study of
28 1990 former lead smelter workers. This cohort was made up of predominantly white men who
29 had worked in a lead-exposed department for at least 1 year between 1940 and 1965. Mean (SD)
30 blood lead, measured in 1976 in 173 members of this cohort, was 56.3 |ig/dL (12.9). There were
31 8 deaths from chronic kidney disease. Compared to the U.S. white male population, the
May 2006 6-116 DRAFT-DO NOT QUOTE OR CITE
-------
1 standardized mortality ratio was 1.26 (95% CI: 0.54,2.49). The standardized mortality ratio
2 increased with duration of exposure from 0.79 in workers exposed 1-5 years to 2.79 in workers
3 exposed >20 years, although the standardized mortality ratios did not reach significance (CI not
4 reported). Lead exposure in U.S. industries has declined over the years, and this has been
5 hypothesized as an explanation for the reduction in mortality from renal disease observed in this
6 type of study. However, that fact that improved treatments for chronic renal disease have led to
7 a decrease in mortality from end-stage renal disease (U.S. Renal Data System, 2004) may also be
8 a factor. The mortality studies by Steenland et al. (1992) and others are further described in
9 Annex Table AX6-4.4.
10
11 6.4.5 Lead Nephrotoxicity in Children
12 6.4.5.1 Studies in Adults Following Childhood Lead Poisoning
13 Henderson clearly established an increased risk for lead nephropathy in adult survivors of
14 untreated childhood lead poisoning (Henderson, 1955). Lead nephropathy was responsible for
15 substantial mortality in the Queensland, Australia population. However, as noted in the 1986
16 Lead AQCD, other studies of adults who survived childhood lead poisoning have not reported
17 this degree of renal pathology. Studies published since 1986 are presented in Annex Table
18 AX6-4.5 and also have not observed the degree of renal pathology noted in the Queensland
19 work. Chelation when lead poisoning was diagnosed may be an explanatory factor in some of
20 these studies.
21 A study of comparing 21 adults, who had experienced childhood lead poisoning between
22 1930 and 1942, to age, sex, race, and neighborhood-matched controls found no significant
23 differences in blood lead level, serum creatinine, or BUN (Hu, 1991). Mean measured creatinine
24 clearance was unexpectedly higher in the previously lead-poisoned group compared to controls
25 (112.8 versus 88.8 mL/min/1.73 m2 [p < 0.01]). Mean in the lead-exposed group was also higher
26 than the predicted value of 94.2 mL/min/1.73 m2 from the nomogram of Rowe et al. (1976).
27 One survivor, who was identified but not included in the study, had been diagnosed with chronic
28 interstitial nephritis on renal biopsy. Her blood lead was 30 |ig/dL and her presentation was thus
29 consistent with actual lead nephropathy. Strengths of this study included clear criteria for lead
30 poisoning and assessment of clinical renal function that included both measured and estimated
31 creatinine clearances. However, the study was limited by small size and the fact that the number
May 2006 6-117 DRAFT-DO NOT QUOTE OR CITE
-------
1 enrolled was a very small subset of the initially identified cohort of 192. At least 43 (22.4%) of
2 the 192 were confirmed to be deceased. That group had evidence of higher initial lead exposure,
3 which raises concern regarding survivor bias in the study group. More importantly, the higher
4 mean creatinine clearance in the lead exposed group provides further evidence for lead-related
5 hyperfiltration. Again, as discussed in the occupational study section, this may hamper attempts
6 to detect associations between lead dose and adverse renal effects.
7
8 6.4.5.2 Lead Body Burden in Children with Chronic Renal Disease
9 Scharer et al. (1991) reported higher lead content in deciduous teeth in 22 German
10 children, age 5-14 years, with varying degrees of renal insufficiency compared to a control group
11 of 20 siblings or neighbors and a group of 16 children without known lead exposure. Mean
12 dental lead content was 2.8, 1.7, and 1.4 |ig/g, in the three groups, respectively. Lead levels in
13 teeth were significantly higher in both the patient and sibling/neighbor control groups compared
14 to the unexposed control group. Mean blood lead in the renal patients was only 2.9 |ig/dL
15 (range 1.1-10.1 |ig/dL). Lead in teeth was not correlated with duration of renal impairment.
16 The authors attributed elevated lead levels to both exposure and accumulation from decreased
17 renal excretion.
18
19 6.4.5.3 Environmental Studies in Children
20 The insensitivity of the clinical renal outcome measures for early renal damage is a
21 particular problem in children who do not have many of the other renal risk factors, such as
22 hypertension and diabetes, that older adults do. As a result, recent studies in children have
23 favored early biological effect markers over clinical renal measures. However, data to determine
24 the predictive value of such biomarkers for subsequent renal function decline in lead exposed
25 populations are extremely limited. Coratelli et al. (1988) reported a decline in urinary NAG in
26 association with a 1 month period of decreased occupational exposure in 20 adult lead battery
27 factory workers followed over a 1 year period. Clinical renal function measures were not studied
28 however. Sarasua et al. (2003) studied 526 adults and children, a mean of 4.5 years after an
29 initial evaluation of renal function including measurement of urinary albumin, NAG, RBP, and
30 alanine aminopeptidase. These participants were drawn from three populations exposed to
31 volatile organic compounds and explosives via groundwater and controls. Follow-up was
May 2006 6-118 DRAFT-DO NOT QUOTE OR CITE
-------
1 performed to determine if the EBE markers remained elevated and whether the presence of
2 elevated EBE markers at baseline was associated with abnormalities in serum creatinine, serum
3 cystatin C, 24 h creatinine clearance, and urine osmolality at follow-up. Among children who
4 had elevated EBE markers at baseline, renal EBE markers remained elevated in 38%. However,
5 none remained elevated in the 32 who had completed adolescence by the time of the follow-up.
6 The authors noted the potential for puberty related biomarker changes. Further, abnormalities in
7 the clinical measures were rare at follow-up.
8 The environmental studies in children generally focused on children living near industrial
9 areas and controls. These studies are summarized in Table AX6-4.5. Three studies that included
10 analysis of clinical renal outcomes are of note. Pels et al. (1998) found no difference in mean
11 serum creatinine between 62 exposed and 50 control children; correlations, if assessed were not
12 reported. Staessen etal. (2001) studied 200 17-year-old Belgian children. The two exposed
13 groups were recruited from industrialized suburbs, whereas, the control group was recruited from
14 a rural area. Mean blood lead levels were 1.5, 1.8, and 2.7 |ig/dL in controls, and exposed
15 groups one and two, respectively. Although blood lead levels were low, after adjustment for sex
16 and smoking status, blood lead was positively associated with both urinary p2-microglobulin and
17 serum cystatin-C. Blood cadmium was not associated with either outcome. In contrast,
18 De Burbure et al. (2006) observed associations between higher blood lead and lower serum
19 creatinine and cystatin C in models with 300-600 European children (depending on outcome).
20 The authors considered this suggestive of hyperfiltration. Additional research in children,
21 including longitudinal follow-up, is needed.
22
23 6.4.6 Mechanisms for Lead Nephrotoxicity
24 Individuals who have been heavily exposed to lead are at increased risk for both gout and
25 renal disease (Shadick et al. 2000; Batuman 1993). Lead is thought to increase serum uric acid
26 (urate) by decreasing its renal excretion (Emmerson, 1965; Ball and Sorensen, 1969; Emmerson
27 and Ravenscroft, 1975). As discussed above, research in the last decade indicates that lead is
28 nephrotoxic at lower levels than previously recognized. The same is true for uric acid (Johnson
29 et al., 2003). Therefore, it is possible that one mechanism for lead-related nephrotoxicity, even
30 at current lower levels of lead exposure, is via increasing serum uric acid.
May 2006 6-119 DRAFT-DO NOT QUOTE OR CITE
-------
1 In order to address this question, Weaver et al. (2005a) analyzed data from 803 current
2 and former lead workers to determine whether lead dose was associated with uric acid and
3 whether previously reported associations between lead dose and renal outcomes (Weaver et al.,
4 2003a) were altered after adjustment for uric acid. Outcomes included uric acid, blood urea
5 nitrogen, serum creatinine, measured and calculated creatinine clearances, and urinary NAG and
6 RBP. Mean uric acid, tibia lead, and blood lead levels were 4.8 mg/dL (SD 1.2), 37.2 jig/g bone
7 mineral (SD 40.4), and 32.0 |ig/dL (SD 15.0), respectively. None of the lead measures (tibia,
8 blood, and DMSA-chelatable lead) were associated with uric acid, after adjustment for age,
9 gender, body mass index, and alcohol use. However, when effect modification by age on these
10 relations was examined, both blood and tibia lead were significantly associated in participants in
11 the oldest age tertile ((3 = 0.0111 [95% CI: 0.003, 0.019] and (3 = 0.0036 [95% CI: 0.0001,
12 0.007]) for blood and tibia lead, respectively). These models were further adjusted for blood
13 pressure and renal function. Hypertension and renal dysfunction are known to increase uric acid.
14 However, they are also risks associated with lead exposure. Therefore, adjustment for these
15 variables in models of associations between lead dose and uric acid likely results in overcontrol.
16 On the other hand, since non-lead-related factors contribute to both renal dysfunction and
17 elevated blood pressure, lack of adjustment likely results in residual confounding. Therefore, as
18 expected, associations between lead dose and uric acid decreased after adjustment for systolic
19 blood pressure and serum creatinine, although blood lead remained borderline significantly
20 associated ((3 = 0.0071 [95% CI: -0.001, 0.015]). However, when the population was restricted
21 to the oldest tertile of workers with serum creatinine greater than the median (0.86 mg/dL), likely
22 the highest risk segment of the population, blood lead remained significantly associated with uric
23 acid even after adjustment for systolic blood pressure and serum creatinine ((3 = 0.0156).
24 Next, in models of renal function in all workers, uric acid was significantly associated with all
25 renal outcomes except NAG. Finally, in the oldest tertile of workers, after adjustment for uric
26 acid, associations between lead dose and NAG were unchanged, but fewer of the previously
27 significant (p < 0.05) associations noted between lead dose and the clinical renal outcomes in
28 Weaver et al. (2003a) remained significant.
29 Data from the Normative Aging Study indicate that lead dose, at levels lower than those
30 known to increase the risk for gout or in the study of Weaver et al. (2005a), is associated with
31 increased uric acid (Shadick et al., 2000). Mean blood, patella, and tibia lead levels were
May 2006 6-120 DRAFT-DO NOT QUOTE OR CITE
-------
1 5.9 |ig/dL, 30.2 |ig/g bone mineral, and 20.8 |ig/g bone mineral, respectively, in 777 participants.
2 A significant association between patella lead and uric acid ((3 = 0.007 [[95% CI: 0.001, 0.013];
3 p = 0.02) was found, after adjustment for age, BMI, diastolic blood pressure, alcohol ingestion,
4 and serum creatinine. Borderline significant associations between tibia (p = 0.06) and blood lead
5 (p = 0.1) and uric acid were also observed. Notably these associations were significant even
6 after adjustment for blood pressure and renal function, providing further evidence that low-level
7 lead increases uric acid.
8 These data suggest that older workers comprise a susceptible population for increased uric
9 acid due to occupational lead exposure. Uric acid may be one mechanism for lead-related
10 nephrotoxicity. However, this is not the only mechanism, since in Weaver et al. (2005a), the
11 association between blood lead and serum creatinine remained significant even after adjustment
12 for uric acid. These mechanistic relations have more than just theoretical importance. Clinically
13 relevant therapies may be possible since EDTA chelation has been reported to improve both
14 renal function and urate clearance in patients with renal insufficiency and gout, even when
15 EDTA-chelatable lead body burdens were low (Lin et al., 2001b).
16
17 6.4.7 Susceptible Populations for Lead Nephrotoxicity
18 6.4.7.1 Chronic Medical Diseases
19 The general population studies by Tsaih et al. (2004) and Muntner et al. (2003) (discussed
20 in section 6.4.4.1 General Population Studies above) indicate that patient populations with
21 diabetes and hypertension are at increased risk for adverse renal effects of lead. Lin et al.
22 (200la, 2002) indicate that patients with CRI and gout are also at increased risk. In these
23 settings, lead appears to acts as a cofactor with other renal risk factors to cause early onset of
24 renal insufficiency and/or a steeper rate of renal function decline. It is likely that the presence of
25 larger high risk populations within general populations is an important factor in the lower lead
26 dose thresholds noted for the adverse effects of lead on the kidney in environmental compared to
27 occupational research.
28
29 6.4.7.2 Age
30 Weaver et al. (2003a, 2005a,b) found older age to be a risk factor for adverse renal effects
31 in Korean lead workers. This is consistent with research in general populations (Lindeman et al.,
May 2006 6-121 DRAFT-DO NOT QUOTE OR CITE
-------
1 1985) and is biologically plausible, since most renal risk factors increase with age. Gonick and
2 Behari (2002) have summarized the data regarding the potential contribution of lead exposure to
3 essential hypertension; similar issues may be involved with the renal dysfunction observed in
4 aging.
5
6 6.4.7.3 Genetic Polymorphisms
7 S-Aminolevutinic Acid Dehydratase (ALAD)
8 Research in the last two decades suggests that several genetic polymorphisms affect lead
9 toxicokinetics (i.e., modify the relation between lead exposure and dose). Of those that are
10 potentially relevant to the kidney, data on the gene that encodes for 8-aminolevulinic acid
11 dehydratase (ALAD) are the most important in this regard. The ALAD enzyme is a principal
12 lead binding protein; the isozymes in those with the ALAD2 allele are more electronegative and
13 bind a greater proportion of blood lead than does the protein in individuals with the ALAD 11
14 genotype (Bergdahl et al., 1997). Research to date indicates that individuals with the ALAD2
15 allele generally have higher blood lead levels than those with the ALAD 11 genotype, although
16 this may not be the case at lower levels of lead exposure (i.e., mean blood lead levels <10 |ig/dL)
17 (Kelada et al., 2001). Participants with the ALAD2 allele have been found to have lower bone
18 lead levels in some studies (Hu et al., 2001; Kamel et al., 2003); other toxicokinetic differences
19 have also been reported (Fleming et al., 1998; Hu et al., 2001; Schwartz et al., 1997; Smith et al.,
20 1995). Overall, these data suggest that tighter binding of lead by the isozymes of the ALAD2
21 allele decreases lead sequestration in bone.
22 In contrast, data to determine whether the ALAD polymorphism impacts the renal toxicity
23 of lead are still quite limited. The only environmentally exposed population in which this has
24 been addressed is the Normative Aging Study. Wu et al. (2003a) (discussed in detail in section
25 6.4.4.1.2 above) analyzed data to determine whether the ALAD genetic polymorphism modified
26 associations between lead dose and uric acid, serum creatinine, and estimated creatinine
27 clearance, 114 (16%) of the study group were either homozygous or heterozygous for the variant
28 ALAD2 allele. None of the three outcomes were significantly different by genotype. However,
29 effect modification by genotype on the association between tibia lead and serum creatinine was
30 observed; the P coefficient (and slope) was greater in the group with the variant allele ((3 = 0.002
31 [SE not provided]; p = 0.03). Effect modification of borderline significance (p < 0.1) on
May 2006 6-122 DRAFT-DO NOT QUOTE OR CITE
-------
1 relations between of patella and tibia lead with uric acid was observed; this was significant in
2 participants whose patella lead levels were above 15 jig/g bone mineral ((3 = 0.016 [SE not
3 provided]; p = 0.04). Similar to the serum creatinine model, patella lead was associated with
4 higher uric acid in those with the variant allele. Genotype did not modify lead associations in
5 models of estimated creatinine clearance.
6 The impact of the ALAD polymorphism on renal outcomes has been studied in four
7 occupationally-exposed populations to date. The two that assessed both associations and effect
8 modification by genotype are discussed here. Weaver et al. (2003b) analyzed data from 798 lead
9 workers. Lead and renal function measures, as well as mean lead levels, were described in
10 Weaver et al. (2003a) in Section 6.4.4.2 above. A total of 79 (9.9%) participants were
11 heterozygous for the ALAD2 allele (none was homozygous). After adjustment, participants with
12 the ALAD2 allele had lower mean serum creatinine and higher calculated creatinine clearance.
13 Effect modification by ALAD on associations between blood lead and/or DMSA-chelatable lead
14 and three of six renal outcomes was observed. Among those with the ALAD12 genotype, higher
15 lead measures were associated with lower BUN and serum creatinine and higher calculated
16 creatinine clearance. Among older workers (age > median of 40.6 years), ALAD genotype
17 modified associations between lead dose and uric acid levels. Higher lead dose was significantly
18 associated with higher uric acid in workers with the ALAD 11 genotype; associations were in the
19 opposite direction in participants with the variant ALAD12 genotype (Weaver et al., 2005c).
20 Ye and colleagues (2003) assessed effect modification by ALAD on associations between
21 blood lead with urinary NAG and albumin in a study of 216 lead workers. Geometric mean
22 blood lead was 37.8 |ig/dL in 14 workers with the ALAD12 genotype and 32.4 |ig/dL in workers
23 with the ALAD 11 genotype. After adjustment for age, NAG was borderline statistically higher
24 in those with the variant allele whose blood lead levels were >40 |ig/dL. In all lead workers,
25 after adjustment for age, gender, smoking, and alcohol ingestion, a statistically significant
26 positive association between blood lead and creatinine adjusted NAG was observed in the
27 workers with the ALAD 12 genotype but not in lead workers with the ALAD 11 genotype (the
28 groups were analyzed separately rather than in an interaction model).
29 Thus, two of the three studies reported steeper slopes for one or more associations
30 between lead dose and adverse renal function in participants with the ALAD2 allele compared to
31 those with the ALAD11 genotype which suggests that the variant ALAD gene confers additional
May 2006 6-123 DRAFT-DO NOT QUOTE OR CITE
-------
1 risk for adverse renal outcomes in lead exposed populations. If the associations of Weaver et al.,
2 (2003b) represent lead-induced hyperfiltration their results could be consistent with increased
3 risk from the variant allele as well. Ultimately, analysis of longitudinal data in the Korean lead
4 worker population will be required to understand these complex relations.
5
6 6.4.8 Confounding of the Renal Effects of Lead by Other Potential
7 Risk Factors
8 Studies selected for discussion in Section 6.4 above have generally controlled for at least
9 the most basic risk factors known to affect renal function such as age, gender, and body mass
10 index (or weight and height separately). Some have controlled for many other potentially
11 important risk factors. In addition, exposure to other nephrotoxicants must be considered.
12 Notably, although these are listed under confounders, some may be effect modifiers as well.
13
14 6.4.8.1 Cadmium
15 Similar to lead, cadmium is an ubiquitous nephrotoxi cant that accumulates in the body.
16 Environmental exposure in the United States occurs primarily through food and smoking
17 (Agency for Toxic Substances and Disease Registry, 1993). Cadmium in food is a result of soil
18 pollution from a variety of human activities such as phosphate fertilizer use, industrial releases
19 from smelting, and fuel combustion. An analysis of NHANES III data, collected in a
20 representative sample of the U.S. population from 1988-1994, indicates that mean urinary
21 cadmium is 0.48 |ig/g creatinine and 97.7% of the population has a level <2.0 |ig/g creatinine
22 (Paschal et al., 2000). Also similar to lead, cadmium causes proximal tubule pathology and is a
23 risk factor for CRT
24 The existing data indicate that cadmium, at exposure levels common in the U.S.,
25 confounds associations between lead exposure and at least one renal outcome, NAG. Roels et al.
26 (1994) reported higher mean NAG in their lead-exposed group; however, NAG was correlated
27 with urinary cadmium but not blood or tibia lead, despite the fact that mean urinary cadmium
28 was only 1.04 and 0.53 |ig/g creatinine in workers and controls, respectively. Cardenas et al.
29 (1993) reported a similar finding. Bernard et al. (1995a) found an association between urinary
30 cadmium and the NAG-B isoenzyme (released with breakdown of proximal tubular cells) in
31 49 cadmium workers and 20 age-matched controls. In multiple linear regression, urinary
May 2006 6-124 DRAFT-DO NOT QUOTE OR CITE
-------
1 cadmium, but not lead, was associated with NAG-B, after adjustment for age. The association
2 was significant even in the 44 participants with levels <2 |ig/g creatinine. However, NAG-A
3 (released by exocytosis) was correlated with urinary lead (the only lead measure), but not
4 cadmium. Roels et al. (1995) reviewed data pertinent to the potential for cadmium confounding
5 of associations between lead and NAG. In more recent work, Weaver et al. (2003a) measured
6 urinary cadmium in a subset of 191 of the 803 workers in their study (mean urinary cadmium
7 was 1.1 |ig/g creatinine). Higher urinary cadmium levels were associated with higher NAG.
8 Of the lead measures obtained, only tibia lead was significantly associated with NAG in the
9 cadmium subset. When urinary cadmium and tibia lead were entered as covariates in the same
10 model, both remained associated with NAG (p < 0.05). However, in comparing the effects,
11 a 0.5 |ig/g creatinine increase in cadmium had the same effect on NAG as a 66.9 jig/g bone
12 mineral increase in tibia lead. When compared by ranges of exposure in this population,
13 environmental level cadmium dose had a larger impact on NAG than did occupational lead dose.
14 Cadmium exposure may confound relations between lead exposure and other renal
15 outcomes as well, although the data are too limited to draw firm conclusions. Positive
16 associations between urinary cadmium, which is thought to be the best measure of cumulative
17 cadmium exposure in the absence of cadmium-related renal damage, and low molecular weight
18 (LMW) proteinuria are well established in the occupational setting. LMW proteinuria, most
19 commonly assessed by (32-microglobulin, is generally progressive at levels >1,500 |ig/g
20 creatinine in workers with substantial body burdens (one or more historical urinary cadmium
21 >20 |ig/g creatinine) but may also be progressive at lower levels (Roels et al., 1997; Bernard,
22 2004). More importantly, clinical renal function also declines as evidenced by decreasing GFR
23 in cadmium exposed workers followed longitudinally after removal from exposure due to LMW
24 proteinuria (Roels et al., 1989; 1997).
25 In contrast to the clear evidence that cadmium is a renal toxicant at occupational levels of
26 exposure, the renal risk from lower level cadmium exposure remains uncertain. Most studies of
27 environmental cadmium exposure are cross-sectional and have assessed EBE markers, rather
28 than clinical renal outcomes (Alfven et al., 2002; Jarup et al., 2000; Noonan et al., 2002; Olsson
29 et al., 2002). The Cadmibel study, a general population study of exposed residents from both
30 cadmium polluted and unpolluted areas (discussed in Section 6.4.4.1.1 above), found correlations
May 2006 6-125 DRAFT-DO NOT QUOTE OR CITE
-------
1 between urinary cadmium and several urinary EBE markers (NAG, RBP, p2-microglobulin,
2 calcium, and amino acids) (Buchet et al., 1990). In those models, after adjustment for urinary
3 cadmium and other covariates, blood lead was significant in models of (32-microglobulin and
4 amino acids but not NAG. However, in this same population, blood lead was inversely
5 associated with creatinine clearance, whereas urinary and blood cadmium were not (Staessen
6 et al., 1992). A 5 year follow-up was conducted to determine the significance of the EBE
7 abnormalities (Hotz et al., 1999). In this study, models of renal function (two dichotomized
8 outcomes: a 20% decline in creatinine clearance and a 20% increase in albumin excretion) in
9 relation to quartiles of urinary cadmium and the EBE markers at baseline were analyzed by
10 likelihood ratios. Baseline variables did not predict adverse renal outcomes. However, 25% of
11 the original population was lost to follow-up; available data indicated that their baseline renal
12 function was worse than those who participated in the follow-up study. This may have biased
13 the study towards the null.
14 Three recent publications suggest that low-level cadmium exposure is associated with
15 adverse clinical renal outcomes. Elevated urine cadmium levels were associated with prevalent
16 microalbuminuria and decreased calculated creatinine clearance after adjustment for age, sex,
17 race, smoking, and use of diuretics in an analysis of 16,094 participants in the NHANES III
18 study (Young et al., 2004). Hellstrom et al. (2001) reported increased rates of renal dialysis
19 and transplantation in residents of cadmium-polluted areas in Sweden. Compared to the
20 "no-exposure group" (domicile >10 km from a battery plant), age-standardized rate ratios were
21 1.4 (95% CI: 0.8, 2.0) in the low-exposure group (domicile 2 to 10 km) and 1.9 (95% CI: 1.3,
22 2.5) in the moderate-exposure group (domicile <2 km). Exposure categorization was based on
23 environmental monitoring in the study areas. Cadmium dose was not directly measured although
24 occupationally exposed participants were considered in a separate group. The third study,
25 (Akesson et al., 2005), also assessed lead exposure as a covariate, an important approach given
26 the Cadmibel results (Staessen et al., 1992). Blood and urinary cadmium were associated with
27 worse GFR and creatinine clearance. The association for blood cadmium and decreased
28 creatinine clearance remained statistically significant even in non-smokers, suggesting a public
29 health remedy, in addition to smoking cessation, may be of value.
30 In conclusion, cadmium clearly confounds associations between lead dose and NAG.
31 Given the similarities in both nephrotoxicants, cadmium may confound and/or modify
May 2006 6-126 DRAFT-DO NOT QUOTE OR CITE
-------
1 associations between lead and other renal outcomes. However, data regarding the concentration-
2 response relationship between environmental cadmium and the kidney are too limited to assess
3 the potential for this at present. Future studies assessing both lead and cadmium are needed.
4
5 6.4.9 Summary of the Epidemiologic Evidence for the Renal Effects of Lead
6 During the past two decades, the quality of research on the renal impact of lead exposure
7 has advanced dramatically. As a result, a much more accurate assessment of the adverse renal
8 impact of lead exposure can now be made. General population studies are the most important
9 advance in this regard. As discussed in Section 6.4.4.1.5, the studies in this category, overall,
10 have numerous strengths ranging from large study size to statistical approaches that utilize a
11 range of exposure and outcome measures, while adjusting for numerous renal risk factors.
12 Studies involving the longitudinal assessment of renal function decline in susceptible patient
13 populations in relation to baseline chelatable lead body burden and therapeutic chelation
14 constitute the other major advance in lead-renal research in the last two decades. These studies
15 also have a number of strengths but this line of research is still relatively new and far fewer
16 participants have been studied at lower lead dose levels. However, the fact that these studies,
17 despite different research approaches, reached similar conclusions to those in the general
18 population literature provides important confirmation.
19 In contrast, research in the occupational setting is far less consistent and, overall, fewer
20 epidemiologic strengths are present in this literature. However, a notable finding from several of
21 these studies is the observation of inverse associations (higher lead dose with lower BUN, serum
22 creatinine, and/or higher creatinine clearance). This may indicate lead-related hyperfiltration and
23 have mechanistic implications. Regardless, significant associations could be obscured if
24 opposite direction associations are present in different segments of the study population and
25 interaction models to address this are not performed. This is a valid concern, since the settings in
26 which these inverse associations are most likely are not well defined. Finally, there are a number
27 of other areas for which the data are too limited. These include the renal effects of blood lead
28 levels <10 |ig/dL in children, genetic susceptibility, co-exposures to cadmium, and mechanisms
29 for the adverse renal effects of lead in humans.
May 2006 6-127 DRAFT-DO NOT QUOTE OR CITE
-------
1 In summary:
2 • Studies published since the 1986 Criteria Document provide strong evidence that renal
3 effects occur at much lower blood lead levels than previously recognized.
4
5 • Risk assessment for this target organ can no longer focus solely on lead nephropathy.
6 Lead-related nephrotoxicity from lead as co-factor in susceptible populations, such as
7 those with diabetes, hypertension, and chronic renal insufficiency from non-lead related
8 causes, is much more common.
9
10 • The majority of studies in general and patient populations published in the last two
11 decades have observed associations between lead dose and worse renal function. Other
12 explanations, such as residual confounding or reverse causality, are less likely (discussed
13 above in Section 6.4.4.1.5.2).
14
15 • The threshold for lead-related nephrotoxicity cannot be determined based on current data.
16 Increased odds ratios for clinically relevant renal outcomes were observed in a population
17 that is representative of hypertensives in the U.S. civilian, non-institutionalized
18 population in the quartile with a blood lead range from 2.5 to 3.8 |ig/dL (Muntner et al.,
19 2003). Associations between blood lead as a continuous variable and worse clinical renal
20 function have been reported in women at a mean of 2.2 |ig/dL (Akesson et al. 2005).
21 Mean blood (4.2 |ig/dL) and EDTA chelatable lead levels (99.1 |ig/72 hr) were
22 associated with decline in glomerular filtration rate over a 4-year follow-up period in
23 patients with chronic renal insufficiency (Yu et al., 2004).
24
25 o Adjustment for blood pressure and, in longitudinal studies, baseline serum
26 creatinine, may result in an underestimate of renal risk from lead exposure.
27 Lead-induced hyperfiltration may have the same effect.
28
29 o The cumulative effect of higher blood lead levels from past exposure may be a
30 factor in nephrotoxicity observed at current blood lead levels. However, Kim
31 et al. (1996) noted associations between blood lead and concurrent serum
32 creatinine in participants whose peak blood lead levels were < 10 |ig/dL between
33 1979 and 1994.
34
35 • The magnitude of the effect of lead on renal function ranged from 0.2 to -1.8 mL/min
36 change in creatinine clearance per |ig/dL increase in blood lead in general population
37 studies. The size of the effect was relatively consistent across the studies although only
38 five provided data useful for this determination (three were at different time points in the
39 Normative Aging Study population) and a form of publication bias may be present in
40 studies that provided no data and reported only that associations were not significant.
41 Yu et al. (2004) reported a similar effect of blood lead longitudinally on yearly decline in
42 glomerular filtration rate.
43
44 • This effect is clinically relevant in U.S. subpopulations who continue to have higher lead
45 exposure than the general population. At levels of exposure in the general U.S.
46 population overall, lead combined with other risk factor, such as diabetes, hypertension,
May 2006 6-128 DRAFT-DO NOT QUOTE OR CITE
-------
1 or chronic renal insufficiency from non-lead related causes, will result in clinically
2 relevant effects in individuals with two or more risk factors. Notably, the size of such
3 susceptible populations is increasing in the U.S. due to obesity.
4
5
6 6.5 CARDIOVASCULAR EFFECTS OF LEAD
7 6.5.1 Summary of Key Findings of the Cardiovascular Effects of Lead from
8 the 1985 Lead AQCD and Addendum, and 1990 Supplement
9 The greater part of the evidence reviewed up to 1990 included analyses of the largest
10 datasets available at the time, the National Health and Nutrition Evaluation Survey II (NHANES
11 II), studying the U.S. population between 1976 and 1980, and the British Regional Heart Study
12 (BRHS), studying men aged 40-59 years from 24 British towns. Analyses of the Welsh Heart
13 Programme, a regional Welsh study, and the Caerphilly Collaborative Heart Disease Study, a
14 cohort study of men aged 45-59 years living in one town in Wales, as well as smaller population
15 and occupational exposure studies in the U.S., Canada, and Europe provided supporting
16 evidence. These studies set enduring design and analysis standards by example for evaluating
17 cardiovascular effects associated with blood lead levels in samples from diverse populations.
18 In general, the reviewed studies used multiple linear regression modeling of blood
19 pressure and multiple logistic regression modeling of hypertension, cardiovascular mortality, and
20 other cardiovascular disease, allowing adjustment of the blood lead effect on outcome by other
21 factors known or suspected to be related to the exposure and outcome under study. The most
22 commonly considered potential confounding factors were age, body mass index (BMI), alcohol
23 use, and cigarette smoking.
24 These studies were almost exclusively cross-sectional, measuring cardiovascular outcome,
25 blood lead, and control variables once, though one Canadian occupational study and one Danish
26 birth-year cohort study used a longitudinal design. Studies sometimes presented analyses
27 stratified by sex or age, by both sex and age, or by race. Other analyses only reported results for
28 one particular stratum. Separate analyses of datasets partitioned by stratified variables always
29 reduce sample size available for statistical models, and, thereby, may reduce power to detect real
30 effects.
31 Evaluated as a whole, the blood pressure studies supported a small but significant
32 association between increasing blood lead concentrations and increasing blood pressure in study
May 2006 6-129 DRAFT-DO NOT QUOTE OR CITE
-------
1 groups. The effect was more consistent across studies in middle-aged men than in other groups,
2 ranging from a 1.5 to 3.0 mm Hg increase in systolic blood pressure for each doubling of blood
3 lead from the mean blood lead level, and from a 1.0 to 2.0 mm Hg increase in diastolic blood
4 pressure for each blood lead doubling, across a wide range of blood lead concentration down to
5 7 |ig/dL. Most studies using multiple regression analyses stratified by sex were unable to find
6 significant associations between blood pressure and blood lead in females, though one reanalysis
7 of the NHANES II dataset did report a statistically significant relationship between diastolic
8 blood pressure and lead in women aged 20 to 74 years. In studies reporting the use of different
9 blood lead-blood pressure concentration-response relationships, log blood lead terms had lower
10 probability values than linear blood lead terms, suggesting that increases in blood pressure with
11 fixed increases in blood lead might be greater at lower blood lead concentrations than at higher
12 concentrations.
13 Three studies of groups with occupational exposure reported mixed results. One study
14 found significant excess mortality due to cardiovascular disease during the period 1946-1965 in a
15 case-control study in the United Kingdom, but not 1966-1985. A study of U.S. battery and lead
16 production workers from 1947-1980 found significant excess mortality due to "other
17 hypertensive disease" (codes 444-447 in the ICD 1955 classification system), but not due to
18 hypertensive diseases outside those classifications. No excess mortality due to hypertension was
19 found in a study of U.S. smelter workers between 1940 and 1965.
20 The BRHS study failed to reveal significant associations between blood lead and ischemic
21 heart disease and stroke, though low power to detect such an effect should be noted. However,
22 electrocardiogram abnormalities associated with left ventricular hypertrophy were found related
23 to blood lead in a subset of the NHANES II data, confirming an earlier study finding significant
24 associations between ischemic changes and blood lead in lead workers.
25 Noninvasive measurement of bone lead concentration using XRF techniques was still
26 maturing during the literature review period covered by the 1986 AQCD document and later
27 addendum and supplement. No cardiovascular studies were reported using bone lead as a marker
28 for lead exposure.
29
May 2006 6-130 DRAFT-DO NOT QUOTE OR CITE
-------
1 Summary of Cardiovascular Findings: 1986 Lead AQCD/Addendum and 1990 Supplement
2 • Multiple regression modeling of the relationship between blood lead and cardiovascular
3 outcome was widely used.
4 • Most studies found a small positive relationship between blood lead and blood pressure.
5 • The few studies reporting blood lead and cardiovascular mortality/morbidity also found
6 small positive associations.
7 • It was concluded that there was a small but real relationship between blood-lead level and
8 adverse cardiovascular outcome.
9 • The need for further research was noted with large samples, identification of susceptible
10 populations, more precise quantitative estimation of effect size, and better definition of
11 the dose-response relationship.
12
13 6.5.2 Effects of Lead on Blood Pressure and Hypertension
14 6.5.2.1 Introduction
15 Blood lead concentration remained the most widely used exposure index in blood
16 pressure/hypertension epidemiologic studies from 1990 to present. Epidemiologic studies of the
17 cardiovascular effects of lead reviewed in this section are further summarized in Annex Table
18 6-5.1. Obtaining the sample is relatively noninvasive and quick, measurement techniques are
19 well standardized and inexpensive, there is wide access to external quality assurance programs,
20 and existing regulation and medical decision-making are based on blood lead levels. If
21 exogenous lead exposure were the only determinant for blood lead concentration, it could be fair
22 to state that a single blood lead measurement represented exposure to lead during the 30-90 day
23 period preceding the measurement. However, blood lead concentration represents a combination
24 of recent exposure to external sources and the influence of internal sources, principally bone
25 lead. As detailed in Chapter 4, bone is a long-term storage depot for much of the lead absorbed
26 by the body from external sources, and by weight can represent over 95% of the total body
27 burden of lead in middle-aged persons, especially where current external exposures are low.
28 Bone lead has residence times of years to decades. Bones constantly absorb lead from and
29 release lead to the circulatory system. Consequently, blood lead concentration is not only
30 determined by current and recent past external exposure but is also influenced by existing bone
31 lead concentration to a degree determined by current external exposure, accumulated past
32 exposure stored in bones, and the physiological state of the bones due to aging, disease,
May 2006 6-131 DRAFT-DO NOT QUOTE OR CITE
-------
1 pregnancy, and lactation, among others. Studies using only blood lead concentration, as an
2 exposure index cannot determine the relative contributions of current exogenous exposure and
3 endogenous exposure to blood lead. Thus, they are unable to assess what part of measured blood
4 lead effect on the circulatory system is due to possibly higher long duration past exposure and
5 what part is due to the possibly immediate toxic effects of currently circulating lead. They are,
6 instead, assessing a combined effect of past and present exposure in a proportion that will differ
7 among subjects according to their past and present exposure, health history, and age.
8 The recently developed in vivo technique of XRF measurement of bone lead
9 concentration has been used in a handful of studies to better assess the role of past exposure to
10 lead on blood pressure and hypertension in essentially cross-sectional studies. Bone lead
11 concentration provides a record of cumulative past exposure due to the long residence times of
12 lead in bones, though the specific temporal pattern of past exposure cannot be readily determined
13 from the measurement. Primarily cortical bones such as tibia have residence times measured in
14 decades, whereas primarily trabecular bones such as calcaneus and patella have residence times
15 measured in years to decades, reflecting different metabolic rates of the two bone types. As there
16 is continual interchange of lead in bone and lead in blood, studies combining the measurement
17 and modeling of both bone lead and blood lead have the best chance of dissecting out the roles of
18 past and present lead exposure on blood pressure and hypertension.
19 Elevated blood pressure can be evaluated as a continuous measure (mm Hg) or as a
20 dichotomized measure (hypertension). The definition of hypertension involves a categorical cut
21 point of mm Hg above which one is hypertensive and below normotensive. Kannel (2000a,b)
22 notes that this number has dropped over time for systolic/diastolic pressure and further notes a
23 continuous graded influence of blood pressure on health even within what is regarded as the
24 normotensive range. The hypertension definition is to some extent arbitrary as the cut point has
25 changed over time. However defined for any given study, regardless of medical definition for
26 the year of the study, hypertension classification offers a different perspective than blood
27 pressure per se. Hypertension has a different clinical relevance than blood pressure changes
28 themselves. The disease condition as an outcome and a change in mm Hg in relation to exposure
29 both offer the opportunity for insight into the clinical relevance of the relationships. Biomarkers
30 like bone lead and blood lead also help to distinguish acute and chronic exposure effects.
May 2006 6-132 DRAFT-DO NOT QUOTE OR CITE
-------
1 Blood pressure is an inherently variable measure. Even when measured with indwelling
2 catheters, blood pressure varies on a minute to minute interval in the same individual. Extrinsic
3 sources of blood pressure variability include measurement technique, the tester, and the
4 conditions under which the measurements are taken. All the sources of measurement error are
5 additive, but the expected total error will be symmetrically distributed about some true blood
6 pressure, i.e., unbiased. Under conditions where the size of the expected lead effect is in the
7 same range as the total measurement error, large studies with high power are required for
8 detecting real effects where they exist. These factors favor studies with large numbers of
9 subjects. Using blood lead as a surrogate for brain lead biases the blood lead regression
10 coefficient towards zero. This is an example of classical measurement error. Smaller blood
11 pressure studies may fail to detect lead effects simply because of low power. As noted in the
12 1985 document with supplement and addendum, stratification of data sets always reduces power.
13 The growing field of toxicogenetics now includes lead exposure epidemiology. The
14 several studies combining subject evaluation of polymorphisms of genes thought to play a role in
15 either the origin of cardiovascular disease, the toxicokinetics of lead or both are also reviewed.
16
17 6.5.2.2 Blood Pressure and Hypertension Studies Using Blood Lead as Exposure Index
18 Table 6-5.1 lists studies showing estimates of the relationship between systolic blood
19 pressure and blood lead level. The table focuses on the key studies with low blood lead in the
20 United States to include studies of the general population; the Boston NAS; and the international
21 Nawrot meta-analysis. Studies were included if the population was not all occupationally
22 exposed or limited to women during pregnancy, or children. Effects were included only if they
23 were based on the entire studey group or secondly, the subgroup had more than 500 people.
24 Other studies are discussed in the text and presented in Annex Table 6AX-5-1.
25 NHANES Studies
26 NHANES contributed the largest datasets analyzed in this review. As the surveys are also
27 representative of the U.S. population, their results may be more readily applied to the general
28 U.S. population than smaller cohort or occupational studies. The several papers using this
29 dataset sometimes come to different conclusions, depending on the statistical techniques used in
30 analysis, including logarithmic or linear specification of the lead variable, stratification of
May 2006 6-133 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-5.1. Summary of Studies with Quantitative Relationships of
Systolic Blood Pressure and Blood Lead
Reference
Vupputuri et al.
(2003)
Den Hond et al.
(2002)
Nash etal. (2003)
Soreletal. (1991)
Cheng etal. (2001)
Proctor etal. (1996)
Nawrot et al. (2002)
Study Location and gender
NHANES III*
White Males
NHANES III
White females
NHANES III
Black Males
NHANES III
Black females
NHANES III 1988-94
White males
NHANES III 1988-94
White females
NHANES III 1988-94
Black males
NHANES III 1988-94
Black females
NHANES II
Females
NHANES II
Males
NHANES II
Females
Boston normative aging
Males (about 97% white)
US Boston Normative aging
study Males
3 1 US and European Studies
(includes occupationally
exposed)
n
5,360
5,188
2,104
2,300
4,685
5,138
1,761
2,197
1786
2,044
2,056
519
798
>58,490
Blood lead
arithmetic mean
and (25 and 75th
percentiles)
4.4 (1.0,4.9)
3.0 (0.5,2.9)
5.4 (1.2,6.0)
3.4 (1.0,4.0)
3.6 (2.3,5.3)
2.1 (1.3,3.4)
4.2 (2.7,6.5)
2.3 (1.4,3.9)
2.9 range 0.5-31.1
Black: 20.1
White: 16.8
Black: 13.2
White: 12.1
5.9 (3.4,7.4)
6.5(3.8,8.1)
Meta-analysis
Estimated Slope and
(95% CI) mmHg per
change in blood lead
from 5 to 10 ng/dL
0.43 (-0.36,1.26)
0.52 (-0.74,1.77)
1.24(0.29,2.18)
2.35 (0.71,4.00)
0.3 (-0.2,0.7)
0.1 (-0.4,0.5)
0.9 (0.04,1.8)
1.2 (0.4,2.0)
1.60(0.05,3.15)
0.40 (-0.15,0.95)
0.20 (-1.40,1.00)
-0.16 (-1.67,1.35)
0.59 (-0.76,1.87)
1.0(0.5,1.4)
NHANES - United States population sample.
May 2006
6-134 DRAFT-DO NOT QUOTE OR CITE
-------
1 analyses according to sex or ethnic groups or use of interaction terms to define these groups,
2 use of survey-design corrected models, choice of covariates in the models, and different age
3 ranges analyzed.
4
5 NHANESII (1976-1980)
6 In one NHANES II-based study, males and females (number unreported but less than
7 9,000 combined) aged 20 to 74 years were studied with separate stepwise multiple regression
8 models adjusted for sampling design (Schwartz, 1991). Mean blood lead levels and ranges were
9 not reported. Covariates common to both male and female models were age and age2, BMI, race,
10 family history, cholesterol, zinc, tricep fold, and natural log lead. Models for men also included
11 height and cigarette smoking. Natural log blood lead was significantly associated with diastolic
12 blood pressure (systolic not reported) in males, with a 2.03 mm Hg diastolic (95% CI: 0.67,
13 3.39) increase for every doubling of blood lead, and for females a 1.14 mm Hg increase (95% CI:
14 0.13, 2.08). Interactions between blood lead and sex and between blood lead and race in a
15 combined model were insignificant (not shown). The conclusion from these interaction terms is
16 that the association between blood lead and diastolic blood pressure was not significantly
17 different between men and women or between races. Stepwise modeling may inflate statistical
18 Type I error.
19 The other NHANES II-based study focused on black-white differences in blood pressure
20 related to blood lead (Sorel et al., 1991). There were 473 blacks and 3,627 whites in the study,
21 each nearly evenly divided by sex, aged 18 to 74 years. Blood lead means and ranges were not
22 given. As is usual in U.S.-based studies, race/ethnicity was based on self-report. Survey design-
23 adjusted multiple regression models were stratified on sex and included age, BMI, and linear
24 blood lead as covariates. Effects of race and poverty index were assessed by including their
25 terms in models with and without blood lead and determining change in race or poverty
26 coefficients by comparing confidence intervals. Each 1 |ig/dL increase in linear blood lead
27 significantly predicted increased systolic blood pressure for both males (0.13 mm Hg/|ig/dL) and
28 females (0.08 mm Hg/jig/dL), but not diastolic blood pressure. The differences in black and
29 white (race variable) blood pressure coefficients did not significantly change when lead was in or
30 out of the model, either for subjects below the poverty index or above the poverty index. Race
31 did not appear to significantly modify the relationship between blood lead and systolic blood
May 2006 6-135 DRAFT-DO NOT QUOTE OR CITE
-------
1 pressure. There were reporting inconsistencies in the female-stratified models, in which the
2 coefficients and 95% CI did not correspond.
3
4 NHANES III (1988-1994)
5 A study using the NHANES III dataset from all adults 20 years of age and up examined
6 the effect of natural log blood lead on systolic and diastolic blood pressure (Den Hond et al.,
7 2002). Multiple regression analyses for each blood pressure measurement were stratified by sex
8 and race, yielding four models for each blood pressure measurement. The mean blood levels
9 were 3.6 |ig/dL in white males (n = 4,685), 2.1 |ig/dL in white females (n = 5,138), 4.2 |ig/dL in
10 black males (n = 1,761), and 2.3 |ig/dL in black females (n = 2,197). Overall blood lead range
11 was < 0.8 to > 20.0 |ig/dL. One group of covariates (age, age-squared, BMI, hematocrit,
12 smoking, alcohol consumption, and an indicator variable for use of antihypertensive
13 medications) were first entered as a block regardless of significance in each model, then another
14 group of variables (coffee consumption, dietary calcium, dietary sodium/potassium ratio, total
15 serum protein, total serum calcium, diabetes, and poverty index) was entered stepwise in the
16 model without lead and the variable retained only if it was statistically significant (p < 0.05).
17 Then log-transformed blood lead was forced into each model. The model building procedure
18 resulted in eight distinct models, each with their own unique mix of covariates. Adjustment of
19 results by survey sample weights and design was not reported. Only blacks had significant lead-
20 systolic blood pressure associations; each doubling in blood lead was associated with a 0.90 mm
21 Hg (95% CI: 0.04, 1.8) and 1.20 mm Hg (95% CI: 0.4, 2.0) increase in males and females
22 respectively. The association of lead-diastolic blood pressure was also significant for black
23 females (0.50 mm Hg [95% CI: 0.01, 1.1]). Interestingly, increasing blood lead was associated
24 with significantly decreased diastolic blood pressure in white males (-0.6 mm Hg [95% CI:
25 -0.9, -0.3]). The authors did not comment on their finding that the significant total serum
26 calcium covariate in these two groups had opposite signs too (white male serum calcium
27 P = 6.50 mm Hg/mmol/L, black female serum calcium P = -5.58 mm Hg/mmol/L). Though the
28 authors offered no formal test of the difference between the two serum calcium coefficients,
29 since both were significantly different than the null hypothesis coefficient of 0 and different in
30 sign, it could be concluded that those coefficients were significantly different between the two
31 groups. As the authors do not present the serum calcium coefficients before forcing lead into the
May 2006 6-136 DRAFT-DO NOT QUOTE OR CITE
-------
1 models, it is not certain that blood lead in the model was associated with the significant sign
2 difference of the calcium coefficients or if the calcium coefficients had opposite signs between
3 the two groups without lead in the model. As each model had a different set of covariates, the
4 presence or absence of one of the other covariates could have produced the same results.
5 Nevertheless, this pattern of results may indicate significant confounding between serum calcium
6 and blood lead associations with blood pressure. Though the study suggested differences
7 between blacks and whites in response to lead, no statistical tests were performed of differences
8 in lead coefficients based on race. In addition, the black-white effect differences associated with
9 blood lead may be due to possible confounding in some or all of the models.
10 Limiting the study sample from NHANES III to women aged 40 to 59 years, another
11 group of researchers addressed the relationship between blood lead and both blood pressure
12 (n = 1,786) and hypertension (n = 2,165) over a blood-lead range of 0.5 to 31.1 |ig/dL (mean
13 2.9 ji/dL) (Nash et al., 2003). Blood pressure models excluded women who reported being under
14 treatment for hypertension. Separate blood pressure multiple regression models were presented
15 for diastolic and systolic blood pressure, each with and without stratification for dichotomous
16 premenopausal/postmenopausal status. One block of covariates was entered without regard to
17 statistical significance (age, race/ethnicity, BMI, and serum creatinine). Another block of
18 covariates (education, poverty income ratio, alcohol use, and cigarette smoking status) was
19 entered second but only retained if variables were significantly associated with blood pressure.
20 Finally, linear blood lead was forced in last. Logistic regression models for hypertension used
21 the same covariate entry scheme with and without stratification on the menopause variable, but
22 using a blood lead quartile exposure variable. Despite the stated procedure for covariate
23 selection, all models used the same set of covariates: linear (or quartile) lead, age, race/ethnicity,
24 alcohol use, cigarette smoking status, BMI, and serum creatinine. All models were adjusted for
25 survey weights and design. Linear lead was significantly associated with systolic blood pressure
26 only in the entire study sample; each 1 |ig/dL increase in blood lead was associated with a 0.32
27 mm Hg (95% CI: 0.01, 0.63) increase in blood pressure. No associations were observed in the
28 menopause-stratified analyses. Linear lead also was significantly associated with diastolic blood
29 pressure in the entire study sample (0.25 mm Hg [95% CI: 0.07,0.43]). Odd ratios of diastolic
30 hypertension (>90 mm Hg) in logistic regression models was significantly related to blood lead
31 with an odds ratio of 4.26 (95% CI: 1.36, 12.99) comparing the 1st quartile blood lead group
May 2006 6-137 DRAFT-DO NOT QUOTE OR CITE
-------
1 (0.5-1.6 |ig/dL) to the 4th quartile blood lead group (4.0-31.1 |ig/dL) in all women not taking
2 antihypertensive medications. Further stratification produced occasional significant odds ratios
3 for either diastolic or systolic hypertension. There were some differences in table and text
4 reporting of results and an inconsistency between the SE and the p-values.
5 Another study using the NHANES III database was notable for its formal testing of race
6 and sex differences in lead effect by interactions terms (Vupputuri et al., 2003). The study used
7 5,360 white men (mean blood lead 4.4 |ig/dL), 2,104 black men (mean blood lead 5.4 jig/dL),
8 5,188 white women (mean blood lead 3.0 |ig/dL), and 2,300 black women (mean blood lead
9 3.4 |ig/dL). Blood ranges were not given. Multiple linear and logistic regression models of
10 blood pressure and hypertension (systolic > 140 mm Hg, diastolic >90 mm Hg, and/or taking
11 antihypertensive medication), respectively, were adjusted for age, high school education, BMI,
12 alcohol, leisure-time physical activity, and dietary intake of sodium, potassium, and total energy.
13 The models used linear lead, except for one set of hypertension models with a cut point for
14 "high" lead exposure at >5 |ig/dL. Subjects taking antihypertensive medication (n = 2,496) were
15 not included in linear regression models of blood pressure. Neither age nor blood lead range
16 were reported, nor was the technique of selecting and entering covariates in multiple regression
17 models. Only coefficients for linear lead effect for each model were reported. Significant
18 interactions in multivariate models were found between lead and race and between lead and sex,
19 though these analyses were not shown. Only black men and women had significant linear lead-
20 blood pressure effects in adjusted systolic (0.25 mm Hg [95% CI: 0.06, 0.44] for black men and
21 0.47 mm Hg [95% CI: 0.14, 0.80] for black women with each 1 |ig/dL increase in blood lead)
22 and diastolic blood pressure (0.19 mm Hg [95% CI: 0.02, 0.36] for black men and 0.32 mm Hg
23 [95% CI: 0.11, 0.54] for black women). Linear blood lead association with hypertension was
24 significant only in women. The odds ratios were 1.09 (95% CI: 1.04, 1.13) for white women
25 and 1.10 (95% CI: 1.06, 1.16) for black women for each 1 |ig/dL increase in blood lead. The
26 authors presented insufficient detail to evaluate this pattern of results.
27
28 Other U.S. Studies
29 U.S. Cohort Studies. The Boston-based Normative Aging Study, part of a longitudinal
30 study of male veterans, examined the effects of blood lead on blood pressure in 798 men, aged
31 45-93 years old, with blood lead between 0.5 and 35.0 |ig/dL (Proctor et al., 1996). Using
May 2006 6-138 DRAFT-DO NOT QUOTE OR CITE
-------
1 multiple regression modeling with forced entry of natural log lead and other covariates (age,
2 age2, BMI, dietary calcium, exercise, smoking, alcohol, heart rate, and hematocrit), the authors
3 found a significant increase of only diastolic blood pressure (0.83 mm Hg [95% CI: 0.08, 1.52])
4 for each doubling of blood lead. Though the relationship between blood lead and systolic blood
5 pressure was positive, it was not significant. Nearly half the blood lead measures were derived
6 from frozen red blood cells collected previously (up to several years earlier) and corrected for
7 hematocrit determined at the time blood pressure was measured. Possible errors in correction of
8 these samples and the non-contemporaneous nature of the resulting blood lead concentrations
9 may have compromised the results.
10 Cheng et al. (2001), using the same Normative Aging Study data and stepwise multiple
11 regression, found a near-zero association between systolic blood pressure and linear blood lead
12 (-0.03 mm Hg for each |ig/dL increase in blood lead) in 519 men aged 48 to 93. The subjects
13 selected for this analysis were all free of hypertension (systolic > 160 mm Hg or diastolic
14 > 95 mm Hg). Differences in subject selection procedures and modeling techniques may have
15 accounted for the different results between Cheng et al. and Proctor et al. They also reported on
16 incidence of hypertension developing between 1991 and 1997 using Cox proportional hazards
17 models. Controlling for age, age2, BMI, and family history of hypertension, linear blood lead
18 was not significantly associated with risk of developing hypertension (systolic > 140 mm Hg or
19 diastolic > 90 mm Hg) in subjects normotensive at the start of the period (rate ratio of 0.98 [95%
20 CI: 0.91, 1.06]) for each 1 |ig/dL increase in blood lead.
21 Gerr et al. (2002) similarly reported near-zero linear blood lead effects on blood pressure
22 on a combined group of 19-29 year old males and females (n = 502), half of whom had lived
23 around active lead smelters as children, using forced entry of all covariates. Mean blood lead
24 was 2.2 |ig/dL with a range from <1 to >7 |ig/dL. Among the covariates forced into the model
25 was tibia lead concentration, expected to be significantly correlated with blood lead. This may
26 have reduced or confounded the effects of blood lead.
27 Korrick et al. (1999) examined linear and natural log blood lead, mean 3 |ig.dL, range
28 <1 to 14 |ig/dL, effect on hypertension, defined as self-reported or physician diagnosis of
29 hypertension or systolic or diastolic > 140/90 mm Hg, in 284 middle-aged women from the
30 Nurse Health Study based in Boston. The association of hypertension and blood lead was not
31 significant. The study had low power (n = 284).
May 2006 6-139 DRAFT-DO NOT QUOTE OR CITE
-------
1 Rothenberg et al. (1999) tested a group of 1,527 women, aged 15 to 42 years, in their third
2 trimester of pregnancy, with blood lead ranging from 0.5 to 40.4 |ig/dL. They stratified testing
3 into immigrant (n = 1,188) and nonimmigrant (n = 439) groups. They used forced entry of all
4 covariates in multiple regression models, including natural log lead, age, BMI, coffee, iron
5 supplement, and job stress, and found lead-related significant increases in systolic (1.18 mm Hg
6 [95% CI: 0.45, 1.91] for each doubling of blood lead) and diastolic (1.02 mm Hg [95% CI:
7 0.37, 1.34]) blood pressure only in immigrants. The small size of the nonimmigrant group may
8 have reduced power to detect significant effects. In a follow-up of 668 women returning for
9 postpartum testing (Rothenberg, et al., 2002a), using multiple regression models with forced
10 entry of natural log blood lead, tibia and calcaneus lead, age, BMI, parity, smoking, immigrant
11 status, and education, the authors found significant decreases in systolic (-1.05 mm Hg [95% CI:
12 -1.96, -0.14]) and diastolic (-1.16 mm Hg [95% CI: -1.98, -0.35]) blood pressure associated
13 with doubling in blood lead in the postpartum women. This subgroup of women had no
14 significant blood lead effects in the third trimester. Although the covariate pattern was different
15 from the larger prenatal study (Rothenberg et al., 1999), thorough testing of possible
16 confounding, especially with the bone lead measures, revealed no significant change in blood
17 lead effects. This study finding is similar to that reported by Den Hond et al. (2002) for
18 white males. No significant effect of blood lead on prenatal or postpartum hypertension
19 (> 140/90 mm Hg) was found.
20 Morris et al. (1990) recruited a group of 105 women and 145 men, aged 18-80 years, from
21 a clinic specializing in nondrug hypertension treatment. Blood lead ranged from 5-40.5 |ig/dL.
22 Multiple regression was performed with forced entry of natural log lead, age, BMI, dietary
23 calcium, "other nutrients," serum ionized calcium, and erythrocyte protoporphyrin. Only men
24 were found to have lead-related significant increases in systolic (3.17 mm Hg [95% CI:
25 -2.13, 8.48] for each doubling of blood lead) and diastolic (1.32 mm Hg [95% CI: -2.12, 4.75])
26 blood pressure. Small study size limits conclusions based on nonsignificant findings in women.
27 Dietary calcium is associated with reduced blood lead in many studies and could be considered a
28 confounder with blood lead. Erythrocyte protoporphyrin is a biomarker of lead exposure and
29 correlates with blood lead over at least part of the blood range in study subjects. There were at
30 least two variables collinear with blood lead, a high proportion of covariates to subjects, and
31 possible subject selection bias.
May 2006 6-140 DRAFT-DO NOT QUOTE OR CITE
-------
1 European Studies
2 European Cohort Studies. The Glostrup Population Study (Copenhagen) studied 1,009
3 men and women (all born in 1936) longitudinally from 1976 to 1987 (M011er and Kristensen,
4 1992). Blood lead ranged from 2 to 62 |ig/dL, depending on the year and sex stratum studied,
5 with mean concentration dropping by -40% over the study period. They used multiple
6 regression with forced entry of natural log lead, BMI, tobacco use, and physical activity.
7 Strongest associations between a doubling of blood lead and blood pressure were found early in
8 the study period. In 1976, a doubling of blood lead was associated with 3.42 mm Hg (95% CI:
9 1.25, 5.58) increase in systolic blood pressure and 2.95 mm Hg (95% CI: 1.08, 4.83) increase in
10 diastolic blood pressure in women. For men in 1981, a doubling of blood lead was associated
11 with an increase of 1.89 mm Hg (95% CI: 0.00, 3.78) in systolic blood pressure and 1.14
12 mmHg(95%CI: -0.37, 2.65) in diastolic blood pressure. No formal longitudinal analyses were
13 performed, only analyses stratified by year and sex and analyses relating change in lead and
14 other covariates to change in blood pressure from one study period to the next. As the relative
15 risk of mortality was associated with increasing blood lead over the study period (see below), the
16 general reduction in lead-associated blood pressure increase over the study period may have been
17 related to lead-associated mortality.
18 The Europe New Risk Factor Project in Rome collected data from 1,319 males aged
19 55-75 years with blood lead between 4.0 and 44.2 |ig/dL (Menditto et al., 1994). They reported
20 significantly increased systolic (4.71 mm Hg [95% CI: 2.81, 6.61]) and diastolic (1.25 mm Hg
21 [95% CI: 0.33, 2.16]) blood pressure associated with a doubling of blood lead.
22 The Cadmibel studies from Belgium specifically selected part of their study group from
23 those living near nonferrous smelters. Staessen et al. (1993) reported on 827 men and
24 821 women, aged 20 to 88 years, with blood lead ranging from 2.7 to 84.9 |ig/dL for men and
25 1.3 to 42.4 |ig/dL for women. They forced natural log blood lead into stepwise multiple
26 regression models stratified by sex. Covariates available for selection were age, age2, BMI,
27 pulse rate, log gamma-glutamlytranspeptidase, serum total calcium, log serum creatinine, urinary
28 potassium, smoking, alcohol, contraceptive use, and menopause. Near-zero nonsignificant
29 relationships were found between blood lead and blood pressure for systolic blood pressure for
30 women and diastolic blood pressure for men and women. They reported a significant decrease in
31 men's systolic blood pressure with increasing blood lead (-1.1 mm Hg for a doubling of blood
May 2006 6-141 DRAFT-DO NOT QUOTE OR CITE
-------
1 lead), similar to the relationship found by Den Hond et al. (2002) for white men and by
2 Rothenberg et al. (2002a) for postpartum women. Stepwise regression results in different
3 covariate patterns for each stratum and capitalizes on chance significance due to multiple testing.
4 A follow-up of the Cadmibel study, the PheeCad study, evaluated 359 men and
5 369 women, aged 20 to 82 years (Staessen et al., 1996a). Fifty-nine percent of the men had
6 occupational exposure. They were measured twice, at baseline and at follow-up about 5 years
7 later. Women's mean blood lead at baseline and follow-up was 6.6 |ig/dL (range 3.3-24.50 and
8 4.8 |ig/dL (range 1.7-11.8). Men's mean blood lead at baseline and follow-up was 11.4 |ig/dL
9 (range 5.6-28.8) and 7.7 |ig/dL (range 3.7-20.1). Multiple regression models were stratified on
10 sex and in women on menopausal status. Time-integrated blood pressure measurements were
11 used. Each doubling of blood log lead was significantly associated with a 5.19 mm Hg (95% CI:
12 1.05, 9.34) increase in diastolic blood pressure in 187 pre- and perimenopausal women. None of
13 the other strata showed significant blood lead-related effects. Using 24-h ambulatory blood
14 pressure readings during the follow-up showed significant associations between natural log
15 blood lead and diastolic blood pressure in the group of all 345 women (2.42 mm Hg [95% CI:
16 0.00, 4.84]). There were no significant lead effects on systolic blood pressure in women or all
17 blood pressure in men. Change in blood pressure and change in covariates between baseline and
18 follow-up were used to assess the effect of change of blood lead in longitudinal analyses, similar
19 to M011er and Kristensen (1992) above. No significant effects of change in blood lead on change
20 in blood pressure were found. Due to stratification and resulting small groups, there may have
21 been reduced power to detect significant effects of lead.
22 The Health Survey for England 1995 examined a representative sample of the English
23 population living in private households and provided up to 2,563 men and 2,763 women with a
24 mean age of 47.6 years in a study of blood lead-blood pressure relationships (Bost et al., 1999).
25 Precise blood lead range was not given but was at least from less than 1.5 |ig/dL to greater than
26 8.5 |ig/dL with geometric means of 2.6 |ig/dL (females) and 3.7 |ig/dL (males). The study used
27 stepwise multiple regression modeling of diastolic and systolic blood pressure stratified by sex,
28 with and without adjustment for alcohol, and with and without subjects on antihypertensive
29 medications. Candidate covariates, selected from a larger pool, included age, alcohol use (heavy
30 drinkers versus all other drinkers and nondrinkers), SES (manual classes versus non-manual
31 classes), location of residence in country (northern resident versus non-northern resident),
May 2006 6-142 DRAFT-DO NOT QUOTE OR CITE
-------
1 smoking, and common log blood lead. As nonsignificant variables did not remain in the models,
2 each model contained a unique mix of covariates. A doubling in blood lead in men was
3 associated with an increase in diastolic blood pressure of 1.07 mm Hg (95% CI: 0.37, 1.78)
4 when alcohol consumption was not in the model and 0.88 mm Hg (95% CI: 0.13, 1.63) when
5 alcohol consumption was in the model. Women had a significant response to lead only for
6 diastolic blood pressure in the model without adjustment for alcohol and with subjects using
7 antihypertensive medication. There were no significant effects of lead on systolic blood pressure
8 in any model. The authors provided no statistical justification for stratified modeling nor did
9 they test for significant differences in lead coefficients as a result of the stratification.
10
11 Occupational Studies
12 U.S. Occupational Studies. Glenn et al. (2003) was one of the few studies to use a
13 prospective design and was the only study using statistical techniques designed for repeated
14 measures. They studied 496 male workers from New Jersey with former organolead exposure.
15 Using generalized estimating equations with baseline linear blood lead, age, BMI, smoking,
16 education, antihypertensive medication, measurement technician, and number of years to follow-
17 up measurement of blood pressure (range 10 months-3.5 years), they found that every 1 |ig/dL
18 increase in baseline blood lead was associated with 1.13 mm Hg/year (95% CI: 0.25, 2.02)
19 increase in blood pressure over the observation period.
20 Schwartz et al. (2000c) reported significant blood lead associations with 543 male former
21 organolead workers. Stepwise backward multiple regression showed an increase of 2.3 mm Hg
22 in systolic blood pressure for each doubling in blood lead. The association with diastolic blood
23 pressure was not significant.
24 Sharp et al. (1990) studied 132 black bus drivers (blood lead range 3.1-20.9 |ig/dL) and
25 117 nonblack bus drivers (blood lead range 2.0 to 14.7 |ig/dL) in San Francisco, aged 30 to
26 60 years. They used natural log blood lead in multiple regression models and found for each
27 doubling of blood lead an increase of 5.22 mm Hg (95% CI: 0.60, 9.84) in systolic blood
28 pressure among blacks, 3.27 mm Hg (95% CI: 0.10, 6.44) in diastolic blood pressure among
29 blacks, and -3.96 mm Hg (95% CI: -8.32, 0.42) in systolic blood pressure among nonblacks.
30 Sokas et al. (1997) reported a possible race interaction (p = 0.09) on systolic blood
31 pressure with linear blood lead in 264 construction workers aged 18-79 years. Each 1 |ig/dL
May 2006 6-143 DRAFT-DO NOT QUOTE OR CITE
-------
1 increase in blood lead increased systolic blood pressure in blacks by 0.86 mm Hg more than in
2 whites. Neither the black or white lead coefficients were significant.
3
4 European Occupational Studies. Maheswaran et al. (1993) reported on 809 male
5 factory workers with blood lead between less than 21 to more than 50 |ig/dL from Birmingham,
6 England. Unfortunately, the inclusion of other factors strongly related to blood lead, including
7 an additional direct measure of lead exposure in addition to linear blood lead (years working in
8 factory) and inclusion of zinc protoporphyrin, may have biased the blood lead effect and resulted
9 in nonsignificant lead effects on blood pressure.
10 Telisman et al. (2004) also reported nonsignificant effects of natural log blood lead on
11 blood pressure in 115 male industrial workers with blood lead between 9.9 and 69.9 |ig/dL, but
12 included erythrocyte protoporphyrin in models, a variable correlated with blood lead over much
13 of the observed blood lead range. Coefficients were not given, as lead did not enter into stepwise
14 regression models. The study had very low power.
15
16 Asian Occupational Studies. Male and female factory workers (n = 798) from Chonan,
17 Korea (blood lead between 17.8 and 64.8 |ig/dL) were studied principally for the effects of
18 genotype of ALAD and vitamin D receptor on cardiovascular response to lead (Lee et al., 2001).
19 These aspects are covered more thoroughly below. As part of their work, the authors developed
20 multiple regression models examining the effect of linear blood lead on blood pressure with
21 forced entry of age and age2, BMI, sex, antihypertensive medication, lifetime alcohol, and
22 ALAD and vitamin D genotypes. A marginally significant effect of blood lead on systolic blood
23 pressure (diastolic blood pressure not modeled) was noted, with a 10 |ig/dL increase in blood
24 lead associated with a 0.7 mm Hg (95% CI: -0.04, 1.4) increase in blood pressure.
25 Nomiyama et al. (2002) used a combined group of 193 female crystal glass workers and
26 nonexposed controls, aged 16 to 58 years, with blood lead between 3.8 and 99.4 |ig/dL. The
27 authors used a stepwise multiple regression with a novel technique to reduce collinearity among
28 covariates. From a large group of covariates, they selected covariates eligible to enter the
29 regression from a factor analysis. Although the stepwise entry of these variables resulted in
30 different models for systolic and diastolic blood pressure, both models included linear blood
31 lead, age, urine protein, and plasma triglycerides. The diastolic model additionally included
May 2006 6-144 DRAFT-DO NOT QUOTE OR CITE
-------
1 family hypertension and low density lipoprotein. Each 10 |ig/dL increase in blood lead was
2 significantly associated with a 1.26 mm Hg (95% CI: 0.58, 1.94) increase in systolic blood
3 pressure and a 1.05 mm Hg (95% CI: 0.52, 1.57) in diastolic blood pressure. In alternative
4 models with ordered categories of blood lead, systolic blood pressure was 7.5 mm Hg (95% CI:
5 3.0, 12.0) and diastolic blood pressure was 6.3 mm Hg (95% CI: 3.4, 9.1) higher in workers with
6 blood lead >60 |ig/dL than in controls with <11.4 |ig/dL. Models did not control for BMI.
7 Wu et al. (1996) examined the effect of ordered blood lead category on blood pressure of
8 112 male (aged 18-67 years) and 110 female (aged 18-71 years) lead battery factory workers in
9 multiple regression models. Blood lead ranged from 8.3 to 95.4 |ig/dL. Nonsignificant blood
10 lead effects were found possibly due to the inclusion of two additional lead exposure
11 measurements, ambient air lead and work history, likely leading to substantial collinearity with
12 blood lead.
13
14 Meta-A nalysis of Blood Lead-Blood Pressure Studies
15 The most recent meta-analysis of the blood lead-blood pressure literature analyzed
16 31 studies from a large pool of studies published up to 2001 (Nawrot et al., 2002). Two other
17 meta-analyses were also published during this reporting period (Schwartz, 1995; Staessen et al.,
18 1994), covering many of the earlier papers cited in Nawrot et al. (2002), and derived similar
19 coefficients for the lead effect, so they will not be reviewed here. The meta-analysis authors
20 selected studies with 50 or more subjects, with subjects 10 years of age and up, with blood
21 pressure and blood lead measurement techniques presented in sufficient detail to estimate effect
22 sizes, and with preference given to papers with models adjusting for age, BMI, and "additional
23 factors of proven importance." Where possible, studies with stratified analyses based on sex and
24 race were entered in the meta-analysis as separate subgroups. Studies were weighted by the
25 number of subjects to arrive at estimates and CIs for lead effect on diastolic and systolic blood
26 pressure. Nearly half the studies reported lead effects from linear lead terms, the remainder from
27 log-transformed lead. To include both types of studies in the analyses, the authors reported
28 effect sizes based on doubling the mean blood lead concentration. For models using logarithmic
29 blood lead, this doubling has the same effect anywhere in the range of blood lead in the study.
30 For models using linear blood lead, the doubling effect was referenced from the mean blood lead
31 reported. Figures 6-5.1 and 6-5.2 depict the effect estimates for systolic and diastolic blood
May 2006 6-145 DRAFT-DO NOT QUOTE OR CITE
-------
Study
Population n
Reference
Reimer and Tittelbach (1989) M
Weiss etal. (1986) M
deKorteta!. (1987) M
Morris el al. (1990) F
Lockett and Arbuckle (1987) M
Sharp etal. (1990) M,W
Sharp etai. (1990) M, 8
Staessenetal. (1990) F
Morris etal. (1990) M
Sokas etal. (1997) M, W
Apostoli etal. (1990) M
Apostoli etal. (1990) F
Neri etal. (1988) M, FW
Staessen et al. (1996a) F, P
Staessen et al. (1996a) M, P
Gartside(1988) M, B
Staessen etal. (1990) M
Gartside(1988) F, B
Parkinson et al. (1987) M
Orssaud etal. (1985) M
Wtoller and Kristensen (1992) M
Rothenberg et al. (1999) F, Nl
Grandjean et al. (1989) M
Schwartz et al. (2000b) M
Grandjean et al. (1989) F
Kromhoutetal. (1985) M
Proctor etal. (1996) M
Maheswaran et al. (1993) M
Elwoodetal. (1988a,b) F, HP
Elwoodetal. (1988a,b) M, HP
Elwood et al. (1988a,b) M, C
Rothenberg et al. (1999) F, I
Menditto etal. (1994) M
Chu etal. (1999) F
Chu etal. (1999) M
Hense etal. (1993) F
Hense etal. (1993) M
Den Hond et al. (2002) M, B
Neri etal. (1988) M/F
Den Hond et al. (2002) F, B
Bost etal. (1999) M
Gartside(1998) M, W
Bost etal. (1999) F
Gartside(1998) F, W
Rabinowitzetal. (1987) F
Den Hond et al. (2002) M, W
Den Hond et al (2002) F, W
Pococketal. (1984) M
All
Systolic Blood Pressure
Figure 6-5.1. Change in the systolic pressure (effect estimate in mm Hg) associated with
a doubling of the blood lead concentration. Studies arranged vertically by
increasing study size.
89
105
106 (
117 ! •
132
145
°5<1 t
°71 i
'sqq i
350 K
407 |
428 H
431
439
439 t-
504 t—
543
546 i—
752
798 i—
QAQ K
856 H
865 n
1136 *
1188
1319
1329
1471
1661 "-
1703
1761
2193 <
2197
OSRT .
2705
2827 ••
3851
4685 i-
5138 i
7379
58518
I I I
-15 -10 -5 (
>
^
, — . — ,
-i
i
»— i
• i
• i
«— i
M
M
H
M-l
1
1
> 1
-»-l
)
h»H
1 » 1
-• — 1
h»H
»— 1
H
M
•
1 1 1 1 1 1
) 5 10 15 20 25 30
Study key:
Source: Nawrot et al. (2002).
C = Caerphilly Study, HP = Welsh Heart Program, P = PheeCad Study,
W = whites, B = blacks, NI = nonimmigrants, I = immigrants,
FW = foundry workers, CS = civil servants.
May 2006
6-146
DRAFT-DO NOT QUOTE OR CITE
-------
Study
Reference Population
Raimar CinrJ TrHc»IHcij"h /"IQftQ^ fcjl
KSaJTlSr 3F1O f IllGlQelCn \ rauUJ
WVoieo A} a1 ^1QftR^
l/VGISS 61 3J. i, (yoOJ
n*a K'Art sat al M Qft7\
Lf@ r\on si ai. ^ > yo i f
Morris etai, (1990)
Lockett and Arbuckle (1987)
Sharp et al (1990)
Sharp etal. (1990)
SteJGSSGH ©1 31, {IsraO)
Morris etal. (1990)
Krcunhout ©t 3i, (1985)
Sokasetal. (1997)
Apostoli et al. (1990)
Apostoli et al, (1990)
Nerietal. (1988)
Staossen et al, (1996a)
Q fa *»*.*, Art Al al j'lQQRa's
£>id©55en si ai, \ fyyosi^
Gartside(1888)
Staessen et al. (1990)
Gartside(1988)
Parkinson etal. (1987)
Orssaud st al (1985)
Moller and Kristensen (1992)
Rothenberg et at. (1999)
Grandjean et a!. (1989)
Schwartz et al. (ZOOOb)
Grandjean et al. (1989)
Proctor etai. (1996)
Maheswaran etal. (1993)
Elwoodetal. (1988a,b)
Elwoodetai. (1988a,b)
Elwoodetal. (1988a,b)
Rothenberg et ai, (1999)
Menditto et al. (1994)
Chuelal. (1999)
Chuetal. (1999)
Henseetal. (1993)
Henseetal. (1993)
Den Hond et al. (2002)
Nerietal. (1988)
Deo Hond et al. (2002)
Bost etal. (1999)
Gartside(1988)
Bost etal. (1999)
Gartside(1988)
Rabinowitz et al. (1987)
Den Hond et al. (2002)
Den Hond et al. (2002)
Pococketal. (1984)
All
IV!
F
M
M W
M, B
M
MT W
M
F
M, FW
F, P
M P
M, B
M
F, B
M
M
M
F, Nl
M
M
F
M
M
F, HP
M, HP
M, C
F, I
M
F
M
F
M
M, B
y
F, B
M
M, W
F
F, W
F
M, W
F, W
M
n
-IflC t
1 Uu 1
106
118 H*
1 1"* i
132
J -5-> 1 fl
145
1 *i"5
IS*
1 r*n i A
254
">Tl
£. t t
288
lAR
O*+U
350
398 1—
407 1 —
428 1
A"** I
439 1
439 M
504 | •
543 1
546
798
809 1 •—
856 I
866 I
1136 (•
1188
1319
1329
1471 i
1661
1703 H
1760 I
2193 h
2187
2563
2705
2763 I
2827
3851 i
4681 •
5126 i
7379 1
58491
I
"1
•, i
i-«-i
__|
I
1 • t
1
-• 1
•* 1
^ ,
i
t— i
-i
—» — 1
— • 1
h»H
-1
M
•H
H
m
l-•^
i
i • i
••— i
M
-• — 1
•1
I— • 1
h»l
— • — 1
t+4
)
•
II 1 1 I 1 I
-10 -5 0 5 10 15 20 25
Diastolic Blood Pressure
Figure 6-5.2. Change in the diastolic pressure (effect estimate in mm Hg) associated with
a doubling of the blood lead concentration. Studies arranged vertically by
increasing study size.
Study key:
Source: Nawrot et al. (2002).
C = Caerphilly Study, HP = Welsh Heart Program, P = PheeCad Study,
W = whites, B = blacks, NI = nonimmigrants, I = immigrants,
FW = foundry workers, CS = civil servants.
May 2006
6-147
DRAFT-DO NOT QUOTE OR CITE
-------
1 pressure, respectively, included in the meta-analysis from Nawrot et al. (2002). Ninety-five
2 percent CIs overlapped for males and females and for blacks and whites, suggesting to Nawrot et
3 al. no significant differences in lead effect by gender or race. In the group of studies as a whole,
4 the combined meta-analysis coefficients for each doubling of blood lead were highly significant
5 for both systolic (1.0 mm Hg [95% CI: 0.5, 1.4]) and diastolic (0.6 mm Hg [95% CI: 0.4, 0.8])
6 blood pressure. The meta-analysis supports the statistical association between increased blood
7 lead and increased blood pressure over a wide range of populations in many studies.
8 Figures 6-5.1 and 6-5.2 graphically depict the results of the studies used by Nawrot et al.
9 meta-analysis. Quantitative estimates for the effect of doubling the mean blood lead
10 concentration on systolic and diastolic blood pressure from many of the studies discussed here
11 are summarized in Figure 6-5.3. Figure 6-5.3 presents results published since Nawrot et al.
12 (2002). The studies shown in Figure 6-5.3 were selected to include those studies with subjects
13 having contemporary blood lead with contemporary blood pressure, published 1990 to present.
14 Effects for the entire study population are presented unless only effects in subsamples are
15 reported. Other selection criteria used are detailed in the legend of Figure 6-5.3. Results from
16 these individual studies also generally appear to agree with the results of the meta-analysis by
17 Nawrot et al. that increased blood lead levels are significantly associated with increased systolic
18 and diastolic blood pressure.
19 A random effects meta-analysis was preformed to examine the use of log-linear and linear
20 blood lead models in blood pressure studies. A significant blood lead effect on systolic blood
21 pressure was observed both the log-linear (p = 0.05) and linear models (p < 0.001).
22 Heterogeneity was significant for the log-linear model (p = 0.0002), but not the linear model
23 (p = 0.319). The log-linear and linear effects were 0.62 mm Hg (95% CI: 0.12, 1.11) and
24 0.55 mm Hg (95% CI: 0.33, 0.772) per 5 |ig/dL respectively, for systolic blood pressure.
25 The difference between these effect estimates using linear or log linear models is non-significant.
26 A meta-regression analysis was done using the geometric mean of the blood lead in each study.
27 Geometric mean blood lead was insignificant indicating that the heterogeneity found is not due
28 to the slopes varying with the mean level of blood lead. These meta-analyses suggest there may
29 be some differences between the studies, but overall there is an effect of blood lead on systolic
30 blood pressure. The meta-analysis result indicates that studies not detecting an effect may be due
May 2006 6-148 DRAFT-DO NOT QUOTE OR CITE
-------
Natural Log Lead in Model
Linear Lead in Model
Sharp eta!. (1990): notiBM i-
Sharpetal (1990): BM
Rotltenberg etal. (1999): nonIM
Mailer etal. (1992): M
Mailer etal.(1992) :F
Proctor etal. (1996): M
Staessen etal. (1993): F
Staessen etal. (1993): M
Ro(henbeigetal.(1999):IMM
Den Hond et al. (2002): BM
Den Hone) el al. (2002): BF
Den Hone) et ai, (2002): WM
Den Hond et ai. (2002): WM
Henseelal. (1994):M
Nomiyama et al. (2002}: F
Geirelal. (2002): M/F
Chsngelal. (2001):M
Schwartz etal. (2000c):M
Henseetal. (1994): F
Lee et ai. (2001): f*F
Maheswaran et al. (1993): M
Nash et al. (2003): F
Soretetal.(1991): M
Vupputurielal. (2003): BM
Vupputuri et ai (2003): BF
Vuppuluri etal. (2003): WF
Vupputori et al. (2003): WM
-10 -5 0 5 10
Change in Systolic Blood Pressure
-10 -5 0 5 10
Change in Systolic Blood Pressure
Sharp etal. (1990): nonBM
Sharp etal. (1990): BM
Rottenberg el al. (1999): noniMM
Mailer etal. (1992): M
Mater el al. (1992): F
Proctor etal. (1996): M
Staessen el al. (1993):F
Staessen etal. (1993): M
Rothenberg et al. (1999): IMM
Den Hond et al. (2002): BM
Den Hond ei al. (2002): BF
Bostetal. (1999): M/F
Schwartz (1991): F
Den Hond et ai. (2002): WM
Schwartz (1991): M
Den Horn! et al. (2002): WM
Henseetal. (1994):M
Nomiyama et al. (2002): F
Geirelal. (2002): M/F
Schwartz et al. (2000c): M
Henseetal, (1994): F
Maheswaran el al. (1993): M
Nash et al. (2003): F
Soreletal(1991): M
Vuppulurietal. (2003): BM
Vuppiituri et al. (2003): BF
Vypputuri et al. (2003): WF
Vupputuri et al. (2003): WM
-10 -5 0 5 10
Change in Diastolic Blood Pressure
-10 -5 0 5 10
Change in Diastolic Blood Pressure
Figure 6-5.3. Effect of doubling mean blood lead on estimate of blood pressure change
with 95% CIs. In studies using linear blood lead terms the effect size was
calculated using blood lead doubling from 5 to 10 ug/dL. Studies not
reporting sufficient information to present coefficients and CIs were not
included. Studies arranged vertically by increasing study size. Where
multiple models from the same study were presented, such as repeated
measures over time or adding a confounding variable, only the effect
estimate from the first model is shown. When the same study was multiply
published with subsamples, only the effect estimate from largest study
is shown.
Study key: B = blacks, W = whites, M = males, F = females, IMM = immigrants,
noniMM = nonimmigrants.
May 2006
6-149
DRAFT-DO NOT QUOTE OR CITE
-------
1 to a small sample size or other factors affecting the precision of the estimation of the
2 effect/exposure relationship.
3
4 6.5.2.3 Blood Pressure and Hypertension Studies Using Bone Lead as Exposure Index
5 Korrick et al. (1999) used a case-control design to study the relationship between
6 hypertension and three measures of lead exposure (blood lead, tibia [cortical bone] lead, and
7 patella [trabecular bone] lead in women. The final study sample consisted of 89 hypertension
8 cases and 195 controls, excluding those with history of hypertension, cardiovascular disease,
9 renal disease, diabetes, or malignancy, use of antihypertensive medications, BMI >29, and
10 incomplete data, aged from 47 to 74 years. Cases were selected through a randomization
11 procedure that produced approximately equal numbers of cases for each of three blood pressure
12 categories, hypertensive (> 140 mm Hg or 90 mm Hg), high normal (> 121/75 mm Hg up to
13 hypertension limit), and low normal (<121/75 mm Hg). As many as four controls were matched
14 to cases by 5 year age grouping. Though they did not match cases and controls on other
15 potential confounding variables, they included these variables in their models. The dependent
16 variable was constructed by placing blood pressure measurements into the three groups. The
17 mean blood lead level was 3.1 |ig/dL; the mean tibia and patella lead levels were 13.3 jig/g and
18 17.3 |ig/g, respectively. An ordered logistic regression with proportional odds assumptions was
19 used to asses linear blood lead, patella and tibia bone lead effects on odds of hypertension,
20 controlling for age, BMI, dietary calcium, alcohol use, dietary sodium, smoking, and family
21 hypertension. They presented results from four models with the same covariates determined
22 a priori, but with each lead variable tested separately. Only patella lead concentration
23 significantly (p = 0.03) predicted increased odds for hypertension, but the effect was small.
24 Each 10 jig/g increase in patella lead was associated with an odds ratio of 1.28 (95% CI:
25 1.03, 1.60). Separate analyses testing interactions of alcohol use, age, and menopausal status
26 showed no significant interaction with patella lead, though the small sample size had little power
27 to detect significant interaction effects. Model diagnostics were given for justifying the use of
28 proportional odds ordinal regression but none were given justifying use of a linear blood lead
29 term in the models.
30 Rothenberg et al. (2002) investigated associations between both hypertension and blood
31 pressure with blood lead, tibia lead, and calcaneus lead in 668 women, aged 15-44 years, in the
May 2006 6-150 DRAFT-DO NOT QUOTE OR CITE
-------
1 third trimester of pregnancy and during a 3-month postpartum period using a cohort design and
2 multiple logistic and multiple linear regression modeling. Subject exclusion criteria were blood
3 lead > than 5 geometric SDs from the geometric mean, documented renal disease, cardiovascular
4 disease, diabetes, use of stimulant drugs, and extreme postnatal obesity (BMI >40). Geometric
5 mean prenatal and postnatal blood lead levels were 1.9 |ig/dL and 2.3 |ig/dL, respectively. Mean
6 tibia and calcaneus lead levels were 8.0 jig/g and 10.7 |ig/g, respectively. Variables in all
7 models were selected a priori and retained in the models regardless of significance level. Control
8 variables were education, smoking status, immigrant status, parity, age, and BMI in all models.
9 Prenatal models also controlled for postpartum hypertension in lieu of family history of
10 hypertension. None of the subjects used antihypertensive medications during the study.
11 All three lead variables were simultaneously tested in all models. Third trimester blood lead
12 ranged from 0.4 to 30.0 |ig/dL, postpartum blood lead ranged from 0.2 to 25.4 |ig/dL. Calcaneus
13 lead ranged from -30.6 to 49.9 |ig/g and tibia lead ranged from -33.7 to 42.5 |ig/g. Only
14 calcaneus lead was significantly associated with an increase in hypertension (either > 140 mm Hg
15 systolic or >90 mm Hg diastolic) during pregnancy, with an odds ratio of 1.86 (95% CI: 1.04,
16 3.32) for each 10 jig/g increase of calcaneus lead. No association between calcaneus lead and
17 hypertension was found postpartum. The authors found the same pattern of trabecular lead
18 concentration association with blood pressure during but not after pregnancy in normotensive
19 women. A 10 jig/g increase in calcaneus lead was associated with -0.75 mm Hg (95% CI:
20 0.04, 1.46) increase in systolic and -0.58 mm Hg (95% CI: 0.01, 1.16) increase in diastolic
21 blood pressure in the third trimester. Thorough diagnostic testing was performed for all models.
22 Only linear age terms were used in the models without exploration of age2 terms. The authors
23 did not use the repeated measures nature of the design in their analyses; instead they analyzed
24 third trimester pregnancy data and postpartum data separately. They did not statistically test
25 differences in coefficients from the same variables in the two parts of the study.
26 Two studies examined a subset of subjects participating in the Normative Aging Study.
27 Hu et al. (1996) used a cross-sectional design of 590 men with median age in the mid-60s (range
28 48-92 years). Blood lead ranged from 1 to 28 |ig/dL, tibia lead from <1 to 96 |ig/g, and patella
29 lead from 1 to 142 |ig/g. Logistic regression models were initially constructed by adding age,
30 race, BMI, family history of hypertension, smoking, alcohol use, and dietary sodium and
31 calcium. Testing linear blood lead, tibia lead, and patella lead one by one against hypertension
May 2006 6-151 DRAFT-DO NOT QUOTE OR CITE
-------
1 status (systolic >160 mm Hg, diastolic >96 mm Hg, or taking antihypertensive medication), they
2 found no significant relationships with any of the lead variables, each entered separately. Only
3 when they used backward elimination of nonsignificant variables did they find a significant odds
4 ratio of 1.50 (95% CI: 1.09, 2.10) for each doubling of tibia lead from the mean (20.8 |ig/g) for
5 hypertension. Later, Cheng et al. (2001) followed up the same group, constructing a multiple
6 linear regression model for systolic blood pressure (diastolic blood pressure was not mentioned
7 in model descriptions) in subjects not hypertensive at baseline measurement. They used a fixed
8 set of control variables, including age and age terms, BMI, family history of hypertension, and
9 alcohol and calcium intake, selected by univariate and bivariate testing of a larger set. After
10 entering linear blood lead, tibia, and patella bone lead separately into the models, they reported a
11 significant association only with tibia lead (1.60 mm Hg [95% CI: 0.00, 4.44] increase in
12 systolic blood pressure for each doubling of tibia lead from the mean). Several years later (not
13 specified in methods but no more than 6 years), the group of subjects that was originally not
14 classified as having definite hypertension was retested for presence of definite hypertension
15 (> 160/95 mm Hg). Each lead measure was separately entered into a Cox's proportional hazards
16 model of incident definite hypertension. Only patella lead showed a significant increase in the
17 rate ratio in subjects with no history of definite hypertension, 1.14 (95% CI: 1.02, 1.28) for each
18 10 |ig/g increase in patella lead. Similar results were obtained when the borderline hypertensive
19 group (> 140/90 mm Hg) was combined with the definite hypertension group in patella lead.
20 A rate ratio of 1.23 [95% CI: 1.03, 1.48]) was estimated. Use of linear lead terms may have
21 affected the ability of the studies to detect significant blood lead effects.
22 A pair of studies using the same group of male workers (age range 42-74 years)
23 previously exposed to organic and inorganic lead at an industrial plant in the U.S. investigated
24 the role of blood lead and bone lead on blood pressure. Blood lead ranged between 1 and
25 20 |ig/dL and tibia lead ranged from -1.6 to 52 |ig/g. The study by Schwartz et al. (2000c)
26 controlled for age, BMI, current smoking, and current use of antihypertensive medication in
27 backward elimination linear multiple regression models for blood lead, tibia lead, and DMSA-
28 chelatable lead, forcing each lead term into separate models. Only blood lead was a significant
29 predictor of blood pressure. In multiple logistic regression models, only blood lead in workers
30 <58 years of age was significant in predicting hypertension (>160/96 mm Hg). Although this
31 study used linear blood lead in one model, it used another model with both linear and squared-
May2006 6-152 DRAFT-DO NOT QUOTE OR CITE
-------
1 blood lead. Both lead terms were significant in the respective models. In a follow-up study
2 (Glenn et al., 2003) with most of the same subjects from the first study, subsequent
3 measurements of blood pressure occurred at intervals of 4-12 months for 10.2 months to 3.5
4 years. The study was notable not only for its prospective nature but in the use of statistical
5 models adjusting for repeated measurements. Models were constructed by adding to a base
6 model containing age at start of study, race, BMI, and indicator variables for technician. Lead
7 variables were always forced in the models, but it is not clear if they were each tested separately.
8 Other potential confounder variables were added stepwise to the model if they met a probability
9 criterion. Both increasing linear blood lead and tibia lead were significantly associated with
10 increasing systolic blood pressure times the number of years of follow-up blood measurement,
11 but not with change in diastolic blood pressure. Each 10 jig/g increase in tibia lead was
12 associated with a 0.78 mm Hg, year (95% CI: 0.24, 1.31) increase in systolic blood pressure for
13 workers followed for the longest time.
14 Gerr et al. (2002) tested the effect of blood lead and tibia lead only in young adults (age
15 19-29 years), both males and females, on blood pressure. Half the subjects had grown up around
16 an active lead smelter. Multiple linear regression models always used age, sex, height, BMI,
17 current smoking status, frequency of alcohol consumption, current use of birth-control
18 medication, hemoglobin level, serum albumin, and income, regardless of significance levels.
19 Both blood lead (as a linear term) and bone lead (a four category ordinal variable from <1 jig/g
20 to >10 |ig/g) were tested together. Tibia lead concentration in the highest group was associated
21 with a significant increase in both systolic (4.26 mm Hg) and diastolic (2.80 mm Hg) blood
22 pressure when compared to the lowest tibia lead group.
23
24 6.5.3 Other Cardiovascular Outcomes
25 Cardiovascular morbidity studies that are reviewed in this section are further summarized
26 in Annex Table 6.5.2 and mortality studies in Annex Table 6.5.2.
27
28 6.5.3.1 Ischemic Heart Disease
29 A community-based case-referent study taken from the Stockholm Heart Epidemiology
30 Program compared survivors of first-time myocardial infarction with matched referents based on
31 sex, age, year of study enrollment, and hospital catchment area (Gustavsson et al., 2001). The
May 2006 6-153 DRAFT-DO NOT QUOTE OR CITE
-------
1 authors assessed lead exposure by a three category ordinal scale based on lead levels in airborne
2 dust. In the comparison of unexposed to >0-0.03 mg/m3 (mean 0.01 mg/m3) and unexposed to
3 >0.04 mg/m3 (mean 0.10 mg/m3), the relative risk was 0.88 (95% CI: 0.69, 1.12) and 1.03
4 (95% CI: 0.64, 1.65), respectively.
5 In a reanalysis of the NHANES II dataset, the influence of linear blood lead in the
6 diagnosis of left ventricular hypertrophy (LVH) based on examination of electrocardiograms and
7 body habitus data in less than 9,900 subjects (exact number not given) of age 25-74 years was
8 tested in a survey-adjusted stepwise logistic regression model (Schwartz, 1991). The final model
9 adjusted LVH by age, race, and sex. The odds ratio for LVH was 1.33 (95% CI: 1.20, 1.47) for
10 each 10 |ig/dL increase in blood lead over an unreported blood lead range. The author reported
11 no significant interactions between blood lead and race or between blood lead and sex, though
12 the article noted that the number of cases of LVH was small. The linear lead effect had greater
13 significance than the natural log lead effect, the reverse of the relationship between the two lead
14 specifications usually seen when blood pressure is the outcome variable.
15 In another study of electrocardiograms in 775 men (mean age 68 years, range 48-93) from
16 the Normative Aging Study, patella and tibia lead concentrations were significantly associated
17 with increased heart rate-corrected QT and QRS intervals in men under 65 years but not over
18 65 years in multiple regression stepwise analysis (Cheng et al., 1998). Only tibia lead
19 concentration was significantly associated with an increased odds ratio of intraventricular
20 conduction deficit (2.23 [95% CI: 1.28, 3.90]) for every 10 |ig/g increase in tibia lead), but only
21 in men under 65 years. In contrast, both tibia and patella lead concentration were significantly
22 associated with atrioventricular conduction deficit (odds ratio of 1.22 [95% CI: 1.02, 1.47] and
23 1.14 [95% CI: 1.00, 1.29] for each 10 jig/g increase in tibia and patella lead, respectively), but
24 only for men greater than or equal to 65 years. None of the lead measurements were
25 significantly associated with arrhythmia. Linear blood lead terms were not significantly
26 associated with any of the above outcomes. Though the authors reported examining both
27 saturated models (models with all considered control and confounding variables, significant or
28 not) and stepwise models, only stepwise models were presented or discussed with each lead term
29 forced into separate models. Thus, each model had an individual mix of control/confounding
30 variables, though age was common to all models. Despite using age as a control/confounding
31 variable in all models, the article offered no statistical justification for the age-stratified analysis.
May 2006 6-154 DRAFT-DO NOT QUOTE OR CITE
-------
1 A group of male and female battery factory workers (n = 108) working for at least
2 10 years and who were hired from 1960 to 1983 had blood lead levels from 1970 to 1994 ranging
3 from 5 to 93 |ig/dL (Tepper et al., 2001). Using a fixed covariate multiple logistic regression
4 model, including age, BMI, sex, and family history of hypertension, the authors found a
5 nonsignificant odds ratios for risk of hypertension (> 165/96 mm Hg or self-reported use of
6 hypertension medications) comparing the first tertile (138-504 jig/dL'year) cumulative blood
7 lead index with the third tertile (747-1447 jig/dL'year) index. Echocardiogram left ventricular
8 mass was not significantly related to cumulative blood lead index or time-weighted average
9 blood lead. The study had very low power to detect significant effects.
10 The discrepancy in blood lead results between the two electrocardiogram studies by
11 Schwartz (1991) and Cheng et al. (1998) could well be explained by population differences.
12 Though both used large datasets, the age range of the NHANES II subject pool was between
13 25 and 74 years and used both men and women, whereas the age range for the Normative
14 Aging study was 48 to 93 years and used only men. Furthermore, the Cheng et al. study had
15 775 subjects whereas the Schwartz had a much larger, though unspecified number. The Tepper
16 et al. (2001) study had the least number of subjects (n = 108), which may have resulted in not
17 detecting significant effects on a different measure of LVH. Nonetheless, the two
18 electrocardiogram studies each reported a significant lead effect, and the study with bone lead
19 (Cheng et al., 1998) is particularly interesting, not only for its older sample but because the bone
20 lead exposure measure reflected accumulated past exposure, which blood lead only partly
21 reflects. The two studies are in agreement that lead exposure, either past or present, is
22 significantly associated with ischemic heart disease.
23
24 6.5.3.2 Cardiovascular/Circulatory Mortality (including stroke)
25 A recent follow-up of the NHANES II cohort provided mortality data used to associate
26 past blood lead concentration with increased circulatory mortality in the U.S. population
27 (Lustberg and Silbergeld, 2002). Blood lead concentration as measured during 1976-1980 was
28 divided into three categories (<10 |ig/dL, 10-19 |ig/dL, and 20-29 |ig/dL) after eliminating
29 109 subjects with blood lead >30 |ig/dL, leaving 4,190 subjects 30-74 years of age in the
30 mortality sample followed to the end of 1992. During the follow-up period, 929 subjects died of
31 all causes. ICD-9 codes 390-459 (circulatory) accounted for 424 deaths. Proportional hazards
May 2006 6-155 DRAFT-DO NOT QUOTE OR CITE
-------
1 models using a priori selected potential confounding variables (age, sex, race, education, income,
2 smoking, BMI, exercise, and location) were used to calculate risk ratios of cardiovascular
3 mortality for the two higher lead categories compared to a < 10 |ig/dL reference. The
4 20-29 ng/dL category showed significantly elevated relative risk of 1.39 (95% CI: 1.01,1.91)
5 for cardiovascular mortality.
6 Another longitudinal study combined fatal and nonfatal coronary heart disease (ICD-8
7 codes 410-414) and cardiovascular disease (ICD-8 codes 410-414 and 430-435) categories from
8 a Danish 1936 birth cohort (N = 1052) followed from 1976-1990 (M011er and Kristensen, 1992).
9 During the study period, 54 cases of cardiovascular disease with 19 deaths were reported.
10 Log-transformed blood lead was used in a Cox proportional hazards model, controlling for a
11 priori selected variables of tobacco use, cholesterol, physical activity, sex, systolic blood
12 pressure, and alcohol. Two other models were also examined, those leaving out alcohol or both
13 alcohol and systolic blood pressure. None of the adjusted models showed significant risk hazard
14 for combined fatal and nonfatal cardiovascular disease, though blood lead was significantly
15 associated with outcome in all models except the one containing both alcohol and systolic blood
16 pressure for "total mortality" risk hazard. This article is notable for its detailed discussion of
17 using confounding variables, such as hemoglobin and alcohol use, in multivariate models of
18 lead-cardiovascular associations. Small sample size and low death rate may have contributed to
19 the nonsignificant results.
20 An occupational study, using 1,990 male workers who worked at least 1 day between
21 1940 and 1965 in an active lead smelter in the U.S. (mean length of employment at smelter
22 13.8 years; mean estimated length of lead exposure 9.9 years), failed to show an association with
23 lead and standardized mortality ratios compared to the U.S. population reference group up to
24 1988 (Steenland et al., 1992). Neither mortality from ischemic heart disease (ICD-9 410-414),
25 hypertension with heart disease (ICD-9 402 and 404), hypertension with no heart disease (ICD-9
26 401, 403, and 405), nor cerebrovascular disease (ICD-9 430-438) were significantly higher in the
27 study group than in the U.S. population when examined in their totality or stratified by "high
28 lead exposure" (>0.2 mg/m3 lead in air, surveyed in 1975) or "duration of exposure." Imprecise
29 estimation of lead exposure may have contributed to the nonsignificant results.
30 A study of 664 male workers in a Swedish lead smelter from 1942-1987 examined
31 standardized mortality ratios for cardiovascular disease compared to the county population
May 2006 6-156 DRAFT-DO NOT QUOTE OR CITE
-------
1 mortality figures from 1969-1989 (Gerhardsson et al., 1995). Blood lead measurements were
2 available from the workers since 1969 (mean 62.1 |ig/dL) and dropped steadily from that date to
3 1985 (mean 33.1 |ig/dL). The consecutive blood lead measurements in the subjects allowed
4 construction of a cumulative blood lead index. Standardized mortality ratios were significantly
5 elevated in the group for all cardiovascular diseases (ICD-8 390-458) and for ischemic heart
6 disease (ICD-8 410-414), 1.46 (95% CI: 1.05, 2.02) and 1.72 (95% CI: 1.20, 2.42),
7 respectively. However, there were no indications of a concentration-response relationship when
8 analyses were stratified by cumulative blood lead index, peak blood lead, or other exposure
9 indices.
10 In a study of 1,261 male newspaper linotype operators working in 1961 and followed until
11 1984, 38% had died from all causes (Michaels et al., 1991). Compared to the New York City
12 population reference group, there was a marginally significant increased standardized mortality
13 ratio in the printers of 1.35 (95% CI: 0.98, 1.82) for cerebrovascular disease (ICD-8 430-438),
14 which became highly significant in those with 30 or more years exposure (1.68 [95% CI: 1.18,
15 2.31]; 37 of the total 43 deaths due to cerebrovascular disease). Atherosclerotic heart disease
16 (ICD-8 410-414) mortality in printers was significantly below that expected from the general
17 population, with a standardized mortality ratio of 0.63 (95% CI: 0.59, 0.73).
18 Mortality studies need to follow large groups over extended periods to achieve adequate
19 statistical power. When large groups with well characterized exposure are followed for long
20 periods, results of mortality studies assess the effects of long cumulative lead exposure. Without
21 detailed exposure histories stretching over decades, it is nearly impossible to determine if past
22 peak exposure, time-integrated exposure or average exposure plays the critical role in producing
23 greater then expected mortality. Noting that both population and occupational lead exposure
24 were greater than current levels when the mortality studies reported here were begun, we can
25 expect a 20-30 year lapse before we can asses the effect of current population and occupational
26 exposure on cardiovascular morbidity and mortality.
27
28 6.5.3.3 Other Cardiovascular Effects
29 Peripheral arterial disease (PAD), flow-limiting atherosclerosis in lower limb muscular
30 arteries, was studied using Phase 1 (1999-2000) of the NHANES IV, the most recent NHANES
31 dataset (Navas-Acien et al., 2004). PAD was categorized as a ratio of brachial artery (arm)
May 2006 6-157 DRAFT-DO NOT QUOTE OR CITE
-------
1 systolic blood pressure to posterior tibial artery (ankle) systolic blood pressure < 0.90. One
2 hundred thirty-nine subjects were classified as having PAD; there were 1,986 subjects without
3 the disease. Blood lead was classified by quartile, with the 1st quartile containing subjects with
4 blood lead <1.4 |ig/dL and the 4th quartile containing subjects with blood lead >2.9 |ig/dL.
5 Age range was 40 to >70 years. Three sets of covariates were tested in separate models. The
6 first set, common to all models, included age, sex, race, and education. The second set included
7 the first set and added BMI, alcohol intake, hypertension, diabetes, hypercholesterolemia, and
8 glomerular filtration rate. The third set added self-reported smoking status and serum cotinine.
9 Compared to first quartile blood lead, 4th quartile blood lead subjects had significant odds ratios
10 for PAD of 3.78 (95% CI: 1.08, 13.19) and 4.07 (95% CI: 1.21, 13.73) for the first two models.
11 The odds ratio of 2.88 (0.87, 9.47) for the third model was not statistically significant. However,
12 the increasing odds ratio trend from 1st through 4th quartile was significant for all 3 models
13 (p<0.02).
14
15 6.5.4 Lead and Cardiovascular Function in Children
16 Despite the potential importance of identifying the effects of lead on cardiovascular
17 function in children, only three studies addressed the issue.
18 Factor-Litvak et al. (1996) studied the association of blood lead on blood pressure in
19 260 children at age 5.5 years from a prospective study of lead on child development from two
20 cities in Serbia. They used multiple linear regression of contemporary linear blood lead (range:
21 4.1 - 76.4 |ig/dL) on systolic and diastolic blood pressure, apparently stepwise as diastolic and
22 systolic models had different covariates. Systolic models controlled for height, BMI, gender,
23 ethnic group, and birth order, while diastolic models controlled for waist circumference, ethnic
24 group, and birth order. Additional models further adjusting for maternal blood pressure,
25 maternal hemoglobin, and for town were also presented, but not discussed here. Every one
26 ng/dL increase in blood lead was associated with 0.054 mm Hg and 0.042 mm Hg increase of
27 systolic and diastolic blood pressure, respectively. Though no diagnostics were reported, the
28 authors did try combined linear and quadratic blood lead terms in alternative models and found
29 the quadratic term non-significant. These marginally significant results may partially obscure
30 early indications of altered cardiovascular health in young children exposed to lead due to small
31 sample size and use of linear lead and stepwise regression in models.
May 2006 6-158 DRAFT-DO NOT QUOTE OR CITE
-------
1 Gump et al. (2005) studied the effect of blood lead on resting and induced-stress
2 cardiovascular function in 122 children 9.5 years old from Oswego, NY. The effect of linear
3 cord blood lead (mean [SD] = 3.0 [1.8] |ig/dL; range not given) and contemporary blood lead
4 (range: 1.5-13.1 |ig/dL) on blood pressure and other cardiovascular functions were tested in
5 stepwise multiple regression models. The response to stress was evaluated by taking the
6 difference between baseline and post-stress scores on the cardiovascular evaluations. Diastolic
7 blood pressure change from baseline to stress condition increased 0.07 mm Hg for every one
8 |ig/dL increase in contemporary blood lead. Change in total peripheral resistance between
9 baseline and stress conditions was 0.09 dyn-s/cm3 for every one |ig/dL increase in contemporary
10 blood lead. Authors reported testing blood lead with linear, quadratic, and cubic terms that "did
11 not add significantly to the prediction of these cardiovascular effects." Nonetheless, the
12 scatterplot of the lead effect on peripheral resistance change shows a notable non-linear effect, as
13 does an alternative analysis of the same outcome using blood lead quartiles, in which the
14 significant effect was seen between the group with 1.5-2.8 |ig/dL and all higher blood lead
15 groups, as might be expected from a log-linear like blood lead-peripheral resistance dose-
16 response curve. The stepwise modeling technique and small sample size likely combined to
17 over-fitting of the models. For instance, the total vascular resistance model had 12 covariates.
18 The model might be difficult to replicate with an independent sample. Due to the study location,
19 investigators had reason to believe that the children also had significant exposure to mercury and
20 pesticide residues from eating contaminated lake fish.
21 A randomized succimer chelation trial of 780 12-33 month old children with baseline
22 blood lead from 20-44 |ig/dL resulted in significantly lower blood lead in the treated group for
23 only the first 9-10 months of the 60-month follow up period (Chen et al., 2006). No difference
24 in blood pressure was noted between succimer and placebo groups during treatment.
25 Longitudinal mixed models showed systolic blood pressure 1.09 mm Hg (95% CI: 0.27-1.90)
26 higher in the succimer treated group than in the placebo treated group from month 12-60 of
27 follow up and near zero coefficient for diastolic blood pressure. Cross-sectional regression
28 analyses of blood pressure and linear blood lead adjusted for clinical center, treatment group,
29 race, sex, parents' education, single parent, age at test, height and BMI during follow up revealed
30 near-zero lead coefficients for systolic and diastolic blood pressure. The authors note the short
31 duration of significant blood lead difference between the groups, the overall downward trend in
May 2006 6-159 DRAFT-DO NOT QUOTE OR CITE
-------
1 blood lead with age in both groups, and the relatively short duration of elevated blood lead in
2 both groups as possible factors for the non-significant results. The lack of positive chelation
3 effect in this study mirrors the results of chelation trials in same children showing no benefit in
4 IQ and neurobehavioral performace. No diagnostics were mentioned though non-parametric
5 fitting of blood pressure and blood lead with non-adjusted data were shown.
6
7 6.5.5 Potential Confounding of the Cardiovascular Effects of Lead
8 6.5.5.1 Confounding by Copollutants
9 High on the list of other metals that might be associated with cardiovascular disease is
10 cadmium, through its known effects on kidney function. If blood lead and blood cadmium
11 strongly covary in a sample by sharing a common source (e.g., when the study sample is drawn
12 from a population living near a nonferrous smelter emitting both metals), including simultaneous
13 blood lead and cadmium measurements in the same model would likely show a significant
14 reduction in both coefficients when compared to either metal alone. If, however, blood cadmium
15 and lead do not covary in the sample, their coefficients in the model together would be much the
16 same as when tested separately. In a study of PAD (Navas-Acien et al., 2004) discussed in
17 Section 6.5.3.3, investigators not only tested both lead and cadmium in separate models but also
18 tested them simultaneously. The correlation coefficient between natural log lead and natural log
19 cadmium was 0.32 (p < 0.001), highly significant, though leaving 90% of the variance between
20 them unexplained. In addition, they tested possible interactions between lead and cadmium, and
21 between the two metals and sex, race-ethnicity, smoking status, renal function, and C-reactive
22 protein. Although none of the interactions were significant, when blood lead and blood cadmium
23 were in the same model together they both had significant trends of increasing odds ratios with
24 increasing quartile of each metal, but the nonsignificant point estimate of the odds ratio for blood
25 lead comparing 1st and 4th lead quartile tested alone dropped further when tested with cadmium
26 (odds ratio of 2.88 versus 2.52). Cadmium between 1st and 4th quartile, on the other hand,
27 showed a similar drop from cadmium tested alone to cadmium tested with lead (odds ratio of
28 2.82 versus 2.42), but both point estimates remained significant. Thus, though point estimates of
29 both lead and cadmium were approximately the same whether tested alone or together, the larger
30 variance associated with the lead coefficients rendered them nonsignificant. Part of the
31 difference in variance between the two metals could be explained by noting that the reference
May 2006 6-160 DRAFT-DO NOT QUOTE OR CITE
-------
1 group (lowest quartile) for lead contained a little over half the number of subjects (n = 472;
2 18 cases, 454 noncases) than the reference group for cadmium (n = 856; 27 cases, 829 noncases).
3 The odds ratios for PAD with smoking status dropped from 4.13 (95% CI: 1.87, 9.12) to 3.38
4 (95% CI: 1.56, 7.35) when lead was added to the model, but both odds ratios remained highly
5 significant and the difference was not statistically tested. The failure to find a significant
6 interaction between the two metals and between smoking status and both metals suggests that
7 none of the odds ratio changes discussed above were significant. The same pattern of results was
8 found when using cotinine blood levels instead of self-reported smoking habit. Adding cadmium
9 alone or cadmium and lead together resulted in nonsignificant odds ratios for both indices of
10 smoking.
11 The Belgian Cadmibel studies also were ideally situated to test possible interactions
12 between blood lead and cadmium, but the technique of stepwise addition of variables to the
13 multiple regression models of blood pressure did not allow retention of both metal variables
14 together in the same model (Staessen et al., 1996b). From the lack of both cadmium and lead in
15 any one model, it can be inferred that, if both variables had been forced into the model together,
16 they both would have had nonsignificant coefficients.
17
18 6.5.5.2 Confounding by Smoking Status
19 Most studies reviewed in this section have controlled for tobacco use, where it often
20 appears related to lower blood pressure. The majority of reviewed studies including smoking as
21 a covariate never present the coefficients of smoking or related covariates. Only the Navas-
22 Acien et al. (2004) study discussed in the previous section systematically addressed the issues
23 related to possible confounding or effect modification with tobacco use.
24
25 6.5.5.3 Confounding by Alcohol Consumption
26 Possible confounding by alcohol use, generally associated with increased blood pressure,
27 was thoroughly discussed in the 1990 Supplement (Grandjean et al., 1989). Alcohol, especially
28 in Europe, contained substantial lead during much of the 20th century. This can be seen in the
29 MONICA Augsberg, Germany cohort study (Hense et al., 1994). The study group was stratified
30 by sex and then, only in men, by rural-urban location. Within each strata, the blood lead range
31 differed by alcohol use. In women, for example, the 10th and 90th percentile values of blood
May 2006 6-161 DRAFT-DO NOT QUOTE OR CITE
-------
1 lead were approximately (as estimated from graphs) 3.5 and 8.5 |ig/dL for self-reported
2 abstainers, 4.5 and 10.5 |ig/dL in those drinking from 1 to 39 g/day, and 6.0 to 14.0 |ig/dL in
3 those drinking 40 plus g/day. Despite the finding that only women in the highest alcohol-use
4 group had a significant lead effect, it cannot be determined if the increase in lead coefficient is
5 significant because the three coefficients associated with use of alcohol strata were not tested for
6 differences among themselves; they were only tested for their significance from the null
7 hypothesis of 0. Another study was based on subjects from the New Risk Factors Survey from
8 the area around Rome, intended to determine confounding effects of a number of social and
9 biochemical variables on the blood lead-blood pressure relationship (Menditto et al., 1994).
10 Alcohol consumption, as well as BMI, heart rate, non-HDL cholesterol, and HDL cholesterol,
11 triglycerides, cigarettes smoked/day, and skinfold thickness were all examined. A doubling of
12 blood lead was associated with an increase of 4.71 mm Hg in systolic and 1.25 mm Hg in
13 diastolic blood pressure. As covariates were successively added to the model, the systolic
14 coefficient was 4.6 (+BMI), 4.9 (+age), 5.1 (+heart rate), 4.3 (+high density lipids),
15 4.2 (+triglycerides), 3.9 (+glucose), 4.4 (+cigarettes/day), 4.1 (+skinfold), and 3.9 (+non-high
16 density lipids). Similar changes were found upon adding covariates to the diastolic model.
17 Alcohol never entered the models, but was significantly and positively associated blood lead in
18 bivariate testing. Unfortunately, neither standard errors or confidence intervals were given and
19 the significance of the changes in the lead coefficient could not be determined.
20 Alcohol as a true confounding variable is likely limited to studies in areas where alcohol
21 contributes significantly to blood lead. In a study of 249 bus drivers in San Francisco, CA,
22 natural log lead coefficients against blood pressure changed less than 10% when alcohol use was
23 included as a covariate (Sharp et al., 1990). Blood lead according to alcohol use was not
24 reported. Another study based on a U.S. population found a significant increase in blood lead of
25 a mixed group of males and females according to alcohol use, ranging from mean blood lead of
26 7.3 |ig/dL in nonusers to 9.2 |ig/dL in those reporting more than 2 ounces/day over 3 days
27 (Morris et al., 1990), with no report of significant effects of alcohol on blood pressure.
