Integrated Science Assessment for Lead Appendix 9: Effects on Other Organ Systems and Mortality


United States
Environmental Protection
Jf lkAgency

EPA/600/R-23/375
January 2024

www.epa.gov/isa

Integrated Science
Assessment for Lead

Appendix 9: Effects on Other
Organ Systems and Mortality

January 2024

Center for Public Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency

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DISCLAIMER

This document has been reviewed in accordance with the U.S. Environmental Protection Agency
policy and approved for publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.

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DOCUMENT GUIDE

This Document Guide is intended to orient readers to the organization of the Lead (Pb) Integrated
Science Assessment (ISA) in its entirety and to the sub-section of the ISA at hand (indicated in bold). The
ISA consists of the Front Matter (list of authors, contributors, reviewers, and acronyms), Executive
Summary, Integrated Synthesis, and 12 appendices, which can all be found at https://assessments.epa.gov/
i sa/ctoeume nt/&de id=3 5 95 3 6.

Front Matter

Executive Summary

Integrated Synthesis

Appendix 1. Lead Source to Concentration

Appendix 2. Exposure, Toxicokinetics, and Biomarkers

Appendix 3. Nervous System Effects

Appendix 4. Cardiovascular Effects

Appendix 5. Renal Effects

Appendix 6. Immune System Effects

Appendix 7. Hematological Effects

Appendix 8. Reproductive and Developmental Effects

Appendix 9. Effects on Other Organ Systems and Mortality

Appendix 10. Cancer

Appendix 11. Effects of Lead in Terrestrial and Aquatic Ecosystems
Appendix 12. Process for Developing the Pb Integrated Science Assessment

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CONTENTS

DOCUMENT GUIDE 	9-iii

LIST OF TABLES 	9-vi

LIST OF FIGURES 	9-vii

ACRONYMS AND ABBREVIATIONS	9-viii

APPENDIX 9 EFFECTS ON OTHER ORGAN SYSTEMS AND MORTALITY	9-1

9.1	Effects on the Hepatic System	9-2

9.1.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-2

9.1.2	Scope	9-2

9.1.3	Epidemiologic Studies on the Hepatic System	9-4

9.1.4	Toxicological Studies on the Hepatic System	9-7

9.1.5	Biological Plausibility	9-8

9.1.6	Summary and Causality Determination	9-11

9.2	Metabolic Effects	9-16

9.2.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-16

9.2.2	Scope	9-16

9.2.3	Epidemiologic Studies on Metabolic Effects 	9-18

9.2.4	Toxicological Studies on Metabolic Effects	9-23

9.2.5	Summary and Causality Determination	9-24

9.3	Effects on the Gastrointestinal System	9-25

9.3.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-25

9.3.2	Scope	9-25

9.3.3	Epidemiologic Studies on the Gastrointestinal System	9-27

9.3.4	Toxicological Studies on the Gastrointestinal System	9-27

9.3.5	Summary and Causality Determination	9-27

9.4	Effects on the Endocrine System	9-28

9.4.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-28

9.4.2	Scope	9-28

9.4.3	Epidemiologic Studies on the Endocrine System	9-30

9.4.4	Toxicological Studies on the Endocrine System	9-32

9.4.5	Summary and Causality Determination	9-32

9.5	Effects on the Musculoskeletal System	9-34

9.5.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-34

9.5.2	Scope	9-35

9.5.3	Epidemiologic Studies on the Musculoskeletal System	9-36

9.5.4	Toxicological Studies on the Musculoskeletal System	9-40

9.5.5	Biological Plausibility	9-41

9.5.6	Summary and Causality Determination	9-45

9.6	Effects on Ocular Health	9-50

9.6.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-50

9.6.2	Scope	9-50

9.6.3	Epidemiologic Studies on Ocular Health	9-52

9.6.4	Toxicological Studies on Ocular Health	9-53

9.6.5	Summary and Causality Determination	9-54

9.7	Effects on the Respiratory System	9-55

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9.7.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-55

9.7.2	Scope	9-55

9.7.3	Epidemiologic Studies on the Respiratory System 	9-57

9.7.4	Toxicological Studies on the Respiratory System	9-59

9.7.5	Summary and Causality Determination	9-60

9.8	Mortality	9-61

9.8.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current Review	9-61

9.8.2	Scope	9-62

9.8.3	Total (non-Accidental) Mortality	9-63

9.8.4	Cause-Specific Mortality	9-68

9.8.5	Biological Plausibility	9-69

9.8.6	Summary and Causality Determination	9-70

9.9	Evidence Inventories - Data Tables to Summarize Study Details	9-74

9.10	References	9-149

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LIST OF TABLES

Table 9-1	Evidence that is suggestive of, but not sufficient to infer, a causal relationship between Pb

exposure and hepatic effects	9-14

Table 9-2	Summary of evidence for a likely to be causal relationship between Pb exposure and

musculoskeletal effects 	9-48

Table 9-3	Summary of evidence for a causal relationship between Pb exposure and total mortality	9-73

Table 9-4	Epidemiologic studies of exposure to Pb and hepatic effects	9-74

Table 9-5	Animal toxicological studies of exposure to Pb and hepatic effects	9-82

Table 9-6	Epidemiologic studies of exposure to Pb and metabolic effects	9-86

Table 9-7	Animal toxicological studies of exposure to Pb and metabolic effects	9-100

Table 9-8	Animal toxicological studies of exposure to Pb and gastrointestinal effects	9-102

Table 9-9	Epidemiologic studies of exposure to Pb and endocrine effects	9-103

Table 9-10	Animal toxicological studies of exposure to Pb and endocrine effects	9-112

Table 9-11	Epidemiologic studies of exposure to Pb and musculoskeletal effects	9-115

Table 9-12	Animal toxicological studies of exposure to Pb and musculoskeletal effects	9-127

Table 9-13	Epidemiologic studies of exposure to Pb and ocular effects	9-128

Table 9-14	Animal toxicological studies of Pb exposure and ocular effects	9-133

Table 9-15	Epidemiologic studies of Pb exposure and respiratory effects	9-134

Table 9-16	Animal toxicological studies of exposure to Pb and respiratory effects 	9-139

Table 9-17	Epidemiologic studies of Pb exposure and total mortality	9-141

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LIST OF FIGURES

Figure 9-1	Potential biological pathways for hepatic effects following exposure to Pb.	9-11

Figure 9-2	Potential biological pathways for musculoskeletal effects following exposure to Pb.	9-44

Figure 9-3	Effect estimates for associations of blood Pb with all-cause mortality.	9-64

Figure 9-4	Dose-response relationship between blood Pb levels and all-cause mortality.	9-65

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ACRONYMS AND ABBREVIATIONS

AAS	atomic absorption spectrometry

AD	Alzheimer's disease

ALAD	S-aminolevulenic acid dehydratase

ALP	alkaline phosphatase

ALT	alanine aminotransferase

AMD	age-related macular degeneration

AOPP	advanced oxidation protein products

AQCD	Air Quality Criteria Document

ARCA	Automobile Racing Clube of America

AST	aspartate aminotransferase

AV/TV	adipocyte volume/total volume

BLL	blood lead level

BMD	bone mineral density

BMI	body mass index

BMP	bone morphogenic protein

BV/TV	bone volume to total volume

C2C	serum cleavage neoepitope of type II
collagen

Ca2+	calcium ion(s)

CAT	catalase

C-R	concentration-response

CAR	Cortisol awakening response

Cd	cadmium

CD	control diet

CHEER	Children's Health and Environmental
Research

CHF	congestive heart failure

CI	confidence interval

CK18	cytokeratin 18

COMP	cartilage oligomeric matrix protein

CPU	carboxypropeptide of type II collagen

CRP	C-reactive protein

CVD	cardiovascular disease

CYP	Cytochrome P450

d	day(s)

DBP	diastolic blood pressure

DMFS	Delayed, missing, and filled surfaces

DMFT	decayed, missing, and filled teeth

DXA	Dual-energy X-ray absorptiometry

ECRHS	European Community Respiratory
Health Survey

EDTA	ethylenediaminetetraacetic acid

EGF	epidermal growth factor

eGFR	estimated glomerular filtration rate

ELEMENT	Early Life Exposure in Mexico to
Environmental Toxicants

ER	endoplasmic reticulum

ERSD	end-stage renal disease

F#	filial generation

FBG	fasting blood glucose

FEV1	forced expiratory volume in one second

FIB-4	fibrosis-4

FT3	free triiodothyronine

FT4	free thyroxine

FVC	forced vital capacity

GADA	glutamic acid decarboxylase antibodies

GD	gestational day

GDM	gestational diabetes mellitus

GDS	Gesell Developmental Schedules

GFAAS	graphite furnace atomic absorption
spectrometry

GFR	glomerular filtration rate

GGT	gamma-glutamyl transferase

GH	growth hormone

GI	gastrointestinal

GM	geometric mean

GPx	glutathione peroxidase

GSH	glutathione

GSH-PX	glutathione peroxidase

Hb	hemoglobin

HDL	high-density lipoprotein

HDL-C	high-density lipoprotein cholesterol

HF	hepatic fibrosis

HOMA- p	HOMA of P-cell function

HOMA-IR	Homeostatic Model Assessment for
Insulin Resistance

HR	hazard ratio

HS	hepatic steatosis

ICP-MS	inductively coupled plasma mass
spectrometry

ID	iron deficient

IHC	immunohistochemistry

IHD	ischemic heart disease

i.p.	intraperitoneal

IOP	intraocular pressure

ISA	Integrated Science Assessment

KARE	Korean Association Resource

KNHANES	Korea National Health and Nutrition
Examination Survey

K-XRF	K-shell X-ray fluorescence

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LDL	low-density lipoprotein

LDL-C	low-density lipoprotein cholesterol

LOD	limit of detection

mo	month(s)

MDA	malondialdehyde

MetS	metabolic syndrome

METS	Modeling the Epidemiologic Transition
Study

MI	myocardial infarction

microCT	micro-computed tomography

mRNA	messenger ribonucleic acid

NAAQS	National Ambient Air Quality

Standards

NAFLD	nonalcoholic fatty liver disease

NANC	noncholinergic

NAS	Normative Aging Study

NASCAR	National Association for Stock Car

Auto Racing

NHANES	National Health and Nutrition

Examination Survey

NF -kB	nuclear factor kappa B

NP	nanoparticle

OA	osteoarthritis

OLD	obstructive lung disease

OLF	obstructive lung function

OR	odds ratio

Pb	lead

PbO	lead oxide

PCNA	proliferating cell nuclear antigen

PCR	polymerase chain reaction

PD	Potential difference

PECOS	Population, Exposure, Comparison,

Outcome, and Study Design

PSS	perceived stress score

PIR	poverty-income ratio

PM	particulate matter

PND	postnatal day

PROGRESS Programming Research in Obesity,
Growth, Environment and Social
Stressors

PTE!	parathyroid hormone

PTElrP	parathyroid hormone-related protein

qRT-PCR	real-time quantitative reverse

transcription-polymerase chain reaction

RBC	red blood cell

RCT	randomized control trial

RR	relative risk

RT-PCR	reverse transcription-polymerase chain
reaction

SBP	systolic blood pressure

SBEE1C	Shiwha and Banwol Environmental
Elealth Cohort

SD	standard deviation

SE	standard error

SES	socioeconomic status

SNP	single nucleotide polymorphism

SOD	superoxide dismutase

SPECT	single photon emission computed
tomography

SSBI	sugar sweetened beverage intake

T-SOD	total superoxide dismutase

T#	tertile #

TACT	Trial to Assess Chelation Therapy

TB	total bilirubin

TBARS	thiobarbituric acid reactive substance

TC	total cholesterol

TEM	transmission electron microscopy

Tg	thyroglobulin

TGAb	thyroglobulin antibody

TGF-pi	transforming growth factor-beta 1

TNF	tumor necrosis factor

TRI	Toxics Release Inventory

TSH	thyroid-stimulating hormone

TPOAb	thyroid peroxidase antibody

Q	quartile

wk	week(s)

yr	year(s)

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APPENDIX 9 EFFECTS ON OTHER ORGAN SYSTEMS

AND MORTALITY

Summary of C ausality Determinations for Ph Kvposure and ilffects on Other Organ Systems and

Mortality

This appendix characterizes the scientific ev idenee lluil supports causahlv dclorniiiiliI 1011s for
lead (IMi) exposure and hepatic effeels. metabolic efleels. Liaslrmnleslinal effeels. endocrine svsleni
efleels. effeels on bone and leelh. effeels nil ocular health, and respirators effeels The l\ |vs of siudles
evaluated wilhin llns appendix are consistent willi llie overall scope of die ISA as delai led in the

(see Seelion 12 4) In assessing llie overall ev idenee. strengths aikl liniilalions of
iikliv idual studies were evaluated based on seieiilille considerations detailed in the Table 12-5 of the

(Seelion 12 <-> I) More details on the causal framework used to reach these
conclusions are included in llie Preamble to the ISA ( ) The ev idenee presented

throughout this appendix supports the following causalilv conclusions

Outcome Group

Causality Determination

Hepatic Effects

Suggestive of, but not sufficient to infer, a causal
relationship

Metabolic Effects

Inadequate

Gastrointestinal Effects

Inadequate

Endocrine System Effects

Inadequate

Musculoskeletal Effects

Likely to be Causal

Ocular Health Effects

Inadequate

Respiratory Effects in
Populations without Asthma

Inadequate

Total (Nonaccidental) Mortality

Causal

The I Acculive Summarv. Integrated S\ nlhesis. and all other appendices of the 2<)24 Ph ISA can be
found al

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9.1

Effects on the Hepatic System

9.1.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current
Review

The 2013 Integrated Science Assessment for Lead (hereinafter referred to as the 2013 Pb ISA)
concluded that "because of the insufficient quality of studies, the available evidence was inadequate to
determine if there is a causal relationship between Pb exposure and hepatic effects" ("U.S. EPA. 2013).
Epidemiologic evidence from a limited number of occupational studies demonstrated impaired liver
function in Pb-exposed workers. However, the internal validity and generalizability of these studies was
limited by cross-sectional study designs, lack of consideration for potential confounders, and notably
higher blood Pb levels (BLLs) (>29 (ig/dL) than the general population. Similarly, toxicological studies
observed changes in liver function enzymes and other markers of liver health in animals exposed to Pb,
but the use of bolus injections as a common route of exposure and high BLLs (>30 (ig/dL) introduced
uncertainty regarding their relevance to human exposures.

9.1.2	Scope

The scope of this section is defined by Population, Exposure, Comparison, Outcome, and Study
Design (PECOS) statements. The PECOS statement defines the objectives of the review and establishes
study inclusion criteria, thereby facilitating identification of the most relevant literature to inform the Pb
ISA.1 In order to identify the most relevant literature, the body of evidence from the 2013 Pb ISA was
considered in the development of the PECOS statements for this Appendix. Specifically, well-established
areas of research; gaps in the literature; and inherent uncertainties in specific populations, exposure
metrics, comparison groups, and study designs identified in the 2013 Pb ISA inform the scope of this
Appendix. The 2013 Pb ISA used different inclusion criteria than the 2024 Pb ISA, and the studies
referenced therein often do not meet the current PECOS criteria (e.g., due to higher or unreported
biomarker levels). Studies included in the 2013 Pb ISA, including many that do not meet the current
PECOS criteria, are discussed in this appendix to establish the state of the evidence prior to this
assessment. Except for supporting evidence used to demonstrate the biological plausibility of Pb-
associated effects on the hepatic system, recent studies were only included if they satisfied all the
components of the following discipline-specific PECOS statements:

'The following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

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Epidemiologic Studies:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

Exposure: Exposure to Pb2 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure;3 or intervention groups in randomized trials and quasi-experimental studies.

Comparison: Populations, population subgroups, or individuals with relatively higher versus
lower levels of the exposure metric (e.g., per unit or log unit increase in the exposure metric,
or categorical comparisons between different exposure metric quantiles).

Outcome: Effects on the hepatic system.

Study Design: Epidemiologic studies consisting of longitudinal and retrospective cohort studies,
case-control studies, cross-sectional studies with appropriate timing of exposure for the health
endpoint of interest, randomized trials and quasi-experimental studies examining
interventions to reduce exposures.

Experimental Studies:

Population: Laboratory nonhuman mammalian animal species (e.g., mouse, rat, guinea pig,
minipig, rabbit, cat, dog) of any lifestage (including preconception, in utero, lactation,
peripubertal, and adult stages).

Exposure: Oral, inhalation, or intravenous routes administered to a whole animal (in vivo) that
results in a BLL of 30 (ig/dL or below.4'5

Comparators: A concurrent control group exposed to vehicle-only treatment or untreated
control.

Outcomes: Effects on the hepatic system.

Study design: Controlled exposure studies of animals in vivo.

2Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the National Ambient Air Quality Standards (NAAQS) review (e.g., longitudinal studies designed to
examine recent versus historical Pb exposure).

3Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM25) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure (Section 2.5.3 (U.S. EPA. 20.1. 2)].
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with blood Pb levels (BLLs) are lacking.
4Pb mixture studies are included if they employ an experimental arm that involves exposure to Pb alone.

5This level represents an order of magnitude above the upper end of the distribution of U.S. young children's BLL.
The 95th percentile of the 2011-2016 National Health and Nutrition Examination Survey (NHANES) distribution of
BLL in children (1-5 years; 11 = 2,321) is 2.66 (ig/dL (Egan et at.. 2021) and the proportion of individuals with BLL
that exceed this concentration varies depending on factors including (but not limited to) housing age, geographic
region, and a child's age, sex, and nutritional status.

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9.1.3 Epidemiologic Studies on the Hepatic System

Epidemiologic evidence evaluated in the 2013 Pb ISA ( 4. 20.1.3') was limited to a small

number of occupational studies that demonstrated impaired liver function in Pb-exposed workers.
However, the internal validity and generalizability of these studies was limited by cross-sectional study
designs, lack of consideration for potential confounders, and notably higher BLLs (>29 (ig/dL) than the
general population. Recent epidemiologic studies of the hepatic system generally examine one of three
groups of endpoints: (1) direct evaluation of liver injury (e.g., nonalcoholic fatty liver disease [NAFLD]
and hepatic fibrosis); (2) serum biomarkers of liver function (e.g., alanine aminotransferase [ALT],
aspartate aminotransferase [AST], alkaline phosphatase [ALP], and gamma-glutamyl transferase [GGT]);
and (3) serum lipids (e.g., fatty acids, lipids, and cholesterol). Results from recent studies provide
inconsistent evidence of an association between BLLs and direct or indirect measures of liver damage.
Recent studies evaluating hepatic effects are generally limited to cross-sectional analyses, which are
unable to establish temporality between exposure and outcome. Additionally, with biomarkers of Pb
exposure, it is difficult to characterize the specific timing, duration, frequency, and level of Pb exposure
that contributed to associations observed with liver function. This uncertainty may apply particularly to
assessments of BLLs, which in nonoccupationally-exposed adults, reflect both current exposures and
cumulative Pb stores in bone that are mobilized during bone remodeling. Measures of central tendency for
Pb biomarker levels used in each study, along with other study-specific details, including study
population characteristics and select effect estimates, are highlighted in Table 9-4. An overview of the
recent evidence is provided below.

9.1.3.1 Direct Evaluation of Liver Injury

A limited number of recent cross-sectional studies examined the association between BLLs and
liver injury, including NAFLD and fibrosis ("Chung et ah. 2020; Reiaet ah. 2020; Werder et ah. 2020;

Zhai et ah. 2017). These studies, which use a variety of diagnostic tools, provide inconsistent evidence of
an association between BLLs and NAFLD and fibrosis. Liver biopsy is the gold standard for evaluating
NAFLD and liver fibrosis, but it is an invasive and cost prohibitive procedure. Therefore, epidemiologic
studies often rely on alternative measurement techniques, including imaging, biomarkers, and biomarker-
based prediction models. Imaging—either ultrasonic or magnetic resonance—generally has greater
sensitivity and specificity than reliance on biomarkers.

A recent cross-sectional study of adults in the Yangtze River Delta in China examined the
relationship between BLLs and NAFLD measured by ultrasound (Zhai et ah. 20.1.7). In addition to using
ultrasonic imaging, this study included a large number of participants (n = 2,011). In sex-stratified
models. Zhai et ah (20.1.7) reported higher odds of NAFLD associated with higher BLL quartiles after
adjusting for a range of demographic and hepatic and metabolic health factors. The observed associations
were stronger in magnitude among men (odds ratio [OR] = 2.168 [95% CI: 0.989, 4.751] quartile 4 versus

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quartile 1) compared with women (OR= 1.613 [95% CI: 1.082, 2.405] quartile 4 versus quartile 1);
however, the effect estimates in men were much less precise due to a smaller sample of men in the study
population. Given the imprecise estimates for men (i.e., wide 95% Cis), it is difficult to draw conclusions
on sex-specific comparisons.

Results from other recent cross-sectional studies are inconsistent. In a small exploratory analysis
of oil spill response workers with low BLLs (mean = 1.82 (ig/dL). Werder et al. (2020) evaluated the
association between BLLs and cytokeratin 18 (CK18), a serologic biomarker of hepatocyte death that has
been used as a marker forNAFLD. The authors observed an association between BLLs and caspase-
cleaved fragment CK18 (CK18 M30), but not whole protein CK18 (CK18 M65). Notably, CK18 M65 has
performed better as a measure of NAFLD than CK18 M30 ("Lee et al.. 2020). adding further ambiguity to
the observed results. Additionally, Werder et al. (2020) examined a range of heavy metals and markers of
inflammation and did not adjust for multiple testing, which increases the likelihood of chance findings
and may explain the inconsistent results. In addition to this weak evidence of an association between
BLLs and markers of NAFLD. (Chung et al.. 2020) analyzed data from the Korea National Health and
Nutrition Examination Survey (KNHANES) and reported null or negative sex-specific associations
between BLLs and scores on the Hepatic Steatosis Index, a validated biomarker-based prediction model
of NAFLD. The authors also observed negative associations between BLLs and Fibrosis 4 Index, a
similarly validated model for fibrosis. This larger analysis (n = 4,420) reported similar mean BLLs
(1.81 (ig/dL) as those reported in Werder et al. (2020).

In addition to studies examining NAFLD and fibrosis separately, (Reia et al.. 2020) used a
biomarker-based index to estimate fibrosis level in National Health and Nutrition Examination Survey
(NHANES) participants with NAFLD. In this case, fibrosis level was used as an indicator of NAFLD
severity. Reia et al. (2020) reported large, but imprecise associations between BLL quartiles and
advanced liver fibrosis. For example, the authors noted that participants in the highest quartile of BLLs
(>1.62 (ig/dL) had nearly 5-fold higher odds of advanced liver fibrosis (OR = 4.93 [95% CI: 1.88, 11.24])
compared to participants in the lowest quartile (<0.64 (ig/dL). Despite having a large sample size, the
authors only examined severe liver fibrosis, which likely resulted in a small number of cases (total cases
not reported) and would have decreased the statistical power of the study. Limited statistical power
resulting from a small sample size reduces the likelihood of detecting a true effect.

9.1.3.2 Serum Biomarkers of Liver Function

Serum biomarkers can be used as indirect evidence of liver damage. For example, elevated levels
of ALT or AST can indicate the presence of necrosis in the liver, and elevated levels of bilirubin, ALP, or
GGT can be associated with cholestasis. However, changes in serum biomarker levels are also related to
effects on other biological systems. Elevated GGT can also occur with chronic heart failure, and elevated
ALP can be used to detect bone disorders. Therefore, studies evaluating these biomarkers in combination

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are more likely to provide evidence of abnormal liver function relative to studies evaluating a single
biomarker.

There have been a limited number of recent epidemiologic studies that evaluated serum
biomarkers of liver function, including a longitudinal study (Pollack et ah. 20.1.5') and a few cross-
sectional analyses ("Chen et aL 20.1.9; Obeng-Gvasi. 20.1.9; Christensen et ah. 20.1.3). Recent studies, which
adjust for a wide range of potential confounders, provide some evidence of an association between BLLs
and serum biomarkers, but results are not entirely consistent, and the implications of some associations
are unclear. Specifically, a small prospective cohort study of premenopausal women evaluated the percent
change in AST, ALT, ALP, and bilirubin over the course of an 8-week follow-up (Pollack et ah. 20.1.5).
The authors reported imprecise positive associations between AST (5.02% [95% CI: -1.36%, 11.41%]),
ALT (6.39% [95% CI: 3.07%, 9.72%]), and ALP (2.14% [95% CI: -5.05%, 9.33%]) and BLLs measured
at baseline (mean = 1.03 |ig/dL). but no association between bilirubin and BLLs (-0.20% [95% CI:
-7.50%, 7.11%]). The clinical relevance of these findings is uncertain given the majority of the study
population fell well within the normal ranges of each of the biomarkers. While small shifts in biomarker
levels may have important public health implications, the importance of these findings would be better
substantiated with evidence of associations between Pb exposure and more direct measures of liver injury.
A recent cross-sectional study of adults living near an e-waste facility in China better addresses clinical
relevance by examining the association between BLLs and abnormal liver function, defined as having two
or more transaminases (AST, ALT, GGT) elevated above the normal range, or having one transaminase at
least twice as high as the upper bound of the normal range (Chen et ah. 20.1.9). In this study, which had
notably higher median BLLs (5.1 to 8.7 (ig/dL across study locations), BLLs were associated with a large,
but imprecise increase in the odds of abnormal liver function (OR = 1.94 [95% CI: 1.00, 3.73] per
1 (ig/dL higher BLL).

Results from recent large cross-sectional NHANES analyses examining a single serum biomarker
of liver function were inconsistent. In an analysis of 2003-2004 NHANES participant's ages 12 years and
older, Christensen et ah (20.1.3) reported null associations between BLL quartiles and ALT levels. An
analysis restricted to adult participants of more recent NHANES survey cycles (2011-2016) observed
higher odds of GGT levels above the study population median (18 U/L) associated with each 1 (ig/dL
higher BLL (OR= 1.94 [95% CI: 1.652, 2.28] for young adults and 1.34 [95% CI: 1.14, 1.58] for middle-
aged adults) (Obeng-Gvasi. 20.1.9). Similar to the Pollack et ah (20.1.5) study, the median GGT levels in
this study were within the normal range.

9.1.3.3 Serum Lipids

Many fatty acids, lipids, and cholesterol are synthesized and eliminated in the liver; the
relationships among them and their relevance to other aspects of human health, including metabolic
effects (Section 9.2) and cardiovascular effects (Appendix 4). are complex. Although increases or

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decreases in serum or liver cholesterol levels may be associated with liver damage, it can be challenging
to determine whether the changes are a consequence of said damage or a contributing factor in disease
progression ("Arguello et ah. 20.1.5; Chrostek et ah. 20.1.4'). Recent epidemiologic studies of serum lipids
have been conducted in populations of adults and children and include a mix of prospective cohorts and
cross-sectional designs. Recent studies also account for a range of potential confounders, including
demographics and socioeconomic status (SES) factors, medical history, and medication use. Associations
between BLLs and serum lipids have been largely inconsistent across both lifestages.

In a recent study including a subset of the Veterans Affairs Normative Aging Study (NAS) cohort
with healthy older adults, Peters et ah (20.1.2) examined the associations between BLLs at baseline and
serum lipid levels after three to four years of follow-up. The authors reported higher odds of clinically
elevated total cholesterol associated with higher BLLs (OR= 1.08 [95%: 0.99, 1.19] per 1 (.ig/dL higher
BLL). Associations with clinical cut points for other serum lipids were either null (elevated triglycerides
and low-density lipoprotein cholesterol [LDL] cholesterol) or negative (low high-density lipoprotein
[HDL] cholesterol). Cross-sectional studies of adult populations, including analyses of nationally
representative health survey data (Xu et ah. 2021; Lee and Kim. 20.1.6) and a small analysis of adults of
African descent (Ettinger et ah. 20.1.4). are also inconsistent. Results across these studies (see Table 9-2)
provide no discernable pattern of associations between BLLs and triglycerides, LDL cholesterol, or HDL
cholesterol. BLL measures of central tendency were low across the evaluated studies (<5 (ig/dL) and do
not appear to explain the inconsistencies.

Results from studies in children are similarly inconsistent. Two recent studies of serum lipids
analyzed data from separate birth cohorts in Mexico - the Early Life Exposure in Mexico to
Environmental Toxicants (ELEMENT) study (Liu et ah. 2020) and the Programming Research in
Obesity, Growth, Environment and Social Stressors (PROGRESS) birth study (Kupseo et ah. 20.1.9). In
children ages 4 to 6, Kupseo et ah (20.1.9) reported null associations between prenatal BLLs and serum
triglycerides and non-HDL cholesterol. In contrast, in an analysis including older children and teens, Liu
et ah (2020) observed higher triglyceride Z-scores in children with prenatal BLLs >5 (.ig/dL compared to
those with BLLs less than 5 (ig/dL (0.58 [95% CI: -0.05, 1.20]). The authors observed negative
associations between prenatal BLLs and cholesterol Z-scores (total, LDL, and HDL). A large cross-
sectional analysis of NHANES participants ages 12 to 19 noted 2.3% (95% CI: 0.3%, 4.2%) higher LDL
cholesterol levels and 0.6% (95% CI: -0.1%, 1.3%) higher total cholesterol levels per 1 (ig/dL higher
BLL (Xu et ah. 20.1.7). The authors observed null (total cholesterol and HDL cholesterol) or negative
(triglycerides) associations between BLLs and other serum lipids.

9.1.4 Toxicological Studies on the Hepatic System

As described in the 2013 Pb ISA, evidence from toxicological studies indicates exposure to Pb
can result in altered liver function and hepatic oxidative stress (	313). A few studies reported

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Pb-induced decreases in cytochrome P450 (CYP) enzymes (Phase I xenobiotic metabolism), as well as
Pb-induced decreases in serum protein and albumin levels and increased AST, ALT, ALP, and GGT
activities (indicators of decreased liver function), increased oxidative stress, and decreased antioxidant
status. A number of recent studies have corroborated findings of Pb exposure and decreased liver function

(Barkaoui et ah. 2020; Dumkova et ah. 2020b; Gao et ah. 2020; Andielkovic et ah. 20.1.9; Laamech et ah.
20.1.7; Long et ah. 20.1.6; Liu et ah. 2C . rafaal et ah. 20.1.1). While impaired lipid metabolism was
reported in the 2013 Pb ISA. results from recent studies of cholesterol have been inconsistent. Laamech et
ah (20.1.7) found an increase in total cholesterol in mice given Pb acetate in their drinking water (BLL:
18 (.ig/dL). Conversely, Dumkova et ah (2020a) found lower levels of total cholesterol in rats that were
given Pb oxide nanoparticles by inhalation (BLLs: 3.1-8.5 (.ig/dL): however, the latter group did report an
increase in lipid droplets by liver histology [BLLs: 3.1-17.8 (.ig/dL; (Dumkova et ah. 2020a; Dumkova et
ah. 2020b; Dumkova et ah. 20.1.7)1. Observation of Pb-associated increases in hepatic oxidative stress, as
indicated by a decrease in glutathione (GSH) levels and catalase (CAT), superoxide dismutase (SOD),
and glutathione peroxidase (GPx) activities has been found in additional recent studies of oral Pb
exposure [drinking water: 21.4-29.0 (ig/dL (Barkaoui et ah. 2020; Andielkovic et ah. 20.1.9; Long et ah.
20.1.6); oral gavage: 18.5-30.2 (.ig/dL (Gao et ah. 2020; Laamech et ah. 20.1.7; Li et ah. 20.1.7)1.

Since the 2013 Pb ISA, several recent studies have reported perturbations related to oxidative
stress in addition to the endpoints noted above. For example, Andielkovic et ah (20.1.9) found changes in
multiple parameters of oxidative stress in liver and kidney tissue in male rats, indicative of an oxidative
stress response to Pb exposure (BLL: 29.0 (.ig/dL). Long et ah (2 also reported several markers of
oxidative damage and response, in mouse liver tissue. They showed in addition, consistent with an
oxidative damage response, attenuation of such response after administration of proanthocyanidins, which
are naturally occurring antioxidant compounds. The same authors reported changes in several markers
that are consistent with a generalized endoplasmic reticulum (ER) response in the liver to environmental
stressors. Likewise, Liu et ah (20.1.3) showed Pb responsiveness of ER stress markers, and the antagonistic
effect of quercetin (a natural flavonoid) on this response. Barkaoui e	20) reported finding

alleviation of Pb-induced oxidative effects from administration of antioxidative, phenolic compounds
extracted from Plantigo albicans.

Cell death by apoptosis may be a downstream result of the molecular sequelae of Pb exposure
described in the preceding paragraph. Indeed, such a result has been reported in mouse livers, both
phenotypically and via molecular markers (Dumkova et ah. 20.1.7; Long et ah. 20.1.6).

9.1.5 Biological Plausibility

This section describes biological pathways that potentially underlie effects of Pb on the liver and
hepatic function. Figure 9-1 depicts the proposed pathways as a continuum of upstream events, connected
by arrows, which may lead to downstream events observed in epidemiologic studies. This discussion of

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how exposure to Pb may lead to hepatic effects contributes to an understanding of the biological
plausibility of epidemiologic results evaluated above. Note that the structure of the biological plausibility
sections and the role of biological plausibility in contributing to the weight-of-evidence analysis used in
the 2024 Pb ISA are discussed in Section IS.4.2.

The hepatic effects of Pb exposure have been studied in many experimental models. The pathway
proposed, outlined in Figure 9-1, involves the induction of oxidative stress and inflammation leading to
downstream cellular loss and metabolic changes that could plausibly be responsible for the development
of health effects in the liver. Oxidative stress control and inflammation are highly regulated processes and
are tightly linked. As discussed above and in both the 2013 Pb ISA and 2006 Pb Air Quality Criteria
Document (AQCD), inflammatory signaling and marker of oxidative stress have been found in the livers
of animals exposed to Pb (see Section 9.1.3 and ("U.S. EPA. 20.1.3. 2006). Hepatic inflammation and
oxidative stress co-occur thus it is difficult to determine if one process precedes the other, thus, they are
grouped in the same grey box in Figure 9-1.

Regulation of inflammation and oxidative stress involve widespread gene expression changes that
could plausibly alter the expression of metabolizing enzymes and proteins necessary for cholesterol
synthesis and maintaining lipid homeostasis which could lead to fat accumulation and subsequent fatty
liver disease. As discussed in the 2013 Pb ISA, Pb treatment can cause elevated cholesterol levels through
changes in cholesterol synthesis pathways in the liver. Pb can also alter the expression and activity of
CYP enzymes that are important in the response to xenobiotics as well as metabolism of cholesterol-
derived steroid hormones. A recent study in knockout mice showed that mice deficient in the 11-1
inflammatory mediators were protected from the hypercholesterolemia in response to Pb compared to
wild type mice (Koiima et ah. 2012). Knockout mice also did not experience the messenger ribonucleic
acid (mRNA) upregulation cholesterol synthesizing enzymes HMGR and Cyp51 or the downregulation of
bile acid synthesizing enzyme Cyp7al. These data support the necessity of inflammation to the regulation
of cholesterol metabolism and are the basis for the solid line from inflammation to the box containing
CYP activity and altered cholesterol synthesis in Figure 9-1.

Excessive damage from oxidative stress and inflammatory responses could lead to cell death
which, in excess, could lead to changes in hepatocyte structure and ultimately decrease liver function. As
discussed above and in the 2013 Pb ISA and 2006 Pb AQCD, many animal studies have shown that Pb
exposure of varying durations and developmental stages results in liver injury, which is most commonly
measured as increased activity of liver enzymes (e.g., AST, ALT, ALP) in the blood serum or plasma.
Increases of liver enzyme activity have been seen in the serum of humans occupationally exposed to Pb
("Mazumdar and Goswami. 20.1.4; U.S. EPA. 20.1.3). As mentioned above, elevated liver enzymes in the
blood can serve as an indirect markers of liver damage. Previous research has shown that exposure to Pb
in animal models can lead to upregulation of cell death pathw ays (U.S. EPA. 20.1.3) and more recent
studies provide additional support (Almasmoum et ah. 20.1.9; Abu-Khudir et ah. ; lasanein et ah.
20.1.6; Long et ah. 20.1.6; Mabrouk et ah. 20.1.6; Liu et ah. 20.1.3; Pal et ah. 20.1.3; Liu et ah. 20.1.2. ).

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Studies have shown that treatment with antioxidants, like vitamin E ("Almasmoum et ah. 20.19). vitamin C
(Upadhvav et ah. 2009). or therapeutic compounds that have anti-inflammatory and antioxidant properties

("Abu-Khudir et ah. 20.1.7; Hasanein et ah. 20.1.6; Long et ah. 20.1.6; Mabrouk et ah. 20.1.6; Liu et ah. 20.1.3;
Pal et ah. 20.1.3; Liu et ah. 20.1.2) can prevent the Pb-induced upregulation of apoptotic pathways and
concomitantly reduced both markers of oxidative damage and serum markers of liver injury. Interestingly,
some therapeutic compounds reduce the liver Pb burden suggesting that the reduction in oxidative stress
may be caused by toxicokinetic changes that reduce the liver Pb exposure concentration (Liu et ah. 20.1.3;
Liu et ah. 20.1.1). however, some studies have seen that antioxidant treatment can reduce oxidative stress
even while live Pb levels remain elevated suggesting that oxidative stress is directly related to
downstream liver damage (Almasmoum et ah. 20.1.9; Long et ah. 20.1.6; Mabrouk et ah. 20.1.6; Reckziegel
et ah. 20.1.6). Together these data provide support for the solid line from the box containing inflammation
and oxidative stress to cell death.

Excessive cell loss can result in changes to liver architecture and trigger repair processes that can
lead to liver scarring, both of which can lead to loss of liver function. The 2013 Pb ISA discussed studies
that showed that Pb treatment led to noticeable histologic changes including signs of increased fibrotic
liver changes (U.S. EPA. 20.1.3). More recent work supports this with evidence that liver histologic
changes are accompanied by increased markers of apoptosis and necrosis (Long et ah. 20.1.6; Mabrouk et
ah. 20.1.6). A study also showed that 4 months of Pb exposure in rats increased wound repair signaling
pathways which corresponded to increased deposition of extracellular matrix proteins in the liver (Perez
Aguilar et ah. 20.1.4). Sufficient damage to the liver can reduce liver function which can be measured as a
reduced level of protein in the blood. Recent studies have shown decreases in serum proteins following
Pb exposure that coincide with molecular or histological signs of liver damage (Almasmoum et ah. 20.1.9;
El-Tantawv. 20.1.6; Hasanein et ah. 20.1.6). Similar evidence is seen in the 2013 Pb ISA. Together, it is
plausible that widespread cell death in the liver can lead to changes in hepatocyte structure that leads to
liver damage and resulting decline in liver function.

The proposed pathway leading from Pb exposure to hepatic health effects begins with the
induction of inflammation and increase in oxidative stress. This results in both changes in metabolizing
enzymes and cholesterol synthesis that could be responsible for fatty accumulation in the liver.
Widespread oxidative damage results in cell loss which could disrupt the normal liver structure and
contribute to loss of liver function. Together, the evidence supports a plausible pathway from Pb exposure
to the hepatic effects seen in epidemiologic and animal tox studies.

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1

Decreased liver function

Liver injury

Altered cholesterol synthesis

Altered CYP activity

Fatty liver disease

CYP = cytochrome P450.

Note: The boxes above represent the effects for which there is experimental or epidemiologic evidence related to Pb exposure, and
the arrows indicate a proposed relationship between those effects. Solid arrows denote evidence of essentiality as provided, for
example, by an inhibitor of the pathway used in an experimental study involving Pb exposure. Dotted arrows denote a possible
relationship between effects. Shading around multiple boxes is used to denote a grouping of these effects. Arrows may connect
individual boxes, groupings of boxes, and individual boxes within groupings of boxes. Progression of effects is generally depicted
from left to right and color coded (white, exposure; green, initial effect; blue, intermediate effect; orange, effect at the population
level or a key clinical effect). Here, population-level effects generally reflect results of epidemiologic studies. When there are gaps in
the evidence, there are complementary gaps in the figure and the accompanying text below. The structure of the biological
plausibility sections and the role of biological plausibility in contributing to the weight-of-evidence analysis used in the 2022 Pb ISA
are discussed in IS.7.2.

Figure 9-1 Potential biological pathways for hepatic effects following
exposure to Pb.

9.1.6 Summary and Causality Determination

The 2013 Pb ISA (U.S. EPA. 2013) concluded that the available evidence was "inadequate to
determine if there is a causal relationship between Pb exposure and hepatic effects." A limited number of
occupational epidemiologic studies evaluated potential associations between higher BLLs and lower
serum protein and albumin levels and higher liver function enzymes, oxidative stress, and antioxidant
status. The implications of the occupational epidemiologic evidence were limited because of the cross-
sectional design of the studies, the high BLLs examined (means >29 |ig/dL). and the lack of consideration
for potential confounding by factors such as age, diet, BMI, smoking, or other occupational exposures.
Similar changes in liver function enzymes were found in mature animals exposed to high levels of Pb
during adulthood, and animals exposed during gestation and lactation. Pb exposure was also shown to
impair lipid metabolism in animals, as evidenced by increased hepatic cholesterogenesis, and altered
triglyceride and phospholipid levels (Sharma et al.. 2010; Ademuviwa et al.. 2009; Khotimchenko and
Kolenchenko. 2007). Multiple toxicological studies observed Pb-related increases in hepatic oxidative

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stress, generally indicated by an increase in lipid peroxidation along with a decrease in GSH levels and
CAT, SOD, and GPx activities (Pandvaet ah. 20.1.0 ; Sharma et ah. 20.1.0; Yu et ah. 2008; Adegbesan and
Adenuga. 2007; Jurczuk et ah. 2007; Kfaotimehenko and Kolenchenko. 2007; Jurczuk et ah. 2006).
However, the relevance of the toxicological evidence was uncertain, as many studies administered Pb as
bolus doses. Additionally, few toxicological studies reported the resulting BLLs and those studies that did
provide this evidence had BLLs of limited relevance to environmentally exposed humans (>30 (.ig/dL).
Thus, despite some evidence of Pb-induced hepatic effects, uncertainties related to the relevance of the
available studies limited the causal conclusions that could be drawn in the 2013 Pb ISA.

