Peer Reviewers:

James V. Bruckner, Ph.D.

Deborah A. Cory-Slechta, Ph.D.

Jamie C. DeWitt, Ph.D.

Jeffrey W. Fisher, Ph.D.

William L. Hayton, Ph.D.

Matthew P. Longnecker, Sc.D, M.D

Angela L. Slitt, Ph.D.

Contract No. EP-C-13-010

Task Order 2013-06

Peer Review Summary Report

External Peer Review of EPA’s Draft Health Effects Documents for

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

November 17, 2014

Prepared for:

U.S. Environmental Protection Agency

Office of Science and Technology/Office of Water

1200 Pennsylvania Avenue, NW

Washington, DC 20460

Prepared by:

Versar, Inc.

6850 Versar Center

Springfield, VA 22151
External Peer Review of EPA’s Draft Health Effects Documents for 

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

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TABLE OF CONTENTS

Contents

EXECUTIVE SUMMARY ................................................................................................ ii

I. INTRODUCTION....................................................................................................... 1

I.1 Background on Draft Health Effects Documents.................................................. 1

I.2 Peer Review Process.............................................................................................. 1

I.3 Peer Review Meeting............................................................................................. 3

II. CHARGE TO REVIEWERS ...................................................................................... 5

III. GENERAL IMPRESSIONS ....................................................................................... 7

IV. RESPONSE TO CHARGE QUESTIONS ................................................................ 17

Charge Questions...................................................................................................... 17

Question 1. ........................................................................................................ 17

Question 2. ........................................................................................................ 22

Question 3. ........................................................................................................ 27

Question 5. ........................................................................................................ 34

Question 6. ........................................................................................................ 36

Question 7. ........................................................................................................ 39

Question 8. ........................................................................................................ 43

Question 9. ........................................................................................................ 47

Question 10. ...................................................................................................... 50

Question 11. ...................................................................................................... 53

Question 12 ....................................................................................................... 55

V. SPECIFIC OBSERVATIONS ..................................................................................... 58

APPENDIX A: PEER REVIEWER BIOSKETCHES ................................................... A-1

APPENDIX B: MEETING AGENDA ........................................................................... B-1

APPENDIX C: MEETING ATTENDEE LIST.............................................................. C-1
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EXECUTIVE SUMMARY 

Versar, Inc. (Versar), a contractor for the Environmental Protection Agency (EPA), coordinated 

an external peer review of EPA’s draft health effects documents for Perfluorooctanoic Acid 

(PFOA) and Perfluorooctane Sulfonate (PFOS), and organized a two-day public peer review 

meeting in Arlington, Virginia on August 21 and 22, 2014. The peer review of EPA’s draft 

health effects documents was initiated with a pre-meeting written peer review managed by 

Versar and conducted by seven independent expert peer reviewers. The role of the peer 

reviewers was to evaluate the scientific and technical merit of the draft documents and provide 

their responses to 12 charge questions. Peer reviewers were charged only with evaluating the 

quality of the science included in EPA’s draft health effects documents and were not charged 

with making any regulatory recommendations or reaching consensus in either their deliberations 

or written comments. The two-day peer review meeting, which directly followed the written 

peer review period, was held to discuss the scientific basis supporting EPA’s draft health effects 

documents and to provide members of the public with an opportunity to observe the peer 

reviewer deliberations.

On the first day of the meeting, Versar began by providing information on the overall peer 

review process and introducing the peer reviewers. In addition, EPA provided background 

information on the draft documents and approach used in the development of the documents. 

Following opening remarks by Versar and EPA, the peer reviewers began their discussions on 

the PFOA draft document, moderated by the Chair, Dr. Deborah Cory-Slechta. The discussions 

centered on individual responses to EPA’s 12 charge questions. Additionally, some comments 

submitted to the public docket prior to the meeting were also discussed. The second day of the 

meeting began with brief remarks from Versar followed by discussions focusing on the PFOS 

draft document. 

The reviewers began the discussion on the first day with the recognition of the significant 

amount of data that is available for both PFOA and PFOS and thus to be considered by the EPA 

for incorporation into the document and for the ultimate derivation of reference dose (RfD) 

values. In general, the reviewers commended EPA in doing a very good job of pulling together 

this significant and extensive body of information and of condensing it into its most critical 

pieces for the derivation of RfD values. This was especially the case given that there is 

significant human and animal data available for both chemicals, as well as inconsistencies in the 

data. 

The reviewers did offer numerous suggestions for improving the documents, many of which are 

applicable to both PFOA and PFOS. In general, the suggestions relate to the statement of the 

problem and defining the database that was utilized, clarity and ease of presentation, and 

transparency of the reports, as well as to issues of modeling, use of human data, and liver weight 

increases as the most sensitive endpoint. These comments are summarized below, but please 

note that this does not reflect a consensus or group perspective. 

 All reviewers agreed that it would be extremely useful to include an opening section of 

the document describing in some detail the literature that was reviewed. More 

specifically, this would include a description of the dates that were included in the 
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literature review, whether requirements for peer-reviewed materials were imposed, and 

what criteria were used in eliminating studies from consideration. This would assist in 

identifying studies that should potentially have been included. Many additional studies of 

importance were suggested for review at the meeting by the peer reviewers. 

 The reviewers also agreed that there are some significant studies that have been 

published recently on PFOA and PFOS that may be relevant, and these should be 

included in the documents during the current revisions.

 Reviewers also felt that the Tables in the documents could be made much more useful to 

readers with the addition of columns that included more study details. This would 

minimize the amount of back-and-forth to the text that was required to assess 

conclusions.

 Additionally, there was a strong agreement that the Hazard Identification section of the 

documents should include a more systematic review of study strengths and limitations. 

These were noticeably absent in the human studies, where all studies were considered 

equivalent but also applicable to animal studies.

 Reviewers also felt that each Chapter should include introductory paragraphs, as well as 

concluding paragraphs, that would provide better integration of the material across the 

Chapters, as well as summarize the conclusions arrived at from the text in the Chapter. 

This would also facilitate the ability of readers to follow the presentations provided in 

Chapter 5 of the derivation of RfDs.

 As pointed out at the peer review meeting, the authors would be well advised to base 

these documents on the new documents being produced by EPA’s National Center for 

Environmental Assessment (NCEA) for the Integrated Risk Information System (IRIS)

program. While the reviewers recognize that the PFOA and PFOA health effect

documents will not be used specifically for the same purpose, they will still likely be 

held to the same standards of presentation, clarity and transparency and thus, the new 

NCEA formats provide good models to follow.

 With respect to content of the documents, there was initial confusion around some of the 

modeling outcomes and assumptions based on values that were provided in the 

documents. However, following explanation from EPA personnel in response to 

clarifying questions from the reviewers at the peer review meeting, it became clear that 

there were errors in these values and once these were corrected, concerns about the 

specific values used in some modeling were allayed. 

 Even with the corrections to the modeling, there were residual concerns among reviewers 

based on toxicokinetic properties of these chemicals, with respect to applying the same 

candidate RfD values to both short and long-term exposures, which in animal studies 

ranged from 11 to 182 days with reviewers expressing a need for this to be reconsidered.

 There were mixed comments by reviewers with respect to the decision not to use human 

data in the derivation of RfD values. All reviewers generally agreed that the rationales 

provided for the exclusion of the human data were not actually appropriate, as it is 

certainly not the case that such use would be precluded by the fact that there were 
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multiple and not sole exposures to either PFOA or PFOS. There was discussion as to the 

possibility of whether human data could be utilized in these assessments, and that ranged 

from an opinion that these data would not be useful to the view that it might be possible 

to use these data, despite the absence of information on route of exposure. Collectively, 

the range of opinions suggests that the issue should be revisited, and that appropriate 

rationales should be provided for the decision that is reached in the revised version. 

 For both PFOA and PFOS, the RfDs were ultimately based on increases in liver weights 

in animal studies. There was significant discussion among reviewers as to the 

appropriateness of this endpoint for the derivation of the RfDs. That range of opinion 

spanned from an interpretation that these did constitute adverse effects in that they are a 

direct effect of a chemical exposure, whereas other reviewers saw these as adaptive 

effects. Collectively, the range of opinions suggests that the issue should be revisited, 

and that appropriate rationales should be provided for the decision that is reached in the 

revised version. 

Following the meeting, peer reviewers were given additional time to complete their individual 

written reviews, which were submitted to Versar upon completion. These final written 

comments are contained in Sections III, IV, V of this report and fall into three categories: 

general impressions, responses to charge questions, and specific observations. Written peer 

review comments, as well as comments submitted to the docket by members of the public, will 

be considered by EPA as it revises the draft documents. 
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I. INTRODUCTION

I.1 Background on Draft Health Effects Documents

On February 28, 2014, the EPA’s Office of Water (OW) announced in the Federal Register the 

release of the draft health effects documents for Perfluorooctanoic Acid (PFOA) and 

Perfluorooctane Sulfonate (PFOS) for purposes of public comment (scientific views) and peer 

review (http://www.gpo.gov/fdsys/pkg/FR-2014-02-28/pdf/2014-04455.pdf). The draft 

documents and charge questions were prepared by the Health and Ecological Criteria Division 

(HECD), within EPA’s OW, in order to support future regulatory evaluations and decisions.

EPA will consider the public comments and peer reviewer comments when revising the 

documents. Once the PFOA and PFOS health effects documents are finalized, they will be 

utilized to develop lifetime health advisory values for each chemical. PFOA and PFOS are listed 

on the third Contaminant Candidate List (CCL3)1and both chemicals are currently being 

monitored under the third Unregulated Contaminant Monitoring Rule (UCMR3)2.

I.2 Peer Review Process

Consistent with guidelines for the peer review of highly influential scientific assessments, 

Versar, an EPA contractor, was tasked with assembling six to seven scientific experts to 

evaluate the draft PFOA and PFOS documents. The purpose of the peer review was to provide a 

documented, independent, and critical review of the draft health effects documents, and identify 

any necessary improvements to the documents prior to being published. In assembling these 

peer reviewers and coordinating the peer review, Versar was charged with evaluating the 

qualifications of peer review candidates, conducting a thorough conflict of interest (COI) 

screening process, independently selecting the peer reviewers, distributing review materials, 

maintaining contact with the peer reviewers, organizing and hosting the public peer review 

meeting, and developing a final peer review report. 

The peer review selection process was initiated with a three-week public nomination period that 

was held from February 28, 2014 to March 21, 2014, as documented in the Federal Register on 

February 28, 2014 (http://www.gpo.gov/fdsys/pkg/FR-2014-02-28/pdf/2014-04455.pdf). During 

this period, members of the public were able to nominate scientific experts with knowledge and 

experience in one or more of the following areas: (1) epidemiology, (2) toxicology (liver effects, 

immunotoxicity, neurotoxicity, developmental and reproductive toxicology, etc.), (3) membrane 

transport, (4) human health risk assessment, (5) pharmacokinetic models, and (6) mode-ofaction for cancer and noncancer effects. Concurrently, Versar conducted an independent search 

for qualified scientific experts to augment the list of publically-nominated candidates. In total, 

Versar evaluated 29 interested and available candidates who were either nominated by the public 

(n=18) or identified by Versar (n=11). 

 

1 CCL3 is a list of contaminants that are currently not subject to any proposed or promulgated national primary drinking water 

regulations, that are known or anticipated to occur in public water systems, and which may require regulation under the Safe 

Drinking Water Act (SDWA). Additional information about the CCL3 can be found at the following website: 

http://water.epa.gov/scitech/drinkingwater/dws/ccl/ccl3.cfm.

2 EPA uses the Unregulated Contaminant Monitoring (UCM) program to collect data for unregulated contaminants suspected to 

be present in drinking water. Results from UCMR3 can be examined as they become available at the following website: 

http://water.epa.gov/lawsregs/rulesregs/sdwa/ucmr/ucmr3/.
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Versar considered and screened all 29 candidates against the selection criteria described in the 

Federal Register dated February 28, 2014, which included: (1) having demonstrated expertise in 

the areas described above, based on information in their submitted resume, biographical sketch 

and/or current publications, (2) being free of any COI and the appearance of the lack of 

impartiality, and (3) being available to participate in-person in a two-day peer review meeting in 

the Washington DC area in the July or August 2014 timeframe. Following the screening process, 

Versar narrowed the list of potential reviewers to 15 candidates and provided to EPA the names 

of the candidates selected by Versar to be on the interim list. Additionally, information on the 15 

candidates, including their professional affiliations, expertise, education, and professional 

experience were provided for the interim list and published in the Federal Register on April 30, 

2014 (http://www.gpo.gov/fdsys/pkg/FR-2014-04-30/pdf/2014-09888.pdf). The Federal 

Register also requested the public to submit relevant information or documentation on the 

interim list of candidates that Versar should consider during the evaluation process of selecting 

the final six to seven reviewers. 

Following the close of the public comment period on the interim list of potential reviewers, 

Versar re-evaluated each interim candidate’s credentials to select the experts who, collectively,

provided expertise spanning the multiple subject matter areas covered in the draft documents 

and provided a balance of perspectives. In addition, Versar evaluated the availability of each 

candidate to ensure all final peer reviewers were available on the same days for the meeting in 

the selected timeframe. Once the evaluation process was completed, Versar narrowed the 

interim list of 15 candidates and selected the seven final peer reviewers. In addition, Versar 

selected Dr. Deborah Cory-Slechta as Chair of the peer review meeting due to her expertise in

toxicology as well as her strong record of chairing and participating in peer review panels, 

scientific meetings, and workshops. A list of the final seven peer reviewers who participated in 

this review is provided below. In addition, each reviewer’s biographical sketch is included in 

Appendix A.

Following the selection process, Versar distributed EPA’s draft PFOA and PFOS documents and 

12 charge questions (see Section II) to the peer reviewers. The peer reviewers were asked to 

evaluate the scientific and technical merit of the draft documents and provide their responses to 

the 12 charge questions. This included evaluating the appropriateness of the quality, accuracy, 

and relevance of the data in the documents. Peer reviewers were not charged with making any 

regulatory recommendations or reaching consensus in either their written comments or public 

deliberations. In addition to being provided the draft documents and charge questions, comments 

submitted to EPA’s public docket (Docket ID number EPA–HQ–OW–2014–0138) during each 

document’s 60-day public comment period were provided to the peer reviewers ahead of the 

meeting for their consideration. Also, a brief summary of the public comments was developed 

by Versar and provided to the reviewers. However, peer reviewers were not asked to evaluate or 

respond to comments submitted to the docket.

Versar managed the pre-meeting peer review period, which provided the peer reviewers 

approximately two months to evaluate the draft health effects document and complete their 

written reviews. Following receipt of the peer reviewers’ draft comments, Versar compiled the 

comments into a pre-meeting peer review report and distributed them to the peer reviewers and 
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EPA to prepare for the public peer review meeting. These preliminary responses to the charge 

questions formed the basis of reviewer discussions on Days 1 and 2 of the public meeting. 

Peer Reviewers:

James V. Bruckner, Ph.D.

University of Georgia

Deborah A. Cory-Slechta, Ph.D.

University of Rochester School of Medicine and Dentistry

Jamie C. DeWitt, Ph.D.

East Carolina University

Jeffrey W. Fisher, Ph.D.

U.S. Food & Drug Administration

William L. Hayton, Ph.D.

The Ohio State University

Matthew P. Longnecker, Sc.D, M.D

National Institute of Environmental Health Sciences

Angela L. Slitt, Ph.D.

University of Rhode Island 

I.3 Peer Review Meeting 

On August 21 and 22, 2014, Versar convened a public peer review meeting in Arlington, 

Virginia. This meeting was held to discuss the scientific basis supporting EPA’s draft health 

effects documents and to provide members of the public with an opportunity to observe the peer 

reviewer deliberations. The meeting followed both the documents’ public comment period, 

during which members of the public were able to submit written comments, and the pre-meeting 

written peer review period, during which the seven selected peer reviewers evaluated EPA’s 

draft health effects documents and provided preliminary comments in response to the charge 

questions. 

Versar managed the pre-meeting registration period, which allowed members of the public to 

register to attend the meeting in person or remotely via teleconference and/or webinar. Members 

of the public were able to register online, via Versar’s registration website

(http://peerreview.versar.com/epa/pfoa/) as well as by telephone, email, or U.S. mail. In advance 

of the meeting, Versar provided all registered attendees with pre-meeting handouts, which 

included the agenda and logistics information. 

On the first day of the meeting, Versar began by providing information on the overall peer 

review process and introducing the peer reviewers. In addition, EPA provided background 
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information on the draft documents and approach used in the development of the documents. 

Following opening remarks by Versar and EPA, the peer reviewers began their discussions on 

the PFOA draft document, which centered on individual responses to EPA’s 12 charge 

questions. The remainder of the day was dedicated to discussions on the PFOA document, which 

were moderated by the Chair, Dr. Deborah Cory-Slechta. The second day of the meeting began 

with brief remarks from Versar followed by discussions focusing on the PFOS draft document. 

Approximately 23 public observers attended the peer review meeting in person and 21 observers 

attended the meeting via teleconference and/or webinar. Please see Appendix B for the meeting 

agenda and Appendix C for a list of public attendees.

Following the public peer review meeting, peer reviewers were given additional time to 

complete their individual written reviews. These final written comments are contained in 

Sections III, IV, and V of this report. Written peer review comments, as well as comments 

submitted to the EPA docket by members of the public, will be considered by EPA as it revises 

the draft health effects documents. 
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II. CHARGE TO REVIEWERS

PFOA and PFOS are environmentally persistent organic fluorocarbons (PFC) that have been 

identified in ambient waters, ground water, drinking water, and biosolids. They are 

metabolically inert but have the ability to bind to and interact with a variety of biomolecules 

leading to responses in living organisms. Both compounds have a substantial database of 

epidemiological, pharmacokinetic, toxicological and mechanistic studies. The two documents 

submitted for peer review include health assessment chapters that will be used 1) to provide 

information to drinking water treatment plant operators regarding the significance of monitoring 

results with respect to potential health outcomes and 2) to determine whether the perfluorinated 

compounds currently being monitored at Public Drinking Water Systems require regulation. The 

health information at that time will be accompanied with chapters on environmental fate, 

occurrence at public drinking water systems and occurrence in other media. The quantitative 

aspects of the Health Assessment documents will also be used to develop lifetime Health 

Advisories for both compounds.

Charge Questions

1. Please comment on the strengths, weaknesses, and characterization of the studies selected as 

key for quantification. 

2. Please provide citations (and, where possible, pdfs or hard copies) for any references you 

suggest EPA consider adding to the document. Describe where you suggest these references 

be incorporated.

3. The OW concluded that the human epidemiology data for PFOS/PFOA do not provide 

adequate quantifiable dose-response information for use as the basis of a candidate RfD 

because of uncertainty regarding the routes, levels and timing of exposures plus the 

confounding influences of other PFCs present in serum. Please comment of the OW 

characterization of the data. 

4. Please comment on the transparency and characterization of the epidemiological data. 

5. The OW has concluded that the cancer classifications for PFOA and PFOS are most 

consistent with respective classifications of suggestive evidence for carcinogenicity as 

described the EPA Guidelines for Carcinogen Risk Assessment (pp. 2-56, 2-57). Please 

comment on the strengths and weaknesses of this classification. 

6. Significant interspecies differences in pharmacokinetics exist for both PFOA and PFOS. 

Adjusting for interspecies differences was an important step in developing candidate RfDs 

given the totality of the human and animal data. Please comment on the strengths and

weaknesses of the pharmacokinetic model adjustments to accommodate the impact of 

albumin binding and renal tubule transporters in determining average serum values.
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7. Table 5-5 in the PFOA document and Table 5-7 in PFOS document list the parameters used 

for the ORD pharmacokinetic models that provide the final serum and AUC values for 

calculating the internal dose point of departure for the RfD calculation. Please comment on 

the strengths and weaknesses of the selected parameters.

8. The volume of distribution (Vd) and half-life values are critical in the derivation of the 

interspecies uncertainty factor applied in derivation of candidate RfDs from a NOAEL, 

LOAEL or a BMDL. The available data for both values are provided in Section 3.5.2 and 

3.5.3 of both documents. Please comment the strengths and weaknesses of the values 

selected.

9. A variety of endpoints and studies were used to compare points of departure and the 

resultant RfDs for both PFOA and PFOS. In addition, comparisons were provided across 

RfD outcomes based on the model outputs compared to those for the NOAEL, LOAEL and 

BMDL points of departure. The range of candidate RfDs derived from the different points of 

departure is fairly narrow. Please comment on the strengths, weaknesses and transparency of 

this analysis.

10. The RfDs for PFOS and PFOA are derived from the modeled steady state serum 

concentrations and their association with effects that include short term and longer term 

exposures with associated diverse effects. The studies considered included effects due to 

exposure durations that ranged from 11 to 182 days, and occur at comparable human 

equivalent dose (HED) levels. The current, draft RfDs do not include an uncertainty factor 

for study duration because of the apparent concordance HEDs despite duration differences. 

Given this pattern of response, is it appropriate to conclude that the candidate RfDs are 

applicable to both short-term and lifetime exposures?

11. In addition to using the average serum values from animal studies to calculate internal doses 

for humans, the animal to human extrapolation can be accomplished by dividing animal 

average serum values by the human to animal clearance ratios to project a human average 

serum point of departure in units of mg/L serum. Please provide recommendations for 

applying uncertainty factors to the extrapolated average human serum values to determine 

serum-based thresholds that are protective for humans. A NOAEL expressed in average 

human serum units would be useful in interpreting NHANES population monitoring data.

12. Please describe any suggestions you have for improving the clarity, organization, and/or 

transparency of the draft documents.
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III. GENERAL IMPRESSIONS

James V. Bruckner

PFOA-specific comments

This is one of the most comprehensive Health Effects Documents I have reviewed. The clarity 

and accuracy of accounts of pertinent research reports/publications are excellent. It is obvious 

considerable time and efforts were devoted to its composition. If anything, the amount of detail 

is so great that it is difficult to distill the mass of information on each topic and capture its 

“essence”. This is likely the result of directions the authors were given for writing the document. 

Some topics in the Hazard Identification section do have summarizing sentences, in which the 

key/critical studies and their finding(s) are integrated and conclusions reached. It would be very 

helpful to devote much more attention to this for more topics, perhaps as an addition to Section 

4.4 Hazard Characterization.

I do have a real problem with the scientific basis and soundness of certain conclusions in the 

document. The primary effect of PFOA in different species is increased absolute and/or relative 

liver weight. These are quite modest, reversible, non-specific effects that usually are not 

considered toxicologically significant. Livers of mice and rats dosed with PFOA typically 

exhibited hypertrophy characterized by increased peroxisomes, numerous mitochondria, reduced 

rough endoplasmic reticulum (RER), proliferation of smooth endoplasmic reticulum (SER), and 

increased autophagosomes or lipid-like droplets. Such morphological changes, particularly those 

in RER and SER, are manifestations of microsomal enzyme induction. This is considered 

adaptive, rather than adverse. Hall et al. (2012) points out that activation of a battery of genes 

involved in xenobiotic metabolism and transport serve to maintain homeostasis by enhancing the 

systemic elimination of the foreign chemical. Although PFOA is very poorly metabolized, it 

does persistently induce microsomal enzymes and the accompanying hepatocellular 

morphological changes. Upregulation of genes responsible for biliary excretion may be 

beneficial, since excretion of bilirubin, bile acids and conjugates of toxic chemicals/metabolites 

would be enhanced.