28
29 6.5.5.4 Confounding by Dietary Calcium Intake
30 The main thrust of the previously reported Morris et al. (1990) study was to examine the
31 effects of dietary calcium on the effect of lead on blood pressure in 78 males and 64 females
May 2006 6-162 DRAFT-DO NOT QUOTE OR CITE
-------
1 between 18 and 80 years, many of whom were hypertensive (undisclosed number), though those
2 using medications for hypertension discontinued their use 1 month before testing started.
3 Subjects were excluded if they had "secondary hypertension." The investigators measured
4 serum calcium and assessed dietary calcium intake, among other variables. There were no
5 changes in blood lead or blood pressure noted as a result of dietary calcium supplementation.
6 Proctor et al. (1996), using the Normative Aging Study, examined possible modification
7 of the effect of natural log blood lead (blood lead range 0.5-35 |ig/dL) on blood pressure in
8 798 men aged 45-93 years by dietary calcium intake assessed by food questionnaire. The study
9 used multiple regression models with a fixed set of covariates, including age and age2, BMI,
10 adjusted dietary calcium, exercise, smoking, alcohol use, sitting heart rate, and hematocrit.
11 Increased blood lead was significantly associated with diastolic blood pressure and systolic blood
12 pressure. Only systolic blood pressure significantly decreased with increased dietary calcium
13 (0.004 mm Hg decrease for every 1 mg/day increase of dietary calcium). The authors formed
14 dichotomized calcium intake (cut point at 800 mg/day) and blood lead (cut point at 15 |ig/dL)
15 variables to test the interaction between blood lead and calcium on blood pressure. They did not
16 find a significant interaction nor did they show the interaction coefficients.
17 A study of a subset of the Cadmibel Study with 827 males and 821 females, age 20 to
18 88 years, selected from areas known to represent a wide range of cadmium exposure, specifically
19 studied total serum calcium interactions with blood lead on blood pressure (Staessen et al.,
rj
20 1993). Stepwise regression models, selecting from log blood lead, age and age , BMI, pulse rate,
21 log serum gamma-glutamyltranspeptidase, serum calcium, log serum creatinine, urinary
22 potassium, smoking, alcohol intake, contraceptive pill use (females only), and a menopause
23 indicator variable (females only), were stratified by sex for systolic and diastolic blood pressure.
24 The stepwise procedure resulted in models each with a different mix of covariates. Increased
25 serum calcium was significantly associated with increased systolic blood pressure in both males
26 and females. Every increase of one log unit of blood lead was associated with nonsignificant
27 changes in blood pressure in women but with a significant decrease in systolic blood pressure in
28 men (systolic log blood lead P = -5.2). A separate set of models were constructed with an
29 interaction term between serum calcium and log blood lead (details not shown). In women only,
30 both main effects of lead and calcium and the interaction effect were significant (no coefficients
31 presented). At the 25th percentile of serum calcium (2.31 jimol/L), a doubling of blood lead was
May 2006 6-163 DRAFT-DO NOT QUOTE OR CITE
-------
1 associated with a 1.0 mm Hg increase in systolic blood pressure. At the 75th percentile of serum
2 calcium (2.42 jimol/L) a doubling of blood lead was associated with a 1.5 mm Hg increase in
3 systolic blood pressure. Furthermore, serum calcium may itself be confounded with age in
4 women, as women showed a sharp rise in serum calcium in their sixth decade of life, coincident
5 with menopause, whereas the trend for serum calcium in men was steadily downward for each
6 subsequent decade of age. The authors did not test an interaction term including calcium and age
7 or calcium and menopausal status. Thus, the significant interaction effect between calcium and
8 lead on blood pressure may be a result of differences due to menopause.
9
10 6.5.5.5 Summary of Potential Confounding of the Lead Effect on Cardiovascular Health
11 The effects of cadmium exposure, smoking, alcohol use, dietary and serum calcium levels
12 have all been formally tested in a few studies, without significant effects as confounders of the
13 lead effect. Failure to find a significant confounding effect with lead, however, does not argue to
14 maintain these variables uncritically in models of blood pressure. If alcohol contains lead,
15 increased alcohol use will lead to increased blood lead. In this case, both variables in the model
16 will be collinear and this tends to distort estimated coefficients and standard errors of their effect
17 on cardiovascular outcome. Tobacco use may influence lead levels much more in occupational
18 studies than in community exposure studies, especially if smoking in the factory is allowed.
19 Frequent hand to mouth behavior will increase lead exposure and, consequently, raise blood lead
20 concentrations. Serum calcium may statistically modify the lead effect differentially by gender
21 due to menopause in women. Menopause also affects lead turnover. If serum calcium, blood
22 lead, and blood pressure are all statistically related, serum calcium should not be used in blood
23 lead-blood pressure/hypertension studies.
24
25 6.5.6 Gene-Lead Interactions
26 Study authors characterized sodium-potassium adenosine triphosphatase a2 (ATP1A2)
27 polymorphism in 220 workers formerly exposed to a mix of organic and inorganic lead in the
28 U.S., noted above in other references (Glenn et al., 2001). The ATP1A2 (3') one kilobase probe
29 produced two homozygous (4.3/4.3 and 10.5/10.5) and one heterozygous (4.3/10.5) genotypes
30 and two homozygous (8.0/8.0 and 3.3/3.3) and one heterozygous (8.0/3.3) genotypes for the
31 2.5 kilobase ATP1A2 (5') probe. Of the 209 subjects with data on both polymorphisms, 43.5%
May 2006 6-164 DRAFT-DO NOT QUOTE OR CITE
-------
1 were doubly homozygous for 8.0/8.0 and 4.3/4.3, 34.4% were homozygous for 8.0/8.0 and
2 heterozygous for 4.3/10.5, 11.5% were heterozygous for 8.0/3.3 and homozygous for 4.3/4.3,
3 5.3%. Also, 5.3% were doubly homozygous for 8.0/8.0-10.5/10.5, and 4.8% were doubly
4 heterozygous for the two genotypes. Although only 13 African American workers participated,
5 prevalence of the 10.5 kilobase allele in the ATP1A2 (3') genotype was statistically higher for
6 them than for other races. Prevalence of hypertension (> 160/96 mm Hg or use of hypertension
7 medication) was significantly higher in those with the 10.5/10.5 genotype than in others.
8 Controlling for age, BMI, lifetime number of alcoholic drinks, the 10.5/10.5 genotype was
9 associated with an odds ratio of 7.7 (95% CI: 1.9, 31.4) for hypertension when compared to the
10 4.3/4.3 homozygous genotype, but there were no effects of either blood lead, tibia lead, or their
11 interaction with ATP1A2 (3') genotype. A multiple linear regression model for linear blood lead
12 and systolic blood pressure, controlling for age, use of hypertensive medication, current
13 smoking, quartiles of lifetime alcohol consumption, and season, showed a significant main effect
14 for 10.5/10.5 homozygous contrasted against combined 4.3/4.3 and 4.3/10.5 groups, associated
15 with a 25.5 mm Hg reduction in blood pressure, primarily due to limited blood lead range of the
16 homozygous group (maximum blood lead of the 10.5/10.5 group 9 |ig/dL; maximum blood lead
17 of the contrast group = 20 |ig/dL). But the interaction between linear blood lead and the
18 10.5/10.5 condition resulted in a significant increase of the blood lead effect on blood pressure
19 by 5.6 mm Hg for every 1 |ig/dL blood lead compared to the blood lead effect in the other
20 genotypes. The authors stated, but did not show analysis or coefficients, that the ATP1 A3 (3')
21 polymorphism also significantly interacted with tibia lead and systolic blood pressure. There
22 were no significant relationships using the ATP1A2 (5') gene. Thus, the ATP1A2 (3')
23 polymorphism appears to directly influence both prevalence of hypertension and the effect of
24 lead on blood pressure, though the small group (n = 9 with all measures) with the important
25 10.5/10.5 homozygous pattern would argue for enlarging this important study.
26 Another research group focused on polymorphisms of two genes suspected to be involved
27 in lead toxicokinetics, the vitamin D receptor (VDR) and delta-aminolevulinic acid dehydratase
28 (ALAD) (Lee et al., 2001). Polymorphism of both genes is well studied and prevalence appears
29 associated with race or ethnic background. Nearly 800 Korean workers aged 18-65 years
30 (79.4% males) from lead-using businesses were classified according to ALAD polymorphism
31 (1-1 [homozygous] versus 1-2 [heterozygous]) and VDR polymorphism (bb [predominant
May 2006 6-165 DRAFT-DO NOT QUOTE OR CITE
-------
1 homozygous] versus Bb plus BB [infrequent polymorphisms]). The homozygous 1-1 ALAD
2 polymorphism was found in 90.1% of the group and the homozygous bb polymorphism was
3 found in 88.8% of the group. When compared to a smaller group of non-lead-exposed workers,
4 blood lead concentration (mean exposed 32.0 |ig/dL [range 4-86] mean nonexposed 5.3 |ig/dL
5 [range 2-10] and tibia lead concentration mean exposed 37.2 |ig/g [range -7-338]; and mean
6 nonexposed 5.8 |ig/dL [range -11-27]) were much higher. The study used stepwise multiple
7 regression models, selecting covariates remaining significant in the models from among a large
8 set of potential control and confounding variables. They also allowed potential confounders to
9 remain in the models if "there were substantive changes in the coefficients of predictor
10 variables" with their addition. Systolic models controlled for age and age2, sex, BMI,
11 antihypertensive medication use, and cumulative lifetime alcohol use. Depending on the
12 presence or absence of linear blood lead, tibia lead, and DMSA chelatable lead in the models,
13 and the gene-age interactions tested, blood urea was added to the model. Diastolic models
14 controlled for age, sex, BMI, cumulative alcohol consumption, and linear blood lead.
15 Hypertension (systolic >160 mm Hg or diastolic >96 mm Hg) logistic multiple regression
16 models controlled for age, sex, BMI, tibia lead, and current alcohol use. Among the exposed
17 workers bb VDR genotypes had significantly lower DMSA-chelatable blood lead and lower
18 diastolic and systolic blood pressure than the combined Bb and BB genotypes. The only
19 significant interaction reported between predictor variables and gene polymorphism on blood
20 pressure was with the VDR polymorphism bb allele, who had a less pronounced increase in
21 systolic blood pressure with age than subjects with the B allele. There were only marginally
22 significant associations of systolic blood pressure with tibia lead and linear blood lead. There
23 were no significant associations in models of diastolic blood pressure with linear blood lead,
24 DMSA-chelatable blood lead, or tibia lead. Tibia lead was significantly associated with
25 hypertension (odds ratio of 1.05 [95% CI: 1.00, 1.12] for each 10 |ig/dL increase in tibia lead).
26 Workers with VDR B allele had significantly higher prevalence of hypertension (odds ratio = 2.1
27 [95% CI: 1.0, 4.4]) than workers with the bb genotype, but no other lead variable or interaction
28 with VDR status was reported significant. Though VDR status was significantly related to blood
29 pressure and prevalence of hypertension, there were no significant effects of ALAD
30 polymorphism on blood pressure or hypertension or of VDR interactions with any lead exposure
31 variable.
May 2006 6-166 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lustberg et al. (2004) studied these same Korean lead workers (n = 793) to examine the
2 relationships between the G894-T894 polymorphism in the gene regulating endothelial nitric oxide
3 synthase (eNOS) and blood lead effects on blood pressure and hypertension. Nitric oxide
4 metabolism has been suggested both as a mechanism for altered blood pressure and for
5 moderating the effects of lead on blood pressure, though there is experimental support for and
6 against both hypotheses. After classifying subjects as homogenous for the GG type (85%),
7 heterogeneous for both types (TG) (14%), or homogenous for TT (1%), the TG and TT types
8 were combined into a single group (TG/TT). Diastolic and systolic multiple regression models
9 were constructed with a fixed set of covariates, including smoking, alcohol consumption, age,
10 sex, BMI, and education. Logistic regression models used blood pressure criteria of either
11 > 140 mm Hg diastolic blood pressure, >90 mm Hg systolic blood pressure, or self-report of
12 using antihypertensive medications. There was no effect of genotype on diastolic or systolic
13 blood pressure or on hypertension prevalence in multiple regression models, nor any significant
14 interaction of lead exposure indices with gene status.
15 Because interaction testing in statistical models requires balanced groups for
16 uncomplicated interpretation, further gene-lead interaction exploration should use studies with
17 nearly equal numbers of heterogenous and homogenous groups. Because adequate power for
18 testing significant interactions requires large groups, subsequent studies should draw subjects
19 from the general population. In addition to enlarging the potential subject pool, population
20 studies may more easily avoid the selection biases often found in occupational studies.
21
22 6.5.7 Summary of the Epidemiologic Evidence for the Cardiovascular
23 Effects of Lead
24 The combined blood lead studies using blood pressure/hypertension as an outcome
25 continue to support the conclusions of the 1990 Supplement that there is a positive association
26 between blood lead and increased blood pressure. The occasional finding of significant negative
27 associations of blood lead with blood pressure (e.g., the Cadmibel study, one NHANES III study,
28 the postpartum phase of the Los Angeles pregnancy study) have not been adequately explained
29 and require further confirmation and study. The reported meta-analysis succinctly characterizes
30 the blood pressure findings with blood lead: 1.0 mm Hg systolic pressure increase with each
31 doubling of blood lead; 0.6 mm Hg diastolic pressure increase with each doubling of blood lead.
May 2006 6-167 DRAFT-DO NOT QUOTE OR CITE
-------
1 Although females often show lower lead coefficients than males, and blacks higher lead
2 coefficients than whites, where these differences have been formally tested, they are usually not
3 statistically significant. The tendencies may well arise in the differential lead exposure in these
4 strata, lower in women than in men, higher in blacks than in whites. The same sex and race
5 differential is found with blood pressure.
6 The most promising developments in this field since the 1990 Supplement have been the
7 use of bone lead as a long-term cumulative lead exposure index and the introduction of genetic
8 analysis into the studies as potential lead effect modifiers. With one exception, all studies using
9 bone lead have found a consistently positive and significant effect on blood pressure and/or
10 hypertension. The ability to estimate past exposure in cross-sectional studies is a significant
11 advance. The results of the bone lead studies to date highlight the important role of accumulated
12 lead exposure in the development of cardiovascular problems.
13 Though the study of genetic polymorphisms is still in its infancy in this field, it too holds
14 great promise in accounting for individual variability in development of cardiovascular disease
15 and individual response to lead exposure.
16 Focus of future efforts should be to obtain more efficient and unbiased quantitative
17 estimates of lead effect on cardiovascular outcome, to determine the role of lead on renal
18 function and cardiovascular effects simultaneously in prospective study, and address issues of
19 prenatal and postnatal lead exposure on development of cardiovascular disease in children.
20 Single equation multiple regression techniques cannot completely evaluate confounding.
21 Prior knowledge is required and path analysis or structural equations is helpful in this regard.
22 However, studies should present the estimated coefficients of the covariates and other statistical
23 results so as to clarify the confounding situation as much as possible.
24 Epidemiological studies cannot by themselves determine cause and effect relationships
25 between lead and cardiovascular disease. However, toxicological studies that observe similar
26 phenomena in experimental animals give biological plausibility to the epidemiological results.
27 In addition they may suggest mechanisms by which lead might cause the observed
28 epidemiological effects. Chapter 5.5 details a series of results that run parallel to and give
29 biological plausibility to the results in humans detailed in this section. In intact animals, elevated
30 blood pressure develops only in response to continued exposure to lead. If duration of lead
31 exposure is key to lead-induced hypertension, as suggested by the consistently observed
May 2006 6-168 DRAFT-DO NOT QUOTE OR CITE
-------
1 elevation of blood pressure and increased risk for hypertension associated with increased bone
2 lead (long term exposure) and the difficulty of detecting lead effects on blood pressure in
3 children, these animal studies argue that the lead effects observed in humans are not the result of
4 statistical artifact or confounding. On the other hand, cell, tissue, and organ response to lead is
5 immediate and may provide clues to the mechanisms by which lead is associated with
6 cardiovascular disease in humans. Lead interference in Ca-dependent processes, including ionic
7 transport systems and signaling pathways important in vascular reactivity may only represent the
8 first step in the cascade of lead-induced physiological events that culminates in cardiovascular
9 disease. Lead alteration of endothelial cell response to vascular damage, inducement of smooth
10 muscle cell hyperplasia, alteration of hormonal and transmitter systems regulating vascular
11 reactivity, and its clear role as promoter of oxidative stress suggest mechanisms that could
12 explain the lead-associated increase in blood pressure, hypertension, and cardiovascular disease
13 noted in this section.
14
15 Conclusions
16 • Studies support the relationship between increased lead exposure and increased adverse
17 cardiovascular outcome, including increased blood pressure, increased incidence of
18 hypertension, and cardiovascular morbidity and mortality. For blood lead and blood
19 pressure, every doubling of blood lead is associated with a -1.0 mm Hg increased
20 systolic and -0.6 mm Hg increased diastolic blood pressure for blood lead between 1 and
21 >40 |ig/dL.
22 • Cumulative past lead exposure, measured by bone lead, may be more important than
23 present exposure in assessing cardiovascular effects of lead exposure. Over the range of
24 bone lead concentration of < 1.0 jig/g to 96 |ig/g, every 10 jig/g increase in bone lead was
25 associated with increased odds ratio of hypertension between 1.28 and 1.86, depending
26 upon the study. Two studies measured averaged increased systolic blood pressure of
27 -0.75 mm Hg for every 10 |ig/g increase in bone lead concentration over a range of <1 to
28 52 |ig/g.
29 • Though genotyping has not yet produced results predicting differential cardiovascular
30 response to lead, this field has potential to identify individuals at higher risk of adverse
31 lead effects.
32
33
May 2006 6-169 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.6 REPRODUCTIVE AND DEVELOPMENTAL EFFECTS OF LEAD
2 6.6.1 Summary of Key Findings of the Reproductive and Developmental
3 Effects of Lead from the 1986 Lead AQCD
4 Lead has been implicated as a risk factor for reproductive outcomes for over a century
5 Rom, 1976; Oliver, 1911). As early as 1860, increased rates of stillbirths and spontaneous
6 abortions were found in women with occupational exposure to lead (usually in the ceramics
7 industry) and in women with husbands employed in the lead industry, compared to unexposed
8 women (Rom, 1976). Other early investigations found increased rates of physically and
9 mentally "retarded" offspring among these same groups. In 1910, these findings resulted in the
10 first lead-related occupational regulation; the British Committee on Occupational Health
11 recommended that women not be employed in the lead industry (Oliver, 1911). These
12 observations, however, were based on exposure levels far above those considered acceptable
13 today, and current research now focuses on substantially lower exposure levels.
14 The 1986 Lead AQCD provided evidence that lead, at high exposure levels, exerted
15 significant adverse health effects on male reproductive functions. Several studies observed
16 aberrations in both sperm count and morphology in men occupationally exposed to relatively
17 high levels of lead (blood lead levels of 40-50 jig/dL). However, the effects of lead on female
18 reproductive function and fetal growth were suggestive but equivocal, perhaps due to the small
19 sample sizes and inadequate controlling for potential confounding factors.
20 This section provides a critical review of the literature regarding the associations between
21 exposure to environmental lead and reproductive outcomes. First, the evidence for the placental
22 transfer of lead is reviewed; this is key to providing a basis and mechanism for fetal exposure.
23 Second, the association between exposure and each outcome is reviewed. Outcomes of interest
24 are reproductive function (fertility), spontaneous abortion, fetal growth, preterm delivery, and
25 congenital anomalies. Each section below begins with a summary of the literature up to 1986,
26 the year of the last EPA Air Quality Criteria Document. Then, key studies are reviewed and
27 each section ends with a conclusion based on the evidence provided. The conclusion is based on
28 the generally accepted "Causal Criteria" for bodies of epidemiologic literature (Hill, 1965;
29 Susser, 1991).
30
May 2006 6-170 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.6.2 Placental Transfer of Lead
2 In 1968, Barltrop (1968) demonstrated that lead crosses the placenta beginning as early as
3 gestational week 12. He found that the rate of transfer subsequently increased to term. Lead
4 accumulations were found in the bones, livers, blood, hearts, kidneys, and brains of stillborn and
5 spontaneously aborted fetuses. These observations were replicated by numerous investigators;
6 for example, Casey and Robinson (1978) found lead accumulations in the livers, kidneys, and
7 brains of stillborn fetuses. Lead accumulations were also found in the livers, brains and kidneys
8 of first trimester abort fetuses (Chaube et al., 1972), suggesting placental transfer earlier than
9 12 weeks of gestation. Newer findings, published since 1986, are reviewed below (also see
10 Section 6.2.2.5.2).
11 Placental transfer of lead is confirmed by correlations of maternal blood lead
12 concentrations, umbilical cord blood lead, and placental lead concentrations in a variety of
13 settings. Umbilical cord blood reflects fetal blood. Early studies, prior to 1986, found
14 correlation coefficients between maternal and umbilical cord blood lead ranging from 0.5 to 0.8,
15 all of which were highly statistically significant. More recent studies also find significant
16 correlations between maternal and fetal blood lead. For example, a prospective study in Kosovo,
17 Yugoslavia recruited 1,502 women at mid-pregnancy in two towns — one with high exposure
18 due to the presence of a lead smelter, refinery, and battery plant, and one with relatively low
19 exposure. The correlation between maternal blood lead (either at delivery or at mid-pregnancy)
20 and cord blood lead ranged from 0.8 to 0.9 (Graziano et al., 1990). Among women with
21 substantially lower levels of exposure (e.g., blood lead 1.9 |ig/dL) the correlation between
22 maternal and cord blood lead was 0.79 (Harville et al., 2005).
23 Chuang et al. (2001) propose that while maternal and cord whole blood lead are highly
24 related, fetal exposure may be even more influenced by maternal plasma lead. Using data from a
25 cohort of 615 women in Mexico City recruited in 1994-1995, these investigators used structural
26 equation modeling to estimate the associations between whole blood lead, bone lead (cortical and
27 trabecular), and the latent variable, plasma lead and cord blood lead. They found the strongest
28 associations between whole blood lead and cord blood lead, even after accounting for plasma
29 lead. The greatest contributors to plasma lead were bone lead and airborne lead. However, with
30 declining exogenous lead exposure, these investigators note that the measurement of plasma and
31 bone lead may become increasingly important in assessing fetal exposure.
May 2006 6-171 DRAFT-DO NOT QUOTE OR CITE
-------
1 These data provide little doubt of fetal exposure to lead via placental transport. Further, it
2 appears that lead crosses the placenta throughout pregnancy, leading to continual exposure of the
3 fetus. Indeed, there is evidence to suggest that maternal blood leads during the later half of
4 gestation increase (Gulson et al., 2004; Hertz-Picciotto et al., 2000; Rothenberg et al., 1994;
5 Sowers et al., 2002). The magnitude of the increase ranges from 14-40%, possibly due to the
6 different starting blood leads in each study (Bellinger, 2005). The increase in blood lead in the
7 later half of pregnancy may result from physiologic changes in maternal homeostasis during
8 pregnancy and, in particular, to mobilization of lead stores from other body organs (Bellinger,
9 2005). Indirect evidence for such mobilization comes from the increased rate of bone turnover
10 during the later half of gestation, prompted by the increased fetal need for calcium (Moline et al.,
11 2000). Thus, both the epidemiological evidence and the biological plausibility of the
12 associations support the role of maternal-fetal transfer of lead.
13 Additionally, in populations with greater lead burdens, the fetus may be at even greater
14 increased risk for exposure and possible adverse effects of exposure. Among the variables
15 associated with lead exposure in pregnant (and nonpregnant) women are: smoking and alcohol
16 consumption (Graziano et al., 1990; Rhainds and Levallois, 1997), pica (Rothenberg et al.,
17 1999), use of ethnic remedies and cosmetics (Al-Ashban et al., 2004; Centers for Disease
18 Control and Prevention, 1993), and food preparation in inappropriately lead-glazed pottery
19 (Azcona-Cruz et al., 2000; Rothenberg et al., 2000). There is some evidence that low calcium
20 intake is also associated with higher blood lead (Gulson et al., 2004; Hernandez-Avila et al.,
21 2003; Hertz-Picciotto et al., 2000). Finally, the location where the mother resides (or resided as
22 a child) may increase blood lead (Graziano et al., 1990). Blood leads are elevated among U.S.
23 immigrants, especially those who migrated from countries where lead is still used as a gasoline
24 additive (Centers for Disease Control and Prevention, 2000); indeed, blood leads are inversely
25 associated with the number of years since migration (Centers for Disease Control and
26 Prevention, 2000; Klitzman et al., 2002; Rothenberg et al., 1999).
27 In conclusion, the epidemiologic evidence indicates that lead freely crosses the placenta,
28 resulting in continued fetal exposure throughout pregnancy. Indeed, the evidence is strong that
29 exposure increases during the later half of pregnancy. Exposure to the fetus is more pronounced
30 in high-risk populations, especially those who migrated from countries still using lead as a
31 gasoline additive.
May 2006 6-172 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.6.3 Effects of Lead on Reproductive Function
2 6.6.3.1 Effects on Male Reproductive Function
3 Male reproductive function is measured using the reproductive history of the male (i.e.,
4 number of pregnancies fathered), time to pregnancy and direct measures of semen quality
5 (usually sperm count, motility and morphology). Most studies relating lead exposure to male
6 reproductive function are based on data collected in the occupational setting linked to population
7 birth registries and on studies directly collecting questionnaire exposure and outcome data.
8
9 Sperm Count, Motility and Morphology
10 Recent publications which purport a decline in sperm concentration, motility, and
11 morphology seek the explanation in the rising use of man-made chemical endocrine disrupters
12 (Auger et al., 1995; Fisch et al., 1997; Farrow, 1994; Gyllenborg et al., 1999; Kavlock et al.,
13 1996; Keiding et al., 1994; Kieding and Skakkebaek, 1996; Lerchl, 1995; Olsen et al., 1995;
14 Sherins, 1995). Several studies from the 1970s and early 1980s suggest aberrations in both
15 sperm count and morphology in men exposed to relatively high levels of lead. In the earliest
16 study, Lancranjan et al. (1975) found decreased sperm counts and an increased prevalence of
17 morphologically abnormal sperm among workers heavily exposed to lead (mean blood lead
18 74.5 |ig/dL) as well as those moderately exposed (mean blood lead 52.8 jig/dL). These findings
19 have been corroborated by results of studies in the U.S. (Cullen et al., 1984) and Italy (Assennato
20 et al., 1986) which describe similar effects in workers with blood leads above 60 |ig/dL.
21 More recently, corroborating data was described in a comprehensive review by Apostoli
22 et al. (1998). In studies of men with blood leads above 40 |ig/dL, decreases in sperm count and
23 concentration, motility and morphologic aberrations were found. Chowdhury et al. (1986) found
24 a significant decrease in sperm count and motility and an increase in the number of sperm with
25 abnormal morphology in 10 men with occupational lead exposure; the average blood lead in the
26 exposed group was 42.5 |ig/dL compared to 14.8 |ig/dL in the unexposed. Similar results were
27 found in a group of 30 lead-exposed factory workers compared to controls (Lerda, 1992). In a
28 large study of male lead smelter workers, Alexander et al. (1996a) found a decreasing trend of
29 sperm concentrations with increasing lead exposure. In this cohort, 152 workers provided blood
30 specimens and 119 also provided semen samples. Geometric mean sperm concentrations were
31 79.1, 56.5, 62.7, and 44.4 million cells/mL for blood leads of <15, 15-24, 25-39, and >40 |ig/dL,
May 2006 6-173 DRAFT-DO NOT QUOTE OR CITE
-------
1 respectively. Long-term body lead burden was estimated from current blood lead concentrations
2 and historical blood lead monitoring data. Using this measure of long-term lead body burden, a
3 similar trend was found for sperm concentration, total sperm count, and total motile sperm count.
4 No associations were found for sperm morphology or serum concentrations of reproductive
5 hormones. A study of traffic police in Peru, where leaded gasoline is still in use, found decreases
6 in sperm morphology, concentration, motility and viability among men with blood lead
7 >40 |ig/dL compared to men with blood lead <40 |ig/dL.
8 Using data from an international study of 503 men employed in the lead industry,
9 Bonde et al. (2002) considered the lowest adverse effect level associated with perturbed semen
10 parameters. Median sperm concentration was reduced by 49% in men with blood lead
11 >50 |ig/dL; regression analysis indicated a threshold value of 44 |ig/dL. These investigators
12 conclude that adverse effects on sperm quality were unlikely at blood leads <45 |ig/dL.
13 In a population of couples undergoing either artificial insemination or in vitro fertilization,
14 Benoff et al. (2003a,b) found higher concentrations of lead in seminal fluid in the male partner
15 among couples who did not conceive, compared to those who did conceive. While not directly
16 measuring the adverse effects of lead on sperm per se, these data suggest a possible mechanism
17 for the transfer of lead from paternal exposure to the fetal environment. Hernandez-Ochoa et al.
18 (2005) also provide evidence that lead concentrations in seminal fluid may be a better indicator
19 of exposure than blood lead. Mean blood lead in this sample was lower than in most other
20 studies, 9.3 |ig/dL. Decreases in sperm concentration, motility, morphology, and viability were
21 correlated with seminal fluid lead or lead in spermatozoa, but not with blood lead.
22 Overall, the available evidence suggests a small association between exposure to lead,
23 usually in the workplace, and perturbed semen quality. It appears that sperm count and
24 morphology (% normal forms) may be decreased at exposures >45 |ig/dL. Future research
25 should focus on studies of men exposed to lower levels of lead, as exposures in the very high
26 range are associated primarily with occupational exposure. These studies should also account for
27 variables known to be associated with semen quality and which may also be associated with
28 exposure, e.g., social class, other environmental exposures such as heat and vibration, and
29 lifestyle variables such as cigarette smoking and alcohol use.
30
May 2006 6-174 DRAFT-DO NOT QUOTE OR CITE
-------
1 Time to Pregnancy
2 Time to pregnancy represents a sensitive measure of fecundity. Time to pregnancy is
3 important because it measures the end effect of perturbed reproductive function. While it is
4 important and necessary to understand the associations between prenatal exposures and
5 endocrine abnormalities and semen characteristics, they represent possible antecedents to the
6 occurrence of pregnancy. Previous reports demonstrate good validity and reliability for reports
7 of time to pregnancy in both males and females and when time to recall has been both long and
8 short (Weinberg et al., 1993, 1994).
9 One advantage to the use of this parameter, as compared to just an infertility measure, is
10 that it does not require categorization of men into fertile and infertile groups. Among couples
11 that succeed in establishing pregnancy, there is considerable variability in the time between
12 discontinuation of contraception and conception (Weinberg et al., 1994). With the possible
13 exception of cigarette smoking and age, very little is known regarding this intercouple
14 variability. Delays in time to pregnancy may be indicative of a range of reproductive
15 abnormalities of both partners, including impaired gametogenesis, hormonal disruptions, and
16 very early unrecognized pregnancy loss. Time to pregnancy has the menstrual cycle as its
17 natural unit and is thus measured in integer units of menstrual cycles.
18 Usually, time to the most recent pregnancy is taken as the outcome (Baird et al., 1986).
19 The measure of exposure in these studies usually is the fecundity density ratio, which is similar
20 to an incidence density ratio. Fecundity density ratios can be interpreted as the risk of pregnancy
21 among the exposed during an interval, compared to the risk of pregnancy among the unexposed
22 during the same interval. In such studies, the intervals of interest are menstrual cycles.
23 Fecundity density ratios less than one indicate reduced fecundity (i.e., longer time to pregnancy)
24 among the exposed compared to the unexposed, while those greater than one indicate enhanced
25 fecundity (i.e., shorter time to pregnancy) in the exposed. Usually fecundity density ratios are
26 calculated using discrete time Cox proportional hazards regression models.
27 Several recent studies evaluate time to pregnancy when the male partner is occupationally
28 exposed to lead. The Asclepios Project, a large European collaborative cross-sectional study,
29 evaluated time to pregnancy in 1,108 men of whom 638 were exposed to lead (Joffe et al., 2003).
30 The reference group consisted of lead workers for whom exposure did not coincide with time of
31 pregnancy. The investigators only included pregnancies which resulted in live births. Fecundity
May 2006 6-175 DRAFT-DO NOT QUOTE OR CITE
-------
1 density ratios were 1.12 (95% CI: 0.84, 1.49), 0.96 (95% CI: 0.77, 1.19), 0.88 (95% CI: 0.70,
2 1.10) and 0.93 (95% CI: 0.76, 1.15) for blood leads <20, 20-29, 30-39, and >40 |ig/dL,
3 respectively. These results indicate that no association was found between blood lead and
4 delayed time to pregnancy. Similar results were found when duration of exposure or cumulative
5 exposure was used as the exposure metric.
6 A separate report was published in the Italian group of men included in the Asclepios
7 project (Apostoli et al., 2000). Blood lead at the time closest to conception was used as the
8 measure of exposure. Lead-exposed men (n = 251) who had experienced at least one completed
9 pregnancy were compared to nonexposed men (n = 45). Contrary to what was expected, time to
10 pregnancy was significantly shorter among couples in which the male partner was exposed to
11 lead compared to those in which the male partner was not exposed. In secondary analyses, time
12 to pregnancy was longer among men with the highest blood lead (i.e., >40 |ig/dL). Limiting
13 the analysis solely to exposed men, time to pregnancy was longer among men with higher
14 blood leads.
15 Among 502 couples identified by Sallmen et al. (2000) from the Finnish Institute of
16 Occupational Health in which the male partner was exposed to lead, time to pregnancy was
17 reduced among those with blood leads >10 |ig/dL compared to those with blood leads
18 < 10 |ig/dL. However, when blood lead was stratified, no concentration-response relationship
19 was found. Fecundity density ratios were 0.92 (95% CI: 0.73, 1.16), 0.89 (95% CI: 0.66, 1.20),
20 0.58 (95% CI: 0.33, 0.96) and 0.83 (95% CI: 0.50, 1.32) for exposures of 10-20, 21-30, 31-40,
21 and >40 |ig/dL, respectively. In this study, blood leads close to the time of conception were
22 available on 62% of men, while in 38% it was estimated using blood leads obtained at other
23 points or based on j ob descriptions.
24 Among 280 pregnancies in 133 couples in which the male partner was employed in a
25 battery plant, 127 were conceived during exposure while the remainder conceived prior to
26 exposure (Shiau et al., 2004). Time to pregnancy increased with increasing blood lead,
27 especially when blood leads were >30 |ig/dL. Fecundity density ratios were 0.50 (95% CI:
28 0.34, 0.74) and 0.38 (95% CI: 0.26, 0.56) for blood leads 30-39 and >39 |ig/dL, respectively.
29 In 41 couples, one pregnancy occurred prior to exposure and one during exposure - time to
30 pregnancy during exposure was significantly longer. Of note, this is the only study to estimate
May 2006 6-176 DRAFT-DO NOT QUOTE OR CITE
-------
1 decreases in time to pregnancy when blood lead was below 40 |ig/dL; time to pregnancy
2 increased by 0.15 months for each 1 |ig/dL increase in blood lead between 10 and 40 |ig/dL.
3
4 Reproductive History
5 Population-based birth registries in the Scandanavian countries provide data on medically
6 diagnosed pregnancies. These registries provide a basis for linking occupational data on lead
7 exposure obtained by place and duration of employment or by direct measures of blood lead
8 relative to the timing of marriage or conception. Using a roster of men employed in three battery
9 plants in Denmark, Bonde and Kolstad (1997) matched all births to the 1,349 employees when
10 they were age 20-49 years. A control group of 9,656 men who were not employed in a lead
11 industry was chosen. No associations were found between employment or, among those
12 employed in the lead industry, duration of employment in the lead industry and birth rate.
13 A similar study in Finland (Sallmen et al., 2000) examined the association between
14 conception and blood lead among men monitored for occupational exposure at the Finnish
15 Institute of Occupational Health (n = 2,111). Men were categorized as probably exposed and
16 possibly exposed based on their measured blood lead in relation to the time of marriage.
17 A nonexposed group of 681 men with blood lead < 10 |ig/dL was similarly evaluated. Among
18 men in the probable exposure group, the risk of failing to achieve a pregnancy increased with
19 increased blood lead in a monotonic concentration-response fashion. Compared to the
20 nonexposed, the risk ranged from 1.3 to 1.9 for blood leads 10-20 |ig/dL and >50 |ig/dL,
21 respectively.
22 Lin et al. (1996) linked records from the Heavy Metal Registry in New York State to birth
23 certificates from the New York State Office of Vital Statistics for the period 1981 to 1992.
24 Exposure was defined as having at least one blood lead measurement above 25 |ig/dL and
25 identified 4,256 men. A reference group of 5,148 men was frequency matched for age and
26 residence. The exposed group had fewer births than expected, and was especially pronounced
27 among men employed in the lead industry for over 5 years.
28 Among 365 men occupationally exposed to metals, Gennart et al. (1992) identified
29 74 exposed continuously for more than 1 year and with at least one blood lead measurement
30 >20 |ig/dL. Compared to a reference group with no occupational exposure, the probability of at
31 least one live birth was significantly reduced. Fertility decreased with increasing duration of
May 2006 6-177 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposure but no concentration-response relationship with blood lead was found (possibly due to
2 the small sample size of exposed men).
3 A study of men exposed to lead in a French battery plant (Coste et al., 1991) reported no
4 effect on fertility. However, this study did not adequately control for potentially confounding
5 variables, particularly those related to the women. Further, nonexposed workers were defined as
6 those with no blood leads recorded which likely resulted in exposure misclassification.
7 One potential mechanism to explain the associations between lead exposure and male
8 reproductive outcomes may be through an effect of lead on circulating pituitary and testicular
9 hormones. Several studies have evaluated this hypothesis in groups of workers (Braunstein
10 et al., 1978; Cullen et al., 1984; Erfurth et al., 2001; Ng et al., 1991; Rodamilans et al., 1988).
11 In general these studies find perturbations in concentrations of follicle stimulating hormone,
12 luteinizing hormone, and testosterone. Although many of these studies were limited by small
13 sample sizes, lack of control groups, and admixtures of exposure, taken together, they provide
14 evidence for this possible mechanism.
15
16 6.6.3.2 Genotoxicity and Chromosomal Aberrations
17 The potential genotoxicity and ability to induce chromosomal aberrations speak to the
18 mechanisms by which lead is a potential reproductive toxin. Two possible mechanisms by
19 which lead may affect reproduction are through affinity with proteins and ability to mimic the
20 actions of calcium (Silbergeld et al., 2000).
21 Data from occupational studies regarding the effects of lead on chromosomes are
22 contradictory; however, the bulk of evidence suggests that there may indeed be a genotoxic
23 effect. Early studies in occupational groups find associations between lead exposure and
24 increased frequency of sister chromatid exchanges (Grandjean et al., 1983; Huang et al., 1988;
25 Leal-Garza et al., 1986; Maki-Paakkanen et al., 1981). Similar results were found in a group of
26 environmentally-exposed children with blood leads ranging from 30 to 63 |ig/dL (Dalpra et al.,
27 1983). Increased frequencies of chromosomal aberrations, particularly chromatid aberrations,
28 were found in battery plant workers and were correlated with increased blood lead (Huang et al.,
29 1988). A more marked increase was found when blood leads were above 50 |ig/dL. Other
30 occupational studies find similar associations (Al-Hakkak et al., 1986; Forni et al., 1976, 1980;
31 Nordenson et al., 1978; Schwanitz et al., 1970). Other studies find no evidence of chromosomal
May 2006 6-178 DRAFT-DO NOT QUOTE OR CITE
-------
1 aberrations when blood leads ranged from 38 to 120 |ig/dL (Bauchinger et al., 1977; Maki-
2 Paakkanen et al., 1981; O'Riordan and Evans, 1974; Schmid et al., 1972; Schwanitz et al., 1975).
3 More recently, two studies in battery plant workers (mean blood lead 40.1 |ig/dL) and controls
4 (mean blood lead 9.8 |ig/dL) found an increase in high-frequency cells and sister chromatid
5 exchanges among the workers, indicating the cytogenetic toxicity of lead (Duydu et al., 2001,
6 2005). An increase in sister chromatid exchanges, although not statistically significant, was also
7 found in individuals exposed to lead and/or alcohol and tobacco (Rajah and Ahuja, 1995, 1996).
8 In the Lithuanian populations exposed to either environmental or occupational lead, a higher
9 incidence of sister chromotid exchanges and chromosomal aberrations was found (Lazutka et al.,
10 1999), although these populations were also exposed to other potentially genotoxic substances.
11 Recent data also indicates that lead may inhibit DNA repair responses among lead-exposed
12 workers (Karakaya et al., 2005).
13 Occupational exposure to lead, particularly when blood leads were high (i.e., over
14 40 |ig/dL) was associated with increased mitotic activity in peripheral lymphocytes and with an
15 increased rate of abnormal mitosis (Forni et al., 1976; Minozzo et al., 2004; Sarto et al., 1978;
16 Schwanitz et al., 1970). Again, to the extent these changes influence the production of gametes,
17 this is a potential mechanism explaining associations between lead exposure and decreased male
18 fecundity.
19
20 Issues Concerning Studies of Male Fecundity Related to Lead Exposure
21 In examining studies of fecundity and fertility, several issues relating to interpretation and
22 bias must be addressed. Infertility usually is defined as 12 months of continuous unprotected
23 intercourse without pregnancy. Fecundity represents both a characteristic of the individuals and
24 a characteristic of a couple, meaning that both partners must be biologically able to procreate.
25 Thus, one possible explanation for observations of reduced fecundity related to occupational lead
26 exposure in the male partner is the exposure he "takes home" via transport of dust on clothing
27 and shoes, ultimately resulting in an effect related to the female partner. Other possible
28 interpretations need to account for measurement error, especially related to the outcomes of
29 reproductive history and time to pregnancy, bias in the selection of subjects for study, and the
30 control for potentially confounding variables.
May 2006 6-179 DRAFT-DO NOT QUOTE OR CITE
-------
1 Both reproductive history and time to pregnancy are subject to errors of recall and rely on
2 the veracity of the subject. Several studies have evaluated recall and veracity of the male partner
3 using the female partner as the "gold standard." In general, these find good reliability between
4 the male and female (Weinberg et al., 1993, 1994). Nevertheless, it is possible, at least for
5 studies using men as the sole informant, that the number of pregnancies a man has fathered is
6 underreported. If reporting is nondifferential with regard to lead exposure, then associations will
7 generally be biased towards the null value; however, since characteristics such as social
8 circumstances, ethnicity, and age may affect both exposure and reporting, it is difficult to
9 evaluate the role of bias.
10 It was not clear from many of the studies that men with medical conditions which affect
11 fecundity/fertility were excluded. Further, several prescription and over-the-counter medications
12 also affect fecundity as does a history of surgery in the genital area (e.g., varicocele). To the
13 extent that these conditions are related to the absence of employment in lead-industries, then the
14 results may be subject to a type of "healthy worker" effect. Because it is unclear whether many
15 of these studies asked about these conditions, this cannot be ruled out as a possible source
16 of bias.
17 In retrospective studies it is often useful to use the outcome of the most recent pregnancy
18 in the primary analysis. The reason for this is to reduce any possible recall bias. This type of
19 bias may also be an issue in studies which use occupational registry data, i.e., men may have
20 fathered an additional pregnancy after employment in the industry ceased.
21 Variables considered potential confounders in studies of fertility and fecundity include
22 sociodemographic characteristics (e.g., age, ethnicity, education, occupation); prenatal and recent
23 lifestyle variables such as cigarette smoking, alcohol use, and medication use; exposures through
24 occupation and hobby, and recent medication use. Also important in these studies is control for
25 factors which may affect the partner's fertility, e.g., cigarette smoking. Many of the studies
26 reviewed did not carefully measure or adjust for confounding variables.
27 The issues presented above potentially limit the interpretation of results from studies
28 examining the association of lead exposure with male fecundity and fertility. Nevertheless, most
29 studies find small associations between lead exposure at high levels (i.e., >45 |ig/dL) and slightly
30 reduced male fecundity or fertility.
31
May 2006 6-180 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.6.3.3 Effects on Female Reproductive Function
2 Few data directly address the effects of lead exposure on fecundity in the female.
3 A recent retrospective study of time to pregnancy among wives of lead workers provides limited
4 support that lead exposure is associated with increased time to pregnancy. Fecundity density
5 ratios were 0.92 (95% CI: 0.72, 0.16), 0.89 (95% CI: 0.66, 1.20), 0.58 (95% CI: 0.33, 0.96),
6 and 0.83 (95% CI: 0.50, 1.32) for blood leads in the male partners of 10-20, 21-30, 31-38 and
7 >39 |ig/dL compared to <10 |ig/dL, respectively. Note however, that exposure here is measured
8 in the male partners and not the females.
9 Time to pregnancy was evaluated in 121 women biologically monitored for lead exposure
10 at the Finnish Institute of Occupational Health between 1973 and 1983 (Sallmen et al., 1995).
11 Fecundity did not differ with level of exposure (defined as <10 |ig/dL, 10-19 |ig/dL and
12 >20 |ig/dL), but among women with blood leads between 29 and 50 |ig/dL, there was a
13 suggestion of reduced fecundity (longer time to pregnancy). However, only a small number of
14 subjects (n = 8) were exposed in this range.
15 In the limited number of studies, there is little evidence regarding the associations
16 between lead exposure and fertility in the female to draw any conclusions at this time.
17
18 6.6.4 Spontaneous Abortion
19 6.6.4.1 Spontaneous Abortion and Maternal Exposure to Lead
20 Historical observations suggest increased rates of spontaneous abortion among lead-
21 exposed women, particularly those employed in cottage industries (Rom, 1976). Two early
22 studies in a smelter town in Sweden (Nordstrom et al., 1978a, 1979) suggest elevated rates of
23 spontaneous abortion among female employees at the smelter and among female residents living
24 in close proximity to the smelter. Neither of these studies used biological markers of lead
25 exposure. Moreover, the Swedish smelter study included other exposures such as arsenic, zinc,
26 and cadmium; thus the conclusions for these analyses should be tempered.
27 In contrast, a prospective study in and around a smelter town in Port Pirie, Australia
28 (McMichael et al., 1986) did not find an association between blood lead concentration and
29 spontaneous abortion. However, it was likely that complete ascertainment of spontaneous
30 abortions was not obtained (Rowland and Wilcox, 1987) since most women were recruited for
31 this study after the first trimester of pregnancy. A retrospective cohort study in two towns in the
May 2006 6-181 DRAFT-DO NOT QUOTE OR CITE
-------
1 former Yugoslavia (Murphy et al., 1990) showed no associations between lead exposure and
2 spontaneous abortion in the first reported pregnancy. One of these towns was a smelter town
3 with relatively high lead exposure (at recruitment during mid-pregnancy, the mean blood lead
4 concentration was 17.1 |ig/dL, while in the control town the mean blood lead was 5.1 jig/dL).
5 A similar study in Poland (Laudanski et al., 1991) evaluated the association between lead-
6 exposed and nonexposed areas for their reproductive histories. Among women in the exposed
7 areas, 11% reported having at least one prior spontaneous abortion, compared to 19.5% of
8 women in the unexposed areas.
9 Two studies in Finland (Lindbohm et al., 1991a; Taskinen, 1988) used hospital registry
10 data to ascertain women with either spontaneous abortions or livebirths. Either maternal job
11 histories (Taskinen, 1988) or both maternal and paternal job histories were obtained from a
12 registry of occupational blood lead measurements. Neither study found evidence of an
13 association between maternal exposure and spontaneous abortion. In the Lindbohm et al.
14 (199 la) study, maternal exposure was extrapolated from the occupation of the father.
15 In Bulgaria, pregnant women residing in or near lead smelting areas or petrochemical
16 plants were prospectively followed for pregnancy outcomes (Tabacova and Balabaeva, 1993).
17 The investigators compared blood leads in those women with spontaneous abortions and those
18 without. Blood lead concentrations in cases were significantly higher than in controls (mean
19 blood lead 7.1 |ig/dL versus 5.2 |ig/dL, respectively). However, this study did not fully describe
20 the selection of women nor the definition for cases.
21 Women employed by the U.S. Forest Service and exposed to lead-based paint (to mark
22 trees for clearing) were studied using self-reported questionnaires (Driscoll, 1998). Adjustment
23 was made for potential confounders and generalized estimating equations were used to adjust for
24 multiple pregnancies per woman. Significant associations were found for three types of paint
25 containing lead pigment (odds ratios of 4.3 [95% CI: 2.0, 9.3], 2.0 [95% CI: 1.2, 3.3] and
26 1.8 [95% CI: 1.2, 2.6]). While these findings are intriguing, the response rate was only 59%
27 (with no evaluation of selection bias) and the paint also contained solvents thought to be
28 associated with spontaneous abortions.
29 Borja-Aburto et al. (1999) examined the association between blood lead concentrations
30 and spontaneous abortions in a nested case-control study using incidence density methods and
31 matching for age, calendar time of study entry, public versus private clinic, and gestational age at
May 2006 6-182 DRAFT-DO NOT QUOTE OR CITE
-------
1 study entry. They ascertained 668 women during the first trimester of pregnancy in Mexico
2 City. After contacting women biweekly to update pregnancy status, they found 35 cases (6.4%)
3 of spontaneous abortion among women not lost to follow up. An odds ratio of 1.8 (95% CI: 1.1,
4 3.1) per 5 |ig/dL increase in blood lead was observed after adjustment for spermicide use, active
5 and passive smoking, use of alcohol and coffee, maternal age, education, income, physical
6 activity, hair dye use, use of video display terminals, and medical conditions. Mean blood lead
7 in cases (12.0 |ig/dL, range 3.1-29 |ig/dL) was slightly higher than in controls (10.1 |ig/dL, range
8 1.3-26 |ig/dL). Further, after categorizing blood lead into 5 |ig/dL intervals, a concentration-
9 response relationship was evident.
10 More recently, a small study of 57 female workers in a battery plant in China and
11 62 controls found that 6 spontaneous abortions occurred in the exposed group, compared to none
12 in the controls (Tang and Zu, 2003). A long-term follow-up of survivors of acute plumbism
13 (Hu, 1991) found increased risk of spontaneous abortions or stillbirths (odds ratio of 1.6
14 [95% CI: 0.6,4.0]). Although the study was based on small numbers, the data suggest a
15 persistent association between childhood exposure and outcomes later in life.
16 A review of eight studies (Borja-Aburto et al., 1999; Driscoll, 1998; Laudanski et al.,
17 1991; Lindbohm et al., 1991a; McMichael et al., 1986; Murphy et al., 1990; Tabacova and
18 Balabaeva, 1993; Taskinen, 1988) evaluating maternal exposure to lead (blood lead >30 |ig/dL)
19 and spontaneous abortion concluded that there was little evidence that lead exposure at these
20 relatively high levels was associated with an increased risk in spontaneous abortions (Hertz-
21 Picciotto, 2000). However, Hertz-Picciotto also concluded that methodological difficulties in
22 most of these studies (i.e., small sample sizes, inadequate ascertainment of outcome, and possible
23 residual confounding) limited the confidence in these data. Further, she noted that exposure in
24 many of these studies was either measured in an ecologic fashion or biological measures were
25 available, but they were not ascertained during a biologically meaningful period.
26 Collectively, there is little evidence to support an association between lead exposure in the
27 female and spontaneous abortion. The only well-designed study which finds an association is
28 that of Borja-Aburto et al. (1999); however, these results need to be confirmed in other
29 populations. Studies of spontaneous abortion need be done carefully to avoid possible bias due
30 to recall, use of pregnancies other than the first, and confounding. Retrospective studies, for
31 example, should take full pregnancy histories, including probing for spontaneous abortions
May 2006 6-183 DRAFT-DO NOT QUOTE OR CITE
-------
1 versus induced abortions versus stillbirths. In some cultures, for example, induced abortions are
2 frowned upon and women may report spontaneous abortions instead. Additionally, some women
3 may confuse a stillbirth with spontaneous abortion, especially if she is unable to adequately date
4 her pregnancy using date of last menstrual period. Although the use of the most recent
5 pregnancy may curtail problems of recall, other concerns dictate that the first pregnancy be used
6 in studies of spontaneous abortion because the risk of subsequent spontaneous abortion depends
7 on the history of spontaneous abortion. Finally, while few variables are known confounders of
8 this relationship, the following should be controlled: maternal age, education and other
9 socioeconomic indicators, cigarette smoking, and alcohol use. Several studies of spontaneous
10 abortion did not properly adjust for these potentially confounding variables.
11 One final concern regards the type of spontaneous abortion. Very early spontaneous
12 abortions, i.e., before a clinical pregnancy is diagnosed, may be missed; assuming, however, that
13 both exposed and unexposed women have the same rates of early spontaneous abortions, this
14 would bias the association towards the null. Indeed, this may be true, as many very early
15 spontaneous abortions may be chromosomally abnormal and probably not attributable to lead
16 exposure.
17
18 6.6.4.2 Spontaneous Abortion and Paternal Exposure to Lead
19 Three studies evaluated paternal exposure to lead and spontaneous abortion. Lindbohm
20 et al. (1991a), using national databases to identify pregnancy outcomes among 99,186 births in
21 Finland, found no association between paternal employment in jobs with lead exposure and
22 spontaneous abortion (odds ratio of 0.9 [95% CI: 0.9, 1.0]). In a follow up case-control study
23 (Lindbohm et al., 1991b), they ascertained paternal exposure status during the period of
24 spermatogenesis in 213 cases of spontaneous abortion and 500 controls. Exposure was
25 ascertained using blood lead concentrations measured during spermatogenesis for 6% of men;
26 for the remaining 94%, exposure was estimated using a regression model where the independent
27 variables were blood leads measured either prior to or after the period of spermatogenesis.
28 Blood lead (either measured or estimated) was not associated with spontaneous abortion.
29 When analysis was restricted to men with measured blood lead, blood lead concentrations
30 >30 |ig/dL were associated with an increased odds of spontaneous abortion (odds ratio of
31 3.8 [95% CI: 1.2, 2.0]); however, this result was only based on 12 cases and 6 controls.
May 2006 6-184 DRAFT-DO NOT QUOTE OR CITE
-------
1 The third study (Alexander et al., 1996b) found no association between men employed in
2 a lead smelter and spontaneous abortion. For men with "moderate" exposure jobs the estimated
3 odds ratio was 0.8 (95% CI: 0.5, 1.5) and for those with "high" exposure jobs, the estimated
4 odds ratio was 1.4 (95% CI: 0.7, 2.5). Further when blood lead 1 year prior to the pregnancy
5 was used as the exposure measure, no increased odds of spontaneous abortion was found. These
6 results, however, are based on a low participation rate in eligible workers (37%) and should be
7 interpreted with caution. Overall, the available studies provide little evidence for an association
8 between lead exposure in the male and spontaneous abortions.
9
10 6.6.5 Fetal Growth
11 The results of epidemiologic studies regarding the association between lead exposure and
12 birth weight are inconsistent. Cross-sectional studies (Clark, 1977; Gershanik et al., 1974;
13 Moore et al., 1982; Rajegowda et al., 1972) did not find significant correlations between blood
14 lead and birth weight, nor did a study using placental lead as the exposure variable (Wibberley
15 et al., 1977). A case-control study (Bogden et al., 1978) comparing 25 low birth weight babies
16 (1,500-2,500 grams) to 25 controls (>2,500 grams) matched on maternal age, race and social
17 class found a small, nonsignificant difference in maternal and cord blood leads. Mean maternal
18 blood lead concentrations were 16.2 + 4.5 |ig/dL and 15.3 + 5.2 |ig/dL and mean cord blood
19 leads were 13.8 + 4.4 |ig/dL and 13.1 + 4.3 |ig/dL in cases and controls, respectively. A further
20 study (Huel et al., 1981) found no differences in maternal and fetal hair lead concentrations
21 between infants born small-for-gestational-age compared to those of normal birth weight.
22 In 1984, Needleman et al. (1984) reported on a cross-sectional study of 5,183 births of at
23 least 20 weeks gestation in Boston, MA. No associations were found between the proportion of
24 births under 2,500 grams and cord blood lead. Exposure levels in this study were relatively low
25 for the time; cord blood leads ranged from <1 to 35 |ig/dL. A reanalysis of these data found no
26 relationship between cord blood lead and birth weight when birth weight was considered as a
27 continuous variable (Bellinger, et al., 1991). However, when birth weight was categorized as
28 low birth weight (<2,500 grams), small for gestational age (<10th percentile for gestational age),
29 or intrauterine growth retarded (>2 standard deviations below the mean for gestational age),
30 relative risks of 1.6 (95% CI: 1.0, 2.6), 1.2 (95% CI: 0.8, 1.6) and 1.9 (95% CI: 1.0, 3.4),
31 respectively, were found for each 10 |ig/dL increase in cord blood lead levels. Increased relative
May 2006 6-185 DRAFT-DO NOT QUOTE OR CITE
-------
1 risks also were found for cord blood lead levels > 15 |ig/dL, compared to cord blood lead
2 <15 |ig/dL; however, only 83 of the 5,183 women had exposures in the high range, resulting in
3 imprecise estimates. These data suggest that lead-related modest reductions in birth weight are
4 perhaps plausible when birth weight is expressed as a function of gestational age.
5 The prospective study of lead exposure in and around Port Pirie, Australia (McMichael
6 et al., 1986) followed 749 pregnancies of at least 20 weeks duration. Mean maternal blood leads
7 at mid-pregnancy were 10.1 |ig/dL and 7.0 |ig/dL for women residing in Port Pirie and the
8 surrounding communities, respectively. After excluding 9 sets of twins and 10 cases for which
9 the maternal last menstrual period could not be ascertained, no relationship was found between
10 either cord blood lead or maternal blood lead measured at mid-pregnancy or at delivery and birth
11 weight in a multivariate regression model controlling for known determinants of birth weight.
12 A prospective study in two towns in Kosovo, Yugoslavia evaluated relationships between
13 birth weight (adjusted for gestational age using last menstrual period) and (a) maternal blood
14 lead at mid-pregnancy and delivery and (b) cord blood lead (Factor-Litvak et al., 1991). The
15 towns were vastly different in exposure patterns, as one was the site of a lead smelter, refinery
16 and battery plant (n = 401, mean mid-pregnancy blood lead 19.0 |ig/dL) and one was relatively
17 unexposed (n = 506, mean mid-pregnancy blood lead 5.6 |ig/dL). No associations were found
18 between any of the biomarkers of lead and birth weight in either crude analyses or analyses
19 adjusted for potentially confounding variables.
20 While the aforementioned studies generally found no association between environmental
21 lead exposure and birth weight, three other studies have shown large reductions in birth weight
22 related to lead exposure. These studies, however, have questionable study designs. Nordstrom
23 et al. (1978b, 1979) in a series of ecologic analyses known as the Swedish Smelter Study, found
24 significant reductions in birth weight between the offspring of women either working at or living
25 in close proximity to the smelter. The 125 gram deficit in birth weight among the offspring of
26 women living closest to the smelter was confined to those with parity three or more, an
27 observation which does not appear to be biologically plausible. Moreover, the ecological nature
28 of the study did not allow for individual measurements of blood lead or for control of potentially
29 confounding variables. Hence, while suggestive, these data do not provide strong evidence for a
30 causal association between lead exposure and birth weight.
May 2006 6-186 DRAFT-DO NOT QUOTE OR CITE
-------
1 In a cross-sectional study of 100 "normal" singleton births, a negative correlation was
2 found between placental lead concentration and birth weight (Ward et al., 1987). Mean placental
3 lead concentration in 21 infants weighing less than 3,000 grams was 2.35 + 0.9 |ig/g compared to
4 1.12 + 0.4 |ig/g in 10 infants weighting more than 4,000 grams. This study has several
5 limitations. First, no statistical adjustment was made for multiple comparisons (many exposures
6 were studied). Second, potentially confounding variables were not controlled. Third, only 31 of
7 the 100 infants, representing the extremes of the birth weight distribution, were studied. Hence,
8 this study also does not provide strong evidence for an association.
9 In Cincinnati, OH, the association between lead exposure and birth weight was examined
10 in offspring of a cohort of young (mean maternal age = 22.7 years), inner city women,
11 85% African American, 86% on public assistance, with a mean IQ of 75 (Dietrich et al., 1987a).
12 The mean gestational period of the neonates, as determined by physical examination, was
13 39.5 weeks. A decrement in birth weight of 172 grams was associated with an increase in blood
14 lead from 10 to 30 |ig/dL. Lead exposure in this group was relatively low with a mean blood
15 lead of 8.0 + 3.7 |ig/dL. In a sample of women from this cohort, the interaction between blood
16 lead and maternal age was significantly associated with birth weight; the effect varied from a
17 decrease of 64 grams for 18 year old mothers to 660 grams for 30 year old mothers, as blood lead
18 rose from 10 to 30 |ig/dL (Bornschein et al., 1989). Although the Cincinnati study is highly
19 suggestive of an effect (especially an effect which varies by maternal age) three factors should be
20 considered in the interpretation of their findings. First, length of gestation was estimated by
21 examining the neurological and physical maturity of the neonate (Ballard et al., 1979); other
22 investigators find assessment of gestational age using this scale overestimates gestational age in
23 preterm infants (Constantine et al., 1987; Kramer et al., 1988; Shukla et al., 1987; Spinnato et al.,
24 1984). Second, it is possible that the association between lead and birth weight differs by
25 maternal characteristics such as race, ethnicity, and SES; however, no study has provided a
26 population sufficiently heterogeneous to examine this possible source of difference. Finally, it is
27 possible that confounding by unmeasured maternal lifestyle characteristics may account for the
28 reported association.
29 A hospital-based study of cord blood lead and pregnancy outcomes in Quebec, Canada,
30 between June 1993 and January 1995 found a slight increase in cord blood lead levels among
31 infants with birth weight <2,500 grams (Rhainds et al., 1999). For those infants with birth
May 2006 6-187 DRAFT-DO NOT QUOTE OR CITE
-------
1 weight <2,500 grams, the geometric mean blood lead was 1.8 |ig/dL (95% CI: 1.6, 2.9)
2 compared to 1.6 |ig/dL (95% CI: 1.5, 1.7), 1.6 |ig/dL (95% CI: 1.5, 1.7), and 1.5 |ig/dL
3 (95% CI: 1.5, 1.6) among those with birth weights 2,500-2,990, 3,000-3,499, and >3,500 grams,
4 respectively. Although suggestive, the study did not control for potentially confounding
5 variables. The investigators also measured cord blood levels of mercury and organochlorine
6 compounds, and observed that mean levels of these toxicants were higher as well in infants who
7 weighed <2,500 g.
8 More recently Irgens et al. (1998) using data from the Norwegian birth registry found that
9 women occupationally exposed to lead (none/low compared to moderate/high) were more likely
10 to deliver a low birth weight infant (odds ratio of 1.3 [95% CI: 1.1, 1.6]). No association was
11 found for paternal occupational lead exposure. Parental occupational exposure to lead was not
12 associated with low birth weight in the Baltimore-Washington Infant Study database (Min et al.,
13 1996), although subgroup analysis suggested that high paternal exposure may be associated with
14 small-for-gestational-age infants (odds ratio of 2.9 [95% CI: 0.9, 9.2]). Similar findings were
15 reported by Lin et al. (1998) who compared offspring of lead-exposed workers with those of bus
16 drivers. No associations were reported between lead exposure and low birth weight except
17 among the group of men with blood lead levels >25 |ig/dL for over 5 years (relative risk of 3.4
18 [95% CI: 1.4,8.4]).
19 Using bone lead as the metric of exposure, Gonzalez-Cossio et al. (1997) found
20 associations with tibia bone lead (but not with patella bone lead or umbilical cord blood lead)
21 and reduced birth weight. Bone lead was measured one month after delivery. Infants with tibia
22 bone lead in the highest quartile (> 15.15 jig lead/g bone mineral) were, on average, 156 g lighter
23 than those in the lowest quartile (<4.50 jig lead/g bone mineral). Further analyses of these data
24 (Hernandez-Avila et al., 2002) found an association between infants in the highest quintile of
25 tibia bone lead and shorter birth length (odds ratio of 1.8 [95% CI: 1.1, 3.2]).
26 Two studies have considered the relationship between lead exposure and head
27 circumference (Hernandez-Avila et al., 2002). Among 233 women in Mexico City, high
28 maternal patella bone lead was associated with increased risk of a low head circumference score
29 at delivery (1.02 per jig lead / g bone mineral [95% CI: 1.01, 1.04]). Similar findings were
30 reported by Rothenberg et al. (1999) who found a reduction in six-month head circumference of
31 1.9 cm (95% CI: 0.9, 3.0) as maternal blood lead rose from 1 to 35 |ig/dL. This study, however
May 2006 6-188 DRAFT-DO NOT QUOTE OR CITE
-------
1 was plagued by multiple comparisons as head circumference was measured nine times and
2 prenatal blood lead six times - only one statistically significant result was found.
3 Potential confounders need to be adjusted for to properly assess the relationship between
4 lead exposure and fetal growth. Factors consistently associated with fetal growth include gender,
5 ethnic origin, maternal body build (i.e., pre-pregnancy weight, height), parity, SES, gestational
6 weight gain and nutritional intake during pregnancy, maternal illness, and cigarette smoking
7 (Kramer, 1987). Factors with less established associations include alcohol consumption (Kline
8 et al., 1987; Kramer, 1987) and street drug use (Kline et al., 1987; Kramer, 1987; Zuckerman
9 et al., 1989). To the extent that these factors are associated with blood lead as well as with fetal
10 growth, they must be accounted for in the analysis.
11 A further problem pertains to the measure of exposure used in most of these studies.
12 Blood lead concentration reflects relatively recent (i.e. in the past 90 days) exposure; thus it does
13 not reflect exposure over the mother's lifetime. Indeed, there is some evidence suggesting that
14 bone lead, a measure of cumulative exposure, may be mobilized during pregnancy (Silbergeld,
15 1991). A single blood lead measure will not reflect such mobilization, particularly if
16 mobilization is not constant over the course of pregnancy. Thus, in all studies, excepting that of
17 Gonzalez-Cossio et al. (1997), exposure may be misclassified. The effect of such
18 misclassification will be to strengthen the findings of studies which support the null hypothesis.
19 For those studies which find an association between blood lead concentration and fetal growth,
20 the inference would be to higher exposure levels. It is difficult to examine the extent of this
21 misclassification as no studies have sufficient numbers of serial blood lead measures to estimate
22 the variation during pregnancy.
23 Studies to date are inconsistent regarding the association between lead exposure and birth
24 weight. Several large prospective studies find no association (Factor-Litvak et al., 1991;
25 McMichael et al., 1986), while at least one (Bornschein et al., 1989) did find an association in
26 specific subgroups of women. However, there is limited evidence (Bellinger et al., 1991) for an
27 association between lead exposure and low birth weight (i.e., <2,500 g), small for gestational age
28 (i.e., <10th percentile for gestational age), and intrauterine growth retardation (i.e., >2 standard
29 deviations below the mean for gestational age). These prospective studies were all well-
30 conducted, adequately measured exposure and outcome, and controlled for potential confounding
31 variables. They did, however, take place in very different populations, suggesting that the
May 2006 6-189 DRAFT-DO NOT QUOTE OR CITE
-------
1 association between lead and fetal growth may depend on the population being studied. The
2 Yugoslavia study (Factor-Litvak et al., 1991) took place in two towns in Kosovo, Yugoslavia,
3 which were divergent on exposure and somewhat comparable on other variables. The Port Pirie
4 study took place in a middle class area of Australia (McMichael et al., 1986). The Boston study
5 (Bellinger et al., 1991) took place in a range of social strata in Boston; the exposure in the
6 highest social group was attributable to renovation of older housing stock. Finally, in the
7 Cincinnati study (Bornschein et al., 1989), the study sample was comprised of lower social class
8 African Americans; the mean IQ of the mothers was 75. It is possible that in this latter study,
9 there was some unmeasured variable which accounts for the observed interaction. Thus, the
10 evidence suggests at most a small effect of lead exposure on birth weight and possibly a small
11 association between lead exposure and several dichotomized measures of fetal growth.
12
13 6.6.6 Preterm Delivery
14 Early evidence regarding an association between environmental lead exposure and
15 preterm delivery was inconsistent. In 1976, Fahim et al. found a preterm delivery rate of 13% in
16 254 pregnant women living near a lead mining community in Missouri, compared to 3% in
17 249 women living in a control location. These investigators also found higher concentrations of
18 lead in amniotic membrane, but not higher placental or cord lead in preterm compared to term
19 deliveries, regardless of the women's residential locale. This observation prompted other studies
20 of lead and preterm delivery.
21 Of the cross-sectional studies, the three which show no association employed cord blood
22 lead as the exposure measure and restricted gestational age (Angell and Lavery, 1982; Bellinger
23 et al., 1991; Needleman et al., 1984; Rajegowda et al., 1972). In contrast, three other studies
24 used different exposure markers (placental lead, maternal and cord blood lead, and maternal and
25 fetal hair lead) and found statistically significant associations (Huel et al., 1981; Moore et al.,
26 1982; Ward et al., 1987). Other studies evaluated pregnancy outcomes in relation to maternal
27 delivery blood lead (McMichael et al., 1986; Rahman and Hakeem, 2003).
28 Of the prospective studies, the Cincinnati study (Bornschein et al., 1989) found no
29 association between both maternal blood lead at mid-pregnancy or maternal blood lead during
30 the neonatal period (10 days post delivery) and preterm delivery. However, gestational age was
31 estimated by examining the neurological and physical maturity of the neonates (which tends to
May 2006 6-190 DRAFT-DO NOT QUOTE OR CITE
-------
1 overestimate gestational age) and not actual dates. In Port Pirie, Australia (McMichael et al.,
2 1986), a concentration-response relationship between maternal delivery blood lead and preterm
3 delivery was reported. Odds ratios ranged from 2.1 to 4.4 in women with blood leads of
4 7.7-10.6 |ig/dL and >13.5 |ig/dL, respectively, compared to those with blood lead <7.7 |ig/dL.
5 Savitz et al. (1990) used data from the National Natality Survey and found an odds ratio of
6 2.3 (95% CI: 0.7, 7.0) between maternal occupational exposure to lead and preterm delivery;
7 however, the estimated odds ratio was based on only 7 cases. In the Yugoslavia study (Factor-
8 Litvak et al., 1991) no associations were found between cord blood lead or blood lead measured
9 at mid pregnancy or delivery and either preterm delivery (defined as delivery <37 completed
10 weeks) or gestational age. A registry study in Norway (Irgens et al., 1998) which linked births
11 between 1970 and 1993 to census-based occupation records found a slightly increased odds of
12 preterm delivery among moderate/high lead-exposed women, compared to those with no or low
13 exposure (odds ratio of 1.13 [95% CI: 0.98, 1.29]). Paternal exposure was not found to increase
14 the risk of preterm birth.
15 An ecologic study in Canada (Philion et al., 1997) examined 30 years of birth records,
16 corresponding to 9,329 births in a smelter city and a control city. Outcome variables were
17 intrauterine growth retardation defined as small for gestational age. The odds ratio for
18 intrauterine growth retardation in the smelter city compared to the control city was 0.83.
19 Further analysis, stratifying time into 5-year intervals also revealed no associations.
20 A case control study in Mexico City (Torres-Sanchez et al., 1999) evaluated 161 preterm
21 births and 459 full term births. Cord blood lead was significantly higher in the preterm group
22 (9.8 + 2.0 |ig/dL) compared to the full term group (8.4 + 2.2 |ig/dL) only among primiparous
23 women.
24 Using data from the Baltimore-Washington Infant Study database, Min et al. (1996)
25 found a small association between paternal occupational exposure in the high range and preterm
26 delivery with appropriate weight for gestational age (odds ratio of 2.1 [95% CI: 0.7, 6.5]) and
27 preterm delivery with small for gestational age (odds ratio of 2.4 [95% CI: 1.9, 3.1]). Similar
28 findings were reported by Lin et al. (1998). Comparing the offspring of lead exposed workers
29 with those of bus drivers, they found an elevated relative risk for preterm delivery (3.0 [95% CI:
30 1.6, 6.8]) only among men with blood leads >25 |ig/dL for over 5 years.
May 2006 6-191 DRAFT-DO NOT QUOTE OR CITE
-------
1 In contrast to fetal growth, few factors are consistently related to preterm delivery; thus in
2 both developed and developing countries the majority of preterm deliveries remain unexplained
3 (Kramer 1987; Van Den Berg and Oechsli, 1984). Factors which are inconsistently associated
4 with preterm delivery include maternal age, SES, pre-pregnant weight, prior history of preterm
5 delivery or spontaneous abortion, and cigarette smoking (Kline et al., 1987; Kramer, 1987).
6 Thus, these factors must be evaluated as potentially confounding factors in studies of lead
7 exposure and preterm delivery.
8 For preterm delivery, or reduced length of gestation, the evidence for an association with
9 lead exposure is contradictory. Several of the prospective studies find no evidence of an
10 association (Bornschein et al., 1989; Factor-Litvak et al., 1991) while one finds a concentration-
11 response relationship (McMichael et al., 1986). Further, two well-done registry studies (Irgens
12 et al., 1998; Savitz et al., 1990) find some evidence of an association, albeit the number of
13 exposed cases was small. It seems unlikely that the association between lead exposure and
14 preterm delivery is large, but, more research is clearly necessary.
15
16 6.6.7 Congenital Abnormalities
17 Needleman et al. (1984) found an association between cord blood lead and minor
18 congenital anomalies among 4,354 infants born in a single hospital in Boston, MA. All data
19 were obtained from hospital records, not from direct examination of the infants. The most
20 common anomalies were hemangiomas, lymphangiomas, minor skin problems (tags and
21 papillae), and undescended testicles. Blood lead levels were not found to be associated with
22 individual anomalies.
23 More recently, a number of studies have considered parental lead related to occupational
24 exposure and risk of congenital anomalies in the offspring. In Finland, Sallmen et al. (1992)
25 evaluated the associations between congenital malformations and paternal exposure during the
26 time of spermatogenesis. The overall estimated unadjusted odds ratio for men with blood lead
27 levels >20 |ig/dL was 2.4 (95% CI: 0.9, 6.5). Due to small sample sizes, the investigators could
28 only adjust for one potentially confounding factor at a time; this resulted in odds ratios ranging
29 from 1.9 to 3.2. Of note is the lack of consistency of malformations among the five men with the
30 highest blood lead. The malformation observed included congenital heart disease, oral cleft, club
31 foot, polydactyly, and anomalies of the adrenal gland. The breadth of these anomalies suggests
May 2006 6-192 DRAFT-DO NOT QUOTE OR CITE
-------
1 either that lead affects physical development throughout gestation or that this association
2 represents a chance finding. Among 2,021 pregnancies, Alexander et al. (1996b) found slightly
3 elevated odds ratios for congenital defects among men in the lead smelting industry with
4 moderate exposure (odds ratio of 1.9 [95% CI: 0.6, 6.3]) and high exposure (odds ratio of
5 2.7 [95% CI: 0.7, 9.6]). These estimates are based on 30 birth defects and 12 stillbirths.
6 No analyses were presented which considered individual birth defects. In Norway, neither
7 maternal (odds ratio of 1.25 [95% CI: 0.8, 1.9]) nor paternal (odds ratio of 0.94 [95% CI:
8 0.8, 1.1]) occupational lead exposure was associated with serious birth defects (Irgens et al.,
9 1998). Similar results were reported by Kristensen et al. (1993) between paternal lead exposure
10 and birth defects, with the exception of a fourfold increase in the risk of cleft lip among male
11 offspring.
12 The risk of parental lead exposure and neural tube defects was evaluated in a case-control
13 study of 88,449 births (363 neural tube defects) over a 25-year period in Fylde, England (Bound
14 et al., 1997). Women living in areas in which the water lead concentration was >10 |ig/L were
15 more likely to deliver a child with a neural tube defect. The association was consistent for
16 anencephaly (n = 169) and spina bifida/cranium bifidum (n = 195), even after adjusting for social
17 class. These authors posit that the association could be a direct effect of lead on neural tube
18 closure or an indirect effect, the latter meaning a reduction in uptake of zinc (due to lead
19 exposure) leading to a reduction in folate uptake. Irgens et al. (1998) partially confirmed these
20 effects on neural tube defects in mothers occupationally-exposed to lead (relative risk of 2.87
21 [95% CI: 1.05, 6.38]), but not for paternal lead exposure.
22 The association between total anomalous pulmonary venous return and parental lead
23 exposure during pregnancy (self reported, obtained from industrial hygiene measures, or from a
24 job exposure matrix) was examined in the Baltimore-Washington Infant Study (Jackson et al.,
25 2004). In this case-control study, maternal periconceptional (i.e., 3 months prior to conception
26 through the first trimester) exposure to lead resulted in an estimated odds ratio of 1.57 (95% CI:
27 0.64, 3.47). For lead-exposed men, the estimated odds ratio was 1.83 (95% CI: 1.00, 3.42).
28 Findings from this study support a possible association between paternal lead exposure and total
29 anomalous pulmonary venous return.
30 Taken together, the evidence suggests few associations between periconceptional or
31 prenatal exposure to lead and congenital anomalies. There is a suggestion of small associations
May 2006 6-193 DRAFT-DO NOT QUOTE OR CITE
-------
1 with high levels of exposure, but many of those studies relied on occupational histories rather
2 than on actual measures of blood lead levels.
3
4 6.6.8 Summary of the Epidemiologic Evidence for the Rep reductive and
5 Developmental Effects of Lead
6 Overall, since the 1986 Lead AQCD, a substantial body of work has evaluated the
7 associations between lead exposure and reproductive outcomes. It is now clear that lead clearly
8 crosses the placenta during all trimesters and maternal exposure results in fetal exposure.
9 For many other outcomes, the observed associations are relatively small, especially at the levels
10 of exposure that are currently of interest. .
11 Further, there may be populations with increased fetal susceptibility, including
12 populations with high rates of smoking and alcohol use, those using ethnic remedies and
13 cosmetics, and those who use lead glazed pottery. Low levels of calcium intake may also
14 increase fetal exposure.
15 • The available evidence suggests small associations between exposure to lead and male
16 reproductive outcomes. These include perturbed semen quality and increased time to
17 pregnancy. These associations appear at blood lead levels greater the 45 |ig/dL, as most
18 studies only considered exposure in the occupational setting. More research is needed
19 regarding possible male reproductive effects at exposure levels in the lower (and
20 currently more relevant) range. There are no adequate data to evaluate associations
21 between lead exposure and female fertility.
22 • With one exception, there is no evidence to suggest an association between either
23 maternal or paternal lead exposure and increased risk of spontaneous abortions. One
24 study in Mexico where the mean maternal blood leads were in the moderate range (i.e.
25 10-12 |ig/dL) suggests an association.
26 • To date, the evidence suggests at most a small association between lead exposure and
27 birth weight and possibly small associations between lead exposure and several
28 dichotomized measures of fetal growth. The reviewed studies occurred in very different
29 populations, and the small associations may reflect some unmeasured or unknown
30 confounding variable. It is unlikely that further epidemiologic research will fully resolve
31 this question. However, several factors, such as maternal SES, maternal education,
32 smoking prevention and reduced use of alcohol, related to lead exposure are associated
33 with increases in birth weight (and decreases in blood lead) and are candidates for
34 intervention.
35
May 2006 6-194 DRAFT-DO NOT QUOTE OR CITE
-------
1 • The evidence suggests at most a small association between lead exposure and preterm
2 delivery or reduced length of gestation. The available data also suggest limited
3 associations between either periconceptional or prenatal lead exposure and congenital
4 anomalies. There is a suggestion of small associations with high levels of exposure, but
5 many of those studies relied on occupational histories rather than on actual measures of
6 blood lead.
9 6.7 GENOTOXIC AND CARCINOGENIC EFFECTS OF LEAD
10 6.7.1 Summary of Key Findings from the 1986 Lead AQCD
11 The 1986 EPA Lead AQCD reviewed five epidemiologic studies of occupationally
12 exposed workers (Cooper and Gaffey, 1975; Davies, 1984a; Selevan et al., 1985; Sheffet et al.,
13 1982; McMichael and Johnson, 1982). These workers were exposed to inorganic lead
14 compounds such as lead oxides and lead sulfides. The EPA noted that Cooper and Gaffey
15 reported a significant increase in lung and gastrointestinal cancer among battery and smelter
16 workers in the U.S. (standardized mortality ratios of 1.50 and 1.48 respectively among smelter
17 workers, and 1.32 and 1.23 among battery workers). Further, much of this exposure was by
18 inhalation and ingestion of lead oxides, which are relatively insoluble, adding some plausibility
19 to the occurrence of cancer at these two sites. Sheffet et al. (1982) found a nonsignificant excess
20 of stomach cancer among U.S. lead chromate pigment workers. However, Davies (1984a) did
21 not find any cancer excess among lead chromate pigment workers in the U.K. The EPA noted
22 that Selevan et al. (1985) found a significant excess of kidney cancer among U.S. lead smelter
23 workers based on 6 cases. This finding was judged striking because it mimicked the findings of
24 kidney cancer in animals. The EPA judged that the McMichael and Johnson (1982) study of
25 lead poisoned workers was not particularly informative because the non-poisoned workers may
26 have had substantial lead exposure and no details were given on how lead poisoning was
27 determined. In summary the EPA felt the evidence was insufficient, stating that "little can now
28 be reliably concluded from available epidemiologic studies."
29 The studies by Cooper and Gaffey (1975) and Selevan et al. (1985), which are both
30 important because they are large occupational cohorts with documented high exposure, have
31 been updated and are further reviewed below. A cohort study of U.K. battery workers (Malcolm
32 and Barnett, 1982) is also reviewed below.
May 2006 6-195 DRAFT-DO NOT QUOTE OR CITE
-------
1 EPA in 1986 also presented data on human cytogenetic studies, reproducing data from
2 an earlier 1980 International Agency for Research on Cancer (IARC) monograph for metals and
3 metallic compounds (IARC, 1980). For lead, 10 chromosomal aberration studies were judged to
4 be "positive" and 6 such studies were judged to be "negative." On the whole the EPA
5 considered that "under certain conditions lead compounds are capable of inducing chromosomal
6 aberrations in vivo and in tissue cultures." The EPA also reviewed more limited data from two
7 human studies of sister chromatid exchange (Dalpra et al., 1983; Grandjean et al., 1983), one of
8 which was positive and one negative.
9
10 6.7.2 Summary of Key Findings by the International Agency for Research
11 on Cancer and the National Toxicology Program
12 IARC reviewed inorganic and organic lead compounds in its monograph number 87 in
13 February of 2004 (IARC, 2005), and concluded that inorganic lead compounds were probable
14 human carcinogens (Group IIA). The IARC classification of inorganic lead compounds as
15 probable human carcinogens was based on limited evidence in humans and sufficient evidence in
16 animals. Regarding organic lead compounds (e.g., tetraethyl lead), IARC concluded that there
17 was insufficient information to make any judgment.
18 Regarding the human studies, IARC based its evaluation largely on six occupational
19 cohort studies of highly-exposed workers, which were felt to be particularly informative (battery
20 workers in U.S. and U.K., smelter workers in Italy, Sweden, and the U.S.). The IARC
21 assessment focused on four cancer sites, lung, stomach, kidney, and brain. IARC noted that lung
22 showed a significant elevation in one study (Lundstrom et al., 1997) and nonsignificant
23 elevations in a number of others. However, the significant elevation of lung cancer in
24 Lundstrom et al. appeared to be inextricably associated with arsenic in addition to lead exposure
25 (Englyst et al., 2001). IARC concluded that the strongest epidemiologic evidence for lead
26 carcinogenicity was for stomach cancer, noting that four cohort studies showed a consistent
27 30-50% excess of stomach cancer vs. external referent populations. IARC noted that
28 confounding by ethnicity, diet, Helicobacter pylori infections, or SES could have played a role in
29 the stomach cancer excesses. Finally, IARC noted that while one cohort study showed a 2-fold
30 excess of renal cancer (Steenland et al., 1992), the other studies showed no excess. Similarly,
31 there were no consistent excesses of brain cancer, although one study did find a significant
May 2006 6-196 DRAFT-DO NOT QUOTE OR CITE
-------
1 positive dose-response between glioma and blood leads, based on small numbers (Anttila et al.,
2 1996).
3 The National Toxicology Program (NTP) in 2003 evaluated the carcinogen!city of lead
4 and lead compounds. A summary of its evaluation can be found in NTP's Report on
5 Carcinogens (NTP, 2004), and the detailed evaluation is also available (NTP, 2003). NTP, like
6 IARC, concluded that "lead and lead compounds are reasonably anticipated to be human
7 carcinogens based on limited evidence from studies in humans and sufficient evidence from
8 studies in experimental animals." The NTP considered that "the strongest epidemiologic
9 evidence was for lung and stomach cancer, which are consistently but weakly associated with
10 occupations and industries entailing lead exposure and with indices of individual lead exposure,
11 including job history and biological monitoring of occupationally exposed and general
12 populations. However, most studies of lead exposure and cancer reviewed had limitations,
13 including poor exposure assessment and failure to control for confounders (other factors that
14 could increase the risk of cancer, including lifestyle factors and concurrent occupational
15 exposure to other carcinogens), and did not demonstrate relationships between the amount of
16 exposure (concentration or duration, for example) and the magnitude of cancer risk." NTP, like
17 IARC, also relied heavily on occupational cohort studies in its evaluation of the epidemiologic
18 evidence. NTP (2003) noted that "the mechanisms by which lead causes cancer are not
19 understood. Lead compounds do not appear to cause genetic damage directly, but may do so
20 through several indirect mechanisms, including inhibition of DNA synthesis and repair,
21 oxidative damage, and interaction with DNA-binding proteins and tumor-suppressor proteins."
22 Both the IARC and NTP evaluations of human evidence relied primarily on occupational
23 studies of highly exposed workers, in which limited evidence of stomach and to some extent lung
24 carcinogenicity was found. There are seven such studies with relatively large populations
25 (Anttila et al., 1995; Carta et al., 2005; Fanning, 1988; Gerhardsson et al., 1995; Lundstrom
26 et al., 1997; Steenland et al., 1992; Wong and Harris, 2000). A further study (Ades and
27 Kazantzis, 1988) also addresses lead exposure in a large occupational cohort, albeit
28 compromised by the strong correlation between arsenic and lead exposure in the cohort.
29 It should be noted that the blood lead levels among these workers were generally three to five
30 times higher than the blood lead levels in the two studies of the general U.S. population (Jemal
31 et al., 2002; Lustberg and Silbergeld, 2002; both based on NHANES II) with environmental
May 2006 6-197 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposures. For example, mean blood levels in two studies of U.S. lead smelter workers averaged
2 56 |ig/dL in Steenland et al. (1990) in 1976 and 80 |ig/dL in Cooper et al. (1985) during the
3 period 1947-1972, while the U.S. population enrolled in NHANES II in late 1976-1980 averaged
4 14 |ig/dL. General population blood lead levels have decreased markedly since the 1970s in
5 many industrial countries with the banning of leaded gasoline. U.S. general population
6 levels in the early 1990s thus averaged 3 |ig/dL according to NHANES III (ATSDR, 1999), see
7 lead toxicological profile, page 409). Regarding the occupational studies, while exposure is well
8 documented, detailed exposure-response data are generally not available, precluding quantitative
9 inference about likely effects in low exposure groups based on these studies. The high exposure
10 occupational cohorts are the most informative for deciding whether lead is likely to cause cancer,
11 simply because high doses are more likely to show detectable effects than low doses, if effects
12 exist. If lead does cause cancer, and assuming there is no threshold below which exposure does
13 not cause cancer (which is generally true for human carcinogens), current low level exposures
14 among the general public may produce some level of lead-related cancers due to the potential
15 exposure of a large number of people.
16
17 6.7.3 Meta-Analyses of Lead and Cancer
18 There have been two published meta-analyses of the carcinogenicity of lead and lead
19 compounds. Their major findings are summarized in Table 6-7.1. Steenland and Boffeta (2000)
20 relied on eight occupational cohort studies of highly-exposed workers (seven cohort studies, one
21 nested case-control), all of which had documentation of exposure levels. Meta-analyses were
22 conducted for lung, stomach, kidney, and brain cancer. The combined lung cancer relative risk
23 was 1.30 (95% CI: 1.15, 1.46), based on 675 lung cancer deaths. However, the authors noted
24 that the lung cancer findings were not consistent across studies, and were influenced highly by
25 one study (Lundstrom et al., 1997) in which confounding by arsenic was likely. Exclusion of
26 this study dropped the combined lung cancer relative risk to 1.14 (95% CI: 1.04, 1.73). The
27 strongest positive evidence was for stomach cancer (relative risk 1.34 [95% CI: 1.14, 1.57],
28 181 observed deaths). There was little positive evidence for renal cancer (relative risk 1.01
29 [95% CI: 0.72, 1.42], 40 deaths), or brain cancer (relative risk 1.06 [95% CI: 0.81, 1.40]).
30 All meta-analyses used fixed effects models, given that no evidence of heterogeneity was found
31 across studies (as long as Lundstrom et al's. lung cancer results were excluded).
May 2006 6-198 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-7.1. Results of Meta-Analyses Addressing the Association Between
Lead Exposure and Cancer
Risk Estimate (95% CI) for indicated outcome
[Number of studies utilized in estimate]
Meta-Analysis
Fu and Boffetta
(1995)
Fu and Boffetta
(1995)
Steenland and
Boffetta (2000)
Lung Cancer
1.24(1.16, 1.33)
[n=15]
1.42(1.05, 1.92)
[battery /smelter only]
1.30(1.15, 1.46)
[n = 8 - cohort only]
Stomach Cancer
1.33(1.18, 1.49)
[n=10]
1.50(1.23, 1.83)
[battery/smelter only]
1.34(1.14, 1.57)
[n = 8 - cohort only]
Renal Cancer
1.19(0.96,1.48)
[n=5]
1.26(0.70,2.26)
[battery /smelter only]
1.01 (0.72, 1.42)
[n = 7 - cohort only]
1 Fu and Boffetta (1995) conducted an earlier meta-analysis in which they reviewed
2 16 cohort and 7 case-control studies. Different numbers of studies were used for meta-analyses
3 of different outcomes, dependent on whether that outcome was reported separately, among other
4 factors. Twelve occupational studies were used in a meta-analysis of lung cancer, resulting in a
5 combined relative risk of 1.29 (95% CI: 1.10, 1.50) (random effects model, reflecting significant
6 heterogeneity of lung cancer results across studies). Meta-analyses using fixed effects (no
7 significant heterogeneity between studies) resulted in relative risks of 1.33 (95% CI: 1.18, 1.49)
8 for stomach cancer (10 studies), of 1.19 (95% CI: 0.96, 1.48) for kidney cancer (5 studies), and
9 1.41 (95% CI: 1.16, 1.71) for bladder cancer (5 studies). No meta-analysis was conducted for
10 brain cancer. Restricting analyses for stomach, lung, and kidney cancer to those studies with the
11 highest occupational exposure to lead (3 to 5 studies of battery and smelter workers) resulted in
12 slightly higher relative risks. The authors concluded that "the findings from the workers with
13 heavy exposure to lead provided some evidence to support the hypothesis of an association
14 between stomach and lung cancer and exposure to lead. The main limitation of the present
15 analysis is that the excess risks do not take account of potential confounders, because little
16 information was available for other occupational exposures, smoking, and dietary habits. The
17 excess risk of stomach cancer may also be explained, at least in part, by nonoccupational factors.
18 For bladder and kidney cancers, the excess risks are only suggestive of a true effect because of
19 possible publication bias."
20
May 2006 6-199 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.7.4 Genotoxicity of Lead
2 The NTP reviewed in some detail the genotoxicity studies over the period 1970-2002.
3 These studies are cross-sectional studies, mostly of occupationally exposed workers compared to
4 a control population. Usually blood lead levels are available to document exposure. Outcomes
5 consisted of chromosomal aberrations (CA), sister chromatid exchange (SCE), micronuclei
6 formation (MN), and studies of DNA damage (often via the comet assay) and/or measures of the
7 mitotic activity. Of these outcomes, only CAs have been shown to have a positive relationship to
8 subsequent cancer (Hagmar et al., 2004, Rossner et al., 2005). SCEs are generally considered a
9 marker of exposure to environmental agents which affect DNA, but do not necessarily predict
10 cancer risk. MN and DNA damage are thought to indicate genotoxicity with unknown effect on
11 cancer risk. The informativeness of these outcomes regarding the possible human
12 carcinogenicity of lead are thus clearly secondary to direct information on cancer risk from
13 epidemiologic studies.
14 Since the NTP review, there have been three additional cytogenetic studies which are
15 informative regarding lead (Palus et al., 2003, Minozzo et al., 2004, and Fracasso et al., 2002),
16 as well as one mutation study (Van Larebeke et al., 2004). As detailed in Annex Table AX6-7.2,
17 all four of these studies (two of DNA damage, one of MN, and one of a specific mutation
18 frequency) were positive in significantly linking lead exposure to the outcome. Treatment of
19 potential confounding factors varied across studies, but there was no indication that more
20 extensive adjustment for such factors was associated with weaker relationships between lead
21 exposure and genotoxic endpoints. Potential coexposure to other potentially genotoxic metals
22 remains an issue, although Paulus et al. (2003) found as much or more evidence of genotoxicity
23 for each major endpoint examined among heavily Pb-exposed workers as among those expected
24 to have the heaviest exposure to Cd.
25 The results of the four most recent studies as well as those reviewed by the NTP are
26 summarized in Table 6-7.2. Of eleven studies of chromosomal aberrations (CA), six were
27 judged to show a positive relationship between CA and lead, four were judged negative, and one
28 was neither clearly positive nor negative. In general, these studies were done in the 1970s and
29 980s; only one dates from the 1990s. There were nine studies of sister chromatid exchange.
30 Of these, four were judged positive, three negative, and two could not be judged clearly one way
31 or the other. It is notable that the positive studies were generally the most recent. There were
May 2006 6-200 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-7.2. Results of Epidemiologic Studies on the Genotoxicity of Lead Exposure3
Studied Outcome
Chromosomal Aberrations
(CA)
Sister Chromatid Exchange
(SCE)
Micronucleus Formation
(MM)
DNA Damage/Mitosis
Gene Mutation
Positive
6
4
5
10
1
Results
Mixed
1
2
0
0
0
Negative
4
3
0
1
0
Results summarize the overall findings of epidemiologic studies addressing the potential genotoxic effects of
lead exposure. Some studies addressed multiple aspects of genotoxicity; for these studies, their results for each
of the listed categories of genotoxic outcomes are presented separately.
1 four MN studies, all of which were judged positive. Finally, there were nine studies of DNA
2 damage and/or mitotic activity. These varied in the specific outcome, although many used a
3 comet assay to measure oxidative damage to DNA. Eight of these nine studies were judged
4 positive in the sense that increased DNA damage or mitotic activity was related to lead exposure,
5 while one was judged negative.
6 While the overall the evidence from cytogenetic studies is mixed, more recent studies
7 which were focused on DNA damage or mitotic activity have tended to be largely positive.
8 However, it is not known whether these outcomes predict subsequent cancer risk.
9
10 6.7.5 Review of Specific Studies on the Carcinogenicity of Lead Since the
11 1986 Lead AQCD
12 6.7.5.1 Introduction
13 The epidemiologic studies of lead exposure and cancer are listed in Table 6-7.3. The most
14 relevant studies focus on exposure through occupational sources, wherein the most intense
15 exposure to lead can be expected to occur. This exposure predominantly involves inorganic lead
16 species. Relevant studies are discussed below, beginning with the most key occupational and
17 general population studies, followed by a brief summary of other relevant studies.
May 2006
6-201
DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-7.3. Epidemiologic Studies of Lead Exposure and Cancer in Specific
Populations, by Geographic Region and Study Design3
Epidemiologic Study Design
Specific Study Population
Cohort
Nested Case-control
Case-control
United States
Battery and lead production
workers
Copper workers (Utah)
Lead and zinc pigment plant
workers
Lead smelter workers (Idaho)
Sample of deaths due to cancer
vs. noncancer deaths (Illinois)
Brain cancer
Central nervous system cancer
Stomach cancer
NHANES II cohort mortality
follow-up, general U.S.
population
Canada
Population-based cases
Specific cancers versus all
cancers
Europe
Glass workers (Finland)
Registry-derived liver cancer
cases vs. stomach cancer or
myocardial infarctions (Finland)
Workers via Cancer Registry
(Finland)
Renal-cell cancer vs. population
controls (Germany)
Laryngeal cancer among
persons with no history of lead
exposure (Greece)
Cooper and Gaffey (1975), Cooper Cooper et al. (1989),
et al. (1985), Wong and Harris Wong and Harris (2000)
(2000) (same publication as
cohort study)
Rencheretal. (1977)
Sheffetetal. (1982)
Selevan et al. (1985), Steenland
etal. (1992)
Jemal et al. (2002), Lustberg and
Silbergeld (2002)
Sankilaetal. (1990)
Anttilaetal. (1995)
Kauppinen et al. (1992)
Anttila etal. (1996)
Mallinetal. (1989)
Coccoetal. (1998a)
Coccoetal. (1998b)
Coccoetal. (1999)
Risch etal. (1988)
Siemiatycki et al. (1991)
Pesch et al. (2000)
Kandiloris et al. (1997)
May 2006
6-202
DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-7.3 (cont'd). Epidemiologic Studies of Lead Exposure and Cancer in Specific
Populations, by Geographic Region and Study Design3
Epidemiologic Study Design
Specific Study Population
Cohort
Nested Case-control
Case-control
Europe (cont'd)
Glass workers (Italy)
Lead and zinc miners: females
only (Sardinia)
Lead and zinc miners: male only
(Sardinia)
Lead and zinc smelter workers
(Sardinia)
Lead and zinc smelter workers
(Sardinia, but different from
Coccoetal. 1996)
Glass workers (Sweden)
Copper and lead smelter workers
(Sweden)
Copper and lead smelter workers
(Sweden) (Lundstrom: full
cohort; Englyst: sub-cohort)
Lead-acid battery workers (U.K.)
Chromate (including lead-
chromate) workers (U.K.)
Zinc, cadmium, and lead smelter
workers (U.K.)
Asia
Gliomas vs. noncancer patients
(China)
Meningiomas vs. noncancer
patients (China)
Gall bladder cancer vs. gallstone
patients (India)
Prostate cancer cases versus
benign prostate hyperplasia cases
and normal controls (India)
Cordiolietal. (1987)
Coccoetal. (1994b)
Cocco et al. (1994a), Carta et al.
(1994); Cartaetal. (2003;
Coccoetal. (1996)
Coccoetal. (1997)
Wingren and Englander (1990) Wingren and Axelson
(1985, 1987, 1993)
Gerhardsson et al. (1995)
Gerhardsson et al. (1986),
Lundstrom et al. (1997), Englyst
etal. (2001)
Dingwall-Fordyce and Lane
(1963), Malcolm and Bamett
(1982)
Davies(1984a, 1984b)
Fanning (1988)
Ades and Kazantzis (1988)
Ades and Kazantzis
(1988) (same publication
as cohort study)
Huetal. (1998)
Huetal. (1999)
Shuklaetal. (1998)
Siddiqui et al. (2002)
a Within regions, study populations are listed in chronological order based on the earliest published study on that specific
worker population. Publications considered to be key studies are italicized.
May 2006
6-203
DRAFT-DO NOT QUOTE OR CITE
-------
1 6.7.5.2 Key Studies of Occupational Populations in the U.S.
2 There are seven key occupational studies based on highly exposed worker populations;
3 these are all cohort studies with adequate numbers to address lung and/or stomach cancer.
4 There are two cohorts based in the U.S. and five based outside it. Studies reviewed in this
5 section are summarized briefly in Table 6-7.4 and in more detail in Annex Table AX6-7.2.
6 Steenland et al. (1992) followed up 1,990 male U.S. lead smelter workers, employed from
7 1940 to 1965, through 1988. Standardized mortality ratios indicated an excess of lung, stomach,
8 kidney, and bladder cancer that did not reach statistical significance. Focusing on workers
9 classified as highly lead exposed based on air-monitoring records yielded a significant excess for
10 kidney cancer (standardized mortality ratio of 2.39 [95% CI: 1.03, 4.71]), although it did not
11 appear to increase with duration of exposure. Estimates for the other cancers (standardized
12 mortality ratio of 1.11 [95% CI: 0.82, 1.47] for lung; 1.28 [95% CI: 0.61, 2.34] for stomach;
13 1.33 [95% CI: 0.48, 2.90] for bladder) showed little change with restriction to the high-exposure
14 group. While neither arsenic nor cadmium exposure could be controlled for, 1975 NIOSH
15 monitoring data indicated less intense exposure to airborne cadmium or arsenic than to lead.
16 Lead averaged 3.1 mg/m3 and arsenic 14 |ig/m3, compared to current OSHA standards of
17 0.05 mg/m3 for lead and 10 |ig/m3 for arsenic. It is notable that a 1996 review of studies
18 (Steenland et al., 1996) on arsenic-exposed workers concluded that significantly elevated rates of
19 lung cancer were concentrated in studies where average exposures greatly exceeded OSHA
20 standards (e.g., hundreds of |ig/m3). No data on workers' smoking status were available.
21 Wong and Harris (2000) extended follow-up on the battery and smelter worker cohort
22 previously reported on by Cooper et al., 1985 through 1995, an additional 15 years. With the
23 additional follow-up, standardized mortality ratios for lung, tracheal, or bronchial cancer
24 decreased to 1.14 (95% CI: 0.99, 1.30) for battery workers but showed little change for smelter
25 workers at 1.22 (95% CI: 1.00,1.47). An elevated standardized mortality ratio for stomach
26 cancer (1.53 [95% CI: 1.12, 2.05]) persisted among battery workers, with a lesser elevation
27 among smelter workers (1.33 [95% CI: 0.75, 2.20]). Among other cancers, only thyroid cancer
28 among all workers combined showed a significantly elevated standardized mortality ratio
29 (3.08 [95% CI: 1.33,6.07]). Cancer mortality did not increase with earlier year of hire. Lung
30 and stomach cancer mortality peaked among workers with 10 to 19 years of factory employment
31 and declined with longer employment duration. Thyroid cancer mortality occurred exclusively
May 2006 6-204 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-7.4. Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
to
o
o
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis Major findings
Oi
to
o
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Steenlandetal. (1992)
U.S.
1,990 male workers employed
for at least 1 year in a lead-
exposed department at a U.S.
lead smelter in Idaho during
1940-1965.
Wong and Harris (2000)
U.S.
Lead battery plant (4,518) and
smelter (2,300) workers
Mean blood lead 56 ng/dL in 1976.
High-lead-exposure subgroup: 1,436
workers from departments with average
of at least 0.2 mg/m3 airborne lead or
>50% of jobs showing 0.40 mg/m3
or greater in 1975 monitoring.
Mortality traced through 1988 to
determine cause of death.
Mean blood lead 80 ng/dL during 1947-
72 among smelter workers, 63 ng/dL
among battery workers.
Mortality traced from 1947 through
1995, with cause of death then identified
from death certificates.
(See additional entry for nested case-
control study of stomach cancer.)
SMR computed for workers vs. national
rates for age-comparable counterparts.
SMR computed based on U.S. national
age-, calendar-year-, and gender-
specific mortality rates. Workers
evaluated as a whole, and also as
separate battery plant and smelter
worker populations.
Job histories were also used to stratify
workers by cumulative years of
employment (1-9,10-19,20+), date of
hire (pre-1946 vs. 1946 on), and lag
between exposure and cancer (<20, 20-
34, >34 years).
High-lead-exposure subgroup SMR (95% CI); no. of
deaths:
2.39 (1.03,4.71); 8
1.33 (0.48, 2.90); 6
1.28(0.61,2.34); 10
1.11 (0.82, 1.47); 49.
Kidney
Bladder
Stomach
Lung
Total cohort:
SMRs for kidney, bladder, stomach, and lung cancer
exceed 1 but do not reach nominal statistical
significance.
Battery plant workers SMR (95% CI):
All cancer 1.05(0.97,1.13)
All respiratory 1.13 (0.98, 1.29)
Stomach 1.53 (1.12, 2.05), significant
Lung, trachea, bronchus
1.14(0.99,1.30)
Thyroid, Hodgkin's: nonsignificant
Bladder 0.49 (0.23, 0.90), significant depression
Smelter -workers:
Digestive, respiratory, thyroid: nonsignificant
Lung 1.22(1.00, 1.47), nonsignificant
Battery plant and smelter -workers combined:
All cancer 1.04(0.97,1.11)
All respiratory 1.15 (1.03, 1.28), significant
Stomach 1.47 (1.13, 1.90), significant
Lung, trachea, bronchus
1.16(1.04, 1.30), significant
Thyroid/endocrine 3.08 (1.33, 6.07), significant
Lung and stomach risks higher for workers employed
10-19 years than <10, but lower for >19 years.
-------
Table 6-7.4 (cont'd). Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
to
o
ON
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis Major findings
ON
to
o
Wong and Harris (2000)
U.S.
(Nested in Wong and Harris
200 cohort.)
30 stomach cancer cases and
120 controls from Philadelphia
battery plant.
Fanning (1988)
U.K.
2,073 deceased males identified
through pension records of lead
battery and other factory
workers in the U.K., 1926-1985
See blood leads for cohort, preceding.
Job titles were used to classify lead
exposure as low, intermediate, or high;
total months of any exposure, of
intermediate or high exposure only, and
of intensity-weighted cumulative
exposure.
Workers were classified as having high
or moderate lead exposure vs. little or no
exposure based on job titles.
Proportional mortality/cohort design.
Odds of exposure were computed for
increasing quartiles of cumulative
exposure.
Controls were age-matched to cases.
Workers dying from a specific cancer
were compared with workers dying
from all other causes to determine their
proportional mortality.
Mean months of employment, of intermediate or high
exposure, or of weighted exposure to lead were all
nonsignificantly lower among cases.
Stomach cancer OR for cumulative weighted exposure
in the 10 years prior to death:
First quartile 1.00
Second quartile 0.62
Third quartile 0.82
Fourth quartile 0.61
p for trend = 0.47; ORs showed no positive association
with any index of exposure.
OR (95% CI) [Number of deaths]
Lung cancer: 0.93 (0.8, 1.1) [76 deaths]
Stomach cancer 1.34 [31 deaths]
No associations were noted for other cancer types.
Elevations in stomach and total digestive cancers were
limited to the period before 1966.
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
-------
Table 6-7.4 (cont'd). Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
to
o
o
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis Major findings
Oi
to
o
Anttilaetal. (1995)
Finland
20,700 workers with at least
one blood lead measurement
between 1973 and 1983.
Mean blood lead 26 ng/dL
Workers were linked to the Finnish
Cancer Registry for follow-up through
1988, with decedents' cause of death
identified from death certificates.
Mortality and incidence were compared
with gender-, 5-year age, and 4-year
calendar-year matched national rates.
Case-referent analyses for lung cancer
also controlled for smoking.
Exposure was categorized according to
the highest peak blood level measured:
Low: 0-0.9
[Oto 18.6ng/dL]
Moderate: l-1.9|imol/L
[20.7 to 39.4 ng/dL]
High: 2-7.8 (imol/L
[41.4tol61.6ng/dL]
Total cohort:
No elevation in total or site-specific cancer
mortality
Moderately exposed:
Total respiratory and lung cancer:
SIR =1.4 (95% CI: 1.0, 1.9) for both
Total digestive, stomach, bladder, and nervous
system: nonsignificant elevations
Highly exposed:
No increase in risks
All cancer:
RR=1.4(95%CI: 1.1,1.8)
Lung or tracheal:
RR = 2.0(95%CI: 1.2,3.2)
No increase in high-exposure group
No RRs reported for other cancers
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Case-referent substudies:
Highly exposed: squamous-cell lung cancer
OR = 4.1 (95% CI: 1.1, 15), smoking-adjusted.
Lung cancer ORs increased with increasing
cumulative exposure to lead.
Short follow-up period limits statistical power,
offset to a large degree by the substantial sample
size. No control for exposure to other potential
carcinogens.
-------
Table 6-7.4 (cont'd). Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
to
o
o
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis Major findings
Oi
to
o
oo
Anttilaetal. (1996)
Finland
26 Finnish men with CNS
cancer and 200 without CNS
cancer selected from Antilla et
al. 1995cohort.l973-1988
(Nested analysis based on
Antilla et al. 1995 cohort)
See Antilla et al. (1995) for general
description. Interviews were used to
obtain occupational history and other
risk-factor data for study cases and
controls from patients or their next of
kin.
Odds ratios for CNS incidence and
death were computed, adjusted for age,
smoking, and occupational exposure to
other potential CNS carcinogens (e.g.
cadmium, gasoline)
Peak blood lead levels used to
categorize exposure as 0.1-0.7,
0.8-1.3, and 1.4-4.3 ug/L.
Cumulative exposure estimated by
using mean annual blood lead level to
categorize exposure as 0, 1-6, 7-14, or
15-49 ug/L.
OR (no. of cases or deaths)
CNS cancer incidence (26 cases):
Rose with increasing peak lifetime blood lead
measurements; not significant
Glioma mortality (16 deaths):
Rose consistently and significantly with peak and
mean blood lead level, duration of exposure, and
cumulative exposure.
Mortality by cumulative exposure, controlled for
cadmium, gasoline, and year monitoring began:
Low (13 subjects) 2.0(2)
Medium (14 subjects) 6.2 (2)
High (16 subjects) 12.0(5)
1 death among 26 subjects with no exposure: test for
trend significant at/> = 0.02.
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
-------
Table 6-7.4 (cont'd). Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
-<
to
o
o
ON
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis
Major findings
Oi
to
o
VO
Gerhardsson et al. (1995)
Sweden
684 male Swedish secondary
lead smelter workers with lead
exposure.
Blood lead level: any worker with a Incidence was compared with gender
detectable blood lead level was classified and age-specific county rates to
as exposed. compute an SIR.
Cancer incidence among workers was
traced from 1969 through 1989.
SIR (95% CI); no. of cases
All malignancies:
1.27(0.91, 1.74); 40
Respiratory:
1.32 (0.49, 2.88); 6
All gastrointestinal:
cohort 1.84 (0.92, 3.29; 11
highest quartile 2.34 (1.07, 4.45); 9
Stomach:
1.88(0.39, 5.50); 3
Colon:
1.46 (0.30, 4.28); 3
SIRs for all other sites except brain were
nonsignificantly elevated..
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
-------
Table 6-7.4 (cont'd). Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
to
o
o
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis Major findings
Oi
to
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Lundstrom et al. (1997)
(see also subcohort analyses of
Englystetal.,2001).
Sweden
3,979 copper and lead smelter
workers.
Englystetal. (2001)
(follow-up and sub-analysis of
Lundstrom etal., 1997).
Sweden
1,093 smelter lead department
workers
1928-1987
Mean blood lead 60 ng/dL in 1959.
Mean blood lead monitoring test results
across time were also used to single out a
"highly exposed" group of 1,026 workers
with blood lead levels >10 nmol/L [>207
Hg/dL].
Mortality and incidence were traced from
1928 through 1987.
Lead department workers were classified
as exposed, and work histories were used
to classify them as ever or never having
worked in departments with exposure to
other known carcinogens. Detailed
individual assessment of arsenic
exposure was then made for all lung-
cancer cases.
Standardized mortality and incidence
ratios were computed for workers
compared with age-, year-, gender-, and
county-specific rates for the general
population Job histories were also used
to single out workers belonging to
departments thought to be exposed to
"lead only."
Incidence was compared with county
rates to compute age-specific SIRs
(including 15-year lag).
SMR (95% CI); no. of deaths
Lung:
Total cohort 2.8 (2.0, 3.8); 39
Highly exposed 2.8 (1.8, 4.5); 19
SIR (95% CI); no. of cases
Lung -with 15-year lag:
Total cohort 2.9 (2.1,4.0); 42
Highly exposed 3.4 (2.2, 5.2); 23
Lead-only 3.1 (1.7, 5.2); 14
Lead-only highly exposed 5.1 (2.0, 10.5); 7
Other highly exposed (total cohort),
•with 15-year lag:
Brain 1.6 (0.4,4.2); 4
Renal pelvis, ureter, bladder 1.8 (0.8, 3.4); 9
Kidney 0.9 (0.2, 2.5); 3
All cancer 1.1 (0.9, 1.4); 83.
SIR (95% CI); no. of cases
Worked in department(s) with known carcinogen co-
exposure:
Lung 2.4 (1.2, 4.5); 10
Worked in department(s) not classified as having
carcinogen co-exposure:
Lung 3.6(1.2, 8.3); 5
Subjects with lung cancer found to have history of
"considerable" exposure to arsenic: 9/10 among
Subcohort I, 4/5 among Subcohort II.
-------
Table 6-7.4 (cont'd). Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
to
o
o
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis Major findings
Oi
to
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Carta et al. (2003)
Sardinia
918 lead smelter workers
1972-2001
Smelter workers considered exposed.
Mortality was traced from 1972 through
2001.
Jemal et al. (2002)
U.S.
3,592 white participants from
the 1976-1980 NHANES II
survey who had blood lead
measured at entry.
Median blood lead 12 |ig/dL
Mortality of participants was traced
through 1992 by use of Social Security
and National Death Index data.
Standardized mortality ratios were
computed.
Job histories also used to categorize
degree of exposure based on
environmental and blood lead
measurements for specific departments
and tasks during
1985-2001.
RRs were calculated for the various
exposure groups compared to survey
participants with the lowest exposure,
adjusted for age and smoking.
Blood lead (ng/dL) was used to classify
subjects into exposure quartiles or
groups above vs. below median
exposure.
SMR; number of cases
Smelter workers as a whole
All cancer 1.01 ; 108
Gastric cancer 1.22 ; 4
Lymphoma/leukemia 1.82 ; 6
Lung cancer 1.21 ; 18
Highly exposed workers
Lung cancer 1.96 (95% C.I. 1.02, 3.68) for highest
exposure group, with statistically significant upward
trend.
Analyses for worker population as a whole supported
by presence of dose-response pattern for lung cancer
based on estimated exposure.
RR (95% CI); no. of deaths
Lung (above vs. below median):
Total cohort 1.5 (0.7, 2.9); 71
M 1.2 (0.6, 2.5); 52
F 2.5(0.7, 8.4); 19
Stomach (above vs. below median):
Total cohort 2.4 (0.3, 19.1); 5
M 3.1(0.3, 37.4); 4
F no deaths in referent group
All cancer: total cohort by quartile (age-adjusted) 1.0,
1.2, 1.3, 1.5 (P for trend 0.16).
-------
Table 6-7.4 (cont'd). Summary of Key Studies on Lead Exposure and Cancer Occurrence in Human Populations
to
o
o
Reference
Study location
Study population
Sample size
Mean exposure and outcome measures
Analysis methods
Covariates adjusted for in analysis Major findings
Oi
to
Lustberg and Silbergeld (2002)
U.S.
4,190 U.S. participants from
the 1976-1980 NHANES II
health and nutrition survey who
had blood lead measured at
entry and whose levels fell
below 30
Mean blood lead 14 |ig/dL.
Mortality of participants was traced
through 1992 by use of Social Security
and National Death Index data.
RRs were calculated for the various
exposure groups compared to survey
participants with the lowest exposure,
adjusted for age, smoking and other
factors.
RRs were calculated for the various
exposure groups compared to survey
participants with the lowest exposure,
adjusted for age, smoking and other
factors
Blood lead (ng/dL) was used to classify
subjects into the following exposure
groups:
Low: <10
Medium: 10-19
High: 20-19
RR (95% CI)
All cancer, vs. low exposure:
Medium 1.5(0.9,2.5)
High 1.7(1.0,2.8)
Lung, vs. low exposure:
Medium 1.7(0.6,4.8)
High 2.2(0.8,6.1)
Non-lung, vs. low exposure:
Medium 1.5(0.8,2.8)
High 1.5(0.8,2.8).
Significant upward trends noted for all-cause and for
cardiovascular mortality with increasing lead category.
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
-------
1 among workers with 20 or more years of exposure. As with earlier analyses based on this
2 cohort, concomitant exposures to other compounds could not be controlled for, but as these were
3 likely to be most intense among lead production workers, whose standardized mortality ratios
4 were similar to or lower than those for battery workers, any bias resulting from such exposure
5 probably was minimal. No data were available to assess the possible role of smoking, diet, or
6 other potential nonoccupational risk factors in the results.
7 A nested case-control analysis was also conducted to further explore stomach cancer
8 mortality within workers employed at the Philadelphia lead battery plant in the cohort (Wong
9 and Harris, 2000). Among 30 workers who died of stomach cancer and 120 age-matched
10 controls, duration of employment and estimated degree of lead exposure based on job histories
11 showed no elevation among workers who died of stomach cancer, nor did mortality increase
12 across increasing tertiles of lead exposure. Little information appeared to be available on
13 potential confounders. The authors suggested that in light of historically higher stomach cancer
14 rates in Ireland and Italy, a higher proportion of Irish and Italian immigrants (as observed among
15 lung cancer cases in the case-control study) may have contributed to the elevated standardized
16 mortality ratios seen in the cohort as a whole. The recent IARC Working Group (IARC, 2005)
17 concluded that, based on the ethnic composition of the control population (23% Irish or Italian),
18 confounding by race could account for only part of the observed association, however.
19 The extended follow-up and nested case-control analyses on the original Cooper et al.
20 (1985) cohort thus continued to provide evidence for some increase in lung and stomach cancer
21 among these lead workers, but no consistent evidence of increasing cancer risk with increasing
22 exposure within the lead worker cohort itself, especially for stomach cancer.
23 Fanning (1998) studied deaths due to specific cancer types among U.K. battery and other
24 factory workers. High to moderate lead exposure resulted in odds ratios for lung and digestive
25 cancer of 0.93 and 1.13, respectively, with the latter elevation due mainly to stomach cancer
26 (odds ratio of 1.34). No odds ratios reached nominal statistical significance, and no associations
27 were noted for other cancer types. The excess of digestive cancer deaths was restricted to the
28 1926 to 1965 period, during which lead exposures would have been most intense. Odd ratios for
29 other cancers did not vary by period. Because each cancer case group was compared with a
30 control group consisting of subjects who died from all other causes, including other cancers,
31 odds ratios would have been biased downward if some of these other deaths also were lead-
May 2006 6-213 DRAFT-DO NOT QUOTE OR CITE
-------
1 related. However, most deaths were due to nonmalignant respiratory or circulatory diseases
2 other than hypertension, mitigating the potential impact of such a bias.
3 Anttila et al. (1995) linked 20,700 Finnish workers whose blood lead was monitored
4 during 1973 to 1983 by the Finnish Institute of Occupational Health to the Finnish Cancer
5 Registry. Exposure was subdivided according to highest peak blood level measured: low (0 to
6 0.9 |imol/L [0 to 18.6 jig/dL]), moderate (1.0 to 1.9 |imol/L [20.7 to 39.4 jig/dL]), and high
7 (2.0 to 7.8 |imol/L [41.4 to 161.6 |ig/dL]). The total cohort showed no elevation in cancer
8 mortality based on standardized mortality ratio analyses. Among male workers with moderate
9 exposure; however, incidence of total respiratory cancer and lung cancer both were elevated
10 (standardized incidence ratio of 1.4 [95% CI: 1.0, 1.9 for both]). Risks of total digestive,
11 stomach, bladder, and nervous-system cancer also were modestly elevated. Risks of mortality
12 for all cancer for both men and women (relative risk 1.4 of [95% CI: 1.1, 1.8]) and lung or
13 tracheal cancer (relative risk of 2.0 [95% CI: 1.2, 3.2]) were even stronger when a person-year
14 analysis was applied to compare workers with moderate lead exposure to those with low
15 exposure. Risks did not increase in the highest exposure group, although the power of analyses
16 specific for this group were limited by its relatively small size (e.g., lung or tracheal cancer
17 deaths among men in the low-, moderate-, and high-exposure groups numbered 25, 34, and 11,
18 respectively, for the person-year-based analyses).
19 Gerhardsson et al. (1995) followed up 664 male Swedish secondary lead smelter workers,
20 tracing their cancer morbidity through 1989. Compared to the surrounding county, the workers'
21 standardized incidence ratio for all cancers was 1.27 (95% CI: 0.91,1.74). Standardized
22 incidence ratios for cancers at all specific sites examined except the brain were elevated, notably
23 those for the respiratory system (1.32 [95% CI: 0.49, 2.88]), stomach (1.88 [95% CI: 0.39,
24 5.50]), and colon (1.46 [95% CI: 0.30,4.28]). Because of the small numbers of tumors (only 6,
25 3, and 3, respectively for the aforementioned sites), the reliability of estimates for most sites is
26 limited. Restricting analyses to workers in the highest quartile of exposure based on routine
27 blood lead monitoring data yielded a higher standardized incidence ratio for total gastrointestinal
28 cancer (2.43 [95% CI: 1.11, 4.62]; 9 tumors), but not respiratory cancer. Availability of blood
29 lead measurements is an advantage of this study, along with a lead-exposed worker population
30 unlikely to have much exposure to arsenic, chromium, or cadmium. However, the cases were
May 2006 6-214 DRAFT-DO NOT QUOTE OR CITE
-------
1 too few for detailed exposure-response analyses by cancer type. Lack of data on smoking further
2 restricts interpretation of the results.
3 Lundstrom et al. (1997) followed 3,979 Swedish smelter workers from 1928 to 1987.
4 Workers were further subdivided into those with high cumulative blood lead scores, and those
5 thought exposed to "lead only" (excluding those from departments thought to have significant
6 exposures to other potential carcinogens, such as arsenic, or little exposure to lead). The lung
7 cancer standardized mortality ratio was 2.8 (95% CI: 2.0, 3.8) for the total cohort, 2.8 (95% CI:
8 1.8, 4.5) for the high-exposure subgroup, and reportedly similar for the lead-only subgroup.
9 Incorporating a 15-year latency period, results differed little between the total cohort and high-
10 exposure subgroup; however, among workers with exposure to lead only, the standardized
11 incidence ratio rose from 3.1 (95% CI: 1.7, 5.2; 14 cases) for all workers to 5.1 (95% CI: 2.0,
12 10.5; 7 cases) for those with the highest exposure. With a 15-year latency period, elevated
13 standardized incidence ratios also were observed for cancer of the brain and nervous system and
14 renal pelvis, ureter, or bladder (1.8 [95% CI: 0.8, 3.4]) among the high-exposure subgroup.
15 Non-respiratory cancers were too infrequent (5 total) in the high-exposure lead-only subgroup
16 for meaningful analysis. This study's size, extensive follow-up, and ability to integrate
17 blood-based and job-based exposure indices give it unusual power. The higher estimated risk
18 observed when workers thought to be potentially exposed to other metals, were excluded also
19 appeared to strengthen the evidence for a specific link between lead and respiratory cancer.
20 A subsequent study by Englyst et al. (2001), however, cast doubt on the efficacy of the "lead
21 only" grouping.
22 Englyst et al. (2001) conducted additional analyses on one element of the Lundstrom et al.
23 (1997) cohort. A total of 1,093 workers from the smelter's lead department was followed up
24 through 1997. Significantly elevated lung cancer standardized incidence ratios were observed
25 in all subcohorts, including the subcohort who had never worked in arsenic-exposed areas
26 (3.6[95%CI: 1.2, 8.3]; 5 cases). This subcohort is the same as the "lead-only" subgroup
27 evaluated by Lundstrom et al. (1997). A review of detailed job histories obtained for all workers
28 with lung cancer, however, indicated that 13 of the 15 had "considerable" exposure to arsenic as
29 well as lead, including all but 1 in the "lead only" subcohort.
30 Carta et al. (2003) followed up the mortality of 918 Sardinian lead smelter workers from
31 1972 through 2001. Smelter workers as a whole displayed an overall cancer mortality no higher
May 2006 6-215 DRAFT-DO NOT QUOTE OR CITE
-------
1 than expected based on regional rates (standardized mortality ratio of 1.01). Cancer-specific
2 standardized mortality ratios were, however, nonsignificantly elevated for cancers of the lung
3 (1.21) and stomach (1.22) as well as for lymphoma and leukemia (1.82). Use of blood and
4 ambient lead monitoring data available by department and task to categorize estimated exposure
5 yielded a statistically significant upward trend with increasing lead exposure for lung cancer; no
6 significant trend was seen for the other cancers, although in light of the small number of gastric
7 cancer and lymphoma/leukemia deaths (4 and 6, respectively) interpretation of dose-response is
8 problematic for these outcomes.
9 In summary, the strongest evidence in the key occupational studies linking lead exposure
10 to actual human cancers is that for cancers of the lung and those of the stomach. Of seven large
11 occupational cohort studies available (Ades and Kazantzis, 1988; Anttila et al., 1995; Carta et al.,
12 2005; Gerhardsson et al., 1995; Lundstrom et al., 1997; Steenland et al., 1992; Wong and Harris,
13 2000), for example, all showed results consistent with an increase in lung cancer risk among
14 lead-exposed workers, and in four of these studies the association was statistically significant.
15 Further, where workers could be categorized as to their level of lead exposure, the greatest
16 magnitude of association for lung cancer was usually seen for the highest exposure category.
17 However, the modest elevation of lung cancer risk seen in most relevant studies is in the range of
18 possible confounding due to smoking or other occupational exposures, particularly arsenic,
19 which precludes the evidence from these studies being seen as conclusive. In particular, the one
20 occupational study with the highest lung cancer risk (Lundstrom et al.) has been subsequently
21 shown to be highly confounded by arsenic, and without this study, the combined evidence for a
22 lung cancer elevation across studies is considerably reduced (e.g., the estimated relative risk falls
23 from 1.30 to 1.14). A moderate elevation of stomach cancer is also found in most studies of
24 occupationally exposed populations with applicable data on this outcome. As with lung cancer,
25 it is possible that other risk factors such as intake of smoked meats or H. pylori infection could
26 have contributed to the observed associations, but the observed elevation (meta-analysis of 1.33
27 or 1.34) coupled with the known effect of diet makes it unlikely that the elevation in stomach
28 cancer is entirely due to confounding by diet. Data for other sites such as kidney, brain, and
29 bladder show some indications of an excess, but the results across studies are not consistent and
30 are based on small numbers.
31
May 2006 6-216 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.7.5.3 Key Studies of the General Population
2 There are two key general population cohort studies in which lead exposure is assessed
3 via blood lead levels (see Annex Table AX6-7.3 for additional details). Jemal et al. (2002)
4 conducted the first biomarker-based general population cohort study of lead exposure and
5 cancer. The study employed the subsample of 3,592 white U.S. participants in NHANES II
6 (1976 to 1980) who had undergone blood lead level determinations at time of entry. Deaths
7 among this population were enumerated through 1992 by linkage to the National Death Index
8 (NDI) and Social Security Administration Death Master File. Median blood lead levels in this
9 population were 12 |ig/dL. Adjusted for age, smoking, drinking, region, year, and gender, risk of
10 mortality from any cancer rose across quartiles of blood lead level, but this trend was not
11 statistically significant. The trend across quartiles was not consistent in gender-specific analyses,
12 although relative risks were elevated for the highest quartile of blood lead level in both men and
13 women (relative risk 2.0 for men and 1.6 for women). The relative risk for lung cancer based on
14 comparison of subjects with blood lead levels above or below the median was 1.5 in the
15 combined population, with higher risk observed among women than men. The highest relative
16 risks were observed for cancer of the esophagus (3.7 [95% CI: 0.2, 89]), pancreas (3.6 [95% CI:
17 0.6, 19.8]), and stomach (2.4 [95% CI: 0.3, 19.1]); no elevations were noted for cancers of other
18 sites. Total cancer mortality was also addressed through a spline regression (Figure 6-7.1 A
19 and B). The mortality curves were visually suggestive of an upward trend at low blood lead
20 levels (<20 jig/dL), but no statistically significant dose-response pattern was present except for
21 analyses restricted to women.
22 The lack of statistically significant results reflects the small number of deaths during follow-up,
23 which limited the study's power; of the nine major sites examined, the number of deaths ranged
24 between 5 and 16 for all sites except the lung. Further, only 4 and 16 deaths occurred among
25 men and women, respectively, with blood leads below 9.8 |ig/dL, precluding assessment of
26 potential effects within that range. Detailed exposure-response analyses were restricted to all
27 cancers combined, although potential effects could have been strongly target-organ specific. In
28 addition, the use of quartile cut points based on the distribution of lead concentrations estimated
29 for the total U.S. population resulted in relatively small numbers in the referent group (lowest
30 exposure quartile) for males and in the high-exposure quartile for females. Use of a biomarker
31 provided an objective measure of lead exposure. Nevertheless, reliance on a single blood lead
May 2006 6-217 DRAFT-DO NOT QUOTE OR CITE
-------
100
10
RJ
N
(0
I
Q>
Of
0.1
0,01
0.001
100
10
0.1
0 10 20 30 40 50 60 70 80
Blood Lead Level (pg/dL)
0.01
B
10 20 30 40 50 60
Blood Lead Level (pg/dL)
Figure 6-7.1. Five-knot cubic spline regression models of total cancer mortality and blood
lead level by gender, based on analyses of the NHANES II cohort. Relative
risk of all cancer mortality for different blood lead levels compared with
referent blood lead level of 8 ug/dL (the 12.4th percentile) among white men
A and while women B in the United States (NHANES II). The solid line
shows the fitted 5-knot spline relationship; the dashed lines are the point
wise upper and lower 95% confidence limits.
Source: Jemal et al. (2002).
1 measurement produces less reliable estimates than would be obtained through multiple
2 measurements and precludes addressing temporal changes in lead exposure over the follow-up
3 period. Lack of control for exposure to occupational carcinogens other than lead and potential
4 residual confounding by duration and intensity of tobacco smoking also could have biased the
5 results, especially for men.
6 Lustberg and Silbergeld (2002) carried out another biomarker-based general population
7 study based on the same NHANES II mortality cohort used by Jemal et al. (2002). This study
8 did not exclude nonwhites, however, and employed more extensive adjustment for potential
May 2006
6-218
DRAFT-DO NOT QUOTE OR CITE
-------
1 confounding factors than the Jemal et al. (2002) analyses (i.e., education, body mass index, and
2 exercise were included in the regression models, although alcohol intake was not). In addition,
3 persons with blood lead levels of 30 |ig/dL or higher were excluded in order to restrict
4 comparisons to levels below the OSHA standard for lead exposure. Persons with levels below
5 10 |ig/dL served as the referent group. Survival analyses adjusted for potential confounders
6 found a relative risk for cancer mortality of 1.5 (95% CI: 0.9, 2.5) for those with blood lead
7 levels of 10 to 19 |ig/dL and 1.7 (95% CI: 1.0, 2.8) for those with levels of 20 to 29 |ig/dL.
8 Separate analyses of lung-cancer and non-lung-cancer deaths yielded estimates of increased risk
9 for moderate- or high-exposure groups, compared with the referent population, both for lung
10 cancer and non-lung cancer. However, none of the estimates reached the P < 0.05 level of
11 statistical significance, and the results for non-lung cancers showed no evidence of an exposure-
12 response relationship.
13 As with Jemal et al. (2002), the use of a biomarker for exposure and the prospective
14 design of the study are strengths. Its attempts to control for potential confounders were more
15 extensive, and its choice of cut points for the referent category yielded more males in the referent
16 group, although that group still included less than 20% of the study population. However, it is
17 notable that blood lead levels rose significantly with smoking level. The models included terms
18 for former smoking, current light smoking, and current heavy smoking (>1 pack per day).
19 Nevertheless, some degree of residual confounding due to smoking might have remained, which
20 could have contributed to the estimated risk of lung cancer for the highest exposure category
21 (relative risk of 2.2 [95% CI: 0.8, 6.1]). Such residual confounding would have had less effect
22 on the results for non-lung cancer. As noted regarding the other NHANES-based study,
23 however, mortality due to cancers of other sites was too uncommon to allow for reliable
24 site-specific comparisons. In the Lustberg and Silbergeld analysis, all cause and cardiovascular
25 mortality increased monotonically with blood lead level, which might indicate residual
26 confounding from SES or smoking affecting both heart disease and cancer.
27
28 6.7.5.4 Other Lead Studies
29 There are a variety of other epidemiologic studies of lead exposure, which are less
30 important than the key studies above but which offer some information. Studies reviewed in this
31 section are summarized in Annex Table AX6-7.4. The weaknesses in these studies largely stem
May 2006 6-219 DRAFT-DO NOT QUOTE OR CITE
-------
1 from potential confounding by other metals in the cohort studies and likely misclassification of
2 lead exposure in the case-control studies.
3 Some studies have examined the potential link between parental lead exposure and
4 childhood cancer. These are briefly described in Section 5.6.2.1, but are not further detailed
5 here. Lack of direct measures of child exposure, the fact that many of the same interpretational
6 problems (e.g., potential coexposures) noted for occupational studies as a whole, and low
7 statistical power due to the rarity of the outcome under study render the available evidence less
8 relevant than that from direct study of exposed occupational and general populations.
9
10 6.7.6 Confounding of Occupational Lead Studies Due to Other Occupational
11 Exposures: Arsenic, Cadmium
12 A number of studies of lead workers come from smelters, where exposures to other metals
13 are common. Of particular concern are other lung carcinogens, especially arsenic (workers
14 exposed to high levels of arsenic historically have had a lung cancer relative risk of 3-4, see
15 Steenland et al. 1996), but also cadmium. Glass workers are also of limited use for inference
16 about lead effects, as they are also typically exposed to arsenic, cadmium, chromium, and nickel,
17 all of which are lung carcinogens (e.g., see Wingren and Axelson, 1993).
18 In some smelters, measurements have been taken which indicate clearly that exposures to
19 these other carcinogens was minimal and the main suspect is lead (e.g., Steenland et al., 1992).
20 In others, however, one is unable to disentangle the effects of arsenic and lead (Ades and
21 Kazantis, 1988, Lundstrom et al., 1997). As a result, these studies cannot yield strong evidence
22 regarding the possible relation between lung cancer and lead specifically. The study by
23 Lundstrom et al., 1997 is particularly important in this regard, because it had a high relative risk
24 of 2.8 (95% CI: 2.0, 3.8), and had an important effect in raising the overall result when included
25 in meta-analyses (e.g., Steenland and Boffetta [2000], where exclusion of the Lundstrom et al.
26 study lowered the estimated combined lung cancer relative risk from 1.30 to 1.14). A subsequent
27 publication by Englyst et al. (2001) indicated that the smelter workers studied by Lundstrom
28 et al. (1997) were likely to have had significant exposure to arsenic, and the authors concluded
29 that it was impossible to separate the effects of lead and arsenic.
30
May 2006 6-220 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.7.7 Confounding of Lead Studies: Smoking and Other Factors
2 The most informative studies of lead carcinogenicity are those comparing highly exposed
3 workers to general populations. In these comparisons one must consider typical differences
4 between worker populations and the general populations, in particular differences due to
5 smoking and diet. Smoking can be a major confounder for lung cancer, while diet or SES can
6 be a confounder, albeit weaker, for stomach cancer.
7 Regarding smoking, it has been shown both theoretically and empirically that
8 confounding due to smoking differences between workers and the general population will
9 typically account for an observed relative risk of approximately 1.1 to 1.2, with a possible
10 maximum of about 1.4 (Axelson and Steenland, 1988; Siemiatycki et al., 1988). Furthermore,
11 most occupational cohort studies are retrospective and have little information on smoking,
12 making it impossible to control directly for potential confounding by this strong risk factor.
13 As noted above, the lung cancer relative risk in the meta-analysis of Steenland and Boffetta
14 (2000), after excluding the Lundstrom et al. study, was 1.14 (95% CI: 1.04, 1.73), based on
15 seven occupational cohort studies, six of which used a non-worker external referent population,
16 and none of which controlled for smoking as a confounder. This relatively small excess relative
17 risk could plausibly be due to confounding by smoking. Unfortunately the occupational cohort
18 studies were usually not followed by nested-case control studies of lung cancer which could have
19 controlled for smoking, and furthermore they usually did not involve internal exposure-response
20 analyses, wherein confounding by smoking is usually minimal. An exception was the lung
21 cancer case-control study conducted by Anttila et al. (1995) within a large cohort of Finnish
22 workers with known blood lead levels. In this case-control study smoking-adjusted lung cancer
23 odds ratios were increased among workers with higher estimated cumulative blood lead or higher
24 peak blood lead exposure compared to workers with the lowest exposure, and the authors noted
25 that smoking actually appeared to be a "weak negative confounder" for the high peak blood lead
26 group. Also, in one large population-based case-control study with extensive information on
27 other cancer risk factors, there remained an elevated odds ratio for lung cancer with substantial
28 lead exposure after controlling for smoking (Siemiatycki et al., 1991). Hence there is some
29 evidence that confounding by smoking does not explain the modest excess lung cancer risk seen
30 in many studies.
May 2006 6-221 DRAFT-DO NOT QUOTE OR CITE
-------
1 Diet high in salt or smoked meats, Helicobacter pylori infection, and SES are possible
2 confounders for stomach cancer. Those of highest SES compared to those of lower SES have
3 been shown to have a relative risk of about 3 (Tomatis, 1990). None of the occupational cohort
4 studies, in which again stomach cancer in workers was compared to the general population,
5 controlled for these potential confounders. However, these potential confounding factors are
6 much less powerful risk factors in respect to stomach cancer than smoking is with respect to lung
7 cancer, and hence are unlikely to account for relative risks higher than perhaps 1.1 or at most 1.2.
8 Given that the occupational cohort studies had a combined relative risk of 1.34 (95% CI: 1.14,
9 1.57) in the meta-analysis of Steenland et al. (2002) and 1.33 (95% CI: 1.18, 1.49) in that of Fu
10 and Boffetta (1995), it seems unlikely that confounding by these factors can fully account for the
11 excess stomach cancer risk observed in the occupational studies.
12
13 6.7.8 Summary of Epidemiologic Evidence for the Genotoxic and
14 Carcinogenic Effects of Lead
15 The availability of studies of cancer in lead-exposed populations was relatively limited at
16 the time of the 1986 Lead AQCD. The number and range of studies has notably expanded since
17 that time, including extended follow-ups of major extant cohorts, new cohort and case-control
18 studies, and analyses addressing not only cancer but genotoxicty. These new human data greatly
19 expand our knowledge of possible lead carcinogenicity. Animals studies are primarily based on
20 dermal exposure to lead acetate. While the animal studies clearly show a carcinogenic effect,
21 they are of less relevance here because human exposures are usually to inhaled lead oxides.
22 • Studies of genotoxicity consistently link lead exposed populations with DNA damage and
23 micronuclei formation, although less consistently with the more established indicator of
24 cancer risk, chromosomal aberrations. Epidemiologic studies, particularly those of the
25 high exposed occupational cohorts, are the most informative for determining whether
26 lead causes cancer, because in general we assume that any cancer effect will be strongest
27 and most easily detected when exposure is highest. There are only two general
28 population cohort studies at ambient levels, and these are of the same population
29 (NHANES II in the late 1970s). These general population studies at lower exposure
30 levels show internal dose-response trends but suffer at times from small numbers for site-
31 specific analyses or lack of site-specific analyses altogether and, also, from possible
32 residual confounding by SES and smoking.
33 • The epidemiologic data reviewed above from key high lead exposure occupational
34 studies suggest a relationship between lead exposure and cancers of the lung and the
35 stomach. These are supported by two meta-analyses. This is limited by potential
May 2006 6-222 DRAFT-DO NOT QUOTE OR CITE
-------
1 confounders such as other occupational exposures (arsenic, cadmium), smoking, and
2 dietary habits. General population cohort studies in which low lead exposure was
3 assessed via blood levels and adjusted for confounders showed trends suggestive of a
4 relationship, but were limited by relatively small numbers for site-specific analysis.
5 A cancer assessment on lead has not been conducted using the U.S. EPA Guidelines for
6 Carcinogen Risk Assessment (U.S. Environmental Protection Agency, 2005). However,
7 the most recent IARC (2005) review concluded that inorganic lead compounds were
8 probable human carcinogens (Group IIA), based on limited evidence in humans and
9 sufficient evidence in animals.
10
11
12 6.8 EFFECTS OF LEAD ON THE IMMUNE SYSTEM
13 6.8.1 Summary of Key Findings of the Effects of Lead on the Immune
14 System from the 1986 Lead AQCD
15 The 1986 Lead AQCD concluded that studies conducted in laboratory animal models
16 provided evidence for immunosuppressive effects of lead; however, evidence for such effects in
17 humans was lacking. Since then, the epidemiological study of immunological effects of lead has
18 progressed considerably. The currently available epidemiologic and clinical observations are
19 consistent with the greater body of evidence derived from studies in experimental animals
20 indicating that lead can suppress cellular and humor immunity and decrease host resistance to
21 infection agents and tumor cells (see Section 5.9). Findings from the epidemiologic studies
22 suggest that lead exposure (as reflected in blood lead concentration) may be associated with
23 effects on cellular and humoral immunity. These effects include changes in serum
24 immunoglobulin levels (e.g., elevated serum IgE); perturbation of peripheral lymphocyte
25 phenotype profiles, including decreases in peripheral blood T-cell abundance and changes in
26 T-cell:B-cell abundance ratios; suppression of lymphocyte activation; and suppression of
27 neutrophil chemotaxis and phagocytosis.
28 Available studies of associations between lead exposure and immunological outcomes are
29 summarized in Annex Tables AX6-8.1 and AX6-8.2. In general, while the studies provide
30 support for associations between lead exposure and immunological outcomes, the studies have
31 numerous limitations that complicate the assessment of the strength of the associations and
32 causation. Furthermore, the health consequences of outcomes that have been associated with
33 lead exposure are uncertain. All studies have been cross-sectional in design and most included
34 relatively small cohorts. The studies implemented varying degrees of quantitative analysis of
May 2006 6-223 DRAFT-DO NOT QUOTE OR CITE
-------
1 potential covariables and confounders. In most studies, a detailed analysis of covariables and
2 confounding was lacking, and many of the reports offered no analysis of covariables or
3 confounding. Covariables that were considered (but not consistently) in multivariate analyses or
4 controlled by stratification included age, sex, race, smoking habits, alcohol consumption, and
5 illness and/or medications that might affect the immune system. Studies that offer the strongest
6 designs are discussed in greater detail below.
7
8 6.8.2 Host Resistance, Hypersensitivity, and Autoimmunity
9 Associations between lead exposure and host resistance have not been rigorously
10 examined in humans. Two analyses of illness surveys in children (Rabinowitz et al., 1990) and
11 lead workers (Ewers et al., 1982) have been reported. Both studies relied on personal surveys for
12 assessment of illness and neither study considered covariates or confounders in the analyses.
13 In the Rabinowitz et al. (1990) study, the highest relative risks (blood lead concentration
14 > 10 |ig/dL compared to <10 |ig/dL) were: other respiratory tract illnesses, 1.5 (95% CI: 1-2.3);
15 severe ear infections, 1.2 (95% CI: 1-1.4); illnesses other than cold or influenza, 1.3 (95% CI:
16 1.0-1.5). The Ewers et al. (1982) reported mean frequency of self-reported colds and influenza
17 per year of employment in lead workers (blood lead concentration range 21-85 |ig/dL) compared
18 to a reference group (range: 6-21 |ig/dL). Mean frequency of 2-4 illnesses per year was higher
19 among the lead workers 28.8% vs. 16.1%); however, a statistical analysis of the data was not
20 reported. Collectively, these studies do not provide convincing evidence for a strong association
21 between lead exposure and disease resistance in humans.
22 Two studies have been reported that have examined possible associations between lead
23 exposure (e.g., blood lead concentration) and asthma. In the Rabinowitz et al. (1990) study
24 described above, the relative risk of asthma (blood lead concentrations <5 |ig/dL compared to
25 >5 or > 10 |ig/dL) were not significant in Caucasian or African American cohorts. In the
26 Caucasian cohort, the hazard ratios were 1.4 (95% CI: 0.7-2.9, blood lead, >5 |ig/dL) and
27 1.1 (95% CI: 0.2-8.4, blood lead, > 10 (ig/dL). In the African American cohort, the
28 corresponding hazard ratios were 1.0 (95% CI: 0.8-1.3, >5 (ig/dL) and 0.9 (95% CI: 0.5-1.4,
29 > 10 |ig/dL). Hazard ratios for asthma incidence in African Americans, compared to Caucasians
30 (<5 |ig/dL), were 1.6 (95% CI: 1.4-2.0, <5 |i/dL), 1.4 (95% CI: 1.2-1.6, >5 jig/dL), and
31 2.1 (95% CI: 1.2-3.6, >10 jig/dL). Thus, while there appeared to be an elevated risk of asthma
May 2006 6-224 DRAFT-DO NOT QUOTE OR CITE
-------
1 in the African-American cohort, relative to the Caucasian cohort, a significant effect of blood
2 lead concentration on risk in African-Americans or Caucasians was not evident in this study.
3 Covariates included in the analysis were average annual income, birth weight and gender.
4 Similar results were obtained when a more stringent definition of asthma was applied to the
5 subjects. Collectively, these studies do not provide convincing evidence for a strong association
6 between lead exposure and asthma in children.
7
8 6.8.3 Humoral Immunity
9 A characteristic immunological response to lead exposure in animals is an increase in
10 production of IgE, immunoglobulin that has been assoicated with allergy and allergic airway
11 disease (see Section 5.9.3.2). Although epidemiological literature is not conclusive regarding the
12 dose-response relationships for lead effects on immunoglobulin production in humans, studies in
13 children have consistently found significant associations between increasing blood lead
14 concentration and increasing serum IgE levels (Table 6 8.1; Karmaus et al., 2005; Lutz et al.,
15 1999; Sun et al., 2003). These effects were evident at blood lead concentrations <10 |ig/dL.
16 Increasing serum IgE levels also have been observed with increasing blood lead concentration
17 (blood lead >30 |ig/dL) in association with occupational exposures to lead (Heo et al., 2004).
18 Outcomes for other immunoglobulin indices in adults have been less consistent (Pinkerton et al.,
19 1998; Sarasua et al., 2000).
20 Possible associations between lead exposure and biomarkers of humoral immunity in
21 children have been examined in several cross-sectional studies (Annesi-Maesano et al., 2003;
22 Karmaus et al., 2005; Lutz et al., 1999; Reigart and Graher, 1976; Sarasua et al., 2000; Sun et al.,
23 2003; Wagnerova et al., 1986). Four studies warrant particular attention because they examined
24 a relatively low range of blood lead concentrations and applied multivariate analyses to the data
25 in attempts to control for possible covariables (Karmaus et al., 2005; Lutz et al., 1999; Sarasua
26 et al., 2000; Sun et al., 2003). Three studies found significant associations between increasing
27 blood lead concentration and serum IgE levels (Karmaus et al., 2005; Lutz et al., 1999; Sun
28 et al., 2003). The reported percent increase in serum IgE levels measured in these studies ranged
29 from approximately 50 to 400%. The Lutz et al. (1999) study measured serum IgE and IgG
30 (against Rubella) in 270 children (age range 9 months to 2 years; blood lead range 1-45 |ig/dL).
31 The observed blood lead-age-IgE relationship is shown in Figure 6-8.1. The highest IgE levels
May 2006 6-225 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-8.1. Summary of Results of Selected Studies of Associations Between Lead Exposure
to
o
o
ON
ON
to
to
ON
O
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Study
C/z/Wrat
Annesi-Maesano et al. (2003)
Karmaus et al. (2005)
Lutzetal. (1999)
Sarasua et al. (2000)
Sun et al. (2003)
Adults
Heo et al. (2004)
Pinkerton et al. (1998)
Sarasua et al. (2000)
-, decrease; +, increase; o, no effect;
Subjects
neonates
children, 7-10 yr
children, 9 mo-6 yr
children, 6-35 mo
children, 3-6 yr
batter manufacture workers
smelter workers
general population
Blood Lead (jig/dL)
n Mean (SD) Range
374 67 (48)b NR
331 3 l-5e
270 NR 1-45
372 7 ~2-16d
73 NR -3-40
606 -22 (~10)e NR
229 39f <2-55
433 4.3 ~l-10d
IgA IgE IgG IgM
NR +c NR NR
0 + 0 0
NR + NR NR
+ NR + +
NR +
0 + 0 0
o NR o
o NR o o
NR, not reported, Ig, serum immunoglobulin level
a total number of subjects (including reference group)
b infants cord blood (maternal blood lead mean was 96 ug/dL (SD 58)
0 in association with increasing neonatal hair lead
d 5-95th percentile range
e mean of age-group means and SDs
f median
-------
„--•-.
~v- -• \
A— ~
Age (in months)
Figure 6-8.1. Relationship between blood lead concentration (PbB), age, and serum IgE
level in children. Spearmen partial correlation between blood lead and
serum IgE is 0.22 p = 0.0004, n = 221).
Source: Lutzetal. (1999).
1 (mean 211 lU/mL, SD 441, n = 17) were observed in children who had blood lead concentrations
2 in the range 15-19 |ig/dL; by comparison, mean IgE levels were blood lead concentrations in the
3 range of 15-19 |ig/dL; by comparison, mean IgE levels were 52 ITJ/mL (SD 166) for subjects
4 who had blood lead concentrations <10 |ig/dL (n = 174). The Karmaus et al. (2005) study
5 measured serum IgA, IgE, IgG, and IgM levels in 331 children (age range 7-10 years). Blood
6 lead concentrations were lower in this study than in the Lutz et al. (1999) study (1-5 |ig/dL).
7 A multivariate linear regression analysis revealed a significant association between blood lead
8 (p < 0.05) and serum IgE (but not IgA, IgG, or IgM). The change in serum IgE level may appear
9 not to be monotonic with increasing blood lead concentration (Figure 6-8.2). However, the
10 two lowest means are not significantly different so that apparent non-monotonicity of the
May 2006
6-227
DRAFT-DO NOT QUOTE OR CITE
-------
70
60
50
j"
3
5. 40 -
ill
_O)
E 30-
8
to
20-
10-
0
<2.2(n=82) 2.2-2.8 (n=81) 2.8-3.4 (n=86)
Blood Lead Cateqorv (uq/dU
>3.4 (n=82)
Figure 6-8.2. Relationship between blood lead concentration and serum IgE level in
children. Mean serum IgE levels (standard deviations not reported) are
adjusted for age, number of infections in the previous 12 months, exposure
to passive smoke in the previous 12 months, and serum lipids (sum of
cholesterol and triglycerides). Means of serum IgE levels in blood lead
categories were significantly different (F-test p = 0.03).
Source: Karmaus et al. (2005).
1 effect/exposure relationship does not have statistical support. The highest IgE levels (adjusted
2 mean 59 IU/L) were observed in the children who had blood lead concentrations ranging from
3 2.8-3.4 |ig/dL (n = 86) and >3.4 jig/dL (n = 82). Sun et al. (2003) measured serum IgE, IgG,
4 and IgM levels in children, ages 3-6 years (blood lead concentration range 2.6-44 |ig/dL,
5 n = 73). A nonparametric comparison of immunoglobulin levels between low (<10 |ig/dL) and
6 high (> 10 |ig/dL) blood lead strata revealed significantly higher IgE levels (Figure 6-8.3) and
7 significantly lower IgG and IgM levels in the high blood lead stratum.
8 The study by Annesi-Maesano et al. (2003) provides further suggestive evidence for
9 an association between lead exposure and increasing IgE levels. The study included 374 mother-
10 infant pairs who had relatively high mean blood lead levels (maternal mean 96 |ig/dL, SD 58;
May 2006
6-228
DRAFT-DO NOT QUOTE OR CITE
-------
EDC
2DC-
200H
13C-
c-
-'JC_
.4
e
1C
Pb
1.2
1.4
-.3
1.8
Figure 6-8.3. Relationship between blood lead concentration (lead) and serum IgE level
in children. Mean serum IgE levels in female children whose blood lead
concentrations were in the range 10-40 ug/dL (20.4 IU/L; n = 16) were
significantly higher than for children whose blood lead concentrations
<10 ug/dL (13.1 IU/L; n = 17).
Source: Sun et al. (2003).
1 infant cord 67 |ig/dL, SD 48). Serum IgE level was significantly associated with increasing
2 infant hair lead (p < 0.001), but not with cord blood lead or placental lead level. The association
3 between IgE and hair lead levels was evident in a subset of mother-infant pairs, in which mothers
4 were classified as nonallergenic, and was unrelated to maternal smoking (i.e., urinary cotinine).
5 The ATSDR Multisite Lead and Cadmium Exposure Study (ATSDR, 1995) is one of the largest
6 studies to assess humoral immune status in association with lead exposures; however, it did not
7 include an assessment of IgE. The study included a cross-sectional analysis of serum IgA, IgG,
8 and IgM levels in 1,561 subjects (age range 6 months to 75 years) who resided in areas impacted
9 by lead mining and/or smelting operations and in 480 demographically-matched controls
May 2006
6-229
DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
(Sarasua et al., 2000). A multivariate linear regression analysis of immunoglobulin levels and
blood lead concentration (exposed and control groups combined) revealed associations between
increasing blood lead and increasing serum IgA, IgG, and IgM levels in subjects 6-35 months of
age (blood lead 5th-95th percentile range 1.7-16 |ig/dL, Figure 6-8.4).
0.9
0.6-4.9
5-9.9 10-14.9
Blood Lead Category (ug/dL)
>=15
Figure 6-8.4. Relationship between blood lead concentration and serum immunoglobulin
(Ig) levels in children. Shown are relative changes in serum Ig levels,
adjusted for age, sex, and exposure location. P-values reflect comparison
to <5 ug/dL blood lead category mean (<5 mg/dL, n = 165; 5-9.9 ug/dL,
n = 136; 10-14.9 ug/dL, n = 47; ;>15 ug/dL, n = 24).
Source: Sarasua et al. (2000).
7 Possible associations between lead exposure and biomarkers of humoral immunity also
8 have been examined in several cross-sectional studies of lead workers (Alomran and Shleamoon,
9 1988; Anetor and Adeniyi, 1998; Ayatollahi, 2002; Coscia et al., 1987; Ewers et al., 1982;
10 Heo et al., 2004; Kimber et al., 1986; Pinkerton et al., 1998; Undeger et al., 1996). Outcomes
11 from these studies, with respect to humoral immune parameters, measured as serum and/or
12 salivary immunoglobulin levels, are mixed. Some studies finding positive associations with
May 2006
6-230
DRAFT-DO NOT QUOTE OR CITE
-------
1
2
3
4
5
6
7
8
9
10
11
12
13
blood lead (Heo et al., 2004), negative associations (Anetor and Adeniyi, 1998; Ewers et al.,
1982; Pinkerton et al., 1998), or no (or mixed) effects (Alomran and Shleamoon, 1988; Kimber
et al., 1986; Queiroz et al., 1994b; Sarasua et al., 2000; Undeger et al., 1996). Based on study
design considerations (e.g., cohort criteria, size, treatments of covariates), three studies warrant
particular attention (Heo et al., 2004; Pinkerton et al., 1998; Sarasua et al., 2000). Of these, only
Heo et al. (2004) assessed serum IgE levels consistent with outcomes reported in children,
increasing blood lead concentration was significantly associated with increasing serum IgE
levels (Figure 6-8.5). The study measured serum IgE, IL-4 and IFNy in 606 battery manufacture
workers. Serum IgE levels were significantly higher in the blood lead stratum (>30 |ig/dL)
compared to lower strata (<10 or 10-29 |ig/dL) for the age strata 30-39 years, >40 years, and for
all ages combined.
LLJ
_0>
E
3
G
10-29
>=30
Blood Lead Category (pg/dL)
Figure 6-8.5. Relationship between blood lead concentration and serum IgE level in
lead workers. Mean serum IgE levels in high blood lead category were
significantly higher for all ages (shown), and within age categories
^40 years and 30-39 years, but not within age category <30 years.
Source: Heo et al. (2004).
May 2006
6-231
DRAFT-DO NOT QUOTE OR CITE
-------
1 Although the Pinkerton et al. (1998) study did not assess IgE outcomes, it offers the
2 strongest study design of the three for assessment of other immunoglobulin classes. Although it
3 is a relatively small cross-sectional study, it considered immune illnesses and immune
4 suppressant drugs in the construction of the cohorts and examined a relatively large number of
5 potential covariates in the data analysis. Serum immunoglobulin levels were measured in male
6 smelter (n = 145) workers and hardware workers (n = 84). Excluded (by blind evaluation) from
7 the study cohorts were individuals who had "serious" illnesses of the immune system, who were
8 taking immune suppressant drugs, or who had chemical exposures (other than to lead) that might
9 affect immune function. Median blood lead concentrations were 39 |ig/dL (range 15-55) in the
10 lead workers and <2 |ig/dL (range <2-12) in the reference group. Covariate-adjusted (logistic
11 regression) geometric mean serum IgA, IgG, and IgM, and salivary IgA levels in the lead
12 workers were not significantly different from the reference group; however, the adjusted
13 regression coefficient for serum IgG and time-integrated (but not current) blood lead
14 concentration was negative and significant.
15 The Sarasua et al. (2000) study, described above for its assessment of children, also
16 included a cross-sectional analysis of serum IgA, IgG, and IgM levels in adults (age 16-75 years,
17 n = 433; blood lead 5th-9th percentile range 1-10 |ig/dL) and found no significant associations
18 between blood lead and serum immunoglobulin levels (serum IgE outcomes were not assessed).
19 Also germane to the evidence for effects of lead on humoral immunity in humans are the
20 results of a clinical study in which serum immunoglobulin levels were repeatedly measured in a
21 lead smelter worker who underwent CaEDTA chelation therapy three times per week for a
22 period of 10 weeks (Sata et al., 1998). Serum IgA, IgG, and IgM were significantly higher when
23 assessed 24 h after each CaEDTA treatment compared to assessments made prior to treatment.
24 Furthermore, serum IgG levels were significantly negatively correlated with blood lead
25 concentration during the treatment period. Before-treatment and after-treatment blood lead
26 concentration means were 45.1 |ig/dL (SD 16.0) and 31.0 |ig/dL (SD 9.8), respectively.
27
28 6.8.4 Cell-Mediated Immunity
29 Studies conducted in animals and in vitro experimental models indicate that lead
30 preferentially targets macrophages and T lymphocytes (see Section 5.9.4). However, the
31 prominent effects are largely on immune system function, rather than overt cytotoxicity to
May 2006 6-232 DRAFT-DO NOT QUOTE OR CITE
-------
1 lymphoid tissues. Lead suppresses Thl-dependent responses (e.g., delayed type
2 hypersensitivity) and production of Thl cytokines; and stimulates macrophages into a
3 hyperinflammatory state. These types of functional changes have not been rigorously evaluated
4 in human epidemiological studies, which have relied, for the most part, on changes in
5 lymphocyte abundance as the main outcomes for assessing status of cellular immune systems.
6 Lead-induced functional changes in immune responses may not be reflected in changes in
7 lymphocyte abundance and, correspondingly, specific functional changes may not be readily
8 discerned from observed changes in lymphocyte abundance. Studies of children have found
9 significant associations between increasing blood lead concentration and decreases in T-cell
10 abundance, with corresponding increases in B-cell abundance (Karmaus et al., 2005; Sarasua
11 et al., 2000; Zhao et al., 2004). These effects have been observed in children whose blood lead
12 concentrations were below 10 |ig/dL (Karmaus et al., 2005; Sarasua et al., 2000), although not
13 all studies (e.g., Lutz et al., 1999) have found such associations at higher blood lead
14 concentrations (e.g., 10-45 jig/dL). Studies of occupational lead exposures have also found
15 associations between increasing blood lead concentration and changes (increases or decreases) in
16 T-cell abundance (Fischbein et al., 1993; Pinkerton et al., 1998; Sata et al., 1997). Effects were
17 observed in association with blood lead concentrations below 25 |ig/dL (Fischbein et al., 1993)
18 and in populations whose blood lead concentrations ranged from approximately 7 to 55 |ig/dL
19 (Pinkerton et al., 1998; Sata et al., 1997). Outcomes from these studies are qualitatively
20 summarized in Table 6-8.2 and are discussed in greater detail below.
21 Several cross-sectional studies have examined possible associations between lead
22 exposure and biomarkers of cellular immunity in children (Karmaus et al., 2005; Lutz et al.,
23 1999; Sarasua et al., 2000; Zhao et al., 2004). Three studies (Karmaus et al., 2005; Sarasua
24 et al., 2000; Zhao et al., 2004) found significant associations between increasing lead exposure
25 and decreases in T-cell abundance (Table 6-8.2). The largest study (Sarasua et al., 2000)
26 examined abundance of total lymphocytes, T-cells (CD3+), B-cells (CD20+), NK cells, and CD4+
27 and CD8+ T-cell phenotypes in infants, children, and adolescents. Associations between
28 increasing blood lead concentration and increasing B-cell abundance (% and number), and
29 decreasing T-cell abundance (%) were found for children 6-35 months of age (n = 312), after
30 adjustment for age, sex, and study site (of four mining/smelting sites). Comparison of adjusted
31 means for outcomes across blood lead strata revealed that the differences were significant for the
May 2006 6-233 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-8.2. Summary of Results of Selected Studies of Associations Between Lead Exposure
to
o
o
Oi
ON
to
OJ
J^.
^ r
Blood Lead (jig/dL)
Study
Children
Karmaus et al. (2005)
Lutzetal. (1999)
Sarasua et al. (2000)
Zhao et al. (2004)
Adults
Fischbein et al. 1993)
Pinkerton et al. (1998)
Sarasua et al. (2000)
Sataetal. (1997)
Subjects
children, 7-10 yr
children, 9 mo-6 yr
children, 6-35 mo
children, 3-6 yr
firearms instructors
smelter workers
general population
lead stearate workers
na
331
270
372
73
87
229
433
99
Mean (SD)
3
NR
7
NR
3 1(4?
39k
4.3
19
PTib
Range
1-51
1-45 o
-2-161
-3-40 o
NR
<2-55 o
-1-101 o
7-50 o
TC PTI d PTI C
H AC AHC
o - NR
NR NR NR
o o NR
- + -
o NR
000
000
o + NR
T f
AM
0
NR
NR
NR
NR
+
NR
-
NKg
0
NR
0
NR
0
0
0
NR
Bh
-
0
+
0
+
+
0
0
-, decrease; +, increase; o, no effect; NR, not reported; SD, standard deviation.
H
6
o
o
H
O
o
H
W
O
O
r-H
H
W
a total number of subjects (including reference group)
b T-cells (CD3+)
c T-helper cells (CD4+)
d Cytotoxic T-cells (CD8+)
e CD4+CD8+
f T-memory cells (CD45RO+, CD45RA+)
g Natural killer cells (e.g., CD16+, CD56+)
h B-cells (e.g., CD19+, CD20+)
1 5-95* percentile range
1 high exposure group
k median
-------
1 > 15 |ig/dL stratum only, compared to the <5 |ig/dL stratum. The Karmaus et al. (2005) study
2 examined children in the age range 7-10 years (n = 331) who had blood lead concentrations
3 <5 |ig/dL. In addition to age and sex, regression models relating outcomes to blood lead
4 concentration included exposure to environmental tobacco smoke and infections in the previous
5 year as covariates. Similar to the Sarasua et al. (2000) study, Karmaus et al.(2005) found
6 significant associations between blood lead concentration and decreased T-cell abundance
7 (CD3+, CD3+CD8+) and increased B-cell (CD19+) abundance (for the blood lead quartile
8 2.2-2.8 |ig/dL; Figure 6-8.6). Zhao et al. (2004) examined lymphocyte phenotype abundance in
9 children in the age range 3-6 years (n = 73) and found significantly lower % abundance of T-cell
10 phenotypes CD3+CD4+, CD4+CD8+ and significantly higher abundance of D3+CD8+ cells in
11 children whose blood lead concentrations were > 10 |ig/dL compared to <10 |ig/dL. Lutz et al.
12 (1999) found no significant associations between blood lead concentration and age-adjusted
13 T-cell (CD3+) or B-cell (CD 19+) abundance or abundance of various other lymphocyte
14 phenotypes (i.e., CD2+, CD25+, CD28+, CD71+) in children whose blood lead concentrations
15 were 10-14, 15-19, or 20-45 |ig/dL compared to <10 |ig/dL.
16 A larger set of studies have evaluated potential associations between lead exposure and
17 biomarkers of cellular immunity in adults (Basaran and Undeger, 2000; Cohen et al., 1989;
18 Coscia et al., 1987; Fischbein et al., 1993; Kuo et al., 2001; Mishra et al., 2003; Pinkerton et al.,
19 1998; Sarasua et al., 2000; Sata et al., 1998, 1997; Yucesoy et al., 1997b; Undeger et al., 1996).
20 Four studies warrant particular attention because they implemented relatively stronger study
21 designs (i.e., cohort criteria, size, treatment of covariates): Fischbein et al., 1993; Pinkerton
22 et al., 1998; Sarasua et al., 2000; and Sata et al., 1998). With one exception (Sarasua et al.,
23 2000), all were studies of relatively small occupational cohorts. The Sarasua et al. (2000) study
24 included a cross-sectional analysis of abundance of total lymphocytes, B-cells, NK cells, and
25 CD4+ and CD8+ T-cell phenotypes in individuals (n = 433), age 16-75 years. Associations were
26 not found between blood lead concentration and either B-cell or T-cell abundance, after
27 adjustment for age, sex, and study site (of four mining/smelting sites). The study did detect
28 ignificant associations among these variables in infants and children (see above discussion of
29 cellular immunity outcomes in children). However, all three occupational studies found
30 significant associations between increasing blood lead concentration and changes in abundanceof
31 circulating T-cells with either no effect or an increasing B-cell abundance (Fischbein et al., 1993;
May 2006 6-23 5 DRAFT-DO NOT QUOTE OR CITE
-------
1.12
1.08H
i_
O)
2 0.92 -
O
•c 0.88 H
01 0.84-
0.80
-Natural killer cells
-T-cells
• T-helper cells
-Memory T-helper cells
-Cytotoxic T-cells
- B-cells
<2.2(n=82) 2.2-2.8 (n=81) 2.8-3.4 (n=86)
Blood Lead Category (ug/dL)
>3.4 (n=82)
Figure 6-8.6. Relationship between blood lead concentration and T- and B-cell
abundances in children. Shown are relative changes in covariate-adjusted
absolute cell numbers (cells/uL) compared to the lowest blood lead group;
adjusted for age, number of infections in the previous 12 months, exposure
to passive smoke in the previous 12 months, and serum lipids (sum of
cholesterol and triglycerides). Abundances for T-cells, cytotoxic T-cells,
and B-cells in the 2.2-2.8 ug/dL group were significantly different (p <, 0.05)
from the <2.2 ug/dL group. Receptor phenotypes assayed were: T-cells,
CD3+; T-helper cells, CD3+CD4+; cytotoxic T-cells, CD3+CD8+; memory
T-helper cells, CD4+CD45RO+; natural killer cells, CD16+CD56+; B-cells,
CD3+CD5+CD19+.
Source: Karmaus et al. (2005).
4
5
6
Pinkerton et al., 1998; Sata et al., 1997). The strengths of the Pinkerton et al. (1998) study have
been described previously with respect to outcome measures for humoral immunity. The study
included male smelter workers (n = 145, mean blood lead 39 |ig/dL; range 15-55) and hardware
workers (n = 84, mean <2 |ig/dL, range <2-12). Covariate-adjusted significant outcomes were
an increase in B-cell (CD19+) abundance (% and number) and increases in CD4+CD45RA+ cell
abundance (%, number) in association with increasing blood lead concentration. Covariate-
May 2006
6-236
DRAFT-DO NOT QUOTE OR CITE
-------
1 adjusted mean levels of monocytes (%), and T-cells (% D4+CD8+, CD8+CD56+) were lower in
2 lead workers compared to the reference group.
3 The Fischbein et al. (1993) study examined a small group of firearms instructors (n = 51)
4 and age-matched reference subjects (n = 36). Fifteen of the instructors had blood lead
5 concentration >25 |ig/dL (mean 31.4, SD 4.3), the mean of the remaining 21 subjects was
6 4.6 |ig/dL (SD 4.6). Mean blood lead concentration of the reference group was reported as
7 <10 |ig/dL. Increasing blood lead concentration was significantly associated with decreasing
8 covariate-adjusted T-cell (CD4+) abundance (Figure 6-8.7). Covariate-adjusted T-cell (CD3+ %
9 and number, CD4+ % and number, CD4+CD8+ number) abundance was significantly lower
10 and B-cell (CD20+ cells % and number) abundance was higher in the instructors than in the
11 reference group.
12 The Sata et al. (1998) study included male lead stearate manufacture workers (n = 71)
13 and a nonexposed reference group (n = 28). Mean blood lead concentration was 19 |ig/dL
14 (range 7-50) in the lead workers (blood lead concentration for the reference group was not
15 reported). Categorical covariate-adjusted lead exposure classification (exposed, not exposed)
16 was significantly associated with lower T-cell (CD3+CD45RO+) number. Lead workers, relative
17 to the reference group, had significantly lower covariate-adjusted mean CD3+CD45RO+ number
18 and higher CD8+ cells (%).
19 The above observations of decreasing T-cell abundance in association with lead exposure,
20 as assessed from blood lead concentrations, is supported by results of several smaller cross-
21 sectional studies, including Basaran and Undeger (2000), Coscia et al. (1987), and Undeger et al.
22 (1996), as well as a clinical study in which T-cell and NK cell abundance was found to increase
23 after CaEDTA chelation therapy of a lead smelter worker (Sata et al., 1997). Lower serum levels
24 of the cytokines that function in the regulation of cellular immune responses, including IL-1P
25 and IFN-y, in lead workers compared to nonexposed subjects have also been observed (Yiicesoy
26 etal., 1997a).
27
28 6.8.5 Lymphocyte Function
29 Studies conducted in animal models have found mixed effects of lead on mitogen-induced
30 lymphocyte activation, promoting expansion of some types of lymphoid populations, while
31 suppressing other (see Section 5.9.5). Lead promotes the activation of Th2-type lymphocytes
May 2006 6-237 DRAFT-DO NOT QUOTE OR CITE
-------
1,8
1.6 H
.o
E 1.4 H
O i.*
c
i5 1-0 H
as
.c
O
8 0.8 H
n
0)
o:
0.6-
0.4
-B-cells
• Cytotoxic T-cells
- T-helper cells
-Natural killer cells
•T-cells
**
Reference (<10, n=36) Low Exposure (<25, n=36) High Exposure (>-25, n=15)
Exposure Category (Blood Lead, ug/dL)
Figure 6-8.7. Relationship between lead exposure and T- and B-cell abundances in
firearms instructors. Shown are relative changes in absolute cell numbers
compared to the reference group. Comparisons of exposed relative to the
reference group are shown as: * for p < 0.05; ** for p < 0.01; and *** for
p < 0.002. Receptor phenotypes assayed were: T-cells, CD3+; T-helper cells,
CD4+; cytotoxic T-cells, CD8+; natural killer cells, CD16+; B-cells, CD20+.
The CD4+/CD8+ ratio (not shown) was significantly lower in both the low
exposure (1.38 [SD 0.5], p < 0.002) and higher exposure group (0.95
[SD 0.5], p < 0.002), compared to the reference group (1.95 [SD 0.66]).
Source: Fischbein et al. (1993).
1 and suppresses Thl type lymphocytes; it also shifts the balance in the production of cytokines,
2 decreasing Thl cytokines (e.g., IFN, IL-12) and increasing production of Th2 cytokines (e.g.,
3 IL-4, IL-6, IL-10). The above findings are somewhat echoed in the overall findings from
4 epidemiological studies, with mixed outcomes when proliferation of peripheral lymphocytes was
5 the outcome measured, whereas, lead preferentially stimulated Th2 cytokine production and
6 suppressed Thl cytokine production when human peripheral lymphocytes were exposed to lead
7 in vitro.
May 2006
6-238
DRAFT-DO NOT QUOTE OR CITE
-------
1 Several studies (all of adults) have examined associations between lead exposure in adults
2 and lymphocyte activation, assessed as a proliferative response to mitogens and/or antigens
3 (Alomran and Shleamoon, 1988; Cohen et al., 1989; Fischbein et al., 1993; Kimber et al., 1986;
4 Mishra et al., 2003; Pinkerton et al., 1998; Queiroz et al., 1994b). Results of these have been
5 mixed. Three studies found no significant associations between blood lead concentrations in
6 lead workers and lymphocyte proliferative response to activating agents (Kimber et al., 1986;
7 Pinkerton et al., 1998; Queiroz et al., 1994b). Four studies found decreasing proliferative
8 response with increasing blood lead concentration (Alomran and Shleamoon, 1988; Cohen et al.,
9 1989; Fischbein et al., 1993; Mishra et al., 2003). The Alomran and Shleamoon (1988), Cohen
10 et al. (1989), Mishra et al. (2003), and Queiroz et al. (1994b) studies, which found significant
11 lead associations, included subjects who had relatively high blood lead levels (>60 |ig/dL)
12 compared to the Kimber et al. (1986) and Pinkerton et al. (1998) studies. The inclusion of
13 subjects with higher lead concentrations may have contributed to the differences in outcomes.
14 As noted in the previous section, the Fischbein et al. (1993) and Pinkerton et al. (1998)
15 studies are particularly noteworthy because of the strengths of the cohort selection and the data
16 analyses which attempted to account for potential confounders. Also, these are the only reported
17 studies that examined antigen-specific lymphocyte activation in humans. Mean blood lead
18 concentrations in the two studies were similar 31 |ig/dL (SD 4) in the Fischbein et al. (1993)
19 study and 39 |ig/dL (range 15-55) in the Pinkerton et al. (1998) study. Both studies found no
20 significant associations between lead exposures (i.e., blood lead concentration) and antigen-
21 specific lymphocyte proliferation, assessed in the Pinkerton et al. (1998) study with tetanus
22 toxoid as the antigen and in the Fischbein et al. (1993) study with staphylococcus aureus as the
23 antigen. However, the Fischbein et al. (1993) study also measured mitogen-induced lymphocyte
24 proliferation (induced with PHA or PWM) and found a significantly lower proliferative response
25 to the mitogens in association with lead exposure. This study also found a significant association
26 between increasing blood lead concentration and decreasing proliferative response in mixed
27 lymphocyte cultures (i.e., proliferative response of lymphocytes from exposed subjects when
28 incubated with inactivated lymphocytes from a reference subject).
29 Inorganic lead has been shown by in vitro studies to perturb several aspects of lymphocyte
30 function when introduced into primary isolates of human blood monocytes. Activated
31 lymphocytes show altered lysosomal enzyme secretion and altered expression and secretion of
May 2006 6-239 DRAFT-DO NOT QUOTE OR CITE
-------
1 cytokines (Bairati et al., 1997; Guo et al., 1996a; Hemdan et al., 2005). Lymphocytes activated
2 with Salmonella enteritidis or with monoclonal antibodies of CDS, CD28 and CD40, and
3 exposed to inorganic lead had suppressed expression of T-helper cell type TH-1 cytokines,
4 interferon (IFN-y), interleukin (IL-1P), and tumor necrosis factor (TNF-a), whereas activation
5 by CD antibodies increased secretion of Tn-2 cytokines, IL-5, IL-6, and IL-10 (Hemdan et al.
6 2005). Inorganic lead also activates transcription factor NK-KP in CD4+ cells (Pyatt et al., 1996),
7 an important regulator of T-cell activation, and increases expression of MHC class II surface
8 antigens (HLA-DR), an important surface antigen in the CD4+ response to exogenous antigens
9 (Guo et al., 1996b). Lead increases antibody production in cultured human B-cells (McCabe and
10 Lawrence, 1991). These observations suggest that lead may perturb cellular immune function
11 through a variety of mechanisms.
12
13 6.8.6 Phagocyte (Macrophage and Neutrophil) Function
14 Studies conducted in animals and in vitro models have shown that lead can modulate
15 macrophages into a hyperinflammatory phenotype, with increased production of
16 proinflammatory cytokines TNF-a and IL-6, increased release of reactive oxygen intermediates
17 and prostaglandins, and, conversely, depressed production of nitric oxide (see Section 5.9.6).
18 Epidemiologic studies have found associations between blood lead concentrations and modified
19 activation of macrophages in children whose blood lead concentrations ranged from 4 to
20 50 |ig/dL (Pineda-Zavaleta et al., 2004). Consistent with the above experimental observations,
21 outcomes have included decreased stimulated nitric oxide release and increased superoxide anion
22 production. In addition, studies have observed suppressed PMNL chemotaxis in association with
23 occupational exposures that resulted in blood lead concentrations of 12-90 |ig/dL (Bergeret
24 et al., 1990; Queiroz et al., 1994a, 1993).
25 Pineda-Zavaleta et al. (2004) examined mitogen (PHA)- and cytokine (INFy)-induced
26 activation of blood monocytes collected from 65 children (age range 6-11 years) who resided
27 near an active lead smelter. Mean blood lead concentrations of subjects at three schools were:
28 7.0 |ig/dL (range 3-25 |ig/dL; 8,100 meters from smelter complex), 21 |ig/dL (range
29 11-49 |ig/dL; 1,750 meters from smelter), and 30 (range 10-48 |ig/dL; 650 meters from smelter).
30 Endpoints measured were nitric oxide and superoxide anion production, a response generally
31 attributed to activated macrophages. Increasing blood lead concentration was significantly
May 2006 6-240 DRAFT-DO NOT QUOTE OR CITE
-------
1 associated with decreasing PHA-induced nitric oxide production and increasing INFy-induced
2 superoxide anion production. The mitogen, PHA, activates macrophages indirectly through
3 activation of lymphocytes, whereas INFy, a cytokine released from CD44 (TH1) cells, directly
4 activates macrophages. Thus, one interpretation of this outcome is that lead suppressed T-cell
5 mediated macrophage activation and stimulated cytokine-induced macrophage activation.
6 Possible associations between occupational lead exposure and PMNL chemotaxis and
7 phagocytic activity have been explored in several small cross-sectional studies. Consistent
8 findings are significantly reduced chemotactic response and phagocytic activity (i.e., respiratory
9 burst, luminal uptake) in lead workers compared to reference groups. The largest study is that of
10 Queiroz et al. (1994a, 1993) which evaluated PMNL function in several (possibly overlapping)
11 cohorts of lead battery manufacture workers (n = 60). Blood lead concentrations in the study
12 groups ranged from 12 to 90 |ig/dL. PMNL chemotaxis and lytic activity were significantly
13 lower in the lead workers compared to the reference group. Bergeret et al. (1990) assessed
14 PMNL chemotaxis and phagocytosis in a group of battery smelting workers (n = 34) and in a
15 group of reference subjects (n = 34) matched to the lead worker group by age, sex, ethnic origin,
16 smoking and alcohol consumption habits, and intake of antibiotics and NSAIDs. Mean blood
17 lead concentrations were 71 |ig/dL (SD 18) in the lead workers and 9 |ig/dL (SD 4) in the
18 reference group. Significantly lower PMNL chemotactic response to FMLP and phagocytic
19 response in opsonized zymosan were significantly lower in the lead workers than in the reference
20 group. Lead introduced into primary cultures of human PMNLs suppressed chemotaxis and
21 phagocytosis (Governa et al., 1987).
22
23 6.8.7 Summary of the Epidemiologic Evidence for the Effects of Lead
24 on the Immune System
25 Studies conducted in animals and in vitro experimental models have shown that lead can
26 alter immune system function (see Section 5.9). Lead appears to preferentially target
27 macrophages and T lymphocytes; although, effects on B cells and neutrophils have also been
28 reported. The prominent effects are largely on immune system function, rather than overt
29 cytotoxicity to lymphoid tissues. Lead suppresses Thl-dependent responses (e.g. delayed type
30 hypersensitivity) and production of Thl cytokines and shifts the Thl/Th2 balance towards Th2
31 responses; increases the production of IgE and Th2 cytokines (e.g. 11-4); and stimulates
May 2006 6-241 DRAFT-DO NOT QUOTE OR CITE
-------
1 macrophages into a hyperinflammatory state. These types of functional changes have not been
2 rigorously evaluated in human epidemiological studies, which have relied, for the most part, on
3 changes in lymphocyte abundance or circulating immunoglobulin levels, as the main outcomes
4 for assessing status of cellular immune systems. The above outcomes may be relatively
5 insensitive to for detecting disturbances in humoral or cellular immune function. Few studies
6 have attempted to examine associations between lead exposure and integrated immune function
7 (e.g., host resistance, hypersensitivity, autoimmunity) and current epidemiological evidence for
8 associations between lead exposure and compromised immune function in humans, reflected in
9 risk of asthma or infections, is not compelling, but these studies may not have been adequate to
10 address this.
11 • Several epidemiological studies have examined possible associations between lead
12 exposures and various indices of humoral and cellular immune status. Findings from
13 these studies suggest that lead exposure (as reflected in blood lead concentration) may be
14 associated with changes in serum immunoglobulin levels; perturbation of peripheral
15 lymphocyte phenotype profiles, including decreases in peripheral blood T-cell abundance
16 and changes in T-cell :B-cell abundance ratios; modulation of lymphocyte activation
17 (increased stimulated lymphocyte release of reactive oxygen intermediates and
18 suppressed production of nitric oxide; increased production of Th2 cytokines and
19 suppression of Thl cytokines); and suppression of neutrophil chemotaxis and
20 phagocytosis. Observations of increased circulating levels of IgE, increased release of
21 reactive oxygen intermediates and suppressed production of nitric oxide in peripheral
22 lymphocytes are of particular interest in that such effects have been consistently observed
23 in studies conducted in animals and in vitro model (see Section 5.9.11).
24
25 • Studies in children have consistently found significant associations between increasing
26 blood lead concentration and increasing serum IgE (Karmaus et al., 2005; Lutz et al.,
27 1999; Sun et al., 2003). These effects have been observed at blood lead concentrations
28 below 10 |ig/dL. Findings of studies of adults have been mixed with significant
29 associations between blood lead (>30 |ig/dL) and serum immunoglobulin levels (Heo et
30 al., 2004; Pinkerton et al., 1998) and no association in a study group in which blood lead
31 concentrations were <10 |ig/dL (Sarasua et al., 2000).
32 • Studies in children have also found significant associations between increasing blood
33 lead concentration and decreases in T-cell abundance, with corresponding increases in B-
34 cell abundance (Karmaus et al., 2005; Sarasua et al., 2000; Zhao et al., 2004). These
35 effects have been observed in children whose blood lead concentrations were below 10
36 Hg/dL (Karmaus et al., 2005; Sarasua et al., 2000), although not all studies have found
37 such associations at higher blood lead concentrations (e.g., 10-45 |ig/dL; Lutz et al.,
38 1999).
May 2006 6-242 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Studies of occupational lead exposures have also found associations between increasing
2 blood lead concentration and decreasing T-cell abundance (Pinkerton et al., 1998; Sata
3 et al., 1997; Fischbein et al., 1993). Effects were observed in association with blood lead
4 concentrations below 25 |ig/dL (Fischbein et al., 1993) and in populations whose blood
5 lead concentrations ranged from approximately 7 to 55 |ig/dL (Pinkerton et al., 1998;
6 Sata etal., 1997).
7 • Studies of lymphocyte and phagocyte (i.e., macrophage, neutrophil) function have found
8 associations between blood lead concentrations and modulation of the activation of
9 lymphocytes and macrophages in children whose blood lead concentrations ranged from
10 4 to 50 |ig/dL (Pineda-Zavaleta et al., 2004); suppressed PMNL chemotaxis in
11 association with occupational exposures that resulted in blood lead concentrations of 12
12 to 90 |ig/dL (Bergeret et al., 1990; Queiroz et al., 1994a, 1993), and suppressed mitogen-
13 induced activation of peripheral lymphocytes in adults in association with occupational
14 exposures that resulted in blood lead concentrations that ranged from 15 to 55 |ig/dL
15 (Fischbein et al., 1993). Consistent with observations made in animal models, lead
16 exposures in vitro suppressed production of Thl cytokines and stimulated production of
17 Th2 cytokines in isolates of peripheral lymphocytes, (Hemdan et al., 2005).
18
19
20 6.9 EFFECTS OF LEAD ON OTHER ORGAN SYSTEMS
21 6.9.1 Biochemical Effects of Lead
22 6.9.1.1 Summary of Key Findings of the Biochemical Effects of Lead from the
23 1986 Lead AQCD
24 The 1986 Lead AQCD provided an extensive discussion of the effects of lead on heme
25 biosynthesis and on quantitative relationships between exposure and effects in humans. Lead
26 interferes with heme synthesis by inhibiting the enzymes 5-aminolevulinic acid dehydratase
27 (ALAD) and ferrochelatase. As a consequence, heme biosynthesis decreases, relieving the rate-
28 limiting enzyme of the heme synthesis pathway, 5-aminolevulinic synthetase (ALAS), from
29 negative feedback inhibition by heme (Figure 6-9.1). The outcomes of decreased activity of
30 ALAD and ferrochelatase, and increased activity of ALAS are increased urinary excretion of
31 coproporphyrin (CP) and 5-aminolevulinic acid (ALA), increased level of ALA in blood plasma,
32 and increased erythrocyte protoporphyrin (EP) levels.
33 Associations between lead exposure and blood ALAD activity and EP levels, and urinary
34 ALA and CP excretion have been studied extensively in adults and children, and quantitative
35 relationships between exposure and effect are well understood. Much of this information was
36 available prior to completion of the 1986 Lead AQCD and is summarized in that criteria
May 2006 6-243 DRAFT-DO NOT QUOTE OR CITE
-------
MITOCHONDRION
MITOCHONDRIA!- MEMBRANE
GLYCINE
SUCCINYL-CoA
HEM6
Pb
ALA SYNTHETASE
(INCREASE)
_ Pb (DIRECTLY OR
BY DEREPRESSION)
FERRO-
CHELATASE
IRON +• PROTOPORPHYRIN
1
I
AMINOLEVULINIC ACID
(ALA)
ALA
DEHYDRASE
(DECREASE)
i-
CORPROPORPHYRIN
(INCREASE)
PORPHOBILINOGEN
Figure 6-9.1. Effects of lead on heme biosynthesis.
Source: Derived from EPA (1986).
1 document (e.g., Alessio et al., 1976; Hernberg et al., 1970; Lilis et al., 1978; Piomelli et al.,
2 1982; Roels et al., 1979; Selander and Cramer, 1970; Valentine et al., 1982). Numerous studies
3 published since the 1986 AQCD provide additional support for the lead concentration-response
4 relationships in humans described in the 1986 AQCD. The most pertinent studies are
5 summarized in Annex Tables AX6-9.1 and AX6-9.2. The studies that provide the strongest basis
6 for empirically-derived expressions relating blood lead concentration, blood ALAD activity,
7 urinary ALA, and EP are listed in Table 6-9.1 and are discussed below.
8 Since completion of the 1986 Lead AQCD, a literature has developed on the effects of
9 lead on serum and blood lipids, including cholesterol levels and indications of oxidative stress, in
10 the form of lipid peroxides, depletion of erythrocyte reduced glutathione (GSH), and production
11 of reactive oxygen species (ROS). These studies also are summarized in Annex Tables AX6-9.1
12 and AX6-9.2, and key findings are discussed below.
13
May 2006
6-244
DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-9.1. Blood Lead-Response Relationships for Heme Synthesis Biomarkers in Adults and Children
to
o
o
ON
ON
to
[\
L/l
o
^
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Study n
ALAD Activity Decrease
Roels and Lauwerys (1987) 143
Alessio et al. (1976, 1977) 169
Hernberg et al. (1970) 158
Morita et al. (1997) 58
Urinary ALA Increase
Roels and Lauwerys (1987) 37
Alessio et al. (1976, 1977) 3 16
Gennart etal. (1992) 183
Oishietal. (1996) 418
Selander and Cramer ( 1 970) 150
Roels and Lauwerys ( 1 987) 39
Roels and Lauwerys (1987) 36
Age
10-13 yr
Adult (m)
Adult (m, f)
Adult (m)
10-13 yr
Adult (m)
Adult (m, f)
Adult (m, f)
Adult (m, f)
Adult (m)
Adult (f)
Blood Lead Change
Blood Lead (Mg/dL)
(jig/dL) Predicted to Halve or
Range Regression Equation (r) Double Effect Biomarker
5-41 log[ALAD]= 1.864-0.015[blood lead] (r = 0.87)
15-150 log[ALAD]=3. 73-0.031 [blood lead] (r=0.87)
5-95 log[ALAD]=2.274-0.018[blood lead] (r = 0.90)
2-82 log[ALAD]=1.8535-0.00971[blood lead] (r= 0.76)
20^1 log[ALAU]=0.94+0. 11 [blood lead] (r = 0.54)
10-150 log[ALAU]=1.25+0.014[blood lead] (r = 0.62)
4-75 log[ALAU]=0.37+0.008[blood lead] (r = 0.64)
10-99 log[ALAU]= -0.387+0.022[blood lead] (r = 0.71)
6-90 log[ALAU]= -1.0985+0. 157[blood lead] (r= 0.74)
10-60 log[ALAU]=0.37+0.006[blood lead] (r = 0.41)
7-53 log[ALAU]=0.15+0.015[bloodlead] (r= 0.72)
20.1
22.4
16.1
20.1
20.9
49.5
37.6
13.7
19.2
50.2
20.1
-------
Table 6-9.1 (cont'd). Blood Lead-Response Relationships for Heme Synthesis Biomarkers in Adults and Children
to
o
o
ON
ON
to
ON
O
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Study
EP Increase
Marcus and Schwartz
(1987)
Piomelli et al. (1982)
Roels and Lauwerys (1987)
Soldin etal. (2003)
Alessioetal. (1976, 1977)
Alessioetal. (1976, 1977)
Gennart etal. (1992)
Roels and Lauwerys (1987)
Roels and Lauwerys (1987)
Wildt etal. (1987)
Wildt etal. (1987)
n
1,677
2,002
51
4,908
95
93
183
39
36
851
139
Age
2-6
2-12
10-13
0-17
Adult (m)
Adult (f)
Adult (m)
Adult (m)
Adult (f)
Adult (m)
Adult (f)
ALA, 5-aminolevulinic acid; ALAD, 6-aminolevulinic
PbB, blood lead concentration.
""Approximately 20 at low transferrin saturation (<3 1%)
Blood Lead
Oig/dL)
Range
6-65
2-98
15-41
<1-103
10-90
10-70
4-75
10-60
7-53
10-80
10-80
acid dehydratase;
Regression Equation (r)
Non-linear kinetic model
log[EP]=1.099+0.016[blood lead] (r = 0.509)
log[EP]= 1.32 1+0.025 [blood lead] (r = 0.73)
EP = -0.0015[PbB]3+0.1854[blood lead]2-
2.7554[PbB]+30.911 (r = 0.999)
log[EP]=0.94+0.0117[blood lead]
log[EP]= 1.60+0.0 143 [blood lead]
log[EP]=0.06+0.019[bloodlead] (r= 0.87)
log[EP]=1.41+0.014[bloodlead] (r= 0.74)
log[EP]=1.23+0.027[blood lead] (r = 0.81)
log[EP]=1.21+0.0148[blood lead] (r= 0.72)
log[EP]=1.48+0.0113[blood lead] (r= 0.56)
ALAU, urinary 5-aminolevulinic acid; EP, erythrocyte
Blood Lead Change
Oig/dL)
Predicted to Halve or
Double Effect Biomarker
20 -40a
18.8
12.0
20.6
25.7
21.1
15.8
21.1
11.1
20.3
20.6
protoporphyrin;
, approximately 40 at higher transferrin saturation (>3 1%).
-------
6.9.1.2 Heme Biosynthesis
ALAD Inhibition
Numerous studies published since completion of the 1986 AQCD have explored
associations between lead exposure and inhibition of ALAD activity, as assessed from
measurements of blood ALAD activity (Gurer-Orhan et al., 2004; Kim et al., 2002; Lee et al.,
2000; Makino et al., 1997; Roels and Lauwerys, 1987; Schuhmacher et al., 1997), or urinary
ALA excretion (Gennart et al., 1992; Oishi et al., 1996; Schuhmacher et al., 1997; Wildt et al.,
1987; Soldin et al., 2003). Quantitative estimates derived from the larger, more recent studies
are presented in Table 6-9.1. Blood lead concentration is inversely correlated with the log of
blood ALAD activity and log of urinary ALA and quantitative estimates of the change in blood.
ALAD activity per unit change in blood lead concentration are consistent across studies
(observed blood lead range: 5-150 |ig/dL). Halving of blood ALAD activity occurs with an
increase in blood lead concentration of approximately 20 |ig/dL in both children (Roels and
Lauwerys, 1987) and adults (Morita et al., 1997). These estimates are consistent with earlier
studies of adults (e.g., Hernberg et al., 1970) and children (e.g., Alessio et al., 1976, 1977),
discussed in the 1986 AQCD. Greater variability is apparent in estimates of the change in
urinary ALA per unit change in blood lead concentration (Table 6-9.1). This may be related,
in part, to gender-heterogeneity in the relationship. Roels and Lauwerys (1987) estimated that
urinary ALA doubles in association with a 20 |ig/dL increase in blood lead concentration in
females and 50 |ig/dL in males. In a much larger study (Oishi et al., 1996), an analysis that
combined data from males (n = 253) and females (n = 165) found that a doubling of urinary
ALA occurred in association with a 13.7 |ig/dL increase blood lead concentration. Urinary ALA
excretion increases as a linear function of plasma ALA concentration (Oishi et al., 1996); thus,
the gender heterogeneity for the blood lead-urinary ALA relationship may derive from a gender
difference in the effect of lead on plasma ALA concentration or from differences in renal plasma
clearance of ALA.
ALAD Polymorphism
ALAD is a polymorphic enzyme with two alleles (ALAD1 and ALAD2) and three
genotypes: ALAD1,1, ALAD1,2, and ALAD2,2 (Battistuzzi et al., 1981). The corresponding
phenotypes appear to have nearly identical catalytic properties (Battistuzzi et al., 1981). The
May 2006 6-247 DRAFT-DO NOT QUOTE OR CITE
-------
predominant genotype is ALAD1,1 which has a prevalence of approximately 90% (Astrin et al.,
1987; Battistuzzi et al., 1981; Hsieh et al., 2000; Shen et al., 2001). A significantly higher
percentage (p = 0.03) of erythrocyte lead was bound to ALAD in carriers of the ALAD2 allele
(84%) compared to carriers of the ALADl allele (81%); however, no differences were evident in
the distribution of lead between erythrocytes and plasma (Bergdahl et al., 1997), and there is no
evidence that the ALAD genotype confers different sensitivity to inhibition of heme biosynthesis
(Hsieh et al., 2000; Perez-Bravo et al., 2004; Schwartz et al., 1997; Suzen et al., 2003).
Ferrochelatase Inhibition
Lead inhibition of ferrochelatase results in an accumulation of protoporphyrin IX in
erythrocytes (EP, also referred to as zinc protoporphyrin, or ZPP, or iron protoporphyrin, FEP,
depending on the method used to make the measurement). Numerous studies have examined
relationships between blood lead concentration and EP levels in adults and children.
Quantitative estimates based on the most pertinent studies are presented in Table 6-9.1. Results
across these studies are similar (observed blood lead range: <1-103 |ig/dL). In both children and
adults (males and females), a doubling of EP levels occurs in association with an increase in
blood lead concentration of approximately 20 |ig/dL (Marcus and Schwartz 1987; Piomelli et al.,
1982; Soldin et al., 2003; Wildt et al., 1987). However, the relationship between blood lead
concentration and EP level is not linear (Marcus and Schwartz, 1987; Soldin et al., 2003). The
slope of the blood lead concentration range over which a change in EP is relatively small
("threshold") appears to extend to approximately 20 |ig/dL in iron replete children and decreases
with increasing iron deficiency. (Marcus and Schwartz, 1987). A pronounced gender difference
in the relationship between EP and blood lead concentration was observed by Roels and
Lauwerys (1987) which was not observed in the much larger study of Wildt et al. (1987).
Inhibition of ferrochelatase also gives rise to an increase in urinary coproporphyrin, with a
similar relationship to blood lead concentration; a doubling of urinary EP occurs in association
with an increase in urinary coproporphyrin of approximately 20 |ig/dL (Alessio et al., 1976).
6.9.1.3 Effects on Blood Lipids: Cholesterol
Associations between occupational exposure to lead and changes in blood lipid
composition have been observed. These include increased levels of lipid peroxides in blood
May 2006 6-248 DRAFT-DO NOT QUOTE OR CITE
-------
and/or serum (Ito et al., 1985; Jiun and Hsien, 1994; Sugawara et al., 1991) and increased serum
levels of total and HDL cholesterol (Kristal-Boneh et al., 1999). Increased levels of glucose-6-
phosphate dehydrogenase (G6PD) in erythrocytes have also been observed in lead workers
(Cocco et al., 1995; Gurer-Orhan et al., 2004).
Kristal-Boneh et al. (1999) measured serum total, HDL, and LDL cholesterol, and
triglycerides in a group of male battery manufacture workers. Covariate-adjusted serum total-
cholesterol and HDL cholesterol levels were 6% and 12% higher, respectively, in lead workers
(n = 56, mean blood lead 42 |ig/dL, SD 15) compared to reference group (mean blood lead:
2.7 |ig/dL). Increasing blood lead concentration was significantly associated with increasing
covariate-adjusted total cholesterol and HDL cholesterol. A similar outcome was found in a
larger study (Ito et al., 1985) of male steel workers (n = 712, blood lead range 5-62 jig/dL).
When stratified by age, total and HDL cholesterol levels in serum were 3.6% and 7.5% higher,
respectively, in lead workers in the age range 40 to 49 years, compared to corresponding strata of
the office workers (n = 155). Although a smaller study, the Kristal-Boneh et al. (1999) study
considered a larger set of potential covariables (e.g., dietary fat, cholesterol, and calcium intakes,
sport activities, alcohol consumption, cigarette smoking).
Oxidative changes in blood lipids (e.g., increased levels of lipid peroxides and
malondialdehyde levels) as well as decreased levels of erythrocyte superoxide dismutase (SOD),
catalase, G6PD, and GSH peroxidase, indicative of increased oxidative stress, have been
observed in lead workers, in comparison to reference groups (Ito et al., 1985; Jiun and Hsien,
1994; Solliway et al., 1996; Sugawara et al., 1991). However, none of these studies have
developed concentration-response relationships that take into account potential confounders.
The largest study is that of (Ito et al., 1985), described above. When stratified by age, serum
lipoperoxide levels were 16% higher in the lead workers in the age range 40 to 49 years,
compared to corresponding strata of the reference group. Serum lipoperoxide levels also
appeared to increase as blood lead increased above 30 |ig/dL, while erythrocyte SOD appeared to
decrease with increasing blood lead concentration (a statistical evaluation was not reported).
Evidence for increased oxidative stress (increased reactive oxygen species) in
lymphocytes of lead workers has also been reported (Fracasso et al., 2002). Peripheral
lymphocytes collected from battery manufacture workers (n = 37, mean blood lead: 40 |ig/dL)
exhibited increased DNA strand breaks, higher production of ROS and lower GSH levels
May 2006 6-249 DRAFT-DO NOT QUOTE OR CITE
-------
compared to a reference group of office workers (n = 29, mean blood lead 4 |ig/dL). The
covariate-adjusted odds ratios (exposed versus not exposed) were 1.069 (95% CI: 1.020, 1.120)
for increased DNA strand breaks and 0.634 (95% CI: 0.488, 0.824) for lower GSH levels.
6.9.2 Effects of Lead on the Hematopoietic System
6.9.2.1 Summary of Key Findings of the Effects of Lead on the Hematopoietic System
from the 1986 Lead AQCD
The 1986 Lead AQCD concluded that lead decreases heme production and shortens
erythrocyte survival; both effects contributing to lead-induced anemia in children and adults,
which becomes evident in children at blood lead concentrations >40 |ig/dL and, in adults,
>50 |ig/dL. The 1986 Lead AQCD also concluded that effects of lead on blood hemoglobin
level extend below 50 |ig/dL, with effects detected in lead workers at blood lead concentrations
<25 |ig/dL (Baker et al., 1979; Grandjean, 1979). More recent epidemiologic studies,
summarized below, provide additional information on concentration-response relationships for
hematopoietic effects of lead. The studies support the conclusion that clinical anemia can occur
in children in association with blood lead concentrations >40 |ig/dL (Schwartz et al., 1990).
The newer studies suggest that perturbation of erythropoiesis, indicated by changes in serum
erythropoietin, occurs in association with blood lead concentrations <40 |ig/dL and in the
absence of detectable changes in blood hemoglobin levels or hematocrit. Details regarding the
design of these studies and outcomes are presented in Annex Tables AX6-9.3 and AX6-9.4.
Outcomes of the most pertinent studies are discussed below.
6.9.2.2 Blood Hemoglobin Levels
Several studies reported since the completion of the 1986 Lead AQCD have explored
associations between lead exposure and blood hemoglobin levels in children and adults.
Consistent findings have been a lack of discernable depression of blood hemoglobin levels in
study populations whose mean blood lead concentrations were <40 |ig/dL (Table 6-9.2). Of note
is the findings relating patella bone lead to both blood hemoglobin levels and hematocrit.
The Kosovo prospective study of pregnancy outcomes is one of the largest epidemiologic
evaluations of associations between lead exposure and blood hemoglobin levels in infants and
children (Graziano et al., 2004; Factor-Litvak et al., 1998, 1999). The study included pregnant
May 2006 6-250 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-9.2. Summary of Results of Selected Studies of Associations Between Lead Exposure and
to
o
o
ON
ON
to
o
i
H
I
0
o
0
H
O
o
H
W
O
O
H H
H
W
Blood Lead (jig/dL)
Study Subjects
C/z/Wrat
Graziano et al. (2004) ages: 4.5-12 yr
Liebeltetal. (1999) ages: 1-6 yr
Adults
Graziano et al. (1990) pregnant women
Hu et al. (1994) male carpenters
Makino et al. (1997) male VCS workers
Solliway et al. (1996) male battery workers
Gennart et al. (1992) battery workers
Horiguchi et al. (1991) male lead refinery workers
Poulos et al. (1986) male lead workers
"a
311
86
1,502
119
1,573
100
183
40
160
-, decrease; +, increase; Hgb, hemoblogin; NR, not reported; PCV, packed cell
a total number of subjects (including reference group)
b range of means of low and higher exposure groups
0 median
d mean of low- and high-exposure groups
e range of group means (standard deviation estimated for up ran£
Mean (SD)
6-9,31-39b
18C
5,17d
8
13
10
51(8)
54 (16)
18-27 (5)e
Range
3-70
2-84
2-43
2-25
1-39
23-63
40-70
NR
NR
volume SD, standard deviation; VCS,
Blood
Hemoglobin Comment
o + erythropoietin
o - erythropoietin
o - erythropoietin
o - in association with patella
bone lead
+ (+) 1 g/dL per 10 ug/dL blood
lead
o RBC count
- hematocnt
- hematocnt
- hematocnt
vinyl chloride stabilizer
>e based on reported standard error).
-------
1 women (n = 1502) and their children (n = 311) who resided in one of two regions of Kosovo,
2 Yugoslavia; one was heavily impacted by lead industries (high-lead area), the other had
3 relatively little lead contamination (low-lead area). Mean blood lead concentrations of children
4 (measured at birth and at intervals to 12 years of age) ranged from 30 to 40 |ig/dL in the high-
5 lead area and 6 to 9 |ig/dL in the low-lead area. Mean blood hemoglobin levels in the low-lead
6 and high-lead children, measured at 4.5, 6.5, 9.5, and 12 years of age, were not significantly
7 different. These findings are consistent with those from a smaller cross-sectional study (n = 89;
8 blood lead range 2 to 84 |ig/dL, 84% <35 |ig/dL) that also found no association between blood
9 lead concentration and blood hemoglobin levels (Liebelt et al., 1999). Results from these two
10 studies suggest that, in the absence of iron deficiency, lead exposures that result in blood lead
11 concentrations <40 |ig/dL do not produce detectable changes in blood hemoglobin levels
12 in children.
13 Associations between lead exposure and blood hemoglobin levels in adults have been
14 examined in numerous epidemiological studies (Froom et al., 1999; Gennart et al., 1992;
15 Horiguchi et al., 1991; Hu et al., 1994; Makino et al., 1997; Poulos et al., 1986; Romeo et al.,
16 1996; Solliway et al., 1996). The Graziano et al. (1990) and Makino et al. (1997) studies warrant
17 particular attention because of the design (longitudinal), relatively large size (>1000 subjects),
18 and relatively low blood lead levels of the subjects (<40 |ig/dL). Both studies support the
19 general conclusion that blood hemoglobin levels are not depressed in association with blood lead
20 concentrations <40 |ig/dL. In the Kosovo prospective study, no discernable effect of lead on
21 maternal blood hemoglobin levels was evident from a comparison of the high-lead exposure
22 group (mean blood lead 17 |ig/dL, range 7-43 |ig/dL) with the low lead exposure group
23 (meanblood lead 5.1 |ig/dL, range 2-11 jig/dL). Makino et al. (1997) found a positive
24 association between increasing blood lead concentration and increasing blood hemoglobin levels
25 in a longitudinal survey of adult males (n = 1,573) who worked in pigment or vinyl chloride
26 stabilizer manufacture (mean blood lead 13 |ig/dL, range 1-39 |ig/dL). A simple linear
27 regression model predicted a 10 |ig/dL increase in blood hemoglobin per 10 |ig/dL increase in
28 blood lead concentration (typical level 10-20 jig/dL).
29 Two other cross-sectional studies are also notable, because of design considerations
30 and/or blood lead concentration ranges of the subjects. Solliway et al. (1996) observed no
31 differences in mean blood hemoglobin levels in a comparison of adult male battery manufacture
May 2006 6-252 DRAFT-DO NOT QUOTE OR CITE
-------
1 workers (n = 34, mean blood lead 41 |ig/dL, range 23-63 |ig/dL) and a matched reference group
2 (n = 56, mean blood lead 7 |ig/dL, range 1-13 |ig/dL). Hu et al. (1994) conducted a cross-
3 sectional assessment of adult male carpentry workers (n = 119) whose blood lead concentrations
4 were <25 |ig/dL. Blood hemoglobin was not significantly associated with blood lead
5 concentration. Of note, however, was the finding that increasing patella bone lead was
6 significantly associated with decreasing blood hemoglobin levels. Covariate-adjusted blood
7 hemoglobin levels were predicted to decrease by 1.1 g/dL per 37 jig/g increase (mean of first and
8 fourth quartiles) in patella bone lead.
9 Studies of lead workers whose blood lead levels were higher than in the studies noted
10 above have, in general, found lower blood hemoglobin levels in association with increasing
11 blood lead concentrations; these include Gennart et al. (1992) with a blood lead range of 40-70
12 ng/dL, Horiguchi et al. (1991) with a mean blood lead level of 54 |ig/dL (SD 16), and Poulos
13 et al. (1986) with mean blood lead range of 21-27 |ig/dL. In the latter study (Poulos et al.,
14 1986), blood hemoglobin levels decreased by 0.6-0.9 g/dL per 10 |ig/dL increase in blood lead
15 (simple linear regression) in adult males. Analyses or adjustments for potential covariables were
16 not reported for these studies.
17
18 6.9.2.3 Erythrocyte Volume and Number
19 Schwartz et al. (1990) conducted a concentration-response analysis of data collected at the
20 Bunker Hill smelter site in Idaho in 1974, shortly after the failure of the smelter bag house
21 resulted in extensive contamination of the surrounding area with uncontrolled smelter emissions.
22 This analysis is unique in that it collected hematocrit measurements in children (n = 579, age
23 range 1-5 years) who had relatively high blood lead levels (range 11-164 |ig/dL, approximately
24 40% exceeded 40 |ig/dL). A logistic model relating blood lead concentration and age to
25 hematocrit predicted a 10% decrease in hematocrit (from 39.5 to 35.5%) in association with
26 blood lead concentrations of 85, 115, and 145 |ig/dL at ages 1, 3, and 5 years, respectively
27 (Figure 6-9.2). A 10% probability of anemia (hematocrit <35%) was predicted in association
28 with a blood lead concentration of approximately 20 |ig/dL at age 1 year, 50 |ig/dL at age
29 3 years, and 75 |ig/dL at age 5 years (Figure 6-9.2).
30 Numerous studies of associations between lead exposure and erythrocyte volume (e.g.,
31 hematocrit) or number have been reported in adults (Gennart et al., 1992; Horiguchi et al., 1991;
May 2006 6-253 DRAFT-DO NOT QUOTE OR CITE
-------
20 40 60 80 100 120 140
Blood Lead (ug/dL)
Figure 6-9.2.
00
0 50 IOO ISO 200
BLOOD LEAD LEVEL (Mg/dl)
Relationship between blood lead and hematocrit in children. The top panel
shows central tendency predictions based on a logistic regression model
relating hematocrit and blood lead concentration, adjusted for age. The
regression coefficients relating hematocrit and blood lead were (P = 0.0133
[SE 0.0041], p = 0.0005). The bottom panel shows corresponding
concentration-response (hematocrit <35%) relationships.
Source: Schwartz etal. (1990).
May 2006
6-254
DRAFT-DO NOT QUOTE OR CITE
-------
1 Hsiao et al., 2001; Hu et al., 1994; Makino et al., 1997; Osterode et al., 1999; Poulos et al., 1986;
2 Solliway et al., 1996). The Hu et al. (1994) and Makino et al. (1997) studies examined groups of
3 workers that had blood lead concentrations that were relatively low, compared to other studies,
4 and found either no association or weak association between blood lead concentration and
5 hematocrit and/or erythrocyte number. The Hu et al. (1994) cross-sectional study of carpentry
6 workers (n = 119, blood lead concentration range 2-25 ng/dL) found no association between
7 blood lead concentration and hematocrit; however, increasing patella bone lead was associated
8 with a significant decrease in hematocrit. Covariate-adjusted blood hematocrit was predicted to
9 decrease by 0.03% (95% CI: 0.01, 0.05) per 37 |ig/g increase (mean of first and fourth quartiles)
10 in patella bone lead. The Makino et al. (1997) longitudinal study of pigment and vinyl chloride
11 stabilizer manufacture workers (n = 1,573; blood lead concentration range 1-39 |ig/dL) found a
12 positive association between blood lead concentration and hematocrit, and erythrocyte count.
13 A simple linear regression model predicted an increase in hematocrit of 0.6 (typically 43) and an
14 increase in erythrocyte count of 0.07 x 106/mm3 (typically 4-7 x 106/mm3) per 10 |ig/dL increase
15 in blood lead concentration.
16 Studies that included subjects who had higher blood lead concentrations (i.e., >40 |ig/dL)
17 have, in general, found negative associations between blood lead concentration and hematocrit
18 Gennart et al., 1992; Horiguchi et al., 1991; Poulos et al., 1986; Solliway et al., 1996), with two
19 exceptions, Hsiao et al. (2001) and Osterode et al. (1999). Hsiao et al. (2001) conducted an
20 11-year retrospective longitudinal analysis of blood lead concentration, hematocrit, and
21 erythrocyte count in a group of battery manufacture workers (n = 30; mean blood lead
22 concentration 30-60 jig/dL). A repeated measures regression analysis (generalized estimation
23 equation) yielded a significant association between increasing blood lead concentration and
24 increasing hematocrit and erythrocyte count. Osterode et al. (1999) measured erythrocyte
25 number and packed cell volume in a group of lead workers (n = 20) and an age-matched
26 reference group (n = 20). Mean blood lead concentration was 45.5 |ig/dL (range 16-91 |ig/dL)
27 in the lead workers and 4.1 |ig/dL (range 3-14 |ig/dL) in the reference group. Mean erythrocyte
28 number and packed cell volume in the lead workers and reference group were not different.
29
May 2006 6-255 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.9.2.4 Erythropoiesis
2 Several studies have found associations between lead exposure and serum erythropoietin
3 levels in children (Graziano et al., 2004; Liebelt et al., 1999) and adults (Graziano et al., 1991;
4 Osterode et al., 1999; Romeo et al. 1996). A qualitative summary of outcomes from these
5 studies are provided in (Table 6-9.3).
6 Two studies have examined possible association between lead exposure and serum
7 erythropoietin levels in children. In the Kosovo prospective study (Factor-Litvak et al., 1998,
8 1999; Graziano et al., 2004) a significant association was evident between increasing blood lead
9 concentration (3-70 |ig/dL) and increasing serum erythropoietin levels after adjustment for age
10 and blood hemoglobin levels (Figure 6-9.3). The association weakened with age; it was
11 significant at ages 4.5 and 6.5 years, but not at ages 9.5 or 12 years. A multivariate linear
12 regression model predicted a 36% increase in serum erythropoietin per 10 |ig/dL increase
13 (3-13 |ig/dL, hemoglobin 13 g/dL) in blood lead at age 4.5 years, and an 18% increase per
14 10 |ig/dL at age 6.5 years. These outcomes suggest that erythropoiesis is stimulated in children
15 in association with increasing blood lead concentrations below 40 |ig/dL and in the absence of
16 depressed blood hemoglobin levels.
17 A smaller cross-sectional study examined serum erythropoietin levels in a group of
18 children (n = 89), 1 to 6 years of age (Liebelt et al., 1999). The blood lead concentration range in
19 the study group (2-84 |ig/dL) was similar to that in the Graziano et al. (2004) study and,
20 consistent with this study, Liebelt et al. (1999) found no association between blood lead
21 concentration and serum hemoglobin levels. However, in contrast to the Graziano et al. (2004)
22 study, blood hemoglobin-adjusted serum erythropoietin levels decreased in association with an
23 increase in blood lead concentration (0.3 mlU/mL decrease per 10 |ig/dL increase blood lead).
24 The Liebelt et al. (1999) study did not include age as a covariate in the regression model, which
25 was shown in the Kosovo prospective study to be a significant covariable in blood lead-serum
26 erythropoietin relationship (Graziano et al., 2004); this may have contributed to the different
27 outcome in the two studies. Liebelt et al. (1999) studied a convenience sample from a
28 lead/primary care clinic (rather than a prospectively selected cohort) that specifically excluded
29 children who had symptoms of severe iron deficiency, or were taking iron supplements or other
30 bone marrow suppressing drugs. Iron status of the children in the Graziano et al. (2004) study
31 was not reported. However, serum ferritin levels in the mothers, at mid-pregnancy, was not
May 2006 6-256 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-9.3. Summary of Results of Selected Studies of Associations Between Lead Exposure and Serum Erythropoietin
to
o
o
Oi
Oi
to
-------
10 20 30 40
Blood Lead (ug/dL)
50
60
70
Figure 6-9.3. Relationship between blood lead and serum erythropoietin in children.
Coefficients relating erythropoietin and blood lead were significant for
ages 4.5 (p = 0.21 [95% CI: 0.13, 0.30], p < 0.0001) and 6.5 years (p = 0.12
[95% CI: 0.03, 0.20], p < 0.001).
Source: Graziano etal. (2004).
1 indicative of iron deficiency (Graziano et al., 1990). Although the direction of the outcome
2 measure was different in the two studies, both studies (Graziano et al., 2004; Liebelt et al., 1999)
3 found evidence for an effect of lead exposure on serum erythropoietin levels in the absence of
4 significant lead-associated changes in blood hemoglobin levels.
5 Three studies have found associations between lead exposure and changes in
6 erythropoiesis biomarkers in adults. As part of the Kosovo prospective study, serum
7 erythropoietin was measured at mid-pregnancy and at term in a subset of women enrolled in the
8 study (Graziano et al., 1991). The high- and low-lead cohorts were constructed from the six
9 highest and lowest mid-pregnancy blood lead concentrations, within each of four blood
10 hemoglobin strata, ranging from 9.0 to 12.9 g/dL. Mean blood lead concentrations in the strata
May 2006
6-258
DRAFT-DO NOT QUOTE OR CITE
-------
1 ranged from 17 to 39 |ig/dL in the high-lead group and 2.4 to 3.6 |ig/dL in the low lead group.
2 Serum erythropoietin levels significantly decreased in association with increasing blood lead
3 concentration, independently of an effect of blood hemoglobin (Figure 6-9.4). Romeo et al.
4 (1996) also found an association between increasing blood lead concentration and decreasing
5 serum erythropoietin, in the absence of discernable changes in blood hemoglobin levels, in a
6 comparison of group male lead workers (n = 28, blood lead range 30-92 |ig/dL) and a similar-
7 aged reference group (n = 113, mean blood lead 10 |ig/dL, range 3-20). Osterode et al. (1999)
8 examined several measures of erythropoiesis in a group of lead workers (n = 20, mean age
9 46 years) and in an age-matched reference group (n = 20). Mean blood lead concentration was
10 45.5 |ig/dL (range 16-91) in the lead workers and 4.1 |ig/dL (range 3-14) in the reference group.
11 Mean blood hemoglobin levels in the lead worker and reference groups were not different.
12 Lead workers with had blood lead concentrations >60 |ig/dL had significantly lower circulating
13 erythrocyte progenitor cells than the reference group. Also, erythrocyte progenitor cell number
14 was significantly negatively correlated with blood lead concentration and urine lead
15 concentration. Serum erythropoietin levels increased exponentially with decreasing packed
16 blood cell volume in the reference group, but not in the lead workers (i.e., serum erythropoietin
17 level was not significantly correlated with packed cell volume in the lead workers). Thus, unlike
18 the reference group (blood lead concentration < 14 jig/dL), lead workers appeared to have a
19 suppressed erythropoietin response to declining blood cell volume.
20 Collectively, the results of the above studies suggest that lead exposure depresses serum
21 erythropoietin levels, in the absence of significant depression in blood hemoglobin levels. Lead-
22 induced nephrotoxicity may contribute to a suppression of erythropoietin levels in lead-exposed
23 individuals. Although this cannot be entirely ruled out in these studies, both the Romeo et al.
24 (1996) and Osterode et al. (1999) studies excluded people who had a history of hematological or
25 kidney disease. Nevertheless, renal nephrotoxicity, including proximal tubular nephropathy,
26 could have been a confounder in these studies which included subjects whose blood lead
27 concentrations were >40 |ig/dL.
28
29
May 2006 6-259 DRAFT-DO NOT QUOTE OR CITE
-------
g
I
c
4»
*
O
o
c
SJ
80
70-
60-
50-
40-
30 '
20-
(4,4)
0
(231)
K3 -"Lo*"1 Blood Lead
K2 -"High" Blood Lead
( ) - Meon BPb (/xq/dl)
(3.9)
(3.0)
9,0-9,9
0,9
1 1,0-1 1 9
12,0-12,9
Hemoglobin concentration (g/dl) strata
Figure 6-9.4. Association between blood lead concentration and serum erythropoietin in
pregnant women. Shown are combined data for mid-pregnancy and
delivery. Each bar represents the mean (+SD) of 12 subjects. ANOVA of
the data at mid-pregnancy and at delivery showed blood lead effects
(p = 0.049, p = 0.055, respectively) and blood hemoglobin effects (p = 0.0001.
p = 0.009, respectively), with no significant interaction between the two
variables.
Source: Graziano etal. (1991).
1 6.9.2.5 Other Effects on Erythrocyte Metabolism and Physiology
2 Erythrocyte Nucleotide Metabolism
3 Lead inhibits erythrocyte pyrymidine-5 'nucleotidase (P5N) and adenine dinucleotide
4 synthetase (NADS). Inhibition of P5N leads to the accumulation of pyrimidine nuclotides in the
5 eyrthrocyte and hemolysis. Associations between increasing blood lead concentration and
6 decreasing blood P5N and NADS activity have been observed in studies of lead workers (Kim
7 et al. 2002; Mohammed-Brahim et al., 1985; Morita et al., 1997). Mean blood lead
8 concentrations in these study groups were >35 |ig/dL and ranged up to 80 |ig/dL. Inhibition of
May 2006
6-260
DRAFT-DO NOT QUOTE OR CITE
-------
1 P5N has also been observed in children whose blood lead concentrations were >30 |ig/dL (Angle
2 and Mclntire, 1978; Angle et al., 1982; summarized in the 1986 AQCD for Lead).
3
4 Erythrocyte Deformabitity
5 Horiguchi et al. (1991) compared the deformability of erythrocytes collected from adult
6 male secondary lead refinery workers (n = 17, age range 24-58 years) with a reference group of
7 male subjects (n = 13, age range 22-44 years). Erythrocyte deformability was assessed as
8 microfilterability of erythrocytes under a negative (-10 cm H^O) pressure head. Erythrocytes
9 from the lead workers showed significantly lower deformability compared to the reference
10 group. The mean blood lead concentration in the lead workers was 53.5 |ig/dL (SD 16.1); blood
11 lead concentrations in the reference grooup were not reported.
12
13 Erythrocyte Membrane Transport
14 Hajem et al. (1990) measured erythrocyte membrane activities of Na+-K+-ATPase, Na+-
15 K+-co-transport, Na+-Li+-antiport, and passive Na+ and K+ permeability in erythrocytes collected
16 from adult males (n = 122, geometric mean blood lead: 16 |ig/dL, range 8.0-33.0) geometric
17 mean hair lead: 5.3 |ig/g, range 0.9-60). Na+-K+-co-transport activity was negatively correlated
18 with blood lead concentration but not with hair lead (geometric mean 5.3 |ig/g, range 0.9-60),
19 and Na+-K+-ATPase activity was negatively correlated with hair lead, but not with blood lead.
20
21 6.9.3 Effects of Lead on the Endocrine System
22 6.9.3.1 Summary of Key Findings of the Effects of Lead on the Endocrine System from
23 the 1986 Lead AQCD
24 The 1986 Lead AQCD concluded that various endocrine processes may be affected by
25 lead at relatively high exposure levels. These included effects on thyroid hormone levels (e.g.,
26 Refowitz, 1984; Robins et al., 1983), effects on male sex hormone levels (e.g., Braunstein et al.,
27 1978), and impairment of the production of 1,25-dihydroxy vitamin D (1,25-OH-D) (e.g., Rosen
28 et al., 1980). Effects on these endocrine systems were concluded to be apparent only at blood
29 lead concentrations exceeding 30-40 |ig/dL. The 1986 Lead AQCD concluded that studies from
30 which the effects of lead on reproductive hormones in females could be assessed were lacking.
May 2006 6-261 DRAFT-DO NOT QUOTE OR CITE
-------
1 More recent epidemiologic studies have examined possible associations between lead
2 exposure (as reflected by blood and/or bone lead levels) and various biomarkers of endocrine
3 function, including the thyroid, male reproductive, and calcitropic endocrine systems. These
4 studies have examined endocrine outcomes at lower blood lead ranges and in the absence of
5 overt clinical lead toxicity, and have more rigorously attempted to control for confounding
6 factors. Evidence for lead effects on these systems, in association with blood lead concentrations
7 below 30-40 |ig/dL, remains absent. The strongest study designs have yielded no associations,
8 or weak associations, between lead exposure and thyroid hormone status (Erfurth et al., 2001;
9 Schumacher et al., 1998; Tuppurainen et al., 1988; Zheng et al., 2001). Similarly, studies of the
10 male reproductive system that attempted to control for confounding effects of age, have yielded
11 mixed outcomes (Alexander et al., 1996a, 1998; Erfurth et al., 2001; Gustafson et al., 1989;
12 McGregor and Mason, 1990; Ng et al., 1991). Results of a more recent epidemiologic study of
13 the calcitropic endocrine system in children suggest that associations between serum vitamin D
14 status and blood lead may not be present in calcium-replete children who have average lifetime
15 blood lead concentrations below 25 |ig/dL (Koo et al., 1991). In adults, exposures to lead that
16 result in blood lead concentrations >40-60 |ig/dL may increase, rather than decrease, circulating
17 levels of 1,25-OH-D and PTH (Kristal-Boneh et al., 1999; Mason et al., 1990), possibly as a
18 compensatory response to increased urinary calcium losses, secondary to impaired kidney
19 function. Details regarding the design of these studies and outcomes are presented in Annex
20 Tables AX6-9.5 and AX6-9.6. Outcomes of the most pertinent studies are summarized below.
21
22 6.9.3.2 Thyroid Endocrine Function
23 Several studies have examined possible associations between lead exposure and thyroid
24 hormone status. Most of these have been studies of occupational exposures. The results of these
25 studies have been mixed; some studies have found significant associations with lead exposure
26 (e.g., blood lead concentration), but most studies have found none or relatively weak
27 associations. In studies that have controlled for the effects of age, outcomes also have been
28 mixed, with the strongest study designs finding none or weak associations between lead
29 biomarkers and thyroid hormone status (Erfurth et al., 2001; Schumacher et al., 1998;
30 Tuppurainen et al., 1988; Zheng et al., 2001). The strength of the association and, possibly, the
31 direction of the effect (i.e., increase or decrease in hormone levels) may change with exposure
May 2006 6-262 DRAFT-DO NOT QUOTE OR CITE
-------
1 duration or level (Robins et al., 1983; Tuppurainen et al., 1988). The overall picture that
2 emerges is that those studies that have included subjects having blood lead concentrations
3 exceeding 100 |ig/dL have found depression of serum T3 and/or T4 levels, without a detectable
4 increase in serum TSH. However, studies in which the blood lead distribution was dominated by
5 levels well below 100 |ig/dL, have found either no effects or subclinical increases in serum T3,
6 T4, with no change in TSH levels. Outcomes from the most pertinent studies are summarized
7 qualitatively in Table 6-9.4 and are described in greater detail below.
8 Siegel et al. (1989) measured serum total thyroxine (TT4) and free thyroxine (FT4) in
9 children ages 11 months to 7 years (n = 68) who were outpatients at a clinical care facility.
10 Mean blood lead concentration in the study group was 25 |ig/dL (range 2-77). In a simple
11 (univariate) linear regression analysis, hormone levels were not significantly associated with
12 blood lead concentration.
13 Zheng et al. (2001) measured concentrations of TT4 and transthyretin (TTR) in serum and
14 cerebral spinal fluid (CSF) of adult hospital patients (n = 82) admitted for evaluation of CSF
15 clinical chemistry (e.g., for head wounds, tumors, neurological symptoms). Mean blood lead
16 concentration was 14.9 |ig/dL (SD 8.3). Age-adjusted serum TT4 and TTR, and CSF TT4 were
17 not significantly associated with blood lead concentration; however, increasing CSF lead
18 concentration was associated with decreasing CSF TTR levels (r = -0.30, p = 0.023).
19 Possible associations between lead exposure and thyroid hormone status have been
20 examined in several studies of lead workers (Dursun and Tutus, 1999; Erfurth et al., 2001;
21 Gennart et al., 1992; Gustafson et al., 1989; Horiguchi et al., 1987; Lopez et al., 2000; Refowitz,
22 1984; Robins et al., 1983; Schumacher et al., 1998; Singh et al., 2000; Tuppurainen et al., 1988).
23 Of these, six warrant particular attention because the design and/or analysis attempted to control
24 for effects of age (Erfurth et al., 2001; Dursun and Tutus, 1999; Gustafson et al., 1989;
25 Schumacher et al., 1998; Tuppurainen et al., 1988; Robins et al., 1983). Outcomes of these
26 studies are summarized in Table 6-9.4. The largest studies were Erfurth et al. (2001),
27 Schumacher et al. (1998), and Tuppurainen et al. (1988).
28 Erfurth et al. (2001) was a cross-sectional study of secondary smelter workers (n = 62)
29 and a reference group of metal (not lead) workers (n = 26). Excluded from the study were
30 individuals with ongoing thyroid disease or who were taking thyroid hormone supplements or
31 other drugs that would interfere with thyroid hormone levels (e.g., beta-blockers). Median blood
May 2006 6-263 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-9.4. Summary of Results of Selected Studies of Associations Between Lead Exposure and
to
o
o
ON
ON
to
ON
O
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Study
C/z/Wrew
Siegel etal. (1989)
Dursun and Tutus (1999)
Erfurth etal. (2001)
Gustafson etal. (1989)
Robins etal. (1983)
Schumacher etal. (1998)
Tuppurainen et al. (1988)
Zheng etal. (2001)
- , decrease; +, increase; o
Blood Lead (jig/dL)
SubJects "a Mean(SD) Range T3
children, 11 mo-7yrs 68 25 2-77 NR
metal powder manufacture workers 57 17.1(9.0) 1-36 +
secondary smelter workers 88 31.1° 4-93 o
secondary smelter workers 42 39.4(2.1) NR o
brass foundry workers 47 NR 16-127 NR
primary smelter workers 151 24.1 15>40% o
battery manufacture workers 176 55.9(23.8) 5-134
general population 82 14.9(8.3) NR NR
, no effect; NR, not reported; T3, triiodothyronine; T4, thyroxine; TSH, thyroid stimulating hormone
T4 TSH
o NR
+ o/ob
0 0
+ 0
NR
0 0
0
o NR
a Total number of subjects (including reference group)
b basal/thyroid releasing hormone-stimulated
0 median
-------
1 lead concentration in the lead workers was 31 |ig/dL (range 8-93 |ig/dL). Age-adjusted basal
2 serum levels of FT3, FT4, and TSH were not associated with blood, urine, or finger bone lead
3 levels. Thyroid releasing hormone (TRH)-induced TSH secretion (area under serum TSH
4 concentration-time curve) was measured in an age-matched subset of the study group (9 lead
5 workers and 11 reference subjects) and was not significantly different in the two groups. The
6 Schumacher et al. (1998) study measured serum FT4, TT4, and TSH levels in a group of male
7 workers (n = 151) at the Trail British Columbia smelter complex. Excluded from the study were
8 individuals who had ongoing clinical thyroid disease. Mean blood lead concentration in the
9 study group was 24 |ig/dL (15% >40 |ig/dL). Covariate-adjusted (age, alcohol consumption)
10 hormone levels were not significantly associated with current blood lead concentration or
11 10-year average blood lead concentrations. Prevalence of abnormal hormone values was also
12 unrelated to blood lead concentration.
13 Tuppurainen et al. (1988) measured serum total triiodothyronine (TT3), FT4, TT4,
14 and TSH levels in a group of male battery manufacture workers (n = 176). Mean blood lead
15 concentration was 56 |ig/dL (range 14-134 |ig/dL). Although, hormone levels were not
16 significantly associated with blood lead concentrations, increasing exposure (i.e., employment)
17 duration was significantly associated with decreasing FT4 (r2 = 0.071, p = 0.001) and TT4
18 (r2 = 0.059, p = 0.021) levels. The r2 was not improved by including age or blood lead as
19 covariables. Strength of the association was greater when the analysis was restricted to workers
20 who had an exposure duration >7.6 years (FT4: r2 = 0.33, p < 0.002; TT4: r2 = 0.21, p < 0.001).
21 Consistent with the results of the Tuppurainen et al. (1988) study, Robins et al. (1983) found a
22 significant association between increasing blood lead concentration and decreasing FT4
23 (r2 = 0.085, p = 0.048) in a group of brass foundry workers (n = 47). The blood lead range in
24 the subjects was 16-127 |ig/dL. When stratified by race (black, white) the association was
25 significant in the black stratum (r2 = 0.21, p = 0.03), but not in the white stratum (r2 = 0.05,
26 p = 0.27). The strength of association was not changed by including age in the regression model.
27 Both the Robins et al. (1983) and Tuppurainen et al. (1988) included subjects with blood lead
28 concentrations >100 |ig/dL.
29 Blood lead concentrations were lower in the Dursun and Tutus (1999) and Gustafson et al.
30 (1989) studies than in the above studies, and both studies found significant associations between
31 lead exposure and increasing serum TT4 levels. Dursun and Tutus (1999) measured serum FT3,
May 2006 6-265 DRAFT-DO NOT QUOTE OR CITE
-------
1 TT3, FT4, TT4, and TSH in a group of metal powder manufacture workers (n = 27) and a
2 reference group (n = 30). Mean blood lead concentration in the workers was 17 |ig/dL (range
3 9-36 |ig/dL). A linear regression model that included age, blood lead concentration, and
4 exposure duration, indicated a significant association between increasing exposure duration and
5 increasing serum TT4 levels (r2 = 0.3, p = 0.03). The Gustafson et al. (1989) study examined a
6 group of male secondary smelter workers (n = 21) and reference subjects, individually matched
7 to the lead workers by age, sex, and work shift. Mean blood lead concentration in the workers
8 was 39 |ig/dL (SD 2). Serum TT4 levels were significantly higher (p < 0.02) in the lead workers
9 compared to the reference group. The difference strengthened when the analysis was restricted
10 to the age range <40 years (p = 0.01).
11
12 6.9.3.3 Reproductive Endocrine Function
13 Male Reproductive Endocrine Function
14 Low testosterone (TES) levels, blunted sex hormone secretion in response to gonadotropin
15 releasing hormone (GnRH), and defects in spermatogenesis have been observed in humans
16 exhibiting clinical neurological symptoms of lead poisoning (Braunstein et al., 1978; Cullen
17 et al., 1984). However, the effects of lower exposure levels on reproductive endocrine status are
18 less clear. Possible associations between lead exposure and changes in male reproductive
19 hormone levels have been examined in studies of lead workers. Of these, five studies attempted
20 to control for effects of age, an important determinant of testosterone levels (Alexander et al.,
21 1998; Erfurth et al., 2001; Gustafson et al., 1989; McGregor and Mason, 1990; Ng et al., 1991).
22 The outcomes from these studies are qualitatively summarized in Table 6-9.5. Blood lead ranges
23 in the latter studies were similar (4-90 |ig/dL), yet outcomes were mixed, with no change
24 (Erfurth et al., 2001; Gustafson et al., 1989; McGregor and Mason, 1990) or subclinical decrease
25 (Alexander et al., 1996a, 1998; Ng et al., 1991) in serum testosterone (TES) in association with
26 lead exposure. Mixed effects were observed for the effect of lead exposure on serum follicle
27 stimulating hormone (FSH) and luteinizing hormone (LH), increases (McGregor and Mason,
28 1990; Ng et al., 1991), decreases (Gustafson et al., 1989), and with no change (Alexander et al.,
29 1996a, 1998; Erfurth et al., 2001) in hormone levels observed.
30 The inconsistency in the direction of effects on TES and the two androgen regulating
31 pituitary hormones, FSH and LH, is particularly noteworthy, and suggest the possibility of
May 2006 6-266 DRAFT-DO NOT QUOTE OR CITE
-------
to
ON
H
6
o
o
H
O
o
H
W
O
O
HH
H
W
Table 6-9.5. Summary of Results of Selected Studies of Associations Between Lead Exposure and
Male Sex Hormone Levels in Adults
to
<->
0
ON
Study
Alexander et al. (1996a, 1998)
Erfurthetal. (2001)
Gustafson et al. (1989)
McGregor and Mason (1990)
Ngetal. (1991)
Blood Lead (jig/dL)
Subjects
primary smelter workers
secondary smelter workers
secondary smelter workers
lead workers
battery manufacture workers
"a
152
88
42
176
171
Mean (SD)
NR
31. 1°
39.4(2.1)
NR
35(13)
Range FSH LH PRL TES
5-58 o o NR -b
4-93 of-6-* o/od o/od od
NR - - o o
17-77 + + NR o
10-72 + + o -
• +
; o, no effect; NR, not reported, FSH, follicle stimulating hormone, LH, luteinizing hormone; PRL, prolactin; TES, testosterone
total number of subjects (including reference group)
1 in association with increasing semen lead levels, not with blood lead
median
1 basal/gonadotropin releasing hormone-stimulated
effect was evident in comparison between groups, but not in multivariate regression that adjusted for age
-------
1 multiple effect of lead on the hypothalamic-pituitary-gonad axis, consistent with observations
2 that have been made in some experimental animal studies. Erfurth et al. (2001) observed a
3 suppressed FSH response to GnRH in a group of lead workers compared to an age matched
4 reference group; however, the magnitude of the response was not significantly associated with
5 lead exposure indices in a multivariate regression analysis that accounted for age. In rats, lead
6 exposure can suppress serum testosterone levels in the absence of a change in circulating levels
7 of GnRH or LH, even though levels of GnRH mRNA increase in the hypothalamus (Klein et al.,
8 1994; Ronis et al., 1996; Sokol et al. 2002). Thus, changes in GnRH production, at the
9 molecular level, do not necessarily translate to changes in hormone levels. This may be the
10 result of lead inhibition of release of GnRH for nerve terminals in the median eminence (Bratton
11 et al., 1994; Sokol, 1987; Sokol et al., 1998, 2002).
12 Alexander et al. (1996a, 1998) examined serum FSH, LH, and TES in males (n = 152)
13 who worked at the Trail British Columbia smelter complex. Covariate-adjusted hormone levels
14 and prevalence of clinically abnormal values were unrelated (p > 0.05) to blood lead
15 concentration (range 5-58 |ig/dL); however, increasing semen lead concentration (range 0.3-17
16 Hg/dL) was significantly associated with decreasing semen testosterone levels (p = 0.004).
17 Erfurth et al. (2001) measured serum TES, sex hormone binding globulin (SHBG), and GnRH-
18 stimulated changes in serum FS, LH, and PRL in male secondary smelter workers (n = 62) and in
19 a reference group (n = 26). Mean blood lead in the lead workers was 31 |ig/dL (range
20 8-93 jig/dL). Age-adjusted basal hormone levels were unrelated to blood, plasma, or urine lead
21 concentrations. In an age-matched subset of the cohorts (n = 9 lead workers, n = 11 reference),
22 median GnRH-stimulated serum FSH was significantly lower in lead workers than in the
23 reference group; however, GnRH-stimulated LH, FSH, and PRL were not significantly
24 associated with any of the lead measures in a multivariate regression analysis. Gustafson et al.
25 (1989) measured serum FSH, LH, and TES (total and free) in a group of male secondary smelter
26 workers (n = 21) and in a group of reference subjects individually matched to the lead workers
27 by age, sex, and work shift. Mean blood lead concentrations were 39 |ig/dL (SD 2) in the lead
28 workers and 5.0 |ig/dL (SD 0.2) in the reference group. Serum FSH levels were significantly
29 lower (p = 0.009) in lead workers compared to reference group. When the analysis was
30 restricted to the age range <40 years, lead workers had significantly lower FSH and LH
31 compared to the reference group. McGregor and Mason (1990) measured serum FSH, LH, TES,
May 2006 6-268 DRAFT-DO NOT QUOTE OR CITE
-------
1 and SHBG in a group of male lead workers (n = 90) and in a reference group (n = 86). Blood
2 lead range in the lead workers was 17-77 |ig/dL; blood lead concentrations in the reference
3 subjects were <12 |ig/dL. Prevalences of abnormal hormone levels in the lead workers and
4 reference group were not different; however, age-adjusted serum FSH was significantly higher in
5 lead workers compared to reference group and increasing FSH levels were significantly
6 associated with increasing blood lead concentrations. Increasing serum LH was significantly
7 associated with increasing exposure duration but not with blood lead concentration or age.
8 Serum TES or SHBG levels were unrelated to blood lead concentration or exposure duration.
9 Ng et al. (1991) measured serum FSH, LH, PRL, and TES in a group of male battery
10 manufacture workers (n = 122) and a reference group (n = 49). Mean blood lead concentrations
11 were 35 |ig/dL (range 10-77 |ig/dL) in the lead workers and 8 |ig/dL (range 3-15 |ig/dL) in the
12 reference group. When cohorts were stratified by age, serum FSH and LH levels were
13 significantly higher in lead workers <40 years of age compared to corresponding age stratum of
14 the reference group; serum TES was significantly lower in lead workers >40 years of age,
15 compared to the same age stratum in the reference group. Covariate-adjusted (age, tobacco
16 smoking) serum TES levels were significantly lower in lead workers in the 10-year exposure
17 duration stratum, compared to the reference group. Covariate-adjusted serum FSH and LH were
18 significantly higher in lead workers in the < 10-year exposure duration stratum, compared to the
19 reference group.
20
21 Female Reproductive Endocrine Function
22 Although delays in sexual maturation in humans have been associated with increases in
23 blood lead concentrations (Selevan et al., 2003; Wu et al., 2003b), and lead has been shown to
24 alter levels of female sex hormones and the menstrual cycle in nonhuman primates (Foster, 1992;
25 Franks et al., 1989; Laughlin et al., 1987), epidemiologic studies of interactions between lead
26 exposure and reproductive endocrinology in females have not been reported. Lead introduced
27 into cultures of human ovarian granulosa cells suppresses progesterone production (Paksy et al.,
28 2001) and suppresses expression of aromatase and estrogen receptor P (Taupeau et al., 2003).
29
May 2006 6-269 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.9.3.4 Pituitary and Adrenal Endocrine Function
2 Several studies of possible associations between lead exposure and levels of pituitary
3 hormones that regulate production and secretion of thyroid hormones (see Section 6.9.3.2) and
4 reproductive hormones (see Section 6.9.3.3) have been reported. In addition to the above
5 studies, Gustafson et al. (1989) found that serum cortisol levels were lower in a group of male
6 secondary smelter workers (n = 21) compared to a reference group individually matched to the
7 lead workers by age, sex, and work shift. Mean blood lead concentrations were 39 |ig/dL (SD 2)
8 in the workers and 5.0 |ig/dL (SD 0.2) in the reference group. Campbell et al. (1985) measured
9 various biomarkers of status of the renin-angiotensin-aldosterone system in male welders (n = 5)
10 and reference subjects (n = 8). Mean blood lead concentration was 35 |ig/dL (range 8-62 jig/dL).
11 Significant positive correlations were observed between blood lead concentration and plasma
12 aldosterone (r = 0.53, p < 0.002), which may have been, at least in part, secondary to a lead
13 effect on plasma renin activity (r = -0.76, p < 0.001) and angiotensin I levels (r = 0.68,
14 p < 0.002). Saenger et al. (1984) found lower urinary levels of 6-p-OH-cortisol, but not cortisol,
15 in children who had elevated urinary lead in an EDTA provocation test (>500 |ig/24 h),
16 compared to children who did not have elevated urinary lead levels, or whose blood lead
17 concentrations were <30 |ig/dL. The change in urinary excretion of 6-p-OH-cortisol in the
18 absence of a change in cortisol levels may reflect an effect of lead on liver cytochrome P450
19 activity, rather than an effect on the adrenal gland (see Section 6.9.4).
20
21 6.9.3.5 Calcitropic Endocrine Function
22 Children exposed to relatively high level of lead >30 |ig/dL may exhibit depressed levels
23 of circulating 1,25-OH-D (Mahaffey et al., 1982; Rosen et al., 1980). These effects were not
24 detected in a study of calcium-replete children with average lifetime blood lead levels below
25 25 |ig/dL (Koo et al., 1991). In adults, lead exposures that result in blood lead concentrations
26 >40-60 |ig/dL may increase, rather than decrease, circulating levels of 1,25-OH-D and PTH.
27 These studies also are summarized in Annex Tables AX6-9.5 and AX6-9.6. Outcomes from the
28 more pertinent studies are qualitatively summarized in Table 6-9.6 and are discussed in greater
29 detail below.
30 Epidemiologic studies of possible associations between lead exposure and vitamin D
31 status in children have yielded mixed results. Mahaffey et al. (1982) and Rosen et al. (1980)
May 2006 6-270 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-9.6. Summary of Results of Selected Studies of Associations Between Lead Exposure
to
o
o
ON
ON
to
o
(*
H
6
o
0
H
O
o
H
W
O
O
HH
H
W
Blood Lead (jig/dL)
Study Subjects na Mean (SD) Range PTH CAL !'25D
Children
Koo etal. (1991) ages: 21, 27, 33 mo 105 9.7 5-24 o o o
Mahaffey etal. (1982) ages: 1-16 yr 177 NR 12-120 o o -
Rosen etal. (1980) ages: 1-5 yr 45 18, 47, 74b 10-120 + o
Adults
Chalkley etal. (1998) smelter workers' 19 47 21-76 NR NR +c
Kristal-Boneh etal. (1998) battery manufacture workers 140 43 1-77 + NR +
Mason etal. (1990) lead workers 138 NR 15-95 o NR +
-, decrease; +, increase; o, no effect; NR, not reported, PTH, parathyroid hormone; CAL, calcitonin; 1,25D, 1,25-dihydroxyvitaminD; 25D, 25-
hydroxyvitamin D
a total number of subjects (including reference group)
b group means: low, moderate, high
0 cadmium, lead, zinc smelter workers, effect on 1,24D in association with high blood cadmium and lead and high urinary cadmium
25D
0
0
-
0
NR
NR
-------
1 observed lower 1,25-OH-D in association with increasing blood lead concentration. Koo et al.
2 (1991) found no association between 1,25-OH-D and blood lead concentration. The Koo et al.
3 (1991) study was a longitudinal analysis of a subset of a prospective study of pregnancy
4 outcomes. Serum calcium, magnesium, phosphorus, PTH, CAL, 25-OH-D, 1,25-OH-D, and
5 bone mineral content were measured in children (n = 105) at ages 21, 27, and 33 months. Mean
6 lifetime average blood lead concentrations (based on quarterly assessments) was 9.7 |ig/dL
7 (range 4.8-23.6 |ig/dL). The range of highest values observed was 6-63 |ig/dL. A structural
8 equation model was developed that initially considered age, sex, race, sampling season, and
9 dietary intake of calcium, phosphorus, and vitamin D as covariables; the final model retained
10 age, sex, race, and sampling season. Decreasing blood lead (In-transformed) was significantly
11 associated with covariate-adjusted decreasing serum phosphorus. No other covariate-adjusted
12 outcomes were significantly associated with blood lead. The distribution of dietary calcium
13 intakes was 4% for <600 mg/day, 55% for 600-1200 mg/day, and 41% for >1200 mg/day.
14 Intakes of phosphorous were similar, suggesting that the subjects were nutritionally replete with
15 respect to these two nutrients.
16 The different outcomes in Koo et al. (1991) compared to the Mahaffey et al. (1982) and
17 Rosen et al. (1980) studies may reflect, in part, the lower blood lead range in the subjects in
18 Koo et al. (1991) (range of lifetime average 5-24 |ig/dL, range of observed highest values 6-63
19 |ig/dL) compared to the Mahaffey et al. (1982) and Rosen et al. (1980) studies (10-120 (ig/dL).
20 Subjects in the Koo et al. (1991) study also had higher calcium intakes (4% with <600 mg/day,
21 43% with >1200 mg/day) than in the Rosen et al. (1980) study (mean 580 mg/day [SE 15] in
22 high blood lead group). Calcium intake (and/or related nutritional factors) may also have been
23 an uncontrolled confounder in the Rosen et al. (1980) study, as higher blood lead concentration
24 appeared to be associated with lower calcium intakes (Sorrell et al., 1977). Mahaffey et al.
25 (1982) did not report calcium intakes. Thus, the effect of lead exposure on vitamin D status may
26 be more pronounced at higher blood lead concentrations (i.e., >60 |ig/dL) and in combination
27 with lower intakes of calcium (or other nutritional limitations).
28 Studies of lead workers have found evidence for higher serum levels of 1,25-OH-D and
29 PTH in association with increasing blood lead concentration (Chalkley et al., 1998; Kristal-
30 Boneh et al., 1998; Mason et al., 1990). The Chalkey et al. (1998) study was a small study
31 (n = 19) of subjects exposed to both cadmium and lead, and effects of lead and cadmium on
May 2006 6-272 DRAFT-DO NOT QUOTE OR CITE
-------
1 1,25-OH-D could not be isolated. The Kristal-Boneh et al. (1998) and Mason et al. (1990)
2 studies included larger samples of subjects whose exposure was primarily, but not exclusively,
3 to lead. Attempts were made to control for effects of age and, in the Kristal-Boneh et al. (1998)
4 study, other potential covariables. Kristal-Boneh et al. (1998) measured serum calcium,
5 magnesium, phosphorus, PTH, 25-OH-D, and 1,25-OH-D in a group of male battery
6 manufacture workers (n = 56) and a reference group (n = 90). Mean blood lead concentrations
7 were 43 |ig/dL (SD 14, range 1-77 |ig/dL) in the lead worker group and 4.5 |ig/dL (SD 2.6, range
8 1.4-19 (ig/dL) in the reference group. Serum 1,25-OH-D and PTH, but not 25-OH-D, were
9 significantly higher in lead workers compared to the reference group. Increasing blood lead
10 concentration (In-transformed) was significantly associated with covariate-adjusted increasing
11 serum PTH and 1,25-OH-D levels. No effects on serum calcium were apparent. Occupational
12 lead exposure was also significantly associated with increasing PTH and 1,25-OH-D level.
13 Covariates retained in the multivariate model were age, alcohol consumption, smoking; calcium
14 intake, magnesium intake, and calorie intake. Mason et al. (1990) measured serum calcium,
15 phosphate, PTH, and 1,25-OH-D in male lead workers (n = 63) and in a reference group (n = 75)
16 and found significantly higher prevalence of elevated 1,25-OH-D (defined as >2 SD higher than
17 reference mean) in lead workers (13%) compared to the reference group (1.3%). Serum levels of
18 1,25-OH-D were also significantly higher in lead workers compared to the reference group.
19 After stratification of the lead workers into exposure categories (high exposure: blood lead
20 >40 |ig/dL and bone lead >40 |ig/g; low exposure: blood lead <40 |ig/dL and bone lead
21 <40 |ig/g), serum 1,25-OH-D levels were significantly higher in the high lead group. Serum
22 calcium levels were not different in the two groups. Increasing blood lead was significantly
23 associated with increasing 1,25-OH-D levels (r2 = 0.206; with age and bone lead included,
24 r2 = 0.218). After excluding 12 subjects whose blood lead concentrations >60 |ig/dL, the
25 regression coefficient was no longer significant (r2 = 0.162, p = 0.26).
26
27 6.9.4 Effects of Lead on the Hepatic System
28 6.9.4.1 Summary of Key Findings of the Effects of Lead on the Hepatic System
29 from the 1986 Lead AQCD
30 The 1986 Lead AQCD noted that effects of lead on liver function in humans had not been
31 extensively studied. Possible association between lead exposures (blood lead concentrations
May 2006 6-273 DRAFT-DO NOT QUOTE OR CITE
-------
1 >70 |ig/dL) and nonspecific liver injury (i.e., increases in liver enzymes in serum) were noted
2 based on studies of workers (e.g., Cooper et al., 1973; Hammond et al., 1980). Also noted was
3 evidence for possible association of suppression of hepatic cytochrome P450 activity with high
4 blood lead concentrations (>70 |ig/dL) (Meredith et al., 1977).
5 Few studies of hepatic effects of lead on humans have been reported since the 1986 Lead
6 AQCD. Studies of hepatic enzyme levels in serum suggest that liver injury may be present in
7 lead workers; however, associations specifically with lead exposures are not evident (Al-Neamy
8 et al., 2001; Hsiao et al., 2001). Studies of urinary metabolites of cytochrome P450 phenotypes
9 CYP2A6 and CYP3 A4 suggest possible associations between lead exposure and suppression of
10 hepatic enzyme activity. The effect on CYP2A6 activity was observed in children with high lead
11 burdens (i.e., blood lead concentration >40 |ig/dL, EDTA-provoked urinary lead >500 |ig/dL).
12 The effect on CYP3 A4 was observed in association with blood lead ranges of approximately
13 30-112 |ig/dL (based on reported serum lead concentrations). These studies are summarized in
14 Annex Table AX6-9.7 and the most pertinent findings are discussed below.
15
16 6.9.4.2 Nonspecific Hepatic Injury
17 Possible association between occupational lead exposure and liver injury has been
18 assessed from measurements of serum enzymes (Al-Neamy et al., 2001; Hsiao et al., 2001).
19 Al-Neamy et al. (2001) found significantly higher serum activity of alkaline phosphatase (AP)
20 and lactate dehydrogenase (LDH), both within clinically normal ranges, in a group (n = 100) of
21 male lead workers (e.g., gas pump attendants, garage workers, printing workers, construction
22 workers), compared to an age-matched reference group (n = 100). Serum levels of alanine
23 aminotransferase (ALT), aspartate aminotransferase (AST), and y-glutamyl transferase (y-GT)
24 were not different in the two groups. The mean lead concentrations were 78 |ig/dL (SD 43)
25 in the lead workers and 20 |ig/dL (SD 12) in the reference group. Hsiao et al. (2001) found no
26 association between blood lead concentration and ALT activity, in a longitudinal study of a
27 group of battery manufactory workers (n = 30). Mean blood lead concentrations ranged from
28 60 |ig/dL (approximate range 25-100 |ig/dL) at the start of the study (1989) to 30 |ig/dL
29 (approximate range 10-60 |ig/dL) in the final year of the study (1999).
30
May 2006 6-274 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.9.4.3 Hepatic Cytochrome P450 Function
2 Studies conducted in animmals have shown that lead can decrease the activity of hepatic
3 cytchrome P450 and its induction by various inducing agent, through a mechanism that, at least
4 in part, invovles a disruption of heme synthesis (see Section 5.10.1.1). Possible assoications
5 beteeen lead exposure and cytochome P450 activity have been studied in children and adults
6 (Saenger et al., 1984; Satarug et al., 2004). Althjough direct assay of hepatic cytrochrome P450
7 levels is not feasible in epidemiological studies, changes in activities of P450 isozymes can be
8 detected from measurments of urinary metabolites of P450 substrates. Urinary excretion of
9 6-p-hydroxycortisol (6-p-OH-cortisol) derives primarily from oxidation of cortisol through the
10 hepatic cytochrome P450 phenotype CYP3A4. A lower urinary 6-p-OH-cortisol:cortisol ratio is
11 indicative of possible suppression of hepatic CYP3A4 activity. Saenger et al. (1984) found
12 significantly lower (-45% lower) urinary excretion of 6-p-OH-cortisol and lower urinary
13 6-p-OH-cortisol:cortisol ratio in 2-9 year-old children (n = 26) who qualified for chelation
14 (EDTA-provoked urinary lead >500 |ig/24 h) than in children who did not qualify, and
15 significantly lower than in an age-matched reference group. Urinary 6-p-OH-cortisol:cortisol
16 ratio was significantly correlated with blood lead (r = -0.514, p < 0.001), urinary lead, and
17 EDTA-provoked urinary lead (r = -0.593, p < 0.001). Mean blood lead concentrations were
18 46 |ig/dL (range 33-60 |ig/dL), prior to chelation, and 42 |ig/dL (range 32-60 |ig/dL) in the
19 children who did not qualify for chelation.
20 Satarug et al. (2004) measured urinary excretion of 7-hydroxy-coumarin (7-OH-
21 coumarin) following a single oral dose of coumarin to assess effects of cadmium and lead
22 exposure on cytochrome P450 phenotype CYP2A6. The rationale for this approach is that
23 7-hydroxylation of coumarin occurs solely through the CYP2A6 pathway. Coumarin-induced
24 urinary 7-OH-coumarin was measured in a group (n = 118) selected from the general population
25 in Bangkok, Thailand. All subjects were nonsmokers. The study found a significant association
26 between increasing urinary lead and decreasing covariate-adjusted urinary 7-OH-coumarin in
27 males, but not in females. Covariates retained included age and zinc excretion. A significant
28 association, in opposite direction, was found between urinary cadmium and urinary 7-OH-
29 coumarin. Mean urinary lead levels (blood lead concentrations were not reported) were 1.3 |ig/g
30 creatinine (range 0.1-1.2 |ig/dL) in males, and 2.4 |ig/g creatinine (range 0.6-6.8 |ig/dL) in
31 females. Mean serum lead concentrations were 4 |ig/dL (range 1-28 |ig/dL) in males and
May 2006 6-275 DRAFT-DO NOT QUOTE OR CITE
-------
1 3 |ig/dL (range 1-12 |ig/dL) in females. The range 1-28 |ig/L serum would correspond to a
2 blood lead concentration range of approximately 30-112 |ig/dL (U.S. Environmental Protection
3 Agency, 2003). These results are consistent with observations of depressed excretion of
4 metabolites of the CYP2A6 substrate, phenazone, in association with overt clinical lead toxicity
5 in lead workers (Fischbein et al., 1977; Meredith et al., 1977).
6
7 6.9.5 Effects of Lead on the Gastrointestinal System
8 6.9.5.1 Summary of Key Findings of the Effects of Lead on the Gastrointestinal
9 System from the 1986 Lead AQCD
10 The 1986 Lead AQCD described gastrointestinal colic (abdominal pain, constipation,
11 intestinal paralysis) as a consistent early symptom of lead poisoning in humans and noted that
12 such symptoms may be present in association with blood lead concentrations in the range of
13 30-80 |ig/dL. The 1986 Lead AQCD concluded that information was insufficient to establish
14 clear concentration (i.e., blood concentration)-response relationships in the general population in
15 association with environmental exposure. Subsequent to the 1986 AQCD several studies of
16 prevalence of symptoms of gastrointestinal colic in lead workers have been reported that provide
17 evidence for symptoms in association with blood lead concentrations >50-80 |ig/dL (Awad el
18 Karim et al., 1986; Holness and Nethercott, 1988; Lee et al., 2000; Matte et al., 1989).
19 Summaries of these studies are presented in Annex Table AX6-9.8. Similar types of studies of
20 children have not been reported.
21
22 6.9.5.2 Gastrointestinal Colic
23 Lee et al. (2000) collected data on symptoms (self-reported questionnaire) in male lead
24 workers (n = 95) who worked in secondary smelters, PVC-stabilizer manufacture facilities, or
25 battery manufacture facilities. A logistic regression model was applied to the prevalence data for
26 gastrointestinal symptoms (loss of appetite, constipation or diarrhea, abdominal pain). The
27 covariate-adjusted odds ratio for symptoms, in association with blood lead concentration
28 (>versus versus <260.5 |ig/4 h, the group
30 median) was also not significant (1.1, [95% CI: 0.4, 2.5]). However, the odds ratio for
31 neuromuscular symptoms in association with DMSA-provoked urinary lead was significant
May 2006 6-276 DRAFT-DO NOT QUOTE OR CITE
-------
1 (7.8, [95% CI: 2.8, 24.5]), suggesting that neuromuscular symptoms may occur in association
2 with exposures that are insufficient to result in detectable gastrointestinal symptoms. Covariates
3 retained in the final regression models were age, tobacco smoking, and alcohol consumption.
4 Three other studies have attempted to quantify associations between lead exposure and
5 gastrointestinal symptoms in lead workers (Awad el Karim et al., 1986; Holness and Nethercott,
6 1988; Matte et al., 1989). Holness and Nethercott (1988) found a significantly (p < 0.05) higher
7 prevalence of symptoms in a group of demolition workers (n = 119) in association with a blood
8 lead range of 50-70 |ig/dL (n = 87), 37% for abdominal cramps and 42% for constipation, or
9 >70 |ig/dL (n = 19) 77% for abdominal cramps and 62% for constipation compared to a group of
10 workers in which the blood lead concentration was <50 |ig/dL (n = 13), prevalences of 8% and
11 6%. Awad el Karim et al. (1986) found higher prevalence of gastrointestinal symptoms, for
12 abdominal colic and constipation, respectively, in male battery manufacture workers, 41.3% for
13 abdominal colic and 41.4% for constipation, compared to a reference group of workers, n = 40
14 prevalences of 7.5% and 10% for abdominal colic and constipation, respectively. The blood lead
15 ranges were 55-81 |ig/dL in the lead workers and 7-33 |ig/dL in the reference group. Matte et al.
16 (1989) did not find a significant difference in prevalence of gastrointestinal symptoms (decreased
17 appetite, nausea, abdominal pain) among a group of battery manufacture and repair workers
18 (n = 63) when stratified by blood lead concentration (60 |ig/dL, >60 jig/dL). The prevalence
19 ratio (high/low blood lead strata) for abdominal pain was 1.5 (95% CI: 0.5, 4.6).
20 In a small study of environmentally-exposed adults, Bercovitz and Laufer (1991) found
21 that the lead level in the dentine of patients with gastrointestinal ulcers (n = 11), even long after
22 recovery, were significantly higher (mean lead 75.02 |ig/g [SE 8.15]) than that in healthy
23 subjects (mean lead 25.62 jig/g [SE 10.15]). Ten of the 11 peptic ulcer patients had a higher lead
24 level than the healthy subjects. In these 10 patients, increased severity of the ulcer and longevity
25 of suffering was associated with increased tooth lead levels. The authors suggested that
26 increased absorption of lead was associated with damage to the epithelial mucosal cells of the
27 gastrointestinal tract.
28
29
30
May 2006 6-277 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.9.6 Effects of Lead on the Respiratory System
2 6.9.6.1 Summary of Key Findings of the Effects of Lead on the Respiratory System
3 from the 1986 Lead AQCD
4 The 1986 Lead AQCD did not discuss effects of lead on the respiratory tract on humans.
5 Only one study since the 1986 document has examined the association between lead and
6 respiratory health outcomes.
7
8 6.9.6.2 Pulmonary Function
9 Bagci et al. (2004) conducted pulmonary function tests on a group of male battery
10 manufacture workers (n = 22), a group of automobile exhaust repair workers (n = 40), and a
11 group of hospital workers (n = 24). Mean blood lead concentrations were 37 |ig/dL (SD 8) in the
12 battery manufacture group, 27 |ig/dL (SD 9) in the exhaust repair group, and 15 |ig/dL (SD 3) in
13 the hospital workers. Lead workers and the reference group had similar tobacco smoking
14 prevalences (51-56%). Battery manufacture workers had significantly lower forced expiratory
15 volume in one second (FEVi), FEVi:vital capacity (VC) ratio, FEVi/forced vital capacity (FVC)
16 ratio, forced expiration flow (FEF), and maximum voluntary ventilation (MVV) compared to
17 the hospital workers. Blood lead concentration was significantly negatively correlated with
18 FEVi/FVC (r = -0.31, p = 0.006) and FEF (r = -0.30, p = 0.009) after adjusting for age,
19 cigarette smoking, and exposure duration. Results from this study are further summarized in
20 Annex Table AX6-9.9.
21
22 6.9.7 Effects of Lead on Bone and Teeth
23 6.9.7.1 Summary of Key Findings of the Effects of Lead on Bone and Teeth from
24 the 1986 Lead AQCD
25 The 1986 Lead AQCD did not discuss the effects of lead on bone and teeth. Since
26 completion of the 1986 AQCD, an additional development in lead epidemiology has been studies
27 that have explored possible associations between lead exposure and risk of dental caries
28 (Campbell et al., 2000; Dye et al., 2002; Gemmel et al., 2002; Moss et al., 1999). In addition,
29 a limited number of studies also examined the toxic effect of lead on bone. These studies are
30 summarized in Annex Table AX6-9.10.
31
May 2006 6-278 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.9.7.2 Bone Toxicity
2 The number of papers dealing with direct toxicity of lead on bone is limited. Most papers
3 are reviews (Hu et al., 1991; Puzas, 2000; Puzas et al., 1992; Rabinowitz, 1991; Silbergeld,
4 1991; Silbergeld et al., 1993; Vig and Hu, 2000) or based on cellular studies (e.g., Pounds
5 et al., 1991) or animals.
6 Various authors have suggested that lead is a potential risk factor for osteoporosis because
7 of the pivotal role of the skeleton in lead toxicokinetics (Goyer et al., 1994). Bone cells
8 accumulate lead actively and earlier ideas suggested that lead was incorporated into the mineral
9 matrix of the bone (Wittmers et al., 1988). However, in an in vivo iliac bone biopsy using laser
10 microbeam mass analysis on a lead-intoxicated adult female following chelation therapy, Flood
11 et al. (1988) found the extracellular lead was concentrated in the superficial 3 to 6 jim of the
12 osteoid zone of bony trabeculae. As lead was absent from the deeper parts of the mineralized
13 matrix, the authors suggested that lead binds more strongly to the organic matrix than to bone
14 mineral.
15 There is increasing evidence from cell culture experiments, animal studies, and from
16 measurements in humans that lead may exert detrimental effects on bone mineral metabolism.
17 In humans this evidence comes from several studies. Following on from the earlier observations
18 of Rosen et al. (1980) that 1,25 (OHh vitamin D levels are reduced in lead poisoned children,
19 Markowitz et al. (1988) found that osteocalcin levels were inversely related to lead body burden
20 in moderately lead poisoned children. During chelation treatment for lead, the osteocalcin levels
21 were shown to increase.
22 An inverse relationship between blood lead and stature and chest circumference has been
23 observed in children from the NHANES II study (Schwartz et al., 1986). There are several
24 explanations for the inverse correlation between blood lead and growth in children. First, blood
25 lead level may be a composite factor for genetic, ethnic, nutritional, environmental, and
26 sociocultural factors. Second, nutritional deficits that retard growth also enhance lead
27 absorption. Finally, there may be a direct effect of low level lead on growth in children. This
28 condition was explained by Dowd et al. (1994) as resulting from the inhibition by Pb2+ of
29 binding of osteocalcin to hydroxyapatite. Effects similar to those described by Schwartz et al.
30 (1986) were reported by Angle and Kuntzelman (1989), Lauwers et al. (1986), and Shukla et al.
31 (1989).
May 2006 6-279 DRAFT-DO NOT QUOTE OR CITE
-------
1 Puzas et al. (1992) suggested lead could upset the very sensitive interactive metabolic
2 activity of osteoblasts and chondrocytes and thereby affect bone growth. In a later review, Puzas
3 (2000) enlarged upon his earlier paper and described in more detail the potential mechanism of
4 lead on growth plate cartilage metabolism and effects of lead on osteoclasts and osteoblasts,
5 especially associated with osteoporosis.
6 Observational studies by Spencer et al. (1992, 1994) suggested a link between
7 occupational exposure to lead and Paget's disease in both males and females but the authors
8 declined to advocate a causal effect. Later Spencer et al. (1995) found that 92% of a group of
9 48 patients with Paget's disease were exposed to lead either from occupational or environmental
10 sources. Adachi et al. (1998) explored a possible association between lead and bone disease
11 from XRF analyses of cortical and trabecular bone lead content in 117 patients who attended a
12 metabolic bone disease clinic (n = 92) or were undergoing dialysis for renal failure (n = 25).
13 In patients suffering from Paget's disease, cortical bone lead content was higher than it was in
14 controls, patients with osteoporosis, and patients on dialysis. Trabecular bone lead content was
15 lowest in patients with Paget's disease or osteitis fibrosa. However, the authors could not
16 distinguish between two alternatives, the first being that increased bone turnover due to Paget's
17 disease releases lead from trabecular bone that is then available for deposition into cortical bone,
18 or secondly, that an increased lead content in cortical bone may cause increased turnover with
19 release of lead from trabecular bone.
20 In another facet of the Normative Aging Study, Shadick et al. (2000) investigated a
21 possible association between long-term lead accumulation and hyperuricemia and gouty arthritis
22 in 777 male subjects. They found a positive association between patella bone lead and uric acid
23 levels (p = 0.022) but no association between bone or blood lead and gout in this
24 environmentally-exposed group.
25
26 6.9.7.3 Dental Health
27 Caries is considered an infectious disease arising from a multifactorial process involving
28 particular flora, dietary exposures, and a susceptible host (Schafer and Adair, 2000). Increased
29 caries risk has been detected in association with increasing blood lead concentrations in
30 populations whose mean blood lead concentrations are approximately 2-3 |ig/dL (Dye et al.,
31 2002; Gemmel et al., 2002; Moss et al., 1999).
May 2006 6-280 DRAFT-DO NOT QUOTE OR CITE
-------
1 Several studies have examined relationships between lead exposure and the occurrence of
2 dental caries in children and adults. The two largest studies were analyses of data collected in
3 the NHANES III; both found significant associations between increasing caries prevalence and
4 increasing blood lead concentrations in children and adolescent (Moss et al., 1999) and the adult
5 (Dye et al., 2002) populations, whose geometric mean blood lead concentration was -2.5 |ig/dL.
6 In the Moss et al. (1999) study, the odds ratios for caries in association with a 5 |ig/dL increase
7 in blood lead concentration (i.e., from <2 |ig/dL) was 1.8 (95% CI: 1.3,2.5). Outcomes of two
8 smaller studies were mixed, with one study finding no significant association between blood lead
9 and caries prevalence (Campbell et al., 2000) and one study finding significant associations
10 (Gemmel et al., 2002); the latter, in children whose mean blood lead concentration was 2.9
11 |ig/dL (maximum 13 |ig/dL).
12 The Moss et al. (1999) NHANES III analysis included the results of coronal caries
13 examinations on 24,901 subjects, stratified by age: 2-5 years (n = 3,547), 6-11 years (n = 2,894),
14 and > 12 years (n = 18,460). Specific outcomes assessed varied by age group: for children 2-11
15 years who had at least one deciduous tooth, the number of deciduous teeth displaying decayed or
16 filled surfaces (DPS); for subjects >6 years and who had at least one permanent tooth, the
17 number of permanent teeth displaying decayed or filled surfaces; and for subjects > 12 years, the
18 sum of decayed, missing, and filled surfaces on permanent teeth (DMFS). In a multivariate
19 linear regression model, increasing blood lead concentration (log-transformed) was significantly
20 associated with covariate-adjusted increases in dfs in the 2-5 year age group (P = 1.78 [SE 0.59],
21 p = 0.004) and in the 6-11 year age group (P = 1.42 [SE 0.51], p = 0.007). Log-transformed
22 blood lead also was associated with increases in DFS in the 6-11 years age group (P = 0.48
23 [SE 0.22], p = 0.03) and in the > 12 years age group (P = 2.50 [SE 0.69], p<0.001), and increases
24 in DMFS in the > 12 years age group (P = 5.48 [SE 1.44], p = 0.01). The odds ratios (compared
25 to 1 st tertile, < 1.66 |ig/dL) for the binomial outcome, 0 or > 1 DMFS, were 1.36 (95% CI: 1.01,
26 2.83) for the blood lead concentration range 1.66-3.52 |ig/dL, and 1.66 (95% CI: 1.12, 2.48) for
27 the range >3.52 |ig/dL. Corresponding population risks attributable to blood lead concentration
28 were 9.6% and 13.5% in the blood lead strata, respectively. An increase in blood lead of
29 5 |ig/dL was associated with an odds ratio of 1.8 (95% CI: 1.3, 2.5). Covariates included in
30 the models were age, gender, race/ethnicity, poverty income ratio, exposure to cigarette smoke,
May 2006 6-281 DRAFT-DO NOT QUOTE OR CITE
-------
1 geographic region, educational level of head of household, carbohydrate and calcium intakes,
2 and frequency of dental visits.
3 Gemmel et al. (2002) conducted a cross-sectional study of associations between blood
4 lead concentration and dental caries in children, 6-10 years of age (n = 543), who resided either
5 in an urban (n = 290) or rural (n = 253) setting. Mean blood lead concentrations were 2.9 |ig/dL
6 (SD 2.0, maximum 13 |ig/dL) in the urban group and 1.7 |ig/dL (SD 1.0, maximum 7 |ig/dL) in
7 the rural group. Increasing blood lead concentration (In-transformed) was significantly
8 associated with covariate-adjusted number of caries (dfs + DPS) (In-transformed) in the urban
9 group (P = 0.22 [SE 0.08], p = 0.005), but not in the rural group (P = -0.15 [SE 0.09], p = 0.09).
10 When dfs counts were stratified by permanent or deciduous teeth, the blood lead association in
11 the urban group was significant for deciduous teeth (P = 0.28 [SE 0.09], p = 0.002), but not for
12 permanent teeth (P = 0.02 [SE 0.07], p = 0.8). Covariates retained in the linear regression model
13 were age, sex, ethnicity, family income, education of female guardian, maternal smoking,
14 frequency of tooth brushing, firmness of toothbrush bristles, and frequency of chewing gum.
15 Campbell et al. (2000) was a retrospective cohort study in which dfs were assessed in
16 children 7-12 years of age (n = 248) from Rochester, NY. Mean blood lead concentration,
17 measured at ages 18 and 37 months of age, was 10.7 |ig/dL (range 18.0-36.8 |ig/dL). The
18 covariate-adjusted odds ratios for caries associated with a blood lead concentration >10 |ig/dL
19 compared to < 10 |ig/dL were 0.95 |ig/dL (95% CI: 0.43, 2.09) for permanent teeth and
20 1.77 |ig/dL (95% CI: 0.97, 3.24) for deciduous teeth. Covariates retained in the logistic model
21 were age, grade in school, number of tooth surfaces at risk. Other covariates examined in the
22 models, all of which had no significant effect on the outcome, were gender, race/ethnicity, SES,
23 parental education, residence in community supplied with fluoridated drinking water, and
24 various dental hygiene variables. This study did not demonstrate that lead exposure >10 |ig/dL
25 as a toddler was a strong predictor of caries among school-age children, but the authors noted
26 that this might be due to limited statistical power.
27 Dye et al. (2002) analyzed data collected in NHANES III on indices of periodontal bone
28 loss. The analysis was confined to subjects 20-69 years of age (n = 10,033). The geometric
29 mean blood lead concentration of the study group was 2.5 |ig/dL (SE 0.08), with 2.4% of the
30 group having blood lead levels >10 |ig/dL. Increasing log-transformed blood lead was
31 significantly associated with increasing prevalence of covariate-adjusted dental furcation
May 2006 6-282 DRAFT-DO NOT QUOTE OR CITE
-------
1 (P = 0.13 [SE 0.05], p = 0.005). Dental furcation is indicative of severe periodontal disease.
2 Covariates retained in the linear regression model were age, sex, race/ethnicity, education,
3 smoking, and age of home. Smoking status was a significant interaction term when included in
4 the model (P = 0.10 [SE 0.05], p=0.034). When stratified by smoking status, the association
5 between dental furcation and blood lead concentration was significant for current smokers
6 (P = 0.21 [SE 0.07], p = 0.004) and former smokers (P = 0.17 [SE 0.07], p=0.015), but not for
7 nonsmokers (P = -0.02 [SE 0.07], p = 0.747).
8 Some studies examined the relationship between tooth lead concentrations and dental
9 caries. In their compilation of metal concentrations in 1,200 deciduous teeth from a Norwegian
10 population, Tvinnereim et al. (2000) found that carious teeth had higher lead concentrations than
11 noncarious teeth. Gil et al. (1994) measured lead concentrations from 220 whole deciduous and
12 permanent teeth from Coruna, Spain. The geometric mean lead level was 10.36 jig/g of tooth.
13 There was a significant increase in teeth lead levels with advancing age. Permanent teeth
14 showed higher mean lead values (13.09 jig/g [SEM 1.07]) than deciduous teeth (3.96 jig/g
15 [SEM 1.07]). The authors reported a possible relationship between increased lead content and
16 periodontal pathology but did not observe any relationship between caries and lead
17 concentrations.
18
19 6.9.8 Effects of Lead on Ocular Health
20 6.9.8.1 Summary of Key Findings of the Effects of Lead on Ocular Health from the
21 1986 Lead AQCD
22 The 1986 Lead AQCD did not address effects of lead on ocular health in humans.
23 Various disturbances of the visual system have been observed in association with overt clinical
24 lead poisoning, including retinal stippling and edema, cataracts, ocular muscle paralysis, and
25 impaired vision (see Otto and Fox, 1993 for review). Two longitudinal studies completed since
26 1986 provide evidence for possible associations between lead exposure and visual evoked retinal
27 responses in children of mothers whose blood lead concentrations in mid-pregnancy were in the
28 range of 10-32 |ig/dL (Rothenberg et al., 2002b), and evidence for a possible association
29 between lead exposure and risk of cataracts in males whose tibia bone lead levels were in
30 the range 31-126 |ig/g (Schaumberg et al., 2004). These studies are summarized in Annex
31 Table AX6-9.11.
May 2006 6-283 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.9.8.2 Ocular Effects
2 In the Mexico City prospective lead study, Rothenberg et al. (2002b) measured
3 flash-evoked electroretinograms (ERG) in a subset of the study group (n = 45) at ages 7-10
4 years. As part of the prospective study, blood lead concentrations had been measured during
5 pregnancy and in the children, at birth and every 6 months, thereafter. Increasing maternal blood
6 lead, measured at 12 weeks of gestation, was significantly associated with increasing ERG a-
7 wave and b-wave amplitude, with significant increases in a-wave in the second maternal blood
8 lead tertile (range 6.0-10.0 |ig/dL), and a-wave and b-wave in the third maternal blood lead
9 tertile (range 10.5-32.5 jig/dL), compared to the first blood lead tertile (range 2.0-5.5 jig/dL).
10 No other blood lead measurements were significantly associated with any ERG outcomes.
11 As part of the longitudinal Normative Aging Study, Schaumberg et al. (2004) analyzed
12 prevalence of cataracts in adult males (n = 642), mean age 69 years (range 60-93). Subjects
13 were stratified by blood lead, patella bone lead, or tibia bone lead quintiles for a logistic
14 regression analysis of the odds ratios for cataracts (first quintile as reference). Covariate
15 adjusted odds ratio for cataracts in the fifth tibia bone lead quintile was significant (3.19 [95%
16 CI: 1.48, .90]). Odds ratios for cataracts were not significantly associated with patella bone lead
17 (1.88 [95% CI: 0.88, 4.02]) or blood lead (0.89 [95% CI: 0.46, 1.72]). The first and fifth
18 quintile lead levels were 0-11 jig/g and 31-126 jig/g for tibia bone; 1-16 jig/g and 43-165 jig/g
19 for patella bone; and 1.0-3.0 jig/g and 8-35 |ig/dL for blood. Covariates retained in the
20 regression model were age, smoking, history of diabetes; and daily intake of vitamin C, vitamin
21 E, and carotenoids.
22 Cavalleri et al. (1982) measured visual fields of male workers in a polyvinyl pipe
23 manufacturing facility (n = 35) who were exposed to lead stearate. Workers in a reference group
24 (n = 350) were individually matched for age, smoking, and alcohol consumption. Visual
25 sensitivity was significantly lower in lead workers compared to the reference group; however,
26 visual sensitivity index was not significantly associated with blood or urine lead. Prevalence of
27 mesopic scotoma (retinal light insesntivity under low illumination conditions) was 28.5% in the
28 lead workers and 0% in the reference group. Mean blood lead levels were 46 |ig/dL (range
29 21-82 |ig/dL) in the lead workers and 30 |ig/dL (range 21-42 |ig/dL) in the reference group.
30
May 2006 6-284 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.9.9 Summary of the Epidemiologic Evidence for the Effects of Lead
2 on Other Organ Systems
3 The following are a listing of key health outcomes discussed above for the effects of lead
4 on other organ systems.
5
6 • Biochemical Effects of Lead. Evidence for disruption of heme synthesis derives from
7 numerous studies in which lead exposure has been associated with decreased activities of
8 enzymes in the heme synthesis pathway (i.e., ALAS, ferrochelatase, cytochrome P450)
9 and increased levels of substrates for heme synthesis (i.e., ALA, coproporphyrin,
10 erythrocyte protoporphrin) in both children and adults. Quantitative relationships
11 between blood lead concentration and the above biomarkers of impaired heme synthesis
12 are highly consistent across studies (e.g., Alessio et al., 1976, 1977; Gennart et al., 1992;
13 Hernberg et al., 1970; Morita et al., 1997; Oishi et al., 1996; Piomelli et al., 1982; Roels
14 and Lauwerys, 1987; Selander and Cramer, 1970; Sol din et al., 2003; Wildt et al., 1987).
15 Increases in blood lead concentration of approximately 20-30 |ig/dL are sufficient to
16 halve erythrocyte ALAD activity and sufficiently inhibit ferrochelatase to double
17 erythrocyte protoporphyrin levels.
18 • Blood Lipids. Associations between occupational exposure to lead and changes in blood
19 lipid composition have been observed. These include increased levels of lipid peroxides
20 in blood and/or serum (Jiun and Hsien, 1994; Sugawara et al., 1991; Ito et al., 1985) and
21 increased serum levels of total and HDL cholesterol (Kristal-Boneh et al., 1999). Effects
22 on serum cholesterol levels were evident in association with a mean blood lead
23 concentration of 42 |ig/dL (Kristal-Boneh et al., 1999) or a range of 5-62 |ig/dL
24 (approximated mean 14 |ig/dL) (Ito et al., 1985). Oxidative changes in blood lipids (e.g.,
25 increased levels of lipid peroxides and malondialdehyde levels) as well as decreased
26 levels of erythrocyte superoxide dismutase, catalase, G6PD, and GSH peroxidase; and
27 increased lymphocyte reactive oxygen species and depleted GSH levels, indicative of
28 increased oxidative stress, have been observed in lead workers in association with blood
29 lead concentrations >30 |ig/dL (Fracasso et al., 2002; Ito et al., 1985; Jiun and Hsien,
30 1994; Solliway et al., 1996; Sugawara et al., 1991).
31 • Disruption of Hemoglobin Synthesis and Declines in Erythrocyte Numbers. Exposures
32 that result in blood lead concentrations that are <40 |ig/dL appear to be tolerated without
33 a decline in blood hemoglobin levels or hematocrit. However, perturbation of
34 erythropoiesis, indicated by changes in serum erythropoietin and progenitor cells, occurs
35 in association with blood lead concentrations below 40 |ig/dL and in the absence of
36 detectable changes in blood hemoglobin levels or hematocrit in children (Graziano et al.,
37 2004; Liebelt et al., 1999) and adults (Graziano et al., 1990; Osterode et al., 1999; Romeo
38 et al., 1996). Risk of clinical anemia in children becomes appreciable at much higher
39 blood lead concentrations; a 10% decrease in hematocrit has been estimated to occur in
40 association with blood lead concentrations >85 |ig/dL; a 10% probability of anemia
41 (hematocrit <35%) was estimated to be associated with a blood lead concentration of
42 approximately 20 |ig/dL at age 1 year, 50 |ig/dL at age 3 years, and 75 |ig/dL at age 5
43 years. (Schwartz et al., 1990). In adults, with blood lead levels below 25 jig/dL,
May 2006 6-285 DRAFT-DO NOT QUOTE OR CITE
-------
1 increasing patella bone lead, but not blood lead, was associated with a significant
2 decrease in hematocrit.
3 • Effects on the Endocrine System, Several studies have examined possible associations
4 between lead exposures in children and adults and various biomarkers of endocrine
5 function, including the thyroid, male reproductive, and calcitropic endocrine systems.
6 The strongest study designs have yielded no associations, or weak associations, between
7 lead exposure and thyroid hormone status (Erfurth et al., 2001; Schumacher et al., 1998;
8 Tuppurainen et al., 1988; Zheng et al., 2001). Studies of occupational exposures which
9 included subjects having blood lead concentrations exceeding 100 |ig/dL have found
10 depression of serum T3 and/or T4 levels, without a detectable increase in serum TSH;
11 however, studies in which the blood lead distribution was dominated by levels well below
12 100 |ig/dL, have found either no effects or subclinical increases in serum T3, T4, with no
13 change in TSH levels.
14 • Reproductive Endocrine Function. Studies of the male reproductive system that
15 attempted to control for confounding effects of age have yielded mixed outcomes
16 (Alexander et al., 1996a, 1998; Erfurth et al., 2001; Gustafson et al., 1989; McGregor and
17 Mason, 1990; Ng et al., 1991). Blood lead ranges in these studies were similar (4-90
18 Hg/dL), yet outcomes were mixed, with no change (Erfurth et al., 2001; Gustafson et al.,
19 1989; McGregor and Mason, 1990), or subclinical decrease (Alexander et al., 1996a,
20 1998; Ng et al., 1991) in serum testosterone (TES) in association with lead exposure.
21 There are also mixed effects on serum follicle stimulating hormone (FSH) and luteinizing
22 hormone (LH) with increases (McGregor and Mason, 1990; Ng et al., 1991), decreases
23 (Gustafson et al., 1989), and with no change (Alexander et al., 1996a, 1998; Erfurth et al.,
24 2001) in hormone levels observed. The inconsistency in the direction of effects on TES
25 and the two androgen-regulating pituitary hormones, FSH and LH, is particularly
26 noteworthy, in the absence of evidence for effects of lead exposure on GnRH-induced
27 FSH (Erfurth et al., 2001).
28 • Calcitropic Endocrine Function. Children exposed to relatively a high level of lead
29 >30 |ig/dL may exhibit depressed levels of circulating 1,25-OH-D (Mahaffey et al., 1982;
30 Rosen et al., 1980). However, associations between serum vitamin D status and blood
31 lead may not be present in calcium-replete children who have average lifetime blood lead
32 concentrations below 25 |ig/dL (Koo et al., 1991). In adults, exposures to lead that result
33 in blood lead concentrations >40-60 |ig/dL may increase, rather than decrease,
34 circulating levels of 1,25-OH-D and PTH (Kristal-Boneh et al., 1999; Mason et al.,
35 1990).
36 • Effects on the Hepatic System. Few studies of hepatic effects of lead on humans have
37 been reported since the 1986 Lead AQCD. Studies of hepatic enzyme levels in serum
38 suggest that liver injury may be present in lead workers; however, associations
39 specifically with lead exposures are not evident (Al-Neamy et al., 2001; Hsiao et al.,
40 2001). Studies of urinary metabolites of cytochrome P450 phenotypes CYP2A6 and
41 CYP3A4 suggest possible associations between lead exposure and suppression of hepatic
42 enzyme activity. The effect on CYP2A6 activity was observed in children with high lead
43 burdens (i.e., blood lead concentration >40 |ig/dL, EDTA-provoked urinary lead
May 2006 6-286 DRAFT-DO NOT QUOTE OR CITE
-------
1 >500 |ig/dL). The effect on CYP3 A4 was observed in association with blood lead ranges
2 of approximately 30-112 |ig/dL (based on reported serum lead concentrations).
3 • Effects on the Gastrointestinal System, Several studies of prevalence of symptoms of
4 gastrointestinal colic in lead workers provide evidence for symptoms in association with
5 blood lead concentrations >50-80 |ig/dL (Awad el Karim et al., 1986; Holness and
6 Nethercott, 1988; Lee et al., 2000; Matte et al., 1989). Similar types of studies of
7 children have not been reported.
8 • Effect on Bone and Teeth. There is limited, but suggestive evidence of an association
9 between lead exposure and bone toxicity. However, in most studies, it is difficult to
10 assess the direct contribution of lead on bone diseases or reduced growth. Several studies
11 that have explored possible associations between lead exposure and risk of dental caries
12 (Campbell et al., 2000; Dye et al., 2002; Gemmel et al., 2002; Moss et al., 1999).
13 Increased caries risk has been detected in association with increasing blood lead
14 concentrations in populations whose mean blood lead concentrations are approximately
15 2-3 |ig/dL (Dye et al., 2002; Gemmel et al., 2002; Moss et al., 1999).
16 • Ocular Health. Various disturbances of the visual system have been observed in
17 association with overt clinical lead poisoning, including retinal stippling and edema,
18 cataracts, ocular muscle paralysis, and impaired vision (Otto and Fox, 1993). Two
19 longitudinal studies completed since the 1986 Lead AQCD provide evidence for possible
20 associations (a) between lead exposure and visual evoked retinal responses in children of
21 mothers whose blood lead concentrations in mid-pregnancy was 10.5-32.5 |ig/dL
22 (Rothenberg et al., 2002b) and (b) between lead exposure and risk of cataracts in middle-
23 aged males whose tibia bone lead levels were 31-126 jig/g (Schaumberg et al., 2004).
24
25
26 6.10 INTERPRETIVE ASSESSMENT OF THE EVIDENCE IN
27 EPIDEMIOLOGIC STUDIES OF LEAD HEALTH EFFECTS
28 6.10.1 Introduction
29 A remarkable expansion has occurred since the 1990 Lead Supplement in the extent of
30 the database available for drawing inferences about the various expressions of lead toxicity.
31 Moreover, the nature of the evidence available has changed as well. Many of the studies
32 conducted prior to 1990 focused on the issue of whether an observed observation was likely
33 to be real or the result of chance, selection bias, residual confounding, or some other
34 methodological error. The validity of any association still needs to be assured. The studies
35 since 1990 mainly focus on characteristics of the pertinent concentration-response relationships,
36 including the functional forms of the relationships, the slopes of the relationships, the natural
May 2006 6-287 DRAFT-DO NOT QUOTE OR CITE
-------
1 histories of adverse effects, and the confounding or effect modifying influences of various co-
2 exposures and host characteristics.
3
4 6.10.2 Exposure and Outcome Assessment in Lead Epidemiologic Studies
5 6.10.2.1 Assessment of Lead Exposure and Body Burdens Using Biomarkers
6 For any health endpoint of interest, the most useful biomarker of exposure is one that
7 provides information about the lead dose at the critical target organ and, moreover, reflects the
8 exposure averaging time that is appropriate to the underlying pathogenetic processes (e.g.,
9 cumulative over lifetime, cumulative over a circumscribed age range, concurrent). In recent
10 studies of lead and health, the exposure biomarkers most frequently used are lead in blood and
11 bone (see discussion in Chapter 4). For outcomes other than those relating to hematopoeisis and
12 bone health, these biomarkers provide information about lead dose that is some distance from the
13 target organ. For example, given that the central nervous system is considered the critical target
14 organ for childhood lead toxicity, it would be most helpful to be able to measure, in vivo, the
15 concentration of lead at the cellular site(s) of action in the brain. However, because such
16 measurements are not currently feasible, investigators must rely on measurements of lead in the
17 more readily accessible but peripheral tissues. The relationship between brain lead and lead in
18 each of these surrogate tissues is still poorly understood, although the pharmacokinetics clearly
19 differs among these compartments. In both rodents and nonhuman primates, brain lead level
20 falls much more slowly than blood lead level following chelation with succimer and, in the
21 rodent, in nonchelated animals after cessation of exposure. These observations suggest that
22 using blood lead as an index of lead in the brain will result in exposure misclassification,
23 although the magnitude of this bias in any specific setting will be difficult to characterize. The
24 most likely direction, however, would be underestimation of the amount of lead in the brain, at
25 least under scenarios involving chronic exposure.
26 As an exposure biomarker, blood lead level has other limitations. Only about 5% of an
27 individual's total body lead burden resides in blood. Furthermore, blood consists of several sub-
28 compartments. More than 90% of lead in whole blood is bound to red cell proteins such as
29 hemoglobin, with the balance in plasma. From a toxicological perspective, the unbound fraction
30 is likely to be the most important sub-compartment of blood lead because of the ease with which
31 it diffuses into soft tissues. The concentration of lead in plasma is much lower than in whole
May 2006 6-288 DRAFT-DO NOT QUOTE OR CITE
-------
1 blood, however. For example, in a group of pregnant women with blood lead levels below
2 10 |ig/dL, plasma lead levels were less than 0.3% of the whole blood lead level. The greater
3 relative abundance of lead in whole blood makes its measurement much easier (and more
4 affordable) than the measurement of lead in plasma. The use of whole blood lead as a surrogate
5 for plasma lead could be justified if the ratio of whole blood lead to plasma lead were well
6 characterized, but this is not so. At least some studies suggest that it varies several-fold among
7 individuals with the same blood lead level. Moreover, the ability of red cells to bind lead is
8 limited, so the ratio of blood lead to plasma lead would be expected to be nonlinear. Thus,
9 interpreting whole blood lead level as a proxy for plasma lead level, which, itself, is a proxy for
10 brain lead level, will result in some exposure misclassification.
11 Although the use of blood lead may not best reflect the actual dose of lead in the specific
12 target organs of interest, of greater concern are the epidemiologic implications of its use. In a
13 regression model, the variation in lead about its mean is correlated with the variation in outcome
14 about its mean. As only variations about the mean contribute to the association, mean
15 differences between true and estimated levels become irrelevant. The measurement error in
16 considering blood lead as a surrogate for brain lead will bias the blood lead effect towards the
17 null and is an example of classical measurement error. The error will be nonlinear if red cell
18 binding is limited. However, when interest centers on the low blood lead level, the error should
19 be approximately additive, multiplicative, or both. Another example of measurement error with
20 epidemiologic implications is the Berksonian error. Berkson error arises when averages of blood
21 leads are used in a regression rather than individual data. For example, if a regression of IQ is
22 performed on averages of children's blood leads grouped between intervals, the Berkson error
23 model will apply. The slope will be unbiased, but the standard errors will be inflated.
24 There are additional issues to consider in the use of blood as a marker of lead exposure.
25 The residence time of lead in blood is closely linked to red cell lifetime, with a half-time on the
26 order of 30 days. Thus, a high blood lead level does not necessarily indicate a high body lead
27 burden. Similarly, individuals who have the same blood lead level will not necessarily have
28 similar body burdens or exposure histories. The rate at which blood lead level changes with
29 time/age depends on exposure history due to re-equilibration of lead stored in the various body
30 pools. In nonchelated children, the time for blood lead to decline to a value less than 10 |ig/dL
31 was linearly related to baseline blood lead level. A single blood lead measurement might
May 2006 6-289 DRAFT-DO NOT QUOTE OR CITE
-------
1 therefore provide limited information about an individual's lead exposure history, a difficulty
2 frequently cited with respect to the interpretation of cross-sectional studies of pediatric lead
3 toxicity, in which children's blood lead level is often measured only once, and sometimes only
4 well after the period when levels typically peak (18-30 months of age). If it is exposures to lead
5 in the early postnatal years that are most detrimental to children's development, categorizing a
6 child's exposure status based on the blood lead level that is contemporaneous with the
7 measurement of neurodevelopment at school-age could result in exposure misclassification. This
8 concern must be qualified, however, by recent data from some longitudinal studies indicating
9 that concurrent blood lead level, even at ages well beyond 18 to 30 months, is sometimes the
10 strongest predictor of late outcomes (Canfield et al., 2003a; Dietrich et al., 1993a,b; long et al.,
11 1996; Wasserman et al., 2000b). Changes in blood lead concentration in children are found to
12 closely parallel changes in total body burden. Empirical evidence in support of this comes from
13 longitudinal studies in which relatively high correlations (r = 0.85) were found between
14 concurrent or lifetime average blood lead concentrations and tibia bone lead concentrations
15 (measured by XRF) in a sample of children in which average blood lead concentrations exceeded
16 20 |ig/dL; the correlations was much weaker (r = <0.15) among children who had average blood
17 lead concentration < 10 |ig/dL (Wasserman et al., 1994).
18 Age-related changes in vulnerability, and the reasons why it might differ across studies,
19 remain uncertain. It might be that among children with chronically elevated exposure, but not in
20 children with relatively low lifetime exposure, blood lead level measured at school-age is a
21 reasonably good marker of cumulative exposure. That concurrent blood lead level is, under
22 some circumstances, a stronger predictor of school-age outcomes than is blood lead level in the
23 early postnatal years does not necessarily imply greater vulnerability of the brain to ongoing than
24 to past exposure. Due to the high intercorrelation among blood lead measures taken at different
25 time points, it is not feasible to examine exposures during any given age for evidence of a
26 sensitive neurodevelopmental period.
27 The development of X-ray-fluorescence (XRF) methods for measuring lead in
28 mineralized tissues offers another approach for characterization and reconstruction of exposure
29 history. Such tissues are long-term lead storage sites, with a half-life measured in decades and
30 contain approximately 90% of the total body lead burden in adults and 70% in children. Thus,
31 bone lead is an index with a long exposure averaging time. XRF methods have proven useful in
May 2006 6-290 DRAFT-DO NOT QUOTE OR CITE
-------
1 studying individuals with occupational lead exposure, those living in highly polluted
2 environments, and those for whom community lead exposures are or, in the past, were relatively
3 high (e.g., Korrick et al., 1999; Schwartz et al., 2000a,b,c,d). In a relatively highly exposed
4 cohort of pregnant women in Mexico City, higher bone lead levels at one month postpartum
5 were associated with reduced birth weight, less infant weight gain, smaller head circumference
6 and birth length, and slower infant development (Gomaa et al., 2002; Gonzalez-Cossio et al.,
7 1997; Hernandez-Avila et al., 2002; Sanin et al., 2001). Among children living near a large lead
8 smelter in Yugoslavia, IQ at age 10-12 years was more strongly associated, inversely, with tibia
9 lead level than with blood lead level (Wasserman et al., 2003).
10 Current XRF methods for measuring bone lead levels have limitations, however.
11 Temporal features of exposure history cannot readily be discerned. Some progress has been
12 made toward this goal by examining the spatial distribution of lead in teeth in relation to the
13 relative abundance of stable lead isotopes, but the specialized technologies needed to carry out
14 these analyses are unlikely ever to be widely available, and the unpredictability of tooth
15 exfoliation makes this tissue difficult to collect unless the study design involves contact with
16 (and the cooperation of) participants at the appropriate ages. Current XRF methods might not be
17 sufficiently sensitive for studies of the health effects of low-dose community exposures. The
18 bone lead levels of a large percentage of subjects might be below the detection limit, e.g., 80% in
19 a case-control study of bone lead levels and juvenile delinquency in which the minimum
20 detection limit was 21.5 |ig/g bone mineral (Needleman et al., 2002). Even among individuals
21 known to have histories of substantial lead exposures, such as adolescents and young adults who
22 grew up near the Bunker Hill smelter in Idaho (McNeill et al., 2000), bone lead levels tend to be
23 low. Lead appears to be deposited at sites of most active calcification. In children, this is
24 trabecular bone, in which the rate of fractional resorption in early childhood is high. Depending
25 on the amount of the child's ongoing exposure, lead deposited in bone might not remain there for
26 decades, making bone lead level an imprecise index of lifetime lead exposure. This concern also
27 exists in the use of tooth lead to represent cumulative lead exposure in children. Rabinowitz
28 et al. (1993) observed that a child's tooth lead level was more strongly related to blood lead level
29 around the time of tooth exfoliation than to an integrated index of blood lead level prior to
30 exfoliation. Finally, it is difficult to compare the performance of different laboratories using
31 XRF methods to measure bone lead because of the absence of standard reference materials.
May 2006 6-291 DRAFT-DO NOT QUOTE OR CITE
-------
1 Nevertheless, efforts continue to modify the instrumentation or measurement protocols to reduce
2 the detection limit.
3 A major research need is the development and validation of biomarkers of critical dose
4 that, compared to blood lead or bone lead, are fewer toxicokinetic steps removed from the sites
5 of lead's actions in the brain. One promising front in the effort to deduce the contents of the
6 "black box" separating external dose and clinical disease is the measurement of processes and
7 products that potentially mediate the association between them. For example, magnetic
8 resonance spectroscopy (MRS) has been used in small case series to measure the ratio of
9 N-acetylaspartate (NAA) to creatine, which are a marker of neuronal and axonal damage and
10 thus, an early biological effect rather than a biomarker of exposure. In children, higher lead
11 exposures are associated with lower NAA to creatine ratios in the frontal gray matter and, to a
12 lesser extent, in frontal white matter (Trope et al., 1998, 2001). Similarly, an adult who had
13 higher bone and blood lead levels than did his monozygotic twin had both greater
14 neuropsychological deficits and lower NAA to creatine ratios in the hippocampus, frontal lobe,
15 and midbrain (Weisskopf et al., 2004a). While much remains uncertain about the interpretation
16 of MRS, the use of this and other biochemical imaging methods, in combination with more
17 conventional structural and functional imaging methods, might bring us closer to understanding
18 the mechanisms of lead neurotoxicity. With the number of toxicokinetic steps separating lead
19 levels at the critical target organs from the usual exposure biomarkers, the progress made in
20 characterizing the concentration-response relationships is remarkable.
21
22 6.10.2.2 Assessment of Health Outcomes
23 Outcome measurement and outcome classification have generally received less attention
24 from investigators than have exposure measurement and misclassification. The specific
25 problems are, to some extent, endpoint domain-specific. With regard to neurodevelopmental
26 toxicities, critical issues are whether the assessment instruments used are psychometrically sound
27 and appropriate for the study cohort, the data generated will support adequate tests of the study
28 hypotheses, and whether the instruments have been administered and scored consistently and
29 correctly. With regard to the cardiovascular toxicities of increased blood pressure/prevalence of
30 hypertension, the critical issue is whether the blood pressure value recorded for a participant is
31 an accurate estimate. Multiple measurements of blood pressure are frequently made in a study
May 2006 6-292 DRAFT-DO NOT QUOTE OR CITE
-------
1 but investigators usually have not taken advantage of the collected information to quantify the
2 amount of error in the measurements. This information can be used to improve the reliability of
3 the measurements, which would be expected to improve the precision of the associations
4 estimated. Similarly, aggregating scores to estimate latent variables representing, for instance,
5 "language skills" or "visual-spatial skills" is an approach that might take advantage of the
6 overlapping information provided by the multiple tests included in neurobehavioral test batteries,
7 producing more reliable endpoint variables. This approach, however, has not been widely
8 applied in lead studies. Concerns regarding the presence of measurement error in the outcome
9 variable need to be considered in the context of the exposure of interest. If the measurement
10 error in outcome is uncorrelated with exposure, it will not induce bias in the estimate of the
11 effect of lead. However, it should be noted that the measurement error will lead to reduced
12 power to detect a significant effect.
13
14 6.10.3 Concentration-Response Relationship of Lead Health Effects
15 The studies since the 1990 Lead Supplement provide pertinent new data on health effects
16 at levels below 10 |ig/dL and information on concentration-response relationships that provide a
17 basis to examine the functional form that best fits data that serves as a description of the
18 underlying concentration-response relationship.
19 Recent studies have strengthened the consensus that the developing nervous system is the
20 organ system that is one of the most sensitive to lead toxicity in children. Neurobehavioral
21 deficits appear to occur at lower levels of exposure than have been observed earlier. Adverse
22 effects in other organ systems have been observed in some susceptible populations at similarly
23 low levels. Adverse renal outcomes in adults with hypertension or chronic renal insufficiency
24 have been reported at mean blood leads of 4.2 |ig/dL (see discussion in Section 6.4). Study
25 results indicate that increased blood lead levels are significantly associated with increased
26 systolic and diastolic blood pressure in adults (see discussion in Sections 6.5 and 6.10.8.2).
27 The following discussion on the functional form of these relationships discuss these concepts in
28 general and uses IQ blood lead as an example. Other potential examples not discussed of effects
29 at low concentrations which support concentration-response relationships include renal toxicity
30 and changes in blood pressure.
31
May 2006 6-293 DRAFT-DO NOT QUOTE OR CITE
-------
1 Accumulating data appear to validate well the statement made in the 1996 AQCD and
2 Addendum, and the 1990 Supplement that adverse effects occur at blood lead levels of 10 to
3 15 |ig/dL or "possibly lower." In a recent study of 6 to 16 year old children in the NHANES III
4 survey, concentration-related deficits in reading and arithmetic scores were found even when
5 analyses were restricted to children with concurrent blood lead levels below 5 |ig/dL (Lanphear
6 et al., 2000), although these analyses were limited by the fact that adjustments could not be made
7 for potential confounding factors, namely maternal IQ or caretaking quality in the home, whose
8 inclusion in regression models often results in a substantial reduction in the size of the lead
9 coefficient. Canfield et al. (2003a) applied semi-parametric models with penalized splines to
10 their data, essentially allowing the data to reveal the functional form that best described them.
11 These analyses showed that the IQ decline per |ig/dL increase in blood lead was greater below
12 10 |ig/dL than it was above 10 |ig/dL. The estimated slope of the IQ decline per |ig/dL was
13 greatest among children for whom the maximum blood lead level measured over the course of
14 the study never exceeded 10 |ig/dL. A similarly steeper slope at lower than at higher blood lead
15 levels was found in a re-analysis of the Boston prospective study (Bellinger and Needleman,
16 2003).
17 Identifying the functional form that best fits a particular set of data and that presumably
18 serves as the best description of the pertinent underlying concentration-response relationship is
19 clearly important. The linear model (Figure 6-10.1) is, as the name implies, linear over the entire
20 range of the exposure data. For certain tests, the assumption is made that the residuals (observed
21 - predicted response) are normally distributed with constant variance, but violations of this
22 assumption in the presence of heteroscedasticity have no real effect on the estimation and
23 minimal effect on the tests of significance (see Annex Section AX6.10 for further discussion).
24 If heteroscedasticity is present but all other conditions are met, the regression model still yields
25 unbiased estimators, but the standard errors can be larger than when remedial efforts such as
26 using weighted regression are employed. The use of regression requires no assumption
27 concerning the distribution of the independent variable (i.e., lead exposure marker). However,
28 when the form of the heteroscedasticity is an increase in variance with level of blood lead and
29 when the data are lognormally distributed or otherwise skewed, there are possibly a large number
30 of influential data points at high blood lead where the data is least reliable. In this case, a log
31 transformation of blood leads may result in more precise estimation of the slope parameter.
May 2006 6-294 DRAFT-DO NOT QUOTE OR CITE
-------
105
100
0
c
o
0. 95
tf)
0
QC
90
85
10
25
30
15 20
Exposure
— Linear Model ---Log-linear Model
35
Figure 6-10.1. Comparison of a linear and log-linear model to describe the relationship
between exposure and response.
The presence of heteroscedasticity and other departures from assumptions forming the
basis for regression analysis can be detected using diagnostic tests or graphics; however, these
methods are rarely used in epidemiologic studies of lead health effects.
The log-linear model (see Figure 6-10.1) is written as:
Response = a + P ln(lead exposure marker),
(6-1)
6 where In is the natural logarithmic function. The log-linear model is concave upwards (assuming
7 that the estimated coefficient is negative). It approaches a linear function for very high exposure
8 values, but approaches infinity at very low exposure values. In other words, it is assumed that
9 the adverse effect of lead is greater at lower than at higher blood lead levels. Blood lead levels
10 have been shown repeatedly to follow a lognormal distribution (Azar et al., 1975; Billick et al.,
11 1979; Hasselblad and Nelson, 1975; Hasselblad et al., 1980; U.S. Environmental Protection
12 Agency, 1986a; Yankel et al., 1977), but this fact is not an argument for choosing the log-linear
13 model. The choice of either log-linear or linear may be based on the Akaike's Information
May 2006
6-295
DRAFT-DO NOT QUOTE OR CITE
-------
1 Criteria (Akaike, 1973), J-test (Davidson and MacKinnon, 1981), or other statistical tests if the
2 choice is to be based on the best fitting model. Rothenberg and Rothenberg (2005) compared the
3 linear lead model with the log-linear lead model for the pooled data from Lanphear et al. (2005)
4 using the J-test. The J-test showed that the log lead specification was still significant (p = 0.009)
5 in a model that also included the linear lead specification, indicating that the log lead
6 specification described the data significantly better than did the linear lead specification. Other
7 models have been used, such as nonparametric models, spline functions, and polynomial models,
8 but the vast majority of the analyses have used either a linear model or a log-linear model.
9 In a recent publication, Bowers and Beck (2006) discuss the mathematical requirement for
10 a supralinear curve when blood lead is lognormally distributed, IQ is normally distributed, and
11 the correlation between these two variables is not zero. This fact is used to infer that the
12 supralinear model arises due to these conditions rather than being a reason for these conditions.
13 This inference would be plausible, for example, if the process of converting raw scores to IQ
14 points induced a normal distribution; however, such inducement does not occur. Bowers and
15 Beck also state that if IQ is only approximately normally distributed that a supralinear
16 relationship between the percentiles of these distributions will occur. This is true, but has
17 nothing to do with the relationship between the variables. When the error component is normally
18 distributed with a variance as large as seen in the childhood lead/IQ studies and the sample size
19 is roughly 2000 or less, use of a linear model and a lognormal blood lead will yield an IQ
20 variable that is statistically equivalent to a normal distribution, resulting in a percentile plot that
21 will appear supralinear. This indicates that using percentiles as a diagnostic test to check for
22 supralinearity is very insensitive. Another concern they present is that a supralinear relationship
23 is not biologically plausible. However, the supralinear model appears to best describe the
24 epidemiologic data.
25 As examined in the Lanphear et al. (2005) pooled analysis of seven prospective cohort
26 studies (see Section 6.2.13 for a detailed description), epidemiologic studies of actual data
27 collected from individuals indicated that the log-linear best fits the IQ-blood lead relationship for
28 the range of blood lead levels observed. The segmented line model consists of joined straight
29 line segments where the joined points are chosen to best fit the data (Quandt, 1958). The log-
30 linear and the quadratic models have been shown in several cases to better fit the biomarker-
31 response relationship than the linear model. However, these models are not considered
May 2006 6-296 DRAFT-DO NOT QUOTE OR CITE
-------
1 practicable for extrapolation outside the range of the biomarker variable. The segmented line
2 model is suggested as a more reasonable model for extrapolation into the low-concentration
3 sparse-data region.
4 Nonlinear concentration-response relationships are not uncommon in toxicology, although
5 many of these are claimed to be examples of hormesis, with the lowest doses of a toxicant being
6 associated with a beneficial effect rather than a greater adverse effect. Concentration-response
7 curves having shapes similar to the hormetic curve are sometimes referred to as U-shaped, to
8 avoid inferring that the effect opposite to the toxic effect is beneficial. Figure 5-3.4 in Chapter 5
9 shows a graph where the response at lower lead doses is opposite to the response at higher lead
10 doses. By itself, this curve may appear linear or even supralinear, but realizing that the response
11 must return to 100% of control at zero dose indicates that it is U-shaped. To call this curve
12 hormetic depends upon whether an increased rate of fixed interval response is beneficial. Note
13 that Figure 6-2.5 of the blood lead-IQ relationship is similar to the lead dose-fixed interval
14 response curve shown in Figure 5-3.4, but shows no evidence of the curves being U-shaped.
15 Without a control level (i.e., IQ at very low blood lead levels if not at 0 |ig/dL), a determination
16 of whether the curve is U-shaped cannot be made. However, a risk assessment must be done
17 cautiously in view of this toxicological information.
18 A biological mechanism for a steeper slope at lower than at higher blood lead levels has
19 not been identified. It is conceivable that the initial neurodevelopmental lesions at lower lead
20 levels may be disrupting very different biological mechanisms than the more severe effects of
21 high exposures that result in symptomatic poisoning or frank mental retardation (Dietrich et al.
22 2001). Perhaps the predominant mechanism at very low blood lead levels is rapidly saturated,
23 but a different, less rapidly saturated process becomes predominant at blood lead levels greater
24 than 10 |ig/dL. As Kordas et al. (2006) states, this might help explain why, within the range of
25 exposures not producing overt clinical effects, an increase in blood lead beyond a certain
26 concentration might cause less additional impairment in children's cognitive functions.
27 However, one must take care not to interpret this as meaning that higher blood lead
28 concentrations do not induce further toxic harm. For example, blood lead levels in excess of
29 70 |ig/dL are still associated with encephalopathy and a risk for fatal outcome.
30 The ad hoc explanation provided above for the observed nonlinear concentration-response
31 relationship is more descriptive than explanatory, however, and the specific processes that may
May 2006 6-297 DRAFT-DO NOT QUOTE OR CITE
-------
1 produce this result have not yet been identified. Nevertheless, relationships of this apparent form
2 have been observed in several data sets, indicating the need to further examine this issue. There
3 are reasons that a supralinear model could be distorted to some degree. Austin and Hoch (2004)
4 have shown that the use of the detection limit as a substitute values for undetected values can
5 lead to bias of the regression slope away from zero. This can occur in multivariate regressions
6 when there is high correlation and a high percent of non-detects. When regressions involve
7 successively decreasing cut points of blood lead, the percent of nondetects increases, potentially
8 creating a supralinear relationship. An important caveat regarding efforts to specify the
9 functional form of the concentration-response relationship is that the accuracy that can be
10 achieved is constrained by the extent to which the biomarker of lead concentration does, in fact,
11 reflect the concentration at the critical target organ, the brain. The greater the misclassification,
12 the more uncertain will be the biological relevance of the best statistical description of the
13 concentration-response relationship.
14
15 6.10.4 Interindividual Variability in Susceptibility to Lead Toxicity
16 Although increased lead exposure has been linked to adverse health effects in many
17 different organ systems, scatterplots reveal tremendous variability of observed points about the
18 best fit lines representing the concentration-response relationships. In other words, individuals
19 for whom the lead biomarker measured has the same value can have markedly different values
20 on the health indicator measured. Even for neurobehavioral deficits in children, the correlation
21 between biomarker level and test score rarely exceeds 0.2, indicating that the explained variance
22 in the test score generally does not exceed 5%. A major challenge is therefore to decompose this
23 variability, to distinguish components of it that reflect error from components that reflect
24 biological processes that determine an individual's response to lead.
25 Deviation of the observed points from the fitted point can have many sources. Exposure
26 misclassification is one source. The lead biomarker measured might not adequately capture the
27 lead dose delivered to the target organ and at the time that is most appropriate biologically.
28 In general, the error would be expected to be non-differential, i.e., it would not introduce a
29 systematic bias in the estimation of the concentration-response relationship. On average, such
30 misclassification would be expected to result both in an attenuation of the slope of the
31 concentration-response relationship and an increase in the scatter of the observations. As focus
May 2006 6-298 DRAFT-DO NOT QUOTE OR CITE
-------
1 shifts to the risks associated with lower and lower levels of lead exposure, the importance of
2 errors introduced by poor dosimetry will assume greater importance insofar as the effects at such
3 levels will presumably be more subtle and increasingly difficult to detect amid the noise
4 contributed by exposure misclassification. Outcome misclassification is another source of error
5 that is likely to contribute to apparent interindividual variability in response. This results if the
6 indicator of the critical health effect that is measured is fallible, i.e., an imperfect measure of the
7 target function. Such misclassification would generally be expected to be non-differential,
8 introducing random noise rather than a systematic bias.
9 Another likely source of scatter in observed points is true interindividual variability in
10 response to a given lead dose. That is, the magnitude of individual response to lead might
11 depend on other characteristics of that individual. Three major categories of such effect
12 modifying factors that might influence susceptibility to lead toxicity are genetic polymorphisms,
13 nutritional status, and social environmental factors. Adequate data are not available to provide a
14 quantitative estimate of the amount of interindividual variability in susceptibility to lead.
15
16 6.10.4.1 Influence of Genetic Polymorphisms on Risk
17 Genetic polymorphisms that are presumed to influence lead toxicokinetics and/or
18 toxicodynamics have been identified, mostly in studies of adults who were occupationally
19 exposed to lead. The magnitude of lead-associated renal dysfunction appears to vary, in complex
20 ways, with the delta-aminolevulinic acid dehydratase (ALAD) polymorphism (Chia et al., 2005,
21 2006). Lead workers with the ATP1 A2(3') polymorphism appear to be at increased risk of lead-
22 associated effects on blood pressure (Glenn et al., 2001). The slope of the association between
23 floor dust lead and blood lead is steeper among children with the less common variant of the
24 vitamin D receptor (Fok 1 or B) than among children with the wild-type allele (Haynes et al.,
25 2003). In adults, these same alleles are associated with higher blood lead levels and increased
26 blood pressure (Schwartz et al., 2000a; Lee et al., 2001). Greater lead-associated reductions in
27 renal function have been observed in adults with a variant allele of nitric acid synthetase,
28 although cardiovascular outcomes, such as blood pressure and hypertension do not appear to
29 depend on the eNOS (endogenous nitric oxide synthase) allele (Weaver et al., 2003b). Adults
30 with variants of the hemochromatosis gene (C282Y and/or H63D) have higher patella lead levels
31 (Wright et al., 2004). With regard to polymorphisms that modify lead neurotoxicity, workers
May 2006 6-299 DRAFT-DO NOT QUOTE OR CITE
-------
1 with the apolipoprotein E4 allele showed greater lead-associated decreases in neurobehavioral
2 function than did workers with the El, E2, or E3 alleles (Stewart et al., 2002). Chia et al. (2004)
3 speculated that the ALAD2 confers protection again lead neurotoxicity, although Kamel et al.
4 (2003) reported that this variant allele is associated with an increased risk of amyotrophic lateral
5 sclerosis. This work is in its early stages, and while it promises to shed light on bases of
6 susceptibility to lead toxicity, firm conclusions cannot yet be drawn.
7
8 6.10.4.2 Influence of Nutritional Status on Risk
9 Only limited epidemiologic data are available on the role of nutritional status in
10 modifying an individual's risk of lead toxicity. Adjusting for severity of environmental lead
11 contamination, iron-deficient children appear to have higher blood lead levels than iron-replete
12 children (Bradman et al., 2001). One interpretation of these data is that children experiencing the
13 same external lead dose can experience different internal doses. In another study of iron status, a
14 decline in blood lead level was associated with improved cognitive performance in iron-
15 sufficient but not in iron-deficient children (Ruff et al., 1996). Among the possible explanations
16 for this finding is that iron deficiency contributes to pharmacodynamic variability, increasing the
17 toxicity of a given lead dose. Some evidence suggests that the intellectual deficit associated with
18 an elevated blood lead level is greater among undernourished children than well-nourished
19 children (Gardner et al., 1998).
20 Several studies have suggested that dietary calcium may have a protective role by
21 decreasing absorption of lead in the gastrointestinal tract and decreasing the mobilization of lead
22 from bone stores to blood, especially during periods of high metabolic activity of the bone such
23 as pregnancy and lactation. Lower calcium intake during pregnancy, especially the second half,
24 appears to increase the mobilization of lead from bone compartments (Hernandez-Avila et al.,
25 1996). However, in other studies, calcium supplementation had no effect on bone lead levels in
26 pregnant and lactating women (Rothenberg et al., 2000; Tellez-Rojo et al., 2002).
27
28 6.10.4.3 Influence of Health Status on Risk
29 The influence of an individual's health status on susceptibility to lead toxicity has been
30 demonstrated most clearly for renal outcomes. Individuals with diabetes, hypertension, and
31 chronic renal insufficiency are at increased risk of lead-associated declines in renal function, and
May 2006 6-300 DRAFT-DO NOT QUOTE OR CITE
-------
1 adverse effects have been demonstrated at blood lead levels below 5 |ig/dL (Lin et al., 2001a,
2 2003; Muntner et al., 2003; Tsaih et al., 2004). As mentioned in the previous section, children
3 with nutritional deficiencies also appear to be more vulnerable to lead-associated
4 neurobehavioral deficits.
5
6 6.10.4.4 Influence of Coexposures on Risk
7 Epidemiologic studies do not provide an adequate basis for determining whether cigarette
8 smoking and/or alcohol affect the nature or severity of the health effects associated with lead
9 exposure. Both factors have often been included in models of both child and adult health
10 outcomes in order to adjust for potential confounding. In addition, both have been evaluated as
11 pertinent pathways of adult exposure. However, their possible roles as effect modifiers have not
12 been well studied.
13 Although most individuals are not exposed to lead in isolation but rather to lead in
14 combination with other toxicants, e.g., cadmium, arsenic, mercury, and polychlorinated
15 biphenyls, epidemiologic studies generally have focused solely on lead. Other toxicant
16 exposures have sometimes been measured but are usually treated as potential confounders in the
17 statistical analyses, with their status as potential modifiers of lead toxicity left unexplored
18 (Bellinger, 2000). As a result, epidemiologic studies do not provide an adequate basis for
19 determining the extent to which co-exposure to other toxicants may affect the nature or severity
20 of health effects associated with lead exposure.
21
22 6.10.4.5 Influence of Timing of Exposure on Risk
23 Children
24 Available studies do not provide a definitive answer to the question of whether lead-
25 associated neurodevelopmental deficits are the result of exposure during a circumscribed critical
26 period or of cumulative exposure. Although support can be cited for the conclusion that it is
27 exposure within the first few postnatal years that is most important in determining long-term
28 outcomes (Bellinger et al., 1992), other studies suggest that concurrent blood lead level is as
29 predictive, or perhaps more predictive, of long-term outcomes than are early blood lead levels
30 (Canfield et al., 2003a; Dietrich et al., 1993a,b; long et al., 1996; Wasserman et al., 2000b).
31 Because of the complex kinetics of lead, an accumulative toxicant, it is extremely difficult to
May 2006 6-301 DRAFT-DO NOT QUOTE OR CITE
-------
1 draw strong conclusions from these observational studies about windows of heightened
2 vulnerability in children. The high degree of intra-individual "tracking" of blood lead levels
3 over time, especially among children in environments providing substantial, chronic exposure
4 opportunities (e.g., residence near a smelter or in older urban dwellings in poor repair), poses
5 formidable obstacles to identifying the time interval during which exposure to lead caused the
6 health effects measured in a study. It could be that damage occurred during a circumscribed
7 period when the critical substrate was undergoing rapid development, but that the high
8 correlation between serial blood lead levels impeded identification of the special significance of
9 exposure at that time.
10 Under such circumstances, an index of cumulative blood lead level or concurrent blood
11 lead level, which might be a good marker of overall body burden under conditions of relatively
12 steady-state exposure, might bear the strongest association with the effect. Under these
13 circumstances, however, it might be incorrect to conclude that it was the later exposures,
14 incurred around the time that the effect was detected, that was responsible for producing it.
15 While some observations in children as old as adolescence indicate that exposure biomarkers
16 measured concurrently are the strongest predictors of late outcomes, the interpretation of these
17 observations with regard to critical windows of vulnerability remains uncertain. Additional
18 research will be needed to distinguish effects that reflect the influence of later exposures to lead
19 from effects that reflect the persistent of effects resulting from exposure during some prior
20 critical window. Resolving this issue solely on the basis of data from observational studies is
21 likely to be difficult due to the high intercorrelation among blood lead measures taken at
22 different ages.
23 Increasing attention is being devoted to determining the extent to which early childhood
24 lead exposures increases the risk of adverse effects that are only apparent at older ages (i.e.,
25 delayed or latent effects). Among young adults who lived as children in an area heavily polluted
26 by a smelter and whose current lead exposure was low, higher bone lead levels were associated
27 with higher systolic and diastolic blood pressure (Gerr et al., 2002). In adult rats, greater early
28 exposures to lead are associated with increased levels of amyloid protein precursor, a marker of
29 risk for neurodegenerative disease (Basha et al., 2005).
30
May 2006 6-302 DRAFT-DO NOT QUOTE OR CITE
-------
1 Aging Population
2 Increases in blood lead for postmenopausal women have been attributed to release of lead
3 from the skeleton associated with increased bone remodeling during menopause in both
4 occupationally- and environmentally-exposed women (Garrido-Latorre et al., 2003; Popovic
5 et al., 2005). In middle-aged to elderly males from the Normative Aging Study, patella lead
6 accounted for the dominant portion of variance in blood lead (Hu et al., 1996). These findings
7 provide evidence that the skeleton may serve as a potential endogenous source of lead in the
8 aging population.
9 Considerable evidence also suggests that indicators of cumulative or long-term lead
10 exposure are associated with adverse effects in several organ systems, including the central
11 nervous, renal, and cardiovascular systems. Among occupationally-exposed men, higher tibia
12 lead levels have been associated with increased cognitive decline over repeated assessments
13 (Schwartz et al., 2005). With regard to the renal system, increased lead exposure may accelerate
14 the effects of normal aging, producing a steeper age-related decline in function. Weaver et al.
15 (2003a) observed that higher lead exposure and dose were associated with worse renal function
16 in older workers, but with lower blood urea nitrogen and serum creatinine in young workers.
17
18 Pregnancy
19 Potential mobilization of lead from the skeleton also occurs during pregnancy and
20 lactation due to increased bone remodeling (Hertz-Picciotto et al., 2000; Manton, 1985;
21 Silbergeld, 1991). In women who have been exposed to lead in childhood and have accumulated
22 large stores in their bones, there may be significant mobilization of lead from bone to blood
23 during late pregnancy and lactation. The greatest probability of lead toxicity for the mothers will
24 be in postpartum while they are lactating; the infants will be particularly vulnerable during the
25 prenatal period, especially in the last weeks of pregnancy (Manton et al., 2003).
26 A variety of adverse reproductive outcomes have been associated with higher paternal or
27 maternal lead exposures, including reduced fertility, spontaneous abortion, gestational
28 hypertension, congenital malformations, fetal growth deficits, and neurobehavioral deficits in
29 offspring. The levels of exposure at which different adverse outcomes occur vary. Increased
30 risks of spontaneous abortion, neurobehavioral deficits in offspring and, in some studies,
May 2006 6-303 DRAFT-DO NOT QUOTE OR CITE
-------
1 gestational hypertension, have been reported at pregnancy blood lead levels below 10 |ig/dL
2 (Bellinger, 2005).
3
4 6.10.5 Reversibility of Lead Health Effects
5 6.10.5.1 Natural History of Effects
6 The absence of a clear operational definition of "reversibility" is a major impediment to
7 drawing inferences about the natural history of any adverse effect associated with an
8 accumulative neurotoxicant such as lead. Rather than indicating irreversibility, a performance
9 deficit that remains detectable after external exposure has ended could reflect ongoing toxicity
10 due to lead remaining at the critical target organ or lead deposited at the organ post-exposure as
11 the result of redistribution of lead among body pools. As noted earlier, brain lead levels can
12 remain elevated long after blood lead levels fall. A rigorous test of reversibility would require
13 that every lead atom has been cleared from the body. This being unattainable, investigators must
14 exploit opportunities that permit only weaker tests of hypotheses about reversibility. These
15 include assessing the persistence of deficits previously associated with lead biomarkers and
16 evaluating performance changes associated with natural experiments, i.e., events such as
17 chelation or a change in external exposure that would be expected to perturb the equilibrium of
18 lead among different body pools.
19 The likelihood of reversibility, as defined above, appears to be related, at least for the
20 adverse effects observed in certain organ systems, to both the age-at-exposure and the age-at-
21 assessment. In occupationally-exposed adults, the central and peripheral nervous system
22 correlates of higher lead burdens appear to attenuate if exposure is reduced.
23 The prospective studies of childhood lead exposure, involving serial measurements of
24 lead biomarkers and health outcomes, provide the best opportunities available to assess the
25 natural history of adversities associated with low-level lead exposures. In some prospective
26 studies, associations observed in infancy between biomarkers of prenatal exposure and
27 neurodevelopment attenuated by the time children reached preschool age. It can be difficult to
28 determine, however, whether this reflects actual disappearance of the effect or an increased
29 difficulty in detecting it due to the emergence of associations between neurodevelopment and
30 lead biomarkers measured postnatally. It is notable, however, that in some prospective studies of
31 children, associations between biomarkers of prenatal lead exposure and various outcomes in
May 2006 6-304 DRAFT-DO NOT QUOTE OR CITE
-------
1 middle adolescence have been reported, suggesting that the persistence of the associations might
2 be endpoint-specific. For example, among children in Kosovo, Yugoslavia, IQ scores at the age
3 of 8 years were inversely associated with a composite index of prenatal lead exposure (average
4 of mothers' blood lead levels at midpregnancy and at delivery) (Wasserman et al., 2000b). This
5 association was independent of changes in postnatal blood lead levels. Among 15 to 17 year old
6 inner-city children in Cincinnati, OH, maternal blood lead levels (ranging from 1 to -30 |ig/dL)
7 in the first trimester were inversely related to attention and visuoconstruction (Ris et al., 2004)
8 and positively related to the frequency of self-reported delinquent behaviors (Dietrich et al.,
9 2001).
10 The results of the prospective studies are more consistent in showing that higher postnatal
11 lead biomarkers are associated with neurocognitive deficits that persist, in some studies, into
12 early adulthood when the concurrent lead exposures are generally much lower. Ongoing external
13 exposure does not appear to be necessary to maintain the deficits, although, as noted previously,
14 it is not possible to exclude entirely a role for ongoing endogenous exposures of the target organs
15 resulting from the redistribution, over time, of lead stores among different compartments. These
16 data are consistent with those from experimental nonhuman primate studies, in which the
17 temporal characteristics of exposure are manipulated as opposed to merely observed as in the
18 human studies.
19 In most epidemiologic studies, the potential for true longitudinal analysis of the data has
20 not been fully exploited, with the data evaluated in what is effectively a series of cross-sectional
21 analyses.
22 Only limited data are available on the factors that influence the likelihood that an
23 association observed between an early lead biomarker and later outcome will persist among
24 children. In one study, the association between prenatal exposure and cognitive development in
25 infancy and the preschool period appeared to attenuate among children living in more privileged
26 circumstances or in whom postnatal lead exposures were lower (Bellinger et al., 1988, 1990).
27 These observations are consistent with those from cross-sectional epidemiologic studies showing
28 that the effects of a given level of exposure are more severe among disadvantaged children
29 (Lansdown et al., 1986; Winneke and Kraemer, 1984) and from experimental animal studies
30 showing that being raised in an enriched environment can reduce the apparent detrimental impact
31 of lead exposure on learning (Guilarte et al., 2003; Schneider et al., 2001).
May 2006 6-305 DRAFT-DO NOT QUOTE OR CITE
-------
1 6.10.5.2 Medical Interventions
2 Data from the Treatment of Lead Exposed Children (TLC) study, a randomized controlled
3 trial of the late outcomes of children treated for lead poisoning (baseline blood lead levels of
4 20 to 44 jig/dL), support the hypothesis that the deficits associated with exposures of such
5 magnitude are persistent and, possibly, permanent (Dietrich et al., 2004; Rogan et al., 2001).
6 At 36-months post-treatment and at age 7 years, no significant differences in cognition or
7 behavior were noted between the succimer and placebo groups. Current blood lead levels were
8 significantly associated with cognitive performance at baseline, 36-months post-treatment, and at
9 7 years of age, and the regression coefficients were similar in magnitude to those estimated in
10 observational studies (i.e., ~3 point IQ decline per 10 |ig/dL increase in blood lead), providing a
11 linkage between the results of the observational studies and those of this experimental study.
12 However, within-child analyses indicated that changes in developmental test scores over time
13 were not consistently associated with changes over time in blood lead level.
14
15 6.10.6 Confounding of Lead Health Effects
16 6.10.6.1 Adjustment for Confounding in Epidemiologic Studies of Lead
17 The possibility that the adverse health effects associated with increased lead exposure in
18 epidemiologic studies are, in fact, due to risk factors with which increased lead exposure is
19 associated remains the most important impediment to drawing causal inferences. It is important
20 to note that confounding is not an inherent characteristic of an association between lead exposure
21 and a health outcome. Rather it is a bias that arises from the particular setting in which the
22 association is being investigated, and its source is the patterns of covariance between lead, the
23 outcome, and other determinants of the outcome. Therefore, the extent to which it represents an
24 interpretational challenge is, to some extent, study-specific. Various approaches have been taken
25 to reduce the uncertainty this creates. Some investigators have specified the sampling frame or
26 the eligibility criteria so as to increase the homogeneity of the study participants on factors
27 known to be strong risk factors for the outcome of interest, thereby reducing both (a) the
28 correlation between them and lead and (b) their potential to confound any association observed
29 between increased lead exposure and poor outcome. An example is the recruitment of a birth
30 cohort from a maternity hospital that largely served a relatively affluent catchment area, resulting
31 in high umbilical cord blood lead levels being associated with higher, rather than lower, social
May 2006 6-306 DRAFT-DO NOT QUOTE OR CITE
-------
1 class standing (Bellinger et al., 1984). Reducing confounding by means of such design decisions
2 has the disadvantage that an investigator cannot determine whether the impact of lead on the
3 outcome varies depending on the factor whose range of potential values has been restricted.
4 More frequently, however, investigators have relied on statistical procedures, applied post data
5 collection, to identify and control for potential confounding. Unlike sample restriction, this
6 approach preserves the opportunity to explore possible modification of the lead effect by
7 cofactors.
8 Adjustment for confounding has been performed primarily using multiple regression
9 analyses and data stratification. For multiple regression modeling, stepwise regression has been
10 frequently used for covariate selection. Stepwise regression has many faults and is often less
11 acceptable then the use of a few well-chosen covariates. However, the stepwise regression
12 methodology may be considered to have less bias, as it selects from a class of variables that
13 represent a wide scientific viewpoint rather than the narrower one of the investigator. One
14 problem with stepwise regression pointed out by Bellinger (2004) is that the usual adjustment
15 strategy assumes that all the variance in the response shared by the exposure and the confounder
16 belongs to the confounder. In some settings, this is likely to be excessively conservative,
17 because confounders can, to some extent, also be proxies for exposure. This is further discussed
18 in the next section.
19 Splitting the data set into smaller data sets (partitioning or stratification) and analyzing
20 those data sets separately was used in some of the studies examining the relationship between
21 blood pressure and lead. This practice also has some advantages and disadvantages. Use of
22 an advanced statistical method could be helpful to determine how the partitioning should be done
23 (Young and Hawkins, 1998), which could reveal relationships that would otherwise not be
24 possible to detect using usual regression techniques. A disadvantage of partitioning a small data
25 set is that the smaller sample size may lack sufficient power to detect otherwise detectable
26 associations and to yield reliable estimates.
27
28 6.10.6.2 Confounding Adjustment on Lead Health Effect Estimates
29 The ability of the investigator to determine how much of the apparent association between
30 a lead biomarker and an outcome reflects residual confounding by a cofactor depends on the
31 characteristics of the joint distribution of lead and the cofactor. For example, with respect to
May 2006 6-307 DRAFT-DO NOT QUOTE OR CITE
-------
1 neurodevelopment, important cofactors include maternal IQ, quality of the rearing environment,
2 maternal smoking, alcohol use, and birth weight, among others. Some of these cofactors are
3 truly independent predictors and can be adjusted for using multiple regression analyses. Under
4 some circumstances, however, lead and the cofactor may be so highly related that one cannot be
5 confident that their associations with the outcome have been disentangled by the statistical
6 methods applied. Moreover, the true causal relationships among lead, the cofactors, and the
7 outcome might not be sufficiently well understood that the outcome variance shared by lead and
8 the cofactors can be characterized appropriately in the analyses.
9 In studies of lead and neurodevelopment, the magnitude of the lead coefficient, reflecting
10 the decline in test score per unit increase in the lead biomarker, is substantially reduced, often by
11 half or more, by adjusting for markers of the social environment. However, as noted above, the
12 extent of confounding is study-specific, so the impact of adjustment for confounders on the lead
13 coefficient will also be study-specific. With respect to the Port Pirie study, Tong and Lu (2001)
14 observed that adjustment for four factors (i.e., quality of home environment, SES, maternal
15 intelligence, and parental smoking behavior) reduced the magnitude of the estimated association
16 between lead and IQ by 40% and inclusion of additional factors resulted in another 10%
17 reduction. Similarly, in the pooled analysis by Lanphear et al. (2005) that included seven
18 prospective studies, the crude coefficient for concurrent lead and childhood IQ score was -4.66
19 (95% CI: -5.72, -3.60), while the coefficient adjusted for study site, quality of the home
20 environment (HOME score), birth weight, maternal IQ, and maternal education was -2.70 (95%
21 CI: -3.74, -1.66). During the 1980s, adjustment for parental IQ and HOME scores became
22 almost mandatory if the findings of a study of lead and children's cognitive outcomes were to be
23 considered credible. Simulation analyses conducted by Mink et al. (2004) suggested that
24 relatively small differences in confounding variables between "exposed" and "unexposed"
25 groups could produce spurious differences in cognitive test scores if unmeasured and
26 unaccounted for in the analysis. As noted by Bellinger (2004), however, the problem usually is
27 not that such cofactors were unmeasured in a lead study, but that they were not measured well.
28 More important yet is the fact that the conceptual models that frame the interpretation of
29 the resulting models usually fail to reflect adequately the complexity of the associations among
30 lead exposure, the outcome, and the cofactors. Although both HOME score and parental IQ
31 surely strongly influence child outcomes in ways that are independent of lead, a case can also be
May 2006 6-308 DRAFT-DO NOT QUOTE OR CITE
-------
1 made that lead might contribute to the associations. That is, a parent's IQ presumably reflects
2 the parent's early lead exposure and, assuming that the physical environments in which a parent
3 and child grow up are not completely unrelated to one another are likely to provide similar lead
4 exposure opportunities. Adjusting for parental IQ in evaluating the association between a child's
5 lead exposure and his or her IQ, therefore, will result in an underestimate of the contribution of
6 the child's lead exposure to his or her IQ. Similarly, if early lead exposure alters child behavior,
7 the transact!onal model of child development would generate the prediction that the changes will
8 elicit different behaviors from parents, altering the characteristics of the child-rearing
9 environment. For instance, increased lead exposure might result in an infant being more
10 irritable, less soothable, and the parent less nurturing. In so far as measurement of the quality of
11 the rearing environment in studies occurs after the children have experienced some lead
12 exposure, the hypothesis that lead is responsible for shaping some aspects of that environment
13 cannot be entirely dismissed, and control for HOME scores might be excessively conservative.
14 Other aspects of model building in assessing the association of lead with health outcomes
15 also warrant comment. In many studies of lead and cognitive outcomes in children, investigators
16 have adjusted for factors such as birth weight or length of gestation that might, themselves,
17 reflect adverse effects of lead, i.e., mediating factors that lie between lead and condition on the
18 causal pathway. The coefficient estimated for lead in a model that contained such factors would
19 be smaller in magnitude than it would be if terms for such mediating factors had not been
20 included.
21 Recognizing imperfections in the ability to measure such factors well, a concern is
22 expressed that the lead coefficient could be reduced further, perhaps all the way to the null,
23 if better, more comprehensive methods of measurement were applied. On the other hand, the
24 methods used to adjust for such factors may be excessively conservative insofar as they attribute
25 to a factor all of the outcome variance that it shares with lead, despite the likelihood that the true
26 relationships among lead, social factors, and outcome are unlikely to be as simple as this model
27 assumes. Some factors might, in part, be markers of lead exposure opportunities. For example,
28 both lead biomarker levels and lower cognitive function in children are associated with lower
29 social class standing. Social class is a complex construct that conveys information about a
30 multitude of factors that might influence children's health, including the amount of lead in
31 environmental media. Thus, some of the association between lower social class and poorer
May 2006 6-309 DRAFT-DO NOT QUOTE OR CITE
-------
1 health might reflect the effect of higher lead exposure. If so, routine adjustment of health
2 outcome for social class in assessing the association between increased lead exposure and poorer
3 health in children will fail to distinguish these lead-related and non-lead-related components of
4 the association between social class and health, and, in fact, will assume that all of it is non-lead-
5 associated (Bellinger et al., 1989). It is nearly impossible to actually determine if the problem of
6 overadjustment exists in a particular data set. There are several statistical methods which
7 attempt to address this problem. These include using partial F tests, ridge regression, path
8 analysis, and structural equations. None of these methods are completely satisfactory.
9 When expressed as the percentage of variance accounted for in a health outcome, the
10 contributions of lead have been characterized as modest in magnitude. For example, Roller et al.
11 (2004) noted that blood lead typically accounts for 1 to 4% of the variance in child IQ scores,
12 compared to 40% or more by social and parenting factors. Although few would take issue with
13 the greater importance of social and parenting factors than of lead as determinants of this
14 outcome, it is of dubious relevance to the regulatory decision-making process. Increased lead
15 exposure has a somewhat different status than many other risk factors for poor child outcome in
16 that the steps needed to mitigate it are relatively well-known. The strategies for increasing SES
17 or remediating inadequate parenting are not as readily apparent. Moreover, it is important to
18 note that the final regression models developed for outcomes such as child IQ rarely exceed 50%
19 in lead studies, suggesting that lead accounts for 2 to 8% of the variance.
20
21 6.10.7 Inferences of Causality
22 Even with more sophisticated and nuanced models, however, any conclusions about the
23 causal forces generating the results of any observational epidemiologic study are necessarily
24 uncertain. In the absence of random assignment to exposure group, residual confounding will
25 always be a possible explanation of an observed association. As in other areas of epidemiology,
26 a weight-of-evidence approach remains the best option available as a basis for drawing of causal
27 inferences. If the association between a lead biomarker and a health outcome of interest is
28 observed in settings that vary widely in terms of the characteristics of the social environment
29 including sociodemographic and cultural characteristics, characteristics of the study participants,
30 including nutritional status, genetic factors, and lifestyle factors, the likelihood that the
31 association is attributable, in its entirety, to residual confounding is reduced. For instance, the
May 2006 6-310 DRAFT-DO NOT QUOTE OR CITE
-------
1 pooled analyses of data contributed by many of the international prospective studies provide a
2 compelling demonstration that the association between blood lead level and child IQ is
3 remarkably robust across disparate sociocultural settings (Lanphear et al., 2005). Even such
4 consistency in the effect estimate across diverse settings is only indirect and weak evidence of
5 causality, however. In general, epidemiologic studies rarely provide data that enhance our
6 understanding of the "black box" between biomarkers of lead burden and indicators of health
7 status. Epidemiologic data identify associations between exposure biomarkers and health
8 indicators, but are not highly informative regarding possible mechanisms of lead toxicity that
9 underlie the associations. A critical stage in applying the overall weight-of-evidence approach is
10 the examination of the epidemiologic data in the context of data from experimental animal
11 behavioral and mechanistic studies. Although such data have their own limitations, they are not
12 subject to many of the most important potential biases that can becloud the interpretation of the
13 epidemiologic data.
14
15 6.10.8 Effects on the Individual Versus Effects on the Population
16 In studies of lead toxicity, health endpoints have more often been continuously-distributed
17 indices such as blood pressure or IQ. A view that the endpoints should be diagnoses rather than
18 measured values on the underlying indices is that a change in the value of a health index that
19 does not exceed the criterion value defining the diagnosis is therefore without consequence for
20 an individual's health. The World Health Organization (WHO) definition of "health" is:
21 "Health is a state of complete physical, mental and social well-being and not merely the absence
22 of disease or infirmity" (World Health Organization, 1948). By this definition, even decrements
23 in health status that are not severe enough to result in the assignment of a diagnosis might be
24 undesirable if they reflect a decrement in an individual's well-being but are not severe enough to
25 meet diagnostic criteria. The American Thoracic Society (ATS, 2000) discusses similar concepts
26 of shift in distribution and health effects.
27 Sometimes, the importance of a lead-associated change on a health index is evaluated by
28 comparing it to the standard error of measurement of the index, i.e., the statistic that defines the
29 range within which an individual's "true" value on the index is likely to lie. For instance the
30 standard error of measurement for full scale IQ is 3 to 4 points, leading some to conclude that the
31 estimated IQ decrement of 3 points per 10 |ig/dL increase in blood lead level is "in the noise" of
May 2006 6-311 DRAFT-DO NOT QUOTE OR CITE
-------
1 measurement and, therefore, meaningless. A similar claim has been made with regard to the
2 magnitude of the association between lead and blood pressure. The error in this argument is that
3 the estimated decrement of 3 IQ points per 10 |ig/dL applies to grouped, not individual, data.
4 For measurement error to provide an explanation for the observation of an association that is
5 approximately the size of the standard error of mesurement, it would be necessary to postulate
6 that the true association is null, but that, by chance or because of some bias, the measured IQ
7 scores of the individuals with higher lead exposures were systematically underestimated (i.e.,
8 their true IQ scores lie in the upper tails of the 95% CI for the children's observed scores) and
9 that the measured IQ scores of the individuals with lower exposures were systematically
10 overestimated (i.e., their true IQ scores lie in the lower tails of the 95% CI). Thus, this argument
11 requires an assumption that the direction of measurement error is highly correlated with exposure
12 status. The fundamental flaw is using a statistic that pertains to individual-level data to draw
13 inferences about group-level data.
14 Nosology (the classification and naming of diseases) is dynamic as knowledge accrues.
15 The total serum cholesterol level that is considered indicative of hyperlipidemia has dropped
16 steadily over the past 40 years. Second, even within the range of health index values that are
17 sub-diagnostic, variations on the index are significantly associated with health outcomes.
18 For instance, even among children with birth weights greater than the cut-off used to define
19 "low birth weight," birth weight is significantly associated with IQ at age 7 years (Matte et al.,
20 2001). Third, exposure-related changes on a health index can be markers or indicators of other
21 changes that are likely to have occurred whose significance is more certain. For instance, slower
22 completion of a commonly-used neuropsychological test, the Grooved Pegboard, is associated
23 with poorer handwriting, and reduced ability to copy a drawing is associated with a greater risk
24 of a need for remedial school services (Bellinger, 2004).
25 The critical distinction between population and individual risk, an issue pertinent to many
26 questions in chronic disease epidemiology, has frequently been blurred in discussions of the
27 public health implications of lead-associated decrements in health. With respect to
28 neurodevelopment, although a two- or three-point decline in IQ might not be consequential for
29 an individual, it is important to recognize that this figure represents the central tendency of the
30 distribution of declines among individuals. Thus, some individuals might manifest declines that
31 are much greater in magnitude, while others manifest no decline at all, reflecting interindividual
May 2006 6-312 DRAFT-DO NOT QUOTE OR CITE
-------
1 differences in vulnerability. Moreover, the import of a decline for an individual's well-being is
2 likely to vary depending on the portion of the IQ distribution. For an individual functioning in
3 the low range due to the influence of developmental risk factors other than lead, a lead-
4 associated decline of several points might be sufficient to drop that individual into the range
5 associated with increase risk of educational, vocational, and social failure.
6 The point estimate indicating a modest mean change on a health index at the individual
7 level can have substantial implications at the population level. For example, although an
8 increase of a few mmHg in blood pressure might not be of concern for an individual's well-
9 being, the same increase in the population mean might be associated with substantial increases in
10 the percentages of individuals with values that are sufficiently extreme that they exceed the
11 criteria used to diagnose hypertension (Rose and Day, 1990). In other words, the mean value
12 conveys substantial information about the percentage of individuals with clinically relevant,
13 extreme values of the indicator. Moreover, interventions that shift the population mean, in a
14 beneficial direction, by an amount that is without clinical consequence for an individual have
15 been shown to produce substantial decreases in the percentage of individuals with values that are
16 clinically significant (Bellinger, 2004). The following subsections will discuss quantitatively
17 lead-related effects of a population level change in IQ and blood pressure.
18
19 6.10.8.1 Effects of Lead on Intelligence
20 The outcome most often examined to investigate neurotoxic effects of lead is IQ.
21 Although the definition of "intelligence" is quite abstract, IQ remains a useful outcome measure
22 as it is correlated with important measures of life success, such as academic achievement,
23 earnings, and social status (Bellinger, 2003; Weiss, 2000). Several studies reported quantitative
24 relationships between full scale IQ and current blood lead levels for children aged 5 to 11 years
25 old, and these are summarized in Table 6-10.1. The estimated relationships as reported by the
26 authors are used.
27 The curves over a range of blood lead levels from the 10th percentile to the 90th
28 percentile are shown in Figure 6-10.2. The curves are restricted to that range because log-linear
29 curves become very steep at the lower end of the blood lead levels, and this may be an artifact of
30 the model chosen. The percentiles are estimated using various methods and are only
31 approximate values. Studies which estimated a linear relationship are shown as reported, and
May 2006 6-313 DRAFT-DO NOT QUOTE OR CITE
-------
Table 6-10.1. Summary of Studies with Quantitative Relationships for
IQ and Blood Lead
Reference
Study Location
n
Estimated Slope Estimated Slope
(IQ points/fig/dL) - (IQ points/fig/dL) -
Blood Lead 10th to Blood Lead Under
90th Percentile 10
Bellinger etal. (1992)
Canfield et al. (2003a)
Dietrich et al. (1993a)
Ernhartetal. (1989)
Wassermanetal. (1997)
Baghurstetal. (1992)
Silvaetal. (1988)
Al-Salehetal. (2001)
Tellez-Rojo et al. (in
press)
Kordas et al. (2006)
Lanphear et al. (2005)
Boston, Massachusetts 116
Rochester, New York 182
Cincinnati, Ohio 221
Cleveland, Ohio 160
Kosovo, Yugoslavia 231
Port Pirie, South Australia 324
Dunedin, New Zealand 579
Riyadh, Saudia Arabia 532
Mexico City, Mexico 566
Torreon, Mexico 589
International Pooled Analysis 1,333
-0.5
-0.7
-0.3
-0.1
-0.2
-0.2
-0.3
-0.6
-1.0
-0.5
-0.2
NA
-0.8
-0.3
NA
NA
-0.4
-0.3
-0.6
-1.0
-1.1
-0.5
1 similarly for the log-linear relationships. Note that these are not forest plots of slopes or hazard
2 ratios—they are the actual estimated relationships.
