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

oEPA
United States
Environmental Protection
Agency
Office of Water
EPA-842-D-22-003
April 2022
EPA Response to the
External Peer Review of U.S. EPA's
"Draft Aquatic Life Ambient Water Quality Criteria for
Perfluorooctane Sulfonate (PFOS)"
(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 Perfluorooctane Sulfonate (PFOS)"
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 PFOS. Please provide
detailed comments	9
2.3	Please comment on the approach used to derive the draft acute estuarine/marine benchmark
for PFOS. 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	21
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 0	29
2.5	Please comment on the toxicity data used to derive the draft criteria	37
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:	62
2.7	Please comment on the frequency and duration of the criterion elements, in particular the
tissue-based criterion elements	72
2.8	Please provide any additional technical comments that you believe should be considered	80
3.0 REFERENCES CITED BY EPA IN RESPONSES	99
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria
for Perfluorooctane Sulfonate (PFOS)"
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 Aquatic Life Ambient Water Quality Criteria for
Perfluorooctane Sulfonate (PFOS) was conducted by Eastern Research Group, Inc. (ERG), a contractor to EPA
for EPA OW and developed an external peer review report (https://www.epa.gov/wqc/aquatic-life-criteria-
pcrfluorooctanc-sulfonatc-pfos). Independent peer review of the draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA) 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 PFOS 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 Perfluorooctane Sulfonate (PFOS)"
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 review comments on the PFOS criteria document and EPA's responses to those
comments are described in this report. Results of the PFOA external peer 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
Perfluorooctane Sulfonate (PFOS), 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 Perfluorooctane Sulfonate
(PFOS)"
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. Chirilv of Document its it Rehiles to (ho Demotion of Ksicli Criterion
Re\ iewer
Re\ iewer Comments
IT A 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 as a heading in
the table, 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 and headings of tables and
figures decreases clarity, e.g., Figs 3-1, Tables 3-1, 3-2, 3-3, 3-4,
3-5. The use of acronyms in the figure or table is valid to save
space, as long as they are defined in the caption of the figure or
table.
Thank you for your comment. EPA added a list of acronyms to
the draft PFOS Aquatic Life Criteria document. This list of
acronyms can be found on page xii of the revised draft PFOS
Aquatic Life Criteria Document.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.1. ChirilY of Document ;is it kehiles to the l)eri\iition ol' K:uh C rilerion
Ue\ iewer
Re\ iewei' Comments
IT A Response
Reviewer
3
Main Question: Perhaps this was missed in the draft document,
but, is there guidance when one criteria is exceeded and the other
is not? For example, if the tissue based criteria are exceeded yet,
the CCC is not; perhaps this is an unlikely scenario as those
receptors have been accumulating PFOS for a duration likely
under higher water concentrations (> 0.014mg/L). Although if
sediment concentrations remain elevated (but not water column
concentrations) this may also be a likely route of PFOS exposure
to fish with sediment dwelling prey.
There are additional domestic criteria missing from the
previously published criteria section; please review those for
Texas, Florida and California.
Are there two Sharpe et al.'s, I believe this is only one
publication but flipping between Sharpe et al. 2010, Sharpe et al.
2010a and Sharpe et al. 2010b throughout the document. If the
goal is to distinguish between supplemental vs the manuscript
proper I suggest just clarifying in the text instead of the reader
looking for two pubs by Sharpe et al. 2010.
Page 238 - error: The study authors reported a 96-hour LC50 of
58.47 mg/L PFOS, based on the results of the range finding test.
The independently-calculated toxicity value was x.xx mg/L.
Page 296 - error: The independently-calculated toxicity value
was x.xx mg/L.
Table 3-6 is not referenced/described in the text. Additionally,
the title reads "Six" most sensitive and lists "Seven".
Overall comment: ranking of sensitive genera flips back and
forth between most and least sensitive among tables, consistencv
would help the reader.
Thank you for raising the question regarding guidance for
potential scenarios resulting in one criterion being exceeded
while the other criteria are not. All of these PFOS (those for
water column and tissue) are intended to be independently
applicable and no one criterion takes primacy. As such all of the
recommended criteria (acute and chronic water column and
tissue criteria) are intended to be protective of aquatic life. As
for the example provided in the comment, the chronic PFOS
criteria consist of both the water-column based criterion and the
tissue-based criteria (as fish and invertebrate whole-body tissue
criteria and fish muscle tissue criterion). Therefore, given the
independent applicability of the PFOS criteria, if one criterion is
exceeded the PFOS criteria as a whole would be considered to
be exceeded.
Thank you for suggesting that EPA review domestic criteria for
Texas, Florida, and California. EPA will review these criteria
and add relevant details, as appropriate, to the section entitled:
"Previously Derived PFOS Toxicity Values and Thresholds."
Lastly, the editorial items regarding the in text citations and
references for Sharpe et al, the independently-calculated values,
and the text for Table 3-6 will be corrected. In particular, the
following edits were made: (1) there should only be one citation
for Sharpe et al. (2010) and any others will be removed, (2) the
x.xx mg/L placeholders for the independently-calculated values
on pages 238 and 296 will be removed or replaced as
appropriate, (3) the text for Table 3-6 will be updated to reflect
the most sensitive species listed are consistent with the text and
(4) the tables ranking the sensitivity of genera were edited to
ensure that all are consistent with listing genera based on
sensitivity and reordered so that the species are listed as most
sensitive to least sensitive.
4

Reviewer
4
EPA has drafted the PFOS 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 the 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 PFOS precursors in
the aquatic environment
• sources, concentration reported in environment and
existing criteria (both national and international) 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
documented in this report are based on comprehensive
assessment of the toxicological data and consistent with
the Guidelines.
Thank you for your comment describing the specific sections of
the draft PFOS Aquatic Life Criteria Document that you found
to be comprehensive.
5

• Acute and chronic MDRs for PFOS estuarine/marine
criteria derivation were not met due to fewer empirical
PFOS toxicity data. To address this gap, the EPA Team
developed an acute aquatic life benchmark for
estuarine/marine environments based on Interspecies
Correlation Estimation (ICE) model. Such predictive
models should be used when there is limited toxicity
data.
• EPA Team has provided extensive background
information on toxicity data assessment and collated this
information in various Appendices as additional line of
evidence.
• Tables and Figures are very well laid out throughout the
document and provide additional information of the
toxicity data used in developing Water Quality Criteria
for PFOS.

Reviewer
5
Overall, the document is clearly written and generally free of
grammatical errors. I applaud the scientists and EPA for
compiling an impressive amount of work and communicating it
in a reasonably clean and coherent way. That said, there are a
few instances of redundancy - literally, the same sentences
repeated. I have made note of these in the actual report and will
include that along with this document, if requested. Although
these are easy enough to see with careful review. The document
is VERY LONG and very detailed so any efforts to shorten or
make more concise would be welcomed.
As for the clarity of technical elements of the document, I feel
that many of the decisions to use or not use data or endpoints
could be more consistent and/or communicated better. For
example, in some cases the geometric mean of endpoints for a
certain taxa is used for the chronic value (pimephales) but for
Thank you for your comment regarding the general support for
the level of detail and the overall structure of the draft PFOS
criteria for aquatic life. EPA will remove the redundancies to
make the draft PFOS Aquatic Life Criteria Document more
concise and clearer.
EPA made edits to ensure that the technical elements and
decisions in the criteria document are consistent throughout and
are clearly communicated in the draft.
Regarding Reviewer 5's comment that a model was fit to the
four most sensitive endpoints (i.e., four most sensitive GMAVs
and GMCVs) to derive the criteria is not entirely accurate.
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
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other taxa, this is not the case (e.g. daphnia; zebrafish). In other
cases, the decision to not use certain data seems as if it could be
communicated more clearly. So while the language of the
document is pretty clear, the actual technical aspects are less so.
One major concern I have is with the overall approach of using
the 4 most sensitive toxicity values to then derive the final acute
and final chronic values. Using this approach it would seem the
AWQC are then very sensitive to changes in any 1 of the 4
toxicity values. For example, when EPA explored the impact of
different toxicity values on the chronic freshwater water column
criteria, using higher toxicity values (e.g., pimephales in place of
fatmucket Table 4-3) resulted in a lower chronic criteria. This is
nonintuitive and suggests a possible flaw in the approach. It's
possible this is not the case and it makes sense both
mathematically (steeper slope) and perhaps even from a
protection standpoint. Either way, EPA should explain why this
happens and what it means for the overall approach. I suspect the
EPA is somewhat constrained by the 1985 guidelines in
developing the AWQC but I also see that New Approach
Methods (WEB-ICE) were used to derive criteria with limited
data. I wonder if using a species sensitivity distribution approach
in which all the chronic or acute (freshwater)data are used would
result in more defensible criteria that are less impacted by
changes in any one toxicity value? At the very least, I think
including a full SSD would be useful for comparison as part of
the characterization piece. In the PFOA document I mention
revisiting and publishing and updated 1985 guidelines...this is
warranted when EPA has the bandwidth to do so. Having said all
this, I am aware that EPA likely has justification for their
approach of using the 4 most sensitive tox values but it would
perhaps be good to mention this again as I suspect a lot of people
that may read the AWQC will not also read the 1985 guidelines.
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 PFOS Aquatic Life Criteria document. Please
see EPA's response to Reviewer 5's comments to Charge
Question 2.2 below for greater details on how the approach used
to derive the draft PFOS criteria follow the 1985 Guidelines.
Specifically, 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. Further, the reviewer is correct in
assuming that when EPA explored the impact of different
toxicity values on the chronic freshwater criterion (see Section
4.2.2 of the draft PFOS Aquatic Life Criteria Document that
underwent external peer review) the use of some higher toxicity
values resulted in a lower chronic water column value for
freshwater because the change in the chronic toxicity values
used in these additional analyses resulted in a steeper slope. EPA
made edits to the draft PFOS Aquatic Life Criteria Document to
clarify this observation in Section 4.2.2.
Lastly, many of the documented decisions and data requested by
Reviewer 5 to be in a single table can be found in the summary
tables of Appendices A through D. EPA made further edits to
these tables to include additional information requested by the
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 Perfluorooctane Sulfonate
	(PFOS)"	
2.1. ChirilY of Document ;is it kohitos to the l)eri\iition ol' K:uh C rilcrion
Uc\ iewer
Re\ iewer C om mollis
IT A Response

Lastly, I had a hard time keeping track of all the decisions to use
or not use data for each of the tox values that supported the
criteria. I think a more detailed table with all the tox values
considered (data shown in Figure 3-3) and including whether the
data used were author-reported, re-calculated by EPA, along
with the lowest reported/calculated value that wasn't used and
why. This may be asking a lot and this information is throughout
the document but not in a single, easy to locate and read
location.

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
.2.2 Please comment on the approach used to derive the draft criterion for PFOS. Please provide detailed comments.
• Is the technical approach used to derive the criterion elements 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 soil to l)eri\e the Draft Criterion lor I'l'OS
Re\ iewer
Comments
KIW Response
Reviewer
1
• Is the technical approach used to derive the criterion
elements 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:
I believe the Criterion Continuous Concentration (CCC) should
be potentially re-calculated considering my comments provided
in response to charge question 5a.
The science does not support the assumption of a 10-year
recovery time for PFOS in aquatic systems.
The generation of tissue criteria is weakly supported, and the
uncertainty associated with these criteria should be emphasized.
The NAM-generated marine Final Acute Value (FAV) and
FAV/2 values (Appendix L) are highly uncertain.
It is unclear if the EPA-calculated Effective Concentration 10%
(EC 10) values are supported; additional details on the modeling
Thank you comments that state the technical approach used to
derive the PFOS criteria were generally logical and for noting
specific areas were the science is not supportive of the criteria in
a few instances. In addition to EPA's response to this comment,
please see EPA's responses to subsequent Reviewer 1 comments
for specific Charge Questions that follow.
Responses to key instances where Reviewer 1 does not believe
the science is supportive of the draft PFOS Aquatic Life Criteria
Document are described below in corresponding order
mentioned in Reviewer l's comment:
1. See EPA's response to Reviewer l's comments under
Charge Question 2.5.a below
2. See EPA's response to Reviewer 5's comments under
Charge Question 2.7 below. EPA considered the
bioaccumulative nature and persistence of PFOS 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 PFOS criteria. Three of the remaining
Expert Peer Reviewers were supportive of the 10-year
exceedance frequency for the tissue-based PFOS criteria,
with the remaining Reviewer (i.e., Reviewer 3) stating it
was difficult to comment on the tissue-based criteria
frequencies.
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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.2. Tlio Technical Approach I soil to Dome (ho Draft Criterion lor I'l'OS
Ue\ iewer
('oilllllClllS
IT A Response

and the variability and fit of each EC 10 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
PFOS 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.
3. Please see EPA's response to Reviewer l's comments
below to Charge Question 2.6 regarding the generation
of the tissue criteria. As such EPA acknowledges the
inherent uncertainties that are present with the use of
BAFs to derive tissue criteria. For these reasons, 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 (the 2016 Selenium Aquatic Life Criterion
for Freshwaters; U.S. 2016) and human health (U.S.
2000). Thus, given the potential bioaccumulation of
PFOS through the aquatic food web EPA concluded that
tissue based criteria were needed to ensure the protection
of aquatic life to exposures of PFOS.
4. Please see EPA's response to Reviewer l's comments
below to Charge Question 2.3 regarding the NAM-
generated acute saltwater benchmark derived in
Appendix L of the draft PFOS criteria. EPA made edits
to ensure that any uncertainty surrounding the acute
saltwater benchmark is clearly stated.
5. Concentration-response model type and graphs of the
concentration-response data with the fitted model were
provided in draft criteria Appendices A.2 and C.2 for
those tests that were used to quantitatively to derive the
PFOS criteria and were among the four most sensitive
acute and chronic genera, respectively. Moreover, the
graphs of the fitted concentration-response model in
provided in the draft's appendices A.2 and C.2 displayed
95% confidence bands allowing for a visual display of
variability. Reviewer 1 further notes their reviewed
focused on "key portions" of the "Draft of the Aquatic
Life Water Quality Criterion" and may have missed 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 Perfluorooctane Sulfonate
(PFOS)"
2.2. Tlio I cchnicitl Approach I soil to Dome (ho Drsil'l Criterion lor I'l'OS
Uc\ icwir
C'oillllKMllS
IT A Response

concentration-response modeling results presented in
appendices A.2 and C.2 as well as the modeling methods
presented in Appendix K.
Lastly, EPA thanks Reviewer 1 for describing the relative
similarity between the draft PFOS 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 tissue criteria derived in this
draft PFOS criteria are intended to be protective of aquatic life
from the bioaccumulation of PFOS. Currently, there are
insufficient data to derive tissue criteria empirically from the
toxicity literature. Instead, EPA derived the tissue criteria by
translating the empirically derived chronic water column
criterion into tissue concentrations with the use of
bioaccumulation factors (BAFs). While this approach adds some
uncertainty to the tissue criteria that were derived, EPA
summarized the limited empirical tissue-based data for aquatic
life to understand this potential uncertainty. In general, the
comparison of the empirical tissue-based data demonstrates that
the tissue criteria, which are based on fish and invertebrate
whole-body and fish muscle, are protective of aquatic life with
some specific studies indicating that the tissue criteria may not
be protective of certain species, exposures, or endpoints. EPA
will take a closer look at the overall approach to derive the tissue
criteria, including the potential uncertainties, and make the
needed adjustments to ensure that the tissue criteria are
protective of all aquatic life. Furthermore, aquatic life tissue
criteria are intended to be protective of aquatic life; aquatic-
dependent wildlife fall outside the scope of the current draft
PFOS criteria. EPA intends to review PFOS data focused on
aquatic-dependent wildlife in the future and to potentially derive
separate aquatic-dependent wildlife criteria for PFOS if the data
support the derivation of such criteria.
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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 currently available.
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.
Thank for your comment noting the approach used in the draft
PFOS Aquatic Life Criteria Document was "logical and
defensible" and that "the science supports the EPA's
conclusions." EPA noted the studies provided by Reviewer 2
(and all other reviewers) that were not included in the draft
PFOS criteria were considered for possible inclusion in the
derivation of the criteria, as appropriate, based on the data
quality, using the data quality review approach described in the
draft document. To summarize, the review of these
recommended studies was conducted to ensure they met the data
quality objectives outlined by the 1985 Guidelines (U.S.EPA
1985) and the EPA 850 test guidelines (U.S.EPA 2016b). This
further allowed EPA to determine if each individual provided
study should be used quantitively in the derivation of the criteria,
qualitatively as supporting information to the criteria, or not used
in the criteria due to concerns with data quality or test
methodology. Additionally, EPA reviewed all relevant PFOS
toxicity studies currently included in EPA's Office of Research
and Development's ECOTOX database through the September
2021 quarterly update. Between both the recommended and
ECOTOX papers, the number of additional PFOS references that
were reviewed total 41, which resulted in 51 individual new
studies (as two of the references were large industry reports that
contained many individual studies) The review and inclusion of
these additional toxicity studies resulted in an update of the draft
PFOS criteria, in which the acute, freshwater criterion changed
very little (from 3.1 mg/L to 3.0 mg/L) and the chronic,
freshwater criterion decreased slightly (from 0.014 mg/L to
0.0084 mg/L). Additionally, with the decrease in the chronic,
freshwater criterion the tissue criteria decreased as well
(resulting in an invertebrate whole-body criterion of 7.4 mg/kg
12

ww, a fish whole-body criterion of 25.8 mg/kg ww, and a fish
muscle criterion of 15.2 mg/kg ww).
Thank you for your comments on the evaluation of the influence
of non-North American species on the derivation of the criteria.
EPA agrees that "it 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 PFOS criteria.
Reviewer
3
• Is the technical approach used to derive the criterion
elements logical?
This is logical and follows the established GLRI guidance;
however, both Canada and Australia utilize a species sensitivity
distributions to determine the 95th and 99th percentile of species
protection. Is there a defensible reason why EPA did not employ
this approach or at the very least present these distributions and
analysis that would support the currently drafted criteria?
Additionally, thresholds from those SSDs (and others published)
are lower than the draft guidance here, this should be addressed:
Australia - 0.13 (ig/L
Canada - 6.8 (ig/L
Salice et al. 2018 - 1.12 (ig/L
Conder et al. 2020 - 5.85 (ig/L
*Giesy et al. 2010 - 5.1 (ig/L (using CCC based on GLRI
guidance)
• Does the science support the conclusions?
Thank you for your comments that state the technical approach
used to derive the PFOS criteria were generally logical.
However, it should be noted that the derivation of the PFOS
criteria followed the 1985 Guidelines. As such the approach is
generally consistent with the approaches used by both Canada
and Australia, since all utilized species sensitivity distributions
and similar percentiles of species protective (95 percentile for
EPA's and Canada's PFOS criteria and 99th percentile for
Australia's criteria). The observed differences between EPA's
draft PFOS criteria and those derived for both Canada and
Australia are largely due to differences in the toxicity studies and
therefore data that were used.
Based on the literature included in the draft PFOS criteria (those
included in EPA's ORD ECOTOX database as of September
2019), the GMCV for zebrafish of 0.0165 mg/L was the most
sensitive chronic value. However, EPA is aware that more recent
toxicity studies that indicate that there are some more sensitive
toxicity values for some aquatic life species. As noted in EPA's
comment to Reviewer 2's comment to Charge Question 2.2
above, between ECOTOX and recommendations made by
external peer reviewers, the number of additional PFOS studies
13

