EPA/832-B-93-0G5
September 1995
A Guide to the
Biosolids Risk Assessments for the
EPA Part 503 Rule
U.S. Environmental Protection Agency
Office of Wastewater Management
Washington, DC
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Notice
This document has been reviewed by the U.S. Environmental Protection Agency and approved for
publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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Foreword
The U.S. Environmental Protection Agency's (EPA's) Part 503 rule provides comprehensive require-
ments for the use or disposal of biosolids generated during the process of treating municipal
wastewater. Formulation of the final rule benefitted greatly from the input provided by the regulated
and environmental communities, and especially the group of scientific experts who worked closely
with EPA in revising the proposed rule. The final rule is the result of a very effective combination of
public comment, scientific risk assessment, and informed risk management.
The Part 503 rule underwent an extensive multi-pathway risk assessment for evaluating and setting
limits to manage pollutants in biosolids. The scientific approach used in developing the Part 503 re-
quirements attempted to determine an acceptable level of pollutants that could be added to the
environment in biosolids and differs from policy-based approaches used in some other countries.
This "Guide to the Part 503 Risk Assessment" has been prepared to help the public, wastewater
treatment authorities, state regulators, and scientists better understand the risk assessment proc-
ess. It helps explain many of the steps that were taken over a nine-year period to develop the rule,
many of the issues that arose, how they were resolved, and how the risk assessment process was
used in deriving the requirements in the final rule. The issues discussed in greater detail in the
Guide are reflective of the questions that have been asked most often and are provided as exam-
ples to increase the reader's understanding of the nature and conservativeness of the Part 503's risk
assessment process.
The Guide emphasizes the importance of collecting relevant data and using appropriate models and
assumptions (field-verified whenever possible) in the establishment of pollutant limits and manage-
ment practices that protect public health and the environment from reasonably anticipated adverse
effects of pollutants in biosolids. The Guide shows that the Part 503 rule is not only conservative and
protective, but also realistically implementable.
Michael B. Cook, Director
Office of Wastewater Management
Part 503 Risk Assessment «EPA iii
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Acknowledgments
This document represents the efforts of several individuals. Gratitude is extended to each person in-
volved in preparing and reviewing this guide.
The authors are Dr. John Walker, Municipal Technology Branch, Office of Wastewater Management,
U.S. EPA; and Linda Stein of Eastern Research Group, Inc. Special thanks go to Robert M.
Southworth and Dr. James Ryan of U.S. EPA and Dr. Rufus Chaney of the U.S. Department of Agri-
culture whose significant contributions to this effort were very important in the guide's development.
The U.S. Environmental Protection Agency gratefully acknowledges the monetary contributions of the fol-
lowing stakeholders for printing of this document to enable its distribution:
BioCycle Magazine
Brown and Caldwell
CH2M Hill Corp.
The Composting Council Research and Education Foundation
Denver Metro Wastewater Reclamation District
Environmental Waste Recycling, Inc.
Metro: King County (WA) Department of Natural Resources
Metropolitan Water Reclamation District of Greater Chicago
Montgomery Watson Americas, Inc.
New England Fertilizer Co.
Northwest Biosolids Management Association
Wheelabrator Water Technologies, Inc., Bio Gro Division
Iv &EPA Part 503 Risk Assessment
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Table of Contents
Chapter 1 Overview 1
Basis for the Part 503 Risk Assessments 2
Document Organization 5
Chapter 2 The Risk Assessment Process for the Part 503 Biosolids Rule 7
Initial List of Pollutants 7
Biosolids Task Force Study 7
Identification of 200 Pollutants 10
Selection of Pollutants by Scientific Experts for Further Consideration From the
List of 200 Pollutants 10
Hazard Profiles of the 50 Pollutants Selected for Further Evaluation 12
Initial Identification of Exposure Pathways for Hazard Assessment 12
Profile Assessments of 50 Pollutants 12
Use of the Hazard Profile Process To Select Pollutants for Detailed Risk Assessment 12
Risk Assessments Conducted for the Proposed Part 503 Rule 14
EPA Science Advisory Board Review of Risk Assessment Methodology for the
Proposed Rule 14
Risk Assessments for Proposed Part 503 Pollutant Limits 14
Comments on the Proposed Part 503 Rule and EPA's Response 20
Public Review and Comment on the Proposed Part 503 Rule 20
EPA Analysis of Comments on the Proposed Rule and Revision of the Risk Assessments . . 20
The National Sewage Sludge Survey 20
Publication of the NSSS Results and Proposed Changes for the Final Part 503 Rule 21
Revised Risk Assessments Conducted for the Final Part 503 Rule 25
EPA Review of Science and Policy Decisions Used in the Biosolids Risk Assessments
Prior to Issuance of the Final Part 503 Rule 28
Publication of the Final Part 503 Rule in the Federal Register 29
Comments, Lawsuits, and Amendments Regarding the Published Final Part 503 Rule .... 29
Court Remand of Specific Portions of the Rule 30
Chapter 3 Identification and Resolution of Risk Assessment Issues 31
Evaluation of Iron and Fluoride 31
Who Is at Risk? The "Highly" Versus "Most Exposed" Individual 33
Part 503 Risk Assessment ©EPA v
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Cancer Risk Level Used 35
Plant Uptake of Metals: Pot/Salt Vs. Field Studies 36
Pot/Salt Studies Overestimate Risk 36
Plant Response to Metals 36
Calculating Plant Uptake Slopes 38
Food Consumption 40
Pollutants Deleted 41
Organic Pollutants 41
Inorganic Pollutants 41
Inclusion of "Pollutant Concentration Limits" (for Low-Metal Biosolids) for Land Application
in the Part 503 Rule 41
Risk From Exposure to Lead in Land-Applied Biosolids 42
"Biosolids Binding" of Pollutants: Biosolids Decrease Pollutant
Phytoavailability and Bioavailability -43
Biosolids Binding Is Long Lasting and Reduces Risk 43
First-Year Biosolids Field Data Overestimate Risk 43
Additional Conditions That Reduce Risk 43
Ecological Risk Assessment 44
Risks to Animals 44
Risks to Plants (Phytotoxicity) 46
First Procedure for Determining Plant Metal Concentrations That Characterize
Phytotoxicity (the Probability Approach) 46
Second Procedure for Determining Plant Metal Concentrations That Characterize
Phytotoxicity (the Calculation Approach) . 47
Selection of the Most Conservative Loading Rate From the First and Second
Approaches as the Phytotoxicity Limit 48
Holistic Review of Field Data To Determine If Phytotoxicity Limits Were Protective , . 48
Risks to Soil Microbes? 49
Additional Ecological Monitoring Research 50
Allow Use of PSRP and PFRP for Regulating Pathogens 50
Regulation of Non-Agricultural Land Application of Biosolids 51
Ceiling Concentration Limits and Caps on Pollutant Concentration Limits ; . 51
Ceiling Concentration Limits Set After ORD Review 51
Caps: A Risk Management Decision 52
Additional Discussion 52
Protection of Ground Water From Excess Nitrogen 54
Management and Regulation of Nutrients i . 54
USDA Comments, EPA Revisions 54
Lawsuits, Provisions of the Rule Remanded by the Court 56
vi &EPA Part 503 Risk Assessment
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Table ot Contents
Chapter 4 How the Risk Assessments Identified Pollutant Limits For Biosolids 59
How Pollutant Limits Were Derived in the Revised Risk Assessments 59
Parameters, Assumptions, Policy Decisions, and Methods Used 60
Land Application Risk Assessment 60
Risk Assessment Calculations 60
Approach Used For the Surface Disposal Risk Assessment 61
Surface Disposal: Ground-Water Pathway 79
Surface Disposal: Vapor (Air) Pathway 80
Approach Used For the Incineration Risk Assessment 80
Use of Risk Assessment Results and 'The Most Limiting Pathway" Approach To
Establish Part 503 Pollutant Limits 81
Calculating Exposure Pathway Pollutant Limits 81
Land Application Pollutant Limits 81
Using Exposure Pathway Pollutant Limits To Calculate Part 503 Pollutant Limits 86
Detailed Risk Assessment Example: Cadmium, Pathway 2, Land Application 87
The Highly Exposed Individual, Pathway 2 87
Algorithms Used in Pathway 2 87
Calculation of the Adjusted Reference Intake: RIA 88
Parameters Used To Calculate the RIA 88
Calculation of the Pollutant Limit (RP) 89
Parameters Used To Calculate the Reference Application Rate of Pollutant (RP) ... 89
Conservative Parameters Result in a Conservative
Pollutant Limit 92
Summary 94
Chapter 5 How the Biosolids Risk Assessment Results Were Used in the Part 503 Rule ... 95
Synopsis of the Biosolids Risk Assessments 96
History of the Risk Assessment Process 96
Defining Exposure Pathways and Highly Exposed Individuals 96
Choosing Parameters To Identify Pollutant Limits 97
Risks to People and Animals 97
Risks to Plants 97
Choosing a Pollutant Limit 97
Evaluating Inorganic and Organic Pollutants 98
Using Conservative Assumptions 98
The Biosolids Risk Assessments and the Part 503 Rule 98
Pollutant Limits for Land Application 99
Four Types 99
Pollutant Limits for Surface Disposal 102
Pollutant Limits for Incineration 102
Part 503 Risk Assessment wEPA vii
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••.' • ' - -' -'• ¦¦'"" :•:¦ •;. \ ' j' .7- .• -
Other Elements of the Part 503 Rule 102
Operational Standards . 104
The Operational Standards for Pathogen and Vector Attraction Reduction 104
The Operational Standard for THC 104
Management Practices 105
Management Practices for Land Application 105
Management Practices for Surface Disposal 105
Management Practices for Incineration 107
Part 503 Monitoring, Recordkeeping, and Reporting Requirements 107
General Summary 107
Chapters Questions and Answers on the Part 503 Risk Assessments 109
Risk Assessment 109
Risk Level of 1 x 10"4 or 1 x 10"6 . 109
Selection of the Part 503 Pollutant Limits 111
Most Exposed Individual (MEI) vs. Highly Exposed Individual (HEl) 112
What If? .113
Soil pH 113
"Time-Bomb" Theory 114
Phytotoxicity 115
Synergistic Effects of Biosolids Metals 116
Use of Data With Zero or Negative Plant Uptake Slopes . . , 116
Pathogens 116
Determining "Acceptable" Concentrations of Biosolids Pollutants in Soils .116
Chapter 7 References 121
Appendix A Parameters Used in the Land Application Risk Assessment for Biosolids ... 127
Appendix B Parameters, Approach, Assumptions, and Degree of Conservatism Used:
Land Application Risk Assessment 133
Appendix C Team of Experts Who Assisted EPA in the Part 503 Biosolids Risk Assessment 141
Appendix D Conversions Used to Place Pollutant Limits in the Same Units 143
viii «SEPA Part 503 Risk Assessment
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Chapter 1
Overview
The U.S. Environmental Protection Agency (EPA) has developed a compre-
hensive, risk-based rule to protect public health and the environment from
reasonably anticipated adverse effects of pollutants that may be present in
biosolids (sewage sludge) that are used or disposed. Commonly known as the Part
503 rule, the regulation (40 CFR Part 503) was published in the Federal Register
on February 19, 1993. Much of the rule was based on the results of risk assess-
ments that were scientifically conducted to identify what, if any, risks were
associated with the use or disposal of biosolids. Those parts of the rule that were
not based on risk assessment were based on performance- or technology-based
standards or on management, monitoring, and recordkeeping practices shown to
protect human health and the environment.
This guide has been prepared to provide an understanding of the risk assessment
process that was conducted as a basis for the Part 503 biosolids rule. The guide il-
lustrates how extensive the process was and how it has resulted in a reasonable
and protective rule. The document takes the reader through the multiple-step risk
assessment process. Specifically, this guidance document:
• Describes the risk assessment procedures used to develop the Part 503 pol-
lutant limits.
• Provides a historical accounting and discussion of the numerous steps taken
to develop the risk assessments.
• Discusses the issues that arose during the risk assessment process and ex-
plains how these issues were resolved.
• Explains the assumptions and policy decisions involved in the selection and
use of risk assessment data and models and the development of the Part 503
rule.
• Describes the conservativeness of the Part 503 rule and the risk assessment
process on which it is based, providing reasons why the Agency believes that
the pollutant limits set in the Part 503 rule are protective of public health and
the environment and why more restrictive limits are not warranted.
• Addresses commonly asked questions about the risk assessments.
While this guide focuses primarily on the risk assessment conducted for land appli-
cation of biosolids, it also highlights some of the key features of the biosolids
Part 503 Risk Assessment SEPA 1
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Chapter 1
Safely recycled biosoiids can result in healthy lawns and shrubbery, beautiful
flowers, and nutritious food.
surface disposal arid incineration risk assessments. The guide also briefly dis-
cusses the Part 503 non-risk-based requirements. For more detail on the Part 503
risk assessments, consult the appropriate Technical Support Documents (U.S.
EPA, 1992a, 1992b, 1992c).
The reader will notice that throughout this document sewage sludge is referred to
as biosoiids. Biosoiids are the primarily organic solid product yielded by municipal
wastewater treatment processes that can be beneficially recycled (whether or not
they are currently being recycled). The term biosoiids is used in this document to
emphasize the beneficial nature of this valuable, recyclable resource (i.e., the use
of the nutrients and organic matter in biosoiids as a fertilizer or soil conditioner).
Also, it is important to point out that while many of the substances found in
biosoiids are called pollutants throughout this document, many also are beneficial
elements that are essential for the growth of plants and animals. The term pollu-
tants has been used as a result of language in the Clean Water Act.
Basis for the Part 503 Risk
Assessments
Based on the best scientific data available, established EPA risk guidelines, and
the scientific Judgment of experts, an extensive risk assessment was conducted for
each of the following biosoiids use or disposal practices:
• Land application
• Surface disposal
• Incineration
The general process used for conducting the Part 503 risk assessments was
based on well-established procedures described by the National Academy of Sci-
ences (NAS, 1983). The procedures are listed in Box 1. Using this process, EPA
analyzed risks to humans, animals, plants, and soil organisms from exposure to
2 &EPA Part 503 Risk Assessment
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- ; °verv,ew
Box 1
The Four Steps in the Part 503 Risk Assessments
The risk assessments for biosolids followed these four basic steps:
• Hazard identification: Can this pollutant harm human health and/or the environment? Scientists
evaluated available studies on the toxicity (harmful effects) of the pollutant being assessed. For exam-
ple, the hazard identification for biosolids indicated that cadmium does not appear to adversely
impact the growth of plants (i.e., does not cause phy totoxicity) but could impact human health via ad-
verse affects on the kidney andother systems if it is present in sufficiently high quantities.
• Exposure assessment: Who is exposed, how do they become exposed, .and how much exposure oc-
curs? Highly exposed individuals (HEI) were identified and their exposure to pollutants in" biosolids
were evaluated via relevant pathways of exposure. HEIs included humans, large arid small animals,
, plants, and small organisms. A total of 14 pathways of exposure were evaluated for land-applied
biosolids, 2 for surface disposed biosolids, and-1 for incinerated biosolids. The movement of'biosolids
pollutants through the environment was modeled,(using m ath em a t Lea l equ a tion s). Many factors influ-
ence the actual exposure. For example, organisms often respond differently depending on whether
they encounter a pollutant by inhaling it, eating or drinking it, or absorbing it through the skin, and-
also on where the pollutant goes after it enters the body (e.g., Does it enter the liver via the blood-
stream, remaining there to cause liver damage? Or .does it move from the liver to another, more
sensitive organ where damage might occur?). In addition, an organism's response often differs de-
pending on its nutritional status (e.g., levels of nutrients like iron, calcium, arid magnesium can protect
. against cadmium absorption and retention in the human body), and whether it was exposed to a pol-
lutant for long or short periods.
• Dose-response evaluation: If a person, animal, or plant is exposed to this pollutant, what happens?
This part of the risk assessment is based on the likelihood of a person, animal, or plant developing a
particular disease as the amount (dose) and exposure to a pollutant increases. Such dose-response rela-
tionships have been established based on years of-carefuliy conducted .toxicological experiments. The
biosolids risk assessments used the following EPA toxicity factors, whenever available: •
Risk reference doses (RfDs)—daily intake of a chemical that, during ah entire lifetime, appears to be
without appreciable risk on the basis of all known facts at the time.
Cancer potency values (qi*s)—conservative indication of the likelihood of a.chemical inducing or
causing cancer during the lifetime of a continuously exposed individual.
• Risk characterization: What is the likelihood of an adverse effect in the population exposed to a pol-
lutant under the conditions.studied? This step involves putting the information together from the first
tiiree steps. Risk is calculated as:
Risk = Hazard x Exposure
Hazard refers to the toxicity of a substance determined during the hazard identification and dose- -
response evaluation, and exposure is determined through the exposure assessment.
Generally, three types of risks are identified: I * _
- risks to individuals
- risks to the general population
- risks to highly exposed or highly sensitive subgroups
In addition, risk characterization addresses uncertainties associated with some of the information used
(e.g., if only studies of animals were available to assess risks to humans, a "safety factor" might be
*;; used that multiplies the results by a factor of 10,100, or 1,000 to adequately protect humans).
Part 503 Risk Assessment SEPA 3
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Chapter 1
pollutants in biosolids through 14 different pathways (e.g., food, water, soil, air) for
land-applied biosolids, 2 exposure pathways for surface disposal of biosolids, and
1 exposure pathway for incineration of biosolids. The process of selecting and
managing the data, models, assumptions, and approaches used to conduct the risk
assessments for the Part 503 rule underwent extensive refinement during the 7
years in which the final rule was formulated.
The Part 503 rule was developed with the realization that the use or disposal of
biosolids may result in changes in the environment, as does the use of other fertil-
izers, the construction of buildings and other structures, and many other aspects of
human activity. The biosolids risk assessment process provided a scientific basis
for determining acceptable environmental change when biosolids are used or dis-
posed. Acceptable change means that even though changes have occurred as a
result of the use or disposal of biosolids (e.g., increases in nutrients and organic
matter as well as pollutants), public health and the environment are still protected
from reasonably anticipated adverse effects of pollutants in biosolids. This ap-
proach is quite different than the policy-driven approach followed by some
European countries and Canadian provinces. Those policy-driven approaches al-
low only small, incremental increases of pollutants from the use or disposal of
biosolids over background levels of pollutants already in the environment; for ex-
ample, metal concentrations may not exceed either the 95th percentile of
background soil concentrations, or a specified low concentration level assuming
that 100 percent of a person's diet is consumed from biosolids-amended soils un-
der poor management conditions. This latter approach often is not associated with
an attempt to determine the extent or acceptability of environmental change.
In addition to using scientific risk assessment methods to identify acceptable envi-
ronmental change, EPA made policy decisions when necessary to establish
pollutant limits for biosolids that protect highly exposed individuals. EPA also relied
on best professional judgment based on research and operational data to determine
appropriate site restrictions (e.g., requiring waiting periods before harvesting crops
grown on soils where biosolids have been applied) and other requirements necessary
to ensure the safe use or disposal of biosolids. The end result was the Part 503 rule,
which imposes general requirements; pollutant limits; management practices; opera-
Figure 1
Elements of the Part 503 Rule
General Requirements
Recordkeeping
Reporti
Hydrocarbons or Vector Attraction
Frequency of Management Carbon Monoxide Reduction (Land
Monitoring Practices (Incineration Application and
Only) Surface Disposal)
Pollutant Limits
Operational Standards
Pathogen and
4 SEPA Part 503 Risk Assessment
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Overview
tional standards (such as technology-based requirements for pathogen reduction
and vector control); and frequency of monitoring, recordkeeping, and reporting re-
quirements. These elements of the Part 503 rule are presented graphically in
Figure 1.
The basic approach used in the biosolids risk assessments was to identify expo-
sures to highly exposed individuals from pollutants of concern through specific
exposure pathways. This approach involved using a combination of "high-end"
(conservative) and "mid-range" (average) values to provide conservative protection
for highly exposed individuals. This guide provides an explanation of this approach,
including how the risk assessment defined highly exposed individuals, why "highly
exposed" rather than "most exposed" individuals were ultimately used in the risk
assessments, and how the risk-based pollutant limits protect these highly exposed
individuals.
The choice of toxicity data, models, and approaches used; the key assumptions
and policy decisions made; and the management of data all had important impacts
on the risk assessment results. This guide addresses each of these elements, in-
cluding discussions of science-based and policy-based decisions. Strengths and
weaknesses of the risk assessment process also are indicated. One pollutant/path-
way analysis is described in detail to illustrate how the various factors involved in
the biosolids risk assessments were used to develop pollutant limits.
In conclusion, the best scientific data and talent were assembled and used for de-
veloping the final Part 503 rule to ensure that it was based on carefully reasoned
science and policy decisions. This comprehensive process resulted in pollutant lim-
its, management practices, and other provisions that protect public health and the
environment from reasonably anticipated adverse effects of pollutants in biosolids.
Document Organization
Several sections of this guide provide summaries of the biosolids risk assessment
process or key aspects of the process for readers who may want to gain an overall
perspective prior to delving into more detailed explanations, also included in this
guide. These summary sections include: synopses of the risk assessment proc-
ess at the beginning and end of Chapter 5; overviews of the many steps involved in
the process in Table 1 and Figure 2 (see Chapter 2); a summary of the issues
raised during the risk assessments and the resolution of these issues in Table 9
(see Chapter 3); a listing and description of all the parameters used in the risk as-
sessment for land application in Appendices A and B; and a summary at the end of
Chapter 4 on the high degree of protectiveness afforded by the Part 503 rule's pol-
lutant limits. Greater detail on the issues raised, their resolution, the determination
of pollutant limits, and the development of the Part 503 rule is provided in Chapters
2, 3, 4, and 5, while answers to commonly asked questions are given in Chapter 6.
To help the reader track discussions this guide, letters have been assigned to each
individual step and issue listed, as shown in Tables 1 and 9 and in the text of Chap-
ters 2 and 3.
The guide's additional chapters include:
• Chapter 2 describes the extensive process that EPA followed to develop and
conduct the risk assessments for biosolids. This description includes a histori-
cal listing and discussion of each of the important steps in developing the risk
assessments.
• Chapter 3 examines some of the key issues that were raised during the risk
assessment process and development of the Part 503 rule and describes how
EPA resolved these issues.
Part 503 Risk Assessment SERA 5
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Chapter 1
• Chapter 4 describes how the risk assessments were conducted, including how
scientific data, assumptions, policy decisions, and methods were used. The
process of developing the algorithms (i.e., the mathematical equations) used
to calculate pollutant limits is discussed, including the different types of pa-
rameters used in the algorithms and the values assigned to these parameters.
Several example calculations are given for various pollutants and exposure
pathways, including a detailed example (for cadmium in Pathway 2 of the land
application risk assessment) that explores how the parameters relate to each
other and examines the influence of the parameters (both individually and col-
lectively) on the biosolids pollutant limits.
• Chapter 5 summarizes the risk assessment process and discusses how the
risk assessment results were used to develop pollutant limits in the final rule.
This chapter also includes brief discussions of how different provisions of the
Part 503 rule are based on, or support, the biosolids risk assessments. It also
provides descriptions of Part 503 provisions that are not risk-based.
• Chapter 6 addresses commonly asked questions about the biosolids risk as-
sessments.
• The Appendices provide additional information used in developing the
biosolids risk assessments and Part 503 rule.
RISK
6 ©EPA Part 503 Risk Assessment
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Chapter 2
The Risk Assessment Process for
the Part 503 Biosolids Rule
The biosolids risk assessment process involved selecting representative
pathways by which humans, animals, and plants could become exposed to
pollutants of concern that can be present in biosolids. Data on exposures
associated with each pathway were combined with data on allowable doses of a
pollutant to develop a limit for that pollutant. The process by which pollutants of
concern and appropriate exposure pathways were selected, as well as the key sci-
entific analyses, deliberations, and policy decisions involved in the biosolids risk
assessment process, are summarized in Table 1 and outlined in Figure 2. The
large letters to the left of each section heading in the text indicate when in the risk
assessment process the step occurred. These letters also are shown in Table 1
(this chapter) and throughout Chapter 3.
Initial List of Pollutants
Step A Biosolids Task Force Study
The biosolids risk assessment process began in 1982 when the Intra-Agency Biosolids
Task Force was established to assess biosolids management approaches nationwide,
evaluate existing regulatory activities, and identify data needs. In 1983 the task force
recommended that a comprehensive regulatory program be developed by EPA under
the authority of Section 405 of the Clean Water Act and other environmental statutes.
The Agency identified several key components for such a program, including:
• Determining pollutants of concern
• Developing risk assessment methodologies
• Determining appropriate risk-based pollutant limits and management practices
• Issuing comprehensive, risk-based regulations (i.e., the Part 503 rule)
Part 503 Risk Assessment «EPA 7
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Chapter 2
' ¦ i,'
Table 1
The Biosolids Risk Assessment and Rule Development Process
Developmental Step
Mechanism Used
Key Features
Step A
Intra-Agency Sludge
(Biosolids) Task Force
Study
Team within EPA worked directly
under the Assistant Administrators to
develop a biosolids management and
regulatory plan
The Task Force worked intensively to develop a
comprehensive plan with input from all •
impacted groups
StcpB
Identification of 200
pollutants
EPA list
Pollutants placed on list based on expected
toxicity
Step C
Selection of SO pollutants
from 200 for further study
Four panels of experts met to
recommend pollutants for land
application (LA), surface disposal
(SD), incineration (I), and ocean
disposal (OD) of biosolids
Selection based on best professional judgment;
likelihood that environmental and human
exposure will occur via LA, SD, I, or OD; known
pollutant toxicity via relevant exposure
pathways; and availability of exposure and
toxicity data
StepD
Initial identification of
exposure pathways for
each use or disposal
practice
Expert panels identified appropriate
exposure pathways for each pollutant
Selection based on best professional judgment
StcpE
Profile assessment and
hazard indices developed
for 50 pollutants
Hazard indices developed with the
assistance of a contractor
Profile assessment and hazard indices based on:
—pollutant toxicity
—pollutant concentration in soil, water, air, food,
and/or biosolids
—worst-case data
—extreme exposure for most exposed individual
(ME1)
StcpF
Selection of pollutants for
detailed risk assessment
Environmental profiles developed
based on results of hazard indices
If hazard indices were 1 or greater, pollutants
were considered for detailed risk assessment and
regulation
Step G
Risk assessment
methodology review
Review by EPA Science Advisory
Board (SAB)
Reviewed algorithms, exposure routes,
assumptions
StepH
Risk assessments for LA,
SD, I, OD for proposed
Part 503 rule
EPA with contractor assistance
—MEI
—conservative models and assumptions
—worst-case data—e.g., salt data for plant
uptake, use of 98th percentile for
non-agricultural (ag) LA
Step I
Published proposed Part
503 rule for comment
Published in the Federal Register,
February 6,1989, for public comment
and external review
5,500 pages of comments received; LA and SD
peer review; incineration review by SAB
Step J
Risk assessments for final
Part 503 rule revised
based on comments;
expert advisors continue
reviews
EPA/advisors met to review and
modify data selection, models used,
data management
—changed from MEI to highly exposed
individual (HEI)
—changed models
—used field data
—developed data management protocol
—combined distributed-and-marketed, ag, and
non-ag LA data
(Continued)
8 <&EPA Part 503 Risk Assessment
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The Risk Assessment Process tor the Part 503 Biosolids Rule
Table 1 (Continued)
Developmental Step
Mechanism Used
Key Features
StepK
National Sewage Sludge
Survey (NSSS)
$1,2 million study involving biosolids
sample collection and analyses, and
questionnaire
Statistically based groups of publicly owned
treatment works (POTWs) (totaling 180) for
biosolids sampling and analysis, and additional
information from 475 POTWs for data on use and
disposal practices, costs, impacts of the proposed
rule, etc.
Information used to evaluate:
—current pollutant concentrations in
biosolids (412 analytes)
—current biosolids use or disposal practices
—impact of rule on current practices
Step L
Published NSSS results
and proposed changes for
final Part 503 rule for
comment
Published in the Federal Register,
November 9,1990, for public
comment and external review
Comments received from 153 respondents;
Proposed alternate pollutant limit concept for
"clean" biosolids
StepM
Revised risk assessments
for final Part 503 rule
EPA with assistance of team of experts
and contractor
Areas of change included:
—protecting HEI rather than ME1
—greater emphasis on field study data
—refined models, data, assumptions
—use of NSSS results
—revised pathways
Step N
Internal EPA review of
draft final Part 503 rule
All EPA offices reviewed rule and
identified issues of concern
Major issues identified:
—biosolids binding
—phytotoxicity
—concerns about ecological risk
—nitrogen management issues
Major risk management decisions;
—use of 99th percentile concentrations from NSSS
—use of agronomic rate for nitrogen
—"clean" biosolids emphasis
Step O
Published final Part 503
rule
Published final rule in Federal Register,
February 19,1993
40 CFR Part 503 with subparts on: general
provisions, land application, surface disposal,
pathogens and vector attraction reduction, and
incineration
StepP
Amendment to rule to
address lawsuits and EPA
revisions to the final Part
503 rule
Published in Federal Register, February
24,1994
Issues:
—land application: molybdenum, cadmium,
chromium pollutant limits; annual pollutant
loading rates (APLR); selenium
—incineration: THC vs. carbon monoxide (CO)
monitoring
Amendments for: certain molybdenum pollutant
limits for land application;
THC/CO—continuous emission monitoring
(Continued)
Part 503 Risk Assessment -&EPA 9
-------
Table 1 (Continued)
Developmental Step Mechanism Used Key Features
StepQ Remanded portions of the Part 503 Undergoing review by EPA as of August 10,1995
rule for modification or further
Rulings on court cases justification; issues included:
—land application chromium limits
—99th-percentile land application
limit for chromium and selenium
—special land application limits for
heat-dried biosolids -
—special selenium limits for land
application on public contact sites
with a low potential for occupancy
Step B Identification of 200 Pollutants
The process of identifying pollutants of concern began in 1984, when EPA devel-
oped for possible consideration a list of approximately 200 pollutants based on the
following types of available data:
• Human exposure and health effects
• Plant uptake of pollutants
• Phytotoxicity (adverse effects on plants)
• Effects in domestic animals and wildlife
• Effects in aquatic organisms
• Frequency of pollutant occurrence in biosolids
Step C Selection of Pollutants by Scientific Experts for
Further Consideration From the List of 200
Pollutants
In 1984 the Agency submitted its initial list of 200 pollutants for review by four pan-
els of experts covering land application, surface disposal, incineration, and ocean
disposal of biosolids. The panels recommended that approximately 50 of the 200
pollutants listed be studied further. The recommended list of pollutants was based
on:
• The probability that the pollutant would be toxic when exposure occurred
through use or disposal of biosolids.
• The likelihood that human and environmental exposure to the pollutant would
occur via land application, surface disposal, incineration, or ocean disposal of
biosolids.
• The availability of toxicity and exposure data for the pollutants.
• Best professional judgment.
10 &EPA Part 503 Risk Assessment
-------
The Risk Assessment Process for the Part 503 BiosoUds Rule
Figure 2
Steps in the Development of the Part 503 Risk Assessment and Rule
1982
EPA establishes Intra-Agency Sludge (Biosolids) Task Force
1982
EPA publishes results of the "40 Cities Study"
1983
EPA Biosolids Task Force presents recommendations, including need for comprehensive *
regulatory program
March 1984
EPA develops list of 200 pollutants
May 1984
Experts select 50 pollutants for further study and identify exposure pathways
1984-85
EPA conducts worst-case hazard profile assessment
1985
Science Advisory Board approves general risk assessment methodology, including
algorithms, exposure routes, and assumptions, but does not check data selection
1986-88
EPA conducts risk assessments protecting MEI, using worst-case data, assumptions, and models
1988
The ocean dumping option is dropped from the rule due to the Ocean Disposal Ban Act of 1988
Feb.1989
EPA publishes proposed Part 503 rule for comment
July 1989
Peer review of Part 503 is conducted; report points out scientific reasons why pollutant limits
in proposed rule are overly stringent and recommends that more realistic limits be
developed
1988-89
EPA conducts National Sewage Sludge Survey (NSSS)
Jan, 1990
A team of experts is established to assist EPA with revision of rule
1990
EPA selects new data, assumptions, and models to use in revising risk assessments
Nov. 1990
EPA publishes NSSS results and possible changes to the proposed rule for public comment
1990-92
EPA conducts revised risk assessments protecting HEI, using field data, and modified
assumptions and models; incorporates comments in NSSS notice
1992
Internal Agency-wide review of Part 503 rule by EPA completed
Nov. 1992
Administrator approves final Part 503 rule
Feb.1993
EPA publishes final Part 503 rule and notices of availability of supporting documents
Feb.1994
EPA publishes an amendment to Part 503 rule
1993-95
EPA identifies 32 additional biosolids pollutants for regulatory consideration by year 2000.
Further analysis may narrow the focus for consideration primarily to dioxins, furans, and
PCBs
1994-95
EPA considers 4 provisions of Part 503 rule remanded by court for modification or additional
justification
1994-95
EPA begins ecological and field monitoring studies on specific issues identified for additional
investigation during development of Part 503 rule
Nov. 1995
Additional ("Round 2") list of biosolids pollutants developed for regulatory consideration by
the year 2000
Dec. 1999
Proposed "Round 2" amended regulation
Dec. 2001
Final "Round 2" amended regulation
Part 503 Risk Assessment «EPA 11
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Chapter 2
Hazard Profiles of the 50 Pollutants
Selected for Further Evaluation
Step D Initial Identification of Exposure Pathways for
Hazard Assessment
A preliminary exposure assessment was conducted to develop "environmental pro-
files" for each of the 50 pollutants. The exposure assessments were based on
"pathways" by which an individual (person, animal, or plant) could be exposed to a
pollutant in biosolids. To determine appropriate exposure pathways, EPA adapted
existing exposure models and developed new ones to represent the movement of
pollutants in the environment arid ultimately to an affected individual. Identification
by experts of the exposure pathways for each use and disposal practice began in
1984 (conducted by a group that included the same experts that recommended fur-
ther evaluation of 50 pollutants, see above). The exposure assessment was
subsequently used to develop the risk assessments conducted for both the pro-
posed and the final biosolids rule.
Step E Profile Assessments of 50 Pollutants
The environmental profile developed for each of the 50 pollutants included a com-
pilation of data on toxicity, occurrence, and fate and effects of the pollutant.
Information on occurrence (i.e., frequency and concentration of pollutants in
biosolids) was obtained from the "40 Cities Study" (described below), which was
considered the best source for such data at the time. Each environmental profile
also evaluated hazards of pollutants associated with particular exposure pathways.
Not all pollutants were evaluated for each pathway because some pathways were
considered unlikely routes of exposure for certain pollutants.
Using a hazard index (Box 2), the environmental profiles evaluated the hazards
for each of the 50 pollutants in biosolids by comparing a pollutant's concentration in
the environment (in soil, plant or animai tissue, water, or air) with established hu-
man health and other regulatory criteria (e.g., acceptable daily intake for a
noncarcinogen, or a cancer risk-specific intake). EPA assumed worst-case condi-
tions in this initial assessment (i.e., maximum exposure of an individual to a
pollutant in its most bioavailable form via the most sensitive route of exposure, as-
suming maximum toxic effect).
Step F Use of the Hazard Profile Process To Select
Pollutants for Detailed Risk Assessment
Selection of pollutants for detailed risk assessment using the hazard indices evalu-
ation involved a two-part process (EPA, 1985). First, all sources of exposure to a
pollutant was considered, including biosolids and background levels of a pollutant
from sources other than biosolids. A hazard index of less than 1 indicated that the
concentration in the environment was lower than the concentration known to be
toxic to the organism being evaluated. It also indicated that the pollutant was not a
hazard to humans, animals, or plants via the pathway being evaluated, even when
factoring in exposures to background concentrations of the pollutant in soil, water,
air, and plants. Pollutant/pathway combinations with hazard indices of less than 1
were dropped from further consideration.
A hazard index value of 1 or greater indicated that a pollutant was potentially toxic.
Each pollutant in this higher-value group was then further evaluated in the second
part of the process, called hazard ranking, by adjusting the index so that it
12 &EPA Part 503 Risk Assessment
-------
The Risk Assessment Process for the Part 503 Biosottcte Rute
Box 2
Calculation and Use of Hazard Index and Hazard Ranking for Biosolids
Hazard Index:, „
... Estimated concentration-in soil, plant or animal tissue, water, or air
* Pollutant hazard nidex = : : ^ .—— r— r ~r '
Lowest concentration toxic to organism being evaluated
1. The hazard index for pollutants in biosolids was calculated by comparing: -- ,
a.) the estimated,concentration of the pollutant in soil, plant or animal tissue, ground water, surface
• • water, or air (based on the' "40 Cities Study" data oh pollutant concentrations'in biosolids and on
pollutant transport and fate data) to: _
b.) ^ the lowest concentration of a pollutant shown to be toxic to the organism being evaluated (as
indicated by available scientific .data) via the most sensitive "route of exposure (i..e., ingestion,
inhalation, or injection) while,assuming maximum toxic effect.
2. ; Pollutants with hazard index values of less than 1 for "worst-case" conditions via certain pathways were not
. , analyzed further for that pathway because a value of less than i indicated that the pollutant was not toxic to
the organism. For example:
" • Lindane (Soil Biota Predator Toxicity):
- ' , ' • " , I\xUB 0.129950x1.05 nnnn^nn'
- Index = = —a—— = 0.,002728
where: . Ii = Concentration of pollutant in biosolids-amended soil (^tg/g dry .weight [DW])
. i ' . , - UB, Uptake factor of pollutant in soiL biota (jigf pollutant/g (issue DW [(^g pollutant/g soil
1 ' TR v= - Feed concentration toxic to predator (fig pollutant/g tissue DW) ' • . .'
3. Pollutants with hazard index values of 1 or greater for certain pathways were considered to be potentially
toxic and ws:re further evaluated (unless the circumstances did not warrant further study, predominantly
' - - because the data were iivsufficient). For example: '
. Lindane (Human Cancer Risk Resulting from SoiI Ingestion [toddler]):
V V; • UixDS)+DI, 0.129950.+.2.71 • •
¦ 0.053. r6^}52' ¦ '¦
where: la = Concentration of pollutant in sludge-amended soil (ug/g DW)
- . DS = Assumed amount of soil in human diet (g/day)''
DI =- Average daily human dietary intake of pollutant (tig/day)
- . -> "RSI = , Cancer risk-specific intake (ug/day) • c "
DW .= , Dry weight , . _ ; ,* . \ - ... , -
Hazard Ranking:
4. Pollutants with hazard index values of 1 or greater were then evaluated to determine what portion of
the hazard associated with a pollutant was attributable to its presence in biosolids. After adjustment-
- (i.e., subtraction of background values so that pollutant exposure from sources other than biosolids were
excluded from the rankings), indices for-each of the pollutants were ranked (i.e., less than l;.l to 100; 100 to
1,000; and greater than 1,000). Higher rankings indicated greater potential risk from pollutants in biosolids.
Ultimately, all hazard index ranlcings of 1 or greater received addditional evaluation. (Note: Background
pollutant concentrations were considered in the exposure calculations for organisms during the risk ' .
assessments for both the proposed'and the final Part 503 rule.) '
5. If the portion of a pollutant's hazard attributable to biosolids resulted in'a hazard ranking of less than 1, the ¦
pollutant was not analyzed further.
6. Pollutants with hazard rankings of greater than I were evaluated in the risk asessments conducted for
biosolids use or disposal practices, with the exception of fluoride, iron, and pollutants deferred due to
insifficient data (see text).
Part 503 Risk Assessment oEPA 13
-------
Chapter 2
reflected only the pollutant's hazard attributable to biosolids. This adjustment was
made by excluding background exposures to the pollutant from sources other than
biosolids. The remaining value indicated impacts from pollutants in biosolids only.
The adjusted hazard indices then were ranked into one of the four hazard ranking
groups—ranging from less than 1,1 to 100,100 to 1,000, and greater than 1,000—
for the purpose of evaluating those pollutant indices with the highest score first.
The weighted scores, however, were not used. Instead, all pollutant/pathway com-
binations with hazard rankings of 1 or more were evaluated in more detail (as
discussed below and in Box 2), while pollutant/pathway combinations with indices
of less than 1 were eliminated from further consideration.
All pollutant/pathway combinations assigned a hazard ranking of 1 or greater in the
environmental profile process were selected for evaluation in the detailed risk as-
sessments for biosolids, with the exception of fluoride and iron (discussed in
Chapter 3) and pollutants for which further evaluation was deferred because of in-
sufficient data. This process resulted in narrowing the list of pollutants to 22 for
assessing risks from land application of biosolids, 16 for surface disposal, and 14
for incineration (see Table 2). Several additional pollutants were added or deleted
from further analysis, as indicated in Table 3.
Some pollutants were not evaluated for all use or disposal practices (i.e., land ap-
plication, surface disposal, incineration) because different practices may result in
different routes of exposure and different potential risks from the same pollutant.
For example, a pollutant might be toxic if a person inhales it from the air near a
biosolids incinerator, but not be toxic if consumed in a crop grown on soil where
biosolids were used as a fertilizer.
Risk Assessments Conducted for the
Proposed Part 503 Rule
Step G EPA Science Advisory Board Review of Risk
Assessment Methodology for the Proposed Rule
The methodologies used for the risk assessments conducted as a basis for the
Part 503 proposed rule were reviewed and approved by EPA's Science Advisory
Board (SAB). It is important to note that the review of the risk assessment method-
ologies by the SAB did not include the data used for the algorithms because this
information was not available at that time. Algorithms are mathematical equations
used in a risk assessment model to relate various relevant parameters (e.g., of ex-
posure and dose response) for pollutants in applicable pathways. For the biosolids
risk assessments, the algorithms ultimately were used to identify pollutant limits. Al-
gorithms are discussed in detail in Chapter 4.
Step H Risk Assessments for Proposed Part 503 Pollutant
Limits
Based on the SAB's favorable review of the risk assessment methodologies, EPA
conducted separate risk assessments for land application, monofilling, and incin-
eration of biosolids using toxicity and exposure data available at that time. Although
a risk assessment methodology for ocean disposal of biosolids was developed and
reviewed by the SAB, a risk assessment for this biosolids disposal practice was not
conducted once the Ocean Disposal Ban Act of 1988 prohibited this disposal practice.
EPA conducted the initial biosolids risk assessments using highly conservative as-
sumptions and worst-case exposure data in an attempt to ensure protection of
public health and the environment. The conservative approach was adopted
14 SEPA Part 503 Risk Assessment
-------
The Risk Assessment Process for the Part 503 Biosolids Rule
because a court-ordered schedule limited the time available to conduct the risk as-
sessments and then develop the rule.
Factors of Importance in the Risk Assessments for the Proposed Part 503
Rule: Some of the key factors and conservative assumptions and approaches
used in the biosolids risk assessments conducted for the proposed Part 503 rule
are presented below. Many of these factors were the subject of lengthy scientific
and policy deliberations (as discussed in Chapter 3) and, subsequently, were
reevaluated and revised in the risk assessments conducted for the final Part 503
rule (as discussed later in this chapter). The key factors in the risk assessments for
the proposed Part 503 rule included:
• How Organisms Are Exposed: Different exposure pathways (the ways in
which people, animals, and plants can become exposed to pollutants in
biosolids) were evaluated for agricultural land application, non-agricuitural land
application (i.e., forests and reclamation sites), distribution and marketing, sur-
face disposal, and incineration of biosolids. All use or disposal practices
except for non-agricultural land application and surface disposal (monofilis)
were evaluated by formal scientific exposure assessments (use of algorithms).