3 The analysis by Lanphear et al. included the studies of Baghurst et al. (1992), Bellinger
4 et al. (1992), Canfield et al. (2003a), Dietrich et al. (1993a), Ernhart et al. (1989) and Wasserman
5 et al. (1997). The pooled analysis also included the Mexico City study of Schnaas et al. (2000).
6 The results from Schnaas et al. are not included in Table 6-10.1 or Figure 6-10.2 because the
7 authors did not provide regression coefficients in their paper, thus concentration-response
8 relationship were not estimable. The study by Silva et al. (1988) is not included in the pooled
9 analysis of Lanphear et al., but is included in this section as its results are comparable
10 and informative.
May 2006
6-314
DRAFT-DO NOT QUOTE OR CITE
-------
120
115
110
g105
_o 100
8 95 \
CO
= 90 J
"• 85
80
75^
70
.Bellinger et al. (1992)
Silva eta I. (1988)
Baghurst etal. (1992)
Al-Saleh etal.
Canfieldetal. (2003)
^
Dietrich etal. (1993)
Ernhartetal. (1989)
Wasserman et al. (1997)
10 15 20 25
Blood Lead (M9/dL)
30
35
Figure 6-10.2. Concentration-response relationships of IQ to blood lead for the individual
studies and the pooled analysis by Lanphear et al. (2005).
1 Several conclusions can be drawn from these graphs. First, note that the overall IQ levels
2 are quite different. This results from different populations and from different applications of the
3 IQ tests. Second, all studies showed a decreasing IQ score as the blood lead level increased.
4 It is the slope of the studies that is relevant, not the actual IQ scores. Third, for studies with
5 lower blood lead levels, the slopes appear to be steeper. This is the reason that many authors
6 choose to use the log-linear model. However, for those studies where the blood leads were
7 generally high, the log-linear and linear models are almost identical. Thus it is not surprising
8 that some authors chose a linear model instead of a log-linear model. The curves in
9 Figure 6-10.2 do not show evidence of a no-effect threshold because the slopes increase as the
10 blood lead levels become smaller. The observed mean adjusted IQ levels (for blood lead <5, 5 to
11 10, 10 to 15, 15 to 20, and >20 |ig/dL) reported by Lanphear et al. (2005) also show no evidence
12 of a threshold, as seen in Figure 6-10.3.
13
May 2006
6-315
DRAFT-DO NOT QUOTE OR CITE
-------
105
100
o
J»
ro
u
^ 95
3
c
CO
o
90
85
10 15 20 25 30
Blood Lead (M9/dL)
35
40
Figure 6-10.3. Mean blood lead levels adjusted for HOME score, maternal education,
maternal IQ, and birth weight from the pooled analysis of seven studies by
Lanphear et al. (2005). Mean adjusted IQ levels at blood lead levels of <5,
5 to 10,10 to 15,15 to 20, and >20 ug/dL are shown.
1 Weiss (1990) predicted, on purely statistical grounds, that a downward shift of five points
2 in mean IQ, if the amount of dispersion in the distribution remained the same, should be
3 accompanied by a doubling of the numbers of individuals with scores two or more standard
4 deviations below the mean and a reduction by half of the number of individuals with scores
5 twoor more standard deviations above the mean. With respect to lead, the general accuracy of
6 this prediction has been empirically demonstrated in two different datasets by Needleman et al.
7 (1982) and Bellinger (2004). The example below provides further evidence of the change in
8 percentages of individuals with IQ <70 or <50 points after restricting the analysis to those with
9 blood lead levels less than 10 |ig/dL.
10 The average slope was estimated for those studies with a significant portion of the
11 subjects with blood lead levels less than 10 |ig/dL. These average slopes are given in
12 Table 6-10.1. In addition, the results of Lanphear et al. (2005) were considered. The average
13 slope at blood lead levels less than 10 |ig/dL from that pooled analysis was -0.5 IQ points per
May 2006
6-316
DRAFT-DO NOT QUOTE OR CITE
-------
1 |ig/dL. Based on the individual studies and the pooled analysis it appears that the average slope
2 is between -0.3 and -0.5 points per |ig/dL, with the exception of the large negative slope of
3 -0.8 points per 10 |ig/dL from the study by Canfield et al. (2003a). The value of -0.4 points per
4 ng/dL will be used in calculations of the implications of the slope at blood lead levels less than
5 10 |ig/dL.
6 A nonexposed population was assumed to have a standard mean IQ of 100 and standard
7 deviation of 15 at a blood lead exposure of 0 |ig/dL. The fraction of the population that would
8 have an IQ <70 or <50 as a function of blood lead level was then calculated. The results are
9 shown in Figure 6-10.4. Note that the fraction with an IQ level below 70, a level often requiring
10 community support to live (World Health Organization, 1992) increases from a little over
11 2 percent for no lead exposure to about 4 percent with a blood lead level of 10 |ig/dL.
12 In addition, the fraction with an IQ level below 50, a level often requiring continuous support to
13 live (World Health Organization, 1992) increases from a little over 4 per 100,000 for no lead
14 exposure to about 11 per 100,000 with a blood lead level of 10 |ig/dL.
15 A shift in the mean value of a health indicator has substantial importance for both
16 extremes of the distribution. In the case of lead, a downward shift in the mean IQ value is
17 associated not only with a substantial increase in the percentage of individuals achieving very
18 low scores, it is associated as well with a substantial decrease in the percentage achieving very
19 high scores. Based on the study by Bellinger et al. (1987) examining intelligence test scores of
20 lead-exposed children, Weiss (1988) discussed the shift of the population distribution of IQ from
21 a mean of 100 and a standard deviation of 15 to a mean of 95, a 5% reduction. When the mean
22 IQ level is 100, 2.3% of the individuals in a given population would score above 130. However,
23 with the population distribution shift and the resulting mean decline in IQ, only 0.99% of the
24 individuals would score above 130. Weiss states that the implication of such as loss transcends
25 the current circumscribed definitions of risk.
26
27 6.10.8.2 Cardiovascular Effects of Lead
28 In studies investigating the cardiovascular effects of lead, blood pressure has been
29 examined most frequently. Results from the Framingham Heart Study show that higher levels of
30 blood pressure, even within the nonhypertensive range, impose increased rates of cardiovascular
31 disease (Kannel, 2000a,b). A continuous graded increase in cardiovascular risk is observed as
May 2006 6-317 DRAFT-DO NOT QUOTE OR CITE
-------
0.08
V
0 0.06
5 0.04
c
o
u.
o
IO
0.02
0.00
0.0016
0.0012
*§ 0.0008
c
O
o 0.0004
2
u_
0.0000
23456789
Blood Lead (M9/dL)
10
3456789 10
Blood Lead (yg/dL)
Figure 6-10.4. Effect of blood lead on fraction of population with IQ level <70 or
<50 points.
1 blood pressure increases, with no evidence of a threshold value. Most events arise not in the
2 most severe cases, but mainly in those with high normal blood pressure (i.e., mild hypertension).
3 This view is further supported by the Seventh Report of the Joint National Committee on
4 Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (Chobanian et al.,
5 2003). Kannel (2000b) states that reducing even moderate elevation in blood pressure is likely to
6 be beneficial.
7 Kannel (2000a) states that systolic blood pressure exerts a strong, influence on
8 cardiovascular events, as it is the prime causal function of hypertension and its adverse
9 cardiovascular sequelae. Cardiovascular events include coronary disease, stroke, peripheral
May 2006
6-318
DRAFT-DO NOT QUOTE OR CITE
-------
1 artery disease, and cardiac failure. Risk ratios are larger for cardiac failure and stroke, but
2 coronary disease (i.e., myocardial infarction, angina pectonis, sudden death) is the most common
3 and most lethal sequela of hypertension (Kannel, 1996). Kannel (2000a) notes that the
4 Framingham Heart Study has recognized that elevated blood pressure tends to occur alongside
5 other major risk factors of cardiovascular disease such as glucose intolerance, dyslipidemia,
6 abdominal obesity, and left ventricular hypertrophy, among others. If a cluster of multiple risk
7 factors is present, the hazard is formidable for coronary disease and stroke.
8 No critical level of blood pressure is evident. The risk appears to be simply proportional
9 from the lowest to the highest level recorded. In the Multiple Risk Factor Intervention Trial
10 (MRFIT), Neaton et al. (1995) confirmed a continuing and graded influence of systolic blood
11 pressure on cardiovascular disease mortality extending down into the range of <140 mm Hg.
12 The Prospective Studies Collaboration (2002) meta-analysis of 61 prospective studies relates
13 blood pressure to vascular mortality without indication of a threshold down to 115/75 mm Hg.
14 The absence of a demonstrable safe or critical level of blood pressure suggests using the range of
15 blood pressure rather than discrete categories such as hypertension.
16 Many studies have suggested a relationship between blood lead and systolic blood
17 pressure. In particular, the meta-analysis of Nawrot et al. (2002) indicated that a doubling of the
18 blood lead corresponded to a 1 mm Hg increase in systolic blood pressure. Although this
19 magnitude of increase is not clinically meaningful for an individual, a population shift of
20 1 mm Hg is important.
21 The Framingham Heart Study results (Kannel, 2000a) were used to estimate a typical
22 population distribution of systolic blood pressure values (Figure 6-10.5). The distribution of
23 systolic blood pressure values was approximated well by a lognormal distribution for both
24 women and men (p > 0.4). The relationship between systolic blood pressure and the risk of
25 cardiovascular events was also given by Kannel (2000a). The relationships are shown in
26 Figure 6-10.6.
27 To estimate population risk, it was assumed that the effect of blood lead on blood pressure
28 was to shift the entire distribution by the amount given by Nawrot et al. (2002). For each shift in
29 the distribution, the entire distribution was integrated out over the risk given in Figure 6-10.6.
30 The result estimated was expected number of cardiovascular events per 1,000 person years, and
31 this was plotted for blood lead levels ranging from 5 to 15 |ig/dL for both women and men. The
May 2006 6-319 DRAFT-DO NOT QUOTE OR CITE
-------
(0
2
c
o
'•e
o
a.
o
o
c
75 150 225
Systolic Blood Pressure (mm Hg) in Women
ra
cu
o
t
o
a.
o
o
a>
3
cr
cu
75 150 225
Systolic Blood Pressure (mm Hg) in Men
Figure 6-10.5. Distribution of systolic blood pressure in women and men aged 35 to
64 years from the Framingham Heart Study (Kannel, 2000a).
results are shown in Figure 6-10.7. Although the effects are modest, they translate into a large
number of events for a moderate population size. For example, a decrease in blood lead
from 10 to 5 |ig/dL results in an annual decrease of 27 events per 100,000 women and 39 events
per 100,000 men.
May 2006
6-320
DRAFT-DO NOT QUOTE OR CITE
-------
75
c
-------
i
0)
111
o 1
g §
ro -
Oi CL
75
JU.U
27.5
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
n n
8 10 12
Blood Lead (|jg/dL)
14
16
Women
--- Men
Figure 6-10.7. Effect of blood lead on expected annual risk of cardiovascular events per
1,000 person-years.
T3
ro
0)
_i
•a
o
£
CD
45
40
35
30
25
20
15
10
5
• LA Cab Drivers
• Philadelphia Cab Drivers
A LA Office Workers
A Starke, FL Workers
• Barksdale, Wl Workers
0.0 2.0 4.0 6.0 8.0
Air Lead (pg/m3)
10.0
12.0
Figure 6-10.8. Relationship of blood lead levels to personal air lead concentrations in five
occupational cohorts, including office workers, cab drivers, and plant
workers (Azar et al., 1975).
May 2006
6-322
DRAFT-DO NOT QUOTE OR CITE
-------
1 lead would lead to a 0.8 |ig/dL decrease in blood lead levels. Using both the relationship
2 between blood lead levels and blood pressure (i.e., a doubling of the blood lead corresponds to a
3 1 mm Hg increase in systolic blood pressure) and the relationship between blood pressure and
4 cardiovascular events (shown in Figure 6-10.6 for women and men), a decrease of 0.8 |ig/dL in
5 blood lead from 5 |ig/dL to 4.2 |ig/dL would lead to a decrease of 6 cardiovascular events per
6 100,000 for women and 10 events per 100,000 for men.
7
8 6.10.9 Summary of Key Findings and Conclusions Derived from Lead
9 Epidemiology Studies
10 The remarkable progress made since the mid-1980s in understanding the effects of lead on
11 health can be gauged by noting the changes that have occurred over time in the questions
12 investigators have addressed. In the 1980s, the question of interest was often, "Does low-level
13 lead exposure affect health?" The questions asked in recent studies have more often focused on
14 details of the associations, including the shapes of concentration-response relationships,
15 especially at levels well within the range of general population exposures, biological and
16 socioenvironmental factors that either increase or decrease an individual's risk, the prognoses
17 associated with lead-associated effects, the efficacy of interventions to reduce adverse effects,
18 and so on. In fact, "low-level," a term long-used to describe exposures that are not sufficiently
19 high to produce clinical signs and symptoms, is increasingly being recognized as a descriptor
20 that has little biological meaning and is interpretable only in a specific historical context. What
21 was considered "low" in the 1980s is an order of magnitude higher than the current mean level in
22 the U.S. population, and the current mean remains perhaps as much as two orders of magnitude
23 above "natural" background levels in humans. The current CDC screening guideline for children
24 of 10 |ig/dL is not a "bright line" separating toxicity from safety, but merely a risk management
25 tool. There is no level of lead exposure that can be clearly identified, with confidence, as "safe."
26 Recent studies of lead neurotoxicity in infants have observed adverse effects at blood lead levels
27 of only 1 or 2 |ig/dL, and adverse renal outcomes have been reported at blood lead levels below
28 5 |ig/dL. Public health interventions have resulted in declines, over the past 25 years, of more
29 than 90% in the mean blood lead level within all age and gender subgroups of the U.S.
30 population, substantially decreasing the numbers of individuals at risk toxic effects of lead.
May 2006 6-323 DRAFT-DO NOT QUOTE OR CITE
-------
1 The following are a listing of key fmdinds for various classes of health outcomes
2 discussed earlier in this epidemiology chapter:
3 • Neurotoxic effects of lead in children. Lead effects on neurobehavior in children have
4 been observed with remarkable consistency across numerous studies of various designs,
5 populations, and developmental assessment protocols. The negative impacts of lead on
6 neurocognitive ability and other neurobehavioral outcomes persist in most recent studies
7 even after adjustment for numerous confounding factors including social class, quality of
8 caregiving, and parental intelligence. These effects appear to be irreversible and persist
9 into adolescence and young adulthood. An international pooled analysis of seven
10 prospective cohort studies offers evidence that exposure to lead affects the intellectual
11 attainment of preschool and school age children even at blood lead levels below 10 |ig/dL.
12 Epidemiologic studies have demonstrated that lead also may be associated with
13 increased risk for antisocial and delinquent behavior, which may be a consequence of
14 attention problems and academic underachievement among children who have suffered
15 higher exposures to lead during their formative years. Direct measures of brain damage
16 using Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS)
17 also provide evidence suggestive of harm due to lead exposure. Pharmacological or
18 nutritional intervention strategies generally have not been found to reduce or eliminate
19 lead-associated neurodevelopmental morbidities.
20
21 • Neurotoxic effects of lead in adults. In adults, the effect of lead on the nervous system
22 may not be detected through neurobehavioral testing due to cognitive reserve, the ability to
23 compensate for brain impairment. There is no consistent evidence that environmental lead
24 exposure is associated with impaired cognitive performance in the elderly if competing
25 risk factors are considered.
26 Numerous studies of occupational lead exposure observed associations of blood
27 lead with peripheral sensory nerve impairment, visuomotor and memory impairment, and
28 postural sway abnormalities. Past occupational exposure to lead also was associated with
29 increased risk of developing Amyotrophic Lateral Sclerosis (ALS), motor neuron disease,
30 and essential tremor. The odds of developing ALS and essential tremor were significantly
31 increased in individuals with the ALAD2 allele. These neurobehavioral impairments in
May 2006 6-324 DRAFT-DO NOT QUOTE OR CITE
-------
1 occupationally-exposed individuals have typically been associated with higher blood lead
2 levels (-30-40 |ig/dL); however, essential tremor has been found to be associated with
3 much lower blood lead levels (mean 3 |ig/dL).
4
5 • Renal effects of lead. In the general population, both cumulative and circulating lead has
6 been found to be associated with longitudinal decline in renal functions. In the large
7 NHANES III study, renal dysfunction was observed in hypertensives at a mean blood lead
8 of only 4.2 |ig/dL. These results provide strong evidence that the kidney is a target organ
9 for effects from lead in adults at current U.S. environmental exposure levels. The
10 magnitude of the effect of lead on renal function ranged from 0.2 to -1.8 mL/min change in
11 creatinine clearence per 1.0 |ig/dL increase in blood lead in general population studies.
12 The renal impact pf environmental lead exposure in children is difficult to assess, because
13 most studies have only measured early biological effect markers and their prognostic value
14 is uncertain.
15 Studies involving the longitudinal assessment of renal function decline in
16 susceptible patient populations have observed that low levels of blood lead (<5 |ig/dL) and
17 chelatable lead levels were associated with decline in glomerular filtration rate over a
18 4-year follow-up period in patients with chronic renal insufficiency. Renal function in
19 these patients was found to stabilize and, in some cases, improve after therapeutic
20 chelation.
21
22 • Cardiovascular effects of lead. Epidemiologic studies support the relationship between
23 increased lead exposure and increased cardiovascular outcome, including increased blood
24 pressure and increased incidence of hypertension. A recent meta-analysis reported that a
25 doubling of blood lead level was associated with a 1.0 mm Hg increase in systolic blood
26 pressure and a 0.6 mm Hg increase in diastolic pressure. Studies also have found that
27 cumulative past lead exposure (e.g., bone lead) may be as important, if not more, than
28 present exposure in assessing cardiovascular effects. The evidence for an association of
29 lead with cardiovascular morbidity and mortality is limited but supportive.
May 2006 6-325 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Reproductive and developmental effects of lead. The epidemiologic evidence suggests
2 small associations between exposure to lead and male reproductive outcomes, including
3 perturbed semen quality and increased time to pregnancy. These associations appear at
4 blood lead levels greater the 45 |ig/dL, as most studies have only considered exposure in
5 the occupational setting. There are no adequate data to evaluate associations between lead
6 exposure and female fertility. For many other outcomes, the observed associations are
7 fairly small, especially at the levels of exposure that are currently of interest. However,
8 there may be populations that are highly susceptible to lead-related reproductive effects,
9 especially if they have additional risk factors for these outcomes.
10
11 • Genotoxic and carcinogenic effects of lead. Studies of genotoxicity consistently find
12 associations of lead exposure with DNA damage and micronuclei formation; however, the
13 associations with the more established indicator of cancer risk, chromosomal aberrations,
14 are inconsistent. Epidemiologic studies of highly-exposed occupational populations
15 suggest a relationship between lead and cancers of the lung and the stomach; however the
16 evidence is limited by the presence of various potential confounders, including
17 coexposures (e.g., arsenic, cadmium), smoking, and dietary habits. The 2004 IARC
18 review concluded that inorganic lead compounds were a probable carcinogen (Group IIA)
19 based on limited evidence in humans and sufficient evidence in animals.
20
21 • Effects of lead on the immune system. Several studies have examined possible
22 associations between lead exposures and biomarkers of immune function. Findings from
23 recent epidemiologic studies suggest that lead exposure may be associated with effects on
24 cellular and humoral immunity. These effects include changes in serum immunoglobulin
25 levels; perturbation of peripheral lymphocyte phenotype profiles, including decreases in
26 peripheral blood T-cell abundance and changes in T-cell to B-cell abundance ratios;
27 suppression of lymphocyte activation; and suppression of neutrophil chemotaxis and
28 phagocytosis. Studies of biomarkers of humoral immunity in children have consistently
29 found significant associations between increasing blood lead concentrations and serum
30 IgE levels at blood lead levels below 10 |ig/dL.
31
May 2006 6-326 DRAFT-DO NOT QUOTE OR CITE
-------
1 • Effects of lead on the hematopoietic system. Lead exposure has been associated with
2 disruption of heme synthesis in both children and adults. Increases in blood lead
3 concentration of a~20 to 30 |ig/dL are sufficient to halve erythrocyte ALAD activity and
4 sufficiently inhibit ferrochelatase to double erythrocyte protoporphyrin levels.
5 Perturbation of erythropoiesis, indicated by changes in serum erythropoietin and
6 progenitor cells, occurs in the absence of detectable changes in blood hemoglobin levels or
7 hematocrit in children and adults at blood lead levels below 40 |ig/dL. Risk of clinical
8 anemia in children becomes appreciable at much higher blood lead concentrations.
9
10 • Effects of lead on the hepatic and gastrointestinal system. Studies of hepatic enzyme
11 levels in serum suggest that liver injury may be present in lead workers; however,
12 associations specifically with lead exposures are not evident. Studies of urinary
13 metabolites of the cytochrome P450 phenotypes, CYP2A6 and CYP3A4, suggest possible
14 associations between lead exposure and suppression of hepatic enzyme activity in adults
15 and children. Several studies observed an association between occupational lead exposure
16 and prevalence of symptoms of gastrointestinal colic. These hepatic and gastrointestinal
17 effects are largely observed only at high blood lead concentrations (>40 |ig/dL).
18
19 • Effects of lead on the endocrine system. Most studies have yielded no associations, or
20 weak associations, of lead exposure with thyroid hormone status and male reproductive
21 endocrine status in highly-exposed occupational populations. Children exposed to
22 relatively high levels of lead (blood lead >30 |ig/dL) exhibit depressed levels of circulating
23 1,25-dihydroxy vitamin D (1,25-OH-D). However, associations between serum vitamin D
24 status and blood lead were not evident in a study of calcium-replete children who had
25 average lifetime blood lead concentrations below 25 |ig/dL.
26
27 • Effects of lead on bone and teeth. The epidemiologic evidence is limited, but suggestive
28 of an association between lead exposure and bone toxicity. Some studies have found an
29 association between occupational exposure to lead and Paget's disease; but, it is difficult to
30 assess whether increased lead results from bone diseases or the bone disease is a result of
31 increased lead exposure. Increased risk of dental caries has been associated with lead
May 2006 6-327 DRAFT-DO NOT QUOTE OR CITE
-------
1 exposure in children and adults. Lead effects on caries were observed in populations with
2 mean blood lead levels were < 10 |ig/dL.
3
4 • Effects of lead on ocular health. Recent longitudinal studies provide evidence for
5 possible associations between lead exposure and adverse ocular health outcomes in low- to
6 moderately-exposed populations. In children whose mothers had blood lead levels of
7 10.5 to 32.5 |ig/dL in mid-pregnancy, an association was observed between lead exposure
8 and visual evoked retinal responses. Middle-aged males whose tibia bone lead levels were
9 31 to 126 |ig/g had increased risk of cataracts.
10
May 2006 6-328 DRAFT-DO NOT QUOTE OR CITE
-------
1 REFERENCES
2 Abbate, C.; Buceti, R.; Munao, F.; Giorgianni, C.; Ferreri, G. (1995) Neurotoxicity induced by lead levels:
3 an electrophysiological study. Int. Arch. Occup. Environ. Health 66: 389-392.
4 Adachi, J. D.; Arlen, D.; Webber, C. E.; Chettle, D. R.; Beaumont, L. F.; Gordon, C. L. (1998) Is there any
5 association between the presence of bone disease and cumulative exposure to lead? Calcif. Tissue Int.
6 63:429-432.
7 Ades, A. E.; Kazantzis, G. (1988) Lung cancer in a non-ferrous smelter: the role of cadmium. Br. J. Ind. Med.
8 45:435-442.
9 Agency for Toxic Substances and Disease Registry. (1993) Toxicological profile for cadmium. Atlanta, GA:
10 U.S. Department of Health & Human Services, Public Health Service; report no. ATSDR/TP-92/06.
11 Available from: NTIS, Springfield, VA; PB93-182418.
12 Agency for Toxic Substances and Disease Registry. (1995) Multisite lead and cadmium exposure study with
13 biological markers incorporated. Final report. Atlanta, GA: U.S. Department of Health and Human
14 Services.
15 Agency for Toxic Substances and Disease Registry. (1999) Toxicological profile for lead. Atlanta, GA: U.S.
16 Department of Health and Human Services, Public Health Service.
17 Agency for Toxic Substances and Disease Registry. (2005) Toxicological profile for lead [draft]. Atlanta, GA:
18 U.S. Department of Health and Human Services, Public Health Service. Available:
19 http://www.atsdr.cdc.gov/toxprofiles/tpl3.pdf [5 May, 2006].
20 Akaike, H. (1973) Information theory and an extension of the maximum likelihood principle. In: Petrov, B. N.;
21 Csaki, F., eds. 2nd International symposium on information theory; September 1971; Tsahkadsor, Armenia,
22 USSR. Budapest, Hungary: Akademiai Kiado; pp. 267-281.
23 Akesson, A.; Lundh, T.; Vahter, M; Bjellerup, P.; Lidfeldt, J.; Nerbrand, C.; Goran, S.; Stromberg, U.; Skerfving,
24 S. (2005) Tubular and glomerular kidney effects in Swedish women with low environmental cadmium
25 exposure. Environ. HealthPerspect. 113: 1627-1631.
26 Akesson, A. (2006) Personal communication [from Agneta Akesson to Virginia Weaver with attached GFR plots].
27 April 12.
28 Al-Ashban, R. M.; Aslam, M.; Shah, A. H. (2004) Kohl (surma): a toxic traditional eye cosmetic study in Saudi
29 Arabia. Public Health 118: 292-298.
30 Al-Hakkak, Z. S.; Hamamy, H. A.; Murad, A. M.; Hussain, A. F. (1986) Chromosome aberrations in workers at a
31 storage battery plant in Iraq. Mutat. Res. 171: 53-60.
32 Al-Neamy, F. R.; Almehdi, A. M.; Alwash, R.; Pasha, M. A. H.; Ibrahim, A.; Bener, A. (2001) Occupational lead
33 exposure and amino acid profiles and liver function tests in industrial workers. Int. J. Environ. Health Res.
34 11: 181-188.
35 Al-Saleh, L; Nester, M.; DeVol, E.; Shinwari, N.; Munchari, L.; Al-Shahria, S. (2001) Relationships between blood
36 lead concentrations, intelligence, and academic achievement of Saudi Arabian schoolgirls. Int. J. Hyg.
37 Environ. Health 204: 165-174.
38 Alessio, L.; Bertazzi, P. A.; Monelli, O.; Toffoletto, F. (1976) Free erythrocyte protoporphyrin as an indicator of the
3 9 biological effect of lead in adult males. III. Behavior of free erythrocyte protoporphyrin in workers with
40 past lead exposure. Int. Arch. Occup. Environ. Health 38: 77-86.
41 Alessio, L.; Castoldi, M. R.; Buratti, M.; Maroni, M.; Bertazzi, P. A. (1977) Behaviour of some indicators of
42 biological effect in female lead workers. Int. Arch. Occup. Environ. Health 40: 283-292.
43 Alexander, B. H.; Checkoway, H.; VanNetten, C.; Muller, C. H.; Ewers, T. G.; Kaufman, J. D.; Mueller, B. A.;
44 Vaughan, T. L.; Faustman, E. M. (1996a) Semen quality of men employed at a lead smelter. Occup.
45 Environ. Med. 53: 411-416.
46 Alexander, B. H.; Checkoway, H.; Van Netten, C.; Kaufman, J. D.; Vaughan, T. L.; Mueller, B. A.; Faustman, E. M.
47 (1996b) Paternal occupational lead exposure and pregnancy outcome. Int. J. Occup. Environ. Health
48 2:280-285.
49 Alexander, B. H.; Checkoway, H.; Faustman, E. M.; Van Netten C.; Muller, C. H.; Ewers, T. G. (1998) Contrasting
50 associations of blood and semen lead concentrations with semen quality among lead smelter workers.
51 Am. J. Ind. Med. 34: 464-469.
52 Alfven, T.; Jarup, L.; Blinder, C.-G. (2002) Cadmium and lead in blood in relation to low bone mineral density and
53 tubular proteinuria. Environ. Health Perspect. 110:699-702.
54 Alomran, A. H.; Shleamoon, M. N. (1988) The influence of chronic lead exposure on lymphocyte proliferative
55 response and immunoglobulin levels in storage battery workers. J. Biol. Sci. Res. 19: 575-585.
May 2006 6-329 DRAFT-DO NOT QUOTE OR CITE
-------
1 American Educational Research Association, American Psychological Association, National Council on
2 Measurement in Education. (1999) Standards for educational and psychological testing. Washington, DC:
3 American Psychological Association.
4 American Thoracic Society. (2000) What constitutes an adverse health effect of air pollution? Am. J. Respir. Crit.
5 Care Med. 161:665-673.
6 Anetor, J. I.; Adeniyi, F. A. A. (1998) Decreased immune status in Nigerian workers occupationally exposed to lead.
7 Mr. J. Med. Med. Sci. 28: 169-172.
8 Angell, N. F.; Lavery, J. P. (1982) The relationship of blood levels to obstetric outcome. Am. J. Obstet. Gynecol.
9 142:40-46.
10 Angle, C. B.; Kuntzelman, D. R. (1989) Increased erythrocyte protoporphyrins and blood lead; a pilot study of
11 childhood growth patterns. J. Toxicol. Environ. Health 26: 149-156.
12 Angle, C. R.; Mclntire, M. S. (1978) Low level lead and inhibition of erythrocyte pyrimidine nucleotidase. Environ.
13 Res. 17: 296-302.
14 Angle, C. R.; Mclntire, M. S.; Swanson, M. S.; Stohs, S. J. (1982) Erythrocyte nucleotides in children - increased
15 blood lead and cytidine triphosphate. Pediatr. Res. 16: 331-334.
16 Annesi-Maesano, I.; Pollitt, R.; King, G.; Bousquet, J.; Hellier, G.; Sahuquillo, J.; Huel, G. (2003) In utero exposure
17 to lead and cord blood total IgE. Is there a connection? Allergy 58: 589-594.
18 Anttila, A.; Heikkila, P.; Pukkala, E.; Nykyri, E.; Kauppinen, T.; Hernberg, S; Hemminki, K. (1995) Excess lung
19 cancer among workers exposed to lead. Scand. J. Work Environ. Health. 21: 460-469.
20 Anttila, A.; Heikkila, P.; Nykyri, E.; Kauppinen, T.; Pukkala, E.; Hernberg, S.; Hemminki, K. (1996) Risk of
21 nervous system cancer among workers exposed to lead. J. Occup. Environ. Med. 38: 131-136.
22 Apostoli, P.; Maranelli, G.; Dei Cas, L.; Micciolo, R. (1990) Blood lead and blood pressure: a cross sectional study
23 in a general population group. Cardiologia 3 5: 597-603.
24 Apostoli, P.; Kiss, P.; Porru, S.; Bonde, J. P.; Vanhoorne, M.; the ASCLEPIOS study group. (1998) Male
25 reproductive toxicity of lead in animals and humans. Occup. Environ. Med. 55: 364-374.
26 Apostoli, P.; Bellini, A.; Porru, S.; Bisanti, L. (2000) The effect of lead on male fertility: a time to pregnancy (TTP)
27 study. Am. J. Ind. Med. 38:310-315.
28 Armon, C.; Kurland, L. T.; Daube, J. R.; Obrien, P. C. (1991) Epidemiologic correlates of sporadic amyotrophic
29 lateral sclerosis. Neurology 41: 1077-1084.
30 Arnvig, E.; Grandjean, P.; Beckmann, J. (1980) Neurotoxic effects of heavy lead exposure determined with
31 psychological tests. Toxicol. Lett. 5: 399-404.
32 Aro, A. C. A.; Todd, A. C.; Amarasiriwardena, C.; Hu, H. (1994) Improvements in the calibration of 109Cd K x-ray
33 fluorescence systems for measuring bone lead in vivo. Phys. Med. Biol. 39: 2263-2271.
34 Assennato, G.; Paci, C.; Baser, M. E.; Molinini, R.; Candela, R. G.; Altamura, B. M.; Giorgino, R. (1986) Sperm
35 count suppression without endocrine dysfunction in lead-exposed men. Arch. Environ. Health 41: 387-390.
36 Assennato, G.; Baser, M.; Molinini, R.; Candela, R. G.; Altamura, B. M.; Giorgino, R.; Abbaticchio, G.; Paci, C.
37 (1987) Sperm count suppression without endocrine dysfunction in lead-exposed men. Arch. Environ.
38 Health 42: 124-127.
39 Astrin, K. H.; Bishop, D. F.; Wetmur, J. G.; Kaul, B.; Davidow, B.; Desnick, R. J. (1987) 5-aminolevulinic acid
40 dehydratase isozymes and lead toxicity. In: Silbergeld, E. K.; Fowler, B. A., eds. Mechanisms of chemical-
41 induced porphyrinopathies. New York, NY: New York Academy of Sciences; pp. 23-29. (Annals of the
42 New Yord Academy of Sciences: v. 514).
43 Audesirk, G.; Shugarts, D.; Nelson, G.; Przekwas, J. (1989) Organic and inorganic lead inhibit neurite growth in
44 vertebrate and invertebrate neurons in culture. In Vitro Cell Dev. Biol. 25: 1121-1128.
45 Auger, J.; Kunstmann, J. M.; Czyglik, F.; Jouannet, P. (1995) Decline in semen quality among fertile men in Paris
46 during the past 20 years. N. Engl. J. Med. 332: 281-285.
47 Austin, P. C.; Hoch, J. S. (2004) Estimating linear regression models in the presence of a censored independent
48 variable. Stat. Med. 23: 411-429.
49 Awad El Karim, M. A.; Hamed, A. S.; Elhaimi, Y. A.; Osman, Y. (1986) Effects of exposure to lead among lead-
50 acid battery factory workers in Sudan. Arch. Environ. Health 41: 261-265.
51 Axelson, O.; Steenland, K. (1988) Indirect methods of assessing the effects of tobacco use in occupational studies.
52 Am. J. Ind. Med. 13: 105-118.
53 Ayatollahi, M. (2002) Study of the impact of blood lead level on humoral immunity in humans. Toxicol. Ind. Health
54 18:39-44.
May 2006 6-330 DRAFT-DO NOT QUOTE OR CITE
-------
1 Azar, A.; Snee, R. D.; Habibi, K. (1975) An epidemiologic approach to community air lead exposure using personal
2 samplers. In: Griffin, T. B.; Knelson, J. H., eds. Lead. Stuttgart, Federal Republic of Germany: Georg
3 Thieme Publishers; pp. 254-290. (Coulston, F.; Korte, F., eds. Environmental quality and safety:
4 supplement v. 2).
5 Azcona-Cruz, M. I.; Rothenberg, S. J.; Schnaas-Arrieta, L.; Romero-Placeres, M; Perroni-Hernandez, E. (2000)
6 Niveles de plomo en sangre en ninos de 8 a 10 anos y su relation con la alteration en el sistema visomotor
7 y del equilibrio [Relationship of blood lead levels with visual-motor and equilibrium disturbances in
8 children aged 8 to 10 years]. Salud Publica Mex. 42: 279-287.
9 Bagci, C.; Bozkurt, A. L; Cakmak, E. A.; Can, S.; Cengiz, B. (2004) Blood lead levels of the battery and exhaust
10 workers and their pulmonary function tests. Int. J. Clin. Pract. 58: 568-572.
11 Baghurst, P. A.; McMichael, A. J.; Wigg, N. R.; Vimpani, G. V.; Robertson, E. F.; Roberts, R. J.; Tong, S.-L.
12 (1992) Environmental exposure to lead and children's intelligence at the age of seven years: the Port Pirie
13 cohort study. N. Engl. J. Med. 327: 1279-1284.
14 Baghurst, P. A.; McMichael, A. J.; Tong, S.; Wigg, N. R.; Vimpani, G. V.; Robertson, E. F. (1995) Exposure to
15 environmental lead and visual-motor integration at age 7 years: the Port Pirie cohort study. Epidemiology
16 6: 104-109.
17 Bairati, C.; Goi, G.; Bollini, D.; Roggi, C.; Luca, M.; Apostoli, P.; Lombardo, A. (1997) Effects of lead and
18 manganese on the release of lysosomal enzymes in vitro and in vivo. Clin. Chim. Acta 261: 91-101.
19 Baird, D. D.; Wilcox, A. J.; Weinberg, C. R. (1986) Use of time to pregnancy to study environmental exposures.
20 Am. J. Epidemiol. 124: 470-480.
21 Baker, E. L., Jr.; Landrigan, P. J.; Barbour, A. G.; Cox, D. H.; Folland, D. S.; Ligo, R. N.; Throckmorton, J. (1979)
22 Occupational lead poisoning in the United States: clinical and biochemical findings related to blood lead
23 levels. Br. J. Ind. Med. 36: 314-322.
24 Balbus, J. M.; Stewart, W.; Bolla, K. L; Schwartz, B. S. (1997) Simple visual reaction time in organolead
25 manufacturing workers: comparison of different methods of modeling lead exposure and reaction time.
26 Am. J. Ind. Med. 32: 544-549.
27 Balbus, J. M.; Stewart, W.; Bolla, K. L; Schwartz, B. S. (1998) Simple visual reaction time in organolead
28 manufacturing workers: influence of the interstimulus interval. Arch. Environ. Health 53: 264-270.
29 Balbus-Kornfeld, J. M.; Stewart, W.; Bolla, K. L; Schwartz, B. S. (1995) Cumulative exposure to inorganic lead and
30 neurobehavioural test performance in adults: an epidemiological review. Occup. Environ. Med. 52: 2-12.
31 Ball, G. V.; Sorensen, L. B. (1969) Pathogenesis of hyperuricemia in saturnine gout. N. Engl. J. Med.
32 280: 1199-1202.
33 Ballard, J. L.; Novak, K. K.; Driver, M. (1979) A simplified score for assessment of fetal maturation of newly born
34 infants. J. Pediatr. 95: 769-774.
35 Baloh, R. W.; Spivey, G. H.; Brown, C. P.; Morgan, D.; Campion, D. S.; Browdy, B. L.; Valentine, J. L. (1979)
36 Subclinical effects of chronic increased lead absorption - a prospective study. II. Results of baseline
37 neurologic testing. J. Occup. Med. 21: 490-496.
3 8 Barltrop, D. (1968) Lead poisoning in childhood. Postgrad. Med. J. 44: 537-542.
39 Barry, P. S. I. (1975) A comparison of concentrations of lead in human tissues. Br. J. Ind. Med. 32: 119-139.
40 Earth, A.; Schaffer, A. W.; Osterode, W.; Winker, R.; Konnaris, C.; Valic, E.; Wolf, C.; Rtidiger, H. W. (2002)
41 Reduced cognitive abilities in lead-exposed men. Int. Arch. Occup. Environ. Health 75: 394-398.
42 Basaran, N.; Undeger, U. (2000) Effects of lead on immune parameters in occupationally exposed workers. Am. J.
43 Ind. Med. 38: 349-354.
44 Basha, M. R.; Wei, W.; Bakheet, S. A.; Benitez, N.; Siddiqi, H. K.; Ge, Y.-W.; Lahiri, D. K.; Zawia, N. H. (2005)
45 The fetal basis of amyloidogenesis: exposure to lead and latent overexpresson of amyloid precursor protein
46 and p-amyloid in the aging brain. J. Neurosci. 25: 823-829.
47 Battistuzzi, G.; Petrucci, R.; Silvagni, L.; Urbani, F. R.; Caiola, S. (1981) 5-aminolevulinate dehydrase: a new
48 genetic polymorphism in man. Ann. Hum. Genet. 45: 233-229.
49 Batuman, V (1993) Lead nephropathy, gout, and hypertension. Am. J. Med. Sci. 305: 241-247.
50 Batuman, V; Maesaka, J. K.; Haddad, B.; Tepper, E.; Landry, E.; Wedeen, R. P. (1981) The role of lead in gout
51 nephropathy. N. Engl. J. Med. 304: 520-523.
52 Batuman, V.; Landy, E.; Maesaka, J. K.; Wedeen, R. P. (1983) Contribution of lead to hypertension with renal
53 impairment. N. Engl. J. Med. 309: 17-21.
54 Bauchinger, M.; Dresp, J.; Schmid, E.; Englert, N.; Krause, Chr. (1977) Chromosome analyses of children after
55 ecological lead exposure. Mutat. Res. 56: 75-80.
May 2006 6-331 DRAFT-DO NOT QUOTE OR CITE
-------
1 Begerow, I; Freier, I.; Turfeld, M; Kramer, U.; Dunemann, L. (1994) Internal lead and cadmium exposure in
2 6-year-old children from western and eastern Germany. Int. Arch. Occup. Environ. Health 66: 243-248.
3 Behringer, D.; Craswell, P.; Mohl, C.; Stoeppler, M.; Ritz, E. (1986) Urinary lead excretion in uremic patients.
4 Nephron 42: 323-329.
5 Bellinger, D. C. (1995) Interpreting the literature on lead and child development: the neglected role of the
6 "experimental system." Neurotoxicol. Teratol. 17: 201-212.
7 Bellinger, D. C. (2000) Effect modification in epidemiologic studies of low-level neurotoxicant exposures and
8 health outcomes. Neurotoxicol. Teratol. 22: 133-140.
9 Bellinger, D. (2002) Perspectives on incorporating human neurobehavioral end points in risk assessments.
10 Risk Anal. 22: 487-498.
11 Bellinger, D. C. (2003) Perspectives on incorporating human neurobehavioral end points in risk assessments.
12 Risk Anal. 23: 163-174.
13 Bellinger, D. C. (2004) Assessing environmental neurotoxicant exposures and child neurobehavior: confounded by
14 confounding? Epidemiology 15: 383-384.
15 Bellinger, D. C. (2005) Teratogen update: lead and pregnancy. Birth Defects Res. Part A 73: 409-420.
16 Bellinger, D. C.; Needleman, H. L. (2003) Intellectual impairment and blood lead levels [letter]. N. Engl. J. Med.
17 349:500.
18 Bellinger, D.; Rappaport, L. (2002) Developmental assessment and interventions. In: Managing elevated blood lead
19 levels among young children: recommendations from the Advisory Committee on Childhood Lead
20 Poisoning Prevention. Atlanta, GA: Centers for Disease Control; pp. 79-95.
21 Bellinger, D.; Needleman, H. L.; Bromfield, R.; Mintz, M. (1984) A followup study of the academic attainment and
22 classroom behavior of children with elevated dentine lead levels. Biol. Trace Elem. Res. 6: 207-223.
23 Bellinger, D.; Leviton, A.; Waternaux, C.; Allred, E. (1985) Methodological issues in modelling the relationship
24 between low-level lead exposure and infant development: examples from the Boston lead study. In:
25 Bornschein, R. L.; Rabinowitz, M. B., eds. The second international conference on prospective studies of
26 lead; April 1984; Cincinnati, OH. Environ. Res. 38: 119-129.
27 Bellinger, D.; Leviton, A.; Needleman, H. L.; Waternaux, C.; Rabinowitz, M. (1986) Low-level lead exposure and
28 infant development in the first year. Neurobehav. Toxicol. Teratol. 8: 151-161.
29 Bellinger, D.; Leviton, A.; Waternaux, C.; Needleman, H.; Rabinowitz, M. (1987) Longitudinal analyses of prenatal
30 and postnatal lead exposure and early cognitive development. N. Engl. J. Med. 316: 1037-1043.
31 Bellinger, D.; Leviton, A.; Waternaux, C.; Needleman, H.; Rabinowitz, M. (1988) Low-level lead exposure, social
32 class, and infant development. Neurotoxicol. Teratol. 10: 497-503.
33 Bellinger, D.; Leviton, A.; Waternaux, C. (1989) Lead, IQ and social class. Int. J. Epidemiol. 18: 180-185.
34 Bellinger, D.; Leviton, A.; Sloman, J. (1990) Antecedents and correlates of improved cognitive performance in
35 children exposed in utero to low levels of lead. Environ. Health Perspect. 89: 5-11.
36 Bellinger, D.; Leviton, A.; Rabinowitz, M.; Allred, E.; Needleman, H.; Schoenbaum, S. (1991) Weight gain and
37 maturity in fetuses exposed to low levels of lead. Environ. Res. 54: 151-158.
38 Bellinger, D. C.; Stiles, K. M.; Needleman, H. L. (1992) Low-level lead exposure, intelligence and academic
39 achievement: a long-term follow-up study. Pediatrics 90: 855-861.
40 Bellinger, D.; Hu, H.; Titlebaum, L.; Needleman, H. L. (1994a) Attentional correlates of dentin and bone lead levels
41 in adolescents. Arch. Environ. Health 49: 98-105.
42 Bellinger, D.; Leviton, A.; Allred, E.; Rabinowitz, M. (1994b) Pre- and postnatal lead exposure and behavior
43 problems in school-aged children. Environ. Res. 66: 12-30.
44 Bellinger, D. C.; Hu, H.; Kalaniti, K.; Thomas, N.; Rajan, P.; Sambandam, S.; Ramaswamy, P.; Balakrishnan, K.
45 (2005) A pilot study of blood lead levels and neurobehavioral function in children living in Chennai, India.
46 Int. J. Occup. Environ. Health 11: 138-143.
47 Benetou-Marantidou, A.; Nakou, S.; Micheloyannis, J. (1988) Neurobehavioral estimation of children with life-long
48 increased lead exposure. Arch. Environ. Health 43: 392-395.
49 Benoff, S.; Hurley, I. R.; Millan, C.; Napolitano, B.; Centola, G. M. (2003a) Seminal lead concentrations negatively
50 affect outcomes of artificial insemination. Fertil. Steril. 80: 517-525.
51 Benoff, S.; Centola, G. M. (2003b) Increased seminal plasma lead levels adversely affect the fertility potential of
52 sperm in IVF. Hum. Reprod. 18: 374-383.
53 Bercovitz, K.; Laufer, D. (1991) Age and gender influence on lead accumulation in root dentine of human
54 permanent teeth. Arch. Oral Biol. 36: 671-673.
May 2006 6-332 DRAFT-DO NOT QUOTE OR CITE
-------
1 Bergdahl, I. A.; Gerhardsson, L.; Schtitz, A.; Desnick, R. I; Wetmur, J. G.; SkerfVing, S. (1997) Delta-
2 aminolevulinic acid dehydratase polymorphism: influence on lead levels and kidney function in humans.
3 Arch. Environ. Health 52: 91-96.
4 Bergeret, A.; Pouget, E.; Tedone, R.; Meygert, T.; Cadot, R.; Descotes, J. (1990) Neutrophil functions in lead-
5 exposed workers. Hum. Exp. Toxicol. 9: 231-233.
6 Bernard, A. (2004) Renal dysfunction induced by cadmium: biomarkers of critical effects. Biometals 17: 519-523.
7 Bernard, A.; Thielemans, N.; Roels, H.; Lauwerys, R. (1995a) Association between NAG-B and cadmium in urine
8 with no evidence of a threshold. Occup. Environ. Med. 52: 177-180.
9 Bernard, A. M; Vyskocil, A.; Roels, H.; Kriz, J.; Kodl, M; Lauwerys, R. (1995b) Renal effects in children living in
10 the vicinity of a lead smelter. Environ. Res. 68: 91-95.
11 Bhattacharya, A.; Shukla, R.; Dietrich, K.; Bornschein, R.; Berger, O. (1995) Effect of early lead exposure on
12 children's postural balance. Dev. Med. Child Neurol. 37: 861-878.
13 Billick, I. H.; Curran, A. S.; Shier, D. R. (1979) Analysis of pediatric blood lead levels in New York City for
14 1970-1976. Environ. Health Perspect. 31: 183-190.
15 Bleecker, M.; Bolla-Wilson, K.; Kawas, C.; Agnew, J. (1988) Age-specific norms for the mini-mental state exam.
16 Neurology 38: 1565-1568.
17 Bleecker, M. L.; Lindgren, K. N.; Ford, D. P. (1997a) Differential contribution of current and cumulative indices of
18 lead dose to neuropsychological performance by age. Neurology 48: 639-645.
19 Bleecker, M. L.; Lindgren, K. N.; Tiburzi, M. J.; Ford, D. P. (1997b) Curvilinear relationship between blood lead
20 level and reaction time. Differential association with blood lead fractions derived from exogenous and
21 endogenous sources. J. Occup. Environ. Med. 39: 426-431.
22 Bleecker, M. L.; Lindgren, K. N.; Ford, D. P.; Tiburzi, M. J. (2002) The interaction of education and cumulative
23 lead exposure on the mini-mental state examination. J. Occup. Environ. Med. 44: 574-578.
24 Bleecker, M. L.; Ford, D. P.; Lindgren, K. N.; Scheetz, K.; Tiburzi, M. J. (2003) Association of chronic and current
25 measures of lead exposure with different components of brainstem auditory evoked potentials.
26 Neurotoxicology 24: 625-631.
27 Bleecker, M. L.; Ford, D. P.; Lindgren, K. N.; Hoese, V. M.; Walsh, K. S.; Vaughan, C. G. (2005a) Differential
28 effects of lead exposure on components of verbal memory. Occup. Environ. Med. 62: 181-187.
29 Bleecker, M. L.; Ford, D. P.; Baughan, C. G.; Lindgren, K. N.; Tiburzi, M. J.; Walsh, K. S. (2005b) Effect of lead
30 exposure and ergonomic stressors on peripheral nerve function. Environ. Health Perspect. 113: 1730-1734.
31 Boey, K. W.; Jeyaratnam, J. (1988) A discriminant analysis of neuropsychological effect of low lead exposure.
32 Toxicology 49: 309-314.
33 Bogden, J. D.; Thind, I. S.; Louria, D. B.; Caterini, H. (1978) Maternal and cord blood metal concentrations and low
34 birth weight—a case-control study. Am. J. Clin. Nutr. 31: 1181 -1187.
35 Bolla, K. I.; Schwartz, B. S.; Stewart, W.; Rignani, J.; Agnew, J.; Ford, D. P. (1995) Comparison of neurobehavioral
3 6 function in workers exposed to a mixture of organic and inorganic lead and in workers exposed to solvents.
37 Am. J. Ind. Med. 27: 231-246.
38 Bonde, J. P. E.; Kolstad, H. (1997) Fertility of Danish battery workers exposed to lead. Int. J. Epidemiol.
39 26: 1281-1288.
40 Bonde, J. P.; Joffe, M.; Apostoli, P.; Dale, A. Kiss, P.; Spano, M.; Caruso, F.; Giwercman, A.; Bisanti, L.; Porru, S.;
41 Vanhoorne, M.; Comhaire, F.; Zschiesche, W. (2002) Sperm count and chromatin structure in men exposed
42 to inorganic lead: lowest adverse effect levels. Occup. Environ. Med. 59: 243-242.
43 Borja-Aburto, V. H.; Hertz-Picciotto, I.; Lopez, M. R.; Farias, P.; Rios, C.; Blanco, J. (1999) Blood lead levels
44 measured prospectively and risk of spontaneous abortion. Am. J. Epidemiol. 150: 590-597.
45 Bornschein, R. L.; Rabinowitz, M. B. (1985) The second international conference on prospective studies of lead -
46 foreword. Environ. Res. 38: 1-2.
47 Bornschein, R. L.; Grote, J.; Mitchell, T., Succop. P. A.; Dietrich, K. N.; Krafft, K. M.; Hammond, P. B. (1989)
48 Effects of prenatal lead exposure on infant size at birth. In: Smith, M. A.; Grant, L. D.; Sors, A. I., eds.
49 Lead exposure and child development: an international assessment [workshop organized by the
50 Commission of the European Communities and the U.S. Environmental Protection Agency]; September
51 1986; Edinburgh, United Kingdom. Dordrecht, The Netherlands: Kluwer Academic Publishers BV;
52 pp. 307-319.
53 Bost, L.; Primatesta, P.; Dong, W.; Poulter, N. (1999) Blood lead and blood pressure: evidence from the Health
54 Survey for England 1995. J. Hum. Hypertens. 13: 123-128.
55 Bound, J. P.; Harvey, P. W.; Francis, B. J.; Awwad, F.; Gatrell, A. C. (1997) Involvement of deprivation and
56 environmental lead in neural tube defects: a matched case-control study. Arch. Dis. Child. 76: 107-112.
May 2006 6-333 DRAFT-DO NOT QUOTE OR CITE
-------
1 Bowers, T. S.; Beck, B. D. (2006) What is the meaning of non-linear dose-response relations between blood lead
2 concentrations and IQ? Neurotoxicology: in press.
3 Bradman, A.; Eskenazi, B.; Sutton, P.; Athanasoulis, M; Goldman, L. R. (2001) Iron deficiency associated with
4 higher blood lead in children living in contaminated environments. Environ. Health Perspect.
5 109: 1079-1084.
6 Bratton, G. R.; Hiney, J. K.; Dees, W. L. (1994) Lead (Pb) alters the norepinephrine-induced secretion of luteinizing
7 hormone releasing hormone from the medium eminence of adult male rats in vitro. Life Sci. 55: 563-571.
8 Braun, C. M. J.; Daigneault, S. (1991) Sparing of cognitive executive functions and impairment of motor functions
9 after industrial exposure to lead: a field study with control group. Neuropsychology 5: 179-193.
10 Braunstein, G. D.; Dahlgren, J.; Loriaux, D. L. (1978) Hypogonadism in chronically lead-poisoned men. Infertility
11 1:33-51.
12 Brito, J. A. A.; McNeill, F. E.; Stronach, I.; Webber, C. E.; Wells, S.; Richard, N.; Chettle, D. R. (2001)
13 Longitudinal changes in bone lead concentration: implications for modelling of human bone lead
14 metabolism. J. Environ. Monit. 3: 343-351.
15 Brito, J. A. A.; McNeill, F. E.; Webber, C. E.; Wells, S.; Richard, N.; Carvalho, M. L.; Chettle, D. R. (2002)
16 Evaluation of a novel structural model to describe the endogenous release of lead from bone. J. Environ.
17 Monit. 4: 194-201.
18 Brockhaus, A.; Collet, W.; Dolgner, R.; Engelke, R.; Ewers, U.; Freier, I.; Jermann, E.; Kramer, U.; Manojlovic, N.;
19 Turfeld, M.; Winneke, G. (1988) Exposure to lead and cadmium of children living in different areas of
20 north-west Germany: results of biological monitoring studies 1982-1986. Int. Arch. Occup. Environ. Health
21 60:211-222.
22 Brody, D. J.; Pirkle, J. L.; Kramer, R. A.; Flegal, K. M.; Matte, T. D.; Gunter, E. W.; Paschal, D. C. (1994) Blood
23 lead levels in the US population: phase 1 of the third National Health and Nutrition Examination Survey
24 (NHANES III, 1988 to 1991). JAMA J. Am. Med. Assoc. 272: 277-283.
25 Brown, A.; Tompsett, S. L. (1945) Poisoning due to mobilization of lead from the skeleton by leukaemic
26 hyperplasia of bone marrow. Br. Med. J. 2: 764-765.
27 Brown, M. J.; Hu, H.; Gonzales-Cossio, T.; Peterson, K. E.; Sanin, L.-H.; de Luz Kageyama, M.; Palazuelos, E.;
28 Aro, A.; Schnaas, L.; Hernandez-Avila, M. (2000) Determinants of bone and blood lead concentrations in
29 the early postpartum period. Occup. Environ. Med. 57: 535-541.
30 Buchet, J. P.; Lauwerys, R.; Roels, H.; Bernard, A.; Bruaux, P.; Claeys, F.; Ducoffre, G.; De Plaen, P.; Staesen, J.;
31 Amery, A.; Linjen, P.; Thijs, L.; Rondia, D.; Sartor, F.; Saint Remy, A.; Nick, L. (1990) Renal effects of
32 cadmium body burden of the general population. Lancet 336: 699-702.
33 Burns, J. M.; Baghurst, P. A.; Sawyer, M. G.; McMichael, A. J.; Tong, S.-L. (1999) Lifetime low-level exposure to
34 environmental lead and children's emotional and behavioral development at ages 11-13 years. The Port
35 Pirie cohort study. Am. J. Epidemiol. 149: 740-749.
36 Cake, K. M.; Bowins, R. J.; Vaillancourt, C.; Gordon, C. L.; McNutt, N. H.; Laporte, R.; Webber, C. E.; Chettle,
37 D. R. (1996) Partition of circulating lead between serum and red cells is different for internal and external
3 8 sources of lead. Am. J. Ind. Med. 29: 440-445.
39 Calabrese, E. J.; Baldwin, L. A. (2001) The frequency of U-shaped dose responses in the toxicological literature.
40 Toxicol. Sci. 62: 330-338.
41 Campara, P.; D'Andrea, F.; Micciolo, R.; Savonitto, C.; Tansella, M.; Zimmermann-Tansella, C. (1984)
42 Psychological performance of workers with blood-lead concentration below the current threshold limit
43 value. Int. Arch. Occup. Environ. Health 53: 233-246.
44 Campbell, J. R.; Toribara, T. Y. (2001) Hair-root lead to screen for lead toxicity. J. Trace Elem. Exp. Med.
45 14:69-72.
46 Campbell, B. C.; Meredith, P. A.; Scott, J. J. C. (1985) Lead exposure and changes in the renin-angiotensin-
47 aldosterone system in man. Toxicol. Lett. 25: 25-32.
48 Campbell, J. R.; Moss, M. E.; Raubertas, R. F. (2000) The association between caries and childhood lead exposure.
49 Environ. Health Perspect. 108: 1099-1102.
50 Canfield, R. L.; Henderson, C. R., Jr.; Cory-Slechta, D. A.; Cox, C.; Jusko, T. A.; Lanphear, B. P. (2003a)
51 Intellectual impairment in children with blood lead concentrations below 10 ug per deciliter. N. Engl.
52 J. Med. 348: 1517-1526.
53 Canfield, R. L.; Kreher, D. A.; Cornwell, C.; Henderson, C. R., Jr. (2003b) Low-level lead exposure, executive
54 functioning, and learning in early childhood. Child Neuropsychol. 9: 35-53.
55 Canfield, R. L.; Gendle, M. H.; Cory-Slechta, D. A. (2004) Impaired neuropsychological functioning in lead-
56 exposed children. Dev. Neuropsychol. 26: 513-540.
May 2006 6-334 DRAFT-DO NOT QUOTE OR CITE
-------
1 Cantarow, A.; Trumper, M. (1944) Lead poisoning. Baltimore, MD: Williams & Wilkins Co.
2 Cardenas, A.; Roels, H.; Bernard, A. M.; Barbon, R.; Buchet, J. P.; Lauwerys, R. R.; Rosello, J.; Ramis, I.; Mutti,
3 A.; Franchini, I.; Pels, L. M.; Stolte, H.; De Broe, M. E.; Nuyts, G. D.; Taylor, S. A.; Price, R. G. (1993)
4 Markers of early renal changes induced by industrial pollutants. II. Application to workers exposed to lead.
5 Br. J. Ind. Med. 50: 28-36.
6 Cardozo dos Santos, A.; Colacciopo, S.; B6, C. M. R. dal; Santos, N. A. G. dos. (1994) Occupational exposure to
7 lead, kidney function tests, and blood pressure. Am. J. Ind. Med. 26: 635-643.
8 Carta, P.; Cocco, P.; Picchiri, G. (1994) Lung cancer mortality and airways obstruction among metal miners exposed
9 to silica and low levels of radon daughters. Am. J. Ind. Med. 25: 489-506.
10 Carta, P.; Am, G.; Cadeddu, C.; Nieddu, V.; Polizzi, M.; Nurchis, P.; Flore, C.; Salis, S.; Randaccio, F. S. (2003)
11 Mortalita per cancro polmonare in lavoratori di una fonderia di piombo della Sardegna [Follow-up:
12 1972-2001] [Lung cancer mortality among workers of a Sardinian lead smelter]. G. Ital. Med. Lav. Ergon.
13 25(suppl. 3): 17-18.
14 Carta, P.; Am, G.; Nurchis, P.; Cadeddu, C.; Polizzi, M.; Nieddu, V.; Salis, G.; Gaviano, L.; Flore, C.; Randaccio,
15 F. S. (2005) Studio di mortalita per cause specifiche in lavoratori di una fonderia di piombo e zinco della
16 Sardegna. G. Ital. Med. Lav. Ergon. 27(suppl. 1): 43-45.
17 Casey, C. E.; Robinson, M. F. (1978) Copper, manganese, zinc, nickel, cadmium and lead in human foetal tissue.
18 Br. J. Nutr. 39: 639-646.
19 Cavalleri, A.; Trimarchi, F.; Gelmi, C.; Baruffini, A.; Minoia, C.; Biscaldi, G.; Gallo, G. (1982) Effects of lead on
20 the visual system of occupationally exposed subjects. Scand. J. Work Environ. Health 8(suppl. 1): 148-151.
21 Cecil, K. M.; Yuan, W.; Holland, S.; Wessel, S.; Dietrich, K.; Ris, D.; Lanphear, B. (2005) The influence of
22 childhood lead exposure on language function in young adults: an fMRI study. Presented at: International
23 Society for Magnetic Resonance Imaging: 12th scientific meeting and exhibition; May; Miami, FL; A1443.
24 Centers for Disease Control and Prevention. (1991) Preventing lead poisoning in young children: a statement by the
25 Centers for Disease Control. Atlanta, GA: U.S. Department of Health and Human Services; October.
26 Centers for Disease Control and Prevention. (1993) Lead poisoning associated with use of traditional ethnic
27 remedies. Morb. Mortal. Wkly. Rep. 42: 521-524.
28 Centers for Disease Control and Prevention. (1995) Blood lead levels among children — Rhode Island, 1993-1995.
29 Morb. Mortal. Wkly. Rpt. MMWR 44: 788-791.
30 Centers for Disease Control and Prevention. (1995) Blood lead levels among children in a managed-care
31 organization — California, October 1992-March 1993. Morb. Mortal. Wkly. Rep. 44: 627-635.
32 Centers for Disease Control and Prevention. (1997) Adult blood lead epidemiology and surveillance - United States,
33 third quarter, 1996. Morb. Mortal. Wkly Rpt. MMWR 46: 105-107.
34 Centers for Disease Control and Prevention. (1997) Blood lead levels - United States, 1991-1994. Morb. Mortal.
35 Wkly. Rep. MMWR 46: 141-146.
3 6 Centers for Disease Control and Prevention. (2000) Blood lead levels in young children — United States and
37 selected states, 1996-1999. Morb. Mortal. Wkly. Rep. 49: 1133-1137.
3 8 Centers for Disease Control and Prevention. (2005) Third national report on human exposure to environmental
39 chemicals. Atlanta, GA: U.S. Department of Health and Human Services, National Center for
40 Environmental Health. NCEH Pub. No. 05-0570.
41 Chalkley, S. R.; Richmond, I; Barltrop,D. (1998) Measurement of vitamin D3 metabolites in smelter workers
42 exposed to lead and cadmium. Occup. Environ. Med. 55: 446-452.
43 Chamberlain, A. C.; Heard, M. J.; Little, P.; Newton, D.; Wells, A. C.; Wiffin, R. D. (1978) Investigations into lead
44 from motor vehicles. Harwell, United Kingdom: United Kingdom Atomic Energy Authority; report no.
45 AERE-R9198.
46 Chancellor, A. M.; Slattery, J. M.; Fraser, H.; Warlow, C. P. (1993) Risk factors for motor neuron disease: a case-
47 control study based on patients from the Scottish Motor Neuron Disease Register. J. Neurol. Neurosurg.
48 Psychiatry 56: 1200-1206.
49 Chaube, S.; Swinyard, C. A.; Nishimura, H. (1972) A quantitative study of human embryonic and fetal lead with
50 considerations of maternal fetal lead gradients and the effect of lead on human reproduction. Teratology
51 5:253.
52 Chen, A.; Dietrich, K. N.; Ware, J. H.; Radcliffe, J.; Rogan, W. J. (2005) IQ and blood lead from 2 to 7 years of age:
53 are the effects in older children the residual of high blood lead concentrations in 2-year-olds? Environ.
54 HealthPerspect. 113: 597-601.
55 Chen, A.; Rhoads, G. G.; Cai, B.; Salganik, M.; Rogan, W. J. (2006) The effect of chelation on blood pressure in
56 lead-exposed children: a randomized study. Environ. Health Perspect. 114: 579-583.
May 2006 6-335 DRAFT-DO NOT QUOTE OR CITE
-------
1 Cheng, Y.; Schwartz, I; Vokonas, P. S.; Weiss, S. T.; Aro, A.; Hu, H. (1998) Electrocardiographic conduction
2 disturbances in association with low-level lead exposure (the Normative Aging Study). Am. J. Cardiol.
3 82: 594-599.
4 Cheng, Y.; Schwartz, J.; Sparrow, D.; Aro, A.; Weiss, S. T.; Hu, H. (2001) Bone lead and blood lead levels in
5 relation to baseline blood pressure and the prospective development of hypertension: the Normative Aging
6 Study. Am. J. Epidemiol. 153: 164-171.
7 Chia, S. E.; Chua, L. H.; Ng, T. P.; Foo, S. C.; Jeyaratnam, J. (1994a) Postural stability of workers exposed to lead.
8 Occup. Environ. Med. 51:768-771.
9 Chia, K. S.; Mutti, A.; Tan, C.; Ong, H. Y.; Jeyaratnam, J.; Ong, C. N.; Lee, E. (1994b) Urinary N-acetyl-(3-D-
10 glucosaminidase activity in workers exposed to inorganic lead. Occup. Environ. Med. 51: 125-129.
11 Chia, K. S.; Mutti, A.; Alinovi, R.; Jeyaratnam, J.; Tan, C.; Ong, C. N.; Lee, E. (1994c) Urinary excretion of tubular
12 brush-border antigens among lead exposed workers. Ann. Acad. Med. Singapore 23: 655-659.
13 Chia, K. S.; Jeyaratnam, J.; Tan, C.; Ong, H. Y.; Ong, C. N.; Lee, E. (1995a) Glomerular function of lead-exposed
14 workers. Toxicol. Lett. 77: 319-328.
15 Chia, K. S.; Jeyaratnam, J.; Lee, J.; Tan, C.; Ong, H. Y.; Ong, C. N.; Lee, E. (1995b) Lead-induced nephropathy:
16 relationship between various biological exposure indices and early markers of nephrotoxicity. Am. J. Ind.
17 Med. 27: 883-895.
18 Chia, S. E.; Chia, H. P.; Ong, C. N.; Jeyaratnam, J. (1996a) Cumulative blood lead levels and nerve conduction
19 parameters. Occup. Med. 46: 59-64.
20 Chia, S. E.; Chia, H. P.; Ong, C. N.; Jeyaratnam, J. (1996b) Cumulative concentrations of blood lead and postural
21 stability. Occup. Environ. Med. 53: 264-268.
22 Chia, S.-E.; Chia, K.-S; Chia, H.-P.; Ong, C.-N.; Jeyaratnam, J. (1996c) Three-year follow-up of serial nerve
23 conduction among lead-exposed workers. Scand. J. Work Environ. Health 22: 374-380.
24 Chia, S.-E.; Chia, H.-P.; Ong, C.-N.; Jeyaratnam, J. (1997) Cumulative blood lead levels and neurobehavioral test
25 performance. Neurotoxicology 18: 793-803.
26 Chia, S. E.; Yap, E.; Chia, K. S. (2004) 5-aminolevulinic acid dehydratase (ALAD) polymorphism and susceptibility
27 of workers exposed to inorganic lead and its effects on neurobehavioral functions. Neurotoxicology
28 25: 1041-1047.
29 Chia, S. E.; Zhou, H.; Tham, M. T.; Yap, E.; Dong, N. V.; Tu, N. H.; Chia, K. S. (2005) Possible influence of
3 0 5-aminolevulinic acid dehydratase polymorphism and susceptibility to renal toxicity of lead: a study of a
31 Vietnamese population. Environ. Health Perspect. 113: 1313-1317.
32 Chia, S.-E.; Zhou, H. J.; Yap, E.; Tham, M. T.; Dong, N.-V.; Hong Tu, N. T.; Chia, K.-S. (2006) Association of
33 renal function and 5-aminolevulinic acid dehydratase polymorphism among Vietnamese and Singapore
34 workers exposed to inorganic lead. Occup. Environ. Med. 63: 180-186.
35 Chiodo, L. M.; Jacobson, S. W.; Jacobson, J. L. (2004) Neurodevelopmental effects of postnatal lead exposure at
36 very low levels. Neurotoxicol. Teratol. 26: 359-371.
37 Chisolm, J. J., Jr.; Mellits, E. D.; Barrett, M. B. (1976) Interrelationships among blood lead concentration,
3 8 quantitative daily ALA-U and urinary lead output following calcium EDTA. In: Nordberg, G. F., ed.
3 9 Proceedings of third meeting of the subcommittee on the toxicology of metals under the Permanent
40 Commission and International Association on Occupational Health; November 1974; Toyko, Japan.
41 Amsterdam, The Netherlands: Elsevier Publishing Co.; pp. 416-433.
42 Chobanian, A. V; Bakris, G. L.; Black, H. R.; Cushman, W. C.; Green, L. A.; Izzo, J. L., Jr.; Jones, D. W.;
43 Materson, B. J.; Oparil, S.; Wright, J. T., Jr.; Roccella, E. J.; Joint National Committee on Prevention,
44 Detection, Evaluation, and Treatment of High Blood Pressure Institute; National High Blood Pressure
45 Education Program Coordinating Committee. (2003) Seventh report of the Joint National Committee on
46 Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Hypertension 42: 1206-1252.
47 Chowdhury, A. R.; Rao, R. V.; Gautam, A. K. (1986) Histochemical changes in the testes of lead induced
48 experimental rats. Folia Histochem. Cytobiol. 24: 233-237.
49 Christoffersson, J. O.; Schtitz, A.; Ahlgren, L.; Haeger-Aronsen, B.; Mattsson, S.; Skerfving, S. (1984) Lead in
50 finger-bone analysed in vivo in active and retired lead workers. Am. J. Ind. Med. 6: 447-457.
51 Christoffersson, J. O.; Ahlgren, L.; Schwartz, A.; Skerfving, S.; Mattsson, S. (1986) Decrease of skeletal lead levels
52 in man after end of occupational exposure. Arch. Environ. Health41: 312-318.
53 Chu, N.-F.; Liou, S.-H.; Wu, T.-N.; Chang, P.-Y. (1999) Reappraisal of the relation between blood lead
54 concentration and blood pressure among the general population in Taiwan. Occup. Environ. Med.
55 56:30-33.
May 2006 6-336 DRAFT-DO NOT QUOTE OR CITE
-------
1 Chuang, H.-Y.; Schwartz, J.; Tsai, S.-Y.; Lee, M.-L. T.; Wang, J.-D.; Hu, H. (2000) Vibration perception thresholds
2 in workers with long term exposure to lead. Occup. Environ. Med. 57: 588-594.
3 Chuang, H. Y.; Schwartz, J.; Gonzales-Cossio, T.; Lugo, M. C.; Palazuelos, E.; Aro, A.; Hu, H.; Hernandez-Avila,
4 M. (2001) Interrelations of lead levels in bone, venous blood, and umbilical cord blood with exogenous
5 lead exposure through maternal plasma lead in peripartum women. Environ. Health Perspect. 109: 527-532.
6 Chuang, H.-Y.; Yu, K.-T.; Ho, C.-K.; Wu, M.-T.; Lin, G.-T.; Wu, T.-N. (2004) Investigations of vitamin D receptor
7 polymorphism affecting workers' susceptibility to lead. J. Occup. Health 46: 316-322.
8 Chuang, H.-Y.; Chao, K.-Y.; Tsai, S.-Y. (2005) Reversible neurobehavioral performance with reductions in blood
9 lead levels-a prospective study on lead workers. Neurotoxicol. Teratol. 27: 497-504.
10 Clark, A. R. L. (1977) Placental transfer of lead and its effects on the newborn. Postgrad. Med. J. 53: 674-678.
11 Clark, C. S.; Bornschein, R. L.; Succop, P.; Que Hee, S. S.; Hammond, P. B.; Peace, B. (1985) Condition and type
12 of housing as an indicator of potential environmental lead exposure and pediatric blood lead levels.
13 Environ. Res. 38: 46-53.
14 Cocco, P. L.; Carta, P.; Belli, S.; Picchiri, G. F.; Flore, M. V. (1994a) Mortality of Sardinian lead and zinc miners:
15 1960-88. Occup. Environ. Med. 51: 674-682.
16 Cocco, P. L.; Carta, P.; Flore, V.; Picchiri, G. F.; Zucca, C. (1994b) Lung cancer mortality among female mine
17 workers exposed to silica. J. Occup. Med. 36: 894-898.
18 Cocco, P.; Salis, S.; Anni, M.; Cocco, M. E.; Flore, C.; Ibba, A. (1995) Effects of short-term occupational exposure
19 to lead on erythrocyte glucose-6-phosphate dehydrogenase activity and serum cholesterol. J. Appl. Toxicol.
20 15:375-378.
21 Cocco, P.; Carta, P.; Flore, C.; Congia, P.; Manca, M. B.; Saba, G.; Salis, S. (1996) Mortality of lead smelter
22 workers with the glucose-6-phosphate dehydrogenase-deficient phenotype. Cancer Epidemiol. Biomarkers
23 Prev. 5: 223-225.
24 Cocco, P.; Hua, F.; Boffetta, P.; Carta, P.; Flore, C.; Flore, V.; Onnis, A.; Picchiri, G. F.; Colin, D. (1997) Mortality
25 of Italian lead smelter workers. Scand. J. Work Environ. Health 23: 15-23.
26 Cocco, P.; Dosemeci, M.; Heineman, E. F. (1998a) Brain cancer and occupational exposure to lead. J. Occup.
27 Environ. Med. 40: 937-942.
28 Cocco, P.; Dosemeci, M.; Heineman, E. F. (1998b) Occupational risk factors for cancer of the central nervous
29 system: A case-control study of death certificates from 24 U.S. States. Am. J. Ind. Med. 33: 247-255.
30 Cocco, P.; Ward, M. H.; Dosemeci, M. (1999) Risk of stomach cancer associated with 12 workplace hazards:
31 Analysis of death certificates from 24 states of the United States with the aid of job exposure matrices.
32 Occup. Environ. Med. 56: 781-787.
33 Cockcroft, D. W.; Gault, M. H. (1976) Prediction of creatinine clearance from serum creatinine. Nephron6: 31-41.
34 Cohen, N.; Modai, D.; Golik, A.; Weissgarten, J.; Peller, S.; Katz, A.; Averbukh, Z.; Shaked, U. (1989) Increased
3 5 concanavalin A-induced suppressor cell activity in humans with occupational lead exposure. Environ. Res.
36 48: 1-6.
37 Colleoni, N.; D'Amico, G. (1986) Chronic lead accumulation as a possible cause of renal failure in gouty patients.
38 Nephron 44: 32-35.
39 Colleoni, N.; Arrigo, G.; Gandini, E.; Corigliano, C.; D'Amico, G. (1993) Blood lead in hemodialysis patients.
40 Am. J. Nephrol. 13: 198-202.
41 Constantine, N. A.; Kraemer, H. C.; Kendall-Tackett, K. A.; Bennett, F. C.; Tyson, J. E.; Gross, R. T. (1987) Use of
42 physical and neurologic observations in assessment of gestational age in low birth weight infants. J.
43 Pediatr. (St. Louis, MO, U.S.) 110: 921-928.
44 Cooney, G. H.; Bell, A.; McBride, W.; Carter, C. (1989a) Neurobehavioural consequences of prenatal low level
45 exposures to lead. Neurotoxicol. Teratol. 11: 95-104.
46 Cooney, G. H.; Bell, A.; McBride, W.; Carter, C. (1989b) Low-level exposures to lead: the Sydney lead study.
47 Dev. Med. Child Neurol. 31: 640-649.
48 Cooney, G.; Bell, A.; Stavrou, C. (1991) Low level exposures to lead and neurobehavioural development: the
49 Sydney study at seven years. In: Farmer, J. G., ed. International conference: heavy metals in the
50 environment, v. 1; September; Edinburgh, United Kingdom. Edinburgh, United Kingdom: CEP
51 Consultants, Ltd.; pp. 16-19.
52 Cooper, W. C. (1988) Deaths from chronic renal disease in U. S. battery and lead production workers. In: Victery,
53 W., ed. Symposium on lead-blood pressure relationships; April 1987; Chapel Hill, NC. Environ. Health
54 Perspect. 78: 61-63.
May 2006 6-337 DRAFT-DO NOT QUOTE OR CITE
-------
1 Cooper, W. C.; Gaffey, W. R. (1975) Mortality of lead workers. In: Cole, J. F., ed. Proceedings of the 1974
2 conference on standards of occupational lead exposure; February 1974; Washington, DC. J. Occup. Med.
3 17: 100-107.
4 Cooper, W. C.; Tabershaw, I. R.; Nelson, K. W. (1973) Laboratory studies of workers in lead smelting and refining.
5 In: Earth, D.; Berlin, A.; Engel, R.; Recht, P.; Smeets, J., eds. Environmental health aspects of lead:
6 proceedings [of an] international symposium; October 1972; Amsterdam, The Netherlands. Luxembourg:
7 Commission of the European Communities; pp. 517-530; report no. EUR 5004 d-e-f.
8 Cooper, W. C.; Wong, O.; Kheifets, L. (1985) Mortality among employees of lead battery plants and lead-producing
9 plants, 1947-1980. Scand. J. Work Environ. Health 11: 331-345.
10 Cooper, W. C.; Wong, O.; Trent, L. (1989) Case-control study of gastric cancer deaths in a lead battery plant. Report
11 to the International Lead Zinc Research Organization.
12 Coratelli, P.; Giannattasio, M.; Lomonte, C.; Marzolla, R.; Rana, F.; L'Abbate, N. (1988) Enzymuria to detect
13 tubular injury in workers exposed to lead: a 12-month follow-up. In: Bianchi, C.; Bocci, V.; Carone, F. A.;
14 Rabkin, R., eds. Kidney and proteins in health and disease: fifth international symposium in health and
15 disease; July 1987; Montecatini Terme, Italy. Basel, Switzerland: S. Karger; pp. 207-211.
16 Cordioli, G.; Cuoghi, L.; Solari, P. L.; Berrino, F.; Crosignani, P.; Riboli, E. (1987) Mortalita per tumore inuna
17 coorte di lavoratori della industria del vetro [Tumor mortality in a cohort of glass industry workers].
18 Epidemiol. Prev. (Italy) 9(30): 16-18.
19 Cory-Slechta, D. A. (1995) Bridging human and experimental animal studies of lead neurotoxicity: moving beyond
20 IQ. Neurotoxicol. Teratol. 17: 219-221.
21 Coscia, G. C.; Discalzi, G.; Ponzetti, C. (1987) Immunological aspects of occupational lead exposure. Med. Lav.
22 78:360-364.
23 Coste, J.; Mandereau, L.; Pessione, F.; Bregu, M.; Faye, C.; Hemon, D.; Spira, A. (1991) Lead-exposed workmen
24 and fertility: a cohort study on 354 subjects. Eur. J. Epidemiol. 7: 154-158.
25 Counter, S. A.; Buchanan, L. H.; Rosas, H. D.; Ortega, F. (1998) Neurocognitive effects of chronic lead intoxication
26 in Andean children. J. Neurol. Sci. 160: 47-53.
27 Counter, S. A.; Buchanan, L. H. (2002) Neuro-ototoxicity in Andean adults with chronic lead and noise exposure.
28 J. Occup. Environ. Med. 44: 30-38.
29 Cramer, K.; Goyer, R. A.; Jagenburg, R.; Wilson, M. H. (1974) Renal ultrastructure, renal function, and parameters
30 of lead toxicity in workers with different periods of lead exposure. Br. J. Ind. Med. 31: 113-127.
31 Craswell, P. W.; Price, J.; Boyle, P. D.; Behringer, D.; Stoeppler, M.; Ritz, E. (1987) Patterns of lead excretion in
32 patients with gout and chronic renal failure — a comparative German and Australian study. Sci. Total
33 Environ. 66: 17-28.
34 Cristy, M. (1981) Active bone marrow distribution as a function of age in humans. Phys. Med. Biol. 26: 389-400.
35 Cullen, M. R.; Kayne, R. D.; Robins, J. M. (1984) Endocrine and reproductive dysfunction in men associated with
36 occupational inorganic lead intoxication. Arch. Environ. Health 39: 431-440.
37 Dalpra, L.; Tibiletti, M. G.; Nocera, G.; Giulotto, P.; Auriti, L.; Carnelli, V.; Simoni, G. (1983) SCE analysis in
3 8 children exposed to lead emission from a smelting plant. Mutat. Res. 120: 249-256.
39 David, O. J.; Clark, J.; Voeller, K. (1972) Lead and hyperactivity. Lancet (7783): 900-903.
40 David, O. J.; Hoffman, S. P.; Sverd, J.; Clark, J.; Voeller, K. (1976) Lead and hyperactivity. Behavorial response to
41 chelation: a pilot study. Am. J. Psychiatry 133: 1155-1158.
42 David, O. J.; Clark, J.; Hoffman, S. (1979) Childhood lead poisoning: a re-evaluation. Arch. Environ. Health
43 34: 106-111.
44 Davidson, R.; MacKinnon, J. G. (1981) Several tests for model specification in the presence of alternative
45 hypotheses. Econometrica 49: 781-793.
46 Davies, J. M. (1984a) Lung cancer mortality among workers making lead chromate and zinc chromate pigments at
47 three English factories. Br. J. Ind. Med. 41: 158-169.
48 Davies, J. M. (1984b) Long term mortality study of chromate pigment workers who suffered lead poisoning. Br. J.
49 Ind. Med. 41: 170-178.
50 Davis, J. M. (1990) Risk assessment of the developmental neurotoxicity of lead. Neurotoxicology 11: 285-292.
51 Davis, J. M.; Svendsgaard, D. J. (1987) Lead and child development. Nature (London) 329: 297-300.
52 Davis, J. M.; Svendsgaard, D. J. (1990) Nerve conduction velocity and lead: a critical review and meta-analysis.
53 In: Johnson, B. L.; Anger, W. K.; Durao, A.; Xintaras, C., eds. Advances in neurobehavioral toxicology:
54 applications in environmental and occupational health: [selected papers presented at the third international
55 symposium on neurobehavioral and occupational health]; December 1988; Washington, DC. Chelsea, MI:
56 Lewis Publishers, Inc.; pp. 353-376.
May 2006 6-338 DRAFT-DO NOT QUOTE OR CITE
-------
1 Davis, J. M; Otto, D. A.; Weil, D. E.; Grant, L. D. (1990) The comparative developmental neurotoxicity of lead in
2 humans and animals. Neurotoxicol. Teratol. 12: 215-229.
3 De Burbure, C.; Buchet, J. P.; Bernard, A.; Leroyer, A.; Nisse, C.; Haguenoer, J.-M; Bergamaschi, E.; Mutti, A.
4 (2003) Biomarkers of renal effects in children and adults with low environmental exposure to heavy metals.
5 J. Toxicol. Environ. Health Part A 66: 783-798.
6 De Burbure, C.; Buchet, J.-P.; Leroyer, A.; Nisse, C.; Haguenoer, J.-M.; Mutti, A.; Smerhovsky, Z.; Cikrt, M.;
7 Trczinka-Ochocka, M.; Razniewska, G.; Jakubowski, M.; Bernard, A. (2006) Renal and neurologic effects
8 of cadmium, lead, mercury, and arsenic in children: evidence of early effects and multiple interactions at
9 environmental exposure levels. Environ. Health Perspect. 114: 584-590.
10 De Kort, W. L. A. M.; Verschoor, M. A.; Wibowo, A. A. E.; van Hemmen, J. J. (1987) Occupational exposure to
11 lead and blood pressure: a study in 105 workers. Am. J. Ind. Med. 11: 145-156.
12 Delves, H. T.; Campbell, M. J. (1988) Measurements of total lead concentrations and of lead isotope ratios in whole
13 blood by use of inductively coupled plasma source mass spectrometry. J. Anal. At. Spectrom. 3: 343-348.
14 Den Hond, E.; Nawrot, T.; Staessen, J. A. (2002) The relationship between blood pressure and blood lead in
15 NHANES III. J. Hum. Hypertens. 16: 563-568.
16 Denno, D. (1990) Biology and violence. From birth to adulthood. New York, NY: Cambridge University Press.
17 Despres, C.; Beuter, A.; Richer, F.; Poitras, K.; Veilleux, A.; Ayotte, P.; Dewailly, E.; Saint-Amour, D.; Muckle, G.
18 (2005) Neuromotor functions in Inuit preschool children exposed to Pb, PCBs, and Hg. Neurotoxicol.
19 Teratol. 27: 245-257.
20 Dick, R. B.; Pinkerton, L. E.; Krieg, E. F., Jr.; Biagini, R. E.; Deddens, J. A.; Brightwell, W. S.; Grubb, P. L.;
21 Taylor, B. T.; Russo, J. M. (1999) Evaluation of postural stability in workers exposed to lead at a secondary
22 lead smelter. Neurotoxicology 20: 595-608.
23 DiPietro, E. S.; Philips, D. L.; Paschla, D. C.; Neese, J. W. (1989) Determination of trace elements in human hair.
24 Biol. Trace Elem. Res. 22: 83-100.
25 Diamond, G. L. (1988) Biological monitoring of urine for exposure to toxic metals. In: Clarkson, T. W.; Nordberg,
26 G.; Sager, P., eds. Scientific basis and practical applications of biological monitoring of toxic metals.
27 New York, NY: Plenum Press; pp. 515-529.
28 Diamond, G. L. (1992) Review of default value for lead plasma-to-urine transfer coefficient (TPLUR) in the U.S.
29 EPA uptake/biokinetic model. Syracuse, NY: Syracuse Research Corporation. Prepared for Environmental
30 Criteria and Assessment Office, U.S. Environmental Protection Agency.
31 Dietrich, K. N.; Krafft, K. M.; Bier, M.; Succop, P. A.; Berger, O.; Bornschein, R. L. (1986) Early effects of fetal
32 lead exposure: neurobehavioral findings at 6 months. Int. J. Biosoc. Res. 8: 151-168.
33 Dietrich, K. N.; Krafft, K. M.; Shukla, R.; Bornschein, R. L.; Succop, P. A. (1987a) The neurobehavioral effects of
34 early lead exposure. In: Schroeder, S. R., ed. Toxic substances and mental retardation: neurobehavioral
3 5 toxicology and teratology. Washington, DC: American Association on Mental Deficiency; pp. 71-95.
36 (Begab, M. J., ed. Monographs of the American Association on Mental Deficiency: no. 8).
37 Dietrich, K. N.; Krafft, K. M.; Bornschein, R. L.; Hammond, P. B.; Berger, O.; Succop, P. A.; Bier, M. (1987b)
3 8 Low-level fetal lead exposure effect on neurobehavioral development in early infancy. Pediatrics
39 80:721-730.
40 Dietrich, K. N.; Succop, P. A.; Bornschein, R. L.; Krafft, K. M.; Berger, O.; Hammond, P. B.; Buncher, C. R. (1990)
41 Lead exposure and neurobehavioral development in later infancy. In: Conference on advances in lead
42 research: implications for environmental health; January 1989; Research Triangle Park, NC. Environ.
43 Health Perspect. 89: 13-19.
44 Dietrich, K. N.; Succop, P. A.; Berger, O. G.; Hammond, P. B.; Bornschein, R. L. (1991) Lead exposure and the
45 cognitive development of urban preschool children: the Cincinnati lead study cohort at age 4 years.
46 Neurotoxicol. Teratol. 13: 203 -211.
47 Dietrich, K. N.; Succop, P. A.; Berger, O. G.; Keith, R. W. (1992) Lead exposure and the central auditory processing
48 abilities and cognitive development of urban children: the Cincinnati lead study cohort at age 5 years.
49 Neurotoxicol. Teratol. 14: 51-56.
50 Dietrich, K. N.; Berger, O. G.; Succop, P. A.; Hammond, P. B.; Bornschein, R. L. (1993a) The developmental
51 consequences of low to moderate prenatal and postnatal lead exposure: intellectual attainment in the
52 Cincinnati Lead Study Cohort following school entry. Neurotoxicol. Teratol. 15: 37-44.
53 Dietrich, K. N.; Berger, O. G.; Succop, P. A. (1993b) Lead exposure and the motor developmental status of urban
54 six-year-old children in the Cincinnati prospective study. Pediatrics 91: 301-307.
55 Dietrich, K. N.; Ris, M. D.; Succop, P. A.; Berger, O. G.; Bornschein, R. L. (2001) Early exposure to lead and
56 juvenile delinquency. Neurotoxicol. Teratol. 23: 511-518.
May 2006 6-339 DRAFT-DO NOT QUOTE OR CITE
-------
1 Dietrich, K. N.; Ware, J. H.; Salganik, M.; Radcliffe, I; Rogan, W. I; Rhoads, G. G.; Fay, M. E.; Davoli, C. T.;
2 Denckla, M. B.; Bornschein, R. L.; Schwarz, D.; Dockery, D. W.; Adubato, S.; Jones, R. L.; for the
3 Treatment of Lead-Exposed Children Clinical Trial Group. (2004) Effect of chelation therapy on the
4 neuropsychological and behavioral development of lead-exposed children after school entry. Pediatrics
5 114: 19-26.
6 Dietrich, K. N.; Eskenazi, B.; Schantz, S.; Yolton, K.; Rauh, V. A.; Johnson, C. B.; Alkon, A.; Canfield, R. L.;
7 Pessah, I. N.; Berman, R. F. (2005) Principles and practices of neurodevelopmental assessment in children:
8 lessons learned from the Centers for Children's Environmental Health and Disease Prevention Research.
9 Environ. Health Perspect. 113: 1437-1446.
10 Dingwall-Fordyce, L; Lane, R. E. (1963) A follow-up study of lead workers. Br. J. Ind. Med. 20: 313-315.
11 Diouf, A.; Garcon, G.; Thiaw, C.; Diop, Y.; Fall, M.; Ndiaye B.; Siby, T.; Hannothiaux, M. H.; Zerimech, F.;
12 Ba, D.; Haguenoer, J. M.; Shirali, P. (2003) Environmental lead exposure and its relationship to traffic
13 density among Senegalese children: a pilot study. Hum. Exp. Toxicol. 22: 559-564.
14 Discalzi, G. L.; Capellaro, F.; Bottalo, L.; Fabbro, D.; Mocellini, A. (1992) Auditory brainstem evoked potentials
15 (BAEPS) in lead-exposed workers. Neurotoxicology 13: 207-209.
16 Discalzi, G.; Fabbro, D.; Meliga, F.; Mocellini, A.; Capellaro, F. (1993) Effects of occupational exposure to mercury
17 and lead on brainstem auditory evoked potentials. Int. J. Psychophysiol. 14: 21-25.
18 Dowd, T. L.; Rosen, J. F.; Gundberg, C. M.; Gupta, R. K. (1994) The displacement of calcium from osteocalcin at
19 submicromolar concentrations of free lead. Biochim. Biophys. Acta 1226: 131-137.
20 Drasch, G. A.; Bohm, J.; Baur, C. (1987) Lead in human bones. Investigations on an occupationally non-exposed
21 population in southern Bavaria (F. R. G.). I. Adults. Sci. Total Environ. 64: 303-315.
22 Drasch, G.; Wanghofer, E.; Roider, G. (1997) Are blood, urine, hair, and muscle valid biomonitors for the internal
23 burden of men with the heavy metals mercury, lead and cadmium? Trace Elem. Electrolytes
24 14(3): 116-123.
25 Driscoll, R. J. (1998) Epidemiologic study of adverse reproductive outcomes among women in the U.S. Forest
26 Service. In: Driscoll, R. J.; Reh, B. D.; Esswein, E. J.; Mattorano, D. A. Health hazard evaluation report no.
27 93-1035-2686, section 2. Washington, DC: U.S. Department of Agriculture, Forest Service; pp. 33-71.
28 Available from: NTIS, Springfield, VA; PB99-152241.
29 Durbin, P. W. (1992) Distribution of transuranic elements in bone. Neurotoxicology 13: 821-824.
30 Dursun, N.; Tutus, A. (1999) Chronic occupational lead exposure and thyroid function. J. Trace Elem. Exp. Med.
31 12:45-49.
32 Duydu, Y.; Stizen, H. S.; Aydin, A.; Cander, O.; Uysal, H.; Isimer, A.; Vural, N. (2001) Correlation between lead
33 exposure indicators and sister chromatid exchange (SCE) frequencies in lymphocytes from inorganic lead
34 exposed workers. Arch. Environ. Contain. Toxicol. 41: 241-246.
35 Duydu, Y.; Dur, A.; Stizen, H. S. (2005) Evaluation of increased proportion of cells with unusually high sister
36 chromatid exchange counts as a cytogenetic biomarker for lead exposure. Biol. Trace Elem. Res.
37 104: 121-129.
38 Dye,B. A.; Hirsch, R.; Brody, D. J. (2002) The relationship between blood lead levels and periodontal bone loss in
39 the United States, 1988-1994. Environ. Health Perspect. 110: 997-1002.
40 EL-Safty, I. A.; Afifi, A. M.; Shouman, A. E.; EL-Sady, A. K. R. (2004) Effects of smoking and lead exposure on
41 proximal tubular integrity among Egyptian industrial workers. Arch. Med. Res. 35: 59-65.
42 Elwood, P. C.; Davey-Smith, G.; Oldham, P. D.; Toothill, C. (1988a) Two Welsh surveys of blood lead and blood
43 pressure. In: Victery, W., ed. Symposium on lead-blood pressure relationships; April 1987; Chapel Hill,
44 NC. Environ. Health Perspect. 78: 119-121.
45 Elwood, P. C.; Yarnell, J. W. G.; Oldham, P. D.; Catford, J. C.; Nutbeam, D.; Davey-Smith, G.; Toothill, C. (1988b)
46 Blood pressure and blood lead in surveys in Wales. Am. J. Epidemiol. 127: 942-945.
47 ESA Biosciences, Inc. (1998) LeadCare® childhood blood lead testing. Chelmsford, MA: ESA Biosciences, Inc.
48 Ehrlich, R.; Robins, T.; Jordaan, E.; Miller, S.; Mbuli, S.; Selby, P.; Wynchank, S.; Cantrell, A.; De Broe, M.;
49 D'Haese, P.; Todd, A.; Landrigan, P. (1998) Lead absorption and renal dysfunction in a South African
50 battery factory. Occup. Environ. Med. 55: 453-460.
51 Elmarsafawy, S. F.; Tsaih, S.-W.; Korrick, S.; Dickey, J. H.; Sparrow, D.; Aro, A.; Hu, H. (2002) Occupational
52 determinants of bone and blood lead levels in middle aged and elderly men from the general community:
53 the Normative Aging Study. Am. J. Ind. Med. 42: 38-49.
54 Emmerson, B. T. (1965) The renal excretion of urate in chronic lead nephropathy. Australas. Ann. Med.
55 14:295-303.
May 2006 6-340 DRAFT-DO NOT QUOTE OR CITE
-------
1 Emmerson, B. T.; Ravenscroft, P. J. (1975) Abnormal renal urate homeostasis in systemic disorders. Nephron
2 14:62-80.
3 Emory, E.; Ansari, Z.; Pattillo, R.; Archibold, E.; Chevalier, J. (2003) Maternal blood lead effects on infant
4 intelligence at age 7 months. Am. J. Obstet. Gynecol. S26-S32.
5 Endo, G.; Horiguchi, S.; Kiyota, I. (1990) Urinary 7V-acetyl-p-D-glucosaminidase activity in lead-exposed workers.
6 J. Appl. Toxicol. 10: 235-238.
7 Endo, G.; Konishi, Y.; Kiyota, A.; Horiguchi, S. (1993) Urinary di microglobulin in lead workers. Bull. Environ.
8 Contam. Toxicol. 50: 744-749.
9 Englyst, V.; Lundstrom, N. G.; Gerhardsson, L.; Rylander, L.; Nordberg, G. (2001) Lung cancer risks among lead
10 smelter workers also exposed to arsenic. Sci. Total Environ. 273: 77-82.
11 Erfurth, E. M; Gerhardsson, L.; Nilsson, A.; Rylander, L.; Schiitz, A.; Skerfving, S.; Borjesson, J. (2001) Effects of
12 lead on the endocrine system in lead smelter workers. Arch. Environ. Health 56: 449-455.
13 Erkkila, J.; Armstrong, R.; Riihimaki, V.; Chettle, D. R.; Paakkari, A.; Scott, M.; Somervaille, L.; Stark, J.;
14 Kock, B.; Aitio, A. (1992) In vivo measurements of lead in bone at four anatomical sites: long term
15 occupational and consequent edogenous exposure. Br. J. Ind. Med. 49: 631-644.
16 Ernhart, C. B. (1995) Inconsistencies in the lead-effects literature exist and cannot be explained by "effect
17 modification." Neurotoxicol. Teratol. 17: 227-233.
18 Ernhart, C. B. (2006) Effects of lead onlQ in children [letter]. Environ. Health Perspect. 114: A85-A86.
19 Ernhart, C. B.; Greene, T. (1990) Low-level lead exposure in the prenatal and early preschool periods: language
20 development. Arch. Environ. Health 45: 342-354.
21 Ernhart, C. B.; Landa, B.; Wolf, A. W. (1985) Subclinical lead level and developmental deficit; reanalyses of data.
22 J. Learning Disabilities 18: 475-479.
23 Ernhart, C. B.; Wolf, A. W.; Kennard, M. J.; Erhard, P.; Filipovich, H. F.; Sokol, R. J. (1986) Intrauterine exposure
24 to low levels of lead: the status of the neonate. Arch. Environ. Health 41: 287-291.
25 Ernhart, C. B.; Morrow-Tlucak, M.; Marler, M. R.; Wolf, A. W. (1987) Low level lead exposure in the prenatal and
26 early preschool periods: early preschool development. Neurotoxicol. Teratol. 9: 259-270.
27 Ernhart, C. B.; Morrow-Tlucak, M.; Wolf, A. W. (1988) Low level lead exposure and intelligence in the preschool
28 years. Sci. Total Environ. 71: 453-459.
29 Ernhart, C. B.; Morrow-Tlucak, M.; Wolf, A. W.; Super, D.; Drotar, D. (1989) Low level lead exposure in the
30 prenatal and early preschool periods: intelligence prior to school entry. Neurotoxicol. Teratol. 11: 161-170.
31 Espy, K. A. (1997) The Shape School: assessing executive function in preschool children. Dev. Neuropsychol.
32 13:-495-499.
33 Esteban, E.; Rubin, C. H.; Jones, R. L.; Noonan, G. (1999) Hair and blood substrates for screening children for lead
34 poisoning. Arch. Environ. Health 54: 436-440.
35 Ettinger, A. s.; Tellez-Rojo, M. M.; Amarasiriwardena, C.; Gonzalez-Cossio, T.; Peterson, K. E.; Aro, A.; Hu, H.;
3 6 Hernandez-Avila, M. (2004) Levels of lead in breast milk and their relation to maternal blood and bone
3 7 lead levels at one month postpartum. Environ. Health Perspect. 112: 926-931.
38 Ewers, U.; Stiller-Winkler, R.; Idel, H. (1982) Serum immunoglobulin, complement C3, and salivary IgA levels in
39 lead workers. Environ. Res. 29: 351-357.
40 Factor-Litvak, P.; Graziano, J. H.; Kline, J. K.; Popovac, D.; Mehmeti, A.; Ahmedi, G.; Shrout, P.; Murphy, M. J.;
41 Gashi, E.; Haxhiu, R.; Rajovic, L.; Nenezic, D. U.; Stein, Z. A. (1991) A prospective study of birthweight
42 and length of gestation in a population surrounding a lead smelter in Kosovo, Yugoslavia. Int. J. Epidemiol.
43 20:722-728.
44 Factor-Litvak, P.; Stein, Z.; Graziano, J. (1993) Increased risk of proteinuria among a cohort of lead-exposed
45 pregnant women. Environ. Health Perspect. 101: 418-421.
46 Factor-Litvak, P.; Kline, J. K.; Popovac, D.; Hadzialjevic, S.; Lekic, V.; Preteni-Rexhepi, E.; Capuni-Paracka, S.;
47 Slavkovich, V.; Graziano, J. (1996) Blood lead and blood pressure in young children. Epidemiology
48 7:633-637.
49 Factor-Litvak, P.; Slavkovich, V.; Liu, X.; Popovac, D.; Preteni, E.; Capuni-Paracka, S.; Hadzialjevic, S.; Lekic, V.;
50 Lolacono, N.; Kline, J.; Graziano, J. (1998) Hyperproduction of erythropoietin in nonanemic lead-exposed
51 children. Environ. Health Perspect. 106: 361-364.
52 Factor-Litvak, P.; Wasserman, G.; Kline, J. K.; Graziano, J. (1999) The Yugoslavia prospective study of
53 environmental lead exposure. Environ. Health Perspect. 107: 9-15.
54 Fahim, M. S.; Fahim, Z.; Hall, D. G. (1976) Effects of subtoxic lead levels on pregnant women in the state of
55 Missouri. Res. Commun. Chem. Pathol. Pharmacol. 13: 309-331.
56 Fanning, D. (1988) A mortality study of lead workers, 1926-1985. Arch. Environ. Health 43: 247-251.
May 2006 6-341 DRAFT-DO NOT QUOTE OR CITE
-------
1 Farias, P.; Hu, H.; Rubenstein, E.; Meneses-Gonzalez, F.; Fishbein, E.; Palazuelos, E.; Aro, A.; Hernandez-Avila,
2 M. (1998) Determinants of bone and blood lead levels among teenagers living in urban areas with high lead
3 exposure. Environ. Health Perspect. 106: 733-737.
4 Farrow, S. (1994) Falling sperm quality: fact of fiction? Br. Med. J. 309: 1-2.
5 Pels, L. M.; Herbert, C.; Pergande, M.; Jung, K.; Hotter, G.; Rosello, J.; Gelpi, E.; Mutti, A.; De Broe, M.; Stolte, H.
6 (1994) Nephron target sites in chronic exposure to lead. Nephrol. Dial. Transplant. 9: 1740-1746.
7 Pels, L. M.; Wtinsch, M.; Baranowski, J.; Norska-Borowka, L; Price, R. G.; Taylor, S. A.; Patel, S.; De Broe, M.;
8 Elsevier, M. M.; Lauwerys, R.; Roels, H.; Bernard, A.; Mutti, A.; Gelpi, E.; Rosello, J.; Stolte, H. (1998)
9 Adverse effects of chronic low level lead exposure on kidney function—a risk group study in children.
10 Nephrol. Dial. Transplant 13: 2248-2256.
11 Fergusson, D. M.; Horwood, L. J. (1993) The effects of lead levels on the growth of word recognition in middle
12 childhood. Int. J. Epidemiol. 22: 891-897.
13 Fergusson, D. M.; Fergusson, J. E.; Horwood, L. J.; Kinzett, N. G. (1988a) A longitudinal study of dentine lead
14 levels, intelligence, school performance and behaviour. Part II. Dentine lead and cognitive ability. J. Child
15 Psychol. Psychiatry Allied Discip. 29: 793-809.
16 Fergusson, D. M.; Fergusson, J. E.; Horwood, L. J.; Kinzett, N. G. (1988b) A longitudinal study of dentine lead
17 levels, intelligence, school performance and behaviour. Part III. Dentine lead levels and attention/activity.
18 J. Child Psychol. Psychiatry Allied Discip. 29: 811-824.
19 Fergusson, D. M.; Fergusson, J. E.; Horwood, L. J.; Kinzett, N. G. (1988c) A longitudinal study of dentine lead
20 levels, intelligence, school performance and behaviour. Part I. Dentine lead levels and exposure to
21 environmental risk factors. J. Child Psychol. Psychiatry Allied Discip. 29: 781-792.
22 Fergusson, J. E.; Kinzett, N. G.; Fergusson, D. M.; Horwood, L. J. (1989) A longitudinal study of dentin lead levels
23 and intelligence school performance and behavior the measurement of dentin lead. Sci. Total Environ.
24 80:229-242.
25 Fergusson, D. M.; Horwood, L. J.; Lynskey, M. T. (1993) Early dentine lead levels and subsequent cognitive and
26 behavioural development. J. Child Psychol. Psych. Allied Disciplines 34: 215-227.
27 Fergusson, D. M.; Horwood, L. J.; Lynskey, M. T. (1997) Early dentine lead levels and educational outcomes at
28 18 years. J. Child Psychol. Psychiatry 38: 471-478.
29 Fewtrell, L. J.; Pruss-Ustun, A.; Landrigan, P.; Ayuso-Mateos, J. L. (2004) Estimating the global burden of disease
30 of mild mental retardation and cardiovascular diseases from environmental lead exposure. Environ. Res.
31 94:120-133.
32 Fiedler, N.; Weisel, C.; Lynch, R.; Kelly-McNeil, K.; Wedeen, R.; Jones, K.; Udasin, I.; Ohman-Strickland, P.;
33 Gochfeld, M. (2003) Cognitive effects of chronic exposure to lead and solvents. Am. J. Ind. Med.
34 44:413-423.
35 Fisch, H.; Andrews, H.; Hendricks, J.; Goluboff, E. T.; Olson, J. H.; Olsson, C. A. (1997) The relationship of sperm
36 counts to birth rates: a population based study. J. Urol. (Hagerstown, MD, U.S.) 157: 840-843.
37 Fischbein, A.; Alvares, A. P.; Anderson, K. E.; Sassa, S.; Kappas, A. (1977) Lead intoxication among demolition
3 8 workers: the effect of lead on the hepatic cytochrome P-450 systems in humans. J. Toxicol. Environ. Health
39 3:431-437.
40 Fischbein, A.; Tsang, P.; Luo, J.-C. J.; Roboz, J. P.; Jiang, J. D.; Bekesi, J. G. (1993) Phenotypic aberrations of the
41 CD3+ and CD4+ cells and functional impairments of lymphocytes at low-level occupational exposure to
42 lead. Clin. Immunol. Immunopathol. 66: 163-168.
43 Flegal, A. R.; Smith, D. R. (1995) Measurements of environmental lead contamination and human exposure. In:
44 Ware, G. W., ed. Reviews of environmental contamination and toxicology, continuation of residue reviews,
45 v. 143. New York, NY: Springer, pp. 1-45.
46 Fleming, D. E. B.; Boulay, D.; Richard, N. S.; Robin, J.-P.; Gordon, C. L.; Webber, C. E.; Chettle, D. R. (1997)
47 Accumulated body burden and endogenous release of lead in employees of a lead smelter. Environ. Health
48 Perspect. 105: 224-233.
49 Fleming, D. E. B.; Chettle, D. R.; Wetmur, J. G.; Desnick, R. J.; Robin, J.-P.; Boulay, D.; Richard, N. S.; Gordon,
50 C. L.; Webber, C. E. (1998) Effect of the delta-aminolevulinate dehydratase polymorphism on the
51 accumulation of lead in bone and blood in lead smelter workers. Environ. Res. 77: 49-61.
52 Flood, P. R.; Schmidt, P. F.; Wesenberg, G. R.; Gadeholt, H. (1988) The distribution of lead in human hemopoietic
53 tissue and spongy bone after lead poisoning and Ca-EDTA chelation therapy: observations made by atomic
54 absorption spectroscopy, laser microbeam mass analysis and electron microbeam X-ray analysis. Arch.
55 Toxicol. 62: 295-300.
May 2006 6-342 DRAFT-DO NOT QUOTE OR CITE
-------
1 Folstein, M. F.; Folstein, S. E.; McHugh, P. R. (1975) Mini-Mental State: a practical method of grading the state of
2 patients for the clinician. J. Psychiatr. Res. 12: 189-198.
3 Food and Drug Administration. (2002) Guidance for industry: immunotoxicology evaluation of investigational new
4 drugs. Washington, DC: U.S. Department of Health and Human Services. Available:
5 http://www.fda.gov/cder/guidance/4945fnl.PDF [29 March, 2006].
6 Forbes, G. B.; Braining, G. B. (1976) Urinary creatinine excretion and lean body mass. Am. J. Clin. Nutr.
7 29: 1359-1366.
8 Forni, A.; Cambiaghi, G.; Secchi, G. C. (1976) Initial occupational exposure to lead: chromosome and biochemical
9 findings. Arch. Environ. Health 31: 73-78.
10 Forni, A.; Sciame', A.; Bertazzi, P. A.; Alessio, L. (1980) Chromosome and biochemical studies in women
11 occupationally exposed to lead. Arch. Environ. Health 35: 139-146.
12 Fosse, G.; Wesenberg, G. B. R.; Tvinnereim, H. M., Eide, R.; Kristoffersen, 0.; Nag, O. H.; Wierzbicka, M.;
13 Banoczy, J.; De Oliveira, A. A.; Srisopak, C.; Zamudio, A. (1995) Lead in deciduous teeth from larger
14 cities of some countries. Int. J. Environ. Stud. 47: 203-210.
15 Foster, W. G. (1992) Reproductive toxicity of chronic lead exposure in the female cynomolgus monkey. Reprod.
16 Toxicol. 6: 123-131.
17 Fracasso, M. E.; Perbellini, L.; Solda, S.; Talamini, G.; Franceschetti, P. (2002) Lead induced DNA strand breaks in
18 lymphocytes of exposed workers: role of reactive oxygen species and protein kinase C. Mutat. Res.
19 515:-159-169.
20 Franklin, C. A.; Inskip, M. J.; Baccanale, C. L.; Edwards, C. M.; Manton, W. I.; Edwards, E.; O'Flaherty, E. J.
21 (1997) Use of sequentially administered stable lead isotopes to investigate changes in blood lead during
22 pregnancy in a nonhuman primate (Macacafascicularis). Fundam. Appl. Toxicol. 39: 109-119.
23 Franks, P. A.; Laughlin, N. K.; Dierschke, D. J.; Bowman, R. E.; Meller, P. A. (1989) Effects of lead on luteal
24 function in rhesus monkeys. Biol. Reprod. 41: 1055-1062.
25 Froom, P.; Kristal-Boneh, E.; Benbassat, J., Ashkanazi, R.; Ribak, J. (1999) Lead exposure in battery-factory
26 workers is not associated with anemia. J. Occup. Environ. Med. 41: 120-123.
27 Fu, H.; Boffetta, P. (1995) Cancer and occupational exposure to inorganic lead compounds: a meta-analysis of
28 published data. Occup. Environ. Med. 52: 73-81.
29 Fulton, M.; Raab, G.; Thomson, G.; Laxen, D.; Hunter, R.; Hepburn, W. (1987) Influence of blood lead on the
30 ability and attainment of children in Edinburgh. Lancet (8544): 1221-1226.
31 Garcon, G.; Leleu, B.; Zerimech, F.; Marez, T.; Haguenoer, J.-M.; Furon, D.; Shirali, P. (2004) Biologic markers of
32 oxidative stress and nephrotoxicity as studied in biomonitoring and adverse effects of occupational
33 exposure to lead and cadmium. J. Occup. Environ. Med. 46: 1180-1186.
34 Gardner, J. M.; Walker, S. P.; Chang, S. M.; Vutchkov, M.; Lalor, G. C. (1998) Undernutrition and elevated blood
3 5 lead levels: effects on psychomotor development among Jamaican children. Public Health Nutr.
36 1: 177-179.
37 Garrido Latorre, F.; Hernandez-Avila, M.; Orozco, J. T.; Medina, C. A. A.; Aro, A.; Palazuelos, E.; Hu, H. (2003)
3 8 Relationship of blood and bone lead to menopause and bone mineral density among middle-age women in
39 Mexico City. Environ. HealthPerspect. Ill: 631-636.
40 Gartside, P. S. (1988) The relationship of blood lead levels and blood pressure in NHANES II: additional
41 calculations. In: Victery, W., ed. Symposium on lead-blood pressure relationships; April 1987; Chapel Hill,
42 NC. Environ. Health Perspect. 78: 31-34.
43 Gemmel, A.; Tavares, M.; Alperin, S.; Soncini, J.; Daniel, D.; Dunn, J.; Crawford, S.; Braveman, N.; Clarkson,
44 T. W.; McKinlay, S.; Bellinger, D. C. (2002) Blood lead level and dental caries in school-age children.
45 Environ. Health Perspect. 110: A625-A630.
46 Gennart, J. P.; Bernard, A.; Lauwerys, R. (1992) Assessment of thyroid, testes, kidney and autonomic nervous
47 system function in lead-exposed workers. Int. Arch. Occup. Environ. Health 64: 49-57.
48 Gerhardsson, L.; Brane, D.; Nordberg, G. F.; Wester, P. O. (1986) Distribution of cadmium, lead and zinc in lung,
49 liver and kidney in long-term exposed smelter workers. Sci. Total Environ. 50: 65-85.
50 Gerhardsson, L.; Chettle, D. R.; Englyst, V.; Nordberg, G. F.; Nyhlin, H.; Scott, M. C.; Todd, A. C.; Vesterberg, O.
51 (1992) Kidney effects in long term exposed lead smelter workers. Br. J. Ind. Med. 49: 186-192.
52 Gerhardsson, L.; Attewell, R.; Chettle, D. R.; Englyst, V.; Lundstrom, N.-G.; Nordberg, G. F.; Nyhlin, H.; Scott,
53 M.-C.; Todd, A. C. (1993) In vivo measurements of lead in bone in long-term exposed lead smelter
54 workers. Arch. Environ. Health 48: 147-156.
55 Gerhardsson, L.; Hagmar, L.; Rylander, L.; Skerfving, S. (1995) Mortality and cancer incidence among secondary
56 lead smelter workers. Occup. Environ. Med. 52: 667-672.
May 2006 6-343 DRAFT-DO NOT QUOTE OR CITE
-------
1 Gerr, F.; Letz, R.; Stokes, L.; Chettle, D.; McNeill, F.; Kaye, W. (2002) Association between bone lead
2 concentration and blood pressure among young adults. Am. J. Ind. Med. 42: 98-106.
3 Gershanik, J. J.; Brooks, G. G.; Little, J. A. (1974) Blood lead values in pregnant women and their offspring. Am. J.
4 Obstet. Gynecol. 119: 508-511.
5 Gil, F.; Perez, M. L.; Facio, A.; Villanueva, E.; Tojo, R.; Gil, A. (1994) Dental lead levels in the Galacian
6 population, Spain. Sci. Total Environ. 156: 145-150.
7 Glenn, B. S.; Stewart, W. F.; Schwartz, B. S.; Bressler, J. (2001) Relation of alleles of the sodium-potassium
8 adenosine triphosphatase 62 gene with blood pressure and lead exposure. Am. J. Epidemiol. 153: 537-545.
9 Glenn, B. S.; Stewart, W. F.; Links, J. M.; Todd, A. C.; Schwartz, B. S. (2003) The longitudinal association of lead
10 with blood pressure. Epidemiology 14: 30-36.
11 Glickman, L.; Valciukas, J. A.; Lilis, R.; Weisman, I. (1984) Occupational lead exposure: effects on saccadic eye
12 movements. Int. Arch. Occup. Environ. Health 54: 115-125.
13 Gomaa, A.; Hu, H.; Bellinger, D.; Schwartz, J.; Tsaih, S.-W.; Gonzalez-Cossio, T.; Schnaas, L.; Peterson, K.;
14 Aro, A.; Hernandez-Avila, M. (2002) Maternal bone lead as an independent risk factor for fetal
15 neurotoxicity: a prospective study. Pediatrics 110: 110-118.
16 Gonick, H. C.; Behari, J. R. (2002) Is lead exposure the principal cause of essential hypertension? Med. Hypotheses
17 59:239-246.