The GMCV for Zebrafish is 0.0165 mg/L, thus there are studies
that result in chronic toxicity at concentrations lower than this
mean; however, this is very close to the CCC of 0.014mg/L. This
seems borderline protective when considering potential
exposures to this species (and those more sensitive).
• Is it consistent with the protection of freshwater
aquatic life from acute, chronic, and bioaccumulative
effects?
I have confusion over Tables 3-9 and 4-6 calculations. How is it
that the inclusion of Lampsilis with a higher GMAV results in a
lower overall CMC (3.3 mg PFOS/L) compared to the CMC in
table 3-9 (3.6 mg PFOS/L)? Actually, looking more closely at
this, the ln(GMAV)A2 are inconsistent among the tables for
Xenopus, this is likely are result of using table 3-6 as a template
for 4-6.
It is great to see the inclusion of the Burkhard et al. 2021 as this
synthesis has been peer-reviewed and published and is an
exceptional overview of PFOS bioaccumulation; unfortunately,
there are not more current literature used within the draft
document.
that were reviewed totals 51. The review and inclusion of these
additional toxicity studies resulted in an update of the draft
PFOS criteria, in which the acute, freshwater criterion changed
very little (from 3.1 mg/L to 3.0 mg/L) and the chronic,
freshwater criterion decreased slightly (from 0.014 mg/L to
0.0084 mg/L). Specifically, the addition of the new data shifted
the relative sensitivity of genera in both the acute and chronic
criteria derivation. The GMAVs shifted slightly with the
addition of fathead minnow, which is now the most sensitive
genus in the acute PFOS dataset. All of the other GMAVs
among the 5 most sensitive genera did not change from the
previous draft. In the chronic PFOS dataset, the midge and the
zebrafish are the only species among the 4 most sensitive genera
with new data. And all of the other GMCVs for the 4 most
sensitive genera did not change from the previous draft with the
exception of the fatmucket GMCV, which changed from the
estimated ECio of 0.0571 mg/L (calculated using acute mussel
data), to the MATC of 0.0177 mg/L following comments from
external peer reviewers indicating that the MATC and/or data
from a chronic mussel study should be used to estimate an ECio
for this species (see EPA's response to Review l's comment to
Charge Question 2.5.a.ii below for more details).
EPA thanks Reviewer 3 for pointing out the inconsistencies
between Tables 3-9 and 4-6 in the draft PFOS Aquatic Life
Criteria Document and has corrected the values for Xenopus.
Thank you for your comments on the inclusion of Burkhard
(2021). EPA has updated the literature cited throughout the draft
PFOS Aquatic Life Criteria Document to be inclusive of more
recently published studies, though September 2021. Updates in
the literature includes both toxicity literature used to derive the
criteria)and background literature related to topics discussed in
14

the Problem Formulation of the draft PFOS Aquatic Life Criteria
Document.
Reviewer
4
This EPA report provides a critical review of toxicity data
identified in EPA's literature search for PFOS, including the
anionic form (CAS No. 45298-90-6), the acid form (CAS No.
1763-23-1), potassium salt (CAS No. 2795-39-3), an ammonium
salt (CAS No. 56773-42-3), sodium salt (CAS No. 4021-47-0),
and a lithium salt (CAS No. 29457-72-5). It quantifies the
toxicity of PFOS to aquatic life, and provides criteria intended to
protect aquatic life from the acute and chronic toxic effects of
PFOS. 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 PFOS
is very logical and consistent with the protection offered
by acute and chronic aquatic life 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
were included for criteria development. For example,
inclusion of non-resident species such as Planaria,
Dugesia japonica and Japanese swamp shrimp,
Neocaridina denticulata for calculating acute water
quality criteria and zebra fish, Danio rerio for chronic
criteria. The EPA team did not find any influence of
excluding non-North American resident species in
Thank you for your comment describing specific sections of the
draft PFOS Aquatic Life Criteria Document in detail. Please see
responses to the comments pertaining to the acute and chronic
MDRs for the acute estuarine/marine benchmark that Reviewer 4
mentions are described in response to Charge Question 2.3.
Specifically, EPA noted the studies provided by Reviewer 4 (and
all other reviewers) that were not included in the draft PFOS
Aquatic Life Criteria document and all studies provided in the
comments of this external peer review were considered for
possible inclusion in the derivation of the criteria and acute
estuarine/marine benchmark to determine if additional
estuarine/marine MDRs were met.
15

criteria derivations and decided to retain the full acute
and chronic toxicity dataset. This was very rational
decision and non-Northern American species served as
surrogate species for the broad range of the thousands of
untested species present in the freshwater environment
in the U.S.
• 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 as per the Guidelines.
• 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 (ECio). 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 ECio could not be calculated for
the genus.
• Furthermore, EPA independently calculated these
toxicity values if sufficient raw data were available for
EPA to conduct statistical analyses. EPA's
independently-calculated toxicity values were used
preferentially, where available.
• I agree with the authors' decision on not developing
plant criteria based on their lesser sensitivity to PFOS
than in comparison to aquatic vertebrates and

invertebrates. The EPA team evaluated the toxicity data
to plants as an additional line of evidence and confirmed
that the proposed PFOS freshwater acute and chronic
criteria are expected to be protective of freshwater
plants.
• 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).
• Based on comprehensive toxicity data assessment, the
EPA team has developed the following criteria using the
procedures described in the 1985 Guidelines. The
freshwater acute water column-based criterion
magnitude is 3.6 mg/L and the chronic water column-
based criterion magnitude is 0.014 mg/L. The chronic
freshwater criterion also contains tissue-based criteria
expressed as 43.0 mg/kg wet weight (ww) for fish
whole-body, 25.3 mg/L ww for fish muscle tissue, and
12.3 mg/kg ww for invertebrate whole-body tissue.
• Acute and chronic MDRs for PFOS estuarine/marine
criteria derivation were not met and an estuarine/marine
FAV could not be calculated to derive an
estuarine/marine acute criterion. Further benchmark was
developed using predictive approach and discussed in
the follow-up question 3.

Reviewer
5
• Is the technical approach used to derive the criterion
elements logical?
Overall, I think the technical approach is relatively sound
although there are instances where it was difficult to keep track
of all the decisions with regard to data and whether these were
Thank you for your comments that the technical approach used
to derive the PFOS criteria were generally relatively sound and
for noting that there are instances where it is difficult to follow
technical decisions with data. And for stating that "EPA did an
17

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFosr
2.2. Tlio I cchnicitl Approach I soil to Dome (ho Drsil'l Criterion lor I'l'OS
Ue\ iewer
C'oillllKMllS
IT A Response

consistent and logical. Admittedly, I think this is a tough
chemical and a tough dataset and EPA did an excellent job with
the background material and highlighted and used key studies
(but more have been published since and will, I'm sure be
included). Unfortunately, the technical approach to derive
criterion elements is not universally logical. Moreover, as
mentioned, using only the 4 most sensitive toxicity endpoints
followed by a regression (what type? Was this specified?) seems
less robust than using a full species sensitivity distribution with a
more "natural" distribution of sensitivity (s-shaped, for
example). This last statement may not be true so a reasonable
compromise might be to include a full SSD as part of the
characterization piece related to "considering other toxicity
values impact on the FCV, etc.". What really confused me was
that when EPA did what amounts to a sensitivity analysis of the
FCV by replacing toxicity values, the FCV DECREASED when
higher toxicity values were used. While I suspect this happened
because switching to higher toxicity values steepened the slope
(or something), it does not make intuitive sense to me and should
be further explained. Alternatively, an explanation and
justification, even brief, would be helpful in supporting the 4
most sensitive toxicity value approach. I am aware that the 1985
guidelines may include this but I suspect most users of the
AWQC may not be familiar with the details of the guidelines.
With regard to the tissue-based criteria, EPA mentions using
"only PFOS studies in which organisms were exposed in the
diet" (or similar; p. 88) but then go on to say the BAF approach
was used. I would edit this section to start with mentioning that a
BAF approach was used because there were not enough tissue
data from laboratory studies. I mention this because it was
confusing - there was a lot of explanation of using only dietary
exposures and then one sentence (basically) stating... EPA
explored a BAF approach.
excellent job with the background material and highlighted and
used key studies."
Responses to Reviewer 5 comments on question 2.2 described
below in corresponding order of Reviewer 5's comment:
1. EPA thanks for your review for stating the "overall
approach to derive the criteria for PFOS is relatively
sound." Regarding Reviewer 5's comment that a model
was fit to the four most sensitive endpoints (i.e., four
most sensitive GMAVs and GMCVs) to derive the
criteria The derivation of the acute and chronic criteria
followed long established methods outlined in the 1985
Guidelines (U.S.EPA 1985). The established criteria
calculation outlined in the 1985 Guideline uses a log-
triangular fit to determine the 5th centile of a genus
sensitivity distribution. Acute and chronic genus
sensitivity distributions (which included all
quantitatively acceptable toxicity data) were presented in
the Effect Analysis section of the draft PFOS Aquatic
Life Criteria Document. When there are less than 59
genera in a genus sensitivity distribution, the 5th centile
magnitude is inherently based on the four most sensitive
genera, with the remaining tests only influencing the
final acute value (FAV) through the "N" in the
calculation. Please see the excerpt from the 1985
Guidelines below for further explanation.
Order the GMAVs from high to low.
L. Assign ranks, R, to the GMAVs from "1 "for the
lowest to "N" for the highest. If two or more
GMAVs are identical, arbitrarily assign them
successive ranks.
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 Perfluorooctane Sulfonate
(PFOS)"
2.2. Tlio Techniciil Approach I soil to Dome (ho Drsil'l Criterion lor I'l'OS
Ue\ iewer
C'oillllKMllS
IT A Response

• Does the science support the conclusions?
Well, offhand, I think the final chronic value for freshwater
organisms should likely be lower. Importantly, several studies
have been published in 2021 that should likely be included as
toxicity values and they may result in lower toxicity estimates.
The fact that EPA's criteria are higher than all other published
criteria is worrisome. We are all using the same data and many
in the field are quite capable scientists.
These two papers come immediately to mind but I am sure there
are others.
Sensitivity and Accumulation of
Perfluorooctanesulfonate and Perfluorohexanesulfonic
Acid in Fathead Minnows (Pimephales promelas)
Exposed over Critical Life Stages of Reproduction and
Development J.G. Suski. C.J. Salice. M.K. Chanov. J.
Avers. J. Rewerts. J. Field Environmental Toxicoloav
and Chemistry, 2021, pp. 811-819.
Toxicological Response of Chironomus dilutus in
Single-Chemical and Binary Mixture Exposure
Experiments with 6 Perfluoralkyl Substances
Christopher J. McCarthv. Shaun A. Roark. Demitria
Wright. Kellv O'Neal. Brett Muckev. Mike Stanawav.
Justin N. Rewerts. Jennifer A. Field. Todd A. Anderson.
Christopher J. Salice Environmental Toxicoloav and
Chemistry, 2021, pp. 2319-2333.
In my view, it is essential that EPA incorporate newly published
toxicity data for PFOS (and PFOA).
Furthermore, in several cases, EPA's decisions to use what look
like higher estimates of toxicity seem somewhat arbitrary and
not internally consistent. I also noted above and mention here
M. Calculate the cumulative probability, P, for
each GMAVas 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).
2. EPA also thanks you for your suggestions regarding the
approach and data used to derive the PFOS tissue
criteria. Edits were made to this section entitled
"Translation Chronic Water Column Criterion to Tissue
Criteria" in the draft PFOS document to clarify the
approach and the data that were used to derive the tissue
criteria.
3. EPA took note of the studies provided by the external
peer reviewers that were not included in the draft PFOS
criteria and all these studies were considered for possible
inclusion in the draft criteria, as appropriate, based on
the quality of the data.
4. EPA ensured to clearly justify each specific toxicity
value used to derive the acute and chronic criteria in the
draft PFOS Aquatic Life Criteria Document. The
toxicity values used in the derivation of the PFOS
criteria were the most defensible values based on careful
consideration of the test methods, author-reported
results, and EPA's independent analysis of the current
toxicity literature. The toxicity values and the
justifications for each value that was used are detailed in
study summaries in the Effects Analysis section and in
the corresponding appendices (A through D).
5. Your comment noting that the criteria are "nearly
protective" of aquatic life was unclear and
19

again the sensitivity of the criteria development approach to
changes in one of the 4 most sensitive taxa/toxicity values.
• Is it consistent with the protection of freshwater
aquatic life from acute, chronic, and bioaccumulative
effects?
I believe the criteria are "NEARLY" protective of freshwater
aquatic life for acute, chronic and bioaccumulative effects of
PFOS. I say "nearly" because it seems to me that the FCV, in
particular, could and maybe should likely be lower. Also, below
I comment on the appropriateness and utility of the frequency
and duration elements of the criteria. Briefly, in my opinion the
frequency and criteria elements of the criteria certainly help the
criteria concentrations to be protective; it is unlikely that a 4-day
exposure to the FCV would result in adverse effects to any taxa
for which there are data; however, these data are not commonly
reported (hourly or 4-day running average concentrations have
never been reported to my knowledge).
unsubstantiated. EPA assumed based on the comments
provided by Reviewer 5 to this questions that the criteria
appeared to be nearly protective based largely on the
more recent toxicity data that the peer review
recommended that EPA review. Based on ORD's
ECOTOX updates of the PFAS literature since the time
of this draft development and September 2021, and
recommended toxicity studies provided by the external
peer reviewers, the number of additional PFOS studies
that were reviewed totals 51 The additional studies were
included in the subsequent draft, as appropriate, based
on their data quality.
6. See EPA's response to Reviewer 5's comments under
Charge Question 2.7 below. In summary, such an event
that a 4-day exposure to the FCV would result in adverse
effects is conceivable but unlikely considering the
implementation of criteria duration and frequency and
NPDES Permit limits because the four-day duration is
represents the time period over which the chronic
criterion is averaged.
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 Perfluorooctane Sulfonate
(PFOS)"
.2.3 Please comment on the approach used to derive the draft acute estuarine/marine benchmark for PFOS. 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)eri\e the Dral'l Acute Ksl u a rine/Marine Benchmark lor I'l'OS
Re\ iewer
Com mciils
KI'A 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 (0.43 mg/L), this implies
the CMC has about a 90% probability of being within 0.086 to
2.2 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. This suggests a reasonable interim FAV of
approximately 1 mg/L, which is similar to that calculated using
the NAM approach. I place higher confidence in the limited
Thank you for your comments regarding uncertainties associated
with the derivation of the acute estuarine/marine benchmark
using a New Approach Method (NAM). As discussed in
Appendix L of the draft PFOS Aquatic Life Criteria document,
ICE models have undergone extensive peer review and their use
has been supported for multiple similar applications, including
direct toxicity estimation for endangered species (NRC 2013;
Willming et al. 2016) and the development of Species Sensitivity
Distributions (Awkerman et al. 2014; Bejarano et al. 2017; Dyer
et al. 2006; Raimondo and Barron 2020; Raimondo et al. 2010).
EPA has noted and quantified uncertainties associated with the
use of Web ICE data to the extent possible in Appendix L.
Further, EPA 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
are being developed. However, additional text has been added to
further clarify these uncertainties and compare the derived
benchmarks to the available empirical test data.
Further, additional empirical estuarine/marine toxicity test data
have become available since the benchmark value was first
derived. The benchmark has been revised to incorporate the
additional acceptable empirical data.
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 Perfluorooctane Sulfonate
(PFOS)"
2.3. The Technical Approach used to Dome (ho Dral'l Acute Ksluarine/Marine Benchmark lor I'l'OS
Ue\ iewer
Com men Is
IT A Response

empirical data and would suggest EPA emphasize it in addition
to or in place of the values calculated by the NAM.
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.
EPA thanks you for your comments noting that the approach
used to derive the acute estuarine/marine benchmark for PFOS
seems 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 PFOS 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
Thank you for your comments that the derivation of the acute
estuarine/marine benchmark using Web-ICE to determine an
acute estuarine/marine benchmark is logical and includes
sufficient conservatism to address uncertainties in the PFOS
toxicity data for estuarine/marine species. EPA agrees that
additional estuarine/marine test data focused on PFOS would
provide support for the derived benchmark value. As such, EPA
reviewed additional toxicity studies focused on the effects of
PFOS on estuarine/marine species and updated the data used to
derive the acute estuarine/marine benchmark. These updated
data can be found in Appendix B of the revised draft PFOS
22

for estuarine and marine species. That said, the benchmark
should be used cautiously due to the relatively large amount of
uncertainty and effort should be made to generate acute and
chronic toxicity data for PFOS on estuarine and marine species.
Aquatic Life Criteria Document. As a great deal of toxicity
testing is underway, EPA will continue to integrate new
acceptable empirical data as they become available until the
benchmark value is derived as a final value.
Reviewer
3
• Is the technical approach used to derive the
benchmark logical?
After potential inclusion of the data mentioned below this
approach may be appropriate. In the current form with the
limited data it may be misleading. Can this guidance be updated?
I am aware of other researchers investigating PFAS on marine
species (Ed Wirth, NOAA) and maybe others that will be
coming out soon.
• Does the science support the conclusions?
I believe the data are incorrect for Fabbri et al. 2014. In table B. 1
the reported effect concentration is recorded as >1 mg/L.
However, looking at the paper, I read, "The PFCs PFOA and
PFOS induced a dose-dependent effect, with significant
decreases in normal larval development from 0.1 fig/L (17% and
27%, respectively; P 0.01). Maximal effects were observed at
100 fig/L (about 40% and 50%, respectively; P 0.001) with no
further decreases at higher concentrations". There is a
monotonic concentration-response curve. The associated figure
also supports an effect at 0.1 (ig PFOS/L, see below.
Furthermore, if the EC50 of the test organisms is a needed
endpoint (as noted in the PFOA justification, for which is
lacking support in the current form) looking at the figure below
% of normal D-larvae for PFOS (although incorrectly referred to
in the legend as PFOAS) could be inferred at 0.1 mg/L.
Furthermore, has EPA considered calculating the MATC from
this study?
Thank you for your comments indicating that after including
addition data from publications noted in the later sections of the
comment the approach used to derive the acute estuarine/marine
benchmark for PFOS "follows the spirit of the 1985 Guidelines."
Additionally, EPA thanks Reviewer 3 for comments 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). In this work,
the acute (48 h) bivalve embryo toxicity test was applied for
screening the developmental effects of different emerging
contaminants inM galloprovincialis. The assay was adapted to
96-microwell plates, and standardized in order to obtain normal
D-shaped larvae with acceptability of test results based on
negative control and positive control (copper) comparable with
those reported in literature for Mytilus spp. The assay was
adapted from International Standard Guide for Conducting
Static Acute Toxicity Tests Starting with Embryos of Four
Species of Saltwater Bivalve Mollusks - ASTM E724-98 (ASTM
2004). The recorded test endpoint was the percentage of normal
D-larvae in each well in respect to the total, including
malformed larvae and pre-D stages. Larvae were considered
normal when the shell was D-shaped (straight hinge) and the
mantle did not protrude out of the shell, and malformed if had
not reached the stage typical for 48-h (trochophore or earlier
stages) or when some developmental defects were observed
(concave, malformed or damaged shell, protruding mantle). The
acceptability of test results was based on controls for a
percentage of normal D-shell stage larvae >75% (ASTM, 2004).
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 Perflnorooctane Sulfonate
(PFOSr ' ' '
2.3. The Technical Approach used to Derive the Draft Acute Estuarine/Marine Benchmark for PFOS
Reviewer
Comments
EPA Response

% Normal D-larvae
.ssgssssss!
—PFOA
-e-PFOAS
Fabbri et al. (2014) did not report an acute EC50 forM
galloprovincialis from exposure to PFOS (or PFOA) because it
could not be calculated. The percent adverse effect at the highest
concentration of PFOS tested (1,000 (ig/L or 1 mg/L) did not
exceed a 50% reduction in % Normal D-larvae relative to the
negative control treatment. Using the raw data shown in Figure 4
of the publication, % Normal D-larvae in the control treatment
of the acute toxicity test with PFOS was approximately 88%; at
the highest concentration tested (1,000 (.ig PFOS/L, nominal) %
Normal D-larvae was approximately 45% (a decrease of only
48.86% compared to the control). Based on this information,
EPA recorded the acute effect concentration for the test (or 48-h
EC50) as > 1 mg/L in Table B. 1 of the document (Summary
Table of Acceptable Quantitative Estuarine/Marine Acute PFOS
Toxicity Studies). EPA's decision to use the acute value of > 1
mg PFOS/L for this study is 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 EC 50 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 LC 50 should be used in place of the desired 96-hr
EC so- If the duration of the test was between 48 and 96
hr, the EC 50 or LC'50 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 "
0 0,01 0.1 1 10 100 1000
PFCs Oig/L)
Fig. 4. Effects of PFOA and PFOS (0.01 -O.l -1 -10-100-1000 hj/1) on
M. gattoprovincialii normal larval development in 96-multiwell plates. Data are re-
ported as in Fig. 3a.
I did not see data included or the study evaluated for: Robertson
JC (1986) Potential for environmental impact of AFA-6
surfactant. Beak Consultants Ltd. Missassauga, Ontario, Canada.
EPA Docket AR226-1030a043.
There are data for saltwater spp in the ITRC from this citation.
• 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?
No, this is a new approach; however, it follows the spirit of the
1985 guidelines.
24

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	(PFOS)"	
2.3. The Technical Approach used to Dome (ho Drsil'l Acute Ksliiiirine/M.irine lienchniiirk lor I'l'OS
Ue\ iewer
Com men Is
IT A Response


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 for
Fabbri et al. (2014) was the 48-h EC50 of > 1 mg PFOS/L. While
the study clearly demonstrates an effect of PFOS on embryo
development (with an author reported LOEC of 0.1 (ig/L PFOS),
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 the chemicals (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 consideration of a calculated
MATC for the study for development of a chronic criterion. The
reported NOEC and LOEC are provided and the test results
discussed in detail in Section 3.1.1.2 of the draft PFOS Aquatic
Life Criteria Document.
EPA noted the studies provided by Reviewer 3 (and all other
reviewers) that were not included in the draft PFOS Aquatic Life
Criteria document and all studies provided in the comments of
this external peer review were considered for possible inclusion
in the derivation of the criteria and acute estuarine/marine
benchmark, as appropriate, based on the data quality review.
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
Thank you for your comment describing specific derivation of
the draft acute estuarine/marine benchmark for PFOS in detail.
And for noting that draft acute benchmark for estuarine/marine
25

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.3. The Technical Approach used to Dome (ho Dnil'l Acute KsUiiirine/Msirine lienchniiirk lor I'l'OS
Ue\ iewer
Com iiK'ii ts
IT A Response

benchmark recommendations for aquatic life using
procedures consistent with those in the 1985 Guidelines.
A total of 3104 datapoints from 398 models were
evaluated.
• ICE model has been recommended to predict the
sensitivity of an untested taxon (predicted taxa are
represented by the y-axis) from the known, measured
sensitivity of a surrogate species (represented by the x-
axis). The ICE model approach used is very reasonable
to predict toxicity of untested taxa.
• As documented in Section L. 1, ICE-predicted models
have been used by multiple independent, international
groups and further confirms that values developed from
ICE-generated SSDs will provide a level of protection
that is consistent with using measured laboratory data.
• In addition, prediction accuracy and robustness of the
model is evaluated using robust parameters (e.g., mean
square error, R2), that fall within a defined range of
acceptability, and with close prediction confidence
intervals that facilitate evaluating the fit of the
underlying data. This confirms the robustness of the
model.
• ICE models predicted with acceptable accuracy for
PFOS when invertebrates were used to predict to
invertebrate species and vertebrates were used to predict
to vertebrate species in these comparisons.
• The draft acute benchmark for estuarine/marine aquatic
life developed using this approach is 0.43 mg/L PFOS, it
is lower than the recommended acute freshwater
criterion(3.6 mg/L), suggesting that estuarine/marine
species may be more acutely sensitive to PFOS. This is
aquatic indicates that estuarine/marine species may be more
acutely sensitive to PFOS, which is in line with the findings
from Hayman et al. (2021). EPA noted the studies provided by
Reviewer 4 (and all other reviewers) that were not included in
the draft PFOS Aquatic Life Criteria document and all studies
provided in the comments of this external peer review were
considered for possible inclusion in the derivation of the criteria
and acute estuarine/marine benchmark.
26

in line with Hayman et al., (2021), confirming marine
species have a higher sensitivity to PFOS than compared
to the freshwater organisms.
• In this report, Mytilus galloprovincialis was not used in
the FAV calculation because the value was not
definitive, and true sensitivity of this species is
unknown. There are two more studies published
reporting the toxicity values for marine/estuarine
species, including Mytilus galloprovincialis.
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 .ors /10.1016/i .chemosphere .2021.1296
99
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
• Is the technical approach used to derive the
benchmark logical?
Thank you for your comment indicating that given the limited
availability of PFOS toxicity data for estuarine/marine species
the application of Web-ICE to derive an acute benchmark is a
reasonable approach. And for further indicating that overall, the
27