(Much of the data, assumptions, models, and endpoints used in the risk as-
sessments for the proposed rule were refined or changed for the final Part 503
risk assessments.)
• 98th-PercentHe Approach: A 98th-percentile (policy-based) approach was
used by EPA to develop pollutant limits for biosolids applied to non-agricultural
land and placed on a surface disposal site. The 98th-percentile pollutant con-
centrations were calculated based on data from the "40 Cities Study" and were
used as "ceilings" for allowable pollutant concentrations in biosolids for the
proposed regulation. (Changed to the 99th-percentiie for the final rule risk as-
sessments.)
• Who Is at Risk: Two types of risk were chosen for evaluation—individual and
aggregate risks:
- Individual risks were evaluated for the "most exposed individual" (MEI)
for each pollutant and pathway. For humans, this MEI was the most
sensitive individual being continuously exposed over a 70-year lifetime
to a pollutant at its maximum concentration in a given pathway. For
plants and animals, the MEI was the most exposed or most sensitive
species exposed over its critical life period to the maximum pollutant
solubility, bioavailability, and/or concentration. (Changed to the highly
exposed individual [HEI] for the final rule risk assessments.)
- An aggregate risk assessment was conducted to determine the bene-
fits of the regulation in terms of numbers of cancer cases avoided in the
population nationally, as required in the Regulatory Impact Analysis for
the Part 503 rule. The aggregate risk assessment multiplied the risks to
individuals (as described above) by the estimated number of individuals
exposed to determine the number of cases avoided. The aggregate risk
assessment was not used as a basis for determining pollutant limits or
management practices in the final Part 503 rule.
• Quantifying Health Effects: Conservative criteria, such as risk reference
doses (RfDs) and cancer potency values (q-,*s), among others, were used in
algorithms for calculating pollutant exposure limits (see Box 3). (Retained for
the final rule risk assessments.)
Part 503 Risk Assessment SEPA 15
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• Chapter 2
Table 2
Pollutants Remaining After Hazard Index, Hazard Ranking, or Deferral
Land Application8
Surface Disposalb
Incineration
Pollutants Evaluated
Hazard
Index
Hazard
Ranking6
Deferral
(yes =
not
deferred)4
Hazard
Index
Hazard
Ranking
Deferral
(yes =
not
deferred)
Hazard
Index
Hazard
Ranking
Deferral
(yes =
not
deferred)
Aldrin/Dieldrin
yes
yes
yes
e
—
—
yes I'
yes ,
yes
Arsenic
yes
yes
yes
yes ¦
no
NAf
yes
yes
yes
Benzene
—
—
—
yes ';
yes,
fe s- ,
yes
no
NA
Benzo(a)anthracene
no
no
deferred
—
—
—
yes
no
deferred
Benzo(a)pyrene
yes
yes
yes
yes.
yes 7"
yes
yes
yes ,
y^:
Bis(2-ethylhexyl) phthalate
yes
no
deferred
yes
yes
yes •
yes ¦¦
yes
yes
Beryllium
—
—
—
—
—
—
yes,, '•
yes" "
yes
Cadmium
yes
yes
yes
yes •
no
NA
yes
yes
yes'*
Carbon tetrachloride
—
—
—
—
—
—
yes_
yes- ' .
yes
Chlordane
yes
yes
yes
yes..;. •
yes . v.V
yes
yes
yes
Chloroform
—
—
—
—
—
—
yes
yes
yes .
Chromium
yes
yes
yes
yes
no
NA
yes
yes
yes" ;
Cobalt
yes
no
deferred
yes ;
no
deferred
—
—
—
Copper
yes
yes
yes '
-yes.;
yes
yes.
—
—
—
Cyanide
no
no
NA
yes, . .
yes
yes
no
no
NA
DDT/DDE/DDD
yes
yes
yes
yes/-;:..
yes ¦
yes
yes:,;';'
no
NA
2,4-Dichloro-phenoxyacetic
acid
—
—
—
yes;;;::
no
NA
no
no
NA
Dioxins
—
—
deferred
—
—
deferred •
no
no
deferred
Fluoride
yes
yes
yes
—
—
—
—
—
—
Furans
—
—
deferred
—
—
deferred
no
no
deferred
Heptachlor
yes
yes
yes
—
—
—
yes
no
NA
Hexachlorobenzene
yes
yes
yes
—
—
—
—
—
—
Hexachlorobutadiene
yes
yes
—
—
—
—
—
—
—
Iron
yes
yes
yes .
—
—
—
—
—
—
Lead
yes
yes
yes
yes,;.:"y
yes
yes
yes;;;
yes
yes
Lindane
yes
yes
yes
yes
yes
yes; ,
yes
no
NA
Malathion
—
—
—
yes
no
NA
no
no
NA
Mercury
yes
yes .
yes
yes;; -
.yes'1'' ,Jy
yes
ye5,t"„V:
no
NA
Methyl ethyl ketone
—
—
—
no
no
deferred
—
—
Methylenebis(2-chloro-)
aniline
yes
no
deferred
—
—
—
—
—
—
Methylene chloride
no
deferred
yes
no
deferred
no
NA
Molybdenum
yes
yes
yes
yes ..
no
no
—
—
—
(Continued)
16 >3-EPA Part 503 Risk Assessment
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The RiskAssessment Process for the Part 503 Biosolids Rule
Table 2 (Continued)
Land Application®
Surface Disposal
b
Incineration
Pollutants Evaluated
Hazard
Index
Hazard
Rankingc
Deferral
(yes =
not
deferred)*1
Hazard
Index
Hazard
Ranking
Deferral
(yes =
not
deferred)
Hazard
Index
Hazard
Ranking
Deferral
(yes =
not
deferred)
Nickel
yes;
yes'
yes.
yes ,
yes, '
yes
yes ,4,
yes v *
yes,
n-Nitroso-dimethylamine8
yes, ^
no
NA
yes^ I
yes
yes *
—
—
—
Polychlorinated biphenyls
(PCBs)
yes •"
yes'\ ^, r
yes.
yes
ft- <> '
yes
yes ••• ¦
yes 7
yes
* *
yes
Pentachlorophenol
no
deferred
—
—
no
no
NA
Phenanthrene
—
—
—
yes
no
deferred
yes';
no
deferred
Phenol
—
—
—
—
—
—
no
no
NA
Selenium
yes
yes, . „
yes
—
—
—
—
—
—
Tetrachloroethylene
—
—
—
—
—
—
yes
no
NA
Toxaphene
ves
yes f
yes*/ , "
yes
yes
yes- ' «•*
yes; "
y«s.v, ^
yes * " *" :
Trichloroethylene
no
no
NA
—
—
—
no
no
NA
Tricresyl phosphate
lyes
no
deferred
—
—
—
—
—
—
Vinyl chloride
no
no
NA
no
no
NA
yes"
no
deferred
Zinc
ye'S-:
yes "
yes
yes ** •
no
NA
yes
no
NA
includes land application and distribution and marketing; for later risk assessment, these two categories were combined.
bSurface disposal was evaluated as "Landfilling" in the Hazard Index/Ranking.
cPollutants remaining after the hazard ranking had a hazard index/ranking >1 and were included in the Part 503 risk assess-
ment. Pollutants with a hazard index/ranking of <1 were excluded from further analysis, except as discussed in Table 3.
dSome pollutants were deferred after the hazard index/hazard ranking process due to lack of data; pollutants marked "yes" re-
mained for further analysis.
e— = not evaluated for that use or disposal practice.
fNA = deferral not applicable because hazard ranking indicated that pollutant did not pose a hazard (for exceptions, see Table 3).
gAlso known as dimethyl nitrosamine.
• Acceptable Level of Cancer Risk From Potentially Toxic Organic Pollu-
tants: Risks at 1 x 10"4 (1 case of cancer in a population of 10,000), 1 x 10"5
{1 case in 100,000), and 1 x 10~6 (1 case in 1,000,000) were evaluated. For
the proposed Part 503 regulation, EPA made a policy decision to regulate risk
at 1 x 10"4 for land application and surface disposal and at 1 x 10 for incin-
eration. (The cancer risk level for incineration was changed to 1 x 10"4 for the
final rule risk assessments.)
• Type of Data Used: Worst-case plant uptake data were used in the risk as-
sessments for the proposed rule. The worst-case data came predominantly
from greenhouse pot studies and studies using metal salts. The use of data
from biosolids field studies was limited. (This was changed to the use of pre-
dominantly field study data for the final rule risk assessments.)
• Linearity Assumption for Plant Uptake of Inorganic Pollutants: EPA used
the conservative assumption that plant uptake of inorganic pollutants is linear
(i.e., that crops take up a pollutant in a manner that is directly proportional to
the amount of pollutant in biosolids applied to land). (Retained for the final rule
risk assessments.)
Part 503 Risk Assessment 4»EPA 17
-------
Chapter 2
Table 3
Pollutants Added or Deleted From Evaluation After Hazard Index/Ranking Completed
Pollutant
Added or Deleted
Reason
Benzene
Added for:
land application
Evaluated with additional exposure pathways
incineration
Regulated as total hydrocarbon (THC) operational
standard
Bis(2-ethylhexyl) phthalate
Added for land application
Evaluated with additional exposure pathways
Cadmium
Added for surface disposal
Additional data available, and for consistency with
land application risk assessment
Chromium
Added for surface disposal
Additional data available, and for consistency with
land application risk assessment
DDT/DDE/DDD
Added for incineration
Regulated as THC operational standard
Dioxins
Added for incineration
Regulated as THC operational standard
Fluoride
Deleted for land application
Limited data indicating toxicity
Furans
Added for incineration
Regulated as THC operational standard
Heptachlor
Added for incineration
Regulated as THC operational standard
Iron
Deleted for land application
Limited data indicating toxicity
Lindane
Added for incineration
Regulated as THC operational standard
Mercury
Added for incineration
Regulated through NESHAPS3 standard
n-Nitroso-dimethylamine
Added for land application
Evaluated with additional exposure pathways
Trichloroethylene
Added for land application
Evaluated with additional exposure pathways
"NESH APS = National Emissions Standards for Hazardous Air Pollutants
• Food Consumption: EPA used conservative dietary data to determine human
exposure to pollutants in biosolids through food consumption. The risk assess-
ment used the highest daily consumption rate of each of eight food groups
(e.g., consumption of dairy products by the teen-age male) to calculate risk to
humans from consuming plant or animal products grown or raised on soils to
which biosolids were applied. (Refined for the final rule risk assessments.)
• Pollutant Transport: Particularly conservative models were used for predict-
ing pollutant transport into ground water, surface water, and air. (Refined for
the final rule risk assessments.)
• Organic and Inorganic Pollutants: Potential risks from both organic and inor-
ganic pollutants were assessed. (Retained for the final rule risk assessments.)
• The "40 Cities Study": During the initial risk assessment process, the primary
source of information on the presence and concentration of pollutants in
biosolids evaluated in the risk assessments for the proposed Part 503 rule was
the "40 Cities Study," published in 1982 (U.S. EPA, 1982). This study did not
reflect the quality of biosolids used or disposed at the time of the proposed
rule (1989) because:
- The study included primarily data on biosolids in various stages of treat-
ment at publicly owned treatment works (POTWs) prior to final
processing, rather than data on final, processed biosolids leaving
POTWs that were used or disposed.
18 &EPA Part 503 Risk Assessment
-------
The Risk Assessment Process for the Part 503 Biosoiids Rule
Box 3
Quantifying Cancer and Noncancer Effects: Qi*s and RfDs
For many analyses conducted for the biosoiids risk assessments, EPA used cancer potency values (qj*s), or'
' rist reference doses/coneentratioris (RfDs/RfCs) to measure- toxic human' effeete/as-deseribed below..Both • ,
q^s and RfDs/RfCs are conservative measures because they predict greater impacts on human health than
. are likely to actually occur and because both values assume exposure for an entire lifetime (70 years). Qj*s or
RfDs were used in the biosoiids risk assessments to calculate the concentration of pollutant in biosoiids that
¦ is reasonably protective against adverse impacts.
Cancer Effects: Qj*s
Cancer potency values (q-f s) were used to quantify human cancer in the risk assessments for biosoiids. A t]j*
represents the'dose at which an exposed individual would be expected to get cancer (i.e., the relationship be-
tween a specific dose of a carcinogenic [cancer-causing] substance and its associated degree of risk). The
• degree of risk (i.e., 1 x 10 ) is a policy decision made by the Agency that indicates, an acceptable degree of
cancer risk for the most exposed person, based on that person's continual exposure at'that dose for a lifetime
(e.g., 70 years). In evaluating cancer risks, EPA conservatively assumes that any exposure to a carcinogen pro-
duces a measurable risk'- The qj* is a "bounding" (upper-limit) estimate; the true risk to humans is not likely
" to exceed the q^/and probably is lowe£ Qj*s are based on data for the most sensitive animal as well as on
conservative.(i.e., linear) extrapolation from high doses (used in laboratory experiments) to low doses (repre-
sentative of actual human exposure). Q-|*s for specific pollutants are listed in EPA's computerized Integrated,
Risk Information System (IRIS) data base, which can be accessed through the National Library of Medicine.
Noncancer Risks: RfDs/RfCs
Reference dose (RfD) or referettce concentration (RfC) values were used in the biosoiids risk assessments to
indicate health effects other than cancer from exposure to Inorganic pollutants in biosoiids. RfDs/RfCs are
conservative estimates of the amount of a chemical that can be consumed daily without appreciable risk of ill
effects during a lifetime. Thus, these values identify "thresholds" for noncancer health effects; no such thresh-
old was identified for cancer risks discussed above because any dose of a carcinogen is assumed to be
capable of producing a carcinogenic effect. Conservative safety factors ranging from 10 to-10,000 are incorpo-
rated into RfDs/RfCs to addr.ess areas of uncertainty such as extrapolation from short-term to long-'term
exposure, interspecies sensitivity, and variation in sensitivity in humans. Like q1 % RfDs/RfCs are listed in
EPA's IRIS data base. The Clean Water Act requires that EPA protect against reasonably anticipated adverse
effects of each regulated pollutant in biosoiids. For example, the chosen RfD for cadmium protects against re-
nal tubular proteinuria.
- The study was designed to trace the fate of toxics in POTWs that had
received significant volumes of industrial wastewater discharge (and
thus potentially high concentrations of pollutants in resulting biosoiids).
- Many POTWs have initiated pretreatment programs since 1978, result-
ing in cleaner biosoiids.
- Wastewater treatment processes have changed over time.
- Advances in analytical procedures since the "40 Cities Study" allow for
more accurate analyses of pollutants in biosoiids.
Realizing the limitations of the "40 City Study," EPA conducted a much more
representative evaluation of biosoiids from POTWs across the United States
(and pollutants in those biosoiids) via a National Sewage Sludge Survey
(NSSS). (NSSS data were used to help develop tjae final rule.)
Based on the results of the initial risk assessments and numerous policy decisions
described above, EPA developed and published the proposed Part 503 rule for
public comment in the February 6,1989, issue of the Federal Register.
Part 503 Risk Assessment &EPA 19
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Chapter 2
Comments on the Proposed Part 503
Rule and EPA's Response
Step I Public Review and Comment on the Proposed
Part 503 Rule
EPA proposed the Part 503 rule on February 6, 1989 (54 FR 5746), seeking com-
ment and additional data for improving the rule. Many different types of reviews
were undertaken that resulted in more than 5,500 pages of comments received by
the Agency. Some of the most extensive comments were received from expert peer
review groups established by the Agency that included representatives from acade-
mia; federal, state, and local government agencies and research centers; and
environmental organizations.
One of the expert peer review groups was organized by the U.S. Department of
Agriculture's (USDA's) Cooperative State Research Service Technical Committee
W-170 to assess the technical basis of the proposed rule for land application, distri-
bution and marketing, monofilling, and surface disposal. This review group, called
the Peer Review Committee (PRC), identified a number of deficiencies and recom-
mended changes in the data, assumptions, and models used for the risk
assessments. The PRC recommendations (USDA/CSRS, 1989) are listed in Table 4.
A second expert peer review group was assembled by the SAB to review the tech-
nical basis for the proposed incineration rule. This group's recommendations and
findings (U.S. EPA, 1989a) are listed in Table 5.
Step J EPA Analysis of Comments on the Proposed Rule
and Revision of the Risk Assessments
EPA performed an extensive analysis of the comments received and undertook a
series of actions in response to the comments. Perhaps one of EPA's most impor-
tant actions was to assemble a team of experts (Appendix C) with extensive
research and experience related to the issues raised by the PRC and a number of
the other commentors.
The team of experts met a number of times over 3 years to provide EPA with
recommendations for improving the risk assessments, including the data, models,
and assumptions that should be used. The team helped assemble and tabulate the
available relevant data, advised EPA on the proper use of these data, and helped
revise the models and assumptions used in the risk assessments. The experts
recommended a number of significant changes to the proposed Part 503 rule.
These changes were announced along with the results of the NSSS, both of which
are described in the following section. EPA has continued to benefit from the assis-
tance provided by members of this team during internal review and promulgation of
the final rule and in explaining the risk assessment process at numerous meetings
both in the United States and abroad.
Step K The National Sewage Sludge Survey
EPA conducted the NSSS in 1988 and 1989 to obtain a current and reliable data
base on biosolids quality and management that could be used to help develop the
. final Part 503 rule. The NSSS included an analysis of 412 analytes in samples of
* biosolids from 180 POTWs as well as analysis of questionnaire information on use
or disposal practices from 475 POTWs with secondary or more advanced waste-
water treatment. The resulting national estimates of pollutant concentrations in
20 SEPA Part 503 Risk Assessment
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The Risk Assessment Process for the Part 503 Biosolids Rule
biosolids, quantities of biosolids generated, and biosolids treatment, practices, and
related costs permitted a more accurate assessment of the level of risk posed by
current biosolids quality and use or disposal practices.
Step L Publication of the NSSS Results and Proposed
Changes for the Final Part 503 Rule
Upon completion of its analysis of review comments on the proposed Part 503 rule
and the NSSS findings, EPA considered making a number of changes to the Part
503 rule. These changes were published along with the results of the NSSS in the
November 9, 1990, issue of the Federal Register (55 FR 47210-47283) and enti-
tled National Sewage Sludge Survey: Availability of Information and Data, and
Anticipated Impacts on Proposed Regulations. The NSSS results indicated that
pollutants exist at relatively low levels in today's biosolids, and the proposed
changes to the rule reflect these results. The findings in that publication are dis-
cussed in more detail below.
NSSS Results: The NSSS results were significantly different from previous esti-
mates of pollutant concentrations in biosolids. Concentrations of heavy metals,
including cadmium, chromium, lead, nickel, zinc, beryllium, and mercury, were
found to be substantially lower than previous estimates. In particular, lead concen-
trations were found to be only about 40 percent as high as previously estimated.
Concentrations of most chlorinated organic pollutants also were confirmed to be
low. Problems with limits of detection in the NSSS were overcome for the most part
via a statistical procedure called maximum likelihood estimation for multiple cen-
sored points.
Biosolids samples also were analyzed for polychlorinated biphenyl (PCB) conge-
ners. No detectable levels of PCB congeners 1016, 1221, 1232, or 1242 were
found in any of the 198 tested samples. The remaining congeners—PCB 1248,
1254, and 1260—were found to be above the minimum detectible level in about 10
percent of the biosolids samples.
The national estimates of pollutant concentrations from the NSSS are considered
appropriate and essentially unbiased statistically (except for PCBs, which differ
from other pollutants in that they do not show a log normal distribution). The esti-
mates were found to be statistically sound for several reasons:
• The surveyed POTWs were selected from all POTWs with secondary treat-
ment identified by the 1986 Needs Survey, the most complete listing available.
• The POTWs included in the NSSS were selected to equally represent each of
four representative POTW size ranges.
• Analytical protocols used to measure the concentration of pollutants in NSSS
samples were specifically adapted for the biosolids matrix.
• While the wide differences in percent solids in the different biosolids samples
analyzed resulted in detection limit problems, the statistical method used to in-
corporate sample results that were below the detection limit (known as the
maximum likelihood estimation for multiple censored points technique) re-
duced the bias associated with more commonly used estimation procedures.
The NSSS results, particularly those indicating that concentrations of metals in
biosolids were lower than estimated by the "40 Cities Study," were used in impor-
tant ways to revise the final Part 503 rule. For example, the results provided a
basis for (1) excluding organic pollutants from the final Part 503 rule, (2) develop-
ing low pollutant concentration limits for minimally regulated biosolids, and (3)
establishing 99th-percentile ceiling concentration limits, as discussed later in this
chapter.
Part 503 Risk Assessment oEPA 21
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Chapter 2
Table 4
Peer Review Committee Recommendations Concerning the Part 503
Proposed Rule Risk Assessment (USDA/CSRS, 1989)
The Peer Review Committee (PRC) recommended that EPA revise and repropose the Part 503 rule after re-
vision and correction of the risk assessment methodology. The recommended revisions included more
realistic most exposed individuals (MEIs) and models, inclusion of "clean" biosolids, site-specific consid-
erations, and careful selection and use of relevant data. The PRC recommended specifically that EPA
should:
• Enlist working groups consisting of experts in biosolids, risk assessment, and modeling to help re-
view the data, revise the scenarios and models, and obtain more realistic pollutant limits.
• Use risk assessment procedures that lead to best estimates and uncertainty bounds rather than calcu-
lating upper bound estimates. At a minimum, the MEI should be replaced with an approach that
considers exposure situations that are reasonable and that may exist in the United States.
• Use biokinetic models to obtain realistic estimates of absorption, translocation, and excretion of
pollutants.
• Use realistic dietary scenarios in calculating food-chain inputs of pollutants in biosolids to humans.
• Use sensitivity analysis to identify the most critical parameters in risk/exposure computations and
make efforts to obtain reliable and realistic estimates for these parameters.
• Adhere to normal scientific practices in the use of the number of significant figures when making cal-
culations.
• Use results of field studies involving additions of biosolids rather than results of green house or pot
studies involving additions of metal salts or pure organic compounds.
• Use field data to establish Lowest Observed Adverse Effect Levels (LOAELs) or No Observed Ad-
verse Effect Levels (NOAELs) as a basis for calculating pollutant limits.
• Expand the proposed rule to include consideration of potential iron and fluoride toxicity.
• Develop the concept of a "clean" biosolids that allows for minimal regulation.
• Avoid regulating all distributed and marketed (D&M) products as biosolids.
• Require labeling of D&M products to provide consumer information on proper use of the products.
• Drop the MEI scenario for D&M products, a concept that assumes a rural nonfarm family grows 60
percent of their fruit and vegetables in a D&M biosolids-amended home garden for a 70-year lifetime.
• Prepare and address different categories for non-agricultural and D&M practices.
• Exempt from the rule compounds banned from use in the United States that have been shown to pose
insignificant risk (e.g., lindane, chlordane, PCBs, hexachlorobutadiene). This action would be consis-
tent with the screening approach used by EPA (i.e., Environmental Profile and Hazard Indices) to
eliminate low priority pollutants from consideration.
• Develop more realistic data bases, assumptions, and risk exposure models consistent with results
from field studies using biosolids-applied PCB, and perform detailed reevaluation and analyses of
the PCB pathways.
• Use two distinct frameworks to assess risk for non-agricultural land:
— Exposure and significant future conversion very low
— Exposure more likely or conversion more probable
• Allow for exception to the 5-year conversion period in non-agricultural land application on a case-by-
case basis.
• Drop 98th-percentile approach.
22 &EPA Part 503 Risk Assessment
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The Risk Assessment Process for the Part 503 Biosottds Rule
Table 4 (Continued)
• Continue the approach of separating the vector attraction reduction requirements from the pathogen
reduction requirements in the proposed regulation.
• Regulate pathogens on a risk-based approach. In the interim, the existing requirements in 40 CFR 257
should be maintained.
• Replace the air dispersion model with a more realistic model, such as that used for the EPA solid
waste incineration program.
• Adopt a consistent approach for including volatile compounds (e.g., benzene and trichloroethylene)
in models used to predict air and ground-water transport.
• Exclude from the rule chemicals that the Agency assumes to be lost from biosolids during processing
and that are not present in the biosolids in significant amounts.
• Discontinue use of the CHAIN model in SLAPMAN and SLUDGEMAN to model contaminant trans-
port in the unsaturated zone and replace with a more appropriate model, such as PRZM, RUSTIC, or
LEACHM.
• Convert output from the unsaturated zone transport model to input for the AT123D saturated zone
transport model in such a manner that satisfies conservation of mass.
• Use realistic, site-specific geologic, hydraulic, and chemical parameters as inputs to computer simula-
tions of contaminant transport.
• Differentiate between trench and area monofills because of the different potential for leaching from
these types of monofills.
• Modify the proposed definition of surface disposal to reflect the operational difference between stor-
age with no intent for further management and storage as an essential component in an overall
biosolids management scheme.
• Avoid requiring methane monitoring at surface disposal sites where biosolids are applied at high
rates to the soil surface.
• Establish acceptable analytical methodologies and limits of detection for regulated biosolids pollu-
tants.
• Define the limit of detection (LOD) as the lowest concentration that can be determined to be signifi-
cantly different from a blank for an analytical test method and sample matrix.
• Replace the sum of individual limits of detection for multiple pollutant categories (e.g., PCBs) with
the highest level of detection for any individual parameter in the multiple parameter set.
• Develop a consistent method to use data that are reported as less than the limit of detection.
• Consider a POTW reporting a limit of detection less than or equal to the acceptable limit of detection
to be in compliance with any EPA concentration-based pollutant limit derived from that limit of de-
tection,
• Allow the use of zero concentrations from biosolids pollutant data below the limit of detection for
laboratories meeting the Agency's analytical standards.
Proposed Changes to the Part 503 Rule:
Some of the changes listed in the Federal Register notice were:
• Domestic Septage: A less complex and more easily implementable regulatory
approach that would remain protective of public health and the environment.
• Organic Emissions From Biosolids Incinerators: An operational (i.e., tech-
nology-based) standard rather than risk-based limits.
Part 503 Risk Assessment &EPA 23
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Chapter 2
Table 5
Science Advisory Board Recommendations Concerning the Part 503 Regulatory Approach
for Incineration of Biosolids (U.S. EPA, 1989a)
Based on its review of the proposed Part 503 rule's approach for regulating incineration of biosolids, the Sci-
ence Advisory Board (SAB) recommended:
• EPA has the scientific basis for developing enforceable operational standards (rather than risk-based
standards) for organic pollutants that would provide incentives for improving incineration technology
and pollution control equipment. Risk-based standards are not recommended because of the wide range
of uncertainties in the risk analysis used for biosolids incineration.
• EPA should undertake and support epidemiological research to determine the incidence of adverse health
effects in populations residing near existing incineration facilities.
Further, the SAB commended EPA's Office of Water in attempting to develop a risk-based regulation for sew-
age sludge incinerators. Based on its review of the proposed Part 503 rule's approach to regulating
incineration of biosolids, however, the SAB identified several uncertainties associated with the risk analysis
that precluded risk-based regulation, including:
• Numerous safety factors were used in the analysis. While each individual factor appears reasonable, the
multiplicative use of a series of such factors made the final number unreasonable.
• The methodology did not explicitly assign a measure of uncertainty or confidence to the calculations, but
rather a single risk number was used.
• Use of total hydrocarbons (THCs) as a direct indicator of risk is not possible due to the uncertainties asso-
ciated with field implementation of hot flame-ionization detector (FID) systems and the lack of a direct
link between THCs, as measured by FID, and the total spectrum of organics that might be emitted from
sewage sludge incinerators. In addition, it has not been demonstrated that hot FID systems can operate
continuously in the stack gas environment of sewage sludge incinerators. Thus, it is not appropriate to
propose regulations that will demand such operation for compliance.
• THC measurements may at best indicate the combined performance of combustion and air quality control
devices, but how these measured concentrations at the stack relate to environmental concentrations of
carcinogens remains unknown.
• Non-agricultural Land Application of Biosolids; Use of exposure pathway
analyses rather than a 98th-percentile approach to establish numerical pollu-
tant limits for ali non-agricultural land application practices, including forest
and range lands, soil reclamation sites, and public contact sites (e.g., parks,
golf courses).
• Surface Disposal of Biosolids: Use of a risk-based exposure assessment
approach, similar to the one used for monofills in the proposed rule, rather
than a 98th-percentile approach.
• Agricultural Land Application of Biosolids: Numerous revisions were con-
sidered regarding selection of appropriate target organisms, exposure
pathways, transport models, and data, including use of:
- More realistic assumptions that would protect an HEI rather than .an MEI
for each pathway.
- New models for aquatic pathways.
- More plausible dietary data.
- Updated and more relevant plant uptake and phytotoxicity data from
field studies of biosolids-amended soils.
- "No effect" and non-detection data to establish pollutant limits based on
No Observed Adverse Effect Levels (NOAELs) or Lowest Observed Ad-
24
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The Risk Assessment Process for the Part 503 Biosolids Rule
verse Effect Levels (LOAELs) where appropriate, based on results from
numerous studies on phytotoxicity and bioavailability.
- New calculations for the fraction of food derived from biosolids-
amended soils.
- Field measurements for the consumption of biosolids or soils by grazing
livestock.
- Revised rate of soil consumption by children.
• 50 Metric Tonnes per Hectare Limit Proposed dropping of the requirement
to limit the land application rate to 50 metric tonnes per hectare {mt/ha) in the
proposed rule because the use of newer models allowed higher than 50 mt/ha
application rates to be calculated in the risk assessments.
• Combining Land Application Pollutant Limits: Use of only one set of
pollutant limits for biosolids that were distributed and marketed or applied to
agricultural or non-agricultural land.
• Use of the Most Limiting Pathway To Set Pollutant Limits: Selection of the
most limiting exposure pathway to set the limit for each pollutant.
Step M Revised Risk Assessments Conducted for the
Final Part 503 Rule
In response to the extensive public and scientific peer review comments received
on the proposed rule and the information obtained from the NSSS, EPA (working
closely with internationally recognized experts) revised some of the data, models,
and assumptions used in the risk assessments for biosolids. Some of the key revi-
sions, summarized in Table 1 and discussed in more detail in Chapter 3, included:
• Reassessment of Who Is at Risk: EPA used the highly exposed individual
(HEI) instead of the most exposed individual (MEI) as the target organism in
the revised risk assessment because use of the MEI was criticized as being
too conservative, reflecting highly unlikely or unusual circumstances rather
than realistic exposure conditions. The HEI reflects more reasonable risks to
exposed individuals, while remaining a conservative measure (Habicht, 1992).
• Revised Health and Environmental Criteria: EPA reviewed and revised its
use of health and environmental criteria. As a result, the Agency used a new
model for risks associated with lead exposure; developed refined ecological
criteria; and used Recommended Daily Allowances (RDAs) when RfDs/RfCs
were unavailable.
• Reconsideration of Risk Levels: EPA reassessed the cancer risk levels of 1
x 10"5 for incineration and 1 x 10"4 for all other use or disposal practices based
on new information obtained after the initial risk assessment was conducted.
This reassessment indicated minimal risk from all current biosolids use or dis-
posal practices, including incineration. The reassessment resulted in the EPA
policy decision to regulate cancer risks for all biosolids use or disposal prac-
tices at 1 x 10"4 in the final Part 503 rule,
• Revision and Reevaluation of Exposure Pathways, including:
- Replacement of the 98th-percentile approach with formal exposure
pathway assessments for all non-agricultural land application and sur-
face disposal practices, based on new data and modeling techniques.
The number of exposure pathways evaluated for non-agricultural land
application (e.g., forest lands, soil reclamation sites, and public contact
sites) was increased.
- Use of the most stringent of the pollutant limits for each pollutant
from all pathways of exposure for land application based on revised
Part 503 Risk Assessment «EPA 25
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Chapter 2
risk assessments that predicted similar pollutant limits for agricultural
and non-agricultural land application and distribution and marketing.
- Use of one risk assessment for all biosolids surface disposal prac-
tices, including biosolids-only landfilling (monofilling), permanent
lagooning, dedicated high-rate surface application for disposal, and
dedicated beneficial use. Although there was one risk assessment, two
exposure routes were evaluated and the more stringent of the two pol-
lutant limits was chosen as the Part 503 pollutant limit.
- Revision of the exposure pathways for ground water, surface
water, and air in the land application and surface disposal risk assess-
ments to incorporate better fate and transport models and assumptions
and to correct techniques used to calculate how much of a pollutant is
lost to ground water, surface water, and air. The risk assessments for
the proposed rule had used the assumption that 100 percent of any
evaluated pollutant could be simultaneously transferred to ground water,
surface water, and air. This overly conservative approach was changed.
The revised risk assessments used a "mass balance" approach, which
more realistically assessed the portion of the pollutant that is transferred
to ground water, surface water, and air.
- The exposure pathways used in the revised risk assessments for
biosolids are shown in Tables 6 and 7.
tail
Potential risks to people,
plants, and animals from
applying biosolids to
cropland, as well as
numerous other
"exposure pathways/'
were evaluated in the
biosolids risk assessment
(Tables 6 and 7)
26 A EPA Part 503 Risk Assessment
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The Risk Assessment Process for the Part 503 Biosolids Rule
Table 6
Summary of Exposure Pathways Used in Risk Assessment for Land Application of Biosolids
Pathway
Description of HEIa
1, Biosolids —~ Soil —~Plant —~ Human
Human (except home gardener) lifetime ingestion of plants grown
in biosolids-amended soil
2, Biosolids —~ Soil -» Plant —»Human
Human (home gardener) lifetime ingestion of plants grown in
biosolids-amended soil
3. Biosolids —» Human
Human (child) ingesting biosolids
4. Biosolids —* Soil —~ Plant —* Animal —~ Human
Human lifetime ingestion of animal products (animals raised on
forage grown on biosolids-amended soil)
5. Biosolids —» Soil -* Animal -~ Human
Human lifetime ingestion of animal products (animals ingest
biosolids directly)
6. Biosolids -> Soil -* Plant -» Animal
Animal lifetime ingestion of plants grown on biosolids-amended soil
7. Biosolids —~ Soil —* Animal
Animal lifetime ingestion of biosolids
8. Biosolids —* Soil —~ Plant
Plant toxicity due to taking up biosolids pollutants when grown in
biosolids-amended soils
9. Biosolids —* Soil —~ Soil —~ Organism
Soil organism ingesting biosolids/soil mixture
10. Biosolids -* Soil -» Soil -~ Organism -»
Soil —* Organism —» Predator
Predator of soil organisms that have been exposed to
biosolids-amended soils
11. Biosolids —~ Soil —» Airborne Dust —* Human
Adult human lifetime inhalation of particles (dust) (e.g., tractor
driver tilling a field)
12. Biosolids —» Soil —» Surface Water —» Human
Human lifetime drinking surface water and ingesting fish
containing pollutants in biosolids
13, Biosolids —~ Soil —» Air —~ Human
Human lifetime inhalation of pollutants in biosolids that volatilized
to air
14. Biosolids -~ Soil -* Ground Water Human
Human lifetime drinking well water containing pollutants from
biosolids that leached from soil to ground water
a HEI = highly exposed individual
Table 7
Summary of Exposure Pathways Used in Risk Assessments for Surface Disposal and
Incineration of Biosolids
Surface Disposal
Pathway
Description of HEIa Exposure for a 70-Year Lifetime
1. Biosolids -*¦ Soil -»Air -»Human
Adult human breathing volatile pollutants from biosolids
disposed at a surface disposal site
2. Biosolids —* Soil —»Ground Water Human
Adult human drinking water obtained from ground
water beneath a surface disposal site
Incineration
1. Biosolids -»Incineration —* Particulate Air —»
Human
Adult human breathing pollutants in the emissions from
a biosolids incinerator
aHEI = higly exposed individual
Part 503 Risk Assessment &EPA 27
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Chapter 2
• Deletion of Organic Pollutants; Based on comments received on the pro-
posed Part 503 rule, EPA reevaluated the organic pollutants regulated by the
proposed rule to determine whether any should be deleted from the final regu-
lation, This reevaluation resulted in EPA's policy decision to delete all organic
pollutants from land application and surface disposal sections of the final Part
503 rule because these pollutants met one of the following criteria: (1) the pol-
lutant has been banned or restricted for use in the United States or it is no
longer manufactured for use in the United States; (2) the pollutant is not pre-
sent in biosolids at significant frequencies of detection based on data gathered
in the NSSS; or (3) the limit for a pollutant from the biosolids exposure assess-
ment is not expected to be exceeded in biosolids that are used or disposed
based on data from the NSSS.
• Food Consumption Revisited; The methodology and data used to calculate
dietary exposure to pollutants in biosolids were reviewed and revised to reflect
more realistic values representing average lifetime food consumption.
• Greater Reliance on Results of Field Studies: Field study data were used in
the revised risk assessment whenever available (rather than greenhouse pot
or metal salt-addition studies) to determine plant uptake of metals and phyto-
toxicity. New data provided during the public comment and scientific review
period indicated that field studies provide a much more realistic basis on which
to set biosolids pollutant limits than pot/salt study data, with limits that are
more representative of real-world conditions. These new data showed that
plants in the field take up metal pollutants at lower rates than predicted based
on greenhouse pot/salt addition studies (see photographs, next page), and
that these rates remain low over time.
• Revised Evaluation of Biosolids Incineration, including:
- Use of an updated model of incineration of biosolids to evaluate expo-
sure to metal emissions.
- Determination that site-specific modeling and performance testing
to calculate air dispersion factors and control efficiencies (required in
the final rule) are more appropriate than establishing absolute values for
those parameters, as was done in the proposed Part 503 rule.
- Determination that it was infeasible to establish a risk-based numerical
limit for total hydrocarbon (THC) emissions from biosolids incinerators,
as was included in the proposed rule. Instead, a technology-based op-
erational standard for THC was included in the final rule.
• A New Aggregate (Population) Risk Assessment; The aggregate (popula-
tion) risk assessment conducted for the final Part 503 rule indicated that
current use or disposal practices for biosolids pose minimal risk to public
health and the environment.
Many of the revisions summarized above are discussed in more detail in Chapter 3.
Step N EPA Review of Science and Policy Decisions
Used in the Biosolids Risk Assessments Prior to
Issuance of the Final Part 503 Rule
During the review of the final Part 503 rule, several EPA offices raised a number of
issues that needed resolution prior to publication of the final rule. These issues are
summarized in Table 8. Many of these issues and EPA's resolution of them are dis-
cussed in greater detail in Chapter 3.
28 &EPA Part 503 Risk Assessment
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The Risk Assessment Process for the Part 503 Biosolids Rule
Table 8
Questions Raised During Internal EPA Review
Topic
Question
Where Addressed
in this Document
Pathogens
How should pathogens (e.g., bacteria, viruses) in biosolids be
regulated?
Chapter 5
Phytotoxicity
How should phytotoxicity (adverse effects on plants) be defined?
Chapter 3; Chapter 4,
Box 10
Lead risks
What methodology should be used to determine risks from
exposure to lead in land-applied biosolids?
Chapter 3
Biosolids binding of
pollutants
Does "biosolids binding" (the ability of biosolids to strongly react
with pollutants, resulting in less pollutant being taken up by plants)
persist over time?
Chapter 3
Soil pH
Should soil pH be regulated?
Chapter 5
Ecological risks
Is the ecological risk assessment adequate?
Chapter 3
Margin of safety
Can a 98th- or 99th-percentile approach used as an additional
margin of safety be justified?
Chapters 3 and 5
Incineration monitoring
How should incineration monitoring be regulated?
Chapters 2 and 5
Nitrogen in ground water
How should nitrogen that migrates into ground water from
biosolids be regulated?
Chapter 3
"Clean" biosolids
Should special provisions to encourage the production of "clean"
biosolids (i.e., biosolids containing low levels of pollutants) be
included in the final rule?
Chapters 3 and 5
Publication of the Final Part 503 Rule in the
Federal Register
The final Part 503 rule was published in the Federal Register on February 19, 1993
(58 FR 9248). The rule set limits for pollutants that may be present in biosolids that
are land applied, surface disposed, or incinerated, as well as other requirements,
including management practices, operational standards (i.e., pathogen and vector
attraction reduction requirements for land application and surface disposal; THC
emissions testing for incinerators), general requirements, and frequency of moni-
toring, reporting, and recordkeeping requirements (see also Figure 1 in Chapter 1).
In addition to the rule itself, the preamble included informative discussions regard-
ing differences between the proposed and final rule pertaining to public and
scientific comments, EPA responses to comments, and final actions taken to revise
the proposed rule.
Comments, Lawsuits, and Amendments
Regarding the Published Final Part 503 Rule
Comments: EPA received comments on the published final Part 503 rule from 89
respondents in response to a request for comments in the Preamble. The com-
ments raised issues regarding the pollutant limits set for cadmium, selenium, and
chromium; the use of "annual pollutant loading rates"; use of a percentage of the
Maximum Contaminant Level (MCL) for nitrate-nitrogen allowance; and the need
for additional ecological field research (see further discussions in Chapter 3). The
comments also questioned the need for pollutant limits for molybdenum and the
Step O
Step P
Part 503 Risk Assessment #EPA 29
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Chapter 2
requirements for monitoring emissions from biosolids incinerators, as discussed
below.
Lawsuits Regarding Pollutant Limits for Molybdenum and Chromium: Several
POTWs and industry groups as well as the USD A noted errors in the calculation of
the uptake slope for molybdenum that caused an underestimation of allowed
biosolids molybdenum applications to farmland. Several organizations sued, refer-
ring to the error and stating that the limit would significantly restrict the use of
biosolids as fertilizer or impose severe restrictions on molybdenum discharge to
POTWs without need or benefit. In addition, several industry groups and POTWs
initiated lawsuits in which they contended that the land application pollutant limits
set for chromium are overly stringent. In particular, plaintiffs argued that because
the limits set for chromium were based on a risk assessment that did not identify a
limit that would cause harm to public health or the environment, the limits would be
unnecessarily detrimental to their industrial practice. On this basis, plaintiffs con-
tended that the limits should be deleted from the rule.
Lawsuits Regarding Biosolids incinerator Monitoring: Lawsuits also were filed
regarding continuous emission monitoring requirements for measuring total hydro-
carbons in emissions from biosolids incinerators. The incineration lawsuits
questioned the requirement for continuous monitoring of THC emissions from cer-
tain incinerators that already had continuous emission monitoring systems for
carbon monoxide (CO) in place, which plaintiffs claimed achieved the same results.
In addition, arguments were made that EPA was not allowing sufficient time nor
providing adequate instruction for installation, start-up, continuous operation, and
calibration of continuous emission monitoring systems for THC.
Part 503 Amendment: In response to the public comments received and lawsuits
filed, EPA published an amendment to the rule in the Federal Register on February
25, 1994 (59 FR 9095). The amendment states that the Agency is reconsidering
the land application pollutant limits for molybdenum. During the period of reconsid-
eration, only the ceiling concentration limit (Part 503, Table 1) must be met for
molybdenum. The other pollutant limits (i.e., cumulative pollutant loading rates
[Part 503, Table 2], pollutant concentration limits [Part 503, Table 3], and annual
pollutant loading rates [Part 503, Table 4]) for molybdenum have been suspended
pending additional study by EPA.
In addition, the February 25, 1994, amendment allows continuous CO monitoring
to be used as a surrogate for THC monitoring for incinerators that do not exceed
100 ppmv (parts per million, volume basis) of CO in the exhaust gas. Also, opera-
tors of biosolids incinerators are not out of compliance if not monitoring for THC or
CO until either a permit has been issued or other federal action has been taken
(e.g., Federal Register notification).
Step Q Court Remand of Specific Portions of the Rule
The court remanded certain provisions of the rule to EPA for modification or further
justification as a basis for their continued inclusion in the Part 503 rule. These pro-
visions continue to be in effect pending the Agency's review of the remanded
portions of the rule.
