EPA BIOSOLIDS PFOA & PFOS PROBLEM FORMULATION
MEETING SUMMARY

November 10 & 12, 2020

Meeting Overview

•	EPA held a meeting to gather stakeholder input on the PFOA and PFOS problem formulation for
biosolids risk assessment. Day 1 of the meeting on November 10, 2020 brought together 72
participants from states and tribes. Day 2 of the meeting on November 12, 2020 brought
together 170 participants from other biosolids stakeholder groups. The same content was
covered on Days 1 and 2; meeting slides are attached to this summary. The meeting was led by
Elyssa Arnold, EPA's Biosolids Risk Assessment Lead.

•	Assessing the risk of chemicals found in biosolids is the Biosolids Program's top priority. EPA has
heard the concerns about biosolids contaminated with PFAS, and is aware of the resulting
uncertainty for states, treatment plants, land applicators, and other stakeholders. The PFOA and
PFOS biosolids risk assessment is an important step to address that uncertainty and to provide
an informed path forward.

•	The PFOA and PFOS problem formulation for biosolids risk assessment is part of the EPA PFAS
Action Plan.

•	The problem formulation is the first step of risk assessment. It articulates the purpose for the
assessment, defines the problem, determines the conceptual models, and describes the analysis
plan. Problem formulation also includes engagement with states and tribes, risk managers,
scientists, and members of the biosolids community to discuss foreseeable science and
implementation issues.

•	The purpose of the risk assessment is to determine potential risks from PFOA and PFOS in
biosolids to public health and the environment in order to inform risk management options. This
is in line with EPA's obligations under the Clean Water Act Section 405(d).

Defining the Problem

•	PFOS and PFOA are part of a larger group of chemicals called per- and polyfluoroalkyl
substances (PFAS).

•	PFAS are highly fluorinated aliphatic molecules that have been released to the environment
through industrial manufacturing and through use and disposal of PFAS-containing products.

•	While many PFASs have been found in biosolids, PFOS and PFOA are among the most abundant
and have the largest data sets to support risk assessment.

•	PFOS and PFOA do not readily degrade via aerobic or anaerobic processes. The only dissipation
mechanisms in water are dispersion, advection, and sorption to particulate matter such as
biosolids in the wastewater stream.

•	While PFOS and PFOA have largely been phased out of production in the United States, their
resistance to environmental degradation causes a lingering concern for exposure. They can also
be formed from precursors in the environment.

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•	PFOS and PFOA are both highly persistent in the environment and highly mobile. Both
chemicals have a tendency to bioaccumulate in humans, terrestrial organisms, and aquatic
organisms.

•	PFOS and PFOA have been measured in biosolids in multiple published studies.

Questions for Meeting Participants

1.	What sources of PFAS are you concerned about?

2.	Is your state, tribe, or stakeholder group monitoring PFAS in biosolids, soils, surface or
ground water?

3.	Are you collecting other information that you think would be useful to EPA?

4.	What challenges are you experiencing assessing the fate and transport of PFAS?

5.	Is there anything else you would like us to consider as we define the problem of PFOA and
PFOS in biosolids?

Key Input

•	PFAS sources of concern include paper mills and residuals, industrial cleaning products, floor
wax (e.g., in schools), metal coating facilities, consumer products (e.g., textiles), car washes,
and aqueous film forming foam. Some sources of concern cannot be discussed due to
ongoing litigation at the state level.

•	Multiple states provided their PFOA and PFOS monitoring data to EPA.

•	Analysis of concentration data needs to account for the laboratory methods used as well as
changes in concentrations overtime.

•	Challenges in assessing fate and transport of PFAS include:
o developing a measure of plant uptake, and

o understanding transformation of PFAS compounds and precursors through the

wastewater treatment process (oxidation, anaerobic concentration, composting, etc.).

•	Biosolids and pretreatment programs are closely linked and should be considered together.

•	The availability and cost of laboratory methods is an obstacle for states.

Conceptual Models

•	Conceptual models were presented for land application, surface disposal, and incineration,
which are the biosolids use and disposal pathways defined under 40 CFR Part 503.1. Human
health receptors were addressed for all three pathways and ecological receptors were
addressed for land application and incineration (surface disposal is excluded because the
exposure pathways for surface disposal are not relevant for ecological risk assessment). The
conceptual models can be found in the slides at the end of this meeting summary document.

•	The conceptual models define the sources of exposure, routes of exposure, and receptors.

•	Conceptual models are not intended to represent every possible route of exposure, but rather
the primary ones that we are planning to model based on both

1.	the expected major pathways and

2.	the reality of the available data and modeling capabilities.

•	The conceptual models represent the exposure pathways for all chemicals in biosolids and are
not specific to PFOA and PFOS. The goal for the PFOA and PFOS risk assessment is to be
consistent with the approach for all of EPA's biosolids chemical risk assessments going forward.

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Questions for Meeting Participants

1.	Do the conceptual models capture the range of routes of exposure of concern in your state,
tribe, or stakeholder group? If not, what is missing?

2.	Do the conceptual models capture the range of receptors of concern in your state, tribe, or
stakeholder group? If not, what is missing?

3.	Do the conceptual models capture the range of potential health effects of concern in your
state, tribe, or stakeholder group? If not, what is missing?

Key Input

•	Missing exposure pathways include:

o home garden use for biosolids compost,
o occupational exposure for professional land applicators,
o occupational exposure for POTW workers,
o groundwater used as drinking water for animals,
o groundwater used as irrigation water,
o human consumption of cow liver, and

o other animal uses and consumption such as medicine, gelatin, and pet food.

•	The incineration conceptual model is for SSIs and the source term does not currently include
pyrolysis or gasification units.

•	EPA will need more data in order to define PFAS destruction in SSIs.

•	The conceptual model for incineration needs to better define the appropriate human
receptors. The adult farmer and farm child may be less impacted than an urban population
near an incinerator, and there may be disproportionate impacts to disadvantaged
communities.

•	Since PFAS are ubiquitous in the environment, the conceptual models should account for
background levels of PFAS in soil, surface water, and ground water. PFAS may be present on
land application sites due to pesticide applications.

•	Similarly, human receptors have background PFAS exposure from drinking water and
consumer products.

•	The conceptual models do not include release mechanisms that are not regulated by the
Clean Water Act, e.g., disposal of ash or scrubber water from an incinerator (covered under
the Resource Conservation and Recovery Act).

Analysis Plan

•	Toxicity endpoints and bioaccumulation factors for the risk assessment for human health,
aquatic life, and aquatic-dependent wildlife will be consistent with other efforts in the EPA
Office of Water and across the Agency. Human health effects and bioaccumulation data support
both ambient water criteria for human health and Safe Drinking Water Act regulatory
determinations. Aquatic life and aquatic-dependent wildlife effects and bioaccumulation data
support ambient water criteria for aquatic life and aquatic-dependent wildlife.

•	Toxicity endpoints for non-aquatic dependent birds, mammals, terrestrial invertebrates, and
terrestrial plants are currently being evaluated by the Biosolids Program.

•	The modeling approach for biosolids risk chemical assessment is currently under development
for presentation to the Science Advisory Board (SAB) in 2021. The approach includes a (1)
chemical prioritization method, (2) a Biosolids Screening Tool for deterministic, screening-level
assessment and (3) a probabilistic risk assessment framework for chemicals that fail at the
screening level. PFOA and PFOS have already been prioritized for risk assessment, however the

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prioritization method will be applied to all chemicals measured in biosolids including many other
PFAS.

•	Modeling for biosolids will be based on publicly available, previously peer-reviewed models for
leaching, runoff, erosion, air dispersal, and plant uptake to the greatest extent possible.

•	The approach for PFAS will be consistent, to the extent appropriate, with all other chemical risk
assessment for biosolids.

•	EPA will complete the PFOA and PFOS risk assessment after the modeling approach is reviewed
by the Science Advisory Board. The risk assessment will also go through review and public
comment.