Yes, given the lack of PFOS toxicity data for acute
estuarine/marine species, I think applying WEB-ICE is a
REASONABLE APPROACH.. .perhaps the only approach that
is defensible. Clearly, more (or some) data would be a wonderful
contribution. WEB-ICE, as mentioned, has been reviewed and
published quite a bit so I think, as an approach, it has merit and
support of the scientific community. EPA also did a good job
presenting the approach and being clear about the criteria being a
draft. Overall, when data have been lacking, EPA has used state-
of-the-art approaches to developing criteria (my concerns are
mostly when sufficient data are available).
• Does the science support the conclusions?
Yes, the science supports the conclusions. Interestingly, the
acute criteria for estuarine/marine species (o.43 mgPFOS/L) is
almost an order of magnitude lower than the acute criteria for
freshwater organisms (3.6 mg/L). Whether estuarine/marine
species are truly more sensitive remains to be seen but, to me, it
is more reasonable, given the lack of data, that the criteria draft
is lower.
• 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?
Yes, and EPA justified this in the explanation of WEB-ICE that
occurs in Appendix L and, overall, the approach and resulting
criteria are consistent with the protection of estuarine and marine
species.
approach and resulting acute estuarine/marine benchmark for
PFOS is consistent with the protection of estuarine and marine
species.
Additionally, EPA thanks Reviewer 5 for noting that the acute
estuarine/marine benchmark for PFOS is almost an order of
magnitude lower than the acute freshwater criterion. EPA
reviewed Hayman et al (2021), cited by Reviewer 4, and other
studies recommended by the peer reviewers for inclusion of
recommended PFOS toxicity studies, and studies were included
as appropriate, based on their data quality.
28

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	(PFOS)"	
.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 O.
2.4. 1 ho I so ol Measured :tiul I nnieiisureil loxicitv losls lo Dome Respeclne C ritorion
Ro\ iowor
Com mollis
KIW Response
Reviewer
1
The consideration of toxicity data from experiments in which
PFOS measurements were not made seems appropriate. The
Appendix 0 analysis is supportive of the general observation
that actual concentrations in the toxicity test waters
approximated nominal values for freshwater. I agree that actual
concentrations in the toxicity test waters for the marine test may
be lower than nominal values, thus, effect data originating from
marine studies that only report nominal concentrations may be
biased high in some cases. Given the tentative/temporary nature
of the marine criteria developed in this study, this bias is
manageable until additional empirical data from experiment with
measured concentrations in water can be provided.
Thank you for your comment indicating the appropriateness of
using data from toxicity studies that did not measure the PFOS
concentrations and the Appendix 0 of the draft PFOS Aquatic
Life Criteria Document supported this use. EPA intends to
continue the consideration and use of toxicity data with
unmeasured test concentrations so long as all other test quality
guidelines are met in the study.
Also, EPA thanks Reviewer 1 for noting that although the effect
data from estuarine/marine studies that only reported nominal
concentrations may biased high (and therefore the draft acute
estuarine/marine benchmark may be slightly under protective)
As the results from the measured meta-analysis (presented in
Appendix 0 of the draft PFOS Aquatic Life Criteria) indicate
that measured and nominal concentrations from saltwater tests
were not in close agreement, with most measured concentrations
being lower than nominal. However, it should be noted that the
saltwater data were limited compared to the freshwater data. And
therefore, it was difficult to discern if these observed differences
between measured and nominal concentrations was a result of
experimental conditions in saltwater. EPA has reviewed
additional toxicity data, both from studies recommended by the
peer reviewers and identified in recent ECOTOX quarterly
updates and has updated both the freshwater criteria and the
acute estuarine/marine benchmark.
Reviewer
2
I am concerned with the approach of using the agreement of
measured and nominal concentrations from studies that
measured the concentration of PFOS in their tests to determine
whether to use toxicity data from studies that did not measure
the concentration PFOS in their tests. My concern stems from
EPA appreciates the comment noting that by using both
measured and unmeasured toxicity studies in the derivation of
the PFOS criteria the assumption was made that unmeasured
toxicity studies conducted dosing with the same accuracy and
care as those that did measure PFOS test concentrations in their
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 Perfluorooctane Sulfonate
(PFOS)"
2.4. 1 ho I so ol Moiisuroil :tiul I nnioiisuroil loxicitv losls lo Domo Uospoclno C rilorion
Uo\ iowor
C om mollis
KIW Rosponso

this approach having to assume that studies that did not measure
the concentration of PFOS in their experiments performed the
dosing of PFOS with the same care and skill as those studies that
did measure the concentration of PFOS in their experiments and
measured concentrations within 20% of nominal. My concern is
compound by 58% and 65% of the freshwater and saltwater
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 PFOS in their experiment?
I think the approach that the EPA has used to determine the level
of agreement between the nominal and measured concentration
of PFOS 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.
experiments. And EPA acknowledges that the Meta-Analysis of
Nominal Test Concentrations Compared to Corresponding
Measured Test Concentrations in Appendix 0 of the draft PFOS
Aquatic Life Criteria Document does not eliminate this concern.
However, unmeasured studies that were used quantitatively to
derive the PFOS 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 PFOS and/or
difficulty in measuring test concentrations by individual study
authors, there would be insufficient data to derive PFOS 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
Appendix 0 of the draft PFOS 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 and/or experimental conditions that
were previously suggested in the PFOS literature (Boudreau et
al. 2003a; Boudreau et al. 2003b; Hansen et al. 2001; Martin et
al. 2004), 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.
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 Perfluorooctane Sulfonate
(PFOS)"
2.4. 1 ho I so ol Measured :tiul I niiie;isiired loxicitv losls lo l)eri\e Uospoclno C rilorion
Ue\ iowor
C om mollis
KIW Response
Reviewer
3
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.
Thank you for your comment that this analysis and the use of
both measured and unmeasured toxicity tests in the derivation of
the draft PFOS criteria seems acceptable given the data currently
available.
EPA appreciates Reviewer 3 's comment regarding the difficulty
of working with PFOS when mixing the chemical into solutions
and the variability in PFOS measurements. EPA will include
these difficulties in the discussions of PFOS dosing and analytics
in Appendix 0 and the draft PFOS Aquatic Life Criteria
Document. Additionally, EPA noted and reviewed the
recommended publication by Rewerts et al. (2021). Based on
this review, EPA added a statement to Appendix 0 of the draft
PFOS Aquatic Life Criteria Document indicating recent PFAS
literature demonstrates the standard variability between nominal
and measured concentrations may be as high as 30% (Rewerts et
al. 2021; which was referred to Rewerts et al. 2020 in the
comment based on the first online publication of this article) as
suggested by Reviewer 3.
Reviewer
4
PFOS 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 determine if
nominal and measured PFOS concentrations were typically in
close agreement, pairs of nominal and corresponding measured
PFOS 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 authors reported, 22 freshwater studies with PFOS measured
concentrations, yielding 373 pairs of measured and nominal
concentrations. In addition, there were 7 estuarine/marine studies
with measured concentrations, yielding 142 pairs of measured
and nominal concentrations. The data were grouped by
Thank you for your comment summarizing the analysis and
resulting conclusions of the Meta-Analysis of Nominal Test
Concentrations Compared to Corresponding Measured Test
Concentrations in Appendix O and for providing input that the
conclusions of the analysis support the inclusion of unmeasured
toxicity tests in the derivation of the draft PFOS criteria for
aquatic life.
Thank you for your comment regarding your experience
analyzing PFOS in ecotoxicological studies for freshwater
species, which have exhibited strong correlation between
nominal and measured concentrations.
31

classifications including water type (salt/fresh) and experimental
conditions (acute/chronic; solvent/no solvent; fed/unfed, etc.).
Data displayed a high degree of linear correlation and measured,
and nominal concentrations were in close agreement
The analysis conducted by EPA Team showed strong correlation
(correlation = 0.9998) of the 326 pairs of nominal and measured
concentrations from freshwater studies. In addition, the
experimental conditions did not influence the correlation
between nominal and measured concentrations. The detailed
analyses of the data in Appendix 0 and the relevant Tables and
Figures provide very comprehensive analyses - this is very
useful information and will assist ecotoxioclogist in designing
future experiments.
This confirms inclusion of unmeasured PFOS toxicity tests for
quantitative use in criteria derivation.
Personal experience on analyzing PFOS in ecotoxicological
studies using freshwater species have also exhibited strong
correlation between nominal and measured concentrations.
The authors reported the strong correlation (0.8993) of the 142
pairs of nominal and measured concentrations, the ratio of
measured to nominal concentrations from the saltwater dataset
showed bias with a geometric mean value of 0.6178.
Additionally, the median percent difference between measured
and nominal concentration was 30.82%. Furthermore, the
saltwater comparison of nominal and measured concentrations
indicated that these experimental conditions (acute/chronic and
unfed/fed) could influence the observed differences between
measured and nominal concentrations. These results suggest that
measured and nominal concentrations from saltwater tests were
not in close agreement, but this analysis was based on limited set
of data.
EPA noted the recommended papers, both the two toxicity
papers with measured test concentrations and Rewerts et al.
(2021) with details pertaining to potential sources of PFOS
variability. All studies suggested for inclusion by reviewers were
reviewed to ensure they met data quality objectives outlined by
the 1985 Guidelines and EPA's 850 test guidelines (U.S.EPA
1985; U.S.EPA 2016b)., and were included in the draft PFOS
Aquatic Life Criteria document, as appropriate, based on their
data quality..
A statement has been included in Appendix O of the updated
PFOS criteria document indicating recent PFAS literature
designates standard variability between nominal and measured
concentrations may be as high as 30% (citing Coats et al. 2017
and Rewerts et al. 2021). And the following statement was added
to the conclusion of the Meta-Analysis of Nominal Test
Concentrations Compared to Corresponding Measured Test
Concentrations in Appendix O of the draft PFOS Aquatic Life
Criteria Document:
Recent PFAS literature has indicated standard
variability between nominal and corresponding
measured concentrations may even be as high as
30%. For example, Rewerts et al. (2021) states, "To
agree with nominal concentration, measured
concentrations for both stock and exposure solutions
were required to fall within the margin of
100 ± 30%, as specified by the guidelines in the
consolidated Quality Systems Manual for
Environmental Laboratories set by the US
Department of Defense and the US Department of
Energy (Coats et al. 2017)." Further, Rewerts et al.
(2021) conclude the variability between measured
and nominal concentrations may be influenced by
solution homogenization and subsampling
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 Perfluorooctane Sulfonate
(PFOSr ' ' '
2.4. The Use of Measured and Unmeasured Toxicity Tests to Derive Respective Criterion
Reviewer
Comments
EPA Response

The measured concentrations in the recently published paper on
marine/estuarine toxicity of PFOS should also be included in this
assessment:
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
The second paper is on benthic organisms and PFOS is measured
in overlying water, pore water and sediment. This may provide
further guidance on difference between PFOS measured and
nominal concentrations.
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
Additional information for Appendix O based on a recently
published paper:
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 storase. https://doi.ora/10.1002/etc.4667
procedures. And noted that for PFOS, it would
appear that storage container type may influence
agreement between measured and nominal
concentrations based on the concerns stated in
previous literature. However, it should be noted that
container type (as glass or plastic) did not appear to
influence the observed differences between measured
and nominal PFOS concentrations in EPA 'sMeta-
Ana lysis of Nominal Test Concentrations Compared
to Corresponding Measured Test Concentrations.
Reviewer
5
I think the comparison of measured and nominal concentrations
was an interesting read and a useful contribution. That said,
many toxicologists focused on PFAS have commented that
EPA acknowledges that many toxicologists working with
PFASs, particularly those at the SETAC North America Focused
Topic Meeting on Environmental Risk Assessment of PFAS in
33

analytical confirmation is necessary for a high quality study -
this was echoed (loudly) at the SETAC Workshop on Risk of
PFAS that occurred in summer, 2019. As well, in my own
experience there have been challenges in sometimes matching
nominal and measured concentrations for aquatic exposures. The
paper by Rewerts et al. 2020 highlights some of the challenges
and provides recommendations for accurate solutions of PFAS.
As a general rule, we have erred on the side of reporting
measured concentrations.
Two important thoughts. First, several very prominent analytical
chemists that have made a career of measuring PFAS have
indicated to me that the analytical method is only about 30%
accurate - meaning that if the analytical measure was +/- 30% of
nominal, they would be considered "the same". EPA used 20%
as a threshold (for deciding nominal and measured were the
same) and I'm not sure why this is. As far as I can tell, 30% is a
more reasonable threshold.
Second, in the review and derivation of toxicity values for the
MacDonald et al. 2014 paper, EPA elected not to use the 20-day
emergence rate endpoint, in part, because the nominal and
measured did not agree. This makes no sense to me. As long as
the solutions were confirmed analytically and reported, that
should be good enough and, in fact, preferred over nominal
alone.
Paper worth including in the section on nominal vs. measured
PFOS concentrations:
Key Considerations for Accurate Exposures in
Ecotoxicological Assessments of Perfluorinated
Carboxvlates and Sulfonates. Justin N. Rewerts. Emerson
C. Christie. Alix E. Robel. Todd A. Anderson.
the August 2019 in Durham, North Carolina, have 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 PFOS toxicity tests in
the current literature there would be insufficient data to derive
PFOS criteria for aquatic life without the inclusion of both
measured and unmeasured tests. Considering that the results of
the meta-analysis (described in Appendix O of the draft PFOS
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 PFOS
aquatic life criteria.
Responses to key instances where Reviewer 5 provides
particular comments on the Meta-Analysis of Nominal Test
Concentrations Compared to Corresponding Measured Test
Concentrations in Appendix O of the draft PFOS Aquatic Life
Criteria Document are described below in corresponding order
mentioned in Reviewer 5's comment:
1. 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 2016). Adjusting to a 30%
threshold (as opposed ot the 20% threshold difference in
Appendix O of the draft PFOS Aquatic Life Criteria
Document) would not meaningfully alter the
conclusions.
34

Christopher McCarthy. Christopher J. Salice. Jennifer A.
Field Environmental Toxicology and Chemistry. 2020
2. EPA agrees with Reviewer 5' s comment that the
observed differences between the measured and nominal
concentrations in the 20-day emergence endpoint of
MacDonald et al. (2004) should not be the reason this
test endpoint was not considered for use in the
derivation of the chronic water column criterion since
the test was measured and those concentrations could be
used. However, this was not the reason the 20-day
emergence endpoint from this study was not used to
derive the chronic water column criterion for PFOS.
Instead, this endpoint was not used because it is not
considered to be a reliable endpoint at this time given
the disparities in the calculated ECios and the level of
data that was presented in the paper, which made
independent calculation of the toxicity values less
accurate. This particular detail is noted on page C-19 of
the appendices in the draft PFOS Aquatic Life Criteria
document. Further, EPA clarifies that in the Meta-
Analysis of Nominal Test Concentrations Compared to
Corresponding Measured Test Concentrations, the 20-
day test from MacDonald et al. (2004) was determined
to have systematic discrepancies between the measured
and nominal test concentrations. Data suggest that the
20-day test had a dosing issue. Given the apparent
systematic dosing issue in the 20-day test, all five
treatments from this test were removed from the
measured meta-analysis alone.
3. EPA noted and reviewed the recommended publication
by Rewerts et al. (2021), which was referred to as
Rewerts et al. (2020) in the comment based on the first
online publication of this article, for possible inclusion
in the discussions in the draft PFOS Aquatic Life
Criteria document. Please see EPA's response to Review
4's comment to the same Charge Question above
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 Perfluorooctane Sulfonate
	(PFOS)"	
2.4. 1 ho I so ol Moiisuroil :tiul I nnioiisuroil loxicitv losls lo Domo Uospoclno C rilorion
Uo\ iowor
C om mollis
KIW Rosponso


regarding the edits that were made to Appendix 0 of the
draft PFOS Aquatic Life Criteria Document for details
on how Rewerts et al. (2021) was incorporated.
36

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
.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 PFOS criteria, with a particular emphasis on:
2.5.a.i. 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 PFOS exposures. Specifically, Yang et al. (2014)
conducted a 96-hour renewal, measured PFOS acute test with the midge. This study Chironomus plumosus was
not acceptable for quantitative use due to the potential problematic source of the organisms. The reported
LC50 was 182 mg/L for PFOS indicating that insects may not be one of the more sensitive taxonomic groups.
Therefore, this test was excluded from the acute criterion calculation, but used to waive the missing insect
MDR.
2.5.a.ii. the use of the quantitatively acceptable chronic toxicity value for mussel (Lampsilis siliquoidea) from Hazelton
et al. (2012). Specifically, Hazelton et al. (2012) conducted a 36-day renewal, measured PFOS chronic test with
fatmucket, Lampsilis siliquoidea. The estimated EC 10 was 0.05713 mg/L, which was extrapolated from the
author-reported data and the exposure response slope from another PFOS toxicity study focused on another
mussel species (Ellipto complamata) as explained in Section 3.1.1.3.3. Therefore, this test was used in the
chronic criterion calculation.
2.5.a.iii. the use of the quantitatively acceptable chronic toxicity value for damselfly (Enallagma cyathigerum) from
Bots et al. (2010). Bots et al. (2010) conducted a 320-day renewal, unmeasured PFOS chronic test with blue
damselfly nymphs, Enallagma cyathigerum. The MATC was 0.03162 mg/L, which was calculated from the
author-reported value for nymph survival as explained in Section 3.1.1.3.2. Therefore, this test was used in the
chronic criterion calculation.
2.5.a.iv. the use of the quantitatively acceptable chronic toxicity value for midge (Chironomus dilutus) from MacDonald
et al. (2004). MacDonald et al. (2004) conducted a 20-day renewal, measured PFOS chronic test with midge
lava, Chironomus dilutus. The EC10 was 0.05963 mg/L, which was an EPA-calculated value for 10-day growth
as explained in Section 3.1.1.3.4. Therefore, this test was used in the chronic criterion calculation.
37

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.5.b. EPA's approach for fitting concentration-response (C-R) data (described in Appendix K) as well as the specific acute
LC50 values (Appendix A.2) and chronic EC 10 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 lo Dome the Drsil't Crilcrhi
Re\ iewer
Com mciils
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.
• 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 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 PFOS and
may have been more tolerant of PFOS exposures,
which would result in biased-high median lethal
concentration (LC50) values. If so, this should be
explicitly stated. Assuming these Chironomus can
develop tolerance to PFOS, it seems that they would
have to be exposed to rather high mg/L ranges of
Thank you for your comment noting that in most cases the data
selected and/or excluded from the derivation were appropriately
utilized.
And all studies provided in the comments of this external peer
review were considered for possible inclusion in the derivation of
the criteria, following the approach described in the draft
document. To summarize, the review of these recommended
studies was conducted to ensure they met the data quality
objectives outlined by the 1985 Guidelines and the EPA 850 test
guidelines (U.S. EPA 1985 and U.S. EPA 2016, respectively).
This further allowed EPA to determine if each individual study
should be used quantitively in the derivation of the criteria,
qualitatively as supporting information to the criteria, or not used
in the criteria due to concerns with data quality or test
methodology. Additionally, EPA reviewed all relevant PFOS
toxicity studies currently included in EPA's Office of Research
and Development's ECOTOX database through the September
2021 quarterly update. Between both the recommended and
ECOTOX papers, the number of additional PFOS studies that
were reviewed total 51 The review and inclusion of these
additional toxicity studies resulted in an update of the draft PFOS
criteria, in which the acute, freshwater criterion changed very
little (from 3.1 mg/L to 3.0 mg/L) and the chronic, freshwater
criterion decreased slightly (from 0.014 mg/L to 0.0084 mg/L)..
Responses to key instances where Reviewer 1 does not believe
the data were appropriately utilized to derive the draft PFOS
criteria are described below in corresponding order mentioned in
Reviewer l's comment:
38

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.5. The Toxicity lo Dome llic Drsift Crilcriii
Uc\ icwcr
Com incuts
KIW Response

PFOS in water given the reported 96-hour LC50 of
182 mg/L. Based on published literature, I am
unaware of natural ecosystems in China (where the
animals may have been originally harvested) with
concentrations of PFOS 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 PFOS,
and the that LC50 result is unbiased. It does seem
clearly show that insects may be less sensitive to
acute lethality effects of PFOS. 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 chronic data from an
unpublished study by Funkhouser (2015) were
included for quantitative consideration. As noted on
page C-25, the animals in the Funkhouser (2015)
study were "purchased from a private collector" and
then kept for "several" generations prior to testing.
The source of the animals is just as uncertain as the
Yang et al (2014) animals, and it is unclear (if PFOS
tolerance at lethal levels is possible) how many
generations would be needed to shed adaptive
tolerance and how it would compare to "several."
Simply put, if data from experiments like
Funkhouser (2015) are quantitatively included, those
from Yang et al. (2014) should also be
Specific to comments to Charge Question 2.5.a:
2.5.a.i Test organisms were obtained from Yang et al. (2014)
were collected from Beijing City Big Forest Flower
Market and therefore, both the potential exposure to
PFOS and other contaminants was unknown.
Additionally, the test organisms were held 7 days prior
to testing, thus the age of the test organisms was
unknown despite the recommended use of 2nd or 3rd
instar (ASTM 1994). For these reasons, EPA
considered the chironomid toxicity data from Yang et
al. (2014) for qualitative use in the criterion
derivation. Further, EPA also included additional
analyses of the acute criterion which included the LC50
of 182.12 mg/L and concluded the chironomid toxicity
data had very little influence on the derivation (with a
CMC of 3.6 mg/L, which is the same as the draft acute
freshwater criterion).
Further, additional toxicity data for the genus have
become publicly available following the initiation of
this external peer review. These additional data were
reviewed by EPA and included in the draft PFOS
Aquatic Life Criteria Document However, these new
data did not include acute toxicity data for this genus
as the exposure duration was a minimum of 10 days as
opposed to the recommended 4-day exposure duration
stated in chironomid test guidelines (OECD 2004a;
OECD 2004b). Therefore, EPA retained the acute
insect toxicity data discussed previously as qualitative
studies and waived the aquatic insect MDR in the
derivation of the acute freshwater criterion for PFOS.
Regarding Reviewer l's comments related to the use
of the data from Funkhouser (2014), incorrectly
39

quantitatively included (with some notes on the
uncertainty of the animal sources).
2.5.a.ii There were only three exposure levels in this
experiment, including the control. One PFOS dose
(4.5 (ig/L) indicated an absence of detectable effects
on metamorphosis, the other (69.5 (ig/L) indicated
an approximate 35% reduction relative to controls.
This is not a definitive test; there is little dose
response information to fully confirm the
effects/absence of effects and predict an effective
concentration (EC) value with a dose response
model. Application of another study's dose response
curve to generate EC 10 values for this study does
not address this fundamental shortcoming, and
simply carries too much uncertainty. Although there
are only two PFOS doses, which is highly uncertain,
use of a Maximum Acceptable Toxicant
Concentration (MATC) value may be a less
uncertain path to including this study in quantitative
calculations. This would result in a more
conservative chronic value for this study (0.018
mg/L instead of 0.057 mg/L). Given the high
uncertainty of using this result (due to only 2 PFOS
doses), I believe this value should be caveated in
some way and re-evaluated for use or excluded in
future criteria derivation. For example, on page C-
22, the Spachmo and Arukwe (2012) value (which
also featured a limited PFOS dose design), the
document notes that the limited doses "may limit its
future use in the criteria derivation pending
independent verification of the toxicity values by
EPA."
referred to as Funkhouser (2015), EPA acknowledges
that the source of these test organisms should be
considered carefully. However, EPA considered the
source and potential previous exposure to be less of a
concern for Funkhouser (2014) despite the original
source being from a private collector as the test
organisms ultimately used in the PFOS experiment
were from an established laboratory line housed at
Texas Tech University and were reared for several
generations before initiation of the PFOS experiment.
2.5.a.ii Thank you for your comments noting the
shortcomings related to the number of exposure levels
in the chronic experiment in Hazelton et al. (2012b).
EPA noted that this was not a definitive test and that
both the study design (which only included two
treatment groups) and level of data presented (which
are only presented graphically in Figure 2 of the
paper) in the publication lack the details needed to
fully understand the effects of chronic PFOS
exposures to the glochidia and juvenile life stages of
Lampsilis siliquoidea. EPA made edits to the draft
PFOS Aquatic Life Criteria document to ensure that
these concerns are clearly discussed (see edits in
Section 3.1.1.3.3 in revised draft).
2.5.a.iii Reviewer 1 expressed concerns with using another
study's dose response curve to generate an ECio for
the chronic exposures to PFOS from Hazelton et al.
(2012) as this application carries uncertainty and does
not address the shortcomings noted above. The
reviewer instead suggests that EPA use a MATC for
this study. Following the recalculation of the
estimated ECio for Hazelton et al. (2012) using a
chronic study by Liu et al. (2013), which was
40

2.5 .a.iii I agree with the interpretation of the Bots et al.
(2010) study and selection of the MATC.
2.5.a.iv First, on page 104, the document mentioned "an
EC10 of 0.0586 mg/L for growth following 10-days
of exposure", but on page 115, the document noted
"10-day growth with an EC10 of 0.05963 mg/L". In
Appendix C (page C-19), the document states "the
independently-calculated 10-day EC 10 for growth
was 0.0586 mg/L." There's some inconsistencies in
the value being obtained from EPA's EC10
modeling using this reference; please correct or
clarify.
One justification for using the 10-day EC 10 growth
result rather than other results is a lack of being able
to calculate EC 10s. I do think the emergence results
should not be discounted, however. EPA notes "as
for the emergence endpoint, there was a lack of a
concentration-response relationship and there were
very similar levels of observed effects (which
ranged between 42.6 and 50.1%) despite the more
than nine-fold increase in the mid-range treatment
concentrations (0.0023, 0.0144, 0.0217 mg/L,
respectively)." The magnitude of the effect (relative
to controls), and the fact that there were statistically-
detectable differences from controls in some of
these doses (0.0144, 0.0217 mg/L) seems to indicate
an ecologically meaningful adverse effect is
occurring due to PFOS. This range of concentrations
just might be a portion of dose response curve that is
relatively flat. There is a very clear adverse effect at
0.0949 mg/L. I think it would be reasonable to select
the MATC for emergence (0.0071 mg/L reported on
page C-19) and treat it a second study point since it
reviewed following the external peer review, the
estimated ECio was updated to 0.123 mg/L. Given the
similarity between this ECio and the author-reported
MATC for Hazelton et al. (2012), the MATC of
0.0177 mg/L was used instead of the estimated ECio
to derive the chronic criterion for PFOS. Additionally,
as stated in the draft PFOS Aquatic Life Criteria
Document, EPA will further refine the toxicity value
used in the derivation of the chronic freshwater
criterion if EPA is able to obtain the treatment level
data from the study authors. Also, additional chronic
PFOS data for mussels would be useful to better
inform the general use of Hazelton et al. (2012) and
the chronic effects of PFOS to mussels in general.
However, given the data currently available, EPA
included an additional analysis to Section 4.2.2 of the
draft PFOS Aquatic Life Criteria document that used
the recalculated ECio for Hazelton et al. (2012) using a
chronic study by {Liu, 2013 #1137@@author-year
instead of the MATC as part of a line-of-evidence
discussion to consider the effect the toxicity value has
on the chronic freshwater criterion. This additional
analysis yielded a chronic water column concentration
of 0.0071 mg/L, which resulted in a modest influence
when compared the recommended CCC value of
0.0084 mg/L and therefore, the author-reported
MATC was used instead. See Section 4.2.2 of the
revised draft PFOS Aquatic Life Document for more
details Thank you for your comment regarding the
interpretation of Bots et al. (2010) and the use of the
MATC to derive the chronic freshwater criterion.
2.5 .a.iv The inconsistencies in the ECio for chironomid growth
following 10-days of PFOS exposure were corrected.
The correct value of 0.0596 mg/L was used to derive
41

was a completely different experiment from the 10-
day experiment used to provide the EC 10 of
0.05963 (or 0.0586) mg/L value. A Species Mean
Chronic Value using the 0.0071 and 0.0586 mg/L
results would be 0.020 mg/L. This 0.020 mg/L value
would seem to be protective while including the
growth and emergence data from these two
experiments.
2.5.b.
More details need to be provided on the dose response modeling
using R. Appendix K is helpful for providing the reader with
details on the general approach, but where EC 10s 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 EC 10s 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 EC 10 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 EC 10s
(as shown for the most sensitive EClOs estimated). These steps
would be helpful to ensure and demonstrate quality of the model
fits and reproducibility of the modeling work.
Additionally, somewhere in the document (Appendix K),the 22
dose response model equations should be provided to the reader.
Alternately, a reference could be made to a document that
the chronic freshwater criterion and the corresponding
text was updated.
With regards to using the author-reported MATC of
0.0071 mg/L for emergence in addition to the EPA-
calculated ECio of 0.05963 mg/L for growth to
calculate a Species Mean Chronic Value that is
utilized in the derivation of the draft chronic
freshwater criterion, EPA disagrees and continues to
use the EPA-calculated ECio of 0.05963 mg/L for
growth alone, because the concerns EPA provided in
the draft PFOS Aquatic Life Criteria document
remained. Consistent with other aquatic life criteria
for other chemicals, EPA utilized the most sensitive
scientifically-defensible endpoint for this particular
study. EPA determined emergence not to be the most
scientifically-defensible endpoint despite appearing to
be the most sensitive.
Specific to comments to Charge Question 2.5.b:
In instances where EPA independently fit a model to derive a
LC50 or ECio estimates for most sensitive genera to acute and
chronic exposures to PFOS, the model types are displayed in
appendices A and C along with graphs of the data and fitted
model with 95% confidence bands for the fit. Details on the
functions and model specifications within the R.drc package are
available via an internet search or by following the link here:
https://cran.r-proiect.ora/web/packaaes/drc/drc.pdf
Standard errors for both the model parameters and LC50 or ECio
estimates are calculated during evaluation, but this level of
statistical detail was not included in version of the draft
document that underwent peer review. In response to Reviewer
1, Appendix A.2 and C.2 of the updated PFOS criteria document
now include 95% Confidence Intervals (C.I.) as parentheticals
42

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perflnorooctane Sulfonate
(PFOS/' ' ' '
2.5. The Toxicity Data to Derive the Draft Criteria
Reviewer
Comments
EPA Response

clearly provides this information (ideally a peer-reviewed or
EPA document) containing all 22 models.
followii
values)
point es
GMAV
test-spe
Appenc
A.2.1
0.9'
"5
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s
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1
O.J'
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within t
link her
lg discussion of all point estimates (i.e., LC50 and ECX
calculated by EPA (irrespective of whether or not the
timate was used in calculation of the four most sensitive
s and/or GMCVs). Please see below for an example of
cific C-R modeling results that were reported in
ix A.2 and C.2 of the draft PFOS Criteria Document.
1 and Krueger 2000 Concentration Response Curve - Pimephales
(fathead minnow)
Publication:
Species: Fathead minnow, Pimephalespromelas
Genus: Pimephales
EPA-Calculated LCso: 9.012 (95% C I. 7.146315 - 10.892956) mg/L
Drottar and Krueger 2000
3imephnl« promelas
Log Logistic tvpc 1. J para
0.1 1.0 10.0
PFOS ( mg L)
nal details on the functions and model specifications
he R.drc package are publicly available by following the
e: https: //cran. r-proi ect .ora/web/packaae s/drc/drc .pdf
Reviewer
2
• Were the data selected and/or excluded from the
derivation of the criteria appropriately utilized?
Thank you for your comment. Given the high occurrence of
unmeasured PFOS toxicity tests (typically attributed to the
relatively high stability of PFOS and/or difficulty in measuring
43

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 measure the
concentration of PFOS 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.
I have listed a number of papers below that were published in
2020 and 2021 that the EPA may want to consider in their
assessment.
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
Simpson, S.L., Liu, Y., Spadaro, D.A., Wang, X., Kookana,
R.S., Batley, G.E., 2021. Chronic effects and thresholds
for estuarine and marine benthic organism exposure to
perfluorooctane sulfonic acid (PFOS)-contaminated
test concentrations by individual study authors) there would be
insufficient data to derive PFOS criteria for aquatic life without
the inclusion of both measured and unmeasured 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 (see Reviewer
comment to Charge Question 2.4 above). Appendix O of the draft
PFOS 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 not systematically indicate discrepancies between
nominal and measured concentrations of PFOS, EPA used both
measured and unmeasured toxicity studies that otherwise meet
EPA's test quality guidelines to derive the PFOS criteria for
aquatic life.
Additionally, EPA noted the studies provided by Reviewer 2 (and
all other reviewers) that were not included in the draft PFOS
criteria and all studies provided in the comments of this external
peer review were considered for possible inclusion in the
derivation of the criteria,as appropriate, based on study data
quality.. Please see EPA's response to Reviewer l's comments to
the same Charge Question above for a summary of EPA's review
of these studies.
Responses to specific comments related to key studies used to
derive the draft PFOS criteria are summarized below in
corresponding order mentioned in Reviewer 2's comment:
Specific to comments to Charge Question 2.5a:
44

sediments: Influence of organic carbon and exposure
routes. Science of The Total Environment 776, 146008..
doi: 10.1016/j.scitotenv.2021.146008
Li, R., Tang, T., Qiao, W., Huang, J., 2020. Toxic effect of
perfluorooctane sulfonate on plants in vertical-flow
constructed wetlands. Journal of Environmental Sciences
92, 176-186.. doi:10.1016/j.jes.2020.02.018
Aquilina-Beck, A.A., Reiner, J.L., Chung, K.W., Delise, M.J.,
Key, P.B., Delorenzo, M.E., 2020. Uptake and Biological
Effects of Perfluorooctane Sulfonate Exposure in the
Adult Eastern Oyster Crassostrea virginica. Archives of
Environmental Contamination and Toxicology 79, 333—
342.. doi: 10.1007/s00244-020-00765-4
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
Suski, J.G., Salice, C.J., Chanov, M.K., Ayers, J., Rewerts, J.,
Field, J., 2021. Sensitivity and Accumulation of
Perfluorooctanesulfonate and Perfluorohexanesulfonic
Acid in Fathead Minnows (Pimephales promelas )
Exposed over Critical Life Stages of Reproduction and
Development. Environmental Toxicology and Chemistry
40, 811-819.. doi:10.1002/etc.4936
McCarthy, C.J., Roark, S.A., Wright, D., O'Neal, K., Muckey,
B., Stanaway, M., Rewerts, J.N., Field, J.A., Anderson,
T.A., Salice, C.J., 2021. Toxicological Response of
Chironomus dilutus in Single-Chemical and Binary
Mixture Exposure Experiments with 6 Perfluoralkyl
2.5.a.i EPA noted Reviewer 2's support for not
considering the chironomid data from Yang et al.
(2014) for quantitative use in the derivation of the
acute freshwater criterion for PFOS. And the
reviewer raises a good point that aquatic insects
appear to be sensitive to chronic exposures of
PFOS. However, given the toxicity data that were
available during the development of the draft PFOS
Aquatic Life Criteria Document that was peer
reviewed and in the literature review that was
conducted following the external peer review, EPA
concluded that aquatic insects appear not to be
sensitive to acute exposure of PFOS. EPA will
continue to review additional PFOS toxicity
literature as it becomes available to better inform
the effects of acute exposures of PFOS to aquatic
insects.
2.5 .a.ii EPA thanks Reviewer 2 for providing editorial
comments for the summary of Hazelton et al.
(2012). Edits were made to the draft PFOS Aquatic
Life Criteria Document to correct these editorial
issues. Drottar and Krueger (2000) was an acute
toxicity study on Elliptio complanata (formerly,
Unio complamatus). A summary for this study can
be found in Appendix A (specifically Section
A.2.1.1) of the draft PFOS Aquatic Life Criteria
Document. Therefore, the observed endpoints
between Drottar et al. (2000) and Hazelton et al.
(2012) were not the same. Following the external
peer review EPA recalculated the estimated ECio
for Hazelton et al. (2012) using a chronic study by
Liu et al. (2013), which not previously included in
the PFOS draft that underwent review. And the
estimated ECiowas updated to 0.0123 mg/L. Given
45

Substances. Environmental Toxicology and Chemistry
40, 2319-2333.. doi:10.1002/etc.5066^
2.5.a.
2.5.a.i 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.
However, I don't agree with the conclusion that
insects may not be one of the most sensitive taxa.
Chironomus tentans is a relatively sensitive taxa to
chronic exposure to PFOS (MacDonald et al. 2004). In
Table C.l, the EC10 for C. tentans is reported as
0.05963 mg/L. Chironomus tentans was also the
fourth most sensitive species used in calculating the
chronic freshwater criterion (Table 3-6). Also, another
insect, Enallagma cyathigerum, another insect species,
was the second most sensitive species used in
calculating the chronic freshwater criterion (Table 3-
6).
2.5.a.ii EPA used an EC10:EC35.4 from Drottar et al. (2000)
for Elliptio complanata and applied this ratio to derive
an EC 10 from the data reported in Hazelton et al.
(2012) for Lampsilis siliquoidea. The problem is that
EPA have not clearly outlined in section 3.1.1.3.3
what endpoint that Drottar et al. (2000) was measuring
in Elliptio complanata (also note that the genus and
species are not spelled correctly in section 3.1.1.3.3).
Is the endpoint measured in E. complanata the same as
the endpoint measure in L. siliquoidea? I tried to look
up the endpoint measure in Drottar et al. (2000) but I
could not find the study and there was no reference
provided in the reference section for Drottar et al.
(2000). This missing information makes it difficult to
the similarity between the recalculated ECio and
the author-reported MATC for Hazelton et al.
(2012), the MATC of 0.0177 mg/L was used
instead of the estimated ECio to derive the chronic
criterion for PFOS. In addition to these changes in
the toxicity value used, EPA updated the text
related to the updated estimated ECio for Hazelton
et al. (2012) to clarify the specific exposure
duration and test endpoints between the two studies
included in the estimated ECio.
2.5 .a.iii Thank you for your comment regarding the
inclusion and interpretation of Bots et al. (2010) in
the derivation of the chronic freshwater criterion
for PFOS.
2.5.a.iv EPA thanks Reviewer 2 for clarifying the species
tested in MacDonald et al. (2004). The authors
used the species name Chironomus tentans,
however, this particular species name has changed
in recent years to the species name that EPA used
in the draft PFOS Aquatic Life Criteria document
of Chironomus dilutus. EPA edited the text for
MacDonald et al. (2004) in the draft PFOS Aquatic
Life Criteria Document to "Chironomus dilutus,
formerly Chironomus tentans" to clarify the issue
of the species name.
EPA has not been able to obtain additional
treatment level data or clarification regarding study
design details from the study authors for
MacDonald et al. (2004). Instead, EPA
independently calculated toxicity values for these
experiments using the data that was provided in the
publication. As such details for some of the
46

comment on the validity of the approach that EPA has
taken to derive an EC 10 for L. siliquoidea.
2.5 .a.iii Ithinkthe EPA's justification for the use of the
survival data from Bots et al. (2010) is valid. While
control mortality reached 40% in the control, the
plateau in control mortality after 60 days, the total
duration of the test being 200 days, and 82.57%
survival in the control from day 60 to 200, justifies the
inclusion of the MATC derived from Bots et al.
(2010) for Enallagma cyathigerum in the derivation of
a chronic criterion.
2.5.a.iv First, the wrong species is referenced in relation to the
MacDonald et al. (2004) study. MacDonald et al.
(2004) reported the toxicity of PFOS to Chironomus
tentans. The EPA's derivation of a 10-d EC 10 for
Chironomus tentans using the data from MacDonald et
al. (2004) is not clear. In Appendix C, section C.2.4,
the EPA writes, "EPA could not fit a curve to
independently verify the 10-day survival (due to a lack
of a specific sample size for this endpoint as the
number of replicates was not stated in the paper;
however, the number of replicates was between 2 and
4 and EPA sought to obtain clarification and treatment
level data from the study authors)" It is not clear how
EPA got the information necessary, e.g., number of
replicates, to fit a curve. It is also not clear what EPA
means by .. and treatment level data from the study
authors."? Did EPA acquire the raw data for growth
from the 10-day toxicity test with C. tentans? If that is
the case, they have not made that clear. If that is the
case, it would also strengthen their independently
derived EC 10 for growth in C. tentans. I think the
EPA needs to more clearly explain where they got the
endpoints (i.e., survival) were lacking in critical
information relating to sample size and EPA was
not able to reliably fit a model to independently
calculate toxicity values. However, these details
were provided in the paper for other endpoints (i.e.,
growth) and thus EPA was able to reliably fit a
model to independently calculate toxicity values.
EPA ensured that these details were clearly
provided in the study summary for MacDonald et
al. 2004 (see Section 3.1.1.3.4 and Appendix
C.2.4).
Following the external peer review of the draft PFOS Aquatic
Life Document, EPA reviewed recently published PFOS toxicity
literature and updated the PFOS criteria to include new data that
met test quality guidelines. This update includes a recently
published chironomid study by McCarthy et al. (2021). The
inclusion of this additional study changed the chironomid GMCV
from 0.05963 mg/L to 0.009731 mg/L and resulted in this genus
being the most sensitive in the chronic PFOS dataset as opposed
to the fourth most sensitive. Specific to comments to Charge
Question 2.5.b:
Thank you for your comment indicating that EPA's
independently-calculated toxicity values from concentration-
response data was appropriate. Details pertaining to model
specifications can be found here: https://cran.r-
proiect.ore/web/packaees/drc/drc.pdf (Ritz and Strcibie 2016)
In instances where EPA independently fit a model to derive an
ECx estimate, the model types are displayed in appendices A and
C of the draft PFOS Aquatic Life Criteria Document along with
graphs of the data and fitted model with 95% confidence bands
for the fit.
47

data necessary to derive the EC 10 for C. tentans used
in the chronic criterion.
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 K.
I think the LC50 and EC 10 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.

