EPA Response to External Peer Review of U.S. EPA's Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid (PFOA) (April 2022)


oEPA
United States
Environmental Protection
Agency
Office of Water
EPA-842-D-22-004
April 2022
EPA Response to the
External Peer Review of U.S. EPA's
"Draft Aquatic Life Ambient Water Quality Criteria for
Perfluorooctanoic Acid (PFOA)"
(April 2022)
U.S. Environmental Protection Agency
Office of Water
Office of Science and Technology
Washington, D.C.

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA)"
TABLE OF CONTENTS
1.0 INTRODUCTION	1
1.1	Development of the Draft Documents	1
1.2	Peer Reviewers	2
2.0 PEER REVIEWER COMMENTS AND EPA RESPONSES ORGANIZED BY CHARGE
QUESTION	3
2.1	Please comment on the overall clarity of the document as it relates to the derivation of
each criterion	3
2.2	Please comment on the approach used to derive the draft criterion for PFOA. Please
provide detailed comments	8
2.3	Please comment on the approach used to derive the draft acute estuarine/marine
benchmark for PFOA. Given the limited estuarine/marine test data available, a new
approach method was used to support the derivation of an acute estuarine/marine
benchmark to provide states and tribes with a protective value. Please provide detailed
comments	20
2.4	Please comment on the use of measured and unmeasured toxicity tests to derive the
respective criterion. In particular please comment on the supporting justification for using
unmeasured toxicity tests in Appendix L	29
2.5	Please comment on the toxicity data used to derive the draft criteria	34
2.6	Please comment on the translation of the chronic water column criterion elements for
aquatic life to derive the tissue-based criterion elements, considering the bioaccumulation
of PFOA and PFOS. In particular, please comment on:	52
2.7	Please comment on the frequency and duration of the criterion elements, in particular
please comment on the frequency and duration components of the tissue-based criterion
elements	60
2.8	Please provide any additional technical comments that you believe should be considered	66
3 REFERENCES CITED BY EPA IN RESPONSES	81

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria
for Perfluorooctanoic Acid (PFOA)"
1.0 INTRODUCTION
The U.S. Environmental Protective Agency (EPA) Office of Water (OW) is charged with protecting ecological
integrity and human health under the purview of the Clean Water Act (CWA). In support of this mission, EPA
has developed draft water quality criteria to protect aquatic life and aquatic-dependent wildlife from the
presence of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) in freshwater. Because there
were only limited data for estuarine/marine species for PFOA and PFOS, EPA developed benchmarks for PFOA
and PFOS in saltwater. The derivation of these criteria is described in two draft documents: Aquatic Life
Ambient Water Quality Criteria for Perfluorooctanoic Acid (PFOA) and Aquatic Life Ambient Water Quality
Criteria for Perfluorooctane Sulfonate (PFOS).
An independent letter peer review of the EPA's draft Aqua lie Life Ambient Water Quality Criteria for
Perfluorooctanoic Acid (PFOA) was conducted by Eastern Research Group, Inc. (ERG), a contractor for EPA
OW and developed an external peer review report (https://www.epa.gov/wqc/aquatic-life-criteria-
pcrfluorooctanoic-acid-pfoa). Independent peer review of the draft Aquatic Life Ambient Water Quality Criteria
for Perfluorooctane Sulfonate (PFOS) document is covered in a separate set of external peer review and EPA
response documents.
This document provides EPA's responses to external peer review comments on the draft PFOA criteria
document. Section 2.0 of this report presents the individual reviewer comments and EPA's responses organized
by charge question.
.1.1 Development of the Draft Documents
Toxicity studies used to derive the PFOA and PFOS criteria were carefully evaluated and thoroughly reviewed
to ensure studies were of sufficient data quality to use in criteria derivation. Scientists from EPA OW and Office
of Research and Development (ORD) conducted an extensive internal review of the PFOA and PFOS toxicity
studies, primarily based on studies in EPA's ECOTOXicology database through September 2019. Additionally,
EPA obtained replicate-level (or treatment-level, when replicates were unavailable) concentration-response (C-
R) data from publications, supplemental materials, or via contacting authors so that EPA could independently fit
C-R models to estimate acute LC50 and chronic EC10 values that were used to derive the criteria to ensure
endpoints used were statistically sound. Individual C-R models and resultant point estimates were also reviewed
and discussed between OW and ORD to ensure the most statistically robust models informed the derivation of
the PFOA and PFOS criteria. In addition to contacting study authors for C-R data (when not reported in the open
literature), EPA also consulted primary authors for methods clarifications in many instances during the data
quality review phase to ensure that the studies used to derive criteria were of high quality.
Overall, due to the paucity of measured freshwater toxicity data, EPA included a number of tests with
unmeasured treatments to derive criteria to ensure the dataset was representative of a range of taxa and there
were sufficient data to develop criteria. EPA also conducted meta-analyses to evaluate the relationship between
nominal and measured test concentrations using tests with measured treatment concentrations. These meta-
analyses (described in detail as Appendix L of the PFOA criteria document and Appendix O of the PFOS
criteria document) suggested measured concentrations were similar to nominal concentrations and that the use of
unmeasured tests, in light of data limitations, was appropriate. Additionally, estuarine/marine toxicity data
limitations did not allow for the direct derivation of acute or chronic estuarine/marine criteria for PFOA or
PFOS. Therefore, to develop recommendations that states and tribes could use in adopting protective values for
estuarine/marine waters, EPA developed acute PFOA and PFOS protective benchmarks using a New Approach
Methodology (detailed in Appendix K of the PFOA criteria document and Appendix L of the PFOS criteria
document).
Addressing data limitations to derive robust criteria/benchmarks, extensively reviewing studies, and calculating
point estimates meant that the derivation of the PFOA and PFOS aquatic life criteria were developed via
comprehensive, rigorous process that included collaborations across EPA scientists in OW and ORD. Beyond
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria
for Perfluorooctanoic Acid (PFOA)"
detailed discussions between OW and ORD, the PFOA and PFOS drafts also underwent two rounds of review
with the EPA Scoping Workgroup (consisting of additional scientists from both OW and ORD) and one round
of review with a group of internal EPA reviewers that included representatives from the OW, ORD, other EPA
Program Offices, and EPA Regions.
Subsequently, EPA contracted with ERG to organize an independent external peer review of both draft
documents. External peer reviewer comments on the PFOA criteria document and EPA's responses to those
comments are described in this report. Results of the PFOS review are documented in a separate report.
.1.2 Peer Reviewers
ERG identified, screened, and selected the following five experts who met technical selection criteria provided
by EPA and were determined by ERG to have no conflict of interest in performing this review:
• Jason Conder, Ph.D.; Principal, Geosyntec Consultants
• Anu Kumar, Ph.D.; Principal Research Scientist, Environment Protection and Technologies,
Commonwealth Scientific and Industrial Research Organization (CSIRO)
• Ryan Prosser, Ph.D.; Associate Professor, University of Guelph
• Christopher J. Salice, Ph.D.; Director, Environmental Science and Studies Program, Towson
University
• Jamie G. Suski, Ph.D.; Senior Scientist, EA Engineering, Science, and Technology, Inc.
ERG provided reviewers with instructions, the draft Aquatic Life Ambient Water Quality Criteria for
Perfluorooctanoic Acid (PFOA), and the charge to reviewers prepared by EPA. Reviewers worked individually
to develop written comments in response to the charge questions. After receiving reviewer comments, ERG
compiled responses by charge question (see Section 2.0) and included the responses organized by reviewer.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.0 PEER REVIEWER COMMENTS AND EPA RESPONSES ORGANIZED BY CHARGE QUESTION
This section organizes reviewer comments by charge question.
.2.1 Please comment on the overall clarity of the document as it relates to the derivation of each criterion.
2.1. Chiritv of Document ;is it Rehites to the l)eri\;ilion of K:ich Criterion
Re\ iewer
Com meiils
KIW Response
Reviewer
1
Overall, the document is clear and the reader can follow the
logic of criteria derivation, and track the values used back
to the cited research articles or values calculated by EPA.
Thank you for your comment.
Reviewer
2
I thought that the document was well written and laid out. I
thought that the document clearly laid out the approach that
the EPA used to derive each criterion. I thought it clearly
outlined the approach that the EPA chose in deciding
which data to use in their derivation and how these data
would be used in derivation.
The appendices are very useful in providing added detail
and the data that were used in the derivation of the criteria.
The appendices allow for a high level of transparency
around how the criteria were generated.
In Table 3-1, the acronym "GMAV" was used in the
caption, but I could not locate where this acronym was
defined earlier in the document.
The captions of figures and tables are not sufficiently
detailed. Figures and tables should be able to stand on their
own. Also, the use of acronyms in the caption of tables and
figures decreases clarity, e.g., Fig. 3-5. The use of
acronyms in the figure or table is fine, as long as they are
defined in the caption of the figure or table.
Thank you for commenting on the clarity and transparency of the
document, the criteria derivation process, and supporting appendices.
Genus Mean Acute Value (i.e., GMAV) is now specified in the first
in-text use. A list of all acronyms used is now included in the revised
draft PFOA Aquatic Life Criteria document to aid readers in
understanding of the text and figure/table captions.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.1. ('hirilv of Document its it kehiles to (ho Demotion of Ksicli Criterion
Ue\ iewer
Com meiils
KIW Response
Reviewer
3
I have confidence is the PFOA draft criteria, these are more
in-line with thresholds put forth by other agencies.
Importantly, a discussion on the difference in derivation of
the thresholds would be welcome; for instance, others are
derived using Species Sensitivity Distributions of the
complete dataset. In comparison, EPA uses a subset of data
on the genus identified as most sensitive.
Table 1 - does not list units of thresholds.
Define CMC at first use
Table 3-6 reverses order of sensitive taxa compared to the
previous tables.
Thank you for describing your overall confidence in the PFOA criteria
given the relative similarities between the draft PFOA criteria
magnitudes and thresholds put forth by other agencies/jurisdictions.
While other jurisdictions may use species sensitivity distributions
(SSD) to identify hazard concentrations or protective thresholds, EPA
used a genus sensitivity distribution (GSD) approach to derive draft
PFOA criteria, which is consistent with EPA's 1985 Guidelines for
Deriving Numerical National Water Quality Criteria for the
Protection of Aquatic Organisms and Their Uses. Reviewer 3
incorrectly stated a subset of data were used to derive the draft
criteria. The draft acute criterion is based on the final acute value
(FAV), which is the 5th centile of the GSD. The chronic criterion was
also based on the FAV transformed by the final acute to chronic ration
(FACR). Consequently, both draft PFOA freshwater column-based
criteria and were based on the entire distribution of available toxicity
data. The acute and chronic freshwater column-based PFOA criteria
were derived following EPA's 1985 Guidelines. Addition of new
chronic toxicity data in the updated draft PFOA criteria document
al lowed for the calculation of a draft chronic freshw ater criterion
magnitude directly from the chronic GSD rather than basing the
magnitude on the FAV transformed by the FACR. as was done in the
draft PFOA criteria document that underwent peer review.
Table 1-1 has been updated to include a column that describes the
criteria or benchmark and calculation approach in response to
Reviewer 3 suggesting "discussion on the difference in derivation of
the thresholds would be welcome." Table 1-1 has also been updated to
include the units of thresholds as mg/L.
Criterion Maximum Concentration (CMC) is now fully described in
the first in-text use and as a caption in the first table that contains
"CMC." Additionally, a list of all acronyms used is now included in
the revised draft PFOA Aquatic Life Criteria document to aid readers
in understanding of the text and figure/table captions.
4

All tables describing relative species sensitivities are now consistent
with one another where more sensitive species are at the top of the
table and tolerant species are at the bottom of the tables.
Reviewer
4
EPA has drafted the PFOA aquatic life criteria to be
consistent with methods described in EPA's "Guidelines
for Deriving Numerical National Water Quality Criteria
for the Protection of Aquatic Organisms and Their Uses"
(U.S. EPA 1985). I congratulate the EPA Team for a very
thorough, comprehensive analysis of toxicological data to
derive each criterion.
• The report is technically sound and is very clearly
written.
• The criteria have been derived using strong science-
based evidence.
• Sub-sections on overview of PFAS, PFAS
nomenclature, problem formulation, exposure
pathways, transformation and degradation of PFOA
precursors in the aquatic environment sources,
concentration reported in environment and existing
criteria (both nationally and internationally) help to
set the scene before toxicological data is presented
and assessed for developing various criterion.
• The freshwater acute water column-based criterion,
the chronic water column-based chronic criterion,
the chronic fish whole-body tissue criterion, the
chronic fish muscle tissue criterion and the chronic
invertebrate whole-body tissue criterion have been
developed and reported in this report.
• Acute and chronic MDRs for PFOA
estuarine/marine criteria derivation were not met
due to fewer empirical PFOA toxicity data. EPA
Team developed an acute aquatic life benchmark for
Thank you for your comment and thank you for describing specific
sections of the draft PFOA criteria document that you felt were
comprehensive.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.1. ('hirilv of Document its it kehiles to (ho Demotion of Ksicli Criterion
Ue\ iewer
Com meiils
KIW Response

estuarine/marine environments based on
Interspecies Correlation Estimation (ICE) model.
•	The relative sensitivity of freshwater plants to
PFOA exposures indicated plants are less sensitive
than aquatic vertebrates and invertebrates so plant
criteria were not considered.
•	EPA Team has provided extensive background
information on toxicity data assessment and collated
this information in various appendices such as
Appendix A-Summary Table of Acceptable
Quantitative Freshwater Acute PFOA Toxicity
Studies; Appendix B-Detailed PFOA Acute
Toxicity Study Summaries and Corresponding
Concentration-Response Curves (when calculated;
Appendix C: Acceptable Freshwater Chronic PFOA
Toxicity Studies); Appendix D- Acceptable
Estuarine/Marine Chronic PFOA Toxicity Studies;
Appendix E-Acceptable Freshwater Plant PFOA
Toxicity Studies; Appendix F- Acceptable
Estuarine/Marine Plant PFOA Toxicity Studies;
Appendix G-Summary Table of Qualitative
Freshwater PFOA Toxicity Studies; Appendix H-
Other Estuarine/Marine PFOA Toxicity Studies
Unused PFOA Toxicity Studies; Appendix I-
Unused PFOA Toxicity Studies; Appendix J- EPA
Methodology for Fitting Concentration-Response
Data and Calculating Effect Concentration-Fitting
Concentration Response Data in R; Appendix K-
Derivation of Acute Protective PFOA Benchmarks
for Estuarine/Marine Waters through a New
Approach Method (NAM); and Appendix L Meta-
Analysis of Nominal Test Concentrations Compared
to Corresponding Measured Test Concentrations.

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
.2.2 Please comment on the approach used to derive the draft criterion for PFOA. Please provide detailed comments.
• Is the technical approach used to derive the criterion logical?
• Does the science support the conclusions?
• Is it consistent with the protection of freshwater aquatic life from acute, chronic, and bioaccumulative effects?
2.2. The Technical Approach I sod (o l)eri\e (ho Dral'l Criterion lor I'l-'OA
Ue\ iewer
Com nicnls
KIW Response
Reviewer
1
• Is the technical approach used to derive the
criterion logical?
Yes, the technical approach used to derive the criteria
elements is generally logical. I disagree with some of the
elements of the analyses, as noted in my detailed comments
(see below, responses to charge question 8)
• Does the science support the conclusions?
In general, the science is supportive of the general
conclusions. As noted in my below detailed responses to
other charge questions, I believe the science is not
supportive of the work in a few key instances including:
1. I believe the Criterion Continuous Concentration
(CCC) should be potentially re-calculated
considering my comments provided in response to
charge question 5a.
2. The science does not support the assumption of a
10-year recovery time for PFOA in aquatic systems.
3. The generation of tissue criteria is weakly
supported, and the uncertainty associated with these
criteria should be emphasized.
4. The NAM-generated marine Final Acute Value
(FAV) and FAV/2 values (Appendix K) are highly
uncertain.
Thank you for your comment, stating the technical approach was
generally logical. Specific elements referenced by Reviewer 1 are
further described and responded to in section 2.8.
Responses to key instances where Reviewer 1 does not believe the
science is supportive of the draft PFOA Aquatic Life Criteria
document are described below in corresponding numerical order:
1. Reviewer 1 believes the FACR should be 90 (calculated as the
geometric mean of the B. calyciflorus, M. macrocopa, and D.
magna Species Mean Acute to Chronic Rations [SMACR])
rather than 299 as it is in the draft criteria (based directly on
the B. calyciflorus SMACR). Addition of new chronic toxicity
data in the updated draft PFOA criteria document allowed for
the calculation of a draft chronic freshw ater criterion
magnitude directly from the chronic GSD rather than basing
the magnitude on the FAV transformed by the FACR. as was
done in the draft PFOA criteria document that underwent peer
review.
2. EPA responded to this comment from Reviewer 1 in greater
detail in Section 2.7. In short, EPA considered the
bioaccumulative nature and persistence of PFOA in aquatic
systems, in combination with the documented recovery times
of pollutants with similar chemical attributes (Lemly 1997;
Gergs et al. 2016), to set a reasonable and protective
exceedance frequency for tissue-based PFOA criteria.
Furthermore, three of the remaining Expert Peer Reviewers
were supportive of the 10-year exceedance frequency for the
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.2. The Technical Approach I soil to l)eri\e (ho Dral'l Criterion lor I'l-'OA
Ue\ iewer
('ommenls
KIW Response

5. It is unclear if the EPA-calculated Effective
Concentration 10% (ECio) values are supported;
additional details on the modeling and the
variability and fit of each ECio model need to be
provided.
• Is it consistent with the protection of freshwater
aquatic life from acute, chronic, and
bioaccumulative effects?
The criteria derived are aimed at protecting aquatic life
(e.g., fish, invertebrates) from the direct acute and chronic
toxicity of PFOA in water. Generally, the values applied
are protective and are generally similar to protective values
derived by other regulatory organizations and independent
(i.e., academic, private sector) scientists. Although, as
based on my comments, I believe there is room for
improvement. The criteria derived for tissues attempt to
provide criteria that take into account bioaccumulation so
that measurements in tissue can be interpreted with respect
to the potential for potential effects; however, the
uncertainty with the tissue criteria is high. The water and
tissue criteria are not intended protective of
bioaccumulative effects that may affect higher trophic
levels, such as wildlife that may consume aquatic life.
tissue-based PFOA criteria, with the remaining Reviewer (i.e.,
Reviewer 3) stating it was difficult to comment on the tissue-
based criteria frequencies.
3. Please see EPA's response to Reviewer l's comments below
to Charge Question 2.6 regarding the generation of tissue-
based criteria. EPA acknowledges the inherent uncertainties
that are present with the use of bioaccumulation factors (BAF)
to derive tissue criteria. EPA screened the BAF literature in a
manner consistent with the evaluation criteria outlined in
Burkhard (2021). Additionally, the use of BAFs to derive
tissue criteria is consistent with previously derived criteria for
both aquatic life (i.e., 2016 Selenium Aquatic Life Criterion
for Freshwaters; U.S. EPA 2016a) and human health (U.S.
EPA 2000). Given the potential bioaccumulation of PFOA
through the aquatic food web, tissue-based criteria were
needed to ensure the protection of aquatic life to PFOA
exposures.
4. Please see EPA's response to Reviewer l's comments below
to Charge Question 2.3 regarding the New Approach Method
(NAM)-generated acute saltwater benchmark derived in
Appendix K of the draft PFOA Aquatic Life Criteria
document. EPA added text to ensure uncertainty surrounding
the acute saltwater benchmark is clearly stated.
5. Concentration-response (C-R) model type and figures of the
C-R data with the fitted model are displayed in Appendices
A.2 and C.2 for those tests that were used to quantitatively
derive the PFOA criteria and were among the four most
sensitive acute and chronic genera, respectively. Figures of
the fitted C-R models in Appendices A.2 and C.2 are
displayed with 95% confidence bands (relative to the Y-axis)
allowing for a visual display of variability in organisms
responses. Reviewer 1 further notes their review focused on
"key portions of the Draft of the Aquatic Life Water Quality
Criterion" and may have missed the C-R modeling results
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.2. The Technical Approach I soil to l)eri\e (ho Dral'l Criterion lor I'l-'OA
Ue\ iewer
Com nicnls
KIW Response