The remanded portions of the rule include:
• The chromium pollutant limits
• The 99th-percentile cap used as a pollutant concentration limit for selenium
• Pollutant concentration limits for heat-dried biosolids (currently not included
in Part 503)
These issues are discussed in more detail in Chapter 3.
30 ©EPA Part 503 Risk Assessment
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Chapter 3
Identification and Resolution of
Risk Assessment Issues
Determining the risks associated with pollutants in biosolids was a chal-
lenging process. Numerous factors had to be considered, many of which
had not been fully explored previously. This chapter presents some of
the key issues raised during the risk assessment process for biosolids and dis-
cusses how EPA resolved them. These issues are summarized in Table 9 and
addressed in more detail throughout this chapter. The large letters to the left of
each section heading in the text and in the left-hand column of Table 9 refer to the
same risk assessment steps discussed in Table 1 in Chapter 2 and indicate when
in the risk assessment process the issue was raised. Not all letters are shown be-
cause not all of the risk assessment steps discussed in Chapter 2 involved issues
that required further resolution.
Step H Evaluation of Iron and Fluoride
Although the initial biosolids hazard index and ranking process (described in Chap-
ter 2) identified both iron and fluoride as potentially toxic, EPA decided not to
evaluate these two pollutants in the risk assessments for biosolids. EPA made this
decision because toxic effects have only been observed under atypical condi-
tions—in experiments with unusually high concentrations of iron and fluoride and
single high volume applications of biosolids.
For example, cattle in which iron toxicity resulted were grazed on land to which, in
an experiment, high iron content biosolids were land applied a day before grazing.
These cattle received no supplemental feed and were continually rotated to new
fields week after week immediately after the fields had been treated with high iron-
content liquid biosolids.
Such an occurrence of elevated iron toxicity in cattle is highly unlikely other than in
a similar experimental setting. The Part 503 rule requires at least a 30-day waiting
period after application of Class B biosolids (those meeting certain pathogen re-
duction requirements) before allowing grazing. Possibly, Class A biosolids (virtually
pathogen free) could be applied just before grazing; however, Class A biosolids are
usually in a dry state and initially do not tend to stick to the forage, as do liquid
Class B biosolids. Also, it is highly unlikely that biosolids in any form would con-
tinue to be applied week after week to pastures immediately before cattle graze.
Part 503 Risk Assessment -SEPA 31
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Chapter 3
Table 9
Issues Raised During the Biosolids Risk Assessment Process
Issue Raised
During
Issue
Resolution of Issue
StepE
Profile assessment
Retain or drop ocean disposal
Dropped—policy decision because of Ocean Disposal Ban
Act
StepH
Risk assessments for
proposed rule
Drop iron and fluoride, which
had high hazard indices
Iron is ubiquitous and an essential element; two studies
showing high levels (Fe and F) considered to be
unrepresentative; iron and fluoride not regulated
Step J
Expert reviews
(1) Target organism
(2) Use of 1 x io~4'"5'or"6 cancer
risk level
(3) Salt/pot vs. biosolids/pot
vs. field data
(4) Megaeater model
(5) Drop organics from Part 503
rale
Replaced most exposed individual with highly exposed
individual
Used 1 x 10"4 for all use or disposal practices (policy
decision)
Used field data to accurately reflect biosolids pollutant
concentrations in plants because salt data greatly
overestimate actual uptake
Replaced with better data and model
Policy decision—NSSS showed organics not present in
sufficiently high levels in biosolids to exceed risk-based
limits; infrequently detected; or no longer used or
manufactured for use in the United States
Step L
NSSS results, rule
changes
Add concept for land
application of biosolids
containing low pollutant levels
that require less regulatory
control. If such biosolids meet
pollutant concentration limits
and certain pathogen and
vector attraction reduction
requirements, they would be
minimally regulated
"Clean" biosolids concept shown to be viable by risk
assessment for low pollutant concentrations; field data
confirmed that land-applied biosolids containing low
pollutant levels have no observed adverse effects on public
health and the environment; NOAEL biosolids concept
included in final Part 503 rule
StepN
Internal EPA review
(1) Lead risk evaluation not
properly conducted
(2) Whether biosolids binding
of metals is long-term
(3) Whether ecological risks,
especially phytotoxicity, were
properly assessed
Explained how animal data were used to show no impact
on body burden; used EPA IEUBK model; risk
management decision to use 300 ppm from animal data vs.
500 ppm from IEUBK model as land application pollutant
concentration limit
Detailed evaluation of data showed a valid basis for
long-term binding of pollutants by biosolids components
Reviewed and explained EPA procedures for ecological risk
assessment; specifically described how risks to animals,
plants (phytotoxicity), and microbes were determined;
policy decision to add ceiling concentration limits to prevent
worst-case exposure, partly in response to phytotoxicity
concerns (see Step N-6 in text); made plans for additional
future ecological and biosolids metal binding studies
(4) Allow use of PSRP and PFRP Policy decision to use both; made vector attraction
reduction a separate requirement; added monitoring
requirement to preclude regrowth for Class A PFRP
(5) Non-agricultural and surface Changed from 98th percentile to risk-based limits
disposal pollutant limits
(Continued)
32 ©EPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
Table 9 (Continued)
Issue Raised
During
Issue
Resolution of Issue
Step N
Internal EPA review
(cont.)
(6) Ceiling concentration limits
for land application and caps
for pollutant concentration
limits
Policy decision to use 99th percentile as a ceiling
concentration if less stringent than risk-based cumulative
pollutant loading rate; used NSSS to assess impact on 1%
(99th percentile) of POTWs for final rule (vs. 10%, or 98th
percentile, in initial proposed rule); 99th percentile still
limits use or disposal of biosolids with highest
concentrations of metals
(7) Assign fraction of
ground-water nitrate MCL (10
mg NO3-N) to biosolids
nitrogen
Policy decision not to fractionate but to assign entire 10 mg
NO3-N to biosolids; no other EPA rule had fractionated the
MCL for nitrogen, and no agreed upon basis for
fractionization has been established
(8) Use biosolids as model for
nutrient management
Policy decision—too complex an issue for unilateral
decision by EPA; involves all sources of nutrients from
chemical fertilizer, animal manure, and other wastes, as
well as biosolids
Step P
Comments,
lawsuits, EPA
revisions
(1) USDA issues, e.g., cadmium
ceiling concentration limit;
APLR approach
Considering whether to make changes or develop
guidances
(2) Regulation of chromium and
molybdenum
Science basis questioned—need for more definitive data;
land application pollutant limits for molybdenum deleted
except for Part 503 Table 1 ceiling concentration limits
(3) THC-CO monitoring
Allow either CO or THC monitoring for biosolids
incinerators
Step Q
Court remand of .
specific provisions
of rule
(1) Chromium land application
Considering deleting chromium as a regulated metal for
land application because the risk assessment did not show
chromium to be a risk
(2) 99th-percentile caps for
selenium and chromium
Considering deleting chromium from the rule and
changing the capped selenium pollutant concentration
limit from 36 mg/kg (99tli-percentile, policy-based) to 100
mg/kg (risk-based)
(3) Special land application
pollutant limits for heat-dried
biosolids
At the time this document was prepared, no final decision
had been made
(4) Different ceiling
concentration limits for
selenium
At the time this document was prepared, no final decision
had been made
Step J-l Who Is at Risk? The "Highly" Versus "Most
Exposed" Individual
Proposed Rule: For the proposed rule EPA focused its risk assessments on the
most exposed individual (MEI) as the target organism (the individual at risk) to
be protected from pollutants in biosolids. The MEI was defined as the individual
that is most exposed to a pollutant in biosolids for a lifetime (e.g., 70 years, if the
MEI was an adult person; or the critical life period of a plant or animal). Worst-case
Part 503 Risk Assessment &EPA 33
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Chapter 3
estimates of the potential for exposure were assigned to the MEI, resulting in very
stringent pollutant limits in the proposed rule.
As discussed in Chapter 2, experts were critical of the risk assessments EPA used
as a basis for developing the proposed Part 503 rule's pollutant limits. They criti-
cized the use of the MEI as the target organism to be protected, the very
conservative assumptions, and the overly stringent models. Some reviewers
showed that the use of the MEI was so unrealistic that such an individual would not
exist; hence, an assessment of risk to a nonexistent organism would not be mean-
ingful. For example, the MEI used in developing the proposed Part 503 rule for
exposure Pathway 1F (exposure Pathway 2 in the final rule's risk assessment) was
a hypothetical home gardener:
• Who for 70 years produced essentially all of his or her own food grown in a
home garden amended with biosolids.
• Whose biosolids-amended garden soil contained the maximum cumulative
permitted application of each of the evaluated pollutants for that 70-year pe-
riod.
• Whose food harvested from the garden had the highest plant uptake rate for
the 70-year period for each of the pollutants, as calculated using data from salt
and pot studies.
• Who consumed foods grown in that garden for 70 years (the gardener's food
consumption represented both male and female diets simultaneously, and the
gardener was always at the age and physiological state for maximum inges-
tion for each of the food groups [e.g., pregnant, an infant, and a teen-age
male]).
This MEI is illustrated in Figure 3. Because of the highly unlikely combination of all
these conservative assumptions, this MEI very likely represents the worst case
exposure (Ryan and Chaney, 1993).
Final Rule: Because of the many difficulties experienced with the MEI approach,
EPA developed a new paradigm for conducting risk assessments (Habicht, 1992).
This paradigm, which was used to conduct the risk assessments for the final Part
503 rule, involved the protection of a highly exposed individual (HEI) and the use
of a combination of high-end and mid-range assumptions in models and algo-
rithms. The HEI also is depicted in Figure 3. In contrast to the MEI, EPA considers
the HEI to be more representative of that subset of the population of actual indi-
viduals at higher risk than the general population because the HEI models an
individual who has high exposure and can exist. Contrast the data, models, and as-
sumptions used for protecting the highly exposed home gardener (Pathway 2)
during the revised risk assessments and development of the final Part 503 rule with
those previously described for the most exposed home gardener (Pathway 1F). In
the revised risk assessment:
• For 70 years, the home gardener HEI produced up to 59 percent of his or her
own food (depending on the food group) grown in a home garden amended
with biosolids.
• The biosolids-amended garden soil contained the maximum cumulative per-
mitted application of each of the evaluated pollutants for the 70-year period.
• The food harvested from the garden had plant uptake slopes for biosolids pol-
lutants determined using the geometric mean of relevant data from field
studies with both acid and neutral biosolids-amended soils.
• Food consumption was apportioned among several different age groups dur-
ing the 70-year life of the HEI gardener.
34 &EPA Part 503 Risk Assessment
-------
Identification and'Resolution of Risk Assessment Issues
Figure 3
Comparisons of the Highly Exposed Individual (HEI) and the Most Exposed Individual (MEI)
(adapted from U.S. EPA, 1991)
90th
Percentile
\
I Below 90th Percentile
I Not Impacted
98th 100th
Percentile Percentile
Portion of the Exposed Population
That Might Be Impacted
Reasonable Worst Case
Exposure
V
s* e ^ 'I!'. * ,
* i High-End'Exposure •
HEI
Exposu
J
Worst Case
Exposure,
or Bounding
Estimate
MEI
Step J-2 Cancer Risk Level Used
Risks from cancer are typically expressed as a "cancer risk level," such as 1 x 10"4
(meaning that the chance of getting cancer is 1 in 10,000) or 1 x 10"6 (meaning that
the chance of getting cancer is 1 in 1 million). This number indicates the probability
that one additional cancer case (over and above the background cancer risk in in-
dividuals not exposed to the pollutant source being evaluated) could be expected
to occur in a population of a certain size exposed for 70 years. This level is not a
scientific estimate of actual risk but a criterion designed to guide choices among
regulatory alternatives. It is an estimate of the upper limits of actual risk that could
exist given certain assumptions; the actual risk level is likely to be significantly less
than the estimated cancer risk level, and may be zero.
Proposed Rule: EPA's initial biosolids risk assessments conducted for the pro-
posed Part 503 rule evaluated cancer risks associated with pollutants in biosolids
at risk levels of 1 x 10"4 (1 cancer case in a population of 10,000 MEIs), 1 x 10"5 (1
cancer case in a population of 100,000 MEIs), and 1 x 10"6 (1 cancer case in a
population of 1,000,000 MEIs). The pollutant limits in the proposed Part 503 rule
were based on risk levels of 1 x 10"4 for all use or disposal practices except incin-
eration, which was proposed to be regulated at 1 x 10"5 because the aggregate
(population) risk assessment indicated that incineration posed a higher risk than
other use or disposal practices.
Final Rule: Cancer risks were reevaluated in the revised risk assessments con-
ducted for the final Part 503 rule based on new information obtained after the initial
risk assessments were conducted. The new results indicated that minimal risk ex-
ists from all current biosolids use or disposal practices, including incineration.
Thus, EPA made a policy decision to regulate risks for all biosolids use or disposal
practices in the final Part 503 rule at 1 x 10"4. This risk level is the lifetime cancer
risk to a highly exposed individual. EPA believes that a 1 x 10"4 risk level for cancer
Part 503 Risk Assessment v>EPA 35
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Chapter 3
risks from pollutants in biosolids provides adequate protection of human health be-
cause the latest analyses did not indicate a significant carcinogenic risk to the
population as a whole for any biosolids use or disposal practice. EPA estimated
that biosolids use or disposal practices prior to promulgation of the final Part 503
rule could have contributed 0.9 to 5 cancer cases annually and that the rule re-
duces cancer cases by 0.09 to 0.7 annually (see also the questions and answers
on this subject in Chapter 6.)
Step J-3 Plant Uptake of Metals: Pot/Salt Vs. Field Studies
Pot/Salt Studies Overestimate Risk
Proposed Rule: For the initial risk assessments conducted for the proposed rule,
EPA relied primarily on the results of greenhouse studies in which soluble metal
salts were added to soil in pots, rather than on the results of studies conducted in
fields, to determine plant uptake of pollutants and phytotoxicity from pollutants in
biosolids. This approach was taken in part based on the assumption that it was
necessary to obtain adverse effect levels associated with uptake, otherwise the
data would not be suitable for use in the risk assessment. In many cases such ad-
verse effects data were found only in pot/salt studies and not in pot/biosolids or
field/biosolids studies. Many of the field studies showed no adverse effects be-
cause of the binding of pollutants by components of the biosolids matrix. (See
photographs on facing page.)
Final Rule: Careful evaluation of the data and new research conducted since the
initial Part 503 risk assessments indicated that the results of metal salt and pot
studies greatly overestimated phytotoxicity and the bioavailability of pollutants in
biosolids (USDA/CSRS, 1989). This is because certain components in biosolids
(e.g., ferric hydrous oxides, organic matter, phosphates) bind pollutants to the
biosolids, making the pollutants less available to plants, animals, and humans
(Corey et al., 1987; Chaney and Ryan, 1994; Mahler et al., 1987). This biosolids
binding effect is not present when pure metal salts (rather than metals in biosolids)
are added to soil. In addition, conditions of pot studies (e.g., plant root confine-
ment, elevated soil temperature, rapidly changing water environment due to
evaporation and transpiration) tend to increase the uptake of pollutants by plants
compared to uptake under field conditions.
Plant Response to Metals
The differences between plant uptake of metals in field soils amended with
biosolids versus plant uptake of metal salts added to soils in pots or in the field is
also illustrated in Figure 4. When pure metal salts are added to soils, a linear re-
sponse occurs (i.e., as the concentration of metal salts increases in the soil, the
concentration of metal increases in plants). This is because the added metal salts
are not bound as tightly by the soil as are metals in biosolids-amended soils (see
description below) and therefore are taken up more freely by plant roots.
In contrast, a plateau response in plant uptake occurs when plants are grown in
soil-biosolids mixtures (see Figure 4). This plateau response has been observed
repeatedly in numerous field studies. With the plateau effect, the rate of pollutant
uptake by plants in the soil-biosolids mixture decreases with increased biosolids-
metal loadings (Chaney et al., 1982). The plateau effect occurs because the
adsorptive materials in the biosolids become as important or more important than
the adsorptive materials initially in the soil. Hence, the uptake slope for the pollu-
tant levels off because more of the stronger biosolids adsorptive capacity is added
for each unit of the pollutant that is added. More specifically, when soils are first
amended with initial amounts of biosolids, which generally contain low levels of
metals, plants and soils compete for the biosolids-bound metals and uptake of
36 &EPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Jssues
HK ph 5 s ph 6 5 jHM
I 5 \% LEACHED HICH METAL SLUPSEJ
WILLIAMS SOYBEAN4 WEEKS GROWTH
-VUL1AM5 SOYBEAN - 4 WEEKS GROWTH
fACMEO HIGH METAL StUBGI
(Photographs by Rufus Chaney, USD A)
Plants respond very differently in pot studies vs. field studies. Photograph 1 shows plants
grown in pot studies. The plant on the left was grown in low pH soil; the plant on the right
was grown at pH 6.5. Photograph 2 is a close-up of leaves taken from the plants shown in
Photograph 1, with the low pH leaves shown at the bottom. Photograph 3 shows plants
thriving in the field, even though they are being grown in low pH soil. Documented field
study research and operational experience were used in the biosolids risk assessment for
land application for the final Part 503 rule whenever possible because these data are much
more representative of real-world conditions.
Part 503 Risk Assessment &EPA 37
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Chapter 3
Figure 4
Comparisons of the Plateau and Linear Plant Uptake Responses to Metals
Linear extrapolation of data
used for risk assessment.
5
Linear
Response
txl 3
Plateau Response
2
Acutal data not used.
1
~o
0
250
500
750
1000
BI0S0LID APPLICATION RATE, dry t/ha
(Adapted from Chaney, 1993)
metals may increase in plants (e.g., uptake appears to be linear). As more
biosolids are added to the soil, the strong binding sites of the biosolids matrix be-
come dominant over the weaker binding sites in the soil. Consequently,
phytoavailability (the ability of plants to take up metals) no longer increases with
further additions of biosolids, resulting in the plateauing effect. For some elements,
interactions between several pollutants also hinder uptake by plants (e.g., zinc in-
hibits cadmium uptake).
Nevertheless, EPA continued to use the conservative linear response assumption
for land application Pathways 1,2,4, 6, and 8 in the risk assessment for the final
Part 503 rule, even though it significantly overestimates pollutant uptake by plants.
Plateau regression could not be fully estimated because data were not available
from field studies using different rates of application over many years. Hence, lin-
ear response was retained in the final rule. This conservative assumption of
linearity was used in combination with less conservative assumptions, such as us-
ing the geometric mean (rather than the more conservative arithmetic mean) from
a large number of studies to determine input values used in calculating plant up-
take slopes, as described below.
Calculating Plant Uptake Slopes
Prior to calculating plant uptake slopes for pollutants in the revised risk assess-
ment, EPA reviewed, corrected, expanded, and ranked the data from numerous
studies on plant uptake (see Box 4).
Data from Type A (field) studies were used whenever available for the revised risk
assessment because they best represent conditions being regulated. Nonetheless,
for certain categories of studies other types of data were used. Data from Type B
biosolids pot studies were used for mercury and selenium. Type C data were used
for arsenic for all but "leafy vegetables," for which Type A data were used.
38 ©EPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
Box 4
EPA Plant Uptake Data Ranking Classification
Type A: Data from studies conducted in fields where biosoiids had been applied.
Type B: Data from all other studies conducted with biosoiids (i.e., field studies using biosoiids spiked with "
additional metals; greenhouse studies using plants grown in biosoiids in pots).
Type C: Data from all other non-biosoiids metals studies in the field or-greenhouse (e.g., studies using
: - metal salts .or. soils .contaminated or ge'ochemically .enriched from sources other, than-biosoiids).
The plant uptake slope, or response, for each study was then calculated. For stud-
ies with multiple application rates and tissue concentrations, the linear regression
statistical method was used to calculate the plant uptake slope. For studies with
one metal application rate and one plant tissue concentration, the uptake slope
was calculated as shown in Box 5.
If the calculated uptake slope was negative or zero, a default slope of 0.001 was
used. It is quite reasonable that the uptake slope of metals may be negative (i.e.,
that lower amounts of metals are obtained from soil by plants after biosoiids are
added to soils, even though the biosoiids also contain the same metals). A negative
slope would result from the strong binding surfaces in the biosoiids matrix, which
hold metals already present in soils and reduce their availability for plant uptake.
The use of a minimum plant uptake slope was required for calculating geometric
means. Therefore, the conservative assumption of a 0.001 minimum uptake slope
allowed negative uptake data to be included in the risk assessment data set, even
though that assumption caused the uptake slopes for the pollutants analyzed to be
overestimated and the pollutant limits to be conservative.
Plant types were assigned to food groups (garden fruits, grains and cereals, leafy
vegetables, legumes, potatoes, and root vegetables), and the uptake slope for
each food group was calculated for each pollutant using the geometric mean ("av-
erage") of the uptake slopes already calculated for individual studies in the food
group. Box 6 provides an example calculation.
Box 5
Sample Plant Uptake Calculation for a Study With One Observation
Algorithm:
'Pla it if take (UC) " T"ISSU^ Concentration (jig—poUutant/g—plant t,issue, DW) ••
; ' • Metal Application Rate {kg—pollutant /hectare of land, DW)
Variables (for cadmium, swiss chard, pl-l 6.2 [Chancy and Homick, 1978; CAST, 1980]):
Tissue Concentration — 1.675 (ug/g DW),
Metal Application Rate -- 4.43 {kg/ha)
Calculation:
UC = = 0.378 (]Xg/g DW)(kg/ha)~l _ "
Part 503 Risk Assessment &EPA 39
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Chapter 3
Box 6
Sample Plant Uptake Slope Calculation for a Food Group
Algorithm:
(UC1 • UCZ-
... • UCn) n = geometric mean ofslopes, where:
UCn= plant uptake slope calculated in Study1,2, etc. . ,
for a plant species * ' , ¦ ; -''v
Variables (hypothetical):
Study 1 Study2 Study 3 . V, , : , .... ' . :
uc 0.005 0.023 ,, o.oo5 / v,:,'.v
Calculation:
(0.005 • 0.023 • 0.005)-3
= 0.01&5 (iig-pollutant/g-plant tissue DW){kg-pollutant/hectare of land DW)"1
Step J-4 Food Consumption
The assumptions used in the biosolids risk assessments regarding the amounts of
food from different types of food groups that people consume influenced risk calcu-
lations in important ways.
Proposed Rule: For the land application risk assessment conducted for the pro-
posed Part 503 rule, EPA used conservative dietary data to determine human
exposure to pollutants in biosolids through food consumption. The risk assessment
used the highest daily consumption rate of each of eight food groups (e.g., con-
sumption of dairy products by teen-age males, consumption of leafy vegetables by
adult females, milk fat consumption of infants for polychlorinated biphenyl [PCB]
uptake). These assumption rates were used to calculate risks to people from con-
suming plants grown on soils to which biosolids were land applied or animal
products from animals that had consumed such plants.
Further evaluation showed that such an approach resulted in an unrealistic
"megaeater"—a person who is always of the age and physiological state for maxi-
mum ingestion of the pollutant (e.g, simultaneously pregnant, an infant, and a
teen-age male, who ingests maximum rates for an entire 70-year life span). Such
an approach would have overestimated exposure through dietary consumption by
3-to 10-fold.
Final Rule: EPA used an updated methodology and new data to calculate human
dietary exposure to pollutants in biosolids for the final Part 503 rule (see Appendix
B). This approach involved the derivation of more realistic values for dietary expo-
sure by apportioning food consumption among several different age periods during
the 70-year life of the HEI. Consistent with the new EPA paradigm for risk assess-
ment, this less conservative but more realistic approach to assessing dietary intake
was combined with both mid-range values (e.g., geometric mean of pollutant con-
centrations in food) and high-end, more conservative assumptions (e.g., regarding
pollutant toxicity and linearity of pollutant uptake by plants) in calculations used to
determine pollutant loading limits.
40 ©EPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
Step J-5 Pollutants Deleted
Organic Pollutants
Biosolids are known to contain synthetic organic chemicals (e.g., PCBs and poly-
cyclic aromatic hydrocarbons [PAHs]).
Proposed Rule: Comments on the proposed Part 503 rule included recommenda-
tions that some of the organic pollutants proposed for regulation be deleted
because the pollutants are either banned or restricted for use in the United States.
Final Rule: In response, EPA decided to reevaluate all organic pollutants proposed
for regulation in the Part 503 rule. The results of this evaluation, as well as numer-
ous research studies and the National Sewage Sludge Survey (NSSS), showed
that organic pollutants occurred in biosolids in the United States at low levels that
do not pose significant risks to public health or the environment. Thus, EPA de-
cided to delete regulation of organic pollutants in the final Part 503 rule because
organic pollutants met at least one of the following three criteria:
• The pollutant has been banned or restricted for use in the United States, or is
no longer manufactured for use in the United States.
• The pollutant is not present in biosolids at significant frequencies of detection
(i.e., 5 percent) based on data gathered in the NSSS in biosolids.
• The limit for the pollutant identified in the biosolids risk assessments is not ex-
pected to be exceeded in biosolids that are used or disposed, based on data
from the NSSS.
The limits that might have been used based on the risk assessments if the organic
chemical pollutants were included in the rule are listed in Table 11 (in Chapter 4).
Inorganic Pollutants
Final Rule: For surface disposal sites without a liner and leachate collection sys-
tem, in addition to organics, the inorganics cadmium, copper, lead, mercury, and
chromium met one of the three criteria discussed above (i.e., were not expected to
exceed the levels identified in the risk assessment). Thus, EPA determined that
risks from these inorganics in surface-disposed biosolids were negligible. The
Agency believed that meeting these criteria protected human health and the envi-
ronment from reasonably anticipated adverse effects of these pollutants in
biosolids without establishing pollutant limits for them in the Part 503 rule. All pollu-
tants, both inorganic and organic, were deleted from Part 503 regulation for surface
disposal sites with a liner and leachate collection system based on the assumption that
any potential migration of pollutants to ground or surface water would be precluded.
Step L Inclusion of ''Pollutant Concentration Limits"
(for Low-Metal Biosolids) for Land Application
in the Part 503 Rule
Experts who assisted EPA in revising the biosolids risk assessments and the pro-
posed Part 503 rule recommended including a provision that would identify
biosolids containing low levels of pollutants which could be used with minimal regu-
latory oversight. These experts proposed levels of pollutants that, based on the risk
assessment and data from field investigations, showed very low risk from land ap-
plication of biosolids, even when soils were poorly managed. After reviewing these
recommendations, along with results of the NSSS, which showed that pollutant lev-
els in biosolids had dropped, EPA proposed the concept for comment. Known as
the "clean" biosolids concept, this provision was adopted as part of the final Part
503 rule as "pollutant concentration limits."
, Part 503 Risk Assessment -&EPA 41
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Chapter 3
Research conducted over the past decade (Chaney, 1993; Chaney and Ryan,
1991, 1993; Chang et ai., 1992; Korcak and Fanning, 1985; USDA/CSRS, 1989)
has clearly demonstrated that biosolids with low levels of pollutants, such as those
designated by the Part 503 pollutant concentration limits, are associated with no
observed adverse effects in the field. Thus, these biosolids are also known as "no
observed adverse effect level (NOAEL)" biosolids. Chapter 5 discusses how the
pollutant concentration limits for NOAEL biosolids were determined.
Part 503 allows NOAEL biosolids to be used with minimal regulatory oversight (i.e.,
additional cumulative amounts of pollutants added to land are not required to be
tracked). In addition, if certain pathogen and vector attraction reduction require-
ments also are met, these biosolids do not have to meet Part 503 general
requirements and management practices for land application. These simplified land
application provisions provide an incentive to biosolids generators to improve the
quality of biosolids and recycle them. EPA's A Plain English Guide to the EPA
Part 503 Biosolids Rule (U.S. EPA, 1994) provides additional details on these
provisions.
Step N-l Risk From Exposure to Lead in Land-Applied
Biosolids
Prior to Internal EPA Review: The critical exposure pathway for lead was Path-
way 3—children ingesting biosolids that contain lead. Experts assisting EPA with
the Part 503 rule initially recommended a lead limit of 300 milligrams per kilogram
(mg/kg). This level was determined based on observations of absorbed and re-
tained lead in the bodies of cows, sheep, pigs, and chickens whose diets consisted
of up to 10 percent biosolids. In these studies, body burdens of lead (i.e., the con-
tent of lead in blood and bone) did not increase unless the lead concentration of
biosolids fed as part of the animals' diet exceeded 300 mg/kg. It should be pointed
out that if there is no increase in the blood and bone tissue, there can be no in-
crease in any meat or milk from the ingesting animal. Hence, not only are the
ingesting animals protected; individuals who might consume the meat or milk from
these animals are also protected.
After Internal EPA Review: Prior to promulgation of the final Part 503 rule, there
was an extended period during which an internal Agency review took place. EPA
reviewers argued that the Agency should be using the Integrated Exposure Up-
take Biokinetic (lEUBK) model to estimate soil/biosolids lead concentration limits
that would protect against potential risks to children who Ingest biosolids-amended
soils. The IEUBK model is used by EPA's Office of Research and Development
(ORD) to calculate protective limits against lead risks. The IEUBK model, as used
for this calculation, assumed that:
• The lead blood level did not exceed 7.0 micrograms of lead per deciliter of
blood (10 micrograms of lead per deciliter is the current critical level that
should not be exceeded).
• The portion of the lead that is bioavailable is 60 percent as high as lead ab-
sorbed by children if they were to ingest lead from soluble lead salt sources.
• The percentage of the population that could exceed the designated blood level
was 5 percent.
Using these IEUBK values, EPA calculated an allowable lead concentration in
biosolids of 500 parts per million (ppm). EPA made a conservative policy decision
to use the lower of the two sets of lead data—300 ppm—as the pollutant concen-
tration limit in the final Part 503 regulation, thus providing an additional margin of
safety for growing children. Studies on rats fed biosolids that contained up to 300
ppm lead per kilogram of biosolids as part of their diet (about 10 percent) have
shown that the bioavailability of the biosoiids-bound lead is only 5 percent as com-
42 SEPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
pared with the 60 percent bioavailability assumed in the IEUBK model calculations.
This 12-fold overestimation of the actual bioavailability adds even more conserva-
tism to the calculated pollutant limit.
Step N-2 "Biosolids Binding" of Pollutants: Biosolids
Decrease Pollutant Phytoavailability and
Bioavailability
Biosolids Binding Is Long Lasting and Reduces Risk
As previously discussed in this chapter, certain components in biosolids (e.g., iron,
manganese, and aluminum oxides; organic matter; and phosphates) cause pollu-
tants to be tightly adsorbed to the biosolids, making them less available to plants,
animals, and people. This binding property of biosolids is a key reason why re-
search studies have revealed no adverse effects when biosolids containg low
levels of pollutants are land applied. Also, risks associated with phytotoxicity and
bioavailability of pollutants in biosolids are relatively low when biosolids are land
applied at rates commonly used in agriculture and good management practices are
followed (Chaney and Ryan, 1993). For example, phytotoxicity from metals in
biosolids has not occurred when biosolids have been applied to neutral, alkaline, or
acidic soils in accordance with the conditions now required by the Part 503 rule.
Phytotoxicity has only occurred when biosolids with high metals concentrations
were land applied at high rates or when very low soil pH existed (below 5.0, near
4.5). The nutrient imbalance and phytotoxicity resulting from these two extreme
conditions is readily revealed when soils are limed. These conditions are discussed
later in this chapter in the section on "Ecological Risks".
A number of studies have shown that the binding properties of biosolids are envi-
ronmentally stable (long term). Research has shown that biosolids continue binding
metals after being added to soils and that the persistence of binding continues in
the field for decades after biosolids addition ceases, even when the organic matter
added to the soil with the biosolids decreases. This persistence of the increased
metal-binding capacity of biosolids-amended soils also has been determined by
studies of soils amended with biosolids over long periods that were collected from
farmers' fields and laboratory and greenhouse studies of control soils (the same
soils not amended with biosolids) (as discussed in Chaney and Ryan, 1993).
First-Year Biosolids Field Data Overestimate Risk
Not only is the binding of metals in biosolids stable, but binding increases and plant
uptake of pollutants decreases over time following the last biosolids application.
The highest uptake slope often occurs in the first year after biosolids application.
This slope is artificially high during the first year because of metal solubilization,
which results from anaerobic biodegradation byproducts and salts associated with
the freshly applied biosolids (Chang et al., 1987). Thus, using first-year or short-
term data on plant uptake overestimates long-term plant uptake responses. The
biosolids risk assessments used long-term plant uptake data when available. Most
field studies of biosolids, however, were conducted over a short period (i.e., 5
years or less) and thus the risk assessments yielded estimates of plant uptake that
are somewhat conservative.
Additional Conditions That Reduce Risk
Soil-Plant Barrier: The soil-plant barrier concept (described by Chaney, 1980) in-
dicates that plants and/or animals are protected against toxicity from
biosolids-applied metals by natural processes in soils, plants, and animals. At least
two different protective mechanisms are involved:
Part 503 Risk Assessment «*EPA 43
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Chapter 3
• First, some metals are so insoluble or so strongly adsorbed in biosolids-
amended soil (e.g., chromium) or plant roots (e.g., lead) that they are not
transferred into edible plant parts even when their concentrations are greatly
increased in the biosolids/soil mixture.
• Second, when soils are strongly acidic (below pH 5.5) and when the available
metal concentration is high, metals such as copper and nickel can be taken up
by plants at levels that can cause phytotoxicity, in addition to the metal cad-
mium, which may cause harm to animals if ingested in sufficient quantity. The
edible parts of these plants would be very stunted (small), or the plants would
exhibit visible symptoms of phytotoxicity from high levels of metals. As a re-
sult, the quantities of such plants, and plant consumption by animals, would be
reduced.
Biosolids Elemental Balance Protectiveness: Under some conditions, the soil-
plant barrier protection described above does not apply (i.e., risks from excessive
selenium, molybdenum, and cadmium in soils would not be prevented by the soil-
plant barrier). If present in sufficient quantity in soils, these metals can be taken up
by plants at high levels that do not cause toxicity to plants (if available levels of
other potentially phytotoxic metals are not excessively high). Metals such as sele-
nium, molybdenum, and cadmium are, however, potentially toxic to animals
ingesting the plants if the level of these metals is sufficiently high. Fortunately, an-
other kind of protection is available to the ingesting animals. This protection arises
from the significant levels of other substances commonly found in biosolids, such
as zinc, calcium, and iron. These substances are taken up by the plant along with
metals such as cadmium. Zinc, calcium, and iron are beneficial to the ingesting animal
and provide protection by inhibiting absorption of selenium, molybdenum, and cad-
mium from the ingested food into the animal's intestines and blood stream (see Box 7).
Step N-3 Ecological Risk Assessment
EPA evaluated ecological risks (potential adverse effects on plants and animals) in
its risk assessment for land application of biosolids. The risk assessment used the
best available ecological data from the scientific literature. Where data were exten-
sive (e.g., on the phytotoxicity of agricultural crops), a comprehensive risk
assessment was possible. Where data were more limited, such as for small wildlife
and non-agricultural plants in an unmanaged environment, a much more limited
approach had to be used for estimating ecological risk. Another difficulty encoun-
tered was that currently there is no universally approved procedure for assessing
ecological risks.
The general approach followed in conducting the ecological risk assessment for
biosolids is outlined below.
Risks to Animals
For animals, risks were evaluated for:
• Agricultural livestock ingesting crops grown on biosolids-amended soil.
• Small herbivores (e.g., deer mice) that live their entire lives in a biosolids-
amended area feeding on seeds and small plants close to the biosolids/soil
layer in fields, forests, and public contact sites (e.g., parks).
• Animals grazing on forages grown on biosolids-amended forest land or recla-
mation sites.
• Animals ingesting biosolids (i.e., soil) directly while grazing.
• Soil organisms (e.g., earthworms) living in and consuming biosolids-amended
soil.
44 SEPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
Box 7
How Diet Alters the Bioavailability of Cadmium:
Experience in Japan, the United States, and New Zealand
Rice Grown in Japan
Cadmium insoiland food hasbeen a concern since 1969,when subsistence farmers in the Jinzu Valley, Japan, experi-
enced adverse health effectvfrom consumirtg rice containing high levels of cadmium (Cd). Women in these farm
families developed itai itai (or osteomalacia), a painful bone disease, following exposure to excessive,cadmium from
rice grown in paddies contaminated with mining wastes (10 ug-Gd/'g-soii). These families also experienced:renal tu-
bular dysfunction (Fanconi syndrome), a disease in which low molecular iveight proteins are excreted in urine
because of accumulation ot cadmium in the kidney cortex. Scientists now know that several circumstances contrib-
uted to these health effects:
• The properties of rice—The bioavailability of cadmium depends on..the presence of calcium, iron, and zinc (Zn) in
, the rice, which when present are known to interfere with (reduce) cadmium absorption in, the human intestine.
Milling of brown rice into white rice removes-most of these elements but little of the cadmium, Lhus increasing
the bioavailability of cadmium in rice. , - '
• The diet of the jinzu Valley farm families—Malnutrition among the farm families during the pre-war depression,
the World War U period, and the postwar depression'resulted in a low intake of iron, zinc, and calcium. In ad-
dition, the water in Japan is low in calcium. These dietary factors also contributed to increased cadmium
absorption from the rice consumed.
- • Properties offloaded soils in rice paddies—Although the soil in. the Jinzu Valley rice paddies was high in zinc (1,200
Hg-Cd/g-soil), the cadmium in the soil was more easily oxidized and more soluble- than the zinc when the
flooded soil-was drained. The cadmium was translocated to rice grain at high levels, while zinc remained inthe
,sofl or leaves. , " . • ' * v
Crops in Western Diets
In contrast, Western diets more often consist of substantial quantities of wheat and lettuce, which are grown in non-
flooded soils, and rice that is not consumed on a subsistence basis and generally comes from many sources. Zinc
always accompanies tl.ie cadmium into the edible part's of crops such as wheatand lettuce, reducing absorption of
cadmium in the intestine. Usually zinc concentrations are 100 times higher than cadmium levels. Therefore, scien-
tists consider the rice exposure cases in Japan to have no relevance for biosolids risk assessments for Western diets.
This conclusion is borne out by experience in New Zealand, where families fished for and consumed large'amounts
of cadmium-rich oysters, ingesting a leVel of cadmium (250 (ig Cd/day) similar to that ingested by the farm families
in Japan who developed kidney disease. But'because neither oysters nor the New Zealand diet were deficient in
zinc, iron, or calcium, the New Zealand families experienced no adverse health effects from cadmium ingestion,
They did not develop renal tubular dysfunction or accumulate high amounts of cadmium in their kidneys, as did"-
the Jinzu Valley farm families. ' . 1 -- - '
Several studies of cadmium in vegetables also demonstrate the low risk from increased cadmium concentration in •-
crops. Morgan and Simms (1988) evaluated a mining site in the United Kingdom where garden soil cadmium levels
readied 360 mg Cd/kg dry weight, resulting in cadmium concentrations in vegetables 15 to 60 limes higher than in
those grown in ordinary soil. This study and others, such as a study by Strehlow and Barltxop (1983) in Shipham,
England, found no evidence of adverse health effects,in.ihe population consuming these vegetables. The Ca:Zn ra-
tio was 1:200 at the mining site "gardens in Shipham, England. Similar findings of no increased cadmium-induced
kidney dysfunction were found for soils containing 100 mg Cd/kg at a zinc smelter iri Palmerton, Pennsylvania.
THis community included elderly residents who, had ingested homegrown garden vegetables over long periods
(ATSDR,' 1994). The Ca:Zn ratio was 1:100. Also, Chaney and. Ryan (1994) found that only if soil cadmium levels ex- '
- ceeded 100 mg Cd/kg dry weight would'exposure represent a potential risk to the subsistence-Western gardener,
based on data from a zinc smelter site. However, since the site was also contaminated with up to 10,000 mg Zn/kg,
the'zinc prevented the production of high cadmium crops.
Crops Grown in Bio solids-Amended Soils
Soils amended with biosolids that may contain cadmium also may contain zinc (usually at a 1:100 ratio of Cd:Zn by
weight), iron, and calcium. When an animal ingests plants grown in such biosolids-amended soils, the animal ob-
tains sufficient quantities of zinc; iron, and calcium along with the ca'dmium so that the absorption of cadmium is
reduced in the animal's intestine. This contrasts with the high absorption of cadmium in the intestine due to .diets ¦
low in zinc, iron, and calcium, such as the rice-based subsistence Japanese diets described above.
Part 503 Risk Assessment
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Chapter 3
• Animals that eat soil organisms living in biosolids-amended soil (i.e., soil or-
ganism predators). Animals that eat earthworms are more highly exposed to
potential risks from pollutants in soils than animals that only ingest soils be-
cause earthworms bioconcentrate pollutants like cadmium and PCBs. The
initial risk assessment, conducted for the proposed rule, identified ducks eat-
ing earthworms as a key ecological target organism to be protected {i.e., the
MEI); in fact, however, ducks eat grain, aquatic vegetation, and fish rather than
earthworms. This was corrected in the revised risk assessment for the final
Part 503 rule, which identifies shrews eating earthworms (which had assimi-
lated and bioconcentrated PCBs) as one of the highly exposed key ecological
organisms to be protected (i.e., the ecological HEI).
Other important factors in the ecological risk assessment conducted for animals in-
cluded:
• The rate at which animals accumulate pollutants in their organs from consum-
ing plants grown on biosolids land application sites.
• The maximum Intake of a pollutant that would not cause a toxic effect to a
most sensitive/most exposed animal; or, alternatively, determination of thresh-
old contaminant concentrations in organs.
• The fraction of the animal diet that is biosolids or plants grown on biosolids-
amended sites.
• "Bioavailability" and "bioaccumulation" factors to account for: (1) the ability of
animals (particularly earthworms) to accumulate pollutants from soils; (2) the
potential for animals (particularly predators of earthworms) to accumulate pol-
lutants from other animals lower in the food chain; and (3) the binding of
pollutants within the biosolids/soil mixture, which makes the pollutant less
available to plants and animals (see also earlier discussions in this chapter re-
garding biosolids binding).
Risks to Plants (Phytotoxicity)
Pathway 8 in the biosolids land application risk assessment involves the exposure
of plants to pollutants in biosolids added to soils. Adverse effects of these pollu-
tants on plant growth and development are known as phytotoxic effects. EPA
used a comprehensive approach to establish pollutant limits that would protect
plants from the potentially phytotoxic metals in biosolids (zinc, copper, nickel, and
chromium). Alternative procedures were used to establish these limits, and the pro-
cedure yielding the most stringent limit for a given metal was chosen, as the
pollutant limit for Pathway 8, the phytotoxicity pathway.
First Procedure for Determining Plant Metal Concentrations That
Characterize Phytotoxicity (the Probability Approach)
Step 1: EPA searched the literature to identify plant tissue concentrations of metals
associated with amount of growth. In the experiments analyzed, different species
of plants were grown in nutrient solution or pots of soil with and without additions of
different test metal salts for 2- to 6-week periods. The studies determined the con-
centrations of different metals in the vegetative tissues of various plant species
associated with 8, 10, 25, and 50 percent retardation of vegetative growth, meas-
ured as shoot growth. The leaf concentration associated with 50 percent growth
reduction was selected as the phytotoxicity threshold (PT50) for use in the risk as-
sessment for the phytotoxicity pathway.