18 Gonick, H. C.; Cohen, A. H.; Ren, Q.; Saldanha, L. F.; Khalil-Manesh, F.; Anzalone, J.; Sun, Y. Y. (1996) Effect of
19 2,3-dimercaptosuccinic acid on nephrosclerosis in the Dahl rat. I. Role of reactive oxygen species. Kidney
20 Int. 50: 1572-1581.
21 Gonzalez-Cossio, T.; Peterson, K. E.; Sanin, L.-H.; Fishbein, E.; Palazuelos, E.; Aro, A.; Hernandez-Avila, M.;
22 Hu, H. (1997) Decrease in birth weight in relation to maternal bone-lead burden. Pediatrics 100: 856-862.
23 Gordon, C. L.; Chettle, D. R.; Webber, C. E. (1993) An improved instrument for the in vivo detection of lead in
24 bone. Br. J. Ind. Med. 50: 637-641.
25 Governa, M.; Valentino, M.; Visona, I. (1987) In vitro impairment of human granulocyte functions by lead. Arch.
26 Toxicol. 59: 421-425.
27 Govoni, S.; Battaini, F.; Fernicola, C.; Castelletti, L.; Trabucchi, M. (1987) Plasma prolactin concentrations in lead
28 exposed workers. J. Environ. Pathol. Toxicol. Oncol. 7: 13-15.
29 Goyer, R. A.; Epstein, S.; Bhattacharyya, M.; Korach, K. S.; Pounds, J. (1994) Environmental risk factors for
30 osteoporosis. Environ. HealthPerspect. 102: 390-394.
31 Grandjean, P. (1979) Occupational lead exposure in Denmark: screening with the haematofluorometer. Br. J. Ind.
32 Med. 36: 52-58.
33 Grandjean, P.; Arnvig, E.; Beckmann, J. (1978) Psychological dysfunctions in lead-exposed workers: relation to
34 biological parameters of exposure. Scand. J. Work Environ. Health 4: 295-303.
35 Grandjean, P.; Wulf, H. C.; Niebuhr, E. (1983) Sister chromatid exchange in response to variations in occupational
36 lead exposure. Environ. Res. 32: 199-204.
37 Grandjean, P.; Hollnagel, H.; Hedegaard, L.; Christensen, J. M.; Larsen, S. (1989) Blood lead-blood pressure
38 relations: alcohol intake and hemoglobin as confounders. Am. J. Epidemiol. 129: 732-739.
39 Graves, A. B.; VanDuijn, C. M.; Chandra, V.; Fratiglioni, L.; Heyman, A.; Jorm, A. F.; Kokmen, E.; Kondo, K.;
40 Mortimer, J. A.; Rocca, W. A.; Shalat, S. L.; Soininen, H.; Hofman, A. (1991) Occupational exposures to
41 solvents and lead as risk factors for Alzheimer's disease: a collaborative re-analysis of case-control studies.
42 Int. J. Epidemiol. 20(suppl. 2): S58-S61.
43 Graziano, J. H.; Popovac, D.; Factor-Litvak, P.; Shrout, P.; Kline, J.; Murphy, M. J.; Zhao, Y.-H.; Mehmeti, A.;
44 Ahmedi, X.; Rajovic, B.; Zvicer, Z.; Nenezic, D. U.; Lolacono, N. J.; Stein, Z. (1990) Determinants of
45 elevated blood lead during pregnancy in a population surrounding a lead smelter in Kosovo, Yugoslavia.
46 In: Conference on advances in lead research: implications for environmental health; January 1989;
47 Research Triangle Park, NC. Environ. Health Perspect. 89: 95-100.
48 Graziano, J. H.; Slavkovic, V.; Factorlitvak, P.; Popovac, D.; Ahmedi, X.; Mehmeti, A. (1991) Depressed serum
49 erythropoietin in pregnant women with elevated blood lead. Arch. Environ. Health 46: 347-350.
50 Graziano, J.; Slavkovich, V.; Liu X., Factor-Litvak, P.; Todd, A. (2004) A prospective study of prenatal and
51 childhood lead exposure and erythropoietin production. J. Occup. Environ. Med. 46: 924-929.
52 Greene, T.; Ernhart, C. B. (1993) Dentine lead and intelligence prior to school entry: a statistical sensitivity analysis.
53 J. Clin. Epidemiol. 46: 323-339.
54 Greene, T.; Ernhart, C. B.; Boyd, T. A. (1992) Contributions of risk factors to elevated blood and dentine lead levels
55 in preschool children. Sci. Total Environ. 115: 239-260.
May 2006 6-344 DRAFT-DO NOT QUOTE OR CITE
-------
1 Griffin, T. B.; Coulston, F.; Wills, H.; Russell, J. C.; Knelson, J. H. (1975) Clinical studies on men continuously
2 exposed to airborne paniculate lead. In: Griffin, T. B.; Knelson, J. H., eds. Lead. Stuttgart, Federal
3 Republic of Germany: Georg Thieme Publishers; pp. 221-240. (Coulston, F.; Korte, F., eds. Environmental
4 quality and safety: supplement v. 2).
5 Groth-Marnat, G. (2003) Handbook of psychological assessment. 4th ed. Hoboken, NJ: John Wiley & Sons.
6 Guidetti, D.; Bondavalli, M; Sabadini, R.; Marcello, N.; Vinceti, M; Cavalletti, S.; Marbini, A.; Gemignani, F.;
7 Colombo, A.; Ferriari, A.; Vivoli, G.; Solime, F. (1996) Epidemiological survey of amyotrophic lateral
8 sclerosis in the province of Reggio Emilia, Italy: influence of environmental exposure to lead.
9 Neuroepidemiology 15: 301-312.
10 Guilarte, T. R.; Toscano, C. D.; McGlothan, J. L.; Weaver, S. A. (2003) Environmental enrichment reverses
11 cognitive and molecular deficits induced by developmental lead exposure. Ann. Neurol. 53: 50-56.
12 Gulson, B. L.; Mizon, K. J.; Palmer, J. M.; Korsch, M. J.; Taylor, A. J.; Mahaffey, K. R. (2004) Blood lead changes
13 during pregnancy and postpartum with calcium supplementation. Environ. Health Perspect.
14 112: 1499-1507.
15 Gump, B. B.; Stewart, P.; Reihman, J.; Lonky, E.; Darvill, T.; Matthews, K. A.; Parsons, P. J. (2005) Prenatal and
16 early childhood blood lead levels and cardiovascular functioning in 91A year old children. Neurotoxicol.
17 Teratol. 27: 655-665.
18 Gunnarsson, L. G.; Bodin, L.; Soderfeldt, B.; Axelson, O. (1992) A case-control study of motor neurone disease: its
19 relation to heritability, and occupational exposures, particularly to solvents. Br. J. Ind. Med. 49: 791-798.
20 Guo, T. L.; Mudzinski, S. P.; Lawrence, D. A. (1996a) The heavy metal lead modulates the expression of both
21 TNF-d and TNF-d receptors in lipopolysaccharide-activated human peripheral blood mononuclear cells.
22 J. Leukoc. Biol. 59: 932-939.
23 Guo, T. L.; Mudzinski, S. P.; Lawrence, D. A. (1996b) Regulation of HLA-DR and invariant chain expression by
24 human peripheral blood mononuclear cells with lead, interferon-y, or interleukin-4. Cell. Immunol.
25 171: 1-9.
26 Gurer-Orhan, H.; Sabir, H.D.; Ozgunes, H. (2004) Correlation between clinical indicators of lead poisoning and
27 oxidative stress parameters in controls and lead-exposed workers. Toxicology 195: 147-154.
28 Gustafson, A.; Hedner, P.; Schtitz, A.; Skerfving, S. (1989) Occupational lead exposure and pituitary function. Int.
29 Arch. Occup. Environ. Health 61: 277-281.
30 Gustavsson, P.; Plato, N.; Hallqvist, J.; Hogstedt, C.; Lewne, M.; Reuterwall, C.; Scheele, P. (2001) A population-
31 based case-referent study of myocardial infarction and occupational exposure to motor exhaust, other
32 combustion products, organic solvents, lead, and dynamite. Stockholm heart epidemiology program
33 (SHEEP) study group. Epidemiology 12: 222-228.
34 Gwiazda, R.; Campbell, C.; Smith, D. (2005) A noninvasive isotopic approach to estimate the bone lead
3 5 contribution to blood in children: implications for assessing the efficacy of lead abatement. Environ. Health
36 Perspect. 113: 104-110.
37 Gyllenborg, J.; Skakkebaek, N. E.; Nielsen, N. C.; Keiding, N.; Giwercman, A. (1999) Secular and seasonal changes
38 in semen quality among young Danish men: a statistical analysis of semen samples from 1927 donor
39 candidates during 1977-1995. Int. J. Androl. 22: 28-36.
40 Hagmar, L.; Stromberg, U.; Bonassi, S.; Hansteen, I.-L.; Knudsen, L. E.; Lindholm, C.; Norppa, H. (2004) Impact of
41 types of lymphocyte chromosomal aberrations on human cancer risk: results from Nordic and Italian
42 cohorts. Cancer Res. 64: 2258-2263.
43 Hajem, S.; Moreau, T.; Hannaert, P.; Lellouch, J.; Huel, G.; Hellier, G.; Orssaud, G.; Claude, J. R.; Juguet, B.;
44 Festy, B.; Garay, R. P. (1990) Influence of environmental lead on membrane ion transport in a French
45 urban male population. Environ. Res. 53: 105-118.
46 Hammond, P. B.; Lerner, S. I.; Gartside, P. S.; Hanenson, I. B.; Roda, S. B.; Foulkes, E. C.; Johnson, D. R.; Pesce,
47 A. J. (1980) The relationship of biological indices of lead exposure to the health status of workers in a
48 secondary lead smelter. J. Occup. Med. 22: 475-484.
49 Haenninen, H.; Hernberg, S.; Mantere, P.; Vesanto, R.; Jalkanen, M. (1978) Psychological performance of subjects
50 with low exposure to lead. J. Occup. Med. 20: 683-689.
51 Haenninen, H.; Mantere, P.; Hernberg, S.; Seppalainen, A. M.; Kock, B. (1979) Subjective symptoms in low-level
52 exposure to lead. Neurotoxicology 1: 333-347.
53 Hanninen, H.; Aitio, A.; Kovala, T.; Luukkonen, R.; Matikainen, E.; Mannelin, T.; Erkkila, J.; Riihimaki, V. (1998)
54 Occupational exposure to lead and neuropsychological dysfunction. Occup. Environ. Med. 55: 202-209.
May 2006 6-345 DRAFT-DO NOT QUOTE OR CITE
-------
1 Haraguchi, T.; Ishizu, H.; Takehisa, Y.; Kawai, K.; Yokota, O.; Terada, S.; Tsuchiya, K.; Ikeda, K.; Morita, K.;
2 Horike, T.; Kira, S.; Kuroda, S. (2001) Lead content of brain tissue in diffuse neurofibrillary tangles with
3 calcification (DNTC): the possibility of lead neurotoxicity. Neuroreport 12: 3887-3890.
4 Harville, E. W.; Hertz-Picciotto, I.; Schramm, M.; Watt-Morse, M; Chantala, K.; Osterloh, J.; Parsons, P. I;
5 Rogan, W. (2005) Factors influencing the difference between maternal and cord blood lead. Occup.
6 Environ. Med. 62: 263-290.
7 Hasselblad, V.; Nelson, W. (1975) Additional analysis of the seven city lead study. In: Griffin, T. B.; Knelson, J. H.,
8 eds. Lead. Stuttgart, Federal Republic of Germany: Georg Thieme Publishers; pp. 147-151. (Coulston, F.;
9 Korte, F., eds. Environmental quality and safety: supplement v. 2).
10 Hasselblad, V.; Stead, A. G.; Galke, W. (1980) Analysis of coarsely grouped data from the lognormal distribution.
11 JASA J. Am. Stat. Assoc. 75: 771-778.
12 Hatzakis, A.; Salaminios, F.; Kokevi, A.; Katsouyanni, K.; Maravelias, K.; Kalandidi, A.; Koutselinis, A.;
13 Stefanis, K.; Trichopoulos, D. (1985) Blood lead and classroom behaviour of children in two communities
14 with different degree of lead exposure: evidence of a dose-related effect? In: Lekkas, T. D., ed.
15 International conference: heavy metals in the environment, v. 1; September; Athens, Greece. Edinburgh,
16 United Kingdom: CEP Consultants, Ltd.; p. 47.
17 Hatzakis, A.; Kokkevi, A.; Maravelias, C.; Katsouyanni, K.; Salaminios, F.; Kalandidi, A.; Koutselinis, A.;
18 Stefanis, C.; Trichopoulos, D. (1989) Psychometric intelligence deficits in lead-exposed children. In:
19 Smith, M. A.; Grant, L. D.; Sors, A. I., eds. Lead exposure and child development: an international
20 assessment [workshop organized by the Commission of the European Communities and the U.S.
21 Environmental Protection Agency]; September 1986; Edinburgh, United Kingdom. Dordrecht, The
22 Netherlands: Kluwer Academic Publishers BV; pp. 211-223.
23 Haynes, E. N.; Kalkwarf, H. J.; Hornung, R.; Wenstrup, R.; Dietrich, K.; Lanphear, B. P. (2003) Vitamin D receptor
24 Fokl polymorphism and blood lead concentration in children. Environ. Health Perspect. Ill: 1665-1669.
25 He, F. S.; Zhang, S. L.; Li, G.; Zhang, S. C.; Huang, J. X.; Wu, Y. Q. (1988) An electroneurographic assessment of
26 subclinical lead neurotoxicity. Int. Arch. Occup. Environ. Health 61: 141-146.
27 Hellstrom, L.; Blinder, C.-G.; Dahlberg, B.; Lundberg, M.; Jarup, L.; Persson, B.; Axelson, O. (2001) Cadmium
28 exposure and end-stage renal disease. Am. J. Kidney Dis. 38: 1001-1008.
29 Hemdan, N. Y. A.; Emmrich, F.; Adham, K.; Wichmann, G.; Lehmann, I.; El-Massry, A.; Ghoneim, H.; Lehmann,
30 J.; Sack, U. (2005) Dose-dependent modulation of the in vitro cytokine production of human immune
31 competent cells by lead salts. Toxicol. Sci. 86: 75-83.
32 Henderson, D. A. (1955) Chronic nephritis in Queensland. Australas. Ann. Med. 4: 163-177.
33 Hense, H. W.; Filipiak, B.; Keil, U. (1993) The association of blood lead and blood pressure in population surveys.
34 Epidemiology 4: 173-179.
35 Hense, H. W.; Filipiak, B.; Keil, U. (1994) Alcohol consumption as a modifier of the relation between blood lead
36 and blood pressure. Epidemiology 5: 120-123.
37 Heo, Y.; Lee, B.-K.; Ahn, K.-D.; Lawrence, D. A. (2004) Serum IgE elevation correlates with blood lead levels in
38 battery manufacturing workers. Hum. Exp. Toxicol. 23: 209-213.
39 Hernandez-Avila, M.; Gonzalez-Cossio, T.; Palazuelos, E.; Romieu, L; Aro, A.; Fishbein, E.; Peterson, K. E.;
40 Hu, H. (1996) Dietary and environmental determinants of blood and bone lead levels in lactating
41 postpartum women living in Mexico City. Environ. Health Perspect. 104: 1076-1082.
42 Hernandez-Avila, M.; Smith, D.; Meneses, F.; Sanin, L. H.; Hu, H. (1998) The influence of bone and blood lead on
43 plasma lead levels in environmentally exposed adults. Environ. Health Perspect. 106: 473-477.
44 Hernandez-Avila, M.; Villalpano, C. G.; Palazuelos, E.; Villapando, M. E. G. (2000) Determinants of blood lead
45 levels across the menopausal transition. Arch. Environ. Health 53: 355-360.
46 Hernandez-Avila, M.; Peterson, K. E.; Gonzalez-Cossio, T.; Sanin, L. H.; Aro, A.; Schnaas, L.; Hu, H. (2002) Effect
47 of maternal bone lead on length and head circumference of newborns and 1-month-old infants. Arch.
48 Environ. Health 57: 482-488.
49 Hernandez-Avila, M.; Gonzalez-Cossio, T.; Hernandez-Avila, J. E.; Romieu, I.; Peterson, K. E.; Aro, A.;
50 Palazuelos, E.; Hu, H. (2003) Dietary calcium supplements to lower blood lead levels in lactating women:
51 a randomized placebo-controlled trial. Epidemiology 14: 206-212.
52 Hernandez-Ochoa, I.; Garcia-Vargas, G.; Lopez-Carrillo, L.; Rubio-Andrade, M.; Moran-Martinez, J.; Cebrian,
53 M. E.; Quintanilla-Vega, B. (2005) Low lead environmental exposure alters semen quality and sperm
54 chromatin condensation in northern Mexico. Reprod. Toxicol. 20: 221-228.
55 Hernberg, S.; Nikkanen, J.; Mellin, G.; Lilius, H. (1970) 5-aminolevulinic acid dehydrase as a measure of lead
56 exposure. Arch. Environ. Health 21: 140-145.
May 2006 6-346 DRAFT-DO NOT QUOTE OR CITE
-------
1 Hertz-Picciotto, I. (2000) The evidence that lead increases the risk for spontaneous abortion. Am. J. Ind. Med.
2 38:300-309.
3 Hertz-Picciotto, I.; Croft, J. (1993) Review of the relation between blood lead and blood pressure. Epidemiol. Rev.
4 15:352-373.
5 Hertz-Picciotto, I.; Schramm, M; Watt-Morse, M; Chantala, K.; Anderson, J.; Osterloh, J. (2000) Patterns and
6 determinants of blood lead during pregnancy. Am. J. Epidemiol. 152: 829-837.
7 Hill, A. B. (1965) The environment and disease: association or causation? Proc. R. Soc. Med. 58: 295-300.
8 Hirata, M.; Kosaka, H. (1993) Effects of lead exposure on neurophysiological parameters. Environ. Res. 63: 60-69.
9 Hogstedt, C.; Hane, M.; Agrell, A; Bodin, L. (1983) Neuropsychological test results and symptoms among workers
10 with well-defined long-term exposure to lead. Br. J. Ind. Med. 40: 99-105.
11 Holness, D. L.; Nethercott, J. R. (1988) Acute lead intoxication in a group of demolition workers. Appl. Ind. Hyg.
12 3:338-341.
13 Holdstein, Y.; Pratt, H.; Goldsher, M.; Rosen, G.; Shenhav, R.; Linn, S.; Mor, A.; Barkai, A. (1986) Auditory
14 brainstem evoked potentials in asymptomatic lead-exposed subjects. J. Laryngol. Otol. 100: 1031-1036.
15 Horiguchi, S.; Endo, G.; Kiyota, I. (1987) Measurement of total triiodothyronine (T3), total thyroxine (T4) and
16 thyroid-stimulating hormone (TSH) levels in lead-exposed workers. Osaka City Med J. 33: 51-56.
17 Horiguchi, S.; Matsumura, S.; Fukumoto, K.; Karai, L; Endo, G.; Teramoto, K.; Shinagawa, K.; Kiyota, L;
18 Wakitani, F.; Takise, S.; Kawaraya, T. (1991) Erythrocyte deformability in workers exposed to lead.
19 Osaka City Med. J. 37: 149-155.
20 Hotz, P.; Buchet, J. P.; Bernard, A.; Lison, D.; Lauwerys, R. (1999) Renal effects of low-level environmental
21 cadmium exposure: 5-year follow-up of a subcohort from the Cadmibel study. Lancet 354: 1508-1513.
22 Hsiao, C. Y.; Wu, H. D.; Lai, J. S.; Kuo, H. W. (2001) A longitudinal study of the effects of long-term exposure to
23 lead among lead battery factory workers in Taiwan (1989-1999). Sci. Total Environ. 279: 151-158.
24 Hsieh, L. L.; Liou, S. H.; Chen, Y. H.; Tsai, L. C.; Yang, T.; Wu, T. N. (2000) Association between aminolevulinate
25 dehydrogenase genotype and blood lead levels in Taiwan. J. Occup. Environ. Med. 42(2): 151-155.
26 Hu, H. (1991) A 50-year follow-up of childhood plumbism: hypertension, renal function, and hemoglobin levels
27 among survivors. Am. J. Dis. Child. 145: 681-687.
28 Hu, H.; Milder, F. L.; Burger, D. E. (1990) X-ray fluorescence measurements of lead burden in subjects with low-
29 level community lead exposure. Arch. Environ. Health 45: 335-341.
30 Hu, H.; Milder, F. L.; Burger, D. E. (1991) The use of K X-ray fluorescence for measuring lead burden in
31 epidemiological studies: high and low lead burdens and measurement uncertainty. Environ. Health
32 Perspect. 94: 107-110.
33 Hu, H.; Watanabe, H.; Payton, M.; Korrick, S.; Rotnitzky, A. (1994) The relationship between bone lead and
34 hemoglobin. JAMA J. Am. Med. Assoc. 272: 1512-1517.
35 Hu, H.; Aro, A.; Rotnitzky, A. (1995) Bone lead measured by X-ray fluorescence: epidemiologic methods. Environ.
36 Health Perspect. 103(suppl. 1): 105-110.
37 Hu, H.; Aro, A.; Payton, M.; Korrick, S.; Sparrow, D.; Weiss, S. T.; Rotnitzky, A. (1996) The relationship of bone
38 and blood lead to hypertension. The Normative Aging Study. JAMA J. Am. Med. Assoc. 275: 1171-1176.
39 Hu, H.; Rabinowitz, M.; Smith, D. (1998) Bone lead as a biological marker in epidemiologic studies of chronic
40 toxicity: conceptual paradigms. Environ. Health Perspect. 106: 1-8.
41 Hu, J.; La Vecchia, C.; Negri, E.; Chatenoud, L.; Bosetti, C.; Jia, X.; Liu, R.; Huang, G.; Bi, D.; Wang, C. (1999)
42 Diet and brain cancer in adults: a case-control study in northeast China. Int. J. Cancer 81: 20-23.
43 Hu, H.; Wu, M.-T.; Cheng, Y.; Sparrow, D.; Weiss, S.; Kelsey, K. (2001) The 5-aminolevulinic acid dehydratase
44 (ALAD) polymorphism and bone and blood lead levels in community-exposed men: the Normative Aging
45 Study. Environ. Health Perspect. 109: 827-832.
46 Huang, J.; He, F.; Wu, Y.; Zhang, S. (1988) Observations on renal function in workers exposed to lead. Sci. Total
47 Environ. 71:535-537.
48 Huel, G.; Boudene, C.; Ibrahim, M. A. (1981) Cadmium and lead content of maternal and newborn hair: relationship
49 to parity, birth weight, and hypertension. Arch. Environ, health 36: 221-227.
50 Hunter, J.; Urbanowicz, M. A.; Yule, W.; Lansdown, R. (1985) Automated testing of reaction time and its
51 association with lead in children. Int. Arch. Occup. Environ. Health 57: 27-34.
52 Hwang, K.-Y.; Lee, B.-K.; Bressler, J. P.; Bolla, K. I.; Stewart, W. F.; Schwartz, B. S. (2002) Proteinkinase C
53 activity and the relations between blood lead and neurobehavioral function in lead workers. Environ.
54 Health Perspect. 110: 133-138.
May 2006 6-347 DRAFT-DO NOT QUOTE OR CITE
-------
1 Inskip, M. I; Franklin, C. A.; Baccanale, C. L.; Manton, W. I.; O'Flaherty, E. I; Edwards, C. M. H.; Blenkinsop,
2 J. B.; Edwards, E. B. (1996) Measurement of the flux of lead from bone to blood in a nonhuman primate
3 (Macaca fascicularis) by sequential administration of stable lead isotopes. Fundam. Appl. Toxicol.
4 33:235-245.
5 International Agency for Research on Cancer (IARC). (1980) Some metals and metallic compounds. Lyon, France:
6 International Agency for Research on Cancer. (IARC monographs on the evaluation of the carcinogenic
7 risk of chemicals to humans: volume 23).
8 International Agency for Research on Cancer (IARC). (2005) Inorganic and organic lead compounds. Lyon, France:
9 International Agency for Research on Cancer. (IARC monographs on the evaluation of the carcinogenic
10 risk of chemicals to humans: volume 87: in preparation).
11 Irgens, A.; Kriiger, K.; Skorve, A. H.; Irgens, L. M. (1998) Reproductive outcome in offspring of parents
12 occupationally exposed to lead in Norway. Am. J. Ind. Med. 34: 431-437.
13 Ishida, M.; Ishizaki, M.; Yamada, Y. (1996) Decreases in postural change of finger blood flow in ceramic painters
14 chronically exposed to low level lead. Am. J. Ind. Med. 29: 547-553.
15 Ito, Y.; Niiya, Y.; Kurita, H.; Shima, S.; Sarai, S. (1985) Serum lipid peroxide level and blood superoxide dismutase
16 activity in workers with occupational exposure to lead. Int. Arch. Occup. Environ. Health 56: 119-127.
17 Iwata, T.; Yano, E.; Karita, K.; Dakeishi, M.; Murata, K. (2005) Critical dose of lead affecting postural balance in
18 workers. Am. J. Ind. Med. 48: 319-325.
19 Jackson, L. W.; Correa-Villasenor, A.; Lees, P. S. J.; Dominici, F.; Stewart, P. A.; Breysse, P. N.; Matanoski, G.
20 (2004) Parental lead exposure and total anomalous pulmonary venous return. Birth Defects Res. Part A
21 70: 185-193.
22 Ja'rup, L.; Hellstrom, L.; Alfven, T.; Carlsson, M. D.; Grubb, A.; Persson, B.; Pettersson, C.; Spang, G.; Schutz, A.;
23 Blinder, C.-G. (2000) Low level exposure to cadmium and early kidney damage: the OSCAR study. Occup.
24 Environ. Med. 57: 668-672.
25 Jemal, A.; Graubard, B. I.; Devesa, S. S.; Flegal, K. M. (2002) The association of blood lead level and cancer
26 mortality among whites in the United States. Environ. Health Perspect. 110: 325-329.
27 Jiun, Y. S.; Hsien, L. T. (1994) Lipid peroxidation in workers exposed to lead. Arch. Environ. Health 49: 256-259.
28 Joffe, M.; Bisanti, L.; Apostoli, P.; Kiss, P.; Dale, A.; Roeleveld, N.; Lindbohm, M.-L.; Sallmen, M.; Vanhoorne,
29 M.; Bonde, J. P.; Asclepios. (2003) Time to pregnancy and occupational lead exposure. Occup. Environ.
30 Med. 60: 752-758.
31 Johnson, R. J.; Kang, D.-H.; Feig, D.; Kivlighn, S.; Kanellis, J.; Watanabe, S.; Tuttle, K. R.; Rodriguez-Iturbe, B.;
32 Herrera-Acosta, J.; Mazzali, M. (2003) Is there a pathogenetic role for uric acid in hypertension and
33 cardiovascular and renal disease? Hypertension 41: 1183-1190.
34 Jones, S. J.; Williams, A. J.; Kudlac, H.; Hainsworth, I. R.; Morgan, W. D. (1990) The measurement of bone lead
3 5 content in patients with end stage failure. In: Yasumura, S.; Harrison, J. E., eds. In vivo body composition
36 studies: recent advances. New York, NY: Plenum Press; pp. 259-262. (Basic life sciences: v. 55).
37 Joseph, C. L. M.; Havstad, S.; Ownby, D. R.; Peterson, E. L.; Maliarik, M.; McCabe, M. J.; Barone, C.; Johnson,
38 C. C. (2005) Blood lead levels and risk of asthma. Environ. Health Perspect. 113: 900-904.
39 Juarez-Perez, C. A.; Aguilar-Madrid, G.; Smith, D. R.; Lacasana-Navarro, M.; Tellez-Rojo, M. M.; Piacitteli, G.;
40 Hu, H.; Hernandez-Avila, M. (2004) Predictors of plasma lead among lithographic print shop workers in
41 Mexico City. Am. J. Ind. Med. 46: 245-252.
42 Jung, K.-Y.; Lee, S.-J.; Kim, J.-Y.; Hong, Y.-S.; Kim, S.-R.; Kim, D.-I.; Song, J.-B. (1998) Renal dysfunction
43 indicators in lead exposed workers. J. Occup. Health 40: 103-109.
44 Jurek, A. M.; Greenland, S.; Maldonado, G.; Church, T. R. (2005) Proper interpretation of non-differential
45 misclassification effects: expectations vs observations. Int. J. Epidemiol. 34: 680-687.
46 Kamel, F.; Umbach, D.; Munsat, T.; Shefner, J.; Hu, H.; Sandier, D. (2002) Lead exposure and amyotrophic later
47 sclerosis. Epidemiology 13: 311-319.
48 Kamel, F.; Umbach, D. M.; Lehman, T. A.; Park, L. P.; Munsat, T. L.; Shefner, J. M.; Sandier, D. P.; Hu, H.;
49 Taylor, J. A. (2003) Amyotrophic lateral sclerosis, lead, and genetic susceptibility: polymorphisms in
50 the 5-aminolevulinic acid dehydratase and vitamin D receptor genes. Environ. Health Perspect.
51 111:1335-1339.
52 Kandiloros, D. C.; Goletsos, G. A.; Nikolopoulos, T. P.; Ferekidis, E. A.; Tsomis, A. S.; Adamopoulos, G. K. (1997)
53 Effect of subclinical lead intoxication on laryngeal cancer. Br. J. Clin. Practice 51: 69-70.
54 Kannel, W. B. (1996) Blood pressure as a cardiovascular risk factor: prevention and treatment. JAMA J. Am. Med.
55 Assoc. 275: 1571-1576.
56 Kannel, W. B. (2000a) Elevated systolic blood pressure as a cardiovascular risk factor. Am. J. Cardiol. 85: 251-255.
May 2006 6-348 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kannel, W. B. (2000b) Risk stratification in hypertension: new insights from the Framingham Study. Am. J.
2 Hypertens. 13: 3S-10S.
3 Karakaya, A. E.; Ozcagli, E.; Ertas, N.; Sardas, S. (2005) Assessment of abnormal DNA repair responses and
4 genotoxic effects in lead exposed workers. Am. J. Ind. Med. 47: 358-363.
5 Karmaus, W.; Brooks, K. R.; Nebe, T.; Witten, J.; Obi-Osius, N.; Kruse, H. (2005) Immune functionbiomarkers in
6 children exposed to lead and organochlorine compounds: a cross-sectional study. Environ. Health Glob.
7 Access Sci. 4: 1-10.
8 Kaufman, A. S.; Kaufman, N. L. (1983) Kaufman assessment battery for children. Circle Pines, MN: American
9 Guidance Service.
10 Kauppinen, T.; Riala, R.; Seitsamo, J.; Hernberg, S. (1992) Primary liver cancer and occupational exposure. Scand.
11 J. Work Environ. Health. 18: 18-25.
12 Kavlock, R. J.; Daston, G. P.; DeRosa, C.; Fenner-Crisp. P.; Gray, L. E.; Kaattari, S.; Lucier, G.; Luster, M; Mac,
13 M. J.; Maczka, C.; Miller, R.; Moore, J.; Rolland, R.; Scott, G.; Sheehan, D. M.; Sinks, T.; Tilson, H. A.
14 (1996) Research needs for the risk assessment of health and environmental effects of endocrine disrupters:
15 a report of the U.S. EPA-sponsored workshop. Environ. Health Perspect. Suppl. 104(4): 715-740.
16 Kehoe, R. A. (1987) Studies of lead administration and elimination in adult volunteers under natural and
17 experimentally induced conditions over extended periods of time. Food Chem. Toxicol. 25: 425-493.
18 Kelada, S. N.; Shelton, E.; Kaufmann, R. B.; Khoury, M. J. (2001) 5-aminolevulinic acid dehydratase genotype and
19 lead toxicity: a HuGE review. Am. J. Epidemiol. 154: 1-13.
20 Kessler, M.; Durand, P. Y.; Huu, T. C.; Royer-Morot, M. J.; Chanliau, J.; Netter, P.; Due, M. (1999) Mobilization of
21 lead from bone in end-stage renal failure patients with secondary hyperparathyroidism. Nephrol. Dial.
22 Transplant. 14:2731-2733.
23 Khalil-Manesh, F.; Gonick, H. C.; Cohen, A.; Bergamaschi, E.; Mutti, A. (1992) Experimental model of lead
24 nephropathy. II. Effect of removal from lead exposure and chelation treatment with dimercaptosuccinic
25 acid (DMSA). Environ. Res 58: 35-54.
26 Keiding, N.; Skakkebaek, N. E. (1996) Sperm decline-real or artifact? Fertil. Steril. 65: 450-453.
27 Keiding, N.; Giwercman, A.; Carlsen, E.; Skakkebaek, N. E. (1994) Comment on "Farrow, S. (1994) Falling sperm
28 quality: fact of fiction? Br. Med. J. 309: 1-2." Br. Med. J. 309: 131.
29 Kim, R.; Aro, A.; Rotnitzky, A.; Amarasiriwardena, C.; Hu, H. (1995) K x-ray fluorescence measurements of bone
30 lead concentration: the analysis of low-level data. Phys. Med. Biol. 40: 1475-1485.
31 Kim, R.; Rotnitsky, A.; Sparrow, D.; Weiss, S. T.; Wager, C.; Hu, H. (1996) A longitudinal study of low-level lead
32 exposure and impairment of renal function. The Normative Aging Study. JAMA J. Am. Med. Assoc.
33 275: 1177-1181.
34 Kim, Y.; Lee, H.; Lee, C. R.; Park, D. U.; Yang, J. S.; Park, I. J.; Lee, K. Y.; Lee, M.; King, T. K.; Sohn, N. S.; Cho,
35 Y. S.; Lee, N.; Chung, H. K. (2002) Evaluation of lead exposure in workers at secondary lead smelters in
3 6 South Korea: with focus on activity of erythrocyte pyrimidine 5'-nucleotidase (P5N). Sci. Total Environ.
37 286: 181-189.
38 Kimber, I.; Stonard, M. D.; Gidlow, D. A.; Niewola, Z. (1986) Influence of chronic low-level exposure to lead on
39 plasma immunoglobulin concentration and cellular immune function in man. Int. Arch. Occup. Environ.
40 Health 57: 117-125.
41 Klein, D.; Wan, Y.-J. Y.; Kamyab, S.; Okuda, H.; Sokol, R. Z. (1994) Effects of toxic levels of lead on gene
42 regulation in the male axis: increase in messenger ribonucleic acids and intracellular stores of gonadotrophs
43 within the central nervous system. Biol. Reprod. 50: 802-811.
44 Kline, J.; Stein, Z.; Hutzler, M. (1987) Cigarettes, alcohol and marijuana: varying associations with birthweight. Int.
45 J. Epidemiol. 16:44-51.
46 Klitzman, S.; Sharma, A.; Nicaj, L.; Vitkevich, R.; Leighton, J. (2002) Lead poisoning among pregnant women in
47 New York City: risk factors and screening practices. Bull. N. Y. Acad. Med. 79: 225-237.
48 Koller, K.; Brown, T.; Spurgeon, A.; Levy, L. (2004) Recent developments in low-level lead exposure and
49 intellectual impairment in children. Environ. Health Perspect. 112: 987-994.
50 Konishi, Y.; Endo, G.; Kiyota, A.; Horiguchi, S. (1994) Fractional clearances of low molecular weight proteins in
51 lead workers. Ind. Health 32: 119-127.
52 Koo, W. W. K.; Succop, P. A.; Bornschein, R. L.; Krugwispe, S. K.; Steinchen, J. J.; Tsang, R. C.; Berger, O.G.
53 (1991) Serum vitamin D metabolites and bone mineralization in young children with chronic low to
54 moderate lead exposure. Pediatrics 87: 680-687.
May 2006 6-349 DRAFT-DO NOT QUOTE OR CITE
-------
1 Kordas, K.; Lopez, P.; Rosado, J. L.; Vargas, G. G.; Rico, J. A.; Ronquillo, D.; Cebrian, M. E.; Stoltzfus, R. J.
2 (2004) Blood lead, anemia, and short stature are independently associated with cognitive performance in
3 Mexican school children. J. Nutr. 134: 363-371.
4 Kordas, K.; Stoltzfus, R. J.; Lopez, P.; Rico, J. A.; Rosado, J. L. (2005) Iron and zinc supplementation does not
5 improve parent orteacher ratings of behavior in first grade Mexican children exposed to lead. J. Pediatr.
6 147:632-639.
7 Kordas, K.; Canfield, R. L.; Lopez, P.; Rosado, J. L.; Vargas, G. G.; Cebrian, M. E.; Rico, J. A.; Ronquillo, D.;
8 Stoltzfus, R. J. (2006) Deficits in cognitive function and achievement in Mexican first-graders with low
9 blood lead concentrations. Environ. Res. 100: 371-386.
10 Korrick, S. A.; Hunter, D. J.; Rotnitzky, A.; Hu, H.; Speizer, F. E. (1999) Lead and hypertension in a sample of
11 middle-aged women. Am. J. Public Health 89: 330-335.
12 Korrick, S. A.; Schwartz, J.; Tsaih, S.-W.; Hunter, D. J.; Aro, A.;Rosner, B.; Speizer, F. E.; Hu, H. (2002) Correlates
13 of bone and blood lead levels among middle-aged and elderly women. Am. J. Epidemiol. 156: 335-343.
14 Kosnett, M. J.; Becker, C. E.; Osterloh, J. D.; Kelly, T. J.; Pasta, D. J. (1994) Factors influencing bone lead
15 concentration in a suburban community assessed by noninvasive K x-ray fluorescence. JAMA J. Am. Med.
16 Assoc. 271: 197-203.
17 Koster, J.; Erhardt, A.; Stoeppler, M.; Mohl, C.; Ritz, E. (1989) Mobilizable lead in patients with chronic renal
18 failure. Eur. J. Clin. Invest. 19: 228-233.
19 Kovala, T.; Matikainen, E.; Mannelin, T.; Erkkila, J.; Riihimaki, V; Hanninen, H.; Aitio, A. (1997) Effects of low
20 level exposure to lead on neurophysiological functions among lead battery workers. Occup. Environ. Med.
21 54:487-493.
22 Kramer, M. S. (1987) Intrauterine growth and gestational duration determinants. Pediatrics 80: 502-511.
23 Kramer, M. S.; McLean, F. H.; Boyd, M. E.; Usher, R. H. (1988) The validity of gestational age estimation by
24 menstrual dating in term, preterm, and postterm gestations. JAMA J. Am. Med. Assoc. 260: 3306-3308.
25 Krieg, E. F., Jr.; Chrislip, D. W.; Crespo, C. J.; Brightwell, W. S.; Ehrenberg, R. L.; Otto, D. A. (2005) The
26 relationship between blood lead levels and neurobehavioral test performance in NHANES III and related
27 occupational studies. Public HealthRep. 120: 240-251.
28 Kristal-Boneh, E.; Froom, P.; Yerushalmi, N.; Harari, G.; Ribak, J. (1998) Calcitropic hormones and occupational
29 lead exposure. Am. J. Epidemiol. 147: 458-463.
30 Kristal-Boneh, E.; Coller, D.; Froom, P.; Harari, G.; Ribak, J. (1999) The association between occupational lead
31 exposure and serum cholesterol and lipoprotein levels. Am. J. Public Health 89: 1083-1087.
32 Kristensen, P.; Irgens, L. M.; Daltveit, A. K.; Andersen, A. (1993) Perinatal outcome among children of men
33 exposed to lead and organic solvents in the printing industry. Am. J. Epidemiol. 137: 134-144.
34 Kromhout, D.; Wibowo, A. A. E.; Herber, R. F. M.; Dalderup, L. M.; Heerdink, H.; de Lezenne Coulander, C.;
35 Zielhuis, R. L. (1985) Trace metals and coronary heart disease risk indicators in 152 elderly men (the
36 Zutphen study). Am. J. Epidemiol. 122: 378-385.
37 Kumar, B. D.; Krishnaswamy, K. (1995) Detection of occupational lead nephropathy using early renal markers.
38 J. Toxicol. Clin. Toxicol. 33: 331-335.
39 Kuo, H.-W.; Hsiao, T.-Y.; Lai, J.-S. (2001) Immunological effects of long-term lead exposure among Taiwanese
40 workers. Arch. Toxicol. 75: 569-573.
41 Lacey, R. F.; Moore, M. R.; Richards, W. N. (1985) Lead in water, infant diet and blood: the Glasgow Duplicate
42 Diet Study. Sci. Total Environ. 41: 235-257.
43 Lagerkvist, B. J.; Ekesrydh, S.; Englyst, V; Nordberg, G. F.; Soderberg, H.-A.; Wiklund, D.-E. (1996) Increased
44 blood lead and decreased calcium levels during pregnancy: a prospective study of Swedish women living
45 near a smelter. Am. J. Public Health 86: 1247-1252.
46 Lancranjan, I.; Popescu, H. I.; Gavanescu, O.; Klepsch, I.; Serbanescu, M. (1975) Reproductive ability of workmen
47 occupationally exposed to lead. Arch. Environ. Health 30: 396-401.
48 Lanphear, B. P.; Burgoon, D. A.; Rust, S. W.; Eberly, S.; Galke, W. (1998) Environmental exposures to lead and
49 urban children's blood lead levels. Environ. Res. 76: 120-130.
50 Lanphear, B. P.; Howard, C.; Eberly, S.; Auinger, P.; Kolassa, J.; Weitzman, M.; Schaffer, S. J.; Alexander, K.
51 (1999) Primary prevention of childhood lead exposure: a randomized trial of dust control. Pediatrics
52 103:772-777.
53 Lanphear, B. P.; Dietrich, K.; Auinger, P.; Cox, C. (2000) Cognitive deficits associated with blood lead
54 concentrations < 10 ug/dL in U.S. children and adolescents. Public Health Rep. 115: 521-529.
May 2006 6-350 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lanphear, B. P.; Hornung, R.; Khoury, J.; Yolton, K.; Baghurst, P.; Bellinger, D. C.; Canfield, R. L.; Dietrich, K.
2 N.; Bornschein, R.; Greene, T.; Rothenberg, S. J.; Needleman, H. L.; Schnaas, L.; Wasserman, G.;
3 Graziano, J.; Roberts, R. (2005) Low-level environmental lead exposure and children's intellectual
4 function: an international pooled analysis. Environ. Health Perspect. 113: 894-899.
5 Lanphear, B. P.; Hornung, R.; Khoury, J.; Yolton, K.; Dietrich, K. N. (2006) Lead and IQ in children: Lanphear
6 et al. respond [letter]. Environ. Health Perspect. 114: A86-A87.
7 Lansdown, R.; Yule, W.; Urbanowicz, M.-A.; Hunter, J. (1986) The relationship between blood-lead concentrations,
8 intelligence, attainment and behaviour in a school population: the second London study. Int. Arch. Occup.
9 Environ. Health 57: 225-235.
10 Last, J. M. (2001) A dictionary of epidemiology. New York, NY: Oxford University Press.
11 Laudanski, T.; Sipowicz, M.; Modzelewski, P.; Bolinski, J.; Szamatowicz, J.; Razniewska, G.; Akerlund, M. (1991)
12 Influence of high lead and cadmium soil content on human reproductive outcome. Int. J. Gynecol. Obstet.
13 36:309-315.
14 Laughlin, N. K.; Bowman, R. E.; Franks, P. A.; Dierschke, D. J. (1987) Altered menstural cycles in rhesus monkeys
15 induced by lead. Fundam. Appl. Toxicol. 9: 722-729.
16 Lauwers, M. C.; Hauspie, R. C.; Susanne, C.; Verheyden, J. (1986) Comparison of biometric data of children with
17 high and low levels of lead in the blood. Am. J. Phys. Anthropol. 69: 107-116.
18 Lauwerys, R.; Buchet, J. P.; Roels, H.; Hubermont, G. (1978) Placenta! transfer of lead, mercury, cadmium, and
19 carbon monoxide in women: I. comparison of the frequency distributions of the biological indices in
20 maternal and umbilical cord blood. Environ. Res. 15: 278-289.
21 Laxen, D. P. H.; Raab, G. M.; Fulton, M. (1987) Children's blood lead and exposure to lead in household dust and
22 water — a basis for an environmental standard for lead in dust. Sci. Total Environ. 66: 235-244.
23 Lazutka, J. R.; Lekevicius, R.; Dedonyte, V.; Maciuleviciute-Gervers, L.; Mierauskiene, J.; Rudaitiene, S.; Slapsyte,
24 G. (1999) Chromosomal aberrations and sister-chromatid exchanges in Lithuanian populations: effects of
25 occupational and environmental exposures. Mutat. Res. 445: 225-239.
26 Leal-Garza, C.; Moates, D. O. R.; Cerda-Flores, R. M.; et al. (1986) Frequency of sister-chromatid exchanges (SCE)
27 in lead exposed workers. Arch. Invest. Med. 17: 267-276.
28 Lee, B.-K.; Ahn, K.-D.; Lee, S.-S.; Lee, G.-S.; Kim, Y.-B.; Schwartz, B. S. (2000) A comparison of different lead
29 biomarkers in their associations with lead-related symptoms. Int. Arch. Occup. Environ. Health
30 73:298-304.
31 Lee, B.-K.; Lee, G.-S.; Stewart, W. F.; Ahn, K.-D.; Simon, D.; Kelsey, K. T.; Todd, A. C.; Schwartz, B. S. (2001)
3 2 Associations of blood pressure and hypertension with lead dose measures and polymorphisms in the
33 vitamin D receptor and 5-aminolevulinic acid dehydratase genes. Environ. Health Perspect. 109: 383-389.
34 Leggett, R. W. (1993) An age-specific kinetic model of lead metabolism in humans. Environ. Health Perspect.
35 101:598-616.
36 Lerchl, A. (1995) Evidence for decreasing quality of sperm. Presentation of data on sperm concentration was
3 7 flawed. Br. Med. J. 311: 569-570.
3 8 Lerda, D. (1992) Study of sperm characteristics in persons occupationally exposed to lead. Am. J. Ind. Med.
39 22:567-571.
40 Levey, A. S.; Bosc, J. P.; Lewis, J. B.; Greene, T.; Rogers, N.; Roth, D. (1999) A more accurate method to estimate
41 glomerular filtration rate from serum creatinine: a new prediction equation. Ann. Intern. Med.
42 130:461-470.
43 Levey, A. S.; Coresh, J.; Balk, E.; Kausz, A. T.; Levin, A.; Steffes, M. W.; Hogg, R. J.; Perrone, R. D.; Lau, J.;
44 Eknoyan, G. (2003) National kidney foundation practice guidelines for chronic kidney disease: evaluation,
45 classification, and stratification. Ann. Intern. Med. 139: 137-147.
46 Leviton, A.; Bellinger, D.; Allred, E. N.; Rabinowitz, M.; Needleman, H.; Schoenbaum, S. (1993) Pre- and postnatal
47 low-level lead exposure and children's dysfunction in school. Environ. Res. 60: 30-43.
48 Lezak, M. (1995) Neuropsychological assessment. New York, NY: Oxford University Press.
49 Lezak, M. D. (2004) Neuropsychological assessment. 4th ed. New York, NY: Oxford University Press.
50 Lidsky, T. I.; Schneider, J. S. (2003) Lead neurotoxicity in children: basic mechanisms and clinical correlates.
51 Brain 126: 5-19.
52 Liebelt, E. L.; Schonfeld, D. J.; Gallagher, P. (1999) Elevated blood lead levels in children are associated with lower
53 erythropoietin concentrations. J. Pediatr. 134: 107-109.
54 Lilis, R.; Gavrilescu, N.; Nestorescu, B.; Dumitriu, C.; Roventa, A. (1968) Nephropathy in chronic lead poisoning.
55 Br. J. Ind. Med. 25: 196-202.
May 2006 6-3 51 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lilis, R.; Eisinger, J.; Blumberg, W.; Fischbein, A.; Selikoff, I. J. (1978) Hemoglobin, serum iron, and zinc
2 protoporphyrin in lead-exposed workers. Environ. Health Perspect. 25: 97-102.
3 Lim, Y. C.; Chia, K. S.; Ong, H. Y.; Ng, V.; Chew, Y. L. (2001) Renal dysfunction in workers exposed to inorganic
4 lead. Ann. Acad. Med. Singapore 30: 112-117.
5 Lin, J. L.; Huang, P. T. (1994) Body lead stores and urate excretion in men with chronic renal disease. J. Rheumatol.
6 21:705-709.
7 Lin, J.-L.; Lim, P.-S. (1992) Elevated lead burden in Chinese patients without occupational lead exposure. Miner.
8 Electrolyte Metab. 18: 1-5.
9 Lin, J.-L.; Lim, P.-S. (1994) Does lead play a role in the development of renal insufficiency in some patients with
10 essential hypertension? J. Hum. Hypertens. 8: 495-500.
11 Lin, J.-L.; Yeh, K.-H.; Tseng, H.-C; Chen, W- Y.; Lai, H.-H.; Lin, Y.-C; Green Cross Health Service Association
12 Study Group. (1993) Urinary N-acetyl-glucosaminidase excretion and environmental lead exposure. Am. J.
13 Nephrol. 13:442-447.
14 Lin, S.; Hwang, S. A.; Marshall, E. G.; Stone, R.; Chen, J. (1996) Fertility rates among lead workers and
15 professional bus drivers: a comparative study. Ann. Epidemiol. 6: 201-208.
16 Lin, S.; Hwang, S.-A.; Marshall, E. G.; Marion, D. (1998) Does paternal occupational lead exposure increase the
17 risks of low birth weight or prematurity? Am. J. Epidemiol. 148: 173-181.
18 Lin, J.-L.; Ho, H.-H.; Yu, C.-C. (1999) Chelation therapy for patients with elevated body lead burden and
19 progressive renal insufficiency. A randomized, controlled trial. Ann. Intern. Med. 130: 7-13.
20 Lin, J.-L.; Tan, D.-T.; Hsu, K.-H.; Yu, C.-C. (2001a) Environmental lead exposure and progressive renal
21 insufficiency. Arch. Intern. Med. 161: 264-271.
22 Lin, J.-L.; Yu, C.-C.; Lin-Tan, D.-T.; Ho, H.-H. (200Ib) Lead chelation therapy and urate excretion in patients with
23 chronic renal diseases and gout. Kidney Int. 60: 266-271.
24 Lin, J.-L.; Tan, D.-T.; Ho, H.-H.; Yu, C.-C. (2002) Environmental lead exposure and urate excretion in the general
25 population. Am. J. Med. 113: 563-568.
26 Lin, J.-L.; Lin-Tan, D.-T.; Hsu, K.-H.; Yu, C.-C. (2003) Environmental lead exposure and progression of chronic
27 renal diseases in patients without diabetes. N. Engl. J. Med. 348: 277-286.
28 Lin, C.; Kim, R.; Tsaih, S.-W.; Sparrow, D.; Hu, H. (2004) Determinants of bone and blood lead levels among
29 minorities living in the Boston area. Environ. Health Perspect. 112: 1147-1151.
30 Lindbohm, M.-L.; Hemminki, K.; Bonhomme, M. G.; Anttila, A.; Rantala, K.; Heikkila, P.; Rosenberg, M. J.
31 (1991a) Effects of paternal occupational exposure on spontaneous abortions. Am. J. Public Health
32 81: 1029-1033.
33 Lindbohm, M. L.; Sallmen, M.; Anttila, A.; Taskinen, H.; Hemminki, K. (1991b) Paternal occupational lead
34 exposure and spontaneous abortion. Scand. J. Work Environ. Health 17: 95-103.
35 Lindeman, R. D.; Tobin, J.; Shock, N. W. (1985) Longitudinal studies on the rate of decline in renal function with
36 age. J. Am. Geriatr. Soc. 33: 278-285.
37 Lindgren, K.; Masten, V.; Ford, D.; Bleecker, M. (1996) Relation of cumulative exposure to inorganic lead and
38 neuropsychological test performance. Occup. Environ. Med. 53: 472-477.
39 Lindgren, K. N.; Masten, V. L.; Tiburzi, M. J.; Ford, D. P.; Bleecker, M. L. (1999) The factor structure of the profile
40 of mood states (POMS) and its relationship to occupational lead exposure. J. Occup. Environ. Med.
41 41:3-10.
42 Lindgren, K. N.; Ford, D. P.; Bleecker, M. L. (2003) Pattern of blood lead levels over working lifetime and
43 neuropsychological performance. Arch. Environ. Health 58: 373-379.
44 Liu, X.; Dietrich, K. N.; Radcliffe, J.; Ragan, N. B.; Rhoads, G. G.; Rogan, W. J. (2002) Do children with falling
45 blood lead levels have improved cognition? Pediatrics 110: 787-791.
46 Lockett, C. J.; Arbuckle, D. (1987) Lead, ferritin, zinc, and hypertension. Bull. Environ. Contam. Toxicol.
47 38:975-980.
48 Loeber, R.; Stouthamer-Loeber, M.; Van Kammen, W.; Farrington, D. P. (1991) Initiation, escalation and desistance
49 in juvenile offending and their correlates. J. Criminal Law Criminol. 82: 36-82.
50 Loghman-Adham, M. (1998) Aminoaciduria and glycosuria following severe childhood lead poisoning. Pediatr.
51 Nephrol. 12: 218-221.
52 Lopez, C. M.; Pineiro, A. E.; Nunez, N.; Avagnina, A. M.; Villaamil, E. C.; Roses, O. E. (2000) Thyroid hormone
53 changes in males exposed to lead in the Buenos Aires area (Argentina). Pharmacol. Res. 42: 599-602.
54 Louis, E. D.; Jurewicz, E. C.; Applegate, L.; Factor-Litvak, P.; Parides, M.; Andrews, L.; Slavkovich, V.; Graziano,
55 J. H.; Carroll, S.; Todd, A. (2003) Association between essential tremor and blood lead concentration.
56 Environ. Health Perspect. Ill: 1707-1711.
May 2006 6-3 52 DRAFT-DO NOT QUOTE OR CITE
-------
1 Louis, E. D.; Applegate, L.; Graziano, J. H.; Parides, M; Slavkovich, V.; Bhat, H. K. (2005) Interaction between
2 blood lead concentration and 5-amino-levulinic acid dehydratase gene polymorphisms increases the odds of
3 essential tremor. Mov. Disord. 20: 1170-1177.
4 Lucchini, R.; Albini, E.; Cortesi, L; Placidi, D.; Bergamaschi, E.; Traversa, F.; Alessio, L. (2000) Assessment of
5 neurobehavioral performance as a function of current and cumulative occupational lead exposure.
6 Neurotoxicology 21: 805-811.
7 Lundstrom, N.-G.; Nordberg, G.; Englyst, V.; Gerhardsson, L.; Hagmar, L.; Jin, T.; Rylander, L.; Wall, S. (1997)
8 Cumulative lead exposure in relation to mortality and lung cancer morbidity in a cohort of primary smelter
9 workers. Scand. J. Work Environ. Health 23: 24-30.
10 Lustberg, M.; Silbergeld, E. (2002) Blood lead levels and mortality. Arch. Intern. Med. 162: 2443-2449.
11 Lustberg, M. E.; Schwartz, B. S.; Lee, B. K.; Todd, A. C.; Silbergeld, E. K. (2004) The g(894)-t(894)polymorphism
12 in the gene for endothelial nitric oxide synthase and blood pressure in lead-exposed workers from Korea.
13 J. Occup. Environ. Med. 46: 584-590.
14 Lutz, P. M.; Wilson, T. J.; Ireland, A. L.; Gorman, J. S.; Gale, N. L.; Johnson, J. C.; Hewett, J. E. (1999) Elevated
15 immunoglobulin E (IgE) levels in children with exposure to environmental lead. Toxicology 134: 63-78.
16 Lyngbye, T.; Hansen, O. N.; Grandjean, P. (1991) Lead concentration in deciduous teeth from Danish school
17 children. Dan. Med. Bull. 38: 89-93.
18 Mahaffey, K. R.; Annest, J. L.; Roberts, J.; Murphy, R. S. (1982) National estimates of blood lead levels:
19 United States, 1976-1980. Association with selected demographic and socioeconomic factors. N. Engl.
20 J. Med. 307: 573-579.
21 Maheswaran, R.; Gill, J. S.; Beevers, D. G. (1993) Blood pressure and industrial lead exposure. Am. J. Epidemiol.
22 137:645-653.
23 Maizlish, N. A.; Parra, G.; Feo, O. (1995) Neurobehavioural evaluation of Venezuelan workers exposed to inorganic
24 lead. Occup. Environ. Med. 52: 408-414.
25 Makino, S.; Shimizu, Y.; Takata, T. (1997) A study on the relationship between blood lead levels and anemia
26 indicators in workers exposed to low levels of lead. Ind. Health 35: 537-541.
27 Maki-Paakkanen, J.; Sorsa, M.; Vainio, H. (1981) Chromosome aberrations and sister chromatid exchanges in lead-
28 exposed workers. Hereditas 94: 269-275.
29 Malcolm, D.; Barnett, H. A. (1982) A mortality study of lead workers 1925-76. Br. J. Ind. Med. 39: 404-410.
30 Malczyk, E.; Darewicz, B.; Pawlak, D.; Darewicz, J.; Buczko, W. (1999) Investigations of urinary lead
31 concentration in patients with urinary bladder carcinoma. Int. Urol. Nephrol. 31: 661 -663.
32 Mallin, K.; Rubin, M.; Joo, E. (1989) Occupational cancer mortality in Illinois white and black males, 1979-1984,
33 for seven cancer sites. Am. J. Ind. Med. 15: 699-717'.
34 Mantere, P.; Hanninen, H.; Hernberg, S. (1982) Subclinical neurotoxic lead effects: two-year follow-up studies with
35 psychological test methods. Neurobehav. Toxicol. Teratol. 4: 725-727'.
36 Manton, W. I. (1985) Total contribution of airborne lead to blood lead. Br. J. Ind. Med. 42: 168-172.
37 Manton, W. I.; Angle, C. R.; Stanek, K. L.; Kuntzelman, D.; Reese, Y. R.; Kuehnemann, T. J. (2003) Release of
38 lead from bone in pregnancy and lactation. Environ. Res. 92: 139-151.
39 Marcus, A. H.; Schwartz, J. (1987) Dose-response curves for erythrocyte protoporphyrin vs blood lead: effects of
40 iron status. Environ. Res. 44: 221-227.
41 Markowitz, M. E.; Rosen, J. F. (1981) Zinc (Zn) and copper (Cu) metabolism in CaNa2 EDTA-treated children with
42 plumbism. Pediatr. Res. 15: 635.
43 Markowitz, M. E.; Weinberger, H. L. (1990) Immobilization-related lead toxicity in previously lead-poisoned
44 children. Pediatrics 86: 455-457.
45 Markowitz, M. E.; Gundberg, C. M.; Rosen, J. F. (1988) Sequential osteocalcin campling as a biochemical marker
46 of the success of treatment of moderately lead poisoned children [abstract]. Pediatr. Res. 23: 393A.
47 Mason, H. J.; Somervaille, L. J.; Wright, A. L.; Chettle, D. R.; Scott, M. C. (1990) Effect of occupational lead
48 exposure on serum 1,25-dihydroxyvitamin D levels. Hum. Exp. Toxicol. 9: 29-34.
49 Matte, T. D.; Figueroa, J. P.; Burr, G.; Flesch, J. P.; Keenlyside, R. A.; Baker, E. L. (1989) Lead exposure among
50 lead-acid battery workers in Jamaica. Am. J. Ind. Med. 16: 167-177.
51 Matte, T. D.; Bresnahan, M.; Begg, M. D.; Susser, E. (2001) Influence of variation in birth weight within normal
52 range and within sibships on IQ at age 7 years: cohort study. Br. Med. J. 323: 310-314.
May 2006 6-353 DRAFT-DO NOT QUOTE OR CITE
-------
1 McBride, W. G.; Carter, C. I; Bratel, J. R.; Cooney, G.; Bell, A. (1989) The Sydney study of health effects of lead
2 in urban children. In: Smith, M. A.; Grant, L. D.; Sors, A. I., eds. Lead exposure and child development: an
3 international assessment [workshop organized by the Commission of the European Communities and the
4 U.S. Environmental Protection Agency]; September 1986; Edinburgh, United Kingdom. Dordrecht,
5 The Netherlands: Kluwer Academic Publishers BV; pp. 255-259.
6 McCabe, M. J.; Lawrence, D. A. (1991) Lead, a major environmental pollutant, is immunomodulatory by its
7 differential effects on CD4+ T cell subsets. Toxicol. Appl. Pharmacol. Ill: 13-23.
8 McCall, R. B. (1979) The development of intellectual functioning in infancy and the prediction of later IQ. In:
9 Osofsky, J. D., ed. Handbook of infant development. New York, NY: John Wiley; pp. 707-741.
10 McDonald, J. A.; Potter, N. U. (1996) Lead's legacy? Early and late mortality of 454 lead-poisoned children.
11 Arch. Environ. Health. 51:116-121.
12 McGregor, A. J.; Mason, H. J. (1990) Chronic occupational lead exposure and testicular endocrine function.
13 Hum. Exp. Toxicol. 9: 371-376.
14 McMichael, A. J.; Johnson, H. M. (1982) Long-term mortality profile of heavily-exposed lead smelter workers.
15 J. Occup. Med. 24: 375-378.
16 McMichael, A. J.; Vimpani, G. V.; Robertson, E. F.; Baghurst, P. A.; Clark, P. D. (1986) The Port Pirie cohort
17 study: maternal blood lead and pregnancy outcome. J. Epidemiol. Commun. Health 40: 18-25.
18 McMichael, A. J.; Baghurst, P. A.; Wigg, N. R.; Vimpani, G. V.; Robertson, E. F.; Roberts, R. J. (1988) Port Pirie
19 cohort study: environmental exposure to lead and children's abilities at the age of four years. N. Engl. J.
20 Med. 319:468-475.
21 McMichael, A. J.; Baghurst, P. A.; Vimpani, G. V; Robertson, E. F.; Wigg, N. R.; Tong, S.-L. (1992)
22 Sociodemographic factors modifying the effect of environmental lead on neuropsychological development
23 in early childhood. Neurotoxicol. Teratol. 14: 321-327.
24 McMichael, A. J.; Baghurst, P. A.; Vimpani, G. V.; Wigg, N. R.; Robertson, E. F.; Tong, S. (1994) Tooth lead
25 levels and IQ in school-age children: the Port Pirie cohort study. Am. J. Epidemiol. 140: 489-499.
26 McNeill, F. E.; Stokes, L.; Brito, J. A.; Chettle, D. R.; Kaye, W. E. (2000) 109Cd Kx-ray fluorescence measurements
27 of tibial lead content in young adults exposed to lead in early childhood. Occup. Environ. Med.
28 57:465-471.
29 Menditto, A.; Morisi, G.; Spagnolo, A.; Menotti, A.; NFR Study Group. (1994) Association of blood lead to blood
30 pressure in men aged 55 to 75 years: effect of selected social and biochemical confounders. NFR study
31 group. Environ. Health Perspect. 102(suppl. 9): 107-111.
32 Meng, X.-M.; Zhu, D.-M.; Ruan, D.-Y.; She, J.-Q.; Luo, L. (2005) Effects of chronic lead exposure on H MRS of
33 hippocampus and frontal lobes in children. Neurology 64: 1644-1647.
34 Meredith, P. A.; Campbell, B.C.; Moore, M. R.; Goldberg, A. (1977) The effects of industrial lead poisoning on
35 cytochrome P450 mediated phenazone (antipyrine) hydroxylation. Eur. J. Clin. Pharmacol. 12: 235-239.
36 Meyer-Baron, M.; Seeber, A. (2000) A meta-analysis for neurobehavioural results due to occupational lead exposure
37 with blood lead concentrations < 70 ug/100 ml. Arch. Toxicol. 73: 510-518.
38 Michaels, D.; Zoloth, S. R.; Stern, F. B. (1991) Does low-level lead exposure increase risk of death? A mortality
39 study of newspaper printers. Int. J. Epidemiol. 20: 978-983.
40 Min, Y.-L; Correa-Villasenor, A.; Stewart, P. A. (1996) Parental occupational lead exposure and low birth weight.
41 Am. J. Ind. Med. 30: 569-578.
42 Mink, P. J.; Goodman, M.; Barraj, L. M.; Imrey, H.; Kelsh, M. A.; Yager, J. (2004) Evaluation of uncontrolled
43 confounding in studies of environmental exposures and neurobehavioral testing in children. Epidemiology
44 15:385-393.
45 Minozzo, R.; Deimling, L. I.; Gigante, L. P.; Santos-Mello, R. (2004) Micronuclei in peripheral blood lymphocytes
46 of workers exposed to lead. Mutat. Res. 565: 53-60.
47 Miranda-Canis, E.; Mateos, F. A.; Sanz, A. G.; Herrero, E.; Ramos, T.; Puig, J. G. (1997) Purine metabolism in
48 patients with gout: the role of lead. Nephron 75: 327-335.
49 Mirsky, A. F. (1987) Behavioral and psychophysiological makers of disordered attention. Environ. Health Perspect.
50 74: 191-199.
51 Mishra, K. P.; Singh, V. K.; Rani, R.; Yadav, V. S.; Chandran, V.; Srivastava, S. P.; Seth, P. K. (2003) Effect of
52 lead exposure on the immune response of some occupationally exposed individuals. Toxicology
53 188:251-259.
54 Mitchell, C. S.; Shear, M. S.; Bolla, K. L; Schwartz, B. S. (1996) Clinical evaluation of 58 organolead
55 manufacturing workers. J. Occup. Environ. Med. 38: 372-378.
May 2006 6-3 54 DRAFT-DO NOT QUOTE OR CITE
-------
1 Moel, D. I.; Sachs, H. K. (1992) Renal function 17 to 23 years after chelation therapy for childhood plumbism.
2 Kidney Int. 42: 1226-1231.
3 Mohammed-Brahim, B.; Buchet, J. P.; Lauwerys, R. (1985) Erythrocyte pyrimidine 5'-nucleotidase activity in
4 workers exposed to lead, mercury or cadmium. Int. Arch. Occup. Environ. Health 55: 247-252.
5 Moline, J.; Carrillo, L. L.; Sanchez, L. T.; Godbold, J.; Todd, A. (2000) Lactation and lead body burden turnover:
6 a pilot study in Mexico. J. Occup. Environ. Med. 42: 1070-1075.
7 Moller, L.; Kristensen, T. S. (1992) Blood lead as a cardiovascular risk factor. Am. J. Epidemiol. 136: 1091-1100.
8 Moore, M. R.; Goldberg, A.; Bushnell, I. W. R.; Day, R.; Fyfe, W. M. (1982) A prospective study of the
9 neurological effects of lead in children. Neurobehav. Toxicol. Teratol. 4: 739-743.
10 Morgan, J. M. (1975) Chelation therapy in lead nephropathy. South. Med. J. 68: 1001-1006.
11 Morgan, W. D.; Ryde, S. J.; Jones, S. J.; Wyatt, R. M.; Hainsworth, I. R.; Cobbold, S. S.; Evans, C. J.; Braithwaite,
12 R. A. (1990) In vivo measurements of cadmium and lead in occupationally-exposed workers and an urban
13 population. Biol. Trace Elem. Res. 26-27: 407-414.
14 Morita, Y.; Sakai, T.; Araki, S.; Araki, T.; Masuyama, Y. (1997) Nicotinamide adenine dinucleotide synthetase
15 activity in erythrocytes as a tool for the biological monitoring of lead exposure. Int. Arch. Occup. Environ.
16 Health 70: 195-198.
17 Morris, C.; McCarron, D. A.; Bennett, W. M. (1990) Low-level lead exposure, blood pressure, and calcium
18 metabolism. Am. J. Kidney Dis. 15: 568-574.
19 Morrow-Tlucak, M.; Ernhart, C. B. (1987) The relationship of low level lead exposure and language development in
20 the pre-school years. In: Lindberg, S. E.; Hutchinson, T. C., eds. International conference: heavy metals in
21 the environment, v. 1; September; New Orleans, LA. Edinburgh, United Kingdom: CEP Consultants, Ltd.;
22 pp. 57-59.
23 Mortada, W. I.; Sobh, M. A.; El-Defrawy, M. M.; Farahat, S. E. (2001) Study of lead exposure from automobile
24 exhaust as a risk for nephrotoxicity among traffic policemen. Am. J. Nephrol. 21: 274-279.
25 Mortada, W. I.; Sobh, M. A.; El-Defrawy, M. M. (2004) The exposure to cadmium, lead and mercury from smoking
26 and its impact on renal integrity. Med. Sci. Monit. 10: CR112-CR116.
27 Moss, M. E.; Lanphear, B. P.; Auinger, P. (1999) Association of dental caries and blood lead levels. JAMA J. Am.
28 Med. Assoc. 281:2294-2298.
29 Muldoon, S. B.; Cauley, J. A.; Kuller, L. H. ; Morrow, L.; Needleman, H. L. ; Scott, J.; Hooper, F. J. (1996)
30 Effects of blood lead levels on cognitive function of older women. Neuroepidemiology 15: 62-72.
31 Muntner, P.; He, J.; Vupputuri, S.; Coresh, J.; Batuman, V. (2003) Blood lead and chronic kidney disease in the
32 general United States population: results from NHANES III. Kidney Int. 63: 1044-1050.
33 Murata, K.; Araki, S.; Yokoyama, K.; Uchida, E.; Fujimura, Y. (1993) Assessment of central, peripheral, and
34 autonomic nervous system functions in lead workers: neuroelectrophysiological studies. Environ. Res.
35 61:323-336.
36 Murphy, M. J.; Graziano, J. H.; Popovac, D.; Kline, J. K.; Mehmeti, A.; Factor-Litvak, P.; Ahmedi, G.; Shrout, P.;
37 Rajovic, B.; Nenezic, D. U.; Stein, Z. A. (1990) Past pregnancy outcomes among women living in the
3 8 vicinity of a lead smelter in Kosovo, Yugoslavia. Am. J. Public Health 80: 33-35.
39 Mushak, P. (1991) Gastro-intestinal absorption of lead in children and adults: overview of biological and
40 biophysico-chemical aspects. Chem. Speciation Bioavailability 3(3/4): 87-104.
41 Nash, D.; Magder, L.; Lustberg, M.; Sherwin, R. W.; Rubin, R. J.; Kaufmann, R. B.; Silbergeld, E. K. (2003)
42 Blood lead, blood pressure, and hypertension in perimenopausal and postmenopausal women. JAMA J.
43 Am. Med. Assoc. 289: 1523-1532.
44 Nash, D.; Magder, L. S.; Sherwin, R.; Rubin, R. J.; Silbergeld, E. K. (2004) Bone density-related predictors of blood
45 lead level among peri- and postmenopausal women in the United States: the Third National Health and
46 Nutrition Examination Survey, 1988-1994. Am. J. Epidemiol. 160: 901-911.
47 National Institute for Occupational Safety and Health. (1977a) Manual of analytical methods. 2nd ed. Cincinnati,
48 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
49 Control, National Institute for Occupational Safety and Health. DHEW (NIOSH) publication no. 77/157-A.
50 Method No. P&CAM 102. V. 1.
51 National Institute for Occupational Safety and Health. (1977b) Manual of analytical methods. 2nd ed. Cincinnati,
52 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
53 Control, National Institute for Occupational Safety and Health. DHEW (NIOSH) publication no. 77/157-A.
54 Method No. P&CW 195. V. 1.
May 2006 6-355 DRAFT-DO NOT QUOTE OR CITE
-------
1 National Institute for Occupational Safety and Health. (1977c) Manual of analytical methods. 2nd ed. Cincinnati,
2 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
3 Control, National Institute for Occupational Safety and Health, 200-1 to 200-8. Method No. P&CAM 200.
4 Vol. 1.
5 National Institute for Occupational Safety and Health. (1977d) Manual of analytical methods. 2nd ed. Cincinnati,
6 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
7 Control. National Institute for Occupational Safety and Health. 214-1 to 214-6. Method No. P&CAM 214.
8 Vol. 1.
9 National Institute for Occupational Safety and Health. (1977e) Manual of analytical methods. 2nd ed. Cincinnati,
10 OH: U.S. Department of Health, Education and Welfare. Public Health Service, Centers for Disease
11 Control, National Institute for Occupational Safety and Health. Method No. P&CAM 262. Vol. 1.
12 National Institute for Occupational Safety and Health. (1977f) Manual of analytical methods. 2nd ed. Cincinnati,
13 OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease
14 Control, National Institute for Occupational Safety and Health. Method No. P&CAM 208. Vol. 1.
15 National Institute for Occupational Safety and Health. (1984) Manual of analytical methods. 3rd ed. Cincinnati, OH:
16 U.S. Department of Health and Human Services, Centers for Disease Control, National Institute for
17 Occupational Safety andHealth. Method No. 7300, 8003, and 8310. Vol. 1.
18 National Institute for Occupational Safety and Health. (1994) Manual of analytical methods. 4rd ed. Cincinnati, OH:
19 U.S. Department of Health and Human Services, Centers for Disease Control, National Institute for
20 Occupational Safety and Health; DHHS (NIOSH) publication 94-113; method no. 7105.
21 National Institutes of Health. (1994) Consensus development panel on optimal calcium uptake. JAMA J. Am. Med.
22 Assoc. 272: 1942-1948.
23 National Research Council. (2000) Toxicological effects of methylmercury. Washington, DC: National Academy
24 Press. Available: http://www.nap.edu/books/0309071402/html/ [27 March, 2006].
25 National Toxicology Program. (2003) Report on carcinogens background document for lead and lead compounds.
26 Research Triangle Park, NC: U.S. Department of Health and Human Services. Available:
27 http://ntp.niehs.nih.gov/ntp/newhomeroc/rocl 1/Lead-Public.pdf [5 May, 2006].
28 National Toxicology Program. (2004) Lead (CAS no. 7439-92-1) and lead compounds. In: Report on carcinogens,
29 eleventh edition. Research Triangle Park, NC: U.S. Department of Health and Human Services. Available:
30 http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/sl011ead.pdf [28 November, 2005].
31 Navarro, J. A.; Granadillo, V. A.; Salgado, O.; Rodriguez-Iturbe, B.; Garcia, R.; Delling, G.; Romero, R. A. (1992)
32 Bone metal content in patients with chronic renal failure. Clin. Chim. Acta 211: 133-142.
33 Navas-Acien, A.; Selvin, E.; Sharrett, A. R.; Calderon-Aranda, E.; Silbergeld, E.; Guallar, E. (2004) Lead,
34 cadmium, smoking, and increased risk of peripheral arterial disease. Circulation 109: 3196-3201.
35 Nawrot, T. S.; Thijs, L.; DenHond, E. M.; Roels, H. A.; Staessen, J. A. (2002) An epidemiological re-appraisal of
36 the association between blood pressure and blood lead: a meta-analysis. J. Hum. Hypertens. 16: 123-131.
37 Neaton, J. D.; Kuller, L.; Stamler, J.; Wentworth, D. N. (1995) Impact of systolic and diastolic blood pressure on
38 cardiovascular mortality. In: Laragh, J. H.; Brenner, B. M., eds. Hypertension: pathophysiology, diagnosis,
39 and management. 2nd ed. New York, NY: Raven Press Ltd.; pp. 127-144.
40 Needleman, H. L. (1995) Environmental lead and children's intelligence: studies included in the meta-analysis are
41 not representative [letter]. Br. Med. J. 310: 1408.
42 Needleman, H. L.; Bellinger, D. (1988) Recent developments. Environ. Res. 46: 190-191.
43 Needleman, H. L.; Gatsonis, C. A. (1990) Low-level lead exposure and the IQ of children: a meta-analysis of
44 modern studies. JAMA J. Am. Med. Assoc. 263: 673-678.
45 Needleman, H. L.; Gunnoe, C.; Leviton, A.; Reed, R.; Peresie, H.; Maher, C.; Barrett, P. (1979) Deficits in
46 psychologic and classroom performance of children with elevated dentine lead levels. N. Engl. J. Med.
47 300:689-695.
48 Needleman, H. L.; Leviton, A.; Bellinger, D. (1982) Lead-associated intellectual deficit. N. Engl. J. Med. 306: 367.
49 Needleman, H. L.; Rabinowitz, M.; Leviton, A.; Linn, S.; Schoenbaum, S. (1984) The relationship between prenatal
50 exposure to lead and congenital anomalies. JAMA J. Am. Med. Assoc. 251: 2956-2959.
51 Needleman, H. L.; Schell, A.; Bellinger, D.; Leviton, A.; Allred, E. N. (1990) The long-term effects of exposure to
52 low doses of lead in childhood; an 11-year follow-up report. N. Engl. J. Med. 322: 83-88.
53 Needleman, H. L.; Riess, J. A.; Tobin, M. J.; Biesecker, G. E.; Greenhouse, J. B. (1996) Bone lead levels and
54 delinquent behavior. JAMA J. Am. Med. Assoc. 275: 363-369.
55 Needleman, H. L.; McFarland, C.; Ness, R. B.; Fienberg, S. E.; Tobin, M. J. (2002) Bone lead levels in adjudcated
56 delinquents. A case control study. Neurotoxicol. Teratol. 24: 711-717.
May 2006 6-356 DRAFT-DO NOT QUOTE OR CITE
-------
1 Neisser, U.; Boodoo, G.; Bouchard, T. I; Boykin, A. W.; Brody, N.; Ceci, S. I; Halpern, D. F.; Loehlin, J. C.;
2 Perloff, R.; Sternberg, R. J.; Urbina, S. (1996) Intelligence: knowns and unknowns. Am. Psychol.
3 51:77-101.
4 Nenov, V. D.; Taal, M. W.; Sakharova, O. V.; Brenner, B. M. (2000) Multi-hit nature of chronic renal disease.
5 Curr. Opin. Nephrol. Hypertens. 9: 85-97.
6 Neri, L. C.; Hewitt, D.; Orser, B. (1988) Blood lead and blood pressure: analysis of cross-sectional and longitudinal
7 data from Canada. In: Victery, W., ed. Symposium on lead-blood pressure relationships; April 1987;
8 Chapel Hill, NC. Environ. Health Perspect. 78: 123-126.
9 Ng, T. P.; Goh, H. H.; Ng, Y. L.; Ong, H. Y.; Ong, C. N.; Chia, K. S.; Chia, S. E.; Jeyaratnam, J. (1991)
10 Male endocrine functions in workers with moderate exposure to lead. Br. J. Ind. Med. 48: 485-491.
11 Nilsson, U.; Attewell, R.; Christoffersson, J.-O.; Schutz, A.; Ahlgren, L.; Skerfving, S.; Mattsson, S. (1991) Kinetics
12 of lead in bone and blood after end of occupational exposure. Pharmacol. Toxicol. (Copenhagen)
13 68:477-484.
14 Niu, Q.; He, S. C.; Li, H. Y.; Wang, J. Y.; Dai, F. Y.; Chen, Y. L. (2000) A comprehensive neurobehavioral and
15 neurophysiological study for low level lead-exposed workers. G. Ital. Med. Lav. Ergon. 22: 299-304.
16 Noda, H.; Sugiyama, S.; Yamaguchi, M.; Tatsumi, S.; Sano, Y.; Konishi, S.; Furutani, A.; Yoshimura, M. (1993)
17 Studies on secular changes in the concentration of lead accumulated in organs and rib of Japanese.
18 Jpn. J. Leg. Med. 47: 147-152.
19 Nolte, J. (1993) The human brain: an introduction to its functional anatomy. St. Louis, MO: Mosby Year Book
20 Publishers.
21 Nomiyama, K.; Nomiyama, H.; Liu, S. J.; Tao, Y. X.; Nomiyama, T.; Omae, K. (2002) Lead induced increase of
22 blood pressure in female lead workers. Occup. Environ. Med. 59: 734-738.
23 Noonan, C. W.; Sarasua, S. M.; Campagna, D.; Kathman, S. J.; Lybarger, J. A.; Mueller, P. W. (2002) Effects of
24 exposure to low levels of environmental cadmium on renal biomarkers. Environ. Health Perspect.
25 110:151-155.
26 Nordberg, M.; Winblad, B.; Fratiglioni, L.; Basun, H. (2000) Lead concentrations in elderly urban people related to
27 blood pressure and mental performance: results from a population-based study. Am. J. Ind. Med.
28 38:290-294.
29 Nordenson, I.; Beckman, G.; Beckman, L.; Nordstrom, S. (1978) Occupational and environmental risks in and
30 around a smelter in northern Sweden. IV. Chromosomal aberrations in workers exposed to lead. Hereditas
31 (Lund, Swed.) 88: 263-267.
32 Nordstrom, S.; Beckman, L.; Nordenson, I. (1978a) Occupational and environmental risks in and around a smelter in
33 northern Sweden: I. Variations in birth weight. Hereditas (Lund, Swed.) 88: 43-46.
34 Nordstrom, S.; Beckman, L.; Nordenson, I. (1978b) Occupational and environmental risks in and around a smelter
35 in northern Sweden: III. Frequencies of spontaneous abortion. Hereditas (Lund, Swed.) 88: 51-54.
36 Nordstrom, S.; Beckman, L.; Nordenson, I. (1979) Occupational and environmental risks in and around a smelter in
37 northern Sweden. V. Spontaneous abortion among female employees and decreased birth weight in their
38 offspring. Hereditas (Lund, Swed.) 90: 291-296.
39 Nowak, B.; Chmielnicka, J. (2000) Relationship of lead and cadmium to essential elements in hair, teeth, and nails
40 of environmentally exposed people. Ecotoxicol. Environ. Saf. 46: 265-274.
41 Nuyts, G. D.; Van Vlem, E.; Thys, J.; De Leersnijder, D.; D'Haese, P. C.; Elseviers, M. M.; De Broe, M. E. (1995)
42 New occupational risk factors for chronic renal failure. Lancet 346: 7-11.
43 Oishi, H.; Nomiyama, H.; Nomiyama, K.; Tomokuni, K. (1996) Comparison between males and females with
44 respect to the porphyrin metabolic disorders found in workers occupationally exposed to lead. Int. Arch.
45 Occup. Environ. Health 68: 298-304.
46 Oktem, F.; Arslan, M. K.; Dtindar, B.; Delibas, N.; Gtiltepe, M.; Ergurhan Ilhan, I. (2004) Renal effects and
47 erythrocyte oxidative stress in long-term low-level lead-exposed adolescent workers in auto repair
48 workshops. Arch. Toxicol. 78: 681-687.
49 Oliveira, S.; Aro, A.; Sparrow, D.; Hu, H. (2002) Season modifies the relationship between bone and blood lead
50 levels: the Normative Aging Study. Arch. Environ. Health 57: 466-472.
51 Oliver, T. (1911) Lead poisoning and the race. Br. Med. J. 1(2628): 1096-1098.
52 Olsen, G. W.; Bodner, K. M.; Ramlow, J. M.; Ross, C. E.; Lipshultz, L. I. (1995) Have sperm counts been reduced
53 50 percent in 50 years? A statistical model revisited. Fertil. Steril. 63: 887-893.
54 Olsson, I.-M.; Bensryd, I.; Lundh, T.; Ottosson, H.; Skerfving, S.; Oskarsson, A. (2002) Cadmium in blood and
5 5 urine—impact of sex, age, dietary intake, iron status, and former smoking—association of renal effects.
56 Environ. Health Perspect. 110: 1185-1190.
May 2006 6-357 DRAFT-DO NOT QUOTE OR CITE
-------
1 Onalaja, A. O.; Claudio, L. (2000) Genetic susceptibility to lead poisoning. Environ. Health Perspect.
2 Suppl. 108(1): 23-28.
3 Ong, C. N.; Endo, G.; Chia, K. S.; Phoon, W. O.; Ong, H. Y. (1987) Evaluation of renal function in workers with
4 low blood lead levels. In: Foa, V.; Emmett, E. A.; Maroni, M; Colombi, A., eds. Occupational and
5 environmental chemical hazards: cellular and biochemical indices for monitoring toxicity. New York, NY:
6 Halstead Press; pp. 327-333.
7 Orban, B. (1953) Oral histology and embryology. St. Louis, MO: Mosby Year Book Publishers.
8 O'Riordan, M. L.; Evans, H. J. (1974) Absence of significant chromosome damage in males occupationally exposed
9 to lead. Nature (London) 247: 50-53.
10 Orssaud, G.; Claude, J. R.; Moreau, T.; Lellouch, J.; Juguet, B.;Festy,B.(1985) Blood lead concentration and blood
11 pressure. Br. Med. J. 290: 244.
12 Osman, K.; Pawlas, K.; Schiitz, A.; Gazdzik, M.; Sokal, J. A.; Vahter, M. (1999) Lead exposure and hearing effects
13 in children in Katowice, Poland. Environ. Res. 80: 1-8.
14 Osterberg, K.; Borjesson, J.; Gerhardsson, L.; Schiitz, A.; Skerfving, S. (1997) A neurobehavioural study of long-
15 term occupational inorganic lead exposure. Sci. Total Environ. 201: 39-51.
16 Osterloh, J. D.; Selby, J. V.; Bernard, B. P.; Becker, C. E.; Menke, D. J.; Tepper, E.; Ordonez, J. D.; Behrens, B.
17 (1989) Body burdens of lead in hypertensive nephropathy. Arch. Environ. Health 44: 304-310.
18 Osterode, W.; Barnas, D.; Geissler, K. (1999) Dose dependent reduction of erythroid progenitor cells and
19 inappropriate erythropoietin response in exposure to lead: new aspects of anaemia induced by lead. Occup.
20 Environ. Med. 56: 106-109.
21 Otto, D. A.; Fox, D. A. (1993) Auditory and visual dysfunction following lead exposure. Presented at: Ninth
22 international neurotoxicology conference; October 1991; Little Rock, AR. Neurotoxicology 14(2-
23 3): 191-207.
24 Otto, D.; Robinson, G.; Baumann, S.; Schroeder, S.; Mushak, P.; Kleinbaum, D.; Boone, L. (1985) Five-year
25 follow-up study of children with low-to-moderate lead absorption: electrophysiological evaluation.
26 Environ. Res. 38: 168-186.
27 Paksy, K.; Gati, I.; Naray, M.; Rajczy, K. (2001) Lead accumulation in human ovarian follicular fluid, and in vitro
28 effect of lead on progesterone production by cultured human ovarian granulosa cells. J. Toxicol. Environ.
29 Health Part A 62: 359-366.
30 Palus, J.; Rydzynski, K.; Dziubaltowska, E.; Wyszynska, K.; Natarajan, A. T.; Nilsson, R. (2003) Genotoxic effects
31 of occupational exposure to lead and cadmium. Mutat. Res. 540: 19-28.
32 Parkinson, D. K.; Hodgson, M. J.; Bromet, E. J.; Dew, M. A.; Connell, M. M. (1987) Occupational lead exposure
33 and blood pressure. Br. J. Ind. Med. 44: 744-748.
34 Paschal, D. C.; Burt, V.; Caudill, S. P.; Gunter, E. W.; Pirkle, J. L.; Sampson, E. J.; Miller, D. T.; Jackson, R. J.
3 5 (2000) Exposure of the U.S. population aged 6 years and older to cadmium: 1988-1994. Arch. Environ.
36 Contam. Toxicol. 38: 377-383.
37 Payton, M.; Hu, H.; Sparrow, D.; Weiss, S. T. (1994) Low-level lead exposure and renal function in the normative
38 aging study. Am. J. Epidemiol. 140: 821-829.
39 Payton, M.; Riggs, K. M.; Spiro, A., Ill; Weiss, S. T.; Hu, H. (1998) Relations of bone and blood lead to cognitive
40 function: the VA Normative Aging Study. Neurotoxicol. Teratol. 20: 19-27.
41 Perez-Bravo, F.; Ruz, M; Moran-Jimenez, M. J.; Olivares, M.; Rebolledo, A.; Codoceo, J.; Sepulveda, J.; Jenkin, A.;
42 Santos, J. L.; Fontanellas, A. (2004) Association between aminolevulinate dehydrase genotypes and blood
43 lead levels in children from a lead-contaminated area in Antofagasta, Chile. Arch. Environ. Contam.
44 Toxicol. 47(2): 276-280.
45 Pergande, M.; Jung, K.; Precht, S.; Pels, L. M.; Herbert, C.; Stolte, H. (1994) Changed excretion of urinary proteins
46 and enzymes by chronic exposure to lead. Nephrol. Dial. Transplant. 9: 613-618.
47 Pesch, B.; Haerting, J.; Ranft, U.; Klimpel, A.; Oelschlagel, B.; Schill, W.; MURC Study Group. (2000)
48 Occupational risk factors for renal cell carcinoma: agent-specific results from a case-control study in
49 Germany. Int. J. Epidemiol. 29: 1014-1024.
5 0 Philion, J. J.; Schmitt, N.; Rowe, J.; Gelpke, P. M. (1997) Effect of lead on fetal growth in a Canadian smelter city,
51 1961-1990. Arch. Environ. Health 52: 472-475.
52 Pineda-Zavaleta, A. P.; Garcia-Vargas, G.; Borja-Aburto, V. H.; Acosta-Saavedea, L. C.; Vera Aguilar, E.; Gomez-
53 Munoz, A.; Cebrian, M. E. Calderon-Aranda, E. S. (2004) Nitric oxide and superoxide anion production in
54 monocytes from children exposed to arsenic and lead in region Lagunera, Mexico. Toxicol. Appl.
55 Pharmacol. 198: 283-290.
May 2006 6-358 DRAFT-DO NOT QUOTE OR CITE
-------
1 Pinkerton, L. E.; Biagini, R. E.; Ward, E. M.; Hull, R. D.; Deddens, J. A.; Boeniger, M. F.; Schnorr, T. M;
2 MacKenzie, B. A.; Luster, M. I. (1998) Immunologic findings among lead-exposed workers. Am. J. Ind.
3 Med. 33:400-408.
4 Pinto de Almeida, A. R.; Carvalho, F. M.; Spinola, A. G.; Rocha, H. (1987) Renal dysfunction in Brazilian lead
5 workers. Am. J. Nephrol. 7: 455-458.
6 Piomelli, S.; Seaman, C.; Zullow, D.; Curran, A.; Davidow, B. (1982) Threshold for lead damage to heme synthesis
7 in urban children. Proc. Natl. Acad. Sci. U. S. A. 79: 3335-3339.
8 Pirkle, J. L.; Brody, D. J.; Gunter, E. W.; Kramer, R. A.; Paschal, D. C.; Flegal, K. M.; Matte, T. D. (1994) The
9 decline in blood lead levels in the United States: the National Health and Nutrition Examination Surveys
10 (NHANES). JAMA J. Am. Med. Assoc. 272: 284-291.
11 Pirkle, J. L.; Kaufmann, R. B.; Brody, D. J.; Hickman, T.; Gunter, E. W.; Paschal, D. C. (1998) Exposure of the U.S.
12 population to lead, 1991-1994. Environ. Health Perspect. 106: 745-750.
13 Pocock, S. J.; Shaper, A. G.; Walker, M.; Wale, C. J.; Clayton, B.; Delves, T.; Lacey, R. F.; Packham, R. F.;
14 Powell, P. (1983) The effects of tap water lead, water hardness, alcohol, and cigarettes on blood lead
15 concentrations. J. Epidemiol. Community Health 37: 1-7.
16 Pocock, S. J.; Shaper, A. G.; Ashby, D.; Delves, T.; Whitehead, T. P. (1984) Blood lead concentration, blood
17 pressure, and renal function. Br. Med. J. 289: 872-874.
18 Pocock, S. J.; Ashby, D.; Smith, M. A. (1987) Lead exposure and children's intellectual performance. Int. J.
19 Epidemiol. 16: 57-67.
20 Pocock, S. J.; Smith, M.; Baghurst, P. (1994) Environmental lead and children's intelligence: a systematic review of
21 the epidemiological evidence. Br. Med. J. 309: 1189-1197.
22 Pollock, C. A.; Ibels, L. S. (1988) Lead intoxication in Sydney Harbour bridge workers. Aust. N. Z. J. Med.
23 18:46-52.
24 Popovic, M.; McNeill, F. E.; Chettle, D. R.; Webber, C. E.; Lee, C. V.; Kaye, W. E. (2005) Impact of occupational
25 exposure on lead levels in women. Environ. Health Perspect. 113: 478-484.
26 Poulos, L.; Qammaz, S.; Athanaselis, S.; Maravelias, C.; Koutselinis, A. (1986) Statistically significant
27 hematopoietic effects of low blood lead levels. Arch. Environ. Health 41: 384-386.
28 Pounds, J. G.; Long, G. J.; Rosen, J. F. (1991) Cellular and molecular toxicity of lead in bone. Environ. Health
29 Perspect. 91: 17-32.
30 Powell, J. J.; Greenfield, S. M.; Thompson, R. P. H.; Cargnello, J. A.; Kendall, M. D.; Landsberg, J. P.; Watt, F.;
31 Delves, H. T.; House, I. (1995) Assessment of toxic metal exposure following the Camelford water
32 pollution incident: evidence of acute mobilization of lead into drinking water. Analyst (Cambridge, U. K.)
33 120:793-798.
34 Price, J.; Grudzinski, A. W.; Craswell, P. W.; Thomas, B. J. (1992) Bone lead measurements in patients with chronic
3 5 renal disease studied over time. Arch. Environ. Health 47: 330-335.
36 Price, R. G.; Patel, S.; Olivers, I.; Milligan, P.; Taylor, S. A. (1999) Early markers of nephrotoxicity: detection of
37 children at risk from environmental pollution. Renal Fail. 21: 303-308.
38 Proctor, S. P.; Rotnitzky, A.; Sparrow, D.; Weiss, S. T.; Hu, H. (1996) The relationship of blood lead and dietary
39 calcium to blood pressure in the normative aging study. Int. J. Epidemiol. 25: 528-536.
40 Prospective Studies Collaboration. (2002) Age-specific relevance of usual blood pressure to vascular mortality: a
41 meta-analysis of individual data for one million adults in 61 prospective studies. Lancet 360: 1903-1913.
42 Prpic-Majic, D.; Bobic, J.; Simic, D.; House, D. E.; Otto, D. A.; Jurasovic, J.; Pizent, A. (2000) Lead absorption and
43 psychological function in Zabreb (Croatia) school children. Neurotoxicol. Teratol. 22: 347-356.
44 Pueschel, S. M.; Kopito, L.; Schwachman, H. (1972) Children with an increased lead burden. A screening and
45 follow-up study. JAMA J. Am. Med. Assoc. 222: 462-466.
46 Puzas, J. E. (2000) Osteotoxicology: the role of lead in bone disease. Curr. Opin. Orthop. 11: 360-365.
47 Puzas, J. E.; Sickel, M. J.; Felter, M. E. (1992) Osteoblasts and chondrocytes are important target cells for the toxic
48 effects of lead. Neurotoxicology 13: 783-788.
49 Pyatt, D. W.; Zheng, J.-H.; Stillman, W. S.; Irons, R. D. (1996) Inorganic lead activates NF-icB in primary human
50 CD4+ T lymphocytes. Biochem. Biophys. Res. Commun. 227: 380-385.
51 Quandt, R. E. (1958) The estimation of the parameters of a linear regression system obeying two separate regimes.
52 J. Am. Stat. Assoc. 53:873-880.
53 Que Hee, S.S.; Boyle, J.R. (1988) Simultaneous multielemental analysis of some environmental and biological
54 samples by inductively coupled plasma atomic emission spectrometry. Anal. Chem. 60: 1033-1042.
55 Que Hee, S. S.; MacDonald, T. J.; Bornschein, R. L. (1985) Blood lead by furnace-Zeeman atomic absorption
56 spectrophotometry. Microchem. J. 32: 55-63.
May 2006 6-359 DRAFT-DO NOT QUOTE OR CITE
-------
1 Queiroz, M. L. S.; Almeida, M.; Gallao, M. I.; Hoehr, N. F. (1993) Defective neutrophil function in workers
2 occupationally exposed to lead. Pharmacol. Toxicol. 72: 73-77.
3 Queiroz, M. L.; Costa, F. F.; Bincoletto, C.; Perlingeiro, R. C. R.; Dantas, D. C. M.; Cardoso, M. P.; Almeida, M.
4 (1994a) Engulfment and killing capabilities of neutrophils and phagocytic splenic function in persons
5 occupationally exposed to lead. Int. J. Immunopharmacol. 16: 239-244.
6 Queiroz, M. L. S.; Perlingeiro, R. C. R.; Bincoletto, C.; Almeida, M.; Cardoso, M. P.; Dantas, D. C. M. (1994b)
7 Immunoglobulin levels and cellular immune function in lead exposed workers. Immunopharmacol.
8 Immunotoxicol. 16: 115-128.
9 Raab, G. M.; Thomson, G. O. B.; Boyd, L.; Fulton, M.; Laxen, D. P. H. (1990) Blood lead levels, reaction time,
10 inspection time and ability in Edinburgh children. Br. J. Dev. Psychol. 8: 101-118.
11 Rabinowitz, M. B. (1991) Toxicokinetics of bone lead. Environ. Health Perspect. 91: 33-37.
12 Rabinowitz, M.; Bellinger, D.; Leviton, A.; et al. (1987) Pregnancy hypertension, blood pressure during labor, and
13 blood lead levels. Hypertension 10: 447-451.
14 Rabinowitz, M. B.; Allred, E. N.; Bellinger, D. C.; Leviton, A.; Needleman, H. L. (1990) Lead and childhood
15 propensity to infectious and allergic disorders: is there an association? Bull. Environ. Contam. Toxicol.
16 44:657-660.
17 Rabinowitz, M. B.; Bellinger, D.; Leviton, A.; Wang, J.-D. (1991) Lead levels among various deciduous tooth types.
18 Bull. Environ. Contam. Toxicol. 47: 602-608.
19 Rabinowitz, M. B.; Wang, J.-D.; Soong, W. T. (1992) Children's classroom behavior and lead in Taiwan. Bull.
20 Environ. Contam. Toxicol. 48: 282-288.
21 Rabinowitz, M. B.; Leviton, A.; Bellinger, D. (1993) Relationships between serial blood lead levels and exfoliated
22 tooth dentin lead levels: models of tooth lead kinetics. Calcif. Tissue Int. 53: 338-341.
23 Rahman, A.; Hakeem, A. (2003) Blood lead levels during pregnancy and pregnancy outcome in Karachi women.
24 J. Pak. Med. Assoc. 53:529-533.
25 Rajah, T.; Ahuja, Y. R. (1995) In vivo genotoxic effects of smoking and occupational lead exposure in printing press
26 workers. Toxicol. Lett. 76: 71-75.
27 Rajah, T. T.; Ahuja, Y. R. (1996) In vivo genotoxicity of alcohol consumption and lead exposure in printing press
28 workers. Alcohol 13: 65-68.
29 Rajegowda, B. K.; Glass, L.; Evans, H. E. (1972) Lead concentrations in the newborn infant. J. Pediatr. 80: 116-117.
30 Ratzon, N.; Froom, P.; Leikin, E.; Kristal-Boneh, E.; Ribak, J. (2000) Effect of exposure to lead on postural control
31 in workers. Occup. Environ. Med. 57: 201-203.
32 Refowitz, R. M. (1984) Thyroid function and lead: no clear relationship. J. Occup. Med. 26: 579-583.
33 Reigart, J. R.; Graber, C. D. (1976) Evaluation of the humoral immune response of children with low level lead
34 exposure. Bull. Environ. Contam. Toxicol. 16: 112-117.
35 Reimer, W.; Tittelbach, U. (1989) Verhalten von Herzfrequenz, Blutdruck und systolischen Zeitintervallen in Ruhe
3 6 und wahrend Einhandarbeit bei Bleiexponierten und Kontrollpersonen [Heart rate, blood pressure and
3 7 systolic time interval in rest and during single-hand exertion in persons exposed to lead and in control
38 subjects]. Z. Gesamte Hyg. Ihre Grenzgeb. 35: 491-492.
39 Rencher, A. C.; Carter, M. W.; McKee, D. W. (1977) A retrospective epidemiological study of mortality at a large
40 western copper smelter. J. Occup. Med. 19: 754-758.
41 Research Triangle Institute. (1999) Health effects. In: Toxicological profile for lead. Atlanta, GA: U.S. Department
42 of Health and Human Services, Agency for Toxic Substances and Disease Registry.
43 Restek-Samarzija, N.; Momcilovic, B.; Trosic, I.; Piasek, M.; Samarzija, M. (1996) Chronic lead poisoning, renal
44 function and immune response. Arh. Hig. Rada Toksikol. 47: 1-8.
45 Restek-Samarzija, N.; Momcilovic, B.; Turk, R.; Samarzija, M. (1997) Contribution of lead poisoning to renal
46 impairment. Arh. Hig. Rada Toksikol. 48: 355-364.
47 Rhainds, M.; Levallois, P. (1997) Effects of maternal cigarette smoking and alcohol consumption on blood lead
48 levels of newborns. Am. J. Epidemiol. 145: 250-257.
49 Rhainds, M.; Levallois, P.; Dewailly, E.; Ayotte, P. (1999) Lead, mercury, and organochlorine compound levels in
50 cord blood in Quebec, Canada. Arch. Environ. Health 54: 40-47.
51 Rhodes, D.; Spiro, A., Ill; Aro, A.; Hu, H. (2003) Relationship of bone and blood lead levels to psychiatric
52 symptoms: The Normative Aging Study. J. Occup. Environ. Med. 45: 1144-1151.
53 Rico, J. A.; Kordas, K.; Lopez, P.; Rosado, J. L.; Vargas, G. G.; Ronquillo, D.; Stoltzfus, R. J. (2006) The efficacy
54 of iron and/or zinc supplementation on cognitive performance of lead-exposed Mexican school children:
55 arandomized, placebo-controlled trial. Pediatrics 117: e518-e527.
May 2006 6-360 DRAFT-DO NOT QUOTE OR CITE
-------
1 Ris, M. D.; Dietrich, K. N.; Succop, P. A.; Berger, O. G.; Bornschein, R. L. (2004) Early exposure to lead and
2 neuropsychological outcome in adolescence. J. Int. Neuropsychol. Soc. 10: 261-270.
3 Risch, H. A.; Burch, J. D.; Miller, A. B.; Hill, G. B.; Steele, R.; Howe, G. R. (1988) Occupational factors and the
4 incidence of cancer of the bladder in Canada. Br. J. Ind. Med. 45: 361-367.
5 Robins, J. M.; Cullen, M. R.; Connors, B. B.; Kayne, R. D. (1983) Depressed thyroid indexes associated with
6 occupational exposure to inorganic lead. Arch. Intern. Med. 143: 220-224.
7 Rodamilans, M.; Osaba, M. J. M.; To-Figueras, J.; Rivera Filial, F.; Marques, J. M.; Perez, P.; Corbella, J. (1988)
8 Lead toxicity on endocrine testicular function in an occupationally exposed population. Hum. Toxicol.
9 7: 125-128.
10 Roderer, G.; Doenges, K. H. (1983) Influence of trimethyl lead and inorganic lead on the in vitro assembly of
11 microtubules from mammalian brain. Neurotoxicology 4: 171-180.
12 Roelofs-Iverson, R. A.; Mulder, D. W.; Elveback, L. R.; Kurland, L. T.; Molgaard, C. A. (1984) ALS and heavy
13 metals: a pilot case study. Neurology 34: 393-395.
14 Roels, H.; Lauwerys, R. (1987) Evaluation of dose-effect and dose-response relationships for lead exposure in
15 different Belgian population groups (fetus, child, adult men and women). Trace Elem. Med. 4: 80-87.
16 Roels, H.; Hubermont, G.; Buchet, J.-P.; Lauwerys, R. (1978) Placental transfer of lead, mercury, cadmium, and
17 carbon monoxide in women. III. Factors influencing the accumulation of heavy metals in the placenta and
18 the relationship between metal concentration in the placenta and in maternal and cord blood. Environ. Res.
19 16:236-247.
20 Roels, H. A.; Balis-Jacques, M. N.; Buchet, J.-P.; Lauwerys, R. R. (1979) The influence of sex and of chelation
21 therapy on erythrocyte protoporphyrin and urinary 5-aminolevulinic acid in lead-exposed workers.
22 J. Occup. Med. 21:527-539.
23 Roels, H. A.; Lauwerys, R. R.; Buchet, J. P.; Bernard, A. M.; Vos, A.; Oversteyns, M. (1989) Health significance of
24 cadmium induced renal dysfunction: a five year follow up. Br. J. Ind. Med. 46: 755-764.
25 Roels, H.; Lauwerys, R.; Konings, J.; Buchet, J.-P.; Bernard, A.; Green, S.; Bradley, D.; Morgan, W.; Chettle, D.
26 (1994) Renal function and hyperfiltration capacity in lead smelter workers with high bone lead. Occup.
27 Environ. Med. 51:505-512.
28 Roels, H.; Konings, J.; Green, S.; Bradley, D.; Chettle, D.; Lauwerys, R. (1995) Time-integrated blood lead
29 concentration is a valid surrogate for estimating the cumulative lead dose assessed by tibial lead
30 measurement. Environ. Res. 69: 75-82.
31 Roels, H. A.; Van Assche, F. J.; Oversteyns, M.; De Groof, M.; Lauwerys, R. R.; Lison, D. (1997) Reversibility of
3 2 microproteinuria in cadmium workers with incipient tubular dysfunction after reduction of exposure.
33 Am. J. Ind. Med. 31:645-652.
34 Rogan, W. J.; Ware, J. H. (2003) Exposure to lead in children — how low is low enough? N. Engl. J. Med.
35 348: 1515-1516.
36 Rogan, W. J.; Treatment of Lead-Exposed Clinical Trial Group. (1998) The treatment of lead-exposed children
3 7 (TLC) trial: design and recruitment for a study of the effect of oral chelation on growth and develpment in
3 8 toddlers. Paediatr. Perinat. Epidemiol. 12:313-333.
39 Rogan, W. J.; Dietrich, K. N.; Ware, J. H.; et al. (2001) The effect of chelation therapy with succimer on
40 neuropsychological development in children exposed to lead. New Engl. J. Med. 344: 1421-1426.
41 Rom, W. N. (1976) Effects of lead on the female and reproduction: a review. Mt. Sinai J. Med. 43: 542-552.
42 Romeo, R.; Aprea, C.; Boccalon, P.; Orsi. D; Porcelli, B.; Sartorelli, P. (1996) Serum erthropoietin and blood lead
43 concentrations. Int. Arch. Occup. Environ. Health 69: 73-75.
44 Ronis, M. J. J.; Badger, T. M.; Shema, S. J.; Roberson, P. K.; Shaikh, F. (1996) Reproductive toxicity and growth
45 effects in rats exposed to lead at different periods during development. Toxicol. Appl. Pharmacol.
46 136:361-371.
47 Rose, G.; Day, S. (1990) The population mean predicts the number of deviant individuals. Br. Med. J.
48 301: 1031-1034.
49 Rosen, J. F.; Pounds, J. G. (1998) "Severe chronic lead insult that maintains body burdens of lead related to those in
50 the skeleton": observations by Dr. Clair Patterson conclusively demonstrated. Environ. Res. 78: 140-151.
51 Rosen, J. F.; Chesney, R. W.; Hamstra, A.; DeLuca, H. F.; Mahaffey, K. R. (1980) Reduction in 1,25-
52 dihydroxyvitamin D in children with increased lead absorption. N. Engl. J. Med. 302: 1128-1131.
53 Rosen, J. F.; Markowitz, M. E.; Bijur, P. E.; Jenks, S. T.; Wielopolski, L.; Kalef-Ezra, J. A.; Slatkin, D. N. (1989)
54 L-line x-ray fluorescence of cortical bone lead compared with the CaNa2EDTA test in lead-toxic children:
55 public health implications. Proc. Natl. Acad. Sci. U. S. A. 86: 685-689,
56 Rosenthal, R. (1984) Meta-analytic procedures for social research. Beverly Hills, CA: Sage Publications.
May 2006 6-361 DRAFT-DO NOT QUOTE OR CITE
-------
1 Roses, O. E.; Alvarez, S.; Conti, M. I.; Nobile, R. A.; Villaamil, E. C. (1989) Correlation between lead and prolactin
2 in males exposed and unexposed to lead in Buenos Aires (Argentina) area. Bull. Environ. Contam. Toxicol.
3 42:438-442.
4 Rossner, P.; Boffetta, P.; Ceppi, M.; Bonassi, S.; Smerhovsky, Z.; Landa, K.; Juzova, D.; Sram, R. J. (2005)
5 Chromosomal aberrations in lymphocytes of healthy subjects and risk of cancer. Environ. Health Perspect.
6 113:517-520.
7 Rothenberg, S. J.; Rothenberg, J. C. (2005) Testing the dose-response specification in epidemiology: public health
8 and policy consequences for lead. Environ. Health Perspect. 113: 1190-1195.
9 Rothenberg, S. J.; Schnaas, L.; Cansino-Ortiz, S.; Perroni-Hernandez, E.; de la Torre, P.; Neri-Mendez, C.;
10 Ortega, P.; Hidalgo-Loperena, H.; Svendsgaard, D. (1989) Neurobehavioral deficits after low level lead
11 exposure in neonates: the Mexico City pilot study. Neurotoxicol. Teratol. 11: 85-93.
12 Rothenberg, S. J.; Karchmer, S.; Schnaas, L.; Perroni, E.; Zea, F.; Alba, J. F. (1994) Changes in serial blood lead
13 levels during pregnancy. Environ. Health Perspect. 102: 876-880.
14 Rothenberg, S. J.; Manalo, M.; Jiang, J.; Cuellar, R.; Reyes, S.; Sanchez, M.; Diaz, M.; Khan, F.; Aguilar, A.;
15 Reynoso, B.; Juaregui, M.; Acosta, S.; Johnson, C. (1999) Blood lead level and blood pressure during
16 pregnancy in south central Los Angeles. Arch. Environ. Health 54: 382-389.
17 Rothenberg, S. J.; Khan, F.; Manalo, M.; Jian, J.; Cuellar, R.; Reyes, S.; Acosta, S.; Jauregui, M.; Diaz, M.;
18 Sanchez, M.; Todd, A. C.; Johnson, C. (2000) Maternal bone lead contribution to blood lead during and
19 after pregnancy. Environ. Res. 82: 81-90.
20 Rothenberg, S. J.; Kondrashov, V.; Manalo, M.; Manton, W. L; Khan, F.; Todd, A. C.; Johnson, C. (2001) Seasonal
21 variation in bone lead contribution to blood lead during pregnancy. Environ. Res. 85: 191-194.
22 Rothenberg, S. J.; Kondrashov, V.; Manalo, M.; Jiang, J.; Cuellar, R.; Garcia, M.; Reynoso, B.; Reyes, S.; Diaz, M.;
23 Todd, A. C. (2002a) Increases in hypertension and blood pressure during pregnancy with increased bone
24 lead levels. Am. J. Epidemiol. 156: 1079-1087.
25 Rothenberg, S. J.; Schnaas, L.; Salgado-Valladares, M.; Casanueva, E.; Geller, A. M.; Hudnell, H. K.; Fox, D. A.
26 (2002b) Increased ERG a- and b-wave amplitudes in 7- to 10-year-old children resulting from prenatal lead
27 exposure. Invest. Ophthalmol. Vis. Sci. 43: 2036-2044.
28 Rowe, J. W.; Andres, R.; Tobin, J. D.; Norris, A. H.; Shock, N. W. (1976) Age-adjusted standards for creatinine
29 clearance. Ann. Intern. Med. 84: 567-569.
30 Rowland, A.; Wilcox, A. (1987) Maternal blood lead [letter]. J. Epidemiol. Community Health 41: 184.
31 Ruff, H. A.; Bijur P. E.; Markowitz, M.; Ma, Y.-C.; Rosen, J. F. (1993) Declining blood lead levels and cognitive
32 changes in moderately lead-poisoned children. JAMA J. Am. Med. Assoc. 269: 1641-1646.
33 Ruff, H. A.; Markowitz, M. E.; Bijur, P. E.; Rosen, J. F. (1996) Relationships among blood lead levels, iron
34 deficiency, and cognitive development in two-year-old children. Environ. Health Perspect. 104: 180-185.
35 Ryu, J. E.; Ziegler, E. E.; Nelson, S. E.; Fomon, S. J. (1983) Dietary intake of lead and blood lead concentration in
36 early infancy. Am. J. Dis. Child. 137: 886-891.
37 Saenger, P.; Markowitz, M. E; Rosen, J. F. (1984) Depressed excretion of 6Beta-hydroxycortisol in lead-toxic
38 children. J. Clin. Endocrinol. Metab. 58: 363-367.
39 Salkever, D. S. (1995) Updated estimates of earnings benefits from reduced exposure of children to environmental
40 lead. Environ. Res. 70: 1-6.
41 Sallmen, M.; Lindbohm, M.-L.; Anttila, A.; Taskinen, H.; Hemminki, K. (1992) Paternal occupational lead exposure
42 and congenital malformations. J. Epidemiol. Community Health 45: 519-522.
43 Sallmen, M.; Anttila, A.; Lindbohm, M.-L.; Kyyronen, P.; Taskinen, H.; Hemminki, K. (1995) Time to pregnancy
44 among women occupationally exposed to lead. J. Occup. Environ. Med. 37: 931-934.
45 Sallmen, M.; Lindbohm, M. L.; Anttila, A.; Taskinen, H.; Hemminki, K. (2000) Time to pregnancy among the
46 wives of men occupationally exposed to lead. Epidemiology 11: 141-147.
47 Salmon, P. L.; Bondarenko, O. A.; Henshaw, D. L. (1999) DOSE210, a semi-empirical model for prediction of
48 organ distribution and radiation doses from long term exposure to 210Pb and 210Po. Radiat. Prot. Dosim.
49 82: 175-192.
50 Sanchez-Fructuoso, A. I.; Torralbo, A.; Arroyo, M.; Luque, M.; Ruilope, L. M.; Santos, J. L.; Cruceyra, A.;
51 Barrientos, A. (1996) Occult lead intoxication as a cause of hypertension and renal failure. Nephrol. Dial.
52 Transplant. 11: 1775-1780.
53 Sanin, L. H.; Gonzalez-Cossio, T.; Romieu, I.; Peterson, K. E.; Ruiz, S.; Palazuelos, E.; Hernandez-Avila, M.;
54 Hu, H. (2001) Effect of maternal lead burden on infant weight and weight gain at one month of age among
55 breastfed infants. Pediatrics 107: 1016-1023.
May 2006 6-362 DRAFT-DO NOT QUOTE OR CITE
-------
1 Sankila, R.; Karjalainen, S.; Pukkala, E.; Oksanen, H.; Hakulinen, T.; Teppo, L.; Hakama, M. (1990) Cancer risk
2 among glass factory workers: an excess of lung cancer? Br. J. Ind. Med. 47: 815-818.
3 Sarasua, S. M.; Vogt, R. F.; Henderson, L. O.; Jones, P. A.; Lybarger, J. A. (2000) Serum immunoglobulins and
4 lymphocyte subset distributions in children and adults living in communities assessed for lead and
5 cadmium exposure. J. Toxicol. Environ. Health A. 60(1): 1-15.
6 Sarasua, S. M.; Mueller, P.; Kathman, S.; Campagna, D.; Uddin, M. S.; White, M. C. (2003) Confirming the utility
7 of four kidney biomarker tests in a longitudinal follow-up study. Renal Failure 25: 797-817.
8 Sargent, J. D.; Dalton, M. A.; O'Connor, G. T.; Olmstead, E. M.; Klein, R. Z. (1999) Randomized trial of calcium
9 glycerophosphate-supplemented infant formula to prevent lead absorption. Am. J. Clin. Nutr.
10 69: 1224-1230.
11 Sarto, F.; Stella, M.; Acqua, A. (1978) Cytogenetic study of a group of workers with increased lead absorption
12 indices. Med. Lav. 69: 172-180.
13 Sata, F.; Araki, S.; Sakai, T.; Nakata, A.; Yamashita, K.; Morita, Y.; Tanigawa, T.; Miki, A. (1997) Immunological
14 effects of CaEDTA injection: observations in two lead workers. Am. J. Ind. Med. 32: 674-680.
15 Sata, F.; Araki, S.; Tanigawa, T.; Morita, Y.; Sakurai, S.; Nakata, A.; Katsuno, N. (1998) Changes in T cell
16 subpopulations in lead workers. Environ. Res. 76: 61-64.
17 Satarug, S.; Nishijo, M.; Ujjin, P.; Vanavanitkun, Y.; Baker, J. R.; Moore, M. R. (2004) Evidence for concurrent
18 effects of exposure to environmental cadmium and lead on hepatic CYP2A6 phenotype and renal function
19 biomarkers in nonsmokers. Environ. Health Perspect. 112: 1512-1518.
20 Satz, P. (1993) Brain reserve capacity on symptom onset after brain injury: a formulation and review of evidence for
21 threshold theory. Neuropsychology 7: 273-295.
22 Savitz, D. A.; Whelan, E. A.; Rowland, A. S.; Kleckner, R. C. (1990) Maternal employment and reproductive risk
23 factors. Am. J. Epidemiol. 132: 933-945.
24 Schafer, T. E.; Adair, S. M. (2000) Prevention of dental disease. The role of the pediatrician. Pediatr. Clin. North
25 Am. 47: 1021-1042.
26 Schafer, J. H.; Glass, T. A.; Bressler, J.; Todd, A. C.; Schwartz, B. S. (2005) Blood lead in a predictor of
27 homocysteine levels in a population-based study of older adults. Environ. Health Perspect. 113:31-35.
28 Schantz, S. L. (1996) Developmental neurotoxicity of PCBs in humans: what do we know and where do we go from
29 here? Neurotoxicol. Teratol. 18: 217-227.
30 Scharer, K.; Veits, G.; Brockhaus, A.; Ewers, U. (1991) High lead content of deciduous teeth in chronic renal
31 failure. Pediatr. Nephrol. 5: 704-707.
32 Schaumberg, D. A.; Mendes, F.; Balaram, M.; Dana, M. R.; Sparrow, D.; Hu, H. (2004) Accumulated lead exposure
33 and risk of age-related cataract in men. JAMA J. Am. Med. Assoc. 292: 2750-2754.
34 Schmid, E.; Bauchinger, M.; Pietruck, S.; Hall, G. (1972) Die cytogenetische Wirkung von Blei in menschlichen
3 5 peripheren Lymphocyten in vitro und in vivo [The cytogeneticeffect of lead in human peripehral
36 lymphocytes in vitro and in vivo]. Mutat. Res. 16: 401-406.
37 Schnaas, L.; Rothenberg, S. J.; Perroni, E.; Martinez, S.; Hernandez, C.; Hernandez, R. M. (2000) Temporal pattern
38 in the effect of postnatal blood lead level on intellectual development of young children. Neurotoxicol.
39 Teratol. 22: 805-810.
40 Schneider, J. S.; Lee, M. H.; Anderson, D. W.; Zuck, L.; Lidsky, T. I. (2001) Enriched environment during
41 development is protective against lead-induced neurotoxicity. Brain Res. 896: 48-55.
42 Schroeder, S. R.; Hawk, B. (1987) Psycho-social factors, lead exposure, and IQ. In: Schroeder, S. R., ed. Toxic
43 substances and mental retardation: neurobehavioral toxicology and teratology. Washington, DC: American
44 Association on Mental Deficiency; pp. 97-137. (Begab, M. J., ed. Monographs of the American Association
45 on Mental Deficiency: no. 8).
46 Schroeder, H. A.; Tipton, I. H. (1968) The human body burden of lead. Arch. Environ. Health 17: 965-978.
47 Schuhmacher, M.; Hernandez, M.; Domingo, J. L.; Fernandez-Ballart, J. D.; Llobet, J. M.; Corbella, J. (1996)
48 A longitudinal study of lead mobilization during pregnancy: concentrations in maternal and umbilical cord
49 blood. Trace Elem. Electrol. 13: 177-181.
50 Schuhmacher, M.; Patemain, J. L.; Domingo, J. L.; Corbella, J. (1997) An assessment of some biomonitors
51 indicative of occupational exposure to lead. Trace Elem. Electrolytes 14(3): 145-149.
52 Schumacher, C.; Brodkin, C. A.; Alexander, B.; Cullen, M.; Rainey, P. M.; vanNetten, C.; Faustman, E.;
53 Checkoway, H. (1998) Thyroid function in lead smelter workers: absence of subacute or cumulative effects
54 with moderate lead burdens. Int. Arch. Occup. Environ. Health 71: 453-458.
55 Schwanitz, G.; Lehnert, G.; Gebhart, E. (1970) Chromosomenschadenbei beruflicher Bleibelastung [Chromosome
56 damage after occupational exposure to lead]. Dtsch. Med. Wochenschr. 95: 1636-1641.
May 2006 6-363 DRAFT-DO NOT QUOTE OR CITE
-------
1 Schwanitz, G.; Gebhart, E.; Rott, H.-D.; Schaller, K.-H.; Essing, H.-G.; Lauer, O.; Prestele, H. (1975)
2 Chromosomenuntersuchungen bei Personen mit beruflicher Bleiexposition [Chromosome investigations in
3 subjects with occupational lead exposure]. Dtsch. Med. Wochenschr. 100: 1007-1011.
4 Schwartz, J. (1985) Evidence for a blood lead-blood pressure relationship [memorandum to the Clean Air Science
5 Advisory Committee]. Washington, DC: U.S. Environmental Protection Agency, Office of Policy Analysis.
6 Available for inspection at: U.S. Environmental Protection Agency, Central Docket Section, Washington,
7 DC; docket no. ECAO-CD-81-2 IIA.F.60.
8 Schwartz, J. (1991) Lead, blood pressure, and cardiovascular disease in men and women. Environ. Health Perspect.
9 91:71-75.
10 Schwartz, J. (1994) Low-level lead exposure and children's IQ: a meta-analysis and search for a threshold. Environ.
11 Res. 65: 42-55.
12 Schwartz, J. (1995) Lead, blood pressure, and cardiovascular disease in men. Arch. Environ. Health 50: 31-37.
13 Schwartz, J.; Otto, D. (1987) Blood lead, hearing thresholds, and neurobehavioral development in children and
14 youth. Arch. Environ. Health 42: 15 3 -160.
15 Schwartz, J.; Otto, D. (1991) Lead and minor hearing impairment. Arch. Environ. Health 46: 300-305.
16 Schwartz, J.; Angle, C.; Pitcher, H. (1986) Relationship between childhood blood lead and stature. Pediatrics
17 77:281-288.
18 Schwartz, J.; Landrigan, P. J.; Baker, E. L., Jr.; Orenstein, W. A.; von Lindern, I. H. (1990) Lead-induced anemia:
19 dose-response relationships and evidence for a threshold. Am. J. Public. Health 80: 165-168.
20 Schwartz, B. S.; Bolla, K. I.; Stewart, W.; Ford, D. P.; Agnew, J.; Frumkin, H. (1993) Decrements in
21 neurobehavioral performance associated with mixed exposure to organic and inorganic lead. Am. J.
22 Epidemiol. 137: 1006-1021.
23 Schwartz, B. S.; Lee, B.-K.; Stewart, W.; Sithisarankul, P.; Strickland, P. T.; Ahn, K.-D.; Kelsey, K. (1997)
24 5-Aminolevulinic acid dehydratase genotype modifies four hour urinary lead excretion after oral
25 administration of dimercaptosuccinic acid. Occup. Environ. Med. 54: 241-246.
26 Schwartz, B. S.; Stewart, W. F.; Kelsey, K. T.; Simon, D.; Park, S.; Links, J. M; Todd, A. C. (2000a) Associations
27 of tibial lead levels with BsmI polymorphisms in the vitamin D receptor in former organolead
28 manufacturing workers. Environ. Health Perspect. 108: 199-203.
29 Schwartz, B. S.; Stewart, W. F.; Bolla, K. I.; Simon, M. S.; Bandeen-Roche, K.; Gordon, B.; Links, J. M.; Todd,
30 A. C. (2000b) Past adult lead exposure is associated with longitudinal decline in cognitive function.
31 Neurology 55: 1144-1150.
32 Schwartz, B. S.; Stewart, W. F.; Todd, A. C.; Simon, D.; Links, J. M. (2000c) Different associations of blood lead,
33 meso 2,3-dimercaptosuccinic acid (DMSA)-chelatable lead, and tibial lead levels with blood pressure in
34 543 former organolead manufacturing workers. Arch. Environ. Health. 55: 85-92.
35 Schwartz, B. S.; Lee, B.-K.; Lee, G.-S.; Stewart, W. F.; Simon, D.; Kelsey, K.; Todd, A. C. (2000d) Associations of
3 6 blood lead, dimercaptosuccinic acid-chelatable lead, and tibia lead with polymorphisms in the vitamin D
37 receptor and 5-aminolevulinic acid dehydratase genes. Environ. Health Perspect. 108: 949-954.
38 Schwartz, B. S.; Lee, B. K.; Lee, G. S.; Stewart, W. F.; Lee, S. S.; Hwang, K. Y.; Ahn, K.-D.; Kim, Y.-B.; Bolla,
39 K. I.; Simon, D.; Parsons, P. J.; Todd, A. C. (2001a) Associations of blood lead, dimercaptosuccinic acid-
40 chelatable lead, and tibia lead with neurobehavioral test scores in South Korean lead workers. Am. J.
41 Epidemiol. 153:453-464.
42 Schwartz, B. S.; Stewart, W. F.; Bolla, K. I.; Simon, P. D.; Bandeen-Roche, K.; Gordon, P. B.; Links, J. M.; Todd,
43 A. C. (200 Ib) Past adult lead exposure is associated with longitudinal decline in cognitive function
44 (erratum to Neurology 55: 1144-1150). Neurology 56: 283.
45 Schwartz, B. S.; Stewart, W.; Hu, H. (2002) Neurobehavioural testing in workers occupationally exposed to lead
46 [letter]. Occup. Environ. Med. 59: 648-649.
47 Schwartz, B. S.; Lee, B.-K.; Bandeen-Roche, K.; Stewart, W.; Bolla, K. I.; Links, J.; et al. (2005) Occupational lead
48 exposure and longitudinal decline in neurobehavioral test scores. Epidemiology 16: 106-113.
49 Sciarillo, W. G.; Alexander, G.; Farrell, K. P. (1992) Lead exposure and child behavior. Am. J. Public Health
50 82: 1356-1360.
51 Seeber, A.; Meyer-Baron, M.; Schaper, M. (2002) A summary of two meta-analyses on neurobehavioural effects
52 due to occupational lead exposure. Arch. Toxicol. 76: 137-145.
53 Selander, S.; Cramer, K. (1970) Interrelationships between lead in blood, lead in urine, and ALA in urine during
54 lead work. Br. J. Ind. Med. 27: 28-39.
55 Selevan, S. G.; Landrigan, P. J.; Stern, F. B.; Jones, J. H. (1985) Mortality of lead smelter workers. Am. J.
56 Epidemiol. 122: 673-683.
May 2006 6-364 DRAFT-DO NOT QUOTE OR CITE
-------
1 Selevan, S. G.; Rice, D. C.; Hogan, K. A.; Euling, S. Y.; Pfahles-Hutchens, A.; Bethel, J. (2003) Blood lead
2 concentration and delayed puberty in girls. N. Engl. J. Med. 348: 1527-1536.
3 Shadick, N. A.; Kim, R.; Weiss, S.; Liang, M. H.; Sparrow, D.; Hu, H. (2000) Effect of low level lead exposure on
4 hyperuricemia and gout among middle aged and elderly men: the normative aging study. J. Rheumatol.
5 27: 1708-1712.
6 Shapiro, I. M.; Dobkin, B.; Tuncay, O. C.; Needleman, H. L. (1973) Lead levels in dentin and circumpulpal dentin
7 of deciduous teeth of normal and lead poisoned children. Clin. Chimica. Acta. 46: 119-23.
8 Sharma, K.; Reutergardh, L. B. (2000) Exposure of preschoolers to lead in the Makati area of Metro Manila, the
9 Philippines. Environ. Res. A 83: 322-332.
10 Sharp, D. S.; Benowitz, N. L.; Osterloh, J. D.; Becker, C. E.; Smith, A. H.; Syme, S. L. (1990) Influence of race,
11 tobacco use, and caffeine use on the relation between blood pressure and blood lead concentration. Am. J.
12 Epidemiol. 131:845-854.
13 Sheffet, A.; Thind, I.; Miller, A. M.; Louria, D. B. (1982) Cancer mortality in a pigment plant utilizing lead and zinc
14 chromates. Arch. Environ. Health 37: 44-52.
15 Shen, X.-M.; Yan, C.-H.; Quo, D.; Wu, S.-M.; Li, R.-Q.; Huang, H.; Ao, L.-M.; Zhou, J.-D.; Hong, Z.-Y.; Xu, J.-D.;
16 Jin, X.-M.; Tang, J.-M. (1998) Low-level prenatal lead exposure and neurobehavioral development of
17 children in the first year of life: a prospective study in Shanghai. Environ. Res. 79: 1-8.
18 Shen, X.-M.; Wu, S.-H.; Yan, C.-H.; Zhao, W.; Ao, L.-M.; Zhang, Y.-W.; He, J.-M.; Ying, J.-M.; Li, R.-Q.;
19 Wu, S.-M.; Guo, D. (2001) Delta-aminolevulinate dehydratase polymorphism and blood lead levels in
20 Chinese children. Environ. Res. 85: 185-190.
21 Sherins, R. J. (1995) Are semen quality and male fertility changing? N. Engl. J. Med. 332: 327-328.
22 Shiau, C.-Y.; Wang, J.-D.; Chen, P.-C. (2004) Decreased fecundity among male lead workers. Occup. Environ.
23 Med. 61:915-923.
24 Shukla, H.; Atakent, Y. S.; Ferrara, A.; Topsis, J.; Antoine, C. (1987) Postnatal overestimation of gestational age in
25 preterm infants. Am. J. Dis. Child. 141: 1106-1107.
26 Shukla, R.; Bornschein, R. L.; Dietrich, K. N.; Buncher, C. R.; Berger, O. G.; Hammond, P. B.; Succop, P. A.
27 (1989) Fetal and infant lead exposure: effects on growth in stature. Pediatrics 84: 604-612.
28 Shukla, V. K.; Prakash, A.; Tripathi, B. D.; Reddy, D. C.; Singh, S. (1998) Biliary heavy metal concentrations in
29 carcinoma of the gall bladder: case-control study. Br. Med. J. 317: 1288-1289.
30 Siddiqui, M. K.; Srivastava, S.; Mehrotra, P. K. (2002) Environmental exposure to lead as a risk for prostate cancer.
31 Biomed. Environ. Sci. 15: 298-305.
32 Siegel, M.;Forsyth, B.; Siegel, L.; Cullen, M. R. (1989) The effect of lead on thyroid function in children. Environ.
33 Res. 49: 190-196.
34 Siemiatycki, J.; Gerin, M.; Stewart, P.; Nadon, L.; Dewar, R.; Richardson, L. (1988) Associations between several
3 5 sites of cancer and ten types of exhaust and combustion products: results from a case-referent study in
36 Montreal. Scand. J. Work Environ. Health 14: 79-90.
37 Siemiatycki, J.; Gerin, M.; Dewar, R.; Nadon, L.; Lakhani, R.; Begin, D.; Richardson, L. (1991) Associations
3 8 between occupational circumstances and cancer. In: Siemiatycki, J., ed. Risk factors for cancer in the
39 workplace. Boca Raton, FL: CRC Press; pp. 141-145.
40 Silbergeld, E. K. (1991) Lead in bone: implications for toxicology during pregnancy and lactation. Environ. Health
41 Perspect. 91:63-70.
42 Silbergeld, E. K.; Schwartz, J.; Mahaffey, K. (1988) Lead and osteoporosis: mobilization of lead from bone in
43 postmenopausal women. Environ. Res. 47: 79-94.
44 Silbergeld, E. K.; Sauk, J.; Somerman, M.; Todd, A.; McNeill, F.; Fowler, B.; Fontaine, A.; vanBuren, J. (1993)
45 Lead in bone: storage site, exposure source, and target organ. Presented at: Ninth international
46 neurotoxicology conference; October 1991; Little Rock, AR. Neurotoxicology 14(2-3): 225-236.
47 Silbergeld, E. K.; Waalkes, M.; Rice, J. M. (2000) Lead as a carcinogen: experimental evidence and mechanisms of
48 action. Am. J. Ind. Med. 38: 316-323.
49 Silva, P. A.; Hughes, P.; Williams, S.; Faed, J. M. (1988) Blood lead, intelligence, reading attainment, and
50 behaviour in eleven year old children in Dunedin, New Zealand. J. Child Psychol. Psychiatr. Allied Discipl.
51 29:43-52.
52 Singh, B.; Chandran, V.; Bandhu, H. K.; Mittal, B. R.; Bhattacharya, A.; Jindal, S. K.; Varma, S. (2000) Impact of
53 lead exposure on pituitary-thyroid axis in humans. BioMetals 13: 187-192.
54 Smith, F. L., 2nd; Rathmell, T. K.; Marcil, G. E. (1938) The early diagnosis of acute and latent plumbism. Am. J.
55 Clin. Pathol. 8: 471-508.
May 2006 6-365 DRAFT-DO NOT QUOTE OR CITE
-------
1 Smith, C. M; Wang, X.; Hu, H.; Kelsey, K. T. (1995) A polymorphism in the 5-aminolevulinic acid dehydratase
2 gene may modify the pharmacokinetics and toxicity of lead. Environ. Health Perspect. 103: 248-253.
3 Sokas, R. K.; Simmens, S.; Sophar, K.; Welch, L. S.; Liziewski, T. (1997) Lead levels in Maryland construction
4 workers. Am. J. Ind. Med. 31: 188-194.
5 Sokol, R. Z. (1987) Hormonal effects of lead acetate in the male rat: mechanism of action. Biol. Reprod.
6 37: 1135-1138.
7 Sokol, R. Z.; Herman, N.; Okuda, H.; Raum, W. (1998) Effects of lead exposure on GnRH and LH secretion in male
8 rats: response to castration and d-methyl-p-tyrosine (AMPT) challenge. Reprod. Toxicol. 12: 347-355.
9 Sokol, R. Z.; Wang, S.; Wan, Y.-J. Y.; Stanczyk, F. Z.; Gentzschein, E.; Chapin, R. E. (2002) Long-term, low-dose
10 lead exposure alters the gonadotropin-releasing hormone system int he male rat. Environ. Health Perspect.
11 110:871-874.
12 Soldin, O. P.; Pezzullo, J. C.; Hanak, B.; Miller, M.; Soldin, S. J. (2003) Changing trends in the epidemiology of
13 pediatric lead exposure: interrelationship of blood lead and ZPP concentrations and a comparison to the US
14 population. Ther. Drug Monit. 25: 415 -420.
15 Solliway, B. M.; Schaffer, A.; Pratt, H.; Yannai, S. (1996) Effects of exposure to lead on selected biochemical and
16 haematological variables. Pharmacol. Toxicol. 78: 18-22.
17 Sonmez, F.; Donmez, O.; Sonmez, H. M.; Keskinoglu, A.; Kabasakal, C.; Mir, S. (2002) Lead exposure and urinary
18 N-acetyl (3 D glucosaminidase activity in adolescent workers in auto repair workshops. J. Adolesc. Health
19 30:213-216.
20 Sorel, J. E.; Heiss, G.; Tyroler, H. A.; Davis, W. B.; Wing, S. B.; Ragland, D. R. (1991) Black-white differences in
21 blood pressure among participants in NHANES II: the contribution of blood lead. Epidemiology
22 2:348-352.
23 Sorrell, M.; Rosen, J. F.; Roginsky, M. (1977) Interactions of lead, calcium, vitamin D, and nutrition in lead-
24 burdened children. Arch. Environ. Health 32: 160-164.
25 Sowers, M.; Jannausch, M.; Scholl, T.; Li, W.; Kemp, F. W.; Bogden, J. D. (2002) Blood lead concentrations and
26 pregnancy outcomes. Arch. Environ. Health 57: 489-495.
27 Spencer, H.; O'Sullivan, V.; Sontag, S. J. (1992) Does lead play a role in Paget's disease of bone? A hypothesis.
28 J. Lab. Clin. Med. 120: 798-800.
29 Spencer, H.; O'Sullivan, V.; Sontag, S. J. (1994) Occupational exposure to lead: preliminary observations in Paget's
30 disease of bone in women and in family members of affected patients. J. Trace Elem. Exp. Med. 7: 53-58.
31 Spencer, H.; O'Sullivan, V.; Sontag, S. J. (1995) Exposure to lead, a potentially hazardous toxin: Paget's disease of
32 bone. J. Trace Elem. Exp. Med. 8: 163-171.
33 Spinnato, J. A.; Sibai, B. M.; Shaver, D. C.; Anderson, G. D. (1984) Inaccuracy of Dubowitz gestational age in low
34 birth weight infants. Obstet. Gynecol. (Hagerstown, MD, U.S.) 63: 491-495.
35 Spivey, G. H.; Baloh, R. W.; Brown, C. P.; Browdy, B. L.; Campion, D. S.; Valentine, J. L.; Morgan, D. E.; Culver,
36 B. D. (1980) Subclinical effects of chronic increased lead absorption~a prospective study. III. Neurologic
37 findings at follow-up examination. J. Occup. Med. 22: 607-612.
38 Spreen, O.; Risser, A. T.; Edgell, D. (1995) Developmental neuropsychology. New York, NY: Oxford University
39 Press.
40 Staessen, J.; Yeoman, W. B.; Fletcher, A. E.; Markowe, H. L.; Marmot, M. G.; Rose, G.; Semmence, A.; Shipley,
41 M. J.; Bulpitt, C. J. (1990) Blood lead concentration, renal function, and blood pressure in London civil
42 servants. Br. J. Ind. Med. 47: 442-447.
43 Staessen, J. A.; Lauwerys, R. R.; Buchet, J.-P.; Bulpitt, C. J.; Rondia, D.; VanRenterghem, Y.; Amery, A. (1992)
44 Impairment of renal function with increasing blood lead concentrations in the general population. N. Engl.
45 J. Med. 327: 151-156.
46 Staessen, J. A.; Dolenc, P.; Amery, A.; Buchet, J.-P.; Claeys, F.; Fagard, R.; Lauwerys, R.; Lijnen, P.; Roels, H.;
47 Rondia, D.; Sartor, F.; Thijs, L.; Vyncke, G., on behalf of the Cadmibel Study Group. (1993)
48 Environmental lead exposure does not increase blood pressure in the population: evidence from the
49 Cadmibel study. J. Hypertens. 1 l(suppl. 2): S35-S41.
50 Staessen, J. A.; Bulpitt, C. J.; Fagard, R.; Lauwerys, R. R.; Roels, H.; Thijs, L.; Amery, A. (1994) Hypertension
51 caused by low-level lead exposure: myth or fact? J. Cardiovasc. Risk 1: 87-97.
52 Staessen, J. A.; Roels, H.; Fagard, R. (1996a) Lead exposure and conventional and ambulatory blood pressure: a
53 prospective population study. JAMA J. Am. Med. Assoc. 275: 1563-1570.
54 Staessen, J. A.; Buchet, J.-P.; Ginucchio, G.; Lauwerys, R. R.; Lijnen, P.; Roels, H.; Fagard, R. (1996b) Public
5 5 health implications of environmental exposure to cadmium and lead: an overview of epidemiological
56 studies in Belgium. J. Cardiovasc. Risk 3: 26-41.
May 2006 6-366 DRAFT-DO NOT QUOTE OR CITE
-------
1 Staessen, J. A.; Nawrot, T.; Den Hond, E.; Thijs, L.; Fagard, R.; Hoppenbrouwers, K.; Koppen, G.; Nelen, V.;
2 Schoeters, G.; Vanderschueren, D.; VanHecke, E.; Verschaeve, L.; Vlietinck, R.; Roels, H. A. (2001)
3 Renal function, cytogenetic measurements, and sexual developments in adolescents in relation to
4 environmental pollutants: a feasibility study of biomarkers. Lancet 357: 1660-1669.
5 Steenland, K.; Boffetta, P. (2000) Lead and cancer in humans: where are we now? Am. J. Ind. Med. 38: 295-299.
6 Steenland, K.; Thun, M. J.; Ferguson, C. W.; Port, F. K. (1990) Occupational and other exposures associated with
7 male end-stage renal disease: a case/control study. Am. J. Public Health. 80: 153-157.
8 Steenland, K.; Selevan, S.; Landrigan, P. (1992) The mortality of lead smelter workers: an update. Am. J. Public
9 Health 82: 1641-1644.
10 Steenland, K.; Loomis, D.; Shy, C.; Simonsen, N. (1996) Review of occupational lung carcinogens. Am. J. Ind.
11 Med. 29: 474-490.
12 Steenland, K.; Mannetje, A.; Boffetta, P.; Stayner, L.; Attfield, M.; Chen, J.; Dosemeci, M.; DeKlerk, N.;
13 Hnizdo, E.; Koskela, R.; Checkoway, H. (2002) Pooled exposure-response analyses and risk assessmenfor
14 lung cancer in 10 cohorts of silica-exposed workers: an IARC multi-centric study (vol 12, pg 773, 2001).
15 Cancer Causes Control 13: 777.
16 Stevens, L. A.; Levey, A. S. (2005a) Measurement of kidney function. Med. Clin. N. Am. 89: 457-473.
17 Stevens, L. A.; Levey, A. S. (2005b) Chronic kidney disease in the elderly — how to assess risk. N. Engl. J. Med.
18 352:2122-2124.
19 Stewart, W. F.; Schwartz, B. S.; Simon, D.; Bolla, K. I.; Todd, A. C.; Links, J. (1999) Neurobehavioral function and
20 tibial and chelatable lead levels in 543 former organolead workers. Neurology 52: 1610-1617.
21 Stewart, W. F.; Schwartz, B. S.; Simon, D.; Kelsey, K.; Todd, A. C. (2002) ApoE genotype, past adult lead
22 exposure, and neurobehavioral function. Environ. Health Perspect. 110: 501-505.
23 Stiles, K. M.; Bellinger, D. C. (1993) Neuropsychological correlates of low-level lead exposure in school-age
24 children: a prospective study. Neurotoxicol. Teratol. 15: 27-35.
25 Stokes, L.; Letz, R.; Gerr, F.; Kolczak, M.; McNeill, F. E.; Chettle, D. R.; Kaye, W. E. (1998) Neurotoxicity in
26 young adults 20 years after childhood exposure to lead: the Bunker Hill experience. Occup. Environ. Med.
27 55:507-516.
28 Stollery, B. T. (1996) Reaction time changes in workers exposed to lead. Neurotoxicol. Teratol. 18: 477-483.
29 Stollery, B. T.; Banks, H. A.; Broadbent, D. E.; Lee, W. R. (1989) Cognitive functioning in lead workers. Br. J. Ind.
30 Med. 46: 698-707.
31 Stollery, B. T.; Broadbent, D. E.; Banks, H. A.; Lee, W. R. (1991) Short term prospective study of cognitive
32 functioning in lead workers. Br. J. Ind. Med. 48: 739-749.
33 Succop, P.; Bornschein, R.; Brown, K.; Tseng, C.-Y. (1998) An empirical comparison of lead exposure pathway
34 models. Environ. Health Perspect. Suppl. 106(6): 1577-1583.
35 Sugawara, E.; Nakamura, K.; Miyake, T.; Fukumura, A.; Seki, Y. (1991) Lipid peroxidation and concentration of
36 glutathione in erythrocytes from workers exposed to lead. Br. J. Ind. Med. 48: 239-242.
37 Sun, L.; Hu, J.; Zhao, Z.; Li, L.; Cheng, H. (2003) Influence of exposure to environmental lead on serum
38 immunoglobulin in preschool children. Environ. Res. 92: 124-128.
39 Susser, M. (1991) What is a cause and how do we know one? A grammar for pragmatic epidemiology. Am. J.
40 Epidemiol. 133:635-648.
41 Stizen, H. S.; Duydu, Y.; Aydin, A.; Is.imer, A; Vural, N. (2003) Influence of the delta-aminolevulinic acid
42 dehydratase (ALAD) polymorphism on biomarkers of lead exposure in Turkish storage battery
43 manufacturing workers. Am. J. Ind. Med. 43: 165-171.
44 Symanski, E.; Hertz-Picciotto, I. (1995) Blood lead levels in relation to menopause, smoking, and pregnancy
45 history. Am. J. Epidemiol. 141: 1047-1058.
46 Tabacova, S.; Balabaeva, L. (1993) Environmental pollutants in relation to complications of pregnancy. Environ.
47 Health Perspect. 101(suppl. 2): 27-31.
48 Tang, N.; Zhu, Z. Q. (2003) Adverse reproductive effects in female workers of lead battery plants. Int. J. Occup.
49 Med. Environ. Health 16: 359-361.
50 Taskinen, H. (1988) Spontaneous abortions among women occupationally exposed to lead. In: Hogstedt, C.;
51 Reuterwall, C., eds. Progress in occupational epidemiology. New York, NY: Elsevier Science Publishers;
52 pp. 197-200.
53 Tassler, P.; Schwartz, B. S.; Coresh, J.; Stewart, W.; Todd, A. (2001) Associations of tibia lead, DMSA-Chelatable
54 lead, and blood lead with measures of peripheral nervous system function in former organolead
55 manufacturing workers. Am. J. Ind. Med. 39: 254-261.
May 2006 6-367 DRAFT-DO NOT QUOTE OR CITE
-------
1 Taupeau, C.; Poupon, J.; Treton, D.; Brosse, A.; Richard, Y.; Machelon, V. (2003) Lead reduces messenger RNA
2 and protein levels of cytochrome P450 aromatase and estrogen receptor "Beta" in human ovarian granulosa
3 cells. Biol. Reprod. 68: 1982-1988.
4 Telisman, S.; Pizent, A.; Jurasovic, J.; Cvitkovic, P. (2004) Lead effect on blood pressure in moderately lead-
5 exposed male workers. Am. J. Ind. Med. 45: 446-454.
6 Tellez-Rojo, M. M; Hernandez-Avila, M; Gonzalez-Cossio, T.; Romieu, I.; Aro, A.; Palazuelos, E.; Schwartz, J.;
7 Hu, H. (2002) Impact of breastfeeding on the mobilization of lead from bone. Am. J. Epidemiol.
8 155:420-428.
9 Tellez-Rojo, M. M.; Hernandez-Avila, M.; Lamadrid-Figueroa, H.; Smith, D.; Hernandez-Cadena, L.; Mercado, A.;
10 Aro, A.; Schwartz, J.; Hu, H. (2004) Impact of bone lead and bone resorption on plasma and whole blood
11 lead levels during pregnancy. Am. J. Epidemiol. 160: 668-678.
12 Tellez-Rojo, M. M.; Bellinger, D. C.; Arroyo-Quiroz, C.; Lamadrid-Figueroa, H.; Mercado-Garcia, A.; Schnaas-
13 Arrieta, L.; Wright, R. O.; Hernandez-Avila, M.; Hu, H. (2006) Longitudinal associations between blood
14 lead concentrations < 10 ug/dL and neurobehavioral development in environmentally-exposed children in
15 Mexico City. Pediatrics: in press.
16 Tepper, A.; Mueller, C.; Singal, M.; Sagar, K. (2001) Blood pressure, left ventricular mass, and lead exposure in
17 battery manufacturing workers. Am. J. Ind. Med. 40: 63-72.
18 Teruya, K.; Sakurai, H.; Omae, K.; Higashi, T.; Muto, T.; Kaneko, Y. (1991) Effect of lead on cardiac
19 parasympathetic function. Int. Arch. Occup. Environ. Health 62: 549-553.
20 Thacker, S. B.; Hoffman, D. A.; Smith, I; Steinberg, K.; Zack, M. (1992) Effect of low-level body burdens of lead
21 on the mental development of children: limitations of meta-analysis in a review of longitudinal data. Arch.
22 Environ. Health 47: 336-346.
23 Theppeang, K.; Schwartz, B. S.; Lee, B.-K.; Lustberg, M. E.; Silbergeld, E. K.; Kelsey, K. T.; Parsons, P. J.; Todd,
24 A. C. (2004) Associations of patella lead with polymorphisms in the vitamin D receptor, 5-aminolevulinic
25 acid dehydratase and endothelial nitric oxide synthase genes. J. Occup. Environ. Med. 46: 528-537.
26 Thompson, S. G.; Pocock, S. J. (1992) Can meta-analyses be trusted? Lancet 338:1127-1130.
27 Thomson, G. O. B.; Raab, G. M.; Hepburn, W. S.; Hunter, R.; Fulton, M.; Laxen, D. P. H. (1989) Blood-lead levels
28 and children's behaviour - results from the Edinburgh lead study. J. Child Psychol. Psychiatr. 30: 515-528.
29 Todd, A. C.; Carroll, S.; Godbold, J. H.; Moshier, E. L.; Khan, F. A. (2000) Variability in XRF-measured tibia lead
30 levels. Phys. Med. Biol. 45: 3737-3748.
31 Todd, A. C.; Buchanan, R.; Carroll, S.; Moshier, E. L.; Popovac, D.; Slavkovich, V.; Graziano, J. H. (2001)
32 Tibia lead levels and methodological uncertainty in 12-year-old children. Environ. Res. 86: 60-65.
33 Todd, A. C.; Carroll, S.; Geraghty, C.; Khan, F. A.; Moshier, E. L.; Tang, S.; Parsons, P. J. (2002) L-shell x-ray
34 fluorescence measurements of lead in bone: accuracy and precision. Phys. Med. Biol. 47: 1399-1419.
3 5 Tomatis, L. (1990) Cancer: causes, occurrence, and control. Lyon, France: International Agency for Research on
36 Cancer. (IARC scientific publications: v. 100).
37 Tong, S.; Baghurst, P.; McMichael, A.; Sawyer, M.; Mudge, J. (1996) Lifetime exposure to environmental lead and
38 children's intelligence at 11-13 years: the PortPirie cohort study. Br. Med. J. 312: 1569-1575.
39 Tong, S.; Baghurst, P. A.; Sawyer, M. G.; Burns, J.; McMichael, A. J. (1998) Declining blood lead levels and
40 changes in cognitive function during childhood: the Port Pirie cohort study. JAMA J. Am. Med. Assoc.
41 280: 1915-1919.
42 Tong, I. S.; Lu, Y. (2001) Identification of confounders in the assessment of the relationship between lead exposure
43 and child development. Ann. Epidemiol. 11: 38-45.
44 Tong, S.; McMichael, A. J.; Baghurst, P. A. (2000) Interactions between environmental lead exposure and
45 sociodemographic factors on cognitive development. Arch. Environ. Health 55: 330-335.
46 Torres-Sanchez, L. E.; Berkowitz, G.; Lopez-Carrillo, L.; Torres-Arreola, L.; Rios, C.; Lopez-Cervantes, M. (1999)
47 Intrauterine lead exposure and preterm birth. Environ. Res. 81: 297-301.
48 Trope, I.; Lopez-Villegas, D.; Lenkinski, R. E. (1998) Magnetic resonance imaging and spectroscopy of regional
49 brain structure in a 10-year-old boy with elevated blood lead levels. Pediatrics 101(6): E7.
50 Trope, L; Lopez-Villegas, D.; Cecil, K. M.; Lenkinski, R. E. (2001) Exposure to lead appears to selectively alter
51 metabolism of cortical gray matter. Pediatrics 107: 1437-1443.
52 Tsai, S.-Y.; Chen, T.-F.; Chao, K.-Y. (2000) Subclinical neurobehavioral effects of low-level lead exposure in glaze
53 factory workers. ActaNeurol. Taiwan. 9: 122-127.
54 Tsaih, S.-W.; Schwartz, I; Lee, M.-L. T.; Amarasiriwardena, C.; Aro, A.; Sparrow, D.; Hu, H. (1999) The
55 independent contribution of bone and erythrocyte lead to urinary lead among middle-aged and elderly men:
56 the normative aging study. Environ. Health Perspect. 107: 391-396.
May 2006 6-368 DRAFT-DO NOT QUOTE OR CITE
-------
1 Tsaih, S.-W.; Korrick, S.; Schwartz, I; Amarasiriwardena, C.; Aro, A.; Sparrow, D; Hu, H. (2004) Lead, diabetes,
2 hypertension, and renal function: the Normative Aging Study. Environ. Health Perspect. 112:1178-1182.
3 Tuppurainen, M; Wagar, G.; Kurppa, K.; Sakari, W.; Wambugu, A.; Froseth, B.; Alho, I; Nykyri, E. (1988)
4 Thyroid function as assessed by routine laboratory tests of workers with long-term lead exposure. Scand. J.
5 Work Environ. Health 14: 175-180.
6 Tuthill, R. W. (1996) Hair lead levels related to children's classroom attention-deficit behavior. Arch. Environ.
7 Health 51: 214-220.
8 Tvinnereim, H. M.; Eide, R.; Riise, T.; Wesenberg, G. R.; Fosse, G.; Steinnes, E. (1997) Lead in primary teeth from
9 Norway: changes in lead levels from the 1970s to the 1990s. Sci. Total Environ. 207: 165-177.
10 Tvinnereim, H. M.; Eide, R.; Riise, T. (2000) Heavy metals in human primary teeth: some factors influencing the
11 metal concentrations. Sci. Total Environ. 255: 21-27.
12 U.S. Environmental Protection Agency. (1986a) Air quality criteria for lead. Research Triangle Park, NC: Office of
13 Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no.
14 EPA-600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
15 U.S. Environmental Protection Agency. (1986b) Lead effects on cardiovascular function, early development, and
16 stature: an addendum to U.S. EPA Air Quality Criteria for Lead (1986). In: Air quality criteria for lead, v.
17 1. Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria
18 and Assessment Office; pp. A1-A67; EPA report no. EPA-600/8-83/028aF. Available from: NTIS,
19 Springfield, VA; PB87-142378.
20 U.S. Environmental Protection Agency. (1990) Air quality criteria for lead: supplement to the 1986 addendum.
21 Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and
22 Assessment Office; report no. EPA/600/8-89/049F. Available from: NTIS, Springfield, VA; PB91-138420.
23 U.S. Environmental Protection Agency. (2001) Final human health risk assessment for the Coeur d'Alene Basin
24 extending from Harrison to Mullan on the Coeur d'Alene River and Tributaries remedial
25 investigation/feasibility study. Washington, DC: Idaho Department of Environmental Quality.
26 U.S. Environmental Protection Agency. (2003) Evaluation of the ICRP Lead Biokinetics Model: empirical
27 comparisons with observations of plasma-blood lead concentration relationships in humans. Washington,
28 DC: Office of Emergency and Remedial Response; FEDSDVI order no. DABT; Syracuse Research
29 Corporation; contract no. GS-10F-0137K.
30 U.S. Environmental Protection Agency. (2004) Air quality criteria for paniculate matter. Research Triangle Park,
31 NC: National Center for Environmental Assessment; report no. EPA/600/P-99/002aF-bF. 2v. Available:
32 http://cfpub.epa.gov/ncea/ [9 November, 2004].
33 U.S. Environmental Protection Agency. (2005) Guidelines for carcinogen risk assessment. Washington, DC: Risk
34 Assessment Forum; report no. EPA/630/P-03/001F. Available: http://cfpub.epa.gov/ncea/index.cfm
35 [30 November, 2005].
36 U.S. Renal Data System. (2004) Outcomes: hospitalization & mortality. In: Annual data report. Minneapolis, MN:
37 USRDS Coordinating Center; pp. 118-138. Available:
3 8 http://www.usrds.org/2004/pdf/06_hosp_morte_04.pdf [21 November, 2005].
39 Undeger, U.; Bas.aran, N.; Canpinar, H.; Kansu, E. (1996) Immune alterations in lead-exposed workers. Toxicology
40 109: 167-172.
41 Valciukas, J. A.; Lilis, R.; Eisinger, J.; Blumberg, W. E.; Fischbein, A.; Selikoff, I. J. (1978) Behavioral indicators
42 of leadneurotoxicity: results of a clinical field survey. Int. Arch. Occup. Environ. Health 41: 217-236.
43 Valentine, J. L.; Baloh, R. W.; Browdy, B. L.; Gonick, H. C.; Brown, C. P.; Spivey, G. H.; Culver, B. D. (1982)
44 Subclinical effects of chronic increased lead absorption~a prospective study. J. Occup. Med. 24: 120-125.
45 Valentino, M.; Governa, M.; Marchiseppe, I.; Visona, I. (1991) Effects of lead on polymorphonuclear leukocyte
46 (PMN) functions in occupationally exposed workers. Arch. Toxicol. 65: 685-688.
47 VanDe Vyver, F. L.; D'Haese, P. C.; Visser, W. J.; Elseviers, M. M.; Knippenberg, L. J.; Lamberts, L. V.; Wedeen,
48 R. P.; De Broe, M. E. (1988) Bone lead in dialysis patients. Kidney Int. 33: 601-607.
49 Van Den Berg, B.; Oechsli, F. (1984) Prematurity. In: Bracken, M., ed. Perinatal epidemiology. New York, NY:
50 Oxford University Press; pp. 69-85.
51 Van Larebeke, N.; Koppen, G.; Nelen, V.; Schoeters, G.; Van Loon H, Albering H, Riga L, Vlietinck, R.; Kleinjans,
52 J.; Flemish Environment and Health Study Group. (2004) Differences in HPRT mutant frequency among
5 3 middle-aged Flemish women in association with area of residence and blood lead levels. Biomarkers
54 9:71-84.
55 Verberk, M. M.; Willems, T. E. P.; Verplanke, A. J. W.; De Wolff, F. A. (1996) Environmental lead and renal
56 effects in children. Arch. Environ. Health 51: 83-87.
May 2006 6-369 DRAFT-DO NOT QUOTE OR CITE
-------
1 Verschoor, M.; Wibowo, A.; Herber, R.; vanHemmen, J.; Zielhuis, R. (1987) Influence of occupational low-level
2 lead exposure on renal parameters. Am. J. Ind. Med. 12: 341-351.
3 Vig, E. K.; Hu, H. (2000) Lead toxicity in older adults. J. Am. Geriatr. Soc. 48: 1501-1506.
4 Vijayalakshmi, P.; Serrano, J.; Sparrow, D.; Hu, H. (1999) Relationship of lead in drinking water to bone lead levels
5 twenty years later in Boston men: The Normative Aging Study. J. Occup. Environ. Med. 41: 349-355.
6 Vimpani, G. V.; Wigg, N. R.; Robertson, E. F.; McMichael, A. J.; Baghurst, P. A.; Roberts, R. J. (1985) The Port
7 Pirie cohort study: blood lead concentration and childhood developmental assessment. In: Goldwater, L. J.;
8 Wysocki, L. M.; Volpe, R. A., eds. Edited proceedings: Lead environmental health - the current issues;
9 May; Durham, NC. Durham, NC: Duke University; pp. 139-146.
10 Vinceti, M.; Guidetti, D.; Bergomi, M.; Caselgrandi, E.; Vivoli, R.; Olmi, M.; Rinaldi, L.; Rovesti, S.; Solime, F.
11 (1997) Lead, cadmium, and selenium in the blood of patients with sporadic amyotrophic lateral sclerosis.
12 Ital. J. Neurol. Sci. 18: 87-92.
13 Vupputuri, S.; He, J.; Muntner, P.; Bazzano, L. A.; Whelton, P. K.; Batuman, V. (2003) Blood lead level is
14 associated with elevated blood pressure in blacks. Hypertension 41: 463-468.
15 Wagnerova, M.; Wagner, V.; Madlo, Z.; Zavazal, Y.; Wokounova, D.; Kriz, J.; Mohyla, O. (1986) Seasonal
16 variations in the level of immunoglobulins and serum proteins of children differing by exposure to air-
17 borne lead. J. Hyg. Epidemiol. Microbiol. Immunol. 30(2): 127-138.
18 Walkowiak, J.; Altmann, L.; Kramer, U.; Sveinsson, K.; Turfeld, M.; Weishoff-Houben, M.; Winneke, G. (1998)
19 Cognitive and sensorimotor functions in 6-year-old children in relation to lead and mercury levels:
20 adjustment for intelligence and contrast sensitivity in computerized testing. Neurotoxicol. Teratol.
21 20:511-521.
22 Wang, C.-L.; Chuang, H.-Y.; Ho, C.-K.; Yang, C.-Y.; Tsai, J.-L.; Wu, T.-S.; Wu, T.-N. (2002a) Relationship
23 between blood lead concentrations and learning achievement among primary school children in Taiwan.
24 Environ. Res. 89: 12-18.
25 Wang, V.-S.; Lee, M.-T.; Chiou, J.-Y.; Guu, C.-F.; Wu, C.-C; Wu, T.-N.; Lai, J.-S. (2002b) Relationship between
26 blood lead levels and renal function in lead battery workers. Int. Arch. Occup. Environ. Health
27 75: 569-575.
28 Ward, N. L; Watson, R.; Bryce-Smith, D. (1987) Placenta! element levels in relation to fetal development for
29 obstetrically 'normal' births: a study of 37 elements. Evidence for effects of cadmium, lead and zinc on fetal
30 growth, and for smoking as a source of cadmium. Int. J. Biosoc. Res. 9: 63-81.
31 Wasserman, G.; Graziano, J. H.; Factor-Litvak, R.; Popovac, D.; Morina, N.; Musabegovic, A.; Vrenezi, N.;
32 Capuni-Paracka, S.; Lekic, V.; Preteni-Redjepi, E.; Hadzialjevic, S.; Slavkovich, V.; Kline, J.; Shrout, P.;
33 Stein, Z. (1992) Independent effects of lead exposure and iron deficiency anemia on developmental
34 outcome at age 2 years. J. Pediatr. 121: 695-703.
35 Wasserman, G. A.; Graziano, J. H.; Factor-Litvak, P.; Popovac, D.; Morina, N.; Musabegovic, A.; Vrenezi, N.;
36 Capuni-Paracka, S.; Lekic, V.; Preteni-Redjepi, E.; Hadzialjevic, S.; Slavkovich, V.; Kline, J.; Shrout, P.;
37 Stein, Z. (1994) Consequences of lead exposure and iron supplementation on childhood development at age
38 4 years. Neurotoxicol. Teratol. 16: 233-240.
39 Wasserman, G. A.; Liu, X.; Lolacono, N. J.; Factor-Litvak, P.; Kline, J. K.; Popovac, D.; Morina, N.; Musabegovic,
40 A.; Vrenezi, N.; Capuni-Paracka, S.; Lekic, V.; Preteni-Redjepi, E.; Hadzialjevic, S.; Slavkovich, V.;
41 Graziano, J. H. (1997) Lead exposure and intelligence in 7-year-old children: the Yugoslavia prospective
42 study. Environ. Health Perspect. 105: 956-962.
43 Wasserman, G. A.; Staghezza-Jaramillo, B.; Shrout, P.; Popovac, D.; Graziano, J. (1998) The effect of lead exposure
44 on behavior problems in preschool children. Am. J. Pub. Health 88 (3): 481-486.
45 Wasserman, G. A.; Musabegovic, A.; Liu, X.; Kline, J.; Factor-Litvak, P.; Graziano, J. H. (2000a) Lead exposure
46 and motor functioning in 4 1/2-year-old children: the Yugoslavia prospective study. J. Pediatr. 137: 555-
47 561.
48 Wasserman, G. A.; Liu, X.; Popovac, D.; Factor-Litvak, P.; Kline, J.; Waternaux, C.; Lolacono, N.; Graziano, J. H.
49 (2000b) The Yugoslavia prospective lead industry study: contributions of prenatal and postnatal lead
50 exposure to early intelligence. Neurotoxicol. Teratol. 22: 811-818.
51 Wasserman, G. A.; Factor-Litvak, P.; Liu, X.; Todd, A. C.; Kline, J. K.; Slavkovich, V.; Popovac, D.; Graziano,
52 J. H. (2003) The relationship between blood lead, bone lead and child intelligence. Child Neuropsychol.
53 9:22-34.
54 Weaver, V M.; Lee, B.-K.; Ahn, K.-D.; Lee, G.-S.; Todd, A. C.; Stewart, W. F.; Wen, J.; Simon, D. J.; Parsons,
55 P. J.; Schwartz, B. S. (2003a) Associations of lead biomarkers with renal function in Korean lead workers.
56 Occup. Environ. Med. 60: 551-562.
May 2006 6-370 DRAFT-DO NOT QUOTE OR CITE
-------
1 Weaver, V. M; Schwartz, B. S.; Ahn, K.-D.; Stewart, W. F.; Kelsey, K. T.; Todd, A. C.; Wen, J.; Simon, D. I;
2 Lustberg, M. E.; Parsons, P. J.; Silbergeld, E. K.; Lee, B.-K. (2003b) Associations of renal function with
3 polymorphisms in the 5-aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide synthase
4 genes in Korean lead workers. Environ. Health Perspect. Ill: 1613-1619.
5 Weaver, V. M.; Lee, B.-K.; Todd, A. C.; Jaar, B. G.; Ahn, K.-D.; Wen, J.; Shi, W.; Parsons, P. J.; Schwartz, B. S.
6 (2005a) Associations of patella lead and other lead biomarkers with renal function in lead workers. J.
7 Occup. Environ. Med. 47: 235-243.
8 Weaver, V. M.; Jarr, B. G.; Schwartz, B. S.; Todd, A. C.; Ahn, K.-D.; Lee, S.-S.; Wen, J.; Parsons, P. J.; Lee, B.-K.
9 (2005b) Associations among lead dose biomarkers, uric acid, and renal function in Korean lead workers.
10 Environ. Health Perspect. 113: 36-42.
11 Weaver, V. M.; Schwartz, B. S.; Jaar, B. G.; Ahn, K.-D.; Todd, A. C.; Lee, S.-S.; Kelsey, K. T.; Silbergeld, E. K.;
12 Lustberg, M. E.; Parsons, P. J.; Wen, J.; Lee-B.-K. (2005c) Associations of uric acid with polymorphisms
13 in the 5-aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide synthase genes in Korean
14 lead workers. Environ. Health Perspect. 113: 1509-1515.
15 Wedeen, R. P.;Mallik, D. K.;Batuman, V. (1979) Detection and treatment of occupational lead nephropathy. Arch.
16 Intern. Med. 139: 53-57.
17 Wedeen, R. P.; Batuman, V.; Landy, E. (1983) The safety of the EDTA lead-mobilization test. Environ. Res.
18 30:58-62.
19 Weinberg, C. R.; Baird, D. D.; Rowland, A. S. (1993) Pitfalls inherent in retrospective time-to-event studies: the
20 example of time to pregnancy. Stat. Med. 12: 867-879.
21 Weinberg, C. R.; Baird, D. D.; Wilcox, A. J. (1994) Sources of bias in studies of time to pregnancy. Stat. Med.
22 13:671-681.
23 Weiss, B. (1988) Neurobehavioral toxicity as a basis for risk assessment. Trends Pharmacol. Sci. 9: 59-62.
24 Weiss, B. (1990) Risk assessment: the insidious nature of neurotoxicity and the aging brain. Neurotoxicology
25 11:305-314.
26 Weiss, B. (2000) Vulnerability of children and the developing brain to neurotoxic hazards. Environ. Health Perspect.
27 Suppl. 108(3): 375-381.
28 Weiss, S. T.; Munoz, A.; Stein, A.; Sparrow, D.; Speizer, F. E. (1986) The relationship of blood lead to blood
29 pressure in a longitudinal study of working men. Am. J. Epidemiol. 123: 800-808.
30 Weisskopf, M. G.; Hu, H.; Mulkern, R. V.; White, R.; Aro, A.; Oliveira, S.; Wright, R. O. (2004a) Cognitive deficits
31 and magnetic resonance spectroscopy in adult monozygotic twins with lead poisoning. Environ. Health
32 Perspect. 112:620-625.
33 Weisskopf, M. G.; Wright, R. O.; Schwartz, J.; Spiro, A., Ill; Sparrow, D.; Aro, A.; Hu, H. (2004b) Cumulative lead
34 exposure and prospective change in cognition among elderly men. The VA Normative Aging Study. Am. J.
35 Epidemiol. 160: 1184-1193.
36 Wesseling, C.; Pukkala, E.; Neuvonen, K.; Kauppinen, T.; Boffetta, P.; Partanen, T. (2002) Cancer of the brain and
37 nervous system and ocupational exposures in Finnish women. J. Occup. Environ. Med. 44: 663-668.
3 8 Wibberley, D. G.; Khera, A. K.; Edwards, J. H.; Rushton, D. I. (1977) Lead levels in human placentae from normal
39 and malformed births. J. Med. Genet. 14: 339-345.
40 Wigg, N. R.; Vimpani, G. V.; McMichael, A. J.; Baghurst, P. A.; Robertson, E. F.; Roberts, R. J. (1988) Port Pirie
41 cohort study: childhood blood lead and neuropsychological development at age two years. J. Epidemiol.
42 Community Health 42: 213-219.
43 Wildt, K.; Berlin, M.; Isberg, P. E. (1987) Monitoring of zinc protoporphyrin levels in blood following occupational
44 lead exposure. Am. J. Ind. Med. 12: 385-398.
45 Wingren, G.; Axelson, O. (1985) Mortality pattern in a glass producing area in SE Sweden. Br. J. Ind. Med.
46 42:411-414.
47 Wingren, G.; Axelson, O. (1987) Mortality in the Swedish glassworks industry. Scand. J. Work Environ. Health
48 13:412-416.
49 Wingren, G.; Axelson, O. (1993) Epidemiologic studies of occupational cancer as related to complex mixtures of
50 trace elements in the art glass industry. Scand. J. Work Environ. Health 19(suppl. 1): 95-100.
51 Wingren, G. Englander, V. (1990) Mortality and cancer morbidity in a cohort of Swedish glassworkers. Int. Arch.
52 Occup. Environ. Health 62: 253-257.
53 Winker, R.; Earth, A.; Ponocny-Seliger, E.; Pilger, A.; Osterode, W.; Rtidiger, H. W. (2005) No cognitive deficits in
54 men formerly exposed to lead. Wien. Klin. Wochenschr. 117: 755-760.
55 Winker, R.; Ponocny-Seliger, E.; Rtidiger, H. W.; Earth, A. (2006) Lead exposure levels and duration of exposure
56 absence predict neurobehavioral performance. Int. Arch. Occup. Environ. Health 79: 123-127.
May 2006 6-371 DRAFT-DO NOT QUOTE OR CITE
-------
1 Winneke, G.; Kraemer, U. (1984) Neuropsychological effects of lead in children: interactions with social
2 background variables. Neuropsychobiology 11: 195-202.
3 Winneke, G.; Brockhaus, A.; Ewers, U.; Kramer, U.; Neuf, M. (1990) Results from the European multicenter study
4 on lead neurotoxicity in children: implications for risk assessment. Neurotoxicol. Teratol. 12: 553-559.
5 Winterberg, B.; Korte, R.; Bertram, H. P. (1991) Response: bone lead is elevated in renal failure [letter]. Nephron
6 58:496-497.
7 Wittmers, L. E.; Aufderheide, A. C.; Wallgren, I; Rapp, G.; Alich, A. (1988) Lead in bone. IV. Distribution of lead
8 in the human skeleton. Arch. Environ. Health 43: 381-391.
9 Wolf, A. W.; Ernhart, C. B.; White, C. S. (1985) Intrauterine lead exposure and early development. In: Lekkas,
10 T. D., ed. International conference: heavy metals in the environment, v. 2; September; Athens, Greece.
11 Edinburgh, United Kingdom: CEP Consultants, Ltd.; pp. 153-155.
12 Wong, O.; Harris, F. (2000) Cancer mortality study of employees at lead battery plants and lead smelters,
13 1947-1955. Am. J. Ind. Med. 38: 255-270.
14 Work Group of the Advisory Committee on Childlhood Lead Poisoning Prevention. (2004) A review of evidence of
15 health effects of blood lead levels <10 ug/dl in children [draft final for ACCLPP review]. Centers for
16 Disease Control and Prevention, National Center for Environmental Health. Available:
17 http://www.cdc.gov/nceh/lead/ACCLPP/meetingMinutes/lessThanlOMtgMAR04.pdf [6 March, 2006].
18 World Health Organization. (1948) Preamble to the Constitution of the World Health Organization as adopted by the
19 International Health Conference, New York, 19-22 June, 1946. Geneva, Switzerland: Official Records of
20 the World Health Organization, no. 2, p. 100.
21 World Health Organization. (1977) Lead. Geneva, Switzerland: World Health Organization. (Environmental health
22 criteria: v.3). Available: http://www.inchem.org/documents/ehc/ehc/ehc003.htm [11 March, 2005].
23 World Health Organization. (1992) International statistical classification of diseases and related health problems:
24 tenth revision (ICD-10). Geneva, Switzerland: World Health Organization; pp. 369-370.
25 World Health Organization. (1995) Inorganic lead. Geneva, Switzerland: World Health Organization, International
26 Programme on Chemical Safety. (Environmental health criteria 165).
27 Wright, R. O.; Hu, H.; Silverman, E. K.; Tsaih, S. W.; Schwartz, J.; Bellinger, D.; Palazuelos, E.; Weiss, S. T.;
28 Hernandez-Avila, M. (2003) Apolipoprotein E genotype predicts 24-month bayley scales infant
29 development score. Pediatr. Res. 54: 819-825.
30 Wright, R. O.; Silverman, E. K.; Schwartz, J.; Tsaih, S.-W.; Senter, J.; Sparrow, D.; Weiss, S. T.; Aro, A.; Hu, H.
31 (2004) Association between hemochromatosis genotype and lead exposure among elderly men: the
32 Normative Aging Study. Environ. Health Perspect. 112: 746-750.
33 Wu, T.-N.; Shen, C.-Y.; Ko, K.-N.; Guu, C.-F.; Gau, H.-J.; Lai, J.-S.; Chen, C.-J.; Chang, P.-Y. (1996) Occupational
34 lead exposure and blood pressure. Int. J. Epidemiol. 25: 791-796.
35 Wu, M. T.; Kelsey, K.; Schwartz, J.; Sparrow, D.; Weiss, S.; Hu, H. (2003a) A 5-aminolevulinic aciddehydratase
3 6 (ALAD) polymorphism may modify the relationship of low-level lead exposure to uricemia and renal
3 7 function: the Normative Aging Study. Environ. Health Perspect. 111:335-341.
38 Wu, T.; Buck, G. M.; Mendola, P. (2003b) Blood lead levels and sexual maturation in U.S. girls: the Third National
39 Health and Nutrition Examination Survey, 1988-1994. Environ. Health Perspect. Ill: 737-741.
40 Yankel, A. J.; Von Lindern, I. H.; Walter, S. D. (1977) The Silver Valley lead study: the relationship between
41 childhood blood lead levels and environmental exposure. J. Air Pollut. Control Assoc. 27: 763-767'.
42 Ye, X. B.; Wu, C. E.; Fu, H.; Yang, S.-L.; Lu, Y.-W.; Ni, W.-M. (2003) Associations of blood lead levels, kidney
43 function, and blood pressure with 5-aminolevulinic acid dehydratase and vitamin D receptor gene
44 polymorphisms. Toxicol. Mech. Methods 13: 139-146.
45 Yokoyama, K.; Araki, S.; Murata, K.; Morita, Y.; Katsuno, N.; Tanigawa, T.; Mori, N.; Yokota, J.; Ito, A.;
46 Sakata, E. (1997) Subclinical vestibulo-cerebellar, anterior cerebellar lobe and spinocerebellar effects in
47 lead workers in relation to concurrent and past exposure. Neurotoxicology 18: 371-380.
48 Yokoyama, K.; Araki, S.; Aono, H.; Murata, K. (1998) Calcium disodium ethylenediaminetetraacetate-chelated lead
49 as a predictor for subclinical lead neurotoxicity: follow-up study on gun-metal foundry workers. Int. Arch.
50 Occup. Environ. Health 71: 459-464.
51 Young, S. S.; Hawkins, D. M. (1998) Using recursive partitioning to analyze a large SAR data set. SAR QSAR
52 Environ. Res. 8: 183-193.
53 Young, B. A.; Boyko, E. J.; Ross, H. J.; Fihn, S.; Bryson, C. L. (2004) Association of urine cadmium with
54 hypertension, microalbuminuria and reduced renal function: results from the NHANES III study [abstract].
55 J. Am. Soc. Nephrol. 15: 146A.
May 2006 6-372 DRAFT-DO NOT QUOTE OR CITE
-------
1 Yu, C.-C.; Lin, J.-L.; Lin-Tan, D.-T. (2004) Environmental exposure to lead and progression of chronic renal
2 diseases: a four-year prospective longitudinal study. J. Am. Soc. Nephrol. 15: 1016-1022.
3 Yuan, W.; Holland, S. K.; Cecil, K. M; Dietrich, K. N.; Wessel, S. D.; Altaye, M; Hornung, R. W.; Ris, M. D.;
4 Egelhoff, J. C.; Lanphear, B. P. (2006) The impact of early childhood lead exposure on brain organization -
5 an fMRI study of language function. Pediatrics: in press.
6 Yticesoy, B.; Turhan, A.; tire, M.; imir, T.; Karakaya, A. (1997a) Effects of occupational lead and cadmium
7 exposure on some immunoregulatory cytokine levels in man. Toxicology 123: 143-147.
8 Yticesoy, B.; Turhan, A.; tire, M.; imir, T.; Karakaya, A. (1997b) Simultaneous effects of lead and cadmium on NK
9 cell activity and some phenotypic parameters. Immunopharmacol. Immunotoxicol. 19: 339-348.
10 Yule, W.; Lansdown, R.; Millar, I. B.; Urbanowicz, M.-A. (1981) The relationship between blood lead
11 concentrations, intelligence and attainment in a school population: a pilot study. Dev. Med. Child Neurol.
12 23: 567-576.
13 Yule, W.; Urbanowicz, M.-A.; Lansdown, R.; Millar, I. B. (1984) Teachers' ratings of children's behaviour in
14 relation to blood lead levels. Br. J. Dev. Psychol. 2: 295-305.
15 Zhao, Z. Y.; Li, R.; Sun, L.; Li, Z. Y.; Yang, R. L. (2004) Effect of lead exposure on the immune function of
16 lymphocytes and erythrocytes. in preschool children. J. Zhejiang Univ. Sci. 5(8): 1001-1004.
17 Zheng, W.; Lu, Y. M.; Lu, G. Y.; Zhao, Q.; Cheung, 0.; Blaner, W. S. (2001) Transthyretin, thyroxine, and retinol-
18 binding protein in human cerebrospinal fluid: effect of lead exposure. Toxicol. Sci. 61(1): 107-114.
19 Zimmermann-Tansella, C.; Campara, P.; Andrea, F. D.; Savontto, C.; Tansella, m. (1983) Psychological and
20 physical complaints of subjects with low exposure to lead. Hum. Toxicol. 2: 615-623.
21 Zuckerman, B.; Amaro, H.; Cabral, H. (1989) Validity of serf-reporting of marijuana and cocaine use among
22 pregnant adolescents. J. Pediatr. ( St. Louis) 115: 812-815.
23
24
May 2006 6-373 DRAFT-DO NOT QUOTE OR CITE
-------
i 8. ENVIRONMENTAL EFFECTS OF LEAD
2
3
4 8.1 TERRESTRIAL ECOSYSTEMS
5 Surface soils across the United States are enriched in lead (Pb) relative to levels expected
6 from natural (geogenic) inputs (Erel and Patterson, 1994; Francek, 1992; Friedland et al., 1984;
7 Marsh and Siccama, 1997; Murray et al., 2004; Yanai et al., 2004). While some of this
8 contaminant Pb is attributed to paint, salvage yards, shooting ranges, and the use of Pb arsenate
9 as a pesticide in localized areas (Francek, 1997), Pb contamination of surface soils is essentially
10 ubiquitous because of atmospheric pollution associated with waste incineration, metal smelting
11 and production, and the combustion of fossil fuels (Newhook et al., 2003; Polissar et al., 2001).
12 However, lead inputs to terrestrial ecosystems in the United States have declined dramatically in
13 the past 30 years. The primary reason for this decline has been the almost complete elimination
14 of alkyl-lead additives in gasoline in North America. Also, emissions from smelters have
15 declined as older plants have been shut down or fitted with improved emissions controls.
16 Most terrestrial ecosystems in North America remain sinks for lead, despite reductions in
17 atmospheric Pb deposition of more than 95%. Lead released from forest floor soils in the past
18 has been largely immobilized in mineral soils (Miller and Friedland, 1994; Johnson et al., 1995,
19 2004; Johnson and Petras, 1998; Watmough et al., 2004). The amount of Pb that has leached
20 into the mineral soil ranges from 20 to 90% of the total anthropogenic Pb deposition, depending
21 on forest type, climate, and litter cycling. While inputs of Pb to ecosystems are currently low,
22 Pb export from watersheds via groundwater and streams is substantially lower. Reported
23 concentrations of Pb in waters draining natural terrestrial ecosystems have always been low
24 (Bacon and Bain, 1995; Johnson et al., 1995b; Wang et al., 1995; Vinogradoff et al., 2005),
25 generally less than 1 ng L l, even at moderately polluted sites (Laskowski et al., 1995).
26 Therefore, even at current input levels, watersheds are accumulating industrial Pb (Wang et al.,
27 1995; Scudlark et al., 2005).
28 The current chapter summarizes the most relevant information from the 1986 Air Quality
29 Criteria Document (AQCD) (U.S. Environmental Protection Agency, 1986) and reviews new
30 information that has become available on the potential effects of atmospheric lead inputs on the
31 terrestrial ecosystem. It has been organized to address: methodologies used in terrestrial
May 2006 8-1 DRAFT-DO NOT QUOTE OR CITE
-------
1 ecosystem research (Section 8.1.1); the distribution of atmospherically delivered lead in
2 terrestrial ecosystems (Section 8.1.2); lead uptake and mechanisms of action (Section 8.1.3);
3 toxic effects of lead on terrestrial organisms (Section 8.1.4); and, lead effects on natural
4 terrestrial ecosystems (Section 8.1.5). The major conclusions and recommendations from each
5 corresponding Annex section for these subject areas are summarized here.
6
7 8.1.1 Methodologies Used in Terrestrial Ecosystem Research
8 Several methodologies used in terrestrial ecosystems research are described in Section
9 AX8.1.1 with additional discussion in AX8.1.2 of the application of these methods to the study
10 of the distribution of atmospherically delivered Pb. One of the key factors necessary for
11 understanding ecological risks is related to bioavailability. The National Research Council
12 (NRC) 2002 review on bioavailability defined the "bioavailability processes" in terms of three
13 key processes. One of these processes, contaminant interactions between phases, is more
14 commonly referred to as "speciation." For a given metal or metalloid, the term speciation
15 describes the chemical's ability to interact with its biological or chemical surroundings by
16 characterizing its physicochemical properties that are relevant to bioavailability.
17 Methods to address bioavailability (speciation), and methods used to reduce Pb
18 bioavailability, are summarized in this section.
19
20 Analytical Tools and Models
21 A wide variety of analytical tools have been used to characterize a metal's speciation as it
22 is found in various media:
23 • XRD - X-ray diffraction;
24 • EPMA - electron probe microanalysis;
25 • PIXE and //PIXE - particle induced X-ray emission;
26 • XPS - X-ray photoelectron spectroscopy;
27 • XAS - X-ray absorption spectroscopy;
28 • SIMS - secondary ion mass spectrometry;
29 • sequential extractions; and,
30 • single chemical extractions.
May 2006 8-2 DRAFT-DO NOT QUOTE OR CITE
-------
1 EPA techniques provide the greatest information on metal speciation. Other techniques,
2 such as EXAFS (extended X-ray absorption fine structure) and EXANES (extended X-ray
3 absorption near edge spectroscopy), show great promise and will be important in solving key
4 mechanistic questions. In the case of phytotoxicity, the speciation of metals by direct
5 measurement or chemical models of pore water chemistry is most valuable.
6 The tools that have been used most often to evaluate speciation for metal particles in
7 various media include the following computer-based models: SOILCHEM, MINTEQL,
8 REDEQL2, ECOSAT, MINTEQA2, HYDRAQL, PHREEQE, and WATEQ4F.
9
10 Metal Speciation for Plants
11 When considering the bioavailability of a metal to plants from soils and sediments, it is
12 generally assumed that both the kinetic rate of supply and the speciation of the metal to either the
13 root or shoot are highly important. In soils and sediments, generally only a small volume of
14 water is in contact with the chemical form, and although the proportion of a metal's
15 concentration in this pore water to the bulk soil/sediment concentration is small, it is this phase
16 that is directly available to plants. Therefore, pore water chemistry (i.e., metal concentration as
17 simple inorganic species, organic complexes, or colloid complexes) is most important.
18 Tools currently used for metal speciation for plants include (1) in situ measurements using
19 selective electrodes (Gundersen et al., 1992; Archer et al., 1989; Wehrli et al., 1994); (2) in situ
20 collection techniques using diffusive equilibrium thin films (DET) and diffusive gradient thin
21 films (DOT) followed by laboratory analyses (Davison et al., 1991, 1994; Davison and Zhang,
22 1994; Zhang et al., 1995); and (3) equilibrium models (SOILCHEM) (Sposito and Coves, 1988).
23
24 Influence of Soil Amendments on Bioavailability
25 The removal of contaminated soil to mitigate exposure of terrestrial ecosystem
26 components to Pb can often present both economic and logistical problems. Because of this,
27 recent studies have focused on in situ methodologies to lower soil-Pb relative bioavailability
28 (RBA) (Brown et al., 2003a,b). To date, the most common methods studied include the addition
29 of soil amendments in an effort to either lower the solubility of the Pb form or to provide
30 sorption sites for fixation of pore-water Pb. These amendments typically fall within the
31 categories of phosphate, biosolid, and Al/Fe/Mn-oxide amendments.
May 2006 8-3 DRAFT-DO NOT QUOTE OR CITE
-------
1 Phosphate amendments have been studied extensively and, in some cases, offer the most
2 promising results (Brown et al., 1999; Ryan et al., 2001; Cotter-Howells and Caporn, 1996;
3 Hettiarachchi et al., 2001, 2003; Yang et al., 2001; Ma et al., 1995). A number of potentially
4 significant problems associated with phosphate amendments have been recognized. The added
5 phosphate poses the potential risk of eutrophication of nearby waterways from soil runoff. There
6 also may be both phyto- and earthworm toxicity (Ownby et al., 2005; Cao et al., 2002; Rusek
7 and Marshall, 2000), primarily associated with very high applications of phosphorous and/or
8 decreased soil pH. Indications of phytotoxicity are often balanced by studies such as Zhu et al.
9 (2004) that illustrate a 50 to 70% reduction in shoot-root uptake of Pb in phosphate-amended
10 soils. It also has been shown (Impellitteri, 2005; Smith et al., 2002; Chaney and Ryan, 1994;
11 Ruby et al., 1994) that the addition of phosphate would enhance arsenic mobility (potentially
12 moving arsenic down into the groundwater) through competitive anion exchange. Some data
13 (Lenoble et al., 2005) indicate that this problem can be mitigated if arsenic and lead
14 contaminated soils could be amended with iron(III) phosphate, although there could still be
15 issues with drinking water quality.
16 Biosolids have been used historically in the restoration of coal mines (Haering et al.,
17 2000; Sopper, 1993). More recently, workers have demonstrated the feasibility of their use in
18 the restoration of mine tailings (Brown et al., 2000), and urban soils (Brown et al., 2003a; Farfel
19 et al., 2005). As with phosphate amendments, problems with biosolid application have also been
20 documented. Studies have shown that metal transport is significantly accelerated in soils
21 amended with biosolids (Al-Wabel et al., 2002; McBride et al., 1997, 1999; Lamy et al., 1993;
22 Richards et al., 1998, 2000).
23
24 8.1.2 Distribution of Atmospherically Delivered Lead in Terrestrial
25 Ecosystems
26 Advances in technology since the 1986 AQCD (U.S. Environmental Protection Agency,
27 1986) have allowed for a more quantitative determination of the mobility, distribution, uptake,
28 and fluxes of atmospherically-delivered Pb in terrestrial ecosystems.
29
30
May 2006 8-4 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead Speciation in Solid Phases
2 Lead can enter terrestrial ecosystems through natural rock weathering and by a variety of
3 anthropogenic pathways. During the hydrolysis and oxidation of Pb-containing minerals,
4 divalent Pb (Pb2+) is released to the soil solution where it is rapidly fixed by organic matter and
5 secondary mineral phases (Kabata-Pendias and Pendias, 1992). The geochemical form of natural
6 Pb in terrestrial ecosystems will be strongly controlled by soil type (Emmanuel and Erel, 2002).
7 In contrast, anthropogenically-introduced Pb has a variety of different geochemical forms,
8 depending on the specific source. While Pb in soils from battery reclamation areas can be in the
9 form of PbSO4 or PbSiOs, Pb in soils from shooting ranges and paint spills is commonly found
10 as PbO and a variety of Pb carbonates (Vantelon et al., 2005; Laperche et al., 1996; Manceau
11 et al., 1996). Atmospherically-delivered Pb resulting from fossil fuel combustion is typically
12 introduced into terrestrial ecosystems as Pb-sulfur compounds and Pb oxides (Olson and
13 Skogerboe, 1975; Clevenger et al., 1991; Utsunomiya et al., 2004). After deposition, Pb species
14 are likely transformed. Although the specific factors that control the speciation of anthropogenic
15 Pb speciation in soils are not well understood, there are many studies that have partitioned Pb
16 into its different geochemical phases. A thorough understanding of Pb speciation is critical in
17 order to predict potential mobility and bioavailability.
18 Selective chemical extractions have been employed extensively for quantifying amounts
19 of a particular metal phase (e.g., PbS, Pb-humate, Pb-Fe, Mn oxide) present in soil rather than
20 total metal concentration. Selective extractions can be a relatively rapid, simple, and inexpensive
21 means for determining metal phases in soils, and the generated data can be linked to potential
22 mobility and bioavailability of the metal (Tessier and Campbell, 1987). However, some
23 problems persist with the selective extraction technique. First, extractions are rarely specific to a
24 single phase. For example, while peroxide (H2O2) is often used to remove metals bound in
25 organic matter in soils, some researchers have demonstrated that this reagent destroys clay
26 minerals and sulfides (Ryan et al., 2002). Peroxide solutions may also be inefficient at removing
27 metals bound to humic acids, and in fact could potentially result in the precipitation of metal-
28 humate substances. In addition to non-selectivity of reagents, significant metal redistribution has
29 been documented during sequential chemical extractions (Ho and Evans, 2000; Sulkowski and
30 Hirner, 2006), and many reagents may not extract targeted phases completely. Therefore, while
May 2006 8-5 DRAFT-DO NOT QUOTE OR CITE
-------
1 chemical extractions do provide some useful information on metal phases in soil, the results
2 should be treated as "operationally defined," e.g., "H2O2 liberated-Pb" rather than "organic Pb."
3 Synchrotron radiation (X-rays) allows researchers to probe the electron configuration of
4 metals in untreated soil samples. Since different elements have different electron binding
5 energies, X-rays can be focused in an energy window specific to a metal of interest. The precise
6 energy required to dislodge a core electron from a metal will be a function of the oxidation state
7 and covalency of the metal. Since the electron configuration of a lead atom will be directly
8 governed by its speciation (e.g., Pb bound to organics, Pb adsorbed to oxide surfaces, PbS, etc.),
9 X-ray absorption experiments are a powerful in situ technique for determining speciation that
10 does not suffer from some of the problems of chemical extractions (Bargar et al., 1997a,b;
11 Bargar etal., 1998).
12 Selective chemical extractions and synchrotron-based X-ray studies have shown that
13 industrial Pb can be strongly sequestered by organic matter and secondary minerals such as clays
14 and oxides of Al, Fe, and Mn (Miller and McFee, 1983; Jersak et al., 1997; Johnson and Petras,
15 1998; Kaste et al., 2005). More recent X-ray studies have demonstrated the importance of
16 biomineralization of Pb in soils by bacteria and nematodes (Jackson et al., 2005; Templeton
17 et al., 2003a,b; Xia et al., 1997).
18
19 Lead Solid-Solution Partitioning
20 The concentration of Pb species dissolved in soil solution is probably controlled by some
21 combination of a) Pb mineral solubility equilibria, b) adsorption reactions of dissolved Pb phases
22 on inorganic surfaces (e.g., oxides of Al, Fe, Si, Mn, etc., clay minerals), and c) adsorption
23 reactions of dissolved Pb phases on soil organic matter. Dissolved Pb phases in soil solution can
24 be some combination of Pb2+ and its hydrolysis species, Pb bound to dissolved organic matter,
25 and Pb complexes with inorganic ligands such as Cl and SO42 . Alkaline soils typically have
26 solutions supersaturated with respect to PbCO3, Pb3(CO3)2(OH)2, Pb(OH)2, Pb3(PO4)2,
27 Pb5(PO4)3(OH), and Pb4O(PO4)2 (Badawy et al., 2002). Pb phosphate minerals in particular, are
28 very insoluble, and calculations based on thermodynamic data predict that these phases will
29 control dissolved Pb in soil solution under a variety of conditions (Nriagu, 1974; Ruby et al.,
30 1994). However, certain chelating agents, such as dissolved organic matter can prevent the
31 precipitation of Pb minerals (Lang and Kaupenjohann, 2003).
May 2006 8-6 DRAFT-DO NOT QUOTE OR CITE
-------
1 Soil solution dissolved organic matter content and pH typically have a very strong
2 positive and negative correlation, respectively, with the concentration of dissolved Pb species
3 (Badawy et al., 2002; Sauve et al., 1998, 2000a,b, 2003; Tipping et al., 2003; Weng et al., 2002).
4 In the case of adsorption phenomena, the partitioning of Pb2+ to the solid phase is also controlled
5 by total metal loading: high Pb loadings will result in a lower fraction partitioned to the solid
6 phase. Sauve et al. (1998; 1997) demonstrated that only a fraction of the total Pb in solution was
7 actually Pb2+ in soils treated with leaf compost. The fraction of Pb2+ to total dissolved Pb ranged
8 from <1 to 60%, depending on pH and the availability of Pb-binding ligands. In acidic soils,
9 Al species can compete for sites on natural organic matter and inhibit Pb binding to surfaces
10 (Gustafsson et al., 2003).
11
12 Tracing the Fate of A tmospherically Delivered Lead
13 Radiogenic Pb isotopes offer a powerful tool for separating anthropogenic Pb from natural
14 Pb derived from mineral weathering (Erel and Patterson, 1994; Erel et al., 1997). This is
15 particularly useful for studying Pb in mineral soil, where geogenic Pb often dominates. The ore
16 bodies from which anthropogenic Pb are typically derived are usually enriched in 207Pb relative
17 to 206Pb and 208Pb when compared with Pb found in granitic rocks. Uranium-238 series 210Pb
18 also provides a tool for tracing atmospherically delivered Pb in soils. Fallout 210Pb is deposited
19 onto forests via wet and dry deposition, similar to anthropogenic Pb deposition in forests, and is
20 thus useful as a tracer for non-native Pb in soils. 210Pb is convenient to use for calculating the
21 residence time of Pb in soil layers because its atmospheric and soil fluxes can be assumed to be
22 in steady-state at undisturbed sites (Dorr, 1995; Dorr and Munnich, 1989; Kaste et al., 2003).
23 Researchers assessing the fate of atmospheric Pb in soils have also relied on repeated
24 sampling of soils and vegetation for total Pb. This technique works best when anthropogenic Pb
25 accounts for the vast majority of total Pb in a particular reservoir. Johnson et al. (1995), Yanai
26 et al. (2004), and Friedland et al. (1992) used O horizon (forest floor) time series data to evaluate
27 the movement of gasoline-derived Pb in the soil profile. Surface soils sampled relatively
28 recently demonstrate that the upper soil horizons (O + A horizons) are retaining most of the
29 anthropogenic Pb burden introduced to the systems during the 20th century (Evans et al., 2005).
30 Miller and Friedland (1994) and Wang and Benoit (1997) suggested that the movement of
31 organic particulates dominated Pb transport in the soil profile.
May 2006 8-7 DRAFT-DO NOT QUOTE OR CITE
-------
1 8.1.3 Species Response/Mode of Action
2 The current document expands upon and updates knowledge since 1986 related to the
3 uptake, detoxification, physiological effects, and modifying factors of lead toxicity to terrestrial
4 organisms. Terrestrial organisms discussed in this chapter include soil organisms, plants, birds,
5 and mammals.
6
7 Uptake into Plants and Invertebrates
8 Recent work supports previous results and conclusions that surface deposition of lead
9 onto above-ground vegetation from airborne sources may be significant (Dalenberg and Van
10 Driel, 1990; Jones and Johnston, 1991; Angelova et al., 2004). In addition, most lead is taken up
11 by plants via the symplastic route (through cell membranes) (Sieghardt, 1990) and remains in the
12 roots, with little translocation to shoots, leaves, or other plant parts. Different species of plants
13 and invertebrates accumulate different amounts of lead (Pizl and Josens, 1995; Terhivuo et al.,
14 1994; Wierzbicka, 1999).
15 Recent work supports previous conclusions that the form of metal tested, and its
16 speciation in soil, influence uptake and toxicity to plants and invertebrates. The oxide form is
17 less toxic than the chloride or acetate forms, which are less toxic than the nitrate form of lead
18 (Khan and Frankland, 1983; Lock and Janssen, 2002; Bongers et al., 2004). However, these
19 results must be interpreted with caution, as the counted on (e.g., the nitrate ion) may be
20 contributing to the observed toxicity (Bongers et al., 2004).
21
22 Detoxification in Plants and Invertebrates
23 Lead may be deposited in root cell walls as a detoxification mechanism, and this may be
24 influenced by calcium (Antosiewicz, 2005). Yang et al. (2000) suggested that the oxalate
25 content in root and root exudates reduced the bioavailability of lead in soil, and that this was an
26 important tolerance mechanism. Other hypotheses put forward recently include the presence of
27 sulfur ligands (Sharma et al., 2004) and the sequestration of lead in old leaves (Szarek-
28 Lukaszewska et al., 2004) as detoxification mechanisms.
29 Lead detoxification has not been studied extensively in invertebrates. Glutathione
30 detoxification enzymes were measured in two species of spider (Wilczek et al., 2004). Lead may
May 2006 8-8 DRAFT-DO NOT QUOTE OR CITE
-------
1 be stored in waste nodules in earthworms (Hopkin, 1989) or as pyromorphite in the nematode
2 (Jackson et al., 2005).
3
4 Physiological Effects
5 The effects on heme synthesis (as measured by 5-aminolaevulinic acid dehydratase
6 [ALAD] activity and protoporphyrin concentration, primarily) had been well-documented in the
7 1986 AQCD (U.S. Environmental Protection Agency, 1986) and continue to be studied (Schlick
8 et al., 1983; Scheuhammer, 1989; Redig et al., 1991; Henny et al., 1991; Beyer et al., 2000;
9 Hoffman et al., 2000a, b). However, Henny et al. (1991) caution that changes in ALAD and
10 other enzyme parameters are not always related to adverse effects, but simply indicate exposure.
11 Other effects on plasma enzymes, which may damage other organs, have been reported (Brar
12 et al., 1997a, b). Lead also may cause lipid peroxidation (Mateo and Hoffman, 2001) which may
13 be alleviated by Vitamin E, although lead poisoning may still result (Mateo et al., 2003b).
14 Changes in fatty acid production have been reported, which may influence immune response and
15 bone formation (Mateo et al., 2003a).
16
17 Response Modification
18 Genetics, biological factors, physical/environmental factors, nutritional factors and other
19 pollutants can modify terrestrial organism response to lead. Fisher 344 rats were found to be
20 more sensitive to lead than Sprague-Dawley rats (Dearth et al., 2004). Younger animals are
21 more sensitive than older animals (Eisler, 1988; Scheuhammer, 1991), and females generally are
22 more sensitive than males (Scheuhammer, 1987; Tejedor and Gonzalez, 1992; Snoeijs et al.,
23 2005). Monogastric animals are more sensitive than ruminants (Humphreys, 1991).
24 Insectivorous mammals may be more exposed to lead than herbivores (Beyer et al., 1985;
25 Sample et al., 1998), and higher tropic-level consumers may be less exposed than lower trophic-
26 level organisms (Henny et al., 1991). Nutritionally-deficient diets (including low calcium) cause
27 increased uptake of lead (Snoeijs et al., 2005) and greater toxicity (Douglas-Stroebel et al., 2005)
28 in birds.
29 Mycorrhizal fungi may ameliorate lead toxicity until a threshold is surpassed (Malcova
30 and Gryndler, 2003), which may explain why some studies show increased uptake into plants
31 (Lin et al., 2004) while others show no difference or less uptake (Dixon, 1988). Lower soil pH
May 2006 8-9 DRAFT-DO NOT QUOTE OR CITE
-------
1 generally increases uptake of lead into plants and soil invertebrates. However, calcium content,
2 organic matter content, and cation exchange capacity of soils also had a significant influence on
3 uptake of lead into plants and invertebrates (Beyer et al., 1987; Morgan and Morgan, 1988).
4 Interactions of lead with other metals are inconsistent, depending on the endpoint
5 measured, the tissue analyzed, the animal species, and the metal combination (Phillips et al.,
6 2003; An et al., 2004; Garcia and Corredor, 2004; He et al., 2004; Perottoni et al., 2005).
7
8 8.1.4 Exposure/Response of Terrestrial Species
9 The current document expands upon and updates knowledge related to the effects of lead
10 on terrestrial primary producers, consumers and decomposers found in the 1986 Pb AQCD (U.S.
11 Environmental Protection Agency, 1986).
12
13 Primary Producers
14 Effects of lead on terrestrial plants include decreased photosynthetic and transpiration
15 rates, and decreased growth and yield. The phytotoxicity of lead is considered to be relatively
16 low, and there are few reports of phytotoxicity from lead exposure under field conditions.
17 Phytotoxicity data recently were reviewed for the development of the ecological soil screening
18 levels (Eco-SSL) (U.S. Environmental Protection Agency, 2005b). Many of the toxicity data
19 presented in U.S. Environmental Protection Agency (2005b) are lower than those discussed in
20 the 1986 AQCD (U.S. Environmental Protection Agency, 1986), although both documents
21 acknowledge that toxicity is observed over a wide range of concentrations of lead in soil (tens to
22 thousands of mg/kg soil). This may be due to many factors, such as the soil conditions (e.g., pH,
23 organic matter) and differences in bioavailability of the lead in spiked soils, perhaps due to lack
24 of equilibration of the lead solution with the soil after spiking. Most phytotoxicity data continue
25 to be developed for agricultural plant species (i.e., vegetable and grain crops). Few data are
26 available for trees or native herbaceous plants, although two of the five ecotoxicological
27 endpoints used to develop the Eco-SSL were for trees and two were for clover.
28
29 Consumers
30 Effects of lead on avian and mammalian consumers include decreased survival,
31 reproduction, and growth, as well as effects on development and behavior. There remain few
May 2006 8-10 DRAFT-DO NOT QUOTE OR CITE
-------
1 field effects data for consumers, except from sites with multiple contaminants, for which it is
2 difficult to attribute toxicity specifically to lead. Avian and mammalian toxicity data recently
3 were reviewed for the development of Eco-SSLs (U.S. Environmental Protection Agency,
4 2005b). Many of the toxicity data presented by EPA (U.S. Environmental Protection Agency,
5 2005b) are lower than those discussed in the 1986 AQCD, although EPA (U.S. Environmental
6 Protection Agency, 2005b) recognizes that toxicity is observed over a wide range of doses
7 (<1 to >1,000 mg Pb/kg bw-day). Most toxicity data for birds are derived from chicken and
8 quail studies, and most data for mammals are derived from laboratory rat and mouse studies.
9 Data derived for other species would contribute to the understanding of lead toxicity, particularly
10 for wildlife species with different gut physiologies. In addition, data derived using
11 environmentally-realistic exposures, such as from lead-contaminated soil and food may be
12 recommended. Finally, data derived from inhalation exposures, which evaluate endpoints such
13 as survival, growth, and reproduction, would contribute to understanding the implications of
14 airborne releases of lead.
15
16 Decomposers
17 Effects of lead on soil invertebrates include decreased survival, growth and reproduction.
18 Effects on microorganisms include changes in nitrogen mineralization, and changes in enzyme
19 activities. Recent data on lead toxicity to soil invertebrates and microorganisms are consistent
20 with those reported in the 1986 Pb AQCD (U.S. Environmental Protection Agency, 1986), with
21 toxicity generally observed at concentrations of hundreds to thousands of mg Pb/kg soil. Studies
22 on microbial processes may be influenced significantly by soil parameters and the significance of
23 the test results is not clear.
24
25 Ecological Soil Screening Levels (Eco-SSLs)
26 Eco-SSLs are concentrations of contaminants in soils that are protective of ecological
27 receptors (U.S. Environmental Protection Agency, 2005a). They were developed following
28 rigorous scientific protocols, and were subjected to two rounds of peer review. The Eco-SSLs
29 for terrestrial plants, birds, mammals, and soil invertebrates are 120 mg/kg, 11 mg/kg, 56 mg/kg
30 and 1700 mg/kg, respectively. See Annex Section AX8.1.4 for additional information.
31
May 2006 8-11 DRAFT-DO NOT QUOTE OR CITE
-------
1 8.1.5 Effects of Lead on Natural Terrestrial Ecosystems
2 Few significant effects of Pb pollution have been observed at sites that are not near point
3 sources of Pb. At present, industrial point sources such as smelter sites represent the greatest Pb-
4 related threat to the maintenance of sustainable, healthy, diverse, and high-functioning terrestrial
5 ecosystems in the United States. However, assessing the risks specifically associated with Pb is
6 difficult because these sites also experience elevated concentrations of other metals and because
7 of effects related to SC>2 emissions. Terrestrial ecosystems may respond to stress in a variety of
8 ways, including reductions in the vigor and/or growth of vegetation, reductions in biodiversity,
9 and effects on energy flow and biogeochemical cycling.
10
11 Influence of Acidification
12 Like most metals, the solubility of Pb is increased at lower pH (Stumm and Morgan,
13 1995), suggesting that enhanced mobility of Pb should be found in ecosystems under
14 acidification stress. However, reductions in pH may also cause a decrease in the solubility of
15 dissolved organic matter (DOM), due to the protonation of carboxylic functional groups (Tipping
16 and Woof, 1990). Because of the importance of complexation with organic matter to Pb
17 mobility in soils, lower DOM concentrations resulting from acidification may offset the
18 increased solubility of the metal. The increased mobility was only observed in very acidic soils,
19 those with pH <4.5 (Blake and Goulding, 2002). Acidification also may enhance Pb export to
20 drainage water in very sandy soils, with limited ability to retain organic matter (Swanson and
21 Johnson, 1980; Turner et al., 1985).
22
23 Influence of Forest Harvesting
24 Forest harvesting represents a severe distruption of the organic matter cycle in forest
25 ecosystems. However, observations from clear-cut sites in the United States and Europe indicate
26 that forest harvesting causes little or no mobilization or loss of Pb from forest soils (Berthelsen
27 and Steinnes, 1995; Fuller et al., 1988). The principal risk associated with forest harvesting is
28 the loss of Pb in particulate form to drainage waters through erosion.
29
May 2006 8-12 DRAFT-DO NOT QUOTE OR CITE
-------
1 Influence of Land Use and Industry
2 Changes in land use represent potentially significant changes in the cycling of organic
3 matter in terrestrial ecosystems. Conversion of pasture and croplands to woodlands changes the
4 nature and quantity of organic matter inputs to the soil. The introduction of industrial activity
5 may have consequences for organic matter cycling, and subsequently, Pb mobilization. In a rare
6 long-term study of polluted soils, Egli et al. (1999) found that loss of soil carbon can induce the
7 mobilization and loss of Pb from terrestrial ecosystems. However, it is worth noting that the
8 decline in soil Pb was considerably smaller than the decline in organic carbon. This suggests
9 that Pb mobilized during organic matter decomposition can resorb to remaining organic matter or
10 perhaps to alternate binding sites (e.g., Fe and Mn oxides).
11
12 Effects Observed Around Industrial Point Sources
13 The effects of Pb exposure on natural ecosystems are confounded by the fact that Pb
14 exposure cannot be decoupled from other factors that may also effect the ecosystem under
15 consideration. Principal among these factors are other trace metals and acidic deposition.
16 Emissions of Pb from smelting and other industrial activities are accompanied by other trace
17 metals (e.g., Zn, Cu, Cd) and sulfur dioxide (802) that may cause toxic effects independently or
18 in concert with Pb.
19 Natural terrestrial ecosystems near smelters, mines, and other industrial plants have
20 exhibited a variety of effects related to ecosystem structure and function. These effects include
21 decreases in species diversity, changes in floral and faunal community composition, and
22 decreasing vigor of terrestrial vegetation. All of these effects were observed in ecosystems
23 surrounding the Anaconda copper smelter in southwestern Montana, which operated between
24 1884 and 1980 (Galbraith et al., 1995; Kapustka et al., 1995). Similar observations were made in
25 the area surrounding Palmerton, Pennsylvania, where two zinc smelters operated between 1898
26 and 1980 (Jordan, 1975; Sopper, 1989; Storm et al., 1994). Subsequent to the effects on
27 vegetation, wind and erosion may remove litter and humus, leaving bare mineral soil, a nearly
28 sterile environment in which very little energy transfer takes place (Little and Martin, 1972;
29 Galbraith et al., 1995). Metal pollution around a Pb-Zn smelter near Bristol, England has not
30 resulted in the loss of oak woodlands within 3 km of the smelter, despite significant
31 accumulation of Pb, Cd, Cu, and Zn in soils and vegetation (Martin and Bullock, 1994).
May 2006 8-13 DRAFT-DO NOT QUOTE OR CITE
-------
1 However, the high metal concentrations have favored the growth of metal-tolerant species in the
2 woodland.
3 The effects of Pb on terrestrial ecosystems near smelters and other industrial sites
4 decrease downwind from the Pb source. Several studies using the soil Pb burden as an indicator
5 have shown that much of the contamination occurs within a radius of 20 to 50 km around the
6 emission source (e.g., Miller and McFee, 1983; Martin and Bullock, 1994; Galbraith et al., 1995;
7 Spurgeon and Hopkin, 1996).
8
9 Influence of Climate Change
10 Atmospheric Pb is not likely to contribute significantly to global climate change. The
11 potential linkages between climate-related stress and Pb cycling are poorly understood. Effects
12 related to alterations in organic matter cycling may influence Pb migration. For example, an
13 increase in temperature leading to increased rates of organic matter decomposition could lead to
14 temporary increases in DOM concentrations and smaller steady-state pools of soil organic
15 matter. There also is some evidence for recent increases in the frequency of soil freezing events
16 in the northeastern United States (Mitchell et al., 1996). Soil freezing occurs when soils have
17 little or no snow cover to insulate them from cold temperatures and results in an increased
18 release of nitrate and DOC from the O horizons of forest soils (Mitchell et al., 1996; Fitzhugh et
19 al., 2001). Increased fluctuations in precipitation may induce more frequent flooding, potentially
20 increasing inputs of Pb and other metals to floodplain soils (Kriiger and Grongroft, 2004). All of
21 these factors could result in increased concentrations of Pb in waters draining terrestrial
22 ecosystems.
23
24 Influence on Energy Flow and Biogeochemical Cycling
25 Lead can have a significant effect on energy flow in terrestrial ecosystems. In terrestrial
26 ecosystems, energy flow is closely linked to the carbon cycle. The principal input of energy to
27 terrestrial ecosystems is through photosynthesis, in which CO2 is converted to biomass carbon.
28 Because of this link between photosynthesis and energy flow, any effect that Pb has on the
29 structure and function of terrestrial ecosystems influences the flow of energy into the ecosystem.
30 At some sites severely affected by metal pollution, death of vegetation can occur, dramatically
31 reducing the input of carbon to the ecosystem (Jordan, 1975; Galbraith et al., 1995).
May 2006 8-14 DRAFT-DO NOT QUOTE OR CITE
-------
1 Lead influences energy transfer within terrestrial ecosystems, which begins with the
2 decomposition of litter and other detrital material by soil bacteria and fungi, and cascades
3 through the various components of the detrital food web. Numerous investigators have
4 documented significant declines in litter decomposition rates (Cotrufo et al., 1995; Johnson and
5 Hale, 2004) and/or the rate of carbon respiration (Laskowski et al., 1994; Cotrufo et al., 1995;
6 Saviozzi et al., 1997; Niklinska et al., 1998; Palmborg et al., 1998; Aka and Darici, 2004) in
7 acid- and metal-contaminated soils or soils treated with Pb. The resulting accumulation of
8 organic matter on the soil surface can be dramatic.
9 Lower decomposition rates in polluted ecosystems are the result of the inhibition of soil
10 bacteria and fungi and its effects on microbial community structure (Baath, 1989). Decreases in
11 carbon respiration have been observed (Kuperman and Carreiro, 1997). Lead and other metals
12 also inhibit the mineralization of nitrogen from soil organic matter and nitrification (Liang and
13 Tabatabai, 1977, 1978; Senwo and Tabatabai, 1999; Acosta-Martinez and Tabatabai, 2000;
14 Ekenler and Tabatabai, 2002), resulting in lower nitrogen availability to plants. This suggests
15 that the inhibitory effect of Pb and other metals is broad-based, and not specific to any particular
16 metabolic pathway. Because the mobility of Pb in soils is closely tied to organic matter cycling,
17 decomposition processes are central to the biogeochemical cycle of Pb.
18
19
20 8.2 AQUATIC ECOSYSTEMS
21 The overall intent of Section 8.2 is to provide sufficient information to support
22 development of an air quality criterion for lead that is protective of aquatic ecosystems.
23 To achieve this objective, the logical starting points are to (1) gain a general understanding of the
24 current distribution and concentrations of lead in the aquatic environment and (2) identify the
25 threshold levels for lead effects on aquatic populations, communities, and ecosystems. Ambient
26 water quality criteria for lead and other chemicals represent surface water concentrations that are
27 intended to be protective of aquatic communities, including recreationally and commercially
28 important species. The EPA derives AWQC to provide guidance to States and Tribes that are
29 authorized to establish water quality standards under the Clean Water Act (CWA). Similarly,
30 EPA has recommended sediment quality benchmarks for lead and other divalent metals,
31 although not truly criteria, that represent concentrations in sediment that are derived to be
May 2006 8-15 DRAFT-DO NOT QUOTE OR CITE
-------
1 protective of benthic (sediment) organisms. As summarized further below and in subsequent
2 sections, the EPA has increasingly focused on developing AWQC and sediment quality
3 benchmarks for lead and other metals that account for the bioavailability of the metal to aquatic
4 life. These criteria and benchmark concentrations in water and sediment represent appropriate
5 starting points to ensure that air quality criteria for lead are adequately protective of aquatic life.
6 Since publication of the 1986 Pb AQCD (U.S. Environmental Protection Agency, 1986),
7 knowledge has expanded on the fate and effects of lead in aquatic ecosystems and on the
8 distribution and concentrations of lead in surface waters throughout the United States. In
9 addition, chemical, physical, and biological properties of lead are discussed. The following
10 provides a general overview of the key information found in corresponding Annex sections
11 (Sections AX8.2.1 through AX8.2.5).
12
13 8.2.1 Methodologies Used in Aquatic Ecosystem Research
14 Ambient Water Quality Criteria and Bioavailability
15 The U.S. EPA guidelines for developing AWQC (Stephan et al., 1985) were published
16 more than 20 years ago. Scientific advances in aquatic toxicology and risk assessment that have
17 developed since the 1980s. For example, the toxicological importance of dietary metals has been
18 increasingly recognized and approaches for incorporating dietary metals into regulatory criteria
19 are being evaluated (Meyer et al., 2005). Other issues include consideration of certain sublethal
20 endpoints that are currently not directly incorporated into AWQC development (e.g., endocrine
21 toxicity, behavioral responses) and protection of threatened and endangered (T&E) species (U.S.
22 Environmental Protection Agency, 2003). In deriving appropriate and scientifically defensible
23 air quality criteria for lead, it will be important that the state-of-the-science for metals toxicity in
24 aquatic systems be considereed in the development process.
25 The primary form of lead in freshwater and marine environments is divalent lead (Pb2+).
26 In surface waters, the bioavailability of lead to aquatic biota is driven by a variety of factors,
27 including calcium, dissolved organic carbon (DOC), pH, alkalinity, and total suspended solids
28 (TSS). Accounting for the influence of calcium and magnesium ions on lead bioavailability, the
29 current AWQC for lead are normalized to the hardness of the receiving water (Table 8-2.1).
30 More recently, the biotic ligand model (BLM), which considers the binding of free metal ion to
31 the site of toxic action and competition between metal species and other ions, has been
May 2006 8-16 DRAFT-DO NOT QUOTE OR CITE
-------
Table 8-2.1. Summary of Lead Ambient Water Quality Criteria for Freshwater
Organisms at Different Hardness Levels
Hardness Acute Criterion Chronic Criterion
(mg/L as CaCO3) (ug/L) (ug/L)
50 34 1.3
100 82 3.2
200 200 7.7
1 developed to predict the toxicity of several metals under a variety of water quality conditions.
2 The BLM has been incorporated into the draft AWQC for copper and is currently being
3 researched for lead.
4
5 Sediment Quality Benchmarks and Bioavailability
6 As in surface waters, there are a number of factors in sediment that can influence lead
7 bioavailability to benthic (sediment) organisms. Although sediment quality criteria have not
8 been formally adopted, the EPA has published an equilibrium partitioning procedure for
9 developing sediment criteria for metals (U.S. Environmental Protection Agency 2005c).
10 Equilibrium partitioning (EqP) theory predicts that metals partition in sediment between acid
11 volatile sulfide, pore water, benthic organisms, and other sediment phases, such as organic
12 carbon. When the sum of the molar concentrations of simultaneously extracted metal (ZSEM)
13 minus the molar concentration of AVS is less than zero, it can accurately be predicted that
14 sediments are not toxic because of these metals. Further, if ESEM-AVS is normalized to the
15 fraction of organic carbon (i.e., (ZSEM-AVS)/fOC), mortality can be more reliably predicted by
16 accounting for both the site-specific organic carbon and AVS concentrations (Table 8-2.2).
17 An alternative approach for developing sediment quality guidelines is to use empirical
18 correlations between metal concentrations in bulk sediment to associated biological effects,
19 based on sediment toxicity tests (Table 8-2.2). These guidelines are based on total metal
20 concentrations in sediment and do not account for the bioavailability of metals between
21 sediments.
22
May 2006 8-17 DRAFT-DO NOT QUOTE OR CITE
-------
Table 8-2.2. Summary of Sediment Quality Benchmarks and
Guidelines for Lead
Benchmark/
Guideline Type Source Effect Level Value
Equilibrium
partitioning
U.S. Environmental
Protection Agency
(2005c)
Low risk of adverse
biological effects
(SEM-AVS)//OC
130 umol/goc
May have adverse biological 130 umol/goc < (SEM-
effects AVS)//bc < 3,000 umol/goc
Bulk sediment
MacDonald et al.
(2000)
Adverse biological
effects expected
TEC
(SEM-AVS)//OC>3,000
umol/goc
35.8 ug/gdry wt.
Ingersoll et al. (1996)
Long etal. (1995)
PEC
ERL
ERM
ERL
ERM
128 ug/g dry wt.
55 ug/g dry wt.
99 ug/g dry wt.
46.7 ug/g dry wt.
218 ug/gdry wt.
AVS = Acid volatile sulfide; ERL = Effects range - low (sediment concentration below which adverse effects are
rarely observed or predicted among sensitive species, Long et al. [1995]); ERM = Effects range - median
(sediment concentration above which effects are frequently or always observed or predicted among most species,
Long et al. [1995]); oc = Organic carbon (foc = fraction organic carbon, g0c = grams organic carbon); PEC =
Probably effect concentration (sediment concentration above which harmful effects are likely to be observed,
MacDonald et al. [2000]); SEM = Simultaneously extracted metal; TEC = Threshold effect concentration
(sediment concentration below which harmful effects are unlikely to be observed, MacDonald et al. [2000]).
1 8.2.2 Distribution of Lead in Aquatic Ecosystems
2 Speciation of Lead in Aquatic Ecosystems
3 The speciation of lead in the aquatic environment is controlled by many factors, such as,
4 pH, salinity, sorption, and biotransformation processes. Lead is typically present in acidic
5 aquatic environments as PbSC>4, PbCU, ionic lead, cationic forms of lead hydroxide, and ordinary
6 hydroxide Pb(OH)2. In alkaline, waters common species of lead include anionic forms of lead
7 carbonate Pb(CC>3) and hydroxide Pb(OH)2. In freshwaters, lead typically forms strong
8 complexes with inorganic OH" and COs2 and weak complexes with Cl~ (Bodek et al., 1988;
May 2006
8-18
DRAFT-DO NOT QUOTE OR CITE
-------
1 Long & Angino, 1977). The primary form of lead in freshwaters at low pH (<6.5) is
2 predominantly Pb2+ and less abundant inorganic forms include Pb(HCO)3, Pb(SO4)22 , PbCl,
3 PbCO3, and Pb2(OH)2CO3. At higher pH (>7.5) lead forms hydroxide complexes (PbOH+,
4 Pb(OH)2, Pb(OH)3 , Pb(OH)42 ). Lead speciation in seawater is a function of chloride
5 concentration and the primary species are PbCl3 > PbCO3 > PbCl2 > PbCl+ > and Pb(OH)+
6 (Fernando, 1995).
7 Lead sorption to suspended or bed sediments or suspended organic matter typically
8 increases with increasing pH, increasing amounts of iron or manganese; and with the polarity of
9 particulate matter (e.g., clays). Adsorption decreases with water hardness (Syracuse Research
10 Corporation [SRC], 1999). At higher pH, lead precipitates as Pb(OH)+ and PbHCO3+ into bed
11 sediments (Weber, 1993). Conversely, at low pH, lead is negatively sorbed (repelled from the
12 adsorbent surface) (U.S. Environmental Protection Agency, 1979; Gao et al., 2003). In addition,
13 lead may be remobilized from sediment due to a decrease in metal concentration in the solution
14 phase, complexation with chelating agents (e.g., EDTA), and changing redox conditions
15 (Gao et al., 2003). Changes in water chemistry (e.g., reduced pH or ionic composition) can
16 cause sediment Pb to become re-mobilized and potentially bioavailable to aquatic organisms
17 (Weber, 1993). Methylation may result in lead's remobilization and reintroduction into the
18 aqueous environmental compartment and its subsequent release into the atmosphere (SRC,
19 1999). However, methylation is not a significant environmental pathway controlling lead fate in
20 the aquatic environment.
21
22 Lead Concentrations in United States Surface Waters
23 Nationwide lead data in surface waters, from 1991 onward, were compiled using the
24 United States Geological Survey's (USGS) National Water-Quality Assessment (NAWQA)
25 database. Data were compiled from locations categorized as "ambient" or "natural." Ambient
26 refers to data collected from all sampling locations, while natural refers to data collected from
27 sampling locations categorized as forest, rangeland, or reference. Summary statistics for surface
28 water, sediment (bulk, <63 um), and fish tissue (whole body and liver) are summarized in
29 Table 8-2.3. Overall atmospheric sources of lead are generally decreasing as regulations have
30 removed lead from gasoline and other products (Eisenreich et al., 1986); however, elevated lead
31
May 2006 8-19 DRAFT-DO NOT QUOTE OR CITE
-------
Table 8-2.3. Summary of Lead Concentrations in United States Surface Water,
Sediment, and Fish Tissue
Surface Water -
Dissolved
(Mg/L)
Statistic
n
%ND
Min
Mean
95th %ile
Max
Ambient
3,445
86
0.04
0.66
1.10
29.78
Natural
430
88
0.04
0.52
0.50
8.40
Sediment -
Bulk, <63 fim
(jig/g dry wt.)
Ambient
1,466
0.48
0.50
120
200
12,000
Natural
258
1.2
0.50
109
162
12,000
Fish Tissue (jig/g dry wt.)
Whole Organism
Ambient
332
39
0.08
1.03
1.06
22.6
Natural
93
51
0.08
0.95
1.26
22.6
Liver
Ambient
559
71
0.01
0.36
3.24
12.7
Natural
83
89
0.01
0.28
2.50
3.37
%ND = Percentage not detected
1 concentrations remain at sites near ongoing sources, such as near mining wastes or wastewater
2 effluents.
3 Lead concentrations in lakes and oceans were generally found to be much lower than
4 those measured in the lotic waters assessed by NAWQA. Surface water concentrations of
5 dissolved lead measured in Hall Lake, Washington in 1990 ranged from 2.1 to 1015.3 ng/L
6 (Balistrieri et al., 1994). Nriagu et al., 1996 found that the average surface water dissolved lead
7 concentrations measured in the Great Lakes (Superior, Erie, and Ontario) between 1991 and
8 1993 were 3.2, 6.0, and 9.9 ng/L, respectively. Pb concentrations ranged from 3.2 to 11 ng/L
9 across all three lakes. Similarly, 101 surface water total lead concentrations measured at the
10 Hawaii Ocean Time-series (HOT) station ALOHA between 1998 and 2002 ranged from 25 to
11 57 pmol/kg (5 to 11 ng/kg; (Boyle et al., 2005). Based on the fact that lead is predominately
12 found in the dissolved form in the open ocean (<90%; Schaule and Patterson, 1981), dissolved
13 lead concentrations measured at these locations would likely have been even lower than the total
14 lead concentrations reported.
15 In addition to directly measuring lead concentrations in various aquatic compartments, it
16 is useful to study the vertical distribution of lead. Sediment profiling and core dating is a method
17 used to determine the extent of accumulation of atmospheric lead and provides information on
18 potential anthropogenic sources. Sediment concentration profiles are typically coupled with lead
May 2006
8-20
DRAFT-DO NOT QUOTE OR CITE
-------
1 isotopic analysis. The isotope fingerprinting method utilizes measurements of the abundance of
2 common lead isotopes (204Pb, 206Pb, 207Pb, 208Pb) to distinguish between natural lead over
3 geologic time and potential anthropogenic sources. Studies of sediment profiles have suggested
4 that observed increases in lead concentrations in the upper sediment layer are concomitant with
5 increases in anthropogenic inputs (Bloom and Crecelius, 1987; Case et al., 1989; Ritson et al.,
6 1999; Chillrud et al., 2003). Isotopic ratios have been used to link increases in sediment
7 concentrations with specific anthropogenic sources and to estimate historic records of lead fluxes
8 to surface waters and sediments (Flegal et al., 1987, 1989; Blais, 1996; Bindler et al., 1999).
9
10 8.2.3 Species Response/Mode of Action
11 Lead Uptake
12 Lead can bioaccumulate in the tissues of aquatic organisms through ingestion of food and
13 water, and adsorption from water, and can subsequently lead to adverse effects if exposed to
14 sufficiently high concentrations (Vink, 2002; Rainbow, 1996). The accumulation of lead is
15 influenced by pH and decreasing pH favors bioavailability and bioaccumulation.
16 Bioconcentration factors (BCFs) have been reported in the scientific literature for various
17 organisms and range from 840 to 20,000 (aquatic plants), 499 to 3,670 (aquatic invertebrates),
18 and 42 to 45 (fish). Organisms that bioaccumulate lead with little excretion must partition the
19 metal such that it has limited bioavailability, otherwise toxicity will occur if a sufficiently high
20 concentration is reached.
21 Resistance Mechanisms
22 Aquatic organisms have various methods to resist the toxic effects of metals such as lead.
23 Resistance processes include detoxification and avoidance responses. Mechanisms of resistance
24 and detoxification vary among aquatic biota. These processes can include translocation,
25 excretion, chelation, adsorption, and vacuolar storage and deposition. For example, protists and
26 plants produce intracellular polypeptides that form complexes with lead (Zenk, 1996; Morelli
27 and Scarano, 2001). Some macrophytes and wetland plants have developed translocation
28 strategies for tolerance and detoxification (Knowlton et al., 1983; Deng et al., 2004). Various
29 aquatic invertebrates may sequester lead in the exoskeleton (Boisson et al., 2002; Knowlton
30 et al., 1983) or have developed specialized excretion processes (Vogt and Quinitio, 1994).
May 2006 8-21 DRAFT-DO NOT QUOTE OR CITE
-------
1 Fish scales and mucous may chelate lead in the water column and potentially reduce lead uptake
2 (Coello and Khan, 1996).
3 Avoidance responses are actions performed to evade a perceived threat. Some aquatic
4 organisms have been shown to be quite adept at avoiding lead in aquatic systems, while others
5 seem incapable of detecting its presence. Snails have been shown to be sensitive to lead, and
6 avoid it at high concentrations (Lefcort et al., 2004). Conversely, anuran (frog and toad) species
7 lack an avoidance response up to 1000 jig Pb/L (Steele et al., 1991). Fish avoidance of chemical
8 toxicants has been well established, and is a dominant sublethal response in polluted waters
9 (Svecevicius, 2001). However, studies examining avoidance behaviour of lead in fish are
10 lacking. In addition to the presence of toxic metals, light and pH can also alter preference-
11 avoidance responses.
12
13 Physiological Effects of Lead
14 Physiological effects of lead on aquatic biota can occur at the biochemical, cellular and
15 tissue levels of organization. Lead has been shown to affect brain receptors in fish (Rademacher
16 et al. 2005) and serum enzyme activity (e.g., EROD and ALAD) in fish and amphibians (Kutlu
17 and Susuz, 2004; Blasco and Puppo, 1999; Gill et al., 1991; Vogiatzis and Loumbourdis, 1999).
18 Studies examining the effects of lead on fish blood chemistry have indicated alterations from
19 acute and chronic exposures ranging from 100 to 10,000 |ig/L (Gill et al., 1991; Allen, 1993;
20 Gopal et al., 1997). Lead exposure has also been shown to negatively affect the growth of
21 aquatic invertebrates (Arai et al., 2002).
22
23 Factors that Modify Organism Response to Lead
24 There are several factors that may influence organism response to lead exposure. These
25 may include the size or age of an organism, genetics, environmental factors (e.g., pH, salinity),
26 nutrition, and the presence of other contaminants. Lead accumulation in living organisms is
27 controlled, in part, by metabolic rates (Farkas et al., 2003) and by the physiological conditions of
28 an organism. Relationships between age, size and lead body burden in aquatic invertebrates and
29 fish are variable and depend on many environmental variables (e.g., exposure) (Farkas et al.,
30 2003). For example, examination of lead exposure (up to 100 |ig/L) in aquatic invertebrates
31 showed little relationship between body size and lead accumulation (MacLean et al., 1996;
May 2006 8-22 DRAFT-DO NOT QUOTE OR CITE
-------
1 Canli and Furness, 1993) while lead accumulation and fish size was found to be positively
2 correlated (Douben, 1989; Kock et al., 1996).
3 The genetics of an organism and/or population may alter the response to lead exposure
4 through one of two processes: (1) a contaminant may influence selection, by selecting for certain
5 phenotypes that enable populations to better cope with the chemical, or (2) a contaminant can be
6 genotoxic, meaning it can produce alterations in nucleic acids at sublethal exposure
7 concentrations, resulting in changes in hereditary characteristics or DNA inactivation (Shugart,
8 1995). Genetic selection has been observed in aquatic organisms due to lead tolerance. Because
9 tolerant individuals have a selective advantage over vulnerable individuals in polluted
10 environments, the frequency of tolerance genes will increase in exposed populations over time
11 (Beaty et al., 1998). Several studies have shown that heavy metals can alter population gene
12 pools resulting in decreased genetic diversity (Duan et al., 2000; Kim et al., 2003). Laboratory
13 studies have shown that exposure to lead at 10 mg Pb2+/mL of blood leads to chromosomal
14 aberrations in some aquatic organisms (Cestari et al., 2004). Low level (50 ug/L) lead exposure
15 in water over four weeks resulted in DNA strand breakage in the freshwater mussel Anodonta
16 grandis (Black et al., 1996). More recently, Cestari et al. (2004) observed similar results
17 (increase in the frequency of chromosomal aberrations and DNA damage in kidney cell cultures)
18 in fish (Hoplias malabaricus) that were fed lead contaminated food over 18, 41 and 64 days.
19 Environmental factors can alter the availability, uptake and toxicity of lead to aquatic
20 organisms. Van Hattum et al. (1996) studied the influence of abiotic variables, including
21 dissolved organic carbon (DOC) on lead concentrations in freshwater isopods and found that as
22 DOC concentrations increased, BCFs decreased in P. meridianus and A aquations, indicating
23 that DOC acts to inhibit the availability of lead to these isopods. Schwartz et al. (2004) collected
24 natural organic matter (NOM) from several aquatic sites across Canada and investigated the
25 effects of NOM on lead toxicity in rainbow trout (Oncorhynchus mykiss). The results showed
26 that NOM in test water almost always increased LT50 (time to reach 50% mortality), and
27 optically dark NOM tended to decrease lead toxicity more than did optically light NOM in
28 rainbow trout. Studies generally agree that the toxicity of Pb decreases as pH increases
29 (MacDonald et al., 2002; Home and Dunson, 1995a,b,c). As pH decreases, lead becomes more
30 soluble and more readily bioavailable to aquatic organisms (Weber, 1993). Acute and chronic
31 toxicity of lead increases with decreasing water hardness, as lead becomes more soluble and
May 2006 8-23 DRAFT-DO NOT QUOTE OR CITE
-------
1 bioavailable to aquatic organisms (Home and Dunson, 1995c; Borgmann et al., 2005). There is
2 some evidence that water hardness and pH work together to increase or decrease the toxicity of
3 lead. High Ca2+ concentrations have been shown to protect against the toxic effects of lead
4 (Sayer et al., 1989; Rogers and Wood, 2004; MacDonald et al., 2002; Hassler et al., 2004).
5 Ca2+ affects the permeability and integrity of cell membranes and intracellular contents (Sayer
6 et al., 1989). As Ca2+ concentrations decrease, the passive flux of ions (e.g., lead) and water
7 increases. Finally, increasing salinity was found to decrease lead toxicity (Verslycke et al.,
8 2003). The reduction in toxicity was attributed to increased complexation of Pb2+ with Cl ions.
9 Nutrients (e.g., nitrate, carbonate) have been shown to affect lead toxicity in some aquatic
10 organisms. Jampani (1988) looked at the impact of various nutrients (i.e., sodium acetate, citric
11 acid, sodium carbonate, nitrogen, and phosphates) on reducing growth inhibition in blue-green
12 algae (Synechococcus aeruginosus) exposed to 200 mg Pb/L. Results indicated that additional
13 nitrogen, phosphates, and some carbon sources, including sodium acetate, citric acid and sodium
14 carbonate, all protected the algae from lead toxicity. One hypothesis was that nutrients were able
15 to reverse toxic effects. The second hypothesis was that nutrients directly interacted with lead, in
16 some way sequestering the metal so as to inhibit its metabolic interaction with the organism
17 (Rao and Reddy, 1985; Jampani, 1988). Rai and Raizada (1989) investigated the effects of lead
18 on nitrate and ammonium uptake and results indicated that lead exposure can affect the uptake of
19 some nutrients in N. muscorum. Thus, nutrients seem to be capable of reducing toxicity, though
20 the mechanisms have not been well established.
21
22 Interactions with Other Pollutants
23 Predicting the response of organisms to mixtures of chemicals is a daunting task
24 (Norwood et al., 2003). Antagonism, synergism, and additivity are the primary responses that
25 occur following exposure to multiple contaminants. When two or more metals compete for the
26 same binding sites or interfere with transport through cell walls or membranes, the interaction is
27 termed less than strictly additive or antagonistic. Antagonistic interactions can reduce metal
28 bioavailability when metals are present in combination, and may lead to reduced potential for
29 toxicity (Hassler et al., 2004). There are a number of elements (Ca2+, Cd2+, Mg2+, Na+ and CF)
30 that act in an antagonistic fashion with Pb (Niyogi and Wood, 2004; Rogers and Wood, 2003,
31 2004; Ahern and Morris, 1998; Li et al., 2004). For example, Pb is a well-known antagonist to
May 2006 8-24 DRAFT-DO NOT QUOTE OR CITE
-------
1 Ca2+ (Hassler et al., 2004; Niyogi and Wood, 2004). Calcium is an essential element, required
2 for a number of physiological processes in most organisms.
3 Synergism occurs when the interaction of two or more metals causes an effect that is
4 greater than the effect observed from the individual metals themselves (Hagopian-Schlekat et al.,
5 2001). Synergism is likely the result of increased bioavailability of one or more of the metal ions
6 due to the presence of other metals (Hassler et al., 2004). Hassler et al. (2004) reported that in
7 the presence of copper (Cu2+) there was a significantly higher rate of internalization of Pb in the
8 green algae Chlorella kesserii. It was suggested that Cu2+ may have affected organism
9 physiology through the disruption of cell membrane integrity. This would allow increased cation
10 (i.e., Pb2+) permeability and therefore substantially increased internalization of Pb. Synergistic
11 interactions have also been observed with lead and other metals (Cd, Cu, Ni, and Zn) (Hagopian-
12 Schlekat et al., 2001).
13 The combined effects of two or more metals may result in additivity when the observed
14 effects are greater than that observed with individual metals but equivalent to a summation of the
15 effects from multiple metals. Norwood et al. (2003) reported, in a review and re-interpretation of
16 published data on the interactions of metals in binary mixtures (n = 15 studies), that antagonistic
17 (n = 6) and additive interactions (n = 6) were the most common for lead. The two most
18 commonly reported lead-element interactions are between lead and calcium and lead and zinc.
19 Both calcium and zinc are essential elements in organisms, and the interaction of Pb with these
20 ions can lead to adverse effects both by increased Pb uptake and by a decrease in Ca and Zn
21 required for normal metabolic functions.
22
23 8.2.4 Exposure/Response of Aquatic Species
24 Effects of Lead on Primary Producers
25 In the 1986 Pb AQCD (U.S. Environmental Protection Agency, 1986), several authors
26 reported that some algal species (e.g., Scenedesmus sp.) were found to exhibit physiological
27 changes when exposed to high lead or organolead concentrations in situ. The observed changes
28 included increasing numbers of vacuoles, deformations in cell organelles, and increased autolytic
29 activity. Increased vacuolization was assumed to be a tolerance mechanism by which lead was
30 immobilized within cell vacuoles.
May 2006 8-25 DRAFT-DO NOT QUOTE OR CITE
-------
1 Several studies have been conducted since the 1986 Pb AQCD on the toxicity of lead to
2 primary producers (Rai and Raizada, 1989; Jampani, 1988; Adam and Abdel-Basset, 1990; Gaur
3 et al., 1994; Gupta and Chandra, 1994). Effects to algal growth (Chlorella vulgaris, Closterium
4 acerosum, Pediastrum simplex, Scenedesmus quadricaudd), ranging from minimal to complete
5 inhibition, have been reported at lead concentrations between 100 and 200,000 |ig/L (Bilgrami
6 and Kumar, 1997; Jampani, 1988). The toxicity of lead to aquatic plant growth has been studied
7 using Spirodelapolyrhiza, Azolla pinnata, and Lemna gibba (Gaur et al., 1994; Gupta and
8 Chandra, 1994; Miranda and Ilangovan, 1996). Test durations ranged from 4 to 25 days and test
9 concentrations ranged between 49.7 and 500,000 |ig/L (Gaur et al., 1994; Miranda and
10 Ilangovan, 1996). Research on aquatic plants has been focussed on the effects of lead on aquatic
11 plant growth, chlorophyll and protein content.
12 Algae and aquatic plants have a wide range in sensitivity to the effects of lead in water.
13 Both groups of primary producers experience ECso values for growth inhibition between
14 approximately 1,000 and >100,000 |ig/L (Bilgrami and Kumar, 1997; Jampani, 1988; Gaur et al.,
15 1994). The most sensitive primary producers reported in the literature for effects to growth were
16 Closterium acersoum and Azollapinnata (Bilgrami and Kumar, 1997; Gaur et al., 1994).
17 The least sensitive primary producers reported in the literature for effects to growth were
18 Synechococcus aeruginosus and L. gibba (Jampani, 1988; Miranda and Ilangovan, 1996).
19 Exposure to lead in combination with other metals is generally less toxic to growth than
20 exposure to lead alone. Studies have shown that lead adversely affects the metabolic processes
21 of nitrate uptake, nitrogen fixation, ammonium uptake, and carbon fixation (Rai and Raizada,
22 1989). Lead in combination with nickel or chromium produced synergistic effects for nitrate
23 uptake, nitrogenase activities, ammonium uptake, and carbon fixation (Rai and Raizada, 1989).
24
25 Effects of Lead on Consumers
26 The 1986 Pb AQCD (U.S. Environmental Protection Agency, 1986) reported that
27 hematological and neurological responses are the most commonly reported effects to aquatic
28 vertebrates. These effects include red blood cell destruction and inhibition of the enzyme
29 ALAD, required for hemoglobin synthesis. The lowest reported exposure concentration causing
30 either hematological or neurological effects was 8 jig Pb/L (U.S. Environmental Protection
31 Agency, 1986).
May 2006 8-26 DRAFT-DO NOT QUOTE OR CITE
-------
1 Recent literature on the toxicity of lead to fish and aquatic invertebrates has been
2 summarized by Eisler (2000). Exposure of invertebrates to Pb can lead to adverse effects on
3 reproduction, growth, survival, and metabolism (Eisler, 2000). Water-borne lead is highly toxic
4 to aquatic organisms, with toxicity varying, depending on the species and life stage tested,
5 duration of exposure, the form of lead tested, and water quality characteristics. Among the
6 species tested, aquatic invertebrates, such as amphipods and water fleas, were the most sensitive
7 to the effects of lead with adverse effects being reported at concentrations ranging from 0.45 to
8 8000 ng/L. Freshwater fish demonstrated adverse effects at concentrations ranging from 10 to
9 >5400 ng/L, generally depending upon water quality parameters (e.g., pH, hardness, salinity).
10 Amphibians tend to be relatively tolerant of lead, however, may exhibit decreased enzyme
11 activity (e.g., ALAD reduction) and changes in behavior (e.g., hypoxia response behavior).
12 Lead tends to be more toxic in longer-term exposures, with chronic toxicity thresholds for
13 reproduction in water fleas ranging as low as 30 |ig/L (e.g., Kraak et al., 1994).
14
15 8.2.5 Effects of Lead on Natural Aquatic Ecosystems
16 The effects of lead on natural aquatic ecosystems were examined following the conceptual
17 framework developed by the EPA Science Advisory Board (Young and Sanzone, 2002). The
18 essential attributes used to describe ecological condition include landscape condition, biotic
19 condition, chemical and physical characteristics, ecological processes, hydrology and
20 geomorphology and natural disturbance regimes. For the biotic condition, the Science Advisory
21 Board (SAB) framework identifies community extent, community composition, trophic structure,
22 community dynamics, and physical structure as factors for assessing ecosystem health. The
23 majority of the published literature pertaining to lead and natural aquatic ecosystems focuses on
24 the biotic condition and identifies effects on energy flow or nutrient cycling, community
25 structure, community level effects, and predator-prey interactions. Other factors for assessing
26 the biotic condition such as effects of lead on species, populations, and organism conditions
27 (e.g., physiological status) were discussed earlier in Sections 8.2.3 and 8.2.4 (see also Annex
28 Sections AX8.2.3 and AX8.2.4).
29 Recent studies have attributed the presence of lead to reduced primary productivity,
30 respiration, and alterations of community structure. Specifically, lead (6 to 80 mg/L) was found
31 to reduce primary productivity and increase respiration in an algal community (Jayaraj et al.,
May 2006 8-27 DRAFT-DO NOT QUOTE OR CITE
-------
1 1992). Laboratory microcosm studies have indicated reduced species abundance and diversity in
2 protozoan communities exposed to 0.02 to 1 mg Pb/L (Fernandez-Leborans and Novillo, 1992,
3 1994; Fernandez-Leborans and Antonio-Garcia, 1988). Numerous field studies have associated
4 the presence or bioaccumulation of lead with reductions in species abundance, richness, or
5 diversity, particularly in benthic macroinvertebrate communities (Deacon et al., 2001; Mize and
6 Deacon, 2002; Mucha et al., 2003; Poulton et al., 1995; Rhea et al., 2004; Maret et al., 2003).
7 However, in natural aquatic ecosystems, lead is often found coexisting with other metals and
8 other stressors. Thus, understanding the effects of lead in natural systems is challenging given
9 that observed effects may be due to cumulative toxicity from multiple stressors.
10 Exposure to lead in laboratory studies and simulated ecosystems may alter species
11 competitive behaviors, predator-prey interactions, and contaminant avoidance behaviors.
12 Alteration of these interactions may have negative effects on species abundance and community
13 structure. For example, reduced avoidance behaviors have been observed at lead concentrations
14 ranging from 0.3 to 1.0 mg/L (Weber, 1996; Steele et al., 1991; Weis and Weis, 1998). The
15 feeding behaviors of competitive species in some aquatic organisms are also influenced by the
16 presence of lead (Lefcort et al., 2000).
17 The effects of lead have primarily been studied in instances of point source pollution
18 rather than area-wide atmospheric deposition. Thus, the effects of atmospheric lead on aquatic
19 ecological condition remains to be defined. There is a paucity of data in the general literature
20 that explores the effects of lead in conjunction with all or several of the various components of
21 ecological condition as defined by the EPA (Young and Sanzone, 2002). However, numerous
22 studies are available associating the presence of lead with effects on biotic conditions.
23
24
25 8.3 CRITICAL LOADS FOR LEAD IN TERRESTRIAL AND
26 AQUATIC ECOSYSTEMS
27 This section defines critical loads, describes various concepts and methods that are related
28 to the estimation of critical loads, and provides a review of the relevant literature on critical
29 loads.
30
May 2006 8-28 DRAFT-DO NOT QUOTE OR CITE
-------
1 8.3.1 Definitions
2 Critical loads are defined in a variety of ways depending on the chemicals and endpoints
3 of concern (Paces, 1998; Skeffmgton, 1999; U.S. Environmental Protection Agency, 2004).
4 For the purposes of this section, critical loads are defined as threshold deposition rates of air
5 pollutants that current knowledge indicates will not cause long-term adverse effects to ecosystem
6 structure and function. A critical load is related to an ecosystem's sensitivity to anthropogenic
7 inputs of a specific chemical. If future inputs of a chemical exceed the critical load for an
8 ecosystem, the chemical is expected to reach or persist at potentially toxic levels in the future.
9 A critical load indicates a potential for future impacts only; a current exceedance of a critical
10 load does not specify whether the current deposition rate of a chemical presents a hazard to the
11 ecosystem.
12 In order to determine a critical load, the lowest concentration in the receiving medium that
13 poses a potential hazard to a defined ecosystem must first be determined. This concentration,
14 known in the critical loads literature as the critical limit (De Vries et al., 2004), is equal to the
15 effects-based criteria for the most sensitive endpoint in the ecosystem. The critical limit
16 indicates the current potential for adverse effects to an ecosystem.
17 In contrast to a critical load, a stand-still load is the highest deposition rate of a chemical
18 that will not result in future increases of its concentrations in the environmental media,
19 regardless of the potential for adverse effects at those concentrations. Stand-still loads are also
20 called "acceptable loads" or critical loads calculated using a "stand-still" approach (De Vries
21 et al., 2004) and should not be confused with effects-based critical loads.
22
23 8.3.2 Historical Perspective
24 In the 1960s, scientists demonstrated that sulfur emissions on the European continent
25 were contributing to the acidification of Scandinavian lakes. During the 1970s, evidence
26 mounted that air pollutants could travel thousands of miles before deposition occurred, implying
27 that international cooperation was necessary to control acidification. To this end, the European
28 Community (EC) and 34 governments signed the Convention on Long-range Transboundary of
29 Air Pollution (CLRTAP) in 1979 under the auspices of the United Nations Economic
30 Commission for Europe (United Nations Economic Commission for Europe (UNECE), 2004).
May 2006 8-29 DRAFT-DO NOT QUOTE OR CITE
-------
1 CLRTAP has since been extended to include eight protocols that regulate air pollutants
2 such as sulfur, nitrogen oxides, heavy metals, persistent organic pollutants, volatile organic
3 compounds, and ozone. In 1988, CLRTAP adopted the critical-load concept, making it basic to
4 the future development of international agreements concerning limitation of the emissions of air
5 pollutants. In 1991, The Coordination Center for Effects (CCE) issued a Technical Report
6 entitled "Mapping Critical Loads for Europe" which presented the first maps of critical loads that
7 were produced as part of the work conducted under the UNECE. Each individual country
8 created maps detailing critical loads and levels of acidity within its boundaries. The maps were
9 then used by CCE to create a Europe-wide map of critical loads (Hettelingh et al., 1991) that is
10 used in combination with air emissions and deposition data to guide negotiations between
11 nations and reduce the gap between critical loads and deposition (Skeffington, 1999). The first
12 international agreement on pollution control based on critical loads was the second Sulfur
13 Protocol, which was established in Oslo (United Nations Economic Commission for Europe
14 (UNECE), 1994) within CLRTAP.
15 Since 1991, CCE has issued biennial technical status reports on critical loads and critical
16 thresholds of acidification, eutrophication, sulfur, nitrogen, and nitrogen oxide (Coordination
17 Center for Effects (CCE), 2005). Progress on data and methodologies is reviewed annually in
18 CCE Mapping workshops. Recent CCE reports focus on scientific and technical support for the
19 revision of protocols as well as time horizons for recovery from ecosystem damage.
20 Many of the signatory governments to CLRTAP have adopted the critical load concept for
21 determining national emission control polices. Canada has also committed to a critical load
22 approach for controlling acid deposition. In 1998, federal, provincial, and territorial Energy and
23 Environment Ministers signed The Canada-wide Acid Rain Strategy for Post-2000. According
24 to Environment Canada, the primary long-term goal of the Strategy is to achieve critical loads
25 (or the threshold level) for acidic deposition across Canada (Environment Canada, 2003).
26 The Ministry of Environment in the Netherlands took the initiative to develop analogous
27 methods for the calculation of critical loads for heavy metals, methods that would be valid in the
28 context of CLPTRP (De Vries et al., 2004). Beginning in the mid-1990s, these methods were
29 developed through a series of manuals, international workshops, and expert meetings (De Vries
30 et al., 2004). Participating nations completed a voluntary preliminary critical load mapping
31 exercise for Pb and cadmium in Europe in 2002 (Hettelingh et al., 2002).
May 2006 8-30 DRAFT-DO NOT QUOTE OR CITE
-------
1 The 1986 Pb AQCD (U.S. Environmental Protection Agency, 1986) largely predates the
2 development of the concept of critical loads, and does not include this topic. The 2004 AQCD
3 for Particulate Matter (U.S. Environmental Protection Agency, 2004) includes a brief discussion
4 of the key elements of the critical loads framework general to any air pollutant. To date, the
5 critical loads framework has not been used for regulatory purposes in the United States for any
6 chemical.
7
8 8.3.3 Application of Critical Loads to Terrestrial and Aquatic Ecosystems
9 A combinatorial application of critical limit and critical load allows one to assess current
10 risk while simultaneously estimating future risk from exposure to a chemical (De Vries et al.,
11 2004). Figure 8-3.1 shows that four combinations of critical load and limit exceedance or
12 non-exceedance are possible for a given ecosystem (Figure 1 of De Vries et al. [2004]).
13 For example, if a current risk is indicated by an exceedance of the critical limit for Pb due to
14 historical Pb deposition, but current inputs of Pb to the ecosystem are below the critical load
15 (lower left corner), the critical load model predicts that Pb concentrations will fall below the
16 critical limit at some point in the future if Pb deposition is maintained at the present level.
17 If current soil concentrations are below the critical limit (upper right corner), inputs greater than
18 the critical load will not result in exceedance of the critical limit for some period of time, but
19 continued exceedance of a critical load will eventually lead to an exceedance of the critical limit.
20 The time until a critical limit is exceeded (critical time) can also be predicted using the
21 critical load model (Paces, 1998). This requires knowledge of current concentrations, the critical
22 load, and predicted deposition rates. Critical times may be useful for setting priorities between
23 ecosystems with critical load exceedances or between different chemicals.
24
25 8.3.4 Calculation of Critical Loads
26 This section summarizes the various methods used to calculate critical loads (De Vries
27 et al., 2001, 2002, 2004; Groenenberg et al., 2002), with an emphasis on the most recent
28 material.
29
May 2006 8-31 DRAFT-DO NOT QUOTE OR CITE
-------
No critical load
exceedance
Critical load
exceedance
No critical limit exceedance
No damage at present or foreseen:
critical
present
• CL
PL2
PL1
Time
"^ Keep the Present Load
(more stringent than Critical
Load)
Future damage foreseen:
Concentration
critical
present
PL4
PL3
• CL
Time
"^ Consider Critical Load
(emissions must decrease, even if
concentrations in the ecosystem
are allowed to increase further at
critical load)
Critical limit exceedance
Present damage but recovery in progress:
Concentration
present
critical
•CL
PL2
PL1
TT
Time
"^ Keep the Present Load
(more stringent than Critical
! ,oad)
or
•^ Consider TjnjgejJLoad to reach
the critical limit in a defined rime
period (more stringent than
Critical Load)
Present damage, no recovery foreseen:
Concentration
present
critical
PL4
PL3
. CL
TT Time
"^ Consider (juictl Load
(decrease of concentrations in the
ecosystem down to critical limit
in the long term)
or
^ Consider Target 1 .oad to reach
the critical limit in a defined time
period (more stringent than
Critical Load)
CL - Critical load; PI, - present load (2 cases); SI. - Stand-still load; TL - Target load; TT - Target time
Figure 8-3.1. The predicted development of metal concentrations in ecosystems for four
cases of exceedance or non-exceedance of critical limits and critical loads,
respectively.
Source: Taken from DeVries et al. (2004).
May 2006
8-32
DRAFT-DO NOT QUOTE OR CITE
-------
1 8.3.4.1 Critical Limits
2 To determine the critical limit, effects-based criteria for the major ecological endpoints
3 should be developed for the ecosystem of concern. Criteria may be developed for any receptor
4 that is exposed to the chemical of concern deposited in the ecosystem. In terrestrial ecosystems,
5 possible ecological endpoints include effects from direct contact of invertebrates or plants
6 with soil and ingestion of plants by herbivores. Effects-based criteria for use in defining the
7 critical limit should be derived from ecotoxicological data appropriate to the most sensitive
8 endpoint (De Vries et al., 2004). Regardless of the selected endpoint, the critical limit should be
9 defined as a concentration in the medium that receives the depositional load, typically soil in
10 terrestrial ecosystems and surface water in aquatic ecosystems. To derive these values, uptake
11 and/or food- chain modeling may be necessary.
12 Many critical load calculations rely on ecological effects criteria developed by
13 government agencies in individual countries (Paces, 1998; De Vries et al., 1998; Van Den Hout
14 et al., 1999; Skjelkvale et al., 2001). Criteria for Pb vary widely and can be the largest source of
15 uncertainty in a critical load calculation (Van Den Hout et al., 1999). One reason for the wide
16 range in estimates of effects criteria is that Pb speciation is often not taken into account. This
17 can result in variation in estimates of concentration for total Pb that is associated with adverse
18 effects, since the fraction of Pb available to cause a toxic effect depends on chemical factors such
19 as the pH or organic matter content (Lofts et al., 2004). To develop effects-based criteria that are
20 applicable to media with a pH or organic matter content different from the test medium, it is
21 more appropriate to develop criteria based on the free concentration of Pb rather than the total
22 concentration of Pb.
23
24 8.3.4.2 Models
25 Critical loads for heavy metals are typically calculated using a steady state model that
26 ignores internal metal cycling and keeps the calculations as simple as possible (De Vries et al.,
27 2004). The critical load is equal to the atmospheric input flux, which equals the sum of the
28 output fluxes from the system minus the other input fluxes (e.g., weathering) when the
29 concentration of Pb is at the critical limit. The input flux of heavy metals via weathering is
30 sometimes neglected, because quantitative estimates are highly uncertain, and weathering is
31 generally thought to be a relatively minor process (De Vries et al., 2004; Scudlark et al., 2005).
May 2006 8-33 DRAFT-DO NOT QUOTE OR CITE
-------
1 More complex methods may be used to calculate critical loads. For example, dynamic
2 models can be used to model the change of concentrations in soil or water over time (Paces,
3 1998). These models are most valuable when the time to steady state is very long compared to
4 the time of interest. Using these models, the critical load is the deposition rate that leads to
5 concentrations equal to the critical limit as the model approaches steady state. Fate and transport
6 models that include internal cycling can also be used in place of simple mass balance models
7 (Doyle et al., 2003) that may improve the accuracy of the models.
8
9 Terrestrial Model
10 If internal cycling and weathering of Pb is neglected and atmospheric deposition is the
11 only important source of Pb to the system, the critical load in a terrestrial ecosystem is equal to
12 the sum of the most important fluxes out of the system, leaching, and uptake by harvested plants:
13
14 CL(Pb) = Pbu + Pble(cnt) (8-1)
15 where:
16
17 CL(Pb) = critical load of Pb (mass per area-year)
18 Pbu = metal net uptake in harvestable parts of plants at the critical limit
19 (mass per area-year)
20 Pbie(crit) = leaching flux of Pb (dissolved and particulate) from the soil layer at
21 the critical limit (mass per area-year)
22
23 When applying a mass balance model, it is important to define the boundaries of the
24 compartment such that all significant fluxes in and out of the compartment can be accounted for.
25 Uptake of Pb by harvested vegetation may be an important flux out of agricultural soil or
26 forested soil that is actively logged. In ecosystems that are not harvested, the steady state model
27 assumes that uptake by plants is balanced by deposition of Pb from decaying vegetation.
28 The flux out of the system due to uptake in harvested plants (Pbu) is calculated as follows:
29
30 Pbu = fPb;U;Z * Yha * [Pb]ha (8-2)
31 where:
32
33 fpb,u,z = fraction of net Pb uptake from soil within the considered layer
34 (dimensionless)
35 Yha = annual yield of harvestable biomass (mass per area-year)
36 [Pb]ha = metal concentration of harvestable parts of plants (Pb per unit mass)
37
May 2006 8-34 DRAFT-DO NOT QUOTE OR CITE
-------
1 The net fraction of metal uptake from soil within the considered layer corrects for Pb
2 measured in harvested vegetation that is taken up via direct deposition onto the plant or from soil
3 outside of the considered soil layer.
4 The yield of harvestable biomass should only include the parts of plants that are removed
5 from the system. Tree leaves, stalks remaining after harvest of agricultural land, roots, and other
6 parts that remain in the considered terrestrial ecosystem should not be included in the yield.
7 De Vries et al. (2004) recommends that data for metal content in harvestable biomass
8 should be taken from unpolluted areas. This leads to more conservative critical loads than using
9 the metal content at the critical load. If the selected endpoint for the critical limit is related to the
10 concentration in harvested plants rather than a concentration in soil, that critical concentration
11 should be used in place of actual metal content in harvestable biomass.
12 The critical leaching flux from the topsoil can be calculated as follows:
13
14 Mcl(cnt) = Qle * [Pb]tot;Sdw(cnt) (8-3)
15 where:
16
17 Qie = flux of drainage water leaching from the considered soil layer
18 (volume/year)
19 [Pb]tot,sdw(crit) = critical total concentration of Pb in soil drainage water
20 (mass per volume)
21
22 The total concentration of Pb in soil drainage water is the sum of all species of dissolved
23 and particulate Pb that leach out of the system in drainage water. De Vries et al. (2004) suggests
24 that Pb that is sorbed to suspended particulate matter should be neglected so that total Pb is equal
25 to dissolved Pb, as concentrations of suspended solids are difficult to estimate. Dissolved Pb
26 may exist as free ions, organic complexes, or inorganic complexes.
27 The drainage water flux leaching from the topsoil (Qie) can be calculated as follows:
28
29 Qle = P-E1-Es-fEt;Z*Et (8-4)
30 where:
31
32 P = Precipitation (volume per area-time)
33 E; = Interception evaporation (volume per area-time)
34 Es = Soil evaporation within the topsoil (volume per area-time)
35 fEt,z = Plant transpiration (volume per area-time)
36 Et = Fraction of water uptake within the topsoil by roots (unitless)
37
May 2006 8-35 DRAFT-DO NOT QUOTE OR CITE
-------
1 De Vries et al. (2004) recommends default values for some of these parameters and
2 provides an alternative calculation method for sites with detailed hydrologic data as part of the
3 guidance document.
4
5 Aquatic Model
6 If internal cycling and weathering of Pb is neglected and atmospheric deposition is the
7 only important source of Pb to the system, the critical load in an aquatic ecosystem is equal to
8 the sum of the most important fluxes out of the system, uptake by harvested plants in the
9 catchment, sedimentation, and lateral outflow from the catchment:
10
11 CL(Pb) = Pbu + Pbsed(cnt) * A! / Ac + PbloC;Cnt (8-5)
12 where:
13
14 CL(Pb) = critical load of Pb (mass per area-year)
15
16 Pbu = removal of Pb by harvesting of vegetation in the catchment
17 (mass per area-time)
18 PbSed(crit) = removal of Pb by sedimentation at the critical load
19 (mass per area-time)
20 Pbioc,crit = lateral Pb outflow from the catchment at the critical load
21 (mass per area-time)
22 AI = lake area
23 Ac = catchment area
24
25 It is important to carefully define the boundaries of the aquatic system, so that all inflows
26 and outflows may be fully accounted for. Current guidance recommends including the entire
27 watershed within the system, rather than confining the system to a single lake or stream (De
28 Vries et al., 2004). In stream water, removal of Pb due to sedimentation does not need to be
29 considered, simplifying the equation to the following:
30
31 CL(Pb) = Pbu + PbloC;Cnt (8-6)
32
33 De Vries et al. (2004) recommends that critical loads should be calculated for stream
34 waters only, due to a high level of uncertainty in the rate of removal via sedimentation or other
35 removal mechanisms within a lake. Critical loads for streams are protective of nearby lakes,
May 2006 8-36 DRAFT-DO NOT QUOTE OR CITE
-------
1 because the critical loads calculated using this methodology will be lower for streams than
2 for lakes.
3 Calculation of removal of Pb by harvesting of vegetation in the catchment is similar to
4 that in terrestrial ecosystems, with fpt,,u equal to 1, since the entire catchment is now included.
5 The critical lateral Pb outflow from the catchment is the product of the lateral outflow flux
6 of water and the total concentration of Pb in the outflow water at the critical limit. The outflow
7 flux of water is calculated from the outflow divided by the catchment area.
8
9 8.3.5 Critical Loads in Terrestrial Ecosystems
10 Critical loads of Pb have been calculated using simple mass balance, dynamic, and
1 1 probabilistic models for forested and agricultural land in Europe and Canada in a handful of
12 preliminary studies. The methods and model assumptions used to calculate critical loads vary
13 widely between these studies and little attempt has been made to validate the models that were
14 used, so it is not known how much various simplifying assumptions affect the results.
15 Paces (1998) used data from a small agricultural catchment in the Czech Republic that is
16 typical of agricultural land in that country to calculate critical loads for Pb and other heavy
17 metals. The critical loads were calculated using a simple dynamic box model. The fluxes into
18 the system included atmospheric deposition, agricultural inputs, and weathering of bedrock and
19 the fluxes out of the system included biological uptake and runoff. The model assumed that
20 inputs of metals to the system are independent of their concentrations in soil but that outputs are
21 proportional to the concentration of biologically active metal. The author defined biologically
22 active metal as the concentration of metal in soil that can be extracted in a 2 M nitric acid
23 solution. This method was used to set a Czech state norm designed to be protective for soil
24 systems that is used as the critical limit in this study. Using the model, Paces determined that the
25 critical limit was not presently exceeded, but that the critical load is exceeded. However, the
26 critical time was almost 1,000 years. Therefore, the model predicts that Pb will continue to
27 accumulate in Czech agricultural soil and will eventually pose a potential risk if current inputs
28 continue. The author identified the simplifying assumptions used to calculate fluxes out of the
29 system as the major source of uncertainty.
30 Van den Hout et al. (1999) calculated critical loads for Pb and other pollutants in the
3 1 organic and mineral soil layers of forested ecosystems. Atmospheric deposition was assumed to
May 2006 8-37 DRAFT-DO NOT QUOTE OR CITE
-------
1 be the only inflow, and outflows from soil were assumed to occur due to biological uptake and
2 leaching. Net heavy metal uptake by the forest was set equal to the rate of water uptake by
3 vegetation multiplied by the water concentration and a "preference factor" that indicates the
4 preference of the vegetation for the metal relative to water. Water flux was estimated from
5 precipitation, soil evaporation, and transpiration data. An equilibrium speciation model that
6 takes inorganic and organic ligands into account was used to estimate dissolved concentrations
7 ofPb inleachate. Results were strongly dependant on the critical limits that were chosen. Using
8 the most stringent levels, critical loads were exceeded over much of Europe. The time to steady
9 state was estimated to be hundreds of years. Speciation of Pb was identified as an important
10 source of uncertainty.
11 Reinds et al. (2002) used the guidance prepared by De Vries et al. (2002b) to calculate
12 critical loads in the mineral topsoil of forested and agricultural ecosystems across 80,000 areas of
13 the European continent. The median critical load for Pb in Europe was 25 g ha'1 year"1 using
14 this methodology. The drainage water flux leaching from the topsoil was the dominant term in
15 the model, so critical loads followed the spatial pattern of net runoff (excess precipitation) across
16 Europe.
17 Probst et al. (2003) calculated critical loads for Pb for forested sites in France.
18 Weathering rates were determined using a model for representative French soil samples. The
19 biomass uptake of Pb was derived using National Forestry Inventory data for the average annual
20 biomass growth and data for the Pb content in biomass. An uptake factor scaled down to the
21 considered depth was applied. Leaching of Pb was calculated using runoff data and dissolved Pb
22 concentrations in soil solution. Critical loads at the French site varied over a wide range (4.9 to
23 133 g ha- year"1). Critical loads were controlled mainly by net runoff. Weathering rates were
24 small compared to leaching and biomass uptake rates.
25 Doyle et al. (2003) used a probabilistic assessment to calculate critical loads in terrestrial
26 and aquatic (see following section) ecosystems on the Canadian Shield. The terrestrial model
27 used an analytical solution to the convection/dispersion equation. The model only considered
28 soluble metal in the flux to soil and assumed that the insoluble fraction was not available. Metals
29 were assumed to be sorbed onto immobile soil solids according to an equilibrium distribution
30 (Kd) relationship. The input parameters were selected to represent boreal forest and Canadian
31 Shield conditions. Best estimate inputs were used for deterministic evaluation and distributions
May 2006 8-38 DRAFT-DO NOT QUOTE OR CITE
-------
1 of values were used in a probabilistic assessment. The model inputs included net water flux,
2 effective water velocity, moisture content of soil, pH, dispersion coefficient, and Kd. The
3 25th percentile critical loads (47 mg/m3 per year for Pb) were compared to current deposition
4 rates to evaluate risk.
5 In spite of the variation in methods and model assumptions used to calculate critical loads
6 for Pb in the studies discussed above, some general conclusions may be drawn. The critical limit
7 is the most important value for determining the value of the critical load. Wide variations in
8 available effects levels makes this parameter one of the most important sources of uncertainty
9 when calculating critical loads in terrestrial ecosystems. Spatial variations in critical loads for Pb
10 are largely controlled by net runoff. Weathering and uptake by harvestable vegetation were less
11 important. The time to reach steady state is several hundred years in the two studies that used
12 dynamic models to determine critical loads.
13
14 8.3.6 Critical Loads in Aquatic Ecosystems
15 Doyle et al. (2003) modeled critical loads in surface water bodies assuming complete
16 mixing with dilution water entering from the terrestrial catchment area. Loss of metal was also
17 assumed to occur through downstream flushing and burial in sediment. Transfer of metal to
18 sediment was modeled as a first-order process dependant on the dissolved concentration and pH.
19 The inputs to the model included the following: water body area, terrestrial catchment area,
20 water body depth, sediment accumulation rate, thickness of biologically active sediment, net
21 precipitation, and water pH. The fist-order rate constant for transfer to sediment was correlated
22 with pH. The model reached steady state within a few years. Transfer of Pb from the terrestrial
23 catchment to the water body was neglected, because the time to steady state could be on the
24 order of 10,000 years if the model included this source of Pb. However, the authors cited a
25 separate calculation that indicated that neglect of transfer of Pb from the catchment may lead to a
26 5-fold underestimation of Pb concentrations in the surface water.
27 These results indicate that Pb run-off from soil is more important than direct atmospheric
28 deposition to the surface water bodies considered in this study. Due to the long times required to
29 achieve steady state, the critical load methodology may not be appropriate for Pb in aquatic
30 systems.
31
May 2006 8-39 DRAFT-DO NOT QUOTE OR CITE
-------
1 8.3.7 Limitations and Uncertainties
2 The largest sources of uncertainty identified in studies of critical loads for Pb include the
3 following:
4 • Steady-state assumption
5 • Derivation of the critical limit
6 • Lead speciation
7 • Soil runoff as an input to aquatic ecosystems
8 The critical load is calculated for steady state conditions, but the time for Pb to reach
9 steady-state concentrations can be as long as several centuries. Thus, dynamic models are often
10 used to predict Pb concentrations over shorter time frames. Dynamic modeling requires
11 additional knowledge about current concentrations in the considered ecosystem. For regulatory
12 purposes, use of dynamic modeling requires that a target time be set in order to calculate a
13 critical load.
14 Criteria for the protection of soil and for the protection of aquatic organisms vary over a
15 wide range from country to country. Use of the critical loads method for international
16 negotiations will require implementation of a consistent calculation methodology that takes into
17 account the effect of Pb speciation on toxicity over a range of soil types and chemical conditions.
18 Speciation strongly influences the toxicity of Pb in soil and water and partitioning
19 between dissolved and solid phases determines the concentration of Pb in soil drainage water,
20 but it has not been taken into account in most of the critical load calculations for Pb performed to
21 date. Recent guidance for heavy metals has begun to emphasize the importance of speciation to
22 critical load calculations and suggest methods to calculate speciation (De Vries et al., 2004).
23 To this end, Lofts et al., (2004) developed critical limit functions for several metals, including
24 Pb, that take into account the effects of pH, organic matter, and the protective effects of cations
25 on speciation.
26 Runoff of Pb from soil may be the major source of Pb into aquatic systems. However,
27 little attempt has been made to include this source into critical load calculations for aquatic
28 systems due to the complexity of including this source in the critical load models.
29
May 2006 8-40 DRAFT-DO NOT QUOTE OR CITE
-------
1 8.3.8 Conclusions
2 Preliminary efforts to calculate critical loads for Pb in terrestrial and aquatic ecosystems
3 have so far relied on a variety of calculation methods and model assumptions. Efforts are
4 ongoing to refine and standardize methods for the calculation of critical loads for heavy metals
5 which are valid in the context of CLPTRP. At this time, the methods and models commonly
6 used for the calculation of critical loads have not been validated for Pb. Many of the methods
7 neglect the speciation of Pb when estimating critical limits, the uptake of Pb into plants, and the
8 outflux of Pb in drainage water, limiting the utility of current models.
9 Future efforts should focus on fully incorporating the role of Pb speciation into critical
10 load models, and validating the assumptions used by the models.
11
May 2006 8-41 DRAFT-DO NOT QUOTE OR CITE
-------
1 REFERENCES
2 Acosta-Martinez, V.; Tabatabai, M. A. (2000) Arylamidase activity of soils: effect of trace elements and
3 relationships to soil properties and activities of amidohydrolases. Soil Biol. Biochem. 33: 17-23.
4 Adam, M. S.; Abdel-Basset, R. (1990) Effect of lead nitrate and lead acetate on the growth and some metabolic
5 processes of Scenedesmus obliquus. Acta Hydrobiol. 32: 93-99.
6 Ahern, M. D.; Morris, S. (1998) Accumulation of lead and its effects on Na balance in the freshwater crayfish
7 Cher ax destructor. J. Exp. Zool. 281: 270-279.
8 Aka, H.; Darici, C. (2004) Carbon and nitrogen mineralization of lead treated soils in the eastern Mediterranean
9 region, Turkey. Soil Sediment Contam. 13: 255-265.
10 Al-Wabel, M. A.; Heil, D. M.; Westfall, D. G.; Barbarick, K. A. (2002) Solution chemistry influence on metal
11 mobility in biosolids-amended soils. J. Environ. Qual. 31: 1157-1165.
12 Allen, P. (1993) Effects of acute exposure to cadmium (II) chloride and lead (II) chloride on the haematological
13 profile of Oreochromis aureus (Steindachner). Comp. Biochem. Physiol. C: Pharmacol. Toxicol.
14 Endocrinol. 105C: 213-217.
15 An, Y.-J.; Kim, Y.-M.;Kwon, T.-M.; Jeong, S.-W. (2004) Combined effect of copper, cadmium, and lead upon
16 Cucumis sativus growth and bioaccumulation. Sci. Total Environ. 326: 85-93.
17 Angelova, V.; Ivanov, K.; Ivanova, R. (2004) Effect of chemical forms of lead, cadmium and zinc in polluted soils
18 on their uptake by tobacco. J. Plant Nutr. 27: 757-773.
19 Antosiewicz, D. M (2005) Study of calcium-dependent lead-tolerance on plants differing in their level of Ca-
20 deficiency tolerance. Environ. Pollut. 134: 23-34.
21 Arai, T.; Maeda, M.; Yamakawa, H.; Kamatani, A.; Miyazaki, N. (2002) Growth effect on the uptake and
22 elimination of trace metals in the abalones Haliotis. Fish. Sci. 68: 1094-1098.
23 Archer, D.; Emerson, S.; Reimers, C. (1989) Dissolution of calcite in deep-sea sediments: pH and O2 microelectrode
24 results. Geochim. Cosmochim. Acta 53: 2831-2845.
25 Baath, E. (1989) Effects of heavy metals in soil on microbial processes and populations (a review). Water Air Soil
26 Pollut. 47: 335-379.
27 Bacon, J. R.; Bain, D. C. (1995) Characterization of environmental water samples using strontium and lead stable-
28 isotope compositions. Environ. Geochem. Health 17: 39-49.
29 Badawy, S. H.; Helal, M. I. D.; Chaudri, A. M.; Lawlor, K.; McGrath, S. P. (2002) Soil solid-phase controls lead
30 activity in soil solution. J. Environ. Qual. 31: 162-167.
31 Balistrieri, L. S.; Murray, J. W.; Paul, B. (1994) The geochemical cycling of trace elements in a meromictic lake.
32 Geochim. Cosmochim. Acta 58: 3993-4008.
33 Bargar, J. R.; Brown, G. E.; Parks, G. A. (1997a) Surface complexation of Pb(II) at oxide-water interfaces. I. XAFS
3 4 and bond-valence determination of mononuclear and polynuclear Pb(II) sorption products on aluminum
35 oxides. Geochim. Cosmochim. Acta 61: 2617-2637.
36 Bargar, J. R.; Brown, G. E.; Parks, G. A. (1997b) Surface complexation of Pb(II) at oxide-water interfaces. 2. XAFS
3 7 and bond-valence determination of mononuclear and polynuclear Pb(II) sorption products and surface
38 functional groups on iron oxides. Geochim. Cosmochim. Acta 61: 2639-2652.
39 Bargar, J. R.; Brown, G. E.; Parks, G. A. (1998) Surface complexation of Pb(II) at oxide-water interfaces: III. XAFS
40 determination of Pb(II) and Pb(II)-chloro adsorption complexes on goethite and alumina. Geochim.
41 Cosmochim. Acta 62: 193-207.
42 Beaty, B. J.; Black, W. C.; Carlson, J. O.; Clements, W. H. DuTeau, N.; Harrahy, E.; Nucklos, J.; Olson, K. E.;
43 Rayms-Keller, A. (1998) Molecular and genetic ecotoxicologic approaches to aquatic environmental
44 bioreporting. Environ. Health Perspect. 106(86): 1395-1407.
45 Berthelsen, B. O.; Steinnes, E. (1995) Accumulation patterns of heavy-metals in soil profiles as affected by forest
46 clear-cutting. Geoderma 66: 1-14.
47 Beyer, W. N.; Pattee, O. H.; Sileo, L.; Hoffman, D. J.; Mulhern, B. M. (1985) Metal contamination in wildlife living
48 near two zinc smelters. Environ. Pollut. Ser. A 38: 63-86.
49 Beyer, W. N.; Hensler, G.; Moore, J. (1987) Relation of pR and other soil variables to concentrations of Pb, Cu, Zn,
50 Cd, and Se in earthworms. Pedobiologia 30: 167-172.
51 Beyer, W. N.; Audet, D. J.; Heinz, G. H.; Hoffman, D. J.; Day, D. (2000) Relation of waterfowl poisoning to
52 sediment lead concentrations in the Coeur d'Alene River basin. Ecotoxicology 9: 207-218.
53 Bilgrami, K. S.; Kumar, S. (1997) Effects of copper, lead and zinc on phytoplankton growth. Biol. Plant.
54 39:315-317.
May 2006 8-42 DRAFT-DO NOT QUOTE OR CITE
-------
1 Bindler, R.; Brannvall, M.-L.; Renberg, I. (1999) Natural lead concentrations in pristine boreal forest soils and past
2 pollution trends: a reference for critical load models. Environ. Sci. Technol. 33: 3362-3367.
3 Black, M. C.; Ferrell, J. R.; Horning, R. C.; Martin, L. K., Jr. (1996) DNA strand breakage in freshwater mussels
4 (Anodonta grandis) exposed to lead in the laboratory and field. Environ. Toxicol. Chem. 15: 802-808.
5 Blais, J. M. (1996) Using isotopic tracers in lake sediments to assess atmospheric transport of lead in Eastern
6 Canada. Water Air Soil Pollut. 92: 329-342.
7 Blake, L.; Goulding, K. W. T. (2002) Effects of atmospheric deposition, soil pH and acidification on heavy metal
8 contents in soils and vegetation of semi-natural ecosystems at Rothamsted Experimental Station, UK.
9 Plant Soil 240: 235-251.
10 Blasco, J.; Puppo, J. (1999) Effect of heavy metals (Cu, Cd and Pb) on aspartate and alanine aminotransferase in
11 Ruditapesphilippinarum (Mollusca: Bivalvia). Comp. Biochem. Physiol. Part C: Pharmacol. Toxicol.
12 Endocrinol. 122C: 253-263.
13 Bloom, N. S.; Crecelius, E. A. (1987) Distribution of silver, mercury, lead, copper, and cadmium in central
14 Puget Sound sediments. Mar. Chem. 21: 377-390.
15 Bodek, L; Lyman, W. J.; Reehl, W. F.; Rosenblatt, D. H., eds. (1988) Environmental inorganic chemistry properties,
16 processes, and estimation methods. Pergamon Press, pp.7.8.1-7.8-9.
17 Boisson, F.; Cotret, O.; Fowler, S. W. (2002) Transfer and distribution of lead in the asteroid Asterias rubens
18 following ingestion of contaminated food: a radiotracer study. Mar. Pollut. Bull. 44: 1003-1009.
19 Bongers, M. V.; Rusch, B.; VanGestel, C. A. M. (2004) The effect of couterion and percolation on the toxicity of
20 lead for the springtail Folsomia Candida in soil. Environ. Toxicol. Chem. 23: 195-200.
21 Borgmann, U.; Couillard, Y.; Doyle, P.; Dixon, D. G. (2005) Toxicity of sixty-three metals and metalloids to
22 Hyalella azteca at two levels of water hardness. Environ. Toxicol. Chem. 24: 641-652.
23 Boyle, E. A.; Bergquist, B. A.; Kayser, R. A.; Mahowald, N. (2005) Iron, manganese, and lead at Hawaii Ocean
24 Time-series station ALOHA: temporal variability and an intermediate water hydrothermal plume. Geochim.
25 Cosmochim. Acta 69: 933-952.
26 Brar, R. S.; Sandhu, H. S.; Grewal, G. S. (1997a) Biochemical alterations induced by repeated oral toxicity of lead
27 in domestic fowl. Indian Vet. J. 74: 380-383.
28 Brar, R. S.; Sandhu, H. S.; Randhawa, S. S.; Grewal, G. S. (1997b) Effect of repeated oral toxicity of lead on
29 activities of some plasma enzymes in domestic fowls. Indian J. Anim. Sci. 67: 878-879.
30 Brown, S. L.; Chaney, R. L.; Hallfrisch, J. G.; Xue, Q. (2003a) Effects of biosolids processing on the bioavailability
31 of lead in urban soils. J. Environ. Qual. 32: 100-108.
32 Brown, S. L.; Henry, C. L.; Compton, H.; Chaney, R.; DeVoider, P. S. (2003b) Using municipal biosolids in
33 combination with other residuals to restore metal-contaminated mining areas. Plant Soil 249: 203-215.
34 Brown, S. L.; Chaney, R.; Berti, B. (1999) Field test of amendments to reduce the in situ availability of soil lead.
35 In: Wenzel, W. W.; Adriano, D. C.; Doner, H. E.; Keller, C.; Lepp, N. W.; Mench, M. W.; Naidu, R.;
36 Pierzynski, G. M., eds. Abstracts of the 5th international conference on biogeochemistry of trace elements;
37 July; Vienna, Austria. Vienna, Austria: International Society for Trace Element Research.
38 Brown, S. L.; Henry, C. L.; Compton, H.; Chaney, R. L.; DeVolder, P. (2000) Using municipal biosolids in
3 9 combination with other residuals to restore a vegetative cover on heavy metal mine tailings. In: Daniels,
40 W. L.; Richardson, S. G., eds. Proceedings: seventeenth annual meeting of the American Society for
41 Surface Mining and Reclamation; June; Tampa, FL. Lexington, KY: American Society for Surface Mining
42 and Reclamation; pp. 685-670.
43 Canli, M.; Furness, R. W. (1993) Toxicity of heavy metals dissolved in sea water and influences of sex and size on
44 metal accumulation and tissue distribution in the Norway lobster Nephrops norvegicus. Mar. Environ. Res.
45 36:217-236.
46 Cao, X.; Ma, Q. Y.; Chen, M.; Singh, S. P.; Harris, W. G. (2002) Impacts of phosphate amendments on lead
47 biogeochemistry at a contaminated site. Environ. Sci. Technol. 36: 5296-5304.
48 Case, J. M.; Reif, C. B.; Timko, A. (1989) Lead in the bottom sediments of Lake Nuangola and fourteen other
49 bodies of water in Luzerne County, Pennsylvania. J. Pennsylvania Acad. Sci. 63: 67-72.
50 Cestari, M. M.; Lemos, P. M. M.; Ribeiro, C.; Costa, J. R.; Pelletier, E.; Ferraro, M.; Mantovani, M. S.; Fenocchio,
51 A. S. (2004) Genetic damage induced by trophic doses of lead in the neotropical fish Hoplias malabaricus
52 (Characiformes, Erythrinidae) as revealed by the comet assay and chromosomal aberrations. Genet. Mol.
53 Biol. 27: 270-274.
54 Chaney, R. L.; Ryan, J. A. (1994) Risk based standards for arsenic, lead and cadmium in urban soils. Frankfurt,
55 Germany: DECHEMA. (Dechema-Fachgesprache Umweltschutz Series).
May 2006 8-43 DRAFT-DO NOT QUOTE OR CITE
-------
1 Chillrud, S. N.; Hemming, S.; Shuster, E. L.; Simpson, H. I; Bopp, R. F.; Ross, J. M; Pederson, D. C.; Chaky,
2 D. A.; Tolley, L.-R.; Estabrooks, F. (2003) Stable lead isotopes, contaminant metals and radionuclides in
3 upper Hudson River sediment cores: implications for improved time stratigraphy and transport processes.
4 Chem. Geol. 199: 53-70.
5 Clevenger, T. E.; Saiwan, C.; Koirtyohann, S. R. (1991) Lead speciation of particles on air filters collected in the
6 vicinity of a lead smelter. Environ. Sci. Technol. 25: 1128-1133.
7 Coello, W. F.; Khan, M. A. Q. (1996) Protection against heavy metal toxicity by mucus and scales in fish. Arch.
8 Environ. Contam. Toxicol. 30: 319-326.
9 Coordination Center for Effects (CCE). (2005) Methods and models. Available: http://www.rivm.nl/cce/methmod/
10 [22 June, 2005].
11 Cotrufo, M. F.; De Santo, A. V.; Alfani, A.; Bartoli, G.; De Cristofaro, A. (1995) Effects of urban heavy metal
12 pollution on organic matter decomposition in Quercus ilex L. woods. Environ. Pollut. 89: 81-87.
13 Cotter-Howells, J.; Caporn, S. (1996) Remediation of contaminated land by formation of heavy metal phosphates.
14 Appl. Geochem. 11: 335-342.
15 Dalenberg, J. W.; Van Driel, W. (1990) Contribution of atmospheric deposition to heavy-metal concentrations in
16 field crops. Neth. J. Agric. Sci. 38: 369-379.
17 Davison, W.; Grime, G. W.; Morgan, J. A. W.; Clarke, K. (1991) Distribution of dissolved iron in sediment pore
18 waters at submillimetre resolution. Nature (London) 352: 323-325.
19 Davison, W.; Zhang, H. (1994) In situ speciation measurements of trace components in natural waters using thin-
20 film gels. Nature 367: 546-548.
21 Davison, W.; Zhang, H.; Grime, G. W. (1994) Performance characteristics of gel probes used for measuring pore
22 waters. Environ. Sci. Technol. 28: 1623-1632.
23 De Vries, W.; Bakker, D. J.; Groenenberg, J. E.; Reinds, G. J.; Bril, J.; Van Jaarsveld, J. A. (1998) Calculation and
24 mapping of critical loads for heavy metals and persistent organic pollutants for Dutch forest soils. J.
25 Hazard. Mat. 61:99-106.
26 De Vries, W.; Schtitze, G.; Romkens, P.; Hettelingh, J.-P. (2001) Guidance for the calculation of critical loads for
27 cadmium and lead in terrestrial and aquatic ecosystems. In: Hettelingh, J.-P.; Slootweg, J.; Posch, M.;
28 Dutchak, S.; Ilyin, I., eds. Preliminary modelling and mapping of critical loads for cadmium and lead in
29 Europe; RIVM report no. 259101011. Bilthoven, The Netherlands: National Institute of Public Health and
30 the Environment; pp. 17-36.
31 De Vries, W.; Schtitze, G.; Lots, S.; Meili, M.; Romkens, P.; Terytze, K.; Scholz, K.; Farret, R.; Jakubowski, M.
32 (2002a) Critical limits for cadmium, lead and mercury related to ecotoxicological effects on soil organisms,
33 aquatic organisms, plants, animals and humans: background document for the Expert meeting on critical
34 limits for heavy metals and methods for their application. In: Proceedings of the expert meeting on critical
3 5 limits for heavy metals and methods for their application; December; Berlin. Geneva, Switzerland: United
3 6 Nations Economic Commission for Europe (UN-ECE) Convention on long range transboundary air
37 pollution. Available: http://www.oekodata.com/pub/mapping/workshops/ws_berlin/proceedings.pdf
38 [19 October, 2005].
39 De Vries, W.; Schtitze, G.; Romkens, P.; Hettelingh, J. P. (2002b) Guidance for the calculation of critical loads for
40 cadmium and lead in terrestrial and aquatic ecosystems. In: Hettelingh, J. P.; Slootweg, J.; Posch, M.;
41 Dutchak, S.; Ilyin, I., eds. Preliminary modelling and mapping of critical loads for cadmium and lead in
42 Europe. Bilthoven, The Netherlands: National Institute of Public Health and the Environment: RIVM
43 reportno. 259101011, pp. 17-36.
44 De Vries, W.; Schtitze, G.; Lofts, S.; Tipping, E.; Meili, M.; Romkens, P. F. A. M.; Groenenberg, J. E. (2004)
45 Calculation of critical loads for cadmium, lead and mercury: background document to a mapping manual
46 on critical loads of cadmium, lead and mercury. Wageningen, The Netherlands: Alterra report no. 1104.
47 Available: http://www.oekodata.com/pub/mapping/manual/reportl 104.pdf [22 June, 2005].
48 Deacon, J. R.; Spahr, N. E.; Mize, S. V.; Boulger, R. W. (2001) Using water, bryophytes, and macroinvertebrates to
49 assess trace element concentrations in the Upper Colorado River basin. Hydrobiologia 455: 29-39.
50 Dearth, R. K.; Hiney, J. K.; Srivastava, V.; Les Dees, W.; Bratton, G. R. (2004) Low level lead (Pb) exposure during
51 gestation and lactation: assessment of effects on pubertal development in Fisher 344 and Sprague-Dawley
52 female rats. Life Sci. 74: 1139-1148.
53 Deng, H.; Ye, Z. H.; Wong, M. H. (2004) Accumulation of lead, zinc, copper and cadmium by 12 wetland species
54 thriving in metal-contaminated sites in China. Environ. Pollut. 132: 29-40.
55 Dixon, R. K. (1988) Response of ectomycorrhizal Quercus rubra to soil cadmium, nickel and lead. Soil Biol.
56 Biochem. 20: 555-559.
May 2006 8-44 DRAFT-DO NOT QUOTE OR CITE
-------
1 Dorr, H. (1995) Application of 210Pb in Soils. J. Paleolimnol. 13: 157-168.
2 Dorr, H.; Munnich, K. O. (1989) Downward movement of soil organic-matter and its influence on trace-element
3 transport (210Pb, 137Cs) in the soil. Radiocarbon 31: 655-663.
4 Douben, P. E. T. (1989) Lead and cadmium in stone loach (Noemacheilus barbatulus L.) from three rivers in
5 Derbyshire. Ecotoxicol. Environ. Saf. 18: 35-58.
6 Douglas-Stroebel, E. K.; Brewer, G. L.; Hoffman, D. J. (2005) Effects of lead-contaminated sediment and nutrition
7 on mallard duckling behavior and growth. J. Toxicol. Environ. Health Part A 68: 113-128.
8 Doyle, P. J.; Gutzman, D. W.; Sheppard, M. L; Sheppard, S. C.; Bird, G. A.; Hrebenyk, D. (2003) An ecological risk
9 assessment of air emissions of trace metals from copper and zinc production facilities. Hum. Ecol. Risk
10 Assess. 9: 607-636.
11 Duan, Y.; Guttman, S.; Oris, J.; Bailer, J. (2000) Genotype and toxicity relationships among Hyalella azteca: I.
12 acute exposure to metals or low pH. Environ. Toxicol. Chem. 19: 1414-1421.
13 Egli, M.; Fitze, P.; Oswald, M. (1999) Changes in heavy metal contents in an acidic forest soil affected by depletion
14 of soil organic matter within the time span 1969-93. Environ. Pollut. 105: 367-379.
15 Eisenreich, S. J.; Metzer, N. A.; Urban, N. R.; Robbins, J. A. (1986) Response of atmospheric lead to decreased use
16 of lead in gasoline. Environ. Sci. Technol. 20: 171-174.
17 Eisler, R. (1988) Lead hazards to fish, wildlife, and invertebrates: a synoptic review. Washington, DC: U.S.
18 Department of the Interior, Fish and Wildlife Service; biological report 85(1.14); contaminant hazard
19 reviews report no. 14.
20 Eisler, R. (2000) Handbook of chemical risk assessment: health hazards to humans, plants, and animals.
21 Volume 1: metals. Boca Raton, FL: Lewis Publishers.
22 Ekenler, M.; Tabatabai, M. (2002) Effects of trace metals on p-glucosaminidase activity in soils. Soil Biol.
23 Biochem. 34: 1829-1832.
24 Emmanuel, S.; Erel, Y. (2002) Implications from concentrations and isotopic data for Pb partitioning processes in
25 soils. Geochim. Cosmochim. Acta66: 2517-2527.
26 Environment Canada. (2003) What is acid rain? Available: http://www.on.ec.gc.ca/wildlife/acidrain/arl-e.html
27 [19 October, 2005].
28 Erel, Y.; Patterson, C. C. (1994) Leakage of industrial lead into the hydrocycle. Geochim. Cosmochim. Acta 58:
29 3289-3296.
30 Erel, Y.; Veron, A.; Halicz, L. (1997) Tracing the transport of anthropogenic lead in the atmosphere and in soils
31 using isotopic ratios. Geochim. Cosmochim. Acta 61: 4495-4505.
32 Evans, G. C.; Norton, S. A.; Fernandez, I. J.; Kahl, J. S.; Hanson, D. (2005) Changes in concentrations of major
33 elements and trace metals in northeastern U.S.-Canadian sub-alpine forest floors. Water Air Soil Pollut.
34 163:245-267
35 Farfel, M. R.; Orlova, A. O.; Chaney, R. L.; Lees, P. S. J.; Rohde, C.; Ashley, P. J. (2005) Biosolids compost
3 6 amendment for reducing soil lead hazards: a pilot study of Orgro® amendment and grass seeding in urban
37 yards. Sci. Total Environ. 340: 81-95.
38 Farkas, A.; Salanki, J.; Specziar, A. (2003) Age- and size-specific patterns of heavy metals in the organs of
39 freshwater fishAbramis brama L. populating a low-contaminated site. Water Res. 37: 959-964.
40 Fernandez-Leborans, G.; Antonio-Garcia, M. T. (1988) Effects of lead and cadmium in a community of protozoans.
41 ActaProtozool. 27: 141-159.
42 Fernandez-Leborans, G.; Novillo, A. (1992) Hazard evaluation of lead effects using marine protozoan communities.
43 Aquat. Sci. 54: 128-140.
44 Fernandez-Leborans, G.; Novillo, A. (1994) Effects of periodic addition of lead on a marine protistan community.
45 Aquat. Sci. 56: 191-205.
46 Fernando, Q. (1995) Metal speciation in environmental and biological systems. Environ. Health Perspect. Suppl.
47 103(1): 13-16.
48 Fitzhugh, R. D.; Driscoll, C. T.; Groffman, P. M.; Tierney, G. L.; Fahey, T. J.; Hardy, J. P. (2001) Effects of soil
49 freezing disturbance on soil solution nitrogen, phosphorus, and carbon chemistry in a northern hardwood
50 ecosystem. Biogeochemistry 56: 215-238.
51 Flegal, A. R; Rosman, K. J. R.; Stephenson, M. D. (1987) Isotope systematics of contaminant leads in Monterey
52 Bay. Environ. Sci. Technol. 21: 1075-1079.
53 Flegal, A. R.; Nriagu, J. O.; Niemeyer, S.; Coale, K. H. (1989) Isotopic tracers of lead contamination in the Great
54 Lakes. Nature (London) 339: 455-458.
55 Francek, M. A. (1992) Soil lead levels in a small town environment: a case study from Mt. Pleasant, Michigan.
56 Environ. Pollut. 76:251-257.
May 2006 8-45 DRAFT-DO NOT QUOTE OR CITE
-------
1 Francek, M. A. (1997) Soil lead levels in orchards and roadsides of Mission Peninsula, Michigan. Water Air Soil
2 Pollut. 94: 373-384.
3 Friedland, A. I; Craig, B. W.; Miller, E. K.; Herrick, G. T.; Siccama, T. G.; Johnson, A. H. (1992) Decreasing lead
4 levels in the forest floor of the northeastern USA. Ambio 21: 400-403.
5 Friedland, A. I; Johnson, A. H.; Siccama, T. G. (1984) Trace metal content of the forest floor in the Green
6 mountains of Vermont: spatial and temporal patterns. Water Air Soil Pollut. 21: 161-170.
7 Fuller, R. D.; Simone, D. M.; Driscoll, C. T. (1988) Forest clearcutting effects on trace metal concentrations: spatial
8 patterns in soil solutions and streams. Water Air Soil Pollut. 40: 185-195.
9 Galbraith, H.; LeJeune, K.; Lipton, J. (1995) Metal and arsenic impacts to soils, vegetation communities and
10 wildlife habitat in southwest Montana uplands contaminated by smelter emissions: I. Field evaluation.
11 Environ. Toxicol. Chem. 14: 1895-1903.
12 Gao, Y.; Kan, A. T.; Tomson, M. B. (2003) Critical evaluation of desorption phenomena of heavy metals from
13 natural sediments. Environ. Sci. Technol. 37: 5566-5573.
14 Garcia, T. A.; Corredor, L. (2004) Biochemical changes in the kidneys after perinatal intoxication with lead and/or
15 cadmium and their antagonistic effects when coadministered. Ecotoxicol. Environ. Saf. 57: 184-189.
16 Gaur, J. P.; Noraho, N.; Chauhan, Y. S. (1994) Relationship between heavy metal accumulation and toxicity in
17 Spirodelapolyrhiza (L.) Schleid. andAzollapinnata R. Br. Aquat. Bot. 49: 183-192.
18 Gill, T. S.; Tewari, H.; Pande, J. (1991) Effects of water-borne copper and lead on the peripheral bloodin the rosy
19 barb, Barbus (Puntius) conchonius Hamilton. Bull. Environ. Contam. Toxicol. 46: 606-612.
20 Gopal, V.; Parvathy, S.; Balasubramanian, P. R. (1997) Effect of heavy metals on the blood protein biochemistry of
21 the fish Cyprinus carpio and its use as a bio-indicator of pollution stress. Environ. Monit. Assess.
22 48: 117-124.
23 Groenenberg, B. J.; Romkens, P.; Tipping, E.; Pampura, T.; Vries, W. D.; Schuetze, G. (2002) Transfer functions
24 for the calculation of critical loads for lead, cadmium and mercury: background document for the expert
25 meeting on critical limits for heavy metals and methods for their application; December; Berlin, Germany.
26 [draft]. Geneva, Switzerland: United Nations Economic Commission for Europe (UNECE) convention on
27 long range transboundary air pollution.
28 Gundersen, J. K.; Jorgensen, E. L.; Larsen, E.; Jannasch, H. W. (1992) Mats of giant sulfur bacteria on deep-sea
29 sediments due to fluctuating hydrothermal flow. Nature 360: 454-456.
30 Gupta, M.; Chandra, P. (1994) Lead accumulation and toxicity in Vallisneria spiralis (L.) and Hydrilla verticillata
31 (l.f.) Royle. J. Environ. Sci. Health Part A 29: 503-516.
32 Gustafsson, J. P.; Pechova, P.; Berggren, D. (2003) Modeling metal binding to soils: the role of natural organic
33 matter. Environ. Sci. Technol. 37: 2767-2774.
34 Haering, K. C.; Daniels, W. L.; Feagly, S. E. (2000) Reclaiming mined lands withbiosolids, manures, and papermill
35 sludges. In: Barnhisel, R. L; Darmody, R. G.; Daniels, W. L., eds. Reclamation of drastically disturbed
36 lands. Madison, WI: Soil Science Society of America; pp. 615-644. [Agronomy Monograph no. 41].
37 Hagopian-Schlekat, T.; Chandler, G. T.; Shaw, T. J. (2001) Acute toxicity of five sediment-associated metals,
3 8 individually and in a mixture, to the estuarine meiobenthic harpacticoid copepodAmphiascus tenuiremis.
3 9 Mar. Environ. Res. 51: 247-264.
40 Hassler, C. S.; Slaveykova, V. L; Wilkinson, K. J. (2004) Some fundamental (and often overlooked) considerations
41 underlying the free ion activity and biotic ligand models. Environ. Toxicol. Chem. 23: 283-291.
42 He, P. P.; Lv, X. Z.; Wang, G. Y. (2004) Effects of Se and Zn supplementation on the antagonism against Pb and
43 Cd in vegetables. Environ. Int. 30: 167-172.
44 Henny, C. J.; Blus, L. J.; Hoffman, D. J.; Grove, R. A.; Hatfield, J. S. (1991) Lead accumulation and osprey
45 production near a mining site on the Coeur d'Alene River, Idaho. Arch. Environ. Contam. Toxicol.
46 21:415-424.
47 Hettelingh, J.-P.; Downing, R. J.; De Smet, P.A.M. (1991) Mapping critical loads for Europe: CCE technical report
48 no. 1. Bilthoven, The Netherlands: National Institute of Public Health and Environmental Protection;
49 Coordination Center for Effects; RIVM report no. 259101001.
50 Hettelingh, J.-P.; Slootweg, J.; Posch, M., eds. (2002) Preliminary modelling and mapping of critical loads for
51 cadmium and lead in Europe. Bilthoven, The Netherlands: National Institute of Public Health and the
52 Environment; RIVM report no. 259101011.
53 Hettiarachchi, G. M.; Pierzynski, G. M.; Oehne, F. W.; Sonmez, O.; Ryan, J. A. (2001) In situ stabilization of soil
54 lead using phosphorus. J. Environ. Qual. 30: 1214-1221.
May 2006 8-46 DRAFT-DO NOT QUOTE OR CITE
-------
1 Hettiarachchi, G. M; Pierzynski, G. M; Oehne, F. W.; Sonmez, 0.; Ryan, J. A. (2003) Treatment of contaminated
2 soil with phosphorus and manganese oxide reduces lead absorption by Sprague-Dawley rats. J. Environ.
3 Qual. 32: 1335-1345.
4 Ho, M. D.; Evans, G. J. (2000) Sequential extraction of metal contaminated soils with radiochemical assessment of
5 readsorption effects. Environ. Sci. Technol. 34: 1030-1035.
6 Hoffman, D. J.; Heinz, G. H.; Sileo, L.; Audet, D. J.; Campbell, J. K.; LeCaptain, L. J. (2000a) Developmental
7 toxicity of lead-contaminated sediment to mallard ducklings. Arch. Environ. Contam. Toxicol. 39: 221-232.
8 Hoffman, D. J.; Heinz, G. H.; Sileo, L.; Audet, D. J.; Campbell, J. K.; LeCaptain, L. J.; Obrecht, H. H., III. (2000b)
9 Developmental toxicity of lead-contaminated sediment in Canada geese (Branta Canadensis). J. Toxicol.
10 Environ. Health A 59: 235-252.
11 Hopkin, S. P. (1989) Ecophysiology of metals in terrestrial invertebrates. London, United Kingdom: Elsevier
12 Applied Science. (Pollution Monitoring series).
13 Home, M. T.; Dunson, W. A. (1995a) Toxicity of metals and low pH to embryos and larvae of the Jefferson
14 salamander, Ambystomajeffersonianum. Arch. Environ. Contam. Toxicol. 29: 110-114.
15 Home, M. T.; Dunson, W. A. (1995b) The interactive effects of low pH, toxic metals, and DOC on a simulated
16 temporary pond community. Environ. Pollut. 89: 155-161.
17 Home, M. T.; Dunson, W. A. (1995c) Effects of low pH, metals, and water hardness on larval amphibians. Arch.
18 Environ. Contam. Toxicol. 29: 500-505.
19 Humphreys, D. J. (1991) Effects of exposure to excessive quantities of lead on animals. Br. Vet. J. 147: 18-30.
20 Impellitteri, C. (2005) Effects of pH and phosphate on metal distribution with emphasis on As speciation and
21 mobilization in soils from a lead smelting site. Sci. Total Environ. 345: 175-190.
22 Ingersoll, C. G.; Haverland, P. S.; Branson, E. L.; Canfield, T. J.; Dwyer, F. J.; Henke, C. E.; Kemble, N. E.;
23 Mount, D. R.; Fox, R. G. (1996) Calculation and evaluation of sediment effect concentrations for the
24 amphipod (Hyalella azteca) and the midge (Chironomus riparius). J. Great Lakes Res. 22: 602-623.
25 Jackson, B. P.; Williams, P. L.; Lanzirott, A.; Bertsch, P. M. (2005) Evidence forbiogenic pyromorphite formation
26 by the nematode Caenorhabditis elegans. Environ. Sci. Technol. 39: 5620-5625.
27 Jampani, C. S. R. (1988) Lead toxicity to alga Synechococcus aeruginosus and its recovery by nutrients. J. Environ.
28 Biol. 9: 261-269.
29 Jayaraj, Y. M.; Mandakini, M.; Nimbargi, P. M. (1992) Effect of mercury and lead on primary productivity of two
30 water bodies. Environ. Ecol. 10: 653-658.
31 Jersak, J.; Amundson, R.; Brimhall, G., Jr. (1997) Trace metal geochemistry in spodosols of the northeastern United
3 2 States. J. Environ. Qual. 26: 511 -521.
33 Johnson, D.; Hale, B. (2004) White birch (Betulapapyri/era Marshall) foliar litter decomposition in relation to trace
34 metal atmospheric inputs at metal-contaminated and uncontaminated sites near Sudbury, Ontario and
35 Rouyn-Noranda, Quebec, Canada. Environ. Pollut. 127: 65-72.
36 Johnson, C. E.; Petras, R. J. (1998) Distribution of zinc and lead fractions within a forest spodosol. Soil Sci. Soc.
37 Am. J. 62: 782-789.
38 Johnson, C. E.; Siccama, T. G.; Driscoll, C. T.; Likens, G. E.; Moeller, R. E. (1995a) Changes in lead
39 biogeochemistry in response to decreasing atmospheric inputs. Ecol. Appl. 5: 813-822.
40 Johnson, C. E.; Driscoll, C. T.; Fahey, T. J.; Siccama, T. G.; Hughes, J. W. (1995b) Carbon dynamics following
41 clear-cutting of a northern hardwood forest. In: Kelly, J. M.; McFee, W. W., eds. Carbon forms and
42 function in forest soils. Madison, WI: Soil Science Society of America; pp. 463-488.
43 Johnson, C. E.; Petras, R. J.; April, R. H.; Siccama, T. G. (2004) Post-glacial lead dynamics in a forest soil.
44 Water Air Soil Pollut. 4: 579-590.
45 Jones, K. C.; Johnston, A. E. (1991) Significance of atmospheric inputs of lead to grassland at one site in the
46 United Kingdom since 1869. Environ. Sci. Technol. 25: 1174-1178.
47 Jordan, M. J. (1975) Effects of zinc smelter emissions and fire on a chestnut-oak woodland. Ecology 56: 78-91.
48 Kabata-Pendias, A.; Pendias, H. (1992) Trace elements in soils and plants. 2nd ed. Boca Raton, FL: CRC Press, Inc.
49 Kapustka, L. A.; Lipton, J.; Galbraith, H.; Cacela, D.; Lejeune, K. (1995) Metal and arsenic impacts to soils,
50 vegetation communities, and wildlife habitat in southwest Montana uplands contaminated by smelter
51 emissions: II. Laboratory phytotoxicity studies. Environ. Toxicol. Chem. 14: 1905-1912.
52 Kaste, J. M.; Friedland, A. J.; Miller, E. K. (2005) Potentially mobile lead fractions in montane organic-rich soil
53 horizons. Water Air Soil Pollut. 167: 139-154.
54 Kaste, J.; Friedland, A.; Stirrup, S. (2003) Using stable and radioactive isotopes to trace atmospherically deposited
55 Pb in montane forest soils. Environ. Sci. Technol. 37: 3560-3567.
May 2006 8-47 DRAFT-DO NOT QUOTE OR CITE
-------
1 Khan, D. H.; Frankland, B. (1983) Effects of cadmium and lead on radish plants with particular reference to
2 movement of metals through soil profile and plant. Plant Soil 70: 335-345.
3 Kim, S.-J.; Rodriguez-Lanetty, M; Suh, J.-H.; Song, J.-I. (2003) Emergent effects of heavy metal pollution at a
4 population level: Littorina brevicula a case study. Mar. Pollut. Bull. 46: 74-80.
5 Knowlton, M. F.; Boyle, T. P.; Jones, J. R. (1983) Uptake of lead from aquatic sediment by submersed macrophytes
6 and crayfish. Arch. Environ. Contam. Toxicol. 12: 535-541.
7 Kock, G.; Triendl, M.; Hofer, R. (1996) Seasonal patterns of metal accumulation in Arctic char (Salvelinus alpinus)
8 from an oligotrophic Alpine lake related to temperature. Can. J. Fish. Aquat. Sci. 53: 780-786.
9 Kraak, M. H. S.; Wink, Y. A.; Stuijfzand, S. C; Buckert-de Jong, M. C; de Groot, C. J.; Admiraal, W. (1994)
10 Chronic ecotoxicity of Zn and Pb to the zebra mussel Dreissenapolymorpha. Aquat. Toxicol. 30: 77-89.
11 Kriiger, F.; Grongroft; A. (2003) The difficult assessment of heavy metal contamination of soils and plants in Elbe
12 River floodplains. Acta Hydrochim. Hydrobiol. 31: 436-443.
13 Kuperman, R. G.; Carreiro, M. M. (1997) Soil heavy metal concentrations, microbial biomass and enzyme activities
14 in a contaminated grassland ecosystem. Soil Biol. Biochem. 29: 179-190.
15 Kutlu, M.; Susuz, F. (2004) The effects of lead as an environmental pollutant on EROD enzyme in Gammaruspulex
16 (L.) (Crustacea: Amphipoda). Bull. Environ. Contam. Toxicol. 72: 750-755.
17 Lamy, L; Bourgeois, S.; Bermond, A. (1993) Soil cadmium mobility as a consequence of sewage sludge disposal.
18 J. Environ. Qual. 22: 731-737.
19 Lang, F.; Kaupenjohann, M. (2003) Effect of dissolved organic matter on the precipitation and mobility of the lead
20 compound chloropyromorphite in solution. Eur. J. Soil Sci. 54: 139-147.
21 Laperche, V.; Traina, S. J.; Gaddam, P.; Logan, T. J. (1996) Chemical and mineralogical characterizations of Pb in a
22 contaminated soil: reactions with synthetic apatite. Environ. Sci. Technol. 30: 3321-3326.
23 Laskowski, R.; Maryafiski, M.; Nikliriska, M. (1994) Effect of heavy-metals and mineral nutrients on forest litter
24 respiration rate. Environ. Pollut. 84: 97-102.
25 Laskowski, R.; Maryafiski, M.; Nikliriska, M. (1995) Changes in the chemical composition of water percolating
26 through the soil profile in a moderately polluted catchment. Water Air Soil Pollut. 85: 1759-1764.
27 Lefcort, H.; Abbott, D. P.; Cleary, D. A.; Howell, E.; Kellar, N. C.; Smith, M. M. (2004) Aquatic snails from mining
28 sites have evolved to detect and avoid heavy metals. Arch. Environ. Contam. Toxicol. 46: 478-484.
29 Lefcort, H.; Ammann, E.; Eiger, S. M. (2000) Antipredatory behavior as an index of heavy-metal pollution? A test
30 using snails and caddisflies. Arch. Environ. Contamin. Toxicol. 38: 311-316.
31 Lenoble, V.; Laclautre, C.; Deluchat, V.; Serpaud, B.; Bellinger, J. C. (2005) Arsenic removal by adsorption on iron
32 (III) phosphate. J. Hazard. Mater. B 123: 262-268.
33 Li, W.-H.; Chan, P. C. Y.; Chan, K. M. (2004) Metal uptake in zebrafish embryo-larvae exposed to metal-
34 contaminated sediments. Mar. Environ. Res. 58: 829-832.
35 Liang, C. N.; Tabatabai, M. A. (1977) Effects of trace elements on nitrogen mineralisation in soils. Environ. Pollut.
36 12: 141-147.
37 Liang, C. N.; Tabatabai, M. A. (1978) Effects of trace elements on nitrification in soils. J. Environ. Qual. 7: 291-293.
38 Lin, Q.; Chen, Y. X.; He, Y. F.; Tian, G. M. (2004) Root-induced changes of lead availability in the rhizosphere of
39 Oryza sativa L. Agric. Ecosyst. Environ. 104: 605-613.
40 Little, P.; Martin, M. H. (1972) A survey of zinc, lead and cadmium in soil and natural vegetation around a smelting
41 complex. Environ. Pollut. 3: 241-254.
42 Lock, K.; Janssen, C. R. (2002) Multi-generation toxicity of zinc, cadmium, copper and lead to the potworm
43 Enchytraeus albidus. Environ. Pollut. 117: 89-92.
44 Lofts, S.; Spurgeon, D. J.; Svendsen, C.; Tipping, E. (2004) Deriving soil critical limits for Cu, Zn, Cd, and Pb:
45 a method based on free ion concentrations. Environ. Sci. Technol. 38: 3623-3631.
46 Long, D. T.; Angino, E. E. (1977) Chemical speciation of Cd, Cu, Pb, and Zn, in mixed freshwater, seawater, and
47 brine solutions. Geochim. Cosmochim. Acta. 41:1183-1191.
48 Long, E. R.; MacDonald, D. D.; Smith, S. L.; Calder, F. D. (1995) Incidence of adverse biological effects within
49 ranges of chemical concentrations in marine and estuarine sediments. Environ. Manage. 19: 81-97.
50 Ma, Q. Y.; Logan, T. J.; Traina, S. J. (1995) Lead immobilization from aqueous solutions and contaminated soils
51 using phosphate rocks. Environ. Sci. Technol. 29: 1118-1126.
52 MacDonald, D. D.; Ingersoll, C. G.; Berger, T. A. (2000) Development and evaluation of consensus-based sediment
53 quality guidelines for freshwater ecosystems. Arch. Environ. Contam. Toxicol. 39: 20-31.
54 MacDonald, A.; Silk, L.; Schwartz, M.; Playle, R. C. (2002) A lead-gill binding model to predict acute lead toxicity
55 to rainbow trout (Oncorhynchus mykiss). Comp. Biochem. Physiol. Part C: Toxicol. Pharmacol.
56 133C: 227-242.
May 2006 8-48 DRAFT-DO NOT QUOTE OR CITE
-------
1 MacLean, R. S.; Borgmann, U.; Dixon, D. G. (1996) Bioaccumulation kinetics and toxicity of lead mHyalella
2 azteca (Crustacea, Amphipoda). Can. J. Fish. Aquat. Sci. 53: 2212-2220.
3 Malcova, R.; Gryndler, M. (2003) Amelioration of Pb and Mn toxicity to arbuscular mycorrhizal fungus Glomus
4 intraradices\yy maize root exudates. Biol. Plant. 47: 297-299.
5 Manceau, A.; Boisset, M.; Sarret, G.; Hazemann, J.; Mench, M.; Cambier, P.; Prost, R. (1996) Direct determination
6 of lead speciation in contaminated soils by EXAFS spectroscopy. Environ. Sci. Technol. 30: 1540-1552.
7 Maret, T. R.; Cain, D. J.; MacCoy, D. E.; Short, T. M. (2003) Response of benthic invertebrate assemblages to metal
8 exposure and bioaccumulation associated with hard-rock mining in northwestern streams, USA. J. N. Am.
9 Benthol. Soc. 22: 598-620.
10 Marsh, A. S.; Siccama, T. G. (1997) Use of formerly plowed land in New England to monitor the vertical distribution
11 of lead, zinc and copper in mineral soil. Water Air Soil Pollut. 95: 75-85.
12 Martin, M. H.; Bullock, R. J. (1994) The impact and fate of heavy metals in an oak woodland ecosystem. In: Ross,
13 S. M., ed. Toxic metals in soil-plant systems. Chichester, England: John Wiley & Sons; pp. 327-365.
14 Mateo, R.; Hoffman, D. J. (2001) Differences in oxidative stress between young Canada geese and mallards exposed
15 to lead-contaminated sediment. J. Toxicol. Environ. Health Part A 64: 531-545.
16 Mateo, R.; Beyer, W. N.; Spann, J. W.; Hoffman, D. J. (2003a) Relation of fatty acid composition in lead-exposed
17 mallards to fat mobilization, lipid peroxidation and alkaline phosphatase activity. Comp. Biochem. Physiol.
18 C Pharmacol. Toxicol. 135: 451-458.
19 Mateo, R.; Beyer, W. N.; Spann, J. W.; Hoffman, D. J.; Ramis, A. (2003b) Relationship between oxidative
20 stress, pathology, and behavioral signs of lead poisoning in mallards. J. Toxicol. Environ. Health A
21 66: 1371-1389..
22 McBride, M. B.; Richards, B. K.; Steenhuis, T.; Russo, J. J.; Suave, S. (1997) Mobility and solubility of toxic metals
23 and nutrients in soil fifteen years after sludge application. Soil Sci. 162: 487-500.
24 McBride, M. B.; Richards, B. K.; Steenhuis, T.; Spiers, G. (1999) Long-term leaching of trace elements in a heavily
25 sludge-amended silty clay loam soil. Soil Sci. 164: 613-623.
26 Meyer, J. S.; Adams, W. J.; Brix, K. V.; Luoma, S. N.; Mount, D. R.; Stubblefield, W. A.; Wood, C. M. (2005)
27 Toxicity of dietborne metals to aquatic organisms. Pensacola, FL: Society of Environmental Toxicology
28 and Chemistry.
29 Miller, E. K.; Friedland, A. J. (1994) Lead migration in forest soils: response to changing atmospheric inputs.
30 Environ. Sci. Technol. 28: 662-669.
31 Miller, W. P.; McFee, W. W. (1983) Distribution of cadmium, zinc, copper, and lead in soils of industrial
32 northwestern Indiana. J. Environ. Qual. 12: 29-33.
33 Miranda, M. G.; Ilangovan, K. (1996) Uptake ofleadbyLemnagibbaL.: influence on specific growth rate and
34 basic biochemical changes. Bull. Environ. Contam. Toxicol. 56: 1000-1007.
35 Mitchell, M. J.; Driscoll, C. T.; Kahl, J. S.; Likens, G. E.; Murdoch, P. S.; Pardo, L. H. (1996) Climatic control of
36 nitrate loss from forested watersheds in the northeast United States. Environ. Sci. Technol. 30: 2609-2612.
37 Mize, S. V.; Deacon, 1. R. (2002) Relations of benthic macroinvertebrates to concentrations of trace elements in
3 8 water, streambed sediments, and transplanted bryophytes and stream habitat conditions in nonmining and
39 mining areas of the Upper Colorado River Basin, Colorado, 1995-98. Denver, CO: U.S. Geological Survey;
40 Water-Resources Investigations Report 02-4139. Available:
41 http://pubs.usgs.gov/wri/wri024139/pdfAVRI02-4139.pdf [24 October, 2005].
42 Morelli, E.; Scarano, G. (2001) Synthesis and stability of phytochelatins induced by cadmium and lead in the marine
43 diatomPhaeodactylum tricornutum. Mar. Environ. Res. 52: 383-395.
44 Morgan, J. E.; Morgan, A. J. (1988) Earthworms as biological monitors of cadmium, copper, lead and zinc in
45 metalliferous soils. Environ. Pollut. 54: 123-138.
46 Mucha, A. P.; Vasconcelos M. T. S. D.; Bordalo A. A. (2003) Macrobenthic community in the Douro estuary:
47 relations with trace metals and natural sediment characteristics. Environ. Pollut. 121: 169-180.
48 Murray, K. S.; Rogers, D. T.; Kaufman, M. M. (2004) Heavy metals in an urban watershed in southeastern
49 Michigan. J. Environ. Qual. 33: 163-172.
50 National Research Council, Committee on Bioavailability of Contaminants in Soils and Sediments. (2002)
51 Bioavailability of contaminants in soil and sediments: processes, tools and applications. Washington, DC:
52 National Academies Press.
53 Newhook, R.; Hirtle, H.; Byrne, K.; Meek, M.E. (2003) Releases from copper smelters and refineries and zinc plants
54 in Canada: human health exposure and risk characterization. Sci. Total Environ. 301: 23-41.
55 Niklinska, M.; Laskowski, R.; Maryariski, M. (1998) Effect of heavy metals and storage time on two types of forest
56 litter: basal respiration rate and exchangeable metals. Ecotoxicol. Environ. Saf. 41: 8-18.
May 2006 8-49 DRAFT-DO NOT QUOTE OR CITE
-------
1 Niyogi, S.; Wood, C. M. (2004) Biotic ligand model, a flexible tool for developing site-specific water quality
2 guidelines for metals. Environ. Sci. Technol. 38: 6177-6192.
3 Norwood, W. P.; Borgmann, U.; Dixon, D. G.; Wallace, A. (2003) Effects of metal mixtures on aquatic biota: a
4 review of observations and methods. Hum. Ecol. Risk Assess. 9: 795-811.
5 Nriagu, J. O. (1974) Lead orthophosphates—IV. Formation and stability in environment. Geochim. Cosmochim.
6 Acta 38: 887-898.
7 Nriagu, J. O.; Lawson, G.; Wong, H. K. T.; Cheam, V. (1996) Dissolved trace metals in lakes Superior, Erie, and
8 Ontario. Environ. Sci. Technol. 30: 178-187.
9 Olson, K. W.; Skogerboe, R. K. (1975) Identification of soil lead compounds from automotive sources. Environ.
10 Sci. Technol. 9: 227-230.
11 Ownby, D. R.; Galvan, K. A.; Lydy, M. J. (2005) Lead and zinc bioavailability to Eisniafetida after phosphorus
12 amendment to repository soils. Environ. Pollut. 136: 315-321.
13 Paces, T. (1998) Critical loads of trace metals in soils: a method of calculation. Water Air Soil Pollut. 105: 451-458.
14 Palmborg, C.; Bringmark, L.; Bringmark, E.; Nordgren, A. (1998) Multivariate analysis of microbial activity and soil
15 organic matter at a forest site subjected to low-level heavy metal contamination. Ambio 27: 53-57.
16 Perottoni, J.; Meotti, F.; Folmer, V.; Pivetta, L.; Nogueira, C. W.; Zeni, G.; Rocha, J. B. (2005) Ebselen and
17 diphenyl diselenide do not change the inhibitory effect of lead acetate on delta-aminolevulinate
18 dehidratase. Environ. Toxicol. Pharmacol. 19: 239-248.
19 Phillips, C.; Gyori, Z.; Kovacs, B. (2003) The effect of adding cadmium and lead alone or in combination to the
20 diet of pigs on their growth, carcase composition and reproduction. J. Sci. Food Agric. 83: 1357-1365.
21 Pizl, V.; Josens, G. (1995) Earthworm communities along a gradient of urbanization. Environ. Pollut. 90: 7-14.
22 Polissar, A. V.; Hopke, P. K.; Poirot, R. L. (2001) Atmospheric aerosol over Vermont: chemical composition and
23 sources. Environ. Sci. Technol. 35: 4604-4621.
24 Poulton, B. C.; Monda, D. P.; Woodward, D. F.; Wildhaber, M. L.; Brumbaugh, W. G. (1995) Relations between
25 benthic community structure and metals concentrations in aquatic macroinvertebrates: Clark Fork River,
26 Montana. J. Freshwater Ecol. 10: 277-293.
27 Probst, A.; Moncoulon, D.; Godderis, Y.; Hernandez, L.; Party, J.-P. (2003) Critical loads for lead in France: first
28 results on forest soils. J. Phys. IV 107: 1111-1114.
29 Rademacher, D. J.; Weber, D. N.; Hillard, C. J. (2005) Waterborne lead exposure affects brain endocannabinoid
30 content in male but not female fathead minnows (Pimephalespromelas). Neurotoxicology 26: 9-15.
31 Rai, L. C.; Raizada, M. (1989) Effect of bimetallic combinations of Ni, Cr and Pb on growth, uptake of nitrate and
32 ammonia, 14CO2 fixation, and nitrogenase activity of Nostoc muscorum. Ecotoxicol. Environ. Saf. 17: 75-85.
33 Rainbow, P. S. (1996) Heavy metals in aquatic invertebrates. In: Beyer, W. N.; Heinz, G. H.; Redmon-Norwood,
34 A. W., eds. Environmental contaminants in wildlife: interpreting tissue concentrations. Boca Raton, FL:
35 CRCPress;pp. 405-425. [SET AC Foundation for Environmental Education series].
36 Rao, J. C. S.; Reddy, T. R. K. (1985) Response of Scenedesmus incrassatulus to lead toxicity in presence of
37 nutrients. J. Biol. Res. 1: 51-56.
38 Redig, P. T.; Lawler, E. M.; Schwartz, S.; Dunnette, J. L.; Stephenson, B.; Duke, G. E. (1991) Effects of chronic
39 exposure to sublethal concentrations of lead acetate on herne synthesis and immune function in red-tailed
40 hawks. Arch. Environ. Contam. Toxicol. 21: 72-77.
41 Reinds, G. J.; Vries, W.D.; Groenenberg, J. E. (2002) Annex 2: updated assessment of critical loads of lead and
42 cadmium for European forest soils. In: Hettelingh, J. P.; Slootweg, J.; Posch, M.; Dutchak, S.; Ilyin, I., eds.
43 Preliminary modelling and mapping of critical loads for cadmium and lead in Europe; RIVM report no.
44 259101011. Bilthoven, The Netherlands: National Institute of Public Health and the Environment;
45 pp. 123-127.
46 Rhea, D. T.; Harper, D. D.; Brumbaugh, W. G.; Farag, A. M. (2004) Biomonitoring in the Boulder River Watershed,
47 Montana: metal concentrations in biofilm and macroinvertebrates, and relations with macroinvertebrate
48 assemblage. Reston, VA: U.S. Geological Survey; report no. USGS-CERC-91340.
49 Richards, B. K.; Steenhuis, T. S.; Peverly, J. H.; McBride, M. B. (1998) Metal mobility at an old, heavily loaded
50 sludge application site. Environ. Pollut. 99: 365-377.
51 Richards, B. K.; Steenhuis, T. S.; Peverly, J. H.; McBride, M. B. (2000) Effect of sludge-processing mode, soil
52 texture, and pH on metal mobility in undisturbed soil columns under accelerated loading. Environ. Pollut.
53 109:327-346.
54 Ritson, P. I.; Bouse, R. M.; Flegal, A. R.; Luoma, S. N. (1999) Stable lead isotopic analyses of historic and
55 contemporary lead contamination of San Francisco Bay estuary. Marine Chem. 64: 71-83.
May 2006 8-50 DRAFT-DO NOT QUOTE OR CITE
-------
1 Rogers, J. T.; Wood, J. G. (2003) lonoregulatory disruption as the acute toxic mechanism for lead in the rainbow
2 trout (Oncorhynchus mykiss). Aquat. Toxicol. 64: 215-234.
3 Rogers, J. T.; Wood, C. M. (2004) Characterization of branchial lead-calcium interaction in the freshwater rainbow
4 trout (Oncorhynchus mykiss). J. Exp. Biol. 207: 813-825.
5 Ruby, M. V.; Davis, A.; Nicholson, A. (1994) In situ formation of lead phosphates in soils as a method to immobilize
6 lead. Environ. Sci. Technol. 28: 646-654.
7 Rusek, J.; Marshall, V. G. (2000) Impact of airborne pollutants on soil fauna. Annu. Rev. Ecol. System. 31: 395-423.
8 Ryan, J. A.; Zhang, P.; Hesterberg, D.; Chou, J.; Sayers, D. E. (2001) Formation of chloropyromorphite in
9 lead-contaminated soil amended with hydroxyapatite. Environ. Sci. Technol. 35: 3798-3803.
10 Ryan, P. C.; Wall, A. J.; Hillier, S.; Clark, L. (2002) Insights into sequential chemical extraction procedures from
11 quantitative XRD: a study of trace metal partitioning in sediments related to frog malformities. Chem.
12 Geol. 184: 337-357.
13 Sample, B. E.; Beauchamp, J. J.; Efroymson, R. A.; Suter, G. W., II; Ashwood, T. L. (1998) Development and
14 validation of bioaccumulation models for earthworms. Oak Ridge, TN: Oak Ridge National Laboratory;
15 ES/ER/TM-220.
16 Sauve, S.; McBride, M.; Hendershot, W. (1997) Speciation of lead in contaminated soils. Environ. Pollut.
17 98: 149-155.
18 Sauve, S.; McBride, M.; Hendershot, W. (1998) Soil solution speciation of lead(II): effects of organic matter and
19 pH. Soil Sci. Soci. Am. J. 62: 618-621.
20 Sauve, S.; Martinez, C. E.; McBride, M.; Hendershot, W. (2000a) Adsorption of free lead (Pb2+) by pedogenic
21 oxides, ferrihydrite, and leaf compost. Soil Sci. Soc. Am. J. 64: 595-599.
22 Sauve, S.; Hendershot, W.; Allen, H. E. (2000b) Solid-solution partitioning of metals in contaminated soils:
23 dependence on pH, total metal burden, and organic matter. Environ. Sci. Technol. 34: 1125-1131.
24 Sauve, S.; Manna, S.; Turmel, M. C.; Roy, A. G.; Courchesne, F. (2003) Solid—solution partitioning of Cd, Cu,
25 Ni, Pb, and Zn in the organic horizons of a forest soil. Environ. Sci. Technol. 37: 5191-5196.
26 Saviozzi, A.; Levi-Minzi, R.; Cardelli, R.; Riffaldi, R. (1997) The influence of heavy metals on carbon dioxide
27 evolution from a typic xerochrept soil. Water Air Soil Pollut. 93: 409-417.
28 Sayer, M. D. J.; Reader, J. P.; Morris, R. (1989) The effect of calcium concentration on the toxicity of copper, lead
29 and zinc to yolk-sac fry of brown trout, Salmo trutta L., in soft, acid water. J. Fish Biol. 35: 323-332.
30 Schaule, B. K.; Patterson, C. C. (1981) Lead concentrations in the northeast Pacific: evidence for global
31 anthropogenic perturbations. Earth Planet. Sci. Lett. 54: 97-118.
32 Scheuhammer, A. M. (1987) The chronic toxicity of aluminum, cadmium, mercury and lead in birds: a review.
33 Environ. Pollut. 46: 263-295.
34 Scheuhammer, A. M. (1989) Monitoring wild bird populations for lead exposure. J. Wildl. Manage. 53: 759-765.
3 5 Scheuhammer, A. M. (1991) Effects of acidification on the availability of toxic metals and calcium to wild birds
36 and mammals. Environ. Pollut. 71: 329-375.
37 Schlick, E.; Mengel, K.; Friedberg, K. D. (1983) The effect of low lead doses in vitro and in vivo on the d-ala-d
38 activity of erythrocytes, bone marrow cells, liver and brain of the mouse. Arch. Toxicol. 53: 193-205.
39 Schwartz, M. L.; Curtis, P. J.; Playle, R. C. (2004) Influence of natural organic matter source on acute copper, lead,
40 and cadmium toxicity to rainbow trout (Oncorhynchus mykiss). Environ. Toxicol. Chem. 12: 2889-2899.
41 Scudlark, J. R.; Rice, K. C.; Conko, K. M.; Bricker, O. P.; Church, T. M. (2005) Transmission of atmospherically
42 derived trace elements through an undeveloped, forested Maryland watershed. Water Air Soil Pollut.
43 163:53-79.
44 Senwo, Z. N.; Tabatabai, M. A. (1999) Aspartase activity in soils: effects of trace elements and relationships to
45 other amidohydrolases. Soil Biol. Biochem. 31: 213-219.
46 Sharma, N.; Gardea-Torresday, J. L.; Parson, J.; Sahi, S. V. (2004) Chemical speciation and cellular deposition of
47 lead mSesbania drummondii. Environ. Toxicol. Chem. 23: 2068-2073.
48 Shugart, L. R. (1995) Environmental genotoxicology. In: Rand, G. M., ed. Fundamentals of aquatic toxicology:
49 effects, environmental fate and risk assessment. 2nd ed. Washington, DC: Taylor and Francis; pp. 405-419.
50 Sieghardt, H. (1990) Heavy-metal uptake and distribution in Silene vulgaris andMinuartia verna growing on
51 mining-dump material containing lead and zinc. Plant Soil 123: 107-111.
52 Skeffington, R. A. (1999) The use of critical loads in environmental policy making: a critical appraisal.
53 Environ.Sci. Technol. 33: 245A-252A.
54 Skjelkvale, B. L.; Andersen, T.; Fjeld, E.; Mannio, J.; Wilander, A.; Johansson, K.; Jensen, J. P.; Moiseenko, T.
55 (2001) Heavy metal surveys in Nordic lakes; concentrations, geographic patterns and relation to critical
56 limits. Ambio 30: 2-10.
May 2006 8-51 DRAFT-DO NOT QUOTE OR CITE
-------
1 Small, K. A.; Kazimi, C. (1995) On the costs of air pollution from mo tor vehicles. J. Transport Econ. Policy 29: 7-32.
2 Smith, E.; Naidu, R.; Alston, A. M. (2002) Chemistry of inorganic arsenic in soils. II. Effect of phosphorus,
3 sodium, and calcium on arsenic absorption. J. Environ. Qual. 31: 557-563.
4 Snoeijs, T.; Dauwe, T.; Pinxten, R.; Darras, V. M.; Arckens, L.; Eens, M. (2005) The combined effect of lead
5 exposure and high or low dietary calcium on health and immunocompetence in the zebra finch
6 (Taeniopygia guttata). Environ. Pollut. 134: 123-132.
7 Sopper, W. E. (1989) Revegetation of a contaminated zinc smelter site. Landscape Urban Plann. 17: 241-250.
8 Sopper, W. E. (1993) Municipal sludge use in land reclamation. Boca Raton, FL: Lewis Publishers.
9 Sposito, G.; Coves, J. (1988) SOILCHEM: A computer program for the calculation of chemical speciation in soils.
10 Berkeley, CA: University of California, Kerney Foundation of Soil Science.
11 Spurgeon, D. I; Hopkin, S. P. (1996) The effects of metal contamination on earthworm populations around a
12 smelting works: quantifying species effects. Appl. Soil Ecol. 4: 147-160.
13 Steele, C. W.; Strickler-Shaw, S.; Taylor, D. H. (1991) Failure ofBufo americanus tadpoles to avoid lead-enriched
14 water. J. Herpetol. 25:241-243.
15 Stephan, C. E.; Mount, D. I.; Hansen, D. J.; Gentile, J. H.; Chapman, G. A. (1985) Guidelines for deriving
16 numerical national water quality criteria for the protection of aquatic organisms and their uses.
17 Washington, D.C.: U.S. Environmental Protection Agency; report no. EPA/822-R85-100. Available from:
18 NTIS, Springfield, VA; PB85-227049.
19 Storm, G. L.; Fosmire, G. J.; Bellis, E. D. (1994) Persistence of metals in soil and selected vertebrates in the
20 vicinity of the Palmerton zinc smelters. J. Environ. Qual. 23: 508-514.
21 Stumm, W.; Morgan, J. J. (1995) Aquatic chemistry: chemical equilibria and rates in natural waters. 3rd ed.
22 New York, NY: Wiley Interscience. [Schnoor, J. L.; Zehnder, A., eds. Environmental science and
23 technology series].
24 Sulkowski, M.; Hirner, A. V. (2006) Element fractionation by sequential extraction in a soil with high carbonate
25 content. Appl. Geochem. 21: 16-28.
26 Svecevicius, G. (2001) Avoidance response of rainbow trout Oncorhynchus mykiss to heavy metal model mixtures:
27 a comparison with acute toxicity tests. Bull. Environ. Contam. Toxicol. 67: 680-687.
28 Swanson, K. A.; Johnson, A. H. (1980) Trace metal budgets for a forested watershed in the New Jersey Pine
29 Barrens. Water Resour. Res. 16: 373-376.
30 Syracuse Research Corporation (SRC). (1999) The environmental fate of lead and lead compounds. Washington,
31 DC: U.S. Environmental Protection Agency; contract no. SRC 68-D5-0012.
32 Szarek-Lukaszewska, G.; Slysz, A.; Wierzbicka, M. (2004) Response ofArmeria maritima (Mill.) Willd. to Cd,
33 Zn, and Pb. Acta Biol. Cracoviensia Ser. Bot. 46: 19-24.
34 Tejedor, M. C.; Gonzalez, M. (1992) Comparison between lead levels in blood and bone tissue of rock doves
3 5 (Columba livia) treated with lead acetate or exposed to the environment of Alcala-de-Henares. Bull.
36 Environ. Contam. Toxicol. 48: 835-842.
37 Templeton, A. S.; Spormann, A. M.; Brown, G. E. (2003a) Speciation of Pb(II) sorbed by Burkholderia
38 cepac/a/goethite composites. Environ. Sci. Technol. 37: 2166-2172.
39 Templeton, A. S.; Trainor, T. P.; Spormann, A. M.; Newville, M.; Sutton, S. R.; Dohnalkova, A.; Gorby, Y.;
40 Brown, G. E. (2003b) Sorption versus biomineralization of Pb(II) within Burkholderia cepacia biofilms.
41 Environ. Sci. Technol. 37: 300-307.
42 Terhivuo, J.; Pankakoski, E.; Hyvarinen, H.; Koivisto, I. (1994) Pb uptake by ecologically dissimilar earthworm
43 (Lumbricidae) species near a lead smelter in south Finland. Environ. Pollut. 85: 87-96.
44 Tessier, A.; Campbell, P. G. C. (1987) Partitioning of trace-metals in sediments: relationships withbioavailability.
45 Hydrobiologia 149: 43-52.
46 Tipping, E.; Woof, C. (1990) Humic substances in acid organic soils: modelling their release to the soil solution in
47 terms of humic charge. J. Soil Sci. 41: 573-586.
48 Tipping, E.; Rieuwerts, J.; Pan, G.; Ashmore, M. R.; Lofts, S.; Hill, M. T. R.; Farago, M. E.; Thornton, I. (2003)
49 The solid-solution partitioning of heavy metals (Cu, Zn, Cd, Pb) in upland soils of England and Wales.
50 Environ. Pollut. 125: 213-225.
51 Turner, R. S.; Johnson, A. H.; Wang, D. (1985) Biogeochemistry of lead in McDonalds Branch Watershed, New
52 Jersey Pine Barrens. J. Environ. Qual. 14: 305-314.
53 U.S. Environmental Protection Agency. (1979) Water-related environmental fate of 129 priority pollutants.
54 Volume I: Introduction and technical background, metals and inorganics, pesticides and PCBs. Washington,
55 DC: Office of Water Planning and Standards; report no. EPA-440/4-79-029a. Available from: NTIS,
56 Springfield, VA; PB80-204373.
May 2006 8-52 DRAFT-DO NOT QUOTE OR CITE
-------
1 U.S. Environmental Protection Agency. (1986) Air quality criteria for lead. Research Triangle Park, NC: Office of
2 Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no.
3 EPA-600/8-83/028aF-dF. 4v. Available from: NTIS, Springfield, VA; PB87-142378.
4 U.S. Environmental Protection Agency. (2003) Draft strategy: proposed revisions to the "Guidelines for deriving
5 numerical national water quality criteria for the protection of aquatic organisms and their uses" [Draft
6 copy]. Available: http://www.epa.gov/waterscience/criteria/aqlife.htmMguide [6 April, 2006].
7 U.S. Environmental Protection Agency. (2004) Air quality criteria for paniculate matter. Research Triangle Park,
8 NC: National Center for Environmental Assessment; report no. EPA/600/P-99/002aF-bF. 2v. Available:
9 http://cfpub.epa.gov/ncea/ [9 November, 2004].
10 U.S. Environmental Protection Agency. (2005a) Guidance for developing ecological soil screening levels (Eco-
11 SSLs). Washington, DC: Office of Solid Waste and Emergency Response, OSWER directive 9285.7-55,
12 November 2003 -revised February 2005. Available:
13 http://www.epa.gov/superfund/programs/risk/ecorisk/ecossl.pdfp9 September, 2005].
14 U.S. Environmental Protection Agency. (2005b) Ecological soil screening levels for lead. Interim final.
15 Washington, DC: Office of Solid Waste and Emergency Response, OSWER directive 9285.7-70.
16 U.S. Environmental Protection Agency. (2005c) Procedures for the derivation of equilibrium partitioning sediment
17 benchmarks (ESBs) for the protection of benthic organisms: metal mixtures (cadmium, copper, lead,
18 nickel, silver and zinc). Washington, DC: Office of Research and Development; EPA-600-R-02-011.
19 United Nations Economic Commission for Europe (UNECE). (1994) Protocol to the convention on long-range
20 transboundary air pollution on further reduction of sulphur emissions (1994 Sulphur Protocol). Geneva,
21 Switzerland: United Nations Economic Commission for Europe (UNECE). Available:
22 http://www.unece.Org/env/lrtap/full%20text/1994.Sulphur.e.pdf [31 October, 2005].
23 United Nations Economic Commission for Europe (UNECE). ( 2004) Convention on long-range transboundary air
24 pollution. Available: http://www.unece.org/env/lrtap/lrtap_hl.htm [19 October, 2005].
25 Utsunomiya, S.; Jensen, K. A.; Keeler, G. I; Ewing, R. C. (2004) Direct identification of trace metals in fine and
26 ultrafine particles in the Detroit urban atmosphere. Environ. Sci. Technol. 38: 2289-2297.
27 Van Den Hout, K. D.; Bakker, D. I; Berdowski, J. J. M; Van Jaarsveld, J. A.; Reinds, G. I; Bril, I;
28 Breeuwsma, A.; Groenenberg, J. E.; De Vries, W.; Van Pagee, J. A.; Villars, M.; Sliggers, C. J. (1999)
29 The impact of atmospheric deposition of non-acidifying substances on the quality of European forest soils
30 and the North Sea. Water Air Soil Pollut. 109: 357-396.
31 VanHattum, B.; VanStraalen, N. M.; Covers, H. A. J. (1996) Trace metals in populations of freshwater isopods:
32 influence of biotic and abiotic variables. Arch. Environ. Contam. Toxicol. 31: 303-318.
33 Vantelon, D.; Lanzirotti, A.; Scheinost, A. C.; Kretzschmar, R. (2005) Spatial distribution and speciation of lead
34 around corroding bullets in a shooting range soil studied by micro-X-ray fluorescence and absorption
35 spectroscopy. Environ. Sci. Technol. 39: 4808-4815.
36 Verslycke, T.; Vangheluwe, M.; Heijerick, D.; De Schamphelaere, K.; Van Sprang, P.; Janssen, C. R. (2003)
3 7 The toxicity of metal mixtures to the estuarine my sid Neomysis integer (Crustacea: mysidacea) under
38 changing salinity. Aquat. Toxicol. 64: 307-315.
39 Vink, J. P. M. (2002) Measurement of heavy metal speciation over redox gradients in natural water—sediment
40 interfaces and implications for uptake by benthic organisms. Environ. Sci. Technol. 36: 5130-5138.
41 Vinogradoff, S. I.; Graham, M. C.; Thornton, G. J. P.; Dunn, S. M.; Bacon, J. R.; Farmer, J. G. (2005) Investigation
42 of the concentration and isotopic composition of inputs and outputs of Pb in waters at an upland catchment
43 in NE Scotland. J. Environ. Monit. 7: 431-444.
44 Vogiatzis, A. K.; Loumbourdis, N. S. (1999) Exposure ofRana ridibunda to lead I. Study of lead accumulation in
45 various tissues and hepatic 5-aminolevulinic acid dehydratase activity. J. Appl. Toxicol. 19: 25-29.
46 Vogt, G.; Quinitio, E. T. (1994) Accumulation and excretion of metal granules in the prawn, Penaeus monodon,
47 exposed to water-borne copper, lead, iron and calcium. Aquat. Toxicol. 28: 223-241.
48 Wang, E. X.; Benoit, G. (1997) Fate and transport of contaminant lead in spodosols: a simple box model analysis.
49 Water Air Soil Pollut. 95: 381-397.
50 Wang, E. X.; Bormann, F. H.; Benoit, G. (1995) Evidence of complete retention of atmospheric lead in the soils of
51 northern hardwood forested ecosystems. Environ. Sci. Technol. 29: 735-739.
52 Watmough, S. A.; Hutchinson, T. C.; Dillon, P. J. (2004) Lead dynamics in the forest floor and mineral soil in
53 south-central Ontario. Biogeochemistry 71: 43-68.
54 Weber, D. N. (1993) Exposure to sublethal levels of waterborne lead alters reproductive behavior patterns in
55 fathead minnows (Pimephalespromelas). Neurotoxicology 14: 347-358.
May 2006 8-53 DRAFT-DO NOT QUOTE OR CITE
-------
1 Weber, D. N. (1996) Lead-induced metabolic imbalances and feeding alterations in juvenile fathead minnows
2 (Pimephalespromelas). Environ. Toxicol. Water Qual. 11: 45-51.
3 Wehrli, B.; Dinkel, C.; Mtiller, B. (1994) Measurements of benthic gradients in deep lakes with ion-selective
4 electrodes and video endoscopy. Mineral. Mag. 58A: 961-962.
5 Weis, J. S.; Weis, P. (1998) Effects of exposure to lead on behavior of mummichog (Fundulus heteroclitus L.)
6 larvae. J. Exp. Mar. Biol. Ecol. 222: 1-10.
7 Weng, L.; Temminghoff, E. J. M.; Lofts, S.; Tipping, E.; Van Riemsdijk, W. (2002) Complexation with dissolved
8 organic matter and solubility control of heavy metals in a sandy soil. Environ. Sci. Technol. 36: 4804-4810.
9 Wierzbicka, M. (1999) Comparison of lead tolerance mAllium cepa with other plant species. Environ. Pollut.
10 104:41-52.
11 Wilczek, G.; Babczynska, A.; Augustyniak, M.; Migula, P. (2004) Relations between metals (Zn, Pb, Cd and Cu)
12 and glutathione-dependent detoxifying enzymes in spiders from a heavy metal pollution gradient. Environ.
13 Pollut. 132: 453-454.
14 Xia, K.; Bleam, W.; Helmke, P. A. (1997) Studies of the nature of Cu2+ and Pb2+ binding sites in soil humic
15 substances using X-ray absorption spectroscopy. Geochim. Cosmochim. Acta61: 2211-2221.
16 Yanai, R. D.; Ray, D. G.; Siccama, T. G. (2004) Lead reduction and redistribution in the forest floor in
17 New Hampshire northern hardwoods. J. Environ. Qual. 33: 141-148.
18 Yang, J.; Mosby, D. E.; Casteel, S. W.; Blanchar, R. W. (2001) Lead immobilization using phosphoric acid in a
19 smelter-contaminated urban soil. Environ. Sci. Technol. 35: 3553-3559.
20 Yang, Y.-Y.; Jung, J.-Y.; Song, W.-Y.; Suh, H.-S.; Lee, Y. (2000) Identification of rice varieties with high tolerance
21 or sensitivity to lead and characterization of the mechanism of tolerance. Plant Physiol. 124: 1019-1026.
22 Young, T. F.; Sanzone, S., eds. (2002) A framework for assessing and reporting on ecological condition: an SAB
23 report. Washington, DC: U.S. Environmental Protection Agency, Science Advisory Board; report no.
24 EPA SAB-EPEC-02-009. Available: http://www.epa.gov/sab/pdf/epec02009.pdf [9 December, 2003].
25 Zenk, M. H. (1996) Heavy metal detoxification in higher plants—a review. Gene 179: 21-30.
26 Zhang, H.; Davidson, W.; Miller, S.; Tych, W. (1995) In situ high resolution measurements effluxes of Ni, Cu,
27 Fe and Mn and concentrations of Zn and Cd in pore waters by DOT. Geochim. Cosmochim. Acta
28 59:4181-4192.
29 Zhu, Y. G.; Chen, S. B.; Yang, J. C. (2004) Effects of soil amendments on lead uptake by two vegetable crops from
30 a lead-contaminated soil from Anhui, China. Environ. Int. 30: 351-356.
31
May 2006 8-54 DRAFT-DO NOT QUOTE OR CITE
-------
4vEPA
Please make all necessary changes in the below label, PRESORTED STANDARD
detach copy or copy, and return to the address in the upper POSTAGE & FEES PAID
left-hand corner. EPA
United States DCDMIT M^ r* Q^
Environmental Protection m PERMIT Na G'35
Agency If you do not wish to receive these reports CHECK HERE LJ;
detach copy or copy, and return to the address in the upper
left-hand corner.
National Center for
Environmental Assessment
Research Triangle Park, NC 27711
Official Business
Penalty for Private Use
$300
EPA/600/R-05/144aB
May 2006
------- |