EPA RESPONSE TO EXTERNAL PEER REVIEW

COMMENTS

on the

EXTERNAL PEER REVIEW DRAFT AQUATIC LIFE

AMBIENT WATER QUALITY CRITERION FOR

SELENIUM - FRESHWATER 2014

September 25, 2015

Office of Water

U.S. Environmental Protection Agency

Washington, DC
ii

TABLE OF CONTENTS

I. Background on External Peer Review Process and this Response to Peer Review Comments 

Document...................................................................................................................... 1

II. Peer Review Charge Questions.................................................................................................. 1

III. Responses Sorted by Question.................................................................................................. 6

PART I: OVERARCHING CHARGE QUESTIONS FOR THE EXTERNAL PEER 

REVIEWERS................................................................................................................ 6

PART II: FISH TISSUE CRITERION ELEMENTS DERIVATION: DERIVATION OF FISH 

EGG-OVARY, WHOLE BODY AND MUSCLE CRITERION ELEMENT(S) ...... 53

PART III: EVALUATION OF THE TRANSLATION PROCEDURE TO DERIVE THE 

WATER COLUMN ELEMENT(S) ........................................................................... 83

PART IV: SIGNIFICANCE OF SCIENTIFIC VIEWS FROM THE 

PUBLIC/STAKEHOLDERS.................................................................................... 125

IV. References Cited in EPA’s Responses ................................................................................. 142
1

I. Background on External Peer Review Process and this Response to Peer Review 

Comments Document

EPA submitted its External Peer Review Draft Aquatic Life Ambient Water Quality Criterion for 

Selenium – Freshwater 2014 for contractor-led independent, external peer review from August 

2014 to September 2014. Prior to this peer review, EPA had released the document for public 

comment for over 60 days, May 14 to July 28, 2014. The external peer reviewers provided their 

independent responses to EPA’s charge questions. External peer reviewers also considered 

public comments on the 2014 draft document, which EPA shared with them to obtain external 

peer reviewers’ feedback on the public comments. 

The 2014 draft criterion update of selenium provided a chronic criterion that is composed of four 

elements. The recommended elements are: (1) a fish egg-ovary element; (2) a fish whole-body 

and/or muscle element; (3) a water column - element (one value for lentic and one value for lotic 

aquatic systems); and (4) a water column intermittent element to account for potential chronic 

effects from repeated, short-term exposures (one value for lentic and one value for lotic aquatic 

systems).

The following text lists the charge questions submitted to the peer reviewers, the external peer 

reviewers’ comments regarding those questions, and EPA’s responses to the peer reviewer’s

comments. EPA revised the 2014 draft document considering the peer review and public 

comments, and is releasing the revised 2015 draft selenium criterion document for a second 

period of public comment, for 75 days, from July 28 to October 10, 2015.

II. Peer Review Charge Questions

PART I: OVERARCHING CHARGE QUESTIONS FOR THE EXTERNAL PEER 

REVIEWERS

1. Please comment on the overall clarity of the document and construction of the criterion 

statement with its multiple elements.

2. EPA has developed a tiered selenium criterion with four elements, with the fish tissue 

elements having primacy over the water-column elements, and the egg-ovary element 

having primacy over any other element. Inclusion of the fish whole-body or fish muscle 

element into the selenium criterion ensures the protection of aquatic life when fish egg or 

ovary tissue measurements are not available, and inclusion of the water column elements 

ensures protection when fish tissue measurements are not available 

2.a.Please comment on the tiered construction of the selenium chronic criterion; is it 

logical, and scientifically defensible as it applies to protection of freshwater 

aquatic life: 

2.a.i. That is, is the primacy of the egg-ovary element over the other elements 

scientifically sound, given the prevailing toxicological knowledge and the 

data and supporting scientific information currently available to the 

Agency? Please provide detailed comments.
2

2.a.ii. Is the primacy of the whole-body/fish muscle element over the water 

column elements scientifically sound, given the prevailing toxicological 

knowledge and the data and supporting scientific information currently 

available to the Agency? Please provide detailed comments.

2.a.iii. Please comment on the scientific uncertainty that may be associated with 

this tiered approach? Are there other data sources, models, or approaches 

that EPA should consider that would reduce uncertainty? Please provide 

detailed comments.

2.a.iv. Are the draft recommended magnitude, duration, and frequency for each 

criterion element scientifically sound and appropriate? Please provide 

detailed comments.

PART II: FISH TISSUE CRITERION ELEMENTS DERIVATION: DERIVATION OF FISH 

EGG-OVARY, WHOLE BODY AND MUSCLE CRITERION ELEMENT(S)

EPA is requesting a technical review of the methods and procedures used to derive a chronic 

selenium criterion based on an egg-ovary concentration, as well as its translation to a criterion 

element applicable to whole-body and muscle tissue. Please address the following questions:

1. Please comment on EPA’s use of the effects concentration 10th centile (EC10) as the 

measurement endpoint for the fish reproductive toxicity studies used to derive the eggovary element.

2. Data used to derive the final chronic egg-ovary criterion element were differentiated 

based on the type of effect (reproductive vs. non-reproductive effects). Acceptable 

chronic toxicity data on fish reproductive effects are available for a total of nine fish 

genera. The genus Sensitivity Distribution (SD) is predominantly populated with data on 

fish genera because field evidence demonstrates that fish communities can be affected by 

selenium even when there is no observable change in the invertebrate community 

diversity and abundance. As a result, decades of aquatic toxicity research have focused 

primarily on fish. Available field and laboratory studies indicate that invertebrates are 

more tolerant to selenium than most of the tested fish species (Criteria document, Table 

6c, Section 4.1.2). The data set used to derive the selenium criterion marks a change from 

the traditional method used to derive water quality criteria that requires toxicity tests with 

aquatic organisms from 8 phylogenetically distinct taxa (including three vertebrate and 

five invertebrate genera) in order to derive aquatic life criteria (Stephan et al., 1985).

2.a.Given selenium’s more taxon-specific and life stage-specific toxicity, please 

comment on EPA’s use of the available data to derive the egg-ovary tissue 

element.

2.b.Given the greater general sensitivity of oviparous fish to selenium compared to 

aquatic invertebrates, please comment on the appropriateness of EPA’s fish 

tissue-based criterion for affording protection to the aquatic community as a 

whole (e.g., including invertebrates).

2.c.With respect to the tests that quantified non-reproductive effects, did the EPA use 

that data to the best extent possible given its limitations (e.g., relevance compared 
3

to reproductive tests, and data quality concerns which increased uncertainty (e.g., 

Hamilton et al., 1990)?

2.d.EPA also rejected studies that used the injection route of exposure for selenium 

due to uncertainty related to uptake, distribution and metabolism/transformation 

kinetics when compared with the dietary and/or maternal transfer routes of 

exposure. Was this reasonable? Does the panel envision an appropriate and 

scientifically defensible use for this type of data? Please provide detailed 

comments.

3. Was the method (Section 4.1.5, 7.1.7) used to translate the fish egg-ovary criterion 

element into muscle and whole body criterions elements understandable, transparent and 

scientifically defensible? Was there sufficient data for making the translations for each 

element?

PART III: EVALUATION OF THE TRANSLATION PROCEDURE TO DERIVE THE 

WATER COLUMN ELEMENT(S)

EPA is also requesting a technical review of the methods and procedures used to translate the 

egg-ovary element of the chronic selenium criterion to water-column elements. Relevant sections 

of the document include:

 A description of the method used to derive an equation to translate the egg-ovary element 

to a monthly water-column element in perennial (lentic and lotic) waters and an equation 

that can be used to convert the monthly water-column element to an intermittent water 

column element (Sections 3.8.3, 3.8.4, 4.2.1, 4.3, and Appendix G).

 An analysis of the translation equation precision using data obtained from published 

literature (Sections 7.2.1, 7.2.2, and Appendix H).

 A description of the method and data sources used to derive the translation equation 

parameters (Sections 4.2.2, 4.2.3, and Appendix B).

 A description of the method and data sources used to categorize waterbody types where a 

single water-column chronic criterion concentration value would be adequately protective 

in most circumstances (Section 4.2.4).

 A description of the method and data sources used to derive water-column chronic 

criterion concentration values for established categories of waters (Section 4.2.5).

 A description of the method and data sources used to derive water-column chronic 

criterion concentration values for intermittent discharges that may occur in lentic and lotic 

waterbodies (Section 4.3).

Please address the following questions: 

1. Please comment on the scientific defensibility of EPA’s translation equation method for 

translating the concentration of selenium in fish tissue to a concentration of selenium in 

the water-column. Please comment on major sources of uncertainty in applying the 

translation equation to different types of waterbodies (e.g., with differing retention times, 
4

water chemistries, and/or species present). Are there other data sources, models, or 

approaches that EPA should consider that would reduce uncertainty? Please provide 

detailed comments.

2. Regarding the trophic transfer factor (TTF) values, did EPA use a scientifically 

defensible method to derive the TTF values (p. 71-77 of the criteria document)? Were 

the exclusion criteria, (pp. 71-77 of the criteria document) developed by EPA to screen 

the available data applied in a consistent and scientifically defensible manner? In 

particular, EPA noticed that application of the exclusion criteria resulted in TTF values 

for aquatic insect larvae that differ from other published values. Given this, are you 

aware of any other methods of screening data that EPA should consider? Also, are you 

aware of any data that was not considered in this effort and should be screened and 

included, if appropriate? Please provide detailed comments.

3. Regarding the conversion factor (CF) values used, did EPA use an appropriate and 

scientifically defensible method to derive those values (p. 78-79 of the criteria document 

and Appendix B)? Are you aware of any other methods that EPA should consider? Also, 

are you aware of any data that was not considered in this effort and should be screened 

and included? Please provide detailed comments.

4. Regarding the derivation of enrichment factor (EF) values, was the method EPA used to 

screen data from the literature applied appropriately and consistently (see 

inclusion/exclusion criteria on p. 71-77 of the criteria document)? Was the method for 

deriving EF values applied to those data in a consistent manner so as to derive EF values 

for selected waters in a scientifically defensible manner? Is the method that EPA used to 

establish the lentic and lotic categories for EF values reasonable given the available data? 

Are you aware of other methods or relevant data the EPA should consider? Please 

provide detailed comments.

5. Please comment on the scientific defensibility of EPA’s conversion of the selenium fish 

tissue – water translation equation into an equation that allows for calculation of a 

criterion for waters that may be subject to intermittent discharges of selenium. Please 

comment on major sources of uncertainty in this approach. Is this method appropriate, 

given the bioaccumulative nature of selenium? Please comment on the uncertainty 

associated with the application of this conversion equation to intermittent discharges that 

may occur in different types of waterbodies and/or in different locations, particularly with 

respect to loads transported to potentially more sensitive aquatic systems. Does the 

method employed result in criteria that are similarly protective to the 30-day chronic 

criterion? Are there any other models or approaches that EPA should consider that would 

reduce this uncertainty? Please provide detailed comments.

PART IV: SIGNIFICANCE OF SCIENTIFIC VIEWS FROM THE 

PUBLIC/STAKEHOLDERS

EPA will also be providing scientific views and other comments from stakeholders and the 

public received via the public docket to the peer review panel. Although EPA will be providing 

the full contents from the docket, EPA is only requesting a review of any scientific views/public 

comments that may be of technical significance to the selenium criterion.
5

1. Has the peer review panel identified any scientific views from the public or stakeholders 

as being technically significant to the draft of the selenium criterion going forward; that 

is, has information or data been introduced during the comment period that would change 

the scientific direction of the criterion? Is there any information or data that may refine or 

enhance the scientific defensibility of this criterion that EPA should consider further? 

Please provide detailed comments on specific issues of technical significance or 

refinement.
6

III. Responses Sorted by Question

PART I: OVERARCHING CHARGE QUESTIONS FOR THE EXTERNAL PEER REVIEWERS

1. Please comment on the overall clarity of the document and construction of the criterion statement with its multiple 

elements.

External Peer Reviewers’ Comments EPA Response

1. I found the overall clarity of the document to be good, 

although there are several specific areas that require clarification 

(detailed in comments to specific charge questions). I also found 

the construction of the criterion statement to be quite clear and 

logical.

Thank you for your comment.

2. In general the document is clearly written, but there are 

numerous typographical errors, missing references (e.g., EPRI, 

2006 cited first on p. 16), and incorrect citations (e.g., Table 12 

cites Appendix L, but the Appendices only go to K). Some key 

words are poorly chosen (the freshwater criterion parts are called 

“elements”), especially considering that this document concerns 

an aquatic trace ELEMENT, and other elements such as mercury 

are also discussed; I recommend selecting another key word for 

this. The use of acronyms and abbreviations are unavoidable in a 

document like this, and while they provided a table listing them 

all (which should be numbered Table 1 on page xi), it would 

make the document more readable to those only looking for 

some specific details to periodically redefine these in the text, 

for example the first time it is used extensively in a new section. 

The criterion statement (largely in Section 3.8) is clearly written 

and presented, although I have serious scientific problems with 

parts of it to be elaborated below. While this was not directly 

requested in our charge, but has direct bearing on the problems 

Regarding use of the word “element,” EPA maintains that the 

word was used appropriately and specifically referenced the 

components of the criteria statement, and will retain this 

terminology.

Regarding the reviewer’s recommendation to periodically 

redefine acronyms in the document, EPA has adopted that 

practice for those terms that are that are heavily used in the 

document.

Regarding the review of the biogeochemistry of selenium, the 

section has been rewritten to reflect the current scientific 

understanding of selenium chemistry in the environment.

Regarding the role of speciation, the data available in the peer-
7

External Peer Reviewers’ Comments EPA Response

in this document, the review section on the aquatic 

biogeochemistry of selenium (pp. 9-17) has factual errors that 

may reflect on the authors understanding of the selenium or on 

some biases. First, in Section 3.2 the statement that “...the 

effects are integrated across forms of selenium; thus water 

column values are based on total selenium exposure.” is an 

oversimplification that leads to conceptual errors later. The 

amount of dissolved selenium that enters the food web through 

the first trophic level is strongly linked to the speciation of 

dissolved selenium (e.g., Reidel et al., 1991; Baines and Fisher, 

2001; Baines et al., 2001; Baines et al., 2004), which for 

freshwater and marine/brackish species is: selenite=organic 

selenide>>selenate. So for a lotic or lentic water body that is 

dominated by selenate, the incorporation of selenate into the 

phytoplankton biomass is much lower than that if the selenium 

was in the +4 oxidation state. In the next section 3.2.1, it starts 

off with serious errors, in particular “organo-selenide” being 

selenomethionine. Data on the speciation of dissolved organic 

selenide show it to be in soluble peptides and proteins, not free 

amino acids (e.g., Cutter, 1982; Cutter and Cutter, 1995), so 

phytoplankton uptake studies using free selenomethionine are 

not using the actual dissolved forms and likely overestimating 

uptake.

A following sentence says that selenite tends to dominate in 

“slow moving waters”, presumably lentic environments. 

However, there are no data in the literature to support this 

statement (e.g., see compilations in Cutter, 1989a); selenite is 

only dominant when there is a large, fossil fuel-derived input, 

regardless of water residence time (e.g., Cutter, 1989a, 1989b). 

In this respect, on p. 14, 2nd complete sentence, they state that 

geologic AND anthropogenic sources often release mostly 

reviewed literature to EPA for modeling are typically nonspeciated and expressed as “total” selenium. Therefore, EPA 

has derived selenium criteria for fish tissue based on the 

relationship between total selenium and the effect observed in 

fish tissue, which integrates the effect of all selenium species to 

which the organism has been exposed over time. 

Regarding the bioaccumulation section, EPA has corrected the 

language in Section 3.2 (now Section 2.2) to more closely reflect 

our current understanding of speciation of selenium and 

incorporation into the food web by algae.

Regarding the statement that selenite tends to dominate in “slow 

moving waters,” EPA has corrected the text to reflect the 

appropriate geologic source and selenium speciation state as 

available from the current literature. 
8

External Peer Reviewers’ Comments EPA Response

selenate, but most anthropogenic sources produce selenite (e.g., 

Cutter, 1989a, 1989b; Cutter and Church, 1986), only geological 

sources (weathered or irrigated) yield selenate; the presence of 

selenite in surface waters can in fact be used as a fossil fuelcombustion source indicator (e.g., Cutter, 1989a, 1989b). 

Interestingly, the last paragraph on p. 14 is largely correct in 

stating that the concentration of particulate selenium in the first 

trophic level (algae) is highly dependent on the dissolved 

speciation; this begs the question of why the authors later ignore 

speciation and calculate EF on total (presumably dissolved) 

selenium in the water column and particles; see later comments.

In the Bioaccumulation section (3.2.2), the major error, and this 

is significant in terms of bioavailability, is that dissolved 

selenium uptake results in elemental selenium and 

organoselenium (2nd to last sentence on p. 15). Elemental 

selenium is only produced by dissimilatory (heterotrophic) 

reduction under low oxygen conditions (many works of 

Oremland, but they correctly cite Oremland et al., 1989); 

autotrophs perform assimilatory reduction to selenide that is 

then coupled with acetyl CoA, serine, etc to produce seleno 

amino acids. Also, the use of the term “absorbed” is poorly 

chosen in that it implies simple exchange with no chemical 

reactions; dissolved selenium is assimilated (or incorporated) 

into autotrophic organic matter, which in the case of selenite 

uptake/assimilation/incorporation involves a change in oxidation 

state and chemical form (i.e., selenite is reduced to selenide and 

bonded with carbon to produce seleno amino acids like 

selenocysteine).

3. There is a lot of information to digest and it may be difficult 

for non-technical readers to follow, but I feel that the document 

Thank you for your comment.
9

External Peer Reviewers’ Comments EPA Response

was organized in a logical manner and that the approaches were 

adequately described. Although I have technical comments 

relative to the criterion statement, I feel that format for 

presenting the selenium criteria based on multiple elements is 

clearly presented and easily digestible to the reader.

I have included here a few miscellaneous typos and editorial 

suggestions that I noted during my review:

p. 59, Table 7a: Correct spelling of "Onchyrhynchus" to " 

Oncorhynchus "

p. 60, paragraph below Table 7b: Correct spelling of "Leopmis" 

to "Lepomis"

p. 62, 1st paragraph: Correct spelling of "Oncorhyncus" to " 

Oncorhynchus "

p. 89, footnote a in Table 12: Appendix L should be Appendix K

p. 114, 1st paragraph, last sentence: Correct spelling of 

"criteirion" to "criterion"

EPA has noted your suggested edits and corrected the 

typographical errors.

4. Reasonably clear, although some phrases and terms need 

further clarification.

Thank you for your comment. EPA has clarified phrases and 

terms to enhance readability.

5. The document is generally well-written and is based on a 

comprehensive evaluation of the extensive body of freshwater 

Se literature. This said, I found many typographical and other 

errors throughout the document, which I will address in a 

marked-up copy (Adobe would not let me use the edit text 

functions so I simply highlighted the text in yellow and provided 

a comment if necessary). There were also several areas that I 

believe require significant clarification, which I will address in 

Regarding spelling and grammar, EPA has made many 

grammatical and typographical corrections during the most 

recent revisions.

Regarding the tiered criterion: EPA has presented a tiered 

criterion, and is recommending that States and Tribes adopt all 

of the recommended tiers; tiering enhances both the usability 
10

External Peer Reviewers’ Comments EPA Response

my subsequent review comments found below. 

I agree with the concept of the tiered criterion approach, 

particularly that tissue (i.e., ovary, egg, muscle, or whole-body)-

based Se concentrations ([Se]) are key to accurately assess the 

toxicological risk posed to fishes, and that egg/ovary [Se] 

overrides/supersedes whole-body or muscle [Se]. However, I do 

not fully agree with the approach, in the absence of tissue [Se] 

data, that a water-column criterion will be protective of aquatic 

species. There are many examples of aquatic systems, due to 

their specific biogeochemistry, ecology, and physiology, where 

very low dissolved [Se] (i.e., less than the proposed criteria for 

lentic or lotic systems) results in toxicologically significant 

bioaccumulation in fishes and their prey, and elevated 

frequencies of larval abnormalities. I suggest that dissolved [Se] 

be used as a “trigger” to initiate further monitoring (i.e., 

collection of fishes to determine tissue [Se]).

I also do not agree with the intermittent exposure criterion; it is 

unclear why it was developed, how it could be implemented 

consistently and reliably, and in general I think it just adds too 

much complexity to an already complex (indeed perhaps the 

most complex) water quality criterion. These are my general 

comments, and more specific details can be found in my 

subsequent review comments.

and the scientific strength of the criterion.

Regarding system variability with respect to the amount of tissue 

bioaccumulation relative to selenium in water; the water 

criterion element has an additional level of conservatism added, 

so that it is calculated to be protective of the expected tissue 

concentration 80% of the time for the most bioaccumulative fish 

in each system (Section 3.2.5).

Regarding those aquatic systems where fish and their prey 

species can experience significant bioaccumulation of selenium 

despite low water concentrations, EPA recommends fish tissue 

be collected in waters where available data (e.g., unusually large 

EFs) suggest the possibility of “toxicologically significant 

bioaccumulation” despite low selenium water concentrations. 

Furthermore, the national criterion can easily be adapted to sitespecific situations using site-specific data using the modeling 

information provided in the document

Regarding the intermittent exposure criterion, EPA recognizes 

that not all exposures are continuous and developed the 

intermittent criterion element due to concern that intermittent 

discharge sources may not be accounted for with the national 

30-day average chronic criteria, yet intermittent discharges of 

sufficient magnitude and frequency could accumulate through 

the food web and ultimately result in chronic impacts on aquatic 

life. EPA believes it is unnecessary to have an additional acute 

criterion element which addresses acute, water column-only 
11

External Peer Reviewers’ Comments EPA Response

events, because selenium is bioaccumulative and toxicity 

primarily occurs through dietary exposure. Although selenium 

may cause acute toxicity at high concentrations, the most 

deleterious effect on aquatic organisms is due to its 

bioaccumulative properties; these effects are found at lower 

concentrations than acute effects. Chapman et al. (2009) noted

that selenium acute toxicity has rarely been reported in the 

aquatic environment and that traditional methods for predicting 

effects based on direct exposure to dissolved concentrations do 

not work well for selenium.

6. On an overall basis, the 2014 Selenium Criterion is wellorganized and well-written. The major sections of the document 

serve to critically analyze the scientific and regulatory 

background of the issue, and to develop and rigorously justify a 

tiered criterion. Overall, the writing is clear and communicative, 

with key details, data and background information appropriately 

appended to the main document. The included tables and figures 

act to support the analysis of cause for a substantially different 

approach to risk management and furthermore this information 

serves to validate this criterion approach by critically evaluating 

decades worth of peer-reviewed laboratory and field 

observations in a fair and scientifically valid manner. The 

concordance observed in many tables exploring and groundtruthing modeled approaches, available data, and a broad array 

of published study results yields exceptional weight and 

justification for this new approach developed for the protection 

of aquatic life. 

Importantly, the criterion statement on p. 96 does indicate dry 

weight basis for tissue analyses, and this is discussed in the text, 

however Table 15 and the tabular Summary on p. 4 do not carry 

Regarding the comment regarding the overall evaluation of the 

document, EPA thanks you.

Regarding the missing “dw,” it has been added.

Regarding those areas of the document that may require 

additional guidance, EPA recognizes that there are numerous 

aspects of the criteria that will benefit from technical support 

documents to enhance its application, and is planning to develop 

such documents. The intermittent element was developed to 

address a specific concern regarding intermittent discharge 

sources.
12

External Peer Reviewers’ Comments EPA Response

the dry weight basis notation and this should be included. With 

the advantage of subsequent key published selenium research 

targeting trophic transfer and reproductive endpoints in fish, as 

well as the expert panel contributions published in Chapman et 

al., 2009, this current document is a significant improvement 

over the 2004 AWQC draft. In its presentation and treatment of 

a broad and diverse study and data set, the draft criterion 

document can be characterized as exhaustive in its attempt to 

quantitatively and qualitatively address the myriad issues related 

to this task under the CWA. Furthermore the draft criterion 

document addresses that task in a manner that synthesizes a new 

tiered criterion approach well-grounded in our current 

understanding of selenium risks in aquatic ecosystem and best 

available peer-reviewed knowledge. The draft approach balances 

knowns and unknowns, data and data gaps, simplicity and 

complexity in an overall sound attempt to address the time-value 

requirement of regulatory science. Although additional 

implementation guidance for this new tiered approach may be 

necessary, and observing that the discussion of background 

science, data and methods used in the intermittent exposure tier 

of the present criterion needs significant improvement, the draft 

document is overall remarkable for its clarity and completeness, 

in a scientifically driven and defendable analysis of a complex 

risk management challenge. 
13

External Peer Reviewers’ Comments EPA Response

7. The Draft Aquatic Life Ambient Water Quality Criterion for 

Selenium in Freshwater is generally clearly written and logically 

organized. While there are some issues which require 

clarification in the document, these generally arise as technical 

issues (identified in subsequent sections of this review) rather 

than writing clarity within the document. In contrast to some of 

the public comments, this reviewer believes that the document 

clearly states the order of preference for criterion (e.g., 

egg/ovary over muscle and whole body over water column 

concentrations) and the ultimate primacy of the egg/ovary 

criterion. 

The lone issue of clarity in the document concerns the water 

column values of selenium. Table 15 (page 97) specifies that 

water column selenium concentrations are based on “dissolved 

total selenium in water” however, elsewhere in the document the 

criterion is described as including “all oxidation states (e.g., 

selenite, selenate, organic selenium, and any other form)”. While 

clarity regarding the species and analytical methods for 

assessing water column selenium are provided in Appendix J 

(Analytical Methods for measuring Selenium), a more precise 

definition of water column Se is warranted within the body of 

the document.

Regarding the comment on the overall evaluation of the 

document, EPA thanks you.

Regarding the basis of the water column concentrations as 

“dissolved total selenium in water,” EPA recognizes that

clarification of the definition of selenium was needed and has 

revised the draft with a better definition and discussion of 

selenium speciation in the water column in the document. 

Selenium data are collected and analyzed using various methods.

The data available to EPA for modeling is typically nonspeciated and expressed as “total” selenium. EPA has derived 

selenium criteria for fish tissue based on the relationship 

between total selenium and the effect observed in fish tissue, 

which integrates the effect of all selenium species to which the 

organism has been exposed over time. Because of the 

uncertainty as to the form and potential for bioaccumulation, the 

criterion is expressed as total dissolved selenium in water (e.g., 

the total of all oxidation states; selenite, selenate, organic 

selenium, and any other forms), realizing that multiple forms of 

inorganic and organic selenium species may be present in any 

one sample.
14

2. EPA has developed a tiered selenium criterion with four elements, with the fish tissue elements having primacy over the 

water-column elements, and the egg-ovary element having primacy over any other element. Inclusion of the fish wholebody or fish muscle element into the selenium criterion ensures the protection of aquatic life when fish egg or ovary tissue 

measurements are not available, and inclusion of the water column elements ensures protection when fish tissue 

measurements are not available.

2.a. Please comment on the tiered construction of the selenium chronic criterion; is it logical, and scientifically 

defensible as it applies to protection of freshwater aquatic life: 

2.a.i. That is, is the primacy of the egg-ovary element over the other elements scientifically sound, given the 

prevailing toxicological knowledge and the data and supporting scientific information currently available to the 

Agency? Please provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. Yes, primacy of the egg-ovary element is sound and well 

supported by the scientific literature. EPA has cited all of the 

key references for support of this approach.

Thank you for your comment.

2. Given the known, well documented, and published in the 

peer-reviewed literature information, choosing the egg-ovary 

compartment/vector/whatever (not element) is very well 

justified. The accuracy of then selecting a suitable value for 

various fish species depends on a critical evaluation of the 

literature, or new experiments.

Thank you for your comment.

3. Yes, in my opinion the tiered construction of the chronic 

selenium criterion is logical and scientifically defensible. First, 

the critical exposure route for fish is dietary organic selenium 

(Janz et al. 2010), which is the basis for all of the studies in 

which egg or ovary selenium concentrations are linked to 

toxicity in offspring. Dietary organic selenium exposures are 

implicit in those studies in which adult females were exposed in 

the field and explicit in those studies in which adult females 

were exposed in the laboratory (primarily through the use of 

Regarding your support of the tiered construction of the chronic 

criterion, EPA thanks you.

Regarding the relative sensitivity of reproductive and nonreproductive (e.g., larval growth) effects, EPA completed a new 

analysis and found that the reproductive endpoint is protective of 

juvenile survival and growth (see pages 134 and 135 in the 

revised 2015 document). EPA however has noted in the current 
15

External Peer Reviewers’ Comments EPA Response

diets enriched with organic selenium, such as 

selenomethionine). Second, the critical toxicity endpoint for fish 

exposed to selenium is larval mortality, deformities, and/or 

edema following exposure to selenium during absorption of the 

yolk-sac. The selenium concentration in the egg or ovaries is the 

most relevant exposure metric for this exposure route and 

toxicity endpoint. Third, and related to the second point, is that 

fish species partition varying amounts of their total selenium 

burden to the ovaries and eggs (deBruyn et al., 2008). Direct 

measurement of the selenium concentration in the eggs or 

ovaries addresses this between-species variability in selenium 

partitioning within tissues. Fourth, fish egg- or ovary-based 

selenium toxicity values (e.g., EC10s) are not highly variable 

among fish species, regardless of whether adult females were 

exposed to dietary organic selenium in the field or in the 

laboratory or whether species may be considered "warm-water" 

or "cold-water" species.

Some studies have also shown that juvenile fish survival and 

growth can be relatively sensitive to dietary organic selenium. 

For this toxicity endpoint, of course, an egg or ovary selenium 

criterion would not be applicable (but a whole-body selenium 

criterion would be). An important question, therefore, is whether 

compliance with an egg or ovary selenium criterion would be 

protective of juvenile fish. DeForest (2008) evaluated this 

question by comparing dietary Se toxicity data for juvenile 

growth and effects on larvae via maternal transfer. Although 

data were limited to bluegill sunfish (Lepomis macrochirus) for 

that evaluation, it was concluded that juvenile bluegill are not 

more sensitive than bluegill larvae exposed to selenium via

maternal transfer. This would indicate that an egg or ovary 

selenium criterion should be protective of effects on juvenile 

criterion document (see pages 127 and 128 in the revised 2015 

document) that the whole body tissue is the sample of choice to 

assess selenium exposure in freshwater environments in juvenile 

anadromous salmonids (i.e., Pacific Northwest species) from the 

larval swim up to the smolt stage prior to outmigration to the 

marine environment.

Regarding the purpose of the water criterion elements, one of the 

purposes of the water-based criterion element(s) was to facilitate 

having an easily implemented value in permits. If a waterbody 

meets the fish tissue limits yet not a surface water criterion, for 

an existing input source, it is likely that the site specific 

dynamics of selenium bioaccumulation may be different than the 

basis of the national criterion, and this waterbody may be a 

candidate for a site-specific water value. Sufficient samples 

should be collected to evaluate the frequency of exceedance of 

the water value, and the concentration difference between the 

fish tissue sample(s) and the appropriate criterion element. An 

analysis of the available data may indicate that the fish tissue

concentration may be increasing over time and may soon exceed 

the allowable tissue criterion element threshold. For example, if 

the selenium entering the environment is from a recent new or 

increased input, the fish tissue concentrations may not yet reflect 

the ultimate “steady state” accumulation of selenium in fish 

tissue, because of a lag time of accumulating selenium moving 

through the food web.
16

External Peer Reviewers’ Comments EPA Response

survival and growth (if the observations for bluegill are 

translatable across fish species).

Although I agree that the primacy of each criterion element is 

logical, it is not clearly stated whether a water Se criterion could 

be adopted into a permit limit. For example, if compliance with 

the lotic or lentic Se criterion is demonstrated, is measurement 

of fish tissue Se concentrations necessary? If a water body meets 

a fish tissue-based Se criterion, but not a surface water criterion, 

would the water body be considered in compliance? I believe the 

answer to the latter is "yes", but this does not seem to be clearly 

stated in the draft AWQC document.

Literature cited:

deBruyn A, Hodaly A, Chapman P. 2008. Tissue selection 

criteria: Selection of tissue types for the development of a 

meaningful selenium tissue threshold in fish. Tissue 

Selection Criteria, Threshold Development Endpoints, and 

Potential to Predict Population or Community Effects in the 

Field Prepared for the North American Metals Council -

Selenium Working Group, Washington, DC. 

DeForest D. 2008. Threshold development endpoints: Review of 

selenium tissue thresholds for fish: Evaluation of the 

appropriate endpoint, life stage, and effect level and 

recommendation for a tissue-based criterion. Tissue 

Selection Criteria, Threshold Development Endpoints, and 

Potential to Predict Population or Community Effects in the 

Field Prepared for the North American Metals Council -

Selenium Working Group, Washington, DC.

Janz DM, DeForest DK, Brooks ML, Chapman PM, Gilron G, 

Hoff D, Hopkins WA, McIntyre DO, Mebane CA, Palace VP, 
17

External Peer Reviewers’ Comments EPA Response

Skorupa JP, Wayland M. 2010. Selenium toxicity to aquatic 

organisms. 141-231 in Chapman PM, Adams WJ, Brooks ML, 

Delos CG, Luoma SN, Maher WA, Ohlendorf HM, Presser TS, 

Shaw DP, eds. Ecological assessment of selenium in the aquatic 

environment. SETAC Press, Pensacola, FL, USA.

4. The tiered construction makes sense for most natural 

conditions, but not when acutely high Se levels are present (e.g., 

Kesterson reservoir). But for most sublethal concentrations this 

approach makes sense as a general approach for the EPA to 

adopt.

In waterbodies where no fish are present for tissue collection as 

a result of acutely toxic selenium concentrations, the water 

concentration criterion element would be applied.

5. Yes, it has been clearly shown in the scientific literature that 

egg/ovary [Se] provides the greatest certainty in predicting the 

toxicological risk associated with Se exposure in fishes. This is 

because (a) embryo-larval abnormalities are the most sensitive 

toxicological response, and (b) maternal transfer of Se to the 

eggs by adult female fishes provides the ultimate dose received 

by their offspring (i.e., during yolk resorption prior to swim-up). 

In addition, the frequency and severity of early life stage 

abnormalities caused by Se has clear ramifications for 

population dynamics; impaired recruitment of individuals into 

fish populations can alter demographics and ultimately result in 

extirpation. This is Ecotoxicology 101. Indeed, documented Se 

poisoning events (e.g., Belews Lake) provide some of the most 

convincing evidence of a cause-effect relationship between 

exposure to a toxic substance and resulting negative impacts on 

fish populations and communities. This is the goal of aquatic 

ecotoxicology: to protect populations and communities of 

organisms, not individuals.

Thank you for your comment.
18

External Peer Reviewers’ Comments EPA Response

6. The primacy of the egg-ovary element over other elements of 

the selenium chronic criterion is logical and broadly 

scientifically defensible. As identified in the document, 

numerous published studies outline the major aquatic ecosystem 

impact of selenium, beyond its nutritional requirement, as a 

reproductive toxicant. While the specific bio-molecular 

mechanisms of reproductive toxicity and teratogenesis still 

require further work, it is well-established from controlled 

laboratory studies and field studies that the best indicator of the 

potential for reproductive end effects from selenium is in tissue 

concentrations, and specifically in egg-ovary concentrations. 