The PT50 was used because EPA determined that relatively severe initial effects
(50 percent or greater growth reductions) would be necessary to correspond to
later yield reductions, given that short-term growth effects do not necessarily trans-
late into longer term yield reductions at maturity (the actual criterion used to define
46 iSEPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
phytotoxicity). Exceeding the phytotoxicity threshold 1 out of every 100 times was
considered acceptable. Even if the Agency had chosen a 25 percent reduction in
growth (PT25) as the phytotoxicity threshold, the maximum loading rate (i.e., that
would not exceed the threshold leaf concentrations) would not have been meaning-
fully different from that calculated using the PT50. For example, at PT25 for zinc,
the probability that this threshold would be exceeded at a 3,500 kilograms per hec-
tare (kg/ha) loading rate would be 0.0011. This probability is equivalent to 1.1
chances in 1,000 (much less than 1 in 100). The probability of exceeding the PT50
at this same loading rate of 3,500 kg/ha would be <0.0001, or 0.1 chance in 1,000
(again much less than 1 in 100), as shown in Chart C of Box 10 (in Chapter 4).
Thus, the results using PT25 and PTS0 thresholds are not meaningfully different: 3,500
kg/ha would be the maximum loading rate for zinc determined using the probability ap-
proach under either threshold assumption. It is important to note that detection of
significant growth reduction in the field (across seasons for any crop) of less than 25
percent—from any cause—is very difficult.
Step 2: Next, EPA used data from biosolids field experiments in which corn or soy-
beans had been grown. Because EPA had previously determined that uptake of
metals by plants grown on biosolids-amended soils in the field cannot be simulated
by plants grown in pots (see "Pot/Salt Studies Overestimate Risk," earlier in this
chapter), EPA limited uptake data strictly to that obtained from field studies. EPA
calculated geometric means and standard deviations of metal concentrations in
plant tissues corresponding to various soil metal loadings. These data were then
used to determine probabilities of reaching the PT50 for each metal in each plant
species. Com was selected as the focus of the analysis because more field data
were available for corn than for any other plant species. A value of 0.01 was se-
lected as an acceptable level of tolerable risk for exceeding the PT50 (i.e.,
exceeding the PT50 1 out of every 100 times was considered acceptable). The
probabilities of the pollutants in field-grown corn meeting or exceeding the PT50
threshold were significantly less than 0.01 at all biosolids loading rates analyzed,
the highest of which were 3,500 kg/ha.for zinc and 1,500 kg/ha for copper. An ex-
ample of how the probabilities were used to select the limit for zinc is shown in
Chapter 4, Box 10 (see Approach 1 and Chart C).
For chromium and nickel, the probabilities that these metal concentrations in corn
leaf would exceed their PT50s decreased as the cumulative loadings increased.
This might be caused by dilution or by reactions of other biosolids constituents with
chromium and nickel, rendering these metals less bioavailable. Because plant
yields in field experiments did not show any negative effects from biosolids applica-
tion (i.e., in all cases, there was no yield suppression, and in many cases yields
increased), it is probable that phytotoxicity does not occur from chromium or nickel.
Based on maximum loadings used in the evaluated scientific research, EPA deter-
mined that 3,000 kg/ha chromium and 420 kg/ha nickel can be safety applied
without affecting corn yields.
Second Procedure for Determining Plant Metal Concentrations
That Characterize Phytotoxicity (the Calculation Approach)
A problem inherent in the Probability Approach discussed above is that corn is not
very sensitive to phytotoxicity from metals; thus, a second procedure also was
used to characterize phytotoxicity. In EPA's second procedure, plant tissue concen-
trations associated with yield reduction were obtained from the literature to define
an upper bound on phytotoxic effects for sensitive plant species (e.g., lettuce).
Sensitive plant species are more susceptible than corn to metal-induced inhibition
of growth (phytotoxicity). These data were used to develop plant tissue levels of
metals associated with first detectable yield reductions. These concentrations
were identified as the phytotoxicity threshold for each of four metals.
Part 503 Risk Assessment «EPA 47
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Chapter 3
More specifically, using a linear response slope assumption (which is highly con-
servative given the plateau response actually seen for biosolids—see "Plant
Response to Metals," earlier in this chapter), EPA calculated the geometric and
arithmetic means for plant response to each metal, which were used to calculate
the metal loading projected to result in plant tissue concentration associated with
the first detectable yield reduction. The average of these geometric and arithmetic
means were individually calculated for each metal as cumulative load applications
in kg/ha (the phytotoxicity thresholds) (see Chapter 4, Box 10, Approach 2).
Selection of the Most Conservative Loading Rate From the First
and Second Approaches as the Phytotoxicity Limit
For zinc, a mean of 2,800 kg/ha was calculated as the loading rate using the sec-
ond procedure described above (the Calculation Approach; also see Chapter 4,
Box 10), which was compared to the value determined using the Probability Ap-
proach (first procedure, described above). A limit was never actually reached for
zinc using the Probability Approach (i.e., no phytotoxicity was observed even at the
highest loading rate, so the highest loading rate analyzed, 3,500 kg/ha, was identi-
fied as a "limit"). The 2,800 kg/ha value identified by the Calculation Approach was
within the upper loading range (2,500-3,500 kg/ha) of the Probability Approach,
and thus 2,800 kg/ha, the more conservative rate, was chosen as an appropriate
pollutant loading rate for zinc.
For copper, a mean of 2,500 kg/ha was calculated as the pollutant loading rate us-
ing the Calculation Approach, which was compared to the value identified in the
Probability Approach (cumulative loading rates up to 1,500 kg/ha). The more con-
servative of these two values—the 1,500 kg/ha—was chosen as the appropriate
limit for copper.
Similarly, for nickel, a limit of 2,400 kg/ha was calculated using the Calculation Ap-
proach as compared to 420 kg/ha for the Probability Approach. The more
conservative value of the two, 420 kg/ha, was chosen as an appropriate limit for
nickel.
Finally, for chromium, a limit could not be identified using the Calculation Approach.
Thus, the maximum loading rate used in any experiment using the Probability Ap-
proach, 3,000 kg/ha, was used as an appropriate limit for chromium even though
no yield reduction was observed using this procedure either. It should be noted that
chromium will likely be dropped from the Part 503 rule due to the lack of adverse
effects and a recent court action (see also the discussions on chromium in Steps P
and Q of this chapter).
Holistic Review of Field Data To Determine If Phytotoxicity
Limits Were Protective
A comprehensive review was made of plant metal concentration data and yields
from all available biosolids field studies (U.S. EPA, 1992a), including all data re-
flecting various soil types and biosolids sources. This review found no instances of
phytotoxicity concentration limits being exceeded nor yield reductions, even in
crops that tend to accumulate metals and exhibit phytotoxicity symptoms, such as
Swiss chard, lettuce, and soybeans, unless the biosolids contained very high con-
centrations of metals (above Part 503 ceiling concentrations) or the plants were
grown in soils at very low pH,
The studies where phytotoxicity did occur were considered atypical because of
abnormally high metal concentrations in the biosolids or very low soil pH. These
high-metal biosolids can no longer be land applied due to pretreatment standards
and/or because they are excluded from being land applied by the ceiling concen-
tration limits in the Part 503 rule. In addition, the agricultural use of soils with low
pHs (below 5.5) is unlikely because normal agronomic practice calls for maintain-
48 ©EPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
ing soils above pH 6.0 to prevent the solubilization of naturally occurring metals in
soil, such as aluminum and manganese; these metals can have a significant toxic
effect on plants (whether or not biosolids are used). Hence, data from these atypi-
cal field studies were not used in developing the final phytotoxicity pollutant limits.
Risks to Soil Microbes?
Most studies have shown no adverse effects on soil microbial activity associated
with metals in biosolids or soil (including nitrification and mineralization of nitrogen,
as well as normal development and functioning of nitrogen-fixing bacteria for leg-
umes, other than white clover). In one study, however, on land known as the
Woburn experimental plots in England, a strain of Rhizobium lost its ability to fix ni-
trogen on one strain of white clover. This loss in ability was noted after a 19-year
period of biosolids application with moderately high concentrations of metals (e.g.,
100 mg Cd/kg biosolids and 3,000 mg Zn/kg biosolids) to sandy soil on which
vegetable crops were being grown. (Nitrogen-fixing microbes are important in agri-
culture and the environment. They have the unique capability, while in symbiosis in
nodules on the plant root, of converting nitrogen gas from the air into organic nitro-
gen, rather than requiring the plant to absorb fertilizer nitrogen from the soil. The
organisms live on the root in irregular, rounded, lump-shaped growths with mutual
benefit to both the microbes and plant.)
At the Woburn experimental plots, biosolids were applied from 1942 to 1961. The
unique circumstances of the field plots and the findings are as follows:
• No legumes have been seeded into the plots since the initial year of biosolids
application, and no new soil microorganisms had been deliberately introduced
to the plots for over 20 years after the last application of biosolids.
• Researchers have studied the different species of crops that have grown on
these plots long after cultivation of vegetable crops and additions of biosolids
ceased, and they have found:
- One strain of naturally occurring Rhizobium on one strain of white clover
and one strain of blue-green algae were not capable of fixing nitrogen.
- Regarding the strain of Rhizobium affected, no phytotoxicity occurred to
the white clover if nitrogen fertilizer was added.
- If the plots were inoculated with Rhizobium leguminosarum biovar trifoti
(an effective strain of Rhizobium that can form nodules with a group of
plant species that includes white and red clover and Phaseolus beans,
among others), normal nodule formation and fixation of nitrogen oc-
curred (McGrath et al., 1988).
- After inoculation, effective strains of Rhizobium persisted in the soils, at
least as long as clover was regularly grown on the soil (Angle et al.,
1993).
• Strains of white clover Rhizobium on the Woburn plots are considerably more
sensitive to zinc and cadmium than United States strains studied under similar
conditions (Angle et al., cited in Chaney and Ryan, 1993).
Several studies have found effective strains of white clover Rhizobium in farm
fields rich in metals. One such study involved soils near a zinc smelter in Pennsyl-
vania, where zinc and cadmium levels in the soil were much higher than in the
Woburn study (Angle and Chaney, 1988; Angle et al., in Chaney and Ryan, 1993).
Another similar study was reported by Obbard and Jones (1993).
Other research on mine spoils with high levels of metals, analogous to free metal
salts in soil, has shown that nitrogen fixation was inhibited in free-living bacteria
(Rother et al., 1982), but not by white clover Rhizobium until metals levels were so
high that phytotoxicity to white clover plants was observed. For all the above rea-
Part 503 Risk Assessment SEPA 49
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Chapter 3
sons, EPA concluded that it was not appropriate to use data from the Woburn study
to limit metal applications for the Part 503 rule.
A new study (Ibekwe et al., 1995) provides strong evidence that biosolids were not
the cause of Rhizobium becoming ineffective on the Woburn plots. Instead, re-
searchers determined that low soil pH caused selection of ineffective strains of
Rhizobium in both experimental controls (soils without biosolids added) and
biosolids-amended soils.
Additional Ecological Monitoring Research
As noted earlier in this section, ecological data are limited. Moreover, at the time
the Part 503 risk assessments were conducted, EPA did not have an Agency-wide
approved procedure for conducting comprehensive ecological risk assessment. As
a result, the biosolids risk assessments did not examine effects on species popula-
tions or communities; however, EPA did use the best available data on toxicity to
wildlife and plants from pollutants in biosolids in its ecological risk assessment. In
so doing, EPA evaluated risks to the most sensitive or most exposed species for
which such toxicological data existed. EPA believes that its approach of using only
toxicity and uptake data for the same sensitive species was both appropriate and
protective of the environment. EPA did not believe that it was appropriate to apply
pollutant toxicity data obtained for one highly sensitive species to another unrelated
species in situations where exposure and uptake or ingestion was known to be
very high but the pollutant toxicity data were unknown.
As is always the case with limited data sets, additional experimental data would be
desirable. To improve its ability to consider ecological risk from land application of
biosolids in the future, EPA has committed itself to conducting and supporting work
by others on the ecological impacts of biosolids use. EPA also is working on the
further development of a methodology that can gain widespread approval for use in
conducting full ecological risk assessments. Biosolids-related ecological research
on which EPA will be focusing includes:
• Validation of ground-water models
• Validation of surface-water runoff models
• Further investigation of the nature and ability of biosolids matrices to bind met-
al pollutants
• Further review of the procedures for determining phytotoxicity
• Further evaluation of ecosystem impacts resulting from the land application of
biosolids
Step N-4 Allow Use of PSRP and PFRP for Regulating
Pathogens
The regulation of pathogens (e.g., disease-causing organisms such as bacteria
and enteric viruses) in the final Part 503 rule is not based on a risk assessment be-
cause methodologies had not been developed sufficiently to make such
calculations. Instead, the Part 503 pathogen operational standard, which is non-
risk based, includes pathogen controls and monitoring requirements for all
biosolids, and crop-harvesting, animal grazing, and site-access restrictions for cer-
tain biosolids. This operational standard was based on extensive experimental data
and years of experience and, in the judgment of EPA, is protective of public health
and the environment.
Proposed Rule: For the proposed rule, EPA recommended extensive monitoring
of pathogens using one of several different monitoring alternatives. The proposed
rule did not permit the use of the older, established processes prescribed in EPA's
50 &EPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment issues
Part 257 rule to significantly reduce pathogens (PSRP) or to further reduce patho-
gens (PFRP),
Final Rule: The final rule permits a combination of monitoring requirements and
PSRP and PFRP approaches for controlling pathogen densities in biosolids. The
Part 503 rule is different from the Part 257 rule in that it contains separate require-
ments for pathogen reduction and vector attraction reduction. A more complete
description of the requirements for controlling pathogens and vector attraction may
be found in A Plain English Guide to the EPA Part 503 Biosolids Rule (U.S.
EPA, 1994) and Control of Pathogens and Vector Attraction in Sewage Sludge
(Including Domestic Septage) Under 40 CFR Part 503 (U.S. EPA, 1992d).
Step N-5 Regulation of Non-Agricultural Land
Application of Biosolids
Proposed Rule: To protect public health and the environment from pollutants in
biosolids at non-agricuitural land application sites (e.g., forests, reclaimed lands,
public contact sites) or at surface disposal sites, EPA proposed a policy-based ap-
proach in which pollutant limits were set so that they did not exceed the
98th-percentile concentration of pollutants found in the "40 Cities Study" (see
Chapter 2). This approach was recommended because low risk to humans and do-
mestic livestock was expected, given that exposure to pollutants in biosolids at
such sites was negligible and pollutant concentrations were found to be low in most
biosolids. This approach also was proposed because a risk assessment methodol-
ogy for such sites did not exist.
Commentors reacted critically to the proposed 98th-percentile approach. They ac-
knowledged that on a simplistic level the 98th-percentile limit would only result in
elimination of 2 percent of biosolids from non-agricultural land application or sur-
face disposal. The commentors pointed out, however, that it often was a different 2
percent (of the 26 pollutants proposed for regulation in biosolids) that would be
eliminated from use or disposal by this non-risk-based approach, and as many as
52 percent of biosolids could theoretically be eliminated from land application (see
Box 8).
Final Rule: The 98th-percentile approach for regulating non-agricultural application
and surface disposal was dropped from the final rule because of the difficulties de-
scribed above. In addition, refined modeling techniques had been developed that
the Agency used to conduct formal risk assessments for non-agricultural land appli-
cation and surface disposal. Hence, in the final Part 503 rule, pollutant limits for
non-agricultural land and surface disposal were risk based.
Prior to establishing the final Part 503 risk-based limits for land application of
biosolids, the risk-based limits for non-agricultural and agricultural land application
were compared and found not appreciably different. Hence, EPA decided to sim-
plify the final rule by using only one set of limits for both types of land application.
EPA selected the most stringent of the non-agricultural or agricultural land application
limits for each pathway, on which the Part 503 pollutant limits were based regardless
of whether the land is being used for agricultural or non-agricultural purposes.
Step N-6 Ceiling Concentration Limits and Caps on
Pollutant Concentration Limits
Ceiling Concentration Limits Set After ORD Review
ORD raised an important issue during its final review of the Part 503 rule prior to
promulgation regarding the representativeness of the selected plant uptake data.
ORD's concern arose because data from experiments involving the use of
Part 503 Risk Assessment <&EPA 51
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Chapter 3
Box 8
Potential Impact of a 98th-Percentile Approach on a Biosolids Data Set
• A hypothetical data set contains 100 biosolids and 26 regulated pollutants.
• If there was only one regulated pollutant in the data set of 100 biosolids, then the tv\ o biosolids with the
highest concentrations of that pollutant would be prohibited from being applied to non-agricultural land
or surface disposed, based on the 98th-percentile approach. (It should be pointed out that this prohibition
would be imposed regardless of whether those levels were high enough to pose a risk to public health or
the environment.)
• Theoretically, if there were 10 regulated pollutants, 20 different bio olids could be prohibited from being
applied to non-agricultural land or surface disposed. ;
• With 26 regulated pollutants, 52 different biosolids could be prohibited from being applied to non-agri-
cultural land or surface disposed using this approach. ;
• An evaluation of a Michigan data set containing analyses of Over 200 biosolids samples revealed that
nearly 40 percent of the biosolids from POTWs in that data set would have been prohibited from being
applied to non-agricultural land or surface disposed if non-risk-based 98th-percentile concentration limits
were the final pollutant limits in the Part 503 rule.
Thus, the 98th-percentile approach was dropped. Part 503 pollutant limits for non-agricultural land appli-
cation and surface disposal were based on risk assessments.
biosolids with high pollutant concentrations were not included in the data set. EPA
did not include these data because they were viewed as nonrepresentative (i.e.,
uptake of pollutants from high-pollutant concentration biosolids is more like uptake
from metal salt and pot studies, discussed earlier in this chapter). To overcome the
potential problems associated with phytotoxicity data from soils amended with
biosolids containing high pollutant levels or from metal pot/salt studies, a policy de-
cision was made to establish 99th-percentile ceiling concentration limits. These
ceiling limits preclude land application of biosolids if any of the regulated pollutant
concentrations in the biosolids are greater than the 99th percentile of the pollutant
concentrations in the NSSS or the calculated risk-based pollutant concentrations,
whichever is the least stringent (also see Chapter 5).
Caps: A Risk Management Decision
EPA also chose to include caps (as pollutant concentration limits for land applica-
tion, discussed earlier in this chapter and in Chapter 5) at levels that were
previously calculated as permissible by the risk assessment. The pollutant concen-
trations calculated by the risk assessment were compared with the 99th-percentile
pollutant concentrations in the NSSS. If the 99th-percentile concentration was
more stringent than the pollutant concentration identified by the risk assessment,
as was the case for chromium and selenium, then the 99th-percentile number was
used to cap (reduce) the calculated risk-based concentration and became the con-
centration limit for that pollutant. If the risk assessment limit was more stringent
than the NSSS level, the risk assessment number was used as the pollutant con-
centration limit. For chromium and selenium, these determinations will likely be
moot because of court determinations described in Steps P and Q of this chapter.
Additional Discussion
The ceiling concentration limits and the caps on pollutant concentration limits in
biosolids in the Part 503 rule provide an additional margin of safety. The ceilings
and caps also help ensure that the quality of current biosolids is maintained. The
52 •SERA Part 503 Risk Assessment
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NO
BJOSOLIDS
• 30 T°WS OF
S'OSPUDS :
Corn grown without biosolids (left), compared with corn grown in
biosolids-amended soil (right).
decision to use the 99th-percentile ceiling limits and caps was a policy decision, al-
though (as described above) the use of these limits ensures that the biosoiids
being used have pollutant concentrations consistent with the biosolids field data
used for the risk assessment. EPA chose the 99th-percentile rather than the 98th-
percentile limits for caps and ceiling limits for the final rule to reduce the impact on
wastewater treatment facilities. If ceiling limits and caps had been set at the 98th
percentile of the NSSS data, a significantly greater percentage of biosolids gener-
ated in the United States would have been precluded from land application (see
Box 8), Because neither percentile is risk-based, the less restrictive 99th-percentile
limit was chosen. Other means of encouraging the further reduction of metal con-
tent in biosolids include the reduced Part 503 regulatory requirements for biosolids
meeting pollutant concentration limits and Class A pathogen requirements; guid-
ance provided to biosolids generators; and the continued emphasis on
pretreatment and source reduction. As stated above, the determinations pertaining
to caps will likely be moot because of court determinations described in Steps P
and Q below.
EPA believes that the 99th-percentile approach is appropriate for ceiling concentra-
tion limits, given that it prohibits the most contaminated biosolids (which act more
Part 503 Risk Assessment wEPA 53
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Chapter 3
like metal salts) from being land applied. This approach supports the selection of
data from biosolids field experiments used for the risk assessment, which did not
include biosolids with the highest metal content and also did not include metal
pot/salt studies.
Step N-7 Protection of Ground Water From Excess Nitrogen
Ground water is protected from biosolids with nitrogen levels in excess of esti-
mated crop needs by the Part 503 rule's requirement that biosolids be land applied
at the agronomic rate. Ground water also is protected by Part 503's requirement
that nitrate-nitrogen be monitored at biosolids surface disposal sites.
Some commentors on the biosolids rule proposed assigning a fraction of the ni-
trate-nitrogen Maximum Contaminant Level (MCL) for ground water (which is 10
ppm) to biosolids that are used or disposed. EPA found no basis for such an as-
signment. Therefore, as EPA does for all pollutant sources of nitrate-nitrogen, the
Agency assigned the entire 10-ppm MCL for nitrate-nitrogen content in ground
water to biosolids. The Agency agreed to review this decision based on further
analysis at a later time.
Step N-8 Management and Regulation of Nutrients
The Part 503 requirement for the application of biosolids at the agronomic rate ap-
propriate for the yield and crop being grown is consistent with sound management
of the nutrient nitrogen. Although EPA considered using the Part 503 rule as part of
an overall nutrient management model (i.e., for regulating the application of a num-
ber of nutrients from various sources), the Agency made a policy decision not to
address this complex issue in the Part 503 rule. Many other sources of nutrients
would need to be involved in a nutrient management program (e.g., chemical fertil-
izers, animal manures, other wastes), which EPA does not have the authority to
regulate under the Clean Water Act. Moreover, EPA believes that other agencies
and knowledgeable parties should be involved in developing such a program. In
addition, EPA felt that biosolids should not be singled out from other nutrient
sources, particularly because biosolids tend to pose less of a public health and en-
vironmental risk due to lower nutrient levels in biosolids than many other sources
and because currently no EPA nutrient requirements address these other sources
of nutrients.
Step P USDA Comments, EPA Revisions
Issues regarding the final, promulgated Part 503 rule were raised by a number of
outside commentors. Some of the issues and recommendations by the U.S.
Department of Agriculture (USDA) are presented below to illustrate the interaction
between risk assessment and risk management in establishing the Part 503 pollu-
tant limits.
Cadmium: USDA recommended that the ceiling concentration limit for cadmium in
biosolids land applied to soils be limited to 21 mg-Cd/kg-soil, dry-weight basis,
rather than the current Part 503 limit of 39 mg Cd/kg.
USDA noted that certain European Union (EU) and other potential international
markets for U.S. grains and sunflower kernels have established very low cadmium
concentration limits for imported grains, even though no risk has been identified
from ingestion of grains with such low cadmium levels in careful scientific research.
Hence, grains produced in the United States with cadmium contents in excess of
the imposed standards of other countries could not be exported to those countries.
USDA agrees that grain produced on soils amended with biosolids containing 39
mg Cd/kg does not pose a risk (unless the cadmium to zinc ratio is much higher
than normal levels [<0.0145]). Nonetheless, because of these international market
54
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Identification and Resolution of Risk Assessment Issues
restrictions, USDA has recommended lowering the cadmium limit. USDA suggests
that a 21 mg Cd/kg limit would be relatively easy to attain given that 91 percent of
U.S. wastewater treatment facilities that generate biosolids could meet this limit
(based on data from the NSSS).
USDA pointed out that exporting grains containing cadmium is already a problem
because some regions of the United States currently cannot meet the EU limits
due to naturally occurring levels of cadmium in soils. In addition, certain crop spe-
cies accumulate higher cadmium levels in their grain than do other crops. USDA is
concerned that use of biosolids containing levels of cadmium as high as 39 mg/kg
(particularly on acidic soils, which may result in plants taking up more cadmium)
could further exacerbate current exportation problems by causing the production of
even more grains with cadmium levels above the EU limits.
Changing the limit from 39 mg Cd/kg could be problematic because, as discussed
in the next section (see "Provisions of the Rule Remanded by the Court"), the court
challenged EPA's use of non-risk-based means for setting certain limits. USDA and
EPA are planning to issue guidance on this issue.
Molybdenum: USDA also recommended that EPA reduce the ceiling concentration
limit for molybdenum (Mo) in biosolids to 54 mg Mo/kg, the 98th percentile in the
NSSS. This recommendation was made because some of the field studies from
which plant uptake slopes for molybdenum for sensitive crop species were calcu-
lated did not involve alkaline soil pH. USDA was concerned that because
molybdenum uptake is much greater at pH 8 than at pH 7, an HEI ruminant animal
might not be protected from biosolids with higher concentrations of molybdenum
applied to alkaline soils.
EPA deleted all requirements from the Part 503 rule for molybdenum except the
ceiling concentration limits as a result of the February 25,1995, amendment, pend-
ing careful additional study and consideration of new data (see Chapter 2). No final
decision on establishing new pollutant limits for the deleted molybdenum limits had
been reached by EPA at the time of this document's preparation. EPA does not ex-
pect to change the existing ceiling concentration limit for molybdenum.
98th Instead of 99th Percentile as a Cap on Pollutant Concentration Limits:
USDA believes that lowering the cap on pollutant concentration limits for additional
protection (from the current 99th percentile to the 98th percentile, as was pre-
viously proposed by EPA) would be a prudent policy decision.
The recent remand by the court that would preclude EPA's use of policy-based
99th-percentile NSSS concentration limits as caps to pollutant concentration limits
would suggest that use of 98th-percentile NSSS concentration limits as caps would
not be possible (see Step Q below on court remands).
Annual Pollutant Loading Rate Limits: USDA recommended that annual pollu-
tant loading rate (APLR) limits should be deleted from the final Part 503 rule. USDA
pointed out the limited usefulness of the APLR approach for regulating the use of
biosolids in bags or containers, which was originally devised prior to the develop-
ment of the "pollutant concentration limit" approach (discussed earlier in this
chapter and in Chapter 5). USDA recommends deleting the APLR approach be-
cause its use would allow distribution to the public of biosolids containing higher
levels of pollutants than the pollutant concentration limit approach.
EPA believes that the likelihood of the APLR approach being used has greatly di-
minished now that the pollutant concentration limit approach has been adopted in
the final rule. The Agency has made no decision about whether to drop the APLR
approach from the rule at the time of this document's preparation.
Part 503 Risk Assessment
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Chapter 3
Chromium; USDA has recommended that chromium limits be deleted from the
Part 503 rule because there is no evidence of damage to plants or animals from
the levels of chromium currently found in biosolids. The court remanded the chro-
mium limits to EPA for modification or additional justification.
EPA plans to delete all chromium limits for land-applied biosolids from the Part 503
rule. An important reason for imposition of the chromium limits by EPA was a pol-
icy-based desire to reduce levels of chromium in wastewater effluents and
biosolids via pretreatment.
Soil pH: USDA recommended that EPA reconsider its decision not to impose soil
pH requirements in the Part 503 rule for biosolids that contain an insufficient lime
equivalent to neutralize the acidity generated during oxidation of biosolids in
biosolids-amended soils.
EPA has decided not to make this recommended change. (See also the discussion
regarding pH earlier in this chapter.)
Selenium: USDA recommended limiting the addition to soil of selenium in biosolids
to 28 kg/ha to avoid excessive plant uptake and possible poisoning of certain sen-
sitive livestock or wildlife.
No decision on this issue had been reached by EPA at the time of this document's
preparation.
Arsenic: USDA recommended increasing the pollutant concentration limit for arse-
nic in the Part 503 rule because the conservative policy decision to use a relative
effectiveness (RE) value of 1 (i.e., implying that arsenic is highly bioavailabie, see
Chapter 4) caused the current Part 503 pollutant concentration limit to be much
lower than if calculated using experimentally derived RE values (i.e., the bioavail-
ability of biosolids-applied arsenic is much lower than assumed).
EPA has no current plans to change the pollutant concentration limit for arsenic in
the Part 503 rule.
Step Q Lawsuits, Provisions of the Rule Remanded by
the Court
The provisions of the Part 503 rule remanded to EPA for modification or additional
justification by the court are still applicable while EPA studies the remanded issues
and decides whether to (1) agree with the court recommendations, (2) justify the
provisions, or (3) recommend no or partial change. The remanded provisions are
summarized below.
Chromium: The court stated that EPA should drop chromium from the Part 503
rule because the biosolids risk assessment did not identify any chromium level as-
sociated with risk to public health or the environment. EPA agrees and plans to
delete all chromium limits for land-applied biosolids from the Part 503 rule.
Selenium: In response to the pleadings of a plaintiff that the EPA selenium limits
posed a special hardship to certain communities because of naturally occurring
high levels of selenium in the area, the court reviewed the various selenium limits
in the rule. The court stated that the capped 99th-percentile pollutant concentration
limit for selenium was based on a policy decision and should be eliminated. In light
of other comments by USDA that the current ceiling limit is too high and may cause
a problem for animal life (see preceding section), EPA has a difficult decision to
make. If the only basis for lowering the limit is a policy decision, EPA may recom-
mend changing the capped selenium pollutant concentration limit from 36 to 100
mg/kg biosolids.
The court also remanded to EPA the potential for a special provision to allow in-
creased selenium pollutant limits on public contact sites with a low potential for
exposure.
56 -SEPA Part 503 Risk Assessment
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Identification and Resolution of Risk Assessment Issues
Heat-Dried Biosolids: The court remanded to EPA the issue of whether to estab-
lish a special provision that would set higher pollutant concentration limits for
heat-dried biosolids. The reason for the remand was a plaintiff's pleading that heat-
dried biosolids would always be used at low rates and therefore should be allowed
higher pollutant concentration limits. Most likely, EPA will not make this change.
Dedicated Beneficial Use of Biosolids: The court asked that EPA consider mov-
ing the category of "dedicated beneficial use of biosolids" from the surface disposal
to the land application section of the Part 503 rule. A plaintiff argued in his pleading
to the court that having dedicated beneficial use of biosolids in the surface disposal
section of the Part 503 rule is very detrimental to efforts for gaining public accep-
tance for using biosolids to improve highly acidic disturbed lands that are also
particularly low in organic matter and plant nutrients.
The court agrees that EPA does not need to move the "dedicated beneficial use of
biosolids" category from the surface disposal to the land application section of the
rule. Moving this category to the land application section of the rule, however,
would help encourage beneficial use of biosolids and reclamation of disturbed
lands, another important EPA goal. No decision on this issue had been reached by
EPA at the time of this document's preparation.
Part 503 Risk Assessment SEPA 57
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Chapter
4
How the Risk Assessments
Identified Pollutant Limits for
Biosolids
The goal of the Part 503 biosolids risk assessments was to establish risk-
based pollutant limits that protect human health and the environment from
reasonably anticipated adverse effects of pollutants in biosolids. EPA used
four types of information in its biosolids risk assessments:
• Available Scientific Data (e.g., toxicity factors commonly used by EPA, such
as RfDs or q-|*s, were used to identify adverse effects associated with specific
concentrations of pollutants; field study data were used to determine plant up-
take of pollutants from biosolids-amended soils).
• Assumptions when specific information was not available (e.g., 70-year life-
time exposure was assumed for most pathways; assumptions were made
regarding quantities of food grown on land amended with biosolids; and linear
uptake of pollutants by plants was assumed).
• Policy decisions when specific scientific data regarding risks were unavail-
able (e.g., a cancer risk level of 1 x 10"4 was used).
• New or existing methodologies (e.g., development of a new method for esti-
mating food consumption; for the ground-water pathway, the VADOFT and
AT123D computer models were used to estimate pollutant transport through
the environment).
How Pollutant Limits Were Derived
in the Revised Risk Assessments
This chapter explains how EPA used the revised biosolids risk assessments to de-
velop pollutant limits for evaluated exposure pathways, from which the final Part 503
pollutant limits were selected. The process of developing pollutant limits involved:
• Determining and defining factors to be used in calculating pollutant limits
• Selecting key data, assumptions, and methods to be used, and making related
policy decisions as needed
Part 503 Risk Assessment SEPA 59
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Chapter 4
* Performing risk assessment calculations
In describing each of these steps, this chapter provides example risk assessment
calculations for several exposure pathways; explanations of how a Part 503 pollu-
tant limit was selected for land application, surface disposal, and incineration of
biosolids; and a detailed discussion of the risk assessment conducted for cadmium
in land-applied biosolids, exposure pathway 2.
Parameters, Assumptions, Policy
Decisions, and Methods Used
The biosolids risk assessments used a series of algorithms, or equations, that
mathematically represented each exposure pathway to calculate pollutant limits. A
biosolids pollutant limit is the pollutant loading rate or concentration of a particular
pollutant in biosolids that would not be expected to harm public health or the envi-
ronment via the pathway being evaluated when biosolids are land applied or
placed on a surface disposal site. Pollutant limits for the incineration of biosolids
protect only public health because ecoiogicai pathways were not evaluated.
Each set of algorithms contained a sufficient number of parameters (appropriate input
factors) for calculating the pollutant limits. Some of the parameters used in the algorithms
were readily available, such as standard toxicity factors used by EPA (i.e., RfDs or qi*s).
Other parameters had to be calculated using an appropriate methodology, or were se-
lected based on assumptions and/or policy decisions. An example of an assumption is
the percentage of food grown on biosolids-amended soils—known as the FC parameter.
Table 6 (in Chapter 2) summarizes the exposure pathways used in the risk assessment
for land application and provides a quick reference regarding when certain parameters
were used (e.g., for pathways evaluating human, animal, or plant exposures.) For more
information on the development of the exposure pathways, see Chapter 2.
Land Application Risk Assessment
AH of the parameters used in the different algorithms for conducting the biosolids
land application risk assessment are defined in Appendix A. The methodologies
(i.e., approach or basis), assumptions, and policy decisions used to establish nu-
meric values for the parameters in the land application risk assessment are
described in Appendix B; this table also indicates whether a parameter is conserva-
tive or average, and why. How these parameters were used is discussed below.
Risk Assessment Calculations
For all exposure pathways for land application, an allowable dose of each pollutant
was identified (e.g., based on an RfD or q^ for humans; or an appropriate repre-
sentation of allowable dose for animals, such as a "threshold pollutant intake," or
TPI). Initially, this allowable dose included pollutant exposure from all sources
(biosolids, food, air, and water). Exposure from sources other than biosolids were
then subtracted from the total allowable dose. The resulting .value indicated the al-
lowable dose of a pollutant from biosolids only (e.g., an RIA, see Appendices A and
B). This health parameter was then combined with pollutant intake information (e.g.,
the amount of a pollutant in biosolids taken up by plants that are then ingested by hu-
mans; the amount of a particular food consumed) to derive a pollutant limit.
The selected or calculated values for the parameters (e.g., see Box 9, Chart A, and
Box 10, Chart B) were used in algorithms specific to each exposure pathway to cal-
culate pollutant limits. For many of the exposure pathways, calculating pollutant
60 i&EPA Part 503 Risk Assessment
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How the Risk Assessments Identified Pollutant Limits for Biosolids
limits involved two or more algorithms. For example, the first algorithm might in-
volve calculating a health-based parameter (e.g., an R1A), followed by one or more
interim calculations that relate the health parameter to a pollutant concentration,
and a final algorithm that calculates a pollutant limit (an RP or RSC).
Examples of several biosolids risk assessment calculations for land application are
shown in Boxes 9 through 14. These examples illustrate how different parameters and
algorithms were used to calculate limits for organic and inorganic pollutants that would
protect humans, animals, and plants from reasonably anticipated adverse effects via
the different exposure pathways. As shown in Box 9, two algorithms were needed to
calculate the pollutant limit for arsenic for exposure involving an adult eating crops via
Pathway 1. As shown in Box 14, seven different algorithms were needed to calculate
the PCB pollutant limit for an adult drinking surface water and ingesting fish from water
that had been subjected to runoff from biosolids-amended soils.
Approach Used for the Surface
Disposal Risk Assessment
Thus far, examples of how the biosolids risk assessments were conducted have fo-
cused on land application. Somewhat different approaches were used to determine
pollutant limits for surface disposal and incineration of biosolids, as discussed below.
The risk assessment for surface disposal of biosolids evaluated risks associated
with:
• MonofUis (which contain biosolids with a solids content generally of 20 percent or
greater) and surface impoundments (which contain liquid and sediment layers),
both lined and unlined, to represent the variety of surface disposal sites.
• Human exposure to pollutants in biosolids through ground water (from drink-
ing water from different classes of ground water, i.e., Class I, II, and 111,
according to EPA's ground-water classification system). For the ground-water
pathway, lined units generally reduced pollutant transport risks to ground water
but increased volatilization risks.
• Human exposure to pollutants in biosolids through inhalation of air containing
pollutants present in biosolids (the vapor, or air, pathway).
Risk-based criteria were developed for Class I and Class ll/lll ground water. A
framework established by EPA for federal and state policymaking efforts concern-
ing ground-water protection (Ground-Water Protection Strategy, 54 FR 5812,
February 6,1989) provides the following category definitions:
• Class I. An existing source of drinking water of unusually high value that is vul-
nerable to contamination and is either irreplaceable as a source of drinking
water for substantial numbers of people or is ecologically vital (i.e., as habitat
for rare or endangered species).
• Class II. All non-Class I ground water currently used for, or potentially available
for, drinking water.
• Class III. Ground water that is not being used as a source of drinking water
due to high concentrations of total dissolved solids or pollutants or because
the yields are too low to meet the needs of an average household.
Upon completion of the biosolids risk assessment, EPA made a policy decision to
regard ail ground water as drinkable in accordance with EPA's Class II designation.
Part 503 Risk Assessment &EPA 61
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Chapter 4
Box 9
Example Risk Assessment Calculation: Arsenic for an Adult Person Ingesting
Crops Grown in Biosolids-Amended Soils (Pathway 1)
This example illustrates the method used to calculate pollutant limits for inorganic, noncarcinogenic pollutants.
Goal: Calculate the amount of pollutant in biosolids that can be applied to a given area of land (e.g., hectare)
without reasonably anticipated adverse effects to humans. This level is defined as the reference application rate,
ofapollutant (RP). If the pollutant in question is inorganic (like arsenic), then it does not degrade in the envi-
ronment but accumulates as additional biosolids are added to soils.
Note: The exposure pathway discussed in this example is Pathway 1, in which biosolids are applied to soils,
plants are grown in the biosolids-amended soils, and humans eat the plants growia there. Appendices A and B
provide additional information on how the parameters presented below were used to determine pollutant
limits for biosolids.
Description of the Algorithm
Step 1:
RIA =
RfD-BW
RE
\
-TBI
•Mo3
Adjusted, reference
intake of pollutant =
in humans (RIA)
Oral
reference
dose (RfD)
Body
weight
(BW)
Relative effectiveness of
ingestion exposure (RE)
Total background
intake rate from
all sources (TBI)
x 10
RIA = Amount of additional pollutant ingested by humans without expectation of adverse effects (i.e., the allowable ,
dose). ' ii'
RfD = Amount of intake of a noncarcinogenic, usually inorganic, pollutant without appreciable risk. RfDs usually are
developed in specialized, small animal studies to determine the level of a pollutant above which toxic
responses begin to occur. These studies involve extrapolation and the application of safety factors to estimate
the safe level of pollutant intake by humans.
BVV = Human body weight.
RE = Relative effectiveness of exposure, which accounts for differences in bioavailability if a pollutant is ingested in
food or water or is inhaled. Because of limited data, this value was set at 1.0.
TBI = Total pollutant intake from all background sources in water, food, and air. >
Step 2:
RPc =
RIA =
UC =
DC =
FC =
RPc =
RIA
Sum(UC- DC • FC)
Reference cumulative
application rate of —
pollutant (RPC)
Adjusted reference intake of pollutant in humans(RIA)
Fraction of food
Uptake response
of pollutant
in plants (UC)
Daily dietary
consumption oj
food group (DC)
E - - . • „ ¦,. grown in
of pollutant x consumption of x , , ,
Jr „ , biosolids-amended
: soils (FC) . ;
The cumulative amount of a pollutant that can be land applied without adverse effects from biosplids exposure
via the pathway evaluated.
Amount of pollutant ingested by humans without expectation of adverse effects (i.e., allowable dose).
Plant uptake slope for pollutant from soils/biosolids. ' -
Dietary consumption of different food groups grown in soils amended with biosolids.
Fraction of different food groups assumed to be grown in soils amended with biosolids. ;'
62 &EPA Part 503 Risk Assessment
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How the Risk Assessments Identified Pollutant Limits for Biosolids
Box 9 (Continued)
Calculation of the Arsenic Pollutant Limit for Pathxvay 1
Step 1 Parameters:
Parameter
Value
Units
RfD
0.0008
milligrams per kilogram per day (mg/kg ¦ day). _ ' '
BW
70 .
kilograms (kg)
RE
1.0
no units - " _
TBI .
0.012
" milligrams pollutant per day (mg/day). -
103' '
103
conversion factor, micrograms per milligram (ug/mg)
Step 1 Calculation:
„„ RfD ¦ BW ^rti , 0.0008-70
RIA —— - TBI ¦ 10 = — ¦ - 0.012 10 =44 Li# arsentc/g-day
Kb . .1 .1). . ¦
Step 2 Parameters:
Parameter
Value
Units
RIA
44
: micrograms .pollutant.per day(jig/day)
UC
micrograms pollutant per gram of dry plant tissue (}ig/g DW)/kg-pollutant/hectnre
DC
', dry grams oi food group in the diet per day (g DW/day)
FC
no units'
J[UC ¦ DC ¦ FC = 0.00654 from Chart A
Chart A
Values for Parameters Used in Calculating the Pollutattt Limit for Arsenic, Pathway 1
Food Group
UC
DC
FC
UC DC FC 1
Other Variables
,
Potatoes ¦ -
0.002
15.5954-
0-025
0.00073 J
RfD
0.0008
Leafy vegetables
0.018 .
, 1.9672 '¦
0.025
O.00O91 . J
; BW
70
Legumes :
0.001
8.7462
' 0.025 ,
0.00024 j
RE
1
Root vegetables
0.004
' 1.5950 -
0.025
0.00015 " |
- - TBI,
0.121
Garden fruits _ -
0.001
" 4.1517
0.025''
0.00015 - , j
RIA
44 -
Peanuts
0.001
2.2538
0.025
0.00006 ; J
RPC
6,700 '
Grains and cereals
0.002 ,
- 96.6802
-0.025 •
0.00430 - j
-
Sum UC DC FC
" . '
0.00654 •
Step 2 Calculation:
RPC
RfA 44
00065?" kg/ha of arsenic biosolids {rounded).
"Y_UC ¦ DC - FC
Note: The most limiting pathway for arsenic was Pathway 3 (seeBox 11),
Part 503 Risk Assessment ®EPA 63
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Chapter 4
Box 10
Example Risk Assessment Calculation: PCBs for an Adult Person Ingesting Crops
Grown in Biosolids-Amended Soils (Pathway 1)
This example illustrates the method used to calculate pollutant limits for degradable, carcinogenic organic
pollutants.
Goal: Calculate the amount of pollutant in biosolids that can be applied to a given area of land (e.g., hectare)
without reasonably anticipated adverse effects to humans. This level is defined as the reference application rate of.
a pollutant (RP). The RP for organic pollutants (e.g., PCBs), which degrade in the environment, is an annual ap-
plication rate (rather than a cumulative loading rate as was used for inorganic pollutants, as in Box 9).