Recent toxicological studies include more relevant routes of exposure (i.e., drinking water, oral
gavage, and inhalation) and exposures resulting in lower BLLs than those available for the 2013 Pb ISA
(BLL range: 3.6-30.2 (.ig/dL). These studies provide consistent evidence of Pb-induced increases in AST,
ALT, ALP, and GGT activities, which are indicative of reduced liver function (Barkaoui et ah. 2020;

Dumkova. et ah. 2020b; Gao et ah. 2020; Andielkovic et ah. 20.1.9; Laamech et ah. 20.1.7; Long et ah.
20.1.6; Liu et ah. 20.1.3; Berrahal et ah. 20.1.1'). Additionally, recent studies provide consistent evidence of
Pb-associated increases in hepatic oxidative stress, as indicated by decreases in GSH levels and CAT,
SOD, and GPx activities ("Barkaoui et ah. 2020; Gao et ah. 2020; Andielkovic et ah. 20.1.9; Laamech et ah.
20.1.7; Li et ah. 20.1.7; Long et ah. 20.1.6"). While impaired lipid metabolism was reported in the 2013 Pb
ISA, a limited number of recent studies of cholesterol have reported contrasting results, one indicating
Pb-induced increases in total cholesterol ("Laamech et ah. 2017) and the other reporting decrements in
total cholesterol (Dumkova et ah. 2020a").

In contrast to toxicological evidence, recent epidemiologic studies evaluating the relationship
between BLLs and hepatic effects are generally inconsistent or inconclusive. Similar to studies evaluated
in the 2013 Pb ISA, most recent studies implement cross-sectional designs, although they include more
robust adjustment for potential confounders and populations with much lower mean BLLs. Still, these
studies do not establish temporality between exposure and outcome or address potentially large
differences in past versus current exposures. There is therefore uncertainty as to the specific timing,
duration, frequency, and level of Pb exposure that contributed to any observed associations. The strongest
evidence for direct liver injury comes from a large cross-sectional analysis of adults in China that reported
a positive association between BLLs and NAFLD prevalence measured by ultrasound (Zhai et ah. 20.1.7").
Other analyses used biomarkers or biomarker indices to assess NAFLD, which are less accurate than
ultrasonic imaging and may introduce non-differential misclassification. Non-differential
misclassification of a dichotomous outcome is likely to bias results toward the null. The available
biomarker studies of NAFLD did not provide convincing evidence that BLLs are associated with NAFLD
prevalence ("Chung et ah. 2020; Reia et ah. 2020; Werder et ah. 2020"). Results from studies that examined
serum biomarkers of general liver function (e.g., AST, ALT, ALP, GGT, and bilirubin) provided some
evidence that BLLs are positively associated with biomarker levels (Chen et ah. 20.1.9; Obeng-Gvasi.
20.1.9; Pollack et ah. 20.1.5). but the inference that can be drawn from these studies is limited in light of
less consistent evidence from more direct measures of hepatic function. There are also a few recent

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studies that examined serum lipids in adults or children and the results are inconsistent. Across studies,
contrasting associations were observed between BLLs and specific lipids, with no discernable pattern of
associations between BLLs and triglycerides, LDL cholesterol, HDL cholesterol, or total cholesterol.

Overall, the collective evidence is suggestive of, but not sufficient to infer, a causal
relationship between Pb exposure and hepatic effects. This conclusion is based on the strength of the
toxicological evidence and some remaining inconsistencies and uncertainties in the epidemiologic
evidence. Recent toxicological studies build upon evidence from the 2013 Pb ISA and provide largely
consistent evidence that indicates exposure to Pb can result in altered liver function and hepatic oxidative
stress. Compared to the 2013 Pb ISA, recent toxicological studies include routes of exposure and BLLs
that are more relevant to humans. Results from a limited number of recent epidemiologic studies
examining liver enzymes are generally coherent with the toxicological evidence, indicating Pb-associated
increases in enzymes that are consistent with altered liver function. However, due to the reported liver
enzyme levels in the epidemiologic studies and inconsistent evidence of an association between BLLs and
direct liver injury, there is uncertainty as to whether the observed changes in enzymes are indicative of
liver damage. The key evidence, as it relates to the causal framework, is summarized in Table 9-1.

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Table 9-1 Evidence that is suggestive of, but not sufficient to infer, a causal relationship between Pb
exposure and hepatic effects

Rationale for Causality
Determination3

Key Evidence13

References'3

Pb Biomarker Levels Associated with Effects0

Consistent evidence from Toxicological studies in rodents provide
animal toxicological	largely consistent evidence that indicates

studies at relevant BLLs exposure to Pb can result in:

Altered liver function

Increases in hepatic oxidative stress, as
indicated by decreases in GSH levels and
CAT, SOD, and GPx activities

Berrahal etal. (2011)
Liu et al. (2013)

Long et al. (2016)
Andjelkovic et al. (2019)
Gao et al. (2020)
Dumkova et al. (2020b)
Laamech et al. (2017)
Barkaoui et al. (2020)

Li etal. (2017)

Long et al. (2016)
Andjelkovic et al. (2019)
Barkaoui et al. (2020)
Gao et al. (2020)
Laamech et al. (2017)

Range of mean BLLs across studies:
18.0 to 29.0 [jg/dL

Range of mean BLLs across studies:
3.6 to 30.2 [jg/dL

Limited or inconsistent
evidence from
epidemiologic studies at
relevant BLLs

Inconsistent evidence of associations
between BLLs and NAFLD

Some evidence that BLLs are associated
with increased levels of serum biomarkers
of liver function, but limited inference due to
study populations that had biomarkers well
within normal ranges

See Section 9.1.3.1

Pollack etal. (2015)
Chen et al. (2019)
Obeng-Gvasi (2019)

Range of mean BLLs across studies:
1.0 to 5.29 [jg/dL

Range of mean BLLs across studies:
1.0 to 8.7 [jg/dL

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Rationale for Causality
Determination3

Key Evidence13

References'3

Pb Biomarker Levels Associated with Effects0

Biological Plausibility The proposed pathway leading from Pb See Section 9.1.4
exposure to hepatic health effects begins
with the induction of inflammation and
increase in oxidative stress. This results in
both changes in metabolizing enzymes and
cholesterol synthesis that could be
responsible for fatty accumulation in the
liver. Widespread oxidative damage results
in cell loss which could disrupt the normal
liver structure and contribute to loss of liver
function.

BLLs = blood lead levels; CAT = catalase; GSH = glutathione; GPx = glutathione peroxidase; NAFLD = nonalcoholic fatty liver disease; Pb = lead; SOD = superoxide dismutase.
"Based on aspects considered in judgments of causality and weight-of-evidence in causal framework in Table I and Table II of the Preamble to the IS As (U.S. EPA, 2015).
bDescribes the key evidence and references, supporting or contradicting, contributing most heavily to causality determination and, where applicable, to uncertainties or
inconsistencies. References to earlier sections indicate where the full body of evidence is described.

°Describes the Pb biomarker levels at which the evidence is substantiated.

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9.2

Metabolic Effects

9.2.1 Introduction, Summary of the 2013 Pb ISA, and Scope of the Current
Review

The 2013 Pb ISA (U.S. EPA. 20.1.3') did not have a separate discussion of potential metabolic
effects of exposure to Pb. However, evidence relevant to metabolic effects was provided by a small
number of studies that examined glucose and insulin homeostasis, lipids, cholesterol, and liver health
endpoints. These studies provided evidence for modes of action and were discussed across a few sections
of the 2013 Pb ISA (U.S. EPA. 20.1.3). including Section 4.4 (Cardiovascular Effects). Section 4.5 (Renal
Effects), and Section 4.9.1 (Effects on the Hepatic System). There was no causality determination for
metabolic effects in the 2013 Pb ISA (U.S. EPA. 2013).

The metabolic effects reviewed in this section include diabetes mellitus and insulin resistance
(Section 9.2.3.1), metabolic syndrome and its components (Section 9.2.3.2), and effects on body weight
measures (Section 9.2.3.3). Other metabolic indicators, such as changes in liver function, serum lipids,
and neuroendocrine signaling, are discussed in other sections of this appendix (Sections 9.2 and 9.4).

9.2.2 Scope

The scope of this section is defined by PECOS statements. The PECOS statement defines the
objectives of the review and establishes study inclusion criteria thereby facilitating identification of the
most relevant literature to inform the Pb ISA.6 In order to identify the most relevant literature, the body of
evidence from the 2013 Pb ISA was considered in the development of the PECOS statements for this
Appendix. Specifically, well-established areas of research; gaps in the literature; and inherent
uncertainties in specific populations, exposure metrics, comparison groups, and study designs identified
in the 2013 Pb ISA inform the scope of this Appendix. The 2013 Pb ISA used different inclusion criteria
than the 2024 Pb ISA, and the studies referenced therein often do not meet the current PECOS criteria
(e.g., due to higher or unreported biomarker levels). Studies included in the 2013 Pb ISA, including many
that do not meet the current PECOS criteria, are discussed in this appendix to establish the state of the
evidence prior to this assessment. Except for supporting evidence used to demonstrate the biological

6The following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

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plausibility of Pb-associated metabolic effects, recent studies were only included if they satisfied all of the
components of the following discipline-specific PECOS statements:

Epidemiologic Studies:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

Exposure: Exposure to Pb7 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure;8 or intervention groups in randomized trials and quasi-experimental studies.

Outcome: Metabolic effects.

Experimental Studies:

Exposure: Oral, inhalation, or intravenous routes administered to a whole animal (in vivo) that
results in a BLL of 30 (ig/dL or below.910

Comparators: A concurrent control group exposed to vehicle-only treatment or untreated
control.

Outcomes: Metabolic effects.

Study design: Controlled exposure studies of animals in vivo.

'Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the NAAQS review (e.g., longitudinal studies designed to examine recent versus historical Pb
exposure).

8Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM25) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure | Section 2.5.3 (U.S. EPA. 20.1. 2)].
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with BLLs are lacking.

9Pb mixture studies are included if they employ an experimental arm that involves exposure to Pb alone.

10This level represents an order of magnitude above the upper end of the distribution of U.S. young children's BLL.
The 95th percentile of the 2011-2016 NHANES distribution of BLL in children (1-5 years; n= 2,321) is 2.66 (ig/dL
(Egan et at. 2021) and the proportion of individuals with BLL that exceed this concentration varies depending on
factors including (but not limited to) housing age, geographic region, and a child's age, sex, and nutritional status.

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9.2.3

Epidemiologic Studies on Metabolic Effects

9.2.3.1 Diabetes Mellitus and Insulin Resistance

Diabetes mellitus is a chronic condition characterized by an inability to regulate glucose in the
blood by producing or responding to insulin. A number of epidemiologic studies evaluated in the 2013 Pb
ISA (U.S. EPA. 20.1.3') examined diabetes as a potential at-risk factor that could modify the relationship
between Pb exposure and other health outcomes, but none examined the direct relationship between Pb
exposure and diabetes incidence or prevalence. Recent studies have examined this relationship,
commonly categorizing diabetes mellitus status as meeting one or more of the following criteria: (1)
elevated fasting blood glucose (FBG), (2) self-reported use of insulin or oral medications for diabetes, or
(3) self-reported physician diagnosis with diabetes. There are three primary types of diabetes: type I, type
II, and gestational diabetes mellitus (GDM). Some of the evaluated studies distinguished between types of
diabetes mellitus, while others did not. Most studies were cross-sectional in design, meaning temporality
between exposure and outcome could not be established.

Recent epidemiologic studies examining the relationship between Pb exposure and diabetes
mellitus, or insulin resistance have reported mostly null findings across lifestages. In adult populations, a
limited number of case-control and cross-sectional studies examining diabetes prevalence reported null or
inverse associations between BLLs and diabetes mellitus or levels of insulin resistance. Results from
recent studies examining insulin resistance in adolescents and gestational diabetes in pregnant women are
also mostly null. Measures of central tendency for Pb biomarker levels used in each study, along with
other study-specific details, including study population characteristics and select effect estimates, are
highlighted in Table 9-6. An overview of the recent evidence is provided below.

Studies in Adults

In a recent cross-sectional analysis of blood Pb and diabetes using data from the 2009 and 2010
cycles of the KNHANES, Moon (2013) observed a negative trend in diabetes prevalence across blood Pb
quartiles. In reference to the lowest blood Pb quartile (geometric mean (GM): 1.43 |ig/dL). the smallest
Ors were observed in the highest exposure quartile (GM: 4.08 (ig/dL; OR = 0.745 [95% CI: 0.516, 1.077])
and in the second highest quartile (GM: 2.74 (ig/dL) (OR= 0.759 [95% CI: 0.531, 1.086]). Similarly, in
stratified analyses examining effect modification by sex in subjects without diabetes. Moon (2013)
reported slightly lower Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), HOMA of [3-
cell function (HOMA-J3), and fasting insulin per log unit higher BLL. The observed results were
comparable in men and in women.

Two recent cross-sectional case-control studies originating from the Nord-Trondelag Health
Study (HUNT3) evaluated differences in blood Pb measurements between subjects with and without type
11 diabetes and reported results that are also consistent with a null or negative association (Hansen et ah.

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20.1.7; Simic et ah. 20.1.7'). Specifically, Hansen et al. (20.1.7) identified 128 cases of previously
undiagnosed, screening-detected type II diabetes and 755 age- and sex-matched controls. The authors
observed slightly higher, but notably imprecise odds of screening-detected type II diabetes for blood Pb
quartile 4 compared to quartile 1 (OR =1.12 [95% CI: 0.58, 2.16]). As indicated by the wide confidence
intervals, higher odds are difficult to distinguish from chance. In a parallel analysis, Simic e
identified 267 cases of self-reported type II diabetes and 609 frequency-matched controls from the same
HUNT3 cohort. Consistent with results from Moon (20.1.3). (Simic et al.. 20.1.7) observed substantially
lower diabetes prevalence corresponding to participants with BLLs in the highest quartile compared to the
lowest (OR = 0.24 [95% CI: 0.13, 0.47]). The observation of a negative association for Pb and type II
diabetes by Simic et al. (IV I ^ but not Hansen et i! UiM ^ may be related to differences in exposure
contrast between identified cases and controls. Hansen et al. (20.1.7) reported median BLLs of 1.99 (ig/dL
for controls and 1.94 (ig/dL for cases, while Simic et al. (20.1.7) reported median BLLs of 2.02 (ig/dL for
controls and 1.64 (ig/dL for cases. Additionally, the differences could be due to an effect of diabetes
treatment on BLLs, which highlights an uncertainty of these cross-sectional analyses.

Studies in Adolescents

A recent study assessed the relationship between exposure to Pb in utero and insulin resistance in
adolescence (Liu et al.. 2020). Pregnant mothers were enrolled in the ELEMENT project from 1997-1999
and 2001-2003 and their children were followed until 2015. There was a null association between first
trimester maternal blood Pb >5 (ig/dL and HOMA-IR in adolescence. The authors also examined effect
modification by sex and reported null associations for boys and girls.

Studies in Pregnant Women

A number of recent studies have investigated the relationship between Pb exposure and GDM.
These studies, most of which have reported null associations between BLLs and GDM, are discussed in
more detail in Section 8.4. LI .2 of the Reproductive and Developmental Effects Appendix.

9.2.3.2 Metabolic Syndrome and its Components

Metabolic syndrome (MetS) describes a set of cardiometabolic conditions that increase a person's
risk for cardiovascular diseases. Components of MetS include elevated blood pressure, low HDL
cholesterol, elevated blood triglycerides, elevated FBG, and a high waist circumference, also referred to
as abdominal obesity. A MetS diagnosis is commonly defined as meeting three or more of the following
criteria: (1) elevated blood pressure (systolic blood pressure >130 mmHg or diastolic blood pressure
>85 mmHg or current use of blood pressure medication); (2) low HDL cholesterol (<40 mg/dL in women
or <50 mg/dL in men); (3) elevated serum triglycerides (>150 mmHg) or current use of anti-dyslipidemia

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medication; (4) elevated FBG (>100 (.ig/dL): (5) abdominal obesity (waist circumference >90 cm in men
or >85 cm in women). None of the studies evaluated in the 2013 Pb ISA (U.S. EPA. 2013) examined the
relationship between Pb exposure and MetS. Recent evidence for the effects of Pb exposure on MetS and
its components is inconsistent. Measures of central tendency for Pb biomarker levels used in each study,
along with other study-specific details, including study population characteristics and select effect
estimates, are highlighted in Table 9-3. An overview of the recent evidence is provided below.

9.2.3.3 Metabolic Syndrome

A number of recent large, population-based cross-sectional studies have analyzed the relationship
between BLLs and MetS prevalence and provide inconsistent evidence of an association. Across studies,
mean and/or median BLLs were below 5 (ig/dL, including some below 2 (ig/dL. Studies analyzing data
from overlapping cycles of the KNHANES observed higher MetS prevalence in participants with higher
BLLs (Moon. 20.1.4; Rhee et ah. 20.1.3). Specifically, Rhee et al. (20.1.3) reported that 2008 KNHANES
participants with BLLS in the highest exposure quartile (3.07-19.43 |ig/L) were 2.57 (95% CI: 1.46, 4.51)
times more likely to have MetS than subjects in the lowest quartile (0.42-1.73 |ig/L). The authors noted a
consistent concentration-response trend across quartiles. In an analysis incorporating more KNHANES
cycles (2007-2012), Moon (20.1.4) observed higher odds of MetS for subjects in the second highest
exposure quartile (GM 2.51 (ig/dL) (OR= 1.21 [95% CI: 0.90, 1.62]) compared to the lowest (GM
1.23 (ig/dL) but did not observe a clear dose-response trend across quartiles.

In contrast to KNHANES studies, other analyses of data from a variety of large population-based
surveys noted negative associations between BLLs and MetS (Wen et al.. 2020; Bulka et al.. 20.1.9; Shim
et al.. 20.1.9). Bulka el	1.9) used data from two NHANES cycles (2011-2014) to perform a cross-

sectional analysis of blood Pb and MetS prevalence. The authors observed lower odds of MetS at higher
blood Pb quartiles, with the lowest odds observed in subjects in the highest quartile of Pb exposure (1.64-
15.98 (.ig/dL) compared to the lowest quartile (0.18-0.70 (.ig/dL) (OR = 0.81 [95% CI: 0.64, 1.03]). Shim
et al. (20.1.9) and Wen et al. (2020) similarly reported lower odds of MetS associated with higher BLLs in
the Korean National Environmental Health Survey II (KNHANES II) and a survey of adults in Taiwan,
respectively.

Components of Metabolic Syndrome

In addition to cross-sectional studies evaluating MetS prevalence, several recent studies have
assessed the potential effects of Pb on the individual components of MetS (i.e., abdominal obesity [often
measured by waist circumference], low HDL cholesterol, elevated triglycerides, and elevated FBG;
studies evaluating blood pressure and hypertension are discussed in Section 4.3). Similar to studies that
evaluated MetS prevalence, most of these studies analyzed cross-sectional data from nationally

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representative health surveys. In general, results from recent studies were inconsistent across individual
MetS components, with the exception of blood pressure and serum triglycerides.

Waist Circumference

Recent KNHANES analyses of BLLs and waist circumference were inconsistent ("Lee and Kim.
20.1.6. 20.1.3; Rfaee et ah. 2013). In an analysis of KNHANES participants from 2005-2010, Lee and Kim
(20.1.3) observed no apparent association between BLLs and waist circumference. The same authors
evaluated more recent KNHANES cycles (2007-2012) and observed slightly higher odds of waist
circumference >85 cm in the second ( >2.199-3.011 jxg/d) and third (>3.011 (ig/dL) blood Pb tertiles
compared to the first tortile (<2.199 (.ig/dL). but slightly lower odds per twofold higher BLLs ("Lee and
Kim. 20.1.6"). In contrast, in an analysis of 2008 KNHANES participants, Rfaee et	1.3) found a

modest positive association between blood Pb and abdominal circumference as a continuous variable.

Results from two recent NHANES analyses were similarly inconsistent (Bulka et ah. 20.1.9; Wang
et ah. 2018c). Wang et ah (20.1.8c) used data from NHANES cycles between 2003 and 2014 and observed
0.8% (95% CI: 0.6, 1.0%) lower waist circumference per 1-SD higher logio-transformed BLL ((.ig/dL). In
contrast, a study including two NHANES cycles that overlapped with the Wang et ah (20.1.8c) study
(2011-2014) reported negative associations between BLLs and probability of abdominal obesity (Bulka et
ah. 20.1.9).

HDL Cholesterol and Serum Triglycerides

The previously discussed KNHANES analyses also assessed HDL cholesterol and serum
triglycerides. These studies do not provide evidence that BLLs are associated with higher odds of low
HDL cholesterol (Lee and Kim. 20.1.6. 20.1.3; Rfaee et ah. 20.1.3). The same studies did provide consistent
evidence of higher serum triglycerides in association with higher BLLs, although these studies were
notably conducted in overlapping populations (i.e., non-independent samples). Lee and Kim (20.1.3) and
Lee and Kim (20.1.6) observed slightly higher odds of high serum triglycerides (>150 (.ig/dL) with higher
BLLs (analyzed as a continuous variable and as tertiles). Similarly. Rfaee et ah (20.1.3) reported a modest
positive association between serum triglycerides and log-transformed BLLs.

In addition to studies that examined HDL cholesterol and serum triglycerides in conjunction with
MetS, a few other recent studies also evaluated these measures as part of a broader lipids profile. As
discussed in Section 9.1.3.3, these studies were inconsistent for HDL cholesterol and triglycerides,
including a prospective cohort study of older Veterans participating in the NAS that reported null
associations between BLLs at baseline and HDL cholesterol and triglyceride levels after three to four
years of follow-up (Peters et ah. 20.1.2).

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Elevated Fasting Glucose

The majority of recent population-based cross-sectional studies of MetS components did not
observe associations between BLLs and FBG. Specifically, KNHANES analyses ("Lee and Kim. 20.1.6;
Rhee et al.. 20.1.3) and a recent NHANES analysis (Bulka et ah. 2019) reported null associations between
BLLs and FBG. In contrast, in an analysis of earlier KNHANES cycles, Lee and Kim (20.1.3) reported
BLLs to be positively associated with elevated FBG (>100 (ig/dL), with higher odds of elevated FBG
relative to two-fold higher BLLs (OR = 1.118 [95% CI: 0.953, 1.311]). In addition to large cross-sectional
studies, a smaller cross-sectional analysis of adults of African descent across five countries of varying
social and economic development in Africa also examined the relationship between BLLs and elevated
FBG (Ettinger et al.. 20.1.4). Ettinger et al. (20.1.4) reported higher odds of elevated FBG (>100 mg/dL) in
subjects with a blood Pb exposure level above the median (1.66 (ig/dL) compared to those below it
(OR = 4.99 [95% CI: 1.97, 12.69]). However, the small sample size (n = 150) in this study reduces
statistical power and the precision of the effect estimate.

9.2.3.4 Body Weight Measures in Adults

A few epidemiologic studies evaluated in the 2013 Pb ISA ("U.S. EPA. 20.1.3) examined obesity as
a potential risk factor that could modify the relationship between Pb exposure and other health outcomes,
but none examined the direct relationship between Pb exposure and body weight measures in adults.
Recent studies have examined this relationship, commonly assessing body weight using body mass index
(BMI), a measure of body fat that is calculated as a person's weight divided by the square of their height.
For adults, overweight is defined as having a BMI of 25 kg/m2 or greater and obesity is defined as having
a BMI of 30 kg/m2 or greater. Studies examining Pb and body weight measures in children and
adolescents are discussed in the Reproductive and Developmental Effects Appendix of the 2024 Pb ISA
(Section 8.5.1.1).

A limited number of recent studies have examined the relationship between Pb exposure and
body weight measures in adults. Overall, the current evidence for the effects of Pb exposure on body
weight measures is inconsistent, although small sample sizes limit the interpretation of a few of the
studies. Additionally, recent studies are cross-sectional, which reduces confidence in their results because
temporality between exposure and outcome cannot be established. Measures of central tendency for Pb
biomarker levels used in each study, along with other study-specific details, including study population
characteristics and select effect estimates, are highlighted in Table 9-3. An overview of the recent
evidence is provided below.

Recent studies examining Pb exposure and body weight measures in adults utilize cross-sectional
study designs. In an analysis of a large population-based survey of Chinese citizens, Wang et al. (20.1.8a)
observed higher BMI ([3 = 0.24 kg/m2 [95% CI: 0.08, 0.40 kg/m2]) and odds of being overweight or obese
(OR =1.13 [95% CI: 1.02, 1.25]) associated with each natural log unit higher level of blood Pb (|ig/L). In

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order to account for potential reverse causality, the authors used Mendelian randomization to assess the
relationship between BLLs and genetic variants associated with increased BMI. Because the genetic
variants precede exposure, the variants are expected to be associated with BLLs if BMI is a potential
causal factor of increased BLLs. Wang et al. (20.1.8a) reported null associations between BLLs and an
aggregate measure of single nucleotide polymorphisms constructed to represent susceptibility to high
BMIs.

Other recent studies were less informative due to small sample sizes. In a cross-sectional analysis
of adults of African descent across five countries of varying social and economic development in Africa,
Ettinger et al. (20.1.4) compared the prevalence of being overweight (BMI >25) or being obese (BMI >30)
among subjects above versus below the median blood Pb exposure level (1.66 (ig/dL). Among subjects
with above median blood Pb, Ettinger et al. (20.1.4) observed slightly lower odds of being overweight
(OR = 0.88 [95% CI: 0.31, 2.51]), but higher odds of being obese (OR = 2.70 [95% CI: 0.75, 9.75]). The
observed associations, however, were notably imprecise due to the small sample size (n = 150). In
contrast, another small cross-sectional study of 145 adult men living in China observed a null association
between BLLs and BMI (Guo et al.. 20.1.9). As is the case in both of these studies, limited statistical
power resulting from a small sample size reduces statistical power and precision, which might explain the
incongruous results.

9.2.4 Toxicological Studies on Metabolic Effects

The 2013 Pb ISA did not have a section devoted to toxicological studies related to the effect of Pb
on metabolism. However, as discussed in the Section 9.1.4, a few studies evaluated in the 2013 Pb ISA
demonstrated that Pb exposure can impair lipid metabolism in animals, as evidenced by increased hepatic
cholesterogenesis, and altered triglyceride and phospholipid levels ("Sfaanna et al.. 20.1.0; Ademuviwa et
al.. 2009; Khotimchenko and Kolenehenko. 2007). The relevance of the toxicological evidence is
uncertain, as many studies administered Pb as bolus doses and/or results were observed in animals with
high BLLs. In subsequent years, there have been a few PECOS-relevant publications on Pb exposure and
metabolic effects. In general, these studies cover disparate endpoints, but provide some evidence of Pb-
induced changes in metabolic activity in rodents.

In a lifetime study using mice, Faulk et al. (20.1.4) assessed perinatal Pb exposures via Pb acetate
in drinking water from conception to weaning. Average maternal BLLs for exposed groups ranged from
4.1 to 32 (ig/dL. The study findings included sex-specific increases in energy expenditure, food intake,
body weight, total body fat, activity, and insulin response. In addition, a study in weanling rats that
focused on neuropathology found that Pb exposure decreased cholesterol levels in brain tissue (Zhou et
al.. 20.1.8). The latter study, which also used Pb acetate in drinking water, reported BLLs ranging from
14.7 to 28.9 (.ig/dL. Finally, in an investigation of the effects of vitamin D metabolism in rats. Rahman et

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al. (20.1.8) reported that Pb interferes with vitamin D metabolism by affecting the expression of its
metabolizing enzymes.

9.2.5 Summary and Causality Determination

There was no causality determination for metabolic effects in the 2013 Pb ISA (U.S. EPA. 2013).
The number of studies examining Pb exposure and metabolic effects has expanded substantially since the
2013 Pb ISA ("U.S. EPA. 2013). highlighted by a number of recent epidemiologic studies, as well as a few
animal toxicological studies currently available for review. The focus of this causality determination is on
altered glucose resistance, diabetes mellitus, MetS, and obesity. Notably, there is significant overlap
between components of metabolic health and the cardiovascular and hepatic systems. While blood
pressure and serum lipids are important components of MetS, they are also discussed in detail in the
cardiovascular effects appendix (Appendix 4) and hepatic effects section (Section 9.1), and contribute to
the causality determinations therein. For the metabolic effects causality determination, these endpoints are
considered to the extent that they contribute to a diagnosis of MetS.

There is some evidence from a limited number of animal toxicological studies that exposure to Pb
resulting in BLLs relevant to humans alters cholesterol metabolism (Zhou et al.. 20.1.8) and leads to
increases in body weight, body fat. and insulin response (Faulk et al.. 20.1.4'). In contrast, recent
epidemiologic studies are inconsistent across a range of metabolic outcomes and thus not coherent with
the limited toxicological evidence. A limited number of cross-sectional studies examining diabetes
prevalence and insulin resistance in adults reported null (Hansen et al.. 20.1.7; Simic et al.. 20.1.7) and
negative (Moon. 20.1.3) associations with BLLs. Further, results from analyses of MetS in large national
surveys in the United States and Korea were largely inconsistent. Many of these same studies also provide
generally inconsistent evidence of associations between BLLs and individual components of MetS,
though there is substantial epidemiologic and toxicological evidence that exposure to Pb leads to
increased blood pressure and hypertension (Section 4.3). While a limited number of KNHANES analyses
demonstrate consistent associations between BLLs and serum triglycerides (Lee and Kim. 20.1.6. 2013;
Rhee et al.. 2013). these studies include overlapping study populations and therefore do not provide
independent evidence of associations. Additionally, a recent prospective cohort study of older adults
observed null associations between BLLs at baseline and serum triglyceride levels measured three to four
years later (Peters et al.. 2012). Despite observed associations between BLLs and some of the individual
components of MetS, the available evidence examining the cluster of components does not consistently
associate BLLs with MetS. A notable limitation of the current evidence base is the use of concurrent
BLLs as a biomarker for Pb exposure. Given the chronic nature of MetS, a cumulative measure of Pb
exposure, such as bone Pb, might be more relevant.

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Collectively, given the insufficient quantity of toxicological studies and inconsistency in
epidemiologic results, the evidence is inadequate to infer the presence or absence of a causal
relationship between Pb exposure and metabolic effects.

9.3 Effects on the Gastrointestinal System

9.3.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the
Current Review

The 2013 Pb ISA concluded that "because of the insufficient quantity and quality of studies, the
available evidence was inadequate to determine if there is a causal relationship between Pb exposure and
gastrointestinal effects" ("U.S. EPA. 20.1.3'). There were very few studies evaluated in the 2013 Pb ISA that
examined Pb exposure and gastrointestinal (GI) effects in humans or animals. Epidemiologic evidence of
an association between Pb exposure and GI effects was limited to a small number of occupational studies
of prevalent symptoms in Pb-exposed workers. The internal validity and generalizability of these studies
was limited by cross-sectional study designs, lack of consideration for potential confounders, and notably
higher BLLs (>40 (ig/dL) than those experienced by the general population. In addition to the
epidemiologic evidence, there were a limited number of toxicological studies that provide evidence of Pb-
induced effects on mechanisms underlying GI damage and impaired function.

9.3.2	Scope

The scope of this section is defined by PECOS statements. The PECOS statement defines the
objectives of the review and establishes study inclusion criteria thereby facilitating identification of the
most relevant literature to inform the Pb ISA.11 In order to identify the most relevant literature, the body
of evidence from the 2013 Pb ISA was considered in the development of the PECOS statements for this
Appendix. Specifically, well-established areas of research; gaps in the literature; and inherent
uncertainties in specific populations, exposure metrics, comparison groups, and study designs identified
in the 2013 Pb ISA inform the scope of this Appendix. The 2013 Pb ISA used different inclusion criteria
than the 2024 Pb ISA, and the studies referenced therein often do not meet the current PECOS criteria
(e.g., due to higher or unreported biomarker levels). Studies included in the 2013 Pb ISA, including many
that do not meet the current PECOS criteria, are discussed in this appendix to establish the state of the

nThe following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

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evidence prior to this assessment. Except for supporting evidence used to demonstrate the biological
plausibility of Pb-associated effects on the gastrointestinal system, recent studies were only included if
they satisfied all of the components of the following discipline-specific PECOS statements:

Epidemiologic Studies:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

Exposure: Exposure to Pb12 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure13; or intervention groups in randomized trials and quasi-experimental studies.

Outcome: Effects on the gastrointestinal system.

Study Design: Epidemiologic studies consisting of longitudinal and retrospective cohort studies,
case-control studies, cross-sectional studies with appropriate timing of exposure for the health
endpoint of interest, randomized trials, and quasi-experimental studies examining
interventions to reduce exposures.

Experimental Studies:

Population: Laboratory nonhuman mammalian animal species (i.e., mouse, rat, Guinea pig,

minipig, rabbit, cat, dog; whole organism) of any lifestage (including preconception, in utero,
lactation, peripubertal, and adult stages).

Exposure: Oral, inhalation, or intravenous routes administered to a whole animal (in vivo) that
results in a BLL of 30 (ig/dL or below.1415

Comparators: A concurrent control group exposed to vehicle-only treatment or untreated
control.

Outcomes: Effects on the gastrointestinal system.

12Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the NAAQS review (e.g., longitudinal studies designed to examine recent versus historical Pb
exposure).

13Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM2 5) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure | Section 2.5.3 (U.S. EPA. 20.1. 2)].
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with BLLs are lacking.

14Pb mixture studies are included if they employ an experimental arm that involves exposure to Pb alone.

15This level represents an order of magnitude above the upper end of the distribution of U.S. young children's BLL.
The 95th percentile of the 2011-2016 NHANES distribution of BLL in children (1-5 years; n= 2,321) is 2.66 (ig/dL
(Egan et at. 2021) and the proportion of individuals with BLL that exceed this concentration varies depending on
factors including (but not limited to) housing age, geographic region, and a child's age, sex, and nutritional status.

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Study design: Controlled exposure studies of animals in vivo.

9.3.3 Epidemiologic Studies on the Gastrointestinal System

The epidemiologic evidence evaluated in the 2013 Pb ISA was limited to a small number of
occupational cohort studies of prevalent GI symptoms in Pb-exposed workers (U.S. EPA. 20.1.3'). As noted
in Section 9.3.1, these studies had a number of limitations, including cross-sectional study designs, lack
of consideration for potential confounders, and notably higher BLLs (>40 (ig/dL) than those experienced
by the general population. There are no recent PECOS-relevant epidemiologic studies that evaluate
potential associations between exposure to Pb and effects on the gastrointestinal system. A limited
number of studies reported associations between BLLs and gut microbiota diversity, as discussed in the
Immune System Effects Appendix ("Section 6.6). However, these studies do not inform the relationship
between Pb exposure and specific GI health effects.

9.3.4 Toxicological Studies on the Gastrointestinal System

In the 2013 Pb ISA ("U.S. EPA. 20.1.3). specific attention was drawn to a pair of rat studies; one
reporting frequency-dependent inhibition of electric field-stimulated relaxations to nonadrenergic
noncholinergic (NANC) nerve stimulation in rat gastric fundus (possibly due to the modulated release of
NO), and the other focusing on Pb-induced oxidative stress in the gastric mucosa, wherein an increase in
gastric mucosal damage induced by the acidified ethanol was observed. Neither of these studies reported
BLLs. Neither of the two pertinent studies since the 2013 Pb ISA directly addresses these findings
lYReddv et a!.. 20.1.8; Kosik-Bogacka et ah. 20.1.1); see below].

In a chronic exposure study with rats, Kosik-Bogacka et al. i confirmed an inhibitory effect
of Pb on electrophysiological parameters, among other findings. These findings were strengthened by
results showing the ability of L-ascorbic acid to (at least partially) abrogate the effects of Pb exposure.
Mean BLLs in this study were reported at 7 (ig/dL.

In a 2018 microbiome study, Reddv et al. (20.1.8) found that Pb-exposed rats had decreased 8-
aminolevulinic acid dehydratase (ALAD) activity and intestinal lactobacillus levels, irrespective of the
dietary iron supplementation. Withdrawal of Pb exposure increased lactobacilli, whereas re-exposure to
Pb decreased lactobacilli population. BLLs were reported in the range of 19 to 48 (ig/dL.

9.3.5 Summary and Causality Determination

The 2013 Pb ISA concluded that evidence was "inadequate" to determine whether a causal
relationship exists between Pb exposure and GI effects (U.S. EPA. 20.1.3). This causality determination

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was based on an insufficient quantity and quality of studies in the cumulative body of evidence. A limited
number of occupational cohort studies indicated associations between BLLs and prevalent symptoms,
such as stomach pain, gastritis, constipation, and intestinal paralysis. However, the implications of these
findings are limited by the cross-sectional study designs, high BLLs associated with effects (mostly
>40 (ig/dL), and limited consideration of potential confounding by factors such as age, smoking, alcohol
use, nutrition, or other occupational exposures. Toxicological evidence indicates that Pb is absorbed
primarily in the duodenum by active transport and diffusion, although variability is observed by Pb
compound, age of intake, and nutritional factors. There was some coherence between the evidence in Pb-
exposed workers and observations in animals that Pb induces damage to the intestinal mucosal
epithelium, decreases duodenum contractility and motility, reduces absorption of calcium ion(s) (Ca2+),
inhibits NANC relaxations in the gastric fundus, and induces oxidative stress (lipid peroxidation,
decreased SOD and CAT) in the gastric mucosa.

Recent studies are limited in number, and while some provide potential biological plausibility for
Pb-induced GI effects, none directly inform the relationship between Pb exposure and GI effects. Given
the insufficient quantity and quality of studies, the evidence remains inadequate to infer the presence or
absence of a causal relationship between Pb exposure and gastrointestinal effects.

9.4 Effects on the Endocrine System

9.4.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current
Review

The 2013 Pb IS A (U.S. EPA. 2013) evaluated a limited number of studies examining the
relationship between exposure to Pb and effects on the endocrine system. Epidemiologic and
toxicological evidence related to male and female sex hormones, which was generally inconsistent, is
discussed in more detail in Appendix 8 (Sections 8.6.1.1 and 8.7.2). In addition to studies on sex
hormones, results from a small number of epidemiologic and toxicological studies on Pb-associated
endocrine effects such as changes in thyroid hormones, Cortisol, corticosterone, and vitamin D levels were
also inconsistent. Further, epidemiologic studies were mostly cross-sectional and included limited
consideration for potential confounders. As a whole, the limited quantity, quality, and consistency of the
available evidence was "inadequate to determine if there is a causal relationship between Pb exposure and
endocrine effects related to thyroid hormones, Cortisol, and vitamin D."

9.4.2	Scope

The scope of this section is defined by PECOS statements. The PECOS statement defines the
objectives of the review and establishes study inclusion criteria thereby facilitating identification of the

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most relevant literature to inform the Pb ISA.16 In order to identify the most relevant literature, the body
of evidence from the 2013 Pb ISA was considered in the development of the PECOS statements for this
Appendix. Specifically, well-established areas of research; gaps in the literature; and inherent
uncertainties in specific populations, exposure metrics, comparison groups, and study designs identified
in the 2013 Pb ISA inform the scope of this Appendix. The 2013 Pb ISA used different inclusion criteria
than the 2024 Pb ISA, and the studies referenced therein often do not meet the current PECOS criteria
(e.g., due to higher or unreported biomarker levels). Studies included in the 2013 Pb ISA, including many
that do not meet the current PECOS criteria, are discussed in this appendix to establish the state of the
evidence prior to this assessment. Except for supporting evidence used to demonstrate the biological
plausibility of Pb-associated effects on the gastrointestinal system, recent studies were only included if
they satisfied all of the components of the following discipline-specific PECOS statements:

Epidemiologic Studies:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

Exposure: Exposure to Pb17 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure18; or intervention groups in randomized trials and quasi-experimental studies.

Comparison: Populations, population subgroups, or individuals with relatively higher versus
lower levels of the exposure metric (e.g., per unit or log unit increase in the exposure metric,
or categorical comparisons between different exposure metric quantiles).

Outcome: Effects on the endocrine system.

Study Design: Epidemiologic studies consisting of longitudinal and retrospective cohort studies,
case-control studies, cross-sectional studies with appropriate timing of exposure for the health
endpoint of interest, randomized trials and quasi-experimental studies examining
interventions to reduce exposures.

16The following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

1'Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the NAAQS review (e.g., longitudinal studies designed to examine recent versus historical Pb
exposure).

18Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM2 5) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure | Section 2.5.3 (U.S. EPA. 2013)1.
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with BLLs are lacking.

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Experimental Studies:

Exposure: Oral, inhalation, or intravenous routes administered to a whole animal (in vivo) that
results in a BLL of 30 (ig/dL or below.19,20

Comparators: A concurrent control group exposed to vehicle-only treatment or untreated
control.

Outcomes: Effects on the endocrine system.

Study design: Controlled exposure studies of animals in vivo.

9.4.3 Epidemiologic Studies on the Endocrine System

A limited number of epidemiologic studies evaluated in the 2013 Pb ISA (U.S. EPA. 20.1.3)
reported associations between exposure to Pb and measures of endocrine function, including thyroid
hormones, Cortisol, and vitamin D levels. However, most studies were cross-sectional in design, and
many did not consider potential confounding factors. Further, while some studies did find associations
between Pb exposure and endocrine effects, the results for specific hormones were not consistent.

There are several recent epidemiologic studies of Pb exposure and endocrine function, which also
implement cross-sectional analyses but included more robust adjustment for potential confounding
factors. The majority of recent studies are large NHANES analyses that provide generally consistent
evidence of null associations between Pb exposure and thyroid hormone and Cortisol levels. However,
given that these studies examined overlapping study populations, the generally consistent results across
these studies should not be considered independent evidence of a null association. Most recent studies
evaluated potential associations between Pb exposure and thyroid hormone levels, including
triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH). There were a few studies
that looked at associations between Pb exposure and Cortisol levels and no recent PECOS-relevant studies
that looked at Pb exposure and vitamin D levels. Measures of study-specific BLLs and endocrine effect
estimates are highlighted in Table 9-9. An overview of recent evidence is provided below.

The most consistent evidence from recent studies indicates null associations between BLLs and
TSH, T3, and free T4 (FT4) levels in adults. A few recent NHANES analyses, which included nationally
representative study populations of adults over 20 years old, reported null associations between BLL and

19Pb mixture studies are included if they employ an experimental arm that involves exposure to Pb alone.

20This level represents an order of magnitude above the upper end of the distribution of U.S. young children's BLL.
The 95th percentile of the 2011-2016 NHANES distribution of BLL in children (1-5 years; n= 2,321) is 2.66 (ig/dL
(Egan et at. 2021) and the proportion of individuals with BLL that exceed this concentration varies depending on
factors including (but not limited to) housing age, geographic region, and a child's age, sex, and nutritional status.

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TSH levels in adults ("Krieg. 20.1.9; Chen et ah. 20.1.3; Mendv et al.. 20.1.3; Christensen. 2012). Recent
NHANES analyses also provide generally consistent evidence of null associations between BLLs and
FT4 levels ("Luo and Hendrvx. 20.1.4; Chen et al.. 20.1.3; Mendv et al.. 2013) as well as between blood Pb
and T3 levels (Nie et al.. ; uo and Hendrvx. 20.1.4; Chen et al.. 20.1.3; Mendv et al.. 20.1.3;
Christensen. 2012).

Recent NHANES studies evaluating a potential association between BLLs and total T4 levels
were less consistent. While some recent studies reported null associations between BLLs and T4 levels in
adults ("Luo and Hendrvx. 2014; Chen et al.. 2013). others observed negative associations (Krieg. 20.1.9;
Mendv et al.. 2013; Christensen. 20.1.2). For example, Mendv et al. (2013) reported that T4 levels were
0.162 (ig/dL lower (95% CI: -0.321, -0.004 (ig/dL) for each 1 (ig/dL higher level of blood Pb.
Additionally, while Luo and Hendrvx (20.1.4) noted a null association between BLLs and T4 levels in the
total population, the authors observed a significant negative association between blood Pb and T4 levels
among men after stratifying by sex. Krieg (20.1.9) also found a negative association between blood Pb and
T4 levels, reporting 38.91% (95% CI: -51.25, -23.44) lower T4 levels for each 1 (ig/dL higher level of
blood Pb.

A limited number of NHANES analyses evaluated potential associations between blood Pb and
free T3 (FT3) levels (Luo and Hendrvx. 20.1.4; Chen et al.. 20.1.3; Mendv et al.. 20.1.3). In an analysis of
adults, Mendv et al. (20.1.3) reported a null association between blood Pb and FT3 levels in the general
adult population. This is consistent with the findings of Chen et al. (20.1.3). who reported a null
association between BLLs and FT3 levels in both adolescents (12-19 years old) and adults (>20 years
old). Both studies performed analyses on the 2007-2008 continuous NHANES cycle. Luo and Hendrvx
(20.1.4) evaluated 2007-2010 data, reporting a positive association between blood Pb and FT3 in the
general adult population. The authors reported that FT3 levels were 0.04 (ig/dL (95% CI: 0.01, 0.08)
higher in the highest tertile of blood Pb compared to the lowest.

In addition to the NHANES analyses discussed above, another recent cross-sectional study
examined the relationship between BLLs and thyroid hormone levels in a small study of pregnant women
(n = 291) from the Yugoslavia Prospective Study of Environmental Lead Exposure Cohort ("Kahn et al..
20.1.4). Kahn et al. (20.1.4) reported a null association between BLL and TSH levels and a negative
association between blood Pb and FT4 levels.

Two recent cross-sectional studies examined associations between BLLs and Cortisol levels
(Ngueta et al.. 20.1.8; Souza-Talarico et al.. 20.1.7). In a small study of older adults (n = 65) in Montreal,
Canada, Ngueta et al. (20.1.8) reported null associations between BLLs and both diurnal and stress-reactive
Cortisol secretion. In contrast, another small study of non-occupationally exposed Brazilian older adults
(n = 126), Souza-Talarico et al. C reported positive associations between BLLs and both Cortisol
awakening response (CAR) and overall Cortisol concentration. The authors reported that CAR was
0.791 (ig/dL (95% CI: 0.672, 1.073 (ig/dL) higher per 1 (ig/dL higher level of blood Pb. However, it is
worth noting that participants showed an elevated basal circadian level of salivary Cortisol independent of

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Pb exposure, suggesting this population has more repeated exposure to stressful events. Furthermore,
while all participants were older postmenopausal adults, sex was unevenly represented with n = 105
(83%) of the participants being women.

9.4.4 Toxicological Studies on the Endocrine System

The 2013 Pb ISA summarized a few toxicological studies that reported on effects of Pb exposure
on the endocrine system. Specifically, T3 and T4 levels were found to be elevated in cows that were
grazing on land near Pb/operational Zn smelters when compared with cows grazing in unpolluted areas
(Swarup et aL 2007). However, when regression analyses were done to evaluate potential associations
between BLLs and plasma Cortisol levels in these same cows, no association was observed. Another study
conducted in Wistar rats reported that 21 days of intraperitoneal (i.p.) injections with 8.0 mg/kg Pb led to
increased corticosterone levels and adrenal weights [BLLs not reported; (Biswas and Ghosh. 2006)1.

Some recent studies have also investigated the effects of Pb on the endocrine system (Table 9-5). The
only studies that investigated adrenal gland weight were conducted in Sprague Dawley rats that were
dosed from postnatal day (PND) 4 to 28 and reported no effect of Pb treatment on the weight of the
adrenal glands [BLLs 3.27-12.5 (ig/dL; (Amos-Kroohs et aL 20.1.6; Graham et aL 2011)1. Findings
concerning corticosterone levels in recent studies are equivocal. Some studies reported increased
corticosterone in rats exposed to Pb. Specifically, one study that dosed Long-Evans rats starting prior to
conception until 304 days of age reported increases in corticosterone levels in female rats at 2 months of
age but reported no changes in males at any time point [BLLs 11.3 (ig/dL on PND 61 in females; ("Rossi-
George et aL 2011)1. Another study measured corticosterone levels in Sprague Daw ley rats at different
intervals following a shallow water stressor. This study reported that treatment with Pb from PND 4 to 28
increased corticosterone levels in male and female rats 0, 30, and 60 minutes following the stressor on
PND 11,0 and 30 minutes following the stressor on PND 19, and 0 and 30 minutes following the stressor
on PND 29 [BLLs 3.2-12.5 (ig/dL on PND 29; (Graham et aL 2011)1. A single study reported decreases
in corticosterone in F3 female C57 BL/6 mice whose F1 sires were exposed to Pb from gestational day
(GD) -61 to PND 21 [BLLs 0.4 (ig/dL on PND 6-7; (Sobolewski et aL 2020)1. Contrasting these studies
are those that did not report any effects of Pb exposure on corticosterone levels. Interestingly, these
studies used similar dosing paradigms to those that reported effects with one study dosing C57 BL/6 mice
starting preconceptionally through adulthood [ending on PND 365; (Corv-Slechta et aL 20.13)1 and the
other study dosing Sprague Dawley rats from PND 4 to 28 (Amos-Kroohs et aL 20.1.6). and neither study
reported alterations of corticosterone levels in either sex.

9.4.5 Summary and Causality Determination

The 2013 Pb ISA concluded that the evidence was inadequate to determine if there is a causal
relationship between Pb exposure and endocrine effects related to changes in levels of thyroid hormones,

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cortisol/corticosterone, and vitamin D. This causality determination was based on an insufficient quantity
and quality of studies that provided inconsistent or inconclusive evidence for Pb-related endocrine effects.
Epidemiologic evidence presented in the 2013 Pb ISA regarding the effects of Pb on Cortisol levels
consisted of a single study showing a positive association between prenatal Pb exposure and salivary
Cortisol levels in children following an acute stressor ("Gump et ah. 2008'). The few epidemiologic studies
investigating associations between Pb and thyroid hormone levels presented in the 2013 Pb ISA reported
inconsistent associations. Toxicological evidence in the 2013 Pb ISA regarding the effects of Pb on the
endocrine system in animals was sparse. Biswas and Ghosh (2006) reported that Pb exposure increased
corticosterone levels and adrenal gland weights in Wistar rats. A single study evaluating thyroid hormone
levels in animals summarized in the 2013 Pb ISA reported no clear associations between Pb exposure and
thyroid hormone levels in cattle with environmental exposure to Pb ("Swaaip et ah. 2007).

Recent epidemiologic and toxicological evidence evaluating the effects of Pb exposure on the
endocrine system continues to be limited and inconsistent. Most recent epidemiologic studies measured
associations between BLLs and thyroid hormone levels. Results from these studies were mostly null,
though there was some evidence of an inverse association between BLLs and T4 levels in a few studies
(Krieg. 20.1.9; Mendv et ah. 20.1.3; Christensen. 20.12). and a single study noted sex-specific associations
between BLLs and T4 and FT4 levels ("Luo and Hendrvx. 20.1.4). Although most studies reported null
associations, the analyses included overlapping study populations, so they should not be interpreted as
independent evidence of a null association. Additionally, consistent with the studies evaluated in the 2013
Pb ISA, recent studies are cross-sectional in design, which introduces uncertainty regarding the
temporality between exposure and outcome. No recent toxicological studies investigating the effects of Pb
on thyroid hormone levels were available. Only a few recent epidemiologic studies examined Pb effects
on Cortisol levels (Ngueta et ah. 20.1.8; Souza-Talarico et ah. 20.1.7). Results from these studies were
inconsistent, and both had small sample sizes. Multiple toxicological studies reported on the effects of Pb
exposure on corticosterone levels in animals, but results are equivocal. One study reported decreases
("Sobolewski et ah. 2020). two studies reported increases ("Graham et ah. ; Lossi-George et ah. 20.1.1).
and two studies reported no effect (Amos-Kroohs et ah. 20.1.6; Cory-Slechta et ah. 20.1.3) on corticosterone
levels in Pb-intoxicated animals. In terms of the effects of Pb on adrenal gland weights in animals, only
two recent studies investigated the effects of Pb on adrenal gland weight. These studies reported no
effects of Pb on adrenal gland weight in Sprague Dawley rats (Amos-Kroohs et ah. 20.1.6; Graham et ah.
20.1.1). contrasting with the only study that investigated adrenal gland weights in the 2013 Pb ISA (Biswas
and Ghosh. 2006) which reported increased adrenal gland weights. This contrast may be due to variability
in route of exposure used in the experimental design leading to differences in BLLs between the animals
in Biswas and Ghosh (2006). and the more recent studies. Specifically, Biswas and Ghosh (2006) dosed
animals with 8 mg/kg/d of Pb via i.p. injection, whereas the most recent publications dosed animals with
either 1 or 10 mg/kg/d of Pb b via oral gavage (Amos-Kroohs et ah. 20.1.6) or indirectly dosed animals via
Pb in the milk from their dams which were dosed via oral gavage (Graham et ah. 20.1.1). No recent
PECOS-relevant epidemiologic or toxicological studies were identified that measured vitamin D levels.

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In conclusion, recent epidemiologic and toxicological studies continue to provide limited and
inconsistent evidence for endocrine system effects associated with Pb exposure. Due to the insufficient
quantity and quality of the studies available for review and the inconsistent results across those studies,
the evidence remains inadequate to infer the presence or absence of a causal relationship between Pb
exposure and endocrine system effects, including changes in thyroid hormones, cortisol/corticosterone,
and vitamin D levels.

9.5 Effects on the Musculoskeletal System

9.5.1 Introduction, Summary of the 2013 Pb ISA, and Scope of the Current
Review

The 2013 Pb ISA evaluated the effects of Pb exposure on bone and teeth (U.S. EPA. 20.1.3'). In
order to be more inclusive of other health effects related to bone and teeth, the 2024 Pb ISA expands the
considered health outcomes to include effects on the entire musculoskeletal system. The musculoskeletal
system consists of the bones, teeth, muscles, joints, cartilage, and other connective tissues that support the
body, allow for movement, and protect vital organs. Primary effects on the musculoskeletal system
include increases in osteoporosis, increased frequencies of falls and fractures, changes in bone cell
function as a result of replacement of bone calcium with Pb, and depression in early bone growth. Other
effects include tooth loss and periodontitis. Mechanistic evidence from toxicological studies includes
effects on cell proliferation, procollagen type I production, intracellular protein, and osteocalcin in human
dental pulp cell cultures.

A small body of epidemiologic studies evaluated in the 2013 Pb ISA ("U.S. EPA. 20.1.3) provided
consistent evidence of associations between Pb biomarker levels and various effects on bone and teeth,
including an increase in osteoporosis, increased frequencies of falls and fractures, tooth loss, and
periodontitis. The results from these studies, adjusting for potential confounding by age and SES-related
factors, were supported by strong toxicological evidence evaluated in the 2013 Pb ISA and the 2006 Pb
AQCD (U.S. EPA. 2006). which reported effects in bone and teeth in animals follow ing Pb exposure.
Exposure of animals to Pb during gestation and the immediate postnatal period was reported to
significantly depress early bone growth with the effects showing concentration-dependent trends.
Systemic effects of Pb exposure included disruption in bone mineralization during growth, alteration in
bone cell differentiation and function due to alterations in plasma levels of growth hormones and
calcitropic hormones such as l,25-[OH]2D3 and impact on Ca2+- binding proteins and increases in Ca2+
and phosphorus concentrations in the bloodstream. Bone cell cultures exposed to Pb had altered vitamin
D-stimulated production of osteocalcin accompanied by inhibited secretion of bone-related proteins such
as osteonectin and collagen. In addition, Pb exposure caused suppression in bone cell proliferation most

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likely due to interference from factors such as growth hormone (GH), epidermal growth factor (EGF),
transforming growth factor-beta 1 (TGF-(31), and parathyroid hormone-related protein (PTHrP).

As in bone, Pb exposure was found to easily substitute for Ca2+ in the teeth and was taken up and
incorporated into developing teeth in experimental animals. Since teeth do not undergo remodeling like
bones do during growth, most of the Pb in the teeth remains in a state of permanent storage. Pb has also
been shown to decrease cell proliferation, procollagen type I production, intracellular protein, and
osteocalcin in human dental pulp cell cultures. Adult rats exposed to Pb have exhibited an inhibition of
the posteruptive enamel proteinases, delayed teeth eruption times, as well as a decrease in microhardness
of surface enamel. Further discussion of these processes and effects, including corresponding references,
can be found in sections 5.8.7 through 5.8.13 of the 2006 Pb AQCD (U.S. EPA, 2006).

In considering the weight of the evidence, the 2013 Pb ISA (U.S. EPA, 20.1.3) concluded that "a
causal relationship is likely to exist between Pb exposure and effects on bone and teeth."

9.5.2 Scope

The scope of this section is defined by PECOS statements. The PECOS statement defines the
objectives of the review and establishes study inclusion criteria, thereby facilitating identification of the
most relevant literature to inform the Pb ISA.21 In order to identify the most relevant literature, the body
of evidence from the 2013 Pb ISA was considered in the development of the PECOS statements for this
Appendix. Specifically, well-established areas of research; gaps in the literature; and inherent
uncertainties in specific populations, exposure metrics, comparison groups, and study designs identified
in the 2013 Pb ISA inform the scope of this Appendix. The 2013 Pb ISA used different inclusion criteria
than the 2024 Pb ISA, and the studies referenced therein often do not meet the current PECOS criteria
(e.g., due to higher or unreported biomarker levels). Studies included in the 2013 Pb ISA, including many
that do not meet the current PECOS criteria, are discussed in this appendix to establish the state of the
evidence prior to this assessment. Except for supporting evidence used to demonstrate the biological
plausibility of Pb-associated effects on the musculoskeletal system, recent studies were only included if
they satisfied all of the components of the following discipline-specific PECOS statements:

Epidemiologic Studies:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

21The following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

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Exposure: Exposure to Pb22 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure23; or intervention groups in randomized trials and quasi-experimental studies.

Outcome: Effects on the musculoskeletal system.

Experimental Studies:

Exposure: Oral, inhalation, or intravenous routes administered to a whole animal (in vivo) that
results in a BLL of 30 (ig/dL or below.24'25

Comparators: A concurrent control group exposed to vehicle-only treatment or untreated
control.

Outcomes: Effects on the musculoskeletal system.

Study design: Controlled exposure studies of animals in vivo.

9.5.3 Epidemiologic Studies on the Musculoskeletal System

A limited number of cross-sectional epidemiologic studies evaluated in the 2013 Pb ISA ("U.S.
EPA. 20.1.3) provided consistent evidence of associations between Pb biomarker levels and osteoporosis
and tooth loss after adjusting for potential confounding by age and SES-related factors. Uncertainties in

22Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the NAAQS review (e.g., longitudinal studies designed to examine recent versus historical Pb
exposure).

23Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM25) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure | Section 2.5.3 (U.S. EPA. 20.1. 2)].
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with BLLs are lacking.

24Pb mixture studies are included if they employ an experimental arm that involves exposure to Pb alone.

25This level represents an order of magnitude above the upper end of the distribution of U.S. young children's BLL.
The 95th percentile of the 2011-2016 NHANES distribution of BLL in children (1-5 years; n= 2,321) is 2.66 (ig/dL
(Egan et at. 2021) and the proportion of individuals with BLL that exceed this concentration varies depending on
factors including (but not limited to) housing age, geographic region, and a child's age, sex, and nutritional status.

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the evidence base included limited consideration of potential confounding by nutritional factors, a lack of
temporality between exposure and outcome, and uncertainty in the level, timing, frequency, and duration
of Pb exposure that contributed to the observed associations. Recent epidemiologic studies of the
musculoskeletal system generally examine one of three groups of endpoints: (1) bone mineral density
(BMD); (2) joint degeneration; and (3) oral health. Results from recent studies, which adjust for a range
of potential confounders, provide generally consistent evidence of an association between BLLs and
osteoporosis, osteoarthritis, dental caries, and periodontal disease. Recent studies evaluating
musculoskeletal effects are largely cross-sectional analyses, which are unable to establish temporality
between exposure and outcome. Additionally, with biomarkers of Pb exposure, it is difficult to
characterize the specific timing, duration, frequency, and level of Pb exposure that contributed to the
observed associations. This uncertainty may apply particularly to assessments of BLLs, which in
nonoccupationally-exposed adults, reflect both current exposures and cumulative Pb stores in bone that
are mobilized during bone remodeling. Measures of central tendency for Pb biomarker levels used in each
study, along with other study-specific details, including study population characteristics and select effect
estimates, are highlighted in Table 9-11. An overview of the recent evidence is provided below.

9.5.3.1 Bone Mineral Density

A number of recent cross-sectional studies provide generally consistent evidence of an
association between exposure to Pb and BMD in adults. In these studies, BMD (g/cm2) was measured via
X-ray absorptiometry or ultrasound and often converted to a standardized score (i.e., z- and Z-scores)26.
Osteoporosis and osteopenia are characterized by varying degrees of BMD decrements that can
compromise bone microarchitecture. A z-score below -1 often corresponds to osteopenia, whereas a z-
score below -2.0 to -2.5 is categorized as osteoporosis. There are significant sex and age differences in
the incidence of osteoporosis and osteopenia, with postmenopausal women being at greatest risk for
declines in BMD. Because osteoporosis and osteopenia are more common in women, many of the recent
epidemiologic studies evaluating the relationship between BLLs and BMD are either conducted in study
populations comprised of older women or stratified by sex. Importantly, the cross-sectional nature of the
studies does not rule out the possibility that the association is driven by increased BLLs due to higher
bone turnover in individuals with osteoporosis. Additionally, although most analyses include study
populations with mean BLLs <3 (ig/dL, study participants were born prior to the phase-out of leaded
gasoline and therefore likely had much higher past Pb exposures, making it difficult to characterize the
specific timing, duration, frequency, and level of Pb exposure that contributed to the observed
associations.

26Standardized scores are used to analyze BMD data as deviations from average BMD in matched healthy
populations. Underlying populations vary by study.

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A few recent analyses of data from large, nationally representative health surveys provide
generally consistent evidence of an association between BLLs and BMD in women ("Wang et ah. 20.1.9;
Cho et ah. 20.1.2; Lee and Kim. 2012). In an analysis of 2008 KNHANES data, Cho et ah (20.1.2) observed
higher odds of osteoporosis associated with higher BLL quartiles in postmenopausal women. The authors
noted associations at low levels (e.g., Q2 [1.83 to <2.32 |ig/dL| versus quartile 1 [<1.83 |ig/dL|) that were
similar in magnitude to comparisons between the higher quartiles and the first quartile, suggesting a
potentially non-linear association. In a similar study, Lee and Kim (20.1.2) analyzed data from the same
KNHANES cycle but expanded the age range to include premenopausal women. The authors reported
that higher BLLs were associated with lower BMD at several bone sites. Additionally, Pb-related BMD
decrements were consistently higher in postmenopausal women compared to premenopausal women. For
example, 1 (ig/dL higher levels of blood Pb were associated with 0.28 g/cm2 (95% CI: 0.11, 0.45 g/cm2)
lower femoral BMD in postmenopausal women compared to 0.15 g/cm2 (95% CI: -0.03, 0.33 g/cm2)
lower femoral BMD in premenopausal women.

In contrast to KNHANES analyses, an analysis of more recent NHANES cycles (2013-2014)
observed null associations between BLLs and BMD in postmenopausal women (Wang et ah. 20.1.9).
Notably, the authors did not control for hormone therapy, which prevents BMD loss and could impact
BLLs due to changes in bone turnover rates. Wang et ah (20.1.9) did note that a higher BLLs were
associated with slightly lower femoral (-0.06 g/cm2 [95% CI: -0.08, -0.03 g/cm2]) and spinal
(-0.05 g/cm2 [95% CI: -0.08, -0.02 g/cm2]) BMD in premenopausal women, as well as higher 10-year
fracture risk scores in the total population (including adult men and women). The findings in
premenopausal women are somewhat consistent with a recent cross-sectional analysis of premenopausal
women in western New York that observed 0.02 (-0.02, 0.05) g/cm2 lower spinal BMD associated with
1 (.ig/dL higher BLLs (Pollack et ah. 20.1.3). However, in contrast to the results from Wang et ah (20.1.9).
Pollack et ah (20.1.3) reported null associations between BLLs and total hip and wrist BMD in
premenopausal women.

In a smaller cross-sectional analysis of adults from two communities in southwestern China,
including one with a history of Pb mining and smelting, Li et ah (2020b) observed some evidence of sex-
specific differences in Pb-associated BMD levels. Specifically, female study participants with BLLs
>3.4 (ig/dL had higher odds of osteoporosis compared to female study participants with BLLs <3.4 (ig/dL
(OR= 1.33 [95% CI: 0.61, 2.88]); whereas an inverse association was reported for men (OR= 0.60 [95%
CI: 0.24, 1.49]). However, given the imprecise effect estimates (i.e., wide 95% els), it is difficult to draw
firm conclusions on these sex-specific comparisons.

Other recent studies evaluated the relationship between Pb exposure and BMD in analyses
combining men and women. The inferences that can be drawn from these studies are limited due to
established sex-specific differences in osteoporosis incidence. In an analysis of 2008-2011 KNHANES
cycles. Lim et ah (20.1.6) observed higher odds of osteoporosis or osteopenia across higher BLL quartiles,
with the highest odds noted in quartile 4 (>2.93 (ig/dL) compared to quartile 1 (<1.66 (ig/dL; OR = 1.49

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[95% CI: 1.12, 1.98]). In a much smaller study of Korean adults, Lee and Park (20.1.8) similarly reported a
negative association between BLLs and BMD t-scores that was greater in magnitude in participants with a
history of smoking (-0.472 [95% CI-0.85, -0.094]) compared to non-smokers (-0.148 [95% CI: -0.369,
0.073]). The authors also examined over 344,396 single nucleotide polymorphisms (SNPs) mapped to
gene-coding regions to assess potential effect modification of the relationship between BLLs and BMD.
Observed interactions between BLLs and genetic variations were inconsistent after adjustment for
multiple testing, but many implicated interactions with genes and pathways involved in angiogenesis,
bone mass, and nuclear receptor signaling, providing areas of interest for exploring possible mechanisms
that may underlie the observed relationship between BLLs and osteoporosis.

9.5.3.2 Osteoarthritis

A few recent cross-sectional studies examined the association between BLLs and osteoarthritis
(OA) in adults. In an analysis of multiple KNHANES cycles (2010-2012), Park and Choi (20.1.9) reported
that higher natural log BLLs were associated with higher odds of radiographic and symptomatic knee OA
(radiographic osteoarthritis [rOA] and symptomatic osteoarthritis [sxOA]) in postmenopausal women
(OR= 1.77 [95% CI 1.17, 2.67] and 1.50 [95% CI: 0.90, 2.53], respectively). There is some evidence that
the association is mediated by BMI, but there is evidence of a direct association as well (i.e., adjusted for
BMI). The authors noted null associations between BLLs and back OA.

In a cross-sectional analysis of African American and white adults, Nelson et al. (2( also
observed associations between BLL and rOA and sxOA in the knee. In a similar study, the same group
noted associations between BLLs and some biomarkers of joint tissue metabolism, including NTX-I,
which is responsible for bone turnover; CTX-II, which is associated with prevalence of rOA in the knee;
COMP (cartilage oligomeric matrix protein), which is a cartilage biomarker; and CPU (carboxypropeptide
of type II collagen), which is linked with collagen synthesis (Nelson et al.. 20.1. la). Notably, the authors
examined a wide range of biomarkers and stratified their models by sex to examine potential effect
modification, increasing the likelihood of multiple testing bias.

Although all of the studies examining OA had low median BLLs (<2.5 (.ig/dL). study participants
were born prior to the phase-out of leaded gasoline and therefore likely had much higher past Pb
exposures, making it difficult to characterize the specific timing, duration, frequency, and level of Pb
exposure that contributed to the observed associations. Additionally, similar to studies of osteoporosis,
the cross-sectional nature of the studies does not rule out the possibility that the association is driven by
cartilage turnover resulting in increased Pb in blood.

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9.5.3.3

Oral Health

Recent epidemiologic studies of Pb exposure and oral health are split into two major categories:
(1) periodontal disease in adults and (2) dental caries in children.

A limited number of recent studies of periodontal disease in adults examined overlapping
KNHANES cycles from 2008 to 2010 ("Han et al.. 20.1.3; Kim and Lee. 20.1.3; Won et ah. 20.1.3"). These
studies, all of which defined periodontal disease according to the World Health Organization's
Community Periodontal Index, provided consistent evidence of an association between BLLs and the
prevalence of periodontitis. All of the studies included extensive adjustment for potential confounders,
including oral hygiene. Given that these studies examined largely overlapping study populations, the
observed results should not be considered independent evidence of an association. Kim and Lee (20.1.3)
noted associations that were stronger in magnitude in men (OR =1.85 [95% CI: 1.26, 2.71] per two-fold
higher BLLs) compared to women (OR= 1.30 [95% CI: 0.88, 1.91] per two-fold higher BLLs), and that
associations were slightly attenuated, but still positive after adjustment for blood mercury (Hg) and
cadmium (Cd; 1.69 [95% CI: 1.15, 2.50] and 1.24 [95% CI: 0.83, 1.85], respectively). In stratified
analyses to examine effect modification by smoking, effect estimates were imprecise (i.e., wide 95% els),
but comparable in magnitude for smokers and non-smokers ("Han et aL. 20.1.3; Won et aL 2013).

Recent epidemiologic studies of dental caries in children included more diverse study
populations. A prospective analysis of mother-child pairs that recruited from hospitals serving low- to
moderate-income populations in Mexico examined the relationship between Pb biomarkers at different
developmental windows and incidence of decayed, missing, and filled teeth (DMFT) in adolescence [10
to 18 years old; Wu et al. (20.1.9)1. The authors reported 12 to 17% higher risk of DMFT associated with
higher prenatal and early childhood BLLs. No associations were observed with concurrent BLLs or
postnatal maternal bone Pb. Prenatal (mean: 5.24 to 6.36 (ig/dL) and early childhood (mean: 15.18 to
15.48 (ig/dL) BLLs were notably higher than concurrent levels (mean: 3.60-3.34 (.ig/dL). which is
consistent with age-specific patterns of Pb kinetics (Sections 2.2 and 2.4). Wu et al. (20.1.9) additionally
stratified their models by sugar sweetened beverage intake (SSBI) and observed strong effect
modification, with stronger associations between prenatal and early childhood BLLs and DMFT score in
children with high SSBI. A prospective analysis in the same cohort reported positive but imprecise
associations between childhood Pb concentrations and DMFT in adolescence (Yepes et al.. 2020). In
recent cross-sectional studies with lower BLLs (see Table 9-6), BLLs in young children were associated
with increased prevalence of dental caries in deciduous teeth (Kim et al.. 20.1.7; Wiener et al.. 20.1.5). but
not permanent teeth (Kim et al.. 20.1.7).

9.5.4 Toxicological Studies on the Musculoskeletal System

The 2013 Pb ISA (U.S. EPA. 20.1.3) evaluated a number of toxicological studies that
demonstrated changes in bone cell function as a result of replacement of bone calcium with Pb depression

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in early bone growth. Studies also reported Pb-induced effects on cell proliferation, procollagen type I
production, intracellular protein, and osteocalcin in human dental pulp cell cultures. Earlier work,
summarized in the 2006 Pb AQCD ("U.S. EPA. 2006). reported concentration-dependent depression of
early bone growth after gestational exposure of rodents to Pb. Recent evidence is limited. In a study of
lifetime Pb exposure in mice, Beier et al. (20.1.6) reported a reduction in osteoclast activity and a
subsequent disruption in bone accrual in Pb-exposed mice. In another publication, the same group
reported no other musculoskeletal effects resulting from Pb exposure alone (Beier et al.. 2017).

9.5.5 Biological Plausibility

This section describes biological pathways that potentially underlie musculoskeletal effects of Pb.
Figure 9-2 depicts the proposed pathways as a continuum of upstream events, connected by arrows, which
may lead to downstream events observed in epidemiologic studies. This discussion of how exposure to Pb
may lead to musculoskeletal effects contributes to an understanding of the biological plausibility of
epidemiologic results evaluated above. Note that the structure of the biological plausibility sections and
the role of biological plausibility in contributing to the weight-of-evidence analysis used in the 2024 Pb
ISA are discussed in Section IS.4.2.

The proposed pathway, outlined in Figure 9-2, involves both direct and indirect effects of Pb that
could plausibly result in the weakening of bones and increased risk of fractures as well as the dental
effects that are measured in epidemiologic studies. Skeletal bone development and biomechanical
strength is controlled by the balance between osteoblasts, the cells responsible for the production of bone
matrix, and osteoclasts, the cells responsible for bone resorption. Dysregulation of this balance can lead to
bone loss and decreased mineralization. Pb can directly replace Ca2+ in the bone matrix as well as exert
direct effects on bone cells to alter bone development. Pb can also alter bone growth and differentiation
signals that can further disrupt the balance of bone formation and resorption.

As discussed in the 2013 Pb ISA, Pb suppresses the differentiation of osteoblasts and promotes
osteoclast function which could result in delayed bone development and reduced bone mechanical
integrity. Recent literature supports this hypothesis as studies have continued to show that animals treated
with Pb have decreased bone mineralization (Li et al.. 2020a; Sheng et al.. 2020; Oi et al.. 20.1.9;

Olchowik et al.. 20.1.4). bone weight (Alvarez-Lloret etah. 20.1.7; de Figueiredo et al.. 20.1.4). and reduced
trabecular bone (Li et al.. 2020a; Sheng et al.. 2020; Alvarez-Lloret et al.. 2( ; er et al.. 2017). Many
of these studies show concurrent changes in osteoblastic and osteoclastic markers that support an overall
shift to increased bone resorption. For example, recent in vivo studies have seen reductions markers of
osteoblast differentiation (Oi et al.. 20.1.9; Zhang et al.. 20.1.9; Beier et al.. 2017). reductions of proteins
that suppress osteoclast activity (Li et al.. 2020a; Sheng et al.. 2020; Oi et al.. 20.1.9; Kupraszewicz and
Brzoska. 2013). and increases of markers of osteoclast activity (Li et al.. 2020a; Oi et al.. 20.1.9; Zhang et
al.. 20.1.9; Kupraszewicz and Brzoska. 2013) suggesting that bone changes result from dysregulation of

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the balance between bone formation and bone resorptive processes. The mechanism behind the reduced
osteoblastic activity is not fully understood but both direct and indirect mechanisms have been proposed.

Support for a direct action of Pb on osteoblast function comes from in vitro studies showing that
Pb treatment of primary osteoblasts leads to reduction in mineral deposition (Beieret ah, 20.1.5; Abbas et
ah, 20.1.3; Ma et ah, 20.1.2). Previously reviewed data also implicated changes in TGF(3, bone morphogenic
protein (BMP), nuclear factor kappa B (NF-kB), and activator protein-1 signaling ( 313).

Recent studies suggest that Pb-induced suppression of Wnt signaling and upregulation of the protein
sclerostin may also be involved (Sun et ah, 20.1.9; Beier et ah, 20.1.7; Beier et ah, 20.1.5). Similar studies of
dental pulp cultures showed that in vitro treatment with Pb resulted in decreased cell proliferation and
reduced extracellular matrix deposition. This could explain the increased incidence of dental carries in
epidemiology studies.

Indirect mechanisms of Pb treatment have also been discussed in the 2013 Pb ISA. The
replacement of Pb for Ca2+ in cells can lead to Ca2+ release. The 2013 Pb ISA and 2006 Pb AQCD
discussed studies that found that Pb treatment leads to increased systemic Ca2+ levels in the blood stream
( 20.1.3, 2006). Calcium is a cellular signaling molecule involved in mitochondrial function and

cell death and thus changes in calcium signaling could have effects on cells elsewhere in the body. Bone
growth can be affected by systemic signaling of hormones and vitamins that regulate osteoblast formation
as well as storage and release of Ca2+ including parathyroid hormone (PTH), GH, BMP, and vitamin D.
As discussed previously in the 2006 Pb AQCD and the 2013 Pb ISA, Pb exposure can alter these pro-
osteoblastic signals which are thought to be involved in the reduction of bone growth and mineralization
seen following Pb exposure. Recent studies show similar alterations in calcitropic and osteoplastic signals
that could be responsible for reduced bone formation (Zhang et ah, 20.1.9; Kupraszewiez and Brzoska,
20.1.3). Together, these data provide plausible indirect pathway by which Pb exposure can regulate skeletal
bone homeostasis.

The pathway for development of osteoarthritis is less well studied. Osteoarthritis results from
erosion of cartilage and articular bone in the joints. Chondrocytes are responsible for matrix deposition
and joint maintenance. Signaling though TGF(3 is thought to be important in proper joint maintenance. A
recent study showed that Pb treatment in rats induced cartilage loss which was associated with loss of
extracellular matrix proteins (Holz et ah, 20.1.2). In the same study, in vitro treatment of chondrocytes
from rat or chicks resulted in reduced markers of TGF(3 signaling and increased markers of matrix
degradation. These data suggest that Pb-induced osteoarthritis could be a result of Pb effects of
chondrocytes and subsequent cartilage degradation.

Teeth do not undergo the same bone turnover processes as skeletal bone and thus Pb incorporated
into the teeth is permanently sequestered. As discussed in the 2013 Pb ISA, dental effects of Pb are
thought to arise from the effects of Pb on enamel producing cells in combination with the incorporation of
Pb into areas of mineralization ( \, 20.1.3). Previously evaluated studies showed decrease cell

proliferation, procollagen type I production, intracellular protein, and osteocalcin in human dental pulp

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cell cultures ("U.S. EPA. 20.1.3'). A recent study supports the link between Pb exposure and dental effects
by showing reduced molar diameter and increased dental cracks in the offspring of rats treated with Pb
during either gestation or lactation ("Chen et ah. 2012). Together Pb-induced dental effects could result
from effects on dental pulp cells resulting in reduced matrix proteins.

The toxicologic data support Pb-induced alterations in multiple aspects of bone, teeth, and joint
maintenance. For skeletal bones, shift in the balance between bone building osteoblasts and bone
resorbing osteoclasts could be responsible for delayed bone growth and increased bone degeneration seen
in epidemiologic studies. In teeth and joints, Pb appears to suppress the synthesis of cellular matrix
proteins important for joint maintenance and enamel formation which could plausibly contribute to the
osteoarthritic and dental effects seen in some epidemiology studies.

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Pb
Exposure

Depressed cell growth
and mineralization

Altered
osteoblast/osteoclast
balance

Osteoporosis

Increased
falls/fractures

Depressed protein
synthesis

Osteoarthritis

Dental effects/Tooth
loss

Note: The boxes above represent the effects for which there is experimental or epidemiologic evidence related to Pb exposure, and the arrows indicate a proposed relationship
between those effects. Solid arrows denote evidence of essentiality as provided, for example, by an inhibitor of the pathway used in an experimental study involving Pb exposure.
Dotted arrows denote a possible relationship between effects. Shading around multiple boxes is used to denote a grouping of these effects. Arrows may connect individual boxes,
groupings of boxes, and individual boxes within groupings of boxes. Progression of effects is generally depicted from left to right and color coded (white, exposure; green, initial effect;
blue, intermediate effect; orange, effect at the population level or a key clinical effect). Here, population-level effects generally reflect results of epidemiologic studies. When there are
gaps in the evidence, there are complementary gaps in the figure and the accompanying text below. IS.7.2 discusses the structure of the biological plausibility sections and the role of
biological plausibility in contributing to the weight-of-evidence analysis used in the 2022 Pb ISA.

Figure 9-2

Potential biological pathways for musculoskeletal effects following exposure to Pb.

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9.5.6

Summary and Causality Determination

The 2013 Pb ISA concluded that evidence was sufficient to determine "that a causal relationship
is likely to exist between Pb exposure and effects on bone and teeth" (U.S. EPA, 20.1.3). This causality
determination was based on a small body of epidemiologic evidence showing associations between Pb
biomarker levels and effects on bones after adjusting for potential confounding by age and SES-related
factors, as well as strong toxicological evidence that reported effects on bone in animals following Pb
exposure. Specifically, a few epidemiologic studies indicated an association between higher Pb biomarker
levels and lower bone density in adults. A prospective study of older women provided evidence that
higher BLLs (>4 (ig/dL versus <3 (ig/dL) were associated with greater risk of falls and osteoporosis-
related fractures, as well as lower bone density measured after 2-4 years (Khali 1 et ah, 2009). This finding
was supported by cross-sectional associations between higher BLLs and lower BMD (Campbell and
Auinger, 2007) and biochemical biomarkers of higher bone turnover (Nelson et ah, 20.1.1a; Machida et ah,
2009) in adults. In evaluating the cross-sectional epidemiologic evidence, it is difficult to determine
whether an increase in BLLs results from lower bone density or from higher bone turnover, and whether
either of these effects lead to a greater release of Pb from bone into the bloodstream. Exposure of animals
to Pb during gestation and the immediate postnatal period was reported to significantly depress early bone
growth with the effects showing concentration-dependent trends. Systemic effects ofPb exposure
included disruption in bone mineralization during growth, alteration in bone cell differentiation and
function due to alterations in plasma levels of growth hormones and calcitropic hormones such as 1,25-
[OH]2D3 and impact on Ca2+- binding proteins and increases in Ca2+ and phosphorus concentrations in
the bloodstream. Bone cell cultures exposed to Pb had altered vitamin D-stimulated production of
osteocalcin accompanied by inhibited secretion of bone-related proteins such as osteonectin and collagen.
In addition, Pb exposure caused suppression in bone cell proliferation most likely due to interference from
factors such as GH, EGF, transforming growth factor-beta 1 (TGF-(31), and PTHrP.

In addition to effects on bone, epidemiologic and toxicological studies evaluated in the 2013 Pb
ISA provided evidence of Pb-related effects on teeth. A limited number of epidemiologic studies reported
associations between higher BLLs and a higher prevalence of dental caries in children (Moss et ah, .1.999)
and periodontitis in adults (Saraiva et ah, 2007). Additionally, higher patella and tibia Pb levels were
associated with tooth loss in men participating in the NAS (Arora et ah, 2009). This epidemiologic
evidence was based on cross-sectional analyses, which precludes conclusions about the directionality of
effects. However, these findings are supported by toxicological evidence in animals for Pb-induced
increases in Pb uptake into teeth and decreases in cell proliferation, procollagen type I production,
intracellular protein, and osteocalcin in cells exposed to Pb in vitro. Despite evidence for associations
between Pb exposure and effects in bone and teeth at relatively low concurrent BLLs, these outcomes
were most often examined in older adults that have been exposed to higher levels of Pb earlier in life.
Therefore, uncertainty still remains concerning the Pb exposure level, timing, frequency, and duration that
contribute to the observed associations.