There are substantial qualitative and quantitative differences in responses of rodents and humans 

to PPARα activation. Therefore, many of the PFOA-induced alterations in lipid 

metabolism/homeostasis and associated biological processes in mice will be absent or an order 

of magnitude less pronounced at comparable doses in humans. Many of PFOA’s effects on the 

liver of rodents are dependent on PPARα activation, though some effects appear to be PPARαindependent. Studies in PPARα-knockout mice show activation of other nuclear receptors by 

PFOA, including PXR, CAR, LXRA and FXR. Bjork et al. (2011) observed markedly lower 

transcriptional responses of PPARα, PXR, CAR and FXR to PFOA in cultured human than in 

cultured rat hepatocytes. These more subtle effects lead the investigators to conclude the 

changes in human cells reflected an adaptive metabolic remodeling rather than overt metabolic 

dysregulation, or disorder occurring in rat cells. The PFOA document’s authors should go into 

detail discussing and summarizing the relative toxicological significance of non-PPARα effects 

in rodents versus humans.
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It is important to recognize that clearly adverse effects of PFOA are seen. Lovelass et al. 

(2008), Cui et al. (2009) and others have seen focal necrosis and degenerative changes in the 

liver of mice and rats given relatively high doses of PFOA, as well as modest elevations in 

serum (hepatic) enzyme activities. Wolf et al. (2008a) observed a variety of degenerative 

structural changes in the liver of PPARα-null mice dosed with PFOA. Sakr et al. (2007a,b) and 

Olsen and Zobel (2007) reported associations between serum PFOA levels and slightly elevated 

serum enzyme activities in some occupationally-exposed populations. The increases in enzymes 

may have been attributable to factors other than PFOA. In light of the foregoing, it would be 

preferable to utilize hepatic morphological changes in rodents and/or elevated serum enzymes as 

the critical effect(s), rather than increased liver weight. These are clearly adverse effects seen in 

both rodents and humans. 

An international panel of experts (Hall et al., 2012) opined that an increase in liver weight of ≤ 

150%, at doses of chemical that do not produce structural or biochemical evidence of 

hepatocellular damage, would not be considered adverse. Absolute and relative liver weights 

were not increased as much as 50% by most PFOA doses in the majority rodent and monkey 

studies. Perkins et al. (2004), for example, reported dose-dependent increases in liver/body 

weight in rats fed 1, 10, 30 and 100 ppm PFOA for 13 weeks of 0, 10, 30, and 41%, 

respectively. Butenhoff et al. (2002) measured increases of 17, 21 and 37.5% and relative liver 

weight in monkeys given 3, 10 or 30/20 mg PFOA/kg/day for 26 weeks, respectively. Liver 

hypertrophy of this magnitude does not warrant such a low RfD. By adhering to EPA policies of 

calculating a BMDL10 and using multiple UFs, regardless of the (lack of) severity of the critical 

effect and relatively low level of concern about other potential health effects, the end result is a 

vanishingly low RfD (i.e. 0.00002 mg/kg/day). A great deal of time and effort were spent on the 

PFOA hazard assessment, toxicokinetic modeling and extrapolations, dose metric and POD 

considerations, etc. Despite all of these scientifically-credible exercises and deliberations, the 

end result (RfD) seems to this reviewer to have been preordained-- to be extremely low.

Logic expressed on page 5-6, in support of use of liver weight gain as a critical effect and 

biomarker of loss of hepatocellular homeostasis seems flawed. As pointed out in the second 

paragraph, liver weight changes were not observed in PFOA-treated mice with a humanized 

PPARα receptor. It is noted that changes in gene products that modulate lipid metabolism do 

occur in these mice. EPA argues that this supports adoption of increased liver weight as a 

biomarker/critical effect. It has not been established that these changes in gene expression are 

adverse, or whether they are sufficient in magnitude to significantly alter lipid metabolism. It 

would be expected that repeated dosing with enough of a molecule (i.e., PFOA) that resembles a 

fatty acid would affect expression of such genes. Reversible changes in total cholesterol, bile 

acids, bilirubin, etc. have been observed. It has not been established, however, whether mild 

fluctuations in these indices are detrimental. No increases in mortality from cerebrevascular 

disease or ischemic heart disease have been found in PFOA-exposed humans. How then does the 

concurrence of alteration of expression of such genes and of liver weight gain support the latter 

as toxicologically-significant effect that should be prevented by setting the RfD low enough?

PFOS-specific comments

This Health Effects Document, like that for PFOA, is quite comprehensive. Its descriptions of 

the many studies of PFOS are clear, quite complete, and apparently quite accurate. As with the 
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PFOA document, so much detail is given about many studies in the Hazard Identification 

section, that is difficult to compare study designs/dosage regimens/species/indices/findings/etc. 

and to draw conclusions. The summary tables for single and multiple studies, however, are quite 

helpful in this regard. It would also be very useful to have more summary statements or 

paragraphs at the end of each topic. These should address the scientific importance of findings, 

their relevance to humans; and their impact on the weight of evidence on an issue.

The hazard characterization section (4.4) is, for the most part, inclusive and balanced in its 

presentation and integration of findings of the more important studies in each subject area. This 

is true for both non-cancer and cancer effects in humans and animals. It concerns me, however, 

that the document’s authors do not focus in the remainder of the document on science (i.e., the 

candidate critical effects and their relevance to human health), but merely choose the most 

sensitive end-points and stress how similar the RfDs are after dosimetry modeling estimates and 

adjustments. I am not sure how this similarity of derived points of departure and other values, 

calculated from dissimilar endpoints, supports or validates the final RfD.

I recommend that an additional section be written, in which the primary adverse effects of PFOS 

are discussed-- in terms of their relative toxicological significance, their apparent mechanism(s), 

their relevance to humans, their likelihood in realistic exposure scenarios, and implications of 

altered experimental indices to actual organ dysfunction. 

I am quite concerned about the increased rat pup mortality in several studies at relatively low 

maternal doses, but not about reversible liver weight changes or centrilobular hypertrophy. Is the 

decreased pup survival in several studies at relatively low maternal doses of PFOS relevant to 

humans?-- Is the dose-response curve steep, as suggested by Luebker et al. (2005a), such that 

there would be less concern about sub-threshold doses? -- What is the most likely mode of 

action (pulmonary surfactant or maturation, dietary, hormonal)? -- Is decreased survival PPARαrelated? -- Is the mechanism in rats relevant to other species? -- Does pup mortality occur in 

other species at comparable doses? -- Might there be a dose-dependent alteration of maternalfetal partitioning of PFOS?

Deborah A. Cory-Slechta

Both documents, although the PFOA document to some degree more than PFOS, overall are 

more of a tabulation of studies than a critical review of studies from which a rationale is 

presented for a choice of studies to model and from which to derive associated RfDs. The 

Executive summaries are too abbreviated and do not include sufficient rationale, description and

detail to provide the reader with an understanding of how decisions described in Chapter 5 were 

made. Since in some cases, this will be the only sections read, they could provide a more 

informative summary. 

It would be very helpful to provide a section up front that describes all of the parameters of the 

literature search, including the years that are included in the document review, as well as 

descriptions of criteria for studies that were included vs. those that were excluded. In addition, it 

should be indicated whether there was a criterion that studies be peer-reviewed. This is 

particularly important given the voluminous size of the data base that has accumulated for these 
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two chemicals. Given that revisions will be done and that such documents do not get updated 

with any frequency, it would be good to attempt to include as much of the new pertinent 

literature as possible.

The section on Toxicokinetics in the documents present studies in detail, but no real 

conclusions; this is true of most of the sections in these documents. Chapters 3 and 4 in 

particular read like tabulations of studies rather than critical reviews and because of that, the 

documents seem disjointed and Section 5, i.e., derivation of values, tend to be difficult to read 

through and require constant searching back to the original chapters in which they are described. 

It is critical to identify the strengths and weaknesses of the various studies, and which were 

given weight to use in the final determinations. It would be helpful if Sections 3, 4 and 5 

included an introductory paragraph describing the goal of the chapter, and that each ends with an 

overall summary with conclusions. The tables in these chapters also would benefit from the 

inclusion of additional information that ultimately permits comparisons within the Table and 

does not require continually returning to the text to recall the species, sample sizes, etc.

In the sections on Hazard Identification, it is useful that studies are summarized by target organ, 

but there are almost no conclusions and no discussions of strengths or weaknesses of studies and 

therefore their use or not in future decisions. In fact, one is left with the impression that all 

studies are equal, especially in the section describing human studies. Within Chapter 4, the subsections entitled “evaluative and integrative” are actually neither. Data are presented simply as 

positive or negative with no real discussion of the strengths and limitations and what was 

concluded overall. For this reason, Chapter 5 is also lacking. It provides very little in the way of 

rationale and conclusions. Thus, the transparency of the process is really insufficient. 

Jamie C. DeWitt

The information presented throughout the documents appears to be accurate (with one minor 

exception noted in Table 1 of these comments) and is presented clearly. For PFOA, a reference 

dose (RfD) of 0.00002 mg/kg/day was determined and evidence of carcinogenicity is considered 

suggestive with a human equivalent dose (HED) of 0.58 mg/kg/day. The RfD was based on 

changes in liver weight reported as a common denominator in four rodent (three rat and one 

mouse) studies and carcinogenicity was based on a limited number of epidemiology studies 

linking kidney and testicular tumors with exposure and evidence of tumor induction in the liver, 

testes, and pancreas (the “tumor triad”) in rats. For PFOS, a RfD of 0.00003 mg/kg/day was 

determined and evidence of carcinogenicity is considered suggestive but with insufficient 

evidence to determine human carcinogenic potential. The RfD was based on developmental 

neurotoxicity and changes in liver weight.

While the carcinogenicity assessment seems appropriate for the two compounds given the 

limitations of the data sets, changes in liver weight as a basis of both of the RfDs is questionable 

in terms of its significance to exposed humans. Exposure to these agents increases liver weight 

and hepatocellular hypertrophy in rodents (and the definition of these endpoints as “adverse” or 

“toxic” also is contentious); this has been demonstrated across various rodent strains and under 

myriad exposure paradigms. However, there is no consensus in the scientific community 

regarding the mechanism by which exposure to these compounds increases liver weight and 
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induces hepatocellular hypertrophy in rodents and whether any of the putative mechanisms are 

sufficient to induce hepatotoxicity in exposed humans. Proposed mechanisms include 

peroxisome proliferator activated receptor alpha (PPARα) activation, activation of other nuclear 

receptors, peroxisome proliferation (which may or may not be dependent on PPARα activation), 

and oxidative stress. Humans can certainly respond to PPARα agonists (i.e., fibrate drugs are 

used as hypolipidemic agents) and a handful of epidemiological studies of highly exposed 

human populations have reported associations between PFOA/PFOS and alterations in liver 

enzymes, but the clinical relevance of the changes to the liver enzymes reported for these studies 

is uncertain. These liver-related changes in humans generally occur at higher doses than required 

to induce changes in the livers of rodents, which occurs at relatively lower doses than other 

observed effects. Therefore, a critical endpoint that occurs at very low doses in rodents, has no 

agreed upon mechanism that may or may not be relevant in humans at relatively high doses, may 

not be the best choice for the basis of a RfD. Liver weight change has been reported to occur in 

several species, including non-human primates, and at low doses, it may be an adaptive response 

and not a toxicological response. While this response may be protective of human health 

because it is common following low dose exposure to PFOA or PFOS, other endpoints may be 

more relevant to humans, especially endocrine system effects, including changes to thyroid 

hormones and mammary gland development, and immune system effects. Endocrine and 

immune system effects have been reported in exposed humans, suggesting that such endpoints 

may operate via a mechanism that is more relevant to humans than mechanisms related to 

changes in liver weights.

In addition, the one developmental neurotoxicity study used, in part, for the PFOS RfD is only 

weakly supported by additional studies in rodents or other species and is based on behavioral 

responses that could be influenced by factors other than direct effects on the nervous system. 

Additional confirmatory studies are necessary for this observation to be considered a critical 

effect of PFOS exposure.

Finally, while well-written overall, the documents lacked an overall critical analysis or depth 

required of a risk assessment. Why specific studies were included or not should be better 

explicated in the text.

Jeffrey W. Fisher

The document was well written in terms of balance and presenting information. Summary 

statements are needed for chapters; a synthesis/analyses of the data are needed in some cases. A 

more critical evaluation of the human and non-human responses to PFOA/PFOS is required to 

justify not using human or non-human primate data. A rationale for the modeling approaches is 

needed given the more recent PBPK models that are available.

William L. Hayton

The literature that pertains to the health effects of PFOA and PFOS is large and presents a major 

challenge to accurately summarize and analyze it and develop an RfD for PFOA and PFOS. 

Reported health effects in animals and humans, sometimes contradictory, include exposureassociated changes in serum cholesterol, lipids, uric acid, and thyroid hormones, obesity-related 
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metabolism, immune system function, and effects on reproduction, development of the 

mammary gland, the nervous system, and behavior. Target organ effects (e.g., liver, kidney) 

have been reported, as well as associations of PFOA and PFOS exposure with testicular, prostate 

and kidney cancer. Studies in several laboratory animal species have added the complications of 

interspecies comparisons and extrapolation of findings to humans. In humans, there have been a 

Phase I clinical trial of PFOA, and epidemiological studies of populations exposed to PFOA and 

PFOS occupationally and in communities with and without water supplies contaminated with 

PFOA and PFOS. The draft documents have accurately presented in summary form the results 

of many animal and human studies and used pharmacokinetic methods to link PFOA and PFOS 

exposure rates to internal dose metrics such as serum concentration. While the overall effort is 

commendable, there are two issues that the draft documents raise: 1) the literature cited does not 

include many apparently relevant published works. The cut-off date for cited literature was 

early 2013 (this should be indicated in the documents), but commenter’s noted a number of 

pertinent publications in 2011 and 2012 that were not cited, and there have appeared several 

highly pertinent papers since the cut-off date, and 2) while the descriptions of individual studies 

are generally clear and accurate, there is a lack of independent, critical analysis of the studies 

and a lack of synthesis of results from multiple studies common to a particular health effect.

Matthew P. Longnecker

The PFOA and PFOS documents achieve the goal of identifying RfDs that are well founded. 

My main criticism is that the rationale for not using the human data to provide a POD needs to 

be strengthened.

For example, in the PFOA document, on page 5-19, first paragraph below the table, it says 

“human data ... lack the exposure information for dose-response modeling.” This statement is 

logically inconsistent with techniques that were used to estimate HED on the basis of serum 

concentration, as given on page 5-17, near the bottom. Or, in some cases, such as in the C8 

study, the exposure estimates that were calculated based on water district were sufficiently good 

that a dose-response analysis would be possible. In other words, because many human studies 

have serum concentration of PFOA or reasonable estimated exposure values, the corresponding 

HED could be estimated, and hence the dose-response could be modeled. Granted, some 

assumptions would be needed, but the methods could be serviceable (see response to item 3 

below). (Some of the above also applies to pages 5-1 and 5-2). More compelling arguments for 

not basing the POD on human data are, e.g., that: 1) the low probability that humans are 1,000 

times more sensitive to PFOA than other species (the number is based on the last column in 

table 5-9 compared with PFOA values in the C8 study and background exposed populations), 

especially given the relatively tight agreement between LOAEL (average serum concentration 

basis) among other species, 2) the possibility that the observed associations in humans were due 

to unmeasured confounding factors or reverse causality, and 3) other weaknesses in the 

epidemiologic data such as inconsistent results across studies (selected outcomes), unreplicated 

findings, or associations with clinical chemistry results for which corresponding adverse clinical 

correlates (i.e., morbidity) are not clearly established.
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Angela L Slitt

The documents provide a very thorough evaluation of PFOA and PFOS studies. It is logically 

organized, presenting findings in a way that the reader can understand the findings related to 

human, monkey, and rodents. The organization of the document allows the reader to easily find 

information about each species within the subchapters and summarizes key points in table form. 

PFOA is a well-studied compound, with a substantial amount of toxicokinetic and endpoint 

studies in rodents. Mechanistic data describing the role of membrane transporters to understand 

gender differences in PFOA elimination in rats is fairly well written. Little data exist regarding 

contribution of membrane transporters to PFOS disposition and elimination. The documents 

thoroughly describe species differences in PPAR-alpha signaling that might contribute to 

observed endpoints in rats, but not humans or monkeys. Overall, both documents are very 

thorough and provide a reliable basis for PFOS and PFOA evaluation.

For PFOA toxicokinetics, mechanisms of PFOA transport are important for understanding 

species differences in response to PFOA exposure, with focus placed on kidney. Figure 3-2 in 

the PFOA document does not adequately present the localization of renal transporters with 

relationship to their contribution to the urine compartment or renal reabsorption. A very nice 

diagram showing the subcellular localization of renal transporters presented by Klaassen and 

Aleksunes (Pharmacol Rev. 2010 Mar;62(1):1-96) clearly depicts the contribution of various 

transporters to filtrate or blood. This is an easier diagram to put PFOA elimination into context 

than the one presented. Contribution of membrane transporters to species differences in PFOA 

excretion Section 3 (specifically 3.4.1) would be put in better context if a table could be 

generated to compare Km and Vmax values for PFOA for various transporters, with specific 

focus on species information for OATPs and OATs. Data regarding information on contribution 

for OATps in liver accumulation of PFOS and PFOA is lacking, with specific regard to species 

differences. As PFOS is a likely candidate for hepatic uptake transport, understanding a 

mechanism to explain species differences in hepatic effects possibly due to difference in hepatic 

exposure is critical. Understanding impact species specific regulation of OATp expression in 

liver (e.g. whether species difference in PPAR-alpha signaling contributes) is also important in 

putting rodent distribution data into context.

Increased liver weight is considered to be a critical effect, but how increased liver weight relates 

to the observed human and monkey health effects needs to be further explained. First, use of 

liver weight alone might not be substantiate of an effect for point of departure compared to other 

liver effects observed at higher concentrations, such as increased serum ALT or AST. 

The studies that have evaluated these endpoints are well conducted. In layman terms, if 

someone is walking around with an increased liver weight, is he or she at risk for disease? Will 

his/her life span be shortened? To increase transparency of the document, a more 

comprehensive explanation is needed to justify why increased liver weight should be considered 

as a critical endpoint for human health. 

However, it should be noted for future consideration that there are a few publications in mice 

that do also ascribe liver weight changes in increased lipid accumulation along with increased 

expression of genes that contribute to fatty liver disease. This is considered to be a gap in 

knowledge for the field. Will relatively low dose PFOS exposures associated with hepatic 
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steatosis have other endocrine related effects known to be associated with NAFLD (insulin 

resistance, impaired glucose tolerance)? Emerging studies are evaluating whether PFOS induces 

hepatic steaosis and whether it is a PPAR-α mediated effect. For example a study performed by 

Wan et al. (2012) administered 0, 1, 5 or 10 mg/kg/day PFOS to adult male CD-1 mice for 3, 7, 

14 or 21 days. Histological analysis of liver sections, and biochemical/molecular analysis of 

biomarkers for hepatic lipid metabolism were assessed. Overall, the study reported that PFOSadministration induced hepatic steatosis in a time- and dose-dependent manner. The study also 

shows a high correlation between liver weight and lipid content. Increased expression of a 

lipogenic target (CD36/FAT) was observed at 5 and 10 mg/kg PFOS. A second study by 

Bijland et al. (2011) illustrated that PFOS administration increased liver weight (+ 107%, p < 

0.0001), which was accompanied by an increased hepatic TG content (+ 192%, p < 0.0001, 

respectively) in E3L.CETP mice on a C57Bl/6 background. At the age of 8–10 weeks, mice 

were fed a semisynthetic Western-type diet, containing 0.25% (wt/wt) cholesterol, 1% (wt/wt) 

corn oil, and 14% (wt/wt) bovine fat for 4 weeks in three independent experiments. Upon 

randomization according to body weight, plasma TC, and TG levels, mice were fed a Westerntype diet without or with PFOS (0.003%, ∼3 mg/kg/day) for 4–6 weeks. In summary, there is 

evidence that administration of relatively low PFOS doses to mice can result in hepatic lipid 

accumulation in the absence of overt “wasting.”

Data is lacking as to whether higher species, such as monkeys or humans will also develop 

PFOS-induced steatosis, which is confounding. Studies have profiled gene expression in wildtype and PPARα-null mice administered PFOS, finding that there is pathology and gene 

expression consistent with lipid-promoting effects in liver that are independent of PPARα, as 

they are observed in PPARα-null mice (Rosen et al., 2010). Limitations to the studies are that 

they did not specifically quantify hepatic lipid content, but inferred that the PFOS-induced 

vacuolization in liver pathology observed was potentially related to triglycerides. Studies by 

Bjork et al. (2011) comparing rat and human primary hepatocytes treated with PFOS (25 μM) 

demonstrated that human hepatocytes were slightly less responsive to the induction of lipid 

oxidation and synthesis genes, as well as induction of carbohydrate metabolism. It should be 

noted that the hepatocytes from the study are from a single human donor, the hepatocyte lipid 

content was not determine, and hepatocyte culture conditions were standard and not optimized 

to induce steatosis. In summary, the current literature is lacking robust information regarding 

whether PFOS, which highly concentrates in liver, has a steatotic-inducing effect in human or 

monkey liver. The evidence in PPARα-null mice indicates that it might have some PPARα 

independent effects related to hepatic fat accumulation. Because evidence for hepatic lipid 

content in PPARα-null mice after PFOA or PFOS has been described only by pathology, more 

robust studies are needed to conclude whether the effects can occur independent of PPARα and 

the observed increased liver weight is due not only to hypertrophy due to nuclear receptor 

activation, but lipid accumulation. However, this reviewer is noting this as a concern for the 

future and area where a gap in knowledge exists.

Moreover, because the reviewer is noting a concern for hepatic fat accumulation that exists in 

the absence of PPARα, it should be appreciated that traditional markers, such as AST and ALT 

have poor prognosis for NAFLD or toxicant associated steatohepatitis. Most patients with 

NAFLD are asymptomatic and the disease is often diagnosed following findings of elevated 

aminotransferases, especially when combined with other features of metabolic syndrome. These 
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abnormal liver function tests usually require the physician to distinguish between NAFLD and 

alcoholic fatty liver disease (AFLD). Some have suggested that a serum AST/ALT ratio >1 are 

indicative of AFLD. Other possible signs of AFLD include elevated HDL-cholesterol with 

hypertriglyceridemia. While most diagnoses of NAFLD may result from altered liver function 

tests, normal serum aminotransferase tests can be seen in patients with both steatosis and NASH 

(Ipekci, et al., 2003; Mofrad, et al., 2003). Indeed, it is reported that two-thirds of NASH 

patients may have normal aminotransferase levels at any given time (Oh, et al., 2008; Delgado, 

2008; Wieckowska and Feldstein, 2008). Kunde et al. investigated the accuracy of NASH 

diagnosis by serum ALT in women undergoing gastric bypass surgery (Kunde, et al., 2005). 