presented in appendices A.2 and C.2 as well as the modeling
methods presented in Appendix J. Reviewer 5, noted "h'.l'A's
approach to fitting C-R data using the drc package in R is, in
my opinion, state of the art"
EPA thanks Reviewer 1 for describing the relative similarity between
the draft PFOA criteria and protective thresholds from regulatory
organizations and independent scientists.
As noted in EPA's response to this comment above (item # 3 from the
previous list), the draft PFOA tissue criteria are intended to protect
aquatic life from PFOA exposures. EPA derived the tissue criteria by
translating the chronic water column criterion into tissue
concentrations through application of BAFs.
There were insufficient data to derive tissue criteria directly from
empirical toxicity tests with tissue-based exposure concentrations.
However, the draft PFOA Aquatic Life Criteria document contained
an evaluation of the tissue-based criteria relative to the limited tissue-
based toxicity, concluding, "these studies do not provide any evidence
that the PFOA tissue-based criteria are not protective of aquatic
species." Furthermore, aquatic life tissue criteria are intended to be
protective of aquatic life; aquatic -dependent wildlife taxa fall outside
the scope of the current draft PFOA Aquatic Life Criteria document.
EPA intends to review PFOA data focused on aquatic-dependent
wildlife in the future and to potentially derive separate aquatic-
dependent wildlife criteria for PFOA, if the data support the derivation
of such criteria.
Reviewer
2
Yes, the technical approach used by the EPA to derive the
criterion is logical and defensible. The approach is also
clearly laid out in the document. Dividing the 5th centile of
the acute GSD by 2 is sufficiently conservative to ensure
the protection of 95% of species, based on the data
Thank you for the comment noting the approach used in the draft
PFOA criteria document was "logical and defensible." EPA agrees
with Reviewer 2 that use of the Brachionus Acute to Chronic Ratio
(ACR) to derive the Final ACR (FACR) was a valid approach that
resulted in a protective chronic freshwater column criterion in the
draft that underwent peer review. For clarity, EPA notes the FACR
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currently available. The use of the ACR from Brachionus
calyciflorus to construct a chronic GSD is a valid approach,
along with being the most conservative option.
Yes, I think the science supports the EPA's conclusions.
However, there appears to be several studies that were not
considered by the EPA. I have listed these studies below.
Yes, I think the approach taken by the EPA is sufficiently
conservative to be protective of freshwater aquatic life
from acute, chronic, and bioaccumulative effects based on
the data that was available at the time. It was a good idea to
evaluate the influence on non-North American species on
the derivation of the criteria.
did not construct the chronic GSD (as suggested by Reviewer 2) but
was used to transform the Final Acute Value (FAV) to the Final
Chronic Value (FCV), which is a valid approach that is consistent
with the 1985 Guidelines and results in a protective chronic criterion.
Addition of new chronic toxicity data in the updated draft PFO A
criteria document allowed for the calculation of a draft chronic
freshwater criterion magnitude directly from the chronic GSD rather
than basing the magnitude on the FAV transformed by the FACR as
was done in the draft PFOA criteria document that underwent peer
review.
Thank you for reiterating that the science supports EPA's conclusion.
All studies provided by Reviewer 2 (and all other reviewers) were
reviewed to ensure they met data quality objectives outlined by the
1985 Guidelines, EPA 850 test guidelines, etc. and were included in
the PFOA criteria document accordingly. EPA agrees that "/Y was a
good idea to evaluate the influence on non-North American species on
the derivation of the criteria." Including non-North American species
in the acute and chronic criteria derivation did not markedly affect the
draft criteria magnitudes and ensures the fullest, high-quality dataset
available is used to represent the thousands of untested aquatic taxa
present in U.S. ecosystems when deriving the PFOA criteria.
Reviewer
3
• Is the technical approach used to derive the
criterion logical?
Why did EPA derive the LC50 for Chydorus when an EC50
was provided by the authors; however, accepted the EC50s
for the two mussel species? This is an inconsistency.
• Does the science support the conclusions?
See response immediately below
Chydorus was the most sensitive acute genus. EPA calculated a C-R
model because C-R data were available (provided by authors to EPA
on 7/16/2020). Per the draft PFOA Aquatic Life Criteria document:
"Toxicity values, including LC50 and ECw values, were
independently calculated from the data presented in the toxicity
studies meeting the inclusion criteria described above when
adequate concentrations-response data were published in the study
or could be obtained from authors. When concentration-response
data were not presented in toxicity studies, concentration-response
data were requested from study authors to independently calculate
toxicity values. In cases where study authors did not respond to
EPA's request for data or were unable to locate concentration-
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• Is it consistent with the protection of freshwater
aquatic life from acute, chronic, and
bioaccumulative effects?
Overall, the draft criteria are in agreement with other
thresholds generated using the species/genus sensitivity
distributions; which seems like a more robust approach
given data are not restricted to a subset of studies (albeit
most sensitive). Although new data should be evaluated
and potentially incorporated into these criteria calculations
it is unclear if those data would alter these currently drafted
thresholds.
response data, the toxicity values were not independently calculated
by EPA, and the reported toxicity values were retained for criteria
deviation."
EC50 values for the two mussel species (i.e., L. recta andL.
siliquoidea) were not calculable because C-R data were not available
in the publication and could not be provided by authors. For both
species, Appendix A.2 of the draft PFOA criteria document that
underwent peer review stated, the EPA-Calculated LC50S were "Not
calculable, concentration-response data not available."
Thank you for describing your overall confidence in the PFOA criteria
given the relative similarities between the draft PFOA criteria and
thresholds put forth by other jurisdictions. All studies provided by
Reviewer 3 (and all other reviewers) were reviewed to ensure they
met data quality objectives outlined by the 1985 Guidelines, EPA 850
test guidelines, etc., and were included in the PFOA criteria document,
as appropriate.
Reviewer
4
This EPA report provides a critical review of toxicity data
identified in EPA's literature search for PFOA, including
the anionic form (CAS No. 45285-51-6), the acid form
(CAS No. 335-67-1), and the ammonium salt (CAS No.
3825-26-1). It quantifies the toxicity of PFOA to aquatic
life, and provides criteria intended to protect aquatic life
from the acute and chronic toxic effects of PFOA. The
detailed assessment is as follows:
• These criteria have been derived using robust
methods and the best available toxicity data on
aquatic life.
• The approach used to derive the draft criterion for
PFOA is very logical and consistent with the
protection offered by acute and chronic aquatic life
Thank you for your comment and thank you for describing specific
sections of the draft PFOA criteria document in detail. Responses to
the comments pertaining to the tissue-based criteria made by
Reviewer 4 are described in response to charge question 2.5.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
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criteria derived using empirical data, as prescribed
in the 1985 Guidelines.
•	Exclusion and inclusion criteria are appropriately
discussed in the context of the toxicological data
reported in the literature and provide additional
evidence on the selection of toxicity data criteria
development.
•	With limited toxicity datasets to North American
resident species, non-North American resident
species served as taxonomically-related surrogate
test organisms. For example, Oryzias latipes is a
common ecotoxicity test species that served as a
surrogate for untested fish species residing in North
America.
•	The acute measures of effect on aquatic organisms
selected included the lethal concentration (LC50),
effect concentration (EC50), or inhibitory
concentration (IC50) estimated to produce a specific
effect in 50 percent of the test organisms
•	The endpoint for chronic exposures incorporated the
effect concentration estimated to produce a chronic
effect on survival, growth, or reproduction in 10
percent of the test organisms (EC10). This approach
has been also consistent with the harmonized
guidelines from OECD and the generally preferred
effect level for countries such as Canada, Australia,
and New Zealand.
•	Reported (No Observed Effect Concentrations)
(NOECs) and (Lowest Observed Effect
Concentrations) (LOECs) were only used for the
derivation of a chronic criterion when a robust EC 10
could not be calculated for the genus.
•	Furthermore, EPA independently calculated these
toxicity values if sufficient raw data were available

13

for EPA to conduct statistical analyses. EPA's
independently-calculated toxicity values were used
preferentially, where available.
• EPA developed protective tissue-based criteria
through a bioaccumulation factor approach. This
was based on the application of evaluation criteria
for screening bioaccumulation factors (BAFs).
• The freshwater Final Acute Value (FAV) for PFOA
was calculated as 91.34 mg/L and freshwater acute
criterion water column magnitude (criterion
maximum concentration, CMC), as 46 mg/L PFOA,
using the procedures described in the 1985
Guidelines. This values is expected to be protective
of 95% of freshwater genera potentially exposed to
PFOA under short-term conditions of one-hour of
duration, if the one-hour average magnitude is not
exceeded more than once in three years.
• Toxicity data were available for only two families,
an estuarine/marine FAV could not be calculated to
derive an estuarine/marine acute criterion. Further
benchmark was developed using predictive
approach and discussed later in this document.
• Tissue-based criteria were also developed using
comprehensive methods and assessment is provided
as response to charge Question 5.

Reviewer
5
The overall approach to derive criteria for PFOA is
logical... except for the use of only the 4 most sensitive
endpoints and then a model was fitted (unspecified, I
believe) to obtain the 5% most sensitive species (in
general). I am not familiar with this as an approach as I
have not seen other scientists use this and, instead, I have
more commonly seen the application of a species
Thank you for your comment stating the "overall approach to derive
the criteria for PFOA is logical.'" Reviewer 5 commented that a model
was fit to the four most sensitive endpoints (i.e., four most sensitive
GMAVs and GMCVs) to derive the criteria, which was not the case.
Instead, derivation of the acute and chronic criteria followed long-
established methods outlined in the 1985 Guidelines. The established
criteria calculation outlined in the 1985 Guideline uses a log-
14

sensitivity distribution based on more data and usually
following an s-shape. Indeed, many well-cited papers on
toxicity thresholds and criteria have used this approach. I
suspect EPA has justification for the approach used in the
document and that it is well-supported. I would suggest
adding any details, beyond just citing the 1985 guidelines,
that supports a focus on just the 4 most sensitive toxicity
endpoints for the criteria development. My apologies if this
information is in the document and I missed it. .
One point of clarification is needed in the explanation of
the regression analysis (p. 64). The document states:
"When LOECs and NOECs were used, a Max Aceept. Tox
Cone. (MATC) was calculated, with is the geometric mean
of the NOEC and LOEC. For the calculation of chronic
criterion. Doint estimates were selected for use as the
measur of effect in favor of the MATCs..." - WHAT IS
MEANT BYT "POINT ESTIMATES"? Isn't the LOEC or
NOEC a point estimate? This needs to be clarified here
(and for PFOS).
On p. 66 - I also recall that in some cases EPA obtained
data from plots using web plot digitizer software. If I am
correct, this should be explained on this page.
One point worth mentioning with regard to the technical
approach is that I think EPA was correct to consider non-
North American resident species in developing the criteria.
While I can understand why some scientists feel strongly
about focusing on native species, I also cannot think of a
clear example of widely different chemical tolerances
among species from different countries. Sure, organisms
from contaminated environments are likely to differ
compared to the same organisms (species) from
uncontaminated areas but barring this, it seem sensitivity to
triangular fit to determine the 5 th centile of a GSD. Acute and chronic
GSDs (which included all quantitatively acceptable toxicity data) were
presented in the Effect Analysis section of the draft PFOA Aquatic
Life Criteria document. When there are less than 59 genera in a GSD,
the 5th centile is inherently based on the four most sensitive genera,
with the remaining tests only influencing the FAV through the in
the calculation. Please see the excerpt from the 1985 Guidelines below
for further explanation.
"Order the GMAVsfrom high to low.
L. Assign ranks, R, to the GMA Vs from "1 "for the lowest to
"N" for the highest. If two or more GMA Vs are identical,
arbitrarily assign them successive ranks.
M. Calculate the cumulative probability, P, for each
GMAV as R/(N+1).
N. Select the four GMAVs which have cumulative
probabilities closest to 0.05 (if there are less than 59
GMAVs, these will always be the four lowest GMAVs)."
Additionally, research conducted since the 1985 Guidelines were
published has continued to suggest use of a log-triangular distribution
to estimate an HCs from sensitivity distributions is appropriate.
USEPA (2011) concluded:
"Judging by bias at small sample sizes, distributions on
log-transformed data (normal, logistic, triangular,
Gumbel) generally outperformed distributions on
untransformed data (Pareto, Weibull, and Burrni) and of
the former, the log-normal, log-logistic, and log-triangular
showed very similar performance."
Lowest Observed Effect Concentrations (LOEC) and No Observed
Effect Concentrations (NOEC) are determined through hypothesis-
based testing. A LOEC is the lowest test concentration where test
organism responses were statistically different from responses in the
control organisms. A NOEC is the highest test concentration where
15

chemicals is not geographically determinated (again,
barring extremes).
Additionally, I think using the EC 10 makes sense for PFAS
chronic criteria and perhaps other chemicals as well. That
said, I can't say that using a 50% effect level for acute
toxicity/exposures makes sense. To me, using an EC20 or
LC20 for acute would be more reasonable. As I understand
it, the current approach divides the calculated FAVs by 2.0
to further ensure protection. Here again, it would seem
easier and more straight-forward to use the EC20 or LC20.
Perhaps dividing the FAV by 2.0, however, commonly
results in a low threshold (like an LC20, for example). If
this is the case, it would be worth EPA mentioning to give
some sense of magnitude to what could be considered an
arbitrary "safety factor" of 2.0. What highlighted this issue
for me was the estuarine mussel species where there was a
27% effect (malformations) at 0.0001 mg PFOA/L but
because an EC50 could not be determined, EPA chose to
use the highest concentration of 1 mg/L. If I were in charge
of managing resources in an estuary, I can't say I'd have
much confidence in that 1 mg/L value. Or at least, I would
be very uncomfortable. Having said all this, I understand
that the frequency and duration of environmental exposures
would make is such that the acute and chronic criteria
would be protective but please see my comments below
with regard to frequency and duration of exposure.
test organism responses were not statistically different from responses
in the control organisms. A point estimate is an LCX or ECX value
determined through regression analysis. The PFOA Aquatic Life
Criteria document now includes a parenthetical indicating what a
point estimate is, stating "Regression analysis was used preferentially
to characterize a concentration-effect relationship and to estimate
concentrations at which chronic effects are expected to occur (i.e.,
Point Estimates)" Additionally, footnote has been added to the first
mention of webplotdigitizer in the draft PFOA criteria document
describing its general use and providing a link to the application.
EPA agrees that "it was correct to consider non-North American
resident species in developing the criteria." Including non-North
American species in the acute and chronic criteria derivation did not
markedly affect the draft criteria magnitudes and ensures the fullest,
high-quality dataset available is used to represent the thousands of
untested aquatic taxa present in U.S. ecosystems when deriving the
PFOA criteria.
Thank you for your comment "the EC 10 makes sense for PFAS
chronic criteria and perhaps other chemicals as well." EPA notes that
use of a 10% effect concentration for deriving chronic criteria
magnitudes is also consistent with the harmonized guidelines from
OECD and the generally preferred effect level for countries such as
Canada, Australia, and New Zealand (CCMC 2007; Warne et al.
2018).
EPA's PFOA FAV was derived following a long-established approach
described in the 1985 Guidelines. Briefly, the PFOA FAV is based on
the 5th centile of a GSD, which was comprised of GMAVs calculated
from LC50 values. Consistent with the 1985 Guidelines, the FAV was
then divided by 2.0 to calculate the criterion maximum concentration
(CMC). Dividing the FAV by 2.0 ensures the CMC represents a
concentration that will not affect a large portion of sensitive
organisms. This is based on the established analyses demonstrating
that the ratio between LC50 values and corresponding LCi0W values
16

(e.g., LCo - LCio) is typically close to 2.0. Please see the excerpt from
the 1985 Guidelines below for further explanation,
"the Criterion Maximum Concentration is now equal to one-half the
Final Acute Value. The Criterion Maximum Concentration is
intended to protect 95 percent of a group of diverse genera, unless a
commercially or recreationally important species is very sensitive.
However, a concentration that would severely harm 50 percent of
the fifth percentile or 50 percent of a sensitive important species
cannot be considered to be protective of that percentile or that
species. Dividing the Final Acute Value by 2 is intended to result in
a concentration that will not severely adversely affect too many of
the organisms."
Additionally, EPA thanks Reviewer 5 for comments regarding the
study on the,'Adaptation of the bivalve embryotoxicity assay for the
high throughput screening of emerging contaminants in Mytilus
galloprovineialis" by Fabbri et al. (2014). Fabbri et al. (2014) did not
report an acute EC50 for M. galloprovincialis from exposure to PFOA
(or PFOS) because it could not be calculated. The percent adverse
effect at the highest concentration of PFOA tested (1 mg/L) did not
exceed a 50% reduction in % Normal D-larvae relative to the negative
control treatment, only producing about a 37% reduction (calculated
from 83% Normal D-larvae in negative control and 52% Normal D-
larvae in the 1 mg/L treatment; determined from visual inspection of
Figure 4 of Fabbri et al. 2014). EPA's decision to use the acute value
of > 1 mg PFOA/L for this study in the draft criteria document that
underwent peer review was consistent with the 1985 Guidelines.
Specifically,
Under Section IV.E.2. - "The result of a [acute] test with embryos
and larvae of barnacles, bivalve molluscs (clams, mussels, oysters,
and scallops), sea urchins, lobsters, crabs, shrimp, and abalones,
should be the 96-hr EC50 based on the percentage of organisms with
incompletely developed shells plus the percentage of organisms
killed. If such an EC50 is not available from a test, the lower of the
96-hr EC50 based on the percentage of organisms with incompletely
17

developed shells and the 96-hr LC50 should be used in place of the
desired 96-hr EC50. If the duration of the test was between 48 and
96 hr, the EC50 or LC50 at the end of the test should be used. "
And, under Section IV.E.5.- "If the tests were conducted properly,
acute values reported as "greater than " values and those which are
above the solubility of the test material should be used, because
rejection of such acute values would unnecessarily lower the Final
Acute Value by eliminating acute values for resistant species."
Thus, the appropriate acute value for entry into Table B. 1 of the draft
criteria document that underwent peer review for Fabbri et al. (2014)
was the 48-h EC50 of > 1 mg/L PFOA. While the study clearly
demonstrates an effect of PFOA on embryo development, the fact that
a 50% reduction in % Normal D-larvae was not reached in the test
resulted in a "greater than" EC50 value for the acute effect
concentration; which is consistent with the authors being unable to
determine an EC50. Furthermore, the authors note PFOS and PFOA
did not cause an increase in the percentage of malformations, but
rather a reduction in number of fully developed D-larvae, suggesting
delayed development effects rather than viability. NOECs, LOECs,
and Maximum Acceptable Toxicant Concentrations (MATC) from
acute tests are not used in the acute GSD for the derivation of acute
criteria. Furthermore, the short 48-h duration of the test excludes its
consideration in the development of a chronic criterion
estuarine/marine criterion or benchmark.
The Mytilus galloprovincialis SMAY was updated to 17.58 mg/L in
the revised PFOA criteria document following incorporation of new
data published by Hayman et al. (2021). Briefly, Hayman et al. (2021)
exposedM galloprovinvialis embryos to PFOA for 48-hours and
determined an EC50 of 9.98 mg/L (endpoint = normal and surviving).
EPA fit a model to the concentration-response data and determined an
EPA-calculated EC50 of 17.58 mg/L from this test. The acute value
from Hayman et al. (2021) was used preferentially over the acute
value determined by Fabbri et al. (2014) to calculate the M
18

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.2. The Technical Approach I soil to l)eri\e (ho Dral'l Criterion lor I'l-'OA
Ue\ iewer
(omnienls
KIW Response


galloprovinvialis SMAV in the revised PFOA draft criteria. Results
from Fabbri et al. (2014) were not used in the M. galloprovinvialis
SMAV calculation because the EC50 was a relatively low "greater
than" value, while Hayman et al. (2021) provided a definitive EC50
value.
Finally, thank you for reiterating how "the frequency and duration of
environmental exposures would make is such that the acute and
chronic criteria would be protective." EPA has provided further
responses to Reviewer 5's comments on the frequency and duration
components of the PFOA criteria below. EPA also notes M.
galloprovincialis occurs in estuarine/marine habitats and the draft
PFOA document did not contain acute or chronic estuarine/marine
criteria but did include an estuarine/marine acute benchmark.
19

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
.2.3 Please comment on the approach used to derive the draft acute estuarine/marine benchmark for PFOA. Given the limited
estuarine/marine test data available, a new approach method was used to support the derivation of an acute
estuarine/marine benchmark to provide states and tribes with a protective value. Please provide detailed comments.
• Is the technical approach used to derive the benchmark logical?
• Does the science support the conclusions?
• Is it consistent with the protection offered by acute estuarine/marine aquatic life criteria derived using empirical data, as
prescribed in the 1985 Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic
Organisms and Their Uses'?
2.3. The Technical Approach used to l)ori\e (ho Dral'l Acute Kstuarine/Marine Benchmark lor PI-'OA
Uo\ iower
C om mollis
FPA Response
Reviewer
1
• Is the technical approach used to derive the benchmark
logical?
The derivation of the acute marine benchmarks (FAV and Criterion
Maximum Concentration (CMC)) using the New Approach Method
(NAM) is highly uncertain, and I would recommend this analysis
not be included as in this document. I do not feel that the analysis
and subsequent criteria have high confidence for use in a regulatory
application. I understand that similar analyses with other chemicals
have about a 90% probability of the predicted effect value being
within a factor of 5 of the actual value (Raimondo et al., 2010 -
cited in document). Given the calculated CMC (3.4 mg/L), this
implies the CMC has about a 90% probability of being within 0.68
to 17 mg/L. If the NAM approach stays in the document, this
uncertainty and range of values should be acknowledged in the
discussion.
I would rather see tentative or provisional acute criterion developed
from the limited empirical marine acute data highlighted in
Appendix B and other recently published marine acute data. I place
higher confidence in empirical data (even if limited to a few
studies) and would suggest EPA emphasize it in addition to or in
place of the values calculated by the NAM.
Thank you for your comment regarding uncertainties
associated with the derivation of the acute estuarine/marine
benchmark using a NAM. As discussed in Appendix K, ICE
models have undergone extensive peer review and their use
has been recommended for multiple similar applications,
including direct toxicity estimation for endangered species
(NRC 2013, Willming et al. 2016) and the development of
SSDs (Awkerman et al. 2014, Bejarano et al. 2017, Dyer et al.
2006, Dyer et al. 2008, Raimondo et al. 2010, Raimondo et al.
2020).
EPA has noted and quantified the epistemic uncertainty
associated with the use of Web ICE-derived data to the extent
possible in Appendix K, and further, has characterized the
value as a "benchmark" to differentiate it from criteria values
that have been derived solely with empirical test data from the
chemical for which the criteria is being developed. Additional
text has been added to compare the derived benchmarks to the
available empirical test data with estuarine/marine species.
Further, additional empirical estuarine/marine toxicity test
data have become available since the benchmark values were
first derived. The benchmarks have been revised to
incorporate the additional acceptable empirical data. EPA
continued to integrate new acceptable empirical data as they
20

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.3. The Technical Approach used to l)eri\e (ho Dral'l Acule Ks( u a rine/Marine Benchmark lor PI'OA
Ue\ iewer
C om mollis
KIW Response

I am hopeful that as new toxicity information on marine species are
developed, these values can be supplanted with a proper and robust
criteria calculation. If such a future analysis is possible, it should be
noted.
• Does the science support the conclusions?
See above comment.
• Is it consistent with the protection offered by acute
estuarine/marine aquatic life criteria derived using
empirical data, as prescribed in the 1985 Guidelines for
Deriving Numerical National Water Quality Criteria for
the Protection of Aquatic Organisms and Their Uses?
The approach seems to be consistent with the approach in the 1985
guidelines. As noted above, the uncertainty with regards to the
predictive capability of the interspecies correlations should be
acknowledged quantitatively.
became available until the benchmark values were derived as
final values.
Thank you for your comment noting that the approach used to
derive the acute estuarine/marine PFOA benchmark is
consistent with the 1985 Guidelines. As noted above,
additional text has been added to further summarize and
clarify uncertainties associated with derivation of the
benchmark value.
Reviewer
2
The technical approach using Web-ICE to determine an acute
benchmark for estuarine/marine species is logical. The science has
shown that Web-ICE can effectively be used to derive effect
measures for additional species using species for which data is
available. I think the approach taken by EPA has included sufficient
conservatism to address the relatively large amount of uncertainty
around the acute toxicity of PFOA to estuarine and marine species.
The proposed acute benchmark for estuarine and marine species is
an order of magnitude lower than the acute benchmark for
freshwater species, which I think underscores the conservatism used
by EPA in determining an acute benchmark for estuarine and
marine species. That said, the benchmark should be used cautiously
due to the relatively large amount of uncertainty and effort should
Thank you for your comment noting that the approach used to
derive the acute estuarine/marine PFOA benchmark is logical
and sufficiently conservative to account for uncertainties
associated with data limitations. EPA agrees that additional
estuarine/marine test data focused on PFOA would provide
support for the derived benchmark value, or enable
development of a criterion.
21

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.3. The Technical Approach used to Dome (ho Dral'l Acule Ks( u a rine/Marine Benchmark lor PI-'OA
Ue\ iewer
C om mollis
FPA Response

be made to generate acute and chronic toxicity data for PFOA on
estuarine and marine species, particularly fish.