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Recent cross-sectional epidemiologic studies continue to support associations between Pb
exposure and effects on bone. The majority of recent studies of osteoporosis or osteopenia were
conducted in female populations or included models stratified by sex to account for sex-specific
difference in osteoporosis and osteopenia incidence. The evaluated studies provide generally consistent
evidence of a positive association between low BLLs (mean/median ranges cross studies: 1.03 to
3.4 (.ig/dL) and osteoporosis or osteopenia in women (Li et aL 2020b; Wang et aL 20.1.9; Pollack et aL.
20.1.3; Cho et aL 20.1.2; Lee and Kim. 2012). Other studies also observed positive associations in models
including men and women (Lee and Park. 20.1.8; Lim et aL. 20.1.6"). but the inferences that can be drawn
from these studies are limited due to the previously noted sex differences in BMD. A few recent cross-
sectional studies also reported associations between low BLLs and symptomatic and radiographic OA in
the knee (Park and Choi. 20.1.9; Nelson et al.. 20.1. lb). These findings were supported by another study
demonstrating associations between BLLs and some biomarkers of joint tissue metabolism, which could
either lead to OA or be indicative of prevalent OA (Nelson et al.. 20.1. la). These studies of OA represent
an emerging area of research for an endpoint that was not discussed in the 2013 Pb ISA. Recent
epidemiologic evidence is prone to similar uncertainties and limitations identified in the 2013 Pb ISA.
Notably, the cross-sectional design of these studies does not establish temporality between the exposure
and outcome. This may be particularly relevant for health outcomes that correlate with bone turnover
rates that could lead to higher BLLs. Additionally, although a number of recent studies have been
conducted in adult populations with low BLLs, uncertainty regarding past exposures continues to limit the
characterization of the Pb exposure levels, timing, frequency, and duration that contribute to the observed
associations.

The recent toxicological evidence base for effects on bones is smaller, but consistent with
findings from the 2013 Pb ISA and coherent with recent epidemiologic evidence. Notably, a recent study
reported a reduction in osteoclast activity and a disruption in bone accrual in Pb-exposed animals (Beier
et aL. 20.1.6). This finding, along with similar evidence from previous IS As and AQCDs. provides support
for a temporal relationship between Pb exposure and effects on bone accrual and bone density that cannot
be established by the available cross-sectional epidemiologic evidence.

In addition to studies of Pb exposure and effects on bone, recent epidemiologic studies have also
explored the relationship between BLLs and effects on teeth. Recent studies in adults focused on the
prevalence of periodontitis, whereas studies in children examined the prevalence or incidence of dental
caries. A group of studies examining overlapping KNHANES cycles observed positive associations
between low BLLs and periodontitis prevalence in adults (Han et aL. 20.1.3; Kim and Lee. 20.1.3; Won et
al.. 20.1.3). including some evidence of a stronger association in men, and persistent associations in models
adjusting for Hg and Cd (Kim and Lee. 20.1.3). Given the largely overlapping study populations, the
observed results should not be interpreted as independent evidence of an association. Additionally, the use
of BLLs in adult populations with higher past exposures limits the ability to characterize the Pb exposure
levels, timing, frequency, and duration that contribute to the observed associations. In a prospective birth
cohort study of low- to moderate-income mother-child pairs, increases in prenatal and early childhood

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BLLs were associated with increased risk of dental caries in adolescence (Wu et al.. 20.1.9'). The authors
also observed a null association with concurrent BLLs, which suggests that there may be critical windows
of exposure earlier in life. These findings were supported by a few cross-sectional studies that reported
associations between BLLs in early childhood and increased prevalence of dental caries in deciduous
teeth (Kim et al.. : Vleneret al.. 20.1.5'). No recent toxicological studies have examined the effects of
Pb exposure on teeth, but as described earlier, previous and recent mechanistic evidence provides
biological plausibility for the observed epidemiologic associations.

Overall, the collective evidence is sufficient to conclude that there is likely to be a causal
relationship between Pb exposure and musculoskeletal effects. This causality determination is based
on an expanded epidemiologic evidence base that continues to demonstrate associations between BLLs
and various musculoskeletal effects after adjusting for potential confounding, as well as strong
toxicological evidence for effects on bone in animals following Pb exposure. Although the recent
epidemiologic evidence is consistent with the findings highlighted in the 2013 Pb ISA, recent studies do
not thoroughly address uncertainties identified in the 2013 Pb ISA, including unclear temporality of
exposure and outcome resulting from mostly cross-sectional study designs. This uncertainty is
particularly important for studies examining BMD and osteoporosis due to the possibility that
associations could be driven by increased BLLs due to higher bone turnover in individuals with low BMD
or osteoporosis. Although there are not many recent toxicological studies that meet PECOS relevance, the
evaluated studies are consistent with a large evidence base from the 2013 Pb ISA and AQCD, which
provides support for the observed epidemiologic associations. The key evidence, as it relates to the causal
framework, is summarized in Table 9-2.

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Table 9-2 Summary of evidence for a likely to be causal relationship between Pb exposure and
musculoskeletal effects

Rationale for Causality
Determination3

Key Evidence13

Key References'3

Pb Biomarker Levels Associated with
Effects0

Consistent evidence from
epidemiologic studies of
osteoporosis and osteopenia

Evidence from cross-sectional
epidemiologic studies supports
associations between Pb exposure and
osteoporosis or osteopenia in adult
female populations.

Cho et al, (2012)
Wanq et al, (2019)
Lee and Kim (2012)
Pollack et al, (2013)
Li et al, (2020b)

Mean/median BLL ranges cross studies:
1.03 to 3.4 [jg/dL

Supporting evidence from
toxicological studies with
relevant exposures
investigating effects on bone

Toxicological evidence in rodents is
coherent with epidemiologic evidence
and provides support for a temporal
relationship between Pb exposure and
effects on bone accrual and bone density

Beier et al, (2016)
(U.S. EPA, 2013)
(U.S. EPA, 2006)

Mean BLL range of 20.8 to 49.9 [jg/dL

Consistent evidence from
epidemiologic studies of
dental caries in children

A prospective birth cohort study provides
evidence that increases in prenatal and
early childhood BLLs are associated with
increased risk of dental caries in
adolescence

Wu et al, (2019)

Mean BLLs (males, female):
15.48, 15.18 [jg/dL



Supporting cross-sectional evidence of
associations between early childhood
BLLs and dental caries in deciduous
teeth

Kim et al, (2017)
Wiener et al, (2015)

Geometric Mean BLLs: 1.53 [jg/dL

Mean NR (28.2% <2 pg/dL; 48.3% 2 to
<5 ug/dL; 18.4% 5 to <10 ug/dL; 5.1%
>10 [jg/dL)

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Rationale for Causality
Determination3

Key Evidence13

Key References'3

Pb Biomarker Levels Associated with
Effects0

Biological Plausibility	Pb can directly replace Ca2+ in the bone Section 9.5.4.

matrix as well as exert direct effects on
bone cells to alter bone development. Pb
can also alter bone growth and
differentiation signals that can further
disrupt the balance of bone formation
and resorption. Pb has also been shown
to decrease cell proliferation, procollagen
type I production, intracellular protein,
and osteocalcin in human dental pulp cell
cultures.

Preamble to the ISAs (U.S. EPA. 2015).
where applicable, to uncertainties or

BLLs = blood lead levels; Ca2+ = calcium ion(s); NR = not reported; Pb = lead.

aBased on aspects considered in judgments of causality and weight-of-evidence in causal framework in Table I and Table II of the
bDescribes the key evidence and references, supporting or contradicting, contributing most heavily to causality determination and,
inconsistencies. References to earlier sections indicate where the full body of evidence is described.

°Describes the Pb biomarker levels at which the evidence is substantiated.

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9.6

Effects on Ocular Health

9.6.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the Current
Review

This section of effects on ocular health focuses on impairments related to the structure of the eye,
including but not limited to cataracts, glaucoma, macular degeneration, and retinal stippling. Studies
examining effects on vision that are related to sensory processing in the central nervous system can be
found in Appendix 3 of the 2024 Pb ISA (Sections 3.5.6.2 and 3.6.3.2). The 2013 Pb ISA concluded that
because the studies of effects on ocular health were of insufficient quantity and quality, the overall
evidence was "inadequate to determine a causal relationship between Pb exposure and ocular effects"
(	2013). There were very few studies evaluated in the 2013 Pb ISA that examined Pb exposure

and ocular effects in humans or animals. Those studies that were reviewed examined disparate outcomes
and the epidemiologic studies lacked rigorous statistical analyses.

9.6.2	Scope

The scope of this section is defined by PECOS statements. The PECOS statement defines the
objectives of the review and establishes study inclusion criteria thereby facilitating identification of the
most relevant literature to inform the Pb ISA.27 In order to identify the most relevant literature, the body
of evidence from the 2013 Pb ISA was considered in the development of the PECOS statements for this
Appendix. Specifically, well-established areas of research; gaps in the literature; and inherent
uncertainties in specific populations, exposure metrics, comparison groups, and study designs identified
in the 2013 Pb ISA inform the scope of this Appendix. The 2013 Pb ISA used different inclusion criteria
than the 2024 Pb ISA, and the studies referenced therein often do not meet the current PECOS criteria
(e.g., due to higher or unreported biomarker levels). Studies included in the 2013 Pb ISA, including many
that do not meet the current PECOS criteria, are discussed in this appendix to establish the state of the
evidence prior to this assessment. Except for supporting evidence used to demonstrate the biological
plausibility of Pb-associated effects on the ocular health, recent studies were only included if they
satisfied all of the components of the following discipline-specific PECOS statements:

27The following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

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Epidemiologic Studies:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

Exposure: Exposure to Pb28 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure;29 or intervention groups in randomized trials and quasi-experimental studies.

Outcome: Effects on ocular health.

Experimental Studies:

Exposure: Oral, inhalation, or intravenous routes administered to a whole animal (in vivo) that
results in a BLL of 30 (ig/dL or below.30'31

Comparators: A concurrent control group exposed to vehicle-only treatment or untreated
control.

Outcomes: Ocular effects.

Study design: Controlled exposure studies of animals in vivo.

28Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the NAAQS review (e.g., longitudinal studies designed to examine recent versus historical Pb
exposure).

29 Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM2 5) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure | Section 2.5.3 (U.S. EPA. 20.1. 2)].
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with BLLs are lacking.

30Pb mixture studies are included if they employ an experimental arm that involves exposure to Pb alone.

31This level represents an order of magnitude above the upper end of the distribution of U.S. young children's BLL.
The 95th percentile of the 2011-2016 NHANES distribution of BLL in children (1-5 years; n= 2,321) is 2.66 (ig/dL
(Egan et at. 2021) and the proportion of individuals with BLL that exceed this concentration varies depending on
factors including (but not limited to) housing age, geographic region, and a child's age, sex, and nutritional status.

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9.6.3

Epidemiologic Studies on Ocular Health

A limited number of epidemiologic studies evaluated in the 2006 Pb AQCD (U.S. EPA, 2006)
and 2013 Pb IS A (U.S. EPA, 20.1.3) provide some evidence of an association betw een exposure to Pb and
ocular health. As part of the longitudinal Normative Aging Study, Sehaiimberg et al. (2004) analyzed
prevalence of cataracts in adult males in relation to blood Pb, patella bone Pb, or tibia bone Pb levels.
Covariate-adjusted odds ratios for cataracts were elevated for the highest quintiles of tibia (3.19 [95% CI:
1.48, 6.90]) and patella (1.88 [95% CI: 0.88, 4.02]) Pb levels compared to the lowest. A null association
was observed for the highest quintile of blood Pb (0.89 [95% CI: 0.46, 1.72]). This may suggest a role for
past and cumulative long-term exposures, which aligns with the chronic nature of cataracts. Evidence for
other ocular diseases from less robust studies provided inconclusive evidence due to study limitations. A
cross-sectional study of macular degeneration reported higher concentrations of Pb in the retinal tissue of
donors with macular degeneration compared to those without (Erie et al., 2009). However, the authors did
not control for confounders in this comparison of means. Another study measured BLLs in smokers and
non-smokers with cataracts, but the authors did not make comparisons between exposure to Pb and
severity of cataracts (Mosad et al., 20.1.0).

Recent studies provide inconsistent evidence of an association between exposure to Pb and ocular
effects. The majority of recent studies evaluating ocular health and Pb exposures are population-based
cross-sectional analyses, which are unable to establish temporality between exposure and outcome.
Additionally, because many of the observed ocular impairments generally occur in older adult populations
who likely had higher past than current Pb exposure, there is uncertainty regarding the Pb exposure level,
duration, frequency, and timing that may contribute to any observed associations. Measures of central
tendency for blood and/or bone Pb levels used in each study, along with other study-specific details,
including study population characteristics and select effect estimates, are highlighted in Table 9-13. An
overview of the recent evidence is provided below.

A limited number of recent studies have evaluated the relationship between levels of Pb in the
blood or bone and glaucoma. The strongest evidence for an association comes from a longitudinal
analysis of the Veterans Affairs NAS, a prospective cohort study of male Veterans (Wang et al., 2018b).
Wang et al. (20.1.8b) reported that higher tibia and patella Pb were associated with 28% (95% CI: -1%,
65%) and 42% (95% CI: 11%, 82%) higher risk of primary open-angle glaucoma, respectively. These
results are supported by a recent KNHANES mediation analysis that evaluated intraocular pressure,
which is an important risk factor for glaucoma (Park and Choi, 20.1.6). The authors reported that each
1 (ig/dL higher BLL was associated with 0.09 mmHg (95% CI: 0.06, 0.12 mmHg) higher intraocular
pressure, after accounting for indirect effects of exposure to Pb through higher blood pressure. The
estimated total effect (i.e., not controlling for mediation by blood pressure) for a 1 (ig/dL higher level of
blood Pb was 0.11 mmHg (standard error not reported). In contrast, two recent large cross-sectional
studies of the KNHANES did not observe an association between BLLs and glaucoma (Lee et al., 20.1.6;
Lin et al., 20.1.5). However, potential associations with chronic age-related diseases, such as glaucoma.

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may be better evaluated using measurements of Pb in bone, which has a much longer half-life than in
blood and is therefore a better indicator of cumulative exposure.

In addition to studies of glaucoma, there were also a few recent population-based cross-sectional
studies that examined the association between BLLs and age-related macular degeneration (AMD) in
older adults ("Hwang et ah. 20.1.5; Park et ah. 20.1.5; Wti et ah. 20.1.4). AMD is a common eye-disorder in
older adults that is caused by retinal damage, resulting in deteriorated central vision. Two recent studies
of the KNHANES provided evidence of an association between BLLs and AMD ("Hwang et ah. 20.1.5;

Park et ah. 2015). Using data from the 2008-2011 cycles of KNHANES, Park et ah (20.1.5) reported 12%
(95% CI: 2%, 23%) higher odds of early-stage AMD (i.e., damaged macula with no vision loss) and 25%
(95% CI: 5%, 50%) higher odds of late-stage AMD (i.e., damaged macula with vision loss) per 1 (ig/dL
higher BLLs. In a similar study that analyzed one additional year of KNHANES data (2008-2012),
Hwang et ah (20.1.5) similarly observed higher odds of early-stage AMD corresponding to higher quintiles
of Pb exposure. Notably, in stratified analyses examining effect modification by sex, the observed
associations in the total population appeared to be driven by a much stronger association in women. The
authors also reported associations for late-stage AMD, but the case numbers were so low for each quintile
that the reduced statistical power to detect an association made the results unreliable. In contrast to the
results from the KNHANES studies. Wti et ah (20.1.4) reported null associations between BLLs and AMD
in an analysis of older adults in the 2005-2008 cycles of the U.S. NHANES.

Additional cross-sectional studies examined other ocular health effects for disparate outcomes,
including an NHANES analysis of cataract surgery in older adults (Wang et ah. 20.1.6) and a KNHANES
study of dry eye disease (Jung and Lee. 20.1.9). Both of these studies reported null associations between
BLLs and the ocular health outcome of interest.

9.6.4 Toxicological Studies on Ocular Health

The 2013 Pb IS A (U.S. EPA. 20.1.3) made note of a limited number of animal studies finding Pb-
induced mouse retinal progenitor cell proliferation and neurogenesis, as well as increased opacity of rat
lens after Pb exposure.

Two recent toxicological studies were identified since the 2013 Pb ISA for inclusion in the 2024
Pb ISA. Perkins et ah (20.1.2) described remodeling of rod and cone synaptic mitochondria in mice after
postnatal exposure to Pb acetate in drinking water (21 (ig/dL BLL at weaning). The observed Pb-induced
changes are consistent with deficits in range of vision. The effect of Pb on rod and cone mitochondria was
mediation by Bcl-xL, a protein that has been implicated in Pb-induced apoptosis. Using adult rats exposed
to Pb acetate in drinking water (1-20 (.ig/dL BLL), Shen et ah (20.1.6) found increased blood-retinal
permeability. The authors noted an association between long-term increased vascular permeability with
retinal dysfunction and degeneration.

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9.6.5

Summary and Causality Determination

The 2013 Pb ISA concluded that evidence was "inadequate" to determine a causal relationship
between Pb exposure and ocular health effects (U.S. EPA, 20.1.3). This causality determination was based
on an insufficient quantity and quality of studies in the cumulative body of evidence. Although a cross-
sectional epidemiologic study reported higher concentrations of Pb in the retinal tissue of donors with
macular degeneration compared to those without (Erie et ah, 2009), the study did not account for smoking
status as potential confounder. Toxicological studies were limited in number, but reported Pb-induced
retinal progenitor cell proliferation, retinal electroretinograms, and lens opacity.

Since the release of the 2013 Pb ISA, there has been an increase in the number of epidemiologic
studies that examine the relationship between Pb exposure and ocular health effects. Recent
epidemiologic studies provide inconsistent evidence of an association between Pb exposure and ocular
health effects. The strongest evidence comes from a prospective cohort study of male Veterans that
reported large, but imprecise associations between bone Pb levels and glaucoma (Wang et ah, 2018b).
These results are supported by a cross-sectional association between BLLs and intraocular pressure,
which is an important risk factor for glaucoma (Park and Choi, 20.1.6). However, additional population-
based cross-sectional studies in the same population reported null associations between BLLs and
glaucoma (Lee et ah, 20.1.6; Lin et ah, 20.1.5). No recent experimental studies examined endpoints related
to glaucoma.

Findings from a limited number of population-based cross-sectional studies of Pb exposure and
AMD were inconsistent across populations - with null results observed in a U.S.-based study and a
positive association in a South Korean-based study. A recent toxicological study reported Pb-induced
increases in blood-retinal permeability, which may lead to increased risk of macular degeneration.

Although the evidence base has expanded since the completion of the 2013 Pb ISA, the limited
number of studies and the inconsistent results do not provide sufficient information to draw a conclusion
regarding causality. Thus, the evidence remains inadequate to infer the presence or absence of a
causal relationship between Pb exposure and ocular health effects.

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9.7

Effects on the Respiratory System

9.7.1	Introduction, Summary of the 2013 Pb ISA, and Scope of the
Current Review

The 2013 Pb ISA evaluated studies of respiratory effects related to inflammatory and atopic
diseases (like asthma) separately from effects on lung function, morphology, and respiratory symptoms.
Similarly, in this review, studies evaluating the effect of Pb on asthma are discussed with effects on the
immune system in Appendix 6. This section discusses the effects of Pb on the respiratory system in the
otherwise healthy lung. The 2013 Pb ISA concluded that there was "insufficient quantity and quality of
studies" related to the impacts of Pb on the non-asthmatic lung and the evidence was therefore
"inadequate to determine a causal relationship" ("U.S. EPA. 2013). Epidemiologic studies in non-
asthmatics were lacking in number, consistency, and statistical rigor, despite observed associations
between BLLs and respiratory effects in children and asthmatics ("Appendix 6). The few respiratory
toxicological studies described previously were in vivo and in vitro studies that administered concentrated
ambient particulate matter, of which Pb was a component. The ability to evaluate the independent effect
of Pb in these studies was limited due to the inability to account for confounding effects of co-pollutants
and the lack of characterization of Pb particles in the samples. Given the limitations of these studies, the
scope for this review was narrowed to remove toxicological studies that analyzed the health effects of Pb
containing mixtures but lacked a Pb alone treatment group.

9.7.2	Scope

The scope of this section is defined by PECOS statements. The PECOS statement defines the
objectives of the review and establishes study inclusion criteria thereby facilitating identification of the
most relevant literature to inform the Pb ISA.32 In order to identify the most relevant literature, the body
of evidence from the 2013 Pb ISA was considered in the development of the PECOS statements for this
Appendix. Specifically, well-established areas of research; gaps in the literature; and inherent
uncertainties in specific populations, exposure metrics, comparison groups, and study designs identified
in the 2013 Pb ISA inform the scope of this Appendix. The 2013 Pb ISA used different inclusion criteria
than the 2024 Pb ISA, and the studies referenced therein often do not meet the current PECOS criteria

32The following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

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(e.g., due to higher or unreported biomarker levels). Studies included in the 2013 Pb ISA, including many
that do not meet the current PECOS criteria, are discussed in this appendix to establish the state of the
evidence prior to this assessment. Except for supporting evidence used to demonstrate the biological
plausibility of Pb-associated effects on the immune system, recent studies were only included if they
satisfied all of the components of the following discipline-specific PECOS statements:

Epidemiologic Studies:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

Exposure: Exposure to Pb33 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure34; or intervention groups in randomized trials and quasi-experimental studies.

Outcome: Effects on the respiratory system.

Experimental Studies:

Exposure: Oral, inhalation, or intravenous routes administered to a whole animal (in vivo) that
results in a BLL of 30 (ig/dL or below.35'36

33Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the NAAQS review (e.g., longitudinal studies designed to examine recent versus historical Pb
exposure).

34Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM25) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure | Section 2.5.3 (U.S. EPA. 20.1. 2)].
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with BLLs are lacking.

35Pb mixture studies are included if they employ an experimental arm that involves exposure to Pb alone.

36This level represents an order of magnitude above the upper end of the distribution of U.S. young children's BLL.
The 95th percentile of the 2011-2016 NHANES distribution of BLL in children (1-5 years; n= 2,321) is 2.66 (ig/dL
(Egan et at. 2021) and the proportion of individuals with BLL that exceed this concentration varies depending on
factors including (but not limited to) housing age, geographic region, and a child's age, sex, and nutritional status.

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Comparators: A concurrent control group exposed to vehicle-only treatment or untreated
control.

Outcomes: Effects on the respiratory system.

Study design: Controlled exposure studies of animals in vivo.

9.7.3 Epidemiologic Studies on the Respiratory System

A limited number of epidemiologic studies evaluated in the 2013 Pb ISA did not provide strong
evidence of an association between BLLs and airway responses in asthma-free populations. Further, these
studies lacked rigorous statistical analysis and included limited consideration of potential confounders. In
panel and time-series epidemiologic studies considering ambient air Pb (measured in PM2 5 or PM10 air
samples), associations were reported between short-term increases in air Pb and decreases in lung
function and increases in respiratory symptoms and asthma hospitalizations in children but not adults.
Despite this evidence for respiratory effects related to air Pb concentrations, the limitations of air Pb
studies - including the limited data on the size distribution of Pb-PM, the uncertain relationships of Pb-
PM10 and Pb-PM2 5 with BLLs, and the lack of adjustment for other correlated particulate matter (PM)
chemical components - precluded firm conclusions about ambient air Pb-associated respiratory effects.
Recent studies have examined lung function and respiratory symptoms in non-asthmatic children and
adults. While the majority of recent studies utilized cross-sectional designs that are unable to establish
temporality between exposure and outcome, most adjust for a wide range of potential confounders and
examine populations with lower BLLs. In general, recent evidence in children is inconsistent, though
there is some evidence from a prospective cohort study that BLLs are associated with accelerated lung
function decline in adults. Notably, because adult populations likely had higher past than current Pb
exposure, there is uncertainty regarding the Pb exposure level, duration, frequency, and timing that may
contribute to the observed association. Measures of central tendency for blood and/or serum Pb levels
used in each study, along with other study-specific details, including study population characteristics and
select effect estimates, are highlighted in Table 9-15. An overview of the recent evidence, delineated by
lifestage, is provided below.

9.7.3.1 Respiratory Effects in Children

A limited number of recent cross-sectional studies have examined the relationship between BLLs
and pulmonary function or respiratory symptoms in children. Studies conducted in different locations
reported inconsistent evidence of an association between BLLs and pulmonary function. In an analysis of
6- to 17-year-old children participating in the 2011-2012 NHANES survey cycle, Madrigal et al. (20.1.8)
reported modest and imprecise positive associations between BLLs and mean forced expiratory volume
(FEV1) (41.9 mL [95% CI: -46.9, 130.6 mL]) and forced vital capacity (FVC) (45.5 mL [95% CI: -49.2,
140.2 mL]) when comparing children with BLLs in the highest quartile (>0.86 (ig/dL) to children with

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BLLs in the first quartile (<0.44 (ig/dL). Similar comparisons were null for FEV1:FVC and forced
expiratory flow (FEF)25%-75%. Notably, the study population had a very low median BLL (0.56 (.ig/dL).
and there were small exposure contrasts between exposure quartiles, which may have limited the
statistical power to detect an association. In contrast with the NHANES analysis, smaller cross-sectional
studies conducted in preschool-aged children in China ("Zeng et ah. 2017) and 10- to 15-year-old children
in Poland (Little et al.. 2017) observed limited evidence of associations between BLLs and decreased
FVC ("Little et aL 20.1.7; Zeng et aL 2017) or FEV1 ("Zeng et aL 20.1.7). Both studies noted small and
imprecise associations and had small sample sizes. Limited statistical power resulting from a small
sample size reduces the likelihood of detecting a true effect and lowers precision, which might explain the
incongruous results. Additionally, the associations observed by Little etal. ( may have been subject
to unmeasured confounding (e.g., by age, SES factors, environmental tobacco smoke), as the authors only
adjusted their regression models for children's heights.

In addition to studies of pulmonary function, a single study examined respiratory symptoms in
children. Zeng et al. ( reported inconsistent associations between BLLs and respiratory symptoms in
preschool-aged children in China, including some living in a community near an e-waste facility. The
authors compared children with BLLs >5 (ig/dL to those with BLLs <5 (ig/dL and reported that those in
the higher exposure group had lower odds of parental-reported wheeze and dyspnea, slightly higher odds
of parental-reported phlegm, and no perceptible difference in parental-reported cough. Caution is
warranted in interpreting results of parental-reported symptoms in locations with known environmental
contamination due to potential over-reporting of symptoms.

9.7.3.2 Respiratory Effects in Adults

A limited number of recent studies have examined the relationship between blood or serum Pb
levels and respiratory effects in adults. There is evidence from a prospective cohort study that BLLs are
associated with accelerated lung function decline in adults, although a large, population-based cross-
sectional study reports conflicting results. All of the studies evaluated in this subsection reported low
levels of blood or serum Pb levels (mean and geometric mean levels <3 (.ig/dL).

The most compelling evidence of an association between Pb exposure and lung function in adults
comes from a prospective cohort study of adults living adjacent to a large industrial complex in South
Korea (Pak et al.. 2012). The authors reported that BLLs were associated with accelerated lung function
decline, measured as the difference in spirometry measurements taken at baseline and after two-years of
follow-up. Specifically. Pak et al. (2012) noted accelerated decline in FVC (-177 mL [95% CI: -330,
-24]) and FEV1 (-107 mL [95% CI: -215, 1]) per 1 (ig/dL higher BLL at baseline. Notably, because
adult populations likely had higher past than current Pb exposure, there is uncertainty regarding the Pb
exposure level, duration, frequency, and timing that may contribute to the observed association. In
contrast to results from Pak et al. (2012). a recent cross-sectional study of 2008-2012 KNHANES

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participants with low BLLs observed null associations between BLLs and FVC and FEV1 in adults

(Leem et ah. 20.1.5").

Leem et al. (20.1.5) also examined obstructive lung function (FEV1/FVC <0.7) in the same
population and observed a null association with BLLs. In a similar recent analysis of a large population-
based health survey (NHANES), (Rokadia and Agarwat 20.1.3) reported a large, but imprecise association
between serum Pb levels and obstructive lung function (OR= 1.94 [95%: 1.10, 3.42] per 1 (ig/dL higher
level of serum Pb) that appears to be driven by an association in participants with moderate to severe
obstructive lung function (OR = 3.49 [95%: 1.70,7.15] perl (ig/dL higher level of serum Pb). The
observed associations were similar in analyses stratified by smoking status, although the associations in
non-smokers were even less precise due to a smaller number of cases.

9.7.4 Toxicological Studies on the Respiratory System

The 2013 Pb ISA evaluated a limited number of studies investigating the effects of ambient
particulate mixtures of which Pb was a component. The effects directly attributable to Pb were not able to
be distinguished from other confounding mixture components. The PECOS criteria used in the 2024 Pb
ISA to identify new respiratory toxicological studies focused on identifying studies that studied Pb
exposure alone. One study reviewed in the 2013 Pb ISA showed that injection of Pb acetate resulted in
histologic signs of damage and inflammation in the lung although uncertainty regarding the biological
relevance of Pb injection remained A few new experimental studies were identified that investigated the
effect of inhaled Pb and met our PECOS criteria (Table 9-9). The studies, all published by the same
group, assessed the localization and clearance of inhaled ultrafine (>100 nm in diameter) Pb particles and
the corresponding effect on lung (and secondary organ) tissue structure. These studies involved 2-
11 weeks of exposures (24 hours/day, 7 days/week) to inhaled Pb nanoparticles after which the
investigators analyzed lung histology and markers of lung damage. Exposure of female mice to roughly
106particles/cm3 lead oxide (PbO) particles for 6 weeks led to a mean BLL of 132 ng/g (-13.922 (ig/dL)
and corresponded to histological signs of lung damage including alveolar septal wall thickening,
emphysema, perivascular infiltration of immune cells, and signs of thrombosis (Dumkova. et al., 20.1.7).
Exposure to a higher concertation of PbO (2.23 x 106 particles/cm3) for 3 days, 2, 6, and 11 weeks led to
BLLs ranging from 10.4 (ig/dL at 2 weeks up to 17.4 (ig/dL after 11 weeks of exposure. The BLL at
3 days was not reported. Histological signs of cellular infiltration and alveolar septal wall thickening was
observed after 6 and 11 weeks of PbO exposure along with signs of macrophage proliferation (PCNA-
staining) (Dumkova et al., 2020b). These effects were not reported for the two-week exposure or an acute
3-day exposure to PbO. Despite increased signs of lung inflammation, signs of fibrosis and apoptosis
were not observed. Interestingly, a 5-week recovery period with no PbO exposure following 6 weeks of
PbO exposure was able to reduce both the lung Pb concertation and partially recover the histopathological
signs of inflammation seen at 6 weeks of PbO (Dumkova et al., 2020b).

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In a separate experiment, a similar procedure as Dumkova. et al. (2020b) was followed using more
soluble Pb(N03)2nanoparticles in place of PbO. Mice were exposed to Pb(NO:,)2 particles for either
3 days, 2 weeks, 6 weeks, or 11 weeks and a separate recovery group that was exposed to Pb(NOs)2 for
6 weeks and then filtered air for 5 weeks ("Dumkova et al.. 2020a). Similar to the results with PbO,
Pb(NC>3)2 exposure showed an increase in histological signs of inflammation and lung damage.
Histological effects with Pb(NOs)2 particle exposure were seen starting at 2 weeks of exposure and did
not completely resolve in the recovery group. Exposure to Pb(NOs)2 reduced the number of lung
macrophages (CD68 positive stained cells) in the lung tissue which corresponded to an increase in
neutrophils (Myeloperoxidase positive cells) and mastocytes (Toluidine blue staining). Similar to the
findings with PbO, a 5-week recovery period with no Pb(NOs)2 exposure following 6 weeks of Pb(NOs)2
exposure was able to reduce both the lung Pb concertation and partially recover the histopathological
signs of inflammation. While macrophage number was partially restored after a 5-week recovery period,
the level of mastocytes remained elevated. Lung mRNA for inflammatory genes like IL-1B, IL-la, and
tumor necrosis factor-a were largely unchanged however RNA levels of NF-kB and IL6 were suppressed
after 3 days and 11 weeks of Pb(NOs)2 suggesting that Pb(NOs)2 dysregulates the inflammatory response
in the lung. While the data presented in these studies are mostly qualitative, it provides some preliminary
evidence of respiratory effects from inhalation of either Pb(NOs)2 or PbO nanoparticles.

9.7.5 Summary and Causality Determination

The effects of Pb on asthma incidence and host defense, which includes data related to host
response to lung infection, are analyzed in the context of allergic disease and immune suppression

(Secti J Section 6.7.2).

The 2013 Pb ISA determined that the evidence for respiratory effects was "inadequate to
determine a causal relationship between Pb exposure and respiratory effects in populations without
asthma." This determination was based on inconsistent findings among studies and the limited quantity
and quality of both epidemiologic and experimental toxicological evidence of respiratory effects. While
there was some epidemiologic evidence of an association between short-term increases in ambient air Pb
and decreases in lung function, these studies were not informative to the causality determination due to
notable uncertainties regarding the size distribution of ambient air Pb, the relationship between ambient
air Pb and BLLs, and the confounding effects of co-occurring pollutants.

Evidence evaluated in the 2013 Pb ISA showed inconsistent relationships between BLLs and
bronchial responsiveness and lung function. Results from recent epidemiologic studies of the effect of
blood Pb on lung function and respiratory symptoms in children remain inconsistent (Section 9.7.3.1). In
adults, a new prospective cohort study provides evidence of accelerated lung function decline in those
with higher BLLs (Pak et al.. 20.1.2). however the relationship between lung function decrements and
BLLs is inconsistent in a few recent cross-sectional analyses (Section 9.7.3.2). This lack of consistency in

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the epidemiologic literature is compounded by uncertainty related to exposure assessment and relative
lack of adjustment for correlated air pollutants. Toxicological data in the 2013 Pb ISA was mostly
limited to studies of concentrated ambient PM of which Pb was a component within a mixture of
pollutants, leaving uncertainty for the role of Pb in the observed effects. New toxicological studies
evaluating inhalation of Pb particles are limited in number but do provide evidence of gross histologic
signs of transient inflammation and lung damage; however, these data are largely qualitative and the
impact of these changes on lung function are unknown. Uncertainty remains regarding the relative size
distribution of Pb particles in ambient air and thus how well experimental generation of Pb particles
reflects ambient concentrations and particle size distribution.

Given the lack of consistency across a small body of epidemiologic evidence and uncertainty in
the direct relevance of a limited number of toxicological results to human lung function, the evidence is
not sufficient to draw a conclusion regarding causality. Thus, the cumulative body of evidence is
inadequate to infer the presence or absence of a causal relationship between Pb exposure and
respiratory effects in populations without asthma.

9.8 Mortality

9.8.1 Introduction, Summary of the 2013 Pb ISA, and Scope of the
Current Review

In the 2013 Pb ISA (U.S. EPA. 2013). the strongest evidence for Pb-associated mortality was
from studies examining cardiovascular mortality. The evidence did not provide strong support for Pb-
associated mortality other than through cardiovascular pathways, and very few studies examined total
(nonaccidental) mortality. For these reasons, the 2013 Pb ISA evaluated studies of all-cause mortality
together with studies examining cardiovascular mortality, and these studies were all included within the
cardiovascular disease chapter. Although this evidence contributed to the "causal relationship" between
Pb exposure and coronary heart disease, there were no distinct causality determinations for total or cause-
specific mortality. In the 2024 Pb ISA, the strongest evidence for Pb-associated cause-specific mortality
continues to come from studies of cardiovascular mortality. However, additional studies examining total
non-accidental mortality have become available since the 2013 Pb ISA, and this section discusses and
evaluates those studies. Studies that examine cardiovascular-related mortality or other cause-specific
mortality are discussed in detail within the appropriate outcome-specific appendices (e.g., cardiovascular
disease [CVD]-related mortality is discussed in Appendix 4) and are briefly summarized in this section.

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9.8.2

Scope

The scope of this section is defined by PECOS statements. The PECOS statement defines the
objectives of the review and establishes study inclusion criteria thereby facilitating identification of the
most relevant literature to inform the Pb ISA.37 In order to identify the most relevant literature, the body
of evidence from the 2013 Pb ISA was considered in the development of the PECOS statements for this
Appendix. Specifically, well-established areas of research; gaps in the literature; and inherent
uncertainties in specific populations, exposure metrics, comparison groups, and study designs identified
in the 2013 Pb ISA inform the scope of this Appendix. The 2013 Pb ISA used different inclusion criteria
than the 2024 Pb ISA, and the studies referenced therein often do not meet the current PECOS criteria
(e.g., due to higher or unreported biomarker levels). Studies included in the 2013 Pb ISA, including many
that do not meet the current PECOS criteria, are discussed in this appendix to establish the state of the
evidence prior to this assessment. Except for supporting evidence used to demonstrate the biological
plausibility of Pb-associated effects on mortality, recent studies were only included if they satisfied all the
components of the following PECOS statements:

Population: Any human population, including specific populations or lifestages that might be at
increased risk of a health effect.

Exposure: Exposure to Pb38 as indicated by biological measurements of Pb in the body - with a
specific focus on Pb in blood, bone, and teeth; validated environmental indicators of Pb
exposure39; or intervention groups in randomized trials and quasi-experimental studies.

Comparison: Populations, population subgroups, or individuals with relatively higher versus
lower levels of the exposure metric (e.g., per unit or log unit increase in the exposure metric,
or categorical comparisons between different exposure metric quantiles).

Outcome: Mortality.

Study Design: Epidemiologic studies consisting of longitudinal and retrospective cohort studies,
case-control studies, cross-sectional studies with appropriate timing of exposure for the health

37The following types of publications are generally considered to fall outside the scope and are not included in the
ISA: review articles (which typically present summaries or interpretations of existing studies rather than bringing
forward new information in the form of original research or new analyses), Pb poisoning studies or clinical reports
(e.g., involving accidental exposures to very high amounts of Pb described in clinical reports that may be extremely
unlikely to be experienced under ambient air exposure conditions), and risk or benefits analyses (e.g., that apply
concentration-response functions or effect estimates to exposure estimates for differing cases).

38Recent studies of occupational exposure to Pb were considered insofar as they addressed a topic area of particular
relevance to the NAAQS review (e.g., longitudinal studies designed to examine recent versus historical Pb
exposure).

39Studies that estimate Pb exposure by measuring Pb concentrations in particulate matter with a nominal mean
aerodynamic diameter less than or equal to 10 |im3 (PMio) and particulate matter with a nominal mean aerodynamic
diameter less than or equal to 2.5 |im3 (PM2 5) ambient air samples are only considered for inclusion if they also
include a relevant biomarker of exposure. Given that size distribution data for Pb-PM are fairly limited, it is difficult
to assess the representativeness of these concentrations to population exposure | Section 2.5.3 (U.S. EPA. 2013)1.
Moreover, data illustrating the relationships of Pb-PMio and Pb-PM2 5 with BLLs are lacking.

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endpoint of interest, randomized trials and quasi-experimental studies examining
interventions to reduce exposures.

9.8.3 Total (non-Accidental) Mortality

The 2013 Pb IS A (U.S. EPA. 20.1.3') evaluated a small number of studies that examined the
association between biomarkers of Pb exposure and all-cause mortality. Overall, these studies reported
consistently positive associations between Pb biomarkers and all-cause mortality. Specifically. Lustberg
and Silbergeld (2002) indicated an increased risk of all-cause mortality when comparing the highest
tertiles of BLLs (20-29 (.ig/dL) to the lowest (<10 (.ig/dL). Lustberg and Silbergeld (2002) conducted this
analysis among NHANES 11 cohort, which had high BLLs (mean 14 (.ig/dL). Additionally. Schober et al.
(2006) and Menke et al. (2006) both evaluated the NHANES III cohort, which had an overall lower BLL
(mean: 2.6 (.ig/dL). and still identified a positive association between BLLs and all-cause mortality
(Figure 9-1). Notably, both NHANES cohorts included adult study populations with higher past than
recent Pb exposures, making it difficult to characterize the specific timing, duration, frequency, and level
of Pb exposure that contributed to the observed associations. Recent evidence continues to support the
association between Pb biomarkers and all-cause mortality. Study-specific details, including biomarker
Pb levels, study population characteristics, confounders, and select results from these studies, are
highlighted in Figure 9-3 and Table 9-17. Studies in Figure 9-3 are standardized to be interpreted as the
risk of all-cause mortality associated with a 1 (ig/dL increase in BLL. Study details in Table 9-10 include
standardized results as well as results that could not be standardized based on the information provided in
each paper. An overview of the recent evidence is provided below.

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Reference	Study Population Pb distribution

Menke et al, 2006 NHANES III Adults £ 20 Mean: 2.58

Pb measurement -Years of
year	follow-up

Lanphearetal,2018 NHANES III Adults a 20

Schoberetal,2006 NHANES III Adults £40

Geometric Mean: 2.71
Geometric SE: 1.31

Median
T1 (2.6)

T2 (6.3)

T3 (11.8)

Median

van Bemmeletal, 2011 NHANES III Adults £40 <5ug/dL2.6

a 5 ug/dL7.5

Duan et al, 2020*

NHANES Adults 2 20

Median (IQR)
1.49(0.93,2.31)

1988-1994

1988-1994

1988-1994

1988-1994

1999-2014

12

19

8.6

7.1

all cause

all cause

all cause

7.5-7.8 all cause

all cause ALAD GG
all cause ALAD CG/GG

all cause

I	1	1	

0.90	1.00	1.20

Hazard Ratio (95% CI) per 1 ug/dL increase in blood Pb

1.40

ALAD GG and ALAD CG/GG = variants of 5-aminolevulinic acid dehydratase, T# = fertile #, NHANES = National Health and Nutrition Examination Survey.