Reviewer
3
See collective responses below
• Were the data selected and/or excluded from the
derivation of the criteria derivation appropriately
utilized?
Data selection and waiving of the MDR for insect family in the
FAV seem reasonable.
• 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
Thank you for your comment indicating that the screening and
ultimately waiving the aquatic insect MDR was reasonable for the
derivation of the acute freshwater criterion for PFOS.
EPA noted the studies provided by Reviewer 3 (and all other
reviewers) that were not included in the draft PFOS criteria and
all studies provided in the comments of this external peer review
were considered for possible inclusion in the derivation of the
criteria, as appropriate, based on data quality, following the
approach described in the draft document. Further, EPA intends
to continue reviewing PFOS toxicity literature as it becomes
available. Particularly, as Reviewer 3 noted in the comments,
48

latest update)? If so, please provide references for
consideration.
The data selection for the derivation of the draft criteria are
limited to published and/or available studies from 2018 and
prior. This significantly reduces the studies used in the
derivation as a number of publications have become available in
recent years.
For example:
A newly published study is available for fathead minnows
exposed to PFOS for chronic duration and over the course of
reproduction and development. Although, this study was static-
renewal, PFOS concentrations are measured ; importantly, this
study resulted in a NOEC of 8 8 jJ.g/L based on reduced biomass
seen in the second generation (Suski et al. 2020). Importantly,
follow-on work (in prep) indicates that this may be a maternal
transfer impact as PFOS exposures to juvenile fish alone do not
share results.
Also, from the authors noted above is an ongoing full life-cycle
fathead PFOS and PFAS mixture exposure. This study is being
conducted under flow through conditions and is expected to
reach termination in December 2021.
McCarthy et al. 2021 published data on chironomids (EC20 =
1.7fj.g/L), these are also not included here.
Bryan Brooks (Baylor) and Matt Simcik (UMN) also have acute
data on the fathead minnow with measured concentrations, these
are not published just yet.
David Moore (Army Corps) is near completion of a full life-
cycle fish study
since many relevant PFOS toxicity studies are currently
underway and/or in preparation for publication.
Responses to specific comments related to key studies used to
derive the draft PFOS criteria are summarized below in
corresponding order mentioned in Reviewer 3's comment:
Specific to comments to Charge Question 2.5.a:
2.5.a.i EPA noted Reviewer 3's support for not considering
the chironomid data from Yang et al. (2014) based on
the source of the test organisms being problematic.
EPA continued to not consider the chironomid data
from Yang et al. (2014) for quantitative use in the
derivation of the acute freshwater criterion for PFOS
and instead used the data qualitatively as supporting
information.
2.5.a.ii EPA thanks Reviewer 3 for the editorial comment
regarding the summary of the chronic exposures to
fatmucket in Hazelton et al. (2012) and edits were
made to the text to clarify. The text in the draft PFOS
Aquatic Life Criteria Document is now:
"The in marsupia exposure was followed by a
24-hour free glochidia exposure consisting of
a factorial design. As such the free glochidia
from the control group of the marsupia
exposure were divided between a control and
the two PFOS treatments and the PFOS
treatments were split into control and the
same PFOS treatment group as the marsupia
exposure. This factorial design allowed for the
comparison of PFOS effects in two different
life-stages."
49

In particular, SERDP has been funding this research for years
and those data are published, recently published or near final.
EPA should reach out to SERDP Pis for data inquiries and
potential inclusion in these draft criteria.
2.5.a.
2.5.a.i This seems appropriate, the flower market is most
definitely an odd place to purchase research
organisms.
2.5.a.ii From Section 3.1.1.3.3: "The in marsupia exposure
was followed by a 24-hour free glochidia exposure
consisting of a factorial design, such that free
glochidia from the control group of the marsupia
exposure were divided between a control and the two
PFOS treatments and the PFOS treatments were split
into control and the same PFOS treatment group as
the marsupia exposure. " - Comment: This is an
exceptionally long and confusing sentence please
revise to help the reader understand this complex
study and overall approach that EPA took.
The approach seems ok given the limited data
availability at this time.
2.5 .a.iii Given the duration of the study the researchers likely
hovered around the nominal concentrations of PFOS.
Inclusion seems appropriate.
2.5.a.iv I am uncomfortable with this conclusion presented
here, it may be more appropriate to use MacDonald et
al. data from the 20-day endpoint considering recent
publication from McCarthy et al. 2020 as noted above.
2.5.b.
2.5 .a.iii EPA also noted and thanks Reviewer 3 for indicating
that the approach used to estimate an ECio fatmucket
in Hazelton et al. (2012) seem reasonable given the
limited data available. Thank you for your comment
regarding the inclusion of Bots et al. (2010) in the
derivation of the chronic freshwater criterion for
PFOS.
2.5 .a.iv Following the external peer review of the draft PFOS
Aquatic Life Document, EPA reviewed recently
published PFOS toxicity literature, including the study
by McCarthy et al. (2021) and updated the PFOS
criteria to include new data that met test quality
guidelines. This update includes chronic data from
McCarthy et al. (2021). The inclusion of this
additional study changed the chironomid GMCV from
0.05963 mg/L to 0.009731 mg/L and resulted in this
genus being the most sensitive in the chronic PFOS
dataset as opposed to the fourth most sensitive in the
previous draft that underwent external peer review.
Specific to comments to Charge Question 2.5.b:
Thank you for your comment indicating that EPA's
independently-calculated toxicity values from concentration-
response data was appropriate and defensible.
50

This seems like a reasonable and defensible approach if it is
applied consistently across genera.

Reviewer
4
The data selected to derive PFOS 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 and provides
further confidence in data selection process.
The key acceptable exclusion/inclusion criteria used to derive
draft criteria are listed below:
• Only single chemical toxicity tests with PFOS 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.
• PFOS toxicity tests were not excluded from quantitative
use in criteria derivation on the basis of unmeasured test
concentrations alone.
• Due to lower sensitivity, insect MDR was excluded
from the criterion calculation, but were used to waive
the missing insect MDR.
Thank you for your comment summarizing the test quality
guidelines that were considered in the review of PFOS toxicity
data for providing three additional papers that EPA should review
for possible inclusion in the derivation of the draft PFOS criteria.
There is one point in Reviewer 4's comments that EPA would
clarify related to the acute toxicity data for aquatic insects. In the
process of deriving an acute freshwater criterion for PFOS, it was
determined that there were no quantitative acute, PFOS toxicity
data focused on aquatic insects and that one MDR would not be
met given the data available at the time. As the derivation of a
PFOS acute freshwater criterion is important for the protection of
aquatic life exposed to PFOS, EPA considered qualitative data
(see Appendix G of the draft PFOS Aquatic Life Criteria
Document) to determine if the relative sensitivity of aquatic
insects could be ascertained and if the requirement of the missing
MDR group could be waived if there was no evidence to suggest
aquatic insect are among the four most sensitive genera.
As such, there were qualitative data from two acute studies
focused on aquatic insects (Yang et al. 2014 and Olson 2017).
And the relative sensitivity of aquatic insects following acute
exposures to PFOS could not be ascertained as these two
qualitative studies indicated contrasting relative sensitivity of
aquatic insects. However, the data on midge from Yang et al.
(2014) were considered to be more robust as the test was based
on measured exposure concentrations, the author reported LC50
could be assessed by EPA on a statistical basis since model
parameters were provided, and all other study design elements
beyond the source of the test organism met EPA's test quality
recommendations. Therefore, EPA utilized the data on midge
from Yang et al. (2014) to conclude that aquatic insects are likely
51

• 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.
Additional toxicity data published over the last six months is
listed below:
Marine/estuarine
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.ora/10.1016/i.chemosphere.2021.129699
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
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).
https://doi.ora/10.1002/etc.5066
not among the four most sensitive genera and waived the
unfulfilled MDR in the derivation of the acute freshwater
criterion for PFOS that underwent external peer review.
Additional toxicity data aquatic insects have become publicly
available following the initiation of this external peer review.
These additional data were reviewed by EPA and included in the
draft PFOS Aquatic Life Criteria Document However, these new
data did not include acute toxicity data any aquatic insects,
including chironomid as the exposure duration in the one new
test by McCarthy et al. (2021) was a minimum of 10 days as
opposed to the recommended 4-day exposure duration stated in
chironomid test guidelines (OECD 2004a; OECD 2004b).
Therefore, EPA retained the acute insect toxicity data discussed
previously as qualitative studies and waived the aquatic insect
MDR in the derivation of the acute freshwater criterion for
PFOS. Given the recent PFOS toxicity literature that EPA
reviewed Also, EPA noted that additional insect toxicity data for
PFOS would be very useful for further examining the relative
sensitivity of insects to PFOS exposures.
EPA noted the studies provided by Reviewer 4 (and all other
reviewers) that were not included in the draft PFOS criteria and
all studies provided in the comments of this external peer review
were considered for possible inclusion in the derivation of the
criteria, as appropriate, based on study data quality, following the
approach described in the draft document.
Responses to specific comments related to key studies used to
derive the draft PFOS criteria are summarized below in
corresponding order mentioned in Reviewer 4's comment:
Specific to comments to Charge Question 2.5.a:
2.5 .a.i EPA thanks Reviewer 4 for the comments pertaining
to the waiving of the acute MDR for aquatic insects.
52

2.5.a.
2.5.a.i 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). At this stage, I do not
fully agree with the statement that midge larvae are
tolerant to acute exposures. The OECD protocol
recommends 48h acute test for midge larvae and the
48h exposure period is acceptable duration for
assessing acute toxicity. The study by Olson (2017)
has limitations but this study can't be fully ruled out.
The chronic toxicity data exhibits sensitivity of insects
to PFOS and this statement is also supported by the
authors. 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 are among
sensitive taxa to chronic PFOS exposures (with
adverse effects reports at low ug/L)
I support the recommendation 'Additional insect
toxicity data for PFOS would be very useful for
further examining the relative sensitivity of insects to
PFOS exposures''.
Unpublished work from our lab shows acute toxicity
to midge larva, Chironomus tepperi at 1 mg/L PFOS
(48 h EC50 value).
2.5.a.ii The authors have provided detailed assessment of this
study and explained the approach used for the
calculation of chronic toxicity value (section C.2.3-
Third Sensitive Freshwater Genus for Chronic
Toxicity: Lampsilis siliquoidea (mussel). Hazelton et
EPA agrees that the PFOS toxicity date from Olson
(2017) should be taken into consideration for the
derivation of the acute freshwater criterion for PFOS.
However, given the multiple concerns that EPA noted
with this study (specifically that publication was
missing important exposure details, the author
reported LC50 and concentration-response curve could
not be assessed by EPA on a statistical basis since
model parameters were not provided, and there was
insufficient treatment level data to independently
calculate toxicity values) it was considered for
qualitative use and was not used in the derivation of
the criterion. Instead, EPA included this study in the
additional analyses section of the Effects
Characterization of the draft PFOS criteria draft (see
Section 4.2.1). This additional analysis indicated that
the inclusion of data for yellow fever mosquito (Aedes
aegypti) from Olson (2017) affects the calculated
value for the freshwater acute water column criterion
for PFOS, decreasing the criterion magnitude by a
factor of 6.9 below the value calculated when waiving
the unfulfilled MDR. However, EPA decided not to
use data from Olson (2017) in the acute freshwater
criterion derivation and noted that additional toxicity
data on aquatic insects are needed to fully understand
the potential acute effects of PFOS on aquatic insects,
especially considering the comparison between
qualitative data for midge and mosquito, which
indicated very different sensitivities among insects for
which data are available.
As for the results from MacDonald et al. (2004);
Marziali et al. (2019); Stefani et al. (2014), the
reviewer suggests that aquatic insects appear to be
sensitive to chronic exposures of PFOS. However,
53

al. 2012 used robust study design in spite of including
only two concentration of PFOS in this study. The
PFOS exposure concentration was measured, and
metamorphosis success was used as an endpoint for
inclusion in the criteria development. While viability
of free glochidia at 24 hours post removal from
females was a less sensitive endpoint and did not meet
the acceptability criteria. The reduction in
metamorphosis success at the 0.0695 mg/L was
estimated to be 35.4% but EC 10 could not be
calculated based on only two PFOS concentrations
tested in this study. The EPA team has calculated
EC 10 (0.05713 mg/L) using the exposure response
slope from PFOS toxicity study on another mussel
species (Ellipto complamata). The explanation and
logic provided is reasonable to include the calculated
EC 10 value to derive the freshwater chronic criterion
and to better understand the effects of PFOS on
aquatic insects.
2.5 .a.iii As a weight of evidence approach, EPA ran additional
analyses with some of the other toxicity values for E.
cyathigerum to understand the influence of this study
on the overall chronic criterion. The 150-day MATC
was more comparable to the other aquatic insect data
and more representative of life cycle effects than the
10-day MATC or NOEC at 60 and 320 days of
exposure (Table 4.3 of the report). EPA has concluded
that the 150-day MATC should be used quantitatively
to derive the chronic freshwater criterion toxicity. In
addition, the control survival of test organisms was
determined to be acceptable at this time point in the
test. I am in agreement with this decision.
given the toxicity data that were available during the
development of the draft PFOS Aquatic Life Criteria
Document that was peer reviewed, EPA concluded
that aquatic insects appear not to be sensitive to acute
exposure of PFOS and that the relative sensitivity of
aquatic insects may differ between acute and chronic
exposures. Thus, making it difficult to ascertain the
relative sensitivity of aquatic insects given the
available data. And while the recent PFOS toxicity
literature that EPA reviewed following the completion
of the external peer review includes additional data for
aquatic insects these new data did not include acute
toxicity data any aquatic insect species, including
chironomid, In particular, the exposure duration in the
one new test by McCarthy et al. (2021) was a
minimum of 10 days as opposed to the recommended
4-day exposure duration stated in chironomid test
guidelines (OECD 2004a; OECD 2004b). Therefore,
EPA retained the acute insect toxicity data discussed
previously as qualitative studies and waived the
aquatic insect MDR in the derivation of the acute
freshwater criterion for PFOS.
2.5.a.ii Thank you for your comment summarizing the chronic
exposure of PFOS to fatmucket in Hazelton et al.
(2012) and EPA's estimation of an ECio given data
limitations, and for indicating that approach used to
estimate an ECiofor fatmucket from Hazelton et al.
(2012) seems reasonable and aids to better
understanding of the effects of PFOS.
2.5.a.iii Thank you for your comment regarding the inclusion
of Bots et al. (2010) in the derivation of the chronic
freshwater criterion for PFOS.
54

2.5.a.iv The observed effects of PFOS on C. dilutus reported
in the paper by the study authors include survival and
growth as weight (measured as mg of ash-free dry
mass per individual) for both the 10-day and 20-day
exposure durations and emergence and reproduction
over the 20-day exposure duration. The author
reported 10-day growth and survival EC 10s for the
study were 0.0492 and 0.1079 mg/L, respectively. The
study authors also reported NOECs of 0.0491 mg/L,
LOECs of 0.0962 mg/L, and MATCs of 0.0687 mg/L
for both endpoints. The author reported 20-day ECioS
for growth, survival, and total emergence were 0.0882,
0.0864, and 0.0893 mg/L, respectively. And the study
authors also reported NOECs of 0.0217 mg/L for
growth and survival and < 0.0023 mg/L for
emergence, LOECs of 0.0949 mg/L for growth and
survival and 0.0217 mg/L for emergence, and MATCs
of 0.0454 mg/L for growth and survival and 0.0071
mg/L for emergence.
Independent statistical analyses were conducted by
EPA Team for both the 10-day and 20-day exposure
durations using data that were estimated The 20-day
ECioS for survival and emergence were not considered
to be reliable endpoints given the disparities in the
calculated ECioS and the level of data that was
presented in the paper, which made independent
verification of the toxicity values less accurate. The
dosing of the 20-day exposure was more of a concern
than the 10-day exposure, which had measured
concentrations that were much more in line with the
expected nominal concentrations. The independently-
calculated 10-day ECio for growth was 0.0586 mg/L
2.5.a.iv Thank you for your comment summarizing the chronic
toxicity values for chironomid. Following the external
peer review of the draft PFOS Aquatic Life
Document, EPA reviewed recently published PFOS
toxicity literature, including a chironomid toxicity
study by McCarthy et al. (2021) and updated the
PFOS criteria to include new data that met test quality
guidelines. This update includes chronic data for
chironomid, which changed the chironomid GMCV
from 0.05963 mg/L to 0.009731 mg/L and resulted in
this genus being the most sensitive in the chronic
PFOS dataset as opposed to the fourth most sensitive
in the previous draft that underwent external peer
review.
Specific to comments to Charge Question 2.5.b:
Thank you for your comment indicating that EPA's
independently-calculated toxicity values from concentration-
response data were appropriate. EPA noted and corrected the
missing values Reviewer 4 highlighted in comments to Charge
Question 2.8 below.
55

was used quantitatively to derive the chronic aquatic
life criterion.
The EPA team has reviewed publications by Stefani et
al. (2014) and Marziali et al. (2019) as additional
supporting information. These authors conducted
chronic toxicity tests with Chironomus spp. and
reported chronic apical endpoints (at low ug/1) but at
only at one concentration.
Use of the chronic toxicity data for PFOS in a
recent publication should also be considered to
assess the reliability of 20-day endpoints (adverse
effects reported at 2-3 jug/L).
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).
https ://doi .ore/10.1002/etc.5 066
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.
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. As noted in Section 8 some of the values
are missing.

Reviewer
5
• Were the data selected and/or excluded from the
derivation of the criteria derivation appropriately
utilized?
As mentioned, I feel that there are some inconsistencies with
how some data were included or excluded. In the previous
comment, for example, some data were excluded from the
MacDonald et al. 2014 paper because there was some
disagreement between nominal and measured. With regard to
PFAS, I would say measured is almost always better than
nominal and the fact that these sometimes don't agree should
not be too big of a deal as long as they are not wildly different.
EPA put substantial effort into sometimes justifying nominal -
in all cases, excluding studies that had analytical confirmation is
less defensible than including studies that only report nominal,
in my opinion. This last statement is, of course, provided the
analytical methods are robust.
• 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.
Please see EPA's response to Reviewer 5's comments to Charge
Question 2.4 regarding the use of measured and unmeasured
toxicity tests in the derivation of the draft PFOS criteria above.
EPA agrees that the observed differences between the measured
and nominal concentrations in the 20-day emergence endpoint of
MacDonald et al. (2004) should not be the reason this test
endpoint was not considered for use in the derivation of the
chronic water column criterion. Instead, this endpoint was not
used because it is not considered to be a reliable endpoint at this
time given the disparities in the calculated ECios (with EPA's
independently-calculated ECio being 0.0102 mg/L and the
author-reported ECio equaling 0.0893 mg/L) and the level of data
that was presented in the paper, which made independent
calculation of the toxicity values by EPA less accurate. This
particular detail is noted on page C-19 of the appendices in the
draft PFOS Aquatic Life Criteria Document. Further, EPA would
clarify that in the Meta-Analysis of Nominal Test Concentrations
Compared to Corresponding Measured Test Concentrations, the
20-day test from MacDonald et al. (2004) was determined to
have systematic discrepancies between the measured and nominal
test concentrations. Given the apparent systematic dosing issue in
the 20-day test, all five treatments from this test were identified
as outliers and were removed from the measured meta-analysis
alone.
57