Reviewer
3
• Is the technical approach used to derive the benchmark
logical?
See comment immediately below
• Does the science support the conclusions?
The PFOA - LOEC reported for Mytilus in Fabbri et al. 2014 is
0.1 jj.g/L; in the draft criteria this is listed as >1 mg/L. The
justification provided for dismissing this effect given 50% of the
test organisms did not experience is not compelling.
• Is it consistent with the protection offered by acute
estuarine/marine aquatic life criteria derived using
empirical data, as prescribed in the 1985 Guidelines for
Deriving Numerical National Water Oualitv Criteria for the
Protection of Aquatic Organisms and Their Uses?
No, this is a new approach; however, it follows the spirit of the
1985 guidelines.
Thank you for your comment regarding the study on the,
"Adaptation of the bivalve embryotoxicity assay for the high
throughput screening of emerging contaminants in Mytilus
galloprovincialis" by Fabbri et al. (2014). Fabbri et al. (2014)
did not report an acute EC50 for M. galloprovincialis from
exposure to PFOA (or PFOS) because it could not be
calculated. The percent adverse effect at the highest
concentration of PFOA tested (1 mg/L) did not exceed a 50%
reduction in % Normal D-larvae relative to the negative
control treatment, only producing about a 37% reduction
(calculated from 83% Normal D-larvae in negative control
and 52% Normal D- larvae in the 1 mg/L treatment;
determined from visual inspection of Figure 4 of Fabbri et al.
2014). EPA's decision to use the acute value of > 1 mg
PFOA/L for this study in the draft PFOA criteria document
that underwent peer review was consistent with the 1985
Guidelines. Specifically,
Under Section IV.E.2. - "The result of a [acute] test with
embryos and larvae of barnacles, bivalve molluscs (clams,
mussels, oysters, and scallops), sea urchins, lobsters,
crabs, shrimp, and abalones, should be the 96-hr EC50
based on the percentage of organisms with incompletely
developed shells plus the percentage of organisms killed.
If such an EC50 is not available from a test, the lower of the
96-hr EC50 based on the percentage of organisms with
incompletely developed shells and the 96-hr LC50 should
be used in place of the desired 96-hr EC50¦ If the duration
of the test was between 48 and 96 hr, the EC50 or LC50 at
the end of the test should be used. "
And, under Section IV.E.5.- "If the tests were conducted
properly, acute values reported as "greater than " values
22

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.3. The Tcchniciil Approach used to Deme (ho Dnil'l Acule KsUi:irine/M:irine lienchniiirk lor PI-'OA
Ue\ iewer
C om mollis
FPA Response

and those which are above the solubility of the test
material should be used, because rejection of such acute
values would unnecessarily lower the Final Acute Value by
eliminating acute values for resistant species."
Thus, the appropriate acute value for entry into Table B. 1 of
the draft criteria document that underwent peer review for
Fabbri et al. (2014) was the 48-h EC50 of > 1 mg/L PFOA.
While the study clearly demonstrates an effect of PFOA on
embryo development, the fact that a 50% reduction in %
Normal D-larvae was not reached in the test resulted in a
"greater than" EC50 value for the acute effect concentration;
this is consistent with the authors being unable to determine
an EC50. Furthermore, the authors note that PFOS and PFOA
did not cause an increase in the percentage of malformations,
but rather a reduction in number of fully developed D-larvae,
suggesting delayed development effects rather than viability.
NOECs, LOECs, and MATCs from acute tests are not used in
the acute GSD for the derivation of acute criterion.
Furthermore, the short 48-h duration of the test excludes its
consideration in the development of a chronic criterion
estuarine/marine criterion or benchmark.
In response to Reviewer 3 noting the apparent sensitivity of
Mytilus galloprovincialis (with a reported LOEC of 0.1
(.ig/L). EPA notes The Mytilus galloprovincialis SMAY was
updated to 17.58 mg/L in the revised PFOA criteria document
following incorporation of new data published by Hayman et
al. (2021). Briefly, Hayman et al. (2021) exposed M
galloprovinvialis embryos to PFOA for 48-hours and
determined an EC50 of 9.98 mg/L (endpoint = normal and
surviving). EPA fit a model to the concentration-response
data and determined an EPA-calculated EC50 of 17.58 mg/L
from this test. The acute value from Hayman et al. (2021) was
used preferentiallv over the acute value determined by Fabbri
23

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.3. The Tcchniciil Approach used to l)eri\e (ho Dral'l Acule Ks(ii;irine/M:irine lienchniiirk lor PI-'OA
Ue\ iewer
C om mollis
FPA Response

et al. (2014) to calculate the M. galloprovinvialis SMAY in
the revised PFOA draft criteria. Results from Fabbri et al.
(2014) were not used in the M. galloprovinvialis SMAY
calculation because the EC50 was a relatively low "greater
than" value, while Hayman et al. (2021) provided a definitive
EC50 value.
Reviewer
4
• EPA applied The ICE model predictions to supplement the
available test dataset to help fill missing MDRs and allow
the derivation of acute estuarine/marine benchmark
recommendations for aquatic life using procedures
consistent with those in the 1985 Guidelines. Total of 3104
datapoints from 398 models were evaluated.
• The draft acute benchmark for estuarine/marine aquatic life
is lower than the recommended acute freshwater criterion
(46 mg/L), suggesting that estuarine/marine species may be
more acutely sensitive to PFOA. According to Hayman et
al., 2021, marine species, compared to freshwater, may have
a higher sensitivity to PFOA.
• There are two more studies published, the toxicity values for
marine/estuarine species.
o Stuart L. Simpson, Yawen Liu, David A. Spadaro,
Xinhong Wang; Rai S. Kookana and Graeme E.
Batley Chronic effects and thresholds for estuarine
and marine benthic organism exposure to
perfluorooctane sulfonic acid (PFOS)-contaminated
sediments: Influence of organic carbon and
exposure routes
https://doi.ora/10.1016/i.scitotenv.2021.146008
o Nicholas T Hayman , Gunther Rosen , Marienne A
Colvin , Jason Conder , Jennifer A Arblaster
Aquatic toxicity evaluations of PFOS and PFOA
for five standard marine endpoints.
https ://doi .ore/10.1016/i .chemosphere .2021.129699
Thank you for your comment and for summarizing the
derivation of the draft acute estuarine/marine benchmark for
PFOA in detail. Furthermore, Reviewer 4 reiterated the draft
PFOA estuarine/marine benchmark is lower than the draft
acute freshwater PFOA criterion, while noting how this is
consistent with results reported by Hayman et al. (2021).
Thank you for providing additional references. All studies
provided by Reviewer 4 (and all other reviewers) were
reviewed to ensure they met data quality objectives outlined
by the 1985 Guidelines, EPA 850 test guidelines, etc., and
were included in the PFOA criteria document, as appropriate.
This includes recalculation of the acute estuarine/marine
benchmark, as suggested by Reviewer 4, to include suggested
estuarine/marine studies.
24

It is recommended to assess the quality of the toxicity data on
marine/estuarine species and recalculate estuarine criteria
based on this recently available information.

Reviewer
5
The most sensitive estuarine/marine species was Mytilus g. in the
study by Fabbri et al. (2014). EPA chose to use 1 mg/L PFOA
because there was not a 50% effect level even at the highest tested
concentration (1 mg/L). HOWEVER, there was 27% effect at the
LOEC (0.0001 mg/L). Is this not problematic? If I were concerned
about mussels or other bivalves in an estuary, I don't think I would
hang my hat on a 1 mg/L PFOA concentration given there was a
27% decrease in normal D-larvae at a concentration several orders
of magnitude below that. This raises the issue of why EPA is using
a 50% effect level for acute criteria - this seems excessively high,
doesn't it? EPA justified using the ECio for chronic criteria so it
seems reasonable to use the EC/LC20 for acute. A 50% effect, if it
occurs, is likely to manifest as ecologically relevant for any
species... 20% may not be protective depending on the species and
endpoint. As mentioned before, I understand that there is a
frequency/duration element to all the criteria but from a functional
standpoint, I don't see how the ferequency and duration elements
are helpful because nobody collects or reports environmental data
on a relevant temporal scale (every hour; 4-day running average??).
See below for more on frequency and duration.
Given the data, I believe the new approach methods based on
WEB-ICE are appropriate. The estimation tool has been in
development and used for a considerable length of time and several
publications have supported it's use. Of course it would be better to
have more data but, again, given the lack of data for
estuarine/marine species, the WEB-ICE approach is likely the best
available.
Thank you for your comment regarding the study on the,
"Adaptation of the bivalve embryotoxicity assay for the high
throughput screening of emerging contaminants in Mytilus
galloprovincialis" by Fabbri et al. (2014). Fabbri et al. (2014)
did not report an acute EC50 for M. galloprovincialis from
exposure to PFOA (or PFOS) because it could not be
calculated. The percent adverse effect at the highest
concentration of PFOA tested (1 mg/L) did not exceed a 50%
reduction in % Normal D-larvae relative to the negative
control treatment, only producing about a 37% reduction
(calculated from 83% Normal D-larvae in negative control
and 52% Normal D- larvae in the 1 mg/L treatment;
determined from visual inspection of Figure 4 of Fabbri et al.
2014). EPA's decision to use the acute value of > 1 mg
PFOA/L for this study in the draft PFOA criteria document
that underwent peer review was consistent with the 1985
Guidelines. Specifically,
Under Section IV.E.2. - "The result of a [acute] test with
embryos and larvae of barnacles, bivalve molluscs (clams,
mussels, oysters, and scallops), sea urchins, lobsters,
crabs, shrimp, and abalones, should be the 96-hr EC50
based on the percentage of organisms with incompletely
developed shells plus the percentage of organisms killed.
If such an EC50 is not available from a test, the lower of the
96-hr EC50 based on the percentage of organisms with
incompletely developed shells and the 96-hr LC50 should
be used in place of the desired 96-hr EC50¦ If the duration
of the test was between 48 and 96 hr, the EC50 or LC50 at
the end of the test should be used. "
25

And, under Section IV.E.5.- "If the tests were conducted
properly, acute values reported as "greater than " values
and those which are above the solubility of the test
material should be used, because rejection of such acute
values would unnecessarily lower the Final Acute Value by
eliminating acute values for resistant species."
Thus, the appropriate acute value for entry into Table B.l of
the draft PFOA criteria document that underwent peer review
for Fabbri et al. (2014) was the 48-h EC50 of > 1 mg/L PFOA.
While the study clearly demonstrates an effect of PFOA on
embryo development, the fact that a 50% reduction in %
Normal D-larvae was not reached in the test resulted in a
"greater than" EC50 value for the acute effect concentration;
this is consistent with the authors being unable to determine
an EC50. Furthermore, the authors note PFOS and PFOA did
not cause an increase in the percentage of malformations, but
rather a reduction in number of fully developed D-larvae,
suggesting delayed development effects rather than viability.
NOECs, LOECs, and MATCs from acute tests are not used in
the acute GSD for the derivation of acute criterion.
Furthermore, the short 48-h duration of the test excludes its
consideration in the development of a chronic criterion
estuarine/marine criterion or benchmark.
The Mytilus galloprovincialis SMAY was updated to 17.58
mg/L in the revised PFOA criteria document follow ing
incorporation of new data published by Hayman et al. (2021).
Briefly, Hayman et al. (2021) exposedM galloprovinvialis
embryos to PFOA for 48-hours and determined an EC50 of
9.98 mg/L (endpoint = normal and surviving). EPA fit a
model to the concentration-response data and determined an
EPA-calculated EC50 of 17.58 mg/L from this test. The acute
value from Hayman et al. (2021) was used preferentially over
the acute value determined by Fabbri et al. (2014) to calculate
the M. galloprovinvialis SMAY in the revised PFOA draft
26

criteria. Results from Fabbri et al. (2014) were not used in the
M. galloprovinvialis SMAY calculation because the EC50 was
a relatively low "greater than" value, while Hayman et al.
(2021) provided a definitive EC50 value.
EPA's acute estuarine/marine GSD consisted GMAVs
calculated from empirical acute LC50 values supplemented
with estimated LC50 values determined through ICE. The 5th
percentile of the GSD served as the estuarine/marine FAV.
Consistent with the 1985 Guidelines, the estuarine/marine
FAV was then divided by 2.0 to calculate the draft
estuarine/marine benchmark. Dividing the FAV by 2.0
ensures the estuarine/marine benchmark represents a
concentration that will not affect a large portion of sensitive
organisms. This is based on the established premise that the
ratio between LC50 values and corresponding LCi0W values
(e.g., LCo - LC10) is typically close to 2.0. Please see the
excerpt from the 1985 Guidelines below for further
explanation,
"the Criterion Maximum Concentration is now equal to
one-half the Final Acute Value. The Criterion Maximum
Concentration is intended to protect 95 percent of a group
of diverse genera, unless a commercially or recreationally
important species is very sensitive. However, a
concentration that would severely harm 50 percent of the
fifth percentile or 50 percent of a sensitive important
species cannot be considered to be protective of that
percentile or that species. Dividing the Final Acute Value
by 2 is intended to result in a concentration that will not
severely adversely affect too many of the organisms. "
In addition to criteria magnitudes themselves, the frequency
and duration components of criteria ensure species are
adequately protected. For example, the 1985 Guidelines state:
27

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.3. The Tcchniciil Approach used to Deme (ho Dnil'l Acule KsUi:irine/M:irine lienchniiirk lor PI'OA
Ue\ iewer
C om mollis
KPA Response


"Duration components (or averaging periods) "in national
criteria have been made short enough to restrict allowable
fluctuations in the concentration of the pollutant in the
receiving water and to restrict the length of time that the
concentration in the receiving water can be continuously
above a criterion concentrations."
In addition to monitoring, the magnitude, duration, and
frequency components of criteria are particularly important in
the design of wastewater treatment plants. For example, the
1985 Guidelines state:
"one of the most important uses of criteria is for designing
waste treatment facilities. Such facilities are designed
based on probabilities and it is not possible to design for a
zero probability. Thus, one of the important design
parameters is the probability that the four-day average or
the one-hour-average will be exceeded, or, in other words,
the frequency with which exceedences will be allowed. "
Overall, EPA agrees with Reviewer 5's assertion that, "given
the data, the new approach methods based on WEB-ICE
are appropriate" for deriving an acute estuarine/marine
benchmark. In the absence of a large acute estuarine/marine
toxicity dataset, the acute estuarine/marine benchmark
provides information regarding a protective value that States
and Tribes may consider for use.
28

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
.2.4 Please comment on the use of measured and unmeasured toxicity tests to derive the respective criterion. In particular
please comment on the supporting justification for using unmeasured toxicity tests in Appendix L.
2.4. 1 ho I so ol Measured :tiul I niiio;isiirod loxicitv losls lo Dome Uespeclne C ritorion
Ro\ iowor
Com mollis
KIW Response
Reviewer
1
The consideration of toxicity data from experiments in
which PFOA measurements were not made seems
appropriate. The Appendix L analysis is supportive of the
general observation that actual concentrations in the
toxicity test waters approximated nominal values for the
freshwater studies.
Thank you for your comment indicating the appropriateness of using
acute and chronic toxicity data from studies that did not measure the
PFOA treatment concentrations. EPA thanks Reviewer 1 for
indicating "the Appendix L analysis is supportive of the general
observation that actual concentrations in the toxicity test waters
approximated nominal values for the freshwater studies.'"
Reviewer
2
I am concerned with the approach of using the agreement
of measured and nominal concentrations from studies that
measured the concentration of PFOA in their tests to
determine whether to use toxicity data from studies that did
not measure the concentration PFOA in their tests. My
concern stems from this approach having to assume that
studies that did not measure the concentration of PFOA in
their experiments performed the dosing of PFOA with the
same care and skill as those studies that did measure the
concentration of PFOA in their experiments and measured
concentrations within 20% of nominal. My concern is
compound by 79.5% and 60% of the acute and chronic
tests, respectively, only reporting nominal test
concentrations. The EPA's approach uses the agreement of
measured and nominal concentration in a minority of
studies to determine whether to include the majority of
studies on their assessment.
I am assuming that there wouldn't be sufficient data to
determine a criterion without using data from studies that
did not measure the concentrations of PFOA in their
experiment?
Thank you for your comment noting that by using both measured and
unmeasured toxicity studies in the derivation of the draft PFOA
Aquatic Life Criteria, the assumption was made that unmeasured
toxicity studies conducted dosing with the same accuracy and care as
measured toxicity tests. EPA acknowledges that the Meta-Analysis of
Nominal Test Concentrations Compared to Corresponding Measured
Test Concentrations in Appendix L of the draft PFOA criteria
document does not eliminate this concern. However, unmeasured
studies that were used quantitatively to derive the PFOA criteria all
otherwise met EPA's test quality guidelines (EPA's 1985 Guidelines
and 850 Test Guidelines; U.S. EPA 1985 and U.S. EPA 2016b). Given
the relative high occurrence of unmeasured PFOA toxicity tests,
typically attributed to the relatively high stability of PFOA and/or
difficulty in measuring test concentrations by individual study authors,
there would be insufficient data to derive PFOA criteria for aquatic
life without the inclusion of both measured and unmeasured tests.
Therefore, EPA chose to use the best available science to develop
criteria recommendations to support states and stakeholders in
protecting aquatic life.
Thank you for your comment noting the approach EPA used to
determine the level of agreement between nominal and measured
concentrations was logical and valid. With the meta-analysis in
29

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.4. 1 lie I so o 1 Measured :tiul I n measured loxicilv lests lo l)eri\e Uespeclne C rilcrion
Ue\ iewer
Com meiils
KIW Response

I think the approach that the EPA has used to determine the
level of agreement between the nominal and measured
concentration of PFOA in the studies that measured the
concentration is logical and valid. It is encouraging that the
agreement on average is high. Again, my largest concern is
assuming this agreement in a minority of studies is present
in all studies.
Appendix L of the draft PFOA criteria document, EPA evaluated any
potential differences between nominal and measured test
concentrations that may be due to water type (salt or freshwater) or
experimental conditions such as (1) acute and chronic test duration;
(2) whether test organisms were fed or unfed; (3) test vessel material
(e.g., glass or plastic); (4) use of solvent or no solvent; and (5) the
presence of a substrate. Because experimental conditions did
systematically produce differences between nominal and measured
concentrations of PFOA, EPA used both measured and unmeasured
toxicity studies that otherwise meet EPA's test quality guidelines to
derive the PFOA criteria for aquatic life.
Reviewer
3
Reviewer 3's response to this question was provided in this
person's review of the draft PFOS document, with a
statement that the comment also pertained to PFOA;
therefore, it is copied here.
This seems acceptable for the time being. Having worked
in the laboratory with PFOS, I can make a first-hand
testament that mixing PFOS into exposures solutions does
not guarantee a homogenous mixture despite working at
solutions well below the solubility limit. There are nuances
associated with achieving homogeneity of the exposure
solution, we have developed a PFAS mixing protocol to
reduce chemical clumping and this increases uniformity of
the solutions. Furthermore, there is approximately 30%
variability of PFOS quantitatively (see... Rewerts et al.
2020); so, the best measurement still has significant
variability.
A statement has been included in Appendix L of the updated PFOA
criteria indicating recent PFAS literature indicates standard variability
between nominal and measured concentrations may be as high as 30%
(citing Coats et al. 2017 and Rewerts et al. 2021, as suggested by
Reviewer 3).
Reviewer
4
PFOA is a highly stable compound, resistant to hydrolysis,
photolysis, volatilization, and biodegradation (as described
in Section 1.1.1 of the Report) and, therefore, expected to
vary only minimally in the course of a toxicity test. To
Thank you for your comment and summarization of the Meta-Analysis
of Nominal Test Concentrations Compared to Corresponding
Measured Test Concentrations in Appendix L of the draft PFOA
Aquatic Life Criteria document. Thank you for describing your
30

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.4. 1 lie I so o 1 Measured and I n measured loxicilv lests lo l)eri\e Uespeclne C rilcrion
Ue\ iewer
Com meiils
KIW Response

determine if nominal and measured PFOA concentrations
were typically in close agreement, pairs of nominal and
corresponding measured PFOA concentrations were
compared to one another through (1) linear correlation
analysis and (2) an assessment of measured concentrations
as a percent of its paired nominal concentration. The
analysis conducted by EPA Team showed strong
correlation (correlation = 0.9995) of the 79 pairs of
nominal and measured concentrations from freshwater
studies, and similar strong correlation (correlation =
0.9999) of the 11 pairs of nominal and measured
concentrations from saltwater studies (Figure LI in the
Report). In addition, the experimental conditions did not
influence the correlation between nominal and measured
concentrations.
This confirms inclusion of unmeasured PFOA toxicity
tests for quantitative use in criteria derivation.
Personal experience on analyzing PFOA in
ecotoxicological studies using freshwater and saltwater
species have also exhinited strong correlation between
nominal and measured concentrations.
Additional information for L.I.4 summary section could
include additional information based on the two additional
published papers and the key points from these studies are
listed below.
Despite the concerns and avoidance of glass, few
studies have presented data describing the sorption of
perfluorooctanoate (PFOA) to glass and other
container materials (Lath et al. 2019). Lath etal.
(2019), who had reported that sorptive losses of PFOA
for lower concentration (-20 ng/L) aqueous solutions
experience analyzing PFOA in ecotoxicological studies for freshwater
species, which have exhibited strong correlation between nominal and
measured concentrations.
EPA notes the suggestion of Reviewer 4 to consider Rewerts et al.
(2021). A statement has been included in Appendix L of the updated
PFOA criteria indicating recent PFAS literature indicates standard
variability between nominal and measured concentrations may be as
high as 30% (citing Coats et al. 2017 and Rewerts et al. 2021). At the
suggestion of Reviewer 4, a statement has been included in Appendix
L of the updated PFOA Aquatic Life Criteria document that discusses
the results of Lath et al. (2019) in relation to the three tests across two
publications (Oakes et el. 2004 and Colombo et al. 2008) that
exhibited a relatively high number of measured treatment
concentrations that were not within 20% of nominal concentrations. In
short, Colombo et al. (2008) did not report the test vessel material,
while Oaks et al. (2004) reported test vessels were lined with food-
grade PVC. PFOA in treatments described by Oakes et al. (2004) may
have rapidly sorbed to the test vessel (in addition to added substrate
and/or macrophytes). This is consistent with results of Lath et al.
(2019), who determined PFOA was more likely to sorb to plastic test
vessels than glass, stating:
"Contrary to suggestions in the literature, our results indicated that
the greatest sorption losses for PFOA occurred on PP
[polypropylene], whereas losses on glass tubes were much lowerT
31

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.4. 1 lie I so o 1 Measured :tiul I nmeiisiired loxicilv lests lo l)eri\e Uespeclne C rilcrion
Ue\ iewer
Com meiils
KIW Response

were highest in polypropylene centrifuge tubes.
However, the container type did not influence the
measured concentration as reported in section - of this
report. According to Rewerts et al., 2021 additional
handling steps, which are not typically reported for
ecotoxicological studies but may contribute to
variability, include solution homogenization,
subsampling procedures, and the container materials
selected for storage, https://doi.ora/10.1002/etc.4667
Lath S, Knight ER, Navarro DA, Kookana RS,
McLaughlin MJ. 2019. Sorption of PFOA onto
different laboratory materials: Filter membranes and
centrifuge tubes. Chemosphere 222: 671- 678.
DOI: 10.1016/i.chemosphere.2019.01.096

Reviewer
5
Similar to PFOS, the approach EPA used for PFOA was to
consider studies in which the chemical was not measured.
This was justified based on an analysis EPA did comparing
nominal and measured concentrations and finding close
agreement. This generally seems reasonable to me
especially considering the stability of the chemical.
However, EPA used a criteria of 20% (p. 61) which is not
consistent with the analytical precision of most methods
used to analyze PFAS. According to several very prolific
environmental chemists that have made a career of
measuring PFAS, they have communicated to me that the
methods are accurate to within 30%. That means that if the
measured were within 30% of nominal, we basically have
concluded these were nominal. I would encourage EPA to
explore their 20% acceptability threshold and perhaps offer
an explanation as to why this is appropriate.
EPA acknowledges participants of the Society of Environmental
Toxicology and Chemistry (SETAC) North America Focused Topic
Meeting on Environmental Risk Assessment of PFAS (held August
2019, Durham, NC) commented that analytical confirmation of test
concentrations is needed. Additionally, previous aquatic life ambient
water quality criteria for other chemicals have preferentially relied on
measured toxicity tests, particularly those tests with relatively
sensitive taxa. Given the relative rarity of measured PFOA toxicity
tests in the current literature there would be insufficient data to derive
PFOA criteria for aquatic life without the inclusion of both measured
and unmeasured tests. Considering that the results of the meta-analysis
(described in Appendix L of the draft PFOA Aquatic Life Criteria
document) that strongly indicated nominal concentrations were
relatively similar to measured concentrations regardless of
experimental condition, EPA used both measured and unmeasured
toxicity studies that otherwise meet EPA's test quality guidelines to
derive the draft PFOA aquatic life criteria.
32

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.4. 1 lie I so o 1 Measured :tiul I n measured loxicilv lests lo l)eri\e Uespeclne C rilcrion
Ue\ iewer
Com meiils
KIW Response


Thank you for your comment noting that several analytical chemists
have recommended a 30% threshold for determining if measured and
nominal concentrations are different. EPA used the 20% threshold (as
opposed to the 30% threshold) to be consistent with EPA's 850 Test
Guidelines (U.S. EPA 2016b). Moreover, in freshwater 89.9% of
measured concentration were within 20% of the paired nominal
concentration, indicating a high degree of correlation between
nominal and measured concentrations. Adjusting to a 30% threshold
(as opposed ot the 20% threshold difference in Appendix L of the
draft PFOA criteria Document) would not meaningfully alter
conclusions.
33

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
.2.5 Please comment on the toxicity data used to derive the draft criteria.
• Were the data selected and/or excluded from the derivation of the criteria derivation appropriately utilized?
• Are there relevant data that you are aware of that should be added to the analyses (note that EPA is working on updating
the toxicity data to reflect the data in ECOTOX between Sept. 2019 through the latest update)? If so, please provide
references for consideration.
In particular, please comment on:
2.5.a. The toxicity values used to derive the PFOA criteria, with a particular emphasis on:
2.5.a.i. the selection and the Acute to Chronic Ratio (ACR) to serve as the Final Acute to Chronic Ratio (FACR) and
its application to derive the Final Chronic Value (FCV).
2.5.a.ii. the use of the qualitatively acceptable acute midge (Chironomus plumosus) data from Yang et al. (2014) to
suggest aquatic insects are relatively tolerant to acute PFOA exposures. Specifically, Yang et al. (2014)
conducted a 96-hour renewal, measured PFOA acute test with the midge, Chironomus plumosus. This study
was not acceptable for quantitative use due to the potentially problematic source of the organisms. The
reported LCso was 402.24 mg/L PFOA indicating that these insects may not be one of the more sensitive
taxonomic groups. Therefore, this test was excluded from the criterion calculation, but used to waive the
missing insect MDR.
2.5.b. EPA's approach for fitting concentration-response (C-R) data (described in Appendix J) as well as the specific acute
LCso values (Appendix A.2) and chronic EC10 values (Appendix C.2) that were estimated (for sensitive genera when
C-R data were available) and used to derive criteria.
2.5. The Toxicity Dsitsi to l)eri\e the Drsil'l Criterion
Ue\ iewer
C om incuts
El'A Response
Reviewer
1
• Were the data selected and/or excluded from the
derivation of the criteria derivation
appropriately utilized?
In most cases, yes. Please see detailed comments on
particular studies and interpretations in response to other
charge questions.
Thank you for your comment noting data were appropriately utilized
in the draft PFOA Aquatic Life Criteria document in most cases,
Instances where Reviewer 1 believes data may have been used
inappropriately have been addressed in responses to other charge
questions.
All studies provided by Reviewer 1 (and all other reviewers),
including Hayman et al. (2021) were all reviewed to ensure they met
34

• Are there relevant data that you are aware of
that should be added to the analyses (note that
EPA is working on updating the toxicity data to
reflect the data in ECOTOX between Sept. 2019
through the latest update)? If so, please provide
references for consideration.
Hayman, N.T., Rosen, G., Colvin, M.A., Conder, J.,
Arblaster, J.A. 2021. Aquatic toxicity evaluations of
PFOS and PFOA for five standard marine
endpoints. Chemosphere 273:129699.
2.5.a
2.5.a.i As stated in the 1985 guidelines, "the Final Acute-
Chronic Ratio should be calculated as the
geometric mean of the acute-chronic ratios for
species whose SMAVs are close to the Final
Acute Value." The guidance does not quantify
"close", but it also does not specify that the Acute
to Chronic Ratio (ACR) should only be derived
from a single ACR from the studv with the acute
value that is closest to the Final Acute Value
(FAV). In the case of the PFOA document, EPA is
using only one ACR value, which is derived from
the Zhang et al. (2013) rotifer study in which the
LC50 is 150 mg/L. I would agree 150 mg/L
relatively close to the FAV of 94 mg/L. However,
I would also argue that the LC50 of 166 mg/L from
the study with Moina macrocopa is also "close" to
94 mg/L (it is only 11% higher than 150 mg/L).
The Species Mean Acute Value (SMAV) for D.
magna is 253.7 mg/L is well within a factor of 3
of 94 mg/L and could also be considered "close".
These three data points tend to cluster, as shown in
data quality objectives outlined by the 1985 Guidelines, EPA 850 test
guidelines, etc., and were included in the PFOA criteria document as
appropriate based on their data quality.
Responses to key instances where Reviewer 1 does not believe the
data were appropriately utilized to derive the draft PFOA Aquatic Life
Criteria are described below in the corresponding order to those
comments by Reviewer 1.
Specific to comments to charge question 2.5.a:
2.5 .a.i Addition of new chronic toxicity data in the updated draft
PFOA criteria document allowed for the calculation of a
draft chronic freshwater criterion magnitude directly from
the chronic GSD rather than basing the magnitude on the
FAV transformed by the FACR, as was done in the draft
PFOA criteria document that underwent peer review.
2.5.a.ii Based on further consideration and peer reviewer
comments, tests with organisms from Yang et al. (2014)
that were collected from the Beijing City Big Forest Flower
Market and tests from Yuan et al. (2015) where organisms
were collected from a fountain in Quanhetou, Boshan,
China are now both considered qualitatively acceptable for
criteria derivation.
Specific to comments to charge question 2.5.b:
The draft PFOA criteria document reviewed by peer reviewers
contained model type and figures of the C-R data with the fitted model
and corresponding 95% confidence bands for tests that were among
the four most sensitive acute or chronic genera (and C-R data were
reported in the publication or could be obtained from authors).
Appendix A.2 contained test-specific C-R modeling for relatively
sensitive acute tests, while test-specific C-R models for relatively
35

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perflnorooctanoic Acid
fl'l'OAj" ' '
2.5. The Toxicity Data to Derive the Draft Criterion
Reviewer
Comments
EPA Response

Figure 3-5. Taking the geometric mean of the
three ACRs from these three studies, which are
studies that have acute values all within a factor of
2-3 of the 94 mg/L FAV, seems more consistent
with the 1985 guidance to select several ACRs
that are "close" to the FAV, rather than simply
selecting a single ACR. The resulting recalculated
ACR would be approximately 90, which provides
a good, but conservative measure of central
tendency and is higher than all but the highest
ACR (299) shown in Table 3-8. Applying an ACR
of 90 to the FAV would result in a FCV of
approximately 1 mg/L, which is protective of
chronic values shown in Figure 3-6 (note the
Zhang et al.-derived rotifer SMCV is 0.8 mg/L,
which is only slightly lower 1 mg/L). Such as
recalculation would better incorporate variability
in the ACRs and avoid both water-based criteria
being completely driven by the results from a
single organism (rotifers) as reported in a single
study (Zhang et al., 2013).
2.5.a.ii I disagree with excluding this data point from the
acute criteria calculations. I assume this data has
been removed under the assumption that these
animals may have been pre-exposed to PFOA and
may have been more tolerant of PFOA exposures,
which would result in biased-high median lethal
concentration (LC50) values. If so, this should be
explicitly stated. Assuming these Chironomns can
develop tolerance to PFOA, it seems that they
would have to be exposed to rather high mg/L
ranges of PFOA in water given the reported 96-
hour LC50 of 402 mg/L. Based on published
sensitive chronic tests were included in Appendix C.2. Please see
below for an example of test-specific C-R modeling results that was
reported in Appendix A.2 of the draft PFOA Criteria Document.
Publication: Le and Peijnenburg 2013
Species: Cladoceran (Chydorus sphaericus)
Genus: Chydorus
EPA-Calculated LC50- 93.17 mg/L
Concentration-Response Model Fit:
Le and Peijnenberg 2013
Chydorus sphaericus
Log Logistic type 1, 3 para
1.001
\ *
J2 \
I \
I 050- \
1 m,
2 \
• \
029-
000- •
3 10 30 100
PFOA ( uM )
Additional details on the functions and model specifications within the
R.drc package are publicly available by following the link here:
https ://cran .r-proi ect. ors/web/packase s/drc/drc .pdf
Standard errors for both the model parameters and ECx estimates were
calculated during evaluation, but this level of statistical detail was not
included in the Peer Review draft of the PFOA Aquatic Life Criteria
document. In response to Reviewer 1, Appendix A. 1, A.2, C. 1, and
C.2 of the updated PFOA criteria document now include 95%
Confidence Intervals (CI) as parentheticals following discussion of all
point estimates (i.e., LC50 and ECX values) calculated by EPA
(irrespective of whether or not the point estimate was used in
calculation of the four most sensitive GMAVs and/or GMCVs).
36

literature, I am unaware of natural ecosystems in
China (where the animals may have been
originally harvested) with concentrations of PFOA
that approach this order of magnitude range (in
which they could build up a tolerance). The
animals were obtained from a local market, so it is
also possible that they were cultured for several
generations, presumably using uncontaminated
water (which would further reduce the chance that
multiple generations were exposed at these levels).
Overall, I think it is more reasonable to assume
that the animals used in the experiment have not
built up an acute lethal tolerance to PFOA, and the
that LC50 result is unbiased. It does seem clearly
show that insects may be less sensitive to acute
lethality effects of PFOA. As such, I think it
should be included as a quantitative endpoint.
Additionally, it seems inconsistent to exclude this
Yang et al (2014) study, when acute data from a
study by Yuan et al. (2015) were included for
quantitative consideration. As noted on page A-10,
the animals in the Yuan et al. (2015) study were
"collected from a fountain in Quanhetou, Boshan,
China, and acclimated in the laboratory for an
unspecified time period before use". The source of
the animals is just as uncertain as the Yang et al
(2014) animals, and it is unclear (if PFOA
tolerance at lethal levels is possible) how many
generations would be needed to shed adaptive
tolerance and how this time period would compare
to an "unspecified time period." Simply put, if data
from experiments like Yuan et al. (2015) are
quantitatively included, those from Yang et al.

(2014) should also be quantitatively included (with
some notes on the uncertainty of the animal
sources).
2.5.b. More details need to be provided on the dose
response modeling using R. Appendix J is helpful
for providing the reader with details on the general
approach, but where ECios are modeled by EPA, the
model being used (out of the 22 available in the R
software package) needs to be specified. Providing
some indication of variability (such as a 95%
confidence interval) for the model-generated ECios
is standard practice for dose response modeling, and
this information should be provided somewhere in
the document. Showing the R package output of the
goodness of fit statistics (or equivalent) for the
modeling in an Appendix would be helpful; since
this was used to select the model used in each
instance of an ECio calculation, it must be available,
so I would recommend including it for full
transparency and to aid future efforts in
understanding the aquatic toxicology of this
chemical. Additionally, it would be helpful to show
the selected model fits for all calculated ECios (as
shown for the most sensitive ECios estimated).
These steps would be helpful to ensure and
demonstrate quality of the model fits and
reproducibility of the modeling work.

Reviewer
2
• Were the data selected and/or excluded from the
derivation of the criteria appropriately utilized?
I think the data used in the derivation of the criteria were
appropriate. As mentioned above, I am a little concerned
about the use of toxicity data from studies that did not
Given the high occurrence of unmeasured PFOA toxicity tests
(typically attributed to the relatively high stability of PFOA and/or
difficulty in measuring test concentrations by individual study
authors) there would be insufficient data to derive PFOA criteria for
aquatic life without the inclusion of both measured and unmeasured
38

measure the concentration of PFOA in their experiments,
especially considering the proportion of studies that did not
measure the concentrations. The confirmation of exposure
concentrations is an important principle of sound
ecotoxicology.
• Are there relevant data that you are aware of
that should be added to the analyses (note that
EPA is working on updating the toxicity data to
reflect the data in ECOTOX between Sept. 2019
through the latest update)? If so, please provide
references for consideration.
Hayman, N.T., Rosen, G., Colvin, M.A., Conder, J.,
Arblaster, J.A., 2021. Aquatic toxicity evaluations
of PFOS and PFOA for five standard marine
endpoints. Chemosphere 273, 129699..
doi: 10.1016/j .chemosphere .2021.129699
Logeshwaran, P., Sivaram, A.K., Surapaneni, A., Kannan,
K., Naidu, R., Megharaj, M., 2021. Exposure to
perfluorooctanesulfonate (PFOS) but not
perflurorooctanoic acid (PFOA) at ppb
concentration induces chronic toxicity in Daphnia
carinata. Science of The Total Environment 769,
144577.. doi: 10.1016/j.scitotenv.2020.144577
Bartlett, A.J., De Silva, A.O., Schissler, D.M., Hedges,
A.M., Brown, L.R., Shires, K., Miller, J., Sullivan,
C., Spencer, C., Parrott, J.L., 2021. Lethal and
sublethal toxicity of perfluorooctanoic acid (PFOA)
in chronic tests with Hyalella azteca (amphipod) and
early-life stage tests with Pimephales promelas
(fathead minnow). Ecotoxicology and
tests. EPA appreciates Reviewer 2 previously noting the approach
EPA used to determine the level of agreement between nominal and
measured concentrations was logical and valid. Appendix L of the
draft PFOA Aquatic Life Criteria document contained EPA evaluation
of potential differences between nominal and measured test
concentrations that may be due to water type (salt or freshwater)
and/or experimental conditions such as (1) acute and chronic test
duration; (2) whether test organisms were fed or unfed; (3) test vessel
material (glass or plastic); (4) use of solvent or no solvent; and (5) the
presence of a substrate. Because experimental conditions did
systematically produce influence discrepancies between nominal and
measured concentrations of PFOA, EPA use both measured and
unmeasured toxicity studies that otherwise meet EPA's test quality
guidelines to derive the PFOA criteria for aquatic life.
All toxicity studies provided by Reviewer 2 (and all other reviewers)
were reviewed to ensure they met data quality objectives outlined by
the 1985 Guidelines, EPA 850 test guidelines, etc., and were included
in the PFOA criteria document as appropriate based on study data
quality. BAFs used to calculate the tissue criteria were obtained from
the BAF database created Lawrence Burkhard (U.S. EPA, Office of
Research and Development) in support of his publication: Burkhard,
L.P. (2021) Evaluation of Published Bioconcentration Factor (BCF)
and Bioaccumulation Factor (BAF) Data for Per- and Polyfluoroalkyl
Substances Across Aquatic Species. ET&C 40: 1530-1543.
BAFs reported in Prosser et al. 2016 were not in the Burkhard (2021)
database and were therefore not used to calculate BAFs. Upon review
of Prosser et al. (2016), it appears this study was not included in the
BAF database developed by Burkhard (2021) because this addressed
study biota sediment accumulation factors (BSAFs) instead of BAFs.
It is for this same reason EPA did not include Prosser et al. (2016)
among the BAFs that were used to derive the tissue criteria for PFOA.
39

Environmental Safety 207, 111250..
doi:10.1016/j.ecoenv.2020.111250
Tornabene, B.J., Chislock, M.F., Gannon, M.E.,
Sepulveda, M.S., Hoverman, J.T., 2021. Relative
acute toxicity of three per- and polyfluoroalkyl
substances on nine species of larval amphibians.
Integrated Environmental Assessment and
Management 17, 684-690.. doi:10.1002/ieam.4391
Flynn, R.W., Iacchetta, M., Perre, C., Lee, L., Sepulveda,
M.S., Hoverman, J.T., 2021. Chronic Per-
/Polyfluoroalkyl Substance Exposure Under
Environmentally Relevant Conditions Delays
Development in Northern Leopard Frog ( Rana
pipiens ) Larvae. Environmental Toxicology and
Chemistry 40, 711-716.. doi: 10.1002/etc.4690
BAF data provided in the supplementary information of
Prosser et al. 2016 study for three freshwater species does
not appear to have been considered.
Prosser, R.S., Mahon, K., Sibley, P.K., Poirier, D., Watson-
Leung, T., 2016. Bioaccumulation of perfluorinated
carboxylates and sulfonates and polychlorinated
biphenyls in laboratory-cultured Hexagenia spp.,
Lumbriculus variegatus and Pimephales promelas
from field-collected sediments. Science of The Total
Environment 543, 715-726.
doi: 10.1016/j .scitotenv.2015.11.062
2.5.a.
2.5 .a.i I think the approach that led to the selection of the
ACR for Brachionus calyciflorus was appropriate.
It is also the most conservative approach with the
Specific to comments to Charge Question 2.5.a:
2.5.a.i Thank you for your comment.
2.5.a.ii Thank you for your comment. The Chironomusplumosus
test by Yang et al. (2014) has been retained as qualitatively
acceptable because of the atypical source (i.e., Beijing City
Big Forest Flower Market) of the test organisms.
Specific to comments to Charge Question 2.5.b:
Thank you for your comment noting the inclusion of C-R models for
tests with species among the four most sensitive acute and/or chronic
genera in Appendices A.2 and C.2 "generates a high level of
transparency in the derivation of the criterion." Additional details on
the functions and model specifications within the R.drc package are
publiclv available via the link here: https://cran.r-
proiect.ore/web/packaees/drc/drc.pdf
40

ACR for this species being the largest of the four
species with ACRs.
2.5.a.ii I think the EPA's decision that the data from Yang
et al. (2014) was not acceptable for quantitative
use was appropriate. The source of the larvae is
problematic. The conclusion that insects may not
be one of the most sensitive taxa is valid. The
NOEC for Chironomus tentans of 100 mg/L
reported by MacDonald et al. (2004) also supports
this conclusion.
2.5.b.
I think the approach that the EPA used to determine effect
measure from concentration-response data was appropriate.
The use of the drc package in R to fit 22 different models
to the empirical data and then using several criteria (e.g.,
AIC, residual standard errors, confidence intervals) to
evaluate the fit of the different models is robust. It would
have been useful if the EPA reported the 22 different
models in Appendix J.
I think the LC50 and EC10 values determined by the EPA
using the approach mentioned in the previous paragraph
was appropriate. It is valid for these effect measures to be
determined when the concentration-response data has been
provided by the authors of the study. The EPA has also
made is clear in Appendix A.2 and C.2 how they
determined these effect measures using the concentration-
response data provide in the studies. This generates a high
level of transparency in the derivation of the criterion.

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.5. The Toxicity l):il:i lo Dome the Draft Criterion
Ro\ iewer
C om incuts
KIW Response
Reviewer
3
• Were the data selected and/or excluded from the
derivation of the criteria derivation
appropriately utilized?
With the exception of the Fabbri et al. 2014, data currently
evaluated, and the associated decision matrix seem
appropriate. However, as noted below, there are new data
available following this draft.
• Are there relevant data that you are aware of
that should be added to the analyses (note that
EPA is working on updating the toxicity data to
reflect the data in ECOTOX between Sept. 2019
through the latest update)? If so, please provide
references for consideration.
o McCarthy et al. 2021 - freshwater
o Hayman et al. 2021 - marine
o Logeshwaran et al. 2021 - freshwater
o Li et al. 2021 - freshwater/plant
o Etc.
2.5.a.
2.5.a.i The use of ACR is appropriate given data
limitations. However, either I am missing it or it is
unclear as to why Chydorus is not included in the
chronic data set when it is the most sensitive in the
acute.
2.5.a.ii McCarthy et al. 2021 reported midge data for
PFOA with an EC50 of 192 mg PFOA/L
following a 20-day exposure. Following EPA
review of this publication, this may fulfill the
Please see EPA's response to Reviewer 3's comments on the use of
Fabbri et al. (2014) under charge question 2.3. EPA thanks Reviewer
3 for noting remaining data were used appropriately.
Specific to comments to Charge Question 2.5.a:
2.5.a.i Thank you for your comment on the appropriateness of
the selection and use of the FACR to derive the draft
chronic criterion. There were no ACRs for species within
the genus, Chydorus (most sensitive acute genus in the
draft criteria document), because chronic toxicity data
were not available precluding the calculation of an ACR
for any species within the genus, Chydorus. Addition of
new chronic toxicity data in the updated draft PFOA
criteria document allowed for the calculation of a draft
chronic freshwater criterion magnitude directly from the
chronic GSD rather than basing the magnitude on the
FAV transformed by the FACR, as was done in the draft
PFOA criteria document that underwent peer review.
2.5.a.ii All toxicity studies provided by Reviewer 3 (and all other
reviewers), including McCarthy et al. (2021), were all
reviewed to ensure they met data quality objectives
outlined by the 1985 Guidelines, EPA 850 test guidelines,
etc., and were included in the PFOA criteria document as
appropriate, based on their data quality.
Specific to comments to Charge Question 2.5.b:
Thank you for your comment on EPA's independent calculation of
acute LC50 and chronic EC10 values, nothing this "is a sound scientific
approach." Section 2.10.3.3 (Summary of Independent Calculation of
Toxicity Values) of the draft PFOA Aquatic Life Criteria document
describes that EPA independently calculated acute LC50 and chronic
EC10 values when C-R data could be obtained from the publication,
supplemental material, and/or through direct contact with study
42

missing insect MDR; however, still supports the
conclusion of likely not a sensitive taxa.
2.5.b.
This is a sound scientific approach, what is unclear is when
EPA employs this vs other times when it is not used. i.e.
chydorus vs two mussle spp in the acute studies
authors. Acute concentration-response data forZ. siliquoidea andZ.
recta were not reported in Hazelton et al. (2012) and could not be
obtained from authors to inform C-R modeling. Section 2.10.3.3 of the
draft PFOA criteria document states:
"Toxicity values, including LC50 and EC 10 values, were
independently calculated from the data presented in the toxicity
studies meeting the inclusion criteria described above when
adequate concentrations-response data were published in the study
or could be obtained from authors. When concentration-response
data were not presented in toxicity studies, concentration-response
data were requested from study authors to independently calculate
toxicity values. In cases where study authors did not respond to
EPA's request for data or were unable to locate concentration-
response data, the toxicity values were not independently calculated
by EPA, and the reported toxicity values were retained for criteria
deviation."
Reviewer
4
• Were the data selected and/or excluded from the
derivation of the criteria derivation
appropriately utilized?
The data selected to derive PFOA criteria are appropriate.
Studies that did not fully meet the data quality objectives
outlined in the 1985 Guidelines were not considered for
inclusion in the criteria derivation, including some studies
with other PFAS exposures, but were considered
qualitatively as supporting information. A brief summary
of each study describing the experimental conditions and
summary tables providing all the relevant information such
as strengths and limitations of each study, end points
selected for deriving criteria are well documented by the
EPA team.
Thank you for commenting "information such as strengths and
limitations of each study, end points selected for deriving criteria are
well documented by the EPA team" and for summarizing how data
were selected and/or excluded from the derivation of the PFOA
criteria. All toxicity studies provided by Reviewer 4 (and all other
reviewers) were all reviewed to ensure they met data quality
objectives outlined by the 1985 Guidelines, EPA 850 test guidelines,
etc., and were included in the PFOA criteria document as appropriate,
based on their data quality.
Specific to comments to Charge Question 2.5.a:
2.5.a.i Thank you for summarizing the selection and application
of the FACRto derive the chronic PFOA criteria. Thank
you for commenting, "The selection and the Acute to
Chronic Ratio (ACR) to serve as the Final Acute to
Chronic Ratio (FACR) and its application to derive the
Final Chronic Value (FCV) for PFOA is acceptable."
43

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.5. The Toxicity l):il:i lo Dome the Draft Criterion
Ro\ iewer
C om incuts
KIW Response

The key acceptable exclusion/inclusion criteria used to
derive draft criteria are listed below:
•	Only single chemical toxicity tests with PFOA
were considered for possible inclusion in
criteria derivation, studies that tested chemical
mixtures, including mixtures with PFAS
compounds were excluded from criteria
derivation.
•	Both controlled laboratory experiments and
field observations/studies were included.
•	PFOA toxicity tests were not excluded from
quantitative use in criteria derivation on the
basis of unmeasured test concentrations alone.
•	Only single chemical toxicity tests with PFOA
were considered for possible inclusion in
criteria derivation, studies that tested chemical
mixtures, including mixtures with PFAS
compounds were excluded from criteria
derivation.
•	Due to lower sensitivity, insect MDR was
excluded from the criterion calculation, but
were used to waive the missing insect MDR.
•	Further supporting information on acceptable
and unused studies for acute and chronic
endpoints and for freshwater and marine studies
are documented and summarized as appendices
in this report.
• Are there relevant data that you are aware of
that should be added to the analyses (note that
EPA is working on updating the toxicity data to
reflect the data in ECOTOX between Sept. 2019
Addition of new chronic toxicity data in the updated draft
PFOA criteria document allow ed for the calculation of a
draft chronic freshwater criterion magnitude directly from
the chronic GSD rather than basing the magnitude on the
FAV transformed by the FACR, as was done in the draft
PFOA criteria document that underwent peer review.
2.5.a.ii Thank you for summarizing the data used to derive the
criteria and for summarizing the relative tolerance of
aquatic insects to acute PFOA exposures based on data
available in the draft PFOA Aquatic Life Criteria
document.
Specific to comments to Charge Question 2.5.b:
Thank you for summarizing EPA's independent calculation of acute
LC50 and chronic EC20 values and for stating, "This is an excellent
approach utilized by the EPA Team. EPA's approach for fitting
concentration-response (C-R) data resulted in consistent approach
across various ecotoxicological studies."
44

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.5. The Toxicity l):il:i lo Dome the Draft Criterion
Ro\ iewer
C om incuts
KIW Response

through the latest update)? If so, please provide
references for consideration.


Additional toxicity data published over the last six months
is listed below:


Marine/estuarine


Stuart L. Simpson, Yawen Liu, David A. Spadaro,
Xinhong Wang; Rai S. Kookana and Graeme E.
Batley Chronic effects and thresholds for estuarine
and marine benthic organism exposure to
perfluorooctane sulfonic acid (PFOS)-contaminated
sediments: Influence of organic carbon and
exposure routes
https://doi.ora/10.1016/i .scitotenv.2021.146008


Nicholas T Hayman , Gunther Rosen , Marienne A Colvin ,
Jason Conder, Jennifer A Arblaster Aquatic toxicity
evaluations of PFOS and PFOA for five standard
marine endpoints.
httDs://cioi.on . , •• chcmost- . r>99


Fresh water


Christopher J. McCarthy, Shaun A. Roark, Demitria
Wright. Kelly O'Neal. Brett Muckey, Mike
Stanaway, Justin N. Rewerts, Jennifer A. Field.
Todd A. Anderson. Christopher J. Sal ice.
Toxicological Response of Chironomus dilutus in
Single-Chemical and Binary Mixture Exposure
Experiments with 6 Perfluoralkyl Substances,
Environmental Toxicology and Chemistry.
10.1002/etc.5066, 40. 8, (2319-2333), (2021).


2.5.a.

45

2.5.a.i The selection and the Acute to Chronic Ratio
(ACR) to serve as the Final Acute to Chronic Ratio
(FACR) and its application to derive the Final
Chronic Value (FCV) for PFOA is acceptable. The
1985 Guidelines allow the use of a Final Acute-
Chronic Ratio (FACR) to convert the FAV to the
FCV (i.e., FAV/FACR=FCV), which is equivalent
to the chronic criterion (Criterion Continuous
Concentration, CCC), intended to protect 95
percent of the taxa in aquatic ecosystems. For
PFOA, the 8-family MDR requirement was not met
for the chronic dataset, as acceptable chronic
studies for species representing three MDR groups
were not available (benthic crustacean and third
phylum or second insect order not already
represented). Therefore, the Final Chronic Value
(FCV) was calculated with the use of an ACR
(acute-chronic ratio). When more than a single
ACR was calculated for the same species, the
Species Mean Acute-Chronic Ratio (SMACR) was
calculated as the geometric mean value of all ACRs
for that species. . The specifications for derivation
of a FACR for aquatic animals was met for PFOA
based on 1985 Guidelines: ACRs for at least three
different families provided that at least one was a
fish, at least one was an invertebrate, and at least
one was an acutely sensitive freshwater species.
The 1985 Guidelines provides recommendations to
calculate the FACR when SMACRs are dissimilar.
The 1985 Guidelines states that if SMACRs tend to
increase or decrease as the SMAV increases, the
FACR should be calculated as the geometric mean
of the ACRs for species whose SMAVs are close to
the FAV. For PFOA, relationship between SMAV

and SMACR showed that SMACRs decreased as
the SMAVs increased. SMAV of the rotifer B.
calyciflorus was closest to the FAV. The CCC was
calculated by dividing the FAV by the FACR to
determine the FCV (91.34/299.1=0.3054). The
PFOA FCV derived by this method is lower than
the all of the quantitatively-acceptable chronic
values (ranges between 0.76- 40 mg/L) and listed
in listed in Table C. 1.
2.5.a.ii The acute data set for PFOA contained 14 genera
representing seven of the eight taxonomic MDR
groups. The missing MDR was a representative
from an insect family. There was no evidence to
suggest aquatic insect are among the four most
sensitive genera. EPA calculated the PFOA CMC
using all acceptable quantitative studies, but did not
include the insect data in the criterion calculation
(i.e., the relatively tolerant insect LC50 value was
not included in the total count ("n") of Genus Mean
Acute Values in the criterion calculation). In
addition, waiving an unfulfilled MDR when
available data suggest it is not among the four most
sensitive genera is consistent with previous EPA
criteria documents, including U.S. EPA (2016).
In addition, Stefani et al. (2014), Macdonald et al.
(2004), and Marziali et al. (2019) conducted
chronic toxicity tests with Chironomus spp. and
reported apical endpoints. Results of these studies,
taken together, also suggest that insects may not be
among the most sensitive taxa to chronic PFOA
exposures. Therefore, these tests were excluded

from the criterion calculation, but were used to
waive the missing insect MDR.

2.5.b.

• This is an excellent approach utilized by the EPA
Team. EPA's approach for fitting concentration-
response (C-R) data resulted in consistent approach
across various ecotoxicological studies. The R drc
package was used to fit 22 different models to each
individual C-R dataset. A single model was then
selected from the 22 models to serve as the
representative C-R model. The selected model
represented the most statistically-robust model
available. In certain cases, this approach even
improved and helped to select most sensitive
toxicological endpoint, for example,

o Page 85- Ji et al. (2008) conducted a
chronic life-cycle test on the effects of
PFOA (with Moina macrocopa). TheM
macrocopa 7-day NOEC (reproduction:
number of young per adult) reported by
authors was 3.125 mg/L, the LOEC was
6.25 mg/L, and the MATC is 4.419 mg/L.
EPA performed C-R analysis for this study
and determined the number of young per
starting female as the most sensitive
endpoint with an acceptable C-R curve. The
EPA-calculated ECio was 2.194 mg/L
PFOA for M. macrocopa and used it
directly as the Moina GMCV.
o Page 88 Yang et al., 2014 Chronic survival
using EPA's method was more sensitive

than reproduction endpoint related ECio
values reported by the authors.
• In depth analyses and associated dose-response
graphs in Appendix A.2 and Appendix C.2 provides
further in-depth information on the EPA's approach
for fitting concentration-response (C-R) data.

Reviewer
5
In general, the data selected or excluded for criteria
development were appropriately used. A study published
by McCarthy et al. in 2021 reports toxicity of PFOA to
Chironomus dilutus - if I recall correctly, I believe these
data (on an insect) indicate that PFOA is not very toxic to
C. dilutus... even for exposures greater than 96 hours. This
agrees with EPA's assessment of available acute toxicity
data for freshwater insects; that PFOA is generally not
toxic to insects. I would, however, still urge more studies
on aquatic insects as this is an obviously diverse taxa with
many sensitive species. It is very possible that the available
test species of insects are not sensitive but other insects
such as mayflies or damselflies, etc. may, in fact, be quite
sensitive.
The write up of the Zhang et al. (2013 and 2014) papers
has a few grammatical errors and could benefit from
additional editing for clarity. I agree that using the intrinsic
rate of increase (or similar) is a very relevant endpoint but
it reads as though this was based on a 4 day observation
period for the 2014 paper. This does not quite make sense
to me... offhand, I would hypothesize that the
reported/calculated effect level of 1.166 mg/L would
decrease with a longer observation period. I think I may be
misunderstanding the experimental design - some editing
would help clarify. This is an important series of studies
All toxicity studies provided by Reviewer 5 (and all other reviewers),
including McCarthy et al. (2021), were all reviewed to ensure they
met data quality objectives outlined by the 1985 Guidelines, EPA 850
test guidelines, etc., and were included in the PFOA Aquatic Life
Criteria document as appropriate, based on their data quality.
Thank you for your comment, agreeing with EPA's assessment of the
relative tolerance of C. dilutus to acute PFOA exposures based on data
available at the time of the draft PFOA Aquatic Life Criteria
document. EPA agrees further insect toxicity testing would be
beneficial.
The Zhang et al. (2013, 2014) summaries in the updated PFOA
Aquatic Life Criteria draft have been edited for clarity.
Regarding the differences in the intrinsic rate of increase (r) endpoint
observation periods between the two studies, it is correct that the
calculation of "r" was based on full lifecycle observations (5.5-6.0
days for all treatments except for the second highest treatment level,
which was 8.3 days) in Zhang et al. (2013), and following a four-day
experiment in Zhang et al. (2014). In Section 3.2 (p. 117) of Zhang et
al. (2014), the authors argue that four days is of sufficient duration to
calculate "r" for the following reasons:
" The tested rotifer B. calyciflorus can produce multiple broods and
the F1 generation also produces neonates in 4 das we have
observed during a long observation period. This meets the
49

(see below regatding resting egg production) so clarity is
critical.
NOTE: the ECio of 0.076 mg/L for resting egg production
observed by Zhang et al. (2014b) is potentially a big deal.
EPA appears justified in not using this because it was only
one replicate, etc. but these data clearly point to a
potentially relevant effect at a relatively low concentration.
2.5.a.
2.5.a.i The EPA followed the 1985 guidelines allowing
them to calculate the FCV using the ACR
approach as outlined around p. 101. Given the
lack of data, this seems like a reasonable
approach. The actual calculation of the FCV
(based on the data from B. calyciflorus) is
appropriate and the use of this FACR to
determine the FCV of 0.3054 is appropriate.
Morevoer, as stated above, this value is also
generally in line with other criteria for PFOA
published by other jurisdictions.
2.5.a.ii I commented on this above but will mention
again. Overall, I think EPA is correct that the
available data on chironimids (Yange et al. 2014
and McCarthy et al. 2021) indicate that
chironomids are not sensitive to PFOA. That
said, it is probably the case that other insects such
as mayflies or damselflies (or other species?) are
more sensitive than chironomids. In contrast to
this statement, however, is that chironomids are
among the most sensitive to PFOS. Bottom line:
for PFOA and available insect toxicity data, it
appears PFOA is not toxic to insect but, clearly,
requirements of reproductive bioassays (Snell and Moffat, 1992). In
addition, a period offour days is sufficiently long for compounds to
achieve steady-state body burdens (Jones and de Voogt, 1999)
making a 4 d test in favor ofpredicting effects of chronic exposure."
Because the chronic exposure durations used to calculate "r" in Zhang
et al. (2014) and Zhang et al. (2013) were relatively similar, in
combination with the stated appropriateness of the 4-day exposure
duration, EPA has retained use of the chronic ECio (endpoint of
intrinsic rate of natural increase) from Zhang et al. (2013) and Zhang
et al. (2014) to calculate the B. calyciflorus SMCV.
Regarding the resting egg production endpoint, EPA acknowledges
the potential importance of the resting egg production endpoint and
thanks Reviewer 5 for noting, "EPA appears justified in not using this
because it was only one replicate."
Specific to comments to Charge Question 2.5.a:
2.5 .a.i Thank you for noting the reasonableness of the FACR
used to derive the FCV and reiterating the relative
similarities in magnitude between EPA's draft chronic
water column PFOA criterion and "other criteria for
PFOA published by other jurisdictions " Addition of new
chronic toxicity data in the updated draft PFOA criteria
document allow ed for the calculation of a draft chronic
freshwater criterion magnitude directly from the chronic
GSD rather than basing the magnitude on the FAV
transformed by the FACR, as was done in the draft PFOA
criteria document that underwent peer review.
2.5.a.ii All toxicity studies provided by Reviewer 5 (and all other
reviewers), including McCarthy et al. (2021), were all
reviewed to ensure they met data quality objectives
outlined by the 1985 Guidelines, EPA 850 test guidelines,
etc., and were included in the PFOA Aquatic Life Criteria
50

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.5. The Toxicity l):il:i lo Dome the Drsil'l Criterion
Re\ iowor
C om incuts
KIW Response

more data are needed to improve confidence in
this estimate.
2.5.b.
EPA's approach to fitting C-R data using the drc package
in R is, in my opinion, state of the art. The method can
easily test a variety of curves and the fit criteria can be
used to select the best fitting curves. Comments related to
specific studies and LC50 and EC10 estimates are elsewhere
in these comments. In general, my opinion is that the
PFOA criteria are slightly more defensible than the PFOS
criteria; this is explained more in the review of PFOS.
document as appropriate, based on their data quality. EPA
thanks Reviewer 5 for their comment noting that they
agree with EPA's assessment of the relative tolerance of
C. dilutus to acute PFOA exposures based on data
available at the time of the draft PFOA Aquatic Life
Criteria document. EPA agrees further insect toxicity
testing would be beneficial.
Specific to comments to Charge Question 2.5.b:
Thank you for your comment and for denoting the scientific
defensibility of the PFOA criteria. Responses to comments related to
specific studies and LC50 and EC10 estimates that are referenced by
Reviewer 5 are provided elsewhere in this document.
51

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.6 Please comment on the translation of the chronic water column criterion elements for aquatic life to derive the tissue-
based criterion elements, considering the bioaccumulation of PFOA and PFOS. In particular, please comment on:
2.6.a. Uncertainty surrounding the bioaccumulation factors (BAFs) used to translate of the chronic water column criterion
elements into tissue-based criterion elements.
2.6.b. EPA's determination of appropriate BAFs and the tissue types that the tissue criterion elements were based.
2.(>. The Tmnshilion of (ho Chronic Wsiter Column Criterion Elements lor Aqiiitlic Life (o l)eri\e (ho Tissue-li.iseil Criterion Klemenls
Considering liioiucuimilitlion
Re\ iewer
Coin nienls
El'A Response
Reviewer
1
The derivation of the tissue criteria in this manner is highly
uncertain. To my knowledge this is the first time EPA has
applied ambient water quality criteria protective of aquatic
life direct toxicity with uptake factors (bioaccumulation
factors (BAFs), bioconcentration factors (BCFs)) in this
manner to calculate tissue criteria. References are made to
the selenium tissue criteria, but those are used in the
reverse (i.e., criteria based on measured concentrations in
tissue used to calculate water criteria). The use of criteria
for water with a assumed uptake factor carries a large
amount of uncertainty, and in general, the use of measured
concentrations in tissue linked to adverse effects is a more
straightforward approach since it does not involve uptake
model predictions. This needs to be noted in the text. Also,
are the predicted tissue criteria meant to be a temporary
stop-gap until tissue effect data become available? This
should be discussed and clarified.
2.6.a. The use of BAFs derived from field studies is
inherently uncertain due to the wide variety of
techniques used in the compiled studies, their
analytical data quality, the differences in species
and ecosystems, experimental designs, spatial
uncertainties for mobile animals like fish, etc. That
being said, the use of a BAF value (or BCF) in
Thank you for your comment indicating that the derivation of the
tissue criteria by translating the chronic freshwater column criterion to
tissue concentrations with the use of BAFs is highly uncertain.
Reviewer 1 is correct that the derivation of these tissue criteria was the
reverse process of the previously derived criterion for selenium, which
instead translated a fish tissue criterion into corresponding lentic and
lotic water column criteria. The derivation of the PFOA tissue criteria
were translated in the manner presented in the draft criteria document
because measured effect concentrations in tissue were limited, with no
quantitatively acceptable and only 5 qualitatively-acceptable toxicity
studies (across four publications) evaluating tissue-based effects.
Therefore, there were insufficient data to derive a chronic tissue
criterion using a GSD approach from empirical tissue data. These
details were provided in Section 3.2.2 of the draft PFOA Aquatic Life
Criteria document. EPA also included a revised comparative
discussion between the tissue-based criteria magnitudes and the
limited empirical tissue data in Section 4.5 of the draft PFOA Aquatic
Life Criteria document. Section 4.5 of the draft PFOA Aquatic Life
Criteria document states:
"Tissue-based PFOA toxicity data were reported for four species
(three fish and one frog species) across five publications, all of
which were classified as qualitatively acceptable... Tissue PFOA
concentrations reported in these qualitative studies were lower than
52