Note: Red text: Studies published since the 2013 Pb ISA; Black text: Studies included in the 2013 Pb ISA.

Effect estimates are standardized to a 1 |jg/dL increase in blood Pb. If the Pb biomarker is log-transformed, effect estimates are standardized to the specified unit increase for the
10th—90th percentile interval of the biomarker level. Effect estimates are assumed to be linear within the evaluated interval.

*Study estimated relative risk.

Figure 9-3 Effect estimates for associations of blood Pb with all-cause mortality.

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In a recent extended analysis of the NHANES III cohort, Lanphear et al. (2018) increased the
average follow-up time of the Menke et al. (2006) analysis by over 7 years (from 12 to -19 years),
resulting in a substantial increase in the number of total deaths observed (4,222 versus 1,661). Lanphear
et al. (2018) reported that 1 (ig/dL higher BLLs were associated with a hazard ratio (HR) of 1.06 [95%
CI: 1.03, 1.09]) for all-cause mortality. The authors also calculated the population attributable fraction for
both all-cause and cardiovascular mortality, to estimate the proportional reduction in mortality that would
be expected if BLLs in those >20 were reduced to 1 (ig/dL. Lanphear et al. (2018) estimated that the
population attributable fraction for all-cause mortality was 18% (95% CI: 10.9, 26.1%), while the
population attributable fraction for cardiovascular mortality was 28.7% (95% CI: 15.5, 39.5%). Therefore,
given the proportion of all-cause mortality attributable to cardiovascular causes (both in this study [~38%]
and nationally [-33%; NHLBI, 2017, 3980932}]), CVD mortality likely accounts for a large proportion
but not the entirety of the all-cause mortality signal. The authors also used a five-knot restricted cubic
spline analysis to assess potential non-linearities and observed a generally sigmoidal concentration-
response (C-R) relationship between BLLs and all-cause mortality, with some attenuation of the C-R
relationship below 2.5 (ig/dL (Figure 9-4). The general shape of the C-R relationship is consistent with
previous results from Menke et al. (2006).

4~\



0	2.5	5	7.5	10

Concentrations of lead in blood |ig/dL

Note: Restricted cubic spline (5 knots) (red line) and adjusted HRs (black line) with 95% CI's (hatched lines) for all-cause mortality.
Source: Adapted from Lanphear et al. (2018).

Figure 9-4 Dose-response relationship between blood Pb levels and
all-cause mortality.

Other recent studies also evaluated the relationship between blood Pb and total mortality using
NHANES data. Using NHANES III, van Bemmel et al. (2011) estimated an increased association
between BLLs and all-cause mortality (HR: 1.04 [95% CI: 0.98, 1.10]). In addition, van Bemmel et al.

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(2 also evaluated this relationship by polymorphisms in 5-aminolevulinic acid dehydratase (ALAD).
A critical mechanism of Pb toxicity is its ability to interact and inhibit key enzymes, such as ALAD, in
the heme biosynthesis pathway. This study evaluated associations between BLLs, and mortality stratified
by ALAD variant (ALADGG [more common genotype] or ALADCG/GG). However, there was little
difference between the estimates generated when stratified (ALADGG HR: 1.03 [95% CI:0.98, 1.08],
ALADCG/GG HR: 1.09 [95% CI:0.93, 1.28]), when comparing BLLs >5 (ig/dL to levels <5 (ig/dL.

Using more recent NHANES cycles (1999-2014), Duan et al. (2020) also reported a positive association
between blood Pb and all-cause mortality (RR: 1.39 [95% CI: 128, 1.51]). In a similar analysis using
recent KNHANES cycles (2007-2015), 6vi.ro et al. (2020) evaluated the association between BLLs and
total (nonaccidental) mortality using KNHANES (2007-2015) baseline data, and mortality data linked
through 2018. Overall, there were positive associations between higher tertiles of blood Pb exposure and
all-cause mortality. Compared to the first tertile of BLLs (<1.91 (.ig/dL). the HR for all-cause mortality
was 2.02 (95% CI: 1.20, 3.40) forthe second tertile (1.91-2.71 ^ig/dL) and 1.91 (95% CI: 1.13, 3.23) for
the third tertile (>2.71 (.ig/dL).

In addition to studies using nationally representative survey data, a recent study by Hollingsworth
and Rudik (202.1.) implemented a quasi-experimental design to examine the effect of the phase out of
leaded gasoline in automotive racing on mortality rates in older adults. Comparing time periods prior to
and after the phaseout of leaded gasoline in professional racing series (i.e., the National Association for
Stock Car Auto Racing [NASCAR] and the Automobile Racing Club of America [ARCA]), the authors
used a difference-in-differences technique to estimate county-level changes in air Pb concentrations,
elevated BLL prevalence among children, and mortality rates in race counties and counties bordering race
counties relative to control counties. A detailed discussion of results for air Pb concentrations and BLLs is
presented in Section 2.4.1. In short, there were substantial declines in both air Pb concentrations and the
prevalence of children with elevated BLLs associated with the phaseout of leaded gasoline. The authors
also reported significant declines in mortality rates over this same period. Specifically, in the period
following de-leading of gasoline, there was an estimated decline in annual age-standardized all-cause
mortality rates of 91 deaths per 100,000 in race counties and 38 deaths per 100,000 in border counties.
Similar to the exposure results, the mortality estimates appear to demonstrate a distance gradient.
Although this analysis includes county-level data, the difference-in-difference approach controls for
spatially varying confounders by estimating the difference in mortality rates in adjoining years in the
same county and controls for temporally varying confounders by assessing the difference of those
differences between locations. The authors additionally adjust for potential confounders that may vary
spatially and temporally (e.g., unemployment rate and quantity of Toxic Release Inventory [TRI] Pb
emissions). Hollingsworth and Rudik (202.1.) did not adjust for potential co-pollutant exposures, but
provide evidence that there is no differential effect of leaded and unleaded races on other co-pollutant
concentrations (i.e., CO, VOCs, PMio, PM2.5, NO2, and O3) in the weeks leading up to and following the
race. However, because the mortality rates are an annual measure, there is remaining uncertainty
regarding potential differential trends in the long-term average of other pollutants that could be correlated
with the phaseout of leaded gasoline in NASCAR and ARCA. A recent re-analysis of NAS data

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(Weisskopf et al.. 2015). expanded on a similar analysis (Weisskopf et al.. 2009) that was discussed in the
2013 Pb ISA. In the re-analysis, special considerations for selection bias were taken to account for the
probability that older individuals who elected to participate in the study were more likely to be free of
cardiovascular disease than those who declined to participate. Specifically, the authors created four
different models, which controlled for different covariates, additional markers for SES, and restricted by
age. In this analysis, the authors restricted the sample (Model 3 and Model 4) to participants that were
<45 years at the start of the NAS study, since cardiovascular disease-related deaths would be relatively
rare in the younger population and would therefore not impact study participation. This study indicated a
positive association with all-cause mortality (HR: 1.86 [95% CI: 1.12, 3.09]) when comparing the highest
tertile (>31 jxg/g) of patella Pb to the lowest tertile (<20 jxg/g), in the model restricting the age of
participants to participants <45 years at the start of the NAS study. No associations were observed
without the age restriction or with blood or tibia Pb.

Since Pb has been identified as being associated with renal insufficiency, previous studies have
further assessed if Pb accumulates in patients with end-stage renal disease (ERSD). In a recent
prospective cohort study in Taiwan, Lin et al. (20.1.1) followed study subjects on maintenance
hemodialysis for a period of 18 months. Overall, subjects included in the study had higher BLLs (mean:
11.5 (ig/dL) than the general Taiwanese population (mean: 7.7 (ig/dL). It is suspected that hemodialysis
patients may experience higher BLLs since their kidneys may no longer be able to excrete Pb from the
body due to a total loss of renal function ("Appendix 5). Among this group, there was a strong but
imprecise association between BLLs and all-cause mortality when comparing those in the second tertile
of BLLs (8.51-12.64 (ig/dL) to those in the first tertile of BLLs (<8.51 (ig/dL; HR: 2.69 [95% CI: 0.47,
3.44]). This effect was higher in magnitude, but even more imprecise among those in the third tertile of
BLLs (>12.64 (ig/dL) compared with the first tertile (HR: 4.70 [95% CI: 1.92, 11.49]). The imprecise
effect estimates in this analysis are likely due to a combination of the relatively small sample size and
short follow-up period, leading to a small number of deaths included in the analysis. The small number of
cases reduces statistical power, as well as the likelihood that an observed result reflects a true effect.

In addition, several analyses evaluated metal chelation therapy as a treatment for those with
atherosclerotic plaques and evaluated subsequent all-cause mortality outcomes in the Trial to Assess
Chelation Therapy (TACT) study. The TACT study was a randomized control trial (RCT) with a 2 x 2
factorial design evaluating chelation therapy with ethylenediaminetetraacetic acid (EDTA) plus the use of
high dose oral vitamins. The factorial group results indicated that a combination of EDTA and high-dose
vitamins was associated with a reduction in deaths from all causes (Lamas et al.. 20.1.4). In the same trial,
the findings indicated that diabetic patients >50 years had a reduction (10% versus 16% HR: 0.59 [95%
CI: 0.44. 0.79]) in the number of deaths from all-causes following EDTA chelation therapy (Escolar et al..
2014). Although these studies suggest a clear association between chelation therapy and a reduction in
overall deaths, it should be noted that most of these studies did not measure BLL pre and post chelation.
Notably, chelation therapy reduces levels of other heavy metals in the blood and thus does not establish a
direct effect of Pb reduction absent direct measures of metal biomarkers. Thus, chelation therapy in

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populations with low BLLs is an area of research that could be expanded to potentially provide strong
quasi-experimental support for other lines of evidence that quantitatively describe the associations
between Pb biomarkers and all-cause mortality, as well as other health effects. A follow-up RCT,

TACT2, a replicative study in diabetics with a history of MI, is currently underway to confirm the results
reported as a result of TACT ("Lamas and Ergui. ).

In contrast to the generally consistent evidence of an association between BLLs and all-cause
mortality, a small Canadian study evaluating several trace metals observed a null association between all-
cause mortality and BLLs among hemodialysis patients (>18 years of age) (Tonelli et ah. 20.1.8'). Patients
in this cohort had relatively low BLLs (1st decile: 0.06 (ig/dL, 10th decile 1.74 (.ig/dL). and there was no
observed relationship between BLLs and all-cause mortality when comparing the highest to the lowest
decile. The authors only presented quantitative results for statistically significant associations, so it is
unclear whether there was any evidence of a non-statistically significant association. Additionally. Tonelli
et al. (20.1.8) was likely underpowered to detect a HR in the range reported in other studies of BLLs and
all-cause mortality (Figure 9-4).

9.8.4 Cause-Specific Mortality

The mortality studies available for review in the 2013 Pb ISA focused primarily on
cardiovascular mortality, and consistently reported positive associations with overall cardiovascular
mortality and cause-specific cardiovascular mortality. Recent studies also evaluate cardiovascular
mortality in addition to other cause-specific mortality outcomes.

Recent analyses further indicate a positive association between Pb exposure and cardiovascular
mortality and are further described in Sectior . In summary, there were several studies using
nationally representative data with low BLLs (mean <2 (ig/dL) that consistently reported increased
associations between biomarkers of Pb exposure and cardiovascular mortality. However, these
populations were largely similar (mostly from NHANES III or other more recent NHANES cycles) and
still include individuals with sizeable historic exposures to Pb. For specific causes of CVD mortality
(e.g., myocardial infarction (MI), ischemic heart disease (IHD), stroke), the measures of association were
higher in magnitude but were less precise (i.e., wider 95% CIs), likely due to the smaller number of
cause-specific cardiovascular-related deaths. Additionally, in the quasi-experimental study discussed in
Section 9.8.3, deleading of racing gasoline led to declines in county-level cardiovascular mortality rates
(Hollingsworth and Rudik. 2021). Evidence from RCT trials evaluating chelation therapy (Escolar et al..
20.1.4; Lamas et al.. 2014) indicates reductions in cardiovascular mortality following chelation with EDTA
and high doses of oral vitamins, yet the study did not specifically evaluate BLLs before or after chelation
therapy. This evidence helps to strengthen the evidence base indicating an association between
biomarkers of Pb exposure and increased risk of cardiovascular mortality.

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Several recent studies also evaluated the relationship between Pb exposure biomarkers and cancer
mortality, as described in Section .1.0.4. In summary, there were a limited number of studies evaluating Pb
biomarkers of exposure and overall cancer mortality. Most studies relied on nationally representative data
and yielded inconsistent but mostly null associations between Pb exposure and cancer mortality.

However, the follow-up period in many of these analyses was short (<11 years), with a small number of
cancer deaths and a lack of control of some potential influential confounders, such as comorbidities and
BMI.

Additionally, some studies evaluated alternative cause-specific mortality outcomes. A cohort
study analyzed data from five NHANES cycles (1999-2008) and reported a positive, but imprecise
association between blood Pb and Alzheimer"s disease ( AD) mortality rSection 3.5.4; (Horton et al..
20.1.9)1. The imprecise effect estimate is likely due to the small number of AD mortality cases (n = 81)
that resulted from AD mortality being determined by the listing of the immediate cause of death rather
than the underlying cause of death. Additionally. Lin et al. C prospectively evaluated subjects on
maintenance hemodialysis for a period of 18 months and evaluated infection-caused mortality. Among
this group there was an imprecise increase in mortality (HR: 5.35 [95% CI: 1.38, 20.83]) in the highest
tertile (>12.64 (ig/dL) compared to the lowest tertile (<8.51 (ig/dL). This association persisted (HR: 4.72
[95% CI: 1.27, 17.54]) even after correction for hemoglobin (dividing BLL by hemoglobin
concentration). Finally, a quasi-experimental reported a decrease in county-level respiratory mortality
rates in association with the phase out of leaded gasoline in automotive racing (Hollingsworth and Rudik.

202 .n.

9.8.5 Biological Plausibility

In evaluating the biological plausibility of reported associations between Pb exposure and total
non-accidental mortality, this section considers the biological evidence supporting health outcomes likely
to contribute to total mortality. As summarized above, studies consistently report positive associations
between Pb exposures and cardiovascular-related mortality, with much more limited evidence for
associations with other causes of mortality. Overall, cardiovascular mortality is the most common
contributor to total non-accidental mortality (i.e., accounting for about 33% of total mortality) (NHLBI.
2017). As it pertains to Pb exposure, the available evidence provides strong support for Pb-associated
cardiovascular effects and supports a continuum of effects leading to cardiovascular mortality, as
described further in Appendix 4. Direct evidence for cardiovascular effects follow ing Pb exposures comes
from numerous animal toxicological studies, and there is coherence between these animal studies and
epidemiologic studies that report associations with some of the same cardiovascular outcomes
(e.g., increased blood pressure, changes in cardiac electrophysiology). Animal studies additionally
support the biological plausibility of the consistent epidemiologic associations reported between body Pb
concentrations and cardiovascular outcomes such as hypertension and cardiovascular mortality.

Section 4.10 characterizes the strong evidence indicating the mechanisms by which exposure to Pb could

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plausibly progress from initial events to endpoints relevant to the cardiovascular system, such as
hypertension, exacerbation of IHD, and potential MI or stroke. In particular, exposures to Pb can result in
oxidative stress and systemic inflammation, which could potentially lead to impaired vascular function, a
pro-atherosclerotic environment, and increases in blood pressure. There is animal toxicological evidence
demonstrating all of these effects following exposure to Pb ("Section 4.8). Atherosclerosis and increased
blood pressure can then set the stage for an MI or stroke that could result in mortality. Thus, the
progression demonstrated in the available evidence for cardiovascular morbidity supports potential
biological pathways by which Pb exposure could result in cardiovascular mortality.

The current evidence strongly supports a plausible relationship between Pb exposure and
cardiovascular mortality. Additionally, Pb may act on other biological pathways leading to death. There is
some limited evidence that BLLs are associated with other causes of mortality, including AD and
infection. The strongest evidence for biologically supported pathways leading to neurodegenerative
disease include the effect of Pb on cellular protein function and subsequent initiation of oxidative stress-
and inflammation-mediated pathways ("Section 3.3). AD. specifically, has been linked with increased
markers of neuroinflammation. Studies with exposure of postweaning animals to Pb have shown
increased inflammation associated with AD markers, as well as inhibition of AD markers following
postexposure treatment with anti-inflammatory and antioxidative molecules. Regarding infection-related
mortality, biological plausibility for the observed association is provided by toxicological and
epidemiologic studies demonstrating (1) skewing of T cell populations, promoting Th2 cell formation and
cytokine production, (2) decreased IFN-y production, (3) decrements in macrophage function, (4)
production of inflammatory mediators, and (5) disruption of the microbiome, all of which could lead to
immunosuppression ("Section ).

9.8.6 Summary and Causality Determination

The 2013 Pb ISA did not make a causality determination regarding the relationship between Pb
exposure and total (nonaccidental) mortality, but studies examining this relationship did support the
coronary heart disease causality determinations made within the cardiovascular disease chapter. The
evidence available at the time of the last review was limited, but reported consistently positive
associations between Pb biomarkers and all-cause mortality (Menke et al.. 2006; Sehober et ah. 2006).
These results were additionally supported by consistent positive associations between BLLs and overall
cardiovascular mortality (Section 4.10') as well as cause-specific cardiovascular mortality (e.g., MI. IHD.
stroke)). Menke et al. (2006) examined the shape of the C-R relationship between BLLs and all-cause
mortality using quadratic spline models, which generally appeared to support a linear, no-threshold
relationship, although the HRs were somewhat attenuated at BLLs <2.5 (ig/dL. Notably, the majority of
mortality studies analyzed participants from NHANES cohorts, either NHANES II or NHANES III, so
while the results are consistent, they do not represent entirely independent study populations.

Additionally, while some of the studies evaluated in the 2013 Pb ISA examined populations with low

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mean BLLs (<3 |ig/dL). study participants were born prior to the phase-out of leaded gasoline and
therefore likely had much higher past Pb exposures, making it difficult to characterize the specific timing,
duration, frequency, and level of Pb exposure that contributed to the observed associations.

Prospective cohort studies evaluated since the completion of the 2013 Pb ISA continue to provide
consistent evidence of positive associations between Pb exposure and total (nonaccidental) mortality.
Many recent analyses further evaluated the association between BLLs and the risk of mortality using
NHANES cohorts linked to mortality databases, including an extended analysis of the NHANES III
cohort with additional years of follow-up (Lanphear et ah. 20.1.8') and analyses of more recent NHANES
cycles (Bvun et ah. 2020; Duan et ah. 2020; van Bemmel et ah. 20.1.1"). In addition to NHANES analyses,
another analysis of participants from a nationally representative survey [KNHANES; ("Bvun et ah. 1020)]
and a smaller prospective cohort study of hemodialysis patients (Lin et ah. 20.1.1) provide evidence of an
association between BLLs and total (non-accidental) mortality. These findings are supported by a quasi-
experimental study that reported a decline in county-level all-cause mortality rates following the phase
out of leaded gasoline in automotive racing (Hollingsworth and Rudik. 2021). Recent studies continue to
include populations with low mean blood Pb concentrations, but do not address potentially large
differences in past versus current exposures. Thus, there is remaining uncertainty as to the specific timing,
duration, frequency, and level of Pb exposure that contributed to the observed associations. The observed
associations between BLLs and total mortality are large in magnitude (Figure 9-3), though uncertainty in
the levels of Pb exposure that contributed to the observed associations may also introduce uncertainty in
estimating the magnitude of the effect. One recent study examined the C-R relationship between blood Pb
and total mortality ("Lanphear et ah. 2018). Similar to Menke et ah (2006). Lanphear et ah (20.1.8)
observed generally sigmoidal spline curves with some evidence of attenuation of the C-R relationship
below 2.5 (ig/dL (Figure 9-4).

The body of evidence for total mortality is further supported by strong evidence for a causal
relationship between Pb exposures and cardiovascular effects and cardiovascular mortality (Section 4.10).
Cardiovascular mortality comprises a large portion of total mortality (Section 4.10), and recent studies
consistently report positive associations with BLLs. The recent evidence includes a wider range of study
populations and expanded evidence on the C-R relationship that generally supports a linear relationship
between BLLs and cardiovascular mortality, with no evidence of a threshold. There is also coherence of
effects across the scientific disciplines (i.e., animal toxicological, controlled human exposure, and
epidemiologic studies) and biological plausibility for Pb-related cardiovascular disease (Appendix 4).
which provides additional support for the Pb-mortality relationship.

Overall, there is sufficient evidence to conclude that there is a causal relationship between Pb
exposure and total (nonaccidental) mortality. This conclusion is driven by epidemiologic evidence for
Pb-associated all-cause mortality and the strong epidemiologic and experimental animal evidence
supporting a causal relationship with cardiovascular effects and cardiovascular mortality. Recent
epidemiologic studies build upon evidence from the 2013 Pb ISA and provide largely consistent evidence

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of an association between biomarkers of Pb exposure and total mortality. A few uncertainties remain in
the evidence base, including a limited number of studies and analyses of similar or overlapping study
populations. However, these studies are supported by more robust evidence of Pb-related cardiovascular
mortality, which comprises nearly 33% of total mortality. In addition, evidence for cardiovascular
morbidity provides biologically plausible pathways through which Pb exposure could result in mortality.
There is also very limited evidence that Pb exposure is positively associated with other causes of
mortality, including AD and infection. Biological plausibility for these outcomes is demonstrated by
pathways leading from Pb exposure to neurodegenerative disease and immunosuppression, respectively.
However, although there is toxicological evidence that developmental exposure to Pb increases the
expression of proteins related to AD, the epidemiologic evidence relating Pb exposure to incident AD
remains limited. The key evidence, as it relates to the causal framework, is summarized in Table 9-3.

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Table 9-3 Summary of evidence for a causal relationship between Pb exposure and total mortality

Rationale for Causality
Determination3

Key Evidence"

Key References"

Pb Biomarker Levels Associated
with Effects0

Consistent epidemiologic
evidence from multiple studies
at relevant BLLs

Increases in total mortality in multiple nationally
represented studies. Total mortality
associations are further supported by increases

(Hollinasworth and Rudik, 2021: Bvun et
al,, 2020; Duan et al,, 2020; Lanphear et
al,, 2018; van Bemmel et al,, 2011; Menke

Median, Mean, and Geometric
Mean BLLs: 1.49-2.71 pg/dL



in cardiovascular mortality conducted within
nationally represented studies.

et al,, 2006)



Epidemiologic evidence
supports no evidence of a
threshold between Pb
biomarkers of exposure and
total mortality at the
concentration ranges
examined

Recent studies provide direct evidence of a
linear or sigmoidal, no-threshold C-R
relationship at lower concentrations of BLLs.

(Menke et al,, 2006)
(Lanphear et al,, 2018)

Mean BLL: 2.58 pg/dL
Geometric Mean BLL: 2.71 pg/dL

Biological plausibility from
cardiovascular morbidity
evidence

Stronq evidence for coherence of effects across Appendix 4

scientific disciplines and evidence for a range of

cardiovascular effects in response to increases

in biomarkers of Pb exposure, especially for

increases in blood pressure and hypertension.

The collective body of cardiovascular morbidity

evidence provides biological plausibility for a

relationship between biomarkers of Pb

exposure and cardiovascular mortality, which

comprises -33% of total mortality.



BLLs = blood lead levels; C-R = concentration-response; Pb = lead.

"Based on aspects considered in judgments of causality and weight-of-evidence in causal framework in Table I and Table II of the Preamble to the IS As (U.S. EPA, 2015).
bDescribes the key evidence and references, supporting or contradicting, contributing most heavily to causality determination and, where applicable, to uncertainties or
inconsistencies. References to earlier sections indicate where the full body of evidence is described.

°Describes the Pb biomarker levels at which the evidence is substantiated.

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9.9

Evidence Inventories - Data Tables to Summarize Study Details

Table 9-4

Epidemiologic studies of exposure to Pb and hepatic effects

Reference and Study
Design

Study Population

Exposure Assessment Outcome

Confounders

Effect Estimates and 95%
Clsa

Direct Evaluation of Liver Injury

tZhai eta!. (2017)

Yangtze River Delta

Region

China

1 yr (2014)

Cross-sectional

SPECT-China
n = 2011

General population,
>18 yr old with no history
of excessive alcohol
consumption or viral
hepatitis

Blood

Pb measured in venous
whole blood using
atomic absorption
spectrometry
Age at measurement:
>18 yr old

Median:

Males: 5.29 [jg/dL
Females: 4.49 [jg/dL

25th:

Males: 3.61 [jg/dL
Females: 2.98 [jg/dL

75th:

Males: 7.28 [jg/dL
Females: 6.59 [jg/dL

Nonalcoholic fatty liver
disease

Two doctors
performed abdominal
ultrasounds and
categorized liver
status as normal or
fatty using predefined
criteria

Age at outcome:
>18 yr old

Age, region,
education, current
smoking, current
drinking, ALT,
diabetes, waist
circumference, BMI,
LDL cholesterol, HDL
cholesterol,
triglycerides, total
cholesterol, and
blood cadmium levels

ORs for NAFLD prevalence
across blood Pb quartiles

Males



Q1:

Ref.



Q2:

1.70 (0.84,

3.42)

Q3:

1.84 (0.88,

3.86)

Q4:

2.17 (0.99,

4.75)

Females



Q1:

Ref.



Q2:

1.38 (0.96,

2.00)

Q3:

1.50 (1.02,

2.18)

Q4:

1.61 (1.08,

2.41)

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Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tWerder et al.

Gulf Region
United States
2012-2013
Cross-sectional

Gulf Long-Term Follow-up Blood
Study
n = 214

Non-smoking >30 yr old
male oil spill response
workers and oil spill safety
trainees with no history of
liver disease or heavy
alcohol use

Pb measured in venous
whole blood using solid-
phase micro-extraction
with gas

chromatography/mass

spectrometry

Age at measurement:

>30

Liver injury

Cytokeratin 18 (CK18
M65 and CK18 M30)

Age at outcome:

>30

Age, race, alcohol
consumption, serum
cotinine, BMI,
diabetes dx, and
education

Change in CK18 M65 (U/L)

2.4 (-12.69, 17.49)

Change in CK18 M30 (U/L)

21.7 (9.94, 33.46)

Mean: 1.82 (1.76)

tChunq et al. (2020)

South Korea
2 yr (2016-2017)
Cross-sectional

KNHANES
n = 4420

Adults, >20 yr old

Blood

Pb measured in venous
whole blood using
GFAAS

Age at measurement:
>20 yr old

Mean: 1.81 pg/dL
Max: 20.16 pg/dL

Hepatic steatosis and
fibrosis

Hepatic steatosis (HS)
as indicated by an HS
Index = 36

(8 x (ALT/AST ratio) +
BMI (+2 if female; +2
if had diabetes
mellitus)). Hepatic
Fibrosis (HF) as
indicated by a fibrosis-
4 (FIB-4) score >2.67
((age * AST
level)/(platelet level *
v(ALT level)).

Age at outcome:
>20 yr old

Age, smoking status,
alcohol consumption,
hypertension status,
obesity status,
diabetes status,
hypertriglyceridemia
status, blood Hg,
blood Cd.

ORs

Hepatic Steatosis

Men

0.83 (0.66, 1.03)
Women

0.98 (0.80, 1.19)

Fibrosis

Men

0.70 (0.44, 1.09)
Women

0.72 (0.42, 1.26)

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Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tReia et al. (2020)

NHANES
n = 2499

Blood

Liver fibrosis

Age, gender, waist
circumference,

ORs (NAFLD Fibrosis Score
>0.676)

United States



>20 yr old

NAFLD Fibrosis Score

hypertension, liver



5 yr (2011-2016)

General population >20 yr

Mean: 1.01 pg/dL



function test,

Q1: Reference

Cross-sectional

old with nonalcoholic fatty

75th: 1.62 pg/dL

Age at outcome:

hemoglobin A1c,

Q2: 2.79 (1.39, 5.63)
Q3: 3.74 (2.01, 6.96)
Q4: 5.93 (2.88, 12.24)



liver disease (NAFLD)



>20 yr old (concurrent
with exposure)

triglycerides,
smoking, and PIR

Serum Biomarkers of Liver Function

tPollack et al, (2015)

BioCycle

Blood

ALT, ALP, AST,

Linear mixed models

AST (% change):



n =259



Bilirubin

adjusted for age,

5.02 (-1.36, 11.41)

Buffalo, NY



Pb measured in venous



BMI, race, average

ALT (% change):

United States

Premenopausal women

whole blood using ICP-

ALT (U/L), ALP (U/L),

calories, alcohol

2 menstrual cycles (8

followed for 2 menstrual

MS

AST (U/L), Bilirubin

intake, smoking, and

6.39 (3.07, 9.72)

visits per cycle) (2005-

cycles



(mg/dL)

cycle day

ALP (% change):

2007)

Age at measurement:

Cohort



27.4 (SD: 8.2)

Age at outcome:



2.14 (-5.05, 9.33)





27.4 (SD: 8.2)









1.03 pg/dL







tChen et al. (2019)

Guangdong
China
1 yr (2015)
Cross-sectional

n = 267

Hospitalized patients from
two regions in Guangdong
(one e-waste polluted
area and a matched
control area). Patients
with heart or kidney
disease, those taking
drugs with hepatic toxicity,
and those with a history of
alcohol consumption or
smoking were excluded.

Blood

Pb was measured in
venous whole blood
using GFAAS

Age at measurement:
4 to 85 yr old

Median:

Exposed: 8.7 [jg/dL;
Control: 5.1 [jg/dL
75th:

Exposed: 12.2 [jg/dL;
Control: 8.4 [jg/dL

Abnormal liver
function

Abnormal liver
function defined as
two transaminases
(AST, ALT, or GGT)
above normal range
or one at least two
times higher than
normal range (40 U/L)

Age at outcome:
4 to 85 yr old
(concurrent with
exposure)

Age, gender, hepatic
disease, RBC, Hb,
and platelets

OR for Prevalence of
Abnormal Liver Function

1.94 (1.00, 3.73)

9-76

-------
Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tChristensen et al.
(2013)

United States
2 yr (2003-2004)
Cross-sectional

NHANES
n = 1345

General population,
>12 yr old. No chronic
hepatitis or liver disease,
and no high alcohol
intake.

Blood

Pb measured in venous
whole blood using ICP-
MS

Age at measurement:
>12 yr old

Liver function

Serum ALT

Age at outcome:
>12 yr old

Sex, Race/Ethnicity,
Age, PIR, BMI

Change in ALT (U/L)

Q1
Q2
Q3
Q4

Reference

-0.068 (-0.14, 0.004)
-0.039 (-0.113, 0.035)
-0.103 (-0.185, -0.021)

Mean NR

tObenq-Gvasi (2019)

United States
NHANES 2009-2016
Cross-sectional

NHANES

n = 7,730 young adults
(18-44); 5,744 middle-
aged adults (45-65)

General population; ages
18-65

Blood

GGT (U/L)

BLL measured in venous Serum GGT (U/L)
whole blood using ICP-
MS

Age at measurement:
>18 yr old

Mean:

Young adults:
1.03 [jg/dL

Middle-aged adults:
1.62 [jg/dL

Age at outcome:
>18 yr old

Gender, BMI,
income, ethnicity,
and alcohol
consumption

ORs (GGT >18 U/L)

Young Adults
1.94 (1.65, 2.28)

Middle-Aged Adults
1.34 (1.14, 1.58)

9-77

-------
Referen<^and Study stlldy Poplllatlon ExposlIre Assessment	0lItcome	ConfolInders Effec, Es«i™,?s ,„d 95%

Serum Lipids

tPeters et al. (2012)

United States
Blood Pb measured
between 1999-2008;
Serum lipids measured
3 to 4 yr after blood Pb
Cohort

Normative Aging Study
n = 426

Older male Veterans

Blood, Bone

Blood Pb measured in
venous whole blood
using GFAAS

Serum lipids

Triglycerides, total
cholesterol, HDL-C,
LDL-C

Mean: 4.01 ± 2.30 [jg/dL Age at outcome:

3 to 4 yr after blood
Pb

Age at baseline, yr
between baseline
and outcome,
education, BMI,
alcohol intake,
smoking status,
pack-yr of smoking,
hypertension status,
and statin use

ORs

Total C (>200 mg/dL)
1.08 (0.99, 1.19)

LDL-C (>130 mg/dL):
1.02 (0.91, 1.15)

HDL-C (<40 mg/dL):
0.90 (0.80, 1.00)

Triglycerides (>200 mg/dL):
0.99 (0.87, 1.13)

tXu et al. (2021)

United States
NHANES 2005-2016
Cross-sectional

NHANES	Blood

n = 7457

Pb measured in venous
General population; Ages whole blood samples
20 to 79 yr old	using ICP-MS

Age at measurement:
Mean (SD):
43.68 (15.02) yr

GM: 1.23 [jg/dL

Dyslipidemia

Total cholesterol,
LDL-C, non-HDL-C,
triglycerides

Age at outcome:
Mean (SD): 43.68
(15.02)

Age, sex, race, BMI,
education status,
smoking status,
alcohol consumption,
physical activity, PIR,
systolic blood
pressure, serum
cotinine, and Cd

RRs

Total C (>200 mg/dL)

1.01	(1.00, 1.01)

non-HDL-C (>160 mg/dL)
1.00 (0.99, 1.01)

LDL-C (>130 mg/dL)

1.02	(1.00, 1.04)

Triglycerides (>200 mg/dL)
0.99 (0.98, 1.00)

9-78

-------
Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

flee and Kim (2016)

Korea

2005-2010

Cross-Sectional

KNHANES
n = 7559

Korean adults aged 20+

Blood

Pb measured in venous
whole blood using
GFAAS

Age at measurement
Mean (SD):

No MetS: 42.32 (0.294)
yr; MetS: 48.36 (0.574)
yr

Geometric Mean (SD)
No MetS: 2.73 (0.024)
[jg/dL; MetS: 2.96
(0.049) [jg/dL

Serum Lipids

Low HDL cholesterol
(<40 mg/dL in women
or <50 mg/dL in men);
Elevated serum
triglycerides
(=150 mmHg)

Age at outcome
same as age at
exposure assessment

Age, BMI, residence ORs
area, education level,
smoking and drinking
status, exercise,
serum aspartate
aminotransferase,
serum alanine
aminotransferase

HDL-C <40 mg/dL
0.84 (0.66, 1.08)

TG >150 mg/dL
1.12 (0.90, 1.39)

tEttinaer et al. (2014)

Kumasi (Ghana), Cape
Town (South Africa),
Victoria (Seychelles),
Kingston (Jamaica),
Maywood, IL (United
States)

Ghana, South Africa,
Seychelles, Jamaica,
United States

2010-2014

Cross-sectional

Modeling the
Epidemiologic Transition
Study (METS)
n = 150

Adults of African descent
from 5 countries of
varying social and
economic development

Blood

Pb measured in venous
whole blood using ICP-
MS

Age at measurement
Mean (SD):

Males: 34.7 (6.0) yr;
Females: 35.2 (6.2) yr

Geometric Mean:
1.55 [jg/dL
Median: 1.66 [jg/dL
75th: 2.6 pg/dL
Max: 31.82 pg/dL

HDL and LDL
cholesterol, blood
pressure,
triglycerides.

Height and weight
were measured by
physical examination.
Fasting glucose was
measured in blood.
Further outcome
assessment details
not provided.

Age at outcome is the
same as age at
exposure assessment

Age, sex, site
location, marital
status, education,
paid employment,
alcohol use, fish
intake

ORs (>1.66 [jg/dL vs.
<1.66 [jg/dL blood Pb)

LDL-C (>2.59 mmol/L)
0.680 (0.289, 1.597)

Triglycerides (>1.7 mmol/L)
0.09 (0.030, 0.250)

HDC-C (<1.03 [males]; <1.29
[females] mmol/L)

1.93 (0.740, 5.020)

9-79

-------
Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tLiu et al.

Mexico City
Mexico

Pregnant women
recruited between
1997-1999 and 2001-
2003, follow-up among
offspring began in 2015
Cohort

Early Life Exposure in
Mexico to Environmental
Toxicants (ELEMENT)
n = 369

Mother/child pairs from a
birth cohort study of
pregnant women from 2
public hospitals serving
low to moderate-income
populations

Blood

Maternal Blood Pb
measured in venous
whole blood using
GFAAS

Age at measurement:
Maternal age (SD):
26.7 (5.6) yr

Mean of prenatal blood:
4.3 [jg/dL

Serum lipids

Total cholesterol,
triglycerides, HDL-C,
LDL-C

Age at outcome
Child's age (SD):

13.7 (1.9) yr

Child age, sex, BMI,	Change in Z-score (>5 pg/dL

number of siblings at	vs. <5 pg/dL blood Pb)

birth, maternal age,

marital status	__ . .

education, smoking	Triglycerides

history	0.58 (-0.05, 1.20)

Total cholesterol

-0.76 (-1.38, -0.13)

HDL-C

-0.64 (-1.28, 0.01)

LDL-C

-0.96 (-1.59, -0.33)

tKupsco et al. (2019)

Mexico City
Mexico

Maternal blood tested
for metals in 2nd
trimester, children
assessed at age 4-6
Cohort

Research in Obesity,
Growth, Environment and
Social Stressors
(PROGRESS) birth study
n = 548

Mother/child pairs from a
birth cohort study

Blood

Maternal blood Pb
measured second
trimester in venous
whole blood samples
using ICP-MS

Age at measurement
Mean (SD):

28 (5.6) yr

Mean (SD):
3.7 (2.7) [jg/dL
Max: 18 pg/dL

Serum lipids

Triglycerides and non-
HDL cholesterol

Age at outcome:

Mean: 4.8 yr; Range:
4-6 yr

Birth weight,
gestational age, pre-
pregnancy BMI,
education, SES,
parity, environmental
tobacco smoke

Change in Z-score

Triglycerides
0.018 (-0.028, 0.064)

non-HDL-C
-0.015 (-0.058, 0.028)

9-80

-------
Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tXu eta!. (2017)

United States

1999-2012

Cross-sectional

NHANES
n = 11662

General population; 12-
19 yr old

Blood

Serum lipids

Pb measured in venous Total cholesterol,
whole blood using ICP- triglycerides, HDL-C,
MS

Age at measurement:
12-19 yr

Mean (SD):
1.17 (1.20) [jg/dL

LDL-C

Age at outcome:
12-19 yr

% Increase

Age, gender,
ethnicity, PIR, waist

circumference, serum Tota/ cholesterol
cotinine, and physical
activity

0.6% (-0.1%, 1.3%)

HDL-C

0.3% (-0.5%, 1.1%)
LDL-C

2.3% (0.3%, 4.2%)

Triglycerides
-1.1% (-2.4%, 0.2%)

ALP = alkaline phosphatase; ALT = alanine aminotransferase; AST = aspartate aminotransferase; BMI = body mass index; Cd = cadmium; CI = confidence interval;
CK18 = cytokeratin 18; ELEMENT = Early Life Exposure in Mexico to Environmental Toxicants; FIB-4 = fibrosis-4; GFAAS = graphite furnace atomic absorption spectrometry;
GGT = gamma-glutamyl transferase; Hb = hemoglobin; HDL = high-density lipoprotein; HDL-C = high-density lipoprotein cholesterol; HF = hepatic fibrosis; HS = hepatic
steatosis; ICP-MS = inductively coupled plasma mass spectrometry; KNHANES = Korea National Health and Nutrition Examination Survey; LDL = low-density lipoprotein; LDL-
C = low-density lipoprotein cholesterol; MetS = metabolic syndrome; METS = Modeling the Epidemiologic Transition Study; NAFLD = nonalcoholic fatty liver disease;

NHANES = National Health and Nutrition Examination Survey; NR = not reported; OR = odds ratio; Pb = lead; PIR = poverty-income ratio; PROGRESS = Programming Research
in Obesity, Growth, Environment and Social Stressors; RBC = red blood cell; RR = relative risk; SD = standard deviation; SES = socioeconomic status; SPECT = single photon
emission computed tomography; Q = quartile; TG = thyroglobulin; yr = year(s).

aEffect estimates are standardized to a 1 |jg/dL increase in BLL or a 10 |jg/g increase in bone Pb level, unless otherwise noted. For studies that report results corresponding to a
change in log-transformed Pb biomarkers, effect estimates are assumed to be linear within the 10th to 90th percentile interval of the biomarker and standardized accordingly.
fStudies published since the 2013 Integrated Science Assessment for Pb.