They compared two different reference laboratory cutoffs for "normal" ALT levels, the previous 

guideline of 30U/L, and new lower level of 19U/L that was suggested to aid in the diagnosis of 

NAFLD. Importantly, the authors reported that the diagnostic utility of serum ALT remained 

poor even at the new lower cutoff. Sensitivity and specificity of serum ALT levels were found to 

be 42% and 80% (ALT > 30U/L) versus 74% and 42% (ALT > 19U/L). These and other studies 

(Lizardi-Cervera, et al., 2006; Amarapurkar and Patel, 2004; Amarapurka, et al., 2006; Chen, et 

al., 2006; Fracanzani, et al., 2008; Sorrentino, et al., 2004; Mofrad, et al., 2003; Uslusoy, et al., 

2009) illustrate the need for a more effective diagnostic measure for NAFLD, especially the 

NASH stage. In sum, use of ALT and AST elevation to base the point of departure must be 

taken into context because they are poor prognostic markers for increased liver accumulation, 

NAFLD, or even NASH. Use of ALT and AST might not be an appropriate biomarker for 

measurement of PFOA or PFOS-induced adverse effects on liver and should be considered as a 

gap in our knowledge for future work.

In the review panel discussion, there was discussion regarding a publication by Hall et al. 

(2012), which summarized the outcome of a workshop regarding liver hypertrophy and 

hepatocarcinogenesis. Overall, the workshop concluded that “hepatomegaly as a consequence of 

hepatocellular hypertrophy without histologic or clinical pathology alterations indicative of liver 

toxicity was considered an adaptive and a non-adverse reaction”. This conclusion is taken in the 

context of hepatic hypertrophy caused by nuclear receptor activation. This differs from others 

that have concluded in mouse NTP studies where correlations between liver weight increases 

and histological parameters and carcinogenesis were assessed, the authors concluded that ‘‘the 

best single predictor of liver cancer in mice was hepatocellular hypertrophy’’ (Allen et al. 2004). 

Based on the conclusions presented in Hall et al. (2012), increased liver weight might not be 

considered an appropriate POD because of lack of overt toxicity and hepatomegaly being 

considered an adverse effect. It should be noted that this reviewer still has concerns regarding 

this conclusion for PFOS and PFOA because the pathology described in PPARα-null mice 

reflect increased hepatic lipids and not hepatomegaly due to nuclear receptor activation that is 

described in this opinion publication. If one considers the pathology examples of hypertrophy 

presented in Hall et al. (2012), it is quite different from the pathology described for PFOS and 

PFOA. For clarity, the document should try to delineate the cellular components that are 

contributing to increased liver weight caused by PFOA and PFOS administration, if such a 

publication exists (e.g. how much of the liver is associated with protein/peroxisome proliferation 

increase versus lipid increase). Because the literature is not clear regarding what exactly in the 

liver is causing increased liver weight, studies documenting hepatic lipid accumulation should 

not be currently considered for POD. Given the recent opinion cited by Hall et al. (2012), it is 
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recommended that studies documenting liver damage, such as ALT and AST elevation be 

currently used as the POD. 

The documents often have redundancy in information, especially in regard to hormone effects 

(there are very similar write ups in sections about effects on thyroid hormone) and 

metabolic/cardiovascular disease risk factors (e.g. lipid endpoints).
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IV. RESPONSE TO CHARGE QUESTIONS

Charge Questions

Question 1. Please comment on the strengths, weaknesses, and characterization of the 

studies selected as key for quantification. 

James V. Bruckner

PFOA-specific comments

The document’s authors have done a good job describing and integrating the findings of the 

numerous studies in which liver weight gain was observed. Although there is a consensus about 

the effect and the dosage required to elicit it in different species, this reviewer does not believe it 

should be utilized, as described above. There are several clearly adverse effects such as elevated 

serum (hepatic) enzyme activities, focal hepatocellular necrosis, bile duct degeneration and 

fibrosis, etc. These effects are generally seen in response to relatively high PFOA doses, so the 

PODs will be higher than with liver weight increase. Alternatively, a human endpoint such as 

elevated serum cholesterol could be considered. See responses to Charge Question 3.

PFOS-specific comments

There have been a substantial number of well-conducted toxicological studies of PFOS. My 

major concern, as expressed above, is its potential to cause adverse effects in children. Other 

than that, PFOS doesn’t appear to produce effects other than those anticipated from a repetitive, 

cumulative dose of an 8-carbon fatty acid.

Deborah A. Cory-Slechta

In general, it appears that, at least with respect to the animal studies, the choices are appropriate 

both in the case of PFOA and PFOS. The derivation of the RfDs/RfCs are based on studies of 

sufficient strength, duration and represent the most sensitive endpoints. 

Having said that, in both documents, the reader is forced to that conclusion with no real 

assistance from the text itself. There is virtually no discussion of the strengths and weaknesses

of the studies overall. Human study outcomes for the most part are simply enumerated, although 

an occasional statement will be made about a limitation (usually) of one of those studies. There 

is no discussion in the human studies of the power to detect effects, the sample sizes, etc. Much 

weight seems to be given to occupational studies in some cases, being used to essentially 

dismiss effects in a community cohort as the same effect was not seen in occupationally exposed 

workers, when in fact finding effects in a population with seemingly longer, albeit lower 

exposure levels actually makes the outcome more robust. Also, population studies with smaller 

sample sizes that nevertheless find significant effects are in fact more compelling and suggest 

robust effects which can be detected even with a small sample size. This deficiency is manifest 

in statements such as those in the PFOS document (p. 5-1) that ‘in most cases the findings are 

suggestive and not conclusive of an effect’. 
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There is a bit more discussion of the animal studies in both documents, at least with respect to 

methods, but as with the human studies, there is little text addressing which studies represent 

stronger studies or what the weaknesses are. From these increase liver weight has been chosen 

as the endpoint from which to derive RfDs. This reviewer does not have an issue with that 

choice, as while it has been described as adaptive by some, it represents a response to an 

involuntary exposure with a direction of effect that is potentially associated with adverse 

consequences. The fact that it is reversible when exposure ends seems irrelevant as reversal of 

exposure is not happening in the human environment.

Jamie C. DeWitt

Strengths: The studies selected as key for quantification were generally well-conducted studies, 

employing a range of doses and sample sizes large enough for detecting statistical differences. 

Additionally, the doses associated with LOAELs for the identified critical endpoints were not 

associated with signs of overt or systemic toxicity in the animal models and nearly all of the 

studies measured serum and/or tissue concentrations of the parent compounds.

Weaknesses: No obvious experimental design weaknesses were noted in any of the studies 

selected as key for quantification.

Characterization: The studies selected as key for quantification for PFOA are all rodent studies 

while at least one study selected for PFOS quantification includes a non-human primate study. It 

is therefore surprising that the PFOA database does not include, as a study key for 

quantification, the Butenhoff et al. 2002 study of non-human primates. Additionally variability 

in putative mechanisms among species was not adequately addressed in the characterization of 

the selective studies, although all of the selective studies were descriptive and not mechanistic.

Jeffrey W. Fisher

PFOA and PFOS: Data bases are massive and both need to be updated. Several human studies 

and a few non-human primate toxicity studies are available. The authors need to explain why 

these studies are not adequate for causality (dose-response). 

William L. Hayton

An advantage to assessment of health effects for both PFOA and PFOS is the large amount of 

published work that informs the topic. While the draft health-effects documents have 

summarized the results of many pertinent studies, the literature reviewed was not 

comprehensive, which projects an appearance of weakness. The documents do not state whether 

the intention was to include all relevant health-effects literature, or to be selective and 

summarize those studies judged to be most relevant. Such a statement at the beginning of the 

documents would be helpful; a cut-off date for the literature review would also frame 

expectations of readers. If the intention was to be selective, a description of selection criteria 

would help allay concerns of readers about papers that were not included. If the intention was to 

comprehensively review all the PFOA and PFOS health-effects literature, then it appears that 
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more work should be done to include omitted works. Public comments list a number of works 

to consider for inclusion.

A general, albeit minor weakness of the literature is that PFOA and PFOS serum concentrations 

in control animals were not measured for many studies – they were likely non-zero and, since 

there is no information on how high they were, it is possible that baseline health-effects metrics 

were affected and that dose-response relationships were affected, especially in the low dose 

range. It is perhaps worthwhile to mention this shortcoming somewhere in the health effects 

documents.

Matthew P. Longnecker

EPA may want to consider the article by AP Hall et al. 2012, about liver hypertrophy. The 

defense of increased liver weight as the POD (or a POD) could be strengthened by evaluating 

the evidence in the context of Hall’s Figure 9, where evidence regarding hepatoxicity and toxic 

mechanisms are also considered. In this case, the possibility of an unknown mechanism exists 

that could be relevant to humans, and long-term exposure could have effects that have not yet 

been detected. See Hall page 986, where it defines adverse as: “...affects [response] to an 

additional environmental challenge”. Thus, an adverse effect, via an unknown mechanism, by 

this definition is possible and has not been studied in animals or humans.

While AP Hall’s article is not all that supportive of using increased liver weight as a point of 

departure (unless certain criteria are met), they are focused on animal studies, especially those 

done in rodents. If increased relative liver weight were to occur in a human population, I 

suspect that it would be considered an adverse outcome, whether or not there was evidence of 

hepatotoxicity or a specific mechanism. Note also that for PFOA, in monkeys, there was an 

increase in relative liver weight with chronic exposure (PFOA document, page 4-66), so increase 

in liver weight in the animal experiments may be relevant to humans. 

An additional comment of relevance here pertains to whether the human data support 

hepatoxicity. While there are studies that report elevated liver function tests in subjects with 

higher serum concentrations of perfluorakyl substances, these elevations do not clearly support 

the presence of toxicity. Again, AP Hall’s discussion of what constitutes evidence of 

hepatoxicity is relevant here, and takes into account the number of LFTs elevated, the specific 

LFTs involved, and the magnitude of their elevation.

Finally, as discussed at the meeting, for the PFOA document on page 5-23 (“RfD Selection”), 

and the PFOS document on page 5-26 (“RfD selection”), I suggest minor editorial changes to 

deemphasize the “consistency of response” point and instead focus a little more on how the RfD 

is robust to choice of POD endpoints. If the selection of RfD does not hinge on increased liver 

weight as a POD, it will be more defendable. 

Transparency might be increased by saying why (more clearly, or more clearly by implicit 

reasoning) the Macon et al. 2011 study, in which the LOAEL was 0.01 mg PFOA/kg from 

GD10 to GD17, based on delayed mammary gland development, was not considered as a POD, 

and why the Hines et al. 2009 study, in which the LOAEL was 0.01 mg PFOA/kg from GD1 to 
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GD17, based on various outcomes, was not considered as a POD. The PFOS studies with low 

LOAELs were considered in the dose-response assessment (no suggestions for improvement 

there).

Angela L Slitt

My response is basically the same as my General Impressions above.

The documents provide a very thorough evaluation of PFOA and PFOS studies. It is logically 

organized, presenting findings in a way that the reader can understand the findings related to 

human, monkey, and rodents. The organization of the document makes allows the reader to 

easily find information about each species within the subchapters and summarizes key points in 

table form. PFOA is a well-studied compound, with a substantial amount of toxicokinetic and 

endpoint studies in rodents. Mechanistic data describing the role of membrane transporters to 

understand gender differences in PFOA elimination in rats is fairly well written. Little data exist

regarding contribution of membrane transporters to PFOS disposition and elimination. The 

documents thoroughly describe species differences in PPAR-alpha signaling that might 

contribute to observed endpoints in rats, but not humans or monkeys. Overall, both documents 

are very thorough are provide a reliable basis for PFOS and PFOA evaluation.

For PFOA toxicokinetics, mechanisms of PFOA transport are important for understanding 

species differences in response to PFOA exposure, with focus placed on kidney. Figure 3-2 in 

the PFOA document does not adequately present the localization of renal transporters with 

relationship to their contribution to the urine compartment or renal reabsorption. A very nice 

diagram showing the subcellular localization of renal transporters presented by Klaassen and 

Aleksunes (Pharmacol Rev. 2010 Mar;62(1):1-96) clearly depicts the contribution of various 

transporters to filtrate or blood. This is an easier diagram to put PFOA elimination into context 

than the one presented. Contribution of membrane transporters to species differences in PFOA 

excretion Section 3 (specifically 3.4.1) would be put in better context if a table could be 

generated to compare Km and Vmax values for PFOA for various transporters, with specific 

focus on species information for OATps and OATs. Data regarding information on contribution 

for OATps in liver accumulation of PFOS and PFOA is lacking, with specific regard to species 

differences. As PFOS is a likely candidate for hepatic uptake transport, understanding a 

mechanism to explain species differences in hepatic effects possibly due to difference in hepatic 

exposure is critical. Understanding impact species specific regulation of OATp expression in 

liver (e.g. whether species difference in PPAR-alpha signaling contributes) is also important in 

putting rodent distribution data into context.

Increased liver weight is considered to be a critical effect, but how increased liver weight relates 

to the observed human and monkey health effects needs to be further explained. In layman 

terms, if someone is walking around with an increased liver weight, is he or she at risk for 

disease? Will his/her life span be shortened? To increase transparency of the document, a more 

comprehensive explanation is needed to justify why increased liver weight should be considered 

as a critical endpoint for human health.
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Use of humanized PPARα mice are a sexy tool to delineate species differences in effects 

associated with peroxisome proliferation. For transparency, the document should acknowledge 

the limitations of that model. Specifically, lack of response may not necessarily correlate to a

lack of response for human PPARα because of species differences in binding to cogate DNA 

elements (e.g. a human receptor may have lower binding capacity to mouse DNA due to 

structural differences and species differences in co-activator/co-repressor interactions). Wording 

in the documents using these mice should acknowledge this limitation.

The documents often have redundancy in information, especially in regard to hormone effects 

(there are very similar write ups in sections about effects on thyroid hormone) and 

metabolic/cardiovascular disease risk factors (e.g. lipid endpoints). 
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Question 2. Please provide citations (and, where possible, pdfs or hard copies) for any 

references you suggest EPA consider adding to the document. Describe where you suggest 

these references be incorporated.

James V. Bruckner

PFOA-specific comments

Fabrega, F. et al. (2014). PBPK modeling for PFOS and PFOA: Validation with human 

experimental data. Toxicol. Lett. On line. (Hard copy available)

Stahl, T., Mattern D and Brunn, H. (2011). Toxicology of perfluorinated compounds. Environ. 

Sci. Europe 23: 38-60.

Hall, A. P., et al. 2012. Liver hypertrophy: A review of adaptive (adverse and non-adverse) 

changes- Conclusions from the 3rd International ESTP Expert Workshop. Toxicol. Pathol. 40: 

971-994.

Bjork, J. A., Butenhoff, J. L., and Wallace, K. B. 2011. Multiplicity of nuclear receptor 

activation by PFOA and PFOS in primary human and rat hepatocytes. Toxicology 228: 8-17.

PFOS-specific comments

No additional references were located.

Deborah A. Cory-Slechta

For both PFOA and PFOS, the document should include a description of the process through 

which studies were identified and how they were processed for inclusion or not. It is not clear 

what the exact dates of the studies examined included, i.e., what the cut-off date was for these 

studies. This makes it difficult to evaluate whether there are missing studies. That said, this 

reviewer is not aware of any specific omissions in the peer-reviewed literature other than those 

that were discussed at the face-to-face meeting. 

Jamie C. DeWitt

Granum, B., Haug, L.S., Namork, E., et al. 2013. Pre-natal exposure to perfluoroalkyl 

substances may be associated with altered vaccine antibody levels and immune-related health 

outcomes in early childhood. J Immunotoxicol. 10:373–379; Looker, C., Luster, M.I., Calafat, 

A.M., et al. 2014. Influenza vaccine response in adults exposed to perfluorooctanoate and 

perfluorooctanesulfonate. Toxicol. Sci. 138:76–88.

Any time the Grandjean et al. (2012) findings related to PFAS and vaccine responses are 

discussed, these references could/should be discussed as well as they report related findings in 

human populations. Although they also are confounded by multiple PFAS (as was the Grandjean 

et al. study), they lend additional support to immunotoxicity as an endpoint worthy of 

consideration. However, it is noted that these references were published after the cutoff date for 

consideration for inclusion in the document.
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Lopez-Espinosa, M.J., et al. 2012. Thyroid function and perfluoroalkyl acids in children living 

near a chemical plant. Environ.Health Perspect. 120:1036–1041. This study is missing from the 

discussion of thyroid hormone disruption. It reports a positive correlation between 

hypothyroidism and PFOA in children from the C8 population aged 1-17.

Corsini E., et al. 2011. In vitro evaluation of the immunotoxic potential of perfluorinated 

compounds (PFCs). Toxicol. Appl. Pharmacol. 250:108-116. Corsini E. et al. 2012. In vitro 

characterization of the immunotoxic potential of several perfluorinated compounds (PFCs). 

Toxicol. Appl. Pharmacol. 258:248-255.These studies are in vitro/ex vivo studies of humanderived cells that provide evidence that in vitro measures of immunocompetence in mice may be 

relevant to the human experience.

Jeffrey W. Fisher

For completeness sake, at least, please update lab animal studies conducted since 2012. 

William L. Hayton

A review of PFOA health-effects literature (GB Post et al. (2012) Environ. Res. 116: 93-117) 

provides an excellent, in-depth discussion of many issues covered in the PFOA health effects 

document. Consider citing this review in the document. 

The literature on PFOA and PFOS toxicokinetics (Section 3) has been comprehensively covered 

in the health effects documents, with the notable omission of Wambaugh et al., Dosimetric 

Anchoring of In Vivo and In Vitro Studies for Perfluorooctanoate and Perfluorooctanesulfonate. 

Toxicol. Sci. 136:308-327, 2013. This paper informed a significant part of the health effects 

documents.

Commenter’s have suggested a number of references to consider with regard to Section 4 

Hazard Identification. Many recent publications report on toxicity associated with PFOA/PFOS 

exposure. For the Dose-Response Assessment (Section 5) it is desirable to focus on those 

toxicities that have occurred at the lowest PFOA/PFOS exposures. For PFOA, the literature that 

is used in Section 5 to determine an RfD was published prior to 2009 (Tables 5-8 – 5-11). The 

benchmark response chosen based on the Section 4 literature was a 10% increase in liver weight, 

which was the biological response that occurred at the lowest PFOA exposure; it was 

acknowledged that this response “... is a biomarker for systemic exposure in rodents, rather than 

a biomarker of adversity ...” (p. 5-6). More recent studies of hazard have identified potential 

adverse effects that result from, or are associated with, PFOA exposures that are lower than the 

LOAEL for a 10% increase in liver weight. For example, adverse effects on fetal, neonatal and 

early childhood stages of development may occur at lower exposures than does liver weight 

gain, which suffers in addition from not being a biomarker of adversity, and which therefore 

raises a question about the validity of any RfD based upon it. Macon et al. 2011 reported an 

LOAEL for delayed mammary gland development of 0.01 mg/kg administered to pregnant CD-1 

mice during GD10 – GD17. As this relatively brief exposure was well below that required for 

steady state, it is possible that had the dams been at steady state at the time of conception (about 

9 weeks of exposure) a much lower LOAEL may have been observed; i.e., a much lower dose 
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rate at steady state would have produced the same exposure to the fetal pups as did the 0.01 

mg/kg administered to the dams during GD10 – GD17. The steady state situation is more 

relevant to adverse effects in humans than is a brief exposure.

Matthew P. Longnecker

I suggest you include the following citation and include a discussion of the evidence presented:

Paula I. Johnson, Patrice Sutton, Dylan S. Atchley, Erica Koustas, Juleen Lam, Saunak Sen, 

Karen A. Robinson, Daniel A. Axelrad, and Tracey J. Woodruff. The Navigation Guide—

Evidence-Based Medicine Meets Environmental Health: Systematic Review of Human Evidence 

for PFOA Effects on Fetal Growth. Environ Health Perspect; DOI:10.1289/ehp.1307893 (in 

press and available through the journal’s website).

Based on the meta-analysis in this paper, the evidence that PFOA is associated with lower 

birthweight is consistent. Thus, the rationale for not basing the POD on the human data needs to 

be strengthened, as noted above. The Johnson et al. report could be discussed in the section on 

anthropometric endpoints that begins on p 4-22. 

The relationship between birthweight and PFOA or PFOS may be confounded because 

glomerular filtration (and hence excretion of the compounds) is proportional to birthweight, as 

discussed in:

Morken NH, Travlos GS, Wilson RE, Eggesbø M, Longnecker MP. Maternal glomerular 

filtration rate in pregnancy and fetal size. PLoS One. 2014 Jul 8;9(7):e101897

In the PFOA document, on page 4-18, you might want to also cite: 

Taylor KW, Hoffman K, Thayer KA, Daniels JL. Polyfluoroalkyl chemicals and menopause 

among women 20-65 years of age (NHANES). Environ Health Perspect. 2014 Feb;122(2): 145-

50.

The Taylor et al., like the Knox et al. report (already cited in the PFOA document) is from a 

large-cross sectional study. Both studies, in their discussion sections, note that the association of 

PFOA or PFOS concentration in serum with age at menopause could be expected because 

postmenopausal women have lost a route of excretion for the compound and will have higher 

serum concentrations on that basis. It would be worth noting this possible explanation in the 

PFOA document on page 4-18, and in the PFOS document on page 4-8. 

Additional data are available on the potential carcinogenicity of PFOA:

 Steenland K, Woskie S. Cohort mortality study of workers exposed to perfluorooctanoic 

acid. Am J Epidemiol. 2012;176(10):909-17.

 Barry V, Winquist A, Steenland K. Perfluorooctanoic acid (PFOA) exposures and incident 

cancers among adults living near a chemical plant. Environ Health Perspect. 2013;121(11-

12):1313-8

 Hall AP et al. Toxicol Pathol 2012:40:971-94. (About liver hypertrophy.)
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The Steenland and Barry reports could be discussed in Section 4.1.2, on pages 4-28 and 4-29, 

respectively.

Angela L. Slitt

1) Evidence is presented for PFOA and PFOS as substrates for the related OATp1d1 in zebra 

fish. Establishing whether PFOS is an OATp transporter substrate is needed to better 

understand PFOS accumulation in liver. This study suggests that it might be. The following 

finding should be included in the PFOS document in Section 3.2.3 and the PFOA document 

in Section 3.0:

a. Popovic M, Zaja R, Fent K, Smital T. Toxicol Appl Pharmacol. 2014 Interaction of 

environmental contaminants with zebrafish organic anion transporting polypeptide, 

OATp1d1 (Slco1d1).