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.(>. The Tmnshilion of (ho Chronic Wsiter Column Criterion Klenienls lor Aqn;itic l.il'e (o l)eri\e (ho Tissue-liiiseil Criterion Klemenls
Considering liio;uTuniul;ilion
Re\ iewer
Com mollis
KIW Response

criteria derivation is consistent with other criteria
developed by EPA. As noted above, the use of the
tissue criteria needs to be considered carefully, and
I think empirical tissue data from toxicity
experiments should form the basis of a next
iteration of a tissue criteria.
2.6.b. The development of BAFs for invertebrates, fish
(whole body), and fish (muscle) seems reasonable
for the application in estimating a draft or interim
tissue criteria until empirical tissue data can be
used to calculate tissue criteria directly
the tissue-based criteria calculated from BAFs. However, no
statistically significant effects of apical endpoints were observed in
any of these studies. Results of these studies do not provide any
evidence that the aquatic community will experience unacceptable
chronic effects at tissue-based criteria magnitudes. "
Finally, text has been added to the revised PFOA Aquatic Life Criteria
document to highlight the uncertainty of the tissue-based criteria
relative to the water column-based criterion. The revised draft PFOA
Aquatic Life Criteria document now states:
"The freshwater chronic water column criterion is more strongly
supported than the chronic tissue-based criteria because the water
column-based chronic criterion was derived directly from the results
of empirical toxicity tests. The chronic tissue-based criteria are
relatively less certain because they were derived by transforming
the chronic water column criterion into tissue concentrations
through BAFs, with any uncertainty and variability in the
underlying BAFs then propagating into the resultant tissue-based
criteria magnitudes."
Specific to comments to Charge Question 2.6.a:
EPA acknowledges the inherent uncertainties resulting from the use of
BAFs to derive tissue criteria. These uncertainties are present given
the differences in analytical methods used, the specific species and
habitats with paired tissue and water column measurements, and
experimental designs utilized across studies.
For these reasons, EPA screened the BAF literature in a manner
consistent with the evaluation criteria outlined in Burkhard (2021) and
focused on factors relating to: 1) number of water samples collected,
2) number of organism samples collected, 3) water and organism
temporal coordination in sample collection, and 4) water and organism
spatial coordination in sample collection. Additionally, the general
experimental design was evaluated. Further, these screening criteria
53

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.(>. The Tmnshilion of (ho Chronic Wsiter Column Criterion Klenienls lor Aqn;itic l.il'e (o l)eri\e (ho Tissue-liiiseil Criterion Klemenls
Considering liio;uTuniul;ilion
Re\ iewer
Com mollis
KIW Response

were consistent with those used for paired concentrations (both tissue
and water and tissue and diet concentrations) in the 2016 Selenium
Aquatic Life Criterion for Freshwaters (U.S.EPA 2016a). These
screening details are provided in Table 2-3 of the draft PFOA criteria
document that underwent external peer review. These screening
criteria for the BAF data reduce the impacts of the inherent
uncertainties that are present with the use of BAFs to derive tissue
criteria. Section 4.5 of the draft PFOA Criteria Document described a
comparative analysis between empirical tissue-based toxicity data and
the draft PFOA tissue-based criteria, which did not provide any
evidence that the aquatic community will experience unacceptable
chronic effects at tissue-based criteria magnitudes.
Additionally, EPA recognizes differences between field-derived and
experimentally-derived (or those linked to adverse effects) BAFs.
Despite the uncertainties noted in Reviewer l's comments, EPA only
used field-derived BAFs to derive the tissue criteria for PFOA. Use of
field-derived BAFs is consistent with previously derived criteria for
both aquatic life (the 2016 Selenium Aquatic Life Criterion for
Freshwaters; U.S.EPA 2016a) and human health (U.S.EPA 2000).
Although field-derived BAFs have inherent uncertainties discussed
above, field-derived BAFs better represent real-world
bioaccumulation of contaminants, including PFOA, through the
aquatic food web.
Specific to comments to Charge Question 2.6.b:
Thank you for your comment regarding the reasonableness of the
development and use of fish and invertebrate BAFs. Currently there
are insufficient data to derive chronic tissue criteria using a GSD
approach from empirical tissue data from toxicity studies. However,
as described in EPA's response to this comment above, the limited
empirical tissue concentrations were compared to the translated tissue
criteria magnitudes and there was no evidence that the aquatic
54

community will experience unacceptable chronic effects at tissue-
based criteria magnitudes.
EPA agrees additional empirical tissue data linked to adverse effects
would be helpful to better understand the translated tissue criteria
and/or to develop chronic tissue criterion using a GSD approach from
empirical tissue data from toxicity studies.
Reviewer
2
2.6.a. There appears to be an error in sub-section 2.11.3;
"The resulting tissue-based criteria magnitudes
correspond to the tissue type from the geometric
mean BAF used in the equation (see Section
2.12.3.1)." I cannot locate sub-section 2.12.3.1.1
assume the authors meant sub-section 2.11.3.1?
Sub-section 2.12.3 and sub-section 2.12.3.1 are
also referenced on pages 105 & 106, respectively.
I think the EPA has sufficiently addressed the
uncertainty around the use of BAFs and the
chronic water column criterion in the derivation of
tissue-based criterion. They have indicated that
tissue-based criterion should only be observed
once in 10 years. The use of the geometric mean of
the reported BAFs incorporates the range of BAFs
that may be present for different invertebrate and
fish species. The use of the chronic water column
criterion also builds in added conservatism to the
tissue-based criterion.
Prosser et al. (2016) reported BAFs for PFOA in
three freshwater species (two invertebrates and one
fish) (See Tables S29-31 in Supplementary
Information), but it was not considered in this
Thank you for your comment regarding the translation of the chronic
freshwater criterion into tissue-based criteria with the use of BAFs.
Specific to comments to Charge Question 2.6.a:
Section 2.12.3.1 should have read Section 2.11.3.1. The section cross-
references have been updated. The BAFs used to calculate the tissue
criteria were obtained from the BAF database created Lawrence
Burkhard in support of his publication: Burkhard, L.P. (2021)
Evaluation of Published Bioconcentration Factor (BCF) and
Bioaccumulation Factor (BAF) Data for Per- and Polyfluoroalkyl
Substances Across Aquatic Species. ET&C 40: 1530-1543.
BAFs reported in Prosser et al. (2016) were not in the Burkhard
(2021) database and were, therefore, not used to calculate BAFs.
Upon review of Prosser et al. (2016), this study was not included in
the BAF database developed by Burkhard (2021) because this study
reported biota sediment accumulation factors (BSAFs) instead of
BAFs. It is for this same reason EPA did not include Prosser et al.
(2016) among the BAFs that were used to derive the tissue criteria for
PFOA.
Specific to comments to Charge Question 2.6.b:
55

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.(>. The
11'iinsliition of (lie Chronic Wsiter Column Criterion Klenients lor Aqn;itic l.il'e (o l)eri\e (he Tissue-liiiseil Criterion Klenienls
Considering liioiucuimilitlion
Re\ iewer
ConinieiKs
KIW Response

assessment. It is not clear why it was not
considered.
Prosser, R.S., Mahon, K., Sibley, P.K., Poirier, D.,
Watson-Leung, T., 2016. Bioaccumulation of
perfluorinated carboxylates and sulfonates and
polychlorinated biphenyls in laboratory-cultured
Hexagenia spp., Lumbriculus variegatus and
Pimephales promelas from field-collected
sediments. Science of The Total Environment 543,
715-726. doi: 10.1016/j.scitotenv.2015.11.062
Thank you for your comment regarding the evaluation criteria that
were used for the BAFs and the use of fish BAFs for whole-body and
muscle.

2.6.b. The evaluation criteria for BAFs outline in Table
2-3 are appropriate and the decision to only use
high and medium quality BAFs is justified based
on the criteria that would make a BAF low quality.
It was a good idea to use fish BAFs based on the
concentration in muscle and whole body. Muscle
tissue is usually exclusively sampled in large fish,
especially as part of fish consumption guidelines.
The whole body is more appropriate for small fish
and invertebrate species, e.g., minnows, benthic
macroinvertebrates.

Reviewer
3
This sentence is very confusing: "EPA examined the
potential for criteria using only those studies in which test
organisms were exposed to PFOA in their diet, because
such studies would most closely replicate real-world
exposures (diet and/or diet plus water)." The tissue criteria
are based on water exposures, the relevance of this
statement and evaluation is lost on me.
EPA agrees with Reviewer 3 that the original sentence was unclear.
The sentence has since been revised to state:
"EPA considered deriving tissue-based criteria using empirical
toxicity tests with studies that exposed organisms to PFOA in water
and/or diet and reported exposure concentrations based on
measured tissue concentrations."
EPA used the PFOA BAFs that were compiled by and can be found in
Burkhard (2021). As such, tables summarizing the information
requested in Reviewer 3's comment can also be found in the
56

A table summarizing the species used to derive the BAFs
would be helpful to evaluate the comprehensiveness, i.e.,
pelagic vs sediment feeders.
supporting information of the paper (see:
https://doi.org/10.1002/etc.5010). EPA also added an appendix to the
draft PFOA Aquatic Life Criteria document that described the BAFs
used in development of the tissue-based criteria magnitudes.
Reviewer
4
2.6.a. Tissue criteria derived from the chronic water
column concentration (CCC) with the use of
bioaccumulation factors were developed by EPA.
The chronic fish whole-body tissue criterion is
54.1 mg/kg wet weight, the chronic fish muscle
tissue criterion is 9.37 mg/kg wet weight and the
chronic invertebrate whole-body tissue criterion is
23.9 mg/kg wet weight.
The freshwater chronic PFOA toxicity data with
measured tissue concentrations was limited, with
no quantitatively acceptable tissue-based tests.
Qualitatively acceptable tissue-based tests were
reported for four species (three fish species and
one amphibian) across five publications. Therefore,
there were insufficient data to derive tissue-based
criteria using a GSD approach from empirical
tissue data from toxicity studies. EPA thus
developed protective tissue-based criteria through a
bioaccumulation factor approach (Burkhard 2021).
Only BAFs of high and medium quality were used
to derive the tissue criteria. BAFs used in the
derivation of the PFOA tissue-based criteria
consisted of > 2 water and organism samples each
and were collected within one year and 2 km
distance of one another. Criteria for protection of
aquatic life and wildlife will need to use whole-
organism BAFs because the criteria are based on
Thank you for your comment summarizing the translation of the
chronic freshwater criterion to tissue criteria using PFOA BAFs.
Specific to comments to Charge Question 2.6.a:
The draft PFOA aquatic life criteria were derived to be protective of
aquatic life and did not explicitly consider aquatic-dependent wildlife.
If a potential aquatic-dependent wildlife criterion were derived in the
future it would be preferentially based on empirical tissue-based
toxicity data to evaluate effects. Evaluation of exposure potential for
these species, however, would likely consider PFOA exposures in diet
through the consumption of whole animals, in which case, use of
whole-body BAFs would be appropriate (among other possible
options for evaluating exposure via diet such as modeling
approaches). The freshwater tissue-based criteria are all equally
protective of the aquatic community whether they are expressed as
fish whole-body, fish muscle, or invertebrate tissues because these
tissue-based criteria were all translated from the same chronic effects-
based water column concentration (i.e., chronic water column
criterion).
Specific to comments to Charge Question 2.6.b:
EPA did not derive PFOA aquatic life criteria in tissues because these
are the tissues consumed by humans; the draft PFOA Aquatic Life
Criteria were derived to protect aquatic communities from acute and
chronic PFOA exposures and are not intended to be protective of
human health endpoints. Criteria were derived for fish whole-body,
fish muscle, and invertebrate tissues because these are the tissue types
57

whole-body toxicology for aquatic life (e.g., fish)
and for wildlife (e.g., birds), both of which
consume the whole fish (Stephan et al. 1985).
2.6.b. Within the body, PFOA tends to bioaccumulate
within protein-rich tissues, such as the blood serum
proteins and liver. BAFs are different for
muscle/fillet and whole-body tissues. Humans
consume muscle/fillets from fish and soft tissues
from bivalves, therefore the water quality criteria
recommended by EPA used BAFs based on these
tissues. EPA calculated additional tissue values for
liver, blood, and reproductive tissues by
transforming the freshwater chronic water column
criterion (i.e., 0.31 (ig/L) into representative tissue
concentrations using tissue-specific
bioaccumulation factors (BAFs). Furthermore,
EPA team justified to use female reproductive
tissues due to its relevance for potential maternal
transfer to offspring. There additional tissue-based
values were calculated for comparative purposes
and were not proposed as recommended criteria.
most commonly monitored by States and Tribes. Additional tissue-
based values were calculated and were presented in Appendix M of
the draft PFOA Aquatic Life Criteria document for informational
purposes.
Reviewer
5
2.6.a. Overall, this seems like a reasonable approach - to
estimate tissue-based criteria using the water
column criteria multiplied by the bioaccumulation
factors. The difficulty arises when we consider the
accuracy or robustness of the BAFs. I agree with
the criteria in Table 2-3 and especially emphasize
the importance of concurrent collections in space
AND time for tissues and environmental media.
Specific to comments to Charge Question 2.6.a:
Thank you for your comment regarding the translation of the chronic
freshwater criterion into tissue-based criteria with the use of BAFs and
your agreement with the BAF selection criteria in table 2-3 of the draft
PFOA Aquatic Life Criteria document.
Specific to comments to Charge Question 2.6.b:
58

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.(>. The Tmnshilion of (ho Chronic Wsiter Column Criterion Klenienls lor Aqn;itic l.il'e (o l)eri\e (ho Tissue-liiiseil Criterion Klemenls
Considering liio;uTuniul;ilion
Re\ iewer
Com mollis
KIW Response

2.6.b. I am very familiar with the Burkhard (2021) paper
which the PFOA document follows closely in
terms of BAFs. The BAFs used by EPA are
appropriate given the data. I also agree that the
most useful/appropriate tissues for BAFs are
invertebrates, fish muscle and fish whole body -
these are the most commonly analyzed and most
abundant in the literature. For what it's worth, in
my own research in which we collected and
analyzed fish tissues and co-located water samples,
our calculated BAFs for PFOA (and PFOS) were
close to the central tendency BAFs reported by
Burkhard (2021). I also agree that co-located and
sampled at the same time yield the most defensible
BAFs as PFAS concentrations can vary
considerably in space and time (not often shown in
the literature).
Thank you for your comment noting the appropriateness of the tissue
types included in the draft PFOA criteria document.
Thank you for noting your research in calculating PFOA BAFs
yielded similar results to the central tendency BAFs reported by
Burkhard (2021), which served as the BAF dataset for the draft PFOA
aquatic life criteria.
59

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.7 Please comment on the frequency and duration of the criterion elements, in particular please comment on the frequency
and duration components of the tissue-based criterion elements.
2.7. The I rcqucncv mid Duration of the C riterion Klemenls
Ue\ iewer
Com nicnls
KIW Response
Reviewer
1
The 4-day duration seems to be supported by the time scale
of toxicity discussed for the limited chronic studies
selected by EPA. This assumption should be revisited as
more data become available (please note in the document).
For the tissue-based criterion (page 107), there is no clear
support for assuming a 10-year exceedance frequency.
Given the uncertainty with the BAF-predicted tissue
criteria, and how little is known regarding the recalcitrance
of PFOA in aquatic ecosystems and recovery time if PFOA
inputs in water were halted, the assignment of a 10-year
exceedance frequency at this stage seems completely
arbitrary. We simply do not yet know the time frame over
which aquatic ecosystems recover from PFOA. It is not
technically supported to cite recovery times for selenium to
support a 10-year recovery time for PFOA, these are
completely different toxicants that have their own unique
fate and behavior. USEPA (1985) guidance suggests
assuming a 3-year frequency as a default, and the
discussion on page 17-108 is not scientifically convincing
enough to modify it to 10 years.
Additionally, it should be noted that the exceedance
frequency for another organic chemical, Tributyltin (TBT)
was set at 3 years by EPA in derivation of that criteria.
TBT exhibits uptake factors similar to PFOA (i.e., BCF of
approximately 2,000 L/kg, wet weight for goldfish, as
noted in the EPA TBT criteria document, which is higher
than the PFOA BAFs of 30-175 L/kg, wet weight being
used to calculate the fish tissue criteria). TBT is also
persistent in aquatic ecosystems, as noted by EPA. Given
Thank you for your comment stating the 4-day duration for the
chronic water column criterion is appropriate based on available data.
EPA agrees with reviewer 1 that "We simply do not yet know the time
frame over which aquatic ecosystems recover from PFOA" However,
we do know that PFOA is stable in water and air (UNEP 2015), and
thus, unless the source is eliminated, PFOA is likely to remain in
aquatic systems over time. Therefore, EPA considered the
bioaccumulative nature and persistence of PFOA in aquatic systems,
in combination with the documented recovery times of pollutants with
somewhat similar chemical attributes (Lemly 1997; Gergs et al. 2016)
set a reasonable and protective exceedance frequency for tissue-based
PFOA criteria.
As described by Reviewer 1, USEPA (1985) suggests a three-year
exceedance frequency; however, the suggestion of three years in
USEPA (1885) was intended to be for water column-based criteria.
Tissue-based exposures exceeding criteria magnitudes cannot
diminish at a rate of water column-based exposures and initiation of
subsequent recovery is delayed. Therefore, it is logical that the
exceedance frequency for tissue-based criteria for bioaccumulative
pollutants (such as selenium; USEPA 2016) be longer than three
years.
Unlike the draft PFOA Aquatic Life Criteria, the Tributyltin (TBT)
Aquatic Life Criteria (U.S. EPA 2004) does not include tissue-based
criteria. Only the draft tissue-based PFOA criteria specified
exceedance frequencies of 10 years. The 10-year frequency for tissue-
based criteria for PFOA was set to provide time for tissue
concentrations that accumulate through food webs to diminish, if
possible, in source reservoirs lower in the food web before being
60

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.7. The l-'ivqucncv :tiul Duration of I lie Criterion Klemenls
Ue\ iewer
Com mciils
KIW Response

TBT is at least an organic chemical, it is a closer analog
than selenium, which is an element. As such, the
exceedance frequency for the PFOA tissue criterion should
be set at the default of 3 years unless EPA can provide
convincing technical information specific to recovery times
for PFOA.
Additionally, on page 108, the paragraph that begins with
"Metals and other chemical pollutants such as PFOA..." is
not convincing as any quantitative support for EPA's 10-
year exceedance frequency for the chronic tissue-based
criteria. The text as written may give the reader the
conclusion that PFOA recovery may be "on the order of
decades", as EPA notes for selenium. There is no support
for the conjecture that PFOA recovery may be "relatively
slow" or require decades, as noted in my above comment.
eliminated in higher trophic level species and allowing for subsequent
potential ecological recovery.
Unless data suggest otherwise, a three-year recovery interval remains
appropriate for water column criteria where ecological recovery can
begin when chemical concentrations no longer exceed the criteria
magnitudes and durations. Consequently, the draft chronic water
column-based criterion for PFOA and the chronic TBT criterion both
specified a three-year exceedance frequency, as recommended by the
1985 Guidelines.
Based on ecological recovery times for other bioaccumulative and
persistent chemicals, ecological recovery times following elevated
PFOA concentrations in the tissues of aquatic organisms is expected
to be relatively long to allow for the dissipation of PFOA throughout
the food web and subsequent recovery. The draft PFOA Aquatic Life
Criteria document was revised in response to the comment from
Reviewer 1. The full text reference by Reviewer 1 (with added strike
throughs to represent deletions in response to Reviewer 1) is provided
below for informational purposes:
"Metals and other chemical pollutants such as PFOA, may
be retained in the sediment and biota, where they can result in
residual effects over time that further delay recovery. Long-term
uptake and subsequent excretion rates of PFOA has been
extensively studies in humans relative to aquatic life. Li et al.
(2017) reported a median PFOA half-life of 2.7years in human
serum following exposure to PFOA in drinking water, which
authors stated was in the range of previously published estimates.
Due to chemical retention in tissues, As a result, ecosystems
impacted by discharges of bioaccumulative pollutants (such as
PFOA or selenium) recover from chemical disturbances at
relatively slow rates. For example, Lemly (1997) concluded that
although water quality in Belews Lake in North Carolina (a
freshwater reservoir) had recovered significantly in the decade
since selenium discharges were halted in 1985, the threat to fish had
not been eliminated. The selenium dischargers that led to severe
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.7. The l-requency :tiul Duration of I lie Criterion Klemenls
Ue\ iewer
Com mciils
KIW Response

reproductive failure and deformities in fish, was still measurable
(fish deformities) in 1992 (seven years later) and in 1996 (ten years
later). Lemly (1997, pg. 280) estimated based on these data that
"the timeframe necessary for complete recovery from selenium
contamination from freshwater reservoirs can be on the order of
decades."