Questions for Meeting Participants

1.	Are you aware of reliable fate, transport, or toxicity data for various routes of exposure,
receptors, or health effects that EPA should know about? If yes, please share.

2.	Have you used any modeling approaches for PFAS that you would like to share with EPA?

3.	Is there anything else you would like to share regarding modeling of PFOA and PFOS in
biosolids?

Key Input

•	NHDES and USGS are conducting a PFAS soil leaching study to calculate soil partition
coefficients.

•	A fate and transport model evaluation for PFAS in biosolids prepared by Arcadis and NCASI
was completed in June 2020: https://www.ncasi.org/wp-content/uploads/2020/Q3/Arcadis-
PFAS-Residuals-Modeling-vl-l.pdf

•	Minnesota is especially concerned about the body burden of PFAS passed to infants. The
state has a model they use for drinking water values and for water quality criteria protective
offish consumption. See: https://www.nature.com/articles/s41370%20018%200110%205

•	Minnesota is trying to initiate a land-applied biosolids study that would test soil, pore water,
surface water, ground water, and crop uptake. The study would begin during the next
growing season.

•	Vermont DEC, Stone Environmental, and NEBRA partnered to create a model for chemical
leaching to ground water from land applied biosolids.

•	Maine is conducting a small ground water leaching study that may be useful to EPA.

Risk Management and Implementation Considerations

•	Risk assessment is the first step of a larger process and is done to identify risks that exceed the
level of concern for human health and ecological receptors. The risk assessment will go through
review and public comment.

•	If EPA determines that PFOA or PFOS in biosolids may adversely affect public health or the
environment, risk managers will consider options for numerical limitations and best
management practices for these compounds. Any subsequent proposed regulation would go
through a standard rulemaking process including intra-Agency and Office of Management and
Budget review.

Questions for Meeting Participants

1. What considerations or concerns should EPA be aware of during risk management and
implementation?

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2. Do you have any other topics related to risk management or implementation that you would
like to raise?

Key Input

•	The approach to biosolids risk assessment and regulation for PFAS should have a high-level
strategy that includes pretreatment and manufacturing. Source control rather than
continuous removal of chemicals from biosolids is key. Wastewater treatment plant
infrastructure improvements require large economic investments.

•	Stakeholders need EPA to look at the big picture in order to protect the quality of biosolids
for beneficial use. A moratorium on land application is not sustainable for the industry.

•	All three use and disposal practices for biosolids (land application for beneficial use, surface
disposal, and incineration) are critical for successful biosolids management. A fourth option,
such as pyrolysis, would improve the stability of the industry but requires a large capital
cost.

•	PFAS contamination may create problems for incineration and landfilling of biosolids as well
as land application.

•	Environmental justice implications should be considered for incineration and for land
application. The synergistic impacts of other constituents on vulnerable communities
further compounds the issue.

•	Any regulatory limits for PFAS need to be considered within the context of background PFAS
levels in the environment and exposure to PFAS from sources other than biosolids.

Next Steps

•	Problem Formulation meetings completed December 2020; draft document expected Spring
2021.

•	Science Advisory Board review of modeling approach expected to begin in 2021.

•	Estimated completion of the risk assessment in 2022 for internal review, followed by public
comment.

•	If EPA determines that PFOA or PFOS in biosolids may adversely affect public health or the
environment, risk managers will consider options for numerical limitations and best
management practices for these compounds.

•	If regulatory limits are advised, they will go through a standard regulatory process including peer
review, inter-Agency and OMB review as well as public comment.

Attached: Meeting Slides

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Biosolids PFOA & PFOS Problem
Formulation Discussion with
Stakeholders

November 10 & 12, 2020



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Outline

•	Introduction and Purpose

•	Part 1: Defining the Problem

•	Part 2: Conceptual Models

•	Part 3: Analysis Plan

•	Risk Management and Implementation Considerations

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INTRODUCTION AND PURPOSE

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Biosolids Risk Assessment in the PFAS Action Plan

•	Activity: Scoping biosolids risk assessment for PFOA/PFOS

•	Purpose: EPA is in the early scoping stages of risk assessment
for PFOA and PFOS in biosolids to better understand the
implications of PFOA and PFOS in biosolids to determine if
there are any potential risks.

•	Timeframe: 2020

https://www.epa.aov/pfas/epas-pfas-action-plan

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Problem Formulation

Problem Formulation is the part of the risk assessment that:

•	Articulates the purpose for the assessment

•	Defines the problem

•	Chemical sources and occurrence

•	Fate and transport in the environment

•	Toxicity endpoints

•	Determines the conceptual models (sources and routes of exposure) for assessing adverse
effects to human health and ecological receptors {e.g., birds, fish)

•	Describes the analysis plan, documenting the approach for acquiring reliable data and the
models and tools to be used in the analysis

•	Includes engagement with states and tribes, risk managers, scientists, and
members of the biosolids community to discuss foreseeable science and
implementation issues.

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Purpose of the Risk Assessment

Determine potential risks from PFOA and PFOS in biosolids to
public health and the environment in order to inform risk
management options.

Clean Water Act, Section 405(d): EPA "shall identify those toxic pollutants which; on the basis of
available information on their toxicity, persistence>, concentration, mobility or potential for
exposure, may be present in sewage sludge in concentrations which may adversely affect public
health or the environment, and propose regulations specifying acceptable management practices
for sewage sludge containing each such toxic pollutant and establishing numerical limitations for
each such pollutant for each use identified under paragraph (1)(A)."

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DEFINING THE PROBLEM

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PFOS and PFOA

Perfluorooctanesulfonic Acid (PFOS)
C8HF1703S
CASRN: 1763-23-1

F

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Perfluorooctanoic Acid (PFOA)

c8hf15o2

CASRN: 335-67-1

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PFOS and PFOA Sources and Environmental Fate

•	PFOS and PFOA are part of a larger group of chemicals called per- and polyfluoroalkyl
substances (PFAS).

•	PFAS are highly fluorinated aliphatic molecules that have been released to the environment
through industrial manufacturing and through use and disposal of PFAS-containing products.

•	While many PFASs have been found in biosolids, PFOS and PFOA are among the most
abundant and have the largest data sets to support risk assessment.

•	PFOS and PFOA do not readily degrade via aerobic or anaerobic processes.

•	While PFOS and PFOA have largely been phased out of production in the United States, their
resistance to environmental degradation causes a lingering concern for exposure. They can
also be formed from precursors in the environment.

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Concentrations of PFOA and PFOS in Biosolids

Year Sampled

PFOA (ng/g dry wt)

PFOS (ng/g dry wt)

Reference

2001

12-70

308 - 618

Venkatesan, 2013

2004-2007

8-68

80 - 219

Sepulvado, 2011

2005

16-219

8.2 - 110

Loganathan 2007

2005

18 - 241

<10-65

Sinclair, 2006

2006

—

81 - 160

Schultz, 2006

2006-2007

18-69

31 - 702

Yu, 2009

2007

20 -128

32 - 418

Yoo, 2009

2011

1 - 14

4 - 84

Navarro, 2016

2014

10-60

30 - 102

Mills, Dasu (in prep)

2018

1-11

2 - 1,100

EGLE, 2020

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Defining the Problem

•	Chemical sources and occurrence

•	Fate and transport in the environment

•	Toxicity endpoints

Questions

1.	What sources of PFAS are you concerned about?

2.	Is your state, tribe, or stakeholder group monitoring PFAS in bioso/ids, soils; surface or
ground water?

3.	Are you collecting other information that you think would be useful to EPA?

4.	What challenges are you experiencing assessing the fate and transport of PFAS?

5.	Is there anything else you would like us to consider as we define the problem of PFOA
and PFOS in bioso/ids?

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CONCEPTUAL MODELS

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Biosolids Use and Disposal Pathways

1.	Land Application

2.	Surface Disposal

3.	Incineration

40 CFR Part 503.1: "(a) Purpose. (1) This part establishes standards, which consist of general
requirements, pollutant limits, management practices, and operational standards, for the final use
or disposal of sewage sludge generated during the treatment of domestic sewage in a treatment
works. Standards are included in this part for sewage sludge applied to the land, placed on a
surface disposal site, or fired in a sewage sludge incinerator.

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Conceptual Model for the Agricultural Land Application Scenario: Human Exposures

Source

Agricultural
Field

Release Mechanism

Windblown
particles

Runoff and
erosion

Leaching/
infiltration

Media

Soil/biosolids
(ag field)

Exposure Scenarios

Forage

Beef & dairy
cattle

Exposure Routes Receptors Pathway Number

4 & 5

Ingestion of beef
& milk

Adult farmer
Farm child

a

Protected & root
crops

Exposed crops

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Soil (buffer)

Surface water
(index res)

Surface water
(farm pond)

Groundwater

k-

K-

Drinking water

Drinking water

Ingestion of
produce

Volatilization

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Air (vapors &



Inhalation of

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particulates)



ambient air

Ingestion of soil

Ingestion of
drinking water

Ingestion offish

Ingestion of
drinking water

Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer
Farm child

Shower air

fr~+i

Inhalation of
shower vapor



Adult farmer

1 & 2

11 & 13

12

12

14

15

	Dashed arrows and box outlines indicate a pathway or route that has been added since 1993.

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Conceptual Model for the Agricultural Land Application Scenario: Ecological Exposures

Source

Release Mechanism

Media

Exposure Scenarios

Exposure Routes

Receptors

Pathway Number

6 & 7

10

8 & 9

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Fish

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Aquatic

plants

mm





Sediment

Hi



Dashed arrows and box outlines indicate a pathway or route that has been added since 1993.

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Conceptual Model for Biosolids Surface Disposal: Human Exposures

Source	Release Mechanism Media	Exposure Scenarios	Exposure Routes	Receptors Pathway Number

Dashed arrows and box outlines indicate a pathway or route that has been added since 1993.

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Conceptual Model for Biosolids Incineration: Human Exposures

Exposure Scenarios	Exposure Routes Receptors

Source

Release
Mechanism

Media

Forage



Combustion
Unit

Vapors &
Particles in Air

Surface water
(farm pond)

Leaching to
Groundwater

Beef &

ĶĶ

Ingestion of beef

H

Adult farmer

dairy cattle

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& milk

m

Farm child

Protected & root
crops

Exposed crops

	w

Drinking water

I-	+i

Drinking water

Shower air

Dashed arrows and box outlines indicate a pathway or route that has been added since 1993.

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Ingestion of
produce

Ingestion of soil

h-H



Ingestion of
drinking water

Ingestion offish

Ingestion of
drinking water

Inhalation of
shower vapor

Inhalation of
ambient air

h-H

h-H

I--H



Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer
Farm child

Adult farmer

Adult farmer
Farm child

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Conceptual Model for Biosolids Incineration: Ecological Exposures

Source Release Mechanism	Media	Exposure Scenarios	Exposure Routes	Receptors

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Conceptual Models

•	Sources of exposure

•	Routes of exposure

•	Receptors

Questions

1.	Do the conceptual models capture the range of routes of exposure of concern for your
state, tribe, or stakeholder group? If not, what is missing?

2.	Do the conceptual models capture the range of receptors of concern for your state,
tribe, or stakeholder group? If not, what is missing?

3.	Do the conceptual models capture the range of potential health effects of concern for
your state, tribe, or stakeholder group? If not, what is missing?

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Toxicity Endpoints

•	Biosolids assessment inputs for human health, aquatic life, and aquatic-dependent
wildlife will be consistent with other efforts in the EPA Office of Water:

•	Human health effects data support both ambient water criteria for human
health and Safe Drinking Water Act regulatory determinations

•	Aquatic life and aquatic-dependent wildlife effects data support ambient water
criteria for aquatic life and aquatic-dependent wildlife

•	Toxicity endpoints for non-aquatic dependent birds, mammals, terrestrial
invertebrates, and terrestrial plants are currently being evaluated by the Biosolids
Program

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Human Health Toxicity Endpoints

•	EPA developed Health Effects Support Documents (HESDs) for PFOA and PFOS Health
Advisories that were published in 2016.

•	The HESDs determined the Reference Dose (RfD) and Cancer Slope Factor (CSF).

•	As the toxicity literature is constantly evolving, EPA is evaluating new studies and other
available information published since 2013.

•	In March of 2020, EPA sought public comment on an annotated bibliography of
identified studies as well as the protocol used to identify the relevant data published
since 2013 to support efforts for Regulatory Determination 4 under the Safe Drinking
Water Act.

•	An initial title and abstract screen has been completed to identify studies with potentially
relevant health effects information {i.e., human epidemiology studies, animal toxicity
studies, and physiologically based pharmacokinetic [PBPK] studies).

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Ecological Toxicity Endpoints

•	Ecological toxicity endpoints are currently being evaluated

•	Relevant toxicity studies from peer-reviewed literature were identified through ECOTOX
searches fhttps://cfpub.epa.qov/ecotoxA) and reviewed for data quality.

•	Effects on survival, growth, and reproduction are being evaluated.

•	EPA is currently working to develop information to support ambient water quality criteria for
aquatic life and aquatic-dependent wildlife.

•	EPA plans to begin reviewing ecological toxicity data for their quality and sufficiency for
criteria development.

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Bioaccumulation Factor (BAF)

•	EPA is currently compiling paired fish tissue and water samples that can be used to calculate
nationally representative BAFs for trophic levels 2, 3, and 4

•	PFOA and PFOS are ionic organic chemicals

•	National BAFs are calculated from field-measured BAFs or laboratory-measured
bioconcentration factors (BCFs)

•	BAFs are normalized by adjusting for the water-dissolved portions of the chemical; this
provides a common basis for averaging BAFs from several studies

•	Lipid normalization is not applicable to measured PFOA and PFOS BAF values because
these chemicals appear to associate with proteins, not lipids.

•	Kpoc, the partitioning coefficient for particulate organic carbon, for PFOA and PFOS from
peer-reviewed sources can be used to normalize measured BAF values

•	EPA is also compiling paired tissue and water data that can be used to calculate nationally
representative BAFs for other aquatic life and aquatic-dependent wildlife

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Modeling Approach

•	Currently under development for presentation to the Science Advisory Board in 2021

•	Biosolids Screening Tool for deterministic, screening-level assessment

•	Probabilistic Risk Assessment framework for chemicals that fail at the screening level

•	Modeling for biosolids will be based on publicly available, previously peer-reviewed models for
leaching, runoff, erosion, air dispersal, and plant uptake to the greatest extent possible

•	Approach for PFAS will be consistent, to the extent appropriate, with all other chemical risk
assessment for biosolids

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Analysis Plan

• Approach for acquiring reliable data

Models and tools to be used in the analysis

Questions

1.	Are you aware of reliable fate, transport, or toxicity data for various routes of exposure,
receptors, or health effects that EPA should know about? If yes, please share.

2.	Have you used any modeling approaches for PFAS that you would like to share with
EPA?

3.	Is there anything else you would like to share regarding modeling of PFOA and PFOS in
biosolids?

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Risk Management and Implementation Considerations

•	The EPA risk assessment will characterize risk from biosolids on a national scale

•	If EPA determines that PFOA or PFOS in biosolids may adversely affect public health or the
environment, risk managers will consider options for numerical limitations and best
management practices for these compounds (as there are with current Part 503 pollutant
limits)

Clean Water Act, Section 405(d): If "it is not feasible to prescribe or enforce a numerical limitation for
a pollutant identified under paragraph (2), the Administrator may instead promulgate a design,
equipment, management practice, or operational standard, or combination thereof'

Questions

1.	What considerations or concerns should EPA be aware of during risk management and
implementation ?

2.	Do you have any other topics related to risk management or implementation that you
would like to raise ?

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Thank you

Elyssa Arnold

Risk Assessment Lead, EPA Biosolids Program

arnold.elvssa@epa.gov

202-566-1189

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