9-81

-------
Table 9-5

Animal toxicological studies of exposure to Pb and hepatic effects

Study

Species (Stock/Strain),
n, Sex

Timing of
Exposure

Exposure Details BLL as Reported (pg/dL)

Endpoints Examined

jerrahal etal. (2011)

Rat (Wistar)

0 mg/L Pb Acetate, M,
n = 12-16

50 mg/L Pb Acetate, M,
n = 12-16

PND40, 65

Oral, drinking water

1.76 ± 0.33 [jg/100 mL for
0 mg/L Pb Acetate,

12.67 ± 1.68 [jg/100 mL for
50 mg/mL Pb Acetate - PND 40

2.06 ± 0.35 [jg/100 mL for
0 mg/L Pb Acetate,

7.49 ± 0.78 pg/100 mL for
50 mg/mL Pb Acetate - PND 65

Plasma Alanine
Aminotransferase (ALT),
Plasma Aspartate
Aminotransferase (AST),
Plasma Alkaline Phosphatase
(ALP)

Li etal. (2017)

Mouse (BALBc)

0 mg/kg Pb Acetate, F,
n = 8

100 mg/kg Pb Acetate, F,
n = 8

Day 29 from	Oral, gavage	0.43 ± 0.05 |jg/L for 0 mg/kg Pb

exposure start	Acetate

302.20 ± 25.32 pg/L for
100 mg/kg Pb Acetate

Malondialdehyde (MDA)
Levels, Glutathione (GSH),
Glutathione Peroxidase
(GSH-PX), Total Superoxide
Dismutase (T-SOD)

Liu et al. (2013)

Rat (Wistar)

0 ppm Pb, M, n = 10
500 ppm Pb, M, n = 10

Exposure d 75 Oral, drinking water 0.0448 pg/dL for 0 ppm

0.450 pg/dL for 500 ppm

Plasma Alanine
Aminotransferase (ALT),
Plasma Aspartate
Aminotransferase (AST),
GRP78 Protein Levels,
Reactive Oxygen Species
Activity, TBARS Levels, Total
Antioxidant Capacity, ATF6
Protein Levels, ATF4 Protein
Levels, P-IRE1 Protein
Levels, T-IRE1 Protein
Levels, XBP-1 Protein Levels,
P-JNK Protein Levels, JNK
Protein Levels, PI3K Protein
Levels, P-Akt Protein Levels,
T-Akt Protein Levels

9-82

-------
Study

Species (Stock/Strain),
n, Sex

Timing of
Exposure

Exposure Details BLL as Reported (pg/dL)

Endpoints Examined

Long et al. (2016)

Mouse (Kunming)

0% Pb Acetate, M, n = 7
0.2% Pb Acetate, M,
n =21

Six weeks
exposure

Oral, drinking water

36.42 ± 17.48 [jg/L for 0% Pb
Acetate, 214.64 ± 36.24 pg/L for
0.2% Pb Acetate

Plasma Alkaline Phosphatase
(ALP), Plasma Alanine
Aminotransferase (ALT),
Plasma Aspartate
Aminotransferase (AST),
Malondialdehyde (MDA)
Levels, Glutathione (GSH),
Glutathione Peroxidase
(GSH-PX), Total Superoxide
Dismutase (T-SOD),
Apoptosis, Bcl-2 Gene
Expression, Bax Gene
Expression, Bcl-2 Protein
Levels, Bax Protein Levels,
Nrf2 Protein Levels, HO-1
Protein Levels, Gamma-GCS
Protein Levels, Nrf-2 Gene
Expression, HO-1 Gene
Expression, Gamma-GCS
Gene Expression, GRP78
Protein Levels, Grp78 Gene
Expression, Chop Gene
Expression

Andielkovic et al. (2019) Rat (Wistar)	24 h posttreatment Oral, gavage

0 mg Pb Acetate per kg
bw, M, n = 8
150 mg Pb Acetate per
kg bw, M, n = 6

Dehydrogenase (LDH),
Malondialdehyde (MDA)
Levels, Advanced Oxidation
Protein Products Level
(AOPP), Total Thiol (-SH)
Groups Level, Prooxidative-
Antioxidative Balance (PAB),
Total Superoxide Dismutase
(T-SOD)

25 pg/L for 0 mg Pb Acetate per
kg bw, 290 pg/L for 150 mg Pb
Acetate per kg bw

Plasma Aspartate
Aminotransferase (AST),
Plasma Alanine
Aminotransferase (ALT),
Plasma Alkaline Phosphatase

9-83

-------
Study

Species (Stock/Strain), Timing^of Exposure Details BLL as Reported (Mg/dL)	Endpoints Examined

Dumkova et al. (2017)

Mouse (ICR)	Week 6 of

0 particles/cm3, F, n = 10 exPosure
1.23 x 10s particles/cm3,

F, n = 10

Inhalation

1.1 [jg/dL for 0 particles/cm3,
13.2 [jg/dL for 1.23 * 10®
particles/cm3, F, n = 10

Histopathology, Proliferating
Cell Nuclear Antigen (PCNA)
Immunohistochemistry,
Apoptotic Cells (TUNEL-
Positive), Na-KATPase
Expression

Jarkaoui et al.

Rat (Wistar)

0	g/L Pb Acetate, M,
n =6

1	g/L Pb Acetate, M,
n =6

Exposure day 30

Oral, drinking water 11.1 ±0.12 pg/dL for 0 g/L Pb
Acetate

23.8 ± 0.912 [jg/dL fori g/L Pb
Acetate

GSH, CAT, T-SOD, GSH-PX,
MDA Levels, Histopathology,
CAT qRT-PCR, GPx qRT-
PCR, SOD qRT-PCR, NF-kB
qRT-PCR, IL-6 qRT-PCR,
TNF-alpha qRT-PCR

Gao et al. (2020)

Rat (Sprague Dawley)

0 mg/kg bw, Pb2+, M/F,
n = 10

5 mg/kg bw, Pb2+, M/F,
n = 10

Four weeks	Oral, gavage	0.02 mg/kg for 0 mg/kg bw,

postexposure	Pb2+,

0.1 ± 0.03 mg/kg for 5 mg/kg
bw, Pb2+

T-SOD, CAT, MDA Levels,
GSH, Histopathology, Plasma
AST, Plasma ALT, Cr, BUN

Dumkova et al.

Mouse (Not Specified)
0 |jg/m3 PbO NPs, F,
n = NR, 2, 6, 11 wk
78.0 |jg/m3 PbO NPs, F,
n = NR, 6 wk followed by
0 |jg/m3 PbO NPs, 5 wk
78.0 |jg/m3 PbO NPs, F,
n = NR, 2, 6, 11 wk

Exposure week 2,
6, 11

Inhalation

0 [jg/dL for 0 |jg/m3 PbO NPs,
F, n = NR, 2, 6, 11 wk

2.7 [jg/dL for 78.0 |jg/m3 PbO
NPs, F, n = NR, 6 wk followed
by 0 |jg/m3 PbO NPs, 5 wk

10.4 ug/dL for 78.0 ug/m3 PbO
NPs-2 wk

14.8 ug/dL for 78.0 ug/m3 PbO
NPs-6 wk

17.4 [jg/dL for 78.0 |jg/m3 PbO
NPs-11 wk

Plasma Alkaline Phosphatase
(ALP), Plasma Alanine
Aminotransferase (ALT),
Plasma Aspartate
Aminotransferase (AST), Cr

9-84

-------
Study

Species (Stock/Strain),
n, Sex

Timing of
Exposure

Exposure Details BLL as Reported (pg/dL)

Endpoints Examined

Dumkova et al.

Mouse (CD1), (ICR)
0 |jg/m3 Pb(N03)2 NPs,
F, n = 10-3d, 2, 6,
11 wk

68.6 |jg/m3 Pb(N03)2
NPs, F, n = 10 - 3 d, 2, 6
11 wk

68.6 |jg/m3 Pb(N03)2
NPs, F, n = 10 - 6 wk,
followed by 0 |jg/m3
Pb(N03)2 NPs - 5 wk

Exposed 3 d,
11 wk

2, 6,

Inhalation

0 [jg/dL for 0 |jg/m3 - all groups
3.1 [jg/dL for 68.6 |jg/m3 -3d
4.0 [jg/dL for 68.6 |jg/m3 - 2 wk
4.7 [jg/dL for 68.6 |jg/m3 - 6 wk
8.5 pg/dL for 68.6 |jg/m3 -11 wk
1.0 pg/dL for 68.6 |jg/m3 - 6 wk
followed by 0 |jg/m3 - 5 wk

Histopathology, NF-kB qRT-
PCR, TNF-alpha qRT-PCR,
IL-1 alpha, IL-1 beta, IL-6
qRT-PCR, TGFbetal, Plasma
Alkaline Phosphatase (ALP)

Laamech et al. (2017)

Mouse (IOPS)

0 mg/kg body weight/day
Pb Acetate, M, n = 12
5 mg/kg body weight/day
Pb Acetate, M, n = 12

Exposure day 40 Oral, gavage

0.010 pg/mLforO mg/kg body
weight/day Pb Acetate,
0.18 |jg/ml_ for 5 mg/kg body
weight/day Pb Acetate

Histopathology, Plasma
Alanine Aminotransferase
(ALT), Plasma Aspartate
Aminotransferase (AST),
Total Cholesterol (TC), Total
Bilirubin (TB),
Malondialdehyde (MDA)
Levels, Protein Carbonyl
(PCO), Glutathione (GSH),
Catalase, Total Superoxide
Dismutase (T-SOD),
Glutathione Peroxidase
(GSH-PX)

ALP = alkaline phosphatase; ALT = alanine aminotransferase; AOPP = advanced oxidation protein products; AST = aspartate aminotransferase; BUN = blood urea nitrogen;
BLL = blood lead levels; CAT = catalase; Cr = chromium; D = day(s); GSH = glutathione; GSH-PX = glutathione peroxidase; LDH = lactate dehydrogenase; h = hour;
MDA = malondialdehyde; NF-kB = nuclear factor kappa B; NP = nanoparticle; PAB = prooxidative-antioxidative balance; Pb = lead; PCNA = proliferating cell nuclear antigen;
PCO = protein carbonyl; PND = postnatal day; qRT-PCR = real-time quantitative reverse transcription-polymerase chain reaction; TB = total bilirubin; TBARS = thiobarbituric acid
reactive substance; TC = total cholesterol; T-SOD = total superoxide dismutase; wk = week(s).

9-85

-------
Table 9-6 Epidemiologic studies of exposure to Pb and metabolic effects

sffiySS? PopBlon Exposure Assessment	Outcome	Contenders Etteot Estimates and 95%

Diabetes and Insulin Resistance - Adults

tMoon (2013)

Korea

2007-2012

Cross-Sectional

KNHANES
n = 3,184

Adults aged
>30 yr

Blood

Pb was measured in venous
whole blood using GFAAS

Age at measurement
Mean (SD):

No diabetes: 49.4 (12.4) yr
Diabetes: 58.8 (10.9) yr

Geometric Mean (SD):

No diabetes:

2.41 (1.52) [jg/dL

Diabetes:

2.47 (1.59) [jg/dL

Diabetes, HOMA-IR, HOMA-I3 Age, sex, region,

(%), fasting insulin (mlU/L)

Age at outcome is the same
as age at exposure
assessment

smoking, alcohol
consumption, regular
exercise, BMI (sex-
stratified analyses
only)

OR (95% CI) for prevalent
diabetes across blood Pb
quartiles:

Q1 (GM 1.43 pg/dL):
Reference

Q2 (GM 2.13 pg/dL):
0.91 (0.64, 1.29)

Q3 (GM 2.74 pg/dL):
0.76 (0.53, 1.09)

Q4 (GM 4.08 pg/dL):
0.75 (0.52, 1.08);

Change in HOMA-IR,
HOMA-IJ, and Fasting
Insulin per unit increase
in log-blood Pb

log(HOMA-IR)

Men: -0.04 (-0.10, -0.02),
Women: -0.04 (-0.09,
-0.01)

log(HOMA-IJ)

Men: -0.05 (-0.11, 0.01),
Women: -0.05 (-0.10,
0.01)

Fasting insulin (mlU/L)
Men: -0.53 (-1.23, 0.16)
Women: -0.27 (-1.00,
0.46)

9-86

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

tHansen et al, (2017)

Nord-Trondelag



Health Study

Nord-Trondelag

(HUNT3)

County

n = 883

Norway



2006-2008

Adults aged

Nested Case-Control

>20 yr. Cases



(n = 128) were



HUNT3



participants



diagnosed with



diabetes.



Controls



(n = 755) were



age- and sex-



matched HUNT3



participants



without diabetes.

Blood

Pb was measured in venous
whole blood using ICP-MS

Age at measurement
Mean (SD):

Cases: 61.4 (14.1) yr
Controls: 65.2 (10.3) yr

Median (10th—90th
percentile):

Cases: 19.9 (10.8-38.0) pg/L
Controls: 19.4 (11.0-37.2)
pg/L

Type 2 diabetes

Individuals were screened for
diabetes at a physical
examination using an oral
glucose tolerance test.
Diagnosis with type 2
diabetes was defined as
having fasting serum glucose
>7.0 mmol/L and/or 2 h
glucose >11.1 mmol/L as well
as glutamic acid
decarboxylase antibodies
(GADA) <0.08 ai.

Age at outcome is the same
as age at exposure
assessment

Age, sex, BMI, waist-
to-hip ratio,
education, income,
smoking, family
history of diabetes

OR (95% CI) for prevalent
type 2 diabetes Q4 vs.

Q1: 1.12 (0.58, 2.16)

tSimic et al. (2017)

Norway

2006-2008

Nested Case-Control

Nord-Trondelag
Health Study
(HUNT3)
n = 945

Adults aged
>20 yr. Cases
(n = 270) were
HUNT3
participants
diagnosed with
type 2 diabetes.
Controls
(n = 615) were
age- and sex-
matched
participants
without diabetes.

Blood

Pb was measured in venous
whole blood using ICP-MS

Age at measurement
Mean (SD):

Cases: 59.2 (12.2) yr
Controls: 65.4 (10.6) yr

Median (10th-90th
percentile):

Cases: 16.4 (9.7-35.2) pg/L
Controls: 20.2 (11.2-37.9)
pg/L

Type 2 diabetes

Type 2 diabetes was defined
as self-reported diabetes
excluding type I diabetes as
indicated by GADA index,
measured in blood at a
physical examination.

Age at outcome is the same
as age at exposure
assessment

BMI, waist-to-hip
ratio, first-degree
family history of
diabetes, smoking
habits, area,
education, economic
status, alcohol
consumption, blood
calcium

OR (95% CI) for prevalent
type 2 diabetes Q4 vs.

Q1: 0.24 (0.13, 0.47)

9-87

-------
sSEE.S?	Popul^on Exposure Assessment	Outcome	Confounders	Estimates ,„d 95%

Diabetes and Insulin Resistance - Adolescents

tLiu et al. (2020)

Mexico City
Maternal enrollment:
1997-1999 and
2001-2003

Child follow-up: 2015

Prospective Birth
Cohort

Early Life
Exposure in
Mexico to
Environmental
Toxicants
(ELEMENT)
Study
n = 369

Adolescents
aged 10-18 yr

Blood

Maternal Pb (1st trimester)
was measured in venous
whole blood using GFAAS

Age at measurement
Mean maternal age in 1st
trimester of pregnancy (SD):
26.7 (5.6) yr

Geometric Mean (95% CI):
4.3 (4.0, 4.6) [jg/dL

Fasting serum glucose Z-
score (mg/dL), HOMA-IR Z-
score

Serum fasting glucose
(mg/dL) was measured using
an enzymatic method. Serum
insulin (|jU/mL) was
measured using
immunoturbidimetric assay.
HOMA-IR was calculated as
insulin (|jU/mL)*glucose
(mg/dL)/405.

Age at outcome
Mean child age (SD):
13.7 (1.9) yr

Child age, sex, BMI z-
score, number of
siblings at birth,
maternal age, marital
status, education,
smoking history

Change in mean fasting
glucose and HOMA-IR Z-
scores for maternal blood
Pb >5 |jg/dL vs. maternal
blood Pb <5 [jg/dL

Fasting glucose z-score
All: -0.05 (-0.69, 0.60)
Boys: -0.05 (-0.34, 0.25)
Girls: -0.06 (-0.35, 0.23)

HOMA-IR z-score

All: -0.11 (-0.63, 0.42)
Boys: -0.04 (-0.28, 0.20)
Girls: 0.04 (-0.19, 0.27)

9-88

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sSEE.S?	Popul^on Exposure Assessment	Outcome	Confounders	Estimates ,„d 95%

Metabolic Syndrome (MetS) and Its Components

tMoon (2014)

Korea

2007-2012

Cross-Sectional

KNHANES
n = 3,950

Adults aged
>20 yr

Blood

Pb measured in venous
whole blood using GFAAS.

Age at measurement
Mean (SD):

No MetS: 42.7 (14.6) yr;
MetS: 54.4 (12.8) yr

Mean (SD)

No MetS: 2.08 (1.00) pg/dL;
MetS: 2.50 (1.01) pg/dL

Metabolic syndrome

MetS was defined as meeting
at least 3 of the following: (1)
elevated blood pressure (SBP
>130 mmHg or DBP
>85 mmHg or current use of
blood pressure medication),
(2) low HDL cholesterol
(<40 mg/dL in women or
<50 mg/dL in men), (3)
elevated serum triglycerides
(>150 mmHg) or current use
of antidyslipidemia
medication, (4) elevated
fasting plasma glucose levels,
(5) abdominal obesity (waist
circumference >90 cm in men
or >85 cm in women).

Age, sex, region,
smoking, alcohol
consumption, regular
exercise, BMI

OR (95% CI) for prevalent
MetS across blood Pb
quartiles

Q1 (GM 1.23 pg/dL):
Reference

Q2 (GM 1.90 pg/dL):
0.84 (0.62, 1.13)

Q3 (GM 2.51 pg/dL):
1.21 (0.90, 1.62)

Q4 (GM 3.79 pg/dL):
1.07 (0.79, 1.45)

Age at outcome is the same
as age at exposure
assessment

9-89

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

tRhee et al. (2013)

Korea
2008

Cross-Sectional

KNHANES
n = 1,405

Nationally
representative
survey of Korean
adults

Blood

Pb was measured in venous
whole blood using GFAAS

Age at measurement
Mean (SD):

No MetS: 40.3 (13.7) yr
MetS: 47.1 (13.3) yr

Median (25th—75th):
2.35 (1.74-3.06) pg/dL
75th: 3.06 pg/dL
Max: 19.43 pg/dL

MetS, abdominal
circumference, triglycerides,
HDL cholesterol, fasting
glucose

MetS was defined using the
Modified National Cholesterol
Education Program Adult
Treatment Panel III Criteria,
with the exception of waist
circumference measurement
cut-offs of >90 cm for males
and >85 cm for females
based on criteria from the
Korean Society for the Study
of Obesity. TC, triglycerides,
HDL cholesterol, and fasting
plasma glucose were
assessed using an automated
analyzer with enzymatic
assays. Abdominal
circumference was measured
by a professional.

Age at outcome is the same
as age at exposure
assessment

Age, sex, smoking,
education, TC,
creatinine, AST, ALT,
fasting serum insulin

OR for MetS prevalence
across log-transformed
Pb quartiles

Q1 (<1.73 pg/dL):
Reference

Q2 (1.74-2.35 pg/dL):

1.56	(0.90, 2.71)

Q3 (2.35-3.06 pg/dL):
1.63 (0.94, 2.83)

Q4 (>3.07 pg/dL):

2.57	(1.46, 4.51)

Change in outcomes per
unit increase in log-
transformed Pb

Abdominal circumference
0.051 (-0.001, 0.107) cm

Triglycerides

0.080 (0.023, 0.137) mg/dL

HDL Cholesterol
0.033 (-0.020, 0.086)
mg/dL

Fasting Glucose

0.019 (-0.029, 0.067)
mg/dL

9-90

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

tBulka eta!. (2019)

United States

2011-2014

Cross-Sectional

NHANES
n = 1,088

Nationally
representative
survey of U.S.
adults

Blood

Pb was measured in venous
whole blood using ICP-MS

Age at measurement:
20-60 yr

Mean (SD)

NHANES 2011-2012:

1.17 (0.04) [jg/dL;

NHANES 2013-2014:

1.00 (0.03) [jg/dL

MetS, triglycerides, HDL
cholesterol, blood glucose,
abdominal obesity

MetS was defined as meeting
at least 3 of the following: (1)
elevated blood pressure (SBP
>130 mmHg or DBP
>85 mmHg or current use of
blood pressure medication),
(2) low HDL cholesterol
(<40 mg/dL in women or
<50 mg/dL in men), (3)
elevated serum triglycerides
(>150 mmHg) or current use
of antidyslipidemia
medication, (4) elevated
fasting plasma glucose levels,
(5) abdominal obesity (waist
circumference >90 cm in men
or >85 cm in women). Waist
circumference (cm) was
measured at the physical
examination by a trained
professional. Serum HDL
(|jg/dL), triglycerides (mg/dL),
and blood glucose (mg/dL)
were measured in blood
samples obtained in the
morning following an
overnight fast.

Age at outcome:

20-60 yr

Age, race/ethnicity,
family poverty-income
ratio, total caloric
intake, educational
attainment, smoking
status, average
number of drinks per
day past year,
physical activity
status, survey cycle,
BMI (excluding
abdominal obesity
analysis), serum
cotinine

PRs for outcomes across
Pb quartiles

MetS

Q1 (0.18-0.70 pg/dL):
Reference

Q2 (0.71-1.05 pg/dL):
0.90 (0.73, 1.11)

Q3 (1.06-1.63 pg/dL):
0.84 (0.69, 1.05)

Q4 (1.64-15.98 pg/dL):
0.81 (0.64, 1.03)

High Triglycerides

Q1
Q2
Q3
Q4

Reference
0.85 (0.72, 0.99)
0.76 (0.64, 0.92)
0.82 (0.67, 1.01)

Low HDL
Q1: Reference

Q2
Q3
Q4

0.90 (0.76, 1.07)
0.79 (0.65, 0.97)
0.73 (0.59, 0.89)

High Glucose
Q1: Reference

Q2
Q3
Q4

1.03 (0.86, 1.23)
0.86 (0.68, 1.08)
0.95 (0.77, 1.17)

Abdominal Obesity
Q1: Reference

Q2
Q3
Q4

0.93 (0.82, 1.07)
0.91 (0.80, 1.04)
0.66 (0.56, 0.78)

9-91

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

tShim et al. (2019)

Korea

2012-2014

Cross-Sectional

Korean National
Environmental
Health Survey II
(KNEHS)
n = 5,251

Nationally
representative
survey of adults
in Korea

Blood

Pb was measured in venous
whole blood using GFAAS

Age at measurement
Mean (SE):

No MetS: 49.87 (0.22) yr
MetS: 61.59 (0.50) yr

Geometric Mean (SE)
No MetS: 0.71 (0.48) pg/dL
MetS: 0.76 (0.49) pg/dL

MetS

MetS was defined as meeting
at least 3 of the following: (1)
elevated blood pressure (SBP
>130 mmHg or DBP
>85 mmHg or current use of
blood pressure medication),
(2) low HDL cholesterol
(<40 mg/dL in women or
<50 mg/dL in men), (3)
elevated serum triglycerides
(>150 mmHg) or current use
of antidyslipidemia
medication, (4) elevated
fasting plasma glucose levels,
(5) abdominal obesity (waist
circumference >90 cm in men
or >85 cm in women).

Age, sex, education,
income, marital
status, aspartate
aminotransferase,
alanine

aminotransferase

ORs for MetS prevalence
across blood Pb quartiles

Q1
Q2
Q3

Q4

Reference
0.94 (0.72, 1.24)
1.00 (0.76, 1.31)

0.86 (0.65, 1.14)

Quartile levels NR

Age at outcome is the same
as age at exposure
assessment

tWen et al. (2020)

Taiwan
June 2016-
September2018
Cross-Sectional

N = 2444	Blood

General	Pb was measured in venous

population	whole blood using ICP-MS

Age at measurement:

Mean (SD): 55.1 (13.2) yr

MetS

Age, sex, TC, LDL
cholesterol,
hemoglobin, eGFR,
uric acid

OR MetS prevalence per
log unit increase in blood
Pb:

0.86 (0.61, 1.20)

Mean: 1.6 pg/dL

9-92

-------
sSEE.S?	Popul^on Exposure Assessment	Outcome	Confounders	Estimates ,„d 95%

MetS was defined as meeting
at least 3 of the following: (1)
elevated blood pressure (SBP
>130 mmHg or DBP
>85 mmHg or current use of
blood pressure medication),

(2) low HDL cholesterol
(<40 mg/dL in women or
<50 mg/dL in men), (3)
elevated serum triglycerides
(>150 mmHg) or current use
of antidyslipidemia
medication, (4) elevated
fasting plasma glucose levels,

(5) abdominal obesity (waist
circumference >90 cm in men
or >85 cm in women).

Age at outcome:

Mean (SD): 55.1 (13.2) yr

9-93

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

flee and Kim (2016) KNHANES
n = 9,880

Korea

2007-2012	Korean adults

Cross-Sectional	aged >20 yr

Blood

Pb measured in venous
whole blood using GFAAS

Age at measurement
Mean (SD):

Males

No MetS: 43.5 (0.23) yr
MetS: 48.7 (0.48) yr

Females

No MetS: 43.5 (0.25) yr
MetS: 51.4 (0.60) yr

Geometric Mean (SD):
Males

No MetS: 2.57 (0.02) pg/dL
MetS: 2.64 (0.04) pg/dL

Females

No MetS: 1.86 (0.01)

MetS: 1.92 (0.04) pg/dL

MetS, waist circumference
(cm), serum HDL (mg/dL),
serum triglycerides (mg/dL),
blood glucose (mg/dL)

MetS was defined as meeting
at least 3 of the following: (1)
elevated blood pressure (SBP
>130 mmHg or DBP
>85 mmHg or current use of
blood pressure medication),
(2) low HDL cholesterol
(<40 mg/dL in women or
<50 mg/dL in men), (3)
elevated serum triglycerides
(>150 mmHg) or current use
of antidyslipidemia
medication, (4) elevated
fasting plasma glucose levels,
(5) abdominal obesity (waist
circumference >90 cm in men
or >85 cm in women). Waist
circumference (cm) was
measured at the physical
examination by a trained
professional. Serum HDL
(pg/dL), triglycerides (mg/dL),
and blood glucose (mg/dL)
were measured in blood
samples obtained in the
morning following an
overnight fast.

Age at outcome is the same
as age at exposure
assessment

Age, BMI, residence
area, education level,
smoking and drinking
status, exercise, AST,
ALT

OR (95% CI) for outcomes
across blood Pb tertiles

MetS prevalence
T1 (<2.20 pg/dL):

Reference

T2 (2.20-3.01 pg/dL):
1.032 (0.788, 1.352)

T3 (>3.01 pg/dL):
0.817 (0.626, 1.065)

Waist circumference
(>85 cm)

T1
T2
T3

Reference
1.11 (0.83, 1.50)
1.11 (0.81, 1.51)

Serum HDL (<40 mg/dL)

T1
T2
T3

Reference
1.00 (0.80, 1.24)
0.76 (0.59, 0.97)

Serum triglycerides
(>150 mg/dL)
T1: Reference
T2: 1.13 (0.93, 1.39)
T3: 1.08 (0.87, 1.33)

Blood glucose

(>100 mg/dL)
T1: Reference
T2: 0.83 (0.68, 1.02)
T3: 1.04 (0.85, 1.28)

9-94

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

flee and Kim (2013) KNHANES
n = 7,559

Korea

2005-2010	Korean adults

Cross-Sectional	aged >20 yr

Blood

Pb measured in venous
whole blood using GFAAS

Age at measurement
Mean (SD):

No MetS: 42.3 (0.29) yr
MetS: 48.4 (0.57) yr

Geometric Mean (SD):

No MetS: 2.734 (0.024) pg/dL
MetS: 2.957 (0.049) pg/dL

MetS, waist circumference,
serum HDL, serum
triglycerides, blood glucose

MetS was defined as meeting
at least 3 of the following: (1)
elevated blood pressure (SBP
>130 mmHg or DBP
>85 mmHg or current use of
blood pressure medication),
(2) low HDL cholesterol
(<40 mg/dL in women or
<50 mg/dL in men), (3)
elevated serum triglycerides
(>150 mmHg) or current use
of antidyslipidemia
medication, (4) elevated
fasting plasma glucose levels,
(5) abdominal obesity (waist
circumference >90 cm in men
or >85 cm in women). Waist
circumference (cm) was
measured at the physical
examination by a trained
professional. Serum HDL
(pg/dL), triglycerides (mg/dL),
and blood glucose (mg/dL)
were measured in blood
samples obtained in the
morning following an
overnight fast.

Age at outcome is the same
as age at exposure
assessment

Age, BMI, residence
area, education level,
smoking and drinking
status, exercise,
serum aspartate
aminotransferase,
serum alanine
aminotransferase

OR (95% CI) for outcomes
across blood Pb tertiles

MetS Prevalence
T1 (<2.362 pg/dL):
Reference

T2 (>2.362-3.282 pg/dL):
1.267 (0.950, 1.690)

T3 (>3.282 pg/dL:
0.984 (0.735, 1.317)

Waist circumference
(>85 cm)

T1
T2
T3

Reference
1.04 (0.75, 1.45)
0.89 (0.64, 1.24)

Serum HDL (<40 mg/dL)
T1: Reference

T2
T3

0.98 (0.79, 1.23)
0.96 (0.77, 1.20)

Serum triglycerides
(>150 mg/dL)
T1: Reference

T2
T3

1.01 (0.82, 1.24)
1.07 (0.87, 1.32)

Blood glucose

(>100 mg/dL)
T1: Reference
T2: 1.00 (0.81, 1.24)
T3: 1.14 (0.91, 1.44)

9-95

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

tWanq et al.

M

United States

2003-2014

Cross-Sectional

NHANES
n = 9537

NHANES
participants aged
20+,2003-2014

Blood

Pb was measured in venous
whole blood using ICP-DRC-
MS

Age at measurement
Mean (SD): 49.2 (18.0) yr

Geometric mean (SD):
1.32 (2.00) [jg/dL

Waist circumference (cm)

Waist circumference (cm)
was measured during minimal
respiration to the nearest
0.1 cm at the level of the iliac
crest at the time of NHANES
physical examination.

Age at outcome:

Mean (SD): 49.2 (18.0) yr

Age, sex,
race/ethnicity,
education, smoking
status, physical
activity, NHANES
cycle, and urinary
creatinine

Change in waist
circumference (cm) per 1-
SD increase in log(10)-
transformed Pb (SD NR):

0.008 (-0.010, -0.006)

tPeters et al, (2012)

Normative Aging

Blood, Bone

Serum lipids

Age at baseline, yr

ORs

United States

Study
n = 426

Blood Pb measured in venous

Triglycerides, HDL-C

between baseline and
outcome, education,

Low HDL-C (<40 mg/dL):

0.899 (0.804, 1.004)

Blood Pb measured



whole blood using GFAAS



BMI, alcohol intake,

between 1999-2008;

Older male



Age at outcome:

smoking status, pack-



Serum lipids
measured 3 to 4 yr
after blood Pb
Cohort

Veterans

Mean: 4.01 ± 2.30 [jg/dL

3 to 4 yr after blood Pb

yr of smoking,
hypertension status,
and statin use

High Triglycerides
(>200 mg/dL):

0.993 (0.874, 1.129)

tEttinaer et al. (2014)

Kumasi, Ghana; Cape
Town, South Africa;
Victoria, Seychelles;
Kingston, Jamaica;
Maywood, Illinois
(United States)
2010-2014
Prospective Cohort

Modeling the
Epidemiologic
Transition Study
(METS)
n = 150

Adults of African
descent from 5
countries of
varying social
and economic
development

Blood

Pb was measured in venous
whole blood using DRC-ICP-
MS

Age at measurement
Mean (SD):

Males: 34.7 (6.0) yr
Females: 35.2 (6.2) yr

Geometric Mean (95% CI):
1.55 (1.30, 1.85) [jg/dL

Waist Circumference >94 cm
(males) or >80 cm (females),
Fasting Glucose >100 mg/dL

Fasting glucose was
measured in blood. Further
outcome assessment details
not provided.

Age at outcome is the same
as age at exposure
assessment

Age, sex, site
location, marital
status, education,
paid employment,
alcohol use, fish
intake, percent body
fat

ORs for blood Pb above
the median (1.66 (jg/dL)
vs. below the median

Waist Circumference

[ >94 cm (m) or >80 cm (f)]
4.53 (1.06, 19.48)

Fasting Glucose
(>100 mg/dL)

4.99 (1.97, 12.69)

Median (95% CI):
1.66 (1.34, 1.93) [jg/dL

9-96

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

75th: 2.6 pg/dL
Max: 31.82 pg/dL

Body Weight

tWanq et al. (2018a)

China
2014

Cross-Sectional

SPECT-China
n = 3922

Chinese citizens
aged >18 yr who
had lived in their
current area for
6+ mo

Blood

Pb was measured in venous
whole blood using GFAAS

Age at measurement:

Mean (SD):

Normal weight subjects:
50.9 (13.9) yr

Overweight subjects:
54.0 (12.3) yr

Obese subjects:

56.2 (11.2) yr

Median

(25th-75th percentiles)

Normal weight:

3.9 (2.6, 5.6) pg/dL

Overweight subjects:

4.3	(2.9, 6.1) pg/dL

Obese subjects:

4.4	(2.7, 6.2) pg/dL

BMI (kg/m2)

BMI was calculated as weight
(kg) divided by squared
height (m2). Overweight
(including obese) was defined
as BMI >25 kg/m2.

Age at outcome is the same
as age at exposure
assessment

Age, sex, economic
status, rural/urban
residence, current
smoking, diabetes,
hypertension,
dyslipidemia

OR (95% CI) for
overweight or obese (BMI
>25 kg/m2) across blood
Pb quartiles

Q1 (<2.69 pg/dL):
Reference

Q2 (2.69-4.01 pg/dL):
1.09 (0.89, 1.33)

Q3 (4.01-5.60 pg/dL):
1.15 (0.94, 1.40)

Q4 (>5.60 pg/dL):
1.40 (1.14, 1.71)

9-97

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

tEttinqer et al. (2014)

Kumasi, Ghana; Cape
Town, South Africa;
Victoria, Seychelles;
Kingston, Jamaica;
Maywood, Illinois
(United States)
2010-2014
Prospective Cohort

Modeling the
Epidemiologic
Transition Study
(METS)
n = 150

Adults of African
descent from 5
countries of
varying social
and economic
development

Blood

Pb was measured in venous
whole blood using DRC-ICP-
MS

Age at measurement
Mean (SD):

Males: 34.7 (6.0) yr
Females: 35.2 (6.2) yr

Geometric Mean (95% CI):
1.55 (1.30, 1.85) [jg/dL

Overweight (BMI >25), Obese Age, sex, site

(BMI >30)

Height and weight were
measured by physical
examination.

Age at outcome is the same
as age at exposure
assessment

location, marital
status, education,
paid employment,
alcohol use, fish
intake, percent body
fat

ORs for blood Pb above
the median (1.66 (jg/dL)
vs. below the median

Overweight (BMI >25)
0.88 (0.31, 2.51)

Obese (BMI >30)
2.70 (0.75, 9.75)

Median (95% CI):
1.66 (1.34, 1.93) [jg/dL

75th: 2.6 pg/dL
Max: 31.82 pg/dL

9-98

-------
Reference and
Study Design

Study
Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
CIs

tGuo et al. (2019)

China
2015

Cross-Sectional

N = 145

Blood

BMI (kg/m2)

Adult men	Pb was measured using ICP- Age outcome

recruited through	MS	Mean (SD): 39 (12) yr

a physical

examination	Age measurement

center	Mean (SD): 39(12) yr

Age

Change in BMI (kg/m2)
per log increase in blood
Pb:

0.05 (-3.64, 3.74)

Mean (SD): 8.5 (3.8) pg/dL;
Median: 7.9 pg/dL
75th: 10.8 pg/dL
Max: 28.2 pg/dL

ALT = alanine aminotransferase; AMT = ;AST = aspartate aminotransferase; BMI = body mass index; CI = confidence interval; DBP = diastolic blood pressure; DRC-ICP-
MS = dynamic reaction cell for inductively coupled plasma mass spectrometry; eGFR = estimated glomerular filtration rate; ELEMENT = Early Life Exposure in Mexico to
Environmental Toxicants; GADA = glutamic acid decarboxylase antibodies; GFAAS = graphite furnace atomic absorption spectrometry; GM = geometric mean; HDL = high-
density lipoprotein; HDL-C = high-density lipoprotein cholesterol; HOMA-IR = Homeostatic Model Assessment for Insulin Resistance; HOMA- (B = HOMA of (B-cell function; ICP-
MS = inductively coupled plasma mass spectrometry; KNHANES = Korea National Health and Nutrition Examination Survey; MetS = metabolic syndrome; METS = Modeling the
Epidemiologic Transition Study; NR = not reported; OR = odds ratio; Pb = lead; SBP = systolic blood pressure; SD = standard deviation; SPECT = single photon emission
computed tomography; TC = total cholesterol; Q = quartile; yr = year.

aEffect estimates are standardized to a 1 |jg/dL increase in BLL or a 10 |jg/g increase in bone Pb level, unless otherwise noted. For studies that report results corresponding to a
change in log-transformed Pb biomarkers, effect estimates are assumed to be linear within the 10th to 90th percentile interval of the biomarker and standardized accordingly.
fStudies published since the 2013 Integrated Science Assessment for Pb.

9-99

-------
Table 9-7

Animal toxicological studies of exposure to Pb and metabolic effects

Study

Species (Stock/Strain), Timing of Exposure
n, Sex	Exposure Details

BLL as Reported (pg/dL)

Endpoints Examined

Faulk et al.

Mouse (Agouti), 0.0 ppm
Pb, M/F, n = 30
2.1 ppm Pb, M/F, n = 28
16 ppm Pb, M/F, n = 33
32 ppm Pb, M/F, n = 29

(Longitudinal phenotypic
measures were taken
from a total of 120 a/a
mice, on average 2.7
mice per litter)

Mo 3, 6, 9

Oral, drinking
water

Mean maternal BLL,
tested at weaning, were
below the LOD for the
control group, and 4.1
(61.3) [jg/dL, 25.1 (67.3)
[jg/dL, and 32.1 (611.4)
[jg/dL in the three
exposure groups,
2.1 ppm, 16 ppm, and
32 ppm, respectively

Oxygen Consumption, CO2 Production, Food Intake, Body
Weight, Body Fat

Rahman et al.

Rat (Wistar)

0% Pb Acetate, M/F,
n = 37

0.2% Pb Acetate, M/F,
n = 38

PND 21, 30 Oral, drinking 2.2 ± 0.07 pg/dL for 0% Serum 25(OH)D, Serum 1,25(OH)2D, Hepatic 25-

water	Pb Acetate,

12.4 ± 3.3 [jg/dL for 0.2%
Pb Acetate - PND 21
3.3 ± 1.7 [jg/dL for 0% Pb
Acetate, 22.7 ±6.0 pg/dL
for 0.2% Pb Acetate -
PND 30

Hydroxylase Protein Levels, Hepatic 25-Hydroxylase
Immunohistochemistry

9-100

-------
Study

Species (Stock/Strain), Timing of Exposure
n, Sex	Exposure Details

BLL as Reported (pg/dL)

Endpoints Examined

Zhou et al. Rat (Sprague Dawley),
(2018)	0% Pb Acetate, M,

n = 20

0.5% Pb Acetate, M,
n = 20

1% Pb Acetate, M,
n = 20

2% Pb Acetate, M,
n = 20

PND 52	Oral, drinking 11.4 |jg/L for 0%

water	147 |jg/L for 0.5%

226 |jg/L for 1 %
289 |jg/L for 2%

Cholesterol Content, mRNA level of SREBP2 in the
cortex, mRNA level of SREBP2 in the hippocampus,
mRNA level of LDL-R in the cortex, mRNA level of HMG-
CR in the hippocampus, mRNA level of HMG-CR in the
cortex, protein level of SREBP2 in the cortex, mRNA level
of LDL-R in the hippocampus, protein level of HMG-CR in
the cortex, protein level of LDL-R in the cortex, protein
level of SREBP2 in the hippocampus, protein level of
HMG-CR in the hippocampus, protein level of LDL-R in
the hippocampus, immunohistochemistry ofSREBP2 in
the cortex, immunohistochemistry of HMG-CR in the
cortex, immunohistochemistry of LDL-R in the cortex,
immunohistochemistry of SREBP2 in the hippocampus,
immunohistochemistry of HMG-CR LDL-R in the
hippocampus, immunohistochemistry of LDL-R in the
hippocampus, mRNA level of LXR-a in the cortex, mRNA
level of ABCA1 in the cortex, mRNA level of LXR-a in the
hippocampus, mRNA level of ABCA1 in the hippocampus,
protein level of LXR-a in the cortex, protein level of
ABCA1 in the cortex, protein level of LXR-a in the
hippocampus, protein level of ABCA1 in the hippocampus

ABCA1 = ATP-binding cassette transporter ABCA1 (member 1 of human transporter sub-family ABCA); BLL = blood lead level; C02 = carbon dioxide; F = female; HMG-CR = 3-
Hydroxy-3-Methylglutaryl-Coenzyme A Reductase; LDL-R = low-density lipoprotein receptor; LOD = limit of detection; LXR-a = liver X receptor alpha; M = male; mo = month;
mRNA = messenger ribonucleic acid; Pb = lead; PND = postnatal day; SREBP2 = Sterol Regulatory Element Binding Transcription Factor 2.

9-101

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Table 9-8 Animal toxicological studies of exposure to Pb and gastrointestinal effects

Study

Species (Stock/Strain),
n, Sex

Timing of Exposure

Exposure Details

BLL as Reported
(Hg/dL)

Endpoints Examined

Kosik-Boaacka et al,
(2011)

Rat (Wistar), Control
(distilled water), M, n = 9
0.1% Pb, M, n = 9

Day 270

Oral, drinking water

0.34 ± 0.23 pg/dLfor
0.0%, 7.21 ± 1.27 pg/dL
for 0.1%

transepithelial electrical
potential difference (PD),
changes in the
transepithelial electrical
potential difference
during mechanical
stimulation (dPD),
transepithelial electrical
resistance (R)

Reddv et al. (2018)

Rat (Sprague Dawley),
Control Diet (CD), M,
n = 10

Control Diet, F, n = 10
Iron Deficient (ID), M,
n = 10

Iron Deficient, F, n = 10
Control Diet + Pb, M,
n = 10

Control Diet + Pb, F,
n = 10

Iron Deficient + Pb, M,
n = 10

Iron Deficient, F, n = 10

Microbiome Counts at
Week 0, 4, 8, 10, 12
BLL at End of Week 8

Oral, gavage

2.3 ± 1.16 |jg/dL - CD, M
19.3 ±6.23 pg/dL-
CD + Pb, M

2.5 ± 0.89 [jg/dL - ID, M
47.5 ± 3.78 pg/dL-
ID + Pb, M

1.9 ± 0.81 |jg/dL - CD, F
13.5 ± 3.52 pg/dL-
CD + Pb, F

1.5 ± 0.31 [jg/dL - ID, F
29.80 ± 8.30 pg/dL-
ID + Pb, F

Fecal Lactobacilli
(Counts), Fecal E. Coli
(Counts), Fecal Yeast
(Counts)

BLL = blood lead level; CD = control diet; dPD = transepithelial electrical potential difference during mechanical stimulation; F = female; ID = iron deficient; M = male;
PD = transepithelial electrical potential difference; R = resistance

9-102

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Table 9-9

Epidemiologic studies of exposure to Pb and endocrine effects

Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tChen et al. (2013)

United States

2007-2008
Cross-sectional

NHANES
n = 5,418

Adolescents and adults in
the general U.S.
population who had no
reported thyroid diseases,
thyroid medications,
pregnancy, and sex
steroid medications.

Blood Pb

Blood Pb was
measured in venous
whole blood using
GFAAS

Age at measurement:
>12 yr old

Mean: 0.93 [jg/dL
Max: 9.20 [jg/dL

TSH, thyroglobulin (Tg),
and thyroid hormones (T3,
FT3, T4, FT4)

TSH and thyroid
hormones measured in
serum using the Beckman
Immunoassay System.

Age at outcome:

>12 yr old

Age, sex, race/ethnicity,
creatinine-adjusted
urinary iodine, BMI Z-
score, and serum
cotinine level

Change in T4 ([jg/dL)b

Adolescents (12-19 yr old)
(-0.02, 0.04)

Adults (>19 yr old)
-0.01 (-0.02, 0.01)
Change in FT4 (ng/dL)b
Adolescents (12-19 yr old)
(-0.01, 0.04)

Adults (>19 yr old)
0.01 (-0.01, 0.02)

Change in T3 (ng/dL)b
Adolescents (12-19 yr old)
(-0.01, 0.04)

Adults (>19 yr old)
-0.0004 (-0.02, 0.02)
Change in FT3 (pg/ml_)b
Adolescents (12-19 yr old)
(-0.002, 0.04)

Adults (>19 yr old)
0.01 (-0.001, 0.02)
Change in TSH ([jlU/mL)b
Adolescents (12-19 yr old)
-0.05 (-0.18, 0.07)

Adults (>19 yr old)
-0.01 (-0.06, 0.04)
Change in Tg (ng/ml_)b
Adolescents (12-19 yr old)
0.05 (-0.13, 0.24)

Adults (>19yrold)
0.01 (-0.03, 0.06)

9-103

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Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tKrieq (2019)

United States

1988-1994

Cross-sectional

NHANES III
n = 16,573

General population,
>20 yr old

Blood Pb

Blood Pb was
measured in venous
whole blood using
AAS

Age at measurement:
>20 yr old

Mean: 3.55 [jg/dL
(SE = 0.10)

TSH and T4

TSH and thyroid
hormones measured in
serum using the Beckman
Immunoassay System.

Age at outcome:

>20 yr old

Linear regression model
adjusted for race-
ethnicity, sex, age,
session, BMI, pregnant,
menopause, hormone
pill use, vaginal cream
use, hormone patch
use, urinary creatinine

Change in TSH (%)

-1.2 (-5.6, 3.3)

Change in T4 (%)

-38.9 (-51.3, -23.4)

Change in Logio-TSH
(HU/mL)b

Male

0.01 (-0.04, 0.05)
Female (Not pregnant)
-0.04 (-0.08, 0.01)
Female (Pregnant)
-0.03 (-0.26, 0.20)

Change in Logio-T4 ([jg/dL)b

Male

-0.15 (-0.48, 0.18)

Female (Not pregnant)
-0.52 (-0.83, -0.21)

Female (Pregnant)
-2.01 (-3.09, -0.93)

9-104

-------
Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tMendv et al. (2013) NHANES
n = 4,652

United States

2007-2008
Cross-sectional

General population >20 yr
old, excluding pregnant
women, individuals with a
history of thyroid disease,
or under treatment for
thyroid dysfunction

Blood Pb

Blood Pb was
measured in venous
whole blood using
GFAAS

Age at measurement:
>20 yr old

Mean (SD):
1.52 ± 1.20 [jg/dL
Max: 33.12 pg/dL

TSH and thyroid
hormones (T3, FT3, T4,
FT4)

TSH and thyroid
hormones measured in
serum using the Beckman
Immunoassay System

Age at outcome:

>20 yr old

Age, gender,
race/ethnicity, smoking,
alcohol consumption,
BMI, physical activity,
iodine intake,
medications, and bone
mineral density

Change in T3 (ng/dL)

-0.774 (-2.269, 0.722)
Change in FT3 (pg/mL)
0.015 (-0.007, 0.037)
Change in T4 ((jg/dL)
-0.162 (-0.321, -0.004)
Change in FT4 (ng/mL)
(-0.011, 0.011)

Change in TSH (mlll/mL)

0.015 (-0.088, 0.118)

tChristensen (2012)

United States

2007-2008
Cross-sectional

NHANES
n = 1,587

General population,
>20 yr old, excluding
individuals with thyroid
disease or cancer, or
were taking thyroid
medications

Blood Pb

Blood Pb was
measured in venous
whole blood using
GFAAS

Age at measurement:
>20 yr old

Median: 1.3 pg/dL
75th: 2.1 pg/dL

TSH and thyroid
hormones (T3, T4)

TSH and thyroid
hormones measured in
serum using the Beckman
Immunoassay System.

Age at outcome:

>20 yr old

Age, sex, race, BMI,
serum lipids, serum
cotinine, pregnancy and
menopausal status, and
use of selected
medications

Change in ln(T3) (ng/dL)

0.004 (-0.016, 0.023)

Change in ln(FT3) (pg/mL)

0.008 (-0.002, 0.017)

Change in ln(T4) ((jg/dL)

-0.018 (-0.036, 0)

Change in ln(FT4) (pg/mL)

-0.001 (-0.018, 0.015)

Change in In(TSH) (mlU/L)

0.027 (-0.031, 0.085)

9-105

-------
Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tLuo and Hendryx
(2014)

United States

2007-2010

Cross-sectional

NHANES
n = 6,231

General population >20 yr
old, excluding pregnant
women, individuals with
history of thyroid disease,
or missing data.

Blood Pb

Blood Pb was
measured in venous
whole blood using
GFAAS

Age at measurement:
>20 yr old

Mean: 1.82 [jg/dL
Max: 33.10 [jg/dL

TSH, thyroglobulin (Tg),
and thyroid hormones (T3,
FT3, T4, FT4)

TSH and thyroid
hormones measured in
serum using the Beckman
Immunoassay System.

Age at outcome:

>20 yr old

Adjusted for age, sex,
race and ethnicity,
serum cotinine, BMI,
and creatinine-adjusted
urinary iodine

Change in T3 across tertiles
(ng/dL)b

T1: Reference

T2: 1.02 (-0.90, 2.94)

T3: 0.69 (-2.37, 3.76)

Women Only

T1: Reference

T2: -0.36 (-3.72, 3.00)

T3: 0.61 (-5.02, 6.23)

Men Only

T1
T2
T3

Reference
1.96 (-0.98, 4.91)
0.69 (-2.59, 3.97)

Change in FT3 across
tertiles (pg/ml_)b:

T1: Reference

T2: 0.03 (0.001, 0.07)

T3: 0.04 (0.01, 0.08)

Women Only

T1
T2
T3

Reference
0.02 (-0.04, 0.08)
0.03 (-0.04, 0.11)

Men Only

T1
T2
T3

Reference
0.03 (-0.01, 0.07)
0.05 (0.01, 0.09)

Change in T4 across tertiles
(|jg/dL)b:

T1: Reference

T2: 0.01 (-0.16, 0.14)

9-106

-------
Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

T3: -0.09 (-0.28, 0.11
Women Only

T1
T2
T3

Reference
0.12 (-0.10, 0.35)
0.02 (-0.29, 0.33)

Men Only

T1
T2
T3

Reference
-0.14 (-0.35, 0.08)
-0.20 (-0.40, 0.01)

Change in FT4 across
tertiles (ng/dL)b:

T1: Reference

T2: 0.007 (-0.01, 0.02)

T3: 0.002 (-0.01, 0.01)

Women Only

T1: Reference

T2: 0.02 (0.01, 0.04)

T3: 0.02 (-0.003, 0.04)

Men Only

T1: Reference

T2: -0.02 (-0.03, 0.005)

T3: -0.01 (-0.04, 0.008)

Change in Log-Tg across
tertiles (ng/ml_)b:

T1: Reference

T2: 0.04 (-0.04, 0.13)

T3: 0.02 (-0.07, 0.12)

Women Only

T1: Reference

T2: 0.08 (-0.03, 0.19)

9-107

-------
Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

T3: -0.06 (-0.19, 0.08)
Men Only
T1: Reference
T2: -0.001 (-0.13, 0.17)
T3: 0.05 (-0.08, 0.17)

Change in Log-TSH across
tertiles (ulll/mL)b:

T1: Reference

T2: 0.01 (-0.05, 0.07)

T3: 0.02 (-0.06, 0.09)

Women Only

T1: Reference

T2: 0.05 (-0.06, 0.16)

T3: 0.02 (-0.09, 0.14)

Men Only

T1: Reference

T2: -0.04 (-0.13, 0.06)

T3: -0.02 (-0.11, 0.07)

9-108

-------
Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tNie etal. (2017)

Shanghai and 7

provinces

China

2014

Cross-sectional

SPECT-China study
n = 5,628

Residents of these
regions are 99.5% Han
Chinese.

Exclusion criteria
included age under 18 yr
old, less than 6 mo spent
at current residence, and
severe communication
problems or acute illness
(thyroid resection or
iodine-131 therapy,
malignant tumor,
subacute thyroiditis, liver
cirrhosis)

Blood Pb

Whole blood
measured using AAS
Age at measurement:
18-93 yr old

Median:

Men: 44.00 |jg/L
Women: 37.87 |jg/L

Mean:

Men:

29.00 ± 62.18 |jg/L
Women:

25.03 ± 54.61 |jg/L

TSH, thyroid hormones
(T3, T4), thyroid
peroxidase antibody
(TPOAb) and thyroglobulin
antibody (TGAb)

Thyroid dysfunction and
subclinical thyroid
dysfunction were
measured by

immunochemiluminometric
assays

Age at outcome:

18-93 yr old

Linear and logistic
regression model
adjusted for age, BMI
smoking status (men
only) and drinking status Women

1.41 (0.00, 2.84)

Change in TPOAb (%)

Men

0.50 (-0.80, 1.82)

Change in TGAb (%)

Men

-0.60 (-1.88, 0.70)
Women

0.20 (-1.09, 1.51)

Change in TSH (%)

Men

-0.40 (-1.29, 0.40)
Women

1.11 (0.30, 1.82)

tKahn et al. (2014)

Pristina ant
Yugoslavia

1985-1986
Cross-sectional

Yugoslavia Prospective
Study of Environmental
Pristina and Mitrovica Exposure
n = 291

Pregnant women in
second trimester, major
central nervous system
defects, multiple births,
and residence >10 km
from clinic

Blood Pb

Whole blood samples
taken in Yugoslavia
and transported on
wet ice to Columbia
University. Blood Pb
measured using
GFAAS.

Age at measurement:
16-41 yr old

Mean [jg/dL (SD):
Pristina: 5.57 (2.01)
Mitrovica: 20.00 (6.99)

TSH, thyroid hormones
(FT4), and thyroid
peroxidase antibodies
(TPOAb)

FT4 and TPOAb

were measured by a
radioimmunoassay
procedure. TSH was
measured using an
immunoradiometric assay

Age at outcome:

16-41 yr old

Logistic regression
model adjusted for:
FT4: height, ethnicity,
BMI, fetal gestational
age, maternal
education, adults per
room; TSH: hemoglobin,
ethnicity, BMI, fetal
gestational age,
maternal age; TPOAb:
ethnicity, fetal
gestational age,
maternal age, adults per
room.

Change in FT4 (ng/dL)b

-0.074 (-0.10, -0.046)

Change in Log-TSH
(HlU/mL)b

0.026 (-0.065, 0.12)

Change in Log-TPOAb
(IU/mL)b

0.31 (0.17, 0.46)

ORb

TPOAb > vs. <10 lU/mL
2.41 (1.53, 3.82)

9-109

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Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tSouza-Talarico et al.
(2017)

Sao Paulo
Brazil

Cross-sectional

N = 126

105 women and 21 men
ages 50-82 yr old with a
mean of 9.8 (±4.5) yr of
education

Blood Pb

Fasting blood Pb was
measured using ICP-
MS

Age at measurement:
50-82 yr old

Median: 2.1 [jg/dL
(SD: ±0.9)
Max: 6.1 [jg/dL

Cortisol concentration and
allostatic load

Six neuroendocrine,
metabolic, and
anthropometric biomarkers
were analyzed, and values
were transformed into an
AL index using clinical
reference cut-offs. Salivary
samples were collected at
home over 2 d at
awakening, 30-min after
waking, afternoon, and
evening periods to
determine Cortisol levels.

Age, gender, time of
awakening,
socioeconomic status
(SES), GDS, and PSS
scores

Change in CAR (pg/dL min)b

0.791 (0.672, 1.073)

Change in total AUC (jjg/dL
hr)b

0.889 (0.829, 0.953)

Age at outcome:
50-82 yr old

9-110

-------
Reference and
Study Design

Study Population

Exposure
Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tNqueta et al.

Montreal
Canada
2004-2006
Cross-sectional

Study of Genetics, Stress Blood Pb
and Cognitive
Development
n = 65

75% of participants were
women, 95% were
Caucasian, 90% were
current smokers

Blood Pb levels were
determined using
inductively coupled
plasma mass
spectroscopy
Age at measurement:
50-67 yr old

Median: 2.48 [jg/dL
Mean: 2.41 [jg/dL
(SD = 0.15)

Diurnal basal Cortisol
levels and acute Cortisol
responsivity

Basal Cortisol:
Participants were
instructed to collect saliva
five times per day during
three consecutive
weekdays: upon
awakening, 30 min after
awakening, at 2:00 p.m.,
at 4:00 p.m., and at
bedtime

Linear model adjusted
for age, gender, waist-
hip ratio, smoking status
and income levels.

Change in basal Cortisol
levels (|jg/dL)

-0.01 (-0.05, 0.02)

Change in reactive Cortisol
levels (|jg/dL)

-0.01 (-0.03 0.01)

Stress reactivity: A total of
nine saliva samples were
collected for measurement
of salivary Cortisol: two
baseline samples, one
postanticipatory, and six
post-TSST tasks: one after
15 min and then five
sampled every 10 min

Age at outcome:

50-67 yr old

AAS = atomic absorption spectrometry; BMI = body mass index; CAR = Cortisol awakening response; CI = confidence interval; d = day(s); GDS = Gesell Developmental Schedules;
GFAAS = graphite furnace atomic absorption spectrometry; FT3 = free triiodothyronine; FT4 = free thyroxine; ICP-MS = inductively coupled plasma mass spectrometry;

NHANES = National Health and Nutrition Examination Survey; Pb = lead; PSS = perceived stress score;SD = standard deviation; SE = standard error; SES = socioeconomic status;
SPECT = single photon emission computed tomography; Tg = thyroglobulin; T# = fertile #; TGAb = thyroglobulin antibody; TPOAb = thyroid peroxidade antibody;
TSH = thyroid-stimulating hormone; yr = year(s)

aEffect estimates are standardized to a 1 |jg/dL increase in BLL or a 10 |jg/g increase in bone Pb level, unless otherwise noted. For studies that report results corresponding to a
change in log-transformed Pb biomarkers, effect estimates are assumed to be linear within the 10th to 90th percentile interval of the biomarker and standardized accordingly.
bEffect estimate unable to be standardized due to insufficient distribution information.
fStudies published since the 2013 Integrated Science Assessment for Pb.

9-111

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Table 9-10

Animal toxicological studies of exposure to Pb and endocrine effects

Study

Species (Stock/Strain), n, Sex Exposure

Exposure Details
(Concentration,
Duration)

BLL as Reported (jjg/dL)b Corticosterone Levels

Rossi-George et al.
(2011)

Rat (Long-Evans)

Control (untreated), M/F, n = 10

dams

50 ppm, M/F, n = 9 dams
150 ppm, M/F, n = 11 dams

GD-61 to	Dams were dosed

PND 304	starting 2 mo prior to

mating through
lactation. Pups were
weaned on PND 21
and continued on the
regimen of their dam
until euthanasia post-
testing at approximately
10 mo of age.

0.979 |jg/dL for 0 ppm,
19.091 |jg/dL for 50 ppm,
35.245 [jg/dL for 150 ppm ¦
PND 21 Females

I.469	|jg/dL for 0 ppm,

II.259	|jg/dLfor50 ppm,
25.699 [jg/dL for 150 ppm ¦
PND 61 Females

I.713	|jg/dL for 0 ppm,

II.993	|jg/dLfor50 ppm,
29.615 [jg/dL for 150 ppm ¦
PND 304 Females

Adrenal Weight,
Corticosterone Levels

1.935 [jg/dL for 0 ppm,
19.597 [jg/dL for 50 ppm,
31.935 [jg/dL for 150 ppm-
PND 21 Males

2.177 |jg/dL for 0 ppm,
12.581 |jg/dL for 50 ppm,
26.855 [jg/dL for 150 ppm -
PND 61 Males

1.694 |jg/dL for 0 ppm,
15.968 [jg/dL for 50 ppm,
29.274 |jg/dL for 150 ppm -
PND 304 Males

9-112

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Study

Species (Stock/Strain), n, Sex

Timing of
Exposure

Exposure Details
(Concentration,
Duration)

BLL as Reported (jjg/dL)b Corticosterone Levels

Graham et al.

Rat (Sprague Dawley)
Control (vehicle), M/F,
n = 12-18 (6-8/6-8)

1 mg/kg Pb, M/F, n = 12-18
(6-8/6-8)

10 mg/kg Pb, M/F, n = 12-18
(6-8/6-8)

PND 4 to	Rats were gavaged

PND 28	every other day from

P4 until P28.

0.267 [jg/dL for 0 mg/kg,
3.27 |jg/dL for 1 mg/kg
12.5 |jg/dL for 10 mg/kg ¦
PND 29

Adrenal Weight,
Corticosterone Levels

Cory-Slechta et al.

Mouse (C57BL.6)	GD-61 to

Control (untreated), M, n = 8-17 PND 365

Control (untreated), F, n = 8-13

100 ppm Pb, M, n = 8-17

100 ppm Pb, F, n = 8-13

Dams were exposed
starting 2 mo prior to
mating. Offspring were
continued on the same
exposure as their dams
until the end of the
experiment at 12 mo of
age.

0.34 |jg/dL for 0 ppm Fl
males

0.11 [jg/dL for 0 ppm FS
males

0.34 |jg/dL for 0 ppm Fl
females

0.16 [jg/dL for 0 ppm FS
females

6.94 |jg/dL for 100 ppm Fl
males

6.16 [jg/dL for 100 ppm FS
males

9.38 |jg/dL for 100 ppm Fl
females

7.07 |jg/dL for 100 ppm FS
females

Adrenal Weight,
Corticosterone Levels

Amos-Kroohs et al.
(2016)

Rat (Sprague Dawley)

Control (vehicle, see notes),
M/F, n = 16 (8/8)

1 mg/kg Pb, M/F, n = 16 (8/8)
10 mg/kg Pb, M/F, n = 16 (8/8)

P4 until P10,
18, or 28.

Rats were gavaged
every other day from
PND4 until PND10, 18,
or 28.

1.24 |jg/dL for 0 mg/kg Pb
2.79 |jg/dL for 1 mg/kg Pb
9.07 [jg/dL for 10 mg/kg Pb

Corticosterone Levels

9-113

-------
Study

Species (Stock/Strain), n, Sex

Timing of
Exposure

Exposure Details
(Concentration,
Duration)

BLL as Reported (jjg/dL)b Corticosterone Levels

Sobolewski et al.

Mouse (C57BL.6)

FO Control (assume untreated),

F, n = 10

100 ppm Pb, F, n = 10

20 females were in control and
20 received Pb but these groups
were further divided, and some
received prenatal stress and
others did not.

GD -61 to	Exposure started 2 mo

PND 21	prior to mating and

continued through
PND 21 (weaning) of
the F1.

F3 was technically not
directly exposed.

F1 0.0 [jg/dL for Control

12.5 |jg/dL for 100 ppm -
PND 6-7

F3 0.0 [jg/dL for Control

Corticosterone Levels

F# = filial generation; F = female; GD = gestational day; M = male; mo = month(s); Pb = lead; PND = postnatal day.

9-114

-------
Table 9-11

Epidemiologic studies of exposure to Pb and musculoskeletal effects



Reference and
Study Design

Study Population Exposure Assessment Outcome Confounders

Effect Estimates and
95% Clsa

Osteoporosis and Bone Mineral Density

tCho et al. (2012)

South Korea
2008

Cross-Sectional

KNHANES
n = 481

Postmenopausal women

Blood

Blood Pb measured in venous
whole blood using GFAAS

Age at measurement:

Mean (SD):

Q1: 64.03 (8.52) yr
Q2 and Q3: NR
Q4: 61.78 (8.62) yr

Median: 2.32 [jg/dL
25th: 1.83 pg/dL
75th: 2.88 pg/dL

Osteoporosis

BMD measured in hip,
neck, and spine using X-
ray absorptiometry.
Osteoporosis defined as
T-score <2.5 at any of
the measurement sites

Age at outcome is the
same as the age at
exposure assessment

Age, BMI, alcohol
intake, cigarette
smoking, exercise,
use of oral
contraceptive pill,
hormone therapy,
caloric intake,
calcium intake, fish
consumption, and
vitamin D level

OR Osteoporosis
Prevalence

Q1:

Ref.





Q2:

1.41

(0.75,

2.67)

Q3:

1.34

(0.70,

2.56)

Q4:

1.50

(0.79,

2.86)

tWanq et al. (2019)

United States

2013-2014

Cross-sectional

NHANES	Blood, Urine

n = 1859

Blood Pb measured in whole
General population; >40 yr blood using ICP-MS
old

Age at measurement:

>40 yr

Mean: 1.24 pg/dL
75th: 1.81 pg/dL

BMD and fracture risk

BMD measured via DXA
scan; Fracture risk
measured via Fracture
Risk Assessment score -
a composite index of
fracture risk factors

Age at outcome:

>40 yr

Age, race/ethnicity,

BMI, serum 25(OH)D

level, smoking,

drinking, treatment

for osteoporosis, and .. .

r ¦	IVIdIGS

use of prednisone

Change in BMD (g/cm2)

Femur

-0.01 (-0.03, 0.01)

Premenopausal Women
-0.06 (-0.08, -0.03)

Menopausal Women
0.01 (-0.01, 0.03)

Spine
Males

0.01 (-0.01, 0.03)

9-115

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

Premenopausal Women
-0.05 (-0.08, -0.02)

Menopausal Women
0.02 (-0.01, 0.04)

Change in 10-yr
Fracture Risk Score

Hip

0.45 (0.28, 0.62)
Major

1.22 (0.68, 1.77)

flee and Kim

South Korea

2008-2009

Cross-Sectional

KNHANES
n = 832

Women ages >40 yr

Blood

Blood Pb measured in venous
whole blood using GFAAS

Age at measurement:

Mean (SD): 56.1 (10.4) yr

GM: 2.182 pg/dL

BMD

BMD in the femoral neck,
trochanter,
intertrochanter, Ward
triangle, total femur, and
lumbar 1-4. Measured
using DXA

Age at outcome:

Mean (SD): 56.1 (10.4)
yr

Residence area,
obesity, educational
level, smoking status,
drinking status,
number of
pregnancies,
hormone treatment,
contraceptive oral pill
and daily calcium
intake for pre- and
postmenopausal, and
time since
menopause for
postmenopausal

Change in BMD (g/cm2)

Premenopausal Women

Total Femur
-0.15 (-0.33, 0.03)

Trochanter
-0.18 (-0.41, 0.05)

Intertrochanter
-0.11 (-0.25, 0.03)

Femoral Neck
-0.11 (-0.28, 0.07)

Ward's Triangle
-0.11 (-0.26, 0.03)

9-116

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

Lumbar 1-4
-0.09 (-0.24, 0.06)

Menopausal Women

Total Femur
-0.28 (-0.45, -0.11)

Trochanter
-0.30 (-0.55, -0.06)

Intertrochanter
-0.22 (-0.35, -0.08)

Femoral Neck
-0.21 (-0.39, -0.02)

Ward's Triangle
-0.13 (-0.29, 0.03)

Lumbar 1-4
-0.17 (-0.31, -0.04)

tPollack et al.

(2013)

Western New York
United States
2005-2007
Cross-Sectional

Lumbar Spine

BioCycle Study
n = 248

Premenopausal women
ages 18-44 yr

Blood

Blood Pb measured in venous
whole blood using ICP-MS

Age at measurement:

Mean (SD): 27.4 (8.2) yr

Mean: 1.03 [jg/dL

Bone mineral density Age, BMI, race,

BMD in the hip, spine,
wrist, and whole body
(g/cm2) measured via
DXA

Age at outcome:

Mean (SD): 27.4 (8.2) yr

parity, caloric intake,
and age at menarche

Change in BMD (g/cm2)

Whole Body
-0.004 (-0.03, 0.021)

Total Hip

-0.002 (-0.035, 0.031)

9-117

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

-0.016 (-0.048, 0.016)
Wrist

0.001 (-0.012, 0.014)

tLi et al. (2020b)

Sichuan Province
China

Cross-sectional

n = 799

Study area included two
rural towns, one with a
history of heavy metal
contamination. Generally
healthy adults ages 40-
75 yr old who lived in
study area for >15 yr and
subsisted on rice and
vegetables grown in study
area.

Blood, Urine

Blood Pb measured in venous
whole blood using ICP-MS

Age at measurement:
40-75 yr

Median 3.4 [jg/dL
75th: 4.7 pg/dL

BMD

Osteoporosis (BMD T-
score <2.0); BMD
measured via X-ray
absorptiometry

Age at outcome:
40-75 yr

Age, BMI, and
smoking status

OR Osteoporosis
Prevalence (>3.4 pg/dL
vs. <3.4 [jg/dL blood Pb)

Males

0.6 (0.24, 1.49)

Females
1.33 (0.61, 2.88)

Non-Smoking Females
0.94 (0.4, 2.21)

tLim et al. (2016)

South Korea

2008-2011

Cross-Sectional

KNHANES	Blood

n = 2429

Blood Pb measured in venous
General population; >18 yr whole blood using GFAAS
old

Age at measurement:

>18 yr

Median: 2.22 pg/dL

25th: 1.66 pg/dL
75th: 2.93 pg/dL

BMD (osteoporosis and
osteopenia)

Osteopenia (BMD T-
score <—1.0) and
Osteoporosis (BMD T-
score <-2.5)

Age at outcome:

>18 yr

Age, sex, smoking
status, alcohol
consumption,
geographic region,
education level,
occupation, and
family income

ORs for Osteoporosis or
Osteopenia prevalence
across blood Pb
quartiles

Q1
Q2
Q3
Q4

Ref.

1.08 (0.85, 1.37)
1.18 (0.91, 1.53)
1.49 (1.12, 1.98)

9-118

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

flee and Park

Ansung and Ansan
South Korea
2001-2002
Cross-Sectional

Korean Association
Resource (KARE) Cohort
n = 443

Adults aged 40-65 yr from
two South Korean
communities, on rural
(Ansung) and one urban
(Ansan)

Blood

Blood Pb measured in venous
whole blood using GFAAS

Age at measurement:
40-65 yr

GM: 4.44 pg/dL

BMD

Age, sex, geographic Change in BMD T-score

region, income, and

BMD (T-score)	physical activity

measured via ultrasound

Age at outcome:

40-65 yr

All

-0-0.26 (-0.45, -0.07)

Ever Smokers
-0.47 (-0.85, -0.09)

Current Smokers
-0.60 (-1.02, -0.17)

Never Smokers
-0.15 (-0.37, 0.07)

Osteoarthritis

tPark and Choi

South Korea
4 Years (2010—
2012)

Cross-sectional

KNHANES
n = 884

Women, >55 yr old

Blood

BLL measured in venous whole
blood using GFAAS

Age at measurement:

Mean: 62.9 yr

Median: 2.22 pg/dL
Max: 7.84 pg/dL

Osteoarthritis

Radiographic and
symptomatic
osteoarthritis.
Radiographic OA (rOA)
assessed in the hip,
knee, and spine using
the Kellgren-Lawrence
grading system.
Symptomatic OA (sxOA)
assessed using a
combination of
radiographic evidence
and self-reported
symptoms

Age at outcome:

Mean: 62.9 yr

Age, smoking status,
alcohol use, physical
activity, education,
occupation, income,
diabetes,
hypertension, and
BMI

ORs for Osteoarthritis
prevalence per In-unit
increase in blood Pb
(Hg/dL)

rOA Knee
1.77 (1.17, 2.67)

sxOA Knee
1.50 (0.90, 2.53)

rOA Back
1.05 (0.70, 1.59)

sxOA Back
0.68 (0.39, 1.18)

9-119

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tNelson et al.
(2011a)

Johnston County,
N.C.

United States
2003-2004 and
2006-2008
Cross-Sectional

Johnston County
Osteoarthritis Project
n = 668

African American and
white adults ages >45 yr
old

Blood

Blood Pb measured in venous
whole blood using ICP-MS

Age at measurement
Mean (SD):

Females: 62.4 (9.4) yr
Males: 64.5 (10.8) yr

Median:

Females: 1.9 [jg/dL
Males: 2.2 [jg/dL

Max:

Females: 25.4 [jg/dL
Males: 25.1 [jg/dL

Osteoarthritis

Urine and serum
biomarkers of joint tissue
metabolism

Age at outcome:

Mean (SD):

Females: 62.4 (9.4) yr
Males: 64.5 (10.8) yr

Age, race, BMI, and
smoking status

% Change in urine and
serum biomarkers of
joint tissue metabolism

Males

uNTX-l

1.2% (-1.0, 3.4%)
UCTX-II

1.4% (-0.6, 3.4%)

COMP

1.6% (-0.1, 3.2%)

C2C

0.0% (-1.0, 1.0%)

CPU

-0.2% (-1.4, 1.0%)

C2C.CPII
0.0% (-1.4, 1.4%)

HA

0.2% (-2.5, 3.0%)
Females

uNTX-l

7.7% (3.9, 11.7%)

9-120

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

UCTX-II

5.1% (0.8, 9.5%)

COMP

-0.8% (-2.8, 1.2%)
C2C

0.0% (-1.6, 1.6%)
CPII

1.7% (-0.6, 4.1%)
C2C.CPII

-1.2% (-3.5, 1.1%)
HA

-0.8% (-6.6, 5.3%)

9-121

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tNelson et al.

(2011b)

Johnston County,
N.C.

United States
2003-2004 and
2006-2008
Cross-Sectional

Johnston County
Osteoarthritis Project
n = 1635

African American and
white adults ages >45 yr
old

Blood

Blood Pb measured in venous
whole blood using ICP-MS

Age at measurement:

Mean (SD): 65.3 (11.0) yr

Mean: 2.4 [jg/dL

Osteoarthritis

Radiographic and
symptomatic
osteoarthritis.
Radiographic OA (rOA)
assessed in the knee
using the Kellgren-
Lawrence grading
system. Symptomatic OA
(sxOA) assessed using a
combination of
radiographic evidence
and self-reported
symptoms

Age at outcome:

Mean (SD): 65.3 (11.0)
yr

Age, sex, race,
ethnicity, BMI,
current smoking, and
current drinking

ORs for Prevalent
Osteoarthritis of the
Knee

rOA

1.10 (1.00,

sxOA
1.08 (0.96,

1.20)

1.20)

Oral Health - Adults

tWon et al. (2013)

South Korea
2009

Cross-Sectional

KNHANES
n = 1966

General population; >19 yr
old

Blood

Blood Pb measured in venous
whole blood using GFAAS

Age at measurement:

>19 yr

Mean NR
T1: <1.73 [jg/dL

T2: 1.73-3.04 pg/dL

T3: >3.04 pg/dL

Periodontal disease

Community Periodontal
Index (code >3,
corresponding to pockets
>3.5 mm)

Age at outcome:

>19 yr

Age, sex, family
income, education
level, use of floss,
use of interproximal
toothbrush, alcohol
consumption,
smoking status, ETS
in workplace,
diabetes,
hypertension, and
oral health status

ORs for Prevalent
Periodontal Disease
across blood Pb tertiles

T1
T2
T3

Ref.

1.37 (0.97,
1.31 (0.88,

1.93)
1.96)

9-122

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tHan et al. (2013)

South Korea

2008-2010

Cross-Sectional

KNHANES	Blood

n = 4716

Blood Pb measured in venous
General population; >19 yr whole blood using GFAAS
old

Age at measurement:

>19 yr

GM:

Periodontitis: 2.60 [jg/dL
No periodontitis: 2.12 [jg/dL

Periodontal disease

Community Periodontal
Index (code >3,
corresponding to pockets
>3.5 mm)

Age at outcome:

>19 yr

Age, gender, income,
education, frequency
of daily
toothbrushing,
regular dental check-
up, smoking, alcohol
consumption,
physical activity,
fasting plasma
glucose, BMI, white
blood cell count and
urine cotinine
concentration.

ORs for Prevalent
Periodontal Disease
across blood Pb
quintiles

Q1 (<1.59 [jg/dL)

Ref.

Q2 (1.59-2.05 [jg/dL)
1.36 (1.00, 1.85)

Q3 (2.05-2.52 pg/dL)
1.3 (0.96, 1.76)

Q4 (2.52-3.57 pg/dL)
1.55 (1.13, 2.13)

Q5 (>3.17 pg/dL)
1.6 (1.15, 2.22)

tKim and Lee

(2013)

South Korea

2008-2009

Cross-Sectional

KNHANES	Blood

n = 3996

Blood Pb measured in venous
General population; >20 yr whole blood using GFAAS
old

Age at measurement:

>20 yr

GM: 2.31 pg/dL

Periodontal Disease

Community Periodontal
Index (code >3,
corresponding to pockets
>3.5 mm)

Age at outcome:

>20 yr

Age, body mass
index (BMI),
residence area,
education level,
household income,
smoking and drinking
status, hemoglobin,
glucose, use of floss
or interproximal
toothbrush, decayed,
missing, or filled
permanent teeth
(DMFT), and active
caries

ORs for Prevalent
Periodontal Disease
across blood Pb
quintiles

Males

1.854 (1.265, 2.717)

Males (adjusted for Hg,
Cd)

1.699 (1.154, 2.502)
Females

1.301 (0.883, 1.917)

Females (w/ Hg and Cd)

9-123

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

1.242 (0.833, 1.851)

Oral Health - Children and Adolescents

tWu eta!. (2019)

Mexico City
Mexico

Initial Recruitment:
1997-2005; Follow-
up: 2008-2013
Cohort

Early Life Exposure in
Mexico to Environmental
Toxicants (ELEMENT)
n = 173 to 386 (depending
on exposure metric)

Mother/child pairs
recruited from 2 public
hospitals serving low-to
moderate-income
populations

Blood

Maternal and child blood Pb
measured in venous whole
blood using GFAAS. Maternal
bone Pb measured using K-XRF

Age at measurement:

Maternal BLL:

1st, 2nd, and 3rd trimester

Child BLL:

1, 2, 3, and 4 yr, and in
adolescence (10 to 18 yr)

Maternal bone:

Postnatally

Mean (males, females):
1st trimester: 6.06, 6.36 [jg/dL
2nd trimester: 5.24, 5.25 [jg/dL
3rd trimester: 5.67, 5.73 [jg/dL
Childhood: 15.48, 15.18 pg/dL
Adolescence: 3.60, 3.34 pg/dL
Maternal tibia: 8.64, 9.68 pg/g
Maternal patella: 7.18, 8.64 pg/g

Dental caries

Teeth evaluated by
trained examiners who
assigned decayed,
missing, filled tooth
(DMFT) scores

Age at outcome:
Adolescence (10 to
18 yr)

Sex, cohort, mother's Rate Ratio of Decayed,
education, sugar Missing, and Filled
sweetened	Teeth per In-unit

beverages intake increase in blood or
bone Pb

1st Trimester BLL
1.07 (0.90, 1.27)

2nd Trimester BLL
1.12 (0.94, 1.32)

3rd Trimester BLL
1.17 (0.99, 1.37)

Childhood BLL
1.14 (0.94, 1.38)

Adolescent BLL
0.97 (0.81, 1.16)

Maternal Patella Pb
0.95 (0.88, 1.03)

Maternal Tibia Pb
0.98 (0.88, 1.08)

9-124

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tYepes et al. (2020) Early Life Exposure in

Mexico City
Mexico

Initial Recruitment:
1997-2005; Follow-
up: 2008-2013
Cohort

Mexico to Environmental
Toxicants (ELEMENT)
n = 490

Mexican children recruited
from 2 public hospitals
serving low-to moderate-
income populations

Blood

Child blood Pb measured in
venous whole blood using
GFAAS.

Child BLL:

Average of measurements at
ages 1, 2, 3, and 4 yr

Mean (SD): 4.83 (2.2) pg/dL

Dental caries

Teeth evaluated by
trained examiners who
assigned decayed,
missing, filled tooth
(DMFT) scores

Age at outcome:
Adolescence (9 to 17 yr)

Age, sex, BMI,
sugar intake (g/day),
water intake (ml/day),
amount of beverages
with sugar per day
(mL/day), amount of
beverages without
sugar per day
(mL/day), amount of
toothpaste used
regularly from birth to
2 yr, amount of
toothpaste used from
2 to 4 yr, amount of
toothpaste used from
4 to 6 yr, and amount
of current toothpaste
use

D1MFS Beta (increment
not reported)

Mean BLL
0.03 (-0.03,

Peak BLL
0.01 (-0.01,

0.09)

0.04)

tKim et al. (2017)

Seoul, Daegu,
Cheonan, and
Busan

South Korea

2005-2010

Cross-sectional

The Children's Health and
Environmental Research
(CHEER) group
n = 1,565 (children w/
permanent teeth) and
1,241 (children w/
deciduous teeth)

School-aged children from
urban, rural, and
industrialized areas with
BLLs <5 [jg/dL

Blood

Blood Pb measured in venous
whole blood using GFAAS

Age at measurement:
"School-aged"

GM: 1.53 [jg/dL

Dental caries

DMFS sum by trained
dental hygienists

Age at outcome:
"School-aged"

Sex, age
(categorical),
household income
(categorical), and
urinary cotinine level
(categorical)

PR for Decayed and
Filled Surfaces

Deciduous Teeth

Decayed Surfaces
1.16 (0.91, 1.49)

Filled Surfaces
1.11 (0.98, 1.25)

DMFS

1.14 (1.02, 1.27)

Permanent Teeth

Decayed Surfaces
0.69 (0.45, 1.07)

9-125

-------
Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

Filled Surfaces
0.87 (0.73, 1.04)

DMFS

0.83 (0.69, 0.99)

tWiener et al.
(2015)

United States

1988-1994

Cross-Sectional

NHANES III
n = 3127

General population; 2 to
6 yr old

Blood

Blood Pb measured in venous
whole blood using GFAAS

Age at measurement:

2 to 6 yr

Mean NR
28.2% <2 [jg/dL;

48.3% 2 to <5 [jg/dL;
18.4% 5 to <10 [jg/dL;
5.1% >10 [jg/dL

Dental caries

Number of teeth with at
least one decayed or
filled surface as detected
by trained examiners

Age at outcome:

2 to 6 yr

Sex, race/ethnicity,
age, urban status,
census region,
poverty index, family
education, ETS
exposure, birth
weight, breastfed,
dental visit, and
parental perception
of oral health

PR for Decayed and
Filled Surfaces

<2 [jg/dL:

Ref.