Beyond bioaccumulation, chemical-specific considerations
such as degradation vs. persistence may also provide a mechanism
influencing ecological recovery rates. The persistence of PFOA has
been attributed to the strong C-F bond, with no known
biodegradation or abiotic degradation processes for PFOA.
Similarly, metals do not degrade and may persist in aquatic systems
following elevated discharge. The persistence of metals may explain
why metals had the second longest median recovery time of any
disturbance described in a systematic review of aquatic ecosystem
recovery (Gergs et al. 2016). Gergs et al. (2016) showed recovery
times following metal disturbances ranged from roughly six months
to eight years (median recovery time = 1 year; 75th centile ~ 3
years; n = 20)."
Reviewer
2
As per Table 0-1,1 think the chosen durations and
frequencies for the acute and chronic criteria are
appropriate. They will ensure protection of aquatic life.
The duration of the tissue-based criterion is appropriate as
the concentration will be measured when biota is collected.
The 10 year frequency is appropriate considering that for
biota to reach the tissue-based criteria, they would likely to
have be exposed to concentrations at or above the chronic
criteria for an extended period of time.
Thank you for your comment.
Reviewer
3
This is a not an easy statement to comment on, as it may be
unlikely that the aquatic receptors will exceed or reach
these tissue concentrations prior to exceedances from the
CCC. Importantly, PFOA is not particularly
Thank you for your comment. Even if it is unlikely that aquatic
receptors will exceed or reach these tissue concentrations prior to
exceedances from the CCC (as suggested by Reviewer 3), EPA notes
the draft PFOA Aquatic Life Criteria document stated:
62

bioaccumulative compared to PFOS and this likely a less
sensitive threshold.
"All of these water column and tissue criteria are intended to be
independently applicable and no one criterion takes primacy. All of
the above recommended criteria (acute and chronic water column
and chronic tissue criteria) are intended to be protective of aquatic
life."
Because the chronic freshwater criteria are independently applicable,
they are protective of the scenario described by Reviewer 3.
Although PFOA is less bioaccumulative than PFOS (as noted by
Reviewer 3), EPA reiterates the PFOA tissue-based criteria were
derived using PFOA-speciflc BAFs.
Reviewer
4
PFOA concentrations in tissues are generally expected to
change only gradually over time in response to
environmental fluctuations. The chronic tissue-based
criteria averaging periods, or duration components, were
therefore specified as instantaneous, because tissue data
provide point, or instantaneous, measurements that reflect
integrative accumulation of PFOA overtime and space in
population(s) at a given site. It was appropriate for EPA to
inform the recommended ten-year exceedance frequencies
for the chronic tissue-based criteria given the large
variation in possible biological and physical variable
influencing ecological recovery.
Thank you for your comment noting that "It was appropriate for EPA
to inform the recommended ten-year exceedance frequencies for the
chronic tissue-based criteria."
Reviewer
5
Conceptually, the frequency and duration of the criterion
elements seem reasonable - the acute water column
criterion can't be exceeded for more than one-hour of
duration which is then not to be exceeded more than once
in three years. Even though many of the effect levels are
50%, this is likely protective given the duration of most
acute toxicity studies is certainly and convincingly more
than one hour. This applies to the chronic water column
Thank you for your comment. EPA agrees with Reviewer 5 that the
one-hour acute duration is protective since 11 the duration of most acute
toxicity studies is certainly and convincingly more than one hour"
EPA also agrees with Reviewer 5 that the chronic water column
criterion duration is also protective because 4 days is shorter than
typical chronic toxicity tests.
The acute PFOA criterion is not based directly on 50% effect levels.
EPA's PFOA FAY was derived following a long-established approach
63

criteria as well which is based on not exceeding a 4-day
duration; most chronic studies are much longer than 4 days.
The only real issue with this is that, for all intents and
purposes, these frequency and duration elements are not
measured in practice. In other words, I am unaware of
hourly measurements of PFAS in water or 4-day running
averages. So, conceptually, I believe the frequency and
duration elements are protective. However, in practice it is
not clear to me how these would be useful or would help
with regulation because the data related to frequency and
magnitude of PFAS in water is not at a fine enough
temporal resolution.
The frequency and duration for tissue-based criteria is a
little different, however. Tissue concentrations (as
mentioned in the document) represent an integration
through time and so a measure of fish tissues, for example,
provides some insight to exposures that have occurred over
longer than an hour or 4 days. In this case, not exceeding
the tissue-based criteria more than once in 10 years is
likely protective. It is also more likely that monitoring
programs would sample fish at least yearly which means
this criteria is likely the most useful from a monitoring and
clean-up perspective. It is still possible that high
concentrations in tissues will be "missed" with only
sampling once a year but this is far better than the
frequency and duration elements for the water column
criteria.
described in the 1985 Guidelines. Briefly, the PFOA FAV is based on
the 5th centile of a GSD, which was comprised of GMAVs calculated
from LC50 values. Consistent with the 1985 Guidelines, the FAV was
then divided by 2.0 to calculate the CMC. Dividing the FAV by 2.0
ensures the CMC represents a concentration that will not affect a large
portion of sensitive organisms. This is based on the established
premise that the ratio between LC50 values and corresponding LCi0W
values (e.g., LCo - LC10) is typically close to 2.0. Please see the
excerpt from the 1985 Guidelines below for further explanation:
"the Criterion Maximum Concentration is now equal to one-half the
Final Acute Value. The Criterion Maximum Concentration is
intended to protect 95 percent of a group of diverse genera, unless a
commercially or recreationally important species is very sensitive.
However, a concentration that would severely harm 50 percent of
the fifth percentile or 50 percent of a sensitive important species
cannot be considered to be protective of that percentile or that
species. Dividing the Final Acute Value by 2 is intended to result in
a concentration that will not severely adversely affect too many of
the organisms."
Similar to magnitudes, the duration and frequency components of
criteria are based on exposure-response relationships and toxicological
principles, irrespective of monitoring considerations. Absent of
continuous monitoring data, EPA agrees that it may be difficult to
assess PFAS concentrations in water bodies with enough temporal
resolution to continually assess average acute concentrations over the
course of a one-hour duration or average chronic concentrations over
the course of four days. Nevertheless, States and Tribes have adopted
and implemented water column-based water quality standards
containing the standard acute 1-hour and chronic 4-day durations, as
well as the 3-year frequency, dating back to the 1985 Guidelines. In
addition to monitoring, duration and frequency components of criteria
are particularly important for setting National Pollution Discharge
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
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2.7. The l-'ivqucncv :tiul Duration of I lie Criterion Klemenls
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Elimination System (NPDES) permit limits (U.S. EPA 1991). For
example, the 1985 Guidelines state:
"one of the most important uses of criteria is for designing waste
treatment facilities. Such facilities are designed based on
probabilities and it is not possible to design for a zero probability.
Thus, one of the important design parameters is the probability that
the four-day average or the one-hour-average will be exceeded, or,
in other words, the frequency with which exceedences will be
allowed."
Thank you for your comment indicating both the protectiveness and
utility of the magnitude, duration, and frequency components
associated with the tissue-based criteria.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
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2.8 Please provide any additional technical comments that you believe should be considered.
2.S. Acklilioiiitl l och 11 ic;i 1 ('ommenls (o Consider
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Reviewer
1
I have the additional detailed comments:
a) Please note that the comments provided in this file reflect a focus on of key
portions of the "Draft of the Aquatic Life Water Quality Criterion..."
document as directed by the above charge questions provided to me. Given
time and resource constraints and the scope of my review, it was not feasible
to provide a detailed review of the entire document and all of the supporting
references and their associated results and conclusions. As such, I reserve
my right to supplement or amend my comments in future, pending additional
review or new information. Thank you for the opportunity to assist EPA in
its work on this very important matter, and I was honored to be selected as a
reviewer.
b) Page 7: Please note in Figure 1-1 that this is the linear isomer of PFOA. It
would be helpful to note that the PFOA data in this study are likely from
experiments with water spiked with the linear PFOA isomer. It is
hypothesized that toxicity and bioaccumulation may differ between branched
and linear forms of PFCAs and PFASs. Linear PFOA is thought to be more
accumulative (as noted on Page 61) and potentially more toxic to aquatic life
when the dose is expressed as an external water concentration. At some sites,
a portion of the concentrations of PFOA in water (which are reported as the
sum of branched and linear PFOA) can be branched PFOA, so criteria
derived from linear PFOA could be overly protective. Please include this
uncertainty in the discussion in the document.
c) Page 47: With regard to the discussion of biomagnification factors (BMFs),
please acknowledge the Martin et al. 2003 paper where the BMF for fish was
noted to be less than one. This paper is very helpful for understanding
biomagnification from the diet in fish, as it was a controlled PFOA-spiked
food study.
d) Page 51: Starting here on this page and in the rest of this section, most of the
units need to be specified for dry weight or wet weight for concentrations of
Thank you for your comments. Responses to
corresponding alphabetical comments are
provided below.
a) Thank you for your comment. EPA
has received the final peer review
report from the contractor, and there
is no ability to supplement or amend
your comments in the final report.
Thank you for your review.
b) The caption to Figure 1-1 has been
updated to specify that it is the linear
isomer of PFOA. As stated in the
draft PFOA Aquatic Life Criteria
document, the criteria document
provides a critical review of all
aquatic toxicity data identified in
EPA's literature search for PFOA,
including the anionic form (CAS No.
45285-51-6), the acid form (CAS No.
335-67-1), and the ammonium salt
(CAS No. 3825-26-1). Further, EPA
added the requested text to the
Measurement Endpoints section of
draft PFOA Aquatic Life Criteria
document to note that PFOA toxicity
studies typically used the linear
PFOA isomer for dosing with fewer
studies using the branched isomer.
c) Reviewer 1 is assumed to be
referencing the publication; Martin, J.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
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PFOA in tissue. There were other instances of this error in the document as
well. For units of every concentration of PFOA in tissue, please be sure to
specify dry weight or wet weight.
e) Page 61: Regarding "nearly 90% of measured concentrations fell within 20%
of paired nominal concentrations", I believe that applies to the freshwater
studies reviewed (please note).
f) Page 64: The use of ECio values instead of effective concentration 20%
(EC20) values for chronic values is inconsistent with EPA's general practice
for developing aquatic life values. The selection of ECios for the selenium
criteria (EPA, 2016) was associated with the derivation of tissue guidelines.
In the EPA (2016) document, EPA noted "EC20s have historically been used
in the derivation of EPA criteria applicable to the water medium". As noted
in the EPA (2016) selenium guidance ECios were selected over EC20s
"given the nature of exposure and effects for this bioaccumulative
chemical." Additionally EPA (2016) selected ECio for selenium because "it
was found that the dose-response curves for selenium across a broad range
of fish genera are very steep, such that a small change in selenium tissue
concentration yielded a large increase in observed adverse effect."
g) First, all the derivation of aquatic life criteria for "bioaccumulative
chemicals" have not followed the process used for selenium, and there is no
quantitative discussion in the current document that compares the
bioaccumulation values for selenium to those of PFOA in a manner than
justifies the use of ECios. For example, EPA in its 2016 aquatic life criteria
for cadmium noted that cadmium "can bioaccumulate in aquatic organisms",
but EC20s (not ECios) were used as chronic values in the derivation of
aquatic life criteria in that document. Fundamentally, there is a logical
disconnect between adding additional conservativism (i.e., using ECios
instead of EC20S) simply because a chemical has a higher bioaccumulative
potential than another chemical or exceeds a BCF or BAF criteria used to
determine a chemical has "bioaccumulative" status by typical chemical
registration guidelines. The use of chronic exposure toxicology data
generally assumes that concentrations in the organisms have reached steady
W., S. A. Mabury, K. R. Solomon and
D. C. Muir. 2003a. Dietary
accumulation of perfluorinated acids
in juvenile rainbow trout
(Oncorhynchus mykiss).
Environmental Toxicology and
Chemistry: An International Journal.
22(1): 189-195. Following page 47 of
the draft PFOA criteria document
(referenced by Reviewer 1), page 48
of the draft PFOA criteria had cited
Martin et al. 2003a. Please see text
below from the draft PFOA Aquatic
Life Criteria document that
referenced Martin et al. (2003a) when
referring to the lack of PFOA
biomagnification in aquatic food
webs:
"PFOA is nearly always shown
not to biomagnijy (Loi et al.
2011; Martin et al. 2004; Tomy
et al. 2004; Xu et al. 2014; Zhou
et al. 2012), unless aquatic-
dependent species, such as
aquatic-dependent birds, are
included in the food web model
(Houde et al. 2006b; Kelly et al.
2009; Tomy et al. 2009). The
overall lack of biomagnification
in PFOA relative to PFOS is
attributed to its physical-
chemical properties, including a
shorter perfluorinated chain
length and the carboxylate head
group, both of which are
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state and, and thus, any bioaccumulation that has occurred is accounted for
and manifests in toxic action. Coincidentally, the general assumption is that
toxic responses have plateaued as well and that effective doses (measured
via external concentrations in water or concentrations in the organism) will
not change significantly with additional exposure time. The bioaccumulative
nature of the toxicant at that point is a moot point with regards to toxic
effects in an aquatic organism, so there seems no need to add additional
conservatism in the estimation of a threshold for potential ecologically-
significant effects on aquatic life. Adding additional conservatism to the
aquatic life criteria to protect other trophic levels (i.e. wildlife that consume
aquatic life) or human consumers of aquatic life, which does involve
bioaccumulation of chemicals in aquatic organisms, is not justified. Criteria
to protect wildlife and humans exposed via exposure pathways involving
bioaccumulation of chemicals in aquatic life are handled via separate
approaches, and are completely disconnected from the acute and chronic
toxicity data developed to evaluate the risks to aquatic invertebrates and
lower trophic level vertebrates like fish and amphibians.
h)	Second, EPA has not provided any analysis of the dose response curves that
demonstrates the need for ECios versus EC20s (as was mentioned for
selenium). Additionally, justification of the use of ECios by simply
referencing the regulatory policies of other countries seems to be insufficient
as the basis for a US policy, and is unsatisfying from a scientific perspective.
i)	More discussion is needed to support the poorly-supported move from
EC20s to ECios, or alternately, EC20s need to be used in throughout the
document, as consistent with past EPA practice in aquatic life criteria
derivation. ECios are more conservative than EC20s, but there is often
greater variability and uncertainty associated with ECio values given the
typical 50% effect ranges that are generally targeted in the experimental
designs of typical toxicological studies. Additionally, as noted in EPA's
2016 aquatic life criteria document for cadmium, ECios are "rarely
statistically significantly different from the control treatment." A 20% effect
has often been discussed as a point of departure of ecologically-significant
population- and community-level effects (e.g., Suter, 2000: Suter, G.W.,
associated with less efficient
assimilation into tissues and
faster excretion rates (e.g.,
Martin et al. 2003a, 2003b)."
d)	EPA ensured all tissue concentrations
reported in the draft PFOA Aquatic
Life Criteria document were reported
in wet or dry weight (ww or dw,
respectively). EPA specified that the
information was not provided
instances where authors did not
specify whether or not tissue
concentrations were reported in ww
or dw.
e)	Reviewer 1 is correct. Text on page
61 has been updated to include the
underlined text (see below) and more
clearly state the paired nominal and
measured concentrations were from
freshwater tests:
"Linear correlation between
measured and corresponding
nominal concentrations in
freshwater suggests a high
degree of precision between
paired observations across all
test conditions and nearly 90%
of measured concentrations fell
within 20% of paired nominal
concentrations in freshwater
toxicity tests, which represent
the test acceptability threshold
identified by EPA 's OCSPP's
68

Efroymson, R.A., Sample, B.E., & Jones, D.S. (2000). Ecological Risk
Assessment for Contaminated Sites. CRC Press. April).
j) Overall, the adoption of a more conservative 10% effect level (i.e., ECio) for
chronic values used in criteria calculation carries large environmental
management and policy implications. As noted above, clarification and
careful justification is needed. EPA needs to clearly articulate (ideally with
ample scientific support) why the additional conservatism is needed. This
important potential policy matter deserves an open and earnest discourse
among the scientific, stakeholder, and regulated communities.
k) Page 67: It appears that only studies in which organisms exposed via diet
were included for evaluation of tissue criteria. Is this correct? It is
questionable to exclude effect concentrations in tissue from experiments in
which exposure of PFAS was only via water. EPA (2016) took the "dietary
exposure only" approach with selenium because the primary exposure route
for selenium has been shown to be via the diet in natural ecosystems. In
contrast, for many aquatic animals (especially lower trophic level fish and
invertebrates), a significant portion of the exposure to PFOA is via non-
dietary pathways. Part of this is due to the fact that controlled studies (e.g.,
Martin et al., 2003 studies cited in the document) have found that water-to-
organism BCFs for aquatic life such as fish are generally larger than diet-to-
organism biomagnification factors (BMFs). Additionally, there is no reason
to expect dietary or non-dietary exposure pathways would affect toxic
responses given the relatively rapid internal kinetics of PFAS in aquatic life
(i.e., half-life of hours or days), especially for small invertebrates and fish
that are in relative equilibrium with their surrounding exposure water.
1) Page 82: The intrinsic rate of increase (basis of the chronic value from the
Zhang et al. (2013) study is not atypical endpoint used in aquatic life criteria
derivation. This chronic value has a large influence over the criteria
calculated in this document, as noted below. More detail is needed on the
calculation of the endpoints used in the two Zhang et al. papers, and some
additional information should be provided on what this endpoint means
ecologically in comparison to typical reproductive endpoints used in criteria
Ecological Effects Test
Guidelines."
f - j) Response applies to comments "f'
through "j." EPA has retained use of
chronic ECio values to ensure species
protection, considering the long-term
persistence of PFOA in environmental
media. Further, use of a 10% effect
concentration for deriving chronic
criteria magnitudes is also consistent
with the harmonized guidelines from
OECD and the generally preferred
effect level for countries such as
Canada, Australia, and New Zealand
(CCMC 2007; Warne et al. 2018).
EPA also retained use of EC10 values
to further afford protection of aquatic
life from this bioaccumulative
"forever" chemical. Additionally,
steady state is not an assumption of
chronic tests, particularly for
chemicals that take longer to reach
equilibrium. Chronic tests simply
measure the effects of longer-term,
lower exposures, that don't generally
outright produce lethality.
k) EPA agrees the statement referenced
by Reviewer 5 was unclear. The text
within the revised PFOA criteria
document has been updated to state:
"EPA considered deriving
tissue-based criteria using
empirical toxicity tests with
69

derivation. Note that for stable populations, the intrinsic rate is 0, so
achieving a maximal rate of increase is not always ecologically sustainable.
Some additional explanation would be helpful to the reader.
m) Page 98: Both the Criterion Maximum Concentration (CMC) and Criterion
Continuous Concentration (CCC) are heavily influenced by toxicity tests on
a single organism (rotifers, Brachionus calyciflorus) conducted by Zhang et
al. (2013) and Zhang et al. (2014). For example, the rotifer acute value is the
second lowest value of the four values used to calculate the FAV and CMC.
The ACR used to calculate the CCC (using the with the FAV) is derived
entirely from the Zhang et al. (2013) study (Page 101). I would recommend
the ACR be recalculated to reflect more of a central tendency estimate that
incorporates other ACRs, rather than relying solely on the Zhang et al.
(2013) result (see above 5a comment). Regardless, I think a few sentences
should be added to note the strong influence of these rotifer studies on
PFOA criteria. Given this, additional experimentation and verification of the
Zhang et al. results seems would seem to be useful and this is worth
mentioning in the document as well.
n) Page G-l: Please explain the acceptable duration acceptable for tests for
which "Duration too short" is noted. It would be good to provide the
acceptable durations that would be considered acceptable for these species.
Perhaps a summary table for acceptable durations for particular endpoints
could be provided in this document.
o) Appendix G: The endpoints such as "decrease mRNA expression levels of
neural genes DjFoxD, DjotxA and DjotxB" and "decrease in inflammatory
cytokines (IL-1B and IL-21) in spleen" are atypical. These should be noted
under "Deficiencies".
p) Page H-2: First use of "atypical duration" in the table. This entry is
inconsistent with other entries (e.g., "duration too short") and does not
clearly describe why the experiment is not considered. Please explain this
table entry.
studies that exposed organisms
to PFOA in water and/or diet
and reported exposure
concentrations based on
measured tissue
concentrations."
1) The intrinsic rate of increase ("r"),
while not a typical endpoint in criteria
derivation for many species, has been
used as a reproductive endpoint for
rotifer taxa, which have rapid
generation rates, in previous criteria.
While a conventional reproductive
endpoint measures some aspect of
population growth (e.g., egg
production, young per adult), the
intrinsic rate of natural increase is
actually more comprehensive,
accounting for all births and deaths
over a given time interval, as it is
expressed as the net change in a given
population per day. In toxicity
studies, it is commonly applied to
rotifers, as their generation time is at
a similar time scale as many toxicity
studies. Although "r" is typically near
or at zero for a stable population for a
long-lived species, in an experimental
setting with a short-lived, rapidly
reproducing species, intrinsic rate of
increase is an appropriate measure of
reproduction, as test animals are not
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limited by food or physical space


during the test duration.


m) EPA responded to the selection of the


FACR in detail in Section 2.5.a.l.


Addition of new chronic toxicity data


in the updated draft PFOA criteria


document allow ed for the calculation


of a draft chronic freshw ater criterion


magnitude directly from the chronic


GSD rather than basing the


magnitude on the FAV transformed


by the FACR, as was done in the


draft PFOA criteria document that


underwent peer review.


n) Table G. 1 of the draft PFOA Aquatic


Life Criteria document provided


summary information (including test


durations) for those tests that were


considered qualitatively acceptable.


Appendix G.2 subsequently provided


detailed summaries of all studies


referenced in Table G.l. Acceptable


acute and chronic study durations


(including taxa-specific test


protocols) can be found established


test protocols/methods, that were


referenced in EPA's draft PFOA


Aquatic Life Criteria document. The
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
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draft PFOA Aquatic Life Criteria


document specifically stated:


"Studies were then further


reviewed by EPA, Office of


Water (OW) to determine test


acceptability for use in criteria


derivation. Studies that did not


fully meet the data quality


objectives outlined in the 1985


Guidelines, EPA's Office of


Chemical Safety and Pollution


Prevention (OCSPP) 's


Ecological Effects Test


Guidelines (U.S. EPA 2016b),


and EPA OW's internal data


quality standard operating


procedure (SOP; which are


consistent with OCSPP's data


quality review approach; U.S.