Note: The exposure pathway discussed in this example is Pathway 1, in which biosolids are applied to soils,
plants are grown in the biosolids-amended soils, and humans eat the plants grown there. Appendices A and B
provide additional information on how the parameters presented below were used to determine pollutant lim-
its for biosolids. . ,
Description of the Algorithm
Step 1:
MA-
RL-BW
\
q i*
¦RE
-TBI
icr
Adjusted reference
intake of pollutant
in humans (RIA)
Risk level (RL) -t Body weight (BW)
¦¦ Relative
Human cancer effectiveness
potency (gt*) X of ingestion
exposure (RE)
Total
background ^
•. intake. rate
from all
sources (TBI )
X 10
RIA = Amount of additional pollutant ingested per day by humans without expectation of adverse effects (i.e., the
allowable dose). - •
RL = Cancer risk level. The probability that one additional cancer case could be expected to occur in that part of the
population that is exposed. For the biosolids risk assessment, the RL was lx.10"4. This risk is equivalent to the
probability of one additional cancer case in a population of 10,000 exposed individuals. Note: The exposed,
population may be only a small fraction of the total population.
BW m Human body weight.
qi* = Cancer potency value. The qi* factor is the amount of intake of a chemical (organic or inorganic) that results in a
specified estimate of cancer risk The assumption is made that even one molecule of a cancer-causing compound
will have some risk. Qi*s usually are developed in specialized, small-animal studies. These studies involve
extrapolation and the application of safety factors to estimate an acceptable level of pollutant intake by humans.
Ql*s are conservative estimates (i.e., contain relatively large safety factors). ;:
RE = Relative effectiveness of exposure, which accounts for differences in bioavailability if the pollutant is ingested in
food or water or is inhaled. Because of limited data, this value was set at 1.0.
TBI as Total intake of the pollutant from all background sources in water, food, and air—assumed negligible because
organic PCB compounds are considered degradable. - ;
64 SEPA Part 503 Risk Assessment
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How the Risk Assessments Identified Pollutant Limits for Biosoljds
Box 10 (Continued)
Step 2:
RLC = - RIA
J^UCDCFC
Reference
concentration _ Adjusted reference intake of pollutant in humans (RIA)
of pollutant ... :, Daily dietary Fraction of food
in soil (RLC) Uptake response ^
imption group grown in
of pollutant x of food group X blosollds_amended
in plants (UC) ^
soil (FC)
RLC = Pollutant concentration in soil considered to be without expectation of adverse effect for animals or humans.
UC * = Plant uptake slope for pollutant from soils/biosolids.
DC = Dietary consumption of different food groups grown on land amended with biosolids. ;
FC. =. / Fraction of different food groups assumed to be grown on land amended with biosolids.
Step 3:
ln2
, Logarithmfactor (ln2)
First-order decay rate constant (k) = —————¦¦ ¦<.
Time factor (To 5)
k = First-order decay rate constant (yr1)
In = Natural logarithm
T05 = Malf-life of pollutant in soil (yr)
Step 4:
RP - RLC ¦ MS ¦ 1CT9 • [1 + e~k + e^ +...+e{x~n)kYl
¦ Reference annual Reference . ,,. - ~ .
„ ¦ r Weight of Decay
application concentration of „
. * = »t . x upper 15 cm x factor
rate of pollutant in „ ... .
pollutant (RP) soil (RLC) of soil (MS) (k)
RPa = The amount of a pollutant that can be applied to a hectare of land per.year .without expectation of adverse
effects.
MS = Assumed mass of dry soil in the upper 15 centimeters of soil. ¦¦ ¦¦ ¦ >-!¦¦
10"9 = Conversion factor,
e = Base of natural logarithms, 2.718.
k = Loss rate constant. . ; : ¦ • ;
n = Number of years of application until equilibrium conditions reached.
Part 503 Risk Assessment «»EPA 65
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Chapter 4
Box 10 (Continued)
Calculation of the PCB Limit for Pathway 1
Step 1 Parameters:
Parameter Value
Units
RL icr4
no units
BVV 70
kilograms (kg) , .
q,» 7.7
milligrams per kilogram (mg/kg) • day :
RE 1.0
no units
TBI 0.0
milligrams pollutant per day (mg/day) : •
103 103
conversion factor, micrograms per milligram (ng/mg) 7 V.? / '
Step 1 Calculation:
10 3=0-909^ ¦ '' " ": v!'
Step 2 Parameters:
Parameter Value
Units
R1A 0.909
micrograms pollutant per day (ng/day)
UC
micrograms pollutant per gram dry plant tissue (jig/g DW)/kg-pollutant/hectare
DC
dry grams of food group in the diet per day (gDW/day)
FC
no units
2 {UC -DC-FC = 0.00312 from Chart B)
Chart B
Values for Parameters Used in Calculating the Pollutant Limit for PCBs, Pathway 1
Food Group
UC DC FC UC DC FC
Other Variables
Potatoes
0.001 15.5954 0.025 0.00039
rl ¦./ 1 • 10"4 ..;;;
Leafy vegetables
0.001 1.9672 0.025 0.00005
: BW 70 '7/
Legumes
0.001 8.7462 0.025 - 0.00022 . . .
'¦.'•727 : '
Root vegetables
0.001 1.5950 0.025 0.00004
RE - 1 / ' '
Garden fruits
0.001 4.1517 0.025 . 0.00010
DE , 1 : . _ ;//_
Peanuts
0.001 2.2538 0.025 0.00006 .
• MSi ' . . 2 • 10®
Grains and cereals
0.001 90.6802 0.025 0.00227
, ¦ k - .. '0.063. 7 V:>. :
Sum UC • DC • FC
0.00312
ria - * 0.909./' 7 ¦ :
. . RLC / 290.934 7
.'Rpa- 37
66 S-EPA Part 503 Risk Assessment
-------
' , How the Risk Assessments identified Pollutant Limits for Biosolids
Box 10 (Continued)
Step 2 Calculation:
~ % Kfy ¦ ; ' - ^ ^ ^ » r * ^ " *
* ( ^
, ' " ° ^ " ''uV",
RIA ~ 0 QOQ
. . ' RLC ^= 291 ^ *>« DW
X UCDC-FC* 0-00312 ^
x 1 s * ** ** ~ ' / » J
Step 3 Calculation:
<* ~ . ¦
. , . k = 0.063 yrT « C ' *
> -/PV-, • v . r~- '
'v - - - , ' ' *. •
" Step 4 Parameters:
, >- ' • *•
Parameter Value
, RLC - 37
TJjnits -J/' '
...kilogram PCB per hectare per year (kg PCB/ha/yr) " .
-.MS ' 2 • id"9
grams soil dry weight per hectare (g soil DVV/ha) ' - ,
k, . '0.063 ,
v/tyr"1)' . '. n*"- . ¦ ;
*e,. , .-2.718
no units , ^ •'
n ' 100' *
assumed years of application required to reach equilibrium ' ' * ' '
Step 4 Calculation:
* * • «. "* *' *' x
:¦•¦ p'v k-Mv' ...
< ' •<
-''RPa=*RLC-,MS-l0~9-ll+e~k + e~2k+...e(l~n)kri =
*
^ •*'*; " 291(2 -io9) • It)-9 • fc"0;0® + f2 x °'°® ... e(1 ~100)^ 0.063] =
37 ifegPCBsfha/yr '~ \ ' /" , *"',*/ "
Note: The most limiting ;
- (seeChapter3).
»¦ ' >*
pathway for PCBs was Pathway 5; however, PCBs were not included jn the final rule
Part 503 Risk Assessment ®€RA 67
-------
Chapter 4
Box 11
Example Risk Assessment Calculation; Arsenic for a Child Ingesting Biosolids (Pathway 3)
This example illustrates the method used to calculate pollutant limits for children for inorganic chemicals,
based on RfDs (see Box 3); the method is similar for organic pollutants, except that qj*s and cancer risk levels
were used instead of RfDs. The same method was used for inorganic and organic pollutants because this path-
way conservatively assumes the direct ingestion of biosolids by a child without the biosolids pollutants
having had an opportunity to degrade or to otherwise be reduced by being mixed into soils.
Goal: Calculate the concentration of the poEutant in biosolids that can be ingested by a child consuming
biosolids without expectation of adverse effects. This level is known as the reference concentration of a pollu-
tant in biosolids (RSC).
Note: The exposure pathway discussed in this example is Pathway 3, which involves a child eating biosolids
that have not been mixed with soil. Appendices A and B provide additional information about how the pa-
rameters presented below were used to determine pollutant limits for biosolids. '
Description of the Algorithm
Step 1:
ria=M^w_tbi
RE
103
This step is similar to Step 1 in Box 9, which shows an example calculation for an adult ingesting crops grown
on land to which biosolids have been applied. The major difference in this example is that the body weight
for a child is used (versus the adult body weight in the example in Box 9).
Step 2:
RIA
RSC=
Is-DE
Reference concentration of _ " RIA
pollutant in biosolids (RSC) Biosolids ingestion Exposure duration
rate (Is) adjustment (DE)
RSC = The concentration of a pollutant in biosolids that can be ingested without expectation of adverse effects.
RIA ss The amount of pollutant ingested by humans without expectation of adverse effects (i.e., allowable dose),
!s = The rate of biosolids ingestion by children.
DE = Exposure duration adjustment. This parameter attempts to include considerations of less-than-lifetime
exposures by children, because the RfDs used in Step V are based on lifetime (i.e., adult) exposure. Because no
EPA-approved method was available for such adjustments prior to promulgating the Part 503 rule, the DE was
set at 1.
Calculation of the Arsenic Limit for Pathway 3
Step 1 Variables:
Parameter
Value
Units
RfD
0.0008
milligrams pollutant per kilogram BW per day (mg/kg/day)
BW
16
kilograms (kg) for a l-to-6-year-old child
RE
1.0
no units
TBI
0.0045
milligrams pollutant per day (nig/day)
103
103
conversion factor, micrograms per milligram ((.ig/mg)
68 &EPA Part 503 Risk Assessment
-------
How the Risk Assessments identified Pollutant Limits for Biosoiids
Box 11 (Continued)
Step 1 Calculation:
RIA
RfD¦ BW
RE
TBI
103:
0.0008 16 _ q qq4:5 j_ jq3 _ g 3 ^ afsenitfg-day
1.0
Step 2 Parameters:
Parameter
Value
Units
RIA
8.3 , ,
micrograms pollutant per day (ng/day)
-
Is
0.2
grams of soil DW per day (g/day)
- - -
DE.
1
no units
•: • • :: . .»r- . .. i ' - ...-v.
Step 2 Calculation:
RSC — M-£ of arsenic/g of biosoiids DW {rounded)
Is- DE 0.2 -1
Note: .Pathway 3 was the most limiting pathway for arsenic.
Grain is one of many crops grown in soils amended with biosoiids,
Part 503 Risk Assessment SEPA 69
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Chapter 4
Box 12
Example Risk Assessment Calculation: Arsenic for an Animal Ingesting Plants
Grown on Biosolids-Amended Soils (Pathway 6)
This example illustrates one method used to calculate pollutant limits for animals for inorganic chemicals.
The most sensitive/most exposed animal species varied according to the particular pollutant.
Goal: Calculate the amount of each pollutant in biosolids that can be applied to a given area of land (e.g., hec-
tare) without adverse effects to animals. This level is defined as the reference application rate of a pollutant (RP). ^
Note: The exposure pathway discussed in this example is Pathway 6, which involves the application of
biosolids to soil, the uptake of biosolids pollutants in soil by plants, and the consumption of these plants by
animals. In this case, pollutant transfer began with forage plants taking up the pollutant from biosolids-
a mended soils; this forage then constituted 100 percent of the animal's diet Appendices A and .B provide
additional information about how the parameters described below were used to determine pollutant limits .
for biosolids.
Description of the Algorithm
Step 1:
RF = TPI- BC.
Reference concentration of _ Threshold pollutant Background concentration of
pollutant in forage (RF) ~ intake level (TPI) pollutant in forage {BC)
RF = The allowable concentration of a pollutant in the animal diet from forage grown in"biosolids-aniended soils.
TPI = The maximum pollutant intake level in the animal diet without observed toxic effect on the most sensitive or''
most exposed species (based on National Research Council data).
BC m The background concentration of pollutant in forage tissue.
Step 2:
RP=—
UC
RP a The amount of a pollutant that can be applied to a hectare of land without expectation of adverse effects. .
RF = The allowable concentration of a pollutant in the animal diet from forage grown on biosoJids-amended soils,
UC = Plant uptake of pollutants from soil/biosolids (see Chapter 3 for a detailed discussion of plant uptake of
pollutants). . ,
Calculation of the Arsenic Limit for Pathway 6
Step 1 Parameters:
Parameter Value Units ... '
TPI 50 micrograms of pollutant per gram of forage (grown in biosolids-amended soils) in
diet DW (ng/g DW)
BC 0.304 Micrograms of pollutant per gram of forage tissue DW(j_ig/g DW)
Step 1 Calculation:
RF= TPI-BC= 50 - 0.304 = 49.7 (|ig pollutant/g diet DW)
70 &EPA Part 503 Risk Assessment
-------
How the Risk Assessments Identified Pollutant Limits for Biosolids
Box 12 (Continued)
Step 2 Parameters:
Parameter
Value
Units
RF * ,
.49.7
micrograms of pollutant per gram of diet DW (ng/g DW)
UC
0.030
(miciograms of pollutant per gram of plant tissue DW ) (kilograms of pollutant per
hectare)"1 (ng/g DW) (kg/ha)"1 • -
Step 2 Calculation:
Rl 49 7
RPC=777; = - 1 ' A = 1,600 kg arsenic/ha (rounded)
ut U.U3U
Note: The most limiting pathway for arsenic was Pathway 3 (see Box 11).
Carefully replicated field research yielded valid data for the Part 503 risk assessment for land application.
Part 503 Risk Assessment 4»EPA 71
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Chapter 4
Box 13
Example Risk Assessment Calculation: Zinc for Plants Grown in Soils Amended
With Biosolids (Pathway 8)
This example illustrates the method used to calculate pollutant limits for plants for inorganic chemicals; no or-
ganic pollutants were evaluated for this pathway because organics occur in biosolids at very low *
concentrations and are rarely taken up by plants in quantities beyond background levels.
Goal; Calculate the amount of each pollutant in biosolids that can be applied to a given area of land (e.g., hec-
tare) without adverse effects to plants. This level is defined as the reference application rate of a" pollutant (R P).
Note; The exposure pathway discussed in this example is Pathway 8, which involves the application of
biosolids to soil and the uptake of pollutants in biosolids by plants. Pathway 8 involved determining RPs (de-
fined above) by two different approaches and then choosing the more restrictive result from the two
approaches as the pollutant limit. Chapter 3 and Appendices A and B provide more information about how
the parameters described below were used to determine pollutant limits for biosolids.
Approach 1 - The Probability Approach:
1. A phytotoxicity threshold (PT50) value—the concentration of a pollutant in plant tissue associated with a
50 percent retardation in growth of young tissue, which in turn was used to establish the concentration in
plants associated with phytotoxicity—was identified for each pollutant from short-term experiment data
on corn. The relationship between soil metal loading and resulting metal concentration in plant tissue
was established based on studies in which only one metal element, often in the form of a metal salt, had
been added to the growth medium (so that plant damage could be attributed to a specific metal).
2. A calculation was made to determine the probability that the metal concentrations in plants grown on
soils amended with biosolids would exceed the PTS0 at various metal loading ranges, using data only ;
from field studies.
3. An acceptable level of tolerable risk of exceeding the PT50 was set at 0.01. That is, it was deemed accept-
able to exceed the PTgg 1 out of every 100 times.
4. The highest biosolids loading rate having a less than 0.01 probability of causing the PT50 to be exceeded
was the allowable loading rate—theRP,
For Zinc;
1. PTgo for zinc = 1,975 ngzinc/g plant tissue DW.
2. The probability that corn grown on biosolids-amended soils would exceed the PT50 was computed for 12
zinc loading ranges (e.g., from 0, 0-50, through 2,500-3,500 kg/ha).
3. As specified earlier, the acceptable level of tolerable risk for exceeding the PT50 was set at 0.01.
4. None of the loading rates evaluated exceeded the probability of 0.01 (see Chart C). Therefore, the highest
loading rate evaluated was chosen as the allowable loading rate (the RP) for biosolids that would not ,
cause a significant phytotoxic effect in corn: RP = 3,500 kg zinc/ha.
72 £EPA Part 503 Risk Assessment
-------
How the Risk Assessments Identified Pollutant Limits for Biosotids
Box 13 (Continued)
Approach 2 - The Lowest-Observed-Adverse-Effects-Level (LOAEL) Approach:
Description of the Algorithm
Reference cumulative:
application rate of
pollutant (RP)
RP
TPC-BC
Threshold phytotoxic concentration
¦ '[ of' pdllutant inplarii tissue/",
Background concentration of
pollutant in plant tissue
(JSC)
Uptake response, of pollutant in plant tissue (UQ
.-"The ampimt'of a pollutant that
TPC - The concentration of a pollutant in a sensitive plant tissue species (e g., lettuce, as opposed to a less sensitive
iV'-spedes,"such; as'corn, used 'in Approach 1) associatfed-with the LOAEL/.as an indicatidn:of phy totdxicitp ?: ['
• BC r5acKgto.dn3concentration:pf ppUutantmpiantMssue/^;/'*;..'"'"'T..!/','• ~.J:C
' UC;"Plantuptake of pollutants from soil./biosolids (see Cha'pter 3 io.r a' detailed discussiort of plant" uptake of
pollutants)..- -v/-' Yr':'V;V ' ' '
For Zinc:
Parameters
Parameter
Value
'J:.J:. Units ' ' : \ ^ \ •'
: TPC
.micrograms ot.pollutant per gram of plant tissue (lettuce). DW (Hg/g DW)
BC
47.0
" micrograms of pollutant per gram of plant tissue (lettuce) DW ()ig7g DW)
'uc:"i:;
3:125-.:-::'
micrograms of pollutant per gram ot plant tissue (lettuce) (kilograms of pollutant
v:V^?perli«ta!^"r(p^g'-E^)(kg7h^v:'*;; \ - {V .V'l. > '• , "4 - '-V
Calculation:
TPC-BC 400 - 47.0 „ ,
RP - " - p - 2,800 kg zinc/ha (rounded )
Results From Approaches 1 and 2
RP, Approach 1 -3,500 kg zinc/ha RP, Approach 2 -- 2,800 kgzinc/ha
_ The more restrictive result of the .two; approaches was chosen as the pollutant limit: RP - 2,800 kg zinc/ha.
The limit set for Pathway 8 was the pollutant limit used in the Part 503 rule for zinc.
Part 503 Risk Assessment «SEPA 73
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Chapter 4
Box 13 (Continued)
Chart C
Probability of Zinc in Corn Grown on Biosolids-Ametided Soils Exceeding the
Phytotoxicity Tolerance Threshold
Zinc
Loading Range
Probability of Exceeding
Tolerance Threshold , .
(kg/ha)
Number of
Observations
. ¦ pt50 ¦ -
1,975ngig' _; . v-'V'
0
51
<0.0001
0-50
16
' '' : V' <0.0001. ' : :'.r:
50-100
28
<0.0001 V:"/: - :'"V;
100-150
16
;' <0.0to.^
150-200
14
¦ Yj::; ¦
2,500-3,500
10
. <0.0001 ; ; '
¦t-"
74 SEPA Part 503 Risk Assessment
-------
How the Risk Assessments Identified Pollutant Umitsfor BiosoHds
Box 14
Example Risk Assessment Calculation: PCBs for an Adult Person Ingesting Surface Water
and Fish Impacted by Pollutants in Runoff From Biosolids-Amended Soils (Pathway 12)
•This example illustrates the method used to calculate pollutant limits for people (adults) for carcinogenic, or-
ganic pollutants evaluated in the biosolids land application risk assessment for surface water. ,
Goal: Calculate the amount of pollutant in biosolids that can be applied to a given area of land (e.g., kilo-
grams per hectare per year) without adverse effects to humans. This level is defined as the reference application
rate of a pollutant (RP). "
Note: The exposure pathway discussed in this example is Pathway 12, which involves the application of
biosolids to soil, the erosion of soil containing pollutants in biosolids, the transfer of the pollutants contained
in the eroded soil to surface water, and the ingestion of the surface water and fish living in "the surface water
by humans. The calculations for surface water below have been summarized (i.e., not all calculations are pre-
sented) to simplify this example. For the more detailed calculations conducted for this pathway, see the
Technical Support Document for Land Application of Sewage Sludge (U.S. EPA, 1992a). Appendices A and B pro-
vide more information about how the variables described below were used to determine, pollutant limits for
bib'solids. - , _
Description of Algorithm
Step 1: Mass Balance
The relative rates of pollutant loss for the site through erosion, volatilization, and leaching were calculated.
These rates were then combined to give a total loss rate of pollutant from soil at the site (K). For Pathway 12,
the ratio of the erosion loss rate to the total loss rale was then calculated to provide the fraction of pollutant
loss caused by erosion (fero). For the additional calculations involved in the mass balance, see the Technical Sup-
port Document for Land Application of Sewage Sludge (U.S. EPA, 1992a). * , -
• fero —
Kem(yr-l)
Ku>t (yr
-1)
fero = fraction of total loss caused by erosion •
Kero - loss rate coefficient,for erosion (yr-1) ' *¦ , ' 1
Ktot = total loss rate for the pollutant in biosolids-amended soil (yr-1)
Step 2: Reference (Allowable) Intake of Pollutant (RI)
For carcinogenic pollutants (including some inorganics, i.e., arsenic):
For noncarcinogenic pollutants:
RI = RfD - background intake sources other than biosolids
Part 503 Risk Assessment S-EPA 75
-------
Chapter 4
Box 14 (Continued)
Step 3: Reference (Allowable) Water Concentration of Pollutant in Surface Water (RCSW):
RIBW '
BCF FM-Pt -lf +/«,;•
RI = reference (allowable) intake : . 1 •
BW = body weight ;
BCF « pollulant-specific bioconcentration factor
FM = pollutant-specific food chain multiplier
Pf = ratio of pollutant concentration in the edible portion of fish to concentration in whole fish
If = daily consumption of fish
Iw = daily consumption of water
Step 4: Reference Concentration of Pollutant in Eroded Soil Entering the Stream (RCsed):
RCsed — RCSW [KDsw +
Ps
\ J
CD
Pw
V J
1
RCscd = reference concentration of pollutant in eroded soil entering the stream
RC»w = reference water concentration for surface water
KDsw = partition coefficient between solids and liquids within the stream
Pi = percent liquid in the water column
Ps, = percent solids in the water column
p,v = density of water
Step 5: Dilution Factor (DF):
DF--
Ssma + (Aws ~ Asnw) S\vs
DF = dilution factor :
Asm* = area affected by land application of biosolids (SMA=bidsolids management area)
Sjm* = sediment delivery ratio for the SMA
AWs = area of the watershed (ha)
Sws = sediment delivery ratio for the watershed
Note: The dilution factor (DF) describes how eroded soil from the SMA is diluted by soil from the untreated .
remainder of the watershed. It represents the fraction of the stream's sediment originating in the SMA. Step 5
assumes that rates of soil erosion from the SMA and the remainder of the watershed are the same; calcula-
tions for Ssma and Sws were previously calculated but are not shown here (see Technical Support Document cited
above for further information).
76 SEPA Part 503 Risk Assessment
-------
Box 14 (Continued)
'
Step 6: Reference Pollutant Concentration for Soil Eroding From the SMA (RCsma):
V .. : :¦¦¦
RC»,a =
&C$ed
OF
:: -r-v'.v-- v ....
. .¦ ,.,-r ;-
-• RQma' -*= reference pollutant concentration in soil eroding from the(SMA
'RCsed . ¦- = • reference concentration of pollutant in.eroded soil, entering-ffie stream; -•»,'
r' ¦'
„DF = dilution factor.
. ¦' ¦ V' '
r;':''¦ -L"l":iS J".-'-: '
¦
.v"
¦ ¦¦ ¦¦ ¦ ¦¦ . ' ¦
.. • ¦
a'*
RPa = ——
. . ,¦
:y;yy~^\S:&:yy-y
-
RPa
RCsed
' 'MEsma ;• = -. estimated rate of soil loss for the SMA _ ^ %; .' y^ • V 'y' ¦ [~J ¦:
10"6 = conversion factor
RCsma " > .
, ..y>yyy::yy yyy,
ant:- -..... v* - ¦ u-.
-:r'x"r
.
; fero = •, fraction of total loss caused by erosion : • : ~y'¦ j'yy'-y- y.. * ;v/
.. -:w! :v..,
v-'-—y -y-y: y ¦ v---
:
Calculation of the PCB Limit for Pathway 12
/vJ'. [y':-:y;yyy- k.^.'-\'~yyyy 'r'-yA '¦,/ ......~y\ "¦ ¦
Parameter Value
Units
. __
Parameter Value Units
¦ '
W- ^ <• •:
.r.^unitless:-*. =-.
p~*
Ktot
.y-t^yyy^y y. ¦ ^y :
: :-i' 10-'' :: : :::K
lifeHme';;
.-a™, wt '. ha:;-:-'::::
7.7
kg-day/mg
- ¦
y-^Sim^y ' ¦ -¦;"v 0A6'-.:unitless 2;- '•
yr .;.::yy::M*l^.'
:=;:»"g/kg-day
;,JV.
Aws 440,300 , • ha
yy,_ -
VT'-r
7:.:-V ' - v"imitless
• vv ' "av-^- ". ¦ -i .¦-••-•h.1;...--.• -
BCF.:-; : : :j.i/i?;4 '
^,mg/kg;r -y;
•" -/
FM -. •- , 10 -
... -
unitless
- "¦O.OCfeS; !i:;'^unitless,: y'l'.y'?'" -
Pf ; 0.5.
unitless
. - V -• - '...-.v.:.,.,-.--, . . -
RC,m, 1.43 mg/kg
¦ If • . 0.04
,- .leg/day . :
.7
kg/ha-yr C;::.v-
Iw. ' ' 2 • . .
1/day
... conversion factor-';' IOC6', '•.•••;. Mg/mg * -
RCSW , ' 1.5 xlO"7 .
mg/1' • .
-;fero-'- -- : .0-033':-;:--;:.'.'cunitless,-.
KDSW 1,510
l/kg
¦. • . : ¦ ¦¦¦¦ ¦ ¦'
Part 503 Risk Assessment &EPA 77
-------
Chapter 4
Box 14 (Continued)
Step 1 Calculation:
Step 2 Calculation:
r Kero (yr ) 0.004 n
fern = j- = "TT-pr- = 0.033
KM {yr ) °-12
RL 10-4 _ tn-5
Rl= =-=-=-=1.3x10 mg/kg-day-
qx* /./ ;• .. = ,y."
Step 3 Calculation: .
RI BW (1.3 *10"^) (70) . , ^-7 „
/?Q„. = = 4 . . ' \ ¦' = 1.5 X 10 me/kg
BCF ¦ FM -Pf-If-Iw (3.1 x 10~^ (10) (0.5) (0.04)+ (2)
Step 4 Calculation:
fpx\r i \
RCsed — RCsw [KDsw +1 p
Pw
\ /
:(I-5jc 10"7) [(1,510)+ (62,500) (1)] = 9.4* W~Tmg/kg:
Step 5 Calculation:
DF= Asma Ss,m = (1,074) (0.46) — = 0.0066 (tmitless)
Asma Ssina + (Aws ~Asma) Sws ~ (1.074) (0.46) + [(440,300) -(1,074)] (0.17)""
Step 6 Calculation:
Step 7 Calculation:
RCsed 9.4X 10 3 ,
Kl>sma — £fp ~ q QQgg ~ mg/kg
RPa = RCsma.MEsnw.l^ = (1.43) (8.400) 10"6^ ^
Jem (0.033)
Note: The limiting pathway for PCBs is Pathway 3; however, organic pollutants, including PCBs, were not in-
cluded in the final rule for land application (see Chapter 3).
78
-------
How the Risk Assessments Identified Pollutant Limits for Biosoiids
Surface Disposal: Ground-Water Pathway
The risk assessment for the ground-water pathway for surface disposal of biosoiids
began with a mass balance that calculated pollutant loss to ground-water leaching,
volatilization, effluent or water discharge (for surface impoundments), and degrada-
tion. An adjusted reference water concentration (RCgw) for each pollutant, which
was a health-based number based on MCLs or q^s, was calculated. Computer
models (the VADOFT model for the unsaturated soil zone, and the AT123D model
for the saturated zone) were then used to calculate pollutant transport to the
ground water and lateral dispersion of the pollutant in the ground water beneath a
surface disposal site.
Site-specific parameters for biosoiids and ground water were used in the computer
models (e.g., area and active lifetime of facility; thickness and porosity of the cover,
if any; distance to well; solids concentrations of biosoiids; soil type and porosity;
depth to ground water; thickness of aquifer; net recharge or seepage; leaching
rate; hydraulic conductivity). Chemical-specific factors also were used in the
ground-water models (e.g., decay rates, diffusion and soil-water partition coeffi-
cients). The surface impoundment risk assessment also included inflow and
outflow factors and exchange between the liquid and sediment layers.
Pollutant concentrations in nearby, downgradient well water were used to calculate
seepage beneath the surface disposal facility, called the reference concentration
of pollutant in water leaching from the monofill or seeping from the bottom of
the surface impoundment (RC|ec. or RCsep), in milligrams per liter (mg/L). For
monofills, the mass of solids in 1 rrr of biosoiids (MS) and the mass of biosoiids in
1 hectare of a monofill (SC) were then calculated. (The SC was calculated by multi-
plying the depth of a monofill cell by the fraction of its total volume containing
biosoiids and the mass of solids per cubic meter of biosoiids.) The RC, MS, SC,
and well data were used to derive a reference concentration of pollutant in
biosoiids (RCS), expressed in milligrams per kilogram (mg/kg), which was identi-
fied as the risk-based pollutant limit.
Many of the assumptions made for the surface disposal ground-water pathway
were conservative and probably contributed to overestimation of exposure and
hence risk. Some of these assumptions included:
• A 150-meter distance to a downgradient receptor well for Class ll/lll aquifers,
because no one drinks well water on site (based on EPA specifications for fa-
cilities that it regulates or on state requirements based on EPA regulations).
• The site life (i.e., the length of time a monofill receives biosoiids, or the time it
takes to fill a surface impoundment with biosoiids) for monofills was assumed
to be 20 years, and the site life for surface impoundments was assumed to be
7 years. After these periods, maximum pollutant loss (e.g., through leaching
and volatilization) and pollutant concentrations in a receptor well were mod-
eled for a 300-year period assuming a constant release of pollutants.
• For Class ll/lll aquifers, a 1-meter depth to ground water was assumed, which
is less than the depth at most operating facilities. This conservative assump-
tion is designed to protect aquifers at relatively shallow depths.
• Maximum pollutant concentrations at the 150-meter, downgradient well were
calculated within the first 300 years after the life of the surface disposal site
lapsed. In contrast, for the vapor pathway discussed below, a maximum 70-
year average ambient air pollutant concentration was used.
Part 503 Risk Assessment &EPA 79
-------
Chapter 4
Surface Disposal: Vapor (Air) Pathway
For the risk assessment for the vapor pathway for surface disposal of biosolids, the
estimated volatile emissions of organic pollutants was first calculated. Inhalation
volume and dispersion factors also were important parameters used. Expected
concentrations of organic pollutants in ambient air at the property boundary of the
surface disposal site were then calculated (using a simplified ISCLT model).
The health-based parameter for the vapor pathway was the reference air concen-
tration for the pollutant (RCair), expressed in micrograms per cubic meter
(ug/m3), which was based on q-,*s. A reference concentration of pollutant in
biosolids (RCS) was then calculated, which was identified as the risk-based pollu-
tant limit for the vapor pathway for surface disposal.
Approach Used for the Incineration
Risk Assessment
One pathway was evaluated in the biosolids risk assessment for incineration—the
inhalation pathway. A pathway to evaluate exposures to ingested pollutants from
biosolids incineration was not evaluated because of limited procedural and data
availability. In the inhalation pathway risk assessment, health-based risk-specific
concentrations (RSCs) were calculated in an algorithm for arsenic, cadmium,
chromium, and nickel. RSCs represented the allowable increase in average, daily
ground-level ambient air concentrations above background levels for the pollutant
from biosolids incineration. The RSC, based on q-,*s and inhalation rates, was then
used in a second algorithm along with site-specific factors on:
• Pollutant dispersion in the ambient air
• Incinerator control efficiency
• Biosolids feed rate to the incinerator
The second algorithm identified risk-based pollutant limits for biosolids incineration,
calculated as the allowable average daily concentration of the pollutant in
biosolids (C), expressed in mg/kg of total soiids (DW).
In addition to the RSCs and site-specific factors used to develop pollutant limits for
biosolids incineration, an inhalation pathway pollutant limit also was developed for
lead in biosolids that are incinerated based on 10 percent of the National Ambient
Air Quality Standard (NAAQS) for lead. This percentage of the NAAQS for lead
was substituted for the RSC and factored into the second algorithm along with site-
specific factors, as discussed above, to identify a risk-based pollutant limit for lead
in biosolids. Pollutant limits for beryllium and mercury in biosolids that are inciner-
ated also were included in the final Part 503 rule, based on National Emissions
Standards for Hazardous Air Pollutants (NESHAPS) for these two pollutants.
Pollutant limits for organic pollutants also were evaluated in the risk assessment for
biosolids incineration. Organic pollutants associated with biosolids incineration,
however, were regulated in the Part 503 rule through an "operational standard"
(discussed below and in Chapter 5) that requires monitoring for and restrictions on
emissions of total hydrocarbons (THCs) in the stack gas. An operational standard
was used because not all of the organic pollutants in the incineration emissions
(e.g., products of incomplete combustion) are known.
EPA estimated the risk for the technology-based THC operational standard using a
weighted toxicity value for all organic pollutants for which there was a q-,*. This
risk-based analysis first used parameters such as the 100-ppm THC standard and
site-specific dispersion factors and gas flow rates to derive site-specific RSCs (dis-
80 ©EPA Part 503 Risk Assessment
-------
How tjie: Risk AMeSsments Identified Pollutent Limits for Biosolids
cussed above). These RSCs, along with other parameters, including a weighted
q-i*, an inhalation rate, and body weight, were then used to determine the degree
of risk posed by the THC emission standard under site-specific conditions. (The
"weighted" q,* represented the cancer potency value for all organic compounds
emitted from a biosolids incinerator that have the potential to create an adverse
health effect, using data on 21 compounds in tests at eight biosolids incinerators,
as well as data for numerous organics that were potentially present but not de-
tected in the tests. The q-,* for each chemical was weighted in that it was multiplied
by a "weighted fractional concentration" based on the compound's detected or as-
sumed concentration.) The results of this risk assessment indicated that the risk
associated with emissions at a 100-ppm THC level, based on data from 23
POTWs, did not exceed a 1 x 10"4 risk level, which was the level established in
Part 503 to protect public health. Based on these results, in the EPA Administra-
tor's judgment, the THC operational standard is protective of public health.
An amendment to the Part 503 rule allows carbon monoxide (CO) monitoring to be
used in lieu of THC monitoring (see Chapter 2) because of good correlation be-
tween CO and THC levels. This amendment does not change the operational
standard. If the CO is below 100 ppm when the emissions are monitored continu-
ously, THCs in the emissions are assumed to be below 100 ppm.
Use of Risk Assessment Results and
"The Most Limiting Pathway"
Approach To Establish Part 503
Pollutant Limits
Calculating Exposure Pathway Pollutant Limits
Pollutant limits were calculated for each of the exposure pathways evaluated for
the land application, surface disposal, and incineration risk assessments using the
parameters and algorithms discussed above. The numeric results of these calcula-
tions are shown in Tables 10, 12, and 14.
Land Application Pollutant Limits
For land application, the calculation of pollutant limits warrants further explanation.
Pollutant limits were first calculated separately for agricultural and non-agricultural
lands (i.e., forest, public contact, and reclamation sites). The lower of the agricul-
tural or non-agricultural pollutant limits was selected for each exposure pathway
(see Table 10).
The pollutant limits for land application exposure pathways were expressed in dif-
ferent units for inorganic and organic pollutants to account for the fact that many
organics degrade in the environment, in contrast to inorganics, which increase over
time rather than degrade. This difference can be seen in Table 10 by the use of a
cumulative application rate of pollutant (RPC) for inorganics, expressed in kilograms
of pollutant per hectare (kg-pollutant/ha), and an annual application rate of pollu-
tant (RPa) for most organics, expressed in kilograms of pollutant per hectare per
year (kg-pollutant/ha-yr). In Pathways 1, 2, 4, and 11, RPcs are listed for the or-
ganics aldrin/dieldrin and chlordane (and DDT for Pathway 11) because of their
long halflife, while RPas are listed for most other, degradable organics.
In some cases (Pathways 3, 5, and 7), a pollutant concentration in biosolids (an
RSC) was used rather than a pollutant loading rate (a RP) to represent a pollutant
limit when the pathway involved direct ingestion of biosolids. For further information
Part 503 Risk Assessment &EPA 81
-------
Chapter 4
Table 10
Biosolids Risk Assessment Results for Land Application
Inorganic Pollutants:
Exposure
Pathway
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Pollutant
RPc
RPc
RSC
RPc
RSC
RPc
RSC
RPC
RPc
RPc
RPC
RPC
RPc
RPc
Arsenic
6700
930
41
1600
3100
66000
1200
Cadmium
610
120
39
1600
68000
140
650
53
63000
unlimited
Chromium
79000
190000
3000
unlimited
12000
Copper
10000
3700
2000
1500
2900
unlimited
unlimited
Lead
300
11000
1200
5000
unlimited
unlimited
Mercury
180
370
17
1500
24000
1100
unlimited
Molybdenum
400
18
530
Nickel
63000
10000
820
¦ 1800
5400
420
unlimited
13000
Selenium
14000
1200
100
15000
13000
790
130
Zinc
16000
3600
16000
150000
2200000
12000
36000
2800
Organic Pollutants:
Exposure
Pathway
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Pollutant
RPa
RPc
RPa
RPc
RSC
*
cu
&
RPc
RSC
RPa
RPc
RPa
RPa
RPa
Aldrin/
Dioldrin
280
64
7.0
17
2.7
30000
Dcnzo(n)
pyrene
230
54
,
15
1.3
3500
unlimited
Chlordane
3400
790
86
13000
2300
5.3
3.9
unlimited
DDT
560
130
320
46
150
100000
1.2
45
unlimited
Hept.ichlor
990
220
24
65
7.4
Hexaehlono-
benzene
320
75
70
25
29
Hexachloro-
but.idienc
43000
10000
1400
600
Lindane
2300
540
8.4
600
140
2100
110
unlimited
n-N'itrosodi-
methylamlnc
87
20
2.1
29000
22
0.056
PCBs
37
8 S
14
2.4
4.6
0.50
200
0.34
1.4
unlimited
Toxaphene
2800
650
100
43
10
5.0
120
unlimited
Trichloro-
ethylene
220000
51000
10000
unlimited
420
unlimited
Note: All results rounded down to two significant figures.
•RPc * reference cumulative application rate of pollutant (kg-pollutant/ha), used for inorganics and organics that do not degrade.
RSC = reference concentration of pollutant in biosolids (jig-pollutant/g-biosolids DW).
RP* * reference annual application rate of pollutant (kg-pollutant/ha-yr), used for degradable organics.
Unlimited = calculated risk-based pollutant loadings for these media and practices were an unlimited value and therefore not of concern for pub-
lic health or the environment.
Blank = pollutants for these pathways were excluded from the risk assessment based on either earlier hazard screening (e.g., hazard index, see
Chapter 2), very low levels (e.g., oiganics in plant pathways; inorganics in volatilization pathways), or lack of an RFD for lead in Pathways 1
and 2.
82 A EPA Part 503 Risk Assessment
-------
How the Risk Assessments identified Pollutant Limits for Biosoiids
Table 11
Pollutant Limits for Biosoiids Identified in the Land Application Risk Assessment
Inorganic Pollutants
Pollutant
Highly Exposed
Individual of Limiting
Pathway
Most
Limiting
Pathway
Pollutant Limit
(as RPJ
(kg- pollutant/ha)
Pollutant Limit (as RSC)
((ig-pollutant/g-biosolids
DW)a
Arsenic
Child Eating Biosoiids
3
41
41
Cadmium
Child Eating Biosoiids
3
39
39
Chromium1"
Plant Phytotoxicity
8
3,000
3,000
Copper
Plant Phytotoxicity
8
1,500
1,500
Lead
Child Eating Biosoiids
3
300
300
Mercury
Child Eating Biosoiids
3
17
17
Molybdenum0
Animal Eating Feed
6
18
18
Nickel
Plant Phytotoxicity
8
420
420
Selenium
Child Eating Biosoiids
3
100
100
Zinc
Plant Phytotoxicity
8
2,800
2,800
Organic Pollutants
d
Pollutant
Highly Exposed
Individual of Limiting
Pathway
Most
Limiting
Pathway
Pollutant Limit (as RPa)
(ug-pollutant/g-biosolids
DW, except as indicated)
Pollutant Limit (as RSC)
((ig-pollutant/g-biosolids,
DW)
Aldrin/Dieldrin
Adult Eating Animal Products
(animals ate biosoiids)
5
2.7
2.7
Benzo(a)pyrene
Child Eating Biosoiids
3
15
15
Chlordane
Child Eating Biosoiids
3
86
86
DDT /DDD/DDE
Adult Eating Fish/Drinking
Surface Water
12
1.2(kg-poll/ha-yr)
120
Heptachlor
Adult Eating Animal Products
(animals ate biosoiids)
5
7.4
7.4
Hexachlorobenzene
Adult Eating Animal Products
(animals ate biosoiids)
5
29
29
Hexachlorobutadiene
Adult Eating Animal Products
(animals ate biosoiids)
5
600
600
Lindane
Child Eating Biosoiids
3
84
84
n-Nitroso-dimethyi-
amine
Child Eating Biosoiids
3
2.1
2.1
PCBs
Adult Eating Animal Products
(animals ate biosoiids)
5
4.6
4.6
Toxaphene
Adult Eating Animal Products
(animals ate biosoiids)
5
10
10
Trichloroethylene
Child Eating Biosoiids
3
10,000
10,000
aRSC = reference concentration of a pollutant in biosoiids (Jlg-pollutant/g-biosolids, DW). By expressing pollutant limits as RSCs, limits for inor-
ganic and organic pollutants can be compared (see Appendix D for conversion factors used to attain same units).
bChromium may be deleted from the rule because of a court suit (see Section Q, Chapter 3).
cQnly the ceiling concentration limit for molybdenum is currently included in the Part 503 rule pending revaluation of additional data (see Sec-
tion P, Chapters 2 and 3).
dLimits for organic pollutants were not included in the final Part 503 rule (see Chapters 3 and 5).
Part 503 Risk Assessment AEPA 83
-------
Chapter 4
Table 12
Summary of Biosolids Risk Assessment Results For Surface Disposal
Pollutant
Unllned
Lined
Monofill
Surface Impoundment
Monofill
Surface Impoundment
Vapor Inhalation Pathway (Pathway 1)
Arsenic
NAa,b
NA
NA
NA
Benzene
6,100
3,300
6,000
3,400
Benzofajpyrene
unlimited
unlimited
unlimited
unlimited
Bis(2-ethylhexyl)phthalate
unlimited
unlimited
unlimited
unlimited
Cadmium
NA
NA
NA
NA
Chlordane
unlimited
unlimited
unlimited
unlimited
Chromium
NA
NA
NA
NA
Copper
NA
NA
NA
NA
DDT/DDD/DDE
unlimited
unlimited
unlimited
unlimited
Lead
NA
NA
NA.
NA
Lindane
unlimited
28,000
unlimited
28,000
Mercury
NA
NA
NA
NA
Nickel
NA
NA
NA
NA
n-Nitrosodimethylamine
3,000
15
2,300
16
PCBs
unlimited
no
unlimited
100
Toxaphcne
unlimited
26,000
unlimited
26,000
Trichloroethylene
unlimited
10,000
unlimited
10,000
Ground-Water Pathway (Pathway 2)
Arsenic
I—•
O
cr
73
unlimited0
unlimited
Benzene
1,200
140
unlimited
unlimited
Benzo(a)pyrene
unlimited
unlimited
" unlimited
unlimited
Dis(2-ethylhexyl)phthalate
unlimited
unlimited
unlimited
unlimited
Cadmium
unlimited
unlimited
unlimited
unlimited
Chlordane
unlimited
unlimited
unlimited
unlimited
Chromium
unlimited
600
unlimited
unlimited
Copper
unlimited
46,000
unlimited
unlimited .
DDT/DDD/DDE
unlimited
unlimited
unlimited
unlimited
Lead
unlimited
unlimited
unlimited
unlimited
Lindane
unlimited
unlimited
unlimited
unlimited
Mercury
unlimited
unlimited
unlimited
unlimited
Nickel
unlimited
690
unlimited
unlimited
n-N'itrosodimethylamine
0.47
0.88
790
3,400
PCBs
unlimited
unlimited
unlimited
unlimited
Toxaphene
unlimited
unlimited
unlimited
unlimited
Trichloroethylene
unlimited
9,500
unlimited
unlimited
4NA indicates that it was not applicable to conduct a risk assessment on these pollutants for the vapor inhalation pathway because they do not
tend to volatilize.
^Limits are expressed in milligrams per kilogram.
'Unlimited Indicates that the calculated risk-based pollutant concentrations for those media and disposal practices were of an unlimited value
and are therefore not of concern for public health or the environment
84
-------
How the Risk Assessments Identified Pollutant Limits for Biosolids j
Table 13
Pollutant Limits for Biosolids Identified in the Surface Disposal Risk Assessment
Inorganic Pollutants
Pollutant
Pollutant Limit (mg/kg)a
Limiting Pathwayb
Arsenic
73
2
Cadmium
unlimited0
—
Chromium
600
2
Copper
46,000
2
Lead
unlimited
—
Mercury
unlimited
—
Nickel
690
2
"Results are from the risk assessments conducted for Class n/m ground water. Class I results are not included because EPA decided to regulate
all ground water as Class II for the purposes of the Part 503 biosolids rule.
bExposure pathways for surface disposal are described in Table 7 (in Chapter 2). Numbers in this column reflect results of the risk assessment for
unlined surface impoundments (versus lined surface impoundments or unlined or lined monofills) because for all inorganics evaluated, this
pathway resulted in the lowest limits.
cUnlimited indicates that the calculated risk-based pollutant values for the pollutants indicated in the media evaluated (ground water for inor-
ganics) were of an unlimited value (i.e., no risk level identified). Risk assessments for inorganics were not conducted for the inhalation pathway
because these pollutants do not tend to volatilize.
Organic Pollutants
Pollutant
Pollutant Limit (mg/kg)a
Limiting Pathway b
Benzene
140
2 (unlined surface impoundment)
Benzo(a)pyrene
unlimited13
—
Bis(2-ethylhexyl)phthalate
unlimited13
—
Chlordane
unlimited
—
DDT/DDD/DDE
unlimited13
Lindane
28,000
1 (unlined or lined surface
impoundment)
n-Nitrosodimethylamine
0.47
2 (unlined monofill)
PCBs
110
1 (unlined surface impoundment)
Toxaphene
26,000
1 (unlined or lined surface
impoundment)
Trichloroethylene
9,500
2 (unlined surface impoundment)
'Pathways for surface disposal are described in Table 7 (in Chapter 2).
bUnlimited indicates that the calculated risk-based values for the pollutants indicated in the media evaluated (ground water and
vapor for organics) had no limits (i.e., no risk level identified).
Part 503 Risk Assessment &EPA 85
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Chapter 4
Table 14
Risk-Based Results for Biosolids Identified in the Incineration Risk Assessment
Pollutant3
<1 i.
Risk-Specific Concentration (|ig/m )
(vapor inhalation pathway)
Arsenic
0.023
Cadmium
0.057
Chromium
Fluidized-bed with scrubber
0.65
Fluidized-bed with wet scrubber and wet electrostatic precipitator
0.23
Other types with wet scrubber
0.064
Other types with wet scrubber and wet electrostatic precipitator
0.016
Nickel
2.0
"Only inorganic results are listed because organics are regulated in the Part 503 rule through an "operational standard" rather
than pollutant limits identified in a risk assessment (see text).
''Risk-specific concentrations were used along with site-specific information to calculate pollutant limits (see text). Only the inha-
lation pathway (see Table 7) was evaluated for incineration; thus this pathway is the "limiting pathway" (see text) from which
the pollutant limits were calculated.
on the different types of pollutant limits, see Appendices A and B and Boxes 9 to
14.
For some land application exposure pathways, no pollutant limit is given in Table
10. In most cases, this is because these pollutants were excluded from further
evaluation during the hazard index/hazard ranking process (i.e., they were not con-
sidered toxic via that particular exposure pathway, as explained in Chapter 2). In
addition, lead was not evaluated for Pathways 1 and 2 because no RfD was avail-
able. Organic pollutants were not analyzed for Pathway 8 because organics occur
in biosolids at very low levels and are rarely taken up by plants at levels above
background levels. Zinc and aldrin/dieldrin were not evaluated for Pathway 10 be-
cause new data indicated that they were not a concern to predators of soil
organisms. For Pathway 13, no inorganic pollutants were analyzed because metals
do not volatilize at ambient temperatures; therefore, levels would be negligible for
this volatilization pathway.
For some pathways, the pollutant limits in Table 10 are listed as "unlimited." This
means that no application (i.e., loading) rate of pollutants in biosolids (RP) was
identified that would result in adverse effects via that particular pathway.
Using Exposure Pathway Pollutant Limits To Calculate Part
503 Pollutant Limits
For each pollutant evaluated, EPA considered the exposure pathway with the low-
est pollutant limit as the "limiting pathway" for that pollutant for land application and
surface disposal. Tables 11 and 13 list the risk assessment results for inorganic
and organic pollutants for land application and surface disposal of biosolids and the
associated limiting pathways. For example, for nickel in the land application risk as-
sessment, Pathway 8 resulted in the lowest pollutant limit (RP = 420 kg of nickel/ha
86 &EPA Part 503 Risk Assessment
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How the Risk Assessments Identified Pollutant Limits for Biosolids
of land), as shown in Tables 10 and 11. This lowest pollutant limit was used directly
in the Part 503 rule as the "cumulative pollutant loading rate" for nickel for land ap-
plication. For other types of Part 503 pollutant limits for land application, the values
identified in the risk assessment were further modified, as described in Chapter 5.
To allow comparisons between exposure pathways for land application, the pollu-
tant limits for all inorganics in Table 10 were converted to the same unit, RPC, as
shown in Table 11 (conversions are provided in Appendix D). Note that in Table 11,
the pollutant limits have been further converted to the unit RSC, so that inorganics
and organics can be compared. Pollutant limits for organics are shown but were
deleted from the final Part 503 rule for land application, as discussed in Chapters 3
and 5.
Detailed Risk Assessment Example:
Cadmium, Pathway 2, Land
Application
This section provides a detailed example of the analysis conducted for cadmium
for Pathway 2 of the risk assessment for land application. This example provides a
closer look at how the risk assessments were conducted, highlights how key scien-
tific data and EPA assumptions and policy decisions were used, and illustrates why
the risk assessment results are conservative.
The Highly Exposed Individual, Pathway 2
The highly exposed individual (HEI) for Pathway 2 in the land application risk as-
sessment for the final Part 503 rule was the subsistence home gardener who over
a lifetime grows a major portion of his or her diet in biosolids-amended soil. Data
indicate that 5.5 percent of the U.S. population have gardens large enough to pro-
duce a major portion of their annual food consumption. Given that less than 2
percent of the U.S. population live in the same county for a lifetime, the HEI popu-
lation of home gardeners for Pathway 2 is probably between 0.1 percent (5.5 x
0.02) and 2 percent of the population, with estimates pointing to less than 1 per-
cent (Ryan and Chaney, 1993). The actual population of HEIs is probably lower
because these estimates are based on short-term data and only a small number of
home gardeners will garden their entire lifetime. Furthermore, to reach the esti-
mated exposure for a 70-year lifetime, the subsistence gardener would have to
continuously consume crops always produced in garden soil that contains the
maximum amount of any given biosolids pollutant being evaluated (the RP) during
that 70-year period. As illustrated by Ryan and Chaney (1995), this is an unlikely
event.
Algorithms Used in Pathway 2
The algorithms used for Pathway 2 in the land application risk assessment were
the same as those used for Pathway 1 (see Boxes 9 and 10). Because the HEI dif-
fers, however (see Table 6 in Chapter 2), the values of some of the key parameters
used in Pathway 2 vary from the values used in Pathway 1, particularly for the FC
and to some extent for the DC parameters. The values for each of the parameters
used for cadmium in Pathway 2 are presented below, followed by a discussion of
how each of the parameter values were selected; whether they are conservative or
average values; and how the combination of all of the parameters contributed to
making the pollutant limit (RP) conservative.
Part 503 Risk Assessment «>EPA 87
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Chapter 4
Calculation of the Adjusted Reference Intake: RIA
The first algorithm used for cadmium in Pathway 2 was:
RIA =
'RJD-BW N
103 =
°^™-0.01614
1,000 = 53.86 \xg Cd/day
RE
Parameters Used To Calculate the RIA
Adjusted Reference Intake, RIA. The RIA represents the allowable dose of a pol-
lutant in biosolids (e.g., in this pathway, the amount of cadmium ingested in food by
the subsistence home gardener). As discussed previously in this chapter (see also
Appendix B), the RIA was an important health-based parameter used in many algo-
rithms throughout the land application risk assessment to calculate pollutant limits.
The RIA value is inherently conservative because it is designed to protect sensitive
members of the population based on the conservative RfD for inorganic pollutants
or the q^ for organic pollutants (see Chapter 2, Box 3 for a discussion of why RfDs
and q^s are conservative). The RIA was called "adjusted" because a standard (av-
erage) adult male body weight (70 kg) was factored in, and the total background
intake of pollutants from sources other than biosolids (e.g., food, water, air) was
subtracted from the overall allowable dose to determine the allowable dose from
biosolids. Differences in routes of exposure (e.g., ingestion versus inhalation) and
bioavailability also were considered in developing the RIA (using the RE parameter,
see below). All the parameters used to develop the RIA are discussed below.
Oral Reference Dose (RfD) for Cadmium. Like other inorganic pollutants in the
land application risk assessment, cadmium in Pathway 2 was considered a noncar-
cinogen because only noncarcinogenic effects were associated with the pollutant
through this pathway (food ingestion of homegrown crops). Thus, the EPA-estab-
lished threshold for noncarcinogens (the RfD) for cadmium was used: 0.001 mg
pollutant/kg body weight»day (or 0.070 mg Cd/70 kg body weight*day). The RfD is
based on conservative data and is designed to protect even the most sensitive
members of a population, based on data on the most sensitive adverse health ef-
fect. For cadmium, this value was based on the most sensitive adverse effect
known to occur through oral exposure of cadmium, called renal proximal tubular
proteinuria, in which low-molecular-weight proteins appear in the urine, probably in-
dicating decreased protein reabsorption by the tubules in the kidney. Although a
number of studies (Kjellstrom and Nordberg, 1978; Nogawa et al., 1978, 1987;
Sharma et al., 1983) have shown that much higher levels of cadmium (e.g., rang-
ing from 0.2 to 1.0 mg/day) could be ingested daily for a lifetime without adverse
effects, the biosolids risk assessment conservatively used the RfD value of 0.07
mg Cd/70 kg body weight*day.
Human Body Weight (BW). The choice of body weight for use in the risk assess-
ment depended on the definition of the individual at risk, which in turn depended on
exposure and susceptibility to adverse effects. Because the RfD is defined as the
dose of pollutant per unit of body weight that can be tolerated over a lifetime, a
standard adult ("lifetime") average body weight of 70 kg was used in Pathway 2.
(For the child ingestion exposure pathway, Pathway 3, an average body weight of
16 kilograms was used.) An average value for the BW parameter was considered
adequate because it was combined with other, more conservative parameters
(e.g., the RfD).
Relative Effectiveness of Exposure (RE). The RE parameter was used to reflect
differences in toxicological effects due to differences in bioavailability and exposure
routes. For example, the bioavailability of cadmium is greatly lessened when zinc is
also present in the diet. Higher zinc levels in the diet of Japanese subsistence rice
eaters (discussed in Box 7, Chapter 3) probably would have reduced or eliminated
the intestinal absorption of cadmium and the severe itai itai disease experienced by
88 <&EPA Part 503 Risk Assessment
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How the Risk Assessments Identified Pollutant Limjtsfor Biosotfcl4|
this population. In addition, the binding ability of the biosolids matrix reduces the
availability of biosolids metal pollutants (see also Section J-3 in Chapter 3). A policy
decision was made to set the RE conservatively at 1 for the land application risk
assessment. Setting RE at 1 assumes 100 percent bioavailability intake. Hence,
setting the RE equal to 1 underestimates the allowable dose of biosolids pollutants.
Total Background Intake Rate of Pollutant From All Other Sources of Expo-
sure (TBI). The background intake values for water were based on EPA reports on
occurrence of and exposure to pollutants in relation to drinking water regulations,
and the TBI data for dietary exposure were based on U.S. Food and Drug Admini-
stration (FDA) market basket analyses for food and liquids (except drinking water)
from 1988 to 1992. Average values were used for the TBI parameter because it
was combined with other, more conservative parameters. A lifetime TBI average
was not based on a maximum daily intake because daily intake from background
sources is variable throughout a lifetime. Hence, a TBI value represents an aver-
age estimate of pollutant intake. A TBI value for cadmium of 0.0161 mg Cd/day
was used.
Calculation of the Pollutant Limit (RP)
The second algorithm used in the Pathway 2 risk assessment combined the RIA
value from the first algorithm discussed above with additional parameters to calcu-
late a pollutant limit, shown below for cadmium:
RIA 53.86
l\i r —
— = 7777^= 122 kgCd/ha*
• DC, ¦ FQ) °'4408
* Listed as 120 kg Cd/ha in Table 15 due to rounding to two significant figures.
Parameters Used To Calculate the Reference Application
Rate of Pollutant (RP)
Uptake Response Slope of Pollutant in Plant Tissue (UC). The UC parameter
reflected the amount of a pollutant taken up by plants from soil/biosolids. This
value was very important in the biosolids risk assessment for land application be-
cause it was used (in this pathway and others) to help assess human toxicity from
consumption of plants containing pollutants in biosolids. The methodology used for
calculating UC (for Pathways 1 and 2) was shown in Chapter 3 in the section "Cal-
culating Plant Uptake Slopes." For Pathway 2, uptake slopes for the following
seven food groups were evaluated because these were deemed likely to be grown
by the home gardener (the HEI for this pathway): potatoes, leafy vegetables, fresh
legumes, root vegetables, garden fruits, sweet corn, and grains and cereals. Table
15 lists the UC values for these different food groups for cadmium in Pathway 2.
A combination of conservative (very low probability of occurrence) and less conser-
vative (low to average probability of occurrence) assumptions were used to
calculate UC values in the biosolids land application risk assessment. This UC
value is an overestimation of actual plant uptake because several of the key as-
sumptions and data sets used were conservative, including; the assumption that
plant response slope is linear; the use of high-metal-content biosolids data; and the
use of short-term data from field studies (1 or 2 years after application), in which
equilibrium had not been attained (these and other conservative assumptions used
are explained below). Because of this conservatism, the geometric mean, rather
than the more conservative arithmetic mean, was used to statistically represent the
log normal distribution of UC data because the geometric mean provides a better
estimate of central tendency for data with this type of distribution (i.e., by using the
geometric mean, UC reflects median data). If the more conservative arithmetic
mean had been used, a higher UC value would have resulted that reflected higher
Part 503 Risk Assessment &EPA 89
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Chapter 4
Table 15
Parameter Values for Cadmium, Pathway 2, Land Application
Food Group
UC
DC
FC
UC•DC FC
Other Variables
Potatoes
0.004
15.5954
0.37
0.0230
RfD
0.001
Leafy vegetables
0.182
1.9672
0.59
0.2112
BW
70
Fresh legumes
0.002
3.2235
0.59
0.0036
RE
1
Root vegetables
0.032
1.5950
0.59
0.0305
TBI
0.01614
Garden fruits
0.045
4.1517
0.59
0.1104
RIA
53.86
Sweet corn
0.059
1.5969
0.59
0.0552
RPC
120
Grains and cereals
0.018
89.0833
0.0043
0.0070
Sum UC-DGFC
0.4408
percentiles of the data (e.g., possibly 70th to 80th percentiles). (A median value,
which is the same as the 50th percentile, is the point at which one-half of the ob-
servations of the amounts of cadmium taken up by plants are less than this value
and one-half are greater than this value. The 80th percentile is the point at which
80 percent of the observed cadmium uptake values are less than this number and
20 percent are greater.)
Minimum Plant Uptake Value Used. To address data uncertainties, a minimum
value of 0.001 mg/kg for plant uptake of a pollutant was assumed, even when data
indicated no increase in pollutant concentration in plants or when uptake was
negative. This assumption of minimum plant uptake is conservative and results in
an overestimation of UC, because lower UC values would have resulted if the ac-
tual values were used. The precise degree of overestimation is unknown. For
cadmium, 14 percent of the 196 data points used had plant uptake slopes of 0.001;
thus, overestimation might be from 0 to 14 percent. (By comparison, 73 percent of
the 52 data points for lead had UC values of 0.001, representing a much higher
overestimation of risk for lead) (Ryan and Chaney, 1993).
Use of Linear Response Slope, Another conservative assumption in calculating
the value for the UC parameter involved the use of a linear response slope to rep-
resent plant uptake of metals, as discussed in Chapter 3. Briefly, numerous field
studies indicate that plant uptake of metals is curvilinear (i.e., increases up to a
point and then levels off, or plateaus, even if more pollutant is added to the soil),
given the ability of biosolids to bind pollutants in biosolids/soil mixtures. Neverthe-
less, the biosolids risk assessment conservatively assumed a linear response (i.e.,
uptake continues to increase indefinitely). The linear response slope was used be-
cause most of the individual studies used on plant uptake did not have sufficient
rates of application to test for lack of linearity (Ryan and Chaney, 1993). Using a
linear response slope results in an overestimate of plant uptake of metals. For cad-
mium in Pathway 2, overestimation was probably at least RP/20, assuming a
maximum biosolids application rate of 1,000 mt/ha.
Inclusion of Acidic pH Data. The UC data included results from field studies that
represented both low pH (acidic) and neutral soil conditions, even though low pH is
unlikely to occur for very long (certainly not for the 70-year lifetime exposure of the
HEI) because gardeners probably would quickly correct the soil pH (e.g., add lime)
to improve plant health (see Chapter 3, "Ecological Risks," for a more detailed dis-
cussion on biosolids and low pH soils). In addition, increases in the solubility of two
90 iSEPA Part 503 Risk Assessment
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How the Risk Assessments Identified Pollutant Limits for Biosolids
metals, aluminum arid manganese, will cause injury in most plant species in low
pH soil conditions, even if no additional metals are added (e.g., from biosolids).
Thus, including data for low pH conditions overestimates UC values. Nevertheless,
because acidic soil conditions can periodically occur, and because data show that
low pH can result in phytotoxicity, plant response under acid soil conditions was
included in the data set. Forty percent of the data used to calculate UC values was
based on studies with a pH of less than 6.0. Using these low pH data, a garden
would be strongly acidic for approximately 30 of the 70 years of HEI exposure for
Pathway 2, an unlikely occurrence (Ryan and Chaney, 1993).
In addition, in the case of cadmium, if low pH conditions are not corrected (allowing
for high cadmium uptake by plants), the presence of zinc (in a ratio less than or
equal to 0.015 cadmium to zinc), which also is taken up by plants under low pH but
otherwise normal soil conditions, will lower cadmium risks for two reasons. First,
zinc is known to reduce the phytoavailability of cadmium for plant uptake. Second,
the reduction in plant yield resulting from zinc toxicity would reduce potential con-
sumption of crops containing high levels of cadmium (Fox, 1983, 1988; McKenna
et al., 1992a, 1992b; Chaney and Ryan, 1994; Chaney, 1990; Logan and Chaney,
1983; Strehlow and Barltrop, 1988).
Use of Short-Term Data To Predict Long-Term Pollutant Uptake. Bioavailability
of metals for plant uptake is highest in the first year after land application of
biosolids (Chang et al., 1987). Nonetheless, long-term UC values (i.e., for 70 years
of exposure) were conservative, based primarily on short-term data (i.e., from
biosoiids/soil systems established for less than 5 years) in the risk assessment.
Use of these early-year data causes overestimation of long-term UC values.
Impact of Combining Conservative and Less Conservative Factors To Calcu-
late UC, Combining the conservative factors discussed above for UC (e.g., the
0.001 bounding estimate, linearity, short-term data, and acid pH systems) with one
or two less conservative factors (e.g., the geometric mean) to estimate the UC re-
sulted in a calculated value for UC that was greater than the actual UC and, hence,
overestimates risk in exposure pathways that use this parameter.
Dietary Consumption of Food Group (DC). As discussed above, the types of
foods considered likely to be grown by the home gardener and therefore evaluated
for this pathway were potatoes, leafy vegetables, fresh legumes, root vegetables,
garden fruits, sweet corn, and grains and cereals. Determining DC values for Path-
way 2 involved a methodology similar to that used for Pathway 1 (i.e., use of EPA's
reanalysis of the FDA Revised. Total Food Diet list to develop an Estimated Lifetime
Average Daily Food Intake; see Chapter 3, "Food Consumption"), with additional
revisions to account for home garden production. For example, while the Pathway
1 food group listed as "legumes" included both dried and fresh legumes, for Path-
way 2 only fresh legumes were included in this category because home gardeners
are unlikely to grow the dried legumes they consume. Similarly, peanuts were ex-
cluded from the Pathway 2 risk assessment (although included in Pathway 1)
because home gardeners are unlikely to grow peanuts. Also, sweet corn was
added as a separate category for Pathway 2 because many gardeners grow sweet
corn (corn was included in Pathway 1 under the category "grains and cereals," but
was subtracted from this category for Pathway 2 because home gardeners do not
usually grow field corn for processing in the home). The DC values for cadmium for
Pathway 2 are listed in Table 15.
The value used for the DC parameter can be considered average; however, this
average DC value was based on conservative estimates (i.e., short-term dietary
data was used to estimate long-term food consumption) (Ryan and Chaney, 1993).
Extrapolating short-term data to long-term exposure estimates is known to result in
overestimation of actual exposure (U.S. EPA, 1991). These short-term data were
nevertheless used because they represented the best data available.
Part 503 Risk Assessment SEPA 91
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Chapter 4
The subsistence home gardener HEI is likely to be at lower risk than the sensitive
population that the RfD and the biosolids Pathway 2 analysis is designed to pro-
tect. This is because although the home gardener will potentially be adversely
exposed to cadmium in vegetables he or she produces and consumes from his or
her biosolids-amended garden soils, these same vegetables also contain signifi-
cant levels of zinc, calcium, and iron, which are known to reduce cadmium
absorption and hence adverse exposure. (See also Box 7 in Chapter 3.)
Fraction of Food Group Produced on Biosolids-Amended Soil (FC). The value
for the FC parameter in Pathway 2 differed significantly from Pathway 1, even
though the algorithms used were the same (see Boxes 9 and 10). This is because
the percent of food grown for human consumption on biosolids-amended land will
most likely be greater for the home gardener (the HEI for Pathway 2) than for an in-
dividual who consumes only store-bought foods, some of which are produced on
biosolids-amended soils (the HEI for Pathway 1). USDA data from surveys on
homegrown foods were revised to arrive at appropriate food production values for
the FC parameter for Pathway 2. Assuming that 100 percent of gardeners produce
some of their own food (a reasonable worst-case assumption made for the
biosolids risk assessment), the revised USDA values used in the biosolids risk as-
sessment for FC in Pathway 2 were:
Food Percent Homegrown
Group (rounded)
Potatoes3
37
Vegetables'5
59
Flour, cereal
0.43
"Includes sweet potatoes.
bIncludes leafy vegetables, fresh legumes, root vegetables,
garden fuits (e.g., tomotos, eggplant), sweet corn.
The above values for FC are conservative because they represent the percent of
homegrown garden foods for the small segment of home gardeners at the high end
of the food consumption distribution. For example, it would be difficult for most
home gardeners to grow 59 percent of the leafy vegetables they consume annu-
ally, given that (!) the harvesting season for leafy vegetables in most parts of the
country is only several weeks long, while leafy vegetables are consumed fresh all
year round, and (2) only 5.5 percent of the population have gardens large enough
to produce a significant portion of their annual food consumption (Ryan and
Chaney, 1993).
Thus, the conservative assumption of 59 percent homegrown production of leafy
vegetables probably significantly overestimates exposure. If a more reasonable as-
sumption of 10 percent (rather than 59 percent) annual leafy vegetable production
by a home gardener were used, while retaining the 59 percent production for other
foods in this food group, the pollutant limit (RP) could be increased by approxi-
mately a factor of 2 (Ryan and Chaney, 1993).
Conservative Parameters Result in a Conservative
Pollutant Limit
When all of the parameter values discussed above, which are based primarily on
conservative assumptions, are used together to calculate a pollutant limit (RP), it is
apparent that the resultant pollutant limit is also highly conservative. In addition, it
is highly unlikely that all the conservative conditions assumed would exist at the
same time. For example, it is unlikely that a person would grow a large portion of
the vegetables he or she consumes for an entire lifetime on biosolids-amended soil
92 SEPA Part 503 Risk Assessment
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How the Risk
(FC parameter) while gardening on strongly acidic soils for many years (UC pa-
rameter) and adhering to a poor quality diet that favors cadmium absorption (DC
parameter) (Chaney and Ryan, 1993).
Summary. The pollutant limits identified by the biosolids risk assessments are con-
servative and very protective, as illustrated by the analysis done for cadmium,
Pathway 2, for land application. Many of the parameters used to calculate the pol-
lutant limits were based on conservative data sets, assumptions, and/or policy
decisions including:
• HEI Assumption. The HEI for Pathway 2 grows a major portion of his or her
diet on biosolids-amended soil for a lifetime. In reality, data indicate that this
HEI population is small (between 0.1 to 2 percent of the U.S. population)
(Ryan and Chaney, 1993). In addition, few people will have home gardens
their entire lifetimes, and only a small portion of those persons will use
biosolids that can produce the high soil concentrations of biosolids pollutants
that would result in exposures at the pollutant limit. Equally conservative as-
sumptions were made for many of the other pathways in the biosolids risk
assessments.
• RfD and q-f* Data. RfDs and q^s, used in many of the exposure pathways,
are based on conservative data and are designed to protect even the most
sensitive members of a population, based on data on the most sensitive ad-
verse health effect.
• RE Policy Decision. Although the ingestion route of exposure may pose less
risk than other exposure routes, the relative effectiveness of exposure (RE)
parameter was conservatively set at 1 because of limited data. A more accu-
rate RE for pollutants in biosolids via food ingestion might be a value less than
1. Based on known data, the RE was considerably overestimated.
• UC Data and Assumptions. Numerous factors used to calculate plant uptake
of pollutants (metals) were conservative, including:
- Use of a minimum value (0.001 mg/kg) for plant uptake of metals (UC),
even when the data showed no increase, or a decrease, in plant uptake
of metals.
- Use of a linear response slope (which assumes that plant uptake contin-
ues to increase) because of a lack of data on biosolids application rates,
even though numerous data show that in reality plant uptake is curvilin-
ear (increases initially, then levels off, or plateaus).
- Use of data from short-term experiments in which the UC was atypically
high (U.S. EPA, 1992a).
• FC Data. Use of high estimates of homegrown food consumed by the HEI for
Pathway 2, particularly the 59-percent value used for leafy vegetables.
• Short-Term Data To Predict Long-Term Pollutant Uptake and Food Con-
sumption. Short-term data were used to predict long-term uptake by plants
and long-term food consumption by the HEI population for Pathway 2.
• Most Biosolids Cannot Exceed the Pollutant Limit for Cadmium. Data in-
dicate that less than 10 percent of current biosolids, and probably less than 3
percent, could ever reach the pollutant limit for cadmium, expressed as a soil
concentration limit. (This limit is known as the RLC, which is the allowed cu-
mulative soil concentration of a pollutant in p.g/g DW; conversion of the RP
pollutant application rate limit to an RLC soil concentration limit is shown in
Chapter 6 and Appendix D.) In addition, it would take a minimum of 300 years
(and possibly up to 600 years) of continuous application at agronomic rates
(e.g., 10 mt/ha/yr) before the soil concentration of cadmium would become
equal to the biosolids concentration and before it would reach the RLC. It
Part 503 Risk Assessment «EPA 93
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Chapter 4
would also take 300 years under agronomic application rates for the upper 1
percent of biosolids (those containing the highest pollutant concentrations) to
produce dietary increases in excess of the RfD. It is unlikely that continuous
yearly application would occur for this time frame; therefore, soil concentra-
tions are not likely to reach the RLC, and exposure of lifetime subsistence
gardeners is unlikely to reach the RfD in any year, and even less likely for 70
years (Chaney and Ryan, 1993,1994; Ryan and Chaney, 1995).
Summary
This chapter explains how pollutant limits were derived in the risk assessments
conducted for the final Part 503 rule. Included in the discussion are descriptions of
the many parameters involved and several example calculations to show how dif-
ferent types of parameters, models, data, and algorithms .were used to calculate
pollutant limits for different pathways. The conservative nature of many of the pa-
rameters also is discussed. The conservativeness remaining after combining
conservative and less conservative data, assumptions, and parameters to calculate
a pollutant limit is described. Finally, a detailed example is included to show the
high level of protection involved in calculating a pollutant limit (cadmium in Pathway
2 for land application). While the exact degree of conservativeness varies some-
what for each of the pathways and pollutant limits developed as a result of the Part
503 risk assessments, EPA believes that all the pollutant limits conservatively pro-
tect public health and the environment from reasonably anticipated adverse effects
of pollutants in biosolids. The conservative pollutant limits identified in the revised
biosolids risk assessments were used to establish the pollutant limits for the final
Part 503 rule, as discussed in Chapter 5.
94
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Chapter
5
How the Biosolids Risk
Assessment Results Were Used
in the Part 503 Rule
The results of the biosolids risk assessments were used to establish Part
503 pollutant limits. Other elements of the Part 503 rule were established
to provide a more comprehensive and protective regulation (see Figure 1
in Chapter 1), for example:
• To be consistent with data used in the various risk assessments (e.g., an as-
sumption used in the risk assessment calculation was a 10-meter buffer zone
between land-applied biosolids and surface waters. Hence, a Part 503 man-
agement practice was placed in the rule that requires a 10-meter buffer zone
from surface waters for land application).
• To ensure that the information needed to meet pollutant limits would be avail-
able (e.g., some Part 503 monitoring and recordkeeping requirements pertain
to operating conditions and emissions from biosolids incinerators; others en-
sure that biosolids meet cumulative pollutant loading rate limits for land
application).
• To provide protection for areas not addressed by the risk assessments (e.g.,
the Part 503 operational standard for pathogen reduction and vector attraction
reduction, and many of the Part 503 management practices).
This chapter first summarizes the biosolids risk assessments, as discussed
throughout this document. It then briefly presents key aspects of the Part 503 rule
as they relate to the risk assessments, focusing on how the biosolids risk assess-
ment results were used to establish the Part 503 pollutant limits. Some of the Part
503 requirements that were not based on the risk assessments also are discussed.
For more information on the Part 503 rule, see EPA's A Plain English Guide to
the EPA Part 503 Biosolids Rule (U.S. EPA, 1994).
Part 503 Risk Assessment &EPA 95
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Chapter 5
Synopsis of the Biosolids Risk
Assessments
History of the Risk Assessment Process
As discussed in Chapter 2, the process of establishing pollutant limits was exten-
sive. In 1984, EPA produced a preliminary list of 200 pollutants potentially found in
biosolids for which a risk assessment might be appropriate. Experts reviewed this
list and narrowed it down to approximately 50 pollutants to be considered for regu-
lation, based on toxicity and exposure data. After initial evaluations of these 50
pollutants (i.e., a hazard index screening, see Chapter 2, Tables 2 and 3), EPA de-
termined that 31 of these pollutants should undergo a detailed biosolids risk
assessment. From 1986 to 1988, the initial, detailed risk assessments for these 31
pollutants were conducted for the proposed Part 503 rule. After receiving numerous
peer review and public comments on the proposed rule published in 1989, a sec-
ond round of risk assessments was conducted with the assistance of biosolids
experts from outside the Agency from 1990 to 1992 for the final Part 503 rule.
These revised risk assessments incorporated numerous changes based on the re-
view comments (as discussed in Chapters 2 and 3). The results of the revised risk
assessments were the basis for setting pollutant limits in the final Part 503 rule.
Defining Exposure Pathways and Highly Exposed
Individuals
The basic approach for assessing risks from biosolids involved:
• Identifying appropriate pollutants to be evaluated (as discussed above and in
Chapter 2).
• Defining the highly exposed individuals (HEIs) for relevant exposure pathways
(e.g., a child ingesting biosolids or an adult eating crops grown on biosolids-
• amended soils) for pollutants of concern.
• Identifying or developing appropriate parameters (e.g., variables for toxicity,
dietary consumption, and food production) that could be used in algorithms
(equations) to calculate pollutant limits (as discussed in Chapter 4).
• Assessing risks to HEIs in relevant pathways of exposure. (HEIs and the
biosolids exposure pathways used are listed in Chapter 2, Tables 6, 7, and 8).
This approach was used for all types of risks—to people, animals, or plants—asso-
ciated with inorganic and organic pollutants. Defining realistic HEIs (i.e., highly
exposed individuals that really could exist in a population) was one of several key
challenges of the risk assessments. The approach used early on in the biosolids
risk assessment process (i.e., for the proposed rule) was the use of a most ex-
posed individual (MEl). Reviewers of this approach commented that the definition
of the MEl involved so many conservative assumptions that it was highly improb-
able that such an individual could exist. In risk assessment terminology, the MEl
represented bounding estimates. Further evaluation of the MEl showed that his or
her exposure would be higher than the 100th percentile (i.e., higher than 100 per-
cent of the most exposed population). Thus, for the revised risk assessment for the
final Part 503 rule, EPA used the concept of an HEI rather than an MEl to define in-
dividuals that because of their circumstances were at the high end of the exposure
distribution, but still had a finite possibility of existing (i.e., did not exceed the 100th
percentile for exposure). The HEI was defined by a combination of conservative
(high-end) and average (mid-range) assumptions, as recommended in EPA's 1992
96 ©EPA Part 503 Risk Assessment
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" How the Biosolids Risk Assessment Results Were Used in the Part 503 Rule
risk assessment guidance (Habicht, 1992, see Chapter 3). Nevertheless, the HEIs
remain conservative representations of the exposed population (as shown in the
example risk assessment for cadmium in Chapter 4).
Choosing Parameters To Identify Pollutant Limits
Risks to People and Animals
Different parameters were used to calculate pollutant limits for different types of
risks (or, different values were assigned to the same parameter). For example:
• For human health risks, the fundamental health-based parameters used were
the risk reference dose (RfD) for noncarcinogens and the cancer potency
value (q-,*) for carcinogenic pollutants (see Chapter 2). These parameters de-
fine intakes of pollutants that, based on an array of considerations, are
considered acceptable. Both RfDs and q^s include significant safety factors,
which contribute to the conservatism of the Part 503 pollutant limits for protec-
tion of humans in relevant exposure pathways.
• For risks to domestic animals and wildlife, the primary protective health pa-
rameter used was the threshold pollutant intake (TPI) of the most sensitive or
most exposed species. This parameter was the calculated maximum pollutant
intake in the diet associated with no toxic effects. Risks to animals also in-
cluded factors for bioavailability and bioaccumulation to account for the uptake
of pollutants in soil by earthworms and earthworm predators as well as a bio-
concentration factor in fish for the surface-water pathway.
• For risks to soil organisms, a pollutant concentration in soil considered to have
no adverse effects (called the RLC) was developed and used as the protective
health parameter.
Risks to Plants
For risks to plants, a series of comprehensive approaches was used. In conjunc-
tion with other experts, EPA conducted an in-depth review of the scientific literature
on plant uptake of metals (including over 270 journal articles) and field study data
on plant metal concentrations. For such risks:
• EPA first analyzed different levels of vegetative growth reduction (e.g., from 8
to 50 percent reduction in growth) associated with various leaf concentrations
of metals and corresponding soil metal loadings. Maximum loading rates were
identified that would not exceed an acceptable phytotoxicity threshold.
• Next, EPA analyzed data to identify plant tissue levels of metals associated with
first detectable yield reductions in sensitive plant species as an alternate way to
develop phytotoxicity thresholds and pollutant limits. Plant response slopes for the
uptake of metals were then calculated from the thresholds for sensitive species to
identify metals application rates that would not exceed the thresholds.
• As described in Chapter 3 (Section N-3) and Chapter 4 (Box 13), EPA then selected
the more restrictive of the two phytotoxicity limits (as determined by the approaches
noted above) as the pollutant limit for phytotoxicity in the risk assessment.
• In reality, no loading rates for potentially phytotoxic metals were identified in
any of the field studies analyzed that would exceed the established phytotoxic-
ity threshold concentrations. Thus, extra protection was provided by the
conservatively established pollutant limits for phytotoxicity.
Choosing a Pollutant Limit
As described in Chapter 4, a number of different exposure pathways were evalu-
ated for each pollutant. The pathway with the lowest pollutant limit was identified as
Part 503 Risk Assessment &EPA 97
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Chapter 5
the "limiting pathway," and this lowest value was used as the pollutant limit in the
risk assessment for each pollutant. The most limiting pathways and the risk as-
sessment pollutant limits are listed in Tables 11, 13, and 14 (Chapter 4) for land
application, surface disposal, and incineration.
Evaluating Inorganic and Organic Pollutants
Both inorganic and organic pollutants were evaluated in the biosolids risk assess-
ments. For these two types of pollutants, different parameters and algorithms were
used in the risk assessment calculations to reflect the fact that many organic pollu-
tants degrade in the environment. Organic pollutants for land application and
surface disposal were not regulated in the Part 503 rule, however, for the reasons
discussed in Chapter 3. For incineration, organic pollutants were regulated through
a THC (or CO) operational standard (discussed later in this chapter).
Using Conservative Assumptions
For many of the parameters and methodologies used, a number of associated as-
sumptions and policy decisions were made. For example, assumptions were made
regarding plant uptake of pollutants (the UC parameter) and the fraction of food
produced on biosolids-amended land (the FC parameter), as discussed in Chapter
4. In many cases, the assumptions and policy decisions made were conservative
to account for uncertainties that remained in the carefully assembled data sets.
Three examples are:
• The assumption that a certain minimal level of plant uptake of pollutants oc-
curs, even when available data showed no increased plant uptake.
• The assumption that home gardeners produce and consume 59 percent of
their annual yearly leafy vegetable consumption, while a more reasonable as-
sumption might be the production and consumption of 10 percent of their leafy
vegetables.
• The selection of the most exposed or most sensitive species as the HEI for
protection of ecological species.
A number of key assumptions were changed (i.e., made less conservative) after
EPA received comments indicating that the proposed Part 503 pollutant limits were
based on unrealistically conservative assumptions. Thus the revised risk assess-
ments were calculated combining assumptions having conservative high-end (low)
probabilities of occurrence with assumptions having mid-range (average) prob-
abilities of occurrence. Using this approach, the 95th to 98th percentiles of the
subset of the population comprised of individuals who might be adversely effected
by pollutants in biosolids were protected by the final Part 503 rule (such as the sub-
sistence home gardener described in Chapter 4, who might be consuming food
produced in soils where the cumulative pollutant loadings were already at their
maximum permitted level). The revised risk assessments resulted in a final Part
503 rule that was both highly protective and more realistic and less stringent than
the initial proposed rule.
The Biosolids Risk Assessments and
the Part 503 Rule
The pollutant limits identified in the biosolids risk assessments were used either di-
rectly or with modification to establish the pollutant limits in the Part 503 rule, as
discussed below.
98 SEPA Part 503 Risk Assessment
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How the Biosolids Risk Assessment Results Were Used in the Part 503 Rule
Pollutant Limits for Land Application
Four Types
The four types of pollutant limits established for land application in the final Part
503 rule are shown in Table 16 and described below:
• Cumulative pollutant loading rates (CPLRs): One type, called the CPLR,
was taken directly from the biosolids risk assessment results (Table 2 in Part
503). CPLRs apply to biosolids with pollutant concentrations in excess of Part
503's Table 3 values (see also Table 16 in this guidance document) that are
applied to land in bulk. Part 503 requires that accurate records be kept of the
amounts of pollutants applied to a site from biosolids subject to CPLRs, Attain-
ment of the CPLR for a pollutant means that no more CPLR biosolids can be
applied to that site. Even at the CPLR, however, the pollutant loading is pro-
tective of public health and the environment. Other biosolids that meet the
pollutant concentration limits, described below, can still be land applied safely,
even on a site where the CPLR has already been reached.
Table 16
Risk Assessment Results and Part 503 Pollutant Limits for Land Application
Pollutant
Table 2,
Part 503 Rule
Table 4,
Part 503 Rule
Table 1,
Part 503 Rule
Table 3,
Part 503 Rule
Risk
Assessment
Results (RPC,
kg-pollutant/
ha, DW)
CPLR Limit"
(kg-pollutant/
ha, DW)
APLR Limitb
(kg-pollutant/
ha/yr, DW)
Ceiling
Concentration
Limit0
(mg-pollutant/
kg- biosolids, DW)
Pollutant
Concentration Limit
(mg-pollutant/
kg- biosolids, DW)
(monthly average)
Arsenic
41
41
2.0
75
41
Cadmium
39
39
2.0
85
39
Chromium"1
Copper
1,500
1,500
75
4,300
1,500
Lead
300
300
15
840
300
Mercury
17
17
0.85
57
17
Molybdenum8
18
75
Nickel
420
420
21
420
420
Selenium
100
100
5.0
100
»-*
o
o
T,
Zinc
2,800
2,800
140
7,500
2,800
aCPLR limits were taken directly from the risk assessment results and pertain only to biosolids applied in bulk.
bAPLR limits were derived from the CPLR limits (see text) and pertain only to biosolids sold or given away in bags or other con-
tainers.
teiling concentration limits are either the 99th-percentile concentrations in the National Sewage Sludge Survey or the risk as-
sessment pollutant limits, whichever were least stringent (see text and Box 15).
dChromium limits are not shown because they most likely will be deleted from the rule (see also Chapter 3).
eSome molybdenum limits are not shown because they are under reconsideration and are presently not part of the rule (except
for the ceiling concentration limit, which remains in effect).
fA change in the pollutant concentration limit for selenium is expected based on a recent court decision (see also Chapter 3).
Part 503 Risk Assessment 4>EPA 99
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Chapter 5
• Annual pollutant loading rates (APLRs): A second type of Part 503
biosolids pollutant limit is the APLR. The APLRs, which apply only to biosolids
that are sold or given away in a bag or other container, identify the maximum
amounts of pollutants in biosolids that can be applied to a site in any one year.