2) This publication presents the finding that PFOS inhibits Pgp, Mrp1, and Mrp4 activity. The 

following finding should be included in the PFOS document in Section 3.2.3 and the PFOA 

document in Section 3.0: 

a. Dankers AC1, Roelofs MJ, Piersma AH, Sweep FC, Russel FG, van den Berg M, van 

Duursen MB, Masereeuw R. Toxicol Sci. 2013 Dec;136(2):382-91. Endocrine 

disruptors differentially target ATP-binding cassette transporters in the blood-testis 

barrier and affect Leydig cell testosterone secretion in vitro.

3) PFOS induced ABC transporters in grey mullets. 

a. de Cerio OD1, Bilbao E, Cajaraville MP, Cancio I. Gene. 2012 Apr 25;498(1):50-8. 

Regulation of xenobiotic transporter genes in liver and brain of juvenile thicklip grey 

mullets (Chelon labrosus) after exposure to Prestige-like fuel oil and to 

perfluorooctane sulfonate.

4) These are new publications regarding epidemiology findings for PFOS and PFOA exposure 

and serum lipids: 

a. Fitz-Simon N, Fletcher T, Luster MI, Steenland K, Calafat AM, Kato K, Armstrong 

B. Epidemiology. 2013 Jul;24(4):569-76. doi: 10.1097/EDE.0b013e31829443ee. 

Erratum in: Epidemiology. 2013 Nov;24(6):941.

b. Starling AP, Engel SM, Whitworth KW, Richardson DB, Stuebe AM, Daniels JL, 

Haug LS, Eggesbø M, Becher G, Sabaredzovic A, Thomsen C, Wilson RE, Travlos 

GS, Hoppin JA, Baird DD, Longnecker MP. Perfluoroalkyl substances and lipid 

concentrations in plasma during pregnancy among women in the Norwegian Mother 

and Child Cohort Study. Environ Int. 2014 Jan;62:104-12.

c. Fu Y, Wang T, Fu Q, Wang P, Lu Y. Associations between serum concentrations of 

perfluoroalkyl acids and serum lipid levels in a Chinese population. Ecotoxicol 

Environ Saf. 2014 Aug;106:246-52.

5) These are publications regarding PFOS exposure and hepatic steatosis:

a. Lv Z, Li G, Li Y, Ying C, Chen J, Chen T, Wei J, Lin Y, Jiang Y, Wang Y, Shu B, 

Xu B, Xu S. Glucose and lipid homeostasis in adult rat is impaired by early-life 

exposure to perfluorooctane sulfonate. Environ Toxicol. 2013 Sep;28(9):532-42. 

doi: 10.1002/tox.20747. Epub 2011 Aug 24. PMID: 23983163 Select item 22484034
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b. Wan HT, Zhao YG, Wei X, Hui KY, Giesy JP, Wong CK. PFOS-induced hepatic 

steatosis, the mechanistic actions on β-oxidation and lipid transport. Biochim 

Biophys Acta. 2012 Jul;1820(7):1092-101. doi: 10.1016/j.bbagen.2012.03.010. Epub 

2012 Mar 28. PMID: 22484034 [PubMed - indexed for MEDLINE] Free Article

c. Bijland S, Rensen PC, Pieterman EJ, Maas AC, van der Hoorn JW, van Erk MJ, 

Havekes LM, Willems van Dijk K, Chang SC, Ehresman DJ, Butenhoff JL, Princen 

HM. Perfluoroalkyl sulfonates cause alkyl chain length-dependent hepatic steatosis 

and hypolipidemia mainly by impairing lipoprotein production in APOE*3-Leiden 

CETP mice. Toxicol Sci. 2011 Sep;123(1):290-303. doi: 10.1093/toxsci/kfr142. 

Epub 2011 Jun 24.
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Question 3. The OW concluded that the human epidemiology data for PFOS/PFOA do not 

provide adequate quantifiable dose-response information for use as the basis of a candidate 

RfD because of uncertainty regarding the routes, levels and timing of exposures plus the 

confounding influences of other PFCs present in serum. Please comment of the OW 

characterization of the data.

James V. Bruckner

PFOA-specific comments

The document’s authors have done a good job summarizing and accurately characterizing the 

epidemiology literature for various endpoints in Section 4.4 - Hazard Characterization. It is true 

there are a number of confounding factors that make estimation of PFOA exposures difficult. 

The EPA might consider, however, utilization of reverse dosimetry modeling. There is a 

reasonable body of data on serum PFOA levels, which could be used to estimate a range of 

PFOA exposures that would result in such internal doses.

PFOS-specific comments

I agree that human epidemiology data do not provide an adequate basis for calculation of a RfD 

or RfC. A reverse dosimetry modeling approach, however, could be used to estimate a range of 

PFOS exposures that could have resulted in measured body burdens. The human data might then 

be utilized in the risk assessment.

Deborah A. Cory-Slechta

It is not clear that such an assertion should be used in the construction of this document. It is not 

clear why the route of exposure should be raised to a concern in the calculations, in fact in the 

human environment, there are exposures from multiple routes, no doubt and thus this is 

consistent with human environmental exposures. Further, if there is data on serum levels, it 

should reflect that cumulative exposure across exposure routes. Indeed, at the end, the goal is to 

arrive at an RfD based on serum levels. There is, moreover, no guarantee that there is no 

contamination in studies in animals from food, glassware etc.

Furthermore, in many epidemiological studies in which mixed exposures are the norm, 

controlling for other exposures is utilized to address this concern and to therefore make 

conclusions about individual exposures. In point of fact, in every single human study, there will 

invariably be other exposures and not a single exposure, and thus this strategy essentially says 

that no human studies can ever be used for any risk assessments. The stated rationales for not 

using human data based on these statements is not adequate. This is why it is important as well 

to evaluate the strengths and weaknesses of each of the studies in terms of whether appropriate 

controlling for other known exposures was carried out and sample sizes sufficient etc. to arrive 

at some conclusions with respect to their ultimate usability in constructing RfDs.
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Jamie C. DeWitt, Ph.D..

While the OW characterization of the epidemiological data for PFOA/PFOS is, technically, true, 

it also is somewhat misguided. Almost any epidemiological database will contain uncertainty 

regarding the routes, levels, and timing of exposures and will have confounding influences of 

other compounds. Very few epidemiological studies are free from these uncertainties, but when 

similar observations and conclusions are reached from multiple studies with these types of 

uncertainties, the database becomes useful for determining a candidate RfD or other value 

relevant to human health. What is particularly valuable about the PFOA/PFOS database is that it 

is relatively extensive in that it includes data not only from occupationally-exposed humans, but 

from people highly exposed to environmental concentrations of PFOA/PFOS and from people in 

the general population who have detectable concentrations of these compounds. Additionally, 

for establishing an RfD, do all of these uncertainties need to be absent? In other words, do 

animal studies used to derive RfDs lack these uncertainties?

What is missing from the OW characterization of the epidemiological data is a thorough 

evaluation concerning hepatotoxicity and developmental toxicity reported in human populations 

and how these endpoints are relevant to or related to animal studies. 

Jeffrey W. Fisher

The use of non-human and human data is very important for interpreting exposure extrapolations 

from rats. I am not an epidemiologist so I cannot comment with authority on the epidemiology 

data for dose-response. Justify why human data are not suitable for use in the analysis of the 

health hazards of PFOA and PFOS.

William L. Hayton

There are a number of epidemiological studies that have been based on large numbers of 

subjects chronically exposed (over decades in some studies) to the subject compounds over a 

broad range of intakes. Steady state serum concentrations have also been available for 

quantification of the systemic exposure. While the route, levels and timing of the exposures 

may have been uncertain, the long half-lives of PFOA and PFOS in humans and the long periods 

of exposure to them indicate that 1) subject serum concentrations were generally at steady state, 

and 2) daily fluctuations in the amount and timing of the exposure would not produce much dayto-day fluctuation in the serum concentration of PFOA/PFOS. These consequences of the long 

exposure period and long half-life indicate that variability in the route and level of exposure 

would not have led to a measured serum concentration that was unrepresentative of the subjects’

long-term average serum concentration. The serum concentration then should be relatively 

stable over time and it should reflect an integrated measure of the individual’s exposure to 

PFOA and PFOS. 

The serum concentration is a quantitative measure of systemic exposure to the subject 

chemicals, and is arguably a better metric of exposure than are intake rate. The over-all rate of 

intake (R) that produces a particular steady state serum concentration (Css) can readily be 
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calculated from the clearance (CL) of the chemicals, which is about 0.08 mL/d/kg body weight: 

R = Css x CL. The calculated rate of intake would represent all intake routes. 

Confounding influences of other PFCs and indeed other chemicals and life-style factors such as 

smoking, diet, alcohol use, etc. would have to be considered, as is generally the case with 

epidemiological studies. Methodology exists for dealing with such influences.

Thus it appears that the epidemiological results should be used in the RfD determination. Their 

strength is that uncertainties associated with extrapolation from laboratory animal studies are 

avoided. Health effects that are positively associated with serum PFOA/PFOS concentration 

and that are observed in large populations of subjects should seriously be considered as 

potentially arising from PFOA/PFOS exposure. If mode of action studies in lab animals or in 

vitro studies support a cause-effect relationship, then the threshold serum concentration could 

inform the calculation of the RfD.

Matthew P. Longnecker

As noted in the General Impressions section above, the human studies with data on plasma or 

serum concentrations of PFOA and PFOS, especially for several categories of such levels, could 

be used to estimate dose-response information. However, there are other reasons why the 

human data may not be useful for setting the RfD (see above). Either PK or PBPK models 

might be useful for estimating the dose that human are exposed to; an advantage of a PBPK 

model is that it could incorporate information about routes and timing of exposure. Estimates of 

the contribution of various routes are available (e.g., Haug et al. 2011; Lorber & Egeghy 2011), 

and exposure trends could be assumed and evaluated in sensitivity analyses. Some occupational 

studies had data that allowed an estimate of serum levels, or measured them directly. Several 

reports show estimated exposure based on serum concentrations of PFOA or PFOS (Locissano 

et al. 2013; Lorber & Egeghy 2011; Thompson et al. 2010). With respect to confounding, the 

assessment of how likely this is could be informed by: 1) the correlation of serum concentration 

of PFOA, PFOS, and other compounds of this type in a particular study population (or in a series 

of studies), and 2) whether the other compound(s) has been associated with the particular 

outcome being considered. If the correlation is low or the other compound has not been 

associated with the outcome, concern about confounding may not be strongly justified. Without 

additional consideration of data that address these points, it may be premature to assume 

confounding would be a problem. 

Angela L. Slitt

Strengths of the studies: Several studies, which all demonstrate a positive association between 

serum PFOA and/or PFOS and cholesterol or LDL levels are based on drinking water as a route 

of exposure. These studies are in agreement with Nelson et al., 2010, which was analyzing data 

from the 2003-4 NHANES study. Steenland et al., 2009 (Environ Health Perspect. Jul 2009; 

117(7): 1083–1088) as part of the C8 Health Project collected data on 69,030 subjects with 

findings that serum PFOA was higher for males, those consuming local vegetables, and those 

using well water rather than public water, and lower for those using bottled water. The 

estimated response rate for participants >20 years of age was 81% and mean serum PFOA 
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concentration was 83 ng/l. Subjects were eligible to participate in the C8 Health Project if they 

had consumed drinking water for at least one year before 3 December 2004 supplied by Little 

Hocking Water Association (Ohio), City of Belpre (Ohio), Tuppers Plains Chester Water 

District (Ohio), Village of Pomeroy (Ohio), Lubeck Public Service District (West Virginia), 

Mason County Public Service District (West Virginia), or private water sources within these 

areas that were contaminated with PFOA. Subjects were also eligible if they could document 

that they had either worked in a contaminated water district or went to school there for at least 

one year. From this population, which the route of exposure is considered to be primarily via 

drinking water, serum lipids were analyzed with regard to PFOA levels and a positive 

correlation was observed for all serum lipids except HDL. Frisbee further characterized this 

cohort, analyzing 12, 476 children and adolescents included in the C8 Health Project, finding an 

increase in total cholesterol.

A recent epidemiology study (Fitz-Simon et al., 2013), not included in the current documents, 

described positive associations between PFOA and PFOS in serum LDL cholesterol. This study 

examined a study population that consisted of 560 adults living in parts of Ohio and West 

Virginia where public drinking water had been contaminated with PFOA. They had participated 

in a cross-sectional study in 2005-2006, and were followed up in 2010, by which time exposure 

to PFOA had been substantially reduced. Overall, the findings demonstrate a positive 

association between serum PFOA and PFOS levels and serum and LDL cholesterol.

Weaknesses: The studies did not appear to analyze PFOS or PFOA levels in drinking water from 

the participants analyzed and did not analyze data based on the length of exposure.
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Question 4. Please comment on the transparency and characterization of the 

epidemiological data.

James V. Bruckner

PFOA-specific comments

See comments above.

PFOS-specific comments

The document’s authors have done a good job describing and summarizing the designs and 

findings of the epidemiology studies.

Deborah A. Cory-Slechta

The PFOA document in particular and to some extent the PFOS document present all of the 

epidemiological studies but do not actually evaluate them; there is not a consistent indication of 

individual strengths and limitations of the studies, failures or not to adequately control potential 

confounding variables. Furthermore, there is no ‘power analysis’ type of evaluation, i.e., some 

of these studies included very small sample sizes and thus their power to actually detect effects 

may be limited, and yet they all appear to be weighted basically the same, i.e., studies with very 

small sample sizes with obviously extremely limited power to detect any effects appear to be 

considered the same as those with extremely large sample sizes. Studies with small sample sizes 

that nevertheless do find an effect of PFOA or PFOS actually suggest a robust type of effect. 

The discarding of positive associations in human epidemiological studies because they do not 

produce frank clinical disease seems inappropriate and inconsistent with other EPA documents. 

For example, p. 4-3 in the PFOS document states that only a small number of ALT values were 

outside the normal range making the results difficult to interpret in terms of health. 

Physiological changes that are moving in the wrong direction, even if sub-clinical at the time, 

are still adverse effects. Are actual clinical diagnoses required for an adverse effect? This is 

especially the case given that the ranges of normal across populations are extremely broad. 

The latter also raises the question of the cumulative toxicity of PFOA and PFOS and whether 

any consideration is being given to this. 

Another such example is in the PFOS document, where it actually refers to a statistically 

significant, but not toxicologically significant effect (p.4-38); what does that mean? Also, p. 5-4 

appears to dismiss any changes in thyroid function since no evidence of clinical hypothyroidism 

actually occurred. This whole approach with the human studies seems quite inconsistent with 

the reliance on increased liver weight in the absence of clinical pathology as the endpoint in the 

human studies. 

Jamie C. DeWitt

It is not obviously or abundantly clear how the OW characterized the epidemiological data for 

either PFOA or PFOS. The studies were well-described, but the contribution of particular studies 
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to the overall assessment was not. The results of studies described in the hazard characterization 

section (4.4) need to be better characterized. For example, in the PFOA risk assessment:

 An increase in serum lipids associated with PFOA/PFOS exposure in humans is discussed 

as a risk factor for cardiovascular disease in humans; however, no evidence of increased 

cardiovascular disease has been observed in human populations. Additionally, serum lipids

typically are decreased in animal models after PFOA/PFOS exposure, which is thought to 

be associated with/typical of exposure to agents that activate PPAR. If humans are known 

to respond to PPAR activators (i.e., fibrate drugs), why would the results between humans 

and animal models be discordant? This should be discussed.

 Several epidemiological studies reporting changes in liver enzymes clearly state that the 

clinical relevance of the changes in enzymes is unknown. Therefore, stating that the human 

studies “suggest effects on the liver as indicated by increases in liver enzymes” amounts to a 

mischaracterization of the data.

 No direct evidence of hepatotoxicity has been reported in epidemiological studies. This 

should be discussed.

 More in-depth characterizations are needed for the additional sections of the hazard 

characterization, with the exception of the thyroid section, which was well-described.

For example, in the PFOS risk assessment: Similarly to the PFOA risk assessment, the hazard 

characterization section needs to better discussion differences and similarities between effects 

reported in humans and effects reported in animal models.

Jeffrey W. Fisher

I am not an epidemiologist, but it appears to be adequate. Better characterization of the pros and 

cons of the human analyses and interpretation of the outcomes would be helpful.

William L. Hayton

The characterization of the individual epidemiological studies presented seems to be adequate. 

Public comments have identified the need to distinguish positive and negative associations with 

statistical significance, which seems to be a fair criticism. As noted in the response to Question 

2, there are relevant studies that have not been described in the health-effects documents that 

ought to be considered and this includes some epidemiological studies. Most of the cited 

epidemiological studies have focused on healthy adults – workers exposed occupationally, 

residents of communities with or without contaminated water. These populations might be 

expected to be less sensitive to adverse effects than would early life stages and particular disease 

populations. Studies of potentially more sensitive populations would be desirable. The Frisbee

et al. (2010) study of children 1-11.9 years and adolescents 12-17.9 years showed significant 

positive associations with serum lipid levels. Studies such as this one would be informative.
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Matthew P. Longnecker

Please see the long paragraph above, under General Impressions, and some of the comments in 

response to item #2 above. Another point that the authors may want to consider is that studies 

that examine external exposure in relation to health outcomes may have special advantages in 

the case of PFOA and PFOS. While in general it is considered best to have a measure of 

exposure that is based on a biomarker of internal exposure, this may be problematic for several 

outcomes for PFOA and PFOS, because of the possibility of confounding or reverse causality 

that would not be an issue if an external estimate of exposure were used. For example, in 

Steenland K, Zhao L, Winquist A. A cohort study of workers exposed to PFOA. Occup Environ 

Med. 2014 Jun;71 Suppl 1:A55, when an external estimate of exposure was used for the 

Washington Works employees, no association with elevated cholesterol was found. The Viera 

et al. (2013) results are based on external estimates of exposure, whereas the similar study by 

Barry et al. (2013) are based on serum levels or estimates based on serum levels. The fact that 

association with kidney cancer is present in the Viera study decreases concern that the 

association was due to reverse causality. Steenland et al. 2012 used an external estimate of 

exposure to study cancer mortality and also found an association with kidney cancer. Lundin et 

al. (external estimate of exposure) had no cases of kidney cancer, though their study was also 

small.

Angela L. Slitt

The epidemiology data is well described and a thorough read. The data would be put in better 

context for the reader if there are average serum concentrations or ranges for the studies 

summarized in tables in addition to other key pieces of information.

A recent publication should be included in the document for consideration. Simon N, Fletcher 

T, Luster MI, Steenland K, Calafat AM, Kato K, Armstrong B. Epidemiology. 2013 

Jul;24(4):569-76. doi: 10.1097/EDE.0b013e31829443ee.
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Question 5. The OW has concluded that the cancer classifications for PFOA and PFOS are 

most consistent with respective classifications of suggestive evidence for carcinogenicity as 

described the EPA Guidelines for Carcinogen Risk Assessment (pp. 2-56, 2-57). Please 

comment on the strengths and weaknesses of this classification. 

James V. Bruckner

PFOA-specific comments

I agree with EPA’s choice of “Suggestive Evidence for Carcinogenicity.” Epidemiological 

findings in occupationally-exposed and general populations to date are equivocal. Increases in 

Leydig cell tumors and liver adenomas have been reported in high-dose male rats. Increased 

incidences of pancreatic cell hyperplasia/adenomas and ovarian stromal hyperplasia/adenoma 

have been observed in female rats. More studies are necessary to confirm/expand these findings, 

and to assess carcinogenic potential in other species. Most mutagenicity and genotoxicity assays 

have been negative. Thus, there is some, but not undue cause for concern about the human 

carcinogenic potential of PFOA.

PFOS-specific comments

The document’s authors have adequately and convincingly presented evidence for classifying 

PFOS as “suggestive of carcinogenicity.”

Deborah A. Cory-Slechta

The classification of both PFOA and PFOS evidence for carcinogenicity as suggestive seems 

consistent with the clear limitations in the available data bases. In addition, the animal studies 

are limited to one species and mutagenicity does not occur in response to PFOA.

Jamie C. DeWitt

This classification is appropriate for both PFOA and PFOS given the epidemiological evidence, 

which is somewhat limited for PFOA and quite limited for PFOS. For PFOA, there is an 

association between kidney and testicular cancer, but there are limited data in animal models for 

these cancers and there is uncertainty that the mechanism of PFOA-induced carcinogenicity in 

animal models is applicable to humans. Studies of PFOS have the same limitations, but

epidemiological studies have failed to find an association between PFOS exposure and cancer.

Jeffrey W. Fisher

I did not review the cancer studies for PFOA and PFOS.
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William L. Hayton

The classification of “suggestive” is not unreasonable. The epidemiological studies, while 

showing apparent associations between PFOA exposure and cancer incidence in testicle and 

kidney as well as other tissues, do not provide a cause-effect relationship. However, they 

certainly do raise a concern about the carcinogenicity of the subject substances. Studies in 

animals have demonstrated conclusively that PFOA causes liver cancer in rats but the MOA that 

involves PPAR activation is absent in humans and it has been concluded that PFOA and PFOS 

cannot be carcinogenic in humans via this mechanism.

An EPA SAB panel (2006) consideration of this question resulted in a majority of the panel 

members favoring a classification of “likely to be carcinogenic” for PFOA. Board members 

acknowledged the PPAR MOA argument against causation of cancer in humans, but also found 

evidence that liver cancer in rats administered PFOA may also have had a MOA independent of 

PPAR activation. Recent epidemiological studies have added to the weight of evidence for an 

association between PFOA/PFOS exposure and cancer. Therefore a classification of “likely” is 

also not unreasonable to this reviewer. Lacking expertise in the nuances of applying the EPA’s 

classification scheme, it is difficult for this reviewer to argue in favor of either “suggestive” or 

“likely”.

Matthew P. Longnecker

The classification as “suggestive evidence for carcinogenicity” for both PFOA and PFOS is 

consistent with the guidelines put forth in the EPA Guidelines for Carcinogen Risk Assessment 

(2005). There are few pertinent data, including some suggestive but weak human evidence. 

There is clearly not enough evidence to classify these agents as likely human carcinogens.

Angela L. Slitt

Overall, the assessments for each PFOS and PFOA appear to be consistent with the EPA

Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a). 

Strengths: Both classifications use evidence from human studies as guidance. 

PFOS: The limited data that exist regarding PFOS and cancer were presented, the classification 

for PFOS under the EPA Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005a) is 

currently consistent with the suggestive evidence of carcinogenic potential descriptor. This 

assessment is reasonable, given that it is based on two studies that show a slight increase in 

adenomas that occurred in males and females.

PFOA: There is conflicting evidence regarding PFOA exposure and cancer risk. However, 

several human studies have found associations between PFOA exposure and elevation of cancer 

of the bladder and kidney. This is also supported by a chronic bioassay in rats, which 

demonstrated that PFOA was tumorigenic.
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Question 6. Significant interspecies differences in pharmacokinetics exist for both PFOA 

and PFOS. Adjusting for interspecies differences was an important step in developing 

candidate RfDs given the totality of the human and animal data. Please comment on the 

strengths and weaknesses of the pharmacokinetic model adjustments to accommodate the 

impact of albumin binding and renal tubule transporters in determining average serum 

values.

James V. Bruckner

PFOA-specific comments

The adjustments made to accommodate the influence of albumin binding and saturable renal 

tubular resorption of PFOA seem reasonable. I would defer, however, to someone with more 

experience in providing for these processes in PBPK models.

PFOS-specific comments

The PBPK model adjustments to estimate human equivalent doses appear to be appropriate. I 

defer to someone more qualified on the subject.

Deborah A. Cory-Slechta

This falls outside my area of expertise and therefore no significant comments are provided. 

However, at the face-to-face meeting there was significant discussion regarding the modeling, 

including clarifications from Dr. Wambaugh that were found by those panel members with 

expertise to clarify these issues and these particular issues were considered adequately 

addressed. 

Jamie C. DeWitt

Several PK models have been reported in the literature for these compounds and are relatively 

well described in the documents. The documents assert that the existing PK models do not 

consider the impact of renal tubule transporters and albumin binding; while, many of the 

existing models appropriately predict serum concentrations in humans and other species, but 

they are mostly based on empirical models. Please explain the weaknesses of such empirical 

models.

Additionally, numerous studies for both compounds report serum and tissue concentrations in 

humans and other species, which can be compared to existing models. Both documents present a 

revised model that amounts to a reanalysis of data from studies that report serum concentrations. 

A more thorough discussion of the improvements made by the reanalysis is needed to better 

understand if the improved model adequately estimates or predicts the clearance rate and other 

parameters for which confidence is low. Alternatively, the publication (Wambaugh et al., 2013) 

that thoroughly describes the reanalysis could be referenced.
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Jeffrey W. Fisher

Serum protein binding: Both PFOA and PFOS are highly bound in serum proteins across 

species, thus model adjustments seem trivial for interspecies extrapolation. Steady-state 

conditions can be assumed to estimate the free fraction (e.g., 2% based on paper by Han et al., 

2003 for humans). I did not find a discussion about the half-life of serum proteins, which may 

have some influence on the ‘apparent’ serum half-life of PFOA and PFOS. The estimated 

fraction of free PFOA or PFOS is important for describing urinary and fecal elimination in rats 

(and other species) and the plasma concentrations of total PFOA and PFOS. Thus, the model 

predicts total PFOA and PFOS in serum or plasma, but the free fraction estimates drive the 

gradual clearance of total BPA from plasma or serum by describing clearance of free. 

Renal reabsorption: The renal reabsorption hypothesis involving species specific and sometimes 

gender specific transporters to describe the pharmacokinetic data represents sound judgment. 

This departure from normal allometric scaling is suggestive of active transport processes. Few 

PBPK models explicitly describe transporters with drugs or chemicals, although the field is 

moving in this direction. Thus, the approach used for PFOA and PFOS is adequate, that is, a 

hypothesis was evaluated by employing empirical PK-based kinetic analyses. Because the 

mechanistic details are missing for each species/gender, scaling of this biological phenomenon is 

not possible at this time. This is not a weakness, but represents the state of the science. 

William L. Hayton

A very important strength of the documents is the attempt to deal with the interspecies 

differences in pharmacokinetics so that adverse effects across species are compared on the basis 

of internal, systemic exposure to PFOA and PFOS, instead of basing comparisons on the 

administered mg/kg dosages. PFOA and PFOS have complicated pharmacokinetics that have 

proven difficult to model. While a relatively simple one-compartment model appears adequate 

to analyze single, low doses, this model fails when it is extended to higher doses and repeated 

doses. Nonlinearities appear associated with saturable plasma protein binding and with 

saturation of transporters thought to be involved in the reabsorption of the compounds from 

renal filtrate. 

A weakness of the pharmacokinetic model adjustments is the lack of robustness of the models. 

Despite the extensive efforts of talented pharmacokineticists, development of a model that scales 

across species and handles a range of dosages and a variety of administration routes has proven 

elusive. The two compartment model of Andersen et al. (2006) has formed the basis of the 

model used in the draft documents. The model incorporates saturable resorption of PFOA and 

PFOS from renal tubular filtrate. While protein binding is known to be saturable (fraction free 

increases with concentration), the model uses a species-specific but constant free fraction. 

Model parameter values for mouse, rat and monkey were used to predict reasonably well 

measured serum concentrations after a fixed daily dosing regimen, Tables 5-6 – 5-8 for PFOA 

and 5-8 and 5-10 for PFOS. This agreement between predicted and measured serum 

concentrations gives confidence that the model-calculated AUC values and final serum 

concentrations associated with adverse health effects (or in the case of liver weight, biological 

marker of exposure) are realistic and a basis for estimation of RfD. While the model used 
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appears adequate for the purpose, the model parameters that were used have some markedly 

non-physiological values. (Information subsequently provided at the reviewers meeting 

explained some of the departure from expected physiological values, as discussed in a following 

section.)

Matthew P. Longnecker

For PFOA and PFOA, the MCMC model results (predicted final serum value) were compared to 

the measured final serum values, and the agreement was fairly good. For PFOS, the MCMC 

model results were compared to those from Loccisano et al. (2012b) and were found to be 

similar, which is also reassuring. Because the PBPK models of PFOA and PFOS are empirical, 

and have been shown to give results that agree reasonably well with observed data, the 

adjustments to accommodate the impact of albumin binding and renal tubule transporters are not 

critical. More data on albumin binding and renal tubule transporters might allow improved 

understanding of the pharmacokinetics of these compounds, but may not necessarily cause 

substantial improvements in the empirical predictions from current models.

Angela L. Slitt

The current weakness of the models is that data on species differences in PFOA and PFOA for 

various key transporters is limited and the document is also using mRNA data for various 

transport proteins to explain gender differences in urinary elimination. First, with regard to 

PFOS accumulation in the liver compartment, it is necessary to compare affinity of human 

versus rat for OATp mediated transport. This alone is tricky because of species differences in 

OATps. If PFOS-induced liver effects are related to PFOS accumulation in liver, it is would be 

helpful to understand whether a lower affinity of human OATp1b1 and 1b3 compared to rat 

OATp1a1 predicts lower hepatic PFOS accumulation. More is known about PFOA, but a 

similar argument can be made for PFOA. In addition, more comprehensive, controlled 

assessment of renal transporter affinity for PFOA and PFOS is needed to better model the 

species difference in urinary elimination.

The document often speculates about PFOA or PFOS regulation of transporter expression, but 

some papers cited (Cheng and Klaasen) do not have enough data at the protein level to support 

whether these differences in transporter expression are the drivers of toxicokinetic differences 

between males and females.
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Question 7. Table 5-5 in the PFOA document and Table 5-7 in PFOS document list the 

parameters used for the ORD pharmacokinetic models that provide the final serum and 

AUC values for calculating the internal dose point of departure for the RfD calculation. 

Please comment on the strengths and weaknesses of the selected parameters.

James V. Bruckner

PFOA-specific comments

Despite the complexities and unknowns involved in plasma protein binding and renal tubular 

functions (i.e., glomerular filtration, basolateral tubular excretion and resorption, and apical 

tubular excretion and resorption), it is necessary to: (a) simply model only for saturable tubular 

resorption; and (b) use a range, or distribution of parameter values consistent with existing 

kinetic data. Unfortunately, optimization sometimes results in selection of physiological 

parameters that are not biologically-realistic, or plausible.

PFOS-specific comments

The parameters used in the modeling are biologically plausible.

Deborah A. Cory-Slechta

This falls outside my area of expertise and therefore no significant comments are provided. 

However, at the face-to-face meeting there was significant discussion regarding the modeling, 

including clarifications from Dr. Wambaugh that were found by those panel members with 

expertise to clarify these issues and these particular issues were considered adequately 

addressed. 

One unclear component of Table 5-7 in the PFOA document is the column labeled 

Species/Strain Used for prediction, which in every case is the same as the column labeled 

Species/Strain and is not otherwise adequately explained.

Jamie C. DeWitt

It is not clear that the parameters in Table 5-5 in the PFOA document and Table 5-7 in the PFOS 

document are from the Andersen et al. 2006 PK model or if they are parameters used in the 

reanalysis of the data. This needs to be better explained in both documents. Additionally, all of 

the units in the tables need to be explained and re-checked for accuracy.

Jeffrey W. Fisher

The authors should entertain the calculation of data derived AUC (e.g. Table 5-6) to compare to 

the model derived AUC, just as was done with measurement of total PFOA in serum. This 

works for the animal studies. The choice of using the empirical model over the more recent 

physiological models may be a weakness and our understanding of transporters advance. 

The evolution of chemical-specific PBPK models for use in risk assessment and regulatory 

applications has repeated itself several times. This is, the first empirical non-physiological 

model(s) or PBPK models contain hypotheses generating ideas and later models test some of 
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these hypotheses, especially if additional experimental data become available. In the case of 

PFOA and PFOS, the EPA selected not to use the most recent PBPK models for PFOA and 

PFOS, but instead use a computational empirical based model (Andersen et al. 2006) that was 

the first attempt to quantitatively interpret the kinetics of PFOA and PFOS across species of 

laboratory animals. The authors did publish their model (Wambaugh et al., 2013). The authors 

chose not to use a human model because a lack of information for Bayesian analyses. The 

justification for their extrapolation methods should be stated and the published reference for the 

model should be cited.

Model parameter distributions (Bayesian analyses) appear to be biologically implausible in some 

cases, covering many orders of magnitude. The authors should discuss this issue and check the 

units of model parameters in Tables.

Both model parameters tables need to include a description of what the parameter represents and 

cite a figure. The figures showing the Andersen et al. 2006 model do not show all the model 

parameters and have different nomenclature. 

The Andersen et al. 2006 paper is a critical paper offering a quantitative explanation for the 

PFOA and PFOS kinetic data sets. 

William L. Hayton

In the “Pharmacokinetic Model Approach” sections of the documents, it is not made sufficiently 

clear that the parameter values in Table 5-5 (PFOA) and Table 5-7 (PFOS) were from re-fitting 

the published data, rather than using parameter values from the original literature reports. 

PFOA Table 5-5, p. 5-12

Body Weight and Cardiac Output values are reasonable and typical.

ka values for mouse and monkey seem extremely large; absorption half-lives would be on the 

order of 10 seconds, which is physiologically unrealistic. All of an oral dose would be 

absorbed within a minute, mimicking a rapid i.v. bolus dose. Serum concentration-time 

profiles may not be sensitive to these values, however so they are not disconcerting for the 

intended use of the models. The rat values appear reasonable.

Vcc values appear reasonable. The total steady-state volume of distribution value [Vss = Vcc x 

(1 + Rv2:v1)] compares favorably with one-compartment Vd values for CD1 mouse, but Vss

values for the other columns (species) appear too large, due to the large Rv2:v1 values.

k12 values vary a lot across the columns, suggesting that k12 may be highly correlated with 

another parameter (e.g., Rv2:v1).

Rv2:v1 values also vary a lot across the columns.

Tmaxc values are consistent across the columns; expressed in Gm/hr, they seem very large. For 

example, 2032 Gm/hr (4.91 moles x 414 Gm/mole) for the CD1 mouse. Even on a kg body 

weight basis could mouse renal tubules resorb 2 kg PFOA per hour? This maximum rate of 

resorption must far exceed the rate of filtration of PFOA at the glomerulus. (Clarification at 

the reviewers meeting explained this apparent departure from physiological reality. The 

units had been mis-specified in Tables 5-5 and 5-7. They were in fact micromole per hour 
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and micromolar for Tmaxc and kT instead of molar based. Thus Tmaxc mouse value was 2 

mg/hr, which is physiologically plausible.)

kT values are the concentration in glomerular filtrate that half saturates the resorption 

transporters. Expressed in mg/mL, they seem large, much larger than the urine 

concentration that would be expected; e.g., for CD1 mouse, kT is 15 mg/mL where free 

serum concentrations (Free x Cserum) would be about 0.3 μg/mL with 10 mg/kg in the 

mouse. So the transporter would not become saturated except at extreme doses. The value 

used by Andersen et al. (2006) for monkey was 0.00001 mg/mL. Unit specified in Tables 

5-5 and 5-7 should be M, not M.

Free fraction values measured in vitro are 0.01 or less at low PFOA serum concentrations (Table 

3-1). The Free values for rat seem much higher than the measured values.

Qfilc is defined as a fraction of blood flow (renal or cardiac output?) to the filtrate (bottom of p. 

5-11) but has units of flow in Table 5-5. 

Vfilc values are much smaller than the 0.01 L value used by Andersen et al. (2006), although 

Andersen et al. state that the model output is insensitive to this parameter and that their 

value was assumed.

PFOS Table 5-7, p. 5-15

Body Weight and Cardiac Output values are reasonable and typical.

ka values for female mouse and monkey seem extremely large – see comment above for PFOA.

Vcc values appear reasonable. See comment above for PFOA.

k12 values vary a lot across the columns, suggesting that k12 may be highly correlated with 

another parameter.

Rv2:v1 values appear reasonable and consistent with other reports of Vss values for PFOS.

Tmaxc values are highly variable across the columns and seem much higher than physiological 

reality would allow. See comment above for PFOA.

kT values are physiologically unrealistic and highly variable across columns. See comment 

above for PFOA.

Free fraction values have been measured in vitro and are 0.01 or less at low PFOS serum 

concentrations (Table 3-1, p. 3-3). The Free values in Table 5-7 are consistent with the 

measured values.

Qfilc is defined as a fraction of blood flow (renal or cardiac output?) to the filtrate (bottom of p. 

5-14) but has units of flow in Table 5-7. 

Vfilc values are much smaller than the 0.01 L value used by Andersen et al. (2006), although 

Andersen et al. state that the model output is insensitive to this parameter and that their 

value was assumed.

While the parameter values for the pharmacokinetic models predict reasonable serum 

concentrations that generally agree with measured values (Tables 5-6 – 5-8 for PFOA and 

Tables 5-8 and 5-10 for PFOS), their high interspecies variability suggest that the models may 

be unreliable for prediction of internal exposures after other intake regimens and during a 

depuration phase.

Matthew P. Longnecker

Please see the answer to the previous question.
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Angela L. Slitt

The parameters included appear to be appropriate, but this lies outside of my area of expertise.
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Question 8. The volume of distribution (Vd) and half-life values are critical in the 

derivation of the interspecies uncertainty factor applied in derivation of candidate RfDs

from a NOAEL, LOAEL or a BMDL. The available data for both values are provided in 

Section 3.5.2 and 3.5.3 of both documents. Please comment the strengths and weaknesses of 

the values selected.

James V. Bruckner

PFOA-specific comments

The adult male rat data of Kemper (2003), from which the rat half-life and clearance (CL) were 

obtained, appear to be solid. It is reasonable to select the human half-life of 2.3 years reported 

by Bartell et al. (2010), as their study population included equal numbers of males and females. 

Division of the rat CL by the human CL to yield a value of 219 is fine. I did not examine the 

publication of Bartell et al. (2010) to evaluate their data or methodology used to derive a human 

half-life of 2.3 years. Therefore, I am uncertain about its accuracy.

PFOS-specific comments

I would again defer to someone with more expertise.

Deborah A. Cory-Slechta

This falls outside my area of expertise and therefore no significant comments are provided. 

However, at the face-to-face meeting there was significant discussion regarding the modeling, 

including clarifications from Dr. Wambaugh that were found by those panel members with 

expertise to clarify these issues and these particular issues were considered adequately 

addressed. 

Jamie C. DeWitt

While the overview of the individual studies that calculated Vd and half-life for each compound 

was detailed and complete, the rationale and analysis concerning why particular values were 

selected were insufficient. Additionally, as addressed in Charge Question 6, the rate of 

clearance/elimination likely contributes to the differences in half-life that are not associated with 

differences in the Vd. Therefore, a 3-fold uncertainty factor for species differences in 

pharmacodynamics (UFA) was utilized for both compounds. What was the justification for using 

a UFA of 3? The section on UF application needs a more thorough discussion regarding the 

choice of this value given differences in clearance. If the section on model adjustment (a

suggestion in Charge Question 6) is better described, this comment may no longer be applicable.

Jeffrey W. Fisher

The use of this non-compartmental method should be justified. Why not use a PBPK model? 

Assuming steady state in the humans does allow for calculation a human equivalent serum 

concentration associated with a laboratory animal concentration. In what region of the 

exposure-dose range would nonlinearity occur in humans? Some type of discussion is needed 
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about the assumptions of this methodology and why it was used. I would like to see statements 

about if the NOAEL, LOAEL, and a BMDL doses are in the linear range for kinetics. 

The authors should use the Bayesian analysis for animal studies to inform the UF. Use 

percentiles to explore Vd and half-life to support UF values. I did not see any attempt to use 

distribution information generated from the model beyond the central tendency or mean values. 

Please state why this is the case. It seems that the distribution information generated from the 

Bayesian analysis could be used to support UF development.

William L. Hayton

PFOA-specific comments

For male rat, the Kemper (2003) study appears to be the best source of pharmacokinetic 

parameter values, which were obtained by a model-independent analysis of serum 

concentration-time data from rats that were dosed by oral gavage at dosages of 0.1, 1.0, 5.0 and 

25 mg/kg. In addition, there was a 1.0 mg/kg dosage administered intravenously, and a 0.1 

mg/kg oral gavage dose with an extended sampling time. Each treatment used four animals. 

The CL and t1/2 values appeared to be independent of dosage and route of administration. It 

would therefore be reasonable to average all 6 mean values for each parameter to give an overall mean of 24 determinations. The average (n=24) values for male rat were CL = 0.0209 L/kg/d 

and t1/2 = 7.83 d. These values can be used to calculate a Vd value (t1/2 x CL / ln 2), which is 

0.236 L/kg.

It is not apparent on p. 5-20 why a Vd value of 0.17 was used with half-life to calculate CLrat

when Kemper (2003) reported CL values and not t1/2 values. (At the peer review meeting, it was 

clarified that the data of Kemper (2003) were re-analyzed and as a result the parameter values in 

the health effects documents differ somewhat from those published with the data in the original 

reports.)

The CLhuman value was taken to be 0.00014 L/kg/d. There are no direct measurements of this 

parameter. Thompson et al. (2010) assumed that the intake rate of PFOA for subjects using 

PFOA-contaminated water was 91% of the PFOA in 1.4 L/d of water. This intake rate was used 

along with a PFOA half-life of 2.3 years to calculate a Vd value of 0.17 L/kg. This is the same 

value that was used in the health effects document for the rat (p. 5-20). The Vd values available 

in mouse, rat and monkey are about 0.2 L/kg, so the Vd,human set at 0.17 L/kg is not unreasonable 

but it lacks the certainty of the rat Vd value. 

The health effects document used a t1/2 for PFOA in human of 839.5 d (2.3 years), which seems 

to be toward the low end of the range of values that have been reported. Along with Vd = 0.17 

L/kg one arrives at CLhuman = ln 2 x 0.17 / 839.5 = 0.00014 L/kg/d. 

The ratio CLrat / CLhuman calculated using the mean CLrat from Kemper (2003) would be 0.0209 / 

0.00014 = 149, which is about twice the value calculated on p. 5-21. This difference arises 

from the calculation of CLrat using the Vd,human and a half life of 11.5 d instead of using the CLrat

directly from Kemper (2003). The mean half life from Kemper (2003) was 7.8 d.
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The CLmouse / CLhuman ratio is accurate, using Lou et al. (2009) data. A calculation for monkey is 

not shown.

PFOS-specific comments

Chang et al. (2012) appears to be the best source of pharmacokinetic parameter values for 

mouse, rat and monkey. Butenhoff and Chang (2007) is given as the reference for a 48-day halflife in rat; this is a final report, internal to 3M. The Chang paper gives half-life values for male 

and female Sprague-Dawley rat at 2 mg/kg and 15 mg/kg. The average Vd for the four groups of 

three/group was 0.71 L/kg. This is higher than the 0.23 L/kg value used in the draft document 

(p. 5-23). The 0.71 L/kg value is also higher than values for mouse, monkey and human, which 

are closer to the 0.23 L/kg value used in the draft document. The draft document ought to 

acknowledge this difference; it may be that the value in the 3M report is lower than the 

published value; Chang was a co-author for both sources. The Chang et al. (2012) paper gives 

CLrat values that are 0.0051 L/h/kg for female (similar for 2 and 15 mg/kg doses) and for males, 

0.022 and 0.011 L/h/kg for the 2 and 15 mg/kg doses. A single average value for CLrat would be 

0.011 L/h/kg, about 3 times the value used for the UFA calculation in the draft document. The 

male value is about 2-3 times the female value and it may be appropriate to calculate a different 

UFA value for each sex. Using the single CLrat averaged across two doses and both sexes (0.011 

L/H/kg) would give a CLrat / CLhuman ratio of 0.011 / 0.000081 = 135 and a UFA = 407, 

substantially higher than the value of 123 in Table 5-15.

The UFA values calculated for mouse and monkey appear to be in line with the literature values 

for PFOS CL values in these species.

Matthew P. Longnecker

The PBPK model of Loccisano et al. 2013 (for humans) can be used to calculate a volume of 

distribution for PFOA of 177 ml/kg, which is very close to the value of 170 ml/kg based on 

Thompson et al.’s 2010 one-compartment model . For PFOS, the corresponding value from the 

PBPK is 280 ml/kg, compared with the value of 230 ml/kg used in the Health Effects Document. 

This 22% difference could have an impact on some calculations. (Note: the PBPK model-based 

volumes of distribution were calculated by Marc-Andre Verner of the University of Montreal. 

He had calculated these values in the course of a separate project.) 

For humans, the half-life data all depend on the assumption that ongoing exposure is negligible 

compared to baseline exposure, a reasonable assumption in most of the populations used to 

estimate half-life. While the Seals et al. (2011) gave estimates that were slightly different for 

PFOA in some cases, the methods employed in this study were not as strong as for Bartell et al. 

(2010) or the Burris et al. studies (2000; 2002). The agreement within species for the half-life 

estimates for PFOS are reassuring. The animal data on the half-life of PFOA are relatively 

sparse (2 rat studies that agreed reasonably well, 1 mouse study, 1 monkey study). For PFOA, 

the UFAs and RfD that were calculated based on the half-lives (expressed as clearance) would 

not have been substantially altered by alternate choices for specific values. The same is true for 

PFOS.
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Angela L. Slitt

Strengths of the available data is that for the several species thorough evaluated, the half-life 

values are very consistent. For example, the several human studies cited report a range in 

calculated PFOS half-life in humans to be 4.1-8.67 years, two studies putting monkeys at 110-

132 days, and rat generally has a narrow range with 3 out of 4 values provided ranging from 

39.8-48.2 days for PFOS. An inconsistency is the Chang et al., 2012 describing a half-life of 

females of 66.7 days when in general female rodents may have faster elimination of PFOS.
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Question 9. A variety of endpoints and studies were used to compare points of departure 

and the resultant RfDs for both PFOA and PFOS. In addition, comparisons were provided 

across RfD outcomes based on the model outputs compared to those for the NOAEL, 

LOAEL and BMDL points of departure. The range of candidate RfDs derived from the 

different points of departure is fairly narrow. Please comment on the strengths, weaknesses 

and transparency of this analysis.

James V. Bruckner

PFOA-specific comments

The procedure used to calculate PODs adheres to standard EPA guidelines and policy. The 

presentation of their derivation is clear, concise and transparent. It is certainly interesting that 

the range of PODs and resulting candidate RfDs is so narrow. Nevertheless, as discussed 

previously, I do not agree with their selection.

PFOS-specific comments

See my comments under General Impressions.

Deborah A. Cory-Slechta

While it is the case for both PFOA and PFOS that values from different points of departure are 

fairly narrow, the transparency of the analyses in neither case is clear. There is no rationale 

described even as to why these analyses were done on all of the studies, what was the primary 

study and how others related to that etc., i.e., this presentation does not follow the typical 

presentation format of IRIS documents in either its presentation of rationales and strategies, nor 

in the conclusions that it reaches. In both cases, it is only the single sentence indicating that 

modeling from one particular study will be protective of effects at other studies using higher 

exposures. This section in both documents needs introductory paragraphs that describe the 

specific strategy, choices of studies and the rationales for those choices. 

As noted in response to Charge Question 3, the rationale for discarding the human 

epidemiological studies is not sufficient and requires rationale other than that stated and 

therefore, the question of using the human data remains open. As noted in response to Charge 

Question 1, in this reviewer’s opinion, the increased liver weight can be justified as a departure 

point for assessment of RfDs, but as discussed at the face-to-face meeting, additional text 

supporting this choice is needed. 

Jamie C. DeWitt

This particular section contained inadequate detail on why particular studies were or were not

chosen. For example, immunotoxicity as an endpoint was not chosen for PFOS, based on “in 

vitro measures of immunocompetence on mice may not be relevant to the human experience and 

limited human data from epidemiology studies are inconclusive regarding the immunotoxicity of 

PFOS in humans”; however, the breadth of data from in vitro/ex vivo immunotoxicity studies 

for PFOS were not thoroughly discussed (please see Charge Question #2 for two additional in 

vitro studies).
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For both compounds, an increase in absolute liver weight was selected as an endpoint as it was a 

common effect [sic] in both short and long term studies. However, the toxicological relevance of 

an increase in absolute liver weight was not discussed other than to indicate that it was a sign of 

altered homeostasis. Further, the co-occurrence of increases in absolute liver weight with other 

toxicologically-relevant endpoints (i.e., immunotoxicity and/or reproductive/developmental 

toxicity) is not a toxicologically valid justification for the use of liver weight as an endpoint for 

an RfD. Therefore, the analysis was not sufficiently transparent to deduce its relative strengths 

and weaknesses. Certainly, choosing an endpoint that occurs across species and occurs at 

relatively low doses will likely be protective of exposed humans; however, will it be a 

defensible endpoint? As currently written, the choice of this endpoint for an RfD is not 

adequately defended.

Jeffrey W. Fisher

I did not review the toxicity data.

William L. Hayton

For PFOA, a 10% increase in liver weight was selected as the metric for effect, which was “... 

not made based on toxicity but on the desire to find a common denominator against which to 

evaluate dose-response across studies and justified by the fact that other adverse effects 

accompanied the LOAEL for increased liver weight in some cases.” The lowest serum 

concentration associated with an increase in liver weight was calculated for female mouse to be 

20.33 mg/L (p. 5-16, PFOA document). These data are referenced to DeWitt (2008); this paper 

has only summary information on liver weights, all of which exceeded 20% weight gain, going 

as high as 70%; and it is not apparent in PFOA document how these liver weight gains were 

used to estimate an LOAEL for 10% liver weight gain. 

Many of the animal studies of hazard assessment were conducted under conditions where the 

duration of the exposure was relatively short compared with the half-life, and steady state had 

not been achieved. It is not apparent how the NOAEL and LOAEL values from such studies 

were adjusted to account for the non-steady state situation. For example, the 20.33 mg/L PFOA 

concentration associated with a 10% increase in liver weight (Table 5-9) emanated from a 15 

day drinking water exposure to 0.94 mg/kg/day that resulted in an average serum exposure of 

20.33 mg/L (0 – 29.7 mg/L over 15 d, Tables 5-7, 5-9). For a fixed daily dose, the time to 90% 

steady state for mouse would be about 63 days (3.3 x half life, which was 19 days), and after 15 

days the serum concentration would only be about 15% of its steady-state value. This seems to 

suggest that the RfD would have been over-estimated by a factor of 7, since the 0.94 mg/kg/day 

at steady state would have produced a serum concentration of about 150 mg/L, not 20.33 mg/L. 

This analysis is based upon the behavior expected from one-compartment model 

pharmacokinetics. As discussed on p.5-9 of the PFOA document, the steady-state serum 

concentration of PFOA is achieved in a much shorter time than one-compartment model kinetics 

would predict. Whether the target-site steady-state concentration of PFOA also occurs in a 

much shorter time than one-compartment model kinetics would predict (3.3 x half life) is 

apparently unknown.
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Matthew P. Longnecker

This part of the document seemed especially strong and transparent. The agreement between 

methods was reassuring. The weaknesses and assumptions were well discussed. Please see the 

minor editorial comment on this issue given for Charge Question 1, above.

Angela L. Slitt

The RfD Point of Departure was based on animal studies that include monkey and rat. 
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Question 10. The RfDs for PFOS and PFOA are derived from the modeled steady state 

serum concentrations and their association with effects that include short term and longer 

term exposures with associated diverse effects. The studies considered included effects due 

to exposure durations that ranged from 11 to 182 days, and occur at comparable human 

equivalent dose (HED) levels. The current, draft RfDs do not include an uncertainty factor 

for study duration because of the apparent concordance HEDs despite duration differences. 

Given this pattern of response, is it appropriate to conclude that the candidate RfDs are 

applicable to both short-term and lifetime exposures?

James V. Bruckner

PFOA-specific comments

I do not believe it is appropriate to conclude that the candidate RfDs are applicable to both shortterm and lifetime exposures. Steady-state is apparently achieved in monkeys within 4 - 6 weeks 

(Butenhoff et al., 2002). Steady-state likely takes considerably longer in humans. Thus, RfDs for 

shorter periods of exposure should be based upon results of studies of similar duration.

PFOS-specific comments

I do not believe the candidate RfDs, as calculated, are applicable to different durations of 

exposure.

Deborah A. Cory-Slechta

While initially believing that it was appropriate conclusion for PFOA and PFOS, based on the 

correspondences in RfDs across short and longer term exposure, discussion at the face-to-face 

meeting made clear that this approach is not reasonable and requires additional consideration. 

Jamie C. DeWitt

This approach may be appropriate given the relative similarity of serum concentrations attained 

regardless of study duration, i.e., steady state in serum is attained after a relatively short period 

of exposure. This appears to be consistent across studies with various species of animal models. 

However, the document authors might need to reconsider given what we may or may not know 

about liver hypertrophy. In the Hall et al. (2012) paper on liver hypertrophy (discussed during 

the public meeting), increase in liver weight is an adaptive response that may not be adverse 

UNLESS weight increases >150% over a three month or longer period may. Following this large 

and prolonged increase in weight, the end result may be a hepatocarcinogenic response. 

However, none of the studies contained in the documents indicate that longer term exposures 

increase liver weight to this degree.

Jeffrey W. Fisher

The departure from K=CXT (Haber’s law) should be based on the toxicity endpoints of concern 

and what is known about dose-exposure kinetics/responses for these chemicals and other 

chemicals that target the same endpoint, not that the HED values are comparable. The NAS 
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AEGL committee only considered primary irritation for inhaled chemicals as an endpoint that 

was independent of duration of exposure. There is an SOP if needed for reference. 

The time to steady state should be included in a table for the lab animals. Toxicity studies 

conducted for less than 30 days (perhaps?) are not at steady state for the pharmacokinetics of 

PFOA. Thus the measured serum levels would be different than at steady state. The shorter the 

duration of the toxicity test, the more impact this could have on extrapolation to chronic 

exposures in humans. My personal preference would be to use PBPK models for all species and 

consider only long term exposures for extrapolation to humans.

William L. Hayton

This depends in part on how quickly the PFOA/PFOS concentrations at sites of toxicity come to 

steady state. Since the Vd for these chemicals is small (~ 0.3 L/kg) it seems likely that the 

concentrations in tissues rise in pseudo equilibrium with the rise in serum concentration. That 

said, the half lives are relatively long due to the very small clearance (t1/2 = ln2 x Vd / CL). If 

one-compartment kinetics apply, then a guideline for time to 90% steady state is 3.3 t1/2. For 

studies that expose animals for a period of time shorter than 3.3 t1/2, the serum concentration 

would not be at steady state and the internal systemic exposure (serum concentration) would be 

less than what it would be if the exposure were longer than 3.3 t1/2. This effect would seem to 

lead to overestimation of the intake rate that was associated with a particular internal exposure 

and associated biological endpoint. For example, the t1/2 of PFOS in mouse is about 36 days and 

3.3 t1/2 is 120 days. Consider a 28-day exposure using a fixed daily dose that produced an 

LOAEL of “X” mg/kg/day. On Day 28, the body level would only be 42% of the steady state 

level, and the average body level over the 28-day period would be about 21% (approximating 

the increase as linear and not exponential). The true LOAEL would be 0.21 “X” mg/kg/day; i.e., 

intake of 0.21 “X” mg/kg/day would produce a body level at steady state that was the same as 

the average body level produced by X mg/kg/day administered over 28 days. The time to 90% 

steady state for a fixed intake rate is quite long; from the literature in the health effects 

documents, the times in the following table were calculated. From this line of reasoning, 

exposure times less than two half-lives begin to significantly overestimate intake rates 

associated with particular endpoints. This analysis is based upon the behavior expected from 

one-compartment model pharmacokinetics. As discussed on p.5-9 of the PFOA document, the 

steady-state serum concentration of PFOA is achieved in a much shorter time than onecompartment model kinetics would predict. Whether the target-site steady-state concentration 

of PFOA also occurs in a much shorter time than one-compartment model kinetics would predict 

(3.3 x half life) is apparently unknown.
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CL Vd t1/2

Time to 90%

steady state

[mL/d/kg] [mL/kg] [d] [d]

Species PFOA PFOS PFOA PFOS PFOA PFOS PFOA PFOS

Mouse 6.6 5 180 265 19 36 63 120

Rat - Male 23 16 273 947 8.4 40 28 92

Rat - Female 776 5.2 150 476 0.13 66 0.43 218

Monkey 6.3 1.4 190 238 27 121 89 400

Human 0.085 0.08 170 230 1378 2000 12.5 yr 18 yr

In addition, this line of reasoning may be incorrect if the assumption of one-compartment 

kinetics is incorrect. For multi-compartment models the serum concentration and target 

organ/tissue could come to their pseudo steady state levels relatively quickly while slowly 

equilibrating (deep) sites slowly approached steady state. Simulation with PBPK models for 

PFOS and PFOA may help answer this question.

Associated with the uncertainty introduced by exposures that were shorter than the time to 

achieve steady-state concentration at the target site is the exposure time required for the adverse 

effect to be expressed. While some adverse effects may occur immediately and directly in 

proportion to the concentration of PFOA or PFOS at the target site, other adverse effects may be 

slow to become manifest. These “indirect adverse response” behaviors are well known in the 

drug action arena; e.g., certain antidepressant drugs require several weeks exposure to the target 

site before the effect of the drug appears. This lag time is not associated with pharmacokinetics 

(time to steady state) but with indirect-response pharmacodynamics. It could be argued that 

uncertainty factors are needed for both pharmacokinetics (pre-steady state condition) and 

pharmacodynamics (or toxicodynamics) to account for possible indirect response behavior.

Matthew P. Longnecker

EPA might want to consider using an uncertainty factor for duration, for two reasons. First, the 

monkey data for PFOS used for the point of departure were from a study where the duration of 

exposure was relatively short-term relative to the half-life, and it appeared that duration of dose 

affected liver and other adverse outcomes detected at higher doses, and no monkey data were 

used in the POD for PFOA. Second, questions raised by Drs. Hayton and Fisher at the peerreview meeting made me less comfortable with the calculations that used average serum 

concentration derived from the AUC and duration of dosing to compare with humans, who are 

more likely to be near steady-state. 

Angela L. Slitt

Yes, but this lies outside of my area of expertise.
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Question 11. In addition to using the average serum values from animal studies to calculate 

internal doses for humans, the animal to human extrapolation can be accomplished by 

dividing animal average serum values by the human to animal clearance ratios to project a 

human average serum point of departure in units of mg/L serum. Please provide 

recommendations for applying uncertainty factors to the extrapolated average human 

serum values to determine serum-based thresholds that are protective for humans. A 

NOAEL expressed in average human serum units would be useful in interpreting NHANES 

population monitoring data.

James V. Bruckner

PFOA-specific comments

No comment.

PFOS-specific comments

No comment.

Deborah A. Cory-Slechta

In initial response to charge questions, I found it difficult to understand specifically what this 

charge question was asking for a response to: Does this refer to the data in Table 5-10 for 

PFOA? Wouldn’t you include animal to human UF values at the least. Since the data for the 

studies listed in the Table is not clear as to their duration (columns are needed for this 

information, or add to the Study box), it is not clear whether a UF for study duration is 

warranted. It is not clear how sex differences are being accommodated in any of these.

At the face-to-face meeting, however, with some additional input from EPA, it was clear to all 

that there was no need to do such derivations from animal to human, which could instead be 

derived directly from the human data and thus presumably this is no longer an issue.

Jamie C. DeWitt

Would this approach take into account differences between animal studies that have a defined 

exposure duration and data from NHANES, where exposure duration is assumed to be 

continuous (although it may not be), if exposure duration does not appear significantly impact 

serum concentrations? Additionally, how would the half-life estimations from the Seals et al. 

(2011) study, which contained two half-life estimations based on concentration and time, impact 

this approach?

Jeffrey W. Fisher

Again, is the system linear in the exposure/dose ranges of interest? I would try to determine an 

UF by exploring a range of predicted human serum levels. Attempt to use 5,50, and 95% for 

animal serum concentrations with a 5,50, and 95% CL values in the animals and for the human 

perhaps use two CL values representing a high and low. The idea is to use as much information 
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as you can to determine the possible range of values. This will help guide the selection of

uncertainty values. 

William L. Hayton

This calculation is equivalent to dividing the animal dosage by the CLhuman, assuming that the 

animal serum concentration is at steady state (Css,animal) maintained by a constant dose rate (DR). 

Css,animal / CLhuman  CLanimal = CLanimal * Css,animal / CLhuman = DR / CLhuman

This calculation would give the steady-state serum concentration in human that would be 

produced by the animal dose rate. (I will have to study this to understand the question; the 

calculation does not make sense to me.)

At the peer review meeting, the aim of this calculation was clarified. Authors desired a way to 

calculate a steady-state serum concentration (Css,human) that would result from the human 

equivalent dose rate (HED) administered until steady state. The appropriate calculation would 

be:

Css,human = HED / CLhuman

Matthew P. Longnecker

The proposed division by animal clearance ratios does not make sense to me. The average 

serum values from animal studies is already taking pharmacokinetic variability in blood levels 

during the observation period into account, and human blood levels will be relatively constant. 

Thus, it would make sense to directly compare the POD estimated average serum concentrations 

from animal models to the blood levels in NHANES. With respect to uncertainty factors that 

would be need consideration for this approach, it seems that UFH, UFL (For LOAEL and 

HEDLOAEL), UFD, and the component of UFA that takes pharmacodynamics into account would 

all still be applicable. 

Angela L. Slitt

This is outside of my area of expertise.
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Question 12. Please describe any suggestions you have for improving the clarity, 

organization, and/or transparency of the draft documents.

James V. Bruckner

PFOA and PFOS-specific questions

See specific observations.

Deborah A. Cory-Slechta

While the EPA authors are aware of updates in the IRIS process, it might be very helpful to look 

at some of the new documents coming through that process for guidance as to the levels of 

critique and evaluation that are now included in these documents. They also include an 

introductory chapter focused specifically on the literature searches and literature that is included 

vs. excluded.

The Executive summary does not provide sufficient rationale and descriptions to lead a reader 

through the steps to what is concluded and reads more like an abstract than an Executive 

Summary. Since this may be the only section read by many reviewers, it is important that it 

provide a succinct journey through the process. Here again, the new IRIS documents (e.g., 

trimethylbenzene) could provide a useful template. 

Chapters 3, 4 and 5 could each benefit from an opening paragraph describing what the section’s 

goals are, and integration and conclusion sections at the end that establish the basis for the 

presentation in Chapter 5. Currently the Hazard Identification studies generally treat all studies 

as of equal strength/power, which is certainly not the case. These chapters should present that 

kind of critical and transparent assessment as it ultimately serves as the basis for decisions that 

are made. 

The inclusion of sections on in Vitro data did not ultimately seem particularly relevant in the 

outcome for these compounds and could be significantly shortened to add more to Chapter 4 on 

study strengths and weaknesses. However, where pertinent, it would probably be more useful to 

break that section up and insert test where it follows an in vivo discussion. 

Tables could be considerably improved and made far more useful to the reader for comparative 

assessments. As of now, they require going back and forth to the text to capture additional 

details of the studies, e.g., sample sizes, species etc. and could benefit the reader significantly 

with those additions. For the human assessments, it is equally important to include these details 

in the chapter as well as a column of study strengths and limitations. 

While charge questions ask whether the appropriate studies were chosen as key studies, this 

reviewer does not remember that that term was even used in the documents, certainly no explicit 

mention was made as to which studies were considered key studies. This would seem to be a 

section that should be included in Chapter 4 more explicitly. Chapter 5 of both documents, more 

so PFOA, are confusing as almost all studies are subjected to modeling, for reasons that are 
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never presented in sufficient detail and simply followed by statements that a selected study (not 

really well presented in Chapter 4 as a selected study) will protect against other adverse effects. 

Jamie C. DeWitt

The documents lack a critical analysis of differences between findings of epidemiological 

studies and findings of animal models. As stated in the comments to Charge Question #3, what 

is particularly valuable about the PFOA/PFOS database is that it is relatively extensive in that it 

includes data not only from occupationally-exposed humans, but from people highly exposed to 

environmental concentrations of PFOA/PFOS, and from people in the general population who 

have detectable concentrations of these compounds.

Critical to this analysis is a discussion of concordance and lack of concordance between human 

data and animal model data. For example, immunotoxicological findings appear to be consistent 

between humans and rodent models whereas serum lipids are not. How do these differences 

impact the overall confidence in the database and derivation of the RfD?

All of the sections related to the PK models developed by ORD need additional information for 

clarity and transparency. As written, it is not clear that the PK values presented throughout the 

document actually represent a reanalysis of existing data from studies that reported serum 

concentrations. The Wambaugh et al. (2013) study could be referenced to shorten this exercise 

as this publication provides details on the reanalysis of existing data.

Justifications for choosing or not choosing particular values or endpoints need to be more 

thoroughly detailed throughout both documents, especially for endpoints that appear to occur in 

both experimental animal models and exposed humans (i.e., thyroid hormone disruption and 

immunotoxicity).

Jeffrey W. Fisher

These documents represent an enormous undertaking to describe studies with PFOA and PFOS. 

Keep the same writing style for reporting studies. This was very good. A synthesis of the most 

important studies is needed and some statements about why other studies are not used by EPA. It 

is easy to get lost in the document because of its size, but if there was an analysis or synthesis 

section for the key toxicity studies and another for PK modeling rationale, it would help readers. 

William L. Hayton

It would be helpful to use one set of units for test article amount and concentration. The draft 

documents use ng/mL, g/mL, g/L, ppb, ppm, and M for PFOA/PFOS concentration in water, 

diet, and serum. It would be more straightforward to use one concentration term, preferably 

ng/mL, and perhaps g/mL in addition as necessary. But making comparisons among ng/mL, 

ppm, and M is a distraction.

In Section 3 of both documents, it would be helpful to include a summary table of primary 

pharmacokinetic parameter values for the species included in this section. Tables 3-17 – 3-20 in 
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the PFOS draft document are a good start. In the PFOA document, Table 3-23 lacks CL values, 

and Tables 3-24 and 3-25 lack Vd values. For the pharmacokinetic model analyses presented, 

primary parameters values could be limited to CL, Vdss, and half life (see table in response to 

question 10). The CL and Vdss values should be normalized to body weight. Where there are 

multiple models for a species, there should be separate entries for each study. Where there are 

multiple dosages for a species, there should be separate entries for each dosage. For the PBPK 

models, Vdss values are not available and therefore should not be included. Such a table would 

be helpful to show consistency or lack thereof among studies and would facilitate selection of 

the best available values for CL and Vdss for use in a human PK model that would predict 

steady-state serum concentration from intake (dosing) rate and, conversely, predict intake rate 

from steady-state serum concentration. These predictions are probably the primary reason to 

include a pharmacokinetics section in the documents.

The pharmacokinetic sections of both documents lack example graphs of serum concentrationtime data on semilog coordinates for PFOA and PFOS. Inclusion of a few representative graphs 

would help the reader evaluate the consistency of the data used to generate the pharmacokinetic 

parameter values, and where model-based equations have been fitted to the data, the scatter of 

the measured concentrations around the model-predicted line would be informative as to the 

goodness of fit and the validity of the model and its parameters.

Matthew P. Longnecker

I can see advantages to treating this more like a systematic review of the literature, where the 

specific search algorithm for included articles is laid out, as are the range of dates of publication 

to be considered, and any other selection criteria applied for articles considered. In these 

documents, while the review of earlier literature appears to be comprehensive, after some point 

there must have been some decision making about which of the more recent articles to include.

The EPA has many guidelines about how data like these are to be evaluated, yet in the document 

few, if any, references to these guidelines were cited. Because so many guidelines exist, it could 

help readers if the authors cited specific places in critical documents that provide guidance for 

specific decisions. 

Angela L. Slitt

The document reads very well. Although not included in the RfD determination, including a 

table of the observed human effects along with serum concentrations in Section 5.0 would put 

Tables 5-2 and 5-3 into context. Some sort of layman explanation to help understand why only 

non-human exposures are being included would be helpful to the general public. 
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V. SPECIFIC OBSERVATIONS

James V. Bruckner

Specific Observations for Health Effects Document for Perfluorooctanoic Acid

Page Paragraph Comment or Question

3-11 5, lines 7-11 It is stated that the PFOA concentration in bile increased by a factor 

of 12.5 with the increase in PFOA dose from 12.5 to 25 umol/kg in 

wild-type mice and 19.5 in PPARα-null mice. These factors should 

be 2.8 for wild-type and 6.1 for PPARα-null mice. The document’s 

authors may want to rethink their interpretation of the data. The 

results for the wild-type mice do suggest saturation of transport from 

liver to bile ducts, but the PPARα-null results do not, indicating a 

role for PPARα in this process.

In contrast to the foregoing, the findings of Lou et al. (2009) (p. 3-

11, pgr. 2) indicate their highest dose of PFOA is cleared from the 

blood of mice more rapidly than lower doses, suggesting saturation 

of hepatic and/or renal reuptake transporters. 

What is the relative importance of biliary and renal elimination of 

PFOA?

3-12 3, lines 2-4 It should also be stated that upregulation of MRP3&4 and the OATs 

may be beneficial, due to increased biliary excretion of bile acids, 

bilirubin, conjugated metabolites of toxic chemicals, etc.

3-14 1 & 2 It might be stated that the findings of Hinderliter (2004) support 

those of Han (2003), in regards to development of female rats.

3-14& 

3-15

It is problematic to try to compare values in Table 3-14 with values 

referred to at the end of the second paragraph on p. 3-17. Whole pup 

and pup serum PFOA levels decrease between PND 1&18 for each 

dosage in the table. It would be preferable to include another table 

showing the PFOA levels with body weight taken into account.

Table 3 – 14 and other tables should include the species in the title. It 

would also be helpful to include some details of the experimental 

protocol in the footnotes.

3-20 It would be useful at the end of this section (Distribution During 

Pregnancy and Lactation) to summarize the primary findings, or 

conclusions that can be drawn from the data that were presented.

3-23 4, line 2 It should be emphasized that urinary excretion of PFOA was 

substantially higher in female than male rats.

3-28 2, line 4 Replace “receptors” with “transporters”.

3-28 6 Did 10 uM PFOA inhbit PAH and estrone uptake to a greater extent 

than 100 uM PFOA?

3-29 3 & 4 It is not clear what Yang et al. (2009) concluded about the role of 

OATp1a1 in the uptake of PFOA from glomerular filtrate.

3-32 3 & 4 These two summary paragraphs are very helpful.

3-37 1, line 1 Should “adsorption” be “absorption”?
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Specific Observations for Health Effects Document for Perfluorooctanoic Acid

Page Paragraph Comment or Question

4-7 & 

4-9

Tables 

4-1 & 4-2

Tables 4-1 and 4-2 are quite helpful in integrating the results of 

studies of occupationally-exposed populations.

4-13 A concluding sentence should be added to summarize the findings of 

a lack of association of PFOA with diabetes, metabolic syndrome, 

etc.

4-32 The NOAEL and/or LOAEL for this study should be stated at the 

end of the paragraph.

4-34 2 Is the LOAEL for liver effects 1 ppm in the study of Loveless et al. 

(2008)?

4-38 1 Include the meaning of the abbreviation “mPPARα”.

4-39 Inclusion of the table for Minata et al. (2010) would be useful to help 

readers better comprehend the study findings.

4-40 A table of short-term LOAELs and NOAELs should be added here 

or in Section 5.

4-47 2 It is hard to believe, judging from the slight difference in mean 

values and their standard deviations, that absolute and relative liver 

weights are significantly higher than controls in the 1 mg/kg/day 

group.

4-67 2, line 5 Insert “absolute” before “liver weight”.

4-69 1, lines 

1 & 2

It might be worthwhile to point out that the actual study by 

Butenhoff et al. was conducted prior to 2004.

4-73 A summary sentence (or two) should be added at the end of the 

Mutagenicity and Genotoxicity section.

4-83 A summary paragraph should be included at the end of the 

Immunotoxicity section.

4-101 1, line 14 Insert the word “some” before “occupational studies”.

In order to present a more balanced perspective of findings in 

occupational studies, the following sentences could be added at the 

end of the paragraph: “Olson and Zobel (2007) examined groups of 

male workers at 3 fluorochemical production facilities. Serum PFOA 

concentrations were not associated with total cholesterol, LDL or 

HDL in workers at these facilities.”

4-102 4 It should be stated that the increases in serum enzyme activity in 

workers were quite modest/small.

The following sentence should be added at the end of the paragraph: 

“Emmett et al. (2006), however, found no association between serum 

PFOA and liver or renal enzymes”.

4-103 2, line 2 Change “apoptotic or necrotic damage of” to “apoptosis or necrosis 

of”. Apoptosis and necrosis are types of cell death, not 

damage/injury.

4-103 3, line 1 It is true that PFOA may interfere with the biliary excretion of other 

compounds that are transported by the same transporters. 

Upregulation of the genes for these transporters, however, may be 

beneficial in that the excretion of bile acids, bilirubin and conjugates 
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Specific Observations for Health Effects Document for Perfluorooctanoic Acid

Page Paragraph Comment or Question

of toxic chemicals/metabolites may be hastened.

4-103 4, line 2 I would avoid the word “critical” until the section on Dose-Response 

Assessment.

4-103 4 Increases in absolute and relative liver weights were dose-dependent 

(Cui et al., 2009; Elcombe et al., 2010; Wolf et al., 2008a)

4-103 5 It is important to distinguish between effects of PFOA on rough and 

smooth endoplasmic reticulum (RER and SER). RER content was 

diminished, but there was a proliferation of SER.

4-104 2, line 5 This last line should be amended to read “that PFOA has some 

effects of unknown toxicological significance that appear to be 

independent of PPARα activation.

4-104 4, line 3-5 The meaning of the sentence is not clear. Has something been 

omitted?

4-105 3, line 3 Add “of offspring” between “abilities” and “at 6 and 18”.

Include Fei and Olsen’s (2011) finding of no association between 

prenatal PFOA exposure and behavioral or coordination problems in 

children at age 7.

4-109 3 The species (i.e., mice) studied by White et al. (2009) and by Wolf et 

al. (2007) should be stated.

4-111 4, line 2 Replace “examine” with “determine whether there was”.

4-112 2, lines 

1 & 2

The first sentence is misleading and should be rewritten.

Butenhoff et al. (2012) did not see a significant increase in liver 

adenomas or carcinomas. 

Biegel et al. (2001) reported an increased incidence of hepatic 

adenoma but not carcinoma.

4-112 2, line 13 What is hepatic cystoid degeneration?

4-114 2, line 3 Insert “decreased” before “apoptosis”.

4-115 5, line 2 What is meant by “PRAR exposures”?

4-116 There is no mention of PFOA-induced changes in expression of 

genes (e.g., cell cycle control, peroxisomes biogenesis, 

inflammation, etc.) that are PRARα-dependent.

There is no mention of the role of PRARα or peroxisomes in 

oxidative injury and carcinogenesis.

4-120 1, lines 

11 & 12

Insert “these” between “that” and “hormones”.

4-121 3 It would be helpful to give the PFOA dosages of White et al. (2007) 

and one or two other studies, so the reader will have some idea of the 

magnitude of PFOA exposure required to alter mammary gland 

development.

5-1 RfD: Omit the word “wealth” from the bullet pertaining to 

epidemiology studies. There have been relatively few epidemiology 

studies of PFOA-exposed populations.
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Specific Observations for Health Effects Document for Perfluorooctanoic Acid

Page Paragraph Comment or Question

5-2 1, lines 2-6 Another obvious point should be made here, mainly that 

occupational exposures result in much higher plasma PFOA levels 

and body burdens than do environmental exposures. Thus, it would 

be anticipated that adverse effects would be more apparent in PFOA 

facility workers.

5-2 1, line 5 Include the words “in some instances” between the words “shown” 

and “between”. Otherwise, it appears from this paragraph the serum 

PFOA concentrations are consistently/usually associated with the 

various maladies.

5-2 3, line 8 Insert “failure to attain” between the words “with” and 

“developmental”.

5-7 2, line 4 Insert the word “rodent” between “between” and “species”

5-19 1, line 1 Insert “from some studies” between “data” and “have”.

Specific Observations for Health Effects Document for Perfluorooctane Sulfonate

Page Paragraph Comment or Question

3-2 5, lines 

2 & 3

It is stated here that “the ratio of PFOS identified in serum and liver 

tissue are similar”. Do the authors mean that PFOS concentrations in 

the serum and liver are similar?

3-2 6 How does PFOS distribute between plasma lipoproteins and 

proteins/albumin?

3-5 1, lines 

9& 10

How much lower were milk PFOS levels than serum levels?

3-7 1, line 2 Oral and gavage are redundant.

3-16 Figure 3-1 This figure nicely illustrates relative PFOS levels in dams and 

fetuses/pups over time.

3-19 1,line 3 Insert “groups” between “day” and “on”.

3-21 1, line 10 Substitute “longer” for “slower”.

3-23 2 It is not clear who conducted the human PBPK modeling nor which 

model they used.

4-21 2, lines 1-3 What did the 2nd monkey die from?

4-26 3, line 3 The word “concentrations” should be replaced by “doses”.

4-39 1 Does an increase in motor activity on PND 17, but no such effect on 

PND 13, 21 or 61, constitute a toxicologically-significant effect?

4-56 2, lines 

1 & 2

It is stated that “taken together, these studies suggest a PPARαindependent mechanism...” Of the studies reviewed to this point in 

the document, only that of Abbott et al. (2009) supports this premise. 

Qazi et al. (2009), Rosen et al. (2010) and other groups of 

investigators have reported other PPARα-independent effects of 

PFOS.

4-60 2, lines 

15-17

Is oxidative damage likely to be operative to a significant extent at 

lower PFOS doses?
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Specific Observations for Health Effects Document for Perfluorooctane Sulfonate

Page Paragraph Comment or Question

4-61 2, line 4 What is meant by “The concentration...”?

4-61 4, line 2 Change “dose of exposure is” to “levels of exposure are”.

4-62 1, lines 

2 & 3

What did Olsen et al. (2003) find correlation between?

4-62 3, lines 

4 & 5

Identify the species (i.e., rat) studied by Chang et al. (2009) and 

Stein et al. (2012).

4-62 5 The liver of rats and monkeys was examined for histopathological 

changes, but the histological changes should not be considered 

lesions nor pathological.

4-68 4, lines 

5 & 6

The elevated incidence of hepatocellular adenomas/ carcinomas was 

almost entirely due to adenomas. Only 1 of 60 high-dose female rats 

exhibited carcinoma.

4-69 5, lines 

3 & 4

It is stated here that there was no increase in hepatocellular 

proliferation detected in the subchronic study of Seacat et al. (2003).

It is stated previously on page 4-69 that “the data for PFOS are 

adequate to support some but not all key events...” I assume that cell 

proliferation is thought to be a missing event. Seacat et al. (2003) 

reported that the average hepatocyte proliferation index was not 

increased, but that some animals exhibited mild increases. It is clear 

in the current document that PFOS is not as potent a PPARα inducer 

as PFOA.

5-4 2 & 5, line 7 Again the terms “histopathological” and “lesions” are misnomers.

5-4 3, line 9 What is meant by a “biologically significant decrease in survival” at 

0.8 mg/kg?
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Deborah A. Cory-Slechta

Specific Observations for Health Effects Document for Perfluorooctanoic Acid

Page Paragraph Comment or Question

Chapter 

5

The text of Chapter 5 in the PFOA document (and other places) 

continues to state that a 10% increase in liver weight would not be an 

adverse effect, but merely a denominator for loss of homeostasis. On 

what basis was this conclusion derived? What is the support for this 

statement? It appears that benchmark dosing was applied to studies that 

had liver weight as the common denominator, but does this 

accommodate the lowest NOAELS and LOAELS observed for any 

endpoint in the long duration studies? Use of just studies with the 

common denominator because they provide replication ignores the fact 

that some other effect may occur at lower levels but simply hasn’t been 

evaluated in as many studies as focused on PPARa-based targets. If 

this isn’t the case, then the text should clearly address this.

5-7 2 States that the BMDL10 values all fall below the experimental 

LOAELs. So, what does that mean, is there some conclusion that is 

supposed to be reached from this? IF so, please state it.

5-13 1 States “Generally these values were similar.” What does similar 

mean? What is acceptable in this context?

5-16 3 States that the half-life value Bartell et al. (2010) was sued for half-life 

because it seemed more relevant to scenarios where exposure result 

from ingestion of contaminated drinking water by members of the 

general population. 

This rationale does not appear to consider the potential different 

strengths and weaknesses of the other potential studies. Is it necessarily 

the case that general population is more important than occupational 

studies? 

The rationale needs to be described in greater detail. Virtually no 

rationale is provided for the choice of the Thompson et al. (2010) study 

for a volume of distribution value.
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Specific Observations for Health Effects Document for Perfluorooctane Sulfonate

Page Paragraph Comment or Question

1-1 4 There are similar concerns for the PFOS document. Loose 

terminology should be eliminated, e.g., what is a ‘finding of note’ 

as used in the executive summary for PFOS.

Executive 

summary

The PFOS executive summary is of limited utility; for many 

readers this may be as much of the document as they read; as 

currently written it is not clear or transparent nor does it 

sufficiently explain how it arrived at an RfD.

3-3 Table 3-1 Couldn’t a sentence essentially substitute for Table 3-1; it really 

isn’t useful.

3-25 1 Loose terminology should be eliminated, e.g., what is “generally 

good”

3-26 Figure 3-7 Figure 3-7 has no explanation of what is the black vs. gray line.

All tables There is a need to improve all of the tables; they should always 

include study name/year, sample size and exposure duration 

information on them; this would make all of the comparisons 

easier to evaluate and not require the reader to continue to go back 

and forth to the text. 

4-4 Table 4-1 For example, table 4-1 has only study name and year, but what 

really matters is also exposure duration and sample sizes, because 

the comparisons of outcomes in the Table depend upon the power 

of the study to detect effects at the very least.

4-9 Table 4-2 The same comment applies to Table 4-2 and any others with this 

intended purpose.

4-11 Table 4-3 Table 4-3 needs sample sizes, exposure duration etc. 

4-24 Table 4-7 Tables that summarize a significant amount of data from a single 

study (e.g., 4-7) should include the study authors and year in the 

Table title so it doesn’t have to be searched for.

In several instances in the PFOS document, adverse effects early 

that appear to be reversed at a later age are discounted with the 

suggestion that they therefore do not matter; given our increasing 

understanding of the importance of early changes in terms of 

epigenetic changes, this is no longer appropriate and in fact, 

misleading.

5-16 Table 5-8 What do the parentheses signify?

5-17 Table 5-9 What do the parentheses signify?

Jamie C. DeWitt

Specific Observations for Health Effects Document for Perfluorooctanoic Acid

Page Paragraph Comment or Question

4-102 2 & 3 DeWitt et al. 2009 also included data on triglyceride levels in C57BL/6 

mice exposed to PFOA for 15 days; triglyceride levels were doseresponsively decreased.
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Jeffrey W. Fisher

No specific observations. 

William L. Hayton

Specific Observations for Health Effects Document for Perfluorooctanoic acid

Page Paragraph Comment or Question

1-2 Last, line 5 Delete “in”; should read “... in rats was analyzed ...”

3-2 1, lines 6-8 Assumption that fecal excretion represented unabsorbed PFOA is 

problematic; suggest rephrasing this sentence.

3-3 Table 3-1 Protein binding is important for PK modeling, where the fraction 

unbound (fup) is the important parameter, not the fraction bound. 

Suggest listing fup values rather than percent bound.

3-6 Last, line 3 “concentration” should be “dose rate”

3-8 2, line 4 In addition to liver, kidney, and blood, other tissues are prominent. 

E.G., Table 42 of Kemper shows that in male at 1 mg/kg, t=Tmax, 

GI tract, GI contents, muscle, bone and skin contained a greater 

percentage of dose than did the kidney.

3-8 2, line 8 “Blood to kidney” should be “kidney to blood”

3-8 2, line 10-11 In Kemper, Tables 44-45, blood to kidney ratios are not 10 or higher 

in males.

3-8 2 This paragraph reports both percent of dose found in tissues, and 

concentrations found in tissues. But Tables 3-4 and 3-5 present only 

the former. When presenting tissue concentrations, please make it 

clear that those data are not shown.

3-18 Last, line 3 “were” is repeated.

3-19 1, line 1 Technically incorrect to say that the level peaked at PND7; that was 

the earliest sample time. The peak may have occurred before PND7. 

3-19 Table 3-15 The last dose was on GD17; strange that at 1 and 3 mg/kg the serum 

concentration increases from PND7 to PND14.

3-22 4 Last sentence is garbled. 

3-22 4, 5 Agree that biliary elimination is possible, but it could be that 

chloestyramine binds PFOA and PFOS in the GI tract lumen after 

they passively diffuse from the blood to the gut. There seems to be 

no direct evidence of biliary elimination, e.g., bile collected from 

treated animals.

3-23 Last, line 4 Should be Table 3-18.

3-34 Last, line 9 Should be “nonlinear least squares”

3-35 Table 3-23 Column 2, “Adsorption” should be “Absorption”

3-38

3-38

2

Figure 3-7

The arrow from Gut to Liver appears to point in the wrong direction; 

it should represent biliary excretion of PFOA from Liver to Gut.

3-43 Last line “... indicating the absence of active excretion in human kidneys.” 

This does not follow from the observation of renal clearance being 

about 0.001% of GFR. A plasma free fraction of 0.001 would 
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Specific Observations for Health Effects Document for Perfluorooctanoic acid

Page Paragraph Comment or Question

account for the CLr being 0.1% of GFR, and passive tubular 

reabsorption would make it 0.001% of GFR since urine flow is about 

1% of GFR. Other scenarios are possible that do not invoke the 

absence or presence of active excretion.

3-44 Table 3-24 Should report all data values with three significant figures. For 

example, Lambda z values have only one sig. fig., while T1/2 values 

have 5-6.

3-46 2 This reviewer does not follow the derivation and use of a value for 

volume of distribution with regard to intake rate and serum 

concentration of PFOA. If the subjects were at steady state, the body 

burden would have to be known. At steady state, the serum 

concentration would be independent of the volume of distribution, so 

any V value ought to match the intake rate to the steady state serum 

concentration.

4-9 1 Log transformed concentration was 1.51 and 1.48 ng/mL – are these 

the logarithms? IE, are the actual concentrations 10^1.51 = 32 and 

10^1.48 = 30 ng/mL?

4-20 2, line 8 Anderson here is spelled Andersen in the reference list.

4-30 1, line 9 prostrate should be prostate.

4-31 4, line 10 decreased should be decrease.

4-112 1 It would be helpful to restate the serum concentrations for the 

Eriksen and Vieira studies, or refer reader to p. 4-29 where they are 

provided.

4-112 1, line 9 Delete “for”.

4-112 2, line 12 Delete “were”.

4-118 4 Delete “of actions” after MOAs

4-120 3 The broad range of half lives could also be due to person-to-person 

variability in the free fraction of PFOA in serum (fup). This is the 

case for highly bound drugs; e.g., warfarin.

5-1 3 Pharmacokinetic is misspelled.

5-1 5 Disagree – exposure assessment based on the human data is feasible. 

In fact, the serum concentrations are a better measure of exposure 

than are intake measures as they reflect all intake pathways and 

eliminate bioavailability and pharmacokinetic influences on internal 

exposure.

5-12 Last Table numbers should be 5-6, 5-7, and 5-8.
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Specific Observations for Health Effects Document for Perfluorooctane Sulfonate

Page Paragraph Comment or Question

3-5 3 The low CSF : serum concentration ratio could also be due to an 

export transporter that pumps PFOS out of the CSF and/or to 

extensive serum protein binding, where only the free serum 

concentration of PFOS is in equilibrium with the free PFOS 

concentration in the CSF.

3-22 2 The free fraction used for the model is much larger than that 

determined experimentally, Table 3-1; this should be pointed out in 

the text.

3-22

3-23

2

Figure 3-5

The arrow from Gut to Liver appears to point in the wrong direction; 

it should represent biliary excretion of PFOS from Liver to Gut.

3-24 4 Anderson should be Andersen.

4-26 4 “concentrations” should be “dosages”.

5.2 3 Should note for many of these studies, that steady state may not have 

been achieved due to the long half-life of PFOS. Half-life values 

from Section 3 are: mouse, 37 days; rat male, 40 days and female 64 

days; monkey, 120 days. Using a one-compartment PK model, the 

time to 90% steady state is 3.3 half lives.

5-5 3 The NOAEL for liver effects in rats of 0.072 mg/kg/day is not 

consistent with p. 5.4, para. 2, which states that lesions of the liver 

were observed in male rats after 104 weeks at this dosage.

5-7 2 For female rat, the PFOS half life is about 60 d and the period of 

gestation is about 20 d or one-third of a half life. If PFOS is 

administered to the dam only during gestation at a fixed daily dose, 

the serum concentration of PFOS would rise from 0 to 21% of the 

steady-state serum concentration that the fixed dose rate would 

produce at steady state. The exposure of the fetus during gestation 

would average only about 10% of the exposure that would have 

occurred if the dam had received PFOS for 4 half-lives (240 days) 

prior to mating. BMDs based on such a fixed dose could be elevated 

by as much as a factor of 10 compared with the steady state 

situation. Steady state would be the relevant situation for humans. 

For the Luebker study (Table 5-3) the serum concentration during 

gestation would have increased from about 38% to 50% of the 

eventual steady state concentration.
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68

Matthew P. Longnecker

Specific Observations for Health Effects Document for Perfluorooctanoic

Page Paragraph Comment or Question

3-28 1

st complete Should the end of the sentence be “increase the transporters” rather 

than “increase the receptors”? 

3-30 2

nd complete L 3, would insert “transfected” between “OAT3” and “cells”

3-39 1

st complete Next to last sentence: I doubt that Olsen assumed the major source of 

exposure was drinking water in the occupational study

3-41 4

th complete In the first formula listed, the plus sign should be an equal sign

4-9 1

st complete L 3 from bottom: the values of 1.51 and 1.48 given are probably 

better described as geometric means.

4-16 2

nd complete L 3 from bottom: would insert “draw” after “blood”

4-21 2

nd complete L 5: the value of 6.78 ug/L is a water level, not a serum level; this 

issue recurs on P 4-23, paragraph at bottom

4-30 1

st complete L 8: should read “exposure categories” rather than “cancer 

categories”?

4-37 Table Would note dose of PFOA somewhere in table or footnote

4-55 Last para L 3: should the “>” be a “<”?

4-79 Last para Last sentence: should “50 and 25” be “50 and 250”? 

4-80 1

st complete The last sentence does not accurately describe the table. E.G., the 

CD4+CD8+ cells decreased at the 47.21 mg/kg/d dose

4-82 Next to last 

para

Last sentence: the 37.5 mg/kg/dose is not mentioned earlier, so this 

is a little confusing.

4-85 Last para L 2: should “0.5” be “0.05”?; Same issue for L 5.

4-89 4

th para How long were the animals dosed?

4-110 3

rd complete 

para

L 5: should “serum” be “blood”?

4-113 3

rd complete 

para

L 1: insert “in” before “liver cells”

5-4 Last para Were the criteria for inclusion in Table 5.2 the same as for Table 

5.1?

5-12 Para below 

table

8-6, 8-7, and 8-8 should be 5-6, 5-7, and 5-8

5-16 Last line I do not see in the Thompson et al. (2010) study any mention of 

using exposure data from NHANES to calibrate the volume of 

distribution. Other sources of data were used, where the water had 

been contaminated.

5-17 1

st formula “/day” should be deleted from “0.17 L/kgbw/day”

5-20 Table 5-12 The first three values in the UFtotal column need to be corrected; they 

should be 21900, 219000, and 21900

5-21 Paragraph 

above table

Last sentence: UFL should be UFH

5-21 Last 

sentence

UDS should be UFS
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Specific Observations for Health Effects Document for Perfluorooctanoic

Page Paragraph Comment or Question

5-27 Calculations The text says the body weight conversions should be based on the 3⁄4 

power. If so, the HED formulas are incorrect, and the HED should 

be 1.99 x 0.0254 = 0.0506, the dosimetric adjustment factor should 

be 0.0254, and the CSF should be 1.57. All the figures here should 

be checked as should the paragraph on P 5-28. The HED is 2,530-

fold greater than the RfD, not 29,000. 

Specific Observations for Health Effects Document for Perfluorooctane Sulfonate

Page Paragraph Comment or Question

1-1 2

nd 1st sentence: would revise for clarity. Do you mean uncertainties 

exist about whether PFOS-induced peroxisome proliferation is 

involved in causing PFOS-induced hepatic lesions? 

1-1 3

rd 1st sentence: would revise for clarity; the occupational studies were 

done at PFOS production plants, but to my knowledge there are no 

residential populations that have been studied for health effects who 

lived near PFOS production plants. (Mid-Ohio valley factory was a 

source of PFOA.) In the 2ndsentence, I do not believe that exposure 

was mainly through contaminated drinking water in any of these 

studies.

4-66 2

nd The earlier summary of the Bloom et al. study (P 4-10) said the 

results were not statistically significant, whereas here the 

interpretation appears to be that the study found an association. The 

interpretation does not seem consistent across the two sections.

5-17 Below table L 3: the word “terminal” should be deleted from this sentence

5-20 1

st formula The “/day” should come out of “0.23 L/kg bw/day”

5-26 L 2 from 

bottom

This should be 35 ug/L not 35 mg/L

Angela L. Slitt

No specific observations.
External Peer Review of EPA’s Draft Health Effects Documents for 

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

A-1

APPENDIX A: PEER REVIEWER BIOSKETCHES
External Peer Review Meeting on

EPA’s Draft Health Effects Documents for

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

Crystal City Marriott at Reagan National Airport

1999 Jefferson Davis Highway

Arlington, VA, 22202-3526

August 21 and 22, 2014

LIST OF PEER REVIEWERS

James Bruckner, Ph.D. 

University of Georgia 

William Hayton, Ph.D. 

The Ohio State University (Emeritus)

Deborah Cory-Slechta, Ph.D. (chair)

University of Rochester School of 

Medicine and Dentistry

Matthew Longnecker, Sc.D., M.D 

National Institute of Environmental 

Health Sciences

Jamie DeWitt, Ph.D.

East Carolina University

Angela Slitt, Ph.D. 

University of Rhode Island

Jeffrey Fisher, Ph.D.

U.S. Food & Drug Administration

BIOGRAPHICAL SKETCHES OF PEER REVIEWERS

James Bruckner, Ph.D. 

University of Georgia 

Dr. Bruckner is Professor of Pharmacology and Toxicology at the University of Georgia College 

of Pharmacy. He is also Professor in the Department of Physiology and Pharmacology at the 

University of Georgia College of Veterinary Medicine. He received his Ph.D. in Toxicology 

from the University of Michigan in 1974. He has previously held faculty positions at the 

University of Kansas and the University of Texas Medical School at Houston. He is actively 

engaged in graduate education and in federally-funded research projects. Dr. Bruckner’s research 

focus is on the toxicology and toxicokinetics of solvents, drug-solvent interactions at 

occupational exposure levels, and toxicokinetic bases for susceptibility of children to insecticides 

and other chemicals. Dr. Bruckner has published more than 200 journal articles, book chapters, 

and abstracts. He has also served on a variety of expert panels and committees for the EPA, 

National Institutes of Health, National Aeronautics and Space Administration, Agency for Toxic 

Substances and Disease Registry, Food and Drug Administration, and the National Academy of 

Sciences.
Deborah Cory-Slechta, Ph.D. (chair)

University of Rochester School of Medicine and Dentistry

Dr. Cory-Slechta is a Professor in the Department of Environmental Medicine and the 

Department of Pediatrics at the University of Rochester School of Medicine and Dentistry, where 

she also serves as co-director of the Behavioral Sciences Facility Core and director of the Animal 

Behavior Core. Dr. Cory-Slechta received her Ph.D. from the University of Minnesota in 1977

and worked as a junior staff fellow of the National Center for Toxicological Research beginning 

in 1979. She was appointed to the faculty of the University of Rochester Medical School in 1982 

and was appointed Chair of the Department of Environmental Medicine and Director of the 

NIEHS Environmental Health Sciences Center at the University of Rochester in 1998. From 

2000 to 2002, she was the Dean for Research and Director of the AAB Institute for Biomedical 

Sciences. Following her appointment as Dean, she served from 2003 to 2007 as the Chair of the 

Department of Environmental and Occupational Medicine at Robert Wood Johnson Medical 

School and as Director of the Environmental and Occupational Health Sciences Institute, a joint 

Institute of the Robert Wood Johnson Medical School and Rutgers. Dr. Cory-Slechta’s research 

has focused largely on environmental neurotoxicants as risk factors for behavioral disorders and 

neurodegenerative disease. These research efforts have resulted in over 170 papers and book 

chapters to date. Dr. Cory-Slechta has served on numerous national research review and advisory 

panels, including committees of the National Institutes of Health, the National Institute of 

Environmental Health Sciences, the Food and Drug Administration, the National Center for 

Toxicological Research, the Environmental Protection Agency, the National Academy of 

Sciences, the Institute of Medicine, and the Agency for Toxic Substances and Disease Registry, 

Centers for Disease Control. In addition, Dr. Cory-Slechta has served on the editorial boards of 

several journals including Environmental Health Perspectives, Neurotoxicology, Toxicology, 

Toxicological Sciences, Fundamental and Applied Toxicology, Neurotoxicology and Teratology, 

and American Journal of Mental Retardation. She has held the elected positions of President of 

the Neurotoxicology Specialty Section of the Society of Toxicology, President of the Behavioral 

Toxicology Society, and been named a Fellow of the American Psychological Association. She

also previously served on the EPA Science Advisory Board Perfluorooctanoic Acid Risk 

Assessment Review Panel.

Jamie DeWitt, Ph.D.

East Carolina University

Dr. DeWitt is an Assistant Professor in the Department of Pharmacology and Toxicology at the

Brody School of Medicine at East Carolina University (ECU). She is affiliated with The Harriet 

and John Wooten Laboratory for Alzheimer’s and Neurodegenerative Diseases Research and 

holds an adjunct appointment in the ECU Department of Public Health. Dr. DeWitt received her 

Ph.D. in Environmental Science and Neural Science from the School of Public and 

Environmental Affairs and Program in Neural Science at Indiana University in 2004. She also 

completed postdoctoral training in Developmental Cardiotoxicity at Indiana UniversityBloomington and in Immunotoxicology at EPA through a cooperative training agreement with 

the University of North Carolina at Chapel Hill. Dr. DeWitt’s main research focus is on how 

toxicants found in the environment can lead to neurodevelopmental and neurodegenerative

disorders via disruption of the developing immune system. Much of her past research has 
involved the immunotoxicity of perfluorooctanoic acid (PFOA) and related polyfluroalkyl 

substances (PFASs). Dr. DeWitt has published seven peer reviewed research articles, three 

review papers and two book chapters that address the biological effects of PFOA, as well as one 

paper on the effects of PFOS on immune function. Her publications describe effects as well as 

underlying mechanisms following adult and developmental exposure. Her research experience 

and publication record (more than 25 peer reviewed manuscripts, 6 review articles, 9 book 

chapters) extend beyond the effects of PFAAs and working with rodent models. She is currently 

editing a book on the general toxicity of PFASs and is a current member of the mechanistic

working group for Monograph 110 of the International Agency for Research on Cancer, which

will include an assessment of PFOA. She is on the editorial boards of the Journal of 

Immunotoxicology and the Journal of Environmental Toxicology and Health and has reviewed 

grants for the Department of Defense and the National Institute of Occupational Safety and 

Health. She has also been manuscript reviewer for more than 20 journals. Dr. DeWitt is the

current president of the North Carolina chapter of the Society of Toxicology and the Junior 

Councilor for the Immunotoxicology Specialty Section of the Society of Toxicology. She also 

was awarded the Outstanding Young Investigator Award from the Immunotoxicology Specialty 

Section in 2013. 

Jeffrey Fisher, Ph.D.

U.S. Food & Drug Administration

Dr. Fisher is a Research Toxicologist at the U.S. Food and Drug Administration (FDA), National 

Center for Toxicological Research. He was formerly a Professor in the Department of 

Environmental Health Science, College of Public Health at the University of Georgia (UGA). He 

joined UGA in 2000 and served as Department Head of the Department of Environmental Health 

Sciences from 2000 to 2006 and Director of the Interdisciplinary Toxicology Program from 

2006-2010. Prior to joining UGA, he spent most of his career at Wright Patterson Air Force Base 

(AFB), where he was Principal Investigator and Senior Scientist in the Toxics Hazards Division 

and Technical Advisor for the Operational Toxicology Branch. Dr. Fisher's research interests are 

in the development and application of biologically based mathematical models to ascertain health 

risks from environmental, food-borne and occupational chemical exposures. Dr. Fisher’s 

modeling experience includes working with chlorinated and non-chlorinated solvents, fuels, 

pesticides, perchlorate and bisphenol A. He has developed physiologically-based 

pharmacokinetic (PBPK) models for use in cancer risk assessment, estimating lactational transfer 

of solvents, understanding in utero and neonatal dosimetry, quantifying metabolism of solvent 

mixtures and developing biologically motivated models for the hypothalamic-pituitary-thyroid 

axis in rodents and humans. Dr. Fisher has published over 140 papers on pharmacokinetics and 

PBPK modeling in laboratory animals and humans. He has served on several national panels and 

advisory boards for the DoD, ATSDR, USEPA and non-profit organizations. He was a U.S. 

delegate for the North Atlantic Treaty Organization. Dr. Fisher served on the International Life 

Sciences Institute Steering Committee, which evaluated chloroform and dichloroacetic acid 

using EPA-proposed Carcinogen Risk Guidelines. He is Past President of the Biological 

Modeling Specialty Section of the Society of Toxicology, reviewer for several toxicology 

journals, and was Co-Principal Investigator on a National Institutes of Health (NIH)-supported 

workshop on Mathematical Modeling at the University of Georgia in the fall of 2003. Dr. Fisher

was also a member of the National Academy of Sciences subcommittee on Acute Exposure 
Guideline Levels (AEGLs) from 2004-2010 and Science Advisory Board (SAB) for the US EPA 

(2007-2010). He is an ad hoc EPA SAB member for dioxin and perchlorate. Dr. Fisher is a 

Fellow of the Academy of Toxicological Sciences, an associate editor for Toxicological 

Sciences, and on the editorial board of Journal of Environmental Science and Health Part C 

Environmental Carcinogenesis & Ecotoxicology Reviews.

William Hayton, Ph.D. 

The Ohio State University (Emeritus)

Dr. Hayton is a Professor Emeritus in the College of Pharmacy at The Ohio State University. Dr. 

Hayton received a Ph.D. in Pharmaceutics from the State University of New York at Buffalo in 

1967. He was a member of the Washington State University College of Pharmacy faculty for 19 

years, rising to Chair of the Pharmacology/Toxicology Graduate Program in 1982 and Acting 

Dean at the College of Pharmacy in 1987. In 1990, he transferred to the Ohio State University as 

Chair of the Division of Pharmaceutics, where he later served as Associate Dean for the 

Graduate Programs and Research until his retirement in 2010. Dr. Hayton’s expertise is 

pharmacokinetics, particularly construction and validation of mathematical models that describe 

or explain the kinetics of complex biological systems. One recent research interest is 

characterization of the Fc receptor-mediated transport and catabolism of albumin and IgG in wild 

type and FcR knockout mice. A second recent project is the quantitative modeling of the female 

hypothalamus-pituitary-gonad (HPG) axis in the female rainbow trout (Oncorhynchus mykiss). 

The model is based on and integrates the biology of gonadotropin, estrogen, androgen and 

maturational hormone signaling systems, and it includes key intermediate steps in the signaling 

pathways; viz., gonadotropin and sex steroid synthesis, hormone receptors and their 

corresponding mRNA levels. Dr. Hayton’s expertise extends to interspecies scaling of 

pharmacokinetic model parameter values and xenobiotic metabolism. Dr. Hayton is author or coauthor of over 100 peer-reviewed scientific publications and has held peer-reviewed grant 

support from the National Institutes of Health, EPA, Air Force Office of Scientific Research, 

Food and Drug Administration, and U.S. Fish and Wildlife Service. He previously served on the 

EPA Science Advisory Board Perfluorooctanoic Acid Risk Assessment Review Panel.

Matthew Longnecker, Sc.D., M.D 

National Institute of Environmental Health Sciences

Dr. Longnecker, M.D., Sc.D., is the head of the Biomarker-based Epidemiology Group at the 

National Institute of Environmental Health Sciences (NIEHS). Dr. Longnecker received an

M.D. from Dartmouth Medical School and completed a residency in internal medicine at Temple 

University Hospital in Philadelphia. After receiving a Sc.D. in Epidemiology from Harvard 

School of Public Health in 1989, he served as an Assistant Professor in the Department of 

Epidemiology at the University of California, Los Angeles, School Of Public Health. Since 

1996, Dr. Longnecker has served as Adjunct Professor/ Associate Professor in the Department of 

Epidemiology, School of Public Health, University of North Carolina at Chapel Hill. He came to

the NIEHS Epidemiology Branch in 1995, as a tenure-track investigator. Dr. Longnecker's 

research program is focused on the health effects of persistent organic pollutants (e.g., the DDT 

metabolite p,p'-DDE, and polychlorinated biphenyls). He is particularly interested in the effects 

of intrauterine exposure to persistent organic pollutants in relation to intrauterine growth, 
preterm birth, birth defects, neurologic findings at birth, growth, neurodevelopment, intelligence, 

and hearing. Recently, Dr. Longnecker has completed and has ongoing a series of studies on 

perfluorinated alkyl substances in relation to reproductive and pediatric outcomes. In addition, 

he has begun studying the effects of early, low-level exposure to the nonpersistent pollutants, 

bisphenol A and organophosphate pesticides. Dr. Longnecker’s research efforts have resulted in 

over 180 papers and book chapters to date. He has served as a leader for numerous national and 

international committees, such as for the Society for Epidemiologic Research and the 

International Society for Environmental Epidemiology, and has been on numerous national and 

international scientific advisory boards, including the EPA Science Advisory Board for the

Perfluorooctanoic Acid Risk Assessment Review.

Angela Slitt, Ph.D. 

University of Rhode Island

Dr. Slitt is an Associate Professor in the Department of Biomedical and Pharmaceutical Sciences

at the University of Rhode Island. Dr. Slitt received her Ph.D. in Pharmacology and Toxicology 

from the University of Connecticut in 2000, and then served until 2004 as a postdoctoral fellow 

at the University of Kansas Medical Center. Dr. Slitt has been a faculty member at the 

University of Rhode Island since 2006. Dr. Slitt’s graduate and postdoctoral training was heavily 

focused on liver biology and health, with a focus in the area of toxicology, and included research 

in nuclear receptors, biotransformation, and transporter expression. Her current research 

interests focus on how 1) expression of drug transporters affects chemical disposition and 

toxicity, 2) nutrition and intake of dietary antioxidants affects the expression of drug 

transporters, 3) liver disease (i.e., diabetes, cholestasis, and ethanol cirrhosis) affects transporter 

expression and chemical disposition, and 4) transporter expression affects cholesterol transport 

and susceptibility to gallstone formation. She has also recently investigated the effect of PFOS 

on caloric restriction in mice. Dr. Slitt is presently on the Editorial Board of BMC Pharmacology 

and Toxicology, Journal of Biochemical and Molecular Toxicology, and Toxicology Methods 

and Mechanism, and is an ad-hoc reviewer for numerous other journals. She is author or coauthor of over 50 peer-reviewed scientific publications, and was recently awarded the University 

of Rhode Island Early Career Faculty Research Excellence Award.
External Peer Review of EPA’s Draft Health Effects Documents for 

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

B-1

APPENDIX B: MEETING AGENDA
*Time for breaks and lunch are approximate and at the Chair’s discretion.

AGENDA

External Peer Review Meeting on

EPA’s Draft Health Effects Documents for

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

Crystal City Marriott at Reagan National Airport

1999 Jefferson Davis Highway

Arlington, VA, 22202-3526

August 21, 2014

Day 1 – PFOA Health Effects Document

8:30 AM Meeting Sign-In Begins

9:00 AM Welcome, Goals of Meeting, and Introductions

David Bottimore, Versar, Inc. 

9:15 AM Welcome by EPA and Overview of PFOA/PFOS Health Effects Documents

Elizabeth Doyle, Chief, EPA/OST/OW/HECD

9:30 AM Chair’s Introduction and Review of Charge

Deborah Cory-Slechta, Chair

10:00 AM Discussion Session – “Round Table” General Overview Comments 

10:45 AM Break*

11:00 AM PFOA Discussion Session – Responses to Charge Questions: 

Question 1: Strengths, Weaknesses, and Characterization of the Studies Selected

Question 2: Additional References for Consideration

Question 3: Conclusions on Human Epidemiology Data 

Question 4: Transparency and Characterization of Epidemiologic Data

12:15 PM Lunch*

1:15 PM PFOA Discussion Session – Response to Charge Questions: 

Question 5: Cancer Classification

Question 6: Pharmacokinetic Model Adjustments

Question 7: Selected Parameters for Pharmacokinetic Model

Question 8: Volume of Distribution (Vd) and Half-life Values 

2:45 PM Break*

3:00 PM PFOA Discussion Session – Response to Charge Questions: 

Question 9: Points of Departure and RfDs

Question 10: RfDs and Applicability to Short-and Long-term Exposures

Question 11: Uncertainty Factors 

Question 12: Other Suggestions for Improving the Document

5:00 PM Adjourn
*Time for breaks and lunch are approximate and at the Chair’s discretion.

AGENDA

External Peer Review Meeting on

EPA’s Draft Health Effects Documents for 

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

Crystal City Marriott at Reagan National Airport

1999 Jefferson Davis Highway

Arlington, VA, 22202-3526

August 22, 2014

Day 2 – PFOS Health Effects Document

9:00 AM Recap of Day 1 and Agenda for Day 2

David Bottimore, Versar, Inc. 

9:15 AM Chair’s Review of Charge for Day 2

Deborah Cory-Slechta, Chair

9:30 AM Discussion Session – “Round Table” General Overview Comments 

10:00 AM Break*

10:15 AM PFOS Discussion Session – Responses to Charge Questions: 

Question 1: Strengths, Weaknesses, and Characterization of the Studies Selected

Question 2: Additional References for Consideration

Question 3: Conclusions on Human Epidemiology Data

Question 4: Transparency and Characterization of Epidemiologic Data

11:30 PM Lunch Break*

12:30 PM PFOS Discussion Session – Response to Charge Questions: 

Question 5: Cancer Classification

Question 6: Pharmacokinetic Model Adjustments

Question 7: Selected Parameters for Pharmacokinetic Model

Question 8: Volume of Distribution (Vd) and Half-life Values 

2:15 PM Break*

2:30 PM PFOS Discussion Session – Response to Charge Questions: 

Question 9: Points of Departure and RfDs

Question 10: RfDs and Applicability to Short-and Long-term Exposures

Question 11: Uncertainty Factors 

Question 12: Other Suggestions for Improving the Document

5:00 PM Adjourn
External Peer Review of EPA’s Draft Health Effects Documents for 

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

C-1

APPENDIX C: MEETING ATTENDEE LIST
LIST OF OBSERVERS 

ATTENDING MEETING IN PERSON

August 21 and 22, 2014

External Peer Review Meeting on

EPA’s Draft Health Effects Documents for

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

Name Affiliation

Janet Anderson, Ph.D. U.S. Air Force

Robert Bilott Taft Stettinius & Hollister LLP

Norman Birchfield U.S. EPA

John Butenhoff, Ph.D. 3M Company

Sue Chang, Ph.D. 3M Company

C-H Selene Chou, Ph.D. Agency for Toxic Substances and Registry

Steven Chranowski Chemistry Council of New Jersey

Joyce Donohue U.S. EPA

Elizabeth Doyle U.S. EPA

Colleen Flaherty U.S. EPA

Maria Hegstad Inside EPA

Gerald Kennedy DuPont

La Rae Landers Dept of the Navy BRAC PMO

Willington Lin Public

Angela Lynch, Ph.D. American Chemistry Council

Geary Olsen, Ph.D. 3M Company

Gloria Post, Ph.D. New Jersey Department of Environmental Protection

Resha Putzrath, Ph.D. Navy and Marine Corps Public Health Center

Jennifer Seed U.S. EPA

Shalene Thomas AMEC Environment & Infrastructure

Steve Via American Water Works Association

Anthony Walters United Science, LLC

Carol Wood Oak Ridge National Laboratory
LIST OF OBSERVERS 

ATTENDING VIA PHONE

August 21 and 22, 2014

External Peer Review Meeting on

EPA’s Draft Health Effects Documents for

Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS)

Name Affiliation

Matthew Bailor Gilmore & Associates, Inc.

Victoria Binetti U.S. EPA

Stuart Cagen, Ph.D. Shell Health

Andrea Candara New York State Department of Health

Tom Cleveland Decatur Utilities

Jason Conder ENVIRON International Corporation

Michelle Deveau Health Canada

Stiven Foster U.S. EPA

Helen Goeden Minnesota Department of Health

Christopher Lau, Ph.D. U.S. EPA

Anita Meyer, DABT U.S. Army Corps of Engineers

Jonathan Naile, Ph.D. Shell Health

Jessica Nelson Minnesota Department of Health

Bridget O'Brien U.S. EPA

Ramasamy Santhini U.S. EPA

Robert Rickard U.S. EPA

John Wambaugh U.S. EPA

Carol Rowan West, Ph.D. Massachusetts Department of Environmental Protection

Linda Wilson New York State Office of the Attorney General

Virginia Yingling Minnesota Department of Health

Tsedash Zewdie Massachusetts Department of Environmental Protection