Sensitivity and Accumulation of
Perfluorooctanesulfonate and Perfluorohexanesulfonic
Acid in Fathead Minnows (Pimephales promelas)
Exposed over Critical Life Stages of Reproduction and
Development. J.G. Suski. C.J. Salice. M.K. Chanov. J.
Avers. J. Rewerts. J. Field Environmental Toxicoloav
and Chemistry, 2021, pp. 811-819.
Toxicological Response of Chironomus dilutus in
Single-Chemical and Binary Mixture Exposure
Experiments with 6 Perfluoralkyl Substances.
Christopher J. McCarthv. Shaun A. Roark. Demitria
Wriaht. Kellv O'Neal. Brett Muckev. Mike Stanawav.
Justin N. Rewerts. Jennifer A. Field. Todd A. Anderson.
Christopher J. Salice. Environmental Toxicoloav and
Chemistry, 2021, pp. 2319-2333.
2.5.a.
2.5.a.i Given that insects are among the most sensitive
organisms for the chronic exposures to PFOS, it seems
the Yang et al. 2014 paper is not very consistent with
the prevailing data. Additionally, McCarthy et al.
2021 reports toxicity to chironomids similar to that of
MacDonald et al. Additionally, while the Olson 2017
data for Aedes species was not acceptable (for valid
reasons), nonetheless the study shows very high
sensitivity of another insect species to acute exposures
to PFOS. That said, given the EPA's stance and
justification that "nominal generally equal measured
PFOS concentrations", I'm inclined to put more
confidence in Olson's study. Same for the 20-day data
in the MacDonald et al. paper on chironomids. In that
case, there was a "relatively large difference between
measured and nominal concentrations (p. 278)" and so
EPA noted the studies provided by Reviewer 5 (and all other
reviewers) that were not included in the draft PFOS criteria and
all studies provided in the comments of this external peer review
were considered for possible inclusion in the derivation of the
criteria, as appropriate, based on study data quality, following the
approach described in the draft document. Please see EPA's
response to Reviewer l's comments for a summary of EPA's
review of these studies.
Specific to comments to Charge Question 2.5.a:
2.5.a.i EPA thanks Reviewer 5 for the comments pertaining
to the waiving of the acute MDR for aquatic insects
based on the acute toxicity data from Yang et al.
(2014). Please see EPA's response to Reviewer 4's
comments to the same Charge Question (question
2.5a) above regarding the sensitivity of aquatic insects
to PFOS exposure and EPA's previous comments
regarding the use of the 20-day chironomid data from
MacDonald et al. (2004) immediately above. As
mentioned in the comment, additional toxicity data for
the genus have become publicly available following
the initiation of this external peer review. These
additional data were reviewed by EPA and included in
the revised draft PFOS Aquatic Life Criteria
Document However, these new data did not include
acute toxicity data for aquatic insects as the exposure
duration was a minimum of 10 days as opposed to the
recommended 4-day exposure duration stated in
chironomid test guidelines (OECD 2004a; OECD
2004b). Therefore, EPA retained the acute insect
toxicity data discussed previously as qualitative
studies and waived the aquatic insect MDR in the
derivation of the acute freshwater criterion for PFOS.
58

the data were not used. This seems odd to me - as
long as there are measured data, that's what I would
suggest using. Regardless, the MacDonald et al. paper
points to the sensitivity of insects so, collectively, I'd
be disinclined to sav that the Yang et al. paper shows
insects are not sensitive and the data requirement can
be waived. I wonder if it's possible to somehow
estimate an acute toxicity value for aquatic insects
based on chronic toxicity data? Basically, a reverse of
the Acute/Chronic ratio approach.
2.5.a.ii Unfortunately, I cannot find the Drottar et al. (2000)
paper which is the basis of estimating the EC 10 from
the EC35 generated in the Hazelton et al. (2012)
study. And..I think the citation in the document is
incorrect and this should be Drottar and Kreugar
(2000g)... or check to make sure the citations in text
and references match. Moroever, the Drottar paper
appears to be an acute test which is VERY different
than the Fatmucket study. This approach seems like a
"stretch" and, again, somewhat inconsistent with the
approaches and decision matrix EPA has used to
utilize or discard other data and endpoints.
2.5 .a.iii Well, clearly it would have been better to be able to
estimate an EC 10 but this appears appropriate. I note
that for this study the exposure concentrations were an
order of magnitude apart; in other cases, EPA has used
"too big of a difference between exposure
concentrations" to discard a study or two. Somewhere,
it would be good to know at what point there is too
great a difference among exposure concentrations
(lOx, 20x, ?) for the study to be deemed acceptable for
use quantitatively.
2.5.a.ii Please see EPA's response to Reviewer 2's comments
for the same Charge Question. Edits were made to the
draft PFOS Aquatic Life Criteria Document to correct
these editorial issues. Drottar et al. (2000) was an
acute toxicity study on Elliptio complanata (formerly,
Unio complamatus). A summary for this study can be
found in Appendix A (specifically Section A.2.1.1) of
the draft PFOS Aquatic Life Criteria Document. Thus,
the observed endpoints between Drottar et al. (2000)
and Hazelton et al. (2012) were not the same.
Following the external peer review EPA recalculated
the estimated ECio for Hazelton et al. (2012) using a
chronic study by Liu et al. (2013), which not
previously included in the PFOS draft that underwent
review; the estimated ECio was updated to 0.123
mg/L. Given the similarity between the recalculated
ECio and the author-reported MATC for Hazelton et
al. (2012), the MATC of 0.0177 mg/L was used
instead of the estimated ECio to derive the chronic
criterion for PFOS. In addition to these changes in the
toxicity value used, EPA updated the text related to
the updated estimated ECio for Hazelton et al. (2012)
to clarify the specific exposure duration and test
endpoints between the two studies included in the
estimated ECio.
EPA updated the text related to the estimated ECio for
Hazelton et al. (2012) to clarify that the exposure
duration and test endpoints were not the same.
Additionally, EPA is hopeful that additional chronic
toxicity data for mussels will become available to
better inform the estimated ECio for Hazelton et al.
(2012) and the overall relative sensitivity of this taxon.
59

2.5.a.iv I do not agree with the toxicity value used by EPA as
obtained from the MacDonald et al. study. The lowest
toxicity value is the MATC for 20-day emergence of
0.0071 mg PFOS/L. It is not clear why EPA did not
use this value? Emergence is clearly extremely
ecologically relevant, and the value generated seems
as defensible as most of the other endpoints EPA has
chosen to include?
Additionally, and as mentioned above, see the paper
by McCarthy et al. (2021) that was just published in
Environmental Toxicology and Chemistry. Those data
appear robust and should meet acceptability criteria.
2.5.b.
In general, the approach for fitting C-R data that EPA used is
basically state-of-the-art. The drc package is very powerful and
provides a way to test many different curves to then select the
best fit model. Although EPA described some of this in the
several sections related to "fitting x data (K 1.2)", I think more
details would be warranted. The description for the criteria to
select best fit models is rather vague. Perhaps a table of specific
fit criteria would be helpful? Perhaps this is not doable because
every dataset is different.
When I teach modules on Akaike Information Criteria (AIC) I
emphasize that the metric "penalizes" fit for more parameters
within a model. So, using AIC can yield the simplest, best
model that fits the data. This is because models with more
parameters tend to yield a better fit purely based on statistical
properties and not the actual phenomena being studied. I am not
aware that AIC is a measure of the model fit to "true outcomes"
which are only theoretical constructs, I think. If we knew the
"true outcomes" we would not really need the model. Anyway, I
would encourage the authors to review the AIC section and
2.5.a.iii Thank you for your comment regarding the inclusion
of Bots et al. (2010) in the derivation of the chronic
freshwater criterion for PFOS. EPA notes that other
studies that were not considered for quantitative use
(and therefore not used in the derivation of the PFOS
criteria) based on the wide range of the test
concentrations, such as an order of magnitude
difference between each treatment group, also had
other concerns with either the study design or the level
of data provided. These concerns are all noted in the
study summaries of draft PFOS.
2.5.a.iv The mentioned endpoint from MacDonald et al.
(2004) was not used quantitatively to derive the
chronic freshwater criterion for PFOS given the
disparities in the calculated ECios (those reported by
the study authors and independently by EPA) and the
author-reported MATC. The disparities in the ECios
are likely due to the level of data that was presented in
the paper, which made independent calculation of the
toxicity values less certain (e.g., authors used
concentration-response data at replicate level data
while EPA only had treatment mean data available).
As mentioned in the comment, additional toxicity data
for this genus have become publicly available
following the initiation of this external peer review.
These additional data from McCarthy et al.
(2021)were reviewed by EPA and included in the
revised draft PFOS Aquatic Life Criteria Document.
The inclusion of this additional study changed the
chironomid GMCV from 0.05963 mg/Lto 0.009731
mg/L and resulted in this genus being the most
sensitive in the chronic PFOS dataset as opposed to
60

make edits if necessary and certainly cite the source of the
explanation.
For section K.2.2. are there actually any criteria (i.e., numbers)
that are used to determine when a model fit is appropriate? As a
simple example, maybe one would consider an rA2 of 0.8 or
better to be a "good model" for linear regression? Some
statements to this effect and any details regarding actual criteria
used to select "good models" would be helpful. So, overall the
curve fitting approach is appropriate but more, specific details
would be helpful.
the fourth most sensitive in the previous draft that
underwent external peer review.
Specific to comments to Charge Question 2.5.b:
Thank you for your comment indicating that EPA's
independently-calculated toxicity values from concentration-
response data was appropriate. Details pertaining to model
specifications can be found here: https://cran.r-
proiect.ora/web/packaaes/drc/drc.pdf (Ritz and Streibia 2016).
In instances where EPA independently fit a model to derive an
ECx estimate, the model types are displayed in appendices A and
C along with graphs of the data and fitted model with 95%
confidence bands for the fit. The AIC provides an initial ranking
of candidate models to yield a subset of possible models to fit.
Models are then judged on a suite of statistical metrics (detailed
in Appendix K) taken as a whole. There is no one number that
would indicate that a model is appropriate. Further, the reviewer
is correct concerning individual datasets: each dataset presents
distinct challenges in assessing fit. Also, the reviewer is correct
that the "true outcomes" phrasing should be revised. As such,
edits were made by EPA to clarify the model fits and the
selection of toxicity values from these model fits in the derivation
of the PFOS criteria.
61

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
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 Wsiler Column Criterion Elements lor Aqiiitlic Life (o l)eri\e (ho Tissne-li.iseil Criterion Elements
Considering liio;uTiiniul;ilion
Re\ iewer
Comments
EIW 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 bioaccumulation factors (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 fish tissue criterion into water column criterion. The
derivation of the PFOS tissue criteria were translated in the manner
presented in the draft criteria document because measured effect
concentrations in tissue were limited, with only 13 toxicity studies
reporting tissue concentrations linked to adverse effects. From these
studies, only three of the eight MDRs were met. Therefore, EPA
concluded that there are currently insufficient data to derive a chronic
tissue criterion using a GSD approach from empirical tissue data from
toxicity studies. These details were provided in Section 3.2.2 of the
draft PFOS Aquatic Life Criteria Document that underwent external
peer review. EPA included a comparison of the translated tissue
criteria to the empirical tissue data linked to adverse effects in Section
4.6 of the draft PFOS Aquatic Life Criteria Document that underwent
external peer review. This comparison and these studies provided
context to the translation of tissue criteria. EPA updated both the
tissue criteria and the comparison of these criteria to the empirical
tissue data. EPA notes the draft PFOS Aquatic Life Criteria document
62

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
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 liioiucuimilitlion
Re\ iewer
Coninienls
KIW Response

criteria dcrn alion is consistent with oilier 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.
continues lo summarize the comparison between the empirically
measured and translated tissue concentrations, stating:
"Measured PFOS tissue data were reported in 14
publications focused on freshwater species, six of which were
quantitatively acceptable and eight of which were
qualitatively acceptable (Table 4-9). The six quantitatively
acceptable studies included data for one invertebrate, two
fish, and one amphibian species, and the eight qualitatively
acceptable studies included data for two invertebrate and
four fish species. Results of these studies are summarized in
Section 4.6.1 and Section 4.6.2.
Tissue concentration data from these toxicity studies were
compared to the translated tissue values for invertebrates
and fish to better understand the protectiveness of the aquatic
life tissue criteria. While tissue concentrations from toxicity
literature were limited, overall, the comparison indicated
that the translated tissue concentrations for invertebrate
whole-body, fish whole-body and fish muscle were consistent
with those from toxicity studies with direct aqueous exposure.
However, tissue concentrations from toxicity studies focused
on maternal transfer indicated that the tissue criteria may be
under protective and that a reproductive tissue criterion may
be needed to ensure protection from PFOS through this
exposure pathway (Hazelton et al. 2012a; Wang etal. 2011).
Nevertheless, BAF data for reproductive tissues are currently
limited; and therefore, a reliable reproductive tissue
criterion cannot be derived at this time (see Appendix Q).
As for other tissue types and taxa with limited data, tissue
concentrations from available toxicity studies suggest that
the translated tissue concentrations for fish liver and
reproductive tissues may be under protective. And while no
63

amphibian tissue criteria are available, tissue concentrations
from two amphibian toxicity tests indicate that the fish tissue
criteria may not be protective of amphibians. However, tissue
data for these tissues and taxa are limited and additional
data are needed."
Specific to comments to Charge Question 2.6.a:
EPA acknowledges the inherent uncertainties that are present with 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 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). Only studies with greater than two
water and tissue samples were collected for each media type, water
samples collected within one year and within one to two km. These
screening details are provided in Table 2-4 of the draft PFOS Aquatic
Life Criteria Document that underwent external peer review. EPA
determined that 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.
EPA recognizes differences between field-derived and
experimentally-derived (or those linked to adverse effects) BAFs.
Despite the uncertainties that are noted in Reviewer l's comments,
64

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.(>. The Tmnshilion of (ho Chronic Wsiter Column Criterion Klenients lor Aqn;itic l.il'e (o l)eri\e (ho Tissne-liiiseil Criterion Klements
Considering liio;uTuniul;ilion
Re\ iewer
Comments
KIW Response

LPA onl\ used ficld-dcm cd BAFs Lo dcn\ c the tissue criteria for
PFOS. This 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). Additionally, while field-derived BAFs have
inherent uncertainties discussed above, EPA concluded that field-
derived BAFs better represent real-world bioaccumulation of
contaminants, including PFOS, 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 the data indicate that that the PFOS tissue-
based criteria are generally expected to be protective of aquatic
species.
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. 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
Thank you for your comment regarding the translation of the chronic
freshwater criterion into tissue-based criteria with the use of
bioaccumulation factors (BAFs).
Specific to comments to Charge Question 2.6.a:
65

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.(>. The Tmnshilion of (ho Chronic W'siter Column Criterion Klenienls lor Aqn;itic l.il'e (o l)eri\e (ho Tissue-liiiseil Criterion Klemenls
Considering liioiucuimilitlion
Re\ iewer
Coninienls
KIW Response

reported UAFs incorporates the range oi' UAFs llial
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
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
2.6.b. The evaluation criteria for BAFs outline in Table
2-4 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 (Table 3-
12). 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.
The UAl;s used Lo calculate llie lissue crilena were obtained from the
UAF database created Lawrence Uurkhard in support of his
publication: Uurkhard, L.P. (2021) Evaluation of Published
Uioconcentration Factor (UCF) and Uioaccumulation Factor (UAF)
Data for Per- and Polyfluoroalkyl Substances Across Aquatic Species.
ET&C40: 1530-1543.
Further, UAFs reported in Prosser et al. (2016) were not in the
Uurkhard (2021) database and were therefore not used to calculate
UAFs. Upon review of Prosser et al. (2016), it appears this study was
not included in the UAF database developed by Uurkhard (2021)
because only biota sediment accumulation factors (USAFs) were
developed and UAFs were not. It is for this same reason EPA did not
include Prosser et al. (2016) among the UAFs that were used to derive
the tissue criteria for PFOS.
Specific to comments to Charge Question 2.6.b:
Thank you for your comment regarding the evaluation criteria that
were used for the UAFs and the use of fish UAFs for whole-body
and muscle.
66

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	(PFOS)"	
2.(>. The Tmnshilion of (ho Chronic Wsiler Column Criterion Klenienls lor Aqii;ilic l.il'e (o l)eri\e (ho Tissne-liiiseil Criterion Klemenls
Considering liio;uTuniul;ilion
Re\ iewer
Comments
KIW Response
Reviewer
3
Please clarify, the following sentence: "BAFs used in the
derivation of the PFOS tissue criteria consisted of > 2
water and organism samples each and were collected
within one year and 2 km distance." It is unclear if the >2
samples refer to the tissue & water samples being
mismatched temporally or if there where >2 sets of water
and tissue samples that were collected in different years.
If the latter then this approach seems appropriate; if the
former, EPA should discuss differences in water chemistry
between years to alleviate any concerns with matching
tissue concentration data to water samples that may have
significant environmental temporal variability.
A table summarizing the animal tissues used in deriving the
BAFs would be helpful to assess the range of fish species
and their dietary preferences.
The sentence in question refers to the generalized ranking system that
evaluates the number of water samples, the number of organism
samples, and the water and organism temporal and spatial
coordination that were used to classify BAFs of medium and high
quality in Burkhard 2021, which was the source of BAFs used in the
translation of the chronic freshwater criterion to tissue criteria for
PFOS. Details relating to the factors considered in screening and the
overall classification of BAFs were provided by EPA in Table 2-4 of
the draft PFOS Aquatic Life Criteria Document that underwent peer
review.
Regarding the relationship between water quality information for all
time periods when water and tissue samples were not collected
simultaneously, EPA determined this was impossible to know,
because in this scenario water samples were not collected on dates
when only tissue samples were collected. Additionally, in the review
of PFOA and PFOS BAFs by Burkhard (2021) there is no information
regarding the systematic influence of water quality parameters on
measured PFOS concentrations in water or organism tissue. However,
Review 5 provided comments that "there are some datasets that show
considerable temporal and spatial variability in PFAS water
concentrations over the course of a few weeks and over a spatial
distance of less than 0.5 km" indicating that water quality parameters
may influence the concentrations of PFOS.
EPA added a table summarizing the information related to the water
column and/or tissue concentrations used in the calculation of PFOS
BAFs. Further it should be noted that EPA used the PFOS BAFs that
were compiled by and can be found in Burkhard (2021). As such
tables detailing all the information related to the PFOS BAFs can be
found in the supporting information of the paper (see
https://doi.ore/10.1002/etc.5010).
67

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.(>. The Tmnshilion of (ho Chronic Wsiler Column Criterion Klenienls lor Aqii;ilic l.il'e (o l)eri\e (ho Tissne-liiiseil Criterion Klemenls
Considering liio;uTuniul;ilion
Re\ iewer
Comments
KIW Response

Reviewer
4
2.6.a. The freshwater chronic PFOS toxicity data with
measured tissue concentrations was limited, with
no quantitatively acceptable tissue-based tests.
Therefore, there were insufficient data to derive
tissue-based criteria using a GSD approach from
empirical tissue data from toxicity studies.
Tissue criteria derived from the chronic water
column concentration (CCC) with the use of
bioaccumulation factors were developed by EPA.
The chronic freshwater criterion also contains
tissue-based criteria expressed as 43.0 mg/kg wet
weight (ww) for fish whole-body, 25.3 mg/kg ww
for fish muscle tissue, and 12.3 mg/kg ww for
invertebrate whole-body tissue. EPA developed
protective tissue-based criteria through a
bioaccumulation factor approach. The authors
reviewed PFOS BAF literature based on four
criteria 1) number of water samples, 2) number of
organism samples, 3) water and organism temporal
coordination in sample collection, and 4) water and
organism spatial coordination in sample collection
and developed a ranking system. BAFs used in the
derivation of the PFOS tissue-based criteria
consisted of > 2 water and organism samples each
and were collected within one year and 2 km
distance. This scheme assured selection of only
BAFs of high and medium quality to derive the
tissue criteria.
2.6.b. BAFs are different for muscle/fillet and whole-
body tissues. Humans consume muscle/fillets from
Thank you for your comment summarizing the translation of the
chronic freshwater criterion to tissue criteria using PFOS BAFs.
68

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.(>. The Tmnshilion of (ho Chronic Wsiler Column Criterion Klenienls lor Aqii;ilic l.il'e (o l)eri\e (ho Tissne-liiiseil Criterion Klemenls
Considering liio;uTuniul;ilion
Re\ iewer
Comments
KIW Response

iish and soil Ussues from bivalves, therefore the
water quality criteria recommended by EPA used
BAFs based on these tissues. In addition, muscle
and whole-body are the most commonly sampled
tissue types in monitoring programs. These criteria
were developed based on the values reported for
50-60 samples (Table 3-12).
Within the body, PFOS tends to bioaccumulate
within protein-rich tissues, such as the blood
serum proteins and liver. EPA Team calculated
additional tissue values for liver, blood, and
reproductive tissues by transforming the
freshwater chronic water column criterion into
representative tissue concentrations using tissue-
specific bioaccumulation factors (BAFs). Author's
decision uses agreement on the use of female
reproductive tissues due to its relevance for
potential maternal transfer to offspring. These
additional tissue-based values were calculated for
comparative purposes and were not proposed as
recommended criteria.

Reviewer
5
2.6.a. Using the BAF for PFOS to determine the tissue-
based criterion elements is, I think, an interesting
and useful approach given the lack of tissue-based
metrics associated with toxicity data. The
variability in observed bioaccumulation of PFOS is
an active area of research but the work by
Burkhard 2021 (also an author on the AWQC)
provides an excellent synthesis and compendium
of available BAFs for PFOS. That said, I noticed
that the criteria for co-located tissue and water
Thank you for your comment regarding the translation of the chronic
freshwater criterion into tissue based criteria with the use of
bioaccumulation factors (BAFs).
Specific to comments to Charge Question 2.6.a:
In the review of PFOA and PFOS BAFs by Burkhard (2021) there is
no information regarding the systematic influence of water quality
parameters on measured PFOS concentrations in water or organism
tissue. However, Review 5 provided comments that "there are some
datasets that show considerable temporal and spatial variability in
69

samples for PFOS was llial thc\ were collected
within a year of each other and within 2 km
distance (p. 134) - this likely contributes to
significant variability in the BAFs. Although there
are few published datasets, there are some datasets
that show considerable temporal and spatial
variability in PFAS water concentrations over the
course of a few weeks and over a spatial distance
of less than 0.5 km. I wonder if the variability in
BAFs would decrease if the criteria were narrowed
to co-collected samples measured at the same
time? Might be worth the exercise. Given the
variability in PFOS BAFs, why not use something
like the 25% percentile BAF instead of the
geometric mean? When developing a protective
criteria and there is a very noisy data set, it might
be beneficial to err on the side of caution until
better data (many co-located samples in space and
time) were available. So, in summary, I think the
approach of using BAFs to estimate tissue-based
criteria is reasonable but given the variability in
BAFs, I would encourage using a lower BAF
instead of the geometric mean or reconsidering the
data that went into the BAFs used for criteria
development.
2.6.b. Invertebrate whole body, fish whole body, and fish
muscle are appropriate tissues for the tissue-based
criterion. These are the most commonly collected
tissue types and are relevant to monitoring efforts
and are even useful for considerations of fish
advisories. That said, the only other tissue worth
considering would be for liver in fish since this
tissue accumulates considerably more PFOS than
PFAS water concentrations o\ cr the course of a few weeks and o\ cr a
spatial distance of less than 0.5 km" indicating that water quality
parameters may influence the concentrations of PFOS. Please see
EPA's response to Reviewer 3's comment regarding the influence of
water quality parameters on PFOS BAFs above.
The geometric mean of the BAFs were used to be consistent with the
BAF methodology (U.S. EPA 2000).
Specific to comments to Charge Question 2.6.b:Thank you for your
comment regarding the appropriateness of the tissue types included in
the draft PFOS Aquatic Life Criteria Document.
70

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	(PFOS)"	
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 liioiucuimilitlion
Re\ iewer
Coninienls
KIW Response

muscle - lliese are included 111 llie appendices so
this is appropriate. Overall, tissues used for the
tissue-based criteria are appropriate.