While the relationships of tissue and water concentrations can be 

studied, quantified, modeled, and tasked to risk assessment, the 

now well-established relationship of egg-ovary Se levels to 

toxicity endpoints fully justifies this primacy of this indicator.

Thank you for your comment. 

7. The tiered construction of the chronic criterion is logical and 

scientifically defensible, and the primacy of the egg/ovary 

element over all other elements is also defensible. In fact, the 

primacy of the egg/ovary criterion was also recognized by a 

multidisciplinary and international group of selenium experts 

convened at a workshop in 2009. Proceedings from that 

workshop were published (Chapman et al. 2009) and in the 

executive summary it was noted “Selenium concentrations in 

eggs are the best predictors of effects in sensitive egg-laying 

vertebrates”. Additional sections of that volume further supports 

the USEPA’s Draft Document approach by recommending that

measurement endpoints for risk assessment should be as closely 

associated with reproductive endpoints in egg laying vertebrates 

as possible and that measurements in eggs or ovaries, or in the 

absence of these measures, selenium concentrations in muscle or

Regarding your supportive comment on the tiered construction 

of the chronic criterion, EPA thanks you for your comment.

Regarding the interpretation of the “never to be exceeded” 

criteria, this is an issue that will be addressed in the technical 

support documents.
19

External Peer Reviewers’ Comments EPA Response

whole body are required. The scientific evidence supporting 

these conclusions has not changed substantively since the time 

of that volume’s publication and the approach remains the most 

valid scientifically. In fact, this general approach was also 

recently adopted by the British Columbia Ministry of the 

Environment (BC MoE 2014) after an extensive, and peer 

reviewed, analysis of the literature relevant to the ecotoxicology 

of selenium. 

It is unclear however, how the USEPA will interpret the “never 

to be exceeded” criteria. Biological variability, coupled with 

uncertainty regarding the residence of mobile fish species, will 

make it likely that some fish in a given collection may exceed 

the guidelines. It is unclear if a result from one fish (i.e. a single 

exceedance) will render a given management area in noncompliance, or if some average value is intended as the trigger.
20

2.a.ii. Is the primacy of the whole-body/fish muscle element over the water column elements scientifically sound, 

given the prevailing toxicological knowledge and the data and supporting scientific information currently 

available to the Agency? Please provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. Yes, in general a tissue-based criterion should have primacy 

over a water-based criterion for Se due to the complex sitespecific nature for Se bioaccumulation. This is well documented 

in the literature. As discussed by EPA, an egg-ovary based 

criterion is highly desirable but may not always be achievable 

due to logistical constraints or the potentially significant impacts 

on populations of terminal sampling of ovaries for some 

threatened or endangered species. In such cases, whole body or 

muscle plugs provide a reasonable surrogate for the egg-ovary 

element. One item lacking from the WQC is guidance on when 

use of whole body or muscle elements is acceptable. Some 

questions that come to mind:

1.) Can WB or muscle elements be used instead of EO even 

when collection of EO samples is considered logistically and 

environmentally feasible?

2.) Are there seasonal considerations to use of WB and muscle 

samples? For example, is it acceptable to use WB or muscle 

samples collected in the Fall for a species that spawns in the 

Spring?

Regarding your support of the primacy of the tissue-based 

criterion, EPA thanks you for your comment.

Regarding questions 1 and 2 posed by the reviewer. The design 

of the tiered criterion is such that the hierarchy allows for the 

assessment of samples that are available (i.e., muscle, egg ovary, 

or whole body). There are practical and scientific considerations 

for the collection and assessment of specific types of samples

which EPA plans to address in a detailed technical support 

document. For example, whole body or muscle tissue from fish

may provide the best estimate of critical body burdens of 

selenium in fish (male or female) that are not in the process of 

spawning. This and other issues will be discussed in the 

technical support document on fish tissue monitoring which is 

under development by EPA at this time.

2. Again, this is well documented and the only proviso would 

be the choice/selection of the CF value

Regarding your support of the primacy of the tissue-based 

criterion, EPA thanks you for your comment.

Regarding the methodology used to derive a CF value for 

conversion of egg ovary to the whole body or muscle criterion 
21

External Peer Reviewers’ Comments EPA Response

elements; it was based on the most phylogenetically similar 

species for which there were data. There were more individual 

species data available for muscle than for whole body 

conversions. The choice or selection of a different CF value 

may play a role in the calculation of a site-specific criterion.

3. Yes, in my opinion the primacy of the whole-body or muscle 

selenium criterion over the water column criterion is 

scientifically sound. Selenium bioaccumulation potential from 

water to fish is highly site-specific (Brix et al., 2005; Presser and 

Luoma 2010; Stewart et al., 2010), so it is appropriate that a 

whole-body or muscle selenium criterion is given a priority over 

a water column selenium criterion. Consideration of only a 

water column selenium criterion (or a water column selenium 

criterion that is given priority over a fish tissue-based selenium 

criterion) would necessarily have to be very low to ensure 

protection of the sites with the greatest selenium 

bioaccumulation potential. However, this would potentially be 

problematic because it would trigger concerns (i.e., selenium 

criterion exceedances) at locations where selenium 

bioaccumulation potential is lower and not of ecological 

concern.

Literature cited:

Brix KV, Toll JE, Tear LM, DeForest DK, Adams WJ. 2005. 

Setting site-specific water-quality standards by using tissue 

residue thresholds and bioaccumulation data. Part 2. 

Calculating site-specific selenium water-quality standards 

for protecting fish and birds. Environ Toxicol Chem 24:231-

237.

Presser TS, Luoma SN. 2010. A methodology for ecosystemRegarding your support of the primacy of the tissue-based 

criterion, EPA thanks you for your comment.

Regarding your comment on the potential problems associated 

with the adoption of only a water criterion element, EPA

recommends adoption of all four elements of the selenium 

criterion. The hierarchy of the criteria is such that, for an 

existing input, a tissue sample will always supersede the result 

of the water element, because the tissue sample(s) are most 

closely associated with the endpoint of concern: reproductive 

impacts on aquatic species. In the situation the peer reviewer

presented, tissue sample(s) could be collected to confirm or 

refute the result of the water sample(s). It may be necessary to 

collect multiple samples over a period of time to ensure that 

selenium is not building up in the system leading to increased 

bioaccumulation in the biota. For example, if the selenium 

entering the environment is from a recent new or increased 

input, the fish tissue concentrations may not yet reflect the 

ultimate “steady state” accumulation of selenium in fish tissue, 

because of a lag time of accumulating selenium moving through 

the food web.
22

External Peer Reviewers’ Comments EPA Response

scale modeling of selenium. Integr Environ Assess Manag 

6:685-710.

Stewart R, Grosell M, Buchwalter D, Fisher N, Luoma S, 

Mathews T, Orr P, Wang W-X. 2010.

Bioaccumulation and trophic transfer of selenium. 93-139 in 

Chapman PM, Adams WJ, Brooks ML, Delos CG, Luoma SN, 

Maher WA, Ohlendorf HM, Presser TS, Shaw DP, eds. 

Ecological assessment of selenium in the aquatic environment. 

SETAC Press, Pensacola, FL, USA.

4. This approach is wholly justifiable because Se is accumulated 

by animals almost exclusively through diet rather than directly 

from the dissolved phase in ambient water. In fact, Se and 

perhaps methylmercury would be extreme examples in which 

this approach is appropriate.

Thank you for your comment.

5. Yes, in the absence of egg/ovary [Se], the next best thing is 

whole-body or muscle [Se]. Practically, whole-body or muscle 

samples are more reliably collected throughout the year since 

most adult female fishes do not have appreciable ovarian tissue 

mass during non-reproductive periods. This is especially true in 

small-bodied fishes. In addition, muscle tissue can be collected 

non-lethally in larger fishes, which may be particularly relevant 

to threatened species.

It is important to note that [Se] in ovarian tissue containing only 

primary oocytes or pre-vitellogenic ovarian follicles (i.e., during 

the non-reproductive period spanning most of the year in many 

fishes) will likely provide similar information on Se risk as 

whole-body or muscle [Se]. This is because the ultimate Se dose 

is maternally delivered to eggs during the period of 

Regarding your support of the primacy of the tissue-based 

criterion, EPA thanks you for your comment. EPA also thanks 

you for the important information on seasonal considerations of 

collection of egg-ovary versus whole body or muscle tissue and 

will consider this information in the technical support document 

on fish tissue sampling for selenium. EPA also appreciates the 

peer reviewer’s clarification of the type of selenium 

incorporated into vitellogenin. Most of the toxicity studies 

evaluated by EPA for criteria derivation involving selenium 

contaminated food use selenomethionine. This likely results in a 

conservative estimate of the exposure dose, since selenium in 

the environment is in multiple forms, some of which are not as 

toxic as selenomethionine.
23

External Peer Reviewers’ Comments EPA Response

vitellogenesis in fishes. Eggs will not be present in the ovary of

most fish species for much of the year. During vitellogenesis 

(the period of egg “growth”), adult females synthesize the yolk 

precursor protein, vitellogenin, in their liver, where it is 

transported via the bloodstream to the ovary and taken up by 

growing (vitellogenic) ovarian follicles (eggs). Thus, the [Se] in 

the liver of adult female fishes may provide a better predictor of 

Se risk than whole-body or muscle [Se]. To be even more 

scientifically correct, it is the concentration of the seleno-amino 

acid, selenomethionine, in the liver of adult female fishes that is 

incorporated into vitellogenin in a non-specific, dose-dependent 

manner (replacing the amino acid methionine) that defines the 

ultimate dose of Se received by their offspring. For more details 

see the following paper, which was not cited in the EPA 

document:

Janz, D.M. 2012. Selenium. Pp. 327-374 In: C.W. Wood, A.P. 

Farrell and C.J. Brauner (Eds.) Fish Physiology Vol 31A, 

Homeostasis and Toxicology of Essential Metals. Elsevier, 

San Diego, CA.

Thus, I do not agree with the statement on page 27 (line 4) that 

“concentrations of Se in ovaries are considered equivalent to 

concentrations of Se in eggs...” because fish ovarian tissue 

during the non-reproductive phase contains somatic cells 

responsible for ovarian maturation processes (i.e., steroidogenic 

cells), and gametes (primary oocytes and pre-vitellogenic 

follicles), and the [Se] in these cells do not necessarily reflect 

the dose of Se that will be received by the eggs (i.e., in the yolk) 

during vitellogenesis. Further studies are needed to examine the 

relationship between [Se] in ovarian tissue vs. eggs. It is 

strongly suggested that the EPA inspect the ovary and egg data 

Regarding the comment on egg-ovary equivalence, EPA notes 

that the text in the criterion document actually states: “In this 

document, concentrations of selenium in ovaries are considered 

equivalent to concentrations of selenium in eggs because most 

studies measured selenium in the ovaries prior to spawning.” 

The last part of the sentence is the relevant part as to why EPA 

considers theses tissues equivalent in the document. The 

selenium egg values for the studies used in the criteria derivation 

were based on eggs just spawned or ripe for spawning (stripped 

and used for spawning), thus they have selenium levels 

representative of the embryo/larvae exposure. The issue of 

temporal considerations on collection of a specific tissue type 

(egg ripeness) for selected species is relevant and will be 

discussed (to the extent information is available) in the 

information developed for states to aid in the implementation of 

the criterion.
24

External Peer Reviewers’ Comments EPA Response

carefully and attempt to derive the potential relationship 

between [Se] in ovarian tissue vs. eggs.

6. With regards to many chemical exposures in aquatic 

ecosystems, tissue levels in resident or migratory aquatic 

animals often help to assess toxic risk by integrating the 

exposure and revealing the storage, distribution, metabolism, 

and excretion of the toxicant, regardless of the geography, 

hydrograph or acute-to-chronic exposure dynamic of the 

chemical. The bimodal nutrient-toxicant behavior of selenium 

adds to the complexity of evaluating approaches to risk 

management. Metabolic and environmental conditions can also 

add complexity and uncertainty to a full understanding of risk in 

selenium impacts aquatic ecosystems. It is clear from many 

studies that the physiological homeostasis (uptake/efflux) of Se 

is not well controlled and the biochemical metabolic corelationship of Se and S pathways in vivo allows for chronic Se 

exposure to advance to toxic endpoints. A recurring issue in 

aquatic ecosystem Se management has been co-exposure to high 

levels of sulfur, typically as sulfate. While high sulfate coexposure may impact Se toxicosis, tissue Se levels yield a high 

quality, aquatic Se toxic impact potential metric regardless of 

sulfate co-exposure or other co-factors in Se reproductive 

toxicity (e.g., synergists or antagonists), known or unknown. 

This Se fish tissue approach, including eggs, ovary, muscle or 

whole body, is robust with respect to the findings of several

decades of peer-reviewed studies. Selenium levels in fish tissue 

are broadly accepted in the scientific community as a high 

quality indicator suitable for risk management of aquatic life. 

The document supports the tissue approach and key 

toxicological endpoints with a critical review of the peerThank you for your comment.
25

External Peer Reviewers’ Comments EPA Response

reviewed literature and inclusion or rejection of specific studies 

and the data or findings therein, in an overall transparent, logical 

and defendable manner. 

The tier placement of whole-body/fish muscle is appropriate 

since egg/ovary assessment may have practical challenges with 

some ecosystems, with some species, the size of the target fish, 

and with some aspects of the life-cycle of the target fish. The 

inclusion and tier level of fish tissue selenium gives flexibility in 

aquatic ecosystem risk assessment. 

Inclusion of water column Se levels in the tiered criteria will no 

doubt help screen for potential Se impacts in aquatic ecosystems 

that have not had a history or occurrence of selenium 

contamination, and in the prevention of discharges or other 

anthropogenic activities that present an unacceptable risk to 

water quality.

7. Affording primacy to the measurement of selenium in tissues 

over measurements in the water column is scientifically sound. 

While egg/ovary are recognized as the best predictors of 

potential impacts of selenium in oviparous vertebrates, there 

may be situations where these tissues are not available or where 

technical expertise is not sufficient to allow collection. In this 

instance, muscle or whole body measures are the next best 

alternative to egg/ovary as a risk assessment tool. The use of 

water column concentrations of selenium as environmental 

assessment tools or as triggers for additional assessment is 

fraught with uncertainty from several sources, which are 

discussed in subsequent sections of this review. 

However, it is important to recognize that the use of these 

tissues for monitoring purposes introduces a layer of uncertainty 

Regarding your support of the primacy of the tissue-based 

criterion, EPA thanks you for your comment.

Regarding uncertainty associated with the water column 

criterion elements, EPA recognizes this uncertainty, but notes 

that the water column element is useful for implementing in 

permits, and in certain situations water will be the preferred 

sample in the case of water bodies with new discharges of 

selenium or where adequate fish samples are not available. In 

situations where both fish tissue and water samples are 

available, the water column values are backstopped by the fish 

tissue criteria elements in the hierarchal construction of the 

criterion and thus provide a means for reducing the uncertainty.
26

External Peer Reviewers’ Comments EPA Response

with regard to potential reproductive toxicity assessments. This 

uncertainty arises because selenium partitions between 

egg/ovary and muscle/whole body differently in different 

species. For example, regression plots of selenium 

concentrations in eggs versus those in muscle of 8 fish species 

revealed vastly different slopes and strengths of regression 

between species (see figure below reproduced directly from 

North America Metal Council ([NAMC] 2008), y axis scale is 

Egg Se (mg/kg dry weight (dw)). Due to this divergence, in 

order for muscle to be used as an effective surrogate for 

concentrations of selenium in egg/ovary, the specific regression 

for the fish species in question will have to be documented. 

With regard to whole body as a criterion, it is unclear whether 

the USEPA intended to include visceral tissues (e.g., liver, 

kidney, gonads, gastrointestinal tract) with the carcass for whole 

Regarding variability in egg-ovary to whole body conversion 

factors (CFs), in the EPA dataset, variability in egg-ovary to 

whole body CFs was relatively low for the majority of species, 

ranging from 1.38-2.44 for 16 of 17 species. The inter-species 

range of CFs for egg ovary to muscle was comparable. EPA 

will address these and other issues in the technical support 

document on fish tissues monitoring for selenium.

Regarding the definition of a whole body tissue sample, the 

entire fish (carcass and visceral tissue) is homogenized, and then 

a sample of the homogenized tissue is collected and analyzed for 

selenium. The whole body criterion element is ranked as a 

lower tier than the egg-ovary criterion element because of the 

additional uncertainty associated with variable selenium 

concentrations across tissue types.
27

External Peer Reviewers’ Comments EPA Response

body measurements of selenium. Because these tissues can 

account for a significant amount of the whole body pool of 

selenium, when Se concentrations in liver and gonads are 

elevated (especially during oogenesis [i.e. egg formation]), this 

requires clarification.
28

2.a.iii. Please comment on the scientific uncertainty that may be associated with this tiered approach? Are there 

other data sources, models, or approaches that EPA should consider that would reduce uncertainty? Please 

provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. There are of course a number of uncertainties in the tiered 

approach proposed by EPA. I provide specific comments on 

these uncertainties throughout this review. Overall though, I do 

not believe there are any currently available data sources, models 

or alternative approaches that EPA has not considered that 

would significantly reduce the uncertainty. 

Thank you for your comment.

2. While the approach is scientifically justifiable, the 

propagation of errors that combine to make the total uncertainty 

is a bit daunting. Indeed, their frequent use of r or r2values for 

log/log plots completely masks the overall uncertainty; what are 

the correlations for direct concentration comparisons? I suspect 

they are much less than 0.4 and the p values would make them 

far less significant. Having said this, the trophic level transfers 

between higher levels (1 and above) are well described and 

parameterized in the literature, so the authors really should do a 

complete error/sensitivity analysis to quantify the overall 

error/uncertainty.

Thank you for your comment.

EPA has considered the variability and uncertainty inherent with 

this derivation and has made some modifications to the 

document, including incorporation of new data, and modification 

of the Conversion Factor (CF) methodology to better reflect 

taxonomic similarities as described immediately below. 

Regarding development of CF and Trophic Transfer Factor 

(TTF) values that better reflected taxonomic similarities among 

species when species-specific data were not available, to

estimate TTF or CF values, EPA sequentially considered higher 

taxonomic classifications (i.e., species, genus, family, order, 

then class) until one or more taxa for which a calculated TTF or 

CF value was available matched the taxon being considered. If 

the lowest matching taxon was common to more than one 

species with a TTF or CF value available, EPA used the median 
29

External Peer Reviewers’ Comments EPA Response

TTF or CF from the matching species. 

This criterion was designed to allow for easy application to sitespecific conditions; the variability and uncertainty will likely be 

lower with a dataset from a specific site.

3. Overall, I believe that the tiered approach is scientifically 

appropriate. I do have specific comments on the actual selenium 

criteria at each tier, which are provided under specific charge 

questions below.

Thank you for your comment.

4. The EPA can provide further levels of uncertainty with regard 

to toxicity associated with fish egg/ovary contamination. How 

many studies is this approach ultimately reliant upon? The report 

is based on a limited number of studies, but more studies are 

warranted before we can be assured that this approach is rocksolid.

Regarding the number of studies upon which this approach is 

ultimately reliant, EPA evaluated 80 studies on selenium toxicity 

to aquatic organisms, identified in appendices C, D, and E; and 

in section 3.1.3. The 13 GMCVs (not including the 2 

“placeholder” GMCVs used to fulfill missing taxonomic 

minimum data requirements [MDRs] included in the sensitivity 

distribution [SD]) were calculated from 15 SMCVs, which were 

calculated from 19 chronic values obtained from 24 studies. An 

additional 21 non-reproductive toxicity values were obtained 

from 20 studies for 10 species, including 5 species that were not 

used in the SD. Fish reproductive and non-reproductive 

summaries are included in Appendix C and D, respectively, and 

were used to demonstrate that the egg-ovary based criterion 

protects against both reproductive and non-reproductive effects

in aquatic organisms. An additional 21 toxicity values from 22 

studies encompassing 18 species, seven of which were not 

included among the reproductive or non-reproductive studies 

listed above, were evaluated and are included in Appendix E 

(other data). Three field studies with multiple species were also 

evaluated qualitatively to assess the relative sensitivity of 

Cyprinidae to selenium, and are included in Appendix E. 
30

External Peer Reviewers’ Comments EPA Response

Finally, 11 studies encompassing 11 species were qualitatively 

evaluated to assess selenium nutritional requirements and are 

included in Appendix E. While EPA agrees that additional 

studies are always desirable, the selenium criterion is based upon 

a substantial dataset.

5. One major source of uncertainty is the translation of wholebody or muscle [Se] to egg/ovary [Se]. This relationship has 

been documented for 10 fish taxa in the document (Tables 7a 

and 8a). These ratios vary about two-fold among taxa (1.21-2.44 

for EO:WB and 0.95-1.92 for EO:M). Not all fish taxa have been 

studied, and more work is needed in this area. Importantly, in a 

given fish species these ratios may vary considerably among 

aquatic ecosystems due to differences in the food web, 

biogeochemistry of Se, and other factors. These ratios may also 

vary across seasons. Nonetheless, the data sources, models and 

approaches used by the EPA to derive these ratios are valid; we 

simply need more data to more accurately define these 

conversion factors.

The major source of uncertainty in the tiered approach is the 

conversion of tissue (egg, ovary, muscle or whole-body) [Se] to 

water column [Se]. The approach used by the EPA is appropriate 

and uses, for the most part, the recent biodynamic modeling 

approach to derive water column [Se] from tissue [Se]. 

However, to use water column [Se] as a criterion in of itself in 

the absence of tissue [Se] data is a recipe for inappropriate 

conclusions, which may penalize industry (i.e., false positives) 

or cause harm to certain fish populations (i.e., false negatives). I 

strongly believe that water column [Se] should be used more as a 

“trigger” to initiate further monitoring that includes collection of 

fish for tissue [Se] determinations. I also think that a safety 

Regarding inter-species variability in conversion factors, while 

not all fish taxa have been studied, major freshwater fish 

families that are phylogenetically distinct and diverse are 

represented, and yet there is only roughly a two-fold variability 

between them. Given the inherent variability (2-3) fold in 

sensitivity observed even among species with repeated toxicity 

tests, 2-fold variability is a small level of uncertainty compared 

to uncertainty associated with other pollutants. EPA agrees that 

more data for the tissue conversion factors are always desirable. 

EPA is moving forward with the current database to ensure 

protection of aquatic life based on the current state-of-thescience. 

Regarding the tiered approach, the water column criteria is 

backstopped with the hierarchal construction of the tissue 

criteria; exceedance of a water column value, can be confirmed 

via sampling of fish tissue. 

Regarding the lack of clarity in the definitions of lotic and lentic

water bodies. Based on comments received, EPA examined the 

potential for residence time to classify the water bodies in the 

database, but available data were extremely limited. EPA also 

examined each waterbody to ensure that the available 
31

External Peer Reviewers’ Comments EPA Response

factor should be applied to the proposed 1.3 ug/L and 4.8 ug/L 

criteria for lentic and lotic systems, respectively, which would 

reduce these values as triggers for further ecosystem monitoring. 

There are many examples of lentic systems with < 1 ug/L 

dissolved [Se] where negative effects of Se on early life stage 

development of fishes have been demonstrated.

This is an appropriate place to discuss the problems with a crude 

classification of systems as lentic vs lotic. Many rivers in the 

USA are impounded, essentially creating lentic systems for a 

significant portion of their river-miles, although they would still 

be classified as lotic. I think the EPA needs to more clearly 

define these terms. One suggestion is to use water residence time 

and/or mean annual flow velocity as more quantitative 

descriptors. Many of the studies that have shown lower Se 

bioaccumulation in lotic systems have been conducted in fastflowing mountain streams, creeks and rivers. To classify a river 

in the southern USA that has numerous dams as a lotic system 

does not make sense.

characteristics and sample location indicated that it was either a 

lentic or lotic site. EPA’s follow-up analyses ensured that sites

such as run-of-the-river-reservoirs, an example discussed in the 

reviewers comment, were not misclassified as lotic.

6. The tiered approach presented in the criterion embodies the 

best available scientific knowledge of selenium in aquatic 

ecosystems actively studied by a broad range of investigators, 

disciplines and institutions, across a diverse range of water 

environments and potentially impacted organisms, over more 

than three decades of focused effort. While all science has 

uncertainty, the magnitude and diversity of the research effort in 

the environmental toxicology and regulatory science community 

to understand the complex risk dynamic of selenium in aquatic 

ecosystems is unprecedented in the history of U.S. 

environmental law. The 2014 Aquatic Life Ambient Water 

Quality Criterion for Selenium balances the available data, 

Thank you for your comment.
32

External Peer Reviewers’ Comments EPA Response

models, and approaches to risk management. The document and 

the tiered criteria within represent a balanced approach where 

assumptions and data uncertainties are clearly laid out and 

discussed. Published data or results that were not included in 

criterion determination were adequately and satisfyingly 

discussed and defended for exclusion. The data and peerreviewed studies used in the quantitative and qualitative 

development of the criterion are sufficiently robust, sufficiently 

concordant in their conclusions, and sufficiently broad in their 

scope and number to result in a criterion that can protect aquatic 

organisms under the requirements of the Clean Water Act.

7. Uncertainty associated with the US-EPA’s tiered approach 

arises from the species specific disposition of selenium into 

egg/ovary versus muscle and whole body (noted above) and in 

the sampling methods used to obtain these tissues. In terms of 

sampling methods, timing may contribute to variability. A recent 

study showed that some fish may partition selenium to the 

eggs/ovaries more immediately from the diet than from their 

tissue stores (Conley 2014). In these species of fish, 

muscle/whole body might be less reflective of egg/ovary 

selenium concentrations than concentrations in the diet. 

However, the authors noted that spawning strategy may play a 

role in determining the importance of tissue reserves versus 

dietary sources accounting for selenium partitioned to egg/ovary. 

Specifically, for species with longer periods of oogenesis and 

which spawn only once annually, tissue stores may be better 

predictors of egg/ovary selenium concentrations than dietary 

sources. However, for multiple spawners, the diet may be a more 

important determinant. This has relevance to the both the 

egg/ovary and muscle/whole body criteria recommended by the 

Regarding the effect of timing on the variability of selenium 

between tissues, the Conley (2014) reference was not yet 

available when the draft criterion was developed. However, the 

agency is aware that spawning strategy likely plays a role in 

accumulation, and maternal transfer and deposition of selenium

into the eggs. This issue will be addressed in the technical 

support materials under development regarding the timing and 

type of sampling based on species spawning strategy (single 

batch versus multiple smaller batches) and seasonality (spring or 

fall [some salmonids] versus sporadic spring/summer [e.g., 

cyprinids]), while also providing flexibility to states to adapt 

their monitoring programs to address the additional requirements 

for fish tissue monitoring for selenium.
33

External Peer Reviewers’ Comments EPA Response

US-EPA and the variability inherent in each. If muscle/whole 

body were used as a measure of compliance the timing of 

sampling within the fishes’ reproductive cycle could have an 

influence on the concentration of selenium in the tissue, 

especially among single spawners with extended oogenesis 

periods. Therefore, if muscle/whole body were sampled 

immediately following the spawning period lower 

concentrations of selenium might be expected than if the tissues 

were sampled prior to oogenesis. 
34

2.a.iv. Are the draft recommended magnitude, duration, and frequency for each criterion element scientifically 

sound and appropriate? Please provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. I have provided specific comments on these issues in 

response to the questions below.

Thank you for your comment.

2. I found the time and frequency evaluations of the factors (not 

elements) well justified, with the exception of the EF, to be 

explained in later comments.

Thank you for your comment. The EPA response to the 

comment on EF is given below, adjacent to the peer reviewer’s

detailed comments.

3. The comments below are organized first by magnitude, 

duration, and frequency, and then by criterion element (i.e., fish 

egg or ovary, fish whole-body or muscle, and water column) 

within each of these categories.

Magnitude

Fish Egg/Ovary Se Criterion

Brown Trout

The draft fish egg/ovary selenium criterion is 15.2 mg/kg dw. 

This draft criterion is driven by brown trout (Salmo trutta), 

which had an EC10 of 15.91 mg/kg dw in the EPA's draft 

AWQC document. This study, conducted by Formation 

Environmental (2011a), has received tremendous scrutiny in 

how to best interpret the results and derive a defensible EC10. In 

my earlier review of that study on behalf of the Eastern Research 

Group (ERG) and EPA, I had concluded that the most relevant 

egg selenium EC10s that could be derived from that study 

ranged from 20.70-21.60 mg/kg dw. In that same review, 

however, I concluded that an egg selenium EC10 of 16.76 

mg/kg dw was on the lower end of the range of possible EC10s 

Regarding the brown trout study, EPA re-analyzed the available 

data on the Formation 2011 study after issuing the External Peer 

Review Draft Selenium Criterion document in 2014. Several 

analytical approaches were considered based on peer review and 

public comments. Because of uncertainty associated with how to 

best interpret the health and mortality of larval fish lost to an 

overflow event caused by a clogged drain, EPA re-evaluated the 

EC10 for mortality during the hatch through swim up portion of 

the test, and did not include the 15 day post swim up portion of 

the test. The hatch through swim up test is the more 

conventional test duration for these kinds of maternal transfer 

tests, and the resulting EC10 was determined to be 18.09 mg/kg 

dw. The description and supplementary analyses are included in 

the Effects Characterization section of the main text and in 

Appendix C.

Regarding the comment on bluegill, following the peer review, 

EPA reanalyzed the Hermanutz bluegill study using a combined 

endpoint of larval survival and edema. Including larval survival 

in the endpoint eliminated the more variable nest data since it 
35

External Peer Reviewers’ Comments EPA Response

that could be derived from the study. Accordingly, in my 

opinion, the EC10 of 15.2 mg/kg dw used by the EPA is an 

overly conservative interpretation of the brown trout Se toxicity 

study.

Bluegill

The second lowest species mean chronic value (SMCV) was 

18.41 mg/kg dw for bluegill sunfish (Lepomis macrochirus). 

This SMCV was based on the geometric of EC10s from three 

studies: (1) an EC10 of 20.05 mg/kg dw from Doroshov et al. 

(1992); (2) an EC10 of 24.55 mg/kg dw from Coyle et al. 

(1993); (3) an EC10 of 12.68 mg/kg dw from Hermanutz et al. 

(1992, 1996). The latter EC10 is much less than the other two 

EC10s for bluegill and less than even a very conservative 

interpretation of the EC10 for brown trout. I agree with the 

interpretations of the Doroshov et al. (1992) and Coyle et al. 

(1993) studies, but disagree with the interpretation of the 

Hermanutz et al. (1992, 1996) study. The EC10 of 12.68 mg/kg 

dw from Hermanutz et al. (1992, 1996) is driven by two 

treatments from Study 1: these were Streams 3 and 8 which had 

an ovary Se concentration of 17.71 mg/kg dw and 80% edema 

was observed and Steam 4 which had an ovary Se concentration 

of 15.46 mg/kg dw and 50.3% edema was observed. At first 

glance, there are three issues that stand out:

 First, the water Se treatment concentration that resulted 

in an ovary Se concentration of 17.71 mg/kg dw in Study 

I was 10 μg/L—in the 10 μg Se/L treatment in Study II 

the ovary Se concentrations averaged 36.39 mg/kg dw 

and the average rate of edema was 83%. Thus, the rates 

was not possible to measure survival in the nest. The combined 

endpoint fit the TRAP model well with an EC10 of 11.36 mg/kg. 

This EC10 was included in the bluegill SMCV in the 

accompanying 2015 draft criterion document. EPA recognizes 

the discrepancy between the bluegill tissue between Study I and 

II is 10 μg/L in streams. However, the 10 μg/L treatment from 

Study I was only one data point in the analysis and it did fit the 

curve well, so it was included. The 30 μg/L fish all died by the 

end of the test and Se accumulation was apparently affected by 

its toxicity. Overall, EPA recognizes the uncertainties in the 

Hermanutz bluegill study, but believes that the current scientific 

analysis is scientifically defensible and reasonable to include in 

criterion development.

Regarding the use of the Esox data, EPA exhaustively examined 

the data. EPA does not believe that the authors’ EC10 

calculation is scientifically defensible. The spacing between 

exposures is too large to estimate the EC10 either by the 

authors’ linear regression approach, or by EPA’s nonlinear 

regression approach. But based on its cluster of three values 

with concentrations near 34 mg/kg dw, and having a 24% effect, 

EPA estimates that Esox is somewhat sensitive, but not among 

the four most sensitive species.

Regarding the comment on the logic for setting the number of 

GMCVs to 14, the goal of aquatic life criteria is to ensure 

protection of populations of species representing the entire 

aquatic community, and not just fish, as described in the 

methodology for criteria development (Stephan et al. 1985). 
36

External Peer Reviewers’ Comments EPA Response

of edema were consistent between the 10 μg Se/L 

treatments in Study I and II, on average, but the ovary Se 

concentrations were widely different. The mean 

macroinvertebrate Se concentrations in the 10 μg Se/L 

treatments in Study I and II were similar (grand means 

among all invertebrate taxa were 21.6 and 22.8 mg/kg 

dw for Study I and Study II, respectively [Hermanutz et 

al., 1996]). The relatively large difference in the bluegill 

ovary Se concentrations in Study I compared to Study II, 

therefore, is unexpected.

 Second, in Study I, the ovary Se concentration of 17.71 

mg/kg dw in the 10 μg Se/L treatment was greater than 

the ovary Se concentration of 15.46 mg/kg dw in the 30 

μg Se/L treatment. This is also unexpected because the 

grand mean Se concentration in invertebrate taxa 

collected from the 10 and 30 μg Se/L streams were 21.6 

and 44.7 mg/kg dw, respectively. Thus, a higher ovary 

Se concentration in the 30 μg Se/L stream would be 

expected. This basis for this discrepancy is not clear, 

although the ovary Se concentration measured in the 30 

μg Se/L stream was based on a single fish, which may 

have randomly had a lower ovary Se concentration. 

 Third, a potentially more important source of uncertainty 

is that the ovary Se concentrations in the Hermanutz et 

al. (1992, 1996) study were reported on a wet weight 

basis. Dry weight ovary Se concentrations were 

estimated assuming a moisture content of 76%, which 

was based on the average from Gillespie and Baumann 

(1986), 85%, and Nakamoto and Hassler (1992), 67%. If 

the true moisture content was 85%, the bluegill Se EC10 

Estimated egg-ovary concentrations were originally calculated 

for invertebrates as a point of reference to show that they were 

typically less sensitive then the fish represented in the SSD, and 

would therefore be protected by a tissue criterion based on fish. 

In the current draft, fish and invertebrate SMCVs and GMCVs 

are listed in separate tables, and whole body and estimated eggovary values for invertebrates have been removed from the two 

tables showing the distribution of GMCVs used in the SSD for 

egg-ovary and whole body criteria, respectively. A separate 

Table (5b) was added showing the measured whole body 

SMCVs and GMCVs for the three invertebrate taxa with 

relevant test data, as well as what the predicted whole body fish 

tissue concentrations would be after multiplying the measured 

invertebrate SMCV&GMCV by the median tropic level 2 to 

trophic level 3 trophic transfer function of 1.27. The results 

described in sections 3.1.3-3.1.4 and shown in Table 5b 

demonstrate that invertebrates are less sensitive to selenium in 

fish, and while they are used implicitly in the SSD to fulfill 

taxonomic minimum data requirements, they are not included 

with fish values. These studies are taken into account as part of 

the total “N” in the criterion calculations, in accordance with the 

standard methodology for criteria development (EPA 2008). 

Regarding the comment on the inclusion of additional genera, 

the Catostomus and Xyrauchen studies, presented in Appendix D 

of the 2014 draft. EPA determined these studies are not of 

sufficient quality for quantitative use, therefore they have not 

been included in setting N. During development of the 

document, EPA considered increasing the N used in the criterion 

calculation to reflect inclusion of Catostomus, based on the 
37

External Peer Reviewers’ Comments EPA Response

from Hermanutz et al. (1992, 1996) would be 20.3 mg/kg 

dw (almost identical to the EC10 derived from Doroshov 

et al. [1992]). In contrast, if the true moisture content 

was 67%, the bluegill Se EC10 from Hermanutz et al. 

(1992, 1996) would be 9.2 mg/kg dw.

In my opinion, the uncertainty in the moisture content of the 

bluegill ovaries in the Hermanutz et al. (1992, 1996), along with 

uncertainties in the ovary Se concentrations in Study I, are 

sufficiently great that this study should not be included in the 

SMCV for bluegill, as there are two other studies (Doroshov et 

al. [1992] and Coyle et al. [1993]) for which dry weight ovary 

Se concentrations were reported and the EC10s from those two 

studies were very comparable. The SMCV for bluegill based on 

those two studies would be 22.2 mg/kg dw. Alternatively, if data 

from Study I of Hermanutz et al. (1992, 1996) are pooled with 

data from Doroshov et al. (1992) and Coyle et al. (1993), the 

consistency in the concentration-response data is apparent and 

an EC10 of 21.4 mg/kg dw can be derived (Fig.1 ).

Fig. 1. Concentration-response relationship for bluegill based on 

data pooled from Study I of Hermanutz et al. (1992, 1996), 

Doroshov et al. (1992), and Coyle et al. (1993). EC10 = 21.4 

mg/kg dw based on logistic regression analysis in TRAP.

suggestive evidence from the de Rosemond et al. study, but 

decided that it would be more prudent not to, given that

Crutchfield (2000) states that “By the early 1980s, the fish 

community had collapsed in the Hyco Reservoir and species 

such as [names of several taxa]... and suckers (Catostomidae) 

became much reduced throughout the reservoir.” Regarding the 

Hamilton et al. study, EPA does not believe it can come to any 

reliable conclusion about the relative sensitivity of razorback 

suckers. 

Regarding the comment on adding new studies, the authors of 

the mountain whitefish study were contacted by EPA; however, 

the authors declined to provide these data to EPA at this time. 

The Formation Environmental Yellowstone cutthroat trout study 

has been analyzed and added to the database. 

Regarding the suggestion for EPA to consider using empirically 

measured whole-body Se (or muscle Se) data for those species 

where they are available, rather than applying CFs to egg/ovary 

Se data (EPA’s current approach) using conversion factors, EPA 

determined that the approach used was consistent and linked 

criteria for other tissues to egg-ovary concentrations.

Regarding the comment that notes that there are a few 

reproductive studies for which EC10s can be directly calculated 

as muscle or whole-body concentrations measured during the 

study, EPA opted to use the egg-ovary EC10 from such studies 

and then convert the SMCV or GMCV from EO to WB or M 
38

External Peer Reviewers’ Comments EPA Response

Other Fish Species in the SSD

The draft fish egg/ovary Se criterion derived following EPA 

guidelines is based on the four lowest GMCVs and the total 

number of GMCVs. The two lowest GMCVs in the EPA's draft 

document are for Salmo (represented by brown trout) and 

Lepomis (represented by bluegill), which were both discussed 

above. The 3rd and 4th lowest GMCVs are for Micropterus

(represented by largemouth bass) and Oncorhynchus

(represented by cutthroat trout and rainbow trout). I do not 

disagree with EPA's interpretation of the studies for those 

genera.

The Esox GMCV of <34 mg/kg dw, represented by northern 

pike, is an EC24 because the data were not amenable to 

derivation of an EC10 using TRAP. The EPA compared this 

EC24 to the EC24 that could be derived for rainbow trout and 

noted that the two species appear to be similar in sensitivity, 

with northern pike perhaps slightly less tolerant. In contrast, the 

original study authors for the northern pike study, Muscatello et 

using all available WB/EO or M/EO ratios. Although EPA 

recognizes the merits of the commenter’s suggestion, EPA used 

the current approach because it is also scientifically defensible. 

Regarding the fish whole-body and muscle selenium criteria, the 

primary driver for the low translated water numbers at two lentic 

sites were large EFs, which were site specific. The application 

of generic TTFs to site-species combinations was done for 

purposes of consistency, as site-specific TTFs could not be 

calculated in many cases. As noted above in response to the 

comment of Peer Reviewer 2 regarding Part I, Question 2.a.iii.,

EPA modified the TTF methodology in the 2015 draft to better

reflect taxonomic similarities when data were lacking. Also, 

compared to EFs, TTFs are relatively small and less variable, 

and have less influence on a translated water value.

Regarding the surface water selenium criteria monthly average, 

EPA reanalyzed the data after considering this peer review 

comment and recalculated the lentic and lotic water column 

elements of the criterion to reflect appropriate consideration of 

both high and low exposure sites. In the 2014 External Peer 

Review Draft, translated lentic and lotic water criteria were 

calculated from 44 and 88 site-species combinations, 

respectively. A single site could have as many as 8 sampled fish 

species. For example, of the 44 site-species used for the lentic 

derivation via the 20th percentile value, 12 of the lowest 13 

values are for Badin and High Rock. These lakes each have one 

EF, but each of its EFs is used six times, once for each of six 

fish species. The particulate concentrations measured in both of 

L og Egg/Ovary Se (mg/kg dw )

% Edema or L arval Mortal ity

0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8

0

20

40

60

80

100

120
39

External Peer Reviewers’ Comments EPA Response

al. (2006), reported an EC10 of 20.38 mg/kg dw based on linear 

regression. The EC10 of 20.38 mg/kg dw would make the Esox

GMCV the 4th lowest in the EPA's dataset. This change alone, 

however, would have a negligible influence on the draft fish 

egg/ovary Se criterion—it would raise it slightly from 15.2 

mg/kg dw to 15.6 mg/kg dw (lowering the 4th lowest GMCV 

steepens the slope of the line through the four lowest GMCVs, 

which increases the 5th percentile).

Number of GMCVs Assumed in Fish Egg/Ovary Se Criterion 

Calculation

The logic for setting the number of GMCVs to 14 is flawed in 

my opinion. This number is based on 9 fish genera, 3 

invertebrate genera with tissue-based toxicity data available, and 

2 crustacean genera that were waived. In my opinion, a genus 

sensitivity distribution based on Se toxicity values for fish 

eggs/ovaries, and for which the resulting criterion will be a Se 

concentration in fish eggs/ovaries, and for which compliance 

will be determined by measuring Se concentrations in fish 

eggs/ovaries, cannot include data for non-fish taxa. It must be 

remembered that a criterion based on an internal tissue 

concentration is not the same as a criterion based on an external 

concentration to which the entire aquatic community may be 

exposed. One will not be able to measure Se concentrations in 

invertebrates in order to determine compliance with the fish 

tissue-based Se criterion, so they should not be included in the 

SSD. Further, if I understand correctly, the three whole body Se 

EC10s for invertebrates (37.84 mg/kg dw for B. calyciflorus, 

>140 mg/kg dw for L. variegatus, and 24.2 mg/kg dw for C. 

triangulifer) were multiplied by a (1) diet-to-whole body fish 

TTF and (2) a whole body-to-egg/ovary conversion factor in 

these lakes are near the median observed in EPA’s lentic 

database, but their water concentrations are among the lowest. 

Conversely, several lotic sites (e.g., McElmo Cr., Spring Creek 

at LaBoca, etc.) had very low EFs (and by extension, high 

translated water concentrations), but each EF was used several 

times, once for each fish species. As a result of the peer 

reviewer’s comments, EPA completed a reanalysis of the data to 

remove any overweighting of a few key high and low end sites 

in the calculations. To account for overweighting, EPA used 

one fish species per site – the species most sensitive to selenium 

bioaccumulation, to yield an appropriately protective water 

column criterion element for both lentic and lotic values. In 

addition to adjustments to correct for overweighting due to the 

influence of multiple species at high and low EF sites, changes 

to several TTFs and CFs, reflecting incorporation of new 

information, were made yielding site-species lentic and lotic 

values of 0.9 μg/L and 4.2 μg/L, respectively. Subsequent

adjustments to correct for overweighting due to the influence of 

multiple species at high and low EF sites resulted in an increase 

in the translated lentic water concentration criterion from 0.9 

μg/L to 1.2 μg/L, and a decrease in the translated lotic water 

concentration criterion from 4.2 μg/L to 3.1 μg/L. 

Regarding the intermittent criteria, this criterion element fills a 

need to account for intermittent discharges that may be elevated 

but infrequent, and to account for associated potential loadings 

and chronic risk to downstream waters. Modifications of the 

criterion can be made on a site-specific basis, with data from the 

site. As mentioned above, biokinetic modeling, if used should 

be adapted to a site using appropriate data – the values EPA 
40

External Peer Reviewers’ Comments EPA Response

order to estimate the Se concentrations in fish eggs/ovaries that 

may result from the toxicity thresholds for invertebrates. These 

values were then used as "SMCV & GMCV as estimated EO 

concentration in an accompanying fish assemblage (mg Se/kg 

dw EO)" in Table 6b of the draft AWQC document. However, 

these are simply predicted concentrations in fish eggs/ovary and 

are not effect concentrations for fish. I believe that n should 

equal the number of fish genera, which is 9 based on the draft 

AWQC document.

Additional Genera that Could be Added to the Total N

Although the EPA did not include the egg/ovary Se toxicity data 

for white suckers (Catostomus commersonii; de Rosemond et al. 

2005) and razorback suckers (Xyrauchen texanus; Hamilton et 

al. 2005a,b) because reliable toxicity thresholds (EC10s or 

other) could not be derived, there does appear to be sufficient 

evidence that they would be among the four most sensitive 

genera. Thus, the number of GMCVs used in the criterion 

calculation could be increased from 9 fish genera to 11 fish 

genera.

Toxicity Data for an Additional Fish Species

Nautilus Environmental in Burnaby, British Columbia has 

conducted a Se maternal transfer toxicity study with mountain 

whitefish (Prosopium williamsoni). This species does not appear 

to be especially sensitive (i.e., it would not be among the four 

lowest GMCVs), but it would added another genus to the 

sensitivity distribution. I recommend that the EPA investigate 

presented represented default values that will be generally 

protective in these situations.

Regarding the suggested EC10 values for brown trout and 

bluegill, EPA revisited the analyses of these relevant studies and 

made appropriate revisions in the 2015 document.

Regarding the criterion frequency, selenium is persistent, 

however, it may be sequestered in an environmental 

compartment that precludes it from uptake in biota (e.g., burial 

in sediment). EPA’s AWQC are traditionally based on aqueous 

concentrations since toxicity for the chemicals for which criteria 

have been developed is generally due to aqueous exposure. 

These concentrations can vary significantly both short-term and 

long term, allowing organisms in the aquatic community to 

recover. In contrast, selenium is a bioaccumulative pollutant, 

and fish tissue concentrations have been directly correlated with 

the adverse effect. Also reductions in fish tissue concentrations 

occur slowly, even after removal of a selenium source. Since 

exceedance of these concentrations is correlated with adverse 

effect occurs EPA determined that these levels cannot be 

exceeded in order to be protective of the aquatic community.

Technical support information regarding fish tissue sampling 

issue is being developed by EPA.
41

External Peer Reviewers’ Comments EPA Response

whether this study is publically available and, if so, whether it 

meets the EPA guideline for test acceptability and inclusion in 

the sensitivity distribution. The Se toxicity study with 

Yellowstone cutthroat trout (Formation Environmental 2011b) 

should also be considered.

Influence of Potential Changes to GMCVs and N

As summarized above, in my opinion, the most conservative and 

reasonable EC10 that can be derived for brown trout is 16.76 

mg/kg dw (although the weight-of-evidence suggest to me that 

the EC10 falls between about 20.7-21.6 mg/kg dw) and that the 

bluegill SMCV should be 22.2 mg/kg dw. If the four lowest 

GMCVs were 16.76 mg/kg dw for Salmo, 20.35 mg/kg dw for 

Micropterus, 22.2 mg/kg dw for Lepomis, and 22.53 mg/kg dw 

for Oncorhynchus, and the total number of fish genera was set 

equal to 11 (with inclusion of the two sucker genera), the 

resulting criterion would be 16.0 mg/kg dw. Alternatively, if the 

Esox (northern pike) GMCV was adjusted from <34 mg/kg dw 

to 20.4 mg/kg dw, the resulting criterion would change slightly 

to 16.1 mg/kg dw. 

Fish Whole-body and Muscle Se Criteria

The draft fish whole-body and muscle selenium criteria are 8.1 

and 11.8 mg/kg dw, respectively. In general, I believe that the 

approach for deriving these draft criteria is reasonable and that 

the magnitudes of these criteria are consistent with the 

toxicological literature. My only suggestion is that the EPA 

consider using empirically measured whole-body Se (or muscle 

Se) data for those species where it is available, rather than 

applying CFs to egg/ovary Se data. It would be interesting to see 
42

External Peer Reviewers’ Comments EPA Response

whether that has a significant influence on the draft whole-body 

or muscle Se criteria. And of course if any modifications are 

made to the egg/ovary Se GMCVs, this would influence the 

draft whole-body and muscle Se criteria, as would a change to 

the number of genera, if my suggestions above are considered.

Surface Water Se Criteria - Monthly Average

The draft water column selenium criteria are 4.8 and 1.3 μg/L 

for lotic and lentic waters, respectively. In general, I do not 

agree with the approach used by the EPA in deriving these water 

column criteria. Although I do not agree with the approach, I do 

believe that the draft criterion of 4.8 μg/L for lotic waters is

reasonable and consistent with our understanding of the range of 

Se bioaccumulation potential into fish across a wide range of 

lotic sites. However, for the draft lentic Se criterion of 1.3 μg/L, 

the approach used by the EPA results in this criterion being 

almost exclusively driven by data for two reference locations. 

This in turn is mostly due to what I perceive as a flaw in the 

approach, where site-specific Se data in invertebrates and fish 

are ignored and instead non-site-specific TTFs and CFs are 

applied that are inconsistent with the site-specific data. This 

resulted in cases where erroneously high modeled Se 

concentrations in fish tissue are linked with low water Se 

concentrations (i.e., reference site concentrations), and then 

these become the "drivers" for the draft lentic criterion of 1.3 

μg/L. Please see my detailed comments on this issue in Part III.

Surface Water Se Criteria - Intermittent Exposure
43

External Peer Reviewers’ Comments EPA Response

The draft intermittent exposure Se criteria represent a 

mathematical manipulation of the monthly average criteria in 

order to derive values that would still result in 30-day average 

concentrations of 4.8 and 1.3 μg/L for lotic and lentic waters, 

even if those were exceeded for x number of days. A limitation 

of this approach is that it does not consider the uptake and 

elimination kinetics of Se in aquatic food chains and the 

influence of exposure duration and magnitude on these 

biokinetic parameters. In my opinion, a biokinetic modelingbased approach would be more appropriate for deriving 

intermittent, or acute, criteria that are protective against 

exceeding fish tissue-based Se criteria. More details are 

provided in my comments in Part III below.

Duration

Fish Egg/Ovary, Whole-body, and Muscle Se Criteria

The draft fish tissue-based selenium criteria (eggs, ovaries, 

whole-body, muscle) are "instantaneous measurements" as "Fish 

tissue data provide point measurements that reflect integrative 

accumulation of selenium over time and space in the fish at a 

given site" and "Selenium concentrations in fish tissue are 

expected to change only gradually over time in response to 

environmental fluctuations." I agree with the EPA's decision that 

the duration for fish tissue Se measurements should be an 

instantaneous measurement since, for most scenarios and fish 

species, the Se concentrations in fish tissue will be reflective of 

a longer term exposure.

Surface Water Se Criteria - Monthly Average and Intermittent 

Exposures

In my opinion, 30 days for an average exposure duration is 
44

External Peer Reviewers’ Comments EPA Response

reasonable, especially since an intermittent criterion is being 

considered (although, as noted, I believe the intermittent 

criterion would best be derived using a biokinetic modeling 

approach). Biokinetic data for algae and several freshwater 

invertebrates indicate that steady-state Se concentrations in the 

food chain may be achieved within this time frame.

Frequency

Fish Egg/Ovary, Whole-body, and Muscle Se Criteria

Although the EPA's AWQC, including the draft water Se 

criteria, are not to be exceeded more than once in three years, 

the fish tissue-based Se criteria are "never to be exceeded." To 

my knowledge, the "frequency" component of AWQC is rarely 

incorporated into permit limitations, so the implications of fish 

tissue-based Se criteria "never to be exceeded" are not entirely 

clear to me. The "frequency" component was initially 

incorporated into AWQC based on the premise that ecosystems 

will not be harmed if the number of criterion excursions is 

limited and/or there are compensating periods of time below the 

criterion over which the ecosystem can recover. As far as I can 

tell, the draft AWQC document for Se does not explain the basis 

for the "never to be exceeded" frequency decision for fish tissue. 

It seems that there should be some level of consistency between 

the allowable "frequency" for fish tissue-based and water-based 

Se criteria. 

Surface Water Se Criteria - Monthly Average and Intermittent 

Exposures
45

External Peer Reviewers’ Comments EPA Response

The "frequencies" of "not more than once in three years on 

average" are consistent with the EPA guidelines and AWQC for 

other chemicals. As noted above, however, I am not aware of the 

"frequency" component of AWQC being incorporated into most 

effluent limitation so am unsure of the significance of this 

component. The fixed monitoring benchmark (FMB) approach, 

which has initially been developed for copper and biotic ligand 

model (BLM)-based criteria, represents a method that does 

explicitly account for exceedance frequency (USEPA 2012). 

However, this approach is for use under a site-specific context 

and would not apply to the national (non-site-specific) Se 

criteria. A reasonable excursion frequency for Se in water 

should be determined carefully, however, as Se is 

bioaccumulative and has variable persistence depending on 

receiving water conditions. For example, more frequent 

excursion frequencies may not be consequential in lotic systems 

with low biological productivity and short resident times, while 

an excursion frequency greater than once every three years may 

be warranted for lentic systems with high biological productivity 

and long residence times. In summary, I think the "frequency" 

decisions should be evaluated and explained in more detail.

Literature cited:

Coyle JJ, Buckler DR, Ingersoll CG, Fairchild JF, May TW. 

1993. Effect of dietary selenium on the reproductive success 

of bluegills (Lepomis macrochirus). Environ Toxicol Chem 

12:551-565.

de Rosemond SC, Liber K, Rosaasen A. 2005. Relationship 

between embryo selenium concentration and early life stage 
46

External Peer Reviewers’ Comments EPA Response

development in a white sucker (Catostomus commersoni) 

from a northern Canadian lake. Bull Environ Contam 

Toxicol 74:1134-1142.

Doroshov S, Van Eenennaam J, Alexander C, Hallen E, Bailey 

H, Kroll K, Restrepo C. 1992. Development of water quality 

criteria for resident aquatic species of the San Joaquin River. 

University of California, Davis.

Formation Environmental. 2011a. Brown trout laboratory 

reproduction studies conducted in support of development of 

a site-specific selenium criterion. Prepared for J.R. Simplot 

Company. Pocatello (ID): Smoky Canyon Mine.

Formation Environmental. 2011b. Yellowstone cutthroat trout 

laboratory reproduction studies conducted in support of 

development of a site-specific selenium criterion. Prepared 

for J.R. Simplot Company. Pocatello (ID): Smoky Canyon 

Mine.

Gillespie RB, Baumann PC. 1986. Effects of high tissue 

concentrations of selenium on reproduction by bluegills. 

Trans Am Fish Soc 115:208-213.

Hamilton SJ, Holley KM, Buhl KJ, Bullard FA. 2005a. 

Selenium impacts on razorback sucker, Colorado River, 

Colorado. II. Eggs. Ecotoxicol Environ Saf 61:32-43.

Hamilton SJ, Holley KM, Buhl KJ, Bullard FA. 2005. Selenium 

impacts on razorback sucker, Colorado River, Colorado. III. 

Larvae. Ecotoxicol Environ Saf 61:168-189.

Hermanutz RO, Allen KN, Roush TH, Hedtke SF. 1992. Effects 

of elevated selenium concentrations on bluegills (Lepomis 

macrochirus) in outdoor experimental streams. Environ 
47

External Peer Reviewers’ Comments EPA Response

Toxicol Chem 11:217-224.

Hermanutz RO, Allen KN, Detenbeck NE, Stephan CE. 1996. 

Exposure of bluegills (Lepomis macrochirus) to selenium in 

outdoor experimental streams. U.S. Environmental 

Protection Agency, Duluth, MN, USA.

Nakamoto RJH, T.J. 1992. Selenium and other trace elements in 

bluegills from agricultural return flows in the San Joaquin 

Valley, California. Arch Environ Contam Toxicol 22:88-98.

USEPA. 2012. Calculation of BLM fixed monitoring 

benchmarks for copper at selected monitoring sites in Colorado. 

Office of Water, USEPA. 820R12009.

4. I do not see obvious errors in their approach. Thank you for your comment.

5. The egg/ovary criterion of 15.2 mg/kg relies strongly on the 

reassessment of brown trout data, in particular the Formation 

study. It seems that much of the issue is related to the lab 

accident where larval trout were removed from an aquarium due 

to a faulty standpipe. The EPA has chosen to assume the worstcase, that 100% of the fish that escaped were dead and/or 

deformed, resulting in an EC10 of 15.91 mg/kg egg. However it 

is plausible that certain of these fish were not dead or deformed, 

as discussed in certain public comment documents. The EPA has 

reanalyzed these data to account for different scenarios, and 

shown that the EC10 varies from 15.91 to 21.16 mg/kg egg. It 

seems to me that the 15.91 mg/kg EC10 may be overly 

conservative. Due to the lack of knowledge regarding the status 

of these escaped fish (dead, deformed, or healthy), perhaps the 

assumption could be made that 50% of the escaped fish were 

dead/deformed, and 50% were normal. This would only slightly 

The brown trout egg ovary EC10 has been re-evaluated by EPA 

based on recognition of confounding occurring due to the lab 

accident that caused aquaria to overflow. The new EC10 is 

based on larval mortality from hatch to swim up, the normal 

duration for these tests, and no longer includes data from the 

post swim up portion of the test after the lab accident This 

yielded an EC10 of 18.09 mg/kg dw.

Regarding collecting fish tissue samples, EPA agrees that 

technical support information is needed on sampling approaches 

for each element of the tissue criterion, since there are various 

situations where one tissue type may be favored over another, or 

the sample logistics (e.g., fish size) may limit the sample to a 

certain type of tissue sample. EPA is developing information for 

states, tribes and stakeholders to consider when sampling fish 
48

External Peer Reviewers’ Comments EPA Response

increase the EC10 value from which the 15.2 mg/kg egg/ovary 

criterion is being largely driven. This is only a suggestion of a 

reasonable compromise given the diverse opinions on this lab 

occurrence.

For the egg/ovary criterion, the timing of fish sampling is 

absolutely critical, and the EPA provides no guidance on 

sampling design for determining egg/ovary [Se] in the 

document. As discussed above in 2a(ii), it is the [Se] in eggs that 

drives early life stage toxicity, so adult female fish absolutely 

must be collected during the late vitellogenic or preovulatory 

periods of oogenesis for this criterion to be scientifically and 

toxicologically meaningful. Measuring [Se] in ovarian tissue 

during other periods of oogenesis will be much less informative 

(i.e., about as informative as muscle or whole-body [Se]). The 

EPA must provide guidance for specific times of the year to 

collect adult female fish for egg [Se] determinations. For 

synchronous spawning species (e.g., salmonids, esocids, 

catostomids, ictalurids), this will be a defined period of 1-2 

months on average (usually spring). For asynchronous (batch) 

spawning species (e.g., cyprinids), this period will be less 

defined and will usually be 3-6 months (usually spring to late

summer or early fall). 

For the whole-body and muscle criteria, the EPA has used best 

available knowledge and approaches to derive these values, and 

they are of appropriate magnitude, duration and frequency. 

Collecting fish at any time of the year and determining wholebody or muscle [Se] will provide sufficient information on Se 

bioaccumulation. Although there will likely be some variation 

across seasons, due to prey availability, temperature and other 

factors, this approach should work.

tissue for the purposes of implementing the freshwater selenium 

criterion. In addition EPA has derived and is recommending 

that states adopt all of the fish tissue elements to provide 

maximum flexibility for a states monitoring and assessment 

program. Adopting all elements covers all potential logistical, 

spatial, temporal, and species- and life history-specific 

considerations.
49

External Peer Reviewers’ Comments EPA Response

6. The recommended magnitude, duration, and frequency for 

each criterion element are scientifically sound and appropriate. 

The derivation of the tissue based criteria are well-supported by 

including the major published works in the related fields and by 

rejecting with transparent cause and inclusion/rejection 

standards those studies that do not attain the stated benchmark 

for quality and reproducibility (e.g., NOECs). The criterion 

development satisfyingly addresses a diverse range of major fish 

types indicative of aquatic ecosystem health in geographically 

diverse lentic and lotic systems. With chronic exposure, fish 

egg-ovaries are now recognized as the best indicator of toxic 

selenium risk, however practical monitoring may require whole 

body-muscle tissue analysis. Water column selenium values fill 

the need for screening and analysis of potential for risk, 

abatement of new contamination pathways, and managing 

discharge, as well as other activities that may impact water 

quality.

Thank you for your comment.

7. As noted in our response above, there is some confusion 

regarding how “never to be exceeded” concentrations of 

selenium in the tissue based criterion will be applied (i.e., is this 

applied to analysis of single fish or to arithmetic or geometric 

means from sampled populations?). Clarification on this 

question is required before the scientific defensibility of the 

duration and frequency can be assessed for the two tissue based 

criterion. 

With regard to the magnitude of the tissue based elements, it 

would appear that at least two issues may challenge the 

scientific defensibility of these criteria. First, it is our 

understanding that the egg/ovary criterion was developed from 

Selenium is persistent. However, it may be sequestered in an 

environmental compartment that precludes it from uptake in 

biota (e.g., burial in sediment). EPA’s AWQC are traditionally 

based on aqueous concentrations since toxicity, for the 

chemicals for which criteria have been developed, is generally 

due to aqueous exposure. These concentrations can vary 

significantly both short-term and long term, allowing organisms 

in the aquatic community to recover. In contrast, selenium is a 

bioaccumulative pollutant, and fish tissue concentrations have 

been directly correlated with the adverse effect. Also reductions 

in fish tissue concentrations take a long time, even after removal 

of a selenium source. Since exceedance of these concentrations 

is correlated with adverse effect occurs EPA determined that 
50

External Peer Reviewers’ Comments EPA Response

EC10 values derived from the literature. Where multiple results 

of acceptable quality for a given species were available, a 

geometric mean was calculated. In the case of the EC10 for 

bluegill (Lepomis macrochirus), the mean EC10 resulted from 4 

studies, published by three authors: Hermanutz et al., 1992 and 

1996, Doroshov et al. (1992) and Coyle et al. (1993). However, 

the EC10 value calculated from the Hermanutz et al. studies 

(=12.7mg/kg) is quite different from the values rom the other 

two studies (20 and 24.6 mg/kg respectively), indicating cause 

for investigation of the reasons for the difference, especially in 

light of their importance for determining the egg/ovary tissue 

based criterion. One of the supplemental comments provided as 

additional information with this package (Docket ID EPA-HQOW-2004-0019-0331) indicates that the TRAP model plot of the 

Hermanutz et al. data provide a poor fit. While we were not 

afforded access to figure 1, which cited in that docket 

submission, if the data are indeed poorly fit, it is appropriate to 

consider them questionable and eliminate them from the 

geometric mean calculation for this species. 

A second, and potentially more serious issue with regard to the 

magnitude of the egg/ovary tissue based criterion, is the reliance 

on the reanalysis of data from the brown trout (Salmo trutta)

study (Formation 2011). Uncertainty in this study arises because 

some fry escaped from their respective incubation chambers and 

could not be assigned to a given treatment. As a result, several 

scenarios were calculated based on whether the escaped fry had 

similar deformity rates relative to the retained fry, were all 

deformed, or were all normal. While this cannot be resolved, the 

criterion was calculated based upon the most conservative 

these levels cannot be exceeded in order to be protective of the 

aquatic community. Technical support information regarding the 

specifics of fish tissue sampling for selenium is being developed 

by EPA.

Regarding the Hermanutz study, EPA re-analyzed this study and 

removed the nest data, which was introducing substantial 

variability, resulting in the poor fit in the EC10 TRAP model in 

the previous draft. When only egg-cup data were used, EPA 

determined the most appropriate endpoint to be a combined

deformity and mortality endpoint. Figure 1 (now Figure 2) was 

in the Hermanutz et al. chronic summary for bluegill in 

Appendix C of the previous draft, although it was not labeled. 

EPA has labeled all Figures in the Hermanutz et al. bluegill 

summary in the current draft.

Regarding the brown trout data from the Formation 2011 study,

EPA agrees with the reviewer and has re-analyzed the data and 

excluded effects observations of the 15 day post swim-up test

when the lab accident occurred and caused the confounding 

issues. The brown trout egg ovary EC10 has been re-evaluated 

by EPA based on recognition of confounding occurring due to 

the lab accident that caused aquaria to overflow. The new EC10 

is based on larval mortality from hatch to swim up, the normal 

duration for these tests, and no longer includes data from the 

post swim up portion of the test after the lab accident This 

yielded an EC10 of 18.09 mg/kg dw.
51

External Peer Reviewers’ Comments EPA Response

approach: that all fry were dead or deformed. This conservative 

approach to calculating an EC10 value for brown trout result in 

it being the most sensitive species, thereby affecting the overall 

egg/ovary criterion. Subsequently, because other criterion (i.e., 

muscle/whole body and the water based criterion) are back 

calculated based on the egg/ovary value, conservatism is 

compounded in the values for these criterion as well. 

For the water column based criterion, two separate elements are 

prescribed in the Draft Document: a monthly average and a 

separate element for intermittent (discontinuous) exposures. 

Each of these is further delineated to apply to either lentic or 

lotic systems. Presumably the definitions for lotic and lentic 

systems would be based on residence time of water or some 

related criteria, but the Draft Document does not contain an 

explicit definition of either type of system. Back calculating

from egg/ovary to muscle/whole body and then down through 

trophic levels to derive allowable water column criterion for 

each of these types of aquatic systems is not scientifically valid, 

because of the use of generic conversion factors and broadly 

based trophic transfer factors. These generic terms do not 

incorporate site specific information, including concentration 

dependent uptake kinetics and consideration for important 

influencing factors (e.g., sulfate). The water based criterion is 

therefore, conservative and variable. As evidence for this, the 

monthly average exposure value for lentic systems is 1.3 ug/L. 

This value is at the upper end of background values for 

freshwater and may be exceeded even in the absence of 

industrial inputs in areas receiving runoff from seleniferous 

soils. The value is also lower than recently recommended lentic 

Regarding the classification of lentic and lotic waterbodies, there 

were few residence time data available for the water bodies 

evaluated, therefore EPA could not use this parameter for 

classification. Based on the comments of peer reviewers as well 

as stakeholders in the public process, the EPA went through 

each waterbody and determined whether it was lentic or lotic, 

being careful to note specific issues like run of the river 

reservoirs which could cause misclassification. 

Regarding the commenter’s concern of back-calculating 

(translating) the tissue criterion to water, EPA re-evaluated 

conversion factors used and refined the approach to reflect the 

most phylogenetically proximate data in its criterion 

calculations, strengthening its previous draft analyses, as noted 

above EPA also re-evaluated the lentic and lotic water column 

values, and developed values that are based on the best 

available, scientifically defensible science to yield water column 

values that are protective of aquatic life based on available data.
52

External Peer Reviewers’ Comments EPA Response

values based on similar analysis (2 and 2.1 ug/L respectively 

(Deforest et al., 2104, BC MoE 2014).
53

PART II: FISH TISSUE CRITERION ELEMENTS DERIVATION: DERIVATION OF FISH EGG-OVARY, WHOLE

BODY AND MUSCLE CRITERION ELEMENT(S)

EPA is requesting a technical review of the methods and procedures used to derive a chronic selenium criterion based on an 

egg-ovary concentration, as well as its translation to a criterion element applicable to whole-body and muscle tissue. Please 

address the following questions:

1. Please comment on EPA’s use of the effects concentration 10th centile (EC10) as the measurement endpoint for the fish 

reproductive toxicity studies used to derive the egg-ovary element.

External Peer Reviewers’ Comments EPA Response

1. It is unclear to me why EPA has selected the EC10 as the 

measurement endpoint for these studies. EPA argues because it 

is a tissue-based criterion, the measure of exposure is less 

variable than might occur for a water-based criterion. I 

understand the point EPA is making and agree that a tissuebased criterion is more integrative of exposure than a waterbased criterion. However, following this logic, EPA is then 

stating that for a chemical with a water-based criterion in a 

system where the exposure concentration is consistently above 

the EC10 (e.g., very stable at a concentration equivalent to the 

EC15) that it is not sufficiently protective.

It seems to me that the ECx selected should be based on the 

level of protection EPA intends to provide and that this is 

independent of variability in exposure. Variability in exposure 

is more appropriately addressed via averaging periods as EPA 

has done with the intermittent exposure element of the criterion. 

In fact, by considering both an intermittent exposure element 

and using an EC10, EPA is addressing the same issue twice.

Given the above, I do not believe EPA has provided a scientific 

rationale for use of the EC10 in a tissue-based criterion as 

When considering the use of the EC10 versus the EC20, an 

EC10 was determined to be a more appropriate endpoint for 

tissue-based criteria given the nature of exposure and effects for 

this bioaccumulative chemical. EC20s have historically been 

used in the derivation of EPA criteria applicable to the water 

medium. While water concentrations may vary rapidly over 

time, tissue concentrations of bioaccumulative chemicals are 

expected to vary gradually. Thus, where concentrations of 

selenium in fish tissue are used as an effect threshold, there is 

potential for sustained impacts on aquatic systems, relative to 

chemicals that are not as bioaccumulative. This calls for use of 

a lower level of effect to attain sufficient protection. 

Also, detection in fish tissue above these levels can potentially 

have longer-term impacts due to the bioaccumulative nature of 

selenium. This is further demonstrated by field observations 

that reproductive effects in fish can take on the order of a decade 

for a selenium contaminated ecosystem to recover from (e.g., 

Belews Lake, NC). Further, the steepness of the dose-response 

curve for selenium argues for a more protective value, not less, 

because small increases in concentrations can have larger 
54

External Peer Reviewers’ Comments EPA Response

providing an equivalent level of protection as an EC20 in a 

water-based criterion. I recommend EPA evaluate how use of 

the EC20 would affect the final criteria calculations. I suspect 

given the sharp dose-response relationships for Se, it will not 

dramatically change the final criteria calculations. Alternatively, 

if EPA now believes the EC10 is an appropriate level of 

protection for WQC, then this should be applied across 

chemicals.

impacts than for toxicants with shallower dose-response curves.

The EC10 was also preferred for selenium over the NOEC or 

LOEC as these measures of effect are influenced by study 

design, specifically the concentrations tested, the number of 

concentrations tested, the number of replicates for each 

concentration, and the number of organisms in each replicate. 

As noted by Campbell (2011), EC10s and NOECs are generally 

of similar magnitude, but EC10s have the advantage of being 

more reproducible than NOECs (Van der Hoeven et al. 1997; 

Warne and van Dam 2008).

The intermittent criterion was developed to address situations 

where a system is subject to elevated concentrations for short 

durations. The kinetic considerations used to set the averaging 

period for the chronic water criterion, from which the 

intermittent criterion is calculated, address a different (but not 

unrelated) facet of the time variability problem than do the 

considerations for using the EC10. The selection for use of the 

EC10 considered the appropriate level of effect for a criterion 

that fish tissue concentrations may approach for extended 

periods of time, having already contaminated all of the lower 

trophic levels with a bioaccumulative pollutant. The 

environmental concern is thus greater than that involving water 

criteria that typically are only infrequently approached by 

rapidly varying concentrations in the water column. It is for this 

reason that EPA has derived its selenium tissue criteria based on 

the EC10 while it continues to derive water criteria for other 

pollutants based on the EC20. Further, the steepness of the 

dose-response curve argues for a more protective value, not less, 

because small increases in concentrations can have larger 
55

External Peer Reviewers’ Comments EPA Response

impacts than for toxicants with shallower dose-response curves.

The intermittent criterion is meant to protect receiving and 

downstream waters from bioaccumulative impacts by limiting

the amount of selenium that is available to be taken up by biota 

and bioaccumulated to levels of concern in sensitive species. 

Because (a) the derivation of the 30-day averaging period, and 

the subsequent derivation of the intermittent criterion, and (b) 

the considerations upon which EPA based its decision to use the 

EC10 both involve the kinetics of bioaccumulation, EPA 

understands the connection the comment is making between the 

two. However, EPA does not agree that it is addressing the 

same issue twice. Rather EPA is addressing two distinct issues 

that are both affected by bioaccumulation and kinetics. 

For these reasons EPA finds it is reasonable and protective to 

select the EC10 as the measurement endpoint for this tissuebased criterion.

2. This seems like a statistically-valid approach to setting the 

threshold, but toxicology is not my field of expertise.

Thank you for your comment.

3. The draft AWQC document notes that "an EC10 was 

determined to be a more appropriate endpoint for tissue-based 

criteria given the nature of exposure and effects for this 

bioaccumulative chemical. EC20s have historically been used in 

the derivation of EPA criteria applicable to the water medium. 

While water concentrations may vary rapidly over time, tissue 

concentrations of bioaccumulative chemicals are expected to 

vary gradually. Thus, where concentrations of selenium in fish 

tissue approach an effect threshold, there is potential for 

sustained impacts on aquatic systems, relative to chemicals that 

Thank you for your comment.
56

External Peer Reviewers’ Comments EPA Response

are not as bioaccumulative." 

I agree with this logic for using the EC10 as the measurement 

endpoint for tissue-based toxicity values, where this effects 

statistic can be derived. I also agree with the use of an EC10 

rather than a no-observed-effect concentration (NOEC), lowestobserved-effect concentration (LOEC), or geometric mean of the 

two, for the reasons discussed in the draft AWQC document.

4. Strikes me as rather arbitrary. Regarding the use of the EC10, see response to Peer Reviewer 1, 

Part II, Question 1, above.

5. The EC10 is absolutely the appropriate endpoint for early life 

stage toxicity in fish to be used to derive the egg/ovary criterion. 

This is due to the very steep dose-response relationships 

observed for larval abnormalities/mortality as a function of egg 

[Se]. Thus, EC10 provides a toxicologically relevant threshold 

for appearance of such toxicities, that is, only a marginal 

increase in egg [Se] will result in a much greater frequency of 

toxicity. In addition, the main alternative endpoint (EC20) will 

not differ greatly from EC10 for a given species due to this steep 

dose-response relationship.

Something the EPA should consider when developing the genus 

sensitivity distribution is the nature of the experiment for each 

taxa (lab- vs. field-based). In lab studies, adult female fish are 

most commonly exposed to selenomethionine (SeMet), which is 

valid because it is the dominant Se species (60-80% of total Se) 

found in organisms throughout food webs, particularly at higher 

trophic levels. In field studies, fish are exposed to SeMet and 

several other selenium species that likely vary in their toxicity, 

Thank you for your comments.

EPA recognizes the issue noted by the peer reviewer regarding 

differences in laboratory and field exposures. EPA used all of 

the available reliable data for the selenium fish effects analyses. 

Laboratory and field experiments did not yield apparent wide 

differences in predictions of effect level, suggesting that effects 

were more related to the concentrations of selenium in tissues 

rather than the proportions of the forms of selenium in diets.

Thus, EPA considers the current criterion to be protective and 

scientifically defensible. 
57

External Peer Reviewers’ Comments EPA Response

and in fact are likely less toxic than SeMet. Thus, lab exposures 

using pure SeMet may overestimate toxicity (i.e., generate lower 

EC10 values) compared to real-world exposures.

6. The EC10 is an appropriate endpoint to use in the 

development of the egg-ovary element of the tiered criterion. 

Egg-ovary Se concentration is well recognized in the peerreviewed scientific literature as a high quality indicator of 

reproductive toxic risk in fish. Because selenium is a 

reproductive toxicant, special considerations in risk management 

are warranted. For precedent, the Food Quality Protection Act of 

1996 which manages risk of chemical exposure in the human 

food system, uses an extra ten-fold safety factor for chemicals 

used in food production that have reproductive toxicology or 

neurotoxic endpoints. This extra safety factor results from our 

common understanding in toxicology that those chemicals with 

repro- or neuro-toxic activity represent an exceptional risk and 

thus require exceptional safeguards. Reproductive toxicity is a 

significant threat to the population of the impacted aquatic 

organisms and thus to the aquatic food-web. There are valid 

questions whether the EC10 is sufficiently protective of 

endangered aquatic species and the criterion document should 

address these concerns more thoroughly. Overall the EC10 eggovary endpoint is scientifically consistent and defendable with 

the intent and required actions of the CWA.

Thank you for your comment. 

Aquatic life criteria are designed to be protective of 

approximately 95% of aquatic genera present in ecosystems. 

Risk assessment practices that are specifically tailored to the 

particular objectives and requirements of the Food Quality 

Protection Act of 1996 to protect human health are not 

necessarily appropriate models for the implementation of the 

Clean Water Act protection of aquatic life. The extra ten-fold 

safety factor is to ensure protection of children, where data are 

not available and does not establish a precedent for the 

protection of the aquatic community.

Regarding consideration of endangered species, EPA has 

provided a summary of available data on the adverse effects of 

selenium to endangered species, and taxonomically related 

surrogates. EPA identified data for white sturgeon (a species 

with one population listed as endangered, and a closely related 

taxonomic surrogate for other endangered sturgeon), several 

species in the family Salmonidae, Cyprinidae as well as a 

pupfish in the Cyprinodontidae, and several less closely related 

species with tests in the order Perciformes (sunfish and bass) as 

surrogates for endangered darters. 

Regarding the comment that it is possible that the EC10 might 

not be sufficiently protective of a particular endangered aquatic 
58

External Peer Reviewers’ Comments EPA Response

species, the commenter did not recommend any specific studies, 

regarding any particular endangered species, to be addressed 

more thoroughly. Further, published data indicates that 

endangered fish species have not been found to be more 

sensitive to toxicants than common species (Sappington et al 

2001, and other). EPA acknowledges that there may be 

locations where a lower criterion could be applicable on a site 

specific basis due to the site-specific presence of a particularly

sensitive species.

7. The slope of the response curve for selenium rates of 

deformities plotted against selenium concentrations in 

eggs/ovaries rises rapidly above the EC10 value. Therefore, use 

of the 10th percentile as the measurement endpoint is 

scientifically defensible, appropriate and consistent with 

USEPA’s assessment of toxicity of other compounds as well as 

the assessment of reproductive toxicity in other jurisdictions (BC 

MoE 2014).

Thank you for your comment.
59

2. Data used to derive the final chronic egg-ovary criterion element were differentiated based on the type of effect 

(reproductive vs. non-reproductive effects). Acceptable chronic toxicity data on fish reproductive effects are available for a 

total of nine fish genera. The genus Sensitivity Distribution (SD) is predominantly populated with data on fish genera 

because field evidence demonstrates that fish communities can be affected by selenium even when there is no observable 

change in the invertebrate community diversity and abundance. As a result, decades of aquatic toxicity research have 

focused primarily on fish. Available field and laboratory studies indicate that invertebrates are more tolerant to selenium 

than most of the tested fish species (Criteria document, Table 6c, Section 4.1.2). The data set used to derive the selenium 

criterion marks a change from the traditional method used to derive water quality criteria that requires toxicity tests with 

aquatic organisms from 8 phylogenetically distinct taxa (including three vertebrate and five invertebrate genera) in order 

to derive aquatic life criteria (Stephan et al., 1985).

2.a. Given selenium’s more taxon-specific and life stage-specific toxicity, please comment on EPA’s use of the available 

data to derive the egg-ovary tissue element.

External Peer Reviewers’ Comments EPA Response

1. Overall, I found EPA’s use of the available data to derive the 

egg-ovary element to be scientifically sound. However, see 

caveats in b and c below. I did find EPA’s use of the data for 

Gambusia to be questionable. Given the variability in the 

EO:WB ratio across species and the complete lack of data on 

this ratio for ovovivaprous fish, the EO-based threshold for this 

genus is highly questionable. Given this uncertainty and that 

these are the only data used in the WQC calculation in which EO 

Se was not directly measured, in my opinion, data for this genus 

should not be used in the WQC calculation.

EPA did not use Gambusia data directly to derive the selenium 

egg ovary criterion, given they are a viviparous fish. EPA did 

use these data to calculate the whole body criterion, as well as 

counted in the “N” for derivation of the egg-ovary criterion. 

The available data indicates that Gambusia is insensitive 

compared to other species in the database.

2. In as much as fish are the most vulnerable to Se toxicity, and 

it is manifested primarily at reproduction, the egg-ovary focus is 

justified. The availability of data that passed the EPA criteria is 

somewhat limited, but statistically valid. Having said this, I am 

not well-versed in fish toxicity literature, so I rely on the other 

reviewers to point out data sets that may have been overlooked 

Thank you for your comment.
60

External Peer Reviewers’ Comments EPA Response

(e.g., I know they missed many water column data).

3. I agree with the EPA's approach of only considering fish data 

in the genus sensitivity distribution as fish are the most sensitive 

aquatic taxa (although the sensitivity of amphibians relative to 

fish is still uncertain). There is a fundamental difference in a 

criterion that is based on an internal organism concentration 

versus an external environmental concentration (such as a water 

concentration). If fish are accepted to be the most sensitive taxa, 

and if selenium criteria are to be based on the selenium 

concentration in fish tissue (either eggs/ovaries or whole body), 

then the toxicity data and genus sensitivity distribution need to 

necessarily be based only on selenium concentrations in fish 

tissue. Development of a tissue-based genus sensitivity 

distribution that includes toxicity data for other taxa would not 

be relevant to the application of any criterion that could be 

derived using such an approach.

EPA has considered this comment as well as similar comments 

from other reviewers and the public. EPA agrees with the 

reviewer that the SD using fish egg-ovary data should only use 

the fish egg-ovary data. However, criteria are developed to 

protect the entire aquatic community, and the available data 

should reflect the sensitivity range for various components (e.g.,

fish, invertebrates) of the aquatic system. The invertebrate 

whole body data will be portrayed in the whole body SD in that 

it shows the relative sensitivity of invertebrates versus fish.

EPA also identified limited data on amphibians and 

characterized effects in comparison to fish. Data indicate that 

the selenium fish tissue criterion is protective of the aquatic 

community including invertebrates and amphibians.

4. I have no particular insight on this issue. Thank you for your comment.

5. This certainly makes the regulator’s job easier due to the 

exquisite sensitivity of oviparous fish species to Se, and the 

well-established, characteristic and diagnostic response pattern 

in fishes (larval deformities and edema) that have clear links to 

population-level impacts. So yes, the egg/ovary tissue element is 

appropriate. However, it is important to note that we have 

limited data for all species, whether vertebrate or invertebrate. 

Recent work in David Buchwalter’s lab at NC State U has 

observed a certain invertebrate taxon (Ephemeroptera I think) to 

be very sensitive to Se, and should be considered by EPA in the 

future criterion document. Nevertheless, in my opinion 

Thank you for your comment. In responding to peer review and 

public comments, EPA examined Buchwalter’s (Conley et al. 

2013) recent study. There were 2 studies with the same 

exposures but different food rations (1x and 2x). There were 

major differences in the effects levels observed, which seemed 

to be a diet effect, rather than a selenium toxicity effect. These 

data are discussed in the revised draft selenium criterion 

document.
61

External Peer Reviewers’ Comments EPA Response

protecting fish based of an egg/ovary criterion will be protective 

of aquatic ecosystem sustainability. To my knowledge, the EPA 

has used a scientifically sound procedure to use available data on 

9 fish species to derive the egg/ovary criterion.

6. The use of fish data to drive the tiered criteria, and 

specifically the egg-ovary tissue element is fully justified and 

well-supported in the criterion document and the relevant 

scientific literature. While the sources, pathways, receptors and

controls of chemicals impacting water quality have inherent 

diversity, selenium demonstrates significant trophic transfer 

potential and potential for fish reproductive effects in aquatic 

ecosystems. The reproductive endpoints observed in peerreviewed, published controlled and field studies strongly suggest 

the potential for accumulation, magnification, and trophic 

transfer, and thus population level effects in a higher tropic level 

organism such as fish. The concomitant food-web impacts and 

observed impacts to aquatic birds support the criterion approach. 

The guidelines of Stephan et al., 1985 pre-date much of the 

knowledge base of Se in aquatic ecosystems, and the somewhat 

unique behavior and impact potential of this toxicant across 

trophic levels did not come into a more complete understanding 

for nearly two decades since that work. Hence, deviation from 

prior risk assessment approaches that pre-date our current 

knowledge base and the evolution of understanding of Se 

behavior in aquatic ecosystems is broadly justified in the risk 

management of selenium. 

Thank you for your comment. 

While the Guidelines EPA uses to derive aquatic life criteria do 

not specifically address bioaccumulative pollutants like 

selenium, there are several aspects of criteria derivation which 

are similar to or an adaptation of the Guidelines. EPA followed 

the Guidelines and used the conceptual approach from EPA’s 

Ecological Risk Assessment Paradigm in deriving the selenium 

criterion,

1. First EPA gathered all data on the toxic effects of 

selenium on aquatic organisms, as criteria are meant to 

protect the entire aquatic community.

2. Second, EPA recognized that the mode of action of 

selenium and its duality as a nutrient and a toxicant 

would require special consideration in the criteria 

derivation process. Given the available data, and 

deliberations from the 2009 Pellston on selenium, EPA 

was able to focus on toxicity tests that used maternal 

transfer of selenium via diet, and subsequent larval 

toxicity.

3. Using the SD methodology of the Guidelines, we 

assembled a fish egg-ovary SD based on EC10s for all 

available reliable studies. We are also including the 

invertebrate tests implicitly and available data on 

amphibians, although they were not represented in the 

SD.
62

External Peer Reviewers’ Comments EPA Response

4. We also used principles developed in an EPA White 

Paper reviewed by the SAB that provided for considering 

MOA and other characteristics of pollutants like 

Contaminants of Emerging Concern (CECs) (and to 

some extent selenium). (U.S. EPA 2008). We were able 

to apply these principles because we have specific 

information about the action of selenium in aquatic 

ecosystems established at a SETAC Pellston workshop 

(Chapman et al. 2009), specifically, that egg-laying 

vertebrates are the most sensitive to selenium, and that 

reproductive effects are the most sensitive measurement 

endpoint.

7. The use of reproductive effects in fish to derive the 

sensitivity distribution is appropriate because non-reproductive 

effects may arise from mechanisms that are not central to the 

primary ecological effects of selenium; reproductive toxicity in 

oviparous vertebrates manifested by maternal transfer of 

selenium to eggs. Additionally, as noted in the Draft Document, 

non-reproductive effects thresholds are highly variable and 

provide less confidence for deriving threshold values for 

selenium. The use of data from fish as the most sensitive 

organisms is appropriate and likely to be protective of 

invertebrates. However, it should be noted that sensitivity among 

invertebrates is highly variable and that some invertebrate taxa 

do exhibit sensitivity at low g/L concentrations (see BC MoE 

2014 for a review of this data). 

While we agree that the Draft Document predominantly uses

data from fish generally sensitivity, the approach in the Draft 

Document is not a complete departure from the principles 

surrounding the use of eight phylogenetically distinct taxa. The 

Thank you for your comment.

EPA has considered this comment as well as similar comments 

from other reviewers and the public regarding the fish and 

invertebrate values. In the current draft document, fish and 

invertebrate SMCVs and GMCVs are no longer presented on the 

same tables, in agreement with the peer reviewer’s comment, 

and invertebrate SMCVs and GMCVs are presented as whole 

body concentrations. However, criteria are developed to protect 

the entire aquatic community, such that the available data should 

reflect the sensitivity range for various components (e.g., fish, 

invertebrates) of the aquatic system. Towards this end, 

invertebrate sensitivity to selenium was evaluated in terms of 

both measured whole body concentrations as well as in terms of 

what the whole body tissue concentration of a representative fish 

would be were it to consume each invertebrate with a whole 

body concentration at the SMCV & GMCV, by multiplying each 

invertebrate GMCV by 1.27, the median TTF for all fish species. 

When evaluated with or without the trophic level 
63

External Peer Reviewers’ Comments EPA Response

US-EPA has attempted to increase taxonomic coverage of the 

sensitivity distribution by converting results from studies of 

three invertebrate taxa into fish reproductive endpoints. 

Specifically, threshold concentrations of selenium in the 

invertebrates were converted to predicted fish concentrations of 

selenium in egg/ovary based on consumption of the invertebrates 

by fish. These values were then included in the fish distribution 

(Figure 5, page 58). The variability inherent in this calculation is 

large because a generic trophic transfer factor of 1.27 was 

applied to convert invertebrate concentrations to fish whole body 

concentrations and then a generic conversion factor of 1.71 was 

applied to convert whole-body concentrations to egg/ovary. The 

result is a highly variable, and scientifically questionable, series 

of three additional data points that were added to the distribution 

of reproductive effects for fish.

biomagnification, the available data demonstrate that compared 

to fish, invertebrates are not sensitive to selenium, and do not 

comprise any of the four lowest GMCVs. Consistent with the 

1985 Guidelines, they are used to fulfill the taxonomic minimum 

data requirements, and are counted in the total number of genera 

(“N”) in the calculations. We note the numeric impact of 

increasing “N” though inclusion of the invertebrate data in the 

“N” for the criterion calculation is minimal, reflecting an 

approximately 3% change in the egg-ovary criterion element 

value.
64

2.b. Given the greater general sensitivity of oviparous fish to selenium compared to aquatic invertebrates, please 

comment on the appropriateness of EPA’s fish tissue-based criterion for affording protection to the aquatic 

community as a whole (e.g., including invertebrates).

External Peer Reviewers’ Comments EPA Response

1. I agree with EPA that currently available data indicates 

oviparous fish are more sensitive than aquatic invertebrates to 

Se. However, it is important to note that there is a paucity of 

data for invertebrates. I agree with EPA’s approach to translate 

available invertebrate data to an EO threshold for purposes of 

developing a species sensitivity distribution (SSD). However, I 

strongly disagree with the addition of 2 hypothetical crustaceans 

to the SSD. This is scientifically indefensible (just making up 

data) and the WQC calculation should be based only on taxa for 

which there are actually data available. By this logic, why add 

only 2 crustacean taxa, why not 3 or 5?

Note, EPA needs to include the data from Conley et al. (2011, 

2013, and 2014) in its assessment of Se toxicity and trophic 

transfer to mayflies.

Overall, given the limited data, I think EPA has overstated the 

certainty with which we can conclude fish are more sensitive 

than invertebrates. All we can really say is that based on a 

relatively small data set, available data suggests the tissue based 

WQC will be protective of invertebrates.

EPA agrees that the estimated egg-ovary concentrations for 

invertebrates should be deleted. The data available do indicate 

that the invertebrates are somewhat less sensitive to fish on a 

whole-body basis and thus invertebrates are included in the “N” 

for the criterion derivation. Invertebrates are portrayed 

explicitly in the whole body SD with the converted whole-body 

fish tissue concentrations for comparative purposes.

EPA examined Buchwalter’s (Conley et al. 2013) recent study. 

There were 2 studies with the same exposures but different food 

rations (1x and 2x). There were major differences in the effects 

levels observed, which seemed to be a diet effect, rather than a 

selenium toxicity effect. These data are discussed in the revised 

draft selenium criterion document. EPA has also examined the 

Conley data and have included the data that has met the data 

quality requirements for quantitative consideration in the criteria 

derivation process.

EPA agrees that, based on available reliable data, the draft 

selenium fish tissue criterion will be protective of invertebrates. 

EPA further agrees that additional data on invertebrate 

sensitivity to selenium would be useful to further support this 

conclusion.
65

External Peer Reviewers’ Comments EPA Response

2. In the aquatic systems in which I have worked with selenium, 

we have never encountered Se problems with invertebrates, and 

the literature seems to bear this out. So it seems to me that 

setting the criteria for the most at risk population is the best 

approach.

Thank you for your comment.

3. Although it has perhaps not been rigorously evaluated at all 

levels of food chain structure and function, field data indicates 

that adverse Se-related effects on fish can occur when there is no 

evidence of effects to food chain organism communities, 

including invertebrates. Selenium trophic transfer factors (TTFs) 

for invertebrates-to-fish typically average about 1 for whole 

body Se concentrations in fish and ≥2 for egg/ovary Se 

concentrations in fish (with the latter being more variable). 

Thus, a whole body Se criterion of 8.1 mg/kg dw and an 

egg/ovary Se criterion of 15.2 mg/kg dw may, on average, both 

be associated with an invertebrate Se concentration of about 8 

mg/kg dw. 

Based on a review of Se toxicity to invertebrate taxa, deBruyn 

and Chapman (2007) identified two studies in which whole body 

invertebrate Se concentrations of <8 mg/kg dw were associated 

with adverse effects. Both of these studies were based on growth 

effects in larval midges (Chironomus decorus). deBruyn and 

Chapman (2007) reported an EC40 of 1.0 mg/kg dw from 

Alaimo et al. (1994) and an EC15 and EC46 of 2.6 and 4.1 

mg/kg dw, respectively, from Malchow et al. (1995). However, 

in Alaimo et al. (1994), Se was below the detection limit in the 

treatment with a 40% reduction in growth relative to the control, 

which suggests the growth reduction was due to other factors. In 

Malchow et al. (1995), whole-body Se LOECs of 2.6 and 4.1 

Thank you for your analysis and your comments. 
66

External Peer Reviewers’ Comments EPA Response

mg/kg dw in midges were observed after 96-hr exposures. It is 

unclear whether growth effects would be related to tissue 

concentrations under such a short exposure period, but perhaps 

the water concentrations themselves (10 μg/L of either selenate 

or selenite) were directly responsible for the reduced growth. 

More recent data for a mayfly (C. triangulifer) suggest that the 

whole-body Se toxicity threshold for this species is also >8 

mg/kg dw (Conley et al. 2009, 2011, 2013).

Overall, in my opinion, the above provides support that a fish 

tissue-based Se criterion should ensure protection of the aquatic 

community as a whole, including invertebrates. 

Literature cited:

Alaimo J, Ogle RS, Knight AW. 1994. Selenium uptake by 

larval Chironomus decorus from a Ruppia maritima-based 

benthic/detrital substrate. Arch Environ Contam Toxicol 

27:441-448.

Conley JM, Funk DH, Buchwalter DB. 2009. Selenium 

bioaccumulation and maternal transfer in the mayfly 

Centroptilum triangulifer in a life-cycle, periphyton-biofilm 

trophic assay. Environ Sci Technol 43:7952-7957.

Conley JM, Funk DH, Cariello NJ, Buchwalter DB. 2011. Food 

rationing affects dietary selenium bioaccumulation and life 

cycle performance in the mayfly Centroptilum triangulifer. 

Ecotoxicology 20:1840-1851.

Conley JM, Funk DH, Hesterberg DH, Hsu L-C, Kan J, Liu YT, Buchwalter DB. 2013. Bioconcentration and 

biotransformation of selenite versus selenate exposed 

periphyton and subsequent toxicity to the mayfly 
67

External Peer Reviewers’ Comments EPA Response

Centroptilum triangulifer. Environ Sci Technol 47:7965-

7973.

deBruyn AMH, Chapman PM. 2007. Selenium toxicity to 

invertebrates: Will proposed thresholds for toxicity to fish 

and birds also protect their prey? Environ Sci Technol 

41:1766-1770.

Malchow DE, Knight AW, Maier KJ. 1995. Bioaccumulation 

and toxicity of selenium in Chironomus decorus larvae fed a diet 

of seleniferous Selenastrum capricornutum. Arch Environ 

Contam Toxicol 29:104-109.

4. Until we find more Se-sensitive groups of freshwater animals 

than fish, the fish tissue-burden approach seems warranted.

Thank you for your comment.

5. See previous comment regarding aquatic insects. In my 

opinion the tissue-based criteria in fish will protect freshwater 

aquatic communities.

Thank you for your comment.

6. The fish tissue-based criterion affords protection to the 

aquatic community as a whole and is appropriately placed in the 

tiered criterion. Since tissue Se integrates chronic and 

intermittent acute aquatic Se exposure, it provides a good quality 

indicator of impacts and potential impacts to the broader aquatic 

community. The complex interactions of predator-prey 

relationships in these environments rely on nominal stability in 

each tropic level and the food-web as a whole. In field practice 

and in published controlled studies, fish tissue Se has been 

shown to provide a valuable assessment and management tool 

for Se impacted aquatic ecosystems. Except where fish 

populations are absent, very low, endangered or otherwise 

Thank you for your comment.
68

External Peer Reviewers’ Comments EPA Response

insufficient, tissue monitoring is a high quality indicator of water 

quality with regards to selenium.

7. As noted above, the use of data from oviparous fish as the 

most sensitive aquatic organisms to derive criterion is 

appropriate and likely to be protective of invertebrates. 

However, the USEPA may wish to consider sensitivity data for 

some invertebrate taxa that do exhibit sensitivity at low g/L 

concentrations (see BC MoE 2014 for a review of this data).

Thank you for your comment. EPA is aware of the available 

invertebrate data that reported selenium impacts at low 

concentrations, however our review of these data uncovered data 

quality flaws that limit the quantitative use of these studies for 

criteria derivation. This discussion is located in Section 3.1.3.
69

2.c. With respect to the tests that quantified non-reproductive effects, did the EPA use that data to the best extent 

possible given its limitations (e.g., relevance compared to reproductive tests, and data quality concerns which 

increased uncertainty (e.g., Hamilton et al., 1990)?

External Peer Reviewers’ Comments EPA Response

1. I agree with EPA, that generally, the reproductive endpoint is 

more sensitive than other endpoints such as juvenile growth.

However, in the case of salmonids, there is at least some 

evidence (e.g., Hamilton et al., 1990) that juvenile growth is 

comparable in sensitivity to reproduction. It is also worth 

pointing out that these studies did not include pre-exposure of 

the parents and subsequent maternal transfer, so it is possible 

that exposure and subsequent effects on juvenile growth have 

been underestimated. Further, juvenile salmonids have a much 

more limited home range and potentially higher intensity of 

exposure if they rear in Se contaminated areas compared to adult 

salmonids (particularly migratory species). Given this, it is 

unclear to me that placing primacy on the egg-ovary element 

will necessarily be protective of these species. EPA should 

consider the potential that juvenile whole body Se 

concentrations for migratory salmonids may need primacy or at 

least concurrent compliance monitoring to ensure the protection 

of these important species.

EPA had significant concerns with the 90-day endpoint in 

Hamilton et.al. 1990, most significantly that the 90-day control 

survival (67%) was below toxicity test acceptability thresholds, 

such that we could not use those effects data. We did consider 

and use the 60-day time point for this study, and concluded that

the egg-ovary transformed whole body criteria of 8 mg/kg dw 

would protect against growth effects in juvenile salmonids. 

EPA does agree that salmonids, particularly anadromous Pacific 

salmonid species are not represented by the dietary maternal 

transfer model upon which the egg-ovary criterion element is 

based for several reasons: Salmonids migrate as smolts to the 

marine environment mature and then migrate back to reproduce, 

however, they cease feeding before entering the freshwater 

environment resulting in a lack of exposure to these 

contaminants in freshwater. Also, these species are 

semelparous, meaning they die after spawning, so there is no 

opportunity for selenium to be stored. This is different than 

other salmonid species that are freshwater species (e.g., brown 

trout) and do not die after spawning. Since the maturing 

juvenile to the smolt stage is the critical lifestage of interest for 

these species, monitoring of whole body concentrations in 

smolts using the whole body criterion element threshold of 8 

mg/kg dw is expected to insure protection of this critical life 

stage from impacts associated with dietary selenium. EPA also 

completed further analyses of this issue in response to this peer 
70

External Peer Reviewers’ Comments EPA Response

review comment. These analyses are presented in Section 6 of 

the 2015 draft criterion document and conclude that the whole 

body criterion element should be used in combination with 

smolt-stage fish from species of anadromous Pacific salmon to 

ensure their protection from selenium exposure in freshwater. 

Thus, EPA’s selenium criterion is protective of these species if 

applied as recommended.

2. Again, fish toxicity is not my expertise, so I cannot 

adequately respond to this question.

Thank you for your comment.

3. Overall, I generally agree with the EPA's interpretation of the 

non-reproductive effects data and the draft whole-body Se 

criterion appears to be protective of the toxicity endpoints 

evaluated in those studies (at least the GMCVs reported in Table 

17 of the draft AWQC document certainly are). The one study 

that could be interpreted somewhat differently is the juvenile 

Chinook salmon study conducted by Hamilton et al. (1990). The 

EPA derived whole-body Se EC10s of 7.355 and 11.14 mg/kg 

dw for juvenile growth based on a seleno-DL-methionine spiked 

diet and San Luis Drain (SLD)-spiked diet. For comparison, 

DeForest and Adams (2011) had derived a whole-body Se EC10 

of 6.4 mg/kg dw based on the seleno-DL-methionine spiked diet, 

using a different concentration-response model (they excluded 

the SLD-spiked diet due to concerns associated with other 

contaminants). Overall, the model fit by the EPA to the data 

using TRAP appears to be quite good and the greater EC10 that 

they derived based on SLD-diet provides support that other 

contaminants did not adversely affect growth in the juvenile 

Chinook. Accordingly, I do not disagree with the SMCV (and 

GMCV) of 9.052 mg/kg dw that the EPA derived from juvenile 

Thank you for your comment and analysis. See comment to 

reviewer number 1 above.
71

External Peer Reviewers’ Comments EPA Response

Chinook salmon. This would also support that the draft wholebody Se criterion of 8.1 mg/kg dw based on reproductive effects 

would be protective against growth effects in juvenile Chinook.

Literature cited:

DeForest DK, Adams WJ. 2011. Selenium accumulation and 

toxicity in freshwater fishes. 193-229 in Beyer WN, Meador JP, 

eds. Environmental contaminants in biota: Interpreting tissue 

concentrations Second edition. CRC Press, Boca Raton, FL, 

USA.

Hamilton SJ, Buhl KJ, Faerber NL, Wiedmeyer RH, Bullard FA. 

1990. Toxicity of organic selenium in the diet to chinook 

salmon. Environ Toxicol Chem 9:347-358.

4. I’m not sure. Thank you for your comment.

5. Since the non-reproductive effects occur at tissue [Se] equal 

to or more commonly greater than reproductive effects, and 

since reproductive effects have clearer links to population-level 

impacts than non-reproductive effects such as reduced growth or 

altered behavior, the EPA has appropriately chosen not to use 

non-reproductive effects in their derivation of tissue-based 

criteria.

Thank you for your comment.

6. The non-reproductive fish data, limited in scope and 

diversity, were adequately explored and treated in the 

development of the tiered criterion. The increased concerns over 

reproductive effects from a risk management perspective, study 

diversity (e.g., species, geography, lentic/lotic), in addition to the 

quality and quantity of reproductive toxicity endpoint data and 

studies reproductive toxic risk the superior driver of selenium 

Thank you for your comment. We have added a figure to

Section 6 where the reproductive effects and non-reproductive 

effects are compared, demonstrating that the whole body 

criterion element translated from egg ovary criterion threshold is 

expected to be protective against non-reproductive effects.
72

External Peer Reviewers’ Comments EPA Response

risk management in aquatic ecosystems. The summary statement 

that the non-reproductive data were less reproducible (p. 57) 

suggests that including them would have added uncertainty to 

the final criterion values. It is reasonable, acceptable, and 

scientifically defensible to have reproductive toxicity as the 

driving endpoint for criterion development, as these criteria 

appear to afford protection from non-reproductive toxic effects.

7. Because non reproductive tests do not evaluate the most 

sensitive measure of selenium ecotoxicology, their use as 

regulatory criteria are questionable. However, the USEPA has 

provided summaries of non-reproductive tests and compared the 

results from these studies with the criterion derived using 

reproductive data. In most cases, the studies have evaluated 

growth or survival of fish. The species mean chronic values 

(SMCV) and genus mean chronic values (GMCV) from the nonreproductive tests are generally greater than the egg/ovary 

criterion and, therefore, it is expected that the criteria derived 

from the reproductive studies (e.g., Egg/ovary) will be protective 

of non-reproductive endpoints as well.

Thank you for your comment. EPA has provided additional 

description in the 2015 draft criterion document by developing 

and displaying sensitivity distributions with both the egg-ovary 

(reproductive) translated whole body values, as well as the 

whole body values from non-reproductive tests to show the 

relationship between and demonstrate the protectiveness of the 

whole body translated criterion element.
73

2.d. EPA also rejected studies that used the injection route of exposure for selenium due to uncertainty related to 

uptake, distribution and metabolism/transformation kinetics when compared with the dietary and/or maternal 

transfer routes of exposure. Was this reasonable? Does the panel envision an appropriate and scientifically 

defensible use for this type of data? Please provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. Yes, it was reasonable to reject these studies for the reasons 

stated by EPA. In my opinion, there is currently insufficient 

information to have confidence that injection studies replicate 

realistic environmental exposures with respect to Se 

homeostasis. Indeed, the fact that the catfish study resulted in 

such an unusually low effect level suggests there may be 

different processes occurring in these types of studies. EPA has 

adequately documented that catfish do not appear to be uniquely 

sensitive based on available field abundance data in Se-impacted 

systems, counter to the lab-based injection study.

Thank you for your comment.

2. I cannot recommend using any artificial means of introducing 

selenium to tissues; exposure must be through food and the 

assimilation pathways it follows for a given species. In this 

respect, chemical speciation is very important, so the exact form 

of organic selenide (peptide vs free amino acid, seleno 

methionine vs seleno cysteine; cytosol vs proteins) is critical to 

its uptake and eventual assimilation (e.g., Reinfelder and Fisher, 

1994; Luoma et al., 1992).

Thank you for your comment.

3. In my opinion it was reasonable to exclude microinjection 

studies because there are sufficient questions as the 

environmental relevance of the exposure. For example, Linville 

(2006) exposed white sturgeon larvae to selenium using two 

different approaches: (1) by microinjection of Lselenomethionine into larval yolk sacs immediately after 

Thank you for your comment.
74

External Peer Reviewers’ Comments EPA Response

hatching and (2) by exposing parent females to dietary selenium 

(as selenized yeast) for up to six months before they deposited 

eggs (i.e., maternal transfer exposure). In larvae that received Lselenomethionine microinjections, mortality was a more sensitive 

endpoint than developmental- related effects. In contrast, in the 

maternal transfer test, larval developmental effects was a more 

sensitive endpoint than larval mortality. Further the egg Se EC10 

for white sturgeon was 15.8 mg/kg dw in the maternal transfer 

study versus 6.77 mg/kg dw in the microinjection study (as 

derived by Beckon [2012]). The microinjection methodology has 

not been validated in other studies and the results from Linville 

(2006) suggest that it is not an appropriate substitute for 

maternal transfer. Further, to my knowledge, studies on injection 

of Se into muscle tissues and subsequent maternal transfer of Se 

to the ovaries and eggs, and comparison to maternal transfer data 

following dietary Se exposures, have not been conducted.

(Although the data from Linville [2006] are sufficient to make 

some comparisons between maternal transfer and microinjection 

studies, the concentration-response data are too limited to derive 

an EC10 that would be considered reliable in a sensitivity 

distribution for criteria development. Further, the egg Se EC10 

from the maternal transfer test was estimated from the larval Se 

EC10 using a regression relationship between egg and larval Se 

concentrations from a microinjection test.)

Literature cited:

Beckon WN. 2012. Evaluation of the toxicity of selenium to 

white and green sturgeon. U.S. Fish and Wildlife Service, 

Sacramento, CA.

Linville RG. 2006. Effects of excess selenium on the health and 

EPA concluded that the white sturgeon EC10 of 16.3 mg/kg for 

the combined edema + skeletal deformity endpoint from the 

Linville 2006 maternal transfer study were of sufficient quality 

to include in the criterion document. The test fulfilled 

Guidelines requirements, larval control survival was acceptable, 

and the highest test concentration indicated evidence of 

reproductive effects. While an EC10 based on one partial 

response would not ordinarily be included in the chronic data 

set, special consideration was given to these results for the 

following reasons: 1) White sturgeon is listed as endangered in 

specific regions, such as the Kootenai River white sturgeon in 

Idaho and Montana; 2) White sturgeon serves as a surrogate for 

other sturgeon listed as threatened or endangered (e.g., pallid 

and shovelnose sturgeon); 3) Linville 2006 reported a 

statistically significant relationship between selenium 

concentrations in larvae and occurrence of skeletal + edema 

effect incidence, and calculated a similar EC10 using a logit 

model; and 4) there are supporting data (De Riu et al. 2014, 

Appendix E) that suggest the federally threatened green sturgeon 

is also sensitive to selenium. 
75

External Peer Reviewers’ Comments EPA Response

reproduction of white sturgeon (Acipenser transmontanus): 

Implications for San Francisco Bay-delta. Ph.D. Thesis, 

University of California, Davis. 232 pp.

4. It is hard to argue on behalf of egg injection studies in favor 

of dietary uptake (the obviously more natural process) studies. 

This is particularly the case if the Se contents of the tissues and 

eggs are measured during the dietary exposure.

Thank you for your comment.

5. I think the EPA should use studies that use maternal injection 

of Se as the route of exposure (e.g., the Doroshov et al. (1992) 

study in catfish). Whether Se is absorbed from the gut or 

injected into adult female fish, it will reach the systemic 

circulation and become part of the Se pool, some of which will 

be incorporated into vitellogenin in the liver and 

transported/deposited into eggs. Including the Doroshov et al. 

(1992) study is thus scientifically sound, and will add an 

additional fish taxon (ictalurids) into the species sensitivity 

distribution.

EPA has not previously accepted injection studies as a valid 

exposure method for aquatic life criteria development, and this 

exposure route is considered particularly critically regarding 

selenium for several reasons.

1. A 100% selenomethionine exposure does not reflect 

natural dietary sources.

2. Microinjection does not include the natural metabolic 

detoxification and storage processes occurring in the 

female over time in the diet, as opposed to a bolus dose 

of a single form of selenium which likely overwhelms 

the body’s metabolic processes.

We note that most other reviewers agreed with the exclusion of 

the injection route of exposure, and several provided additional 

lines of reasoning for excluding injection studies from 

consideration.

In addition, in the effects characterization EPA describes field 

evidence from Hyco Reservoir that found catfish representing 

multiple year classes present even after most other fish species 

were reproductively extirpated from the lake. This indicates that 
76

External Peer Reviewers’ Comments EPA Response

at a minimum, catfish are no more sensitive than other species 

for which we have reliable egg-ovary data for (i.e., centrarchids 

like bass and bluegill), and that they are likely less sensitive, due 

to their presence in these studies after other species disappeared.

Thus, EPA concluded that the egg-ovary criterion is expected to 

be protective for ictalurids, despite the absence of valid eggovary test data.

6. The rejection of injection exposure route studies is 

reasonable. Injection based toxicology studies have their place in 

understanding the interface of chemistry and biology. They are 

of significant value when metabolism of the toxicant is of 

interest or when digestive and absorption processes (i.e., 

bioavailability) confound or complicate study goals. Since 

controlled feed/water laboratory exposure trials, and field 

observation data and published studies are available in overall 

sufficient quantity, diversity, and quality for establishment of the 

criterion, the rejection of injection-based trials results yield a 

data set more amenable to generalization of aquatic ecosystem 

exposure and dose, as well as the subsequent analysis of trophic 

transfer and potential for toxic end effects. Although injection 

route studies have scientific value, they are not necessary or 

required for a qualitative and quantitative understanding of Se 

aquatic ecosystem risk potential given the other peer-reviewed 

resources presently available.

Thank you for your comment.

7. The US-EPA rejected the Doroshov et al. (1992) study in 

which female catfish were injected intramuscularly with selenomethionine and effects were determined in their offspring. The 

chemical form of selenium was appropriate for injection into 

these fish, but it could be argued that injection circumvents 

EPA has reexamined the study data and determined that it will 

not accept injection studies as a valid exposure method for 

selenium aquatic life criterion development. The majority of the 

other peer reviewers’ comments support this decision. Please see 

EPA comments to reviewer 5 above for more detail.
77

External Peer Reviewers’ Comments EPA Response

dietary uptake, tissue partitioning and timing of muscular uptake 

with respect to reproductive cycle of the fish. Some may 

therefore consider this injection study to be invalid. However, 

relating selenium concentrations in egg/ovary to reproductive 

effects was the primary focus of the USEPA’s assessment. 

While several compromises have been established to allow data 

to be included in the development of the criterion (see discussion 

of the bluegill and brown trout data from earlier comments), the 

exclusion of the data from the Doroshov et al. (1992) study 

appears arbitrary. Moreover, citing abundance of Ictalurids in 

the Hyco Reservoir (Crutchfield (2000) and at Belews Lake 

(Young et al. 2010) at selenium concentrations that may have 

affected abundance of other fish species is not sufficient 

evidence to dismiss the data from the Doroshov et al. (1992) 

study. A reexamination of the data and consideration to include 

them in the egg/ovary criterion is warranted.
78

3. Was the method (Section 4.1.5, 7.1.7) used to translate the fish egg-ovary criterion element into muscle and whole body 

criterions elements understandable, transparent and scientifically defensible? Was there sufficient data for making the 

translations for each element? 

External Peer Reviewers’ Comments EPA Response

1. Yes, I found the egg-ovary to muscle and whole body 

translations to be understandable and scientifically defensible. 

Thank you for your comment.

2. The methodology is well described and documented, but as 

above I would like to see a more thorough error analysis for the 

resulting CFs.

Thank you for your comment. We have expanded the discussion 

and clarified the derivation of the CFs and modified the 

methodology to leverage more of the taxonomic relationships 

available in the dataset. See response to Peer Reviewer 2, in 

Part I, Question 2.a.iii.

3. In general, I am hesitant about considering tissue-to-tissue Se 

relationships in order to estimate toxicity thresholds for one 

tissue based on measured concentrations in another tissue. 

However, the "EO/WB" ratios shown in Table 7a appear bracket 

the ratios typically observed, while still reflecting the variability 

observed between different species and families. The resulting 

draft whole-body Se criterion of 8.1 mg/kg dw is not 

inconsistent with other whole-body fish Se guidelines that have 

been recommended based on direct whole-body Se 

measurements. DeForest and Adams (2011), for example, 

recommended a whole-body fish Se guideline of 8.1 mg/kg dw 

following a different approach. However, per my above 

comment, I believe that the number of GMCVs should be 11 

rather than 14 (or 12 if a recently conducted study for mountain 

whitefish were added to the sensitivity distribution.

In addition, for those species with measured Se concentrations in 

whole-body tissue or muscle, why not use the empirical 

Regarding the comment on the number of GMCVs, EPA agrees 

that the invertebrate and the Gambusia data should not be 

represented in the egg-ovary sensitivity distribution, and they 

have been removed from that distribution. EPA 304(a) criteria 

are developed to protect the entire aquatic community, and so 

the “N” should consider the other less sensitive taxa data 

implicitly; even though they are not represented in the SD, they 

are still protected by the criterion. 

We also evaluated new studies, and so the “N” reflects the 

number of studies that are used quantitatively, and represented 

explicitly in the SD; as well as those less sensitive taxa that

cannot be represented in the SD, but are part of the total number 

of taxa where data are available that show that the criterion is 

protective.
79

measurements? For example, for Dolly Varden, McDonald et al. 

(2010) reported a whole body Se EC10 of 44 mg/kg dw based on 

the site-specific relationship between egg and WB Se in their 

study (this would not influence the draft whole-body Se criterion 

because Salvelinus is not among the four most sensitive genera, 

but it would be more accurate). Likewise, Coyle et al. (1993) 

and Hermanutz et al. (1992, 1996) report whole body Se 

concentrations in bluegills. This could be checked for other 

species as well.

Finally, perhaps it should be noted that, if possible or desired, 

site- and species-specific relationships between egg/ovary Se 

and whole-body or muscle Se could be derived and used in place 

of the draft criteria of 8.1 and 11.8 mg/kg dw.

Literature cited:

Coyle JJ, Buckler DR, Ingersoll CG, Fairchild JF, May TW. 

1993. Effect of dietary selenium on the reproductive success 

of bluegills (Lepomis macrochirus). Environ Toxicol Chem 

12:551-565.

DeForest DK, Adams WJ. 2011. Selenium accumulation and 

toxicity in freshwater fishes. 193-229 in Beyer WN, Meador 

JP, eds Environmental contaminants in biota: Interpreting 

tissue concentrations Second edition. CRC Press, Boca 

Raton, FL, USA.

Hermanutz RO, Allen KN, Roush TH, Hedtke SF. 1992. Effects 

of elevated selenium concentrations on bluegills (Lepomis 

macrochirus) in outdoor experimental streams. Environ 

Toxicol Chem 11:217-224.

Hermanutz RO, Allen KN, Detenbeck NE, Stephan CE. 1996. 

Exposure of bluegills (Lepomis macrochirus) to selenium in 

outdoor experimental streams. U.S. Environmental 

(See responses to questions 2.a.6. and 2.b.1 above for further 

discussion.)

Section 6.1.11 includes a figure showing the distribution of eggovary GMCVs converted to whole body concentrations overlaid 

with the distribution of GMCVs using empirical whole body 

measurements, plus those converted from muscle to whole body. 

Both overlays include invertebrate GMCVs.

EPA supports the development of site-specific criteria, where 

data are available and has specifically designed this criterion so 

that its modification from a national criterion to a site-specific 

value, using site-specific data, could be easily facilitated. The 

discussion on how to develop site specific criteria is presented in 

Appendix K
80

Protection Agency, Duluth, MN, USA.

McDonald BG, deBruyn AMH, Elphick JRF, Davies M, Bustard

D, Chapman PM. 2010. Developmental toxicity of selenium to 

Dolly Varden char (Salvelinus malma). Environ Toxicol Chem 

29:2800-2805.

4. It seemed reasonably clear to me. Thank you for your comment.

5. The EPA used an appropriate approach to translate the 

egg/ovary element to whole-body and muscle elements. 

Unfortunately, data are limited to few fish species. As discussed 

above in 2a(iii), conversion ratios vary by about two-fold for 

both EO:WB and EO:M. In addition, within-species ratios may 

vary throughout the year. These aspects all create uncertainty, 

but these are the data we have and this is the best approach. It is 

suggested that as more studies measure [Se] in egg/ovary, 

whole-body and muscle, that these data be used to update 

criteria through time.

One thing that was not clear. In certain cases it appears that [Se] 

in egg/ovary and whole-body were determined in the same fish. 

If eggs were removed for [Se] determination prior to 

determination of whole-body [Se], then how did the removal of 

eggs influence the whole-body [Se]? Was the absolute quantity 

of Se removed by subsampling eggs added back into the wholebody quantity, and was the mass of eggs removed added back to 

the whole-body?

Thank you for your comment. 

The majority of the data for the E/O to whole body [Se] 

relationship analysis came from Osmundson et al (2007) who 

did have egg data and whole body [Se] data from the same fish. 

The whole body [Se] was calculated by adding back the egg Se 

that was removed for analysis. Osmundson et al (2007) had 9 of 

the 10 species in EPA’s data set for this analysis. Coyle et al 

(1993) also added back egg Se for the whole body same fish 

comparison. Formation (2011) and Doroshov et al. did not 

specify how the whole body [Se] was determined. Hermanutz 

(1996) and Hardy (2005) apparently measured whole body and 

egg Se in different fish with the same exposure. EPA has added 

clarifying discussion to the section discussing fish tissue 

relationships.

6. The approach and method of translating the fish egg-ovary 

criterion into muscle/whole body is transparent and broadly 

scientifically defensible, and there appears to be sufficient data 

to make the translation. Although there is some variability in the 

Thank you for your comment. 

The Figure 5 (now Figure 3.1) that the comment refers to has 

been simplified to eliminate the problem of needing to refer to 
81

calculated results of whole body and muscle calculations, the 

relative consistency across taxon gives significant support to the 

modeling approach and in the data used to derive the values. The 

Figure 5 references to Table 10 and 11 should be introduced and 

explained in the body text prior to using them in a Figure caption 

since the reader has not seen that data. Some editing in this 

regard would improve clarity and help the reader understand and 

follow the approach. The body text of paragraph 1 of page 59 

needs to be rewritten for clarity; statements of “it can be seen” 

assume much and explain little. Because the paragraph 

references a subsequent Section 4.2, editing page 59 to introduce 

and summarize the detail of 4.2 would be an improvement in 

clarity for the reader. Table 7a and 8a would be improved with 

units (mg Se/kg DW) for tissue concentrations. Footnotes on 

these important tables cross-referencing the specific source, 

table or appendix where the data originated would be helpful and 

aid in reader understanding and transparency.

material described later in the document.

7. The methods used to translate egg/ovary to muscle and whole 

body criteria are understandable and transparent, but as we noted 

in our earlier comments, there are scientific issues with some of 

the transformations. The USEPA attempts to use matched pairs 

of muscle and whole body concentrations of selenium for each 

species, but only a few fish species provided data for directly 

assessing the conversion (Page 78). As a result, US-EPA used 

the median conversion value for all species (i.e., 1.27) to convert 

muscle selenium to whole body concentrations where species 

specific data were not available. Continued use of this generic 

ratio would be expected to introduce additional variability and 

uncertainty, particularly for the conversion from egg/ovary to 

whole body because in many cases this requires a two step 

conversion (i.e., from egg/ovary to muscle and then from muscle 

The EPA agrees with the reviewer comment and has revised its 

approach in the 2015 draft criterion document accordingly and

now uses species-specific muscle-to-whole body conversion 

factors where data are available. Where species-specific data 

are not available, the EPA uses the same taxonomic 

classification procedure for the CF as used to estimate TTF 

values for species without data. (See response to Peer Reviewer 

2 above, in Part I, Question 2.a.iii.) Section 3.2.2 of the 2015 

draft criterion document provides a complete description of this 

procedure.
82

to whole body). More specifically, almost half (i.e., 7 of 16) of 

the Conversion Factor (CF) values for egg/ovary to whole body 

were derived by including the generic muscle to whole body 

conversion ratio. The issue is less important for conversion of 

egg/ovary to the muscle criteria because for most species (other 

than desert pupfish) there were data available to calculate the 

conversion directly.
83

PART III: EVALUATION OF THE TRANSLATION PROCEDURE TO DERIVE THE WATER COLUMN ELEMENT(S)

EPA is also requesting a technical review of the methods and procedures used to translate the egg-ovary element of the chronic 

selenium criterion to water-column elements. Relevant sections of the document include:

 A description of the method used to derive an equation to translate the egg-ovary element to a monthly water-column element 

in perennial (lentic and lotic) waters and an equation that can be used to convert the monthly water-column element to an 

intermittent water column element (Sections 3.8.3, 3.8.4, 4.2.1, 4.3, and Appendix G).

 An analysis of the translation equation precision using data obtained from published literature (Sections 7.2.1, 7.2.2, and 

Appendix H).

 A description of the method and data sources used to derive the translation equation parameters (Sections 4.2.2, 4.2.3, and 

Appendix B).

 A description of the method and data sources used to categorize waterbody types where a single water-column chronic 

criterion concentration value would be adequately protective in most circumstances (Section 4.2.4).

 A description of the method and data sources used to derive water-column chronic criterion concentration values for 

established categories of waters (Section 4.2.5).

 A description of the method and data sources used to derive water-column chronic criterion concentration values for 

intermittent discharges that may occur in lentic and lotic waterbodies (Section 4.3).

Please address the following questions: 

1. Please comment on the scientific defensibility of EPA’s translation equation method for translating the concentration of 

selenium in fish tissue to a concentration of selenium in the water-column. Please comment on major sources of uncertainty 

in applying the translation equation to different types of waterbodies (e.g., with differing retention times, water 

chemistries, and/or species present). Are there other data sources, models, or approaches that EPA should consider that 

would reduce uncertainty? Please provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. I appreciate that EPA is dealing with a very difficult issue in 

terms of translating a tissue-based criteria to water for routine 

monitoring and screening purposes. I agree with the general 

conceptual model EPA has developed for making this 

EPA has used all available data in developing a series of site 

specific food chain models in order to derive the national 

criteria. Although there is some uncertainty in the TTFs and 

CFs due to a paucity of species specific data, the EPA believes 
84

External Peer Reviewers’ Comments EPA Response

translation. Having said that, the details of how EPA has 

implemented this conceptual model I think are very problematic. 

My concerns center on two major themes – compounding 

multiple uncertain values in the food chain transfer models and 

lack of transparency on what level of protection the proposed 

water elements provide.

I am very concerned that EPA is placing too much value on 

extrapolated and modeled values. The translation approach 

involves building food chain models for 69 sites that in many 

cases have significant data gaps (e.g., dietary composition, 

extrapolated TTFs, extrapolated CFs, etc.). To address these 

uncertainties, EPA developed a series of protocols for filling in 

the data gaps (e.g., using TTFs for species in the same 

order).While I appreciate the logic and largely agree with these 

protocols, ultimately, information derived in this manner is not 

measured data. This approximated information is then used in a 

very quantitative manner for setting the water-based WQC.

Figure 11 in particular I find very misleading. How many of the 

data points in those two distributions (lotic and lentic) are based 

on sites where all parameters in the food chain models were 

actually measured? I did not take the time to calculate this, but 

EPA must explicitly provide this information. I suspect the 

percentage will be quite low. What do these distributions in 

Figure 11 look like if based on only studies where all parameters 

were directly measured? In my view, use of such data provides 

a potentially very inaccurate picture of what we actually know 

about the distribution of waterborne Se concentrations 

associated with the tissue-based WQC. This seems to be a 

significant departure from previous WQC criteria derivation 

processes where if data for a particular study were insufficient, 

the study was simply excluded and the resulting uncertainty 

using taxonomically related surrogates provides the most 

scientifically defensible approach since the range of variability 

across these parameters is typically small compared to sources 

of variability in other aspects of criteria development (e.g., range 

in sensitivity across species in a given genus for a particular 

toxicant). See response to Peer Reviewer 2 above, in Part I, 

Question 2.a.iii.

The reviewer would like a better accounting of the uncertainty

associated with each step in the translation process. 

Unfortunately, most of the studies that provide the data used in 

the translation do not provide enough information to 

quantitatively estimate the associated uncertainty. The approach 

EPA uses to translate the egg-ovary criterion element into watercolumn measurements represents the best available science, data 

and information on selenium bioaccumulation at the present 

time. EPA has used a peer reviewed approach shown in Presser 

and Luoma (2010). It allows for use of the available data in the 

most scientifically defensible manner possible. The kinetic 

analyses recommended in the comment would be impossible to 

complete nationally because sufficient data do not exist to allow 

for of a rate-based dynamic model using speciated selenium 

data. 

As discussed in response to comment #2 below, EPA believes 

that confining its national assessment to a very small number of 

well-studied sites and to laboratory studies where such 

measurements are available would reduce rather than increase 

confidence in the appropriateness of the national criterion. 
85

External Peer Reviewers’ Comments EPA Response

from having relatively few complete data sets was reflected in a 

lower WQC (e.g., a WQC less than the most sensitive taxa 

tested if n<20). An important element of previous WQC was 

transparency in the level of protection being provided (e.g., 95 

% of taxa) and the assumptions underlying that protection (e.g., 

that tested taxa were representative of aquatic communities in 

the US). It is entirely unclear to me what level of protection is 

being provided by the water element of proposed WQC. The 

proposed water-based WQC is based on the 20th percentile for 

lotic and lentic sites that were modeled (see concerns about this 

in the previous paragraph). But even this is not correct, because 

for some sites, multiple fish species were modeled per site. This 

raises numerous questions regarding independence of values in 

the distribution, whether the sites evaluated are biased towards 

those with known Se issues, etc. EPA has also not made it clear 

why protection of 80% of sites is a desirable regulatory 

objective. Why not 70%, 90%, or 95%? I appreciate that EPA 

has undertaken a ground truthing exercise to evaluate the 

proposed water element WQC. However, it is unclear exactly 

how EPA undertook this analysis. Were there truly over 3,000 

independent sites that EPA evaluated? If this exercise concluded 

that <10% of sites would result in false negatives, then what 

does this say about the representativeness of the 69 sites and 

what is the real level of protection being provided? The overall 

approach of considering selenium’s pathway from the water 

column, dissolved state, through trophic levels, and into tissues 

such as reproductive organs is well justified, particularly the 

trophic transfer model that is dynamic and rate/kinetically based 

(uptake rate * assimilation efficiency/elimination rate); the 

trophic transfer approach largely developed by Nick Fisher and 

collaborators. However, the water to first trophic level approach 

Nevertheless, where sufficient site-specific data are available to 

support rate-based estimates of uptake of separate selenium 

species, interested parties could use those data to develop a sitespecific criterion.

Regarding the reviewer’s comment about the data points in 

Figure 11 being based on estimated values, that figure is clearly 

labeled as model results. There are not sufficient data at any 

single site to derive all the necessary input values to translate 

through all trophic levels to the water value only using 

measurements taken at a particular site. Nevertheless, EPA did 

require that fish be measured at the site and that the EF value be 

measured at the site. Nationally derived TTFs and CFs were 

then applied to the site translation. 

Because Chapman et al. (2010) contains numerous examples of 

(a) EFs and TTFs are not derived from rate data, (b) water 

concentrations expressed as total dissolved selenium, EPA does 

not agree that the Pellston Workshop calls upon EPA to restrict 

itself to the commenter’s recommendation to use only 

kinetically based EFs and TTFs and to use only separately 

measured concentrations of selenite and selenate. EPA believes 

that the tiered structure of its selenium criterion, with the range 

of site-specific options that it offers, is fully consistent with the 

recommendations of the Workshop. 

EPA has addressed the relationship between its approach and the 

kinetic approach with selenite and selenate in the response to the 
86

External Peer Reviewers’ Comments EPA Response

is completely unacceptable in that it is not dynamic or rate-based 

(actually assumes equilibrium) and completely ignores the 

effects of speciation. The latter is curious in that they seem to be 

relying on the Chapman et al (2009 and 2010) recommendations 

from the SETAC Pellston workshop which specifically states, 

“Understanding Se speciation is critical to understanding its 

mobility, transformation, partitioning in the environment, and 

potential risk to aquatic ecosystems.” and “The single largest 

step in the bioaccumulation of Se occurs at the base of food 

webs, characterized by an “enrichment function”; 

thermodynamic or equilibrium-based principles are not 

appropriate for predicting Se bioaccumulation at the base of 

food webs.” The choice of the Presser and Luoma model used in 

this EPA document is completely contrary to these 

recommendations since the water/particle ratio called the 

Enrichment Factor (EF) is only a renamed equilibrium 

distribution coefficient (Kd) that was used long ago for metal 

cations. Dissolved and particulate selenium speciation cannot be 

modeled with equilibrium approaches, it must consider the 

kinetics of the transfers/transformations (e.g., Cutter, 1992). 

Since the transfer of dissolved selenium in any of its chemical 

forms to the particulate state (largely assimilation by 

phytoplankton and conversion to organic selenide – seleno 

amino acids in proteins) changes the chemical forms, how does 

one calculate a distribution coefficient (EF)? For selenium, 

dissolved selenite or selenate are not what are in the particulate 

state (organic selenides), so which dissolved species and which 

particulate species do you use to calculate EF? And, they are 

certainly not reversible (selenite uptake followed by 

regeneration does not return selenite, but rather organic 

selenide...which may later oxidize back to selenite and selenate; 

comment immediately below. It can be seen that under steadystate conditions, the equations of EPA’s approach with dissolved 

selenium can be derived from the equations of the kinetic 

approach with separate selenite and selenate. 

The first advantage of EPA’s approach is that it allows far more 

site data to be brought to bear in the derivation. EPA believes 

that the variability in EF values across sites far exceeds any 

uptake differences attributable to the ratio of selenite to selenate 

across sites. That is, the selenite/selenate ratio is only one factor 

that should not be focused on in a way causes the assessment to 

lose sight of the larger body of site data. Furthermore, site EFs 

represent the composite uptake of all TL1 species at the site, and 

are not reliably captured by measurements of a single TL1 

species in the lab.

The second advantage of EPA’s approach is that it produces a 

criterion that applicable to the selenium water measurements 

commonly available across the U.S. 

Regarding the comment’s question of whether there were “truly 

over 3,000 independent sites:” There were over 3000 wholebody fish tissue measurements that could be coupled with water 

concentrations measured. The 3000 measurements include samesite values of (a) different species measured at the same time, (b) 

the same species measured at different times, and (c) different 

species measured at different times.
87

External Peer Reviewers’ Comments EPA Response

Cutter, 1982; Cutter and Bruland, 1984). In this EPA document, 

they “solve” this issue by only considering total dissolved 

selenium, in contradiction to the recommendations at the 

Pellston workshop.

With regard to the relationship between EPA’s approach and

other facets of more complex approaches, in addition to the 

response to Reviewer 2 immediately below, please see also the 

response to the comment in Part III, Question 2, Reviewer 3, 

which addresses the issue of the model’s linearity.

Regarding the comment’s issue with use of the 20th percentile 

translated water value, the level of protection is determined by 

the egg-ovary criterion element. The water-column element is a 

translation of the egg-ovary element and thus is intended to 

provide the same level of protection as the egg-ovary element. 

However, some level of uncertainty in translating the egg-ovary 

element to the water-column element is unavoidable. To 

address this uncertainty, the EPA chose the 20th percentile of 

translated water-column values using the most bioaccumulative 

food web present at each site to select a protective national water 

column criterion element. Limitations of available data only 

allowed translation of the egg-ovary criterion element at 69 

unique aquatic sites. The 20th %tile was selected because it 

results in a low probability of false negatives, (i.e., low 

probability of failure to indicate exceedance of the egg-ovary 

criterion element via the water column element.) 

In response to the selenium chemistry comments, EPA has 

modified the selenium chemistry section to reflect the uptake 

and transformation of selenium in the aquatic food web. Those 

changes can be found in Section 2.
88

External Peer Reviewers’ Comments EPA Response

2. The use of the Presser and Luoma (2006, 2010) model for 

any aquatic ecosystem to predict dissolved or particulate 

concentrations is questionable for the simple reason that while it 

acknowledges the importance of chemical speciation, and the 

rates of processes (kinetics as opposed to equilibrium 

thermodynamics), it largely ignores them in application. It is a 

totally empirical model designed for the San Francisco BayDelta system, so its application to other systems may not work. 

To reiterate the preceding paragraph in detail, the primary 

problem with this model is the exchange between the dissolved 

and particulate phases, in this case the first trophic level 

(autotrophs/primary producers). While there is some adsorption 

of dissolved selenite and selenate to suspended particles (e.g., 

Doblin et al., 2006), most particulate selenium in organic matter 

is organic selenide in the form of seleno-amino acids in proteins 

(Wrench, 1978). In other words, the uptake of dissolved selenite 

and selenate from the water column by phytoplankton changes 

their chemical forms, it is reductively incorporated (Cutter, 

1982; Cutter and Bruland, 1984). 

Biological uptake of dissolved nutrients such as nitrogen, and 

metals, is best (most accurately) modeled using MichaelisMenten kinetics, or at least pseudo-first order rate expressions. 

The release of this particulate organic selenide back into the 

water column as dissolved organic selenide is coupled to oxic 

(or anoxic) respiration (Cutter, 1982; Cutter and Bruland, 1984), 

which is also modeled using an appropriate rate expression (e.g., 

first order; see discussion in Meseck and Cutter, 2006). The 

critical point here is that the speciation of particulate selenium 

has no relation to that in the water column – reductive 

incorporation and subsequent regeneration obliterates this 

Please see response to reviewer 1 above. In short, EPA has used 

an approach shown in Presser and Luoma (2010). The specific 

applications of the model cited in Presser and Luoma (2006, 

2010) were parameterized using site specific empirical data from 

the SF Bay. However, the model described in those studies is a 

basic food web model that can be applied to any system.

The kinetic analyses recommended in the comment would be 

impossible to complete nationally because sufficient data do not 

exist to allow for of a rate-based dynamic model using speciated 

selenium data. Thus, EPA uses total dissolved selenium to 

reflect the selenium concentration in water that is available for 

uptake and assimilation at TL1. As mentioned above in the 

response to Reviewer 1, the document’s narrative on the uptake 

and transformation of selenium has been rewritten to reflect the 

actual processes in nature.

EPA has followed up on the reviewer’s recommendation that:

“all that is needed is a model that covers dissolved to first 

trophic level interactions, and from there the existing 

biodynamic part of the Presser and Luoma (2006; 2010) 

could be employed. In this case, using Equations 4-6, and 7, 

in the Meseck and Cutter (2006) paper (and related equations 

in the Appendices) could suffice.”

EPA coupled the above with consideration of the reviewer’s 

recommendation to:

“Use ... simple first order rate equations (and values) 
89

External Peer Reviewers’ Comments EPA Response

relationship and only a rate-based (kinetic) approach can 

accurately quantify it. However, the Presser and Luoma (2006, 

2010) model uses equilibrium distribution coefficients (Kd or in 

this EPA document EF) to quantify how particulate selenium in 

the first trophic level reflects the dissolved concentration in the 

water column. The distribution coefficient approach works well 

for divalent metal cations where no oxidation state change 

occurs. For a given Kd value, if the dissolved concentration goes 

up, more adsorbs to the particles (to maintain equilibrium), and 

when the dissolved concentration drops, the particulate-bound 

metal desorbs. But, when there is a redox change between 

dissolved and particulate conversions, the equilibrium concept is 

violated. For example, if the concentration of selenite goes up, 

the rate of uptake increases, and the concentration of particulate 

organic selenide increases; in a crude fashion, the use of a Kd

could mimic this biochemical process. But, when the 

concentration of dissolved selenite goes down, particulate 

organic selenide doesn’t desorb to balance it; they are different 

chemical species. Particulate organic selenide is only released 

through respiration/regeneration, not adsorption/desorption (for 

which the Kd concept was created). So in this scenario, the 

Presser and Luoma (2006) cannot accurately predict the 

response to a change in dissolved concentration, and more 

importantly cannot predict the speciation of selenium. 

Interestingly, Presser and Luoma (2006) note that as more 

recycling (i.e., the regeneration part of the selenium cycle 

depicted in Cutter and Bruland, 1984) occurs, organic selenide 

concentrations increase. Indeed, they do, but their model cannot 

reproduce this, a problem if you “reverse” their model to predict 

water column dissolved concentrations of selenium for a given 

particulate concentration in the food web (e.g., 11.8 ppm Se in 

described in the literature.”

The reviewer’s recommended Equation 7 relates selenium water 

concentrations to sediment flux rates, and although it is 

applicable to reviewer’s San Francisco Bay site, it cannot be 

applied to the national criterion derivation for lack of 

information on the direction and magnitude of sediment flux 

rates in the wide range of sites EPA considered.

However, the implications of the reviewer’s recommended 

equations 4-6 are of interest. Those equations are as follows, 

where D signifies dissolved and P particulate, and Se(-II) is 

organic selenium:

∂DSe(IV)/∂t = k3 [DSe(IV)] - k5 [DSe(VI)]

∂DSe(IV)/∂t = k2 [DSe(-II)] - k3 [DSe (IV)] - k4 [DSe (IV)]

∂DSe(-II)/∂t = k1 [PSe(-II)] - k2 [DSe (-II)] - k6 [DSe (-II)]

The above rate coefficients are for the following reactions:

k1: PSe(-II) → DSe(-II)

k2: DSe(-II) → DSe(IV)

k3: DSe(IV) → DSe(VI)

k4: Phytoplankton uptake rate for DSe(IV)

k5: Phytoplankton uptake rate for DSe(VI)

k6: Phytoplankton uptake rate for DSe(-II)

Lacking information on rates of concentration change, the 

approach is unworkable unless a steady-state assumption is 
90

External Peer Reviewers’ Comments EPA Response

fish muscle; this document). This latter (highlighted) point is 

exactly what Section 4.2 is doing. On a related matter, the 

Presser and Luoma model suggests that it handles selenium 

speciation, but only in the dissolved phase, and then rather than 

using separate Kds for each species, and presumably summing 

the contributions from each from to derive the particulate 

selenium concentration, they simply average the Kds to one 

value and omit speciation. 

To put this modeling approach into another perspective, it has 

been observed (Cutter, 2005) that the aquatic selenium and 

nitrogen cycles are very similar/parallel. Adding N cycling to 

the Se cycle depicted in Cutter and Bruland (1984) gives:

imposed, as commonly done in such problems. At steady state, 

concentrations do not change over time. Consequently, the left 

side of each equation is zero, and the problem becomes 

workable. The equations then reduce to:

k3 [DSe(IV)] = k5 [DSe(VI)] Hence, with first order 

kinetics, [DSe(IV)] ∝ [DSe(VI)]

k2 [DSe(-II)] = k3 [DSe (IV)] + k4 [DSe (IV)] Hence, 

[DSe(-II)] ∝ [DSe (IV)] 

k1 [PSe(-II)] = k2 [DSe (-II)] + k6 [DSe (-II)] Hence,

[PSe(-II)] ∝ [DSe (-II)]

With first-order kinetics and steady-state assumptions, 

particulate organic selenium, PSe(-II), in the primary producers 

is proportional to dissolved organic selenium, DSe(-II), which in 

turn is proportional to dissolved Se(IV), which in turn is 

proportional to dissolved Se(VI).Consequently, under these 

model assumptions, selenium in the primary producers is 

proportional to total dissolved selenium in the water column. 

The reviewer’s recommended approach thus appears to be a 

more detailed articulation of the approach EPA applied, 

provided that the first-order kinetic assumption is taken to be 

one of the acceptable approaches, as the reviewer seems to 

suggest, and if the commonly used steady-state modeling 

assumption is applied, as was done for all other trophic levels.

Reiterating a point made in response comment #1 immediately 

above, this comment is technically incorrect in calling EFs an 

equilibrium concept. EFs, like TTFs and BAFs, are better 

characterized as steady-state concepts. Steady state does not 
91

External Peer Reviewers’ Comments EPA Response

p Org Se(-II)

PON

d Se(VI)

NO3

-

d Se(IV)

NO2

-

d Org Se(-II)

DON

p Org Se(-II)

PON

Atmospheric Input

(SeIV=SeVI) 

(NO3>NH3 Rivers >DON)

(SeVI >Org Se >SeIV)

(NO3>DON)

Mixed Layer

Deep Water

Atmosphere

Phytoplankton

Uptake

Regeneration:

Particle Sinking

Regeneration

?

Recycling

(part<=>diss)

0.1 y-1 0.04 y-1 0.0009 y-1

Upwelling

(SeVI>SeIV)

(NO3

-

 only)

p Org Se(-II)

PON

d Org Se(-II)

DON

d Se(IV)

NO2

-

d Se(VI)

NO3

-

B

If Suboxic/Anoxic

Deep Waters: 

d Se(VI)

NO3

-

p Se(0)

N2

Biogeochemical Cycle of Selenium in a stratified lake

(with nitrogen analogs)

Thus, I ask those who wrote this document if they would use the 

Presser and Luoma (2006, 2010) approach to model nitrogen 

cycling and therefore set N discharge, etc limits? I suspect the 

answer would be no, and my response then would be, why use it 

for selenium?

To be constructive, what modeling approach should be used? In 

Cutter (1992) it was argued that a kinetic/rate approach, and not 

require equilibrium or process reversibility. For example, 

irreversible uptake coupled with growth dilution would still 

yield a steady-state EF.

In site-specific situations where ample measurements are 

available for all forms of Se, EPA recognizes the value of the 

reviewer’s detailed articulation of the organic-inorganic Se 

processes. However, because such data are rarely available, the 

reviewer’s detailed approach is not feasible to capture the wide 

diversity of sites represented via the derivation of the national 

criterion. EPA believes that confining its assessment to a very 

small number of well-studied sites where such measurements are 

available would reduce rather than increase confidence in the 

appropriateness of the national criterion. Likewise, an analysis 

based on a few site- or lab-specific measurements of k1 through 

K6 would also decrease rather than increase confidence, when 

compared to an approach that homogenizes the rate coefficients 

but uses the end-resulting ratios of concentrations observed in 

water and primary producers at a wide diversity of sites.
92

External Peer Reviewers’ Comments EPA Response

an equilibrium thermodynamic one (EFs are an equilibrium 

concept) is the only way to quantify the selenium cycle. There 

are at least two existing kinetic models for the selenium cycle: 

for lakes there is the one described in Porcella et al. (1991) and 

Bowie et al. (1996), and one for estuaries, Meseck and Cutter 

(2006). The Meseck and Cutter model focuses on the dissolved 

to first trophic level dynamics and includes the full speciation of 

selenium in the dissolved and particulate states in an estuary 

(San Francisco Bay/Delta). The Bowie et al. (1996) model uses 

a kinetic approach to modeling selenium speciation and 

dynamics from the dissolved state to all trophic levels in 

freshwaters, and was designed to assist in mitigation/restoration 

efforts. The Meseck and Cutter (2006) model also has direct 

applications to mitigation via scenario modeling (what if...). 

However, this model includes components to simulate sediment 

resuspension, mixing and dispersion, and primary production 

(light-limited in this case), so it may be too complicated for the 

application needed here. Indeed, all that is needed is a model 

that covers dissolved to first trophic level interactions, and from 

there the existing biodynamic part of the Presser and Luoma 

(2006; 2010) could be employed. In this case, using Equations 

4-6, and 7, in the Meseck and Cutter (2006) paper (and related 

equations in the Appendices) could suffice. Or, use simple 

Michealis-Menten equations and values in the literature (e.g., 

Riedel et al., 1991), and simple first order rate equations (and 

values) described in the literature (e.g., Cutter, 1982; Cutter and 

Bruland, 1984; Reinfelder et al., 1993).

3. I believe that the EPA's translation method is not 

unreasonable, but I have three primary concerns: (1) TTFs and 

CFs derived for taxa from other studies are applied to sites 

The model prediction itself is correct with respect to the 

translation calculations. In applying the translation model, the 

egg-ovary criterion element concentration is used to translate 
93

External Peer Reviewers’ Comments EPA Response

regardless of whether those TTFs and CFs are reflective of sitespecific trophic transfer data; (2) the EFs and TTFs are treated as 

constants regardless of exposure concentrations; and (3) the 

level of protection associated with the draft criteria is unclear. 

These are discussed further below (in response to questions 1 

and 2).

Model for translating fish egg/ovary Se criterion to lentic and 

lotic water Se criteria is not always consistent with site-specific 

information:

The EPA identified sites where Se EFs could be calculated 

based on reported co-located Se concentrations in surface water 

and particulates (algae, detritus, sediment). Information on the 

fish species present at those sites was then used to develop food 

web models, which determined the CFs and TTFs that were then 

applied in translating from the draft fish egg/ovary Se criterion 

back to corresponding water Se concentrations. Site-specific 

food web information was used where reported, but the EPA 

mostly relied on the NatureServe database 

(http://www.natureserve.org) for information on the typical diet 

and/or eating habits of the fish at each site.

A limitation of this modeling approach is that it ignored sitespecific information on Se bioaccumulation in fish and their 

diets. The EFs used were site-specific, but Se modeling up the 

rest of the food chain and into fish was based on assumed model 

parameters. This becomes particularly important when 

considering the data "drivers" for the draft lentic Se criterion of 

1.3 μg/L. This value is driven almost exclusively by data for two 

reference lakes (Badin Lake and High Rock Lake, NC, USA). 

Badin Lake was reported to have a water Se concentration of 

0.32 μg/L and High Rock Lake a water Se concentration of 0.67 

that value to a water concentration by dividing that egg-ovary 

criterion element by the product of a species-specific composite 

TTF, a species specific egg-ovary to whole body to CF, and a 

site specific EF). The model values in Table 12 are correct 

calculations.

To maximize the applicability of the available information, EPA 

treated EF as site-specific and TTFs as taxon-specific. Sitespecific food-web observations (prey species consumed by 

predator species) were always used when available. When not 

available from the study, the NatureServe database was used. 

EPA believes it has used the available data in a comprehensive 

and scientifically defensible way.

Regarding the reviewer’s point about EFs and TTFs not varying 

with concentration, see responses in the TTF section (Question 

2) below.

Regarding the influence of Badin and High Rock Lakes, EPA 

agrees that they have a strong influence on the derived lentic 

value. Of the 44 site-species used for the lentic derivation via 

the 20th percentile value, 12 of the lowest 13 values are for 

Badin and High Rock. These lakes each have one EF, but each 

of its EFs is used six times, once for each of six fish species. 

The particulate concentrations measured in both of these lakes 

are near the median observed in EPA’s lentic database, but their 

water concentrations are among the lowest. As a result of the 

peer reviewer’s comments, EPA completed a reanalysis of the 
94

External Peer Reviewers’ Comments EPA Response

μg/L (Lemly 1985). For comparison, the mean water Se 

concentrations translated from a fish egg/ovary Se criterion of 

15.2 mg/kg dw were 0.54 μg/L for Badin Lake and 1.2 μg/L for 

High Rock Lake. The former falls between the water Se 

concentrations reported for these two reference lakes and the 

latter almost equals the draft lentic criterion of 1.3 μg/L. Since 

six fish species were assumed to represent each of these two 

sites, these two reference sites are the drivers for the draft lentic 

Se criterion of 1.3 μg/L.

In addition to two reference sites being the drivers for the draft 

lentic Se criterion of 1.3 μg/L, the model for translating a fish 

egg/ovary Se criterion of 15.2 μg/L to a water Se concentration 

does not appear to be correct for these two sites. Although fish 

egg/ovary Se concentrations were not reported for Badin Lake 

and High Rock Lake, muscle Se concentrations were. Those 

muscle Se concentrations were reported on a wet weight basis 

and converted to a dry weight basis by assuming a moisture 

content of 75%. The muscle-to-egg CFs reported in Table 12 of 

the draft AWQC document were then used to estimate fish egg 

Se concentrations. These estimated fish egg Se concentrations 

for the two reference sites were, on average, less than one-half 

of the draft fish egg/ovary Se criterion of 15.2 mg/kg dw. 

Further, the muscle Se concentrations at the references sites 

ranged from 2.3 to 5.8 mg/kg dw, which are well below the draft 

muscle Se criterion of 11.8 mg/kg dw. The above demonstrates 

that the food web model for these two reference sites does not 

accurately reflect Se bioaccumulation potential at these two sites 

and in fact greatly overestimates Se bioaccumulation potential. 

Overall opinion on method for translating from a fish tissue 

criterion to water Se criteria:

data to remove any overweighting of a few key high and low 

end sites in the calculations. To account for overweighting,

EPA used one fish species per site – the species most sensitive 

to selenium bioaccumulation, to yield an appropriately 

protective water column criterion element.
95

External Peer Reviewers’ Comments EPA Response

In my opinion, the approach should rely more on empirical data 

in order to eliminate cases where the food web models do not 

reflect the site-specific data. One alternative approach is that 

described in DeForest et al. (2014). That approach was also 

based on multi-step Se partitioning, but rather than using EFs 

and TTFs, the empirical relationships between (1) water and 

particulate Se; (2) particulate and invertebrate Se; and (3) 

invertebrate and fish egg/ovary Se were used. Quantile 

regression was used to work backward from an egg/ovary Se 

threshold to conservative Se concentrations in lentic and lotic 

water bodies. This regression-based approach accounts for the 

breadth of data on Se enrichment and trophic transfer potential, 

which can essentially represent the bounds of Se 

bioaccumulation potential from water to fish eggs/ovaries. The 

regression-based approach also accounts for the slopes of the 

relationships between water and particulate Se, particulate and 

invertebrate Se, and invertebrate and fish Se. This would be one

example of an alternative model that could be considered.

Level of protection associated with draft water selenium criteria 

unclear:

The draft lentic and lotic criteria are based on the 20th 

percentiles of the data points plotted in Fig. 11 of the draft 

AWQC document. Those data points in Fig. 11 are for 

individual fish species at a given site. For example, 18 of the 51 

data points for lentic systems (35%) are for just three water 

bodies (six fish species per water body). It is unclear what the 

20th percentiles of those lentic and lotic distributions are 

protective of, as they do not represent 20% protection of sites or 

20% protection of fish species. The latter was presumably not 

the intent, as those levels of protection would not be acceptable 
96

External Peer Reviewers’ Comments EPA Response

for national AWQC recommendations.

Literature cited:

DeForest DK, Brix KV, Gilron G, Hughes SA, Tear LM, 

Elphick JR, Rickwood CJ, DeBruyn AMH, Adams WJ. 

2014. Selenium partitioning between water and fish tissue in 

freshwater systems: Development of water-based selenium 

screening guidelines. 

http://www.namc.org/docs/Selenium%20 

Integrated%20Report%20-%20Final%20(2014-05-20).pdf

Lemly AD. 1985. Toxicology of selenium in a freshwater 

reservoir: Implications for environmental hazard evaluation and 

safety. Ecotoxicol Environ Saf 10:314-338.

4. The EPA is justified in simplifying the bioaccumulation 

equations by eliminating the growth rate constant (g) because it 

is negligible compared to the loss rate constant of Se from 

aquatic animals. This is generally the case for most metals and 

metalloids, with some notable exceptions where the loss rate 

constants are very low (e.g., methylmercury). Their equations 2 

and 3 (pages 64-65) have already been published, and the 

reference for this should be cited. (Reinfelder, J.R., N.S. Fisher, 

S.N. Luoma, J.W. Nichols, and W.-X. Wang. 1998. Trace element 

trophic transfer in aquatic organisms: a critique of the kinetic model 

approach. Science of the Total Environment 219: 117-135.) The 

authors should note that the loss rate constant of some 

contaminants can differ following uptake from the aqueous 

phase and uptake from diet---this is because the contaminant 

may deposit in different tissues from these two uptake routes. As 

such, the term ke should be converted to kef and kew (following 

uptake from food and uptake from water). For Se, fortunately, 

Thank you for your comment. EPA added the reference you 

noted. EPA recognizes that ke consists of kef and kew, but has 

decided to retain the mathematical expression as is for

simplicity. As the reviewer noted, uptake from the aqueous 

phase is negligible. 
97

External Peer Reviewers’ Comments EPA Response

this correction is unlikely to be an important one because uptake 

from the aqueous phase (water) is negligible compared to dietary 

uptake. But strictly speaking, the mathematical expression (Eq. 

2) should reflect two different loss rate constants.

By using tissue concentrations of Se in fish to calculate 

dissolved Se concentrations in ambient water, one must 

ultimately calculate the Se concentration in organisms at the 

base of the food chain, namely phytoplankton. This is because 

none of the animals in the food chain appreciably take up Se 

from the aqueous phase. The problem of inferring Se 

concentrations in water from phytoplankton Se concentrations is 

that the enrichment factors (or bioconcentration factors) of Se in 

phytoplankton can vary by up 2 or 3 orders of magnitude, 

depending on the type of phytoplankton that happen to be 

dominant in the water. Chlorophyceae (green algae), for 

example, bioconcentrate Se far less than diatoms, and so the 

variability in these calculations would depend heavily on which 

types of phytoplankton happen to be dominating the community, 

and this can change temporally and geographically.

5. The EPA has used the modern and scientifically valid 

biodynamic model approach to derive water quality elements 

from tissue-based elements. I am not aware of other data 

sources, models or approaches that would reduce the inherent 

uncertainty. However, based on comments provided above (in 1 

and especially 2a(iii)), relying on water column dissolved [Se] 

has a high likelihood of generating both false positive and false

negative results with respect to regulatory action. I think the 

proposed water column criteria (a) should be used as triggers to 

initiate further monitoring of fish tissue [Se], (b) should be made

more conservative (reduced) by application of a safety factor to 

Thank you for your comment. The water column criterion 

element values were derived using the egg-ovary criterion 

element as the basis of the calculation. EPA developed water 

column criterion values because routine water concentration 

monitoring of selenium is more practically feasible than routine 

tissue monitoring, and used a hierarchal (tiered) approach to 

insure that water column values indicating a selenium problem 

could be vetted using a fish tissue sample, because the fish tissue 

selenium concentrations are indicative of potential effects.. 

Water column values are necessary because they may be the 

only media data available – i.e. streams where fish are absent, or 
98

External Peer Reviewers’ Comments EPA Response

avoid false negatives, and (c) that the simple classification of a 

water body as lentic or lotic should be modified to include more 

quantitative measures of flow such as water residence time 

and/or mean annual water velocity. Given that many impounded 

riverine systems in the USA are essentially lentic systems for 

much of their river-miles, perhaps a water column trigger [Se] 

could be set at 1 ug/L (same as the current Canadian [CCME] 

water quality guideline for Se). If exceeded, this trigger value 

would result in further action in terms of fish collections for 

tissue [Se].

temporally necessary due to a new discharge where selenium has 

not accumulated in the system, and so there is uncertainty in the 

relationship between the discharge and the potential for 

bioaccumulation in fish at the site.

6. The translation equation approach used to convert 

toxicologically relevant fish tissue concentrations to watercolumn concentrations is broadly scientifically sound and 

defensible, and represents our best available understanding of 

these relationships across trophic levels in an aquatic ecosystem 

food web. This may be especially true because the approach is 

based on a straightforward model, and alternative approaches 

that introduce complexity can also introduce uncertainty from 

the requirements of additional data beyond that currently 

available. Risk estimation rarely has perfection due to situational 

variability and uncertainty involving the integration of exposure, 

uptake, and biokinetics. The draft criterion approach uses 

qualified data and reasonable analysis to reduce complexity and 

increase the transparency of criterion. Modeling dynamic 

relationships in complex multi-level systems with innate 

variability is a significant environmental management challenge, 

however the effort can yield a valuable management tool. Figure 

8 (p. 73) graphically demonstrates “hysteresis” with regards to 

aquatic food chain selenium levels and potential for toxic impact 

as well as the temporal relationship to periodic sampling. Any 

Thank you for your comment. 
99

External Peer Reviewers’ Comments EPA Response

challenges in application of this approach across diverse aquatic 

ecosystem types with variable water chemistries and annual 

variability (e.g., flow and flux), are equally met by the 

challenges of sufficiently devising specific criteria to address 

every subset of variables with less or equal uncertainty in the 

protection of aquatic life. The duration and frequency 

requirements of the water column selenium criterion address the 

potential for system variability (e.g., year to year 

weather/hydrograph changes) and propagation of system 

uncertainty (e.g., non-selenium related chemical or biological 

changes) in this risk management.

7. The scientific method for translating concentrations of 

selenium in fish tissues to allowable concentrations in the water 

column is clearly written and understandable. However, while 

we understand the regulatory need for triggers to initiate site 

investigation where selenium is suspected of being an issue, the 

derivation of allowable water column concentrations from eggs 

or ovaries is oversimplified and likely to need site specific 

inputs for refinement. Back calculating from egg/ovary to 

muscle/whole body and then down through trophic levels to 

derive allowable water column criterion for each of these types 

of aquatic systems is not scientifically valid, because of the use 

of generic CF, assumptions regarding proportions of prey items 

consumed by resident fish and broadly applied trophic transfer 

factors. These generic terms do not incorporate site specific 

information, including concentration dependent uptake kinetics 

and consideration for important influencing factors (e.g., sulfate, 

organic carbon, temperature, etc.). The water based criterion 

developed in the Draft Document are therefore, necessarily 

conservative. As evidence for this, the monthly average 

EPA has developed the national criterion based on the bestavailable science. EPA also agrees on the utility of site-specific 

criteria developed using site-specific data to estimate risk in the 

most refined manner possible. EPA has included a discussion of 

the development of site-specific criteria in the criterion 

document main text body, and describes approaches to 

developing site-specific criteria in detail in Appendix K.

In each site-species translation equation an egg-ovary selenium 

concentration is divided by the product of: a species (or closest 

taxonomical surrogate) specific CF, a species-specific 

component TTF, and a site specific EF. At many sites, sitespecific data are not available to calculate site specific CFs and 

TTFs for each species, so the application of CFs and TTFs 

represents the best available information. Also, see response to 

Peer Reviewer 2, in Part I, Question 2.a.iii above.
100

External Peer Reviewers’ Comments EPA Response

exposure value for lentic systems is 1.3 g/L. This value is at the 

upper end of background values for freshwater and may be 

exceeded even in the absence of industrial inputs in areas 

receiving runoff from seleniferous soils. The value is also lower 

than recently recommended lentic values based on similar 

analysis (Deforest et al. 2104, BC MoE 2014).

In effect, EPA is positing that although partitioning from water 

to particulate matter is highly variable and can best be evaluated 

using data gathered from the specific site under consideration (if 

available), selenium partitioning among tissues (CF), and from 

particulate matter to fish through the food chain (TTF) is 

relatively similar for a given species regardless of site. 

Although this introduces some uncertainty to the translated 

values, CFs and TTFs are less variable across sites than EFs

based on available data. (See response to Peer Reviewer 2, in 

Part I, on modification of CF and TTF derivation method to 

incorporate taxonomic proximity.)
101

2. Regarding the trophic transfer factor (TTF) values, did EPA use a scientifically defensible method to derive the TTF values 

(p. 71-77 of the criteria document)? Were the exclusion criteria, (pp. 71-77 of the criteria document) developed by EPA to 

screen the available data applied in a consistent and scientifically defensible manner? In particular, EPA noticed that 

application of the exclusion criteria resulted in TTF values for aquatic insect larvae that differ from other published 

values. Given this, are you aware of any other methods of screening data that EPA should consider? Also, are you aware 

of any data that was not considered in this effort and should be screened and included, if appropriate? Please provide 

detailed comments.

External Peer Reviewers’ Comments EPA Response

1. In general, EPA has used a scientifically defensible method 

to derived TTFs. However, I am concerned that the TTFs 

derived from field data by EPA are biased low and potentially 

not protective. I note that the data in Figure 16 appear to show a 

rather significant bias towards under-prediction of EO selenium 

concentrations, consistent with this concern. As recognized by 

EPA, there is typically an inverse relationship between the 

exposure concentration and the TTF such that low dietary Se 

will result in relatively high TTFs for a given predator-prey 

species pair. Many of the field data sets used by EPA are from 

sites with high levels of Se contamination (10’s to 100’s g l-1

waterborne Se). Conversely, a number of the data sets are from 

extremely low Se environments (e.g., mayfly). Perhaps, for TTF 

derivation purposes, EPA should constrain calculation of the 

median TTF to conditions that approximate the range of WQC 

(e.g., 0.5-10 g l-1in water) that EPA might consider on a sitespecific basis, or the range of concentrations typically associated 

with the EC10 for sensitive fish species. Otherwise, individual 

TTFs have the potential to be biased either low or high 

depending on the site(s) from which they were collected. EPA 

should carefully review the biokinetic data using similar criteria.

EPA used TTFs derived from both lab and field data. TTFs 

derived from field data are expected to be sufficiently protective 

of aquatic life in the field since they are estimates based on realworld conditions, and not controlled experiments in the lab. 

Field data were considered superior to lab data for several 

reasons, such as having representative diets, steady-state 

conditions and an absence of artifacts that can be observed in 

laboratory exposures (e.g., poor nutrition, selenium speciation

issues). 

Although there is a strong correlation between predicted and 

observed egg-ovary concentration values, Figure 16 does show 

more data points above the y = x (observed egg-ovary 

concentration vs predicted egg- ovary concentration) line at low 

selenium concentrations. This result suggests the model 

underestimates bioaccumulation at low selenium concentrations. 

However, within the range of concentrations near the egg-ovary 

criterion element value, the relationship between predicted and 

observed selenium concentrations are evenly dispersed around 

the y = x line. Thus the model is unlikely to result in biased 

estimates near the egg-ovary criterion concentration, the focus 
102

External Peer Reviewers’ Comments EPA Response

of the criterion development.

2. After the dissolved to first trophic level particulate selenium 

part of the model that I am criticizing above, the rest of the 

Presser and Luoma (2006) model (including the derivation of 

TTFs) is excellent and accurately predicts bioaccumulation 

through the various parts of the food web (and earlier 

documented in the Luoma and Rainbow (2005) peer-reviewed 

paper). The reason here is that once into the first trophic level, 

the primary speciation of particulate selenium is organic 

selenide, and the concepts of assimilation efficiency, trophic 

transfer factors, ingestion and depuration (egestion) work well 

for selenium (and any other metal or nutrient). The screening of 

data followed well-set protocols and are quite defensible. I am 

not aware of additional data to be included, but I’m sure there 

must be some in the grey literature. 

Thank you for your comment.

3. Overall, I generally agree with how the EPA derived TTFs 

from either physiological coefficients or from field data. 

Following are specific comments.

TTFs from empirical measurements in laboratory studies:

Laboratory-based TTFs were calculated from physiological 

coefficients (AE, IR, ke), but it does not appear that TTFs were 

calculated from laboratory data in which Se concentrations were 

empirically measured in invertebrates or fish and their diets. 

This approach is analogous to the field-based TTFs calculated 

by the EPA, but there is less uncertainty in the dietary Se 

concentration because the dietary Se concentration is known in 

laboratory studies. Is there a reason why these studies were not 

considered? 

When EPA collected data for calculating TTF values, the search 

was restricted to field data. Field data were considered superior 

to lab data for several reasons, such as: having representative 

diets, steady-state conditions and an absence of artifacts that can 

be observed in laboratory exposures (e.g., poor nutrition, 

selenium speciation issues). 

The dynamic nature of selenium transfer from one trophic level 

to another is better represented in field data than in laboratory or 

mesocosm data. EPA did include TTFs from the multiple 

Conley et al. publications based on the life-cycle exposure of 

selenium to mayflies via a complex periphyton diet. There are 

concerns regarding the Conley mayfly TTFs when insufficient 
103

External Peer Reviewers’ Comments EPA Response

TTFs are not constants across exposure concentrations:

As previously noted, one potential limitation of the modeling 

approach is that TTFs tend to be inversely related to exposure 

concentration (i.e., TTFs are inversely related to the 

corresponding dietary Se concentration). However, the TTFs in 

the model used by the EPA are constants that are specific to the 

exposure concentration in the test from which they were derived. 

The EPA did note, on p. 74, that the "distribution of ratios could 

be biased high toward larger values if the data are obtained from 

aquatic systems with low selenium concentrations" and on p. 75 

a regression-based approach was considered. EPA ultimately 

used what was described as a hybrid approach, in which 

ordinary least squares (OLS) linear regression was used to 

confirm that a significant (p ≤ 0.05) and positive relationship 

was observed, and then the median of individual ratios was used 

to estimate central tendency and avoid bias from systems with 

very low or very high selenium concentrations. This helps to 

partially address the issue, but a regression-based approach may 

still be more appropriate (see previous comment).

TTFs for insect larvae:

The draft AWQC document includes Se TTFs of 1.97 for a 

dragonfly (Anisoptera), 2.88 for a damselfly (Coenagrionidae), 

1.28 for a mayfly (Centroptilum triangulifer), 1.90 for a midge 

(Chironomidae), and 1.48 for a corixid (Corixidae). 

 Dragonflies and damselflies: The dragonfly and 

damselfly TTFs do not always appear to be calculated as 

described. On p. B-63 it is noted that the Se 

concentration in dragonfly and damselfly food is the 

median selenium concentration in all invertebrate tissues 

food resulted in different TTF (and toxicity) measurements,

which illustrate the potential bias with laboratory studies. The 

decision to include the Conley studies was based on the weight 

of evidence of similar TTFs for most of the exposures and the 

need to fill a data gap for a TTF of an important fish prey item. 

Regarding the commenters question on regression versus 

median approaches, ultimately, a hybrid approach (median ratios 

with regression statistics used to screen data quality) was 

selected by EPA because the use of ratios was less sensitive to 

outliers or from regressions where the y-intercept was notably 

different from zero, where the slope of a constrained regression 

(following the approach used by Presser and Luoma) had a poor 

fit. Every approach (median ratios, constrained regression, and 

conventional OLS regression) has inherent strengths and 

weaknesses, and ultimately, the hybrid approach was determined 

to be the most robust. 

EPA has carefully considered its assumption that EFs and TTFs 

do not vary with concentration. The following graphs show the 

water-TL1, TL1-TL2, and TL2-TL3 relationships, from the 

standpoint of total least squares (error in x and y), and ordinary 

least squares (error in y only). One advantage of total least 

squares (TLS) is that the regression relationship is unaffected by 

which variable is assigned to the x and y axes. Another 

advantage is that introducing sampling noise into an underlying 

relationship does not consistently flatten the TLS slope (in 

contrast to its flattening of the OLS slope). Because 

concentrations in both media have essentially equal uncertainty, 
104

External Peer Reviewers’ Comments EPA Response

that co-occur with an Odonate species. For Site 29 in 

Birkner (1978), however, only corixids are considered in 

the damselfly diet, even though data for chironomids are 

available. The damselfly Se concentration at this site was 

55.0 mg/kg dw and the corixid Se concentration was 29.4 

mg/kg dw, which resulted in a TTF of 1.87. However, if 

chironomids were also considered part of the diet, which 

had a Se concentration of 58.2 mg/kg dw, the median Se 

concentration in the damselfly diet would be 43.8 mg/kg 

dw and the TTF would be 1.26. I recommend that the 

EPA double-check the dietary data used to calculate the 

TTFs for these taxa.

 Mayfly (C. triangulifer): The Se TTF of 1.28 for this 

species may be too low. This value was based on 

biokinetic data from Riedel and Cole (2001). However, 

empirical laboratory data from Conley et al. (2009, 2011, 

2013) indicate that the Se TTF may range from about 1-

3, with a mean of about 2 depending on exposure and test 

conditions. I recommend that the EPA consider these 

studies, which may result in a higher Se TTF for C. 

triangulifer.

 Midges (Chironomidae): The Se TTF of 1.90 for this 

taxa may be high when considering laboratory-based 

TTFs, for which the dietary Se concentration is known. 

Based data for chironomids from Malchow et al. (1995) 

and Rickwood and Jatar (2013), mean and maximum Se 

TTFs are 0.3 and 1.4. The chironomid Se TTFs derived 

from field data by the EPA include dietary Se 

assumptions that may underestimate the dietary Se 

concentration and result in relatively high Se TTFs. For 

total least squares might be the preferred approach.

In the graphs below show, (a) the data, (b) the TLS line and its 

formula, (c) the OLS line, and (d) a slope=1 line going through 

the median of x and y.

y = 0.7887x0.8359

0.125

0.25

0.5

1

2

4

8

16

32

64

128

0.125 1 8 64 512

TL 1 Conc (mg/kg)

Water Conc (μg/L)

Data

TLS

OLS

Slope=1
105

External Peer Reviewers’ Comments EPA Response

example, the TTFs from Saiki et al. (1993) average 1.0 

when a detritus-based food chain is assumed, as 

suggested by the study authors. I recommend that the 

EPA consider the dietary assumptions in the field studies 

in light of the laboratory data.

 Corixids (Corixidae): Additional Se TTF data for 

corixids are available from a laboratory study with 

Trichorixa reticulata (water boatman). In this study, the 

TTF was very high (32.6) in the control with a low 

dietary Se concentration of <0.1 mg/kg dw, but then 

TTFs were <1 at dietary Se concentrations of about 6 to 

86 mg/kg dw. It is recommended that this laboratory 

study be included in deriving the corixid and be used to 

check the dietary assumptions in the field studies.

Additional potentially relevant TTF data sources:

Laboratory data:

 Conley et al. (2009, 2011, 2013) - Centroptilum 

triangulifer (mayfly)

 Malchow et al. (1995) - Chironomus decorus

(chironomid)

 Rickwood and Jatar (2013) - Chironomus dilutus

(chironomid)

 Besser et al. (1989) - Daphnia magna (cladoceran)

 Besser et al. (1993) - Daphnia magna (cladoceran)

 Guan and Wang (2004) - Daphnia magna (cladoceran)

 Thomas et al. (1999) - Trichorixa reticulata (water 

y = 3.5313x0.7992

0.125

0.25

0.5

1

2

4

8

16

32

64

128

256

512

0.0625 0.5 4 32

TL2 Conc (mg/kg)

TL1 Conc (mg/kg)

Data

TLS

OLS

Slope=1
106

External Peer Reviewers’ Comments EPA Response

boatman)

Literature cited:

Besser JM, Huckins JN, Little EE, La Point TW. 1989. 

Distribution and bioaccumulation of selenium in aquatic 

microcosms. Environ Pollut 62:1-12.

Besser JM, Canfield TJ, La Point TW. 1993. Bioaccumulation of 

organic and inorganic selenium in a laboratory food chain. 

Environ Toxicol Chem 12:57-72.

Conley JM, Funk DH, Buchwalter DB. 2009. Selenium 

bioaccumulation and maternal transfer in the mayfly 

Centroptilum triangulifer in a life-cycle, periphyton-biofilm 

trophic assay. Environ Sci Technol 43:7952-7957.

Conley JM, Funk DH, Cariello NJ, Buchwalter DB. 2011. Food 

rationing affects dietary selenium bioaccumulation and life 

cycle performance in the mayfly Centroptilum triangulifer. 

Ecotoxicology 20:1840-1851.

Conley JM, Funk DH, Hesterberg DH, Hsu L-C, Kan J, Liu YT, Buchwalter DB. 2013. Bioconcentration and 

biotransformation of selenite versus selenate exposed 

periphyton and subsequent toxicity to the mayfly 

Centroptilum triangulifer. Environ Sci Technol 47:7965-

7973.

Guan R, Wang W-X. 2004. Dietary assimilation and elimination 

of Cd, Se, and Zn by Daphnia magna at different metal 

concentrations. Environ Toxicol Chem 23:2689-2698.

Malchow DE, Knight AW, Maier KJ. 1995. Bioaccumulation 

and toxicity of selenium in Chironomus decorus larvae fed a 

In the above plots, the linear assumption (log-log slope=1 or EF 

and TTF constant with concentration) serves well for water-TL1 

(EF) and for TL2-TL3 (TTF into fish). In the TL1-TL2 

relationship, TTF into invertebrates, the linear assumption at 

high values of x fits the corresponding upper bound values of y, 

indicating environmentally conservative results at high 

concentrations.

Regarding midges, chironomids were considered. The modeled 

diet for site 29 of Birkner 1978 consists of 3 invertebrate taxa: a 

chironomid, a corixid, and an amphipod. The median value of 

29.4 happens to be for the corixid. However, the chironomid 

and amphipod values were used in the determination of the 

median.

y = 1.2104x1.0837

0.125

0.25

0.5

1

2

4

8

16

32

64

128

256

512

0.25 2 16 128

TL3 WB Conc (mg/kg)

TL2 Conc (mg/kg)

Data

TLS

OLS

Slope=1
107

External Peer Reviewers’ Comments EPA Response

diet of seleniferous Selenastrum capricornutum. Arch 

Environ Contam Toxicol 29:104-109.

Rickwood CJ, Jatar M. 2013. Investigation into the fate and 

effects of selenium on the life-cycle of a benthic invertebrate 

(Chironomus dilutus). CanmetMINING, Project: 603994. 

Natural Resources Canada (NRCan), Ottawa, Canada.

Riedel GF, Cole L. 2001. Selenium cycling and impact in 

aquatic ecosystems: Defining trophic transfer and waterborne exposure pathways. Chapter 3 in EPRI Report 2001. 

EPRI, Palo Alto, CA.

Thomas BV, Knight AW, Maier KJ. 1999. Selenium 

bioaccumulation by the water boatman Trichocorixa reticulata

(Guerin-Meneville). Arch Environ Contam Toxicol 36:295-300.

Regarding the new TTF data, EPA thanks you for providing 

additional sources of TTF data. EPA reviewed and used the 

additional data determined to pass data quality and relevance 

screening. EPA has included empirical laboratory data from the 

Conley et al. studies in the 2015 draft criterion to calculate the 

mayfly TTF, which is now 2.48, changed from the TTF 1.28

value used in the 2014 draft.

4. I am more familiar with the marine literature and am not 

well-versed in the freshwater literature regarding Se TTF values.

Thank you for your comment.

5. The method used to derive TTF values is scientifically sound 

by using the widely accepted biodynamic modeling approach, 

which is particularly appropriate for Se. The EPA also 

demonstrated that temporal changes in TTF are for the most part 

not a factor that may cause large data discrepancies. Since the 

EPA used a large dataset to derive TTF values for insects, any 

differences between the EPA-derived values and values reported 

from individual studies are not of concern to this reviewer. I am 

not aware of any other data, other than the recent work by 

Buchwalter mentioned in II2a above. It is suggested the EPA 

include an updated literature search for this and other supporting 

data prior to the next revision of the document.

Thank you for your comment. EPA is providing an updated 

bibliography in the 2015 draft selenium criterion document 

based on literature suggested by the public and the peer 

reviewers, particularly the references detailed by peer reviewer 3 

above.
108

External Peer Reviewers’ Comments EPA Response

6. The trophic transfer factor (TTF) values were developed as 

an application of a peer-reviewed, published approach that 

represents our best available scientific information. The method 

and data used are adequately described, and the approach is 

satisfyingly direct. The confounding dynamic to this approach 

could be the bi-modal essential-toxic behavior of selenium 

where low-level exposure has different metabolic and storage 

behavior that non-essential metals and therefore different 

toxicodynamics across a broad range of exposures. This 

dynamic is adequately discussed (p. 74). The screening criteria 

for data used in TTF calculations appear defensible and 

reasonable, and complete with regard to major published works.

Thank you for your comment.

7. The derivation of Trophic Transfer Factors (TTF) by the USEPA in the Draft Document is clearly outlined and presented. 

However there are several issues which, again, result in the 

introduction of error and therefore an element of conservatism in 

the data that was derived. For example, the USEPA matched 

selenium concentrations in consumers and their likely prey items 

from a thorough investigation of the available data. However, 

where matched data from more than one prey item was 

identified from a site, the median of lower trophic organisms 

was used to calculate a TTF. While we understand the rationale 

for this practice from a data handling perspective, by not 

acknowledging that prey items may comprise different 

proportions of the diet ultimately introduces variability in the 

calculated TTF, with the potential for an influence in either 

direction. Additionally, while the US-EPA presents a statistical 

argument for the validity of matching pairs of samples taken 

from an aquatic site over a year, it is also acknowledged that 

some sites may present selenium loads or bioaccumulation 

EPA used a median of concentrations of lower trophic 

organisms since most predators are opportunistic, preying on the 

organism that they encounter at random. Site-specific studies 

would reveal predator prey preference or prey abundance 

relationships that may warrant consideration of a different 

approach.

EPA used a time limit threshold of 1 year to characterize 

samples as “matched” to maximize the available data that are 

likely to be temporally similar. EPA understands that there are 

uncertainties associated with this assumption, but this approach 

was deemed necessary in order to obtain sufficient data from 

sufficient sites in order to develop water column criteria. It may 

be more appropriate to collect site specific data for a known 

impacted site to insure that both temporal and spatial 

considerations at the site are accounted for. Uncertainties are 

“backstopped” by the egg-ovary criterion, the ultimate indicator 
109

External Peer Reviewers’ Comments EPA Response

kinetics that require different collection time criteria. 

Recognizing that the Draft Document will largely be applied to 

impacted receiving environments that are influenced by 

industrial activity and which present dynamic ranges in selenium 

loading, it appears likely that establishing a precedent to allow 

matching concentrations of selenium in aquatic compartments 

collected a year apart will, in most cases, not be appropriate. 

Finally, the USEPA designated single TTF based on the median 

value of only those regressions that were significant (Page 75). 

While this is a conservative approach, it does not fully 

incorporate consideration for differential uptake among lower 

trophic organisms at varying concentrations of selenium 

exposure.

of ecosystem protection in a waterbody. 
110

3. Regarding the conversion factor (CF) values used, did EPA use an appropriate and scientifically defensible method to derive 

those values (p. 78-79 of the criteria document and Appendix B)? Are you aware of any other methods that EPA should 

consider? Also, are you aware of any data that was not considered in this effort and should be screened and included? 

Please provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. EPA has used a scientifically defensible method for deriving 

CFs. I am not aware of any other data EPA should consider. It 

could be argued that a regression based approach be used instead 

of the ratio approach EPA has adopted. In some cases, it appears 

that residuals are structured, suggesting that assumptions of the 

CF approach may be violated. At least for the 4-5 most sensitive 

taxa, EPA should conduct a sensitivity analysis of the 

regression-based approach versus the ratio approach and 

particularly consider confidence in the CF at concentrations that 

approximate the EC10.

The median ratio approach was used because it was less subject 

to variability in slope imposed using the constrained regression 

(0 intercept) approach, which was problematic when the yintercept was notably different from 0. Also, the median 

approach appeared less sensitive to issues encountered using 

unconstrained regression for those slopes where the y-intercept 

was notably different than zero. EPA considered all approaches, 

and determined the ratio-based approach to be less affected by 

issues related to outliers and y-intercept.

2. The calculation of the CF values was rather straightforward, 

with my only concern, as noted above, being a thorough 

quantification of the resulting errors in the CF values. As an 

overall statement, error propagation seems to have been largely 

ignored in this document.

Thank you for your comment. EPA has clarified the 

uncertainties in the document by providing more information on 

the variability behind the calculation of the factors in the 2015 

draft document.

3. I think the EPA used a reasonable approach for deriving CFs. 

As a partial confirmation of those values, fish species for which 

diet-to-egg TTFs can be derived could be compared to the 

combined CFs and TTFs values.

Thank you for your comment.

4. See my response to question 2. RE - I am more familiar with 

the marine literature and am not well-versed in the freshwater 

literature regarding Se TTF values.

Thank you for your comment.
111

External Peer Reviewers’ Comments EPA Response

5. EO:WB conversion factors ranged from 1.38 to 7.39 with a 

median value of 1.27. As mentioned in II3 above, it was unclear 

how determination of [Se] in both whole-body and egg were 

determined in the same fish, and this should be clarified in the 

document. Similarly when muscle and whole body were 

determined in the same fish. Overall, this is a simple method and 

I am not aware of any alternative methods, nor data sources for 

these analyses.

Thank you for your comment. For 16 of the 17 species for which 

data were available, EO/WB CFs ranged from 1.38-2.44, with 

the EO/WB ratio for mountain whitefish being 7.39. The E/O to 

WB ratio for all fish (based on a hierarchal taxonomic approach 

using available data) is 1.63. (See response to Peer Reviewer 2, 

in Part I, Question 2.a.iii.for additional information regarding the

hierarchal taxonomic approach.) The mountain whitefish has a 

fairly small distribution in the US, when considering overlap 

with Se enriched areas. Thus, median values are considered

more appropriate.

As noted above (response to Question 3, part 2, peer reviewer 

response number 5), regarding determination of selenium 

concentration in both whole-body and egg were determined in 

the same fish. The vast majority of the data for the E/O to whole 

body [Se] relationship analysis came from Osmundson et al 

(2007) who did report egg data and whole body [Se] data from 

the same fish. The whole body [Se] was calculated by adding 

back the egg Se that was removed for analysis. Osmundson et al 

(2007) had 9 of the 10 species in EPA’s data set for this analysis. 

Coyle et al (1993) also added back egg Se for the whole body 

same fish comparison. Formation (2011) and Doroshov et al.

did not specify how the whole body [Se] was determined. 

Hermanutz (1996) and Hardy (2005) apparently measured whole 

body and egg Se in different fish with the same exposure. EPA 

has added a clarifying discussion to the section discussing fish 

tissue relationships.

Please see response to peer review comment 7 below for details 
112

External Peer Reviewers’ Comments EPA Response

on how the CF methodology was improved from the 2014 draft 

approach.

6. There is inherent uncertainty and variability in deriving 

conversion factors given the diversity of fish types, lifecycle 

stage, and environmental conditions. The single 1.27 conversion 

factor approach appears to be a straightforward and reasonable 

approach given the limitations of data and species data sets. This 

is especially true in practice where a criterion will be applied to 

fish types including those not subjected to controlled studies. 

While species specific CFs are desirable, this would require 

considerably more data that currently available especially in 

regards to life cycle of the target fish analyzed. The conversion 

factor (CF) method and input data appear to be a reasonable and 

defendable approach to addressing data limitations and practical 

application of the criterion. Other numerical approaches can also 

rise to developing CFs however it is unclear if the absence of 

data would bias those results or create similar uncertainties as 

well. The calculation approach in the current draft is 

straightforward and robust. Appendix B appears to have most 

freshwater fish data used in the CF analyses addressed in 

multiple published scientific papers or agency reports. Because 

of the critical nature of this calculation to criterion development, 

updating literature searches for new research data is important.

Thank you for your comment. EPA updated literature sources

for the 2015 draft criterion document.

7. As noted in our response to Charge Question #2, almost half 

(i.e., 7 of 16) of the Conversion Factor (CF) values for egg/ovary 

to whole body were derived using a generic (i.e., not species 

specific) muscle to whole body conversion ratio that was 

calculated as the median value of the available data for all fish 

species. This practice will have likely contributed to the 

Thank you for your comment. In the 2015 draft document, EPA 

improved its methodology from the approach used in the 2014 

draft to calculate CF values when matched pairs of selenium 

measurements in eggs and/or ovaries and whole body tissue 

were not available by using species-specific or most-closelytaxonomically-related muscle to whole body and egg-ovary to 
113

External Peer Reviewers’ Comments EPA Response

variability in the dataset. muscle conversion factors. See response to Peer Reviewer 2

above, in Part I, Question 2.a.iii. For those species of fish with 

neither sufficient data to directly calculate an egg-ovary to whole 

body CF, nor data to calculate a conversion factor for egg-ovary 

to muscle or whole body to muscle, EPA estimated CF following 

the approach described for the estimation of TTF values. In this 

approach, EPA sequentially considered higher taxonomic 

classifications until one or more taxa for which a calculated CF 

value was available matched the taxon being considered, and if 

the lowest matching taxon was common to more than one 

species with a CF value available, EPA used the median CF 

from the matching species. For fish species without sufficient 

data to directly calculate an egg-ovary to whole body CF but 

which had sufficient data to calculate a conversion factor for 

either egg-ovary to muscle or whole body to muscle, EPA 

followed a two stage approach based on taxonomic similarity 

similar to that described above. If a fish species had a speciesspecific egg-ovary to muscle conversion factor, but no wholebody data with which to calculate an egg to whole body CF, then 

available data for other species were used to estimate a muscleto-whole-body conversion factor for that species based on 

taxonomic relatedness. The estimated muscle-to-whole-body 

factor would be multiplied by the directly measured egg-ovaryto-muscle factor to estimate an egg-ovary-to-whole-body CF for 

that species.
114

4. Regarding the derivation of enrichment factor (EF) values, was the method EPA used to screen data from the literature 

applied appropriately and consistently (see inclusion/exclusion criteria on p. 71-77 of the criteria document)? Was the 

method for deriving EF values applied to those data in a consistent manner so as to derive EF values for selected waters in 

a scientifically defensible manner? Is the method that EPA used to establish the lentic and lotic categories for EF values 

reasonable given the available data? Are you aware of other methods or relevant data the EPA should consider? Please 

provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. Yes, the method for deriving EFs was scientifically 

defensible and appears to have been applied in a consistent 

manner. However, similar to my comments regarding TTFs, 

there is frequently an inverse relationship between water Se and 

EF. EPA should carefully examine the distribution of EFs as a 

function of water Se and assess whether their data set is unduly 

biased by EFs measured in systems with unusually low or high 

waterborne Se. It would be helpful if Table 12 included the 

mean or median water Se concentration at the site. Note, in the 

section on calculation of EFs, there is no reference to where the 

EFs for the 69 individual sites can be found (i.e., Appendix L).

Thank you for your comment. A figure has been added to

section 3.2.4 that examines the relationship between EF and 

water concentration. There is a statistically significant inverse 

relationship between EF and Se concentration in water.

EPA carefully re-examined the distribution of EFs and corrected

the data for overweighting by EFs measured in systems with 

unusually low or high waterborne selenium, as described above, 

in response to Peer Reviewer 3’s comments to Question 2.a.iv, 

regarding magnitude, duration and frequency. A new appendix 

(G) has been created that lists all of the EF values, by site, and 

the values used to make the calculations.

2. See above comments; I feel the EF values are completely 

useless and in fact incapable of being calculated given that they 

really need to include the chemical speciation of dissolved 

selenium. They did however miss lots of dissolved and 

particulate data, many examples including: Cutter, 1989a; 

Cutter, G. A. 1991., Riedel and Cole, 2001 in their reference list, 

and river data in Cutter, 1989b and Cutter and San DiegoMcGlone that are also in their reference list.

The consequences of the absence of the chemical speciation of 

dissolved selenium has been addressed in a previous response.

Thank you for including a list of references including particulate 

and dissolved Se data. EPA has reviewed these sources to 

determine whether they can be included in our translation 

dataset and included those that were relevant and passed data 

quality review. 
115

External Peer Reviewers’ Comments EPA Response

3. Overall, I believe that the EPA used a reasonable approach in 

calculating EF values. However, I do not necessarily agree that 

Se concentrations should be available for at least two particulate 

types in order to derive an EF. Periphyton, for example, may be 

the dominant particulate in certain lotic systems and in my 

opinion such data should be included. I do agree that Se 

concentrations in sediment alone is insufficient for deriving EF 

values. I have greater reservations in how the EFs (and CFs and 

TTFs) were ultimately used to translate from the draft fish 

egg/ovary Se criterion to water Se criteria.

Potential sources of additional EF data may include:

Bowie GL, Sanders JG, Riedel GF, Gilmour CC, Breitburg DL, 

Cutter GA, Porcella DB. 1996. Assessing selenium cycling 

and accumulation in aquatic ecosystems. Water Air Soil 

Pollut 90:93-104.

Casey R. 2005. Results of aquatic studies in the McLeod and 

Upper Smoky River systems. Alberta Environment. 64 pp.

Fan TW-M, Swee JT, Hinton DE, Higashi RM. 2002. Selenium 

biotransformations into proteinaceous forms by foodweb 

organisms of selenium-laden drainage waters in California. 

Aquat Toxicol 57:65-84.

Greater Yellowstone Coalition. 2005. Technical Reports on 

selenium concentrations in water, macrophytes, 

macroinvertebrates, and fish.

Hamilton SJ, Buhl KJ. 2003a. Selenium and other trace elements 

in water, sediment, aquatic plants, aquatic invertebrates, and 

fish from streams in southeastern Idaho near phosphate 

mining operations: September 2000. US Geological Survey. 

To reduce uncertainty in estimating site-specific EF values, EPA 

limited its analysis to those aquatic sites with at least two 

particulate selenium measurements with corresponding water 

column measurements, and only used sediment measurements if 

there was at least one other measurement from either algae or 

detritus. That is, EPA would calculate an EF from algae (or 

detritus) alone; however, in order to qualify, at least 2 algal (or 

detritus) samples from a site were required. In contrast, 

sediment data alone were insufficient to calculate an EF. In 

order for sediment to be included, additional algal or detrital 

data were also required.

Thank you for providing additional potential data for EF 

determination. EPA added the data from Bowie et al 1996, 

Casey 2005, Fan et al 2002, McDonald and Strosher 1998 and 

Zhang and Moore 1996 to the EF data set. EPA already had 

Minnow Environmental 2007 in the EF data set which includes 

the data contained in Orr et al 2006. 
116

External Peer Reviewers’ Comments EPA Response

64 pp.

Hamilton SJ, Buhl KJ. 2003b. Selenium and other trace 

elements in water, sediment, aquatic plants, aquatic 

invertebrates, and fish from streams in southeastern Idaho 

near phosphate mining operations: May 2001. US 

Geological Survey. 61 pp.

Hamilton SJ, Buhl KJ, Lamothe PJ. 2002. Selenium and other 

trace elements in water, sediment, aquatic plants, aquatic 

invertebrates, and fish from streams in southeastern Idaho 

near phosphate mining operations: June 2000. USGS, 

Yankton, SD and Denver, CO. 72 pp.

McDonald LE, Strosher MM. 1998. Selenium mobilization from 

surface coal mining in the Elk River basin, British 

Columbia: A survey of water, sediment and biota. Ministry 

of Environment, Land and Parks, Cranbrook, BC. 46 pp. + 

appendices.

Orr PL, Guiguer KP, Russel CK. 2006. Food chain transfer of 

selenium in lentic and lotic habitats of a western Canadian 

watershed. Ecotoxicol Environ Saf 63:175-188.

Orr PL, Wiramanaden CIE, Paine MD, Franklin W, Fraser C. 

2012. Food chain model based on field data to predict westslope 

cutthroat trout (Oncorhynchus clarkii lewisi) ovary selenium 

concentrations from water selenium concentrations in the Elk 

Valley, British Columbia. Environ Toxicol Chem 31:672-680.

Presser TS, Luoma SN. 2009. Modeling of selenium for the San 

Diego Creek watershed and Newport Bay, California. US 

Geological Survey, Open-File Report 2009-1114. 48 pp.

Zhang Y, Moore JN. 1996. Selenium fractionation and 
117

External Peer Reviewers’ Comments EPA Response

speciation in a wetland system. Environ Sci Technol 30:2613-

2619.

4. See my response to question 2. RE - I am more familiar 

with the marine literature and am not well-versed in the 

freshwater literature regarding Se TTF values.

Thank you for your comment.

5. EF values were derived from all available data that I am 

aware of and used scientifically valid approaches, including 

inclusion/exclusion criteria. See comments above regarding the 

simple distinction used for lentic vs. lotic systems.

Thank you for your comment. EPA revised the lotic and lentic 

section to better identify the difference between lotic and lentic

in Section 3.2.4. Unfortunately, a parameter like residence time 

was not available for most of the waters in the dataset.

6. The enrichment factor (EF) approach and method is 

scientifically defensible and represents our best understanding of 

selenium dynamics in aquatic ecosystems. While all modeling 

approaches have uncertainties and limits in application, the 

approach is reasonable, transparent, appropriately applied and 

representative of the present selenium knowledge base. The 

criterion document uses available data in a consistent manner, 

and extending the water system terminology used by study 

authors for data used in EF value determinations is a best 

practice. The evaluation of categories of aquatic systems is well 

treated in the analysis. The grouping of streams, drains, washes 

and creeks into a common category is reasonable. The results of 

Figure 9 and 10, and furthermore in Figure 11, help to validate 

the EF approach of the criterion document when measured 

against our cumulative knowledge base of selenium behavior in

different aquatic systems. The use of a 20th percentile approach 

for water column values accommodates system variability and 

system uncertainty that is inherent in all modeling approaches. 

Whereas tissue levels of Se can more reliably predict toxic risk, 

Thank you for your comment.
118

External Peer Reviewers’ Comments EPA Response

a 20th percentile affords adequate protection in many risk 

management situations such as water quality-based effluent 

limits, especially in light of the primacy of the tissue based 

components of the criterion.

7. Derivation of Enrichment Factors (EF) based on paired 

concentrations of selenium determined in water and particulate 

would have been influenced by the practice of allowing data to 

be paired if they were collected up to a year apart. In terms of 

application of EF to categories for lentic and lotic systems it is 

difficult to judge because of the lack of specific criteria to 

distinguish between the two types of systems in the Draft 

Document. While the US-EPA acknowledges the importance of 

residence time for defining aquatic systems as either lentic or 

lotic, the criterion for their initial assignment to each category is 

not apparent (Page 82). Despite statistical comparisons that 

support their aggregation, it is very likely that lakes, reservoirs, 

ponds and marshes will have vastly different selenium kinetics, 

and yet they are all designated as lentic systems. Likewise, 

selenium uptake into aquatic food-webs of creeks, drains, 

washes, rivers and streams may differ markedly. The wide range 

of variability in the aggregated categories (Figure 10, page 84) is 

compelling evidence in support of this point. Additional specific 

guidance is required to distinguish between the two types of 

aquatic systems and the applicability of EFs for each.

Thank you for your comment. As discussed above, EPA has 

rewritten the description of lotic and lentic sites and has 

investigated each site individually since a common delineation 

parameter such as residence time was not available for most of 

the waters for which data were available in the study.
119

5. Please comment on the scientific defensibility of EPA’s conversion of the selenium fish tissue – water translation equation 

into an equation that allows for calculation of a criterion for waters that may be subject to intermittent discharges of 

selenium. Please comment on major sources of uncertainty in this approach. Is this method appropriate, given the 

bioaccumulative nature of selenium? Please comment on the uncertainty associated with the application of this conversion 

equation to intermittent discharges that may occur in different types of waterbodies and/or in different locations, 

particularly with respect to loads transported to potentially more sensitive aquatic systems. Does the method employed 

result in criteria that are similarly protective to the 30-day chronic criterion? Are there any other models or approaches 

that EPA should consider that would reduce this uncertainty? Please provide detailed comments.

External Peer Reviewers’ Comments EPA Response

1. EPA’s proposed method for addressing intermittent and timevarying discharges appears reasonable given available data.

Ideally, intermittent criteria would be based on a biokinetic 

modeling approach and EPA’s effort to evaluate their proposed 

approach using biokinetic modeling is encouraging. However, 

given the limited biokinetic data currently available, it is 

probably premature to implement such an approach for setting 

WQC. Further use of such an approach may be unnecessarily 

complicated if the simpler approach proposed by EPA continues 

to achieve the same objective as the biokinetic approach. A 

major uncertainty in the approach and subsequent biokinetic 

evaluation is the near complete lack of kinetic data for EF. If 

depuration kinetics are slower than EPA has assumed for 

primary producers, then this will have significant impacts on the 

validity of this approach.

The issue of generating pulse loads of Se that may ultimately 

result in Se accumulation in sensitive downstream systems (e.g., 

pulse loads in a river that discharges to a wetland) is a legitimate 

concern. However, in my opinion, this is a site-specific issue and 

it is not reasonable to establish national WQC that ensure 

protection of these sites without dramatically increasing the false 

Thank you for your comment. The intermittent criterion 

elements were developed to address intermittent elevated input 

scenarios that could result in chronic effects via bioaccumulation 

in an ecosystem, effects that may not be captured through 

assessing impacts considering only continuous 30-day exposure 

scenarios. See the response to comment #3 for the relationship 

between the intermittent criterion and the kinetic analysis of the 

2014 Appendix G. EPA has since revised the 2014 Appendix G 

(now Appendix J) kinetic model to include a water-TL1 step. .
120

External Peer Reviewers’ Comments EPA Response

positive rate for the WQC. However, it would be useful for 

EPA to provide specific language on the need to consider 

loading to downstream environments when regulating 

intermittent discharges or developing site-specific WQC.

2. If a realistic concentration can be established using a more 

appropriate modeling approach (as above), then the calculation 

for intermittent discharges is fine. However, the propagation of 

errors must be carefully evaluated.

Thank you for your comment. EPA provided further discussion 

of uncertainty in Appendix J, section 3 of the 2015 draft 

criterion document.

3. I am not sure that the criterion equation for intermittent 

dischargers is meaningful, as it is basically a mathematical 

manipulation and does not in any way account for selenium 

uptake and elimination kinetics. An alternative approach that the 

EPA may want to consider is based on biokinetic modeling, such 

as that described in Brix and DeForest (2008). The method they 

described was based on modeling of a food chain comprised of 

periphyton, an invertebrate (mayfly), and a fish (fathead 

minnow). Inputs to the model include the background water Se 

concentration, the magnitude of an intermittent Se pulse, and the 

duration of the Se pulse. This provides a tool for evaluating 

whether a Se pulse of a given magnitude and duration could 

result in exceedance of a whole-body fish Se criterion, or shortterm Se criteria could be derived for given short-term durations.

For a comparison of the biokinetic-based approach to the 

intermittent criterion equation in the draft AWQC document, I 

assumed that the background water Se concentration is 1 μg/L, 

the lotic criterion is 4.8 μg/L, and the number of days elevated is 

4. The intermittent criterion would be 29.5 μg/L. Just as an

example, if a lotic food chain consisting of 

periphyton→mayflies→fathead minnows were assumed, a 4-d 

Regarding the comment on the biokinetic approach, EPA’s 

kinetic analysis was presented in Appendix G of the 2014 draft. 

It was similar to the work of Brix and DeForest (2008). It has 

since been revised to make it even more similar in structure to 

Brix and DeForest (2008). It continues to have a similar 

response time as Brix and DeForest because the limiting kinetic

rate used in both Brix and DeForest and the 2014 Appendix G is 

based on the same fathead minnow study as referred to in the 

comment: Bertram and Brooks (1986).

Regarding the biokinetic model and intermittent criteria, the 

kinetic analysis of Appendix G of the 2014 draft specifically 

addressed intermittent exposure. When applied to intermittent 

exposure, the analysis demonstrated the protectiveness of the 30-

day averaging period that EPA is recommending. 

The intermittent criterion is a rearrangement of the water chronic 

criterion and its kinetic model-based 30-day averaging period. 

The 2014 intermittent criterion thus hinged on the kinetic model 
121

External Peer Reviewers’ Comments EPA Response

pulse of 29.5 μg Se/L would not be nearly sufficient to reach a 

whole body Se concentration of 8.1 mg/kg dw (Fig. 2). There is 

a rapid increase in predicted Se concentrations in periphyton and 

mayflies and then a rapid elimination, but uptake is slower in 

fathead minnows. 

In my opinion, a biokinetic-based modeling approach would be 

more appropriate for deriving acute or intermittent water Se 

criteria. 

Fig. 2. Example of modeled selenium uptake and elimination in 

a model food chain exposed to a 4-d pulse of 29.5 μg Se/L.

Literature cited:

Brix KV, DeForest DK. 2008. Selenium. Pages 123-172 in 

Gensemer RW, Meyerhoff RD, Ramage KJ, Curely EF, eds. 

Relevance of ambient water quality criteria in ephemeral and 

effluent-dependent watercourses of the arid western US. SETAC 

Press, Pensacola, FL, USA.

of the 2014 Appendix G. In the revised document Appendix G 

is now Appendix J.
122

External Peer Reviewers’ Comments EPA Response

4. See my response to question 1 of Part III. See response provided above in Part III, Question 1, Reviewer 4.

5. EF values were derived from all available data that I am 

aware of and used scientifically valid approaches, including 

inclusion/exclusion criteria. See comments above regarding the 

simple distinction used for lentic vs. lotic systems.

Thank you for your comment.

6. While the need for a criterion tier that addresses intermittent 

discharges is clear, this part of the document is not well 

documented for scientific support as evidenced in the main 

document by no citations in this section beyond that of the 

general Chapman et al. 2009 reference. Appendix G Part 3.0 

documents the modeling approach, however a list of references 

is missing. Since this is original work, further description of 

methods, key data inputs, and model run output may be useful 

The document’s 86-page list of references contains all citations 

used in the main text and the appendices. The bioaccumulation 

modeling approach is rather standard and is similar to Brix and 

DeForest (2008) referred to elsewhere in comments. The 

primary difference is that in EPA’s application, all 

concentrations have been normalized to their criterion (in water 

and TL3) or corresponding benchmarks (in TL1 and TL2). 

Appendix J presents the model equations and input values. 

0.1

1

10

-10 0 10 20 30 40 50 60 70 80 90 100

Tissue Se, μg g

-1 dw

Time, days

Primary producer

Invertebrate

Fish
123

External Peer Reviewers’ Comments EPA Response

for potential replication of the results by others. A citation on 

page G-6 (EPA 1986; should be USEPA 1986) may be 

important to sourcing this modeling approach, but it is unclear in 

the writing whether this is so; without references to Appendix G, 

validation of scientific defensibility of the intermittent watercolumn criterion is not possible. Infrequently, some of the 

writing in Appendix G is informal or tech-speak and should be 

edited for clarity. Figure captions should contain a short 

description of all relevant model inputs to increase 

communication value and transparency. The modeling approach 

and the results of Appendix G appear to be a reasonable and 

defendable approach to developing a criterion for intermittent 

water column selenium values, although the polished execution 

of this important part of the tiered criterion is lacking in 

comparison to the other criterion elements. Thus, there appears 

to be sufficient support for the criterion approach in Appendix G 

and this information should be summarized and referenced in the 

main document body. This part of the tiered criterion is the most 

difficult to study in the field, although our practical and 

experiential knowledge of Se bioaccumulation in aquatic 

ecosystems suggests it has high importance in protecting aquatic 

life. The practical implementation of this tier of the criterion will 

require enhanced guidance and regulatory sensitivity to the cost 

of monitoring.

Appendix J uses a single set of kinetic parameters (explained in 

the text). Its different figures address different assumptions 

about the time series of water concentrations.

In the 2015 draft, the Appendix J (replacing Appendix G in the 

2014 draft document) has been modified, edited, and simplified..

7. It is not clear how the intermittent criterion outlined in the 

Draft Document will be applied. The mathematical expression of 

the criteria on page 93 is clear but the terms surrounding the 

application of the criterion are not. For example, the criterion is 

not intended to apply to “ordinary smoothly varying 

concentrations” (Page 94). However, what specifically will 

The document’s language about the intermittent criterion not 

being intended to apply to ordinary smoothly varying 

concentrations has been deleted. The intermittent criterion 

provides the same protection as the 30-day chronic criterion 

(from which it is derived). Whereas the 30-day chronic 

expresses the criterion in terms of one average of all 
124

External Peer Reviewers’ Comments EPA Response

constitute a discharge curve that is not “smooth” has not been 

defined. It is also not clear what magnitude of selenium 

concentration spikes would designate a discharge as having to be 

regulated as an intermittent discharge. Finally, designation of an 

intermittent criterion appears to contradict the data in Appendix 

G and the statement on page 94 that “kinetics of selenium 

accumulation and depuration are sufficiently slow that 

attainment of the water criterion concentration element by 

ambient 30 day averages will protect sensitive aquatic life 

species even where concentrations exhibit a high degree of 

variability. While outside the area of our expertise it is noted 

that several comments in the public registry suggest that a 

biokinetic model may be more appropriate than the application 

of an expansion of the 30-day average calculation for 

determining intermittent criterion.

concentrations occurring within a 30-day period, the intermittent 

criterion applies to two averages, occurring for two different 

durations within the 30-day period, one labeled the intermittent 

and one labeled background. The intermittent criterion will 

achieve its purpose no matter where the line is drawn between 

intermittent concentration and background concentration. The 

intermittent criterion elements were developed to address 

intermittent elevated input scenarios that could result in chronic 

effects via bioaccumulation in an ecosystem, effects that may 

not be captured when considering only continuous 30-day 

exposure scenarios.

The kinetic model of Appendix G in the 2014 draft was used to 

derive the 30-day averaging period. It specifically evaluated 

intermittent exposure. The validity of the intermittent criterion 

thus hinges on the validity of the derivation of the chronic water 

criterion and the Appendix G (now Appendix J in the revised 

document) kinetic model derivation of the 30-day averaging 

period.
125

PART IV: SIGNIFICANCE OF SCIENTIFIC VIEWS FROM THE PUBLIC/STAKEHOLDERS 

EPA will also be providing scientific views and other comments from stakeholders and the public received via the public docket to the 

peer review panel. Although EPA will be providing the full contents from the docket, EPA is only requesting a review of any 

scientific views/public comments that may be of technical significance to the selenium criterion.

1. Has the peer review panel identified any scientific views from the public or stakeholders as being technically significant to

the draft of the selenium criterion going forward; that is, has information or data been introduced during the comment 

period that would change the scientific direction of the criterion? Is there any information or data that may refine or 

enhance the scientific defensibility of this criterion that EPA should consider further? Please provide detailed comments 

on specific issues of technical significance or refinement.

External Peer Reviewers’ Comments EPA Response

1. After reviewing the public/stakeholder comments, I highlight 

the following comments which I would also make above and 

beyond responses to specific review questions EPA has asked:

1.) Because some states will continue to use an acute WQC for 

Se, I agree EPA needs to clarify its position on the scientific 

credibility of the existing acute WQC.

2.) There were a number of comments indicating that use of an 

instantaneous averaging period and “never to exceed” for the 

tissue element is inappropriate and inconsistent with the 

Guidelines.I disagree with these comments and support 

EPA’s decision.

3.) I agree with several commenters that EPA must develop 

rigorous definitions of lentic and lotic as guidance for 

regulators.

4.) EPA needs to provide some guidance on how small first 

order and ephemeral streams that naturally do not support 

Thank you for considering the public comments and providing 

your feedback. In response to your points 1-4, EPA provides the 

following:

1. EPA has indicated that acute toxicity is not included in the 

assessment (Section 2.6 and Section 2.7.3). Some reviewers 

have stated that the intermittent criterion may serve as a 

surrogate for the acute criterion. 

2. Thank you for your support – additional information is being 

developed regarding frequency and duration as it relates to 

application of the criterion.

3. EPA has revised the lentic and lotic sections of the criterion 

document, and has investigated each waterbody/sample used in 

the criterion derivation.. 

4. EPA is currently working on developing technical information 

that will help in the implementation of the Se criteria.
126

External Peer Reviewers’ Comments EPA Response

fish populations should be regulated. There are a large 

number of these streams in the western US that have Se 

issues. Note, in these types of systems or in small wetland 

systems without fish, aquatic-dependent birds may be the 

most sensitive receptor. This leads to the obvious comment 

that if this WQC is intended to protect all US surface waters, 

EPA must develop guidance on the protection of aquaticdependent wildlife.

2. I examined the public comments AFTER I had reviewed the 

document and written the above comments, so as to not bias my 

own evaluation. The comments (by my count, 429) ranged from 

editorial ones, to simple criticisms, to detailed scientific 

evaluations and suggestions. Of the later, the most common 

concerned “implementation” (16% of total), followed by 

“translation” (to water column criteria; 14%), and site specific 

criteria (13%). If we combine all the “criteria” comments (site, 

tiered, tissue, intermittent), these received the most comments 

(30%). Of these, most dealt with the details of developing the 

criteria (justifying the calculation methods, literature missed, 

apparent oversights or conflicts with existing procedures). Thus, 

the peer-review community (it seems that most of these 

comments came from consulting companies, municipal and state 

agency scientists, and some from the academic sector) feels the 

document needs considerable attention to reformulating the 

criteria. The next most important topic was then implementing 

the criteria (16% by itself) and in this respect most comments 

(actually criticisms) were directed to the water column 

formulation. Related to this was the “translation” of the tissues 

(all)-based criteria to the water column (14% of comments), and 

most of these comments were directed to the inappropriate use 

Thank you for considering the public comments and providing 

your feedback. 

EPA disagrees with the peer reviewer’s view that the public 

comments indicate that the previously peer-reviewed and 

published methodology (Presser and Luoma, 2010) applied by 

EPA to derive the criteria needs to be reformulated. EPA 

worked with the scientists who published the methodology in 

applying their model in the context of a national criterion 

development to ensure appropriate application of their model. 

As acknowledged in the comment, most public comments dealt 

with specific issues with specific data. EPA has responded by 

correcting, modifying, or adding specific items that went into the 

criterion derivation. Further, none of the other six peer 

reviewers has recommended or indicated that EPA needs to 

reformulate the methodology used for setting water column 

criteria.

EPA has made revisions to several sections of the document in 

order to further support the existing defensibility of the science 
127

External Peer Reviewers’ Comments EPA Response

of the Presser and Luoma model. Considering my review above 

and the community response, it would seem that the EPA needs 

to reformulate their methodology for setting water column 

criteria.

used, and also to help clarify and reduce some of the uncertainty

related to the criterion and supporting data. EPA develops 

criteria that are national in scope, based on available 

scientifically-defensible data and approaches. EPA describes the 

appropriate use of the Presser and Luoma model in the criteria 

document. EPA realizes that the nature of selenium 

bioaccumulation may be effectively reflected through the 

development of site-specific criteria. Other public comments 

that reflect implementation issues are beyond the scope of the 

scientific criterion document and will be addressed in technical 

support documents under development by EPA.

In response to comments in Part III, Question 1, Items 1 and 2, a 

description of preferability of the approach EPA used is 

provided, including, why the reviewer’s recommendation to use 

a kinetic-based model in place of EPA’s EF database would not 

strengthen the national applicability of the criterion because it 

would restrict analyses to a small a database. In Part III, 

Question 2, Item 3, EPA addressed another model issue, its 

linearity (implying first-order kinetics), and how the available 

data support such a formulation. Nevertheless, in conclusion, 

EPA encourages the development of site-specific criteria at sites 

with high quality, robust databases indicating the 

appropriateness of alternate model assumptions or formulations.

3. A substantial number of comments from stakeholders and the 

public were provided. These comments covered a large variety 

of topics and were often conflicting. I did not identify any 

comments that would lead me to think that the scientific 

direction of the criterion should be changed. The comments 

Thank you for considering the public comments and providing 

your feedback. EPA, in a parallel process to the criterion 

development, is working to develop technical information that 

will assist in the implementation of the selenium criteria. EPA 

notes that several reviewers viewed the intermittent criterion 
128

External Peer Reviewers’ Comments EPA Response

relative to interpretation of toxicity studies and derivation of 

EC10 values should all be carefully reviewed by the EPA, as 

some suggested that certain EC10 values should be lowered and 

other suggested they should be raised (although I personally 

believe that the GMCVs values derived by the EPA were 

generally conservative, especially for Salmo and Lepomis). 

Aside from the technical comments and disagreements that are 

related to magnitudes of the various Se criterion elements, it 

appears that there is a desire (or need) for the EPA to more 

clearly define how the draft Se criteria should be implemented 

by the states. Perhaps case studies could be provided as 

examples? It is also apparent that the basis of the intermittent 

criterion, and its relationship to an acute criterion (if there is a 

relationship), needs to be more clearly explained. Although 

some comments seem to agree that an acute Se criteria is not 

necessary any longer, there does still appear to be a need for 

acute Se criteria from the perspectives of certain states. Finally, 

again related to implementation, is the question of whether the 

lotic and lentic water Se criteria can be replaced by a different 

metric, such as residence time. In my opinion, the latter would 

be worthy of further consideration by the EPA, although I 

wonder whether more reliable categories could be developed 

based on existing datasets.

element as a reasonable surrogate for an acute criterion for 

protecting aquatic ecosystems, particularly downstream lentic 

waterbodies, from the effects of intermittent discharges of 

selenium. EPA has also further examined the lentic/lotic 

classification issue, and has evaluated each site used in the 

criterion development individually to ensure it was not 

mischaracterized. Unfortunately, residence time was not a 

common metric available in the available studies.

4. Some of the comments made about acute toxicity are valid, 

but are unlikely to be relevant to most real-world situations. 

Note that acute toxicity can affect other than reproduction, but 

such effects are rarely seen (I think).

Thank you for considering the public comments and providing 

your feedback.

5. I have read through the entire package of views from public 

and stakeholders, not just the summarized Excel file but the 

Thank you for considering the public comments and providing 

your feedback.
129

External Peer Reviewers’ Comments EPA Response

actual documents, some of which are >100 pages. The EPA 

should pay close attention to these documents, since some 

excellent scientific issues are raised in many of them. It is good 

to see that there presently exists such good knowledge of the 

aquatic ecotoxicology of Se among stakeholders; 10 years ago 

this would not be true.

The public/stakeholder views represent the classic range, from 

industry-based opinions that the proposed criteria are too 

conservative, to conservation group-based opinions that the 

proposed criteria will not protect all aquatic life. Both sides of 

the argument present many good points that should be 

considered carefully by the EPA. I will provide my views on 

each category of public/stakeholder comments at the end of this 

section.

The bottom line is that industry would prefer the egg/ovary 

criterion to be about 20 mg/kg egg (or greater), whereas 

conservation groups would prefer it to be about 10 mg/kg egg 

(or lower). Perhaps the 15.2 mg/kg criterion represents a 

workable compromise between these two extremes? I believe the 

EPA document for the most part has used current, scientifically 

sound approaches without significant bias in either direction (but 

see my comments regarding the Formation brown trout study). 

Since the proposed EPA criteria would still allow some aspect of 

site-specific assessment at the State level, then there could be 

modifications based on site specific issues such as relatively 

high background [Se] in certain areas, fish species not included 

in derivation of the egg/ovary criterion, lack of fish species 

(“fishless” waters), high aqueous sulfate, the presence of 

listed/threatened/endangered fish species, the presence of critical 

aquatic-dependent wildlife such as birds, or other 

The EPA uses the best available science in its development of 

Water Quality Criteria (WQC); the Agency is also bound to 

rigorous data quality standards under the Data Quality Act. The 

EPA has Guidelines for the use of toxicity data in its derivation 

of WQC for the protection of aquatic life and its uses, and has 

followed those guidelines in the derivation of the selenium 

criterion. The nature of selenium bioaccumulation may vary on 

a site-by-site basis in a manner sufficient to justify development 

of site-specific criteria. The reviewer identifies several 

important issues that will be addressed in the technical 

information to be developed to guide the implementation of the 

criteria.

Regarding public concerns pertaining to the Formation brown 

trout, the study data were re-evaluated. Ultimately, EPA 

determined that the model instabilities resulting in uncertainty 

surrounding the EC10 value, such as multiple minima for the 

optimistic and worst-case deformity endpoint, were the result of 

high variability in deformities at low selenium concentrations, as 

well as the assumptions associated with how to interpret the 

health and survival of fry lost to overflow caused by a clogged 

drain during a 15-day post swim-up feeding trial. Most maternal 

transfer studies do not include a post swim-up test, and for this 

test, the uncertainty introduced by the laboratory accident was 

concluded to outweigh the additional information gained by 

extending the test. EPA performed an analysis, described in 

detail in both Section 6 and Appendix C, showing that there was 

no relationship between fish health and whether or not a given 

fish was lost to the overflow event. EPA recalculated the EC10 
130

External Peer Reviewers’ Comments EPA Response

biological/chemical/physical factors.

Specific comments on public/stakeholder documents:

An acute criterion is not needed and is not relevant. If you are 

releasing Se into the aquatic environment at levels that cause 

acute toxicity to fish, then you have a big problem!

Lentic and lotic systems must be clearly defined and perhaps a 

more quantitative approach should be used as I have discussed 

above.

The EPA should read the public/stakeholder input carefully and 

use these suggestions to come to a final decision on the 

Formation brown trout study. This is of critical importance since 

brown trout was found to be the most sensitive fish species and 

the egg/ovary criteria is driven largely by the brown trout EC10.

Elevated sulfate ion in aquatic systems may reduce Se 

bioaccumulation in food webs by competing with selenate for 

uptake by primary producers, particularly algae. However, if 

regulatory limits are based on fish tissue [Se] then any 

modification of Se uptake by primary producers will be reflected 

in fish tissue [Se]. In my opinion sulfate is not really a regulatory 

issue when fish tissue [Se] is used.

Ideally freshwater criteria for Se should include aquaticdependent wildlife such as birds. However this makes the Se 

criteria more complicated than perhaps it needs to be. The issue 

of birds could be considered on a site-specific basis in certain 

ecosystems inhabited by ecologically significant avian 

populations and migrating water birds.

The EPA must provide guidance on several aspects related to 

implementation of the tiered criteria approach, at the very least 

(18.09 mg/kg dw) for larval survival for the hatch through swim 

up portion of the test, and this recalculation is reflected in the 

2015 draft selenium criterion document.

Regarding risk to aquatic dependent wildlife, EPA understands 

the potential for risk to birds from selenium exposure and has 

begun to investigate the potential for a national criteria that 

would protect aquatic-dependent wildlife.

Regarding key issues pertaining to fish-tissue sampling, EPA is 

developing technical information related to fish-tissue sampling, 

as we realize this is a complex but important subject.

Regarding the zebrafish studies, EPA has evaluated the available 

zebrafish data and identified several important issues with the 

quantitative use of those data. This information is included and 

fully discussed in the revised 2015 draft criterion document. 

This issue was also highlighted in the FR Notice in July 2015 

with a request for additional data on zebrafish and other 

cyprinids. A major problem is that the concentration-response 

curve was so unusually shallow that zebrafish could be 

interpreted to be among the most or least sensitive species 

depending on the level of effect considered. Further, high 

control mortality (47%) at the end of the study raised concerns 

about the health of the fish at the time of testing. In addition, 

since the zebrafish is a non-native cyprinid species, EPA 

assessed the information available on zebrafish sensitivity to 

selenium compared to the sensitivity of native cyprinid 
131

External Peer Reviewers’ Comments EPA Response

including (a) when to sample fish so that females are in 

vitellogenic or pre-ovulatory stages of oogenesis, (b) what 

sample size of fish to collect for tissue [Se] determinations (I 

suggest a minimum of n=10 female fish per site), (c) 

recommended analytical procedures for quantification of Se, (d) 

guidelines for implementation of the 30-day average water 

column criterion element (how, when, where), and (e) guidelines 

for implementation of the intermittent water column criterion, if 

the EPA chooses to keep it in the tiered criterion.

An interesting comment made in one of the public/stakeholder 

documents (US Fish and Wildlife Service, document 354-A2)) 

regards the use of recently published studies in zebrafish, a nonnative cyprinid, in the species sensitivity distribution for larval 

deformities as a function of egg [Se]. They present a compelling 

argument to consider these data in the criterion development.

(minnow) species across the United States (Appendix D in the 

criteria document), including several studies where native 

cyprinids were investigated in selenium-impacted waters. Data 

from these studies suggest that native cyprinids are likely less 

sensitive to selenium than the currently available non-native 

zebrafish data suggest. The results of these analyses, 

particularly a comparison of the concentration response 

relationships of zebrafish versus all of the other fish species for 

which we have similar data, raises a concern. Given these 

concerns, EPA has not used the zebrafish data quantitatively in 

the derivation of the revised criterion. As noted above, EPA is 

seeks additional information on cyprinid taxa sensitivity to 

selenium, and particularly additional data on zebrafish, and 

solicited such information in the Federal Register Notice

announcing the opening of the public comment period on the 

selenium draft criterion in July 2015. Such studies should be 

submitted to the docket in similar fashion as scientific views on 

the criterion document. EPA will then consider this information 

in finalizing the selenium criterion document.

6. Acute criterion: The comments largely support or request 

guidance concerning abandonment of an acute criterion. The 

intermittent water column tier of the draft selenium criterion 

Thank you for your comments.
132

External Peer Reviewers’ Comments EPA Response

does much to address potential ecosystem impact potential from 

discharge concentrations historically regarded as having “acute” 

toxic potential.

Alternative more sensitive endpoint: Comment lacks clarity and 

method/approach publication or peer-review to fully consider the 

point being made. 

Aquatic dependent wildlife: Sound points are made concerning 

the potential for impact to aquatic birds. The author overstates 

that the criterion set a de facto limit for invertebrates. While the 

comments are broadly valid and demonstrate the complexity of 

the Se aquatic impact issue, equal concerns should be weighed 

on the relative balance of over- or under- protection of the draft 

criteria if deployed. The rigor of this present document to 

address aquatic life ambient water quality is significant, broadly 

inclusive and broadly defendable. The tier approach may be 

expected to have significant impact in overall water quality and 

aquatic dependent wildlife because of the integrative exposure 

nature of the tissue criterion. 

Averaging period: Comment reasonably addresses the need for 

clearer implementation guidance of the intermittent water 

column criterion.

Bioaccumulation factors: The context of this question is 

addressed in the document, however additional clarification may 

be useful.

Biphasic modeling: The comment author expresses an opinion 

regarding the modeling approach. The available peer-reviewed 

published studies supporting this approach for selenium in 

fish/aquatic ecosystems are limited and thus of less value in 

setting the criterion. The author may have a good point however 

EPA agrees with your comment regarding the potential 

surrogacy of the intermittent criterion element for the acute 

criterion.

EPA is currently investigating the potential for a national criteria 

for aquatic-dependent wildlife.

EPA is developing information to assist in the implementation of 

this and other criterion aspects.

Regarding comments on the Formation brown trout study, EPA 

has reviewed the comments from the public and other peer 

reviewers on the brown trout study. This resulted in a reanalysis of the available data and a revision of the EC10 from 

15.9 to 18.1 based on larval mortality only from hatch to day 15 

and excluded data beyond the lab overflow accident, which was 

a major confounder.

Regarding the CF (and TTF) methodologies, EPA has revised its 

CF derivation methodology and uses taxonomic proximity to 

make it as species-specific as the data will allow. (See response 

to the comment of Peer Reviewer 2 to Part I, Question 2.a.iii for 

details.) EPA has decided to retain the use of the median rather 

than a higher percentile as the general range of CFs is relatively 

narrow with the exception of the mountain whitefish, so use of a 

higher percentile threshold would allow the CF to be unduly 

influenced by this species. (See 2015 draft, page 72.)
133

External Peer Reviewers’ Comments EPA Response

the availability of published work limits its practical 

consideration. The Atlantic salmon graph referenced appears to 

be a Wikipedia selenium entry without attribution.

Bluegill Hermanutz: The conclusion that the Hermanutz data are 

outliers is not supported in the comment by any 

numerical/statistical analysis and thus must be treated as 

opinion, unless otherwise verified. Data variability in biological 

systems can be tested to determine outliers however it is unlikely 

the data count would support exclusion, thus inclusion is more 

defendable. 

Brown trout study: The presentation and role of the brown trout 

study, related serial reviews, and re-reviews in the draft criterion 

document and supporting resources raises questions in the public 

comments. While some of the questions addressed in public 

comments are broadly addressed in the draft document, 

additional effort should be made by EPA to specifically address 

concerns outlined in these comments. The use of the study data 

is confounded by unfortunate experimental system failure 

encountered during the study. 

Clarification: The comment authors state reasonable requests for 

clarification that can be addressed in the main text body.

Conversion factors: Several of the public comments regarding 

conversion factors represent valid concerns. Some of the issues 

are addressed in the draft document and thus additional 

explanation could be useful. The suggested approach of using 

species specific CFs and determining a 80 or 90th percentile cut 

is a solid suggestion for an alternative approach. 

Correction: These should be validated and corrected.

Regarding consideration of new data, EPA has acquired new 

data through the peer review and public process and has 

included these data, as appropriate, in the derivation of the 

criterion.

Regarding endangered species, EPA recognizes the concern 

regarding protection of listed species. EPA has considered and 

described available data on impacts of selenium on endangered 

species in the criterion document as well as impacts on species 

that are close phylogenetic surrogates of listed species dataset.

EPA notes that site-specific criteria can be developed if sensitive 

endangered species not represented by surrogates in the dataset 

used in the criterion are present at a specific site.

Regarding the concerns over lentic/lotic, MDRs, and mayfly 

data, EPA has addressed the issues of lentic/lotic waters, mayfly, 

new information, Minimum Data Requirements (MDRS), 

particularly the invertebrates issue and several other concerns 

pointed out by the public and other reviewers in the revised 2015 

draft criterion document and above.

Regarding comments on the tissue derivation procedures, EPA 

has reviewed the approaches for both the derivation of the 

muscle as well as the whole body criteria elements and modified 

the criterion document, as appropriate
134

External Peer Reviewers’ Comments EPA Response

Criteria are over-protective: these are speculative comments.

Criteria are under-protective: There are valid concerns 

expressed, especially in the apparent disconnection between 

agencies working towards similar goals. Concerns over the water 

column tier of the criteria are adequately addressed by the 

primacy of the tissue tiers. The risk differentiation argued 

between 4-6 mg/kg and 8.1 whole body/muscle tissue selenium, 

in light of the egg-ovary tissue primacy in the draft criterion, is 

moot. 

Data analysis: This comment should be explored for its validity. 

Data paucity affecting criterion: This comment appears to 

somewhat understate the available data. An additional literature 

search may yield new studies that increase egg-ovary data 

counts. 

Define terms in document: Solid points are made to enhance 

clarity.

Dietary requirements of Se in fish: The identified citations are of 

value.

Document process: No comment.

EC10 clarification: Editing error identified; requires correction.

Endangered species protection: This process observation should 

be considered. 

Exclude invertebrates: Risk assessment using extrapolations 

from animal models is a keystone of toxicology. The approach in 

the document is a modeling effort based on a similar 

extrapolation of available data. While not perfect, the data have 

Regarding concerns over specific studies, See previous 

responses starting on page 33 of this document regarding the 

Hermanutz bluegill study, Hardy cutthroat trout study, inclusion 

of Doroshov catfish study, and zebrafish study.

Regarding the clarity of the criterion as a freshwater criterion, 

EPA provides clarification in the 2015 draft document, but the 

document is clearly labeled freshwater, and the data included in 

the criteria are all freshwater or anadromous/diadromous fish 

that have a significant life history in freshwater.

Regarding implementation issues, EPA is addressing all of the 

issues mentioned (as well as others) in its development of 

technical support documents that will aid in the implementation 

of the selenium criterion.

Regarding the translation procedure, EPA has addressed the 

public and reviewer comments on the translation of the fish 

tissue criterion to water, both in this document as responses to 

the charge question comments specific to translation. EPA has 

also addressed the water column value issues to the extent that 

the available data allow.

Regarding criteria to protect birds, EPA is currently 

investigating the potential for a national criteria for aquaticdependent wildlife. (See response to peer reviewer 5 regarding 

this issue.)
135

External Peer Reviewers’ Comments EPA Response

value. 

General comments: Many opinions expressed. Sulfate impacts 

can be argued to be adequately incorporated into the primacy of 

the egg-ovary criterion.

GMCV alternative: There are several useful comments, 

including apparently revised data that should be addressed. 

Human health: This comment contains information useful in 

addressing human health implications of the draft criterion. 

Implementation: The public comments express thoughtful 

concerns and practical implementation questions that can serve 

as prompts to draft additional guidance. 

Importance of Se speciation: The comment expresses 

academically valid concerns however the practicality and data 

quality issues of speciated Se analyses for routine sampling and 

monitoring discount this concern. There are additional 

confounding issues of analytical sensitivity and result 

uncertainty at the criterion levels. Total dissolved Se sampling 

will filter out selenite that is readily adsorbed to suspended 

sediment particles. 

Intermittent criterion: Several good points are raised in the 

public comments. Suggestions to abandon one model for another 

do not provide adequate support for the suggestion. Practical 

implementation concerns are valid and should be addressed. 

Lentic lotic clarification: The public comments express 

thoughtful concerns and practical questions that can serve as 

prompts to draft additional guidance and supporting information.

Mayfly toxicity: This study should be reviewed for inclusion. 
136

External Peer Reviewers’ Comments EPA Response

Mercury interaction: This observation is not unequivocal in the 

scientific literature and thus does not require significant 

consideration in criterion development. 

Misunderstanding of MDRs: Some points are valid, however the 

practice of extrapolating and translating data is commonplace in 

toxicology. 

Mode of action: The authors correctly identify an 

oversimplification of the wording in the draft criterion 

document.

Natural background: The public comments correctly identify 

concerns of naturally occurring selenium contamination of 

waters and impacted aquatic life. The draft criterion should 

explicitly address these concerns in regards to implementation of 

the draft criterion. 

New information: Some of the submitted information has value 

and should be considered for inclusion. Sulfate modification to 

selenium impacts are addressed in the primacy of the egg-ovary 

criterion which reasonably characterizes endpoint risk regardless 

of modified uptake.

Number of GMCVs in data set: Draft text should be modified to 

address clarification.

Other comments: Most labs report 2 significant figures for water 

Se analysis at these levels.

Rainbow trout study clarification: Clarifying language should be 

added to the draft text.

Recommend other studies: These studies should be reviewed for 

inclusion in the data set. 
137

External Peer Reviewers’ Comments EPA Response

Recommended modifications: This is a summary state of 

previous suggestions in the list. Data updates once validated are 

reasonable requests.

Recommended muscle criterion: The approach should be 

critically reviewed. 

Recommended research: While interesting, the method is not 

used in all studies. Citable references are absent from the 

comment.

Recommended whole body criterion: The approach should be 

critically reviewed. 

Recommends alternative analysis of Hardy cutthroat trout: The 

commenter’s calculation lacks peer review and detail. 

Recommends alternative statistical analysis for Hermanutz 

bluegill: The commenter’s calculation lacks peer review and 

detail. 

Recommends alternatives to Guidelines SSD: Several practical 

comments are contained in this collection that can assist in 

drafting clarifying language and guidance.

Recommends including catfish study: The comments are well 

developed but not necessarily compelling for inclusion, 

especially in light of previous comments directed at lowering the 

outcome of the criterion development. 

Recommends including zebrafish in data set: A sound argument 

is forwarded to include this new dataset. 

Requests clarification of GEI fathead minnow analysis and its 

exclusion: This request can be reasonably addressed in the draft 
138

External Peer Reviewers’ Comments EPA Response

document. 

Salinity freshwater distinction: Guidance should be included to 

address these concerns. 

Se speciation: The comments addressing plant Se speciation are 

correct in that the draft text is overly simplified and dated in its 

discussion of plant Se. Mesocosm studies will also adopt a test 

water that will influence Se speciation and thus similar Se 

species exposure concerns will be present as will transferability 

or differential sediment/particulate/container reactivity of Se 

species in the test system. 

Site-specific criteria: There are numerous public comments that 

should be addressed in guidance for implementation.

Tiered criteria: There are numerous public comments that should 

be addressed in guidance for implementation.

Tissue criterion: There are numerous public comments that 

should be addressed in guidance for implementation.

Translation: There are numerous public comments that should be 

addressed in the draft document.

Update data set: If practical and possible, this is always a 

consideration.

Water column values: The concerns should be addressed in the 

draft document text.

Wildlife criterion: It is apparent from FWS comments that there 

is significant concern with the draft criteria potential for 

protection of aquatic dependent wildlife and fish as well. The 

pathway for further consideration and development of protection 

proposed in the draft document appear reasonable to move CWA 
139

External Peer Reviewers’ Comments EPA Response

requirements forward.

Winter stress: Comments opine on winter stress exclusion.

Ww to dw conversions: The comment should be addressed in the 

draft criterion text as best as possible. It is unlikely that the 

variability of WW-DW can be uniformly captured in a 

standardized approach.

7. Relevant comments from the public or stakeholders have 

been acknowledged where they are relevant to the other charge 

questions above. No further specific issues arising from our 

review of the public comments are noted.

Thank you for your comment.

References

British Columbia Ministry of the Environment (BC MoE) 

Ambient Water Quality Guideline for Selenium; Technical 

Report Update, April 2014, 

http://www.env.gov.bc.ca/wat/wq/BCguidelines/selenium/pd

fs/wqg-update-2014.pdf

Chapman PM et al. 2009. Ecological Assessment of Selenium in 

the Aquatic Environment. CRC Press. Boca Raton FL. 

339pp.

Conley JM, Watson AT, Xie L, Buchwalter DB. 2014. Dynamic 

selenium assimilation, distribution, efflux, and maternal 

transfer in japanese medaka fed a diet of se-enriched 

mayflies.Environ. Sci. Technol. 48:2971-2978.

Deforest DK, Brix KV, Elphick JR, Rickwood CJ, deBruyn 

AMH, Tear LM, Gilron G, Hughes SA, Adams WJ. 2014. 

Final Report: Selenium Partitioning between Water and Fish 
140

External Peer Reviewers’ Comments EPA Response

Tissue in Freshwater Systems: Development of Water-based 

Selenium Screening Guidelines. May 2014. North American 

Metals Council. 41 pp. 

(http://www.namc.org/docs/Selenium%20Integrated%20Rep

ort%20-%20Final%20(2014-05-20).pdf)

North Amreican Metals Council – Selenium Working Group. 

2008. Selenium Tissue Thresholds: Tissue selection criteria, 

threshold development endpoints, and potential to predict 

population or community effects in the field. 178pp.

References for Cutter evaluation that are not in the existing EPA 

reference list:

Baines, S.B., N.S. Fisher, M.A. Doblin, and G.A. Cutter. 2001. 

Uptake of dissolved organic selenides by marine 

phytoplankton. Limnol. Oceanogr., 46: 1936-1944.

Baines, S. B., N.S. Fisher, M.A. Doblin, G.A. Cutter, L.S. 

Cutter, and B. Cole. 2004. Light dependence of selenium 

uptake by phytoplankton and implications for predicting 

selenium incorporation into food-webs. Limnol. Oceanogr., 

49: 566-578..

Cutter, G.A. 1982. Selenium in reducing waters. Science 217: 

829-831.

Cutter, G.A. and T.M. Church. 1986. Selenium in Western 

Atlantic precipitation. Nature 322: 720-722.

Cutter, G.A. 1989a. Selenium in fresh water systems. In:

Occurrence and Distribution of Selenium (M. Ihnat, ed.). 

CRC Press, Florida, Chap. 10.

Cutter, G. A. 1991. Selenium biogeochemistry in reservoirs. 
141

External Peer Reviewers’ Comments EPA Response

Volume 1: Time series and mass balance results. Electric 

Power Research Institute, EPRI EN-7281, 97 pp. 

Cutter, G.A. 1992. Kinetic controls on the speciation of 

metalloids in seawater. Mar. Chem., 40: 65-80.

Cutter, G.A. 2005. Biogeochemistry: now and into the future. 

Palaeogeogr. Palaeoclimatol. Palaeoecol. 219: 191-198.

Meseck, S.C. and G.A. Cutter. 2006. Evaluating the 

biogeochemistry of selenium in San Francisco Bay through 

modeling. Limnol. Oceanogr., 51:2018-2032.

Porcella, D.B., G.L. Bowie, J.G. Sanders, and G.A. Cutter. 1991. 

Assessing Se cycling and toxicity in aquatic ecosystems. Water 

Air Soil Pollut., 57-58: 3-11.
142

IV. References Cited in EPA’s Responses

Bertram, P.E. and A.S. Brooks. 1986. Kinetics of accumulation of selenium from food and water 

by fathead minnows (Pimephales promelas). Water Res. 20(7): 877-884.

Birkner, J.H. 1978. Selenium in aquatic organisms from seleniferous habitats. Ph.D. thesis. 

Colorado State University, Fort Collins, CO. Available from: University Microfilms, Ann Arbor, 

MI. Order No. 78-20841.

Bowie, G.L., J.G. Sanders, G.F. Riedel, C.C. Gilmour, D.L. Breitburg, G.A. Cutter and D.B. 

Porcella. 1996. Assessing selenium cycling and accumulation in aquatic ecosystems. Water Air 

Soil Pollut. 90(1/2): 93-104.

Brix, KV, and DK DeForest. 2008. Selenium. In Relevance of Ambient Water Quality Criteria 

for Ephemeral and Effluent-Dependent Watercourses in the Arid Western United States. WR 

Gensemer, RD Meyerhoff, KJ Ramage, EF Curley (editors). SETAC

Chapman P.M., W.J. Adams, M.L. Brooks, C.G. Delos, S.N. Luoma, W.A Maher, H.M. 

Ohlendorf, T.S. Presser and D.P. Shaw. 2009. Ecological Assessment of Selenium in the Aquatic 

Environment: Summary of a SETAC Pellston Workshop. Pensacola FL (USA): Society of 

Environmental Toxicology and Chemistry (SETAC).

Chapman P.M., W.J. Adams, M.L. Brooks, C.G. Delos, S.N. Luoma, W.A Maher, H.M. 

Ohlendorf, T.S. Presser and D.P. Shaw (eds). 2010. Ecological Assessment of Selenium in the 

Aquatic Environment. SETAC Press, Pensacola, FL, USA.

Conley, J.M., D.H. Funk, D.H. Hesterberg, L-C. Hsu, J. Kan, Y-T. Liu and D.B. Buchwalter. 

2013. Bioconcentration and biotransformation of selenite versus selenite exposed to periphyton 

and subsequent toxicity to the mayfly Centroptilum triangulifer. Environ. Sci. Technol. 47:7965-

7973.

Conley, J.M., A.T.D. Watson, L. Xie, and D.B. Buchwalter. 2014. Dynamic selenium 

assimilation, distribution, efflux, and maternal transfer in Japanese Medaka fed a diet of Seenriched mayflies. Environ. Sci. Technol. 47:7965-7973.

Coyle, J.J., D.R. Buckler, C.G. Ingesoll, J.F. Fairchild and T.W. May. 1993. Effect of dietary 

selenium on the reproductive success of bluegills Lepomis macrochirus. Environ. Toxicol. 

Chem. 12(3): 551-565.

Crutchfield, Jr. J.U. 2000. Recovery of a power plant cooling reservoir ecosystem from selenium 

bioaccumulation. Environ. Sci. Pol. 3: S145-S163.

De Riu, D., L. Jang-Won, Huang, S., Monielloa, G., and Hung, S. 2014. Effect of dietary 

selenomethionine on growth performance, tissue burden, and histopathology in green and white 

sturgeon. Aquat. Toxicol. 148:65-73.
143

Doroshov, S., J. Van Eenennaam, C. Alexander, E. Hallen, H. Bailey, K. Kroll and C. Restrepo. 

1992. Development of Water Quality Criteria for Resident Aquatic Species of the San Joaquin 

River; Part II, Bioaccumulation of Dietary Selenium and its Effects on Growth and Reproduction 

in Bluegill (Lepomis macrochirus). Final Report to State Water Resources Control Board, State 

of California. Contract Number 7-197-250-0.

EPA. 2008. White Paper on Aquatic Life Criteria for Contaminants of Emerging Concern. Part I. 

General Challenges and Recommendation. OW/ORD Emerging Contaminants Workgroup. 

http://water.epa.gov/scitech/swguidance/standards/criteria/aqlife/cec.cfm

Fan, T.W.M., S.J. Teh, D.E. Hinton and R.M. Higashi. 2002. Selenium biotransformations into 

proteinaceous forms by foodweb organisms of selenium-laden drainage waters in California.

Aquatic Toxicol. 57: 65-84.

Formation Environmental. 2011. Brown Trout Laboratory Reproduction Studies Conducted in 

Support of Development of a Site-Specific Selenium Criterion. Prepared for J.R. Simplot 

Company by Formation Environmental. Revised October 2011.

Hardy, R.W. 2005. Effects of dietary selenium on cutthroat trout (Oncorhynchus clarki) growth 

and reproductive performance. Report for Montgomery Watson Harza. December 14.

Hermanutz, R.O., K.N. Allen, N.E. Detenbeck and C.E. Stephan. 1996. Exposure to bluegill 

(Lepomis macrochirus) to selenium in outdoor experimental streams. U.S. EPA Report. MidContinent Ecology Division. Duluth, MN.

Linville, R.G. 2006. Effects of Excess Selenium on the Health and Reproduction of White 

Sturgeon (Acipenser transmontanus): Implications for San Franscisco Bay-Delta. Dissertaiton. 

University of California at Davis.

McDonald, L.E. and M.M. Strosher. 1998. Selenium Mobilization from Surface Coal Mining in 

the Elk River Basin, British Columbia: A Survey of Water, Sediment and Biota. Pollution 

Prevention Ministry of Environment, Lands and Parks, Cranbrook, British Columbia, Canada.

Meseck, S.C. and G.A. Cutter. 2006. Evaluating the biogeochemistry of selenium in San 

Francisco Bay through modeling. Limnology and Oceanography 51:2018-2032.

Minnow Environmental, Inc. 2007. Selenium monitoring in the Elk River watershed, B.C. 

(2006). Report prepared for the Elk Valley Selenium Task Force. Minnow Environmental Inc. 

Mississauga, Ontario.

Orr, P.L., K.R. Guiguer and C.K. Russel. 2006. Food chain transfer of selenium in lentic and 

lotic habitats of a western Canadian watershed. Ecotox. Environ. Safety 63:175-188. 

Osmundson B.C., T. May, J. Skorupa and R. Krueger. 2007. Selenium in fish tissue: Prediction 

equations for conversion between whole body, muscle, and eggs. Poster presentation at the 2007 

Annual Meeting of the Society of Environmental Toxicology and Chemistry, and three 

supporting unpublished spreadsheets. Milwaukee, WI, USA.
144

Presser, T.S. and S.N. Luoma. 2010. A Methodology for Ecosystem-Scale Modeling of 

Selenium. Integrated Environmental Assessment and Management. 6: 685-710.

Presser, T.S. and S.N. Luoma. 2006. Forecasting selenium discharges to the San Francisco BayDelta estuary: ecological effects of a proposed San Luis drain extension. Professional Paper 

1646, U.S. Department of Interior, U.S. Geological Survey, Reston, Virginia.

Sappington, L.C., F.L. Mayer, F.J. Dwyer, D.R. Buckler, J.R. Jones, and M.R. Ellersieck. 2001. 

Contaminant sensitivity of threatened and endangered fishes compared to standard surrogate 

species. Environ. Toxicol. Chem. 20(12):2869-2876.

Stephan, C.E., D.I. Mount, D.J. Hansen, J.H. Gentile, G.A. Chapman and W.A. Brungs. 1985. 

Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic 

Organisms and their Uses. PB85-227049. National Technical Information Service, Springfield, 

VA.

Zhang, Y. and J.N. Moore. 1996. Selenium fractionation and speciation in a wetland system. 

Environ. Sci. Technol. 30: 2613-2619.