2-5 [jg/dL:
1.84 (1.36, 2.50)

5-10 [jg/dL:
2.14 (1.36, 3.36)

>10 |jg/dL:
1.91 (1.17, 3.11)

BLL = blood lead level; BMD = bone mineral density; BMI = body mass index; CHEER = Children's Health and Environmental Research; CI = confidence interval; C2C = serum
cleavage neoepitope of type II collagen; COMP = cartilage oligomeric matrix protein; CPU = carboxypropeptide of type II collagen; DMFS = delayed, missing, and filled surfaces;
DMFT = decayed, missing, and filled teeth; DXA = Dual-energy X-ray absorptiometry; ELEMENT = Early Life Exposure in Mexico to Environmental Toxicants; ETS = environmental
tobaccos smoke; GFAAS = Graphite furnace atomic absorption spectrometry; ICP-MS = inductively coupled plasma mass spectrometry; KARE = Korean Association Resource;
KNHANES = Korea National Health and Nutrition Examination Survey; NHANES = National Health and Nutrition Examination Survey; NR = not reported; OA = osteoarthritis;
OR = odds ratio; Pb = lead; PR = prevalence ratio; rOA = radiographic osteoarthritis; sxOA = symptomatic osteoarthritis; SD = standard deviation; Q = quartile; yr = year(s).
aEffect estimates are standardized to a 1 |jg/dL increase in BLL or a 10 |jg/g increase in bone Pb level, unless otherwise noted. For studies that report results corresponding to a
change in log-transformed Pb biomarkers, effect estimates are assumed to be linear within the 10th to 90th percentile interval of the biomarker and standardized accordingly.
fStudies published since the 2013 Integrated Science Assessment for Lead.

9-126

-------
Table 9-12 Animal toxicological studies of exposure to Pb and musculoskeletal effects

Study

Species	Timing of Exposure

(Stock/Strain), n, Sex Exposure Details

BLL as Reported
(Hg/dL)

Endpoints Examined

3eier et al.(2017)

Mouse (C57BL.6),
0 ppm Pb, M/F, n = NR
100 ppm Pb, M/F,
n = NR

PND 240 Oral, 0.17 ± 0.19 ng/dLfor Serum Protein Levels of Dickkopf-1, Serum Protein Levels of
drinking 0 ppm,	Sclerostin (scl), Serum Protein Levels of C-terminal telopeptide

water 58.67 ± 4.61 ng/dL (CTx-1), Serum Protein Levels of type 1 procollagen (P1NP),
for 100 ppm -	Energy to Femur Failure (Males, 8 moo), Femur Yield Load /

PND 240	Maximum Load (Males, 8 moo), Maximum Femur Stiffness

(Males, 8 moo), Osteoclast Surface/Bone Surface (Oc.S/BS) by
Micro-Computed Tomography (microCT), Osteoclast
Number/Trabecular Area (N.Oc/Tb.Ar) by Micro-Computed
Tomography (microCT), Osteoblast Number/Trabecular Area
(N.Ob/Tb.Ar) by Micro-Computed Tomography (microCT),
Adipocyte size (Ad Size) by Micro-Computed Tomography
(microCT), Adipocyte Volume/Total Volume (AV/TV) by Micro-
Computed Tomography (microCT), Bone Volume to Total Volume
(BV/TV) by Micro-Computed Tomography (microCT)

3eier et al

Mouse (C57BL.6), PND 30, Oral,
0 ppm Pb, F, 200 ppm 90,180, drinking
Pb, F, 500 ppm Pb,/F 360	water

0 ng/mL for 0 ppm, Femur Length, Areal Bone Mineral Density (aBMD), Bone Mass,
50 ng/mL for	Bone Weight, Body Fat, Femur Diameter, P1NP (ng/mL),

100 ppm, 100 ng/mL TRAP5b (U/L), CTx (ng/mL), Calcitonin (pg/mL), 17 beta-estradiol
for 300 ppm -	(ng/mL), Dkk-1 (ng/mL), Femoral BV/TV, Tb.N, Tb.Sp, Conn.D,

PND 28	SMI, Cort Th, Cort BA, Tb Extension, Bone Strength, Beta-

Catenin Protein Levels, TNF-Alpha Protein Levels, NF-kB Protein
Levels, b-catenin RT-PCR, Peroxisome Proliferator-Activated
Receptor-c RT-PCR, CD47 RT-PCR, Nuclear Factor Of Activated
T Cells RT-PCR, CTSK RT-PCR

aBMD = areal bone mineral density; AV/TV = adipocyte volume/total volume; BV/TV = bone volume to total volume; CTx-1 = C-terminal telopeptide; mo = month(s);
microCT = Micro-Computed Tomography; NF-kB = nuclear factor kappa B; N.Oc/Tb.Ar = Osteoclast Number/Trabecular Area; NR = not reported; Oc.S/BS = Osteoclast
Surface/Bone Surface; P1 NP = type 1 procollagen; PND = postnatal day; RT-PCR = reverse transcription-polymerase chain reaction; scl = sclerostin; TNF = tumor necrosis factor.

9-127

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Table 9-13

Epidemiologic studies of exposure to Pb and ocular effects

Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

Glaucoma

tWanq et al, (2018b)

Veterans Affairs NAS

Bone

Glaucoma

Age, BMI,

HRs for Glaucoma



n = 702





education, job

Incidence



United States



Tibia and patella lead

Incident cases of primary

type, pack-yr,





1991-1999 (Follow-up

Healthy male Veterans at

measured using K-XRF

open-angle glaucoma

diabetes mellitus,

Tibia Pb



through 2014)

time of enrollment in the

Age at measurement:
Mean age: 66.8

identified using validated

systemic

1.65)

Cohort

NAS (1963) and without

criteria to assess medical

hypertension, and

1.28 (0.99,



glaucoma at baseline

records

ocular







(time of bone lead

Mean -



hypertension.

Patella Pb





measurement)

Tibia: 21.7 |jg/g
Patella: 31.0 |jg/g





1.42 (1.11,

1.82)

tPark and Choi (2016)

KNHANES

Blood

Intraocular pressure

Age, sex, smoking

Change in intraocular



n = 8371





status, alcohol

pressure (mmHg):

South Korea



Blood Pb was measured in

Intraocular pressure measured

consumption, job

0.088 (0.06, 0.117)

2008-2012

General population,

venous whole blood using

using a Goldmann applanation

status, education,

Cross-sectional

>20 yr old with no history

GFAAS

tonometer

residence,





of glaucoma

Age at measurement:



hypertension







>20 yr old

Age at outcome:

medication use,









>20 yr old

and family history







GM: 2.19 [jg/dL



of glaucoma



tlin et al, (2015)

KNHANES

Blood

Glaucoma

Age, sex, exercise,

OR for Glaucoma



n = 2680





and ferretin and

Prevalence13:

South Korea



Blood Pb was measured in

Presence of glaucoma was

aspartate

1.04 (0.84, 1.29)

2008-2009

General population,

venous whole blood using

assessed by testing of visual

aminotransferase

Cross-sectional

>19 yr old with no history

GFAAS

function using frequency-

levels





of retinal disease or

Age at measurement:

doubling technology.







stroke

>19 yr old













Age at outcome:









Mean -

19 yr old









w/ glaucoma: 2.70 [jg/dL











w/o glaucoma: 2.52 [jg/dL







9-128

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Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

flee et al, (2016)

KNHANES
n = 5198

Blood

Glaucoma

Age group, region
of residence,

ORs for Glaucoma
Prevalence13

South Korea



Blood Pb was measured in

Presence of glaucoma was

occupation,



2008-2012

General population,

venous whole blood using

assessed by testing of visual

education level,

Normal IOP

Cross-sectional

>19 yr old without a

GFAAS

function using frequency-

smoking status,



history of glaucoma or

Age at measurement:

doubling technology.

hypertension,

0.93 (0.65, 1.34)



age-related macular

>19 yr old



family history of





degeneration



Age at outcome:

glaucoma, and

Low-Teen IOP





GM -

>19 yr old

IOP

1.16 (0.74, 1.83)





No Glaucoma: 2.32 [jg/dL;











Glaucoma: 2.28 [jg/dL





High-Teen IOP
0.65 (0.36, 1.18)

Age-Related Macular Degeneration

tPark eta!. (2015)

South Korea

2008-2011

Cross-sectional

KNHANES
n = 3865

General population,
>40 yr old

Blood

Blood Pb was measured in
venous whole blood using
GFAAS

Age at measurement:
>40 yr old

Mean: 2.69 [jg/dL

Age-related macular
degeneration

Macular degeneration was
assessed using retinal
photographs. Photographs
were graded at least twice
using a standardized protocol.

Age at outcome:

>40 yr old

Age, sex, smoking Early-Stage AMD (OR):

status, occupation,
residence,
household income,
anemia, BMI

1.12 (1.02, 1.23)

Late-Stage AMD (OR):

1.25 (1.05, 1.50)

9-129

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Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tHwang et al. (2015)

South Korea

2008-2012

Cross-sectional

KNHANES
n = 4933

General population,
>40 yr old

Blood

Blood Pb was measured in
venous whole blood using
GFAAS

Age at measurement:
>40 yr old

Mean: 3.15 [jg/dL

Quintile

1

<1.75 [jg/dL

Quintile

2

1.75-2.25 [jg/dL

Quintile

3

2.25-2.73 [jg/dL

Quintile

4

2.73-3.38

Quintile

5

>3.38 [jg/dL

Age-related macular
degeneration

Macular degeneration was
assessed using retinal
photographs. Photographs
were graded twice using a
standardized protocol.

Age at outcome:

>40 yr old

NA

ORs (Early-Stage
AMD; Quintiles)

Q1
Q2
Q3
Q4
Q5

Reference
1.04 (0.62, 1.73)
1.14 (0.70, 1.84)
1.26 (0.78, 2.06)
1.55 (0.94, 2.53)

Men Only:

Q1
Q2
Q3
Q4
Q5

Reference
0.66 (0.31, 1.40)
1.32 (0.68, 2.56)
0.80 (0.40, 1.60)
1.32 (0.68, 2.54)

Women Only:
Q1: Reference
Q2: 1.72 (0.86, 3.46)
Q3: 1.83 (0.90, 3.73)
Q4: 1.41 (0.72, 2.77)
Q5: 1.92 (1.06, 3.48)

9-130

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Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tWu eta!. (2014)

United States

2005-2008

Cross-sectional

NHANES
n = 5390

General population,
>40 yr old

Blood

Blood Pb was measured in
venous whole blood using ICP-
MS

Age at measurement:

>40 yr old

GM: 1.61 [jg/dL; Median:
1.77 [jg/dL
75th: 2.61 pg/dL
Max: 26.8 pg/dL

Age-related macular
degeneration

Macular degeneration was
assessed using retinal
photographs. Photographs
were graded twice using a
standardized protocol.

Age at outcome:

>40 yr old

Age, aged-
squared, gender,
race, education,
BMI, pack-yr

ORs for AMD
Prevalence (Quartiles)

Q1
Q2
Q3
Q4

Reference
0.86 (0.60, 1.22)
1.00 (0.68, 1.48)
0.86 (0.59, 1.26)

Quartile 1
Quartile 2
Quartile 3
Quartile 4

0.18-1.2 pg/dL
1.21-1.77 pg/dL
1.78-2.61 pg/dL
2.62-26.8 pg/dL

Other Ocular Effects

(Schaumberq et al.,

United States
1991-1999 (Follow-up
through 2002)

Cohort

Veterans Affairs NAS
n =642

Healthy male Veterans at
time of enrollment in the
NAS

Bone

Tibia and patella lead
measured using K-XRF
Age at measurement:
Mean age: 69 yr

Median -
Tibia: 20 pg/g
Patella: 29 pg/g

Cataract

Documentation for either eye
of cataract surgery or a
cataract, graded clinically as
3+ or higher on a 4-point
scale, diagnosed either after
or within 1 yr prior to bone
lead measurement

Age at outcome:

>60 yr old

Age, pack-yr of
cigarette smoking,
BLLs, diabetes,
and dietary intake
of vitamin C,
vitamin E, and
carotenoids

OR for Cataract

Highest exposure
quintile v lowest
Tibia: 3.19 (1.48, 6.90)
Patella: 1.88 (0.88, 4.02)

9-131

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Reference and Study
Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tWanq et al. (2016)

United States

1999-2008

Cross-sectional

NHANES
n = 9763

General population,
>50 yr old

Blood

Blood Pb was measured in

venous whole blood using AAS

(1999-2002) and GFAAS

(2003-2008)

Age at measurement:

50+ yr old

Cataract surgery

Self-reported cataract surgery

Age at outcome:

>50 yr old

Age, race, gender,
education,
diabetes mellitus,
BMI, serum
cotinine, and pack-
yr

OR for Cataract
Surgery per doubling
of BLL:

0.97 (0.88, 1.06)

GM: 1.97 [jg/dL

tJunq and Lee (2019)

South Korea

2010-2012

Cross-sectional

KNHANES
n = 23376

General population,
>40 yr old

Blood

Blood Pb was measured in
venous whole blood using
GFAAS

Age at measurement:
>40 yr old

GM -

Male: 2.82 pg/dL;

Female: 2.05 pg/dL

Dry eye disease

Self-reported symptoms of dry
eye disease

Age at outcome:

>40 yr old

Age, sex, smoking ORs for Dry Eye

status, alcohol
consumption,
region, education,
occupation, family
income, family
history of
ophthalmologic
disease, and
history of
ophthalmologic
surgery

Disease Prevalence
(Tertiles)

T1: Reference
T2: 1.12 (0.85,
T3: 0.79 (0.56,

1.48)
1.1)

T1
T2
T3

<2.03 pg/dL
2.03-2.82 pg/dL
>2.82 pg/dL

AAS = atomic absorption spectrometry; AMD = age-related macular degeneration; BLL = blood lead level; BMI = body mass index; GFAAS = Graphite furnace atomic absorption
spectrometry; GM = geometric mean; HR = hazard ratio; ICP-MS = inductively coupled plasma mass spectrometry; IOP = intraocular pressure; KNHANES = Korea National Health
and Nutrition Examination Survey; K-XRF = K-shell X-ray fluorescence; NA = not available; NAS = Normative Aging Study; NHANES = National Health and Nutrition Examination
Survey; OR = odds ratio; Pb = lead; Q = quartile; T# = fertile #; yr = year(s).

aEffect estimates are standardized to a 1 pg/dL increase in BLL or a 10 pg/g increase in bone Pb level, unless otherwise noted. For studies that report results corresponding to a
change in log-transformed Pb biomarkers, effect estimates are assumed to be linear within the 10th to 90th percentile interval of the biomarker and standardized accordingly.
bPer natural log unit increase in pg/dL of blood Pb.
fStudies published since the 2013 Integrated Science Assessment for Pb.

9-132

-------
Table 9-14 Animal toxicological studies of Pb exposure and ocular effects

Study	Species (Stock/Strain), n, Timing of Exposure Exposure Details BLL as Reported (pg/dL)	Endpoints Examined

Shen et al. (2016) Rat (Sprague Dawley), 0 ppm
Pb, M, n = 12 (BLL), n = 6
(other endpoints)

55 ppm Pb (0.01%), M, n = 12
(BLL), n = 6 (other endpoints)

109 ppm Pb (0.02%), M,
n = 12 (BLL), n = 6 (other
endpoints)

Blot Protein Levels of
Occludin, Western Blot Protein
Levels of Claudin-5, Western
Blot Protein Levels of pAkt
(Ser473), Western Blot Protein
Levels of pAkt (Thr308)

BLL weeks 1, 2, 3, 4, Oral, drinking water
5, 6; Other
Endpoints week 6

1.11 ±0.08 |jg/dL for 0.00%
12.58 ±2.42 [jg/dL for 0.01 %
19.00 ±2.59 [jg/dL for 0.02%

Retinal Thickness, Blood-
Retina-Barrier Permeability,
Occludin Protein Levels,
Claudin 5 Protein Levels,
Immunofluorescence Protein
Levels of Occludin,
Immunofluorescence Protein
Levels of Claudin 5, Western

Perkins et al. Mouse (C57BL.6), Bcl-xL
(2012)	Transgenic ((C57BL.6),

Background)Wild Type 0.0%
Pb Acetate, M/F, n = 3 to 7,
varying between groups and
between assays
Wild Type 0.015% Pb Acetate,
M/F, n = 3 to 7, varying
between groups and between
assays

Transgenic 0.0% Pb Acetate,
M/F, n = 3 to 7, varying
between groups and between
assays

Transgenic 0.015% Pb
Acetate, M/F, n = 3 to 7,
varying between groups and
between assays

BLL PND 21,
PND60

Other Endpoints
PND 60 to 70

Oral, drinking water

1.9 ± 1.0 pg/dl for 0.0%,

20.6 ± 4.7 |jg/l for 0.015% Pb-

PND21

3.6 ± 1.8 pg/dl for 0.0%,
5.6 ± 2.7 |jg/l for 0.015% Pb-
PND 60

Conventional Transmission
Electron Microscopy (TEM) of
Cell and Organelle Structure,
Three-Dimensional Electron
Microscope Tomography of
Cell and Organelle Structure,
Mitochondrial Cristae
Measurements in Rod
Spherules, Mitochondrial
Cristae Measurements in Cone
Pedicles, Mitochondrial Crista
Junction Diameter and Density
in Rod Spherules,

Mitochondrial Crista Junction
Diameter and Density in Cone
Pedicles, Photoreceptor and
Synaptic Terminal Oxygen
Consumption (Light-Adapted)

BLL = blood lead level; CI = confidence interval; F = female; M = male; pAkt = phosphorylated Akt; Pb = lead; PND = postnatal day; TEM = transmission electron microscopy.

9-133

-------
Table 9-15

Epidemiologic studies of Pb exposure and respiratory effects





Reference and
Study Design

Study Population Exposure Assessment Outcome

Confounders

Effect Estimates and
95% Clsa

Children and Adolescents

tMadrigal et al. (2018) NHANES
n:1234

United States
2011-2012
Cross-sectional

Children and adolescents
aged 6-17 yr

Blood Pb measured in
venous whole blood
using ICP-MS.

Age at measurement:
6-17 yr old

Median:

0.56

pg/dL

25th

percentile:

0.44

pg/dL

75th

percentile:

0.85

pg/dL

Pulmonary function:
FEVi, FVC, FEVi:
FVC, and FEF25% -75%

Spirometry was
performed in the
standing position
using a standardized
protocol according to
the recommendations
of the American
Thoracic Society for
FEV1 and FVC.

Age at outcome:
6-17 yr old

Age, sex, race, height,
family poverty-income
ratio, serum cotinine, use
of anti-asthmatic,
bronchodilator, or inhaler
medications

Change in lung function
parameters across
blood Pb quartiles

FEVi
Q1: Ref.

Q2: 4.8 (-98.3, 107.8)
Q3: 22.3 (-49.3, 93.9)
Q4: 41.9 (-46.9, 130.6)

FVC
Q1: Ref.

Q2: 1.6 (-88.5, 91.7)
Q3: 23.8 (-46.4, 94.0)
Q4: 45.5 (-49.2, 140.2)

FEVr.FVC
Q1: Ref.

Q2: 0.0003 (-0.01, 0.01)
Q3: -0.001 (-0.01, 0.01)
Q4: 0.002 (-0.01, 0.02)

FEF25%-75%

Q1: Ref.

Q2: -8.1 (-229.8, 213.7)

Q3: -28.9 (-160.5,

102.7)

Q4: 0.71 (-193.1, 192.5)

9-134

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Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tZenq et al. (2017)

Guiyu, Xiashan, and
Haojiang

Guangdong Province,
China

November -
December 2013

Cross-sectional

Preschool children aged 5-
7 yr

n = 206 (n = 100 from Guiyu,
n = 54 from Xiashan, n = 52
from Haojiang)

Blood Pb measured in
venous whole blood
using GFAAS

Age at measurement:
5-7 yr old

Median

Exposed (Guiyu):
5.53 [jg/dL

Unexposed (Xiashan
and Haojiang):
3.57 [jg/dL

75th Percentile:

Exposed: 7.04 [jg/dL
Unexposed: 4.86 [jg/dL

Lung function
parameters: FVC and
FEV1

Spirometry was
conducted with a
portable spirometer;
results of three
readings were
recorded and the
highest FVC and
FEV1 was used in the
analysis

Age at outcome:
5-7 yr old

Age, gender, height,
family member daily
smoking, family income
level, parental education
level, daily outdoor play
time, and living area

Change in lung function
parameters per In-unit
increase in blood Pb
(Hg/dL)

FEVi (mL)

-15 (-93, 63)

FVC (mL)

-29 (-100, 43)

tlittle et al. (2017)

Legnica-Glogow

District

Poland

1995 and 2007
Cross-sectional

Polish schoolchildren aged
10-15 yr

n = 184 male
n = 189 female

Blood Pb measured in
venous whole blood
using GFAAS

Age at measurement:
10-15 yr

FVC

A Spiro ProVR unit
was used to measure
pulmonary function.
FVC was computed by
the instrument as a
percentage of gender-
, age- and height-
specific normative
data.

Adjusted for height

Change in FVC (mL) per
logio-unit increase in
blood Pb (|jg/dL)

Boys

-5.1 (-13.9, 3.7)

Girls

-12.9 (-23.2, -2.6)

Age at outcome:
10-15 yr

9-135

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Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tZenq et al. (2016)

Guiyu and Haojiang
China

December 2012 to
January 2013
Cross-sectional

Children age 3-8

n = 470 children
n = 170 from Haojiang and
n = 300 from Guiyu)

Blood Pb measured in
venous whole blood
using GFAAS.

Age at measurement:
3-8 yr old

Medians

Guiyu: 6.24 |jg/dL
Haojiang: 4.75 [jg/dL

75th: BLL:

Guiyu: 8 [jg/dL
Haojiang: 5.76 [jg/dL

Respiratory
symptoms: wheeze,
cough, dyspnea, and
phlegm

The respiratory
symptoms such as
wheeze, cough,
phlegm, and dyspnea
were defined by the
standard

questionnaire from the
European Community
Respiratory Health
Survey (ECRHS)

Age at outcome:
3-8 yr old

Age, gender, passive
smoking, living in Guiyu,
whether use home as
workshop, whether home
close to e-waste recycling
site, and whether child
contact e-waste

OR (>5 [jg/dL vs.
<5 [jg/dL blood Pb)

Wheeze

0.64 (0.32, 1.27)

Dyspnea
0.64 (0.23, 1.79)

Cough

0.95 (0.6, 1.52)

Phlegm

1.2 (0.72, 2.01)

Adults

tPaketal. (2012)

Shiwha and Banwol
Korea

2005 and 2007
(Shiwha) and 2006
and 2008 (Banwol)
Cohort

Shiwha and Banwol
Environmental Health Cohort
(SBEHC)

Men and women over the age
of 30 residing in Shiwha or
Banwoi and completed both
pulmonary function tests
during cycle 1 (2005-2006)
and cycle 2 (2007-2008)

Blood Pb measured in
venous whole blood
using GFAAS

GM (GSD):

Cycle 1: 1.55 (1.76)

pg/dL

Cycle 2: 1.96 (1.66)
pg/dL

FEVi and FVC

Pulmonary function
was measure via
spirometry

Age at outcome: 30+

Age, sex, baseline height,
baseline FVC,
methacholine, cotinine
level

Accelerated FVC
Decline

177.0 (24.1, 329.9)

Accelerated FEVi
Decline

107.0 (-0.8, 214.8)

n = 263 (n = 112 males)

9-136

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Reference and
Study Design

Study Population	Exposure Assessment	Outcome

Confounders

Effect Estimates and
95% Clsa

tleem et al. (2015)

Korea

2008-2012

Cross-sectional

KNHANES
n = 5972

Adults >20 yr who completed
spirometry and had blood
measurements

Blood Pb measured in
venous whole blood
using GFAAS

Age at measurement:
20+

Mean BLL

non-OLF: 2.36 [jg/dL
OLF: 2.77 pg/dL

Obstructive lung
function (OLF)

Spirometry was used
for lung function. OLF
was defined as
FEV1/FVC <0.7

Age at outcome:

20+

Age, sex, BMI, and
smoking status

Change in lung function
parameters per In-unit
increase in blood Pb
(Hg/dL)

FEVi (mL)

0 (-116, 116)

FVC (mL)

9 (-3, 21)

FEVi/FVC (%)
-0.002 (-0.004, 0)

9-137

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Reference and
Study Design

Study Population

Exposure Assessment

Outcome

Confounders

Effect Estimates and
95% Clsa

tRokadia and
Aetarwal (2013)

United States

2007-2010

Cross-sectional

NHANES

n = 9575 (1164 OLD and 8411
non-OLD)

Serum Pb measured
from venous whole blood
samples using ICP-MS

Age at measurement:
General population; >18 yr old <| 8-79 yr

Geom. mean (SE)
non-OLD: 1.18 (1.0)

[jg/dL OLD:
pg/dL

1.73 (1.02)

Obstructive lung
disease (OLD)

Spirometric data were
collected from
NHANES participants;
Participants with OLD
were defined as FEV
1 /FVC <0.7; Mild
OLD: FEV1 = 80%
predicted; Moderate-
severe OLD:
FEV1 < 80% predicted

Age at outcome:
18-79 yr

Age, sex, race, BMI,
chronic kidney disease,
diabetes, hyperlipidemia,
hypertension, stroke,
coronary artery disease,
smoking, serum C-
reactive protein
concentration, and serum
cotinine concentration

ORs for OLD
Prevalence

All OLD
1.94 (1.10,

Mild OLD
1.21 (0.55,

3.42)

2.66)

Moderate-Severe OLD
3.49 (1.70, 7.16)

BLL = blood lead level; BMI = body mass index; CI = confidence interval; ECRHS = European Community Respiratory Health Survey; FEF = forced expiratory flow; FEV1 = forced
expiratory volume; FVC = forced vital capacity; GFAAS = graphite furnace atomic absorption spectrometry; GM = geometric mean; GSD = gestational sac diameter; ICP-
MS = inductively coupled plasma mass spectrometry; KNHANES = Korea National Health and Nutrition Examination Survey; NHANES = National Health and Nutrition Examination
Survey; OLD = obstructive lung disease; OLF = obstructive lung function; OR = odds ratio; Pb = lead; SBEHC = Shiwha and Banwol Environmental Health Cohort; Q = quartile;
yr = year(s).

aEffect estimates are standardized to a 1 |jg/dL increase in BLL or a 10 |jg/g increase in bone Pb level, unless otherwise noted. For studies that report results corresponding to a
change in log-transformed Pb biomarkers, effect estimates are assumed to be linear within the 10th to 90th percentile interval of the biomarker and standardized accordingly.
fStudies published since the 2013 Integrated Science Assessment for Lead.

9-138

-------
Table 9-16 Animal toxicological studies of exposure to Pb and respiratory effects

.	Exposure Details

Study	Species (Stock/Strain), n, Sex	Exposure	(Concentration, BLL as Reported (Mg/dL) b Examined

Duration)

<11 ng/g for control	IHC, Histology

(<1.166 ijg/dL)

132 ng/g for Pb-exposed
(13.992 [jg/dL)

experiment 2

Control (clean air), F, n = 5

0.956 x 10s PbO particles/cm3, F, n = 5

Dumkova et al. (2017) Mouse (ICR)	NR	Mice were exposed to

PbO NPs 24 hr/d for
6 wk.

experiment 1

Control (clean air), F, n = 5

1.23 x 10s PbO particles/cm3, F, n = 5

Dumkova et al.

Mouse (CD1) (ICR)

Control (clean air), F, n = 10 (2 wk, 6 wk,
11 wk)

PbO, F, n = 10 (2 wk, 6 wk, 11 wk)

PbO recovery, F, n = 10 (6 wk PbO, 5 wk
clean air)

NR

Mice were exposed to
clean air or PbO np
24 hr/d 7 d/wk for 2 wk,

6 wk, or11wk. a	„„„ , „ ,

recovery group was	°4 Pb° 2 wk

exposed to PbO for 6 wk < MQ/dL)
and then clean air for

5 wk (11 wk total)	148 ng/g PbO 6 wk

(14.8 [jg/dL)

174 ng/g PbO 11 wk
(17.4 pg/dL)

<3 ng/g in control (2 wk, 6 wk, Western blot,
11 wk) (<0.3 pg/dL)	Histology, IHC,

PCR

27 ng/g PbO recovery
(6 wk/clean air 5 wk)
(2.7 pg/dL)

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Study

Species (Stock/Strain), n, Sex

Timing of
Exposure

Exposure Details
(Concentration,
Duration)

BLL as Reported (pg/dL) b

Endpoints
Examined

Dumkova et al.

Mouse (ICR)

Control (clean air), F, n = 10 (d 3, 2 wk,
6 wk, 11 wk)

Pb(N03)2 (68.6 pg/m3), F, n = 10 (d 3,
2 wk, 6 wk, 11 wk)

Recovery (Pb(N03)2 68.6 |jg/m3), F,
n = 10 (6 wk Pb/5 wk recovery)

6 wk - 8 wk Mice were exposed to
at start	Pb(N03)2 np or clean air

24 hr/d, 7 d/wk for 3 d,
2 wk, 6 wk, or 11 wk. To
assess recovery, a
separate group of mice
were exposed to
Pb(N03)2 for 6 wk and
then clean air for 5 wk.

<3 ng/g for control at all
timepoints (d 3, 2 wk, 6 wk,
11 wk) (<0.3 pg/dL)

31 ng/g for Pb(N03)2 d 3
(3.1 pg/dL)

40 ng/g for Pb(N03)2 2 wk
(4.0 pg/dL)

47 ng/g for Pb(N03)2 6 wk
(4.7 pg/dL)

PCR, Histology,
IHC

85 ng/g forPb(N03)2 11 wk
(8.5 pg/dL)

10 ng/g forPb(N03)2
exposure 6 wk and clean air
for 5 wk (1.0 pg/dL)

BLL = blood lead level; BMI = body mass index; d = day(s); hr = hour(s); IHC = immunohistochemistry; NP = nanoparticle; NR = not reported; Pb = lead; Pb(N03)2 = lead nitrate;
PbO = lead monoxide; PCR = polymerase chain reaction; wk = week(s).

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Table 9-17

Epidemiologic studies of Pb exposure and total mortality

Reference and Study
Design

Study Population Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

Menke et al.(2006)

NHANES III 1988-1994,
mortality follow-up in 2001

-12 yr of follow-up
Cohort

NHANES III
n = 13,946, >20 yr

Average individual
born -1946

Blood (GFAAS with
Zeeman correction)
(Hg/dL)

Mean: 2.58
Tertiles
T1 < 1.93
T2 1.94-3.62
T3 > 3.63

Age of measurement
Mean 44.4

All-cause mortality

Cox proportional hazard	HR

regression analysis adjusted

age, race/ethnicity, sex, urban All-cause 1.09 (1.05, 1.14)

residence, cigarette smoking,

alcohol consumption,

education, physical activity,

household income,

menopausal status, BMI,

CRP, TC, diabetes mellitus,

hypertension, GFR category

Schober et al. (2006)	NHANES III

n = 9,686, >40 yr

NHANES III 1988-1994,
mortality follow-up in 2006 Average individual
-8.55 yr of follow-up

born in or before
-1951

Blood (GFAAS with
Zeeman correction)
(Hg/dL)

Cohort

T1
T2
T3

<5 (median 2.6)
5-9 (median 6.3)
>10 (median 11.8)

All-cause mortality

Cox proportional hazard
regression analysis adjusted
for sex, age, race/ethnicity,
smoking, education level.

Did not evaluate BMI or
cormorbidities

HR

All-cause 1.05 (1.03, 1.08)

Age of measurement
>40 yr

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Reference and Study
Design

Study Population Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

Lustberq and Silberqeld NHANES II
12002,1	n = 4,190, aged 30-

74

NHANES II 1976-1980,

mortality follow-up in 1992 Average individual
Cohort	born -1924

Blood (GFAAS with
Zeeman correction)15
(Hg/dL)

Mean (SD) 14.0 (5.1)
Median: 13
T1: <10
T2: 10-19
T3: 20-29

Age of measurement
Mean (SD) 54.1 (13.2)

All-cause and
circulatory mortality

Cox proportional hazard
regression analysis adjusted
for age, sex, location,
education, race, income,
smoking, BMI, exercise

HR(T1: Referent)0

All-cause

T2: 1.40 (1.16-1.69)
T3: 2.02 (1.62-2.52)

Khalil et al, (2009)

Study of

Blood (GFAAS with

All-cause mortality Cox proportional hazards

HR (>8 [jg/dL vs. <8 [jg/dL



Osteoporotic

Zeeman correction)

regression analysis adjusted

blood Pb)c

Baltimore, MD and
Monongahela Valley, PA

Fractures
n = 533

women, ages 65-
87 yr

(pg/dL)

Mean (SD) 5.3 (2.3)

forage, clinic, BMI, education,
smoking, alcohol intake,
estrogen use, hypertension,
total hip BMD, walking for

All-cause: 1.59 (1.02, 2.49)

Blood Pb measured 1990-

Range 1-21

exercise, and diabetes



1991, mortality follow-up for









-12 yr



Age of measurement
Mean 70





tlanphear et al. (2018) NHANES III
United States	n = 14,289 > 20 yr

1988-1994 mortality follow-

up in 2011	Average individual

-19 yr of follow-up (IQR born-1947

17.6-21.0 yr)

Cohort

Blood (GFAAS with
Zeeman correction)
(pg/dL)

Geometric Mean 2.71
Geometric SE 1.31
10th percentile 1.0
90th percentile 6.7

Age of measurement
Mean 44.1

All-cause, CVD, and Cox proportional hazards
IHD mortality	regression analysis adjusting

forage, sex, household
income, ethnic origin, BMI,
smoking status, alcohol
consumption, physical activity,
concentration of cadmium in
urine, blood pressure, healthy
eating index tertiles, HbA1C,
and serum cholesterol

HR

All-cause: 1.06 (1.03, 1.09)
CVD: 1.10 (1.05, 1.15)
IHD: 1.14 (1.08, 1.20)

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Reference and Study
Design

Study Population Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tvan Bemmel et al. (2011)

United States

1988-1994, follow-up
through 2007

-7.8 yr of follow-up for
those with low blood Pb

-7.5 yr of follow-up for
those with high blood Pb

Cohort

NHANES III
n = 3,349

Adult age >40 yr

Average individual
born -1932

Blood (GFAAS with
Zeeman correction)
(Hg/dL)

Median
<5 [jg/dL 2.6
>5 [jg/dL 7.5

Age of measurement
<5 [jg/dL 57
>5 [jg/dL 61

All-cause and CVD Cox proportional hazards

mortality

adjusting forage, education,
sex, smoking status, and
race/ethnicity

HR

All-cause

All: 1.04 (0.98, 1.10)
ALADGG 1.03 (0.98, 1.08)
ALADCG/GG 1.09 (0.93, 1.28)

tDuan et al. (2020)

United States

1999-2014, follow-up
through end of 2015

- 7.1 yr of follow-up

NHANES
n = 18,602
Age >20 yr

Average individual
born -1960

Blood (ICP-MS) (|Jg/dL)d
Median (IQR)

1.49 (0.93, 2.31)

Age of measurement
Mean (SD) 45.9 (0.3)

All-cause mortality

Poisson regression analyses
adjusted for: sex, age,
ethnicity, education, poverty-
income ratio (PIR), cotinine
category, BMI, physical
activity, hypertension, and
diabetes

RR

All-cause: 1.39 (1.28, 1.51)

Cohort

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Referenc^and Study study Population Exposure Assessment	Outcome

Confounders

Effect Estimates and 95%
Clsa

tByun et al.

Korea

2007-2015, mortality
follow-up in 2018 (between
3-11 yr of follow-up)

Cohort

KNHANES
n = 7,308

Individuals with a
BLL less than
10 [jg/dL, who were
aged 30 yr and over
at the baseline
examination, and
who were not
diagnosed with
cancer or IHD

Average individual
born in or before
-1981

Blood (GFAAS with
Zeeman background
correction) (pg/dL)

Geometric mean: 2.26
Blood Pb tertiles:

All-cause mortality

T1
T2
T3

<1.91

1.91-2.71

>2.71

Age at measurement:
>30 yr

Cox proportional hazard
models adjusted for age and
sex, household income,
education, occupation,
smoking status, drinking
frequency, BMI, and physical
activity, high-lead-containing
food intake (grains,
vegetables, and seafood)

HRC

T1
T2
T3

Reference
2.02 (1.20,
1.91 (1.13,

3.40)
3.23)

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Referenc^and Study study Population Exposure Assessment	Outcome

Confounders

Effect Estimates and 95%
Clsa

tlin et al. (2011)

Taiwan

Years not reported
Cohort (18 mo of follow-up)

n = 927

Taiwanese adult
patients with end-
stage renal disease
(ERSD) on
hemodialysis for
>6 mo, age >18

Baseline blood Pb
(ETAAS) (pg/dL)

Mean: 11.5

Median: 10.4

T1
T2
T3

<8.51

8.51-12.64
<12.64

All-cause, and

Infection-cause

mortality

Age of measurement
Mean (SD) 55.2 (13.5)

Multivariate Cox model
adjusting forage, previous
cardiovascular diseases
(stroke, Ml, PID, congestive
heart failure (CHF)), education
level, hemodialysis vintage,
using fistula, normalized
protein catabolic rate,
hemoglobin, serum albumin,
creatinine, cardiothoracic
ratio, and logarithmic
transformation of high-
sensitivity C-reactive protein
(CRP)

HR(T1: Referent)0

All-cause

T2 2.69 (0.47, 3.44)
T3 4.70 (1.92, 11.49)

Infection-cause
T2 4.33 (0.35, 6.54)
T3 5.35 (1.38, 20.83)

Hemoglobin-corrected:

All-cause:

T2: 3.52 (0.41, 5.01)
T3: 4.98 (1.86, 13.33)

Infection-cause:
T2: 3.02 (0.23, 2.07)
T3: 4.72 (1.27, 17.54)

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Referenc^and Study study Population Exposure Assessment	Outcome

Confounders

Effect Estimates and 95%
Clsa

tTonelli etal. (2018)
Canada

Cohort (2 yr of follow-up)

n = 1,278

Patients on incident
hemodialysis

>18 yr

Plasma Pb (ICP-MS)
(pg/dL)

Deciles

1	0.06

2	0.19

3	0.28

4	0.35

5	0.44

6	0.55

7	0.68

8	0.83

9	1.08

10	1.74

All-cause mortality

Logistic regression adjusting
for age, sex, race/ethnicity,
unemployment prior to
dialysis, yr dialysis initiated,
dialysis duration, predialysis
care, arteriovenous access,
comorbidities (atrial fibrillation,
Ml, BMI, cancer,
cerebrovascular disease,
CHF, lung disease, diabetes,
dementia, hypertension, liver
disease, peripheral vascular
disease, psychiatric disease,
substance misuse), albumin,
and creatinine.

*AII variables were considered
candidate variables and were
included based on stepwise
regression results

Authors indicate a null
relationship between blood
Pb deciles and all-cause
mortality; quantitative
results not reported

9-146

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Reference and Study
Design

Study Population Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

tHollinqsworth and Rudik
(2021) United States

Quasi-experimental design

Elderly population
(>65 yr)

Assessed the
change in deaths
(National Vital
Statistics System)
occurring among
this age group
before and after the
phaseout of leaded
gasoline in
professional racing
(NASCAR, ARCA).

County-level blood Pb
measurements in
children

All-cause mortality

Difference-in-difference
approach controlling for SES
at the county level (median
income, unemployment rates,
percent minority population),
TRI Pb emissions data

Decline in age-standardized
mortality rate per 100,000
population

Race counties: 91
Border counties: 38

Compared mortality
rates in race-
counties to
bordering counties

Average individual
born in or before
-1942

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Reference and Study
Design

Study Population Exposure Assessment

Outcome

Confounders

Effect Estimates and 95%
Clsa

t(Weisskopf et al., 2015)

United States
Cohort

Veterans Affairs
NAS
n = 637

Healthy male
Veterans at time of
enrollment in the
NAS (1963) and
without glaucoma at
baseline (time of
bone lead
measurement)

Bone

Patella lead measured
using K-XRF
Age at measurement:
Mean (SD): 67 yr (7 yr)

Patella Tertiles

T1
T2
T3

<20 ijg/g
20-31 ijg/g
>31 |jg/g

All-cause mortality

Age at K-XRF, age at K-XRF
squared, smoking, education,
occupation and salary at NAS
entry, mother's education and
occupation, father's education
and occupation

HR (T1 Referent)

T2:
T3:

1.41 (0.86, 2.30)
1.86 (1.12, 3.09)

ARCA = Automobile Racing Club of America; BLL = blood lead level; BMD = bone mineral density; BMI = body mass index; CHF = congestive heart failure; CI = confidence interval;
CHF = congestive heart failure; CRP = C-reactive protein; CVD = cardiovascular disease; ERSD = end-stage renal disease; ETAAS = electrothermal atomic absorption spectrometry;
GFAAS = graphite furnace atomic absorption spectrometry; GFR = glomerular filtration rate; HR = hazard ratio; ICP-MS = inductively coupled plasma mass spectrometry;
IHD = ischemic heart disease; IQR = interquartile range; KNHANES = Korea National Health and Nutrition Examination Survey; K-XRF = K-shell X-ray fluorescence; Ml = myocardial
infarction; mo = month(s); NAS = Normative Aging Study ; NASCAR = National Association for Stock Car Auto Racing; NHANES = National Health and Nutrition Examination Survey;
Pb = lead; PIR = poverty-income ratio; RR = relative risk; SD = standard deviation; SES = socioeconomic status, T# = fertile #; TC = total cholesterol; TRI = Toxics Release
Inventory; wk = week(s); yr = year(s).

aEffect estimates are standardized to a 1 |jg/dL increase in BLL or a 10 |jg/g increase in bone Pb level, unless otherwise noted. For studies that report results corresponding to a
change in log-transformed Pb biomarkers, effect estimates are assumed to be linear within the 10th to 90th percentile interval of the biomarker and standardized accordingly.
bBlood Pb analysis method unclear, assumed based on data source.

°Unable to be standardized.

dUnits assumed to be |jg/dL (written as |jg/L in the paper).

fStudies published since the 2013 Integrated Science Assessment for Pb.

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