EPA 2018) were not considered


for inclusion in the criteria


derivation, including some


studies with other PFAS


exposures, but were considered


qualitatively as supporting


information and are


characterized in the Effects


Characterization."


o) Within table G. 1 and H. 1


(qualitatively acceptable freshwater


and estuarine/marine toxicity data),


the deficiencies column now includes


"non-apical endpoint" for studies that


did not report apical endpoint,
72

including the examples described by
Reviewer 1.

p) Use of "atypical duration" occurred
five times within Table H. 1 and once
in Appendix H.2 (i.e., summaries of
studies in Table H.l) and did not
occur elsewhere in to draft PFOA
Aquatic Life Criteria document.
Instances where "atypical duration"
was used in Table H. 1 described tests
with exposure durations of either 6 or
7 days. In these instances, Table H.l
has been revised to state:
"Exposure duration too short
for chronic test and too long for
acute test."
Reviewer
2
I think the EPA's criteria for PFOA are very defensible based on the science and
data available. I think they did a great job clearly laying out how they derived the
criteria and providing all of the data that was used in the derivation.
Thank you for your comments. All previously
mentioned comments have been responded to
and addressed accordingly in the updated
PFOA draft.
Reviewer
3
All technical comments have been previously mentioned
Thank you for your comments.
Reviewer
4
Some additional edits/suggestions are listed below:
1- Appendix list in Table of Contents in missing
2- List of Tables not matching with Tables listed in the text
Table 2-4. is Table 2.1 Measured Perfluorooctanoic acid (PFOA)
Concentrations in Surface Waters Across the United States. .Error! Bookmark
Thank you for your comments. Responses to
corresponding numerical comments are
provided below.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
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not defined.
Table 2-5. is Table 2.2 Summary of Assessment Endpoints and Measures of
Effect Used in the Criteria Derivation for PFOA. 74
Table 2-6 is Table 2.3 . Evaluation Criteria for Screening Bioaccumulation
Factors (BAFs) in the Public Literature. Error! Bookmark not defined.
3- Page xiv Table 0-1. Recommended Freshwater Perfluorooctanoic acid (PFOA)
Aquatic Life Ambient Water Quality Criteria-
Superscript 3 3 listed as footnote in the Table but not referenced in the table
4- Table 2-2. Summary of Assessment Endpoints and Measures of Effect Used
in the Criteria Derivation for PFOA
Assessment
Kndpoinls lor the
Aquatic
Commiinitv
Aquatic Life:
Survival, growth,
and reproduction of
freshwater and
estuarine/marine
aquatic life (i.e.,
fish, amphibians,
aquatic
invertebrates)
Measures of Kfleet
For effects from acute exposure:
1. LC50 concentrations in water, diet,
and/or tissue (e.g., muscle, blood, egg)
2. NOEC and LOEC concentrations in
water, diet, and/or tissue (e.g., muscle,
blood, egg)
For effects from chronic exposure:
1. EC10 concentrations in water, diet,
and/or tissue (e.g., muscle, blood, egg)
1. A list of appendices is now included
at the beginning of the document.
2. The list of tables has been corrected.
3. Table 0-1 of the draft PFOA Aquatic
Life criteria document that underwent
Peer Review contained a superscript
"J" following "Instantaneous" within
the table.
4. Table 2-2 has been revised to only
include assessment endpoints and
measures of effect as they pertain to
water column concentrations, since
only water-column exposures were
used to derive the draft PFOA
criteria.
5. Table 1.1 has been updated to include
current information for Australia and
New Zealand.
6. Section 1.2 of the PFOA Aquatic Life
criteria document has been updated to
refer to OECD (2021), specifically
stating:
"EPA 's Office of Pollution
Prevention and Toxics (OPPT)
defines a PFAS chemical as: "a
structure that contains the unit
R-CF2-CF(R)(R"), where R, R',
andR" do not equal "H" and the
carbon-carbon bond is saturated
(note: branching, heteroatoms,
74

2. NOEC and LOEC concentrations in
water, diet, and/or tissue (e.g., muscle,
blood, egg); Only used when an ECio
could not be calculated for a genus.

and cyclic structures are
included)."
No edits were made to Table 1-2 of
the draft PFOA Aquatic Life Criteria
document as this table reflects the
terminology in OECD (2021),
specifically the general terms used to
simply categorize PFASs based on
simple traits in Figure 11 of OECD
(2021).

Please review if the highlighted muscle, blood and egg would be relevant to this
section.
5- Section 1.1 Previously Derived PFOA Toxicity Values and Thresholds
Table 1.1 to be updated by current information for Australia and new Zealand.
Freshwater values are to be used on an interim basis until final marine guideline
values can be set using the nationally-agreed process under the Australian and
New Zealand Guidelines for Fresh and Marine Water Quality. Marine guideline
values developed by CRC CARE are under consideration through the nationally-
agreed water quality guideline development process. The Australian and New
Zealand Guidelines for Fresh and Marine Water Quality (ANZG, 2018;
ANZWQG, 2000) and Australia's PFAS Environmental Management Plan
(HEPA, 2020) both recommend that a 99% species protection level be used as a
guideline for bioaccumulating substances such as PFOS, PFOA, and PFHxS (as
given below) as a precautionary approach.
7. Table 1-3 was updated to reflect the
latest PFAS nomenclature provided in
OECD (2021), specifically the
addition of PFAAs that were not
considered to be PFASs previously
by Buck et al. (2011) are now
included in Table 1-3 based on those
PFAAs identified in Figures 9 and 10
of OECD (2021).
8. The effects symbol in the conceptual
model now states:
"Deformities, Reproductive and
Growth Impairments,
Mortality."
9. The cross reference has been
corrected.
75

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.S. Acklilioiiitl l och 11 ic;i 1 ('ommcnls (o Consider
Uc\ icwcr
Com niciils
KIW Response




Kxposurc
scen;i rio
PI OA
Kxposurc scenario
Comments find source

Freshwater
19
^g/L
99% species protection -
high conservation value
systems
Australian and New
Zealand Guidelines for
Fresh and Marine Water
Quality - technical draft
default guideline values
for PFOA.
The draft guidelines do
not account for effects
which result from the
biomagnification of
toxicants in air-breathing
animals or in animals
which prey on aquatic
organisms.
The WQGs advise
P40FP40F.1PP that the
99% level of protection
be used for slightly to
moderately disturbed
systems. This approach is
generally adopted for
chemicals that
bioaccumulate and
biomagnify in wildlife.
Regulators may specify
or environmental
legislation may prescribe
220
^g/L
95% species protection -
slightly to moderately
disturbed systems
632
l-lg/L
90% species protection -
highly disturbed systems
1824
^g/L
80% species protection -
highly disturbed systems
1 https://www.waterqualitv.gov.aU/anz-guidelines/guideline-values/default/water-qualitv-toxicants/local-conditions#bioaccumulation
76

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	



2.S. Acklilioiiitl Te
chniciil Comments (o C onsider
Ue\ iewer
(0111 niciils
KPA Response





the level of species
protection, required,
rather than allowing for
case-by-case
assessments.




Kxposure
scciiiirio
I'l OA
Kxposure scenario
Comments ;nul source




Interim
marine
19
^g/L
99% species protection
- high conservation value
systems
As above.
Freshwater values are to
be used on an interim
basis until final marine
guideline values can be
set using the nationally-
agreed process under the
Australian and New
Zealand Guidelines for





220
^g/L
95% species protection
- slightly to moderately
disturbed systems





632
l-lg/L
90% species protection -
highly disturbed systems


77

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.S. Additional l och 11 ic;i 1 Comments (o Consider
Ue\ iewer
C 0111 iiicnls
KPA Response


1824
l-lg/L
80% species protection -
highly disturbed systems
Fresh and Marine Water
Quality.
The WQG advise that in
the case of estuaries, the
most stringent of
freshwater and marine
criteria apply, taking
account of any available
salinity correction.
Marine guideline values
developed by CRC
CARE are under
consideration through the
nationally-agreed water
quality guideline
development process.


6-	Table 1 2. Two Primary Categories of PFAS
Please refer to OECD 2021 to be consistent with PFAS
terminology/nomenclature
OECD (2021), Reconciling Terminology of the Universe of Per- and
Polyfluoroalkyl Substances: Recommendations and Practical Guidance,
OECD Series on Risk Management, No. 61, OECD Publishing, Paris
7-	Table 1.3 page 5
Please review Figure 9 OECD 2021 (also attached as PDF)
8-	Conceptual Model of PFOA in the Aquatic Environment and Effects
Figure 2.7 page 56- Growth as an endpoint missing in the endpoints - first
pentagon

78

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
(PFOA)"
2.S. Acklilioiiitl l och 11 ic;i 1 ('ommenls (o Consider
Ue\ iewer
Com niciils
KIW Response

9- Page 69 last paragraph- Table 2-6 outlines the screening criteria for study
evaluation and ranking. Cross reference to be updated to Table 2.3

Reviewer
5
Overall, I think the PFOA criteria document and the reported criteria are robust
given the constraints imposed by data availability. I agree with most assumptions
made by EPA and the actual criteria values reported. I would, however, suggest that
EPA consider revising the 1985 Guidelines. Re-evaluating the guidelines and
publishing and update, even if changes are minimal would be a valued effort. I am
sure that EPA has more than enough to do but given the importance of AWQC, I
think it would be better to base the science on a more recent effort. There has been
a lot of solid science in the last 35 years with a focus on criteria, species sensitivity
distributions, etc. Although not used heavily for PFOA the use of the 4 most
sensitive taxa and then a linear regression to estimate the criteria seems less robust
than other methods. I could be wrong but here is where an updated Guidelines
would be helpful - that may be an effort worth exploring quantitatively.
Thank you for your comments.
EPA uses the best available science in
developing AWQC.
EPA has initiated an effort to update the 1985
Guidelines. When a draft revision is
completed it will be peer reviewed and made
available for public comment.
Reviewer 5 commented that a model was fit
to the four most sensitive endpoints (i.e., four
most sensitive GMAVs and GMCVs) to
derive the criteria, which was not the case.
Instead, derivation of the acute and chronic
criteria followed long-established methods
outlined in the 1985 Guidelines. The
established criteria calculation outlined in the
1985 Guideline uses a log-triangular fit to
determine the 5th centile of a GSD. Acute and
chronic GSDs (which included all
quantitatively acceptable toxicity data) were
presented in the Effect Analysis section of the
draft PFOA Aquatic Life Criteria document.
When there are less than 59 genera in a GSD,
the 5th centile is inherently based on the four
most sensitive genera, with the remaining
tests only influencing the FAV through the
in the calculation. Please see the excerpt
from the 1985 Guidelines below for further
explanation.
79

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctanoic Acid
	(PFOA)"	
2.S. Acklilioiiitl l och 11 ic;i 1 ( onimcnls (o Consider
Ue\ iewer
C 0111 iiicnls
KIW Response


"Order the GMAVsfrom high to low.


L. Assign ranks, R, to the
GMA Vsfrom "1 "for the lowest
to "N" for the highest. If two or
more GMA Vs are identical,
arbitrarily assign them
successive ranks.


M. Calculate the cumulative
probability, P, for each GMAV
as R/(N+1).


N. Select the four GMAVs which
have cumulative probabilities
closest to 0.05 (if there are less
than 59 GMAVs, these will
always be the four lowest
GMAVs)."


Additionally, research conducted since the
1985 Guidelines were published has
continued to suggest use of a log-triangular
distribution to estimate an HCs from
sensitivity distributions is appropriate.
USEPA (2011) concluded:


"Judging by bias at small
sample sizes, distributions on
log-transformed data (normal,
logistic, triangular, Gumbel)
generally outperformed
distributions on untransformed
data (Pareto, Weibull, and
Burrni) and of the former, the
log-normal, log-logistic, and
log-triangular showed very
similar performance."
80

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA)"
3 REFERENCES CITED BY EPA IN RESPONSES
Awkerman, J. A., S. Raimondo, C. R. Jackson and M. G. Barron. 2014. Augmenting aquatic species
sensitivity distributions with interspecies toxicity estimation models. Environmental toxicology and
chemistry. 33(3): 688-695.
Bejarano, A. C., S. Raimondo and M. G. Barron. 2017. Framework for optimizing selection of interspecies
correlation estimation models to address species diversity and toxicity gaps in an aquatic database.
Environmental science &technology. 51(14): 8158-8165.
Buck, R. C., J. Franklin, U. Berger, J. M. Conder, I. T. Cousins, P. de Voogt, A. A. Jensen, K. Kannan, S. A.
Mabury and S. P. van Leeuwen. 2011. Perfluoroalkyl and polyfluoroalkyl substances in the environment:
terminology, classification, and origins. Integr. Environ. Assess. Manag. 7(4): 513-541.
Burkhard, L. P. 2021. Evaluation of published bioconcentration factor (BCF) and bioaccumulation factor
(BAF) data for per-and polyfluoroalkyl substances across aquatic species. Environmental Toxicology and
Chemistry.
CCME (Canadian Council of Ministers of the Environment). 2007. Protocol for the derivation of water
quality guidelines for the protection of aquatic life. Winnipeg, Manitoba: Canadian Council of Ministers of
the Environment. Available online at: http://ceqg-rcqe.ccme.ca/download/en/220.
Coats, K., G. Long and J. Adelson. 2017. Quality Systems Manual (QSM) for Environmental Laboratories.
Department of Defense, Washington, DC.
Dyer, S. D., D. J. Versteeg, S. E. Belanger, J. G. Chaney and F. L. Mayer. 2006. Interspecies correlation
estimates predict protective environmental concentrations. Environmental science & technology. 40(9): 3102-
3111.
S.D. Dyer, D.J. Versteeg, S.E. Belanger, J.G. Chaney, S. Raimondo, and M.G. Barron. 2008. Comparison of
Species Sensitivity Distributions derived from interspecies correlation models to distributions used to derive
water quality criteria, Environ. Sci. Technol. 42; 3076-3083.
Fabbri, R., M. Montagna, T. Balbi, E. Raffo, F. Palumbo and L. Canesi. 2014. Adaptation of the bivalve
embryotoxicity assay for the high throughput screening of emerging contaminants in Mytilus
galloprovincialis. Mar Environ Res. 99: 1-8.
Gergs, A., S. Classen, R. Strauss, R. Ottermanns, T. Brock, H. Ratte, U. Hommen and T. Preuss. 2016.
Ecological Recovery Potential of Freshwater Organisms: Consequences for Environmental Risk Assessment
of Chemicals. Rev. Environ. Contam. Toxicol. 236: 259-294.
Hayman, N. T., G. Rosen, M. A. Colvin, J. Conder and J. A. Arblaster. 2021. Aquatic toxicity evaluations of
PFOS and PFOA for five standard marine endpoints. Chemosphere. 273: 129699.
Hazelton, P. D., W. G. Cope, T. J. Pandolfo, S. Mosher, M. J. Strynar, M. C. Barnhart and R. B. Bringolf.
2012. Partial Life-Cycle and Acute Toxicity of Perfluoroalkyl Acids to Freshwater Mussels.Environ. Toxicol.
Chem., 31: 1611-1620.
Jones, K.C. and P. de Voogt. 1999. Persistent organic pollutants (POPs): state of the science. Environ. Pollut.
100: 209-221.
Lath S, Knight ER, Navarro DA, Kookana RS, McLaughlin MJ. 2019. Sorption of PFOA onto different
laboratory materials: Filter membranes and centrifuge tubes. Chemosphere 222: 671- 678.
Lemly, A. D. 1997. Ecosystem recovery following selenium contamination in a freshwater reservoir.
Ecotoxicology and Environmental Safety. 36(3): 275-281.
81

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA)"
Li, M.H. 2008. Effects of nonionic and ionic surfactants on survival, oxidative stress, and cholinesterase
activity of planarian. Chemosphere 70(10): 1796-1803.
Li, M.H. 2009. Toxicity of perfluorooctane sulfonate and perfluorooctanoic acid to plants and aquatic
invertebrates. Environ. Toxicol. 24(1): 95-101.
Martin, J. W., S. A. Mabury, K. R. Solomon and D. C. Muir. 2003a. Dietary accumulation of perfluorinated
acids in juvenile rainbow trout (Oncorhynchus mykiss). Environmental Toxicology and Chemistry: An
International Journal. 22(1): 189-195.
McCarthy, C.J., S. A. Roark, D. Wright, K. O'Neal, B. Muckey, M. Stanaway, J. N. Rewerts, J. A. Field, T.
A. Anderson, C. J. Salice. 2021. Toxicological Response of Chironomus dilutus in Single-Chemical and
Binary Mixture Exposure Experiments with 6 Perfluoralkyl Substances. Environ. Contam. Toxicol. 40(8):
2319-2333.
NRC. 2013. Assessing risks to endangered and threatened species from pesticides. National Academies Press
Washington, DC. pp 142
OECD. (Organisation for Economic Co-operation and Development). 2021. Reconciling Terminology of the
Universe of Per- and Polyfluoroalkyl Substances: Recommendations and Practical Guidance. Series on Risk
Management No.61. Paris, France. ENV/CBC/MONO(2021)25. pp.34.
https://www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=ENV/CBC/MONO(2021)25&doc
Language=en
Prosser, R. S., K. Mahon, P. K. Sibley, D. Poirier and T. Watson-Leung. 2016. Bioaccumulation of
perfluorinated carboxylates and sulfonates and polychlorinated biphenyls in laboratory-cultured Hexagenia
spp., Lumbriculus variegatus and Pimephales promelas from field-collected sediments. Sci Total Environ.
543(Pt A): 715-726.
Raimondo, S. and M. G. Barron. 2020. Application of Interspecies Correlation Estimation (ICE) models and
QSAR in estimating species sensitivity to pesticides. SAR and QSAR in Environmental Research. 31(1): 1-
18.
Raimondo, S., C. R. Jackson and M. G. Barron. 2010. Influence of taxonomic relatedness and chemical mode
of action in acute interspecies estimation models for aquatic species. Environmental science & technology.
44(19): 7711-7716.
Rewerts, J. N., E. C. Christie, A. E. Robel, T. A. Anderson, C. McCarthy, C. J. Salice and J. A. Field. 2021.
Key considerations for accurate exposures in ecotoxicological assessments of perfluorinated carboxylates and
sulfonates. Environmental toxicology and chemistry. 40(3): 677-688.
Ritz, C. and J. C. Streibig. 2016. Analysis of dose-response curves.Package 'drc'. 3.0-1. https://cran.r-
proj ect. org/web/packages/drc/drc .pdf
Snell, T.W. and B.D. Moffat. 1992. A 2-d Life cycle test with the rotifer Brachionus calyciflorus Environ.
Toxicol. Chem. 11: 1249-1257
U.S.EPA. (US Environmental Protection Agency). 1985. Guidelines for deriving numerical national water
quality criteria for the protection of aquatic organisms and their uses. Office of Research and Development.
PB85-227049. https://www.epa.gov/sites/default/files/2016-02/documents/guidelines-water-quality-
criteria.pdf
U.S. EPA (United States Environmental Protection Agency). 1991. Technical support document for water
quality-based toxics control. U.S. EPA, Office of Water, Washington, DC. EPA/505/2-90-001, PB91-127415.
U.S.EPA. (U.S. Environmental Protection Agency). 2000. Methodology for Deriving Ambient Water Quality
Criteria for the Protection of Human Health. Office of Water. EPA-822-B-00-004.
https://www.epa.gOv/sites/default/files/2018-10/documents/methodology-wqc-protection-hh-2000.pdf
82

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA)"
U.S.EPA. (U.S. Environmental Protection Agency). 2003. Ambient Aquatic Life Ambient Water Quality
Criterion for Tributyltin (TBT). Office of Water. Washington, DC. EPA 822-R-03-031.
https://www.epa.gov/sites/default/files/2019-02/documents/ambient-wqc-tributyltin-final.pdf
U.S.EPA (United States Environmental Protection Agency). 2011. Review of methods for characterizing
effects of pesticides and other chemical stressors to aquatic organisms. Office of Pesticide Programs.
Washington, D.C. EPA-HQ-OPP-2011-0898-0005.
U.S.EPA. (U.S. Environmental Protection Agency). 2016a. Aquatic Life Ambient Water Quality Criterion for
Selenium - Freshwater. Office of Water. Washington, DC. EPA 822-R-16-006.
https://www.epa.gov/sites/production/files/2016-07/documents/aquatic_life_awqc_for_selenium_-
_freshwater_2016 .pdf
U.S.EPA (U.S. Environmental Protection Agency). 2016b. Series 850 - Ecological Effects Test Guidelines.
Office of Chemical Safety and Pollution Prevention, Washington, DC. Accessed March 2021.
https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/series-850-ecological-effects-test-
guidelines.
Willming, M. M., C. R. Lilavois, M. G. Barron and S. Raimondo. 2016. Acute toxicity prediction to
threatened and endangered species using interspecies correlation estimation (ICE) models. Environmental
science & technology. 50(19): 10700-10707.
Warne, M.St.J., G.E. Batley, R.A. van Dam, J.C. Chapman, D.R. Fox, C.W. Hickey and J.L. Stauber. 2018.
Revised method for deriving Australian and New Zealand water quality guideline values for toxicants -
update of 2015 version. Prepared for the revision of the Australian and New Zealand Guidelines for Fresh and
Marine Water Quality. Australian and New Zealand Governments and Australian state and territory
governments, Canberra, 48 pp.
Yang, S., F. Xu, F. Wu, S. Wang and B. Zheng. 2014. Development of PFOS and PFOA Criteria for the
Protection of Freshwater Aquatic Life in China. Sci. Total Environ. 470/471: 677-683.
Yuan, Z., J. Zhang, Y. Zhang, H. Zhen and Y. Sun. 2015. The effect of perfluorooctanoic acid on the
planarian Dugesia japonica. Pol. J. Environ. Stud. 24(2): 801-807.
Zhang, L., J. Niu, Y. Li, Y. Wang and D. Sun. 2013. Evaluating the sub-lethal toxicity of PFOS and PFOA
using rotifer Brachionus calyciflorus. Environ. Pollut. 180: 34-40.
Zhang, L., J. Niu, Y. Wang, J. Shi and Q. Huang. 2014. Chronic effects of PFOA and PFOS on sexual
reproduction of freshwater rotifer Brachionus calyciflorus. Chemosphere 114: 114-120.
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