71

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.7 Please comment on the frequency and duration of the criterion elements, in particular the tissue-based criterion elements.
2.7. The l-requency :tiul Duration of I lie Criterion Klemenls
Ue\ iewer
Com mciils
KIW Response
Reviewer
1
The 4-day duration seems to be supported by the more
sensitive chronic endpoints used to derive the CCC.
For the tissue-based criterion (page 135), 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 PFOS in aquatic ecosystems and recovery time if PFOS
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 PFOS. It is not
technically supported to cite recovery times for selenium to
support a 10-year recovery time for PFOS, 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 135-136 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 PFOS (i.e., BCF of
approximately 2,000 L/kg, wet weight for goldfish, as
noted in the EPA TBT criteria document, which is similar
to the PFOS BAFs of 1,800-3,100 L/kg, wet weight being
used to calculate the fish tissue criteria). TBT is also
persistent in aquatic ecosystems, as noted by EPA. Given
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 PFOS tissue criterion should
Thank you for your comment noting that 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 PFOS" However,
we do know that PFOS is stable in water and air (UNEP 2015), and
thus, unless the source is eliminated, PFOS is likely to remain in
aquatic systems overtime. Therefore, EPA considered the
bioaccumulative nature and persistence of PFOS in aquatic systems, in
combination with the documented recovery times of pollutants with
somewhat similar chemical attributes (Gergs et al. 2016; Lemly 1997)
set a reasonable and protective exceedance frequency for tissue-based
PFOS criteria. The selection of the 10-year exceedance frequency for
tissue criteria was not arbitrary. Rather, it was based on disturbance to
ecological recovery time relationships with chemicals of similar
properties.
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 PFOS Aquatic Life Criteria, the Tributyltin (TBT)
Aquatic Life Criteria does not include tissue-based criteria. Only the
draft tissue-based PFOS criteria specified exceedance frequencies of
10 years. The 10 year frequency for PFOS tissue-based criteria was set
with the intent to provide time for tissue concentrations that
accumulate through food webs to diminish, if possible, in source
72

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.7. The I rcqucncv mid Duration of the Criterion Klemcnls
Uc\ icwcr
Comments
KIW Response

be set at the default of 3 years unless EPA can provide
convincing technical information specific to recovery times
forPFOS.
Additionally, on page 136, the paragraph that begins with
"Metals and other chemical pollutants such as PFOS..." 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 PFOS recovery may be "on the order of
decades", as EPA notes for selenium. There is no support
for the conjecture that PFOS recovery may be "relatively
slow" or require decades, as noted in my above comment.
reservoirs lower in the food web before being eliminated in higher
trophic level species and allowing for subsequent potential ecological
recovery. 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 criteria for PFOS
and the chronic TBT criteria both specified a three-year exceedance
frequency, as recommended by the 1985 Guidelines (U.S.EPA 1985).
Based on ecological recovery times for other bioaccumulative and
persistent chemicals, ecological recovery times following elevated
PFOS concentrations in the tissues of aquatic organisms is expected to
be relatively long to allow for the dissipation of PFOS throughout the
food web. The draft PFOS Aquatic Life Criteria document was
revised in response to the comment from Reviewer 1. The full text
referenced by Reviewer 1 (with added strike throughs to represent
deletions and bold text to represent insertions to remove conjecture
from the writing) is provided below for information purposes:
"Metals and other chemical pollutants such as PFOS, 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 PFOS has been
extensively studies in humans relative to aquatic life. Li et al.
(2018) reported a median PFOS half-life of 3.4years in human
serum following exposure to PFOS in drinking water, which
authors stated was in the range of previously published estimates.
As a result, Due to chemical retention in tissues, ecosystems
impacted by discharges of bioaccumulative pollutants (such as
PFOS 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 reproductive
failure and deformities in fish, was still measurable (fish
deformities) in 1992 (seven years later) and in 1996 (ten years
73

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 PFOS has
been attributed to the strong C-F bond, with no known
biodegradation or abiotic degradation processes for PFOS.
Somewhat similarly, as elements, 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 been 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.
Thank you for your comment regarding guidance for potential
scenarios resulting in one criterion being exceeded while the other
criteria are not. Even if it is unlikely that aquatic receptors will exceed
or reach these tissue concentrations prior to exceedances from the
74

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	(PFOS)"	
2.7. The I rcqucncv mid Duration of the Criterion Klemenls
Ue\ iewer
Comments
KIW Response

What I am not clear on is, if tissue concentrations exceed
these proposed thresholds yet, PFOS water concentrations
do not exceed the CCC, what would be the proposed
guidance?
CCC (as suggested by Reviewer 3), EPA notes the draft PFOS
Aquatic Life Criteria document stated:
"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."
Reviewer
4
PFOS 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 PFOS 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 nothing that "It was appropriate for
EPA to inform the recommended ten-year exceedance frequencies for
the chronic tissue-based criteria."
Reviewer
5
In my opinion, the frequency and duration of criterion
elements is among the most uncertain and potentially
contentious elements of any type of protective criteria. The
frequency and duration for tissue-based criteria is that the
tissue-based criteria cannot be exceeded more than once in
a 10 year period. This means that if the PFOS criterion for
whole body in fish of 43 mg/kg bw is exceeded more than
once in a 10 year period then the criteria is exceeded. This
also means the fish was likely exposed to the 0.014 mg/1
Thank you for your comments. For clarity EPA has broken down and
responded to various points in Reviewer 5's comment.
Reviewer 5 Comment A: In my opinion, the frequency and duration
of criterion elements is among the most uncertain and potentially
contentious elements of any type ofprotective criteria. The frequency
and duration for tissue-based criteria is that the tissue-based criteria
cannot be exceeded more than once in a 10 year period. This means
that if the PFOS criterion for whole body in fish of 43 mg/kg bw is
75

concentration for longer than an instantaneous exposure
and likely longer than 4 days. So, to me, does this not mean
that if 43 mg/kg bw was measured in a fish tissue, then the
fish was likely exposed to 0.014 mg PFOS/L for longer
than 4 days, doesn't it? And, this also means that if fish
whole body concentrations were 42.5 mg/kg bw for 10
years, the criterion would not be exceeded. I would suspect
that long term PFOS exposures that consistently lead to
42.5 mg/kg bw in fish would likely translate to adverse
ecological impacts in some biota present in the same
system. When I think of it this way, these criteria do not
seem appropriately protective. In my view, the water
column continuous exposure criteria should be adjusted
downward which would then translate to a lower tissue-
based criteria which might be more reasonable. Although,
as mentioned, another protective approach would be to use
something like the 25th percentile BAF or something other
than the mean. That said, at least in many cases fish tissue
monitoring occurs on a yearly basis so there is some
potential for the criteria to be reasonably assessed against
environmental data. It is still possible that fish tissue
concentrations could be exceeded every year and this be
missed by monitoring efforts. Nonetheless, because tissue
concentrations are an intergrative measure and because
many monitoring programs probably do measure fish every
year, this is a better match than the water column criteria.
When we consider the acute and chronic water column
criteria, the frequency and duration elements are protective,
in my opinion. The problem is that nobody knows if the
criteria for acute toxicity are exceeded for more than 1 hour
or whether the chronic criteria was exceeded for more than
4 days - this extent of temporal resolution (hourly
concentrations or 4-day running averages) just does not
exist. So while I agree that conceptually, the frequency and
exceeded more than once in a 10 year period then the criteria is
exceeded.
EPA Response A: Following a single instances of tissue values being
greater than the corresponding criterion would mean that one
excursion (i.e., the event where both criteria magnitude and duration
are not met in situ) has occurred. If no other excursions occur within
the ten-year frequency, then a criterion exceedance will not occur. If
additional excursions reoccur within ten years, on average, then the
criterion will be exceeded and Clean Water Act (CWA) Section
303(d) action may be taken.
Reviewer 5 Comment B: This also means the fish was likely exposed
to the 0.014 mg/l concentration for longer than an instantaneous
exposure and likely longer than 4 days.
EPA Response B: The four-day duration represents the time period
over which the chronic criterion is averaged. Please see the except
from the 1985 Guidelines below for further explanation:
"The Criterion Continuous Concentration (CCC) is intended
to be a good estimate of this threshold of unacceptable effect.
If maintained continuously, any concentration above the CCC
is expected to cause an unacceptable effect. On the other
hand, the concentration of a pollutant in a body of water can
be above the CCC without causing an unacceptable effect if
(a) the magnitudes and durations of the excursions above the
CCC are appropriately limited and (b) there are
compensating periods of time during which the concentration
is below the CCC. The higher the concentration is above the
CCC, the shorter the period of time it can be tolerated. But it
is unimportant whether there is any upper limit on
concentrations that can be tolerated instantaneously or even
for one minute because concentrations outside mixing zones
rarely change substantially in such short periods of time"
76

duration elements definitely would add to the protection of
aquatic life... I just don't see how these can be
implemented or regulated. Perhaps EPA is aware that my
concern is not warranted because in relevant
circumstances, appropriately timed environmental data are
obtained.
Reviewer 5 Comment C: So, to me, does this not mean that if 43
mg/kg bw was measured in a fish tissue, then the fish was likely
exposed to 0.014 mgPFOS/L for longer than 4 days, doesn 't it?
EPA Response C: It's logical to assume a fish would have to be
exposed to PFOS at the chronic criterion magnitude for longer than 4
days for tissue concentrations to reach tissue-criteria magnitudes;
however, the four-day duration component of the chronic criterion
does not specify actual exposure duration, only the time period in
which the chronic criterion is averaged over (see EPA Response B
above).
Reviewer 5 Comment D: And, this also means that if fish whole body
concentrations were 42.5 mg/kg bw for 10 years, the criterion would
not be exceeded. I would suspect that long term PFOS exposures that
consistently lead to 42.5 mg/kg bw in fish would likely translate to
adverse ecological impacts in some biota present in the same system.
When I think of it this way, these criteria do not seem appropriately
protective. In my view, the water column continuous exposure criteria
should be adjusted downward which would then translate to a lower
tissue-based criteria which might be more reasonable. Although, as
mentioned, another protective approach would be to use something
like the 25th percentile BAF or something other than the mean.
EPA Response D: The criteria magnitudes for tissues were based on
the PFOS water column-criterion, which was the fifth centile of the
chronic Genus Sensitivity Distribution (GSD; composed primarily of
ECio values). Consequently, the chronic criterion is protective aquatic
life from unacceptable chronic PFOS exposures in water, including
approximately 95% of taxa at a 10% effect level. Because the tissue
criteria are based on the chronic water column-criterion itself,
Reviewer 5 is incorrect to postulate the water column criterion may
not be protective based on the magnitude, duration, and frequency
components of the tissue-based criteria. The 10-year frequencies of
the tissue criteria do not explicitly imply species will be exposed to
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 Perfluorooctane Sulfonate
(PFOS)"
2.7. The Frequency mid Duration of the Criterion Klemenls
Ue\ iewer
Comments
KIW Response

PFOS in the water column continually for 10 years. Instead, the 10-
year frequency for tissue-based criteria was set to provide time for
tissue concentrations that accumulate up through food webs to
potentially diminish in source reservoirs lower in the food web before
finally being eliminated in higher trophic level species and allowing
for subsequent potential ecological recovery. Finally, EPA notes the
draft PFOS water quality criteria document explicitly stated:
"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. "
Reviewer 5 Comment E: That said, at least in many cases fish tissue
monitoring occurs on a yearly basis so there is some potential for the
criteria to be reasonably assessed against environmental data. It is
still possible that fish tissue concentrations could be exceeded every
year and this be missed by monitoring efforts. Nonetheless, because
tissue concentrations are an integrative measure and because many
monitoring programs probably do measure fish every year, this is a
better match than the water column criteria.
EPA Response E: EPA thanks Reviewer 5 for indicating both the
protectiveness and utility of the magnitude, duration, and frequency
components associated with the tissue-based criteria.
Reviewer 5 Comment F: When we consider the acute and chronic
water column criteria, the frequency and duration elements are
protective, in my opinion. The problem is that nobody knows if the
criteria for acute toxicity are exceeded for more than 1 hour or
whether the chronic criteria was exceeded for more than 4 days - this
extent of temporal resolution (hourly concentrations or 4-day running
averages) just does not exist. So while I agree that conceptually, the
frequency and duration elements definitely would add to the
78

protection of aquatic life... I just don 't see how these can be
implemented or regulated. Perhaps EPA is aware that my concern is
not warranted because in relevant circumstances, appropriately timed
environmental data are obtained.
EPA Response F: 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 an hour duration or average chronic concentrations
of 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
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 exceedances will be allowed."
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 Perfluorooctane Sulfonate
(PFOS)"
2.8 Please provide any additional technical comments that you believe should be considered.
2.S. Addition:i 1 Technic;il Comments lo Consider
Ue\ iewer
Comments
KIW Response
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) In general, the document needs some quality copy editing effort. I
found many typographical errors, issues with formatting,
reference/citation issues, and in some cases, poorly-worded text. I
have noted a few of these instances below.
c) Page xv: "25.3 mg/L ww" is not correct units for a concentration in
tissue.
d) Page 6: "The carbon chain can be fully fluorinated...". Please
specify that this applies to PFAS in general, not to PFOS.
e) Page 6: The reference to "Table 2-1"; should that be Table 1-2?
f) Page 9: Please note in Figure 2-1 that this is the linear isomer of
PFOS. It would be helpful to note that the PFOS data in this study
are likely from experiments with water spiked with the linear PFOS
isomer. It is hypothesized that toxicity and bioaccumulation may
differ between branched and linear forms of PFCAs and PFASs.
Linear PFOS is thought to be more accumulative (as noted on Page
45) and potentially more toxic to aquatic life when the dose is
Thank you for your comments. Responses to the
corresponding alphabetical comments are
provided below:
a. Thank you for your comment. EPA has
received the final peer review report from
the contractor. This peer review has
concluded and comments received are
reflected in this final report. There is no
ability to supplement or amend
comments. Thank you for your review.
b. - e. The grammatical errors and requested
clarifications that were noted by the peer
reviewers have been corrected in the
revision to the draft PFOS Aquatic Life
Criteria document. Thank you for your
comments.
f. EPA edited the caption for Figure 2-1 to
note that this is the linear isomer of
PFOS. And, as stated in the draft PFOS
Aquatic Life Criteria document, the
criteria provides a critical review of all
aquatic toxicity data identified in EPA's
literature search for PFOS, including the
anionic form (CAS No. 45298-90-6), the
acid form (CAS No. 1763-23-1), a
potassium salt (CAS No. 2795-39-3), an
ammonium salt (CAS No. 56773-42-3), a
sodium salt (CAS No. 4021-47-0), and a
lithium salt (CAS No. 29457-72-5).
Further, EPA added the requested text to
note that PFOS toxicity studies typically
80

expressed as an external water concentration. At some sites, a
portion of the concentrations of PFOS in water (which are reported
as the sum of branched and linear PFOS) is branched PFOS, so
criteria derived from linear PFOS could be overly protective. Please
include this uncertainty in the discussion in the document.
g) Page 18: To my knowledge, FTSAs degrade to PFCAs, not PFSAs
like PFOS. See Zhang et al. (2016): Zhang, S., Lu, X., Wang, N., &
Buck, R. C. (2016). Biotransformation potential of 6:2 fluorotelomer
sulfonate (6:2 FTSA) in aerobic and anaerobic sediment.
Chemosphere, 154, 224-230.
doi: 10.1016/j .chemosphere .2016.03.062
h) Page 62: Regarding "The importance of the sediment pathway for
PFOS bioaccumulation..." Larson et al. (2018) conducted some
insightful food web modeling on benthic and pelagic sources of
PFOS. See: Larson, E.S., Conder, J.M., Arblaster, J.A. 2018.
Modeling avian exposures to perfluoroalkyl substances in aquatic
habitats impacted by historical aqueous film forming foam releases.
https://doi.Org/10.1016/j.chemosphere.2018.03.004 Chemosphere
201:335-341.
i) Page 66: 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 PFOS in tissue. There were other instances of
this error in the document as well. For units of every concentration
of PFOS in tissue, please be sure to specify dry weight or wet
weight.
j) Page 73-75: There are a few scientific names on these pages that are
not italicized. Also may occur in other portions of the document.
k) Page 78: USEPA (1998) is not cited in the references section; I fear
there may be other similar omissions.
utilize the linear PFOS isomer for dosing
with fewer studies using the branched
isomer.
g. EPA thanks Reviewer 1 noting that
FTSAs do not appear to degrade to
PFSAs like PFOS and agrees. The
corresponding text was edited in the draft
PFOS Aquatic Life Criteria document to
correct the text.
h. Since the draft PFOS Aquatic Life
Criteria document is solely focused on
exposures to aquatic life, Larson et al.
(2018) was not included in the discussion
of bioaccumulation of PFOS because this
paper focused on food web modeling for
aquatic birds.
i. EPA will ensure that all tissue
concentrations reported in the draft PFOS
Aquatic Life Criteria Document are
reported in either wet or dry weight (ww
or dw, respectively). And in the instances
where this information is not provided by
study authors, EPA will specify that the
information was not provided.
j. EPA edited text throughout the draft
PFOS Aquatic Life criteria Document to
ensure that all species names are
italicized.
k. EPA ensured that all cited references are
included in the references section.
81

1) Page 78: Where the 1985 guidelines are mentioned, please cite to
USEPA (1985).
m) Page 78: Replace the "Stephan et al. (1985)" citation with USEPA
(1985). Also, I believe the surname of senior author of USEPA
(1985) is Stephen, not Stephan.
n) Page 80: At the start of Section 2.10.2, it would be good to discuss
linear and branched PFOS.
o) Page 86: The use of EC 10 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
EC 10s 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 EC 10s were selected over EC20s "given
the nature of exposure and effects for this bioaccumulative
chemical." Additionally EPA (2016) selected EC10 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."
p) 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 PFOS
in a manner than justifies the use of EClOs. For example, EPA in its
2016 aquatic life criteria for cadmium noted that cadmium "can
bioaccumulate in aquatic organisms", but EC20s (not EClOs) 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 EClOs instead of
EC20s) simply because a chemical has a higher bioaccumulative
1. & m. The 1985 Guideline citation was
changed to U.S. EPA 1985.
n. Please see EPA's response to item f.
above.
o. - s. EPA retained the use of the chronic
ECio values to ensure species protection,
considering the long-term persistence of
PFOS in the aquatic environment.
Further, the use of the ECioto derive
chronic criteria magnitudes is also
consistent with the harmonized
guidelines from OECD (OECD 2001)
and the generally preferred effect level
utilized in the derivation of protective
values for contaminants, including
PFOS, in other countries such as
Canada, Australia, and New Zealand
(CRCCare 2017; ECCC 2018; EPAV
2017). EPA also retained use of
EC10 values to further afford
protection of aquatic life from this
bioaccumulative "forever" chemical.
t. EPA agrees that the previous text stating
that empirically derived tissue criteria
would be derived from only studies in
which test organisms were exposure via
diet. This statement has been revised to
state:
"EPA considered deriving tissue-
based criteria using empirical toxicity
tests with studies that exposure test
organisms to PFOS via water, diet,
82

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 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.
q) Second, EPA has not provided any analysis of the dose response
curves that demonstrates the need for EC 10s versus EC20s (as was
mentioned for selenium). Additionally, justification of the use of
EC 10s 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.
r) More discussion is needed to support the poorly-supported move
from EC20s to EC 10s, or alternately, EC20s need to be used in
throughout the document, as consistent with past EPA practice in
and/or maternal transfer and reported
exposure concentrations based on
measured tissue concentrations. "
u. Reviewer 1 is correct that there is only one
citation for Bots et al. (2010). EPA
corrected the citations to reflect this.
v. EPA decided to intentionally leave the
qualitative Aedes data point off of Figure
3-5 as the qualitative Chironomus data
point was considered to be more robust
and was used to conclude that aquatic
insects are likely not among the four most
sensitive genera and used to waive the
unfulfilled MDR. This justification is
described in greater detail in Section
3.1.1.1.8 of the draft PFOS Aquatic Life
Criteria Document. EPA concluded that
including the Aedes data point in Figure 3-
5 would lead to confusion.
w. Reviewer 1 is correct. The noted sentence
should state for PFOS instead of PFOA.
EPA corrected the text.
x. The noted reference to Appendix Q was
incorrect in the draft PFOS Aquatic Life
Criteria Document that underwent external
peer review. This reference was updated to
be Appendix P.
y. EPA ensured that all percent effects
related to controls were added for studies
where the LOEC was used to derive the
criteria. EPA included such text in both
83

aquatic life criteria derivation. EC 10s are more conservative than
EC20s, but there is often greater variability and uncertainty
associated with EC10 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, EC 10s 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., Efroymson, R.A., Sample, B.E., & Jones, D.S.
(2000). Ecological Risk Assessment for Contaminated Sites. CRC
Press. April).
s) Overall, the adoption of a more conservative 10% effect level (i.e.,
EC 10) 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.
t) Page 88: 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 PFOS 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).
the main body and the appendices of the
draft PFOS Aquatic Life Criteria
Document.
z. EPA agrees that the noted endpoints are
non-apical endpoints and therefore were
not used in the derivation of the draft
aquatic life criteria for PFOS. However,
inclusion in Table 4-9 under the
qualitative studies section was meant to be
part of the line-of-evidence discussion
comparing empirically measured tissue
concentrations from toxicity studies to the
tissue-based criteria derived for PFOS.
Therefore, EPA retained these non-apical
endpoints in this particular section and
Table 4-9.
aa. EPA updated the text relating the endpoint
for this study to reflect the specific Gosner
Stage the length was measured.
bb. The endpoint referred to in the comment is
time to a specific Gosner Stage, not just
the Gosner Stage itself as stated in the
comment. EPA edited the text to clarify
the endpoint as "this time (in days) to
reach Gosner Stage 40. " This particular
endpoint as the time to reach a specific
Gosner Stage (in this case of 40) is a
growth endpoint as it speaks to the
development and overall growth of the test
organism.
84