APLR biosolids, like CPLR biosolids, contain pollutant levels in excess of the
Part 503 Table 3 pollutant concentration limits. The APLRs were derived by di-
viding the CPLRs by 20, reflecting an assumed 20 applications annually at the
same rate to a given site. APLRs were established because imposing CPLRs
was not practical, given the difficulty in establishing a chain of control from
preparer to applier of bagged or containerized biosolids. Part 503 requires that
APLR biosolids must be accompanied with labeling information to ensure that
they are used properly and that the APLR is not exceeded.
EPA concluded that 20 yeans is a reasonable conservative assumption for APLRs
because biosolids sold or given away in a bag or other container will probably be ap-
plied to a lawn, home garden, or public contact site and therefore probably will not be
applied longer than 20 years at the same site, particularly not 20 consecutive years.
• Ceiling concentration limits: A third type of pollutant limit for land applica-
tion, called the ceiling concentration limit, identifies biosolids with the
maximum allowable concentrations of pollutants that can be land applied.
These limits were established in Part 503 as minimum-quality limits to prohibit
the lowest quality (highest metal content) biosolids from being land applied.
Biosolids with high metals concentrations are a concern because metals at
high levels might behave more like metal salts, which are taken up by plants
much more readily than metals at the low levels typically found in biosolids
(see Chapter 3). Including ceiling limits also may bolster public confidence in
the land application of biosolids. The ceiling concentration limits are either the
99th-percentile concentration for each pollutant, as defined by the National
Sewage Sludge Survey (NSSS), or the pollutant limits identified in the risk as-
sessment, whichever is the least stringent (see Box 15, this chapter, and
Section N-6 of Chapter 3).
• Pollutant concentration limits: The last and most stringent type of Part 503
limit is called the pollutant concentration limit. These risk-based limits were de-
rived by assuming a 1,000-mt/ha application of biosolids in which the
cumulative pollutant loading rates would be met but not exceeded. The pollu-
tant concentration limits define no-adverse-effect biosolids that can be land
applied safely without the applier keeping track of cumulative pollutant load-
ings, as is required for biosolids meeting CPLRs discussed above (see also
the description of pollutant concentration limits in Chapter 3). The pollutant
concentration limits were derived from the pollutant limits identified in the risk
assessments. (Prior to a recent court decision [see Section Q, Chapter 3], the
99th-percentile NSSS concentrations were imposed as pollutant concentration
limits when they were lower than the risk assessment limits.)
If biosolids can be shown to meet the pollutant concentration limits listed in Ta-
ble 3 of Part 503, as well as certain Part 503 pathogen and vector control
requirements (discussed later in this chapter), these biosolids (sometimes
called exceptional quality [EQ] biosolids) can be land applied as freely as
other fertilizers and soil conditioners without also having to show they meet
the Part 503 management practices and general requirements. Recordkeep-
ing, monitoring, and reporting requirements would still be in effect, but the
burden of these stipulations would be considerably diminished without the
need to track pollutant loadings. Numerous field studies supported this ap-
proach; research results showed no adverse effects from applying biosolids
with the low levels of pollutants defined by the pollutant concentration limits.
100 SEPA Part 503 Risk Assessment
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How the Biosolids Risk Assessment Results Were.Used in the Part 503 Rule
As discussed above, the derivation of ceiling concentration limits was based on
prohibiting the use of lower quality (high metal) biosolids, including pollutants that
would behave more like metal salts. At the same time, the use of pollutant concen-
tration limits encourages the use of high-quality biosolids. The decision to use
ceiling concentration and pollutant concentration limits, whether arising from risk-
based calculations or other data, was an EPA policy decision. This decision helped
implement EPA's comprehensive risk management policy that incorporates the
goals of promoting the use of high-quality biosolids and maintaining the existing
quality of land-applied biosolids. The policy decision to use these types of limits also
added further conservatism to the Part 503 rule. Box 15 provides an example of how
Part 503 ceiling concentration limits and pollutant concentration limits were derived.
To summarize, all land-applied biosolids must meet the Part 503 ceiling concentra-
tion limits. Biosolids also must meet either (1) the Part 503 pollutant concentration
limits, or (2) the Part 503 CPLRs or APLRs, as discussed above. Thus, EPA used
both risk-based limits and policy decisions to develop the land application pollutant
limits in the Part 503 rule.
Box 15
How Part 503 Ceiling and Pollutant Concentration Limits Were Derived
Example for copper: /'V
• The pollutant limit (RPc) identified in the biosolids land application risk assessment for copper was 1,500
; . kg 'ofcopper per hectare (see Chapters 3 and 4); . ,
• To convert the pollutant limit to a pollutant concentration limit, EPA used the assumptions that biosolids
would be applied to asite for 100 ye'ars at a rate of 10 metric tons per year, (a total of 1,000 metric, tonsper
hectare of biOsohds application), which represents "1,500 mg of cppper per kg of biosolids:
1,500 kg of copper per hectare (risk assessment limit)
concentration —— :———— * :— - - — ' - -- -
limit '¦ I00{site life, yrs) - 10(annual application rate, mt—biosolids DW/ha ¦ yr}':- 0,001.;
'¦--•V =T,'500 mgofcopper per leg of biosolids -a.— v-
(Note: 0.001 is a conversion factor) • . : ^
.•.Including, pollutant, concentration limits.encourages' the use of superior quality.biosolids,. because if the
poUutant concentration . limits;, and certain Part 503; pathogen and vector /requirements 'are met/ ; the1
biosolids can be used as :freely as any, other type'offertilizer or soil conditionet • •• :
• To deriv.e the ceiling concentration limits the 99th-percentile,.pollutant concentration in the National"Seiy-";
: : .-age Sludge Survey.;(NSSS) :was Identified. For copper, this was.4,300.mg of copper-per kg. of biosoHds.;The.?
results, of .the risk -assessment" and; the NSSS, survey were' ;then .compared and fee least .stringent
higher) Of the risk assessment,or l^SSS,number (4,300 ;mg/Icg) was- selected the/ceiling concentration.;
.limit; this limit prevents bio^lids with high concentrations of pollutants from beingland applied.
Risk Assessment Part 503 Ceiling Part 503 Pollutant
Pollutant Limit NSSS 99th % Concentration Limit Concentration Limit
Copper . %50i) 4,3(30 . 4,300 ' 1,500*
"All numbers are mg of pollutant/kg of biosolids, :DW. The Part503 pollutant concentration limits are monthly averages.
Part 503 Risk Assessment SEPA 101
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Chapter 5
Pollutant Limits for Surface Disposal
EPA used either the 99th-percentile pollutant concentrations from the NSSS or the
pollutant limits identified in the risk assessment, whichever were more stringent, as
the pollutant limits for unlined surface disposal units in the Part 503 rule. The
Agency determined that risks from surface disposal sites with liners and leachate
collection systems were negligible; thus, the Part 503 approach for surface dis-
posal includes pollutant limits only for biosolids disposed at surface disposal sites
without liners and leachate collection systems.
Surface disposal sites often comprise a number of cells, or units, that accept biosolids
and may or may not be active. Part 503 pollutant limits for active units without liners
and leachate collection systems differ depending on the distance between the unit
boundary and the surface disposal site boundary. The risk assessment proved to be
sensitive to the assumption of distance to the property line for unit boundaries 150 feet
or less from the surface disposal site property line, and thus the Part 503 limits reflect
these distance differences. The Agency made a decision to manage risks by tailoring
limits for active biosolids units within surface disposal sites based on property line dis-
tance, rather than requiring ail surface-disposed biosolids to meet unnecessarily
restrictive limits based on worst-case property line distances. The Agency also de-
termined that risks from the surface disposal of biosolids through the surface-water
pathway could be managed much more efficiently through management practices (dis-
cussed later in this chapter) that prevent biosolids from entering surface water rather
than through substantially more stringent pollutant limits.
Some inorganic pollutants (copper, lead, and mercury) were not regulated in Part
503 for surface disposal because they met one of three criteria that EPA used to
delete pollutants from biosolids regulation (i.e., they were not expected to exceed
the pollutant limits identified in the risk assessment, based on NSSS data; see "De-
letion of Pollutants" in Chapter 3).
Pollutant Limits for Incineration
. Four of the seven inorganic pollutant limits in Part 503 for biosolids incineration
were derived using information from the biosolids risk assessment (i.e., risk-spe-
cific concentrations for arsenic, cadmium, chromium, and nickel), as described in
Chapter 4. Because of the limited number of incinerators affected, the Agency
chose to use site-specific pollutant limit calculations. This approach allows risks to
be managed in accordance with incinerator performance (see Box 16).
Beryllium and mercury pollutant limits were incorporated by reference to the Na-
tional Emission Standards for Hazardous Air Pollutants (NESHAPS) for these
pollutants, which are health-based standards. The pollutant limit for lead was
based on a percentage of the National Ambient Air Quality Standard (NAAQS),
rather than a risk-specific concentration for lead. EPA chose this approach for be-
ryllium, mercury, and lead to be consistent with existing air quality regulations. EPA
concluded that meeting the NESHAPS, or the pollutant limit calculated for lead us-
ing the NAAQS factor and site-specific data, protects public health from reasonably
anticipated adverse effects of these pollutants in biosolids.
Other Elements of the Part 503 Rule
In addition to pollutant limits, other elements of the Part 503 rule include general
requirements; operational standards; management practices; and frequency of
monitoring, recordkeeping, and reporting requirements (see also Figure 1 in Chap-
ter 1), Several of these additional elements are discussed below to highlight their
relationship to the risk-based pollutant limits.
102 ©EPA Part 503 Risk Assessment
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Box 16
Equations Used To Calculate Part 503 Pollutant Limits for Incineration
For arsenic, cadmium, chromium, and nickel;3
- Part 503 pollutant limit'
MC-"86,'40q;,,
For lead;®
Part 503 pollutant limit
"Where: ;
RSC - ; "
NAAQS;
Site-Specific Factors.
DF
CE-
DF- (1 -CE)-SF
0.1-NAAQS -86,400;
DF-Xl~CE).-:SF:
.'
, ¦¦ '
v:v'
' ¦¦ ¦¦ '
\.£:.
= -¦ % Biosolids incinerator control efficiency for arsenic-cadmium,chromium, lead, or nickel; *>
" site-specific (hundredths) ; . •< •
SF ¦ , = ' Biosolids feed rate, sit
Hypothetical example calculation for arsenic:
Parameter
Units
RSC
;v#.;;o.Q23'-'^
ug/m'
.Conversion factor " •' ¦¦"* ''
;v '86,400 ;
.. \ ' Sec/day.;.,.'. .v..'
Site-Specific Factors
DF
" • . : ;ng/m3/g/sec;;
CE
0 975
hundredths
SF
12 86
. ,, .. .
¦ *
. : ¦ . ¦
¦¦¦¦¦¦ . ¦
.. .. . ..
'•¦V.
: . ¦¦¦¦:.:¦
aSee the Part 503 rule for
Part 503 RSCx 86,400 0.023 x 86.400
pollutant limit £>Fx {1-C£) k-SF ~ 34 *(}-$¦? 118.6.';:
' ' .. • '¦ -.:. ....¦¦ ¦¦¦: ' " . ¦
it/ perforr
C-:< V,
1 ii':1 'v ¥''V."
Part 503 Risk Assessment -jvEPA 103
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Chapter 5
Operational Standards
In most cases, EPA determined that risk-based pollutant limits could be calculated
to achieve the goal of protecting public health and the environment from reason-
ably anticipated adverse effects of pollutants in biosolids, given the state of the
science of risk assessment. In three cases, however, risk assessment methodolo-
gies were not sufficiently developed to provide a reasonable estimate of risk. Thus,
EPA determined that the most appropriate way for the Agency to manage risks in
these instances was to use operational standards rather than risk-based pollutant
limits. The Clean Water Act specifically provides for alternatives to numeric limits
for biosolids use or disposal in certain circumstances:
If...it is not feasible to prescribe or enforce a numeric limitation for a pollu-
tant...the Administrator may instead promulgate a design, equipment,
management practice or operational standard [emphasis added]...which in the
Administrator's judgment is adequate to protect public health and the environ-
ment from any reasonably anticipated adverse effect of such pollutant. [Clean
Water Act, Section 405(d)(3)]
The Part 503 rule contains three operational standards. One standard regulates
pathogen reduction in biosolids; the second addresses vector attraction reduction
in biosolids; and the third covers total hydrocarbon (THC) limits in incinerator emis-
sions. Each of these operational standards is discussed below.
The Operational Standards for Pathogen and Vector
Attraction Reduction
EPA determined that a risk assessment approach for pathogen and vector attrac-
tion reduction in biosolids was not yet sufficiently developed to establish risk-based
limits. Thus, EPA chose to manage risks from pathogens (and risks from vectors
spreading those pathogens) through operational standards. The Agency concluded
that the best way to meet the objective of protecting public health and the environ-
ment was to have biosolids meet certain technology-based requirements for
minimizing or eliminating pathogen densities and reducing vector attraction. These
requirements can be met either directly by taking measurements or by using cer-
tain approved processes known to reduce pathogens and vector attraction to levels
judged reasonably safe by EPA.
With respect to pathogens, two levels of control can be met: Class A, which allows
the use of biosolids with fewer restrictions because pathogen densities are below
detectable levels; and Class B, which, because pathogen densities are reduced but
are still detectable, is associated with a number of site and harvesting restrictions
that allow sufficient time for environmental degradation of pathogens prior to con-
tact. Domestic septage is required to meet certain pH requirements and site
restrictions similar to those for Class B biosolids. More information on the Part 503
pathogen and vector attraction reduction requirements can be found in EPA's A
Plain English Guide to the EPA Part 503 Biosolids Rule (U.S. EPA, 1994) and
Control of Pathogens and Vector Attraction in Sewage Sludge (U.S. EPA,
1992d).
The Operational Standard for THC
Based on comments received on the proposed Part 503 rule, the Agency decided
to replace its proposed risk-based THC concentration approach with an opera-
tional, technology-based standard. EPA set the operational standard for THC in
emitted incinerator off-gases at 100 ppm based on testing at three incinerators.
After evaluating the aggregate impact analysis, which indicated minimal health ef-
fects from current biosolids incinerator practices, along with site data on THC
104 ©EPA Part 503 Risk Assessment
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How the Biosolids Risk AssessmentResults Were Used irt the Part 503 Rule
emissions, EPA concluded that this operational standard would protect public
health from any reasonable anticipated adverse effects. As discussed in Chapters
2 and 4, EPA later included carbon monoxide (CO) monitoring (100-ppm limit) as
an alternate, acceptable method of ensuring that the THC emissions operational
standard would be met.
Management Practices
In general, management practices in the Part 503 rule were stipulated for the three
use or disposal practices (land application, surface disposal, or incineration) for
one of three reasons:
• To protect public health and the environment when specific pathways or end-
points were not analyzed in the risk assessment (e.g., threatened or
endangered species requirements for land application and surface disposal of
biosolids).
• To embody assumptions that were incorporated into the risk assessment and
thus need to be met in practice to ensure that risk levels are not exceeded
(e.g., a 10-meter buffer zone around bodies of surface water for land-applied
biosolids).
• To require that information be provided where risk levels might be exceeded if
biosolids were not handled properly (e.g., labeling requirement for bagged or
containerized biosolids for land application).
Thus, management practices were included in Part 503 to (1) constrain risks when
actual risks were not evaluated, (2) support risk modeling assumptions, or (3) en-
sure proper handling of biosolids. Where risks were determined to be negligible (as
discussed below), the Agency considered the appropriate strategy was to refrain
from subjecting the biosolids to management practice requirements. The manage-
ment practice requirements for the three use or disposal practices are listed in
Table 17 and are discussed below.
Management Practices for Land Application
As shown in Table 17, management practices are used in conjunction with pollutant
limits and other elements of the Part 503 rule to govern the land application of
biosolids. Management practices are used to protect threatened or endangered
species; restrict land application on flooded, frozen, or snow-covered land; impose
a 10-meter buffer between land-applied biosolids and U.S. waters; require agro-
nomic rates pertaining to nitrogen; and require labeling for bagged or containerized
biosolids, unless certain conditions, discussed below, are met.
Biosolids that meet the Part 503 pollutant concentration limits and certain Part 503
pathogen and vector attraction reduction requirements are not subject to the gen-
eral requirements and management practices (listed in Table 17) for land
application because the Agency has determined that the risks associated with the
land application of these biosolids are negligible. Also, bagged biosolids applied to
a lawn or home garden are not subject to management practice requirements other
than labeling because the Agency determined that it is unlikely that large amounts
of bagged biosolids would be applied to a lawn or home garden multiple times. The
risks associated with this scenario are thus considered negligible.
Management Practices for Surface Disposal
EPA established the Part 503 management practices listed in Table 17 for surface
disposal of biosolids when risks to human health and the environment were not ad-
dressed by the risk assessment, and to ensure protection of surface water, air
quality, ground water, and human health from pollutants that may be present in
biosolids at surface disposal sites.
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Chapter 5
Table 17
Part 503 Management Practices
Management Practice
Reason Included in Rule
Land Application2
Protection of threatened or endangered species
Consistency with federal regulation (50 CFR 17.11 and 17.12)
Restriction of land application on flooded, frozen, or
snow-covered land
Prevents biosolids from entering surface waters and wetlands
Ton-meter buffer for US. waters
Protects waters of the U.S.; helps ensure risk is no greater than that calculated
in the biosolids risk assessment, which assumed a 10-m buffer zone from
surface waters
Agronomic application rate limit for nitrogen
Protects ground water from nitrate contamination
Labeling requirements for bagged or containerized biosolids
Helps ensure that appliers use proper application rates, which ensure that
pollutant limits are met
Surface Disposal
Protection of threatened or endangered species
Consistency with federal regulation (50 CFR 17.11 and 17.12)
Prohibition against restriction of base flood flow
Protects area's flooding capacity; also protects surface water and public health
from the release of pollutants in biosolids if a base flood occurs
Geological stability requirements
Protects the structural integrity of the surface disposal site and prevents the
release of leachate (which may contain pollutants in biosolids) from the site
Protection of wetlands
Protects wetlands from possible contamination when biosolids are placed in a
surface disposal site
Collection of runoff
Prevents runoff from a surface disposal site (which may contain pollutants in
biosolids) from being released into the environment
Collection of leachate
Prevents leachate from a surface disposal site from being released into the
environment
Methane gas limit
Ensures explosive conditions do not exist at site
Restriction on crop production
If no crop production, prevents pollutants in biosolids at surface disposal sites
from being consumed by humans/animals; if crop production allowed,1* helps
ensure levels of pollutants taken up by crops do not negatively affect the food
chain
Restriction on grazing
If no grazing, prevents animals from ingesting pollutants in biosolids at
surface disposal sites; if grazing allowed,b helps ensure that levels of
pollutants taken up by crops do not negatively affect the food chain
Restriction of public access
Minimizes public contact with pollutants that may be present in biosolids at
surface disposal sites
Protection of ground water
Protects ground water from nitrate contamination
Incineration
Measurement of THC or CO in stack gases
Measurement of oxygen in stack gases
Measurement of moisture content in stack gases
Measurement of combustion temperature
Measurement of operating parameters for pollution control
devices
Protects air quality by ensuring proper incinerator operation
Protection of threatened and endangered species
Consistency with federal regulation (50 CFR 17.11 and 17.12)
*In addition to these management practices, site and harvesting restrictions are included in the pathogen and vector attraction reduction require-
ments to protect human/animal health for crop consumption by ensuring that pathogen concentrations in crops are at or below levels identified
in the risk assessment.
bCrop production or grazing are allowed at surface disposal sites only if the site owner/operator can demonstrate that human health and the en-
vironment are protected from reasonably anticipated adverse effects of pollutants in biosolids.
106 &EPA Part 503 Risk Assessment
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How the Biosolids Risk Assessment Results Were Used in the Part 503 Rule
Management Practices for Incineration
The Part 503 rule requires that management practices relating to the measurement
of key parameters must be followed at biosolids incinerators. The required meas-
urements are necessary to show that the incinerator is operating properly and to
ensure that pollutant limits are being met. They are also a necessary enforcement
tool. The management practices for incineration are listed in Table 17.
Part 503 Monitoring, Recordkeeping, and Reporting
Requirements
Monitoring, recordkeeping, and reporting are necessary to ensure that risks are
properly managed. Further, these requirements form the basis for enforcing the
regulation. Without the ability to enforce the rule, the Agency cannot be sure that
the risk levels specified in the rule will be met. The Agency determined, however,
that the frequency of monitoring, the types of records and reports maintained, and
report submission requirements could vary, given the variable risks posed by differ-
ent practices, quantities of biosolids produced, and classifications of POTWs.
For further information on all of the elements of the Part 503 rule, see EPA's A
Plain English Guide to the EPA Part 503 Biosolids Rule (U.S. EPA, 1994). For
the Part 503 rule's approach for regulating domestic septage (i.e., less burden-
some requirements than for biosolids at certain types of sites), see EPA's
Domestic Septage Regulatory Guidance: A Guide to the EPA Part 503 Rule
(U.S. EPA, 1993).
General Summary
EPA conducted three comprehensive risk assessments for pollutants in biosolids
that are land applied, surface disposed, or incinerated. The risk assessments
evaluated risks to human health through relevant exposure pathways for each of
the three use or disposal practices, as well as ecological risks (to animals and
plants) for land application and surface disposal. Using appropriate parameters
that represented relevant data and assumptions, the risk assessments quantita-
tively identified allowable concentrations or application rates of pollutants in
biosolids that are used or disposed that protect human health and the environment
from reasonably anticipated adverse effects.
The results of the risk assessments were used as a basis for establishing the final
Part 503 pollutant limits, aided in some cases by EPA policy decisions. The risk as-
sessments involved a number of conservative assumptions and data management
decisions that provided protective yet realistic Part 503 requirements. Additional
protective measures also were included in the rule (e.g., operational standards,
management practices, and monitoring and recordkeeping requirements) to ad-
dress areas not included in the risk assessment or to support assumptions made in
the risk assessment. Where risks were negligible, less burdensome requirements
were allowed, such as exempting "clean" (or "exceptional quality") biosolids from
management practices and general requirements for land application and setting
alternate requirements for domestic septage.
Using the best available data, the biosolids risk assessments identified limits for
pollutants in biosolids that protect public health and the environment. The Part 503
rule, based on the risk assessments, sets forth conservative pollutant limits and
other requirements without being overly restrictive, while allowing the beneficial
and safe use of biosolids.
Part 503 Risk Assessment v>EPA 107
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Ongoing monitoring ensures that biosolids are being used in accordance with Part
503 requirements that were established based on the biosolids risk assessments. The
top photograph shows a technician collecting a representative composite sample of
a dried biosolids product. The bottom photograph shows this sample being dry
ashed in preparation for chemical analysis.
108 SEPA Part 503 Risk Assessment
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Chapter
6
Questions and Answers on the
Part 503 Risk Assessments
A number of particular questions are often asked about the Part 503 risk
assessments. This chapter poses many of these questions and provides
answers to them. Additional discussion about many of these issues may
be found elsewhere in this guide.
Risk Assessment
Q: What do the Part 503 risk assessments accomplish?
A: They assess the potential for risk to humans, other animals, and plants from
pollutants in biosolids. The risk assessments evaluated exposure to selected
pollutants in biosolids via 14 exposure pathways for land application, 2 for surface
disposal, and 1 for incineration.
Risk Level of 1 x 10"4 or 1 x 10~6
Q: What does a risk level of 1 x 10~4 mean?
A: For carcinogenic compounds (compounds that are capable of inducing or caus-
ing cancer), a 1 x 10"4 risk level means there is a 1 in 10,000 chance of the highly
exposed individual getting cancer.
Q: Does this 1 x 10"4 risk level mean that as a result of the Part 503 biosolids rule,
2,500 of the 2.5 million persons living in the United States (1 person for each
10,000) could possibly get cancer because of exposure to a pollutant in biosolids?
A: No, the risk of getting cancer is related only to the population that is exposed to
that risk. In the United States, the number of persons highly exposed to risks from
biosolids is actually very small. If, for example, 10,000 individuals were in the
highly exposed population, then there might potentially be one case of cancer aris-
ing in the United States from exposure to a particular pollutant in biosolids. If,
however, the population of highly exposed individuals was 10, then there might po-
tentially be 0.001 case of cancer arising in the United States from that pollutant.
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Chapter 6
Q: Were the limits for metals in the Part 503 rule established based on a 1 x 10"4
risk?
A: No, the Part 503 metals were considered noncarcinogens (they do not cause
or induce cancer) for the exposure pathways evaluated.
Q: If metals were not regulated on a 1 x 10"4 risk basis, then on what basis?
A: The pollutant limits for each of the Part 503 metals in biosolids are based on
threshold limits such as risk reference doses (RfDs), which represent the amount
of daily intake of a particular noncancer-causing substance that is not expected to
cause adverse effects; the RfD is a conservative determination of the upper level of
acceptable intake. The RfD (or other threshold limit) was then combined with
pollutant intake information (e.g., the amount of a pollutant in biosolids taken up by
plants that are then ingested by humans; the amount of a particular food con-
sumed) to derive a pollutant limit. Each pollutant limit is set to protect a highly
exposed individual (plant or animal) from any reasonably anticipated adverse ef-
fects of a pollutant in biosolids.
Q: Understanding now that the limits for metal pollutants in biosolids used or dis-
posed were not based on a 1 x 10"4 risk in the Part 503 rule, were any pollutant
limits established on the basis of a 1 x 10"4 risk?
A: Yes and no. Yes, in that pollutant limit determinations based on a 1 x 10"4 can-
cer risk level were made for potentially toxic organic pollutants that could occur in
biosolids. And, no, because the pollutant limits determined in this way were not in-
cluded in the final rule, as described below.
Land Application: Thirteen pollutant limits were determined for organic pollutants
using the 1 x 10"4 approach, but they were not included in the final Part 503 rule.
The decision to drop these organic pollutants from the final Part 503 rule was made
because: (i) the pollutant has been banned, restricted for use, or is no longer
manufactured for use in the United States; (ii) the pollutant is not present in
biosolids at significantly high frequencies of detection, based on data gathered
from the National Sewage Sludge Survey (NSSS); or (iii) the limit for the pollutant
identified in the biosolids risk assessments is not expected to be exceeded in
biosolids that are used or disposed, based on data from the NSSS.
Surface Disposal: Pollutant limits also were determined for toxic organic pollutants
in surface-disposed biosolids based on a 1 x 10~4 cancer risk. None of the organics
were retained in the final Part 503 rule, and three inorganics were deleted from
regulation because each of these organic and inorganic pollutants met one of the
three criteria described in the previous paragraph.
Incineration: Pollutant limits were also determined for toxic organic pollutants as-
sociated with incinerated biosolids for which qi*s (cancer potency values) exist,
based on a 1 x 10"4 cancer risk. Because of the limitations of the risk assessment
process in reflecting all of the individual toxic organic pollutants emitted from
biosolids incinerators, the EPA's Science Advisory Board recommended using an
operational standard rather than pollutant limits. The recommended operational
standard involves monitoring the emission of total hydrocarbons from biosolids in-
cinerators to ensure the levels from stacks do not exceed 100 ppm. This standard
is believed to be protective of public health for the spectrum of toxic organic pollutants
that are emitted from biosolids incinerators.
110 &EPA Part 503 Risk Assessment
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- Questions arid Answers on the Part 503 Risk Assessments
Q: Why was a risk limit of 1 x 10"4 chosen as a basis for the pollutant limits for
carcinogens instead of a 1 x 10"6 risk (a 1 in 1 million chance of potentially getting
cancer)?
A: The less restrictive 1 x 10"4 risk limit was chosen as a policy decision. The ag-
gregate (overall) risk from biosolids use or disposal in the United States is
especially low (i.e., ranging from only a fraction of a person to several persons be-
ing at risk out of the total U.S. population). Because the risk is especially low, the
less restrictive risk limit still provides adequate protection.
Q: If a risk limit of 1 x 10'4 is sufficient, then why not apply a more protective risk
limit just to be more safe? After all, a 1 x 10"6 risk limit is only 100 times more re-
strictive than the 1 x 10'4 risk limit.
A: In addition to the fact that cancer risk from the use of biosolids is very low, a 1 x
10"6 cancer risk level was not chosen to be more protective because:
• Use of more conservative levels in risk assessment calculations has some-
times led to predictions that the levels of certain substances in the
environment are more hazardous than relevant research indicates. A good dis-
cussion of how risk assessment methodology can predict erroneously that the
levels of certain substances in the environment are too high can be found in a
paper by Ryan and Chaney (1995).
• Although not used as a determining factor during the development of the Part
503 rule, use of a more stringent risk level would require thousands of facilities
to achieve the stricter limit of 1 x 10"6 for a given substance rather than 1 x
10"4, even though the limit is only one hundred times more stringent. It is diffi-
cult to justify such an expense for little or no actual difference in risk to the
highly exposed organism.
Selection of the Part 503 Pollutant Limits
Q: How were the pollutant limits chosen for the Part 503 rule?
A: For all pollutants evaluated, first the highly exposed individual was identified for
each of the applicable pathways of exposure. For example, for land application
practices, a different highly exposed individual was identified for each of the 14 dif-
ferent exposure pathways that were applicable. The risk assessment limit for each
pollutant was selected from the pathway with the highest exposure and lowest per-
mitted dose. For example, the pollutant limit for copper was set at 1,500 kg
copper/hectare of land based on the Pathway 8 pollutant limit being the most strin-
gent (lowest) at 1,500 kg-eopper/ha-land; for all the other copper exposure
pathways, the pollutant limits were greater. For land application, additional pollutant
limits were derived from these values and incorporated into the rule.
Q: Were all pathways evaluated for each pollutant?
A: No. Risk assessments were not conducted for all pathways for each pollutant.
Risk assessment is made up of several components, including hazard identification
and exposure assessment. Where the exposure assessment indicated that expo-
sure to the pollutant was not significant via a certain pathway, or where EPA lacked
data, that pathway was not evaluated for a particular pollutant.
Part 503 Risk Assessment SEPA 111
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Chapter 6
Most Exposed Individual (MEI) vs. Highly Exposed
Individual (HEI)
Q: Was the final Part 503 rule designed to protect the MEI or the HEI?
A: The HEI.
Q: Why not the MEI?
A: The MEI is a hypothetical (imaginary) individual that experts did not believe
could exist. Protecting an individual that does not even exist was believed to be un-
realistic. The Agency's risk assessment policy states that the individual that should
be protected is an HEI. In contrast to the MEI, the HEI may exist, although in small
numbers.
The MEI was used as the target organism to be protected in the proposed Part 503
rule, and was developed with very conservative assumptions and overly stringent
models. As an example, one of the MEIs in the proposed Part 503 rule (for land ap-
plication exposure pathway 1F [later exposure Pathway 2]) was the hypothetical
home gardener:
• Who produced and consumed essentially all of his or her own food for 70
years in a home garden amended with biosolids.
• Whose biosolids-amended garden soil contained the maximum cumulative
permitted application of each of the evaluated pollutants for that 70-year pe-
riod.
• Whose food harvested from the garden had the highest plant uptake rate for
the 70-year period for each of the pollutants, as calculated using data from
pot/salt studies.
• Who for 70 years consumed foods that were grown in that garden, with the
gardener always at the age, sex, and physiological state for maximum absorp-
tion and/or ingestion (e.g., simultaneously male and female, pregnant, an
infant, and a teen-age male).
In contrast, the use of an HEI combines high-end and mid-range assumptions in
models and algorithms (descriptive mathematical equations). The HEI attempts to
be representative of a real individual. This is indicated by the data, models, and as-
sumptions used for protecting the highly exposed home gardener again via
Pathway 2 during the revised risk assessment and development of the final Part
503 rule. In this risk assessment:
• The home gardener HEI produced and consumed up to 59 percent of his or
her own food (depending on the food group) for a 70-year period in a
biosolids-amended garden.
• The biosolids-amended garden soil contained the maximum cumulative per-
mitted application of each of the evaluated pollutants for the 70-year period.
• The food that was harvested from the garden had plant uptake slopes for
biosolids pollutants determined using the geometric mean of relevant data
from field studies, with both acid and neutral biosolids-amended soils.
• The food consumption was apportioned among several different age periods
during the 70-year life of the HEI gardener.
112 SEPA Part 503 Risk Assessment
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Questions and Answers on the Part 503 Risk Assessments
What If?
Q: Do we know everything about the use or disposal of biosolids?
A: No.
Q: Then, how can the Agency determine that it is all right to use or dispose of
biosolids? What if we find that some other pollutant in biosolids is hazardous? Or
what if we find there is a "time-bomb" effect and all the pollutants we now think are
being held in an unavailable form by the biosolids, even after they are added to
soils, later become available?
A: The use of biosolids has been one of the most extensively studied waste man-
agement practices in the United States. Some public uses have occurred in the
United States for 70 years. Throughout this long history of use, biosolids have re-
peatedly been shown to be a valuable soil conditioning and fertilizing product.
While there can be no absolute guarantees, the past use of biosolids has been
very reassuring when biosolids have been used in accordance with practices
known to be acceptable.
In the few instances in the past where problems occurred from biosolids use, the
implementation of various commonly used management practices has rectified
. most situations, as is the case with any farming practice where stewardship of the
land is management-based (i.e., managing soil pH, insect pests and plant disease,
weeds, water, levels of macro- and micronutrients, crops, microclimate, and har-
vesting methods).
The use of biosolids also can be valuable where lands have been mismanaged. It
is commonly known that lands disturbed by mining can be reclaimed through effec-
tive use of biosolids. More recently, it has been determined that arid lands
"devastated by overgrazing" can be recovered considerably with the use of
biosolids. Also, studies now underway suggest that lead in soils from paint and
automotive exhausts can be bound by the application of biosolids, making the lead
less available to children who eat soil.
Science continues to show new uses for waste resources such as biosolids. All
field research to date leads to the conclusion that the agronomic use of high-quality
biosolids is sustainable and safe. Thus, it seems prudent to make informed use of
biosolids as a highly recyclable resource.
Soil pH
Q: Why wasn't soil pH management included as a biosolids land application re-
quirement in the Part 503 rule, especially given that it was a requirement in the
former Part 257 rule?
A: The Part 503 rule was designed to be self-implementing and to cover all prac-
tices that involve the use of biosolids. Hence, the plant uptake values used to
establish the regulatory limits for land application pathways in the Part 503 rule in-
cluded data from acidic, neutral, and alkaline soils (i.e., pH <6.0 to >7.0).
It is possible that some sensitive plant species may exhibit symptoms of phyto-
toxicity when grown in soils amended with biosolids containing high concentrations
of zinc, nickel, or copper at low soil pH and near the cumulative pollutant loading
rates. At the recommendation of experts who assisted EPA, however, the Agency
decided that it would be ill-advised to require pH control. The rationale is that many
other factors offer protection against harmful effects from metals, such as the soil-
plant barrier and other elements present in biosolids that bind pollutants (as
discussed more fully in Chapter 3). In addition, in soils where the pH is below 5.5,
Part 503 Risk Assessment SEPA 113
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Chapter 6
not only do high levels of biosolids pollutants have the potential to become toxic to
plants, but so do the naturally occurring soil metals, such as aluminum and manga-
nese. Given the potential toxicity from these widespread soil metals, most
agronomic plants do not grow well at very low pH. Under these conditions, farmers
and home gardeners would need to add lime to soils to obtain a reasonable yield of
edible food, regardless of whether biosolids are being used for their soil condition-
ing and fertilizing value.
"Time-Bomb" Theory
Q: What is the so-called time-bomb theory?
A: The time-bomb theory involves the belief that the organic matter present in
biosolids is primarily what binds metals and thus reduces their bioavailability. The
basic premise of the theory is that as soon as the organic matter degrades, the
metals will become more bioavailable.
Q: Do pollutants in biosolids become more bioavailable after having been added
to soil and after the organic matter in biosolids has decayed?
A: Evidence does not support this claim. Biosolids are typically about 50 percent
organic and 50 percent inorganic. The experts who assisted EPA in the risk as-
sessments cited evidence that much of the binding that occurs is attributable to the
inorganic part of biosolids, namely from oxides of iron, aluminum, and manganese,
and also from phosphate compounds. This binding effect is so strong that it per-
sists after the biosolids have been applied to soils, except in very low pH situations
as described in the soil pH Question and Answer section above. Examination of
field data, gathered as many as 60 to 100 years after the use of irrigation wastewa-
ter and/or biosolids on soils, supports the concept of binding by the inorganic
fraction of the biosolids and indicates that binding of the metals persists when the
biosolids organic matter has had time to degrade.
A few scientists question this belief, but experimental data exist to support this in-
organic binding concept, and experimental data do not exist to refute it. A leading
proponent (Beckett et al., 1979) of the time-bomb theory who attempted to prove it,
dropped his advocacy of the theory after conducting a series of experiments that
failed to provide support (Johnson et al., 1983).
Q: Is there a direct relationship between the amount of biosolids metals that have
been applied to soil and the amount of metals absorbed by plants?
A: No. Metals are bound by the biosolids matrix, which reduces their phytoavail-
ability. As an example, assume that the total amount of a metal in biosolids does
not change. As more of the biosolids are added to soils, the total amount of that
metal pollutant present in the soil/biosolids mixture increases. However, the metal
phytoavailability (plant uptake of that metal) does not proportionately increase due
to the simultaneous increase of the inorganic part of the biosolids matrix in the
soil/biosolids mixture. This increasing inorganic matrix strongly binds the metal,
and competes with and limits the ability of a plant to absorb the metal. This issue is
discussed more fully in Chapter 3.
Q: Does the Part 503 rule take into account that reduced bioavailability is associ-
ated with the use of biosolids?
A: No and yes. No, because EPA did not adjust Part 503 pollutant limits based on
bioavailability. Yes, because the Agency did, however, use biosolids field data on
plant uptake of pollutants to the extent possible, which invariably showed there to
be less uptake (i.e., a reduced uptake slope) than if only metal salts were added to
soils. Nonetheless, in the Part 503 risk assessments the Agency assumed that the
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Questions and Answers on the Part 503 Risk Assessments
plant uptake slope was linear. Given that in fact the uptake slope is less than linear,
the final rule overestimates the phytoavailability of biosolids metals.
Q: In the risk assessments for the final rule, why weren't more plant uptake data
used from experiments in which metals salts were added to soils?
A: Experts determined that metal salt data are not relevant to biosolids because
metals are bound by the biosolids matrix during generation and processing of the
biosolids. This binding does not occur when metal salts are added to soils. Data
from metal salt studies were used only when no other data were available.
Phytotoxicity
Q: What is phytotoxicity as it relates to the Part 503 biosolids rule?
A: Phytotoxicity refers to the retardation in plant growth that can be caused by
plant toxicity from metal pollutants in biosolids. The Part 503 pollutant limits were
set to preclude phytotoxicity.
Q: Is it true that the risk assessments assumed that phytotoxicity has not occurred
unless there is a 50 percent reduction in plant growth?
A: No. EPA used several procedures to determine the concentration of the poten-
tially phytotoxic metals (zinc, copper, nickel, and chromium) in plants that result in
phytotoxicity. A 50-percent retardation in plant growth of young com and bean
seedling was involved in only one of the alternative approaches used to establish
phytotoxicity limits. Even in this approach, other levels of growth retardation were
evaluated (i.e., 8-, 10-, and 25-percent plant growth retardation), although the 50-
percent level was used. In another approach, data on plant tissue concentrations
associated with yield reduction were taken from the available literature to define
phytotoxic effects for sensitive crops, such as lettuce. These sensitive plant spe-
cies are more susceptible than corn to metal-induced inhibition of growth
(phytotoxicity). These data were used to develop plant tissue levels of metals asso-
ciated with first detectable yield reductions, which were identified as phytotoxicity
thresholds. These data, in turn, were used, in conjunction with data on plant uptake
of metals, to identify metals application rates that would exceed the phytotoxicity
threshold. The more restrictive of the values determined by these approaches was
chosen as the pollutant limit for phytotoxicity in the risk assessment. These proce-
dures are described in more detail in Chapters 3 and 4.
Q: Why is it difficult to set a phytotoxicity limit?
A: The problem facing the experts who assisted EPA with the phytotoxicity risk as-
sessment was that many things can cause phytotoxicity, as well as apparent
phytotoxicity, during the growth of seedlings. Furthermore, the retardations in early
vegetative growth that often occur may or may not be associated with harvestable
crop yield reduction. Factors that can cause phytotoxicity or apparent phytotoxicity
include: cold weather; insoluble salts, low nutrients, high nutrients, and high metals
in soils; pesticides and herbicides; and ozone and other impurities in the air. In
carefully conducted field tests, yields commonly vary by as much as 15 to 25 per-
cent with good fertility and management. An ultimate yield reduction of at least that
much must be attained to support a determination that the reduction was signifi-
cant, especially over several seasons and with various crops being grown.
Part 503 Risk Assessment EPA 115
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Chapter 6
Synergistic Effects of Biosolids Metals
Q: Is there evidence of any synergistic (additive or more than additive) negative
effects associated with metals in soils amended with biosolids?
A: The only evidence of synergy has been observed in soils freshly amended with
metal salts (not biosolids). EPA is not aware of any evidence to suggest that syn-
ergy has occurred even in pot studies where metal-rich biosolids were used as the
soil amendment,
Q: Is there any evidence of positive interactive effects from biosolids metals?
A: Yes. When biosolids are used as a source of fertilizer, there is a built-in protec-
tion for people who eat crops that may accumulate metals, including cadmium.
This is because invariably biosolids also contain iron, calcium, and zinc, which are
absorbed into the edible portion of the plant. The presence of these other three
substances in the crop consumed reduces the potential for cadmium absorption
into a person's intestines and body, and hence reduces the potential health risk
from cadmium.
Use of Data With Zero or Negative Plant Uptake Slopes
Q: Were data used from experiments that had a zero or negative plant uptake
slope?
A: Yes, but such data were given a protective minimum value; that is, when the
slope was negative or zero, a minimum, slightly positive value of 0.001 was used.
This procedure allowed such data to be used in determining plant uptake slopes.
This minimum value, however, overestimates uptake to some degree.
Pathogens
Q: Is the pathogen operational standard risk-based?
A: No. Risk assessment methodologies had not been developed sufficiently
to make such calculations. Instead, the pathogen operational standard,
which is technology-based, requires that pathogens in biosolids be reduced to be-
low detectable levels or to levels that, when coupled with crop harvesting and site
access restrictions, have been demonstrated to be protective of public health and
the environment.
Determining "Acceptable'' Concentrations of Biosolids
Pollutants in Soils
Q: The biosolids risk assessments were designed to determine acceptable pollutant
application rates or pollutant concentrations in biosolids. Based on the risk assess-
ment results and the Part 503 pollutant limits, what are the "acceptable"
concentrations of biosolids pollutants in soils? How are these soil concentrations
derived?
A: Table 18 presents acceptable concentrations of biosolids pollutants in soils
(Column 6). The following equation shows how soil concentrations (RLC) can be
derived from the biosolids risk assessment pollutant limits (RPs), which are equiva-
lent to the Part 503 cumulative pollutant loading rate (CPLR) limits.
np
n = RLC (in \ig/g) X 10 = RLC (in mg/kg)
MSx 10
116 SEPA Part 503 Risk Assessment
-------
Questions and Answers on the Part 503 Risk Assessments
where:
RP = cumulative application rate of pollutant in biosolids (kg/ha)
MS = 2 x 109 g/ha (assumed mass of soil in upper 15 cm)
10 = conversion factor (kg/|j.g)
10 = conversion of RLC from jag/g to mg/kg
RLC = allowed soil concentration of pollutant from biosolids (|xg/g, or mg/kg)
For copper, the soil concentration RLC would be:
RP 1500
— —- = ~~ = 75 (RLC, in [xg/g) x 10=750 (RLC, in mg/kg)
MS x 10 20
The copper pollutant concentration in soil from biosolids (RLC) calculated from the
above equation is further adjusted by adding in the background median (50th per-
centile) soil concentration for the pollutant in question, in this case for copper
(Holmgren et ah, 1993), to determine the "acceptable" concentration for biosolids
pollutants in soils:
RLC for copper of 750 mg/kg in biosolids + median background soil concentration
for copper of 19 mg/kg = an "acceptable" concentration for copper of
769 mg/kg in the soil-biosolids mixture
Table 18
Acceptable Soil Concentrations for Metals Derived from the Biosolids Risk Assessment
(1)
(2)
(3)
(4)
(5)
(6)
Pollutant
Table 3 in Part 503
Table 2 in Part 503
CPLRs as Soil
50th Percentile
Risk Assessment
Pollutant
Concentration
Limits
(mg/kg-biosolids)
Cumulative
Loading Rates
(CPLRs)
(kg/ha-land)
Concentration
Limits
(mg/kg-soil)a
Background Soil
Concentration
(mg/kg-soil)
Acceptable Soil
Concentration
(mg/kg-soil)
Arsenic
41
41
20.5
3b
23.5
Cadmium
39
19.5
0.2C
19.7
J
Chromium
Copper
1,500
1,500
750
19c
769
Lead
300
300
150
llc
161
Mercury
17
17
8.5
0.1®
8.6
Molybdenumf
Nickel
420
420
210
18c
228
Selenium
100
100
50
0.21®
50.21
Zinc
2,800
2,800
1,400
54c
1,454
aAssumes a final 1:1 ratio of biosolidsrsoil in the upper 15 cm (6 in.) plow layer.
bBaxter et al, 1983
cHoimgren et alv 1993
dTo be deleted from the Part 503 rule based on a court decision (see Section Q, Chapter 3).
eU.S.G.S., 1970
fCurrently not in the Part 503 rule; subject to re-evaluation (see Section P, Chapter 2).
gCappon, 1984
Part 503 Risk Assessment ©EPA 117
-------
Chapter 6
m tfeawR.y-
Sg-MMSEiii
The top photograph shows biosolids being used as a fertilizer and soil conditioner
on a residential lawn. The lush lawn achieved as a result of using biosolids is
shown in the bottom photograph. The benefits of using biosolids can be
substantial. The results of the biosolids risk assessment process tell us how to
recycle biosolids safely.
118 <&EPA Part 503 Risk Assessment
-------
Questions and Answers on the Part 503 Risk Assessments
Q: Should people compare soil cleanup standards with Part 503 CPLR limits
(Column 3 in Table 18) or Part 503 pollutant concentration limits (Column 2 in Table
18)? (Note that the relationship between Part 503 CPLRs and pollutant concentra-
tion limits is discussed in Chapter 5.)
A: No. Instead, soil cleanup standards should be compared with "acceptable" soil
concentration values, as derived from the biosolids risk assessments (Column 6 in
Table 18).
Q: How do these acceptable soil concentrations compare with state and other
EPA cleanup standards for soils?
A: In most cases, the acceptable soil concentrations calculated from the Part 503
risk assessments are greater than those for state and other federal EPA programs;
however, some of the state and other federal acceptable soil concentrations are
greater. Almost no set of soil concentrations agree. Furthermore, most of the other
sets of numbers are only preliminary (numbers are not finalized) and have been
calculated for other purposes (e.g., in connection with efforts to cleanup soils con-
taminated by hazardous wastes). Some of the concentration levels have been
calculated based on best available technology and others are based on risk as-
sessments using different data sets, approaches, assumptions, models, and/or
pathways than were used in the Part 503 risk assessments.
Part 503 Risk Assessment «»EPA 119
-------
Intentionally Blank Page
-------
Chapter 7
]? pfpfpri fpc
JL Ml -Mm JL L.^htai' ki r
Adams, M. 1991. FDA total diet study: dietary intakes of lead and other chemicals.
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Angle, J., S. McGrath, A. Chaudri, R. Chaney, and K. Giller. 1993. Inoculation ef-
fects on legumes grown in soil previously treated with sewage sludge. Soil Biology
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Angle, J, and R. Chaney. 1988. Soil microbial-legume interactions in heavy metal
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Baxter, J, M. Aquilar, and K. Brown. 1983. Heavy metals and persistent organics at
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CAST. 1976. Application of sewage sludge to cropland: appraisal of potential haz-
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Part 503 Risk Assessment <>EPA 121
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Chapter 7
Chaney, R. 1990. Public health and sludge utilization-food chain impact. BioCycle
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Chaney, R. and J. Ryan. 1991. The future of residuals management after 1991. In
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and rate, soil pH, and time on heavy metal residues in leafy vegetables. In Proc.
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long-term sludge application on accumulation of trace elements by crops. In Land
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of sludge properties on accumulation of trace elements by crops. In Land Applica-
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Fox, M. 1988. Nutritional factors that may influence bioavailability of cadmium. J.
Environ. Qual. 17:175-180.
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in the earthworm Eisenia foetida. J. Environ. Qual. 9:23-26.
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copper, and nickel in agricultural soils of the United States of America. J. Environ.
Qual. 22:335-348.
122 -SEPA Part 503 Risk Assessment
-------
IJgfe
;p*^r-^':'''J&;
-Mf.'J:-
'-NiiiN.c
•{ji-ii-jy ••-';'y-:r.";.v,.,.-.r.,^
R^i^gisa|
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bium leguminosarum bv. trifolii from different soils using REP and ERIC PGR.
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the human being. Environ. Res. 16:248-296.
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of type of soil material and metal source. Soil Sci. 140:23-34.
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land-metals. In Proc. 1983 Workshop on Ultilization of Municipal Wastewater and
Sludge on Land. A. Page, T. Gleason, J. Smith, I. Iskander, and L. Sommers (eds.).
University of California, Riverside, CA.
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amended soils. I. Effect on yield and cadmium availability to plants. Sci. Total
Environ. 67:117-131.
McDonald, D. 1983. Predation on earthworms by terrestiral vertebrates. In: Earth-
worm Ecology: From Darwin to Vermiculture. J. Satchell, ed. London: Chapman
and Hall.
McGrath, S., P. Hirsch, and K. Giller. 1988. Effect of heavy metal contamination on
the genetics of nitrogen-fixing populations of Hhizobium leguminosarum nodulating
white clover. In Environmental Contamination, CDEP Consultants: Edinburgh,
Scotland, pp. 164-166.
McKenna, I., R. Chaney, S. Tao, R. Leach, and F. Williams. 1992a. Interactions of
plant zinc and plant species on the bioavailability of plant cadmium to Japanese
quail fed lettuce and spinach. Environ. Res. 57:73-87.
McKenna, I., R. Chaney, and F. Williams. 1992b. The effects of cadmium and zinc
interactions on the accumulation and tissue distribution of zinc and cadmium in let-
tuce and spinach. Environ. Pollut. 79:113-120.
Morgan, H. and D. Simms, eds. 1988. The Shipham report: an investigation into
cadmium contamination and its implications for human health. Sci. Total Environ.
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National Academy of Sciences. Washington, D.C.: National Academy Press.
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people eating cadmium in rice, based on epidemiological studies. Trace Subst. En-
viron. Health 21:431-439.
Part 503 Risk Assessment *»EPA 123
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Chapter 7
Nogawa, K., A. Ishizaki, and S. Kawano. 1978. Statistical observations of the dose-
response relationships of cadmium based on epidemiological studies In the
Kakehashi River Basin. Environ. Res. 18:397-409.
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124 -SEPA Part 503 Risk Assessment
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EPA Materials Available From:
Office of Water Resource Center (OWRC)
U.S. EPA
401 M Street SW (RC-4100)
Washington, DC 20460
Phone: (202) 260-7786
Center for Environmental Research Information (CERI)
26 West Martin Luther King Drive
Cincinnati, OH 45268
Phone: (513) 569-7562
Fax: (513) 569-7585
National Technical information Service (NTIS)
U.S. Department of Commerce
5285 Port Royal Road
Springfield, VA 22161
Phone: (800) 553-6847
(703) 487-4650
Fax: (703) 321-8547
Education Resource Information Center (ERIC)
c/o West Virginia University
P.O. Box 6064
Morgantown, WV 26506-6064
Phone: (614) 292-6717
Fax: (614) 292-0263
Part 503 Risk Assessment -&EPA 125
-------
Chapter 7
Specialists To Contact for More Information
About Risk Assessment
Dr. Jim Ryan
EPA Office of Research & Development
(513) 569-7653
Dr. John Walker
EPA Office of Wastewater Management
(202) 260-7283
About Risk Assessment and Derivation of the Rule
Mr. Robert Southworth
EPA Office of Science and Technology
(202) 260-7157
126 &EPA Part 503 Risk Assessment
-------
Appendix
A
Parameters Used in the Land
Application Risk Assessment
for Biosolids
Parameter
Definition
Abbreviation
Used in
Calculation of
Pollutant Limit
Pathway
Where Used
(see Table 6)
Source of
Further
Information
Pollutant Limit Calculated via the Risk Assessment Process:
(1) The amount of a pollutant that can be applied to a
hectare of land without adverse effects
RP
For most pathways
(Pathways 1,2,4,6,8,
9,10,11,12,13,14;
except 3,5,7)
Appendix B (most
parameters);
Chapter 4, Boxes
9-14 (RP or RSC
parameters)
(2) The concentration of pollutant in biosolids that can
be ingested without adverse effects
RSC
(Pathways 3,5,7)
RP & RSC used for Pathways 1-11:
r.r. Allowable Dose of Pollutant
RP or RSC = 1
Plant Uptake x Dietary Consumption x Food Production parameters (whichever is relevant)
or
RP for Pathways 12 (surface water [sw]), 13 (air) and 14 (groundwater [gw]) based on:
Parameters for pollutant concentration(includes health parameters) in eroding soil \forsw]
or air emissions [for air] or beneath site \forgw] x loss rate parameter [for sw and gw]
Rr —
Fraction of total loss parameter (erosion [for sw], volatilization [for air], or leaching [for gw])
The parameters used in the risk assessment calculations are described below:
Part 503 Risk Assessment SEPA 127
-------
Appendix A
Parameter
Definition
Abbreviation
Used in
Calculation of
Pollutant Limit
Pathway
Where Used
(see Table 6)
Source of
_ Further
Information
Health-Based Parameters Used in Risk Assessment Calculations:
For People:
Amount of pollutant ingested by humans without
expectation of adverse effects (based on RfD or qj*,
BYV, RL, RE, TBI, see below)
RIA
Pathways 1,2,3/4,5
Chapter 4, Boxes
9-11
—Risk reference dose (RfD)-daily intake of chemical
that during an entire lifetime appears to be without
appreciable risk on the basis of all the known facts
at the time (Lu, 1983); or cancer potency value
Conservative quantitative indication of the
likelihood of a pollutant inducing or causing
cancer during the lifetime of a continuously
exposed individual
RfD or qi* or
an RDA when
there was no J
RfD for a
pollutant
All human
pathways
(Pathways 1,2,3,4,5,
12,13,14)
Chapter 2, Box 3
— Cancer risk level-the probability that one
additional cancer case could be expected to occur
in an exposed population of a certain size (e.g., the
RL could be set at 1 x 10"4 = 1 add, cancer case in a
population of 10,000 exposed individuals)
RL
In conjunction with
qi*s (Pathways
1,2,3,4,5,12,13,14)
Chapter 3, text
—Human body weight (kg)—average adult male
body weight of 70 kg (154 lbs) was used to
represent a "lifetime" weight, since the RfD/qj*
represents a lifetime dose (70 years)
BW
All human
pathways
(Pathways
1,2,4,5,11,12,13,14)
— Child: average body weight—16 kg (35 lb) for child
(ages 1-6) with respect to agricultural land and 19
kg (42 lb with respect to nonagricultural land (also
see Appendix B)
BW
Pathway 3
—Relative effectiveness of exposure—accounts for
differences in bioavailability and routes of
exposure (e.g., inhalation vs. ingestion); because of
limited data, this value was conservatively set at 1
RE
Pathways 1,2,3,4,5
—Allowable ("reference") concentration of pollutant
in human diet ingested as a result of animal tissue
consumption (based on RIA, and UA, DA, FA, see
below)
RF
Humans eating
animal products
(Pathways 4,5)
— Allowable ("reference") intake of pollutant, based
on qi* and RL, or RfD (RL/qj* or RfD-background
intake)
RI
Surface water
(Pathway 12)
Chapter 4, Box 14
—Allowable ("reference") water concentration of a
pollutant in surface water, air, or ground water
RCsw
RCair
RCgw
Surface water, air,
or ground-water
pathways
(Pathways 12,13,14)
—Allowable ("reference") concentration of pollutant
in:
Surface water or
ground water
Chapter 4, Box 14
soil eroding into the surface water stream
RCsed
(Pathway 12)
soil eroding from the biosolids application area (SMA)
RCsma
(Pathway 12)
leachate beneath the land application site
RQec
(Pathway 14)
128 &EPA Part 503 Risk Assessment
-------
Parameters Used in the Land Application Risk Assessment for Biosoiids
Parameter
Definition
Abbreviation
Used in
Calculation of
Pollutant Limit
Pathway
Where Used
(see Table 6)
Source of
Further
Information
Health-Based Parameters (continued):
For Animals:
Allowable ("reference") concentration of pollutant in
animal diet ingested" as a result of eating plants, based
on:
— Maximum pollutant intake level in animal diet
without observed toxic effect on most sensitive or
most exposed species (threshold pollutant intake)
RF
TPI
Animals eating
plants (Pathways
6,7)
For animal toxicity
(Pathways 6,7)
Chapter 4, Box 12
Environmental Parameters:
For Soil Organisms and Soil Concentration Values:
Pollutant concentration in soil considered to have no
adverse effects on soil organisms, or minimal effects
on animals or humans in pathways where people or
animals are the target organism (e.g., for degradable
organics, or when diet is soil/soil organisms)
RLC
For Pathways
1,2,4,9,10
For Plants:
Toxicity based on:
— (1) Phytotoxicity threshold—Concentration of a
pollutant in plant tissue associated with a 50%
retardation in growth of young vegetative tissue
based on studies of plants grown in pots of metal
amended soil or nutrient solution
PTso
For plant toxicity
(Pathway 8)
Chapter 3, text (see
Pot/Salt vs. Field
Studies, Sludge
Binding, and
Ecological Risk
Assessment);
Chapter 4, Box 13
— (2) Threshold pollutant concentration in plant TPC For plant toxicity Chapter 3; Chapter
tissue assoc. with phytotoxicity, based on lowest (Pathway 8) 4, Box 13
observed adverse effect level (LOAEL) of the most
sensitive/most exposed plant species in field soils
The most limiting number from approaches (1) and (2) above was used to set the pollutant limit for Pathway 8.
Dietary Consumption Parameters:
— Daily consumption by humans of different food
groups grown on land amended with biosoiids
DC
Humans eating
plants (Pathways
1,2)
Chapter 3, text;
Chapter 4
(cadmium example)
Daily human consumption of different types of
animal products
DA
Humans eating
animal products
(Pathways 4,5)
— Rate of soil ingestion by children
Is
Toxicity to child
(Pathway 3)
Chapter 3, text
Chapter 4, Box 11
— Daily consumption of:
fish
water
If
Iw
Surface water
(Pathway 12)
Chapter 4, Box 14
Part 503 Risk Assessment -&EPA 129
-------
Appendix A
Parameter
Definition
Abbreviation
Used in
Calculation of
Pollutant Limit
Pathway
Where Used
(see Table 6)
Source of
Further
Information
Parameters for Fraction of Diet Produced on Biosolids-Amended Land:
—Fraction of different food groups assumed to be
grown on land amended with biosolids
FC
Humans eating
plants (Pathways
1,2)
Chapter 4
(cadmium example)
—Fraction of different animal products assumed to
be raised on forage grown on biosolids-amended
soils
FA
Humans eating
animal products
(Pathways 4,5)
—Fraction of animal diet that is biosolids
FS
Animals eating
biosolids (incl.
animal products
eaten by humans)
(Pathways 5,7)
— Fraction of diet comprised of soil organisms
FD
Animals (soil
organism
predators) eating
soil organisms
(Pathway 10)
Parameters for Plant Uptake of Pollutant:
—Plant uptake slope for pollutants from
soil/biosolids
UC
Humans and
animals eating
plants; plants
themselves
(Pathways 1,2,4,6,8)
Chapter 3, text;
Chapter 4
(cadmium example)
—Uptake factor relating pollutant concentration in
each animal product to pollutant concentration in
forage crop/animal diet consumed by the animal
UA
Humans eating
animal products
(Pathways 4,5)
Loss-Factor Parameters:
—First-order loss rate constant-accounts for amount
of organic pollutant lost to degradation, leaching,
and/or volatilization, based on half-life data
k
For most degradable Chapter 4, Box 10
organic pollutants
(Pathways 1,2,4,5,10)
—Mass balance of pollutant /oss-calculates relative
rates at which a pollutant is removed (lost) from a
site through soil erosion, leaching, volatilization,
and/or degradation
K
Surface water, air,
ground water
(Pathways 12,13,14)
Chapter 4, Box 14
—Mass balance of pollutant loss-calculates fraction
of total loss caused by volatilization
fvol
Air (Pathway 13)
— Mass balance of pollutant loss-calculates fraction
of total loss caused by leaching
flee
Ground water
(Pathway 14)
—Estimated rate of soil loss for the biosolids
management area (SMA)
MEsma
Surface water
(Pathway 12)
Chapter 4, Box 14
—Estimated rate of soil loss for the watershed
MEws
Surface water
(Pathway 12)
Chapter 4, Box 14
—Fraction of total cumulative loading lost in a
human lifetime (inorganics)
fis
Surface water
(Pathway 12)
—Mass of pollutant at end of a human lifetime
(inorganics)
Mls
Surface water
(Pathway 12)
130 iBEPA Part 503 Risk Assessment
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Parameters Used in
the Land Applies
itiiQit Risk Assessrti
lentforBiosoIids
¦
Parameter
Definition
Abbreviation
Used in
Calculation of
Pollutant Limit
Pathway
Where Used
(see Table 6)
Source of
Further
Information
Background Parameters;
— Total background intake rate of pollutants from
sources of exposure other than biosolids (e.g., from
drinking water, food, air)
TBI
All human food
chain pathways
(Pathways 1,2,3,4,5)
Chapter 4, Boxes
9-11
— Background concentration of pollutant in soil
BS
For animal (incl.
soil organism)
toxicity (Pathways
7,9,10)
— Background concentration of pollutant in plant
tissue
BC
For animal and
plant toxicity
(Pathways 6,8)
Chapter 4, Boxes
12,13
Bioavailability and Bioaccumulation Parameters:
— Fractional toxicity of pollutants in biosolids
(compared to metal salt-amended diets)
BAV
Animals eating soil
organisms
(Pathway 10)
Chapter 3, text (see
Ecological Risk
Assessment)
— Pollutant-specific bioconcentration factor
BCF
Surface water
(Pathway 12)
Chapter 4, Box 14
Pollutant-specific food chain multiplier
FM
Exposure Through Inhalation:
Allowable concentration of pollutant in dust, based
on:
MDC, based on:
(Pathway 11)
— NIOSH air quality criteria for the pollutant
NIOSH
— ACGIH total dust standard
TDA
— Ratio relating the concentration of pollutant in
ambient air (at HEI's location) to the rate at which
the pollutant is emitted from biosolids-amended
soil
SSR
(Pathway 13)
— Reference annual flux3 of pollutant emitted from
the site
RFair
(Pathway 13)
Additional Parameters Specific to Surface Water:
— Density of water
Pw
(Pathway 12)
Partition factors (used to derive concentration of
pollutant in surface water):
(Pathway 12)
— partition coefficient between solids and liquids
within the stream
KDsw
— percent liquid and solids in the water column
Pi/ Ps
Additional Parameters Specific to Ground Water:
— Ratio of predicted concentration of pollutant in
well to concentration in leachate
fwel
(Pathway 14)
— Reference annual flux® (net recharge in m/yr) of
pollutant beneath the site
RFgw
(Pathway 14)
Part 503 Risk Assessment -SEPA 131
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Appendix A
Abbreviation
Used in
Pathway
Source of
Parameter
Calculation of
Where Used
Further
Definition
Pollutant Limit
(see Table 6)
Information
Additional Parameters Specific to Ground Water (continued):
— Length of square waveb in which maximum total TP (Pathway 14)
loss rate of pollutant depletes total mass of
pollutant applied on site (inorganics)
*Flux is the amount of air or ground water flowing across a given area per unit of time (RFgw/flee = application rate [RP]).
^Square wave refers to a pulse of constant magnitude representing maximum annual pollutant loss (kg/ha • yr) occurring over
the 300-yr simulation model. Used in VADOFT model to predict concentration of pollutant at the water table.
132 &EPA Part 503 Risk Assessment
-------
Parameters, Approach,
Assumptions, and Degree of
Conservatism Used: Land
Application Risk Assessment
Parameter Used
Parameter Is
in Calculation of
Approach
Assumptions/
Conservative (C) or
Pollutant Limita'b
or Basis
Policy Decisions
Average (A) and Why
Pollutant Limit Is:
RP
or
Cumulative or annual
application rate of pollutant that
can be land applied without
expectation of adverse effects:
cumulative rate—
nondegradable pollutants
(inorganics; aldrin/dieldrin,
chlordane)
annual rate—degradable
pollutants (organics)
Certain pollutants assumed not C—Many of the parameters
to degrade in environment used to calculate RP or RSC are
conservative, resulting in
inherently conservative
pollutant limits
RSC
RSC based on poll. conc. in
biosolids was calculated
(except for lead, Pathway 3) by
relating human or animal
health/exposure parameters
(e.g., RIA, TPI) to exposures
from biosolids/ soil:
—parameter for the ingestion
of poll, in biosolids/soil by
children (Is), or
—uptake of poll, in plant tissue
(consumed by animals) and
of animal tissue consumed
by humans (UA), and
parameter for fraction of
animals' diet that is biosolids
Part 503 Risk Assessment &EPA 133
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Appendix B
Parameter Used
in Calculation of
Pollutant Limita'b
Approach
or Basis
Assumptions/
Policy Decisions
Parameter Is
Conservative (C) or
Average (A) and Why
Pollutant Limit Is (continued):
RSC
(continued)
Lead pollutant limit
determined using EPA's
Integrated Uptake Biokinetic
Model (IEUBK), for lead
(Pathway 3)
Policy decision for lead to set
limit lower than number
derived from IEUBK to
provide additional margin of
safety (i.e., from livestock data
on lead)
Health Parameters:
RIA
Health-based value (e.g., RfD
or qj*) adjusted for body
weight, with exposure to
pollutant from sources other
than biosolids (food, water, air)
subtracted
C—Designed to protect most
sensitive members of
population from biosolids
pollutant; based on
conservative RfD or qj*
RfD orqj*
See Chapter 2, Box 3
If pollutant associated with
both cancer and noncancer
effects, cancer was used as
most sensitive endpoint unless
the cancer was associated with
a different route of exposure
Continuous 70-yr lifetime
Any exposure to carcinogen
has a risk (qj*)
Threshold (i.e., minimal risk)
levels exist for noncarcinogens
(RfDs)
C—Both RfD and qj* predict
greater adverse effects than are
likely to occur; both assume
lifetime exposure, which is
unlikely; qj* based on most
sensitive species and
conservative extrapolation
from high to low dose; RfDs
use safety factors to offset
uncertainties
RL
Standard U.S. Government
scientific approach used to
establish cancer risk level
Lifetime (70 yr) exposure
Risk level of 1 x 10"4 chosen
(policy decision)
A—Risk level of 1 x 10"4 chosen
because related data indicated
minimal risk associated with
biosolids use or disposal
BW
Standard adult male value used
Adult: 70-kg (154 lb) male
(except Pathway 3);
A (adult)—Average value used
Two alternative values for child
weights
Child: for Pathway 3 —
Child (ages 1-6) = 16 kg (35 lb)
for agricultural land and
(ages 4-6) = 19 kg (42 lb) for
nonagricultural land
A (child)—Peak absorption age
is 1.5 years
RE
RE value of 1.0 was based on
EPA policy to be conservative;
REs of less than 1.0 should be
used only where good data
exist on RE or pharmaco-
kinetics; limited data existed
for this risk assessment
Relative effectiveness of
exposure (RE) = 1 (compares
exposure routes, e.g., ingestion
vs. inhalation)
C—A value of 1 probably
overestimates risks through
food consumption
RF Poll. conc. in human or animal 100% of livestock diet consists A—It is not unusual for
diet (RF) was needed to of forage grown on livestock to forage on
calculate soil-based RSC value; biosolids-amended land biosolids-amended land
RF relates health parameter (Pathway 6)
(e.g., RIA, TPI) to uptake (UA)
and dietary (DA, FA)
parameters
134 SEPA Part 503 Risk Assessment
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Parameters,Approach. Assumptions, and Degree of ConservatismUsed: L^rid Application Risk Assessment
Parameter Used
Parameter Is
in Calculation of
Pollutant Limita,b
Approach
Assumptions/
Conservative (C) or
or Basis
Policy Decisions
Average (A) and Why
Health Parameters (continued):
RCSW,
RCSW based on the smaller
value of the risk assessment
calculation, chronic or acute
freshwater criteria for the poll.,
or LOABL; RCair based on qx*
and RL; RC^ based on q^* and
RL for organics, and MCLs for
inorganics
Distance to well = 0
Buffer zone = 10 meters (bet.
biosolids management area
and nearest body of surface
water)
Soil type = sandy soil
C—Based on conservative
health criteria and assumptions
RC
gw
Background pollutant
concentration values
subtracted from MCL to derive
reference (allowable) water
concentration
If background concentration of
pollutant was below the
detection limit, assigned a
value to the background
concentration equal to one-half
of the detection limit
Background conc. of organics = 0
RC,
lec
Models used to simulate flow
and transport of pollutants
through soil and ground water:
— VADOFT (from RUSTIC)
model (unsaturated zone)
— AT123D model (saturated
zone)
The overly conservative
approach in the proposed risk
assessment was changed for the
revised risk assessment to more
realistically assess the portion of
a pollutant transferred to
ground water (e.g., fate and
transport models [CHAIN and
MINTEQ] used for pollutants in
the unsaturated zone were
replaced with a more
appropriate model [VADOFT]);
assumption that 100 percent of a
pollutant could be simul-
taneously transferred to ground
water, surface water, and air, was
changed to a "mass balance"
approach; more realistic,
site-specific geologic, hydraulic,
and chemical parameters were
used as inputs to computer
models).
C—Results well within
acceptable EPA risk levels
TPIC Based on recommendations of
experts about best available
data on most sensitive and
most exposed species
Chickens believed to be a more
representative species (e.g., than
mink) for PCBs (Pathway 10)
Shrews and moles assumed to C—Based on most sensitive or
be the most exposed species for most exposed species
cadmium and lead (most
sensitive species not identified)
(Pathway 10)
Part 503 Risk Assessment wEPA 135
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Appendix B
Parameter Used
Parameter Is
in Calculation of
Pollutant Limita,b
Approach
Assumptions/
Conservative (C) or
or Basis
Policy Decisions
Average (A) and Why
Environmental Parameters:
RLC
Because plant uptake of
organic pollutants was
regressed against soil
concentration, a reference
(allowable) pollutant
concentration in soil was
calculated (RLC), which was
then converted to an annual
application rate (RP)
(Pathways 1,2,4)
Based on best available data
(NOAEL for earthworms)
(Hartenstein et al., 1980),
although no species identified
as the most sensitive/most
exposed (Pathway 9)
Limit based on available data
adequately protects soil
organisms from adverse effects
A—Because data available for
only a few species
PTsoorTPC
Limit based on PTS0 for corn,
or TPC for most
sensitive/exposed species,
whichever resulted in the more
limiting number in calculations
Calculation for TPC based on
biosolids field studies
Based on literature search
(computer databases and 2,713
original articles) (PTS0)
Only PT50 approach used for
chromium because data
unavailable for TPC approach
Short-term retardation in
growth of young plant may
reflect some level of reduced
yield at maturity (PT5q)
0.01 = probability (99 times out
of 100) that the PT50
concentration was not
exceeded in field studies; PT50
was set as the tissue
concentration that was not to
be exceeded
Agricultural pollutant limits
also protect wild species in
nonagricultural settings (based
on lit search) (PT50, TPC)
Uptake of pollutants is through
plant roots (PT5q, TPC)
C—Most conservative result of
PT5o or TPC chosen as poll,
limit; short-term phytotoxicity
often does not result in yield
reduction at maturity; TPC
more sensitive indicator of
phytotoxicity than PT50
Dietary Consumption Parameters:
DC
EPA Estimated Lifetime
A—Food consumption
Average Daily Food Intake,
averaged over a lifetime
based on surveys/studies of
dietary intake (reanalyzed
Pennington 1983): food
consumption for different age
groups among males and
females were averaged and
used to calculate a lifetime
weighted average intake
(Pathways 1,2)
EPA reanalysis of FDA Revised
Total Diet List (1982) (Pathway
2)
136 &EPA Part 503 Risk Assessment
-------
Parameters, Approach, Assumptions, and Degree of Conservatism Used: Land ApplicationRiskAssessment
Parameter Used
Parameter Is
in Calculation of
Pollutant Limita,b
Approach
Assumptions/
Conservative (C) or
or Basis
Policy Decisions
Average (A) and Why
Dietary Consumption Parameters (Continued):
DA
Estimated Lifetime Average
Daily Food Intake (see DC
above); only animal tissue food
groups used for DA
Human food consumption of
products from animals that
have ingested biosolids ranges
from 3-10% depending on food
type (Pathway 5)
HEI consumes animal tissue
foods daily (ag and nonag
pathways) (Pathway 4)
A—Food consumption
averaged over a lifetime
Iw, If
Daily consumption of fish
(Javitz, 1980) and water
(standard EPA assumption).
HEI consumes 2 liters/day
of drinking water and ingests
0.04 kg/day of fish from
surface waters into which soil
eroded from a site where
biosolids were applied
C—The fish value is highly
conservative for the
population, and the water
value is high-end but not as
conservative as the fish value
EPA OSWER recommended
value for amount of soil
ingested by a child each day
for 5 years from age 1 to 6
(U.S. EPA, 1989b)
0.2 g/day = soil ingestion rate
for children
Biosolids not diluted with soil
Child is not a PICA child
C—Designed to protect
children at highest risk, except:
A—Does not consider pica
child (a pica child is one who
has an abnormal craving to eat
materials other than food, such
as soil and dirt)
Parameters for Fraction of Diet Produced on Biosolids-Amended Land:
FC
Adaptation of estimates of % of
human diet crops grown on
biosolids-amended soils (from
CAST 1976) x % of biosolids
land applied (Pierce and Bailey
1982) (Pathway 1)
Based on USDA survey of
homegrown foods (1982)
2.5% = amount of human diet
(vegetables, fruit, grain)
(except for home gardener)
grown on land receiving
biosolids (agricultural)
(Pathway 1)
25% = fraction of evaluated
foods (berries, mushrooms)
produced on biosolids
amended soil (nonagricultural)
(Pathway 1)
HEI produces 37-59% of own
crops grown on biosolids-
amended land, varies
depending on food group
(agricultural; not analyzed for
nonag) (Pathway 2)
A—Amount of food grown
was reduced to exclude crops
not consumed by people (i.e.,
crops consumed by animals)
(Pathway 1)
C—Very few home gardeners
actually grow 59% of the leafy
vegetables they consume, on
land amended with biosolids,
continuously for 70 years
(Pathway 2)
FA
Fraction of food group assumed
to be derived from animals that
ingest forage grown on
biosolids-amended soil ranges
from 3-11% depending on food
type (agricultural) and 100%
(deer) and 50% (elk)
(nonagricultural) (Pathway 4)
A—-for livestock farmers
C—for U.S. population
Part 503 Risk Assessment wEPA 137
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Appendix B
Parameter Used
Parameter Is
in Calculation of
Pollutant Limita,b
Approach
Assumptions/
Conservative (C) or
or Basis
Policy Decisions
Average (A) and Why
Parameters for Fraction of Diet Produced on Biosolids-Amended Land (Continued):
FS
Weighted average chronic
lifetime model, based on cattle
biosolids ingestion studies,
adjusted for % of
biosolids-amended land
Based on 2.5% ingestion of
biosolids from pastures in year
of biosolids application and
1.0% in non-application year
1.5% = fraction of biosolids
ingested by grazing animals on
land amended with biosolids
30 days prior to grazing
(averaged over a season)
(Pathways 6,7)
33% = maximum fraction of a
farm's area amended with
biosolids in any one year
(Pathways 6,7)
A—Averaged over a lifetime
FD
Based on available studies of
earthworm consumption
(McDonald, 1983)
33% = fraction of earthworms
in predator's diet (Pathway 10)
C—Based on maximum
chronic consumption of
earthworms by wildlife
Parameters for Plant Uptake of Pollutants:
UC
Plant tissue concentration
Metal application rate
or, linear regression
Plant uptake is linear (increases
- = Slope as more metal added)
0.001 = default value for plant
uptake slope for inorganics
when slope was negative or
<0.001, or when no data
available, and for all organics
Based primarily on field studies;
some field spiked-metal or
greenhouse/pot studies, or other
non-biosolids metals studies used
when field studies unavailable
Geometric mean used (see UA
below)
C—Plant uptake of metals in
biosolids is, in fact, curvilinear
(plateaus), i.e., metals become
less available to plants over
time, even if more metal added
(see Chap. 3); also, data from
high-metal studies were
included
UA
Animal tissue uptake slopes
calculated (regression):
Geometric mean used to average
plant and animal uptake slopes
from different studies
Concentration of poll, in animal tissue
Concentration of poll, in feed
Loss Factor Parameter:
K Mass balance (see Appendix A) 8.5 mt/ha • yr = annual losses A
to erosion (USDA, 1987)
Mass balance, organics:
assumes equilibrium reached
(annual loading of poll. =
annual loss of poll.); thus
organics could be applied
indefinitely in water or air
because they do not accumulate
Mass balance, inorganics: assumes
equilibrium not achieved; conc. of
poll, assumed to increase with
repeated applications until limit
reached; based on max. predicted
av. conc. of poll, in surface water
over 70 yrs.
138 &EPA Part 503 Risk Assessment
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Parameters, Approach, Assumptions, and Degree of Conservatism Used: Land Application Risk Assessment
Parameter Used
in Calculation of
Pollutant Limita,b
Approach
or Basis
Assumptions/
Policy Decisions
Parameter Is
Conservative (C) or
Average (A) and Why
Background Parameters:
TBI
Background intake rate of
pollutants from sources of
exposure other than biosolids
was subtracted from
RfDs/qj*s; remainder = amt. of
poll, from biosolids that will
not exceed threshold
A—Average background
values used
BS
Background concentration of
pollutant in soil (BS) subtracted
from allowable soil
concentration to determine
allowable pollutant
concentrations in soil from
biosolids
Median background inorganic
pollutant concentrations in
agricultural soils used
(Holmgren et al., 1993)
Background soil levels of
organic pollutants = 0 (i.e., for
organics the amount of
pollutant applied annually is
assumed to be degraded at the
same rate it is applied—is in
equilibrium)
A—Average values used
BC
Geometric mean of
background pollutant
concentration in plants grown
in Monbiosolids-amended soil =
BC
A—Average values used
Bioavailability and Bioaccumulation Parameters:
BAY
Based on available studies,
which indicate that pollutants
are not 100% available
Bioavailability factors:
Cadmium = 21.4% for a highly
contaminated heat-dried
biosolids (the BAV for Part 503
Table 3 biosolids = near 0%)
Lead = 40% (BAV usually far
under 5%; cows retain less than
1% of ingested Pb)
PCBs = 100% (biosolids PCBs =
50%)
C—Assumptions overestimate
pollutant availability in biosolid
BACC
Analogous to use of uptake
slope in other parts of the risk
assessment; BACC describes
conc. of poll, present in
earthworms because of
bioavailable poll. conc. in soil
Bioaccumulation factors:
Cadmium = 6
Lead = 0.45
PCBs = 3.69
(p.g-pollutant/g-soil biota DW)
(|J.g-pollutant/g-soil DW)"1
Parameter for Exposure Through Inhalation:
MDC, based on:
1 meter = distance from tractor
driver to soil surface (Pathway
11)
NIOSH
TDA
NIOSH-recommended
standards (Pathway 11)
American Conf. Gov. Indus.
Hygienists (ACGIH)
recommendation
10 mg/m = max. dust level
exposure (above this level,
ACGIH recommends closed
cab) (Pathway 11)
C—Within acceptable
government risk levels
Part 503 Risk Assessment <>EPA 139
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Appendix B
Parameter Used
Parameter Is
in Calculation of
Pollutant Limit'
Approach
Assumptions/
Conservative (C) or
or Basis
Policy Decisions
Average (A) and Why
Parameter for Exposure Through Inhalation (continued):
R^air
(Pathway 13)
Only organic pollutants
evaluated because inorganics
do not volatilize at ambient air
temperatures
Inhalation rate = 20 m /day of
air contaminated with
pollutants from biosolids
Wind direction assumed never
to change, keeping HEI
downwind of site
HEI lives at downwind
boundary of biosolids
management area
C—Exposure will not always
occur downwind of the site
and at the site boundary
Parameter for Exposure Through Ground Water:
TP
See Appendix A
300-yr. ground-water
contamination simulation
model used
Site receives worst-case 1,000
mt/ha application (over 60 cm
on surface) (policy decision)
Depth to ground water = 1
meter
Soil type = loamy sand
Porosity = 0.4
C—Depth to ground water
may be more than 1 meter;
worst-case application rate
used; based on pollutant
transport over 300 years
"Appendix A describes the parameters used; Chapter 3 discusses issues involving some of the key parameters.
bBoxes 9 to 14 (in Chapter 4) provide examples of how the parameters were used to calculate pollutant limits for biosolids.
'Threshold pollutant intake level (TPI), or tolerable conc. of poll, in whole kidney, DW used (Pathway 10); also, cadmium = 4 dif-
ferent approaches, most limiting # used (Pathway 10).
140 &EPA Part 503 Risk Assessment
-------
Appendix
C
Team of Experts Who Assisted
EPA in the Part 503 Biosolids
Risk Assessment
Dr. Rufus Chaney
Research Scientist
USDA-ARS
Beltsvilie, MD
Dr. Willard Chapped
Professor
Center for Environmental Science
University of Colorado
Denver, CO
Dr. Robert Griffin
Professor
Department of Chemical Engineering
University of Alabama
Birmingham, AL
Dr. Terry Logan
Professor
School of Natural Resources
Ohio State University
Columbus, OH
Dr. Al Page
Professor
Department of Soil and Environmental Science
University of California
Riverside, CA
Dr. Robert Wagenett
Department Chairman
College of Agricultural and Life Science
Cornell University
Ithaca, NY
Dr. Andrew Chang
Professor of Soil Science
Department of Soil and Environmental Science
University of California
Riverside, CA
Dr. Lawrence Gratt
IWG Corporation
San Diego, CA
Dr. Charles Henry
Assistant Professor
College of Forestry Resources
University of Washington
Seattle, WA
Dr. George O'Connor
Chairman
Department of Soil Science
University of Florida
Gainesville, FL
Dr. Jim Ryan
Soil Scientist
Risk Reduction Engineering Laboratory
U.S. EPA
Cincinnati, OH
Dr. John Walker
Physical Scientist
Office of Wastewater Management
U.S. EPA
Washington, DC
Dr. Mel Webber
Wastewater Technology Center
Burlington
Ontario, Canada
Part 503 Risk Assessment &EPA 141
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Intentionally Blank Page
-------
Conversions Used To Place
Pollutant Limits in the Same
Units
1) Conversions for Inorganic Pollutants
Pollutant limits originally expressed in RSCs were converted to RPcs using the fol-
lowing equation:
RPC = RSC x AWSAR x 0.001 x SL
where:
RPC
cumulative reference application rate of pollutant in biosolids
(kg-pollutant/ha-land)
RSC
reference concentration of pollutant in biosolids
(mg-pollutant/kg-biosolids DW)
AWSAR =
annual whole biosolids application rate (mt-biosolids DW/ha/yr)
0.001
conversion factor
SL
number of years of site life
The annual whole biosolids application rate (AWSAR) is the maximum amount of
biosolids that can be applied to a hectare in a year, as defined in the Part 503 rule.
An AWSAR of 10 mt-biosolids DW/ha/yr, which is somewhat higher than the typical
application rate of 7 mt, and a site life of 100 years, a reasonable maximum site
life, were used. Therefore:
RPC = RSC x 0.001 x 10 x 100
Because of the factors used, the RPcs for Pathways 3,5, and 7 are the same num-
bers as the analogous RSCs, but the units differ. The RPcs and RSCs for
inorganics are shown in Chapter 4, Table 11.
Part 503 Risk Assessment <&EPA 143
-------
Appendix D
2) Conversions for Organic Pollutants
Pollutant limits originally expressed in RSCs were converted to RPas using the fol-
lowing equation:
RPa = RSC x A WSAR x 0.001
where;
RPa = reference annual application rate of pollutant (kg-pollutant/ha/yr)
RSC = reference concentration of pollutant in biosolids
(mg-pollutant/kg-biosolids DW)
AWSAR = annual whole biosolids application rate (mt-biosolids DW/ha/yr)
0,001 = conversion factor
Therefore, based on the same assumption regarding the AWSAR discussed above
(10 mt-biosolids DW/ha/yr):
RPa = RSC x 10x0.001
A "site life" was not used for degradable organic pollutants (as it was for inorganics
above) because for organics that degrade, there is no limit on site life. The RPas
and RSCs for organics are shown in Chapter 4, Table 11.
3) Additional Useful Conversions
Additional conversions derived from the above two conversions were useful for
comparing pollutant limits, including:
For inorganics:
RP
Rpc = -~= 100 X RPa
For organics:
RPc
a ~ 100
4) Equation Used To Express Pollutant Limit as a
Soil Concentration
MS x 10 9
where:
RLC = allowed soil concentration of pollutant (jig-pollutant/g-soil DW)
RP = reference application of pollutant (kg-pollutant/ha-land)
MS = 2 x 109 g/ha (assumed mass of soil in upper 15 cm)
10"9 = conversion factor (kg/ng)
144 ©EPA Part 503 Risk Assessment
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Guide to the Biosolids
Risk Assessments for the
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Municipal Technology Branch 4204
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In order for the Municipal Technology Branch to be effective in meeting your needs, we need to under-
stand what your needs are and how effectively we are meeting them. Please take a few minutes to tell
us if this document was helpful in meeting your needs, and what other needs you have concerning
biosolids, wastewater treatment, stormwater best management practices, or water reuse.
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EH Consultant EH State official EH Student
~ Other
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EH This document is what I was looking for.
EH I would like a workshop/seminar based on this document.
EH The document was especially helpful in the following ways:
EH The document could be improved as follows:
~ I was unable to meet my need with this document. What I really need is:
EH I found the following things in this document which I believe are wrong:
EH What other types of technical assistance do you need?
We thank you for helping us serve you better. To return this questionnaire, tear it out, fold it, staple it, put
a stamp on it, and mail it. Otherwise, it may be faxed to (202) 260-0116.
Guide to the Biosolids
Risk Assessments for the
EPA Part 503 Rule
-------
Staple Here
Fold Here
Municipal Technology Branch 4204
United States Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Fold Here
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Environmental Protection Agency
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