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
J i :
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
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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
16
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
Ķ
& 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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