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.
u) Page 112: There's only one "Bots et al. 2010" in the references
section. Multiple instances of "Bots et al 2010b" are cited in this
document. I believe there is only one Bots et al. 2010 paper. Please
clarify.
v) Page 125: The Aedes data point is missing from Figure 3-5. If the
qualitative Chironomus data point is included please include Aedes.
w) Page 132: "expected to protect P. primulas from chronic time-
variable PFOA exposures"... should that be "PFOS" instead?
x) Page 135: A reference for "Appendix Q" is made. Please provide
Appendix Q.
y) The percentage effect for LOECs (relative to controls) needs to be
clearly noted in the Appendices, for example, in Table C. 1 and in the
detailed summary text for the reviews of each paper. This should be
provided when LOECs or MATCs are used as chronic values.
z) Page 173: "Reduction in superoxide dismutase" and "Changes in
protein expression" are atypical endpoints not well tied to
ecologically significant effects. These should be removed from the
table and subsequent discussion, or presented separately as
qualitative analyses only.
aa) Page 173: It is not appropriate to refer to the Gosner stage endpoint
as "Length at metamorphosis" in the table. Refer to it as "Gosner
stage" if it is to be included.
cc. Please see EPA's response to comment y
above.
dd. EPA provided additional details to clarify
how the SMAV/SMCVs were calculated
for this and all other species.
ee. EPA provided details relating to the
additional treatment-level data requested
from individual study authors, but has not
shared these data publicly as part of the
draft PFOS Aquatic Life Criteria
Document as these data are subject to
copyright by the individual publishing
journals and EPA was not granted
permission to share data publicly beyond
the scope of the request to the individual
authors.
ff A model figure for the chronic tests from
Hazelton et al. (2012) is not missing from
Section C.2.3.1 as the ECio was not
estimated like the other studies in the draft
PFOS Aquatic Life Criteria through model
fitting, but was estimated by assuming the
0.0695 mg/L treatment represents an
EC35.4, and estimating the EC10 using the
exposure response slope from another
PFOS toxicity study focused on another
mussel species (Perna viridis). Please see
the summary under Charge Question
2.5.a.ii above and Section 3.1.1.3.3 of the
draft PFOS Aquatic Life Criteria
Document for additional details.
85

bb) Page 176: Gosner stages are not a typical endpoint, and the use of
the growth data would be much more supportable. See comment
below regarding Page C-42.
cc) Page C-2: When the MATC is used in tables in the Appendices, it
would be helpful to provide the percent effect level (relative to
control) for the LOEC associated with the MATC. Also, in cases in
which the LOEC is provided as the chronic value, please provide the
percent effect level.
dd) Page C-3: How was the Species Mean Chronic Value (SMCV) for
leopard frog calculated? There is only one chronic value that is
bolded in the data, and it does not equal the SMCV. Please add text
to clearly discuss which values are included (and how the ">" values
are used in subsequent calculations like geometric means).
ee) Page C-7: For Wang et al., since this value is the lowest used in the
criterion derivation, please share a table of the raw data graphed in
the Figure on page C-7.
ff) Page C-16: Appears to be a missing figure.
gg) Page C-29: Typo "XX.XX mg/L". There are other typos like this in
the document (search for "XX").
hh) Page C-42: The amount of detail for the review of the Hoover et al.
(2017) experiment is insufficient. The selection of the Gosner stage
as an endpoint requires additional detail. The relationship between
Gosner stage and more typical endpoints clearly linked to ecological
health (growth, reproduction, and survival is unclear). The effects on
Gosner stage in this study are subtle; all dosed animals indicated
they had reached tadpole stage (Gosner stages 25-41) at the 40-day
endpoint noted. The maximum difference in Gosner stages noted in
the study was approximately 2 (control Gosner stage result of -30,
100 and 1000 (ig/L Gosner stage results of -28). A 7% difference in
Gosner stages (especially when both 28 and 30 values fall within a
tadpole Gosner stage development range) is difficult to translate to
gg. The noted typo of XX.XX mg/L was
intended to be placeholder for a value. All
instances of these placeholders have been
updated throughout the draft PFOS
Aquatic Life Criteria Document.
hh. EPA thanks you for your comment on
(Hoover et al. 2017). EPA reconsidered
the study and the endpoints that were used
to derive the draft PFOS aquatic life
criteria. This re-evaluation of this study
will also take other recently published
studies on amphibians.
ii. The noted repeated text was deleted.
jj. EPA thanks you for your comment on Han
et al. (2015). EPA reconsidered the study
and the endpoints that were used to derive
the draft PFOS aquatic life criteria. The
revised criteria document now states:
The publication is unclear about the
method used for the reproduction
test endpoint and whether it was an
independently conducted 10-day test
or a subsample of reproducing
adults were observed from the 20-
day test. EPA sought but did not
receive responses to clarifying
questions posed to the authors.
Additionally, the authors were asked
if control survival for the test was
above 80% and if the authors could
provide the data. Based on the
information presented in the paper
without additional information and
86

adverse ecological impact. As shown in the Gosner stage chart for
anurans (Virginia Herpetological Society,
http://www.virginiaherpetologicalsociety.com/amphibians/amphibia
n-development/amphibian-development.htm) the difference between
stage 28 and stage 30 is the shape of the tail. It is unclear if this
statistically detectable difference in the tail shape that distinguishes
Gosner stage 28 and 30 would result in an ecologically significant
decrease in the overall time period required to reach sexual maturity
or ultimately translate to a developmental malformation that would
result in an ecologically meaningful population-level effect (decrease
in survival, decrease in reproductive output, etc.). The uncertainty
with this atypical endpoint is high, and given the slight difference
(-7%) between NOEC and LOEC exposures, I would recommend
this datum be removed from the quantitative analysis. Notably,
Figure S2 of this paper presents results for a measurement of growth
via the Snout Vent Length (SVL) measurement endpoint. This
endpoint provide more a continuous measurement of growth and is
more typical of endpoints used in criteria derivation.
ii) Page C-44: "In the later phases of the tests, (Bots et al. 2010a)" is
repeated.
jj) Page D-3: Regarding the Han et al (2015) study, I disagree with the
selection of the less conservative growth endpoint. The reproductive
effect does look to be valid and a reasonable endpoint to consider.
EPA's reasoning to exclude it is not compelling and is unclear. The
exposure duration was at least 10 days, which is likely sufficient for
many marine invertebrates with relatively short life cycles (i.e.,
mysids). Perhaps EPA could reach out to the study authors to clarify
the uncertainty around the exposure time (10 days or 20 days?). At
any rate, I think the MATC should rely on the reproductive endpoint,
and given the good dose-response for the reproductive data, a robust
EC 10 or EC20 value could likely be calculated.
kk) Page G-3: Seems like the Olson (2017) snail experiment provides
some useful chronic (21-day exposure?) data for a relevant sublethal
data provided by the authors to
clarify adherence to EPA data
quality objectives and independent
calculation and verification of point
estimates, the developmental stage
is considered for quantitative use
and the reproductive endpoint for
qualitative use. The use of the
reproductive endpoint could be
changed based on input on
clarifying questions from the study
authors. The 20-day MATC (based
on time to reach development stage)
was 0.7071 mg/L and currently
recommended by EPA as acceptable
for quantitative use.
kk. & 11. Table G.l of the draft PFOS 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 in established test
protocols/methods, that were referenced in
EPA's draft PFOS Aquatic Life Criteria
document. The draft PFOS Aquatic Life
Criteria document specifically stated:
"All studies were evaluated for data
quality generally as described by
U.S.EPA (1985) in the 1985
Guidelines and in EPA 's Office of
Chemical Safety and Pollution
87

growth endpoints. Please explain why this data was excluded from
the chronic evaluation. Simply listing "Duration" in this table does
not provide enough detail.
11) Page H-l: Please explain the acceptable duration acceptable for the
urchin test and other tests. Simply listing "Duration too short"
without noting the acceptable duration that would be considered is
not helpful. Perhaps a summary table for acceptable durations for
particular endpoints could be provided in this document.
mm) 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.
nn) Page P-12: The Hoover et al. (2017) paper is included twice. There
may be more errors like this in the document, it needs to be reviewed
closely by a technical editor.
oo) Appendix L: The references cited in this section seem to be missing.
Prevention (OCSPP) 's Ecological
Effects Test Guidelines (U.S.EPA
2016b), and EPA OW's internal
data quality SOP, which is
consistent with OCSPP's data
quality review approach (U.S.EPA
2018). These toxicity data were
further screened to ensure that the
observed effects could be primarily
attributed to PFOS exposure.
mm. Use of "atypical duration" occurred 15
times within Table H. 1 and twice in
Appendix H.2 (i.e., summaries of studies
in Table H. 1) and did not occur
elsewhere in to draft PFOS 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. 1 has been revised to
state:
"Exposure duration too short for
chronic test and too long for acute
test."
nn. The in-text citations and references have
been updated to remove any duplicates as
noted with Hoover et al. (2017).
oo. EPA ensured that all cited references,
including those in Appendix L, are
included in the reference section of the
88

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
(PFOS)"
2.S. Additional l och 11 ic:iI ( omiiicnls (o C onsidci
Uc\ iewei
Comments
KI'A Response
draft PFOS Aquatic Life Criteria
Document.
Reviewer I think the EPA's criteria for PFOS 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 comment.
Reviewer
3
All technical comments have been previously mentioned
Thank you for your comment.
Reviewer
4
Additional suggestions are listed below:
1. The species listed in the table is Mytilus galloprovincialis not M. edulis
Table 3-1. The Three Most Sensitive Acute Estuarine/Marine Genera.
Kiink
(.onus
Spocios
(;\1AY
PI-OS)
( (llllllH'lKS

Mytilus1
Mediterranean
mussel,
M. edulis
Mytilus
galloprovincialis
> 1
\ol a resjideiil s>pecies> in
North America, but other
species in this genus are
resident, commercially, or
ecologically important
species
2. Page 115- second paragraph (values highlighted in red and underlined
are not consistent)
Thank you for your comment. Responses to
corresponding numerical order are provided
below:
1. The species name for Mediterranean mussel
was changed from M. edulis to M.
galloprovincialis.
2.The noted values were changed to ensure that
they are consistent. The first noted value of
0.0271 mg/L is the correct value.
3. The units were corrected in the noted text to
state:
"The chronic freshwater criteria also
contain tissue-based criteria expressed as
43.0 mg/kg wet weight (ww) for fish
whole-body, 25.3. mg/kg ww for fish
muscle tissue, and 12.3 mg/kg ww for
invertebrate whole-body tissue. "
4. The noted text was a placeholder for text and
was replaced with the following text:
89

The author reported 10-day growth and survival EC10S for the study were
0.0492 and 0.1079 mg/L, respectively. The study authors also reported
NOECs of 0.0491 mg/L, LOECs of 0.0962 mg/L, and MATCs of 0.0687
mg/L for both endpoints. And the author reported 20-day ECioS for growth,
survival, and total emergence were 0.0882, 0.0864, and 0.0893 mg/L,
respectivelv. And the studv authors also reported NOECs of 0.0217 ma/L for
growth and survival and < 0.0023 mg/L for emergence, LOECs of 0.0949
mg/L for growth and survival and 0.0217 mg/L for emergence, and MATCs
of 0.0454 mg/L for growth and survival and 0.0071 mg/L for emergence.
Also, it should be noted, the paper reported contrasting NOECs for 20-day
survival. The text in the paper stated that the NOEC was 0.0271 ma/L and
Table 2 of the paper stated 0.0949 mg/L. EPA assumed the NOEC in Table 2
of the paper was not correct and that 0.0217 mg/L was the correct NOEC
based on the data presented in Figure 3A of the paper. This assumption was
applied to the summary of the study results presented in this PFOS draft
criteria.
3. Page 138-middle of the paragraph The chronic freshwater criteria also
contain tissue-based criteria expressed as 43.0 mg/kg wet weight (ww)
for fish whole-body, 25.3 mg/ —ww for fish muscle tissue and 12.3
mg/kg ww for invertebrate whole-body tissue.
4. Page A-21 last paragraph The noted toxicity values provided in each
study summary above (ADD NUMBERS), comprising of both author-
reported and independently-calculated LC50 values, were used to
calculate the GMAV value (as the geometric mean of the three LC50
values previously mentioned) of 22.48 mg/L, which was used to derive
the freshwater aquatic life criterion.
5. Page A-24- Fourth line from bottom-The study author reported LC50
was 22.2 ± 4.6 mg/L for PFOS. The independently-calculated toxicity
value was x.xx mg/L. The study author reported value was used
quantitatively to derive the draft acute water column criterion.
"The noted toxicity values provided in
each study summary above (17, 22.68,
and 29.46 mg/L), comprising of both
author-reported and independently-
calculated LC50 values, were used to
calculate the GMAV value (as the
geometric mean of the three LCsovalues
previously mentioned) of22.48 mg/L,
which was used to derive the freshwater
aquatic life criterion."
5-11. The noted text of x.xx mg/L were
placeholders that were either replaced with
relevant independently-calculated toxicity
values or were removed if independently-
calculated toxicity values could not be
calculated by EPA.
12. Table 2-3 was 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 PFOS
criteria at this time given the toxicity
literature that is currently available, which
focus largely on direct aqueous exposures.
13. The noted protective values for Australia and
New Zealand were updated Section 1.1 of
the draft PFOS Aquatic Life Criteria
Document to reflect the updated values and
information.
14. Section 1.2 of the draft PFOS Aquatic Life
Criteria document was updated, specifically
stating:
90

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perflnorooctane Sulfonate
(PFOSr ' ' '
2.8. Additional Technical Comments to Consider
Reviewer
Comments
EPA Response

6. Page A-25- Fourth line from bottom The study author reported 96-hour
LC50 was 50.51 mg/L PFOS. The independently-calculated toxicity value
was x.xx mg/L. The study author reported value was used quantitatively
to derive the draft acute water column criterion.
7. Page A-27- Fourth line from bottom. The independently-calculated
toxicity value was x.xx mg/L. The study author reported value was used
quantitatively to derive the draft acute water column criterion.
8. Page A-29- First paragraph For comparison, the 7-day LC50 was 39.71
mg/L. The independently-calculated toxicity value was x.xx mg/L. The
96-hour study author reported value was used quantitatively to derive the
draft acute water column criterion.
9. Page A-30- First paragraph The independently-calculated toxicity value
was x.xx mg/L. The study author reported value was used quantitatively
to derive the draft acute water column criterion.
10. Page A-36- 5th line from bottom in complete data x.xx mg/L.
11. Also at A-37 in complete data x.xx mg/L.
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, Rr,
andR" do not equal "H" and the carbon-
carbon bond is saturated (note:
branching, heteroatoms, and cyclic
structures are included).
Further, no additional edits were made to
Table 1-2 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).
15. 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).
16. The effects symbol in the conceptual model
(Figure 2-9) of the draft PFOS Aquatic Life
Criteria Document now states:
" Deformities. Reproductive and Growth
Impairments. and Mortality. "
Table 2-3. Summary of Assessment Endpoints and Measures of Effect Used in
the Criteria Derivation for PFOS
Assessment Endpoints for Measures of Effect
the Aquatic Community

Aquatic Life: Survival,
growth and reproduction of
freshwater and
estuarine/marine aquatic life
(i.e., fish, amphibians, aquatic
invertebrates)
For effects from acute exposure:
1. LCso 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. ECio 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); Only used when
an ECio could not be
calculated for a genus.
Note: only chronic exposures were
considered for derivation of the tissue-
based criteria since PFOS is a
bioaccumulative chemical. These
chronic tissue-based criteria are
expected to be protective of acute
effects, because acute effects were
obser\>ed at much greater
concentrations than chronic effects.

Please review if the highlighted muscle, blood and egg would be relevant to
this section interns ofLC50, EC 10, LOEC andNOEC endpoints .
12. 1.1.2 and page 3- Previously Published Chronic Water Criteria for
Direct Aqueous Exposure
The information on Australian guidelines to be updated based on NEMP2
published in 2020.1 will attach it as a PDF.
92

-------
EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	 (PFOS/' 	[	' 	'
2.8. Additional Technical Comments to Consider
Reviewer
Comments
EPA Response
https://www.environment.gov.au/svstem/files/resources/2fadflbc-b0b6-44cb-
al92-78c522d5ec3f/files/pfas-nemp-2.pdf
"Previously published freshwater chronic values were available for two
states (Minnesota and Michigan) and three countries or geographic
regions (Australia/New Zealand, Canada, and Europe). These publicly
available values for other jurisdictions were 0.019 mg/'L and 0.14 mg/'L
for Minnesota (STS/MPCA 2007) and Michigan (EGLE 2010),
respectively, and were 0.00013 mg/'L in Australia/New Zealand (CRC
CARE 2017; EPAV2016), 0.00680 mg/'L in Canada (ECCC 2018), and
0.000023 mg/L in Europe (RLVM 2010). Previously published
estuarine/marine chronic values were available for two geographic
regions (Australia/New Zealand and Europe). These publicly available
values were 0.0000046 mg/L in Europe (RLVM2010) and 0.0078 mg/'L in
Australia/New Zealand (CRC CARE 2017; EPAV2016) "
The CRC marine guidelines are not valid as they are not based on the
framework Freshwater values are to be used on an interim basis
13. Page 4- Table 1.1 to be updated accordingly
Exposure
scenario
PFOS
Exposure
scenario
Comments and source
Freshwater
0.00023
(ig/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 PFOS
and PFOA.



Note 1: The 99% species
protection level for PFOS is close
to the level of detection. Agencies
may wish to apply a 'detect'
threshold in such circumstances

0.13
(ig/L
95% species
protection -
slightly to
moderately
disturbed
systems
93

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	(PFOS)"	
2.S. Additional l och 11 ic:iI ( omiiicnls (o Consider
Uc\ iewei
Comments
KIW Response
Kxposmv
scenario
2 (ig/L
31 (ig/L
PI-OS
90% species
protection -
highly
disturbed
systems
80% species
protection -
highly
disturbed
systems
l-'xposiire
scciiiirio
rather than a quantified
measurement.
Note 2: The draft guidelines do
not account for effects which
result from the biomagnification
of toxicants in airbreathing
animals or in animals which prey
on aquatic organisms.
Note 3: The WQGs advise3 that
the 99% level of protection be
used for slightly to moderately
disturbed systems. This approach
is generally adopted for chemicals
that bioaccumulate and
bio magnify in wildlife.
Regulators may specify or
environmental legislation may
prescribe the level of species
protection required, rather than
allowing for case by-case
assessments.
( iimiiK'iiio mill MiuiYi'
94

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EPA Response to the External Peer Review of U.S. EPA's "Draft Aquatic Life Ambient Water Quality Criteria for Perfluorooctane Sulfonate
	(PFOS)"	
2.S. Additional l och 11 ic:iI ( omiiicnls (o Consider
Ue\ iewei
Comments
KIW Response
Interim
marine
0.00023
99% species
(ig/L
protection

-high

conservation

value systems
0.13
95% species
(ig/L
protection

- slightly to

moderately

disturbed

systems
2 Jig/L
90% species

protection -

highly

disturbed

systems
31 (ig/L
80% species

protection -

highly

disturbed

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
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.
ahttps://www.waterqualitv.gov.au/anz-guidelines/guideline-
values/default/water-qualitv-toxicants/local-conditions#bioaccumulation
14. Table 1 2. Two Primary Categories of PFAS
Please refer to OECD 2021 to be consistent with PFAS
terminology/nomenclature
95

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
15. Table 1.3 Page 8
Please review Figure 9 OECD 2021 (also attached as PDF)
16. Conceptual Model of PFOS in the Aquatic Environment and Effects
Figure 2.9 page 77- Growth as an endpoint missing in the endpoints - first
pentagon

Reviewer
5
Specific comments to the various elements of the PFOS AWQC are above.
Here, I want to suggest that EPA revisit the 1985 Guidelines and publish
either an updated version or an amendment. Basing critically important
criteria on documents published in 1985 and then using this to justify
decisions seems like it would not pass muster in the scientific community.
I've had papers rejected because they did not include enough recent citations,
for example. Moreover, I've mentioned my concerns with the 4- most
sensitive taxa + linear regression for criteria derivation. No paper I've read on
generating the 5th percentile most sensitive species has used this approach.
Granted, I may have missed them but my sense is that it is more common to
use a full SSD. It would be helpful, for example, if the revised Guidelines
explored this further or other means of criteria development (including new
approach methods) and published, used, and cited and updated guidelines
document. I'd like to think we still generally lead the world (more or less) in
environmental protection so having an updated document would be
welcomed.
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.
Thank you for your 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 PFOS Aquatic Life Criteria document.
When there are less than 59 genera in a GSD, 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 Perfluorooctane Sulfonate
	(PFOS)"	
2.S. Additional l och 11 ic:i 1 (ommenls (o Consider
Ue\ iewer
Comments
KIW Response


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 in EPA's response to Reviewer 5's
comments to Charge Question 2.2.
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. (U.S.EPA 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
Burrm) and of the former, the log-normal,
log-logistic, and log-triangular showed very
similar performance."
97

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