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# P EER 

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PEER REVIEW SUMMARY REPORT July 28 , 2015

Submitted to: 

### U.S. Environmental Protection Agency Office of Water, Office of Science and Technology Health and Ecological Criteria Division 1200 Pennsylvania Avenue, NW Washington, DC 20460 Attn: Joe Beaman Beaman.Joe@epa.gov

Submitted by: Eastern Research Group, Inc. 110 Hartwell Avenue Lexin gton, MA 02421

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## CONTENTS

1.0 INTRODUCTION

................................ ................................ ................................ .............................. 1

1.1 BACKGROUND

................................ ................................ ................................ ............................... 1

1.2 PEER REVIEWERS

................................ ................................ ................................ ............................ 1

2.0 SUMMARIES ORGANIZED BY CHARGE QUESTION

................................ ................................ ............ 2 Overall Document Organization and Structure

................................ ................................ ......................... 2
2.1 Please comment on the overall construction and clarity of the document, i.e., is the layout of the document logical and is the document clearly written? Are there better ways to ar range and/or present the information? If so, please explain and describe.

............... 2 Questions on Use of Ecosystem

- Scale Selenium Model

................................ ................................ ........... 4
2.2 Overall Toxicity Benchmarks/Development: The salinity throughout the San Francisco Bay and Delta (SFBD) varies from fresh to brackish to marine, and many of the species (or close relatives of the species) evaluated for the draft national freshwater criterion (USEPA, 2014 pp 57

- 62; 78

- 79 provided as supporting material), live in the estuary. Given these considerations, discuss w hether it is reasonable to use the draft national freshwater selenium criterion (tissue elements) for aquatic life in the SFBD. Are there better ways to estimate toxicity benchmark values for key aquatic life species, many of which are anadromous, in the e stuary? Please explain.

................................ .......................... 4
2.3 Toxicity Benchmarks/Green Sturgeon: For green sturgeon in the SFBD, juvenile growth is most likely the most sensitive endpoint. A recent study, De Riu et al. (2014) (provided), using green sturgeon observed selenium concentrations of 6

– 7 mg/kg dw (whole body) in the control treatment, whic h appears to reflect essentially a ‘no

effect’ concentration for growth or other effects, and is similar to the draft national whole body criteria of 8.1 mg/kg dw (USEPA, 2014 pp. 57

- 62; 78

- 79). In light of this study (and any other relevant data on green sturgeon), is the draft national benchmark value of 8.1 mg/kg dw protective of the juvenile growth endpoint for green sturgeon? Please explain your answer.

................................ ................................ .............. 7
2.4 Toxicity Benchmarks/Model: EPA uses log

- logistic modeling to determine EC10 values from environmental data. FWS has suggested that a biphasic model (Beckon et al., 2008 and Brian and Cousens, 1989, cited in review document) may be a better model to represent effects of selenium, since a biphasic model shows a more representative progression of effect to living species (selenium is a micronutrient, but is toxic in both deficit conce ntrations and excessive concentrations). Studies on selenium effects in the literature (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document) do not appear to consider this issue, and study designs do not appear to t ake the issue into account.

................................ ................................ ....................... 10

a. Given that many of the studies in the literature often use a small (or zero) control concentrati on of selenium, and a low level of effect is observed (reflective of a deficient concentration), is the response to increasing levels of selenium (into the excessive toxic amounts) better represented using a biphasic model or log

- logistic model? Would the slope of the regression be skewed in either model, due to incomplete modeling of deficit effects?

................................ ................................ .............. 10

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b. Discuss whether it would b e reasonable and appropriate to use a biphasic model to determine EC10 values for studies in the literature on representative or key species for the SFBD (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document), or whe ther the results of using a standard log

logistic model would produce more representative results.

............................................... 13
2.5 Species and Diet: Discu ss whether the appropriate key species and food chains (webs) have been identified and appropriately applied for the SFBD.

.................................................. 14

a. Discuss whether the diets of the key species chosen in each of the identified food webs are reasonable based on the literature (sources cited in review document) and whether the calculations of the Trophic Transfer Factors (TTFs) are scientifically support able based on those diets (see specific questions below). Are there better ways to calculate TTFs for mixed diets for the key species? Please explain.

................................................................................................ ................................ . 14 Specifically for Clam

- eating Fish:

................................................................................................ 15 b. Are the diet mixes (i.e., percentage of Corbula ) for adult whit e sturgeon, juvenile white and green sturgeon, and splittail scientifically supportable based on the available literature (Zeug et al., 2014, provided; USFWS, 2008 pp. 51

- 59, provided as supporting material; and Feyrer et al., 2003, cited in review documen t)? Is it scientifically supportable to postulate that splittail do not consume as much Corbula , and are therefore not as much at

- risk as sturgeon?

............................................. 15

c. Recent literature indicates that green sturgeon are more sensitive to selenium than white sturgeon (De Riu et al., 2014, provided; and Silvestre et al., 2010, cited in review document). Studies have also shown that adult green sturgeon primarily use the SFBD as a migratory corridor to freshwaters for spawning (http://exxexpartnership.com/wp

- content/uploads/2010/10/GreenSturgeon

- _1_.pdf , cited in review document). If it is known that egg maturation in adult green sturgeon is completed prior to entering the estuary, discuss whether it is scientifically supportable to conclude that adult white sturgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFBD (please provide references). Please comment on and discuss the potential for selenium exposure of adult green sturgeon during migration to play a role in reproductive toxicity, given the current state of knowledge on the reproductive biology and life history of green sturgeon.

.............................................................................................................................. 17 Specifically for Clam

- eating Birds:

.............................................................................................. 19 d. Discuss whether the diet mixes for the California Ridgway’s rail, scoter and scaup are scientifically defensible based on the literature (sources cited in review document).

........................................................................................................................... 19 Rails: Specifically, discuss whether it is scientifically supportable to assume that California Ridgeway’s rails do not consume a larg e percentage of Corbula, given that their littoral feeding habitat does not overlap with the preferred habitat of Corbula

. ................................................................................................ ................................ 19
Sco ter/Scaup: It has been observed that in the early part of the winter, scoter and scaup live mainly in the shallower, northern parts of the Bay (Suisun Bay and San Pablo Bay) where Corbula are prevalent, and consume mostly Corbula . However,

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iii in the latter pa rt of the winter and early spring prior to migration, they move down to the deeper, Central Bay area where Corbula are not as available, and the scoter and scaup are thought to consume mostly herring that do not bioaccumulate selenium as effectively. They then follow the coast north and continue to feed on herring prior to breeding and nesting. It appears that selenium moves directly from the diet of water birds into their eggs and not from internal tissue stores (Chapman et al., 2010). Given that scoter an d scaup switch to a low selenium diet for a period prior to migration as well as during migration, and that selenium may be depurated at a higher rate during migration, and that scoter and scaup are likely to continue to feed on low selenium fish sources i n the breeding and nesting grounds, is it reasonable to decrease the percentage of Corbula in scoter and scaup diet by 1⁄2 (from 90% to 45%), with respect to selenium exposure that could impact reproductive endpoints? Please discuss.

................................ 20 Specifically for Insect

- eating Fish:

................................ ................................ .............................. 21

e. Are the diet mixes for SFBD steelhead, Chinook salmon and delta smelt used in the model scientifically supportable based on the literature (sources cited in review document)? Please explain.

................................ ................................ ..................... 21
2.6 Trophic Transfer Factors (TTFs): Discuss whether the TTF values taken from the literature for individual species based on their food prey are scientifi cally supportable, i.e., are the TTF factors in Table 4

- 3 (values taken from USGS, 2010, Figure 11 and pp. 21

– 24; Presser and Luoma, 2010, Table 3; and USEPA, 2014, pp. 71

- 77, each provided as supporting material) scientifically supportable and appropria te? Are you aware of any other or more applicable data?

................................ ................................ ........................... 22 The TTF for Corbula (17) was developed and discussed in USGS (2010) pp . 21

- 23 (provided as supporting material). Discuss whether this analysis is scientifically supportable. Would you recommend a different or better way to develop a site

- specific TTF for Corbula , given the available data? Are there additional data that the Agency should consider for developing a site

- specific TTF for Corbula ?

................................ ................................ .......... 24
2.7 Partitioning Coefficients (K d s): In general, seleniu m is more bioavailable for accumulation into the food chain during dry/low flow (lentic) conditions, which is represented by higher K d values. Is it scientifically supportable to use the 75 th percentile of the K d values for each of the landward and seaward transects in the modeling, since data representing critical (very dry) conditions are not available? Would the use of median or mean K d values be more appropriate? Please explain your

answer.

................................ ................................ ................................ ................................ ....... 26
2.8 Corbula Concentrations: Information in Fuller et al. (2012) and in Thompson and Parchaso (2010) (both provided) indicate that populations and population densities of Corbula appear to decline in wet years, and increase in dry years. The articles suggest that Corbula may be sensitive to flow into the estuary and/or the salinity of the estuary (and other factors). The model shows that when the system has higher K d values (repre sentative of dryer years), more selenium is available for bioaccumulation and more selenium accumulates in the food chain (which would drive the draft criteria to protect the use downward), and thus, we are concerned with accounting for critically dry cond itions. Please comment on the articles and these statements.

..................... 28
2.9 Transects: Discuss whether it is reasonable and representativ e to use the focused seaward transects to model the clam

- based food webs, in order to eliminate the end

-

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member variability at the ocean (at the Golden Gate Bridge, the entrance to San Francisco Bay). Does the geology of the focused area (a wide Suisun Bay flowing into a constricted Carquinez Strait), and the importance of the area (the location of refinery discharges), favor the use of focused transects to best represent the clam

- based food web for the estuary? Please discuss.

................................ ................................ .......................... 29 Results and Application

................................ ................................ ................................ ........................... 30
2.1 0 Results: Discuss whether the model input and results scientifically support the water quality criteria for the three food chains represented. Are there better ways to represent the three food webs in the modeling? Please explain.

................................ ............. 30 Discuss whether it is scientifically supportable to use the modeling results for the clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish (all three food webs) in addition to the clam

- eating fish themselves. Discuss whether there are other scientifically defensible ways to use the modeling results to protect all the categories of species for the SFBD.

................................ ................................ ................................ .............. 3 2
2.11 Draft Criteria: The USGS Ecosystem

- Scale Selenium model was originally developed and validated for SFBD, and a considerable amount of site

- spec ific data are available and are used to model the estuary. EPA is using the model results to inform the criteria development process, and presents draft multi

- media criteria in Chapter 4. These criteria are a whole body or muscle fish tissue value and a cl am tissue value that directly reflect selenium levels that are considered to be protective of aquatic biota; and corresponding chronic and intermittent water column values, as well as a particulate concentration value to facilitate regulatory controls of s elenium sources.

............ 33 Given the relevance and detail of the USGS model and the abundance of site

- specific data, discuss whether th e criteria in the different media are scientifically defensible and protective for this aquatic ecosystem.

................................ ................................ ....................... 33
2.12 Translator (Per mits): EPA regulations generally call for NPDES permit limits to be expressed in terms of total recoverable values (40 CFR 122.45(c)). The model applied in this document yields calculations of water column values in the dissolved form. For most metals, EPA recommends dissolved values for water quality criteria, because the dissolved form better represents the bioavailable fraction in the water column to aquatic biota. However, for selenium, aquatic biota can take in the dissolved and particulate fractions i n the water column, which are then moved into and up the food chain.

................................ ................................ ................................ ................................ .......... 34 For most metals, EPA allows a translator to be used on t he dissolved criteria value, to determine a total recoverable permit limit; the translator is the fraction of the total recoverable metal in the downstream water (downstream of a discharge) that is dissolved.

................................ ................................ ................................ ................................ .... 34 Given that selenium has different bioaccumulation dynamics, what is an appropriate method to derive a translator? Explain your answer.

................................ ................................ ............. 34
2.13 Other Comments Provided

................................ ................................ ................................ ............ 38

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v 3.0 NEW INFORMATION PROV IDED BY REVIEWERS

................................ ................................ ............. 38

APPENDIX A CHARGE T O REVIEWERS

................................ ................................ ................................ ...... 1

APPENDIX B INDIVIDU AL REVIEWER COMMENTS

................................ ................................ .................... 1
R eviewer 1

. ................................ ................................ ................................ ................................ ............. B

- 3
Reviewer 2

................................ ................................ ................................ ................................ ............ B

- 11 Reviewer 3

................................ ................................ ................................ ................................ ............ B

- 2 5 Reviewer 4

................................ ................................ ................................ ................................ ............ B

- 3 5
Reviewer 5

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- 4 3

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1 **1.0 INTRODUCTION** 

This report document s the results of an independent p eer r eview of the Draft Aquatic Life and Aquatic

Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014) , developed by the U.S . Environ mental Protection Agency (EPA)

. Eastern Research Group, Inc. ( ERG, a contractor to EPA) organized this review and developed this report. Section 2 of this report provides a summary of reviewer comments and the individual reviewer comments for each charge question

. N ew information provided by the reviewers is presented in Section 3. Appendices A and B provide , respectively, the charge to reviewers and the complete set of comments submitted by each reviewer.

**1.1 Background** 

EPA ’s Office of Water is charged with protecting ecological integrity and human health from adverse anthropogenic, water

- mediated effects, under the purview of the Clean Water Act (CWA) and Safe Drinking Water Act. T he Agency has been revising the CWA section 304(a) recommende d aquatic life water quality criterion for selenium to reflect the latest science. States may adopt EPA’s recommended criteria, use it to develop site

- specific criteria, or develop their own scientifically defensible criteria. Once adopted and approved, a s tate’s Water Quality Standards are used to determine the level of pollution control necessary to attain the aquatic life designated use in a waterbody and to assess whether the waterbodies are impaired. EPA Region 9, assisted by EPA H eadquarters , develop ed the Draft Aquatic Life and Aquatic

- Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014) , and then contracted with ERG to organize an independent, external peer review o f the draft criteria document

. The draft selenium criterion is intended to protect the aquatic communities of the San Francisco Bay Delta generally, and also focuses on aquatic

- dependent waterfowl, consistent with current science and the available data for the Bay and Delta Region. The document is not intended to address concerns about selenium toxicity to human health, nor selenium contamination in other areas outside the Bay and Delta . For this reason, comments on human health or selenium

- related aquatic issues (unless clearly relatabl e) were beyond the scope of this review. In addition, not long before this peer review, EPA released a national external peer review draft of a selenium chronic criterion for the protecti on of freshwater aquatic life. This document was provided to reviewer s as supporting information . Comments on the national external peer review draft criterion w ere outside the scope of this review.

**1.2 Peer Review**  **ers**

ERG search ed , identified, and select ed five reviewers who met the technical selection criteria provided by EPA and who had no conflict of interest in performing the review :

• Kevin V. Brix, Ph.D.; Post

- Doctoral Fellow, Department of Zoology, University of British Columbia

• Nicholas Fisher, Ph.D.; Distinguished Professor, School of Marine and Atmospheric Sciences, State University of New York

• Gregory Möller, Ph.D.; Professor of Environmental Chemistry and Toxicology, University of Idaho

• Michael C. Newman, Ph.D.; A. Marshall Acuff, Jr. Professor of Marine Science, Virginia Institute of Marine Science, The College of William and Mary

• Daniel Schlenk, Ph.D.; Professor of Environmental Toxicology, Department of Environmental Sciences, University of California, Riverside

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2 ERG provided reviewers with instructions, the review document, the charge to reviewers (Appendix A) pr epared by EPA, and supporting reference materials as described in the charge. R eviewers worked individually to develop written comments in response to the charge questions. After receiving reviewer comments, ERG summarized reviewers’ responses to the charge questions, noting areas of agreement and disagreement, where relevant (Section 2).

**2.0 SUMMARIES**  **ORGANIZED BY CHARGE QUESTION** 
This section presents overall summaries of reviewer comments organized by charge question. Each summary is followed by a table presenting the individual reviewer comments organized by charge question. Individual c omments are copied directly from written comments as submitted by each reviewer and presented in Appendix B

. **Overall Document Organization and Structure**

**2.1 Please commen**  **t on the overall construction and clarity of the document, i.e., is the layout of the document logical and is the document clearly written? Are there better ways to**  **arrange and/or present the information? If so, please explain and describe.**

F ive reviewers responded to this question

. All five noted that the document is well written and has a logical layout. One reviewer pointed out that the format and conceptual flow are similar to EPA’s External Peer Review Draft Aquatic Life Ambient Water Quality Criterion for Selenium

— Freshwater 2014 , making it easier to read. Two reviewers suggested that EPA improve its treatment of uncertainty. One suggested that EPA better quantify uncertainty during computational steps; the other recommended that EPA add a chapter ded icated to uncertainty analysis to examine the strengths and weaknesses of the assumptions used in the model. A reviewer suggested that the outline should more clearly communicate that the topics of “fate and exposure” and “effects” are addressed separatel y (in Chapters 2 and 3, respectively). He also commented that Chapter 3 could be clearer if it included more figurative descriptions of thresholds. Another reviewer commented that the document should include more background information concerning selenium flux, loading, and discharge, as well as additional discussion of water column concentrations and estuarine fresh

salt water dynamics that influence selenium sedimentation. Three reviewers pointed out minor editorial mistakes.

Reviewer Comments

Reviewer 1 I found the writing to be quite good

— that is the layout of logical argument and the clarity of the statements made. Considering the many other documents I have seen, this document is much better written than many others.

Reviewer 2 The format and concept ual flow are generally similar to those of the federal WQC – Selenium draft, making it easily read and understood by those who have reviewed the federal treatment of the issue. In my opinion, the writing was clear and logical. There seemed to be a richer d iscussion and handling of uncertainties than in the federal document. It helped substantially to have significant components of the material already published in the open literature (e.g., Luoma and Presser (ES&T 43:8483, 2009) and Presser and Luoma (IEAM 6:685, 2010). Those publications were polished and concise

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3 discussions of the central themes, especially the methodology applied for ecosystem

scale modeling. Unlike the federal document that focused on taxonomic groupings, this draft document categorized species first based on their ecological qualities such as trophic ecology and movement patterns. Species were considered based on how much they consumed high (e.g., bivalves) or low (e.g., insects) selenium prey. Diet composition, species movements and lif e histories were considered throughout the draft. This made it much easier to understand and logically move through the materials. Whereas the federal draft document could not develop a comprehensive treatment of aquatic

- dependent wildlife (birds), the SFB D draft document was able to consider such important wildlife. This was a welcome addition that rounded

- out the entire treatment. In my opinion, the draft SFBD document (and federal document) might have quantified the propagation of uncertainty more during the numerous computational steps so that the reader had a sound understanding with which to decide whether any modest differences in calculated values were real or simply reflective of the variation generated during the uncertain computations in the proce ss. Question 3 below can be used as an example. Is the difference between 6

- 7 and 8.1 trivial relative to the uncertainty that emerges during computations? The 0.1 digit in the 8.1 suggests very high certainty that, given the details of the derivation, is dubious.

Reviewer 3 The document is well constructed and relatively well written. While the document (Chapter 2) separately addresses fate and exposure (based on modeling) and effects in separate sections (Chapter 3), these are not clearly delineated in the outline. For example, the outline should separate environmental fate and models used to assess particulate vs. dissolved concentrations from bioaccumulation models that estimate body burdens. While Figure 2

- 1 attempts to provide an overall conceptual a model, a more simplified model documenting the estimation of water criteria from tissues would be a better representation, and would probably be better suited in Chapter 1. Chapter 3 is relatively well

- written. However, more figurative descriptions for t hresholds would provide better clarity. For example, copies of the species sensitivity distribution (SSD) which were used to obtain EC10s would be very helpful. As a template, please see the EPA 2014 document.
As a minor editorial comment, the outline for Chapter 4 is missing a subheading C. A chapter should be dedicated to Uncertainty Analyses at some point in the document. What are the strengths and weaknesses of the assumptions used in the model? It was difficult to find a specific section where validat ions of the models were provided.

Reviewer 4 Overall the document is well written and well organized. It could be enhanced with additional summary information concerning selenium flux, loading and discharge in this complex ecosystem, as well as additiona l discussion of water column concentrations and estuarine fresh

- salt water dynamics that impact Se sedimentation. The major routes of fish and avian wildlife dietary exposure are very well treated. USGS Professional Paper 1646, USGS 2010 and the CA Water B oard TMDL documents for the North Bay can be the source of some of this water column and loading information. Note: p13 “across the full

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4 range of bay salinities (<1 to 33 parts per trillion, ppt)” should be parts per thousand.

Reviewer 5 I found the over all construction and clarity of the document to be quite good. There was a nice logical progression beginning with background and then describing and assembling all the various components needed to develop a Se WQC for SFBD. One very minor comment, paginat e the whole document rather than just within a section.

**Questions on Use of Ecosystem**

**- Scale Selenium Model** 

**2.2 Overall Toxicity Benchmarks/Development:**  **The salinity throughout the San Francisco Bay and Delta (SFBD) varies from fresh to brackish to marine, and many of the species (or**  **close relatives of the species) evaluated for the draft national freshwater criterion (USEPA, 2014 pp 57** 

**- 62; 78** 

**- 79 provided as supporting material), live in the estuary.**  **Given these considerations, discuss whether it is**  **reasonable to use the draft national freshwater selenium criterion (tissue elements)**  **for aquatic life in the SFBD. Are there better ways to**  **estimate toxicity benchmark values for key aquatic life species, many of which a re**  **anadromous, in the estuary? Pleas**  **e explain.**
All five reviewers responded to this question. Three reviewers said that it is reasonable to use the draft national criterion. One reviewer said that the national freshwater selenium criterion was used and adjusted in a reasonable manner for the SFBD. He wondered, however, whether an exposure adjustment for duration of time within the estuary or freshwater regions could have included more detail. Another reviewer noted that it is reasonable to use the draft national criterion (tissue elements) be cause sediment selenium exposure is a prime pathway in the SFBD ecosystem. A third reviewer thought it was reasonable to use the freshwater criterion for SFPB; he was not aware of any evidence suggesting that anadromous species are more or less sensitive to selenium than freshwater species and, given the mechanism of action for selenium, saw no reason to hypothesis this might be the case

. Two reviewers presented reasons why the draft national freshwater selenium criterion (tissue elements) would not be reas onable for aquatic life in the SFBD. One reviewer noted that sulfate is more abundant in saline waters than freshwater, resulting in higher selenate uptake by phytoplankton cells at the base of the food chain in saline waters. He also noted that estuarine organisms may respond to potentially toxic levels of selenium differently than freshwater organisms. Another reviewer agreed, noting that there may be differences in developmental toxicity between saltwater

- adapted fish and freshwater fish. He also pointed out that acclimation to hyper - and hypo

- saline conditions has a significant impact on endocrine and physiological responses in anadromous fish, including altered development of offspring and diminished reproduction. He suggested that it may be more approp riate to differentiate criteria based on returning adults (ocean to stream) or outgoing younger life stages (i.e. smolts; stream to ocean), and noted that the proposed SFBD criteria fails to recognize in ovo exposure within returning salmonid females.

Rev iewer Comments

Reviewer 1 It is not appropriate to apply Se bioaccumulation data from freshwater studies to estuarine or saline waters. This is because sulfate is abundant in saline waters but not in fresh water environments. Thus, selenate , which comes into phytoplankton cells, at the base of the food chain, is not appreciably taken up by cells in seawater where the sulfate

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5 concentration exceeds that of selenate by 10 million times (approx.). Selenite is the main species of inorganic seleni um that is acquired by marine phytoplankton, which can also take up organic selenides. Thus, selenate uptake in freshwater regions may be quite appreciable (due to the lack of competition from sulfate) but not in saline waters. However, once the Se is in o rganisms, it is not clear whether freshwater organisms would respond to potentially toxic levels in the same way as would estuarine organisms. The abundance of potentially competing ions in saline waters may result in different sensitivities for the estuar ine organisms, but I am unaware of a rigorous comparison of animal sensitivities to a given tissue Se concentration among marine vs. freshwater organisms. The ideal comparison would be for a euryhaline species in which Se toxicity is compared for the same species at freshwater and estuarine salinities. I am unaware if such a comparison has been made.

Reviewer 2 Although the national freshwater selenium criterion was used, its use and adjustments for the SFBD were reasonable and effectively incorporated. Th e challenge with some species of concern being anadromous is a difficult one and I wondered while reading the document whether an exposure adjustment for duration of time within the estuary or freshwater regions might have included more detail. Try as I mi ght, I could not think of an alternative that might have been materially more accurate. As an example, the EPA 540/1

- 89/002 for human risk assessment can incorporate more exposure duration and frequency details in its calculation of intake. But, given the lack of knowledge about bioaccumulation kinetics of the species of concern, this approach would likely not improve accuracy of estimates for the SFBD species. Perhaps a formal expert elicitation would further refine estimates. As a very minor point related to the use of freshwater concepts and computations for the estuarine or marine regions of the SFBD, equating μ g/L and μ g/kg is fine for freshwater as done on page 11 for partition coefficients but water density differences in saline waters makes the equating of liters and kilograms slightly biased. (An average liter of Pacific seawater weighs roughly 1025 g, not 1000 g.)

Reviewer 3 It is clear that salinity values have significant variance throughout SF Bay and the Delta. Acclimation to hyper and hypo saline conditions has significant impacts on endocrine and physiological responses in anadromous fish. Two of the most sensitive toxicity benchmarks for selenium in freshwater are altered development of offspring and diminished reproduction, both unde r endocrine control. The National Se criteria was estimated based on reproductive and developmental endpoints using a species distribution of 9 freshwater fish genera with an N=14 Genus Mean Chronic Values (GMCVs) (EPA 2014). Most of the exposures included a dietary component, which would allow all forms of Se (organic species) to be present and transported to the gonad. The 5th percentile projection yielded criterion lower than the most sensitive fish species tested, brown trout ( Salmo trutta ) and Oncorhyn chus , which has two anadromous species in SFBD (Steelhead and Chinook Salmon). Since at least two andromous species were evaluated with reproduction and developmental endpoints utilized in the evaluation, the National value is likely conservative. However, some uncertainty exists with the value as some have suggested many of the studies used dietary selenomethionine as the primary source of Se, and this may underestimate Se toxicity as other organic forms may also contribute to the toxic responses observed in fish (Ridby et

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6 al. 2014). In addition, there may be some underestimation in Saltwater acclimated animals. When embryos of Japanese medaka ( Oryzia latipes ) were acclimated to hypersaline conditions and treated with concentrations of 0.05 mM SeMe (derive d from concentrations observed in mosquito fish ( Gambuis affinis) from the San Joaquin River) for 12 hours (Kupsco and Schlenk 2014) and 24 hours (Lavado et al. 2012), significant enhancement of developmental toxicity was observed. While this species is no t endemic to SFBD, it demonstrates that there may be significant differences in developmental toxicity between saltwater adapted fish and those of freshwater fish, particularly at early life stages (Larvae, alevin, smolt). And since many anadromous fish at young ages must acclimate to hypersaline conditions in areas where exposure to Se may still occur either through prior maternal transfer in ovo, or via diet, combined exposure to both stressors may occur, particularly in the SFBD. Alternatively, since an adromous adult female fish are likely gravid prior to returning to freshwater to spawn, it is unknown whether acclimation to freshwater impairs endocrine signaling, which could affect maternal transfer of Se to offspring or have any reproductive impact on Se toxicity in the returning adults. The endocrine responses would not be due to accumulation or feeding preferences on the adult females but due to the effects of hypersaline conditions on the physiology and susceptibility of anadromous species.
Thus, it may be more appropriate to differentiate criteria based on returning adults (ocean to stream) or outgoing younger life stages (i.e. smolts; stream to ocean). In addition, the assumption of the SFBD criteria assumes that for salmonids juvenile (fry, alevi n, smolt) life stages are the more sensitive to Se toxicity and assumes dietary exposures via insects. The proposed SFBD criteria fails to recognize in ovo exposure within returning females, which is likely more critical (Thomas and Janz 2014). If in ovo

e xposure occurs, then models must incorporate a more complex food web (inclusion of fish to returning adults, rather than exclusively insects as in outgoing fish).

Reviewer 4 In the SF Bay estuarine system, the interface of marine and freshwater from the Delta causes sedimentation of much of the freshwater suspended particulate load and many dissolved ions. The major concern of Se toxicological impact modulation would come from the presence of dissolved sulfate at the lowest trophic levels. With sedimentat ion however, sulfate reducing bacteria come into play in the sediment forming reduced sulfur compounds reacting with co

- precipitating dissolved metal salts and mineral adsorbents (see for example: Chambers, et al. Sulfate reduction and sediment metabolism in Tomales Bay, California. Biogeochemistry 1994, Volume 25, Issue 1, pp 1

- 18). Thus, it is reasonable to suggest that marine

- freshwater interface sedimentation caused by common ion effect and other solution processes, would increase the sedimentation of d issolved and suspended Se, forming the well

- recognized sediment Se exposure pathway of the SF Bay, while providing for a sulfate reduction pathway (and Se as well) that would decrease sulfate competition in selenium exposure as well as modifying Se oxidati on state and chemical forms (see for example: Meseck & Cutter. 2012. Selenium Behavior in San Francisco Bay Sediments. Estuaries and Coasts (2012) 35:646

– 657). With sediment Se exposure as a prime pathway in this ecosystem, it is reasonable to use the draf t national

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7 freshwater selenium criterion (tissue elements) for aquatic life in the SFBD.

Reviewer 5 Yes, I think it is reasonable to use the draft national freshwater selenium tissue criterion for SFBD. I am not aware of any evidence that suggests anadromous species are more or less sensitive to Se than freshwater species. Further, considering the mechan isms of action for Se, I can think of no reason to hypothesize that this might be the case.

**2 .3**  **Toxicity Benchmarks/Green Sturgeon: For green sturgeon in the SFBD, juvenile growth is**  **most likely the most sensitive endpoint**

**. A recent study, De Riu**  **et al. (2014) (provided), using green sturgeon**  **1 observed selenium concentrations of 6**  **– 7 mg/kg dw (whole body)**  **in the control treatment, which appears to reflect essentially a ‘no**

**- effect’ concentration**  **for growth or other effects, and is similar to the draft national whole body criteria of 8.1 mg/kg dw (USEPA, 2014 pp. 57** 

**- 62; 78** 

**- 79).**  **In light of this study (and any other relevant data on green sturgeon), is the draft national benchmark value of 8.1 mg/kg dw protective**  **of the juvenile grow th endpoint for g**  **reen sturgeon? Please explain your answer.** 
All five reviewers responded to this question. Three reviewers agreed that the national benchmark value of 8.1 mg/kg dw should be protective of the juvenile growth endpoint for green sturgeon. One of these reviewe rs noted that the draft national benchmark was based on reproduction and development, which are more sensitive than juvenile growth. Another of these reviewer s pointed out that De Riu et al. (2014) has a very high range of exposure diets that lack clear environmental dietary relevance. He commented that De Riu et al. (2014) is not definitive as a single study for lower diet concentration growth effects in clam

- eating fish, but that the no

- observable

- effects level of 6

- 7 mg/kg dw (whole body) is protected by the draft national benchmark value. The third reviewer disagreed that juvenile growth is likely the most sensitive endpoint for green sturgeon, noting that larval abnormality is generally the most sensitive endpoint for fish. However, he thought it clear that the draft national benchmark value would be protective of juvenile green sturgeon growth

. The real concern , he noted, is that this value is likely statistically indistinguishable from background selenium in juvenile green sturgeon.
The comments of the two other reviewers suggest that they were less certain that the draft national benchmark value would be protective. One of these reviewer s noted that the difference between 8.1 and 6

- 7 mg/kg is probably not significant, considering the data variability and the fact that the 5th percentile projection of 8.1 is a projection, so sturgeon appear to be barely protected by the draft national benchmark value. Another reviewer noted that the methods in the draft national benchmark value and De Riu et al. (2014) focus on individuals, not populations, and that i ndividual

- based metrics are often protective of populations (although this may not be true for ma ny species ).

R ev i e w er C o mme n t s

R ev i e w er 1 Th e d i f f er en c e b e tw een 8

. 1 a n d 6

- 7 m g / k g is p r o b ab ly n o t s ig n ific an t, es p ec i a l l y g i v en th e
v ariab ilit y in t h e s e d at a an d t h e fac t t h at t h e 5 th p e rc e n t ile p ro j e c t i o n o f 8

. 1 is a p r o j e c t i o n , n o t a h a r d n u m b e r

. T h u s , t h e gr e e n s t u r ge o n h a v e S e c o n c e n t r a t i o n s a r e
a b o u t e q u a l t o t h e 5 th p er c en ti l e p r o j ec ti o n o f 8

. 1 wh o l e b o d y c r i ter i o n a n d th es e g r een
s t u r ge o n w o u l d a p p e a r t o b e j u s t b a r e l y p r o t e c t e d b y t h e d r a f t n a t i o n a l b e n c h m a r k v a l u e

1 Green sturgeon larvae were obtained from the offspring of three males and one female originating from the Klamath River along the Pacific Coast.

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8 of 8.1 ppm.

Reviewer 2 The methods used in the federal draft criterion document and De Riu et al. (2014) focus on effects to individuals, not populations. Indeed, these documents often obfuscate this distinction by using laboratory study results that allow inferences about the statistical population of tested individuals to suggest protection of the ecologica l population . It is often the case that individual

- based metrics will be protective of populations but that could easily not be true for many species. This point was made very clearly by Kammenga et al. (1996) and others almost twenty years ago. Most labor atory

- derived testing is done with species (“r

- strategists”) that are quite different from the green sturgeon. The sturgeon has a life history in which individuals take several years to mature, develop eggs over several years, do not spawn annually, live f or a long time, but produce many eggs upon spawning. It is not a species for which an expedient heuristic like “if you protect the individual’s most sensitive life stage, you protect the species population viability” can be confidently applied.

Fortunatel y, because of concerns of conservationists about the endangered green sturgeon, information has been gathered about the vital rates of most concern for this species, e.g., Beanesderfer et al (2007) and Heppell (2007). Beanesderfer et al. (2007) used demogr aphic models to conclude, “The model highlights the extreme sensitivity of a green sturgeon population to even small incremental increases in mortality where multiple ages are affected.” Heppell (2007) used a technique called elasticity analysis to identif y vital rates that most influence the growth rate (log λ ) of green sturgeon populations, concluding that “Elasticity analysis [demonstrated ] a high sensitivity of population growth rate to changes in the survival rate of subadult and adult fish.” The fede ral and SFBD proposed criteria focus on the less critical vital rate (reproduction and YOY) so they are likely protective and might even be overprotective. Beamesderfer, RCP, ML Simpson, and GJ Kopp. 2007. Use of life history information in a population m odel of Sacramento green sturgeon. Environ Biol Fish 79:315

- 337. Heppell, SS. 2007. Elasticity analysis of green sturgeon life history. Environ Biol Fish 79:357

- 368. Kammenga, JE, M Busschers, NM Van Straalen, PC Jepson, and J Baker. 1996. Stress induced f itness is not determined by the most sensitive life

- cycle trait. Funct. Ecol. 10:106

- 111.

Reviewer 3 The estimated value (EC5) should be protective of growth for juvenile green sturgeon. This is because the National benchmark was based on the more sensitive response of reproduction/development. Since growth is likely a less sensitive endpoint, the predicted value should be conservative and protective. In addition, the National criteria is similar to the criteria obtained from Linville (2006), which also used a feeding study and offspring development to estimate tissue values in white sturgeon.

Reviewer 4 De Riu et al. (2014) is an solid Se aquatic toxicity study (lacking genetic diversity due to green sturgeon listing and single egg donor), however the exposure diets of 0 (common 1

- 2 mg/kg Se diet formulation background), 50, 100 and 200 (2.2 ± 0.2, 19.7 ± 0.6, 40.1 ±

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9 1.5, and 77.7 ± 3.6 mg Se/kg dw tested) are a very high exposure range that lack clear environmental dietary relevance. Indeed Kleckner, et al. 2010 (Selenium Concentrations and Stable Isotopic Compositions of Carbon and Nitrogen in the Benthic Clam Corbula amurensis from Northern San Francisco Bay, California: May 1995

– February 2010. USGS Open

- File Report 2010

– 1252) observe a max Corbula Se concentration of 22 mg/kg dw. Thus there is really only a two point dose response curve (2.2 and 19.7 mg/kg) f or the major dose

- response range dynamic in the SFBD area of interest for clam feeding fish. The data of Table 1 for fixed ration Growth Performance in De Riu et al. (2014) for the 0 and 50 exposure groups through 8 weeks appear to have very high variabili ty and a very large 95% confidence interval that includes zero. The ANOVA used assumes normality but the data appeared skewed and may require transformation to explore effects estimation. The effect of time in this study is also not adequately explored. Th us the Control and 50 dose group data for %BWI/d as presented in Table 1 are far less than definitive and not justified to warrant the summary conclusion of the paper characterized as “the low SeMet diet (19.7 ± 0.6 mg Se/kg dw), which caused severe advers e effects in green sturgeon”. Hence De Riu et al. (2014) is not definitive as a single study for lower (<20 mg/kg Se) diet concentration growth effects in clam eating fish.

%BWI/d 2wk 4wk 6wk 8wk
0 control 4.5 ±1.8 (± 40%) 11.9 ± 6.1 (± 51%) 6.3 ± 15.9 (± 252%) 6.6 ± 14.9 (± 226%)

50 3.8 ± 3.9 (± 103%) 6.8 ± 8.4 (± 123%) 3.1 ± 14.8 (± 477%) 2.6 ± 16.0 (± 615%)

The control (2.2 mg/kg Se dw diet) green sturgeon total body Se at 4 weeks (6.5 ± 0.9) and 8 weeks (7.1 ± 0.9) have upper confidence bounds of 7.4 mg/kg and 8.0 mg/kg respectively and thus in close proximity to the draft national benchmark value of 8.1 mg/kg dw. Given the noted genet ic variability limitations of De Riu et al. (2014) as well as their observation of potential fixed ration study impacts to the rapid growth phase of juvenile green sturgeon, as well as expected routine laboratory sampling variability and method bias, the p rotection of juvenile green sturgeon is qualitatively and quantitatively afforded by the draft national benchmark value. In light of the lack of precision of the De Riu et al. (2014) study to benthic clam Se concentration range in this ecosystem, and the v ariability of the Table 1 data, the NOEL of 6

- 7 mg/kg dw (whole body) is protected by the draft national benchmark value of 8.1 mg/kg dw.

Reviewer 5 I disagree with the assertion that juvenile growth is likely the most sensitive endpoint for green sturgeo n. In general, larval abnormality is the most sensitive endpoint for fish. Using the micro

- injection to maternal transfer ratio for white sturgeon and applying it to green sturgeon suggests larval abnormality may be a more sensitive endpoint. I agree with EPA’s current assessment that while the FWS analysis suggests this may be the case, the uncertainty in this extrapolation precludes its use in setting a Se WQC. The fact that background Se in juvenile sturgeon is higher than the estimated whole body thresh old

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10 using the micro

- injection to maternal transfer ratio further increases the uncertainty in this analysis. I think it is clear that the draft national benchmark value of 8.1 mg/kg dw is protective of juvenile green sturgeon growth. The real concern is th at this value is likely statistically indistinguishable from background Se in juvenile green sturgeon. Based on the error estimates for week 8 whole body measurements in the De Rui et al. study (Table 2), it is likely that at least one control sample excee ded the 8.1 mg/kg dw threshold. This raises concerns that some relatively large fraction (e.g., 30% based on n=3 from De Rui et al.) of background tissue measurements exceed the proposed Se WQC.

**2.4 Toxicity Benchmarks/Model:**  **EPA uses log**

**- logistic modeli**  **ng to determine EC10 values from**  **environmental data. FWS has suggested that a biphasic model (Beckon et al., 2008 and Brian and Cousens, 1989, cited in review document) may be a better model to**  **represent effects of selenium, since a biphasic model shows a more representative**  **progression of effect to living species (selenium is a micronutrient, but is toxic in both deficit concentrations**  **and excessive concentrations). Studies on selenium effects in the literature (Heinz et al., 1989, Hilton et al., 1980, and**  **Hamilton et al., 1990, cited in review document) do not appear to consider this issue, and study designs do not appear to take**  **the issue into account.**

**a. Given that many of the studies in the literature often use a small (or zero) control**  **concentration o f selenium, and a low level of effect is observed (reflective of a**  **deficient concentration), is the response to increasing levels of selenium (into the excessive toxic amounts) better represented using a biphasi**  **c model or log**

**- logistic**  **model? Would the slop**  **e of the regression be skewed in either model, due to incomplete**  **modeling of deficit effects?**
Four reviewers responded to this question. Two of them noted that a biphasic model would likely represent the response to increasing levels of selenium better than a log

- logistic model, but the data are insufficient to warrant a biphasic model. One of thes e reviewer s clarified that exposure concentrations were not established to produce a sufficient number of observations. He suggest ed codifying more formal methods to guide users to decide which model is best for their particular data set. The second reviewer noted that data are lacking to identify EC10 values. These two reviewers prefer red a log

- logistic model until data are sufficient to warrant biphasic modeling.
A third reviewer noted several issues with the use of biphasic modeling for selenium. F or example, selenium appears to have very poor regulatory homeostasis as an essential trace element, which confounds the use of biphasic models for selenium. He cited Beckon et al. (2008) 2 , who note that the complexity of dietary selenium exposure makes it a poor choice for biphasic modeling. He also pointed out that the narrow toxic reproductive endpoints found in selenium exposure limit the usefulness of biphasic modeling. The fourth reviewer thought that EPA should consider using “non - standard” models i f the models better describe the data and there is a viable mechanism justifying the use of such a model.

R ev i e w er C o mme n t s

2 Beckon et al. 2008

. Environ. Sci. Technol. 42 : 1308

– 1314

.

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11 Reviewer 1 I do not know.

Reviewer 2 This concern crossed my mind several times during the review of the EPA draft federal WQC document. However, many of the data sets presented in that draft document were not designed to generate or sufficient for generating a reliable biphasic model. Exposures concentrations were not established to produce the number of observations needed in th e region where the deviation from a conventional log

- logistic model would be observed. So, the log

- logistic is generally the best model if the data are inadequate for fitting a more complicated one. The USFWS document (Beckon and Maurer, 2008) does contai n relevant data sets (e.g., Figure 23 for weights of juvenile rainbow trout) that would allow a biphasic model to be fit. In such cases, the biphasic model does seem best. The supplied FWS report by Beckon (2009, Selenium effect levels for selected represe ntative/surrogate species) has some examples illustrating my point. Figure 9 (salmon survival) and perhaps Figure 1 (mallard hatchability) show data for which a biphasic model would be warranted. If additional supportive information were available, a bipha sic model might be fit to the salmon survival data shown in Figure 10. A biphasic model for Figure 2 (mallard hatchability) would be an over parameterization given the nature of the data set. Given the above discussion, it seems that professional judgment might be used to decide which model is warranted. I suggest that more formal methods be codified to guide a user in deciding which model is best for their particular data set(s).

a. If one possessed a data set with which a biphasic model could be successfully fit, the biphasic model would be best. Obviously the slope derived from an inadequate data set for fitting the deficit response dynamics would be biased. But, if one forced a biphasic model onto an inadequate data set, the uncertainty in parameter estimat es would increase. Many of the species response data sets illustrated in the federal draft document would be inadequate for fitting a biphasic model. As stated above, I suggest that formal methods be established to aid users in deciding which model is best for their particular data set.

Reviewer 3 Se is clearly an essential nutrient and likely fits a “bi

- phasic” model showing non

montonicity or a U

- shape (Eaton and Gilbert 2013). While this is likely the most accurate description of the relationship of Se to development, the data are significantly lacking to identify EC10 values. The Beckon et al. (2008) manuscript compares 3 log

- logistic models with varied EC10 estimates. For each comparison there are limited data points showing the classic U

- shape that es sential nutrients should have with only one point showing reduced hatch at low concentrations. Consequently, until studies can be conducted to provide statistically adequate data to generate a biphasic curve, standard log

- logistic modeling should still be utilized.

Reviewer 4 Biphasic models have good potential to address toxicological impacts from essential trace elements (ETEs). However the broad range of existing and published aquatic toxicology studies were not experimentally set up with the broad ran ge of dosage required to explore effects with this model. Log

- logistic models are acceptable common practice,

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12 although all models have limitations. Selenium appears to have very poor regulatory homeostasis as an essential trace element, compared to for exa mple copper or manganese, and this confounds the use of biphasic models for selenium. The 2008 work of Beckon notes that the complexity of dietary selenium exposure makes it a poor choice for biphasic modeling: “Although biphasic relationships are common, it should not be assumed that dose

- response relationships are biphasic as a general rule, even for substances that are well known to cause biphasic responses. For example, dietary exposure to selenium is widely understood to have biphasic effects on the health and survival of animals ... However, although embryonic malformations are one of the effects of high levels of selenium, such defects are not known to be among the effects of selenium deficiency. Therefore, d ata relating selenium exposure to developmental defects ... may be best represented by a monotonic dose response model. Affecters of organisms are more likely to exhibit biphasic dose

response relationships if the effect or “endpoint” assessed is a general

m easurement of health, growth, or fecundity rather than a narrower effect such as embryonic deformities, liver lesions, or thrombosis. This is because broad measures of effect are more likely to represent a combination of individual beneficial low

- dose and deleterious high

- dose mechanisms or responses. A narrow end point is more likely to capture the consequence of a particular mechanism or response that may be only beneficial or only deleterious to the organism, and would be represented better by a monotoni c dose

- response model.” (Beckon, et al. Environ. Sci. Technol. 2008, 42, 1308

– 1314) As noted, biphasic models work best when the response tracked in the study appears in both deficiency and toxicity realms of exposure. The somewhat narrow toxic reproductiv e endpoints found in Se exposure limit the usefulness of the biphasic approach. Thus a) the Se dose response analysis is better represented log

- logistic model. Skewing of the slope of the regression due to incomplete deficit dosing maybe unlikely since all experimental diets will have a baseline Se concentration from the protein and other constituents in the diet formulation prior to test agent fortification (i.e. addition of selenate, Se

- methionine or other quantified Se substance). Dietary formulations fo r deficiency studies are very difficult with ETEs since they are ubiquitous at low, often required, levels in many healthy plants and animals. The cautions of Beckon , et al. 2008 concerning the application of biphasic modeling to selenium suggest b) it is not reasonable and appropriate to use a biphasic model to determine EC10 values for studies in the literature on representative or key species for the SFBD . A standard log

- logistic model is appropriate and acceptable in the exploration of high dose Se repr oductive toxicity.

Reviewer 5 For some data sets, a biphasic model may better describe the data and there is a potential mechanistic underpinning (i.e., Se essentiality) for why such a model would be appropriate. It is possible for model slopes to differ depending on the data set and the interpretation of what constitutes a 10% effect can be quite different. The data from Hilton et al. (1980) (Figure 23; USFWS 2008) is the clearest example of such a data set although this particul ar study is problematic because fish were fed an inorganic Se diet. In contrast, it is not clear that use of a biphasic model on data for Chinook salmon (Figure 11; USFWS 2008) and mallards (Figure 1; USFWS 2008) is more appropriate than a

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13 standard log

- log istic model. In general, I think EPA should consider use of “non

- standard” models if they better describe the data and there is a viable mechanism for why such a model should be used. In my opinion, only the Hilton et al. study meets both criteria.

**b. Dis**  **cuss whether it would be reasonable and appropriate to use a biphasic model to determine EC10 values for studies in the literature on representative or key species**  **for the SFBD (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in**
**r eview document), or whether the results of using a standard log** 

**- logistic model**  **would produce more representative results.**
Four reviewers responded to this question , with varying levels of caveat or concern about the use of biphasic models for selenium. On e reviewer described numerous concerns that would make it neither reasonable n or appropriate to use a biphasic model for this purpose

. A standard log

- logistic model would, in his opinion, be appropriate and accept able in the exploration of high

- dose selenium reproductive toxicity. A second reviewer recommended that EPA consider use of “non

- standard” models if they better describe the data and there is a viable mechanism for why such a model should be used ; however, few studies meet both criteria. Anot her reviewer commented that a biphasic model would more accurately predict selenium influences on biological systems if data sets contained sufficient points in lower

- dose regions. The fourth reviewer noted that biphasic modeling would be preferable if suf ficient data were available to provide adequate statistical power.

Reviewer Comments

Reviewer 1 I do not know and have no opinions on this.

Reviewer 2 Yes. Fitting a biphasic model to data sets with enough points in the lower dose regions would result in a model that more accurately made predictions and conformed to our current understanding of the mechanisms of selenium influences on biological systems.

Reviewer 3 As mentioned above, a biphasic model would be preferred if the data were available to provide adequate statistical power.

Reviewer 4 See response provided under 2 .4. a

.

Reviewer 5 See response provided under 2 .4.a.

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14 **2.5 Species and Diet:**  **Discuss whether the appropriate key species and food chains (webs) have been identified and appropriately applied for the SFBD.** 

**a. Discuss whether the diets of the key species chosen in each of the identified food**  **webs are reasonable based on the literature (sources cited in review document) and whether the calculations of the Trophic Transfer Factor**  **s (TTFs) are scientifically supportable based on those diets (s**  **ee specific questions below). Are there better**  **ways to calculate TTFs for mi xed diets for the key species?**  **Please explain.** All five reviewers responded to this charge question. T hree reviewers noted that the diet information used in the document was reasonable and the TTF values we re appropriate. One of these reviewer s noted that the seminal works of Luoma and Presser have characterized selenium behavior, impacts, and risks in the SFBD , and subsequent studies have explored pathways and endpoints for selenium in the SFBD. TTFs are therefore derived from the best available information and, given this body of work, are generally scientifically supportable. A second reviewer thought the ide ntified food webs we re reasonable , and did not think there was a better way to calculate TTFs for mixed diets for the key species. Th e third, who clarified that he was not an expert in trophic ecology, thought that the diet information appear ed reasonable and t he TTF values well chosen , but suggested it might be useful to have some indication of the uncertainty associated with each estimate.
Two reviewers were not convinced that the TTF values we re appropriate. One of these reviewer s commented that it is possible to calculate TTFs for mixed diets, but was not sure that it would be worth doing, because the considerable variability in single predator/prey combinations is compounded when multiple combinations are considered, confounding TFF derivation. The fif th reviewer stated that specification of the targeted life stage is necessary to refine the food chains proposed in the document (e.g., because larval or Young of the Year fish moving from freshwater into saltwater are likely to have a different diet than adults moving back into freshwater to spawn )

.

R ev i e w er C o mme n t s

R ev i e w er 1 I t is p o s s ib le t o m at h e m at i c ally c al c u lat e T T F s f o r m ix e d d ie t s f o r a g iv e n s p e c i e s , b u t I a m
n o t s u r e t h a t i t i s w o r t h d o i n g s o , e v e n t h o u gh m a n y a n i m a l s c o n s u m e m o r e t h a n o n e p re y it e m

... . t h a t is , n a t u re i s m o re c o m p le x t h an m o d e ls t y p ic all y d e p ic t

. T h e re as o n I h av e c o n c e rn s in d o in g s o f o r m ix e d d i e t s is t h at t h e re is c o n s id e rab le v ariab ilit y f o r an y
o n e p r e d a t o r / p r e y c o m b i n a t i o n

. I f o n e wer e t o c o n s i d er tw o o r m o r e p r ey i te m s , th e
v ariab ilit y c o m p o u n d s i t s e l f a n d d o e s n o t h e l p p i n p o i n t o r q u a n t i f y a m o r e “ r e a l ” T T F

. A n
e x a m p le o f t h is s o r t o f v ari ab ilit y c an b e s e e n f o r 6 d iffe re n t m e t als in fis h c o n s u m in g d iv e rs e p re y , w h e re ab o u t an o rd e r o f m ag n it u d e d iffe re n c e s are s e e n , la rg e ly b as e d o n t h e v a riab ilit y in t h e m e t al c o n c e n t rat i o n s in t h e d iffe r e n t fo rm s o f p re y

. [ s e e M a t h e w s & F is h e r, S c i. T o t al E n v ir o n

. 4 0 7 : 5 1 5 6

- 516 1 ( 20 09 )

. ]

R ev i e w er 2 I a m n o t a n exp e r t o n th e t r o p h i c ec o l o g y o f th es e s p e c i es s o th e a n s w er h er e i s b a s ed o n t h e i n f o r m a t i o n s e n t w i t h t h e s u p p l e m e n t a l m a t e r i a l s a n d t h a t s h o w n i n t a b l e s o f t h e d raft S F BD d o c u m e n t

. B as e d o n t h o s e d a t a, t h e d ie t in fo rm at io n ap p e ars t o b e
r ea s o n a b l e. Th e TTF v a l u es s ee m wel l c h o s en ; h o we v e r , i t m i g h t b e u s ef u l t o h a v e s o m e i n d i c at io n o f t h e u n c e rt ain t y as s o c iat e d w i t h e ac h e s t i m at e

. I n f u tu r e r ep o r ts , th e
u n c e r t a i n t y o f e a c h c o m p o n e n t go i n g i n t o t h e v a r i o u s c a l c u l a t i o n s c o u l d b e i n c o r p o r a t e d in t o a M o n t e C arlo re s a m p l in g ro u t in e t o p r o v id e e s t i m at e s o f t h e u n c e rt ain t y ar o u n d

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15 eac h calculated TTF. The uncertainty is likely large relative to that variation in TTF values among species. One conventional addition would be to use end member analysis involving N, C and perhaps S stable isotopes to estimate dietary components for each ke y species. The UC

Davis campus has an excellent facility to do the analyses and others have the required software such as the EPA’s IsoSource package. This being said, my judgment is that such an approach would not provide much better information than the one taken in the draft document.

Reviewer 3 Overall, the criteria focuses on ocean

- going early life stage organisms for the salmonid anadromous fish species. As discussed above, larval or Young of the Year fish moving from freshwater into saltwater ( smolts) are likely to have a different diet (only one TTF) than adults moving back into freshwater to spawn (Mixture 4

- trophic level

- see Fig 7 USEPA, 2014). Specification of the targeted life stage is necessary to refine the food chains proposed in this do cument.

Reviewer 4 The seminal works of Luoma and Presser have wonderfully characterized Se behavior, impacts and risks in the SFBD. Building on these works, the SFBD is exceptionally well characterized through several decades of modeling, samplings and s cientific analyses exploring pathways and endpoints for selenium in this complex and important ecosystem. The body of SFBD work has been thorough in its analysis of key species and the related food webs that contribute to our understanding of Se impacts. T he dietary information for the key species analyzed are well cited and well explored. More recent work with sturgeon (Zeug et al, 2014) fills data gaps with this key species. The resulting TTFs thus represent the use of best available data. Opportunistic f eeding and food web dynamics related to the hydrograph and climate variability add variability to dietary understanding, however it is unlikely that precise quantitative analysis that addresses the full range of variables is possible. Thus a) TTFs derived from best available information, such as done in the current analysis is generally scientifically supportable.

Reviewer 5 Yes, based on the literature provided the identified food webs are reasonable. No, I don’t think there are better ways to calculate T TFs for mixed diets for the key species. Also see specific responses below.

**Specifically for Clam**

**- eating Fish:** 

**b. Are the diet mixes (i.e., percentage of**  Corbula **) for adult white sturgeon, juvenile white and green sturgeon, and splittail**  **scientifically supportable based on the available literature (Zeug et al., 2014, provided; USFWS, 2008 pp. 51** 

**- 59, provided as**  **supporting material; and Feyrer et al., 2003, cited in review document)? Is it scientifically supportable to postulate that split**  **tail do not consume as much** Corbula **, and are therefore not as much at** 

**- risk as sturgeon?** 

All five reviewers commented that the diet mixes for these species are scientifically supportable based on the available literature. One reviewer clarified that the amo unt of selenium

- containing food that a cold

-

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16 blooded fish consumes would be substantially less than that consumed by warm

- blooded birds, so it was confusing that the TTF values for fish were close to those of birds. Another reviewer specified that the propo sed diet mixes are scientifically supportable, but the available data do not necessarily preclude consideration of other dietary mixes. He suggested it would be useful for EPA to perform a sensitivity analysis.
All five reviewers agreed that it is scienti fically supportable to assume that splittail do not consume as much Co r bula. One of these reviewers, however, disagreed that this necessarily equates to splittail being at a lower risk than sturgeon. The species could have different sensitivities to selenium.

R ev i e w er C o mme n t s

R ev i e w er 1 Th i s s ee m s r ea s o n a b l e to m e, b u t s e e m y c o m m en t b el o w ( u n d er “ c ” )

.

R ev i e w er 2 A b rie f c larific a t io n o f o n e p o in t w o u ld h e lp r e lat i v e t o t h e g e n e ral T T F v alu e s fo r c lam

e at in g fis h an d b ird s

. T h e fi s h are c o ld

- b l o o d e d a n d t h e b i r d s a r e w a r m

- b l o o d e d

. T h e
a m o u n t o f s e l e n i u m

- c o n t ai n in g fo o d t h a t a fis h c o n s u m e s t o m ain t ain it s e lf w o u l d b e
s u b s t a n t i a l l y l e s s t h a n t h a t c o n s u m e d b y t h e w a rm

- b l o o d e d b i r d s

. S in c e s e le n iu m is

ac c u m u lat e d m o s t ly f ro m f o o d , it w as c o n fu s in g t o m e t h at t h e T T F v alu e s f o r fis h w e re
s o c l o s e t o t h o s e o f b i r d s

. F o r fis h an d b ird s e at in g C o r bul a as 4 0

- 4 5 % o f t h e ir d ie t , T ab le 4

- 8 g i v es TTF fi sh = 1

. 1 a n d T T F duc k e gg = 1

. 8

. Bas e d o n a p h y s io l o g ic al ru le

- o f

- t h u m b , m y i n f o r m a l gu e s s w o u l d h a v e b e e n a 5

- to 1 0

- f o ld d iffe re n c e , n o t t h e lo w 2

- fo ld d iff e re n c e in t h e t ab le s

. C le arl y , t h e re is an u n e x p lain e d f e at u re o f t h e c alc u lat e d T T F v alu e s t h at
re s u lt s in t h is ap p are n t i n c o n gr u i t y

. b

. Y e s

. B a s e d o n m y r e v i e w o f t h e s u p p l i e d m a t e r i a l s a n d t h e d i s c u s s i o n s i n t h e d r a f t d o c u m en t, th e d i e t m i xes s ee m r ea s o n a b l e, i n c l u d i n g th e d i f f er en c es b etw een
s t u r ge o n a n d s p l i t t a i l c o n s u m p t i o n s o f C o r bul a

.

R ev i e w er 3 B a s ed o n th e l i ter a tu r e, th es e a s s u m p ti o n s s ee m a p p r o p r i a te.

R ev i e w er 4 Th e d i et m i xes a p p ea r t o b e r ep r es en ta ti v e o f o u r c u r r en t u n d er s ta n d i n g o f c l a m

- e at in g f i s h i n t h e S F B D

. N e w e r w o r k s u c h a s Z e u g e t al. , 2 0 1 4 are v alu ab l e as s e t s in m o d e lin g d i eta r y exp o s u r e a n d th u s TTF s

. W i th o u t c l ea r a n d d e f i n i ti v e d a ta a d d r es s i n g s y s tem
v ariab ilit y , s u c h as t h e c as e fo r m an y o rg an is m ’ s d ie t , b e s t in fo r m e d e s t im a t e s t h at b alan c e w h at is k n o w n ag ain s t w h at is u n k n o w n o r u n q u an t ifie d , is a r e as o n ab le

a p p r o a c h

. T h i s a p p e a r s t o b e t h e a p p r o a c h t a k e n w h e n t h e ; U S F W S , 2 0 0 8 a n d F e y r e r e t al. w o r k is u s e d :

D i e t : S pl i t t ai l ar e be nt hi c ( b o t t o m ) f e e de r s

. S t o m ach c o nt e nt s f r o m 7 0 s pl i t t ai l

co l l e ct e d i n S ui s un M ar s h b e t w e e n M a r ch 1 9 9 8 and J a nuar y

1 9 9 9 i ndi cat e t hat t he i r di e t co ns i s t e d m ai nl y ( 4 3 % ) o f

uni de nt i f

i e d m at e ri al , pr o babl y

de t r i t us

. T he

o v e r bi t e cl am ( As i an cl a m ) , P o t a m o co r bul a am ur e ns i s , and o t he r m o l l us k s
co ns t i t ut e d 3 4 % o f

t h e di e t ( Fe y r e r and M a t e r n 2 0 0 0 , F e y r e r e t a l

. 20 03 )

. T h u s b) it i s s c i e n t ific ally s u p p o rt ab le t o p o s t u la t e t h a t s p lit t ail d o n o t c o n s u m e as m u c h C o rb u la, an d are t h e r e fo r e n o t as m u c h at

- ris k as s t u rg e o n

.

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17 R ev i e w er 5 T h e d ie t m i x e s p r o p o s e d b y US E P A are s c ie n t ific ally s u p p o rt ab le , al t h o u g h I w o u ld n o t s a y t h e av ailab le d at a p re c lu d e s c o n s id e rat i o n o f o t h e r d i e t ary m i x e s

. I t w o u ld b e u s e fu l t o p e rfo r m an d p r o v id e t h e r e s u lt s o f a s e n s it iv i t y an al y s i s o n t h is is s u e

. F o r exa m p l e , i f th e
s t u r ge o n d i e t w a s 5 0 % C o r bul a , h o w m u c h l o w er w o u l d th e p r o p o s ed W Q C n eed to b e? I als o ag re e t h a t s p lit t ail d o n o t c o n s u m e as m u c h C o r b u la a s s t u r ge o n , b u t d o n o t a gr e e t h is n e c e s s arily e q u at e s t o t h e m b e in g at l o w e r ris k

. R i s k is an in t e g r a ti o n o f exp o s u r e
an d e ffe c t ( i. e

. , s e n s it i v it y )

. Giv e n t h e li m it e d s t u d ie s o n s t u rg e o n an d s p lit t ail in g e n e ral, it is p re m at u r e t o c o n c lu d e t h e y are l e s s o r e q u ally s e n s it iv e t o S e c o m p are d t o s t u rg e o n

. T h e re f o re , t h e l e v e l o f ris k fo r s p lit t ail is u n k n o w n

.

**c. Recent literature indicates that green sturgeon are more sensitive to selenium than**  **white sturgeon (De Riu et al., 2014, provided; and Silvestre et al., 2010, cited in review document). Studies have also shown that adult green sturgeon primarily u**  **se the SFBD as a migratory corridor to freshwaters for spawning**  (http://exxexpartnership.com/wp

- content/uploads/2010/10/GreenSturgeon

- _1_.pdf **, cited in review document). If it is known that egg maturation in adult green sturgeon**  **is completed prior to entering the estuary, discuss whether it is scientifically supportable to conclude that adult white sturgeon and juvenile white and green**  **sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in**  Corbula **in the SFBD (please pr ovide references). Please comment on and**  **discuss the potential for selenium exposure of adult green sturgeon during migration to play a role in reproductive toxicity, given the current state of knowledge on the**  **reproductive biology and life history of gree n sturgeon.** 
Four reviewers responded to this question. Two reviewers commented that adult white sturgeon and juvenile white and green sturgeon will likely be more affected by elevated levels of selenium in Corbula in the SFBD than adult green sturgeon, tho ugh both reviewers qualified their comments. For example, one of these reviewers commented that EPA cannot rule out the possibility that eggs will have significant selenium exposure during migration of adults.
Another reviewer noted that it is not clear whether diet

- derived selenium continues to accumulate in animals even after maturation of gonads. The fourth reviewer referred to his response in Section 2 .3 (De Riu et al. [2014] has a very high range of exposure diets that lack clear environmental dietary relevance ) to describe why De Riu et al. (2014) is neither definitive nor quantitatively precise in assessing green sturgeon selenium exposure risk in the SFBD.

R ev i e w er C o mme n t s

R ev i e w er 1 Th es e q u e s ti o n s a r e o u ts i d e m y exp er ti s e.

R ev i e w er 2 Yes

. Th e j u d gm e n t i s s o u n d t h a t “ adul t w hi t e s t ur ge o n and j uv e ni l e w hi t e and gr e e n
s t ur ge o n w i l l be m o r e af f

e c t e d t han adul t gr e e n s t ur ge o n. ” A s d i s c u s s e d a b o v e , o n e w a y
o f h an d lin g t h e m ig rat o ry c h arac t e ris t i c s o f e a c h s p e c i e s w o u ld b e t o q u an t it at i v e ly i n c l u d e m o re d e t ails f o r e x p o s u re d u rat i o n an d fre q u e n c y

. T h e E P A d o c u m e n t d e alin g
w it h h u m an ris k as s e s s m e n t ( E P A 5 4 0 / 1

- 8 9 / 0 0 2 ) i n c l u d e s e x p o s u r e d u r a t i o n a n d fre q u e n c y in i t s c al c u lat io n o f in t ak e

. G i v en th e l a c k o f k n o wl ed g e a b o u t s el en i u m b io ac c u m u lat io n k in e t i c s i n t h e s t u r ge o n , t h i s a p p r o a c h w o u l d l i k e l y n o t i m p r o v e t h e

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18 accuracy of estimates. Perhaps a formal expert elicitation would improve future estimates.

Reviewer 3 Since Se is likely transported to gonads via the egg

- yolk precursor vitellogenin (Linville 2006: Janz et al. 2010), one could assume that animals that do not require vitellogenin any longer would not continue to increase gonadal concentrations of Se. However, it is unclear whether vitellogenin is continually deposited into “mature” gonads of gr een sturgeon. Studies in zebrafish indicate vitellogenin is constantly turned over throughout embryogenesis (Han et al. 2010) which would argue diet

- derived Se would continue to accumulate in animals even after maturation of gonads.

In the recent Linares

- Casenave et al. 2015 publication, of 26 female white sturgeon collected between San Pablo Bay and Suisun Bay, 18 were pre

- vitellogenic indicating most fish did not have sexually mature gonadal development. It was not documented whether the animals were com ing from saltwater to freshwater for spawning or vice

versa. If animals are returning to spawn, then it can presumed that gonadal development and selenium burdens would be higher than in animals exciting the estuary. Animals with vitellogenic oocytes did h ave higher concentrations of Se.

Reviewer 4 While of value, De Riu et al., 2014 for reasons stated above, is neither definitive nor quantitatively precise in assessing green sturgeon Se exposure risk in the SFBD. If there is high confidence in the observa tion that sturgeon use the “SFBD as a migratory corridor to freshwaters for spawning” and that egg maturation is primarily complete before entering the estuary, then there is cause to c) scientifically support a conclusion that adult white sturgeon and juv enile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFBD. The 0 and 50 group dose

- response data in De Riu et al., 2014 compared to the observed Corbula Se concentrations in Kleck ner, et al. 2010, suggest lower level risks for juvenile growth toxic endpoints.

Reviewer 5 I think given our understanding of adult green and white sturgeon use of SFBD, it is likely that juvenile white and green sturgeon will be more affected than adult s of either species. I understand that it is likely green sturgeon eggs mature while adults are in the ocean and that the adults appear to primarily use SFBD as a migration corridor. However, I think we cannot rule out the potential for toxicologically sig nificant Se exposure (with respect to the eggs) during this migration. We simply don’t have any information on this issue and so it would be prudent not to rule out this potential exposure pathway. I don’t think there is enough information to address this issue in a quantitative manner, but it should be highlighted that this is a potentially significant uncertainty that needs further study rather than eliminating it as an issue for concern as the document currently does.

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19 **Specifically for Clam**

**- eating Birds:** 

**d. Discuss whether the diet mixes for the California Ridgway’s rail, scoter and scaup are**  **scientifically defensible based on the literature (sources cited in review document).**

**Rails: Specifically, discuss whether it is scientifically supportable to assum**  **e that California Ridgeway’s rails do not consume a large percentage of**  Corbula, **given that their littoral feeding habitat does not overlap with the preferred habitat of**  Corbula

**.** Four reviewers responded to this question. Three supported the assumption that California Ridgeway’s rails do not consume a large percentage of Corbula . One of these reviewers noted that the review document presents a defensible understanding of diet mix a nd dietary exposure for the three avian species. He also pointed out that it appears reasonable to decrease the percentage of Corbula in scoter and scaup diet by a half for selenium exposure and the potential for reproductive endpoints. The fourth reviewer noted that the 20 percent Corbula diet is speculative and the actual percentage could be higher or lower. He suggested conducting a sensitivity analysis to understand the implications of this assumption.

Reviewer Comments

Reviewer 1 This definitely makes sense.

Reviewer 2 Yes. This assumption seems defensible for the rail.

Reviewer 3 I cannot comment on this section as I am unfamiliar with the life histories of these avian species.

Reviewer 4 The review document presents a solid and defensible understanding of diet mix and this dietary exposure for the California Ridgway’s rail, scoter and scaup. While habitat choice and thus exposure potential from Corbula are beyond my area of expertise, d) i t seems plausible and reasonable to assess exposure potential in this manner. My work with aquatic birds in this ecosystem (Möller, G. 1996. Biogeochemical Interactions Affecting Hepatic Trace Element Levels in Aquatic Birds. Environmental Toxicology and C hemistry 15:1025

- 1033) suggests a complex dietary and environmental correlation of Cd

– Mn

– Se

– Hg

– As in vivo that may confound simple monotonic dose response models. Indeed, the tissue data for several of the sediment feeding birds demonstrated very high Se l evels compared to other species. While complex, d) it does appear reasonable to decrease the percentage of Corbula in scoter and scaup diet by one half for Se selenium exposure and the potential for reproductive endpoints.

Reviewer 5 While the 20% Corbul a diet used in the model is not unreasonable given the available data, it is entirely speculative and could be either lower or higher. A sensitivity analysis would be useful to understand the implications of this assumption. If all of the mollusk component of the rail diet (60%) were Corbula , would they become the driver of the proposed WQC? If so, what percentage Corbula in the diet causes this to be the case?

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20 **Scoter/Scaup: It has been observed that in the early part of the winter, scoter and scaup**  **live mainly in the shallower, northern parts of the Bay (Suisun Bay and San Pablo Bay) where**  Corbula **are prevalent, and consume mostly** Corbula **. However, in the latter part of the winter and early spring prior to migration, they move down to the deeper, Ce**  **ntral Bay area where**  Corbula **are not as available, and the scoter and scaup are thought to consume mostly herring that do not bioaccumulate selenium as effectively. They then**  **follow the coast north and continue to feed on herring prior to breeding and nest ing. It**  **appears that selenium moves directly from the diet of water birds into their eggs and not from internal tissue stores (Chapman et al., 2010). Given that scoter and scaup switch to**  **a low selenium diet for a period prior to migration as well as during migration, and that selenium may be depurated at a higher rate during migration, and that scoter and scaup**  **are likely to continue to feed on low selenium fish sources in the breeding and nesting grounds, is it reasonable to decrease the percentage of**  Cor bula **in scoter and scaup diet by 1⁄2 (from 90% to 45%), with respect to selenium exposure that could impact**  **reproductive endpoints? Please discuss.**
Four reviewers responded to this question. Two thought that this reduction seemed reasonable. One referenced h is earlier comment that it appear s reasonable to reduce the percentage of Corbula in scoter and scaup diet by one half for selenium exposure and the potential for reproductive endpoints . The second reviewer noted that decreasing the percentage of Corbula s eems reasonable, but that exposure frequency and duration could be considered more fully in the future, as in human risk assessments. He also suggested that additional bioaccumulation/elimination pharmacokinetics models combined with knowledge of migratory movement of the species might enhance the certainty of reducing the percentage of Corbula in scoter and scaup diet. Two other reviewers expressed concerns about this reduction. One of these reviewer s commented that it would be speculative and possibly no t protective of the species to decrease the percentage of Corbula in scoter and scaup diet by half. He noted that species respond to whatever concentration of a toxic substance they have in their tissue at a given time, not to the average concentration ove r time. The other reviewer wa s not convinced that the reduction in Corbula is accurate, and suggested that EPA should consider when egg proteins are deposited relative to the timing of ducks feeding on Corbula . Ducks may also depurate selenium relatively r apidly.

Reviewer Comments

Reviewer 1 It strikes me as rather speculative to do so, and possibly not protective of these species. Bear in mind that animals do not respond to average concentrations of toxic substances in their tissues, but rather to whatever concentration they have in their tis sue at any particular time. So, when they are feeding on Corbula, their Se concentrations is high and at that time they are vulnerable. It is not appropriate to average the Se that they see, and respond to, by including herring for part of the time. Imagine if you drank one glass of water each day for 100 consecutive days, but only one of those glasses had a toxic level (concentration X) of arsenic. You would die after drinking that one glass of arsenic. You should not conclude that you would respond to X/1 00 arsenic (the average arsenic concentration of the ten glasses) and be safe. 99 of those glasses would be harmless, and one would be lethal. The same may occur with the Se in these birds.

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21 Reviewer 2 Yes. It seems reasonable and is consistent with my earlier comments about adjusting intake estimates based on knowledge of exposure duration and frequency. But exposure frequency and duration might be considered more fully in the future as done with human risk assessment (EPA 540/1

- 89/002). The treatment i n “D. Draft Criteria. A. Applicable Waters; Magnitude, Duration and Frequency” reflects the approach in the federal draft document. However, a more granular treatment of the duration/frequency of exposure issues could improve the accuracy of judgments in m y opinion. In the future, additional bioaccumulation/elimination pharmacokinetics models combined with knowledge of the migratory movement of the species between habitats differing in selenium levels might enhance the certainty in this judgment.

Reviewer 3 See response provided under 2 .5.d.

Reviewer 4 See response provided under 2 .5.d.

Reviewer 5 While I follow the thinking used by EPA in setting the Corbula diet at 45% for scoter and scaup, I’m not convinced it is particularly accurate. In assessing po tential exposure of green sturgeon, EPA asserted that sturgeon eggs mature while adults are in the open ocean where Se exposure is low. It seems a similar line of thinking should be used in assessing risks to scoters and scaups. When are egg proteins depos ited relative to the timing of duck feeding on Corbula . If Corbula feeding occurs during this period, then exposure should be high, if not, then there is no relevant exposure with respect to the SFB WQC. It should also be pointed out that even if exposure is relatively high, there is evidence that ducks depurate Se relatively rapidly (19 d half life for mallards; (Heinz et al. 1990) ) and marine ducks deposit a low percentage of Se in eggs relative to freshwater species (Henny et al. 1995)

.

**Specifically for Insect**

**- eating Fish:** 

**e. Are the diet mixes for SFBD steelhead, Chinook salmon and delta smelt used in the**  **model scientifically supportable based on the literature (sources cited in review document)?**  **Please explain.**
All five reviewers responded to this question. Three generally agreed with this statement. Two reviewers commented that the insect diet mixes are well studied and scientifically supportable . One of these reviewers thought that EP A could have high confidence that these species were not consuming mollusks . The other thought the diet mixes seemed sound, but noted that he was not an expert in fish trophic ecology and habits. A third reviewer “supposed” that the diet mixes were scienti fically supportable but noted that diet depends on the abundance of prey insects at the particular place and time, which probably accounts for much of the variability in selenium concentrations observed in predator fish.
The fourth reviewer did not respon d directly to the statement but expressed the concern that, at least for salmonids, the diet mixes of forage fish and insects depend on the life

- stage of the animal. He suggested revising the models to separate adult and early life stages.

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22 Reviewer Comm ents

Reviewer 1 I suppose so, but again, how much of any given diet these fish happen to consume in any one location and any one time depends on the abundance of those prey insects at that particular time and place. These things vary enormously and probab ly account for much of the variability that one sees in Se concentrations in predator fish.

Reviewer 2 Based on a review of the supplied documents and tabulations in the draft SFBD document, the diet mixes do seem sound. However, I am not an expert on fish trophic ecology and habits.

Reviewer 3 As discussed above, at least for salmonids, the diet mixes will differ based on the life

stage of the animal. Returning adults will have a much larger forage fish component than insects and likely continual depo sition of Se into ova. In contrast, early life

- stage salmonids will have a greater insect component. The models should be revised to separate adult and early life stages.

Reviewer 4 With several decades of monitoring, the insect diet mixes for SFBD insect eating fish are e) scientifically supportable and well discussed and referenced in FWS, 2008.

Reviewer 5 The diets of SFBD steelhead, Chinook salmon and delta smelt are relatively well studied. These are probably the most reliable diet mixes of any of the species evaluated by EPA. Most importantly, there is high confidence that these species are not consuming mollusks.

**2 .6**  **Trophic Transfer Factors (TTFs): Discuss whether the TTF va**  **lues taken from the literature for individual species based on their food prey are scientifically supportable,**  **i.e., are the TTF factors in Table 4**

**- 3 (values taken from USGS, 2010, Figure 11 and pp. 21** 

**– 24; Presser and Luoma, 2010, Table 3; and USEPA, 201**  **4, pp. 71**

**- 77, each provided as**  **supporting material) scientifically supportable and appropriate? Are you aware of any other or more applicable data?** 

All five reviewers commented that the TTF values are scientifically supportable. One reviewer commented that the extraction and derivation of the TTF values were well founded, but suggested including stable isotope information for the trophic transfer for the spec ies in this report. He said that such information is readily available and provided several examples. Another reviewer noted that the TTFs are scientifically supportable, but that a four

- trophic

- level mixture should be used for adult returning salmonids. A third reviewer suggested that EPA not use the same TTF for fish in all cases, because species

- specific TTFs are available in some circumstances.

Reviewer Comments

Reviewer 1 These TTFs look good to me.

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23 Reviewer 2 The extraction and derivation of the TTF values seem well founded although the reason for such a small difference in TTF values for warm

- blooded birds and cold

- bolded fish mentioned earlier is not apparent. The TTF value computations are straightforward and consistent with our understanding o f trophic transfer of selenium. I do wonder if there is useful stable isotope information available for the trophic transfer for the key species in this report. Several such studies exist including those by authors of several supporting documents for this review. Perhaps their discussion was not prominent enough for me to recognize the inclusion of stable isotope information in the draft SFBD document. (A search of the 96 page draft pdf did not find the word “isotope.”) In the future, it might be useful to explore and discuss more the insights available from published stable isotope studies of these or similar species. These kinds of data might provide reinforcing detail to the estimated TTF values. Numerous publications of stable isotope studies of the subj ect area were found with a quick Google search. Some examples include the following:
Cloern, JE,EA Canuel and D Harris. 2002. Stable carbon and nitrogen isotope composition of aquatic and terrestrial plants of the San Francisco Bay estuarine system. Limnol

. Oceanogr., 47(3): 713

– 729
Croteau, MN, SN Luoma, and AR Stewart.2005. Trophic transfer of metals along freshwater food webs: Evidence of cadmium biomagnification in nature. Limnol. Oceanogr., 50(5): 1511

– 1519 Davis, JA et al. 2012. Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds. Environmental Research 119: 3

– 26 Gegrke, GE. 2011. Sources of mercury to San Francisco Bay surface sediment as revealed by mercury stable isotopes. Geochimica et Cosmochimica Act a, 75:691

- 705

Stewart ,AR et al. 2004. Food Web Pathway Determines How Selenium Affects Aquatic Ecosystems: A San Francisco Bay Case Study. Environ. Sci. Technol., 38 (17): 4 519

– 4526

Reviewer 3 The TTFs appear valid and are scientifically supportable. However, as discussed above, a 4 trophic level mixture should be used for adult returning salmonids (Figure 7; USEPA 2014).

Reviewer 4 The TTFs taken from the work of Presser and Luoma, USGS and the 2014 Draft Criteria are to my knowledge the best available TTF values that could be applied in a SFBD model; I am not aware of any additional TTF values that would supplant this data. The addi tional Corbula TTF values developed in USGS 2010 pp21

- 23 is coherently presented and contains well supported assumptions (e.g. dissolved Se exposure is trivial). The USGS 2010 Corbula TTF analysis is explicitly developed and cited in this reference and I a m not aware of any additional analyses of this caliber and quality.

Reviewer 5 In general, the TTFs taken from the literature and used in the WQC derivation are scientifically supportable. Specific to Corbula , yes I agree with the novel approach taken

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24 by USGS and adopted by EPA in this analysis. One issue of concern is that EPA has opted to use a TTF fish of 1.1 in all cases despite species

- specific TTFs being available in some circumstances. For example, USGS derived a TTF for white sturgeon of 0.8. It is unclear why EPA selected to use a mean value from across species, as generally in WQC derivation, spe cific

- specific data is given preference.
Also, see comments below on K d s and the need to consider concentration

- dependent TTFs.

The TTF for Corbula (17) was developed and discussed in USGS (2010) pp. 21

- 23 (provided as supporting material). Discuss wheth er this analysis is scientifically supportable. Would you recommend a different or better way to develop a site

- specific TTF for Corbula , given the available data? Are there additional data that the Agency should consider for developing a site

specific TTF for Corbula ?

All five reviewers noted that the TTF for Corbula is scientifically supportable. One reviewer pointed out that the TTF values are consistent with the general approach in the federal draft criterion document and are well

- tailored for the SFBD. He suggested supplementing relevant materials with stable isotope end member analyses, considering use of an expert elicitation exercise to improve the estimates.

Reviewer Comments

Reviewer 1 I don’t know of any involving Corbula beyond what is here.

Reviewer 2 The TTF values are consistent with the federal draft document’s general approach. They are tailored very logically for the SFBD. Reading the relevant materials such as Luoma and Presser (2009) and Presser and Luoma (2010) for more details reinfo rces this conclusion of consistency. I can think of no better way to estimate TTF values. Supplementing the current i n formation with stable isotope end member analyses might enhance insights. An expert elicitation exercise might improve TTF estimates if do ne carefully. Perhaps future reports could calculate and present the quantitative uncertainties in TTF estimates. More specific comments can be made below about the components (IR,AE, ke) going into the calculations as discussed in the USGS(2010) document.

IR Estimation “IR is determined by filtration rate (125 L/g clam/d, Cole et al., 1992) multiplied by C (median = 0.4 mg C/L) to achieve the units (g C/g clam/d) in the suspended particulate material at each sampling. In the average condition in the estuary, clams ingest 5% of their body weight per day in C across all days for which data is available. At an average of 2% C in suspended particulate material (again, the average across all data) they ingest 2.5 times their body weight per day in total suspended particulate

m aterial. If IR is calculated at each of three low river discharge months where data is available, the average is 1.7 g suspended particulate material/g clam/d. Experience has indicated that the ingestion model is more accurate when actual outcomes are used (or averaged) for the generic situation (i.e., 1.7 g suspended particulate

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25 material/g clam/d) as compared to taking the average of each component of the outcome and calculating a generic average. Therefore, we recommend using 1.7 g suspended particulate m aterial/g clam/d for modeling.”
Again I wonder about the variation in features such as filtration rates as a function of factors like temperature or salinity. Until provided with contrary information, it would be reasonable for a reader to suppose that fil tration rate varies substantially. Also variation associated with the general estimate of 0.4 mg C/L might be important to describe. Given the wide variation in k d values throughout the region of interest, this value might have substantial variation associ ated with it. Finally, according to classic Holling’s predator functional responses, the efficiency of removing particles during filtration can vary with the density of those particles in the waters. Some additional scrutiny of the uncertainty in the chose n values seems warranted.

AE Estimation “The derivation of a refined site

- specific AE based on individualized bioavailabilities of Selenium in suspended particulate material uses observed fractions of particulate organo

- Selenium, adsorbed Se, or elemental Se found in the estuary (Doblin et al., 2006) combined with individual AEs for those particulate Se species from the literature (living phytoplankton, AE = 60%; adsorbed on seston, AE = 40%; elemental, AE = 0%; Schlekat et al., 2004; Wang et al., 1996). Th e equation is: AE = (fraction organic particulate Se) (AE organic particulate Se) + (fraction adsorbed particulate Se) (AEadsorbed particulate Se) + (fraction elemental particulate Se)(AEelemental particulate Se). For example, if a site

- specific sample of suspended particulate material collected in the estuary contains 45% Se in phytoplankton at an assumed AE of 60%; 30% Se adsorbed on seston at an assumed AE of 40%; and 25% elemental Se in sediment at an assumed AE of 0%, then the composite AE = (0.45 x 0. 6) + (0.30 x 0.40) + (0.25 x 0) = 0.39 or 39% AE.”

This manner of estimating AE seems reasonable although the variation in the distribution of selenium among the three phases will likely change temporally and spatially. Future documents might spend more t ime discussing the variation expected in this and the resulting variation in AE.

K e Estimation



### “ We apply the efflux rate constant derived experimentally (Lee et al., 2006): k e = 0.03/d.”
Seems like a reasonable value chosen from a peer

- reviewed publicatio n.
Calculations “When we model for times when all data are available from the estuary, we use all data from that sampling date. When we model generically we employ mean parameters.” This is fine; however, insight might be enriched by more detail about the variation as well as the mean parameters. During the calculations, general decisions involving variation

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26 were made such as calculating values for specific regions or “ 

### excluding April, 1999 transects data as out of the norm (i.e., El Niño condition in the estuary). ” Relative to the last decision, one could argue that El Niño years are normal occurrences and clams will be there during those times.
Nonetheless, the handling of the calculations is fine and the report does provide some useful information about the expected variation, that is, “ We assume a TTF C.amurensis of 17 in modeling scenarios here. The range of TTFs across all estuarine conditions was 14

- 26. These values are higher than laboratory

- derived values primarily because ingestion rates are higher in these field systems than in experiments. This is the first calculation of a field

- derived TTF for a marine bivalve species. ”

Reviewer 3 The site

- specific model used to calculate TTF for Corbula is scientifically sound.

Reviewer 4 See r esponse provided under 2 .6

Reviewer 5 See response provided under 2 .6

.

**2**

**. 7**  **Partitioning Coefficients (K d**  **s): In general, selenium is more bioavailable for accumulation**  **into the food chain during dry/low flow (lentic) conditions, which is represented by higher K**  **d values. Is it scientifically supportable to use the 75**  **th percentile of the K**  **d values**  **for each of the landward and seaward transects in the modeling, since data representing critical (very dry) conditions are not available? Would the use of median or mean K**  **d values be more appropriate? Please explain your answer.** 
All five reviewers responded to this question. T wo reviewers noted that the 75 th percentile seems appropriately protective. One commented that this allows for precaution in dry/low

- flow higher

- known

- risk conditions, which is important considering the exceptionally dry conditions that are currently impacting the SFBD hydrograph. The other suggested that EPA evaluate concentration dependency in the assessment and consider using a quantile regression ap proach for determining the 75 th percentile K d .

Two reviewers comment ed that it is inappropriate to use the 75 th percentile of the K d values. One of them noted that K d s assumes that the element in question is in equilibrium between dissolved and particulate phases, which is not the case for suspended particles such as phytoplankton, to which the authors are apparently referring. He recommended that the authors refer to these values as concentration factors and that they use a range of values (rather than med ian of mean concentration factors), because the mean varies with phytoplankton assemblage and these natural communities typically change with the seasons. The other reviewer pointed out that the rationale for using the 75 th percentile is not clearly stated and that, given the uncertainties, use of a 95th percentile would be more conservative.
The fifth reviewer pointed out that the natural variation in K d values is high, and that means, if used, would not represent the populations of K d values. He suggests using a probabilistic or conservative approach (e.g., use of the 75 th percentile value would be better than using the mean or median).

Reviewer Comments

Reviewer 1 I think it is inappropriate to use Kds, or at least to call them Kds. This is because Kds

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27 assume that the element in question

— in this case, Se

— is in equilibrium between the dissolved and particulate phases. That may be the case for sediments, but it is not the case for suspended particles, which in many case would probably be phytoplankton, and I believe that this is the case to which the authors are referring. Se uptake by phytoplankton (and also other microorganisms at the base of the food chain). It is m ore appropriate to call them concentration factors. However, Se CFs can vary enormously (several orders of magnitude) among different types of phytoplankton, with chlorophytes being the lowest and diatoms and dinoflagellates among the highest (for selenite ). As for median or mean CFs, I would instead use a range of values, since a mean for some types of phytoplankton would be wholly inappropriate for another phytoplankton assemblage, and these natural communities typically change with season (seasonal succe ssion patterns among the phytoplankton communities) and nutrient concentrations.

Reviewer 2 The natural variation in the K d values is quite high. The constrained transects have k d values from 712 to 7,725 and the landward transect models use k d values from 554 to 12,650. Table 8 in USGS (2010) indicates means that if used, would be unrepresentative of the populations of K d values. In such a case, I would have suggested that a probabilistic approach be taken or that a conservative approach be app lied. The conservative approach of using the 75% percentile value seems better than using the mean or median.

Reviewer 3 The rationale for selection of the 75 th percentile is not clearly stated. Given the significant uncertainties in Kd as well as other c omponents within these systems (i.e. percentage of microalgae, peryphyton etc), one would think a 95 th percentile would be mor e conservative.

Reviewer 4 Without data, median or mean values build on absent data estimate that may underestimate risk without cause. Using the 75th percentile of the Kd values seems to be an appropriately protective estimate, allowing for precaution in dry/low flow higher know risk conditions. Point of Clarification
Without data, median or mean values build on absent data estima tes that may underestimate risk without cause. There is currently a significant absence of data for dry and critically dry seasonal impacts on sediment transects that are important in calculating Kd values. Table 4

- 7 has some limited data [C. Insect

- Eating Fish (see USGS, 2010 Table 10)] for below average water

- year types and the increase in observed Kd is consistent with our knowledge base of lentic/lotic flow dynamics on aquatic food web Se dynamics. While additional Se flux or mass balance analysis for t he impact of less flow into the SFBD during dry years that would be helpful, it is reasonable to assume that system hysteresis from existing sediment load and potential point discharges will maintain or more likely increase Kd in below average water

- years. Thus, using the 75th percentile of the Kd values seems to be an appropriately protective estimate, allowing for precaution in dry/low flow higher known risk conditions, especially in light of the exceptionally dry conditions that are currently impacting t he SFBD hydrograph.

Reviewer 5 Yes, I think it is appropriate to use the 75 th percentile K d in the modeling given the

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28 variability in K d s both seasonally and annually, and the uncertainty regarding K d s during very dry conditions. One uncertainty with K d s that EPA has not considered is that they tend to be inversely related to exposure concentration (see Poster by DeForest et al. provided with comments). EPA should evaluate concentration dependency in their assessment and consider using a quantile regressi on approach for determining the 75 th percentile K d . It is also worth noting that if EPA were to use this type of approach at each step in the model (i.e., 75 th percentile at each step), this would equate to a 98 th percentile site/condition (assuming each s tep is independent), which I believe most would consider adequately protective.

**2 .8**  Corbula **Concentrations: Information in Fuller et al. (2012) and in Thompson and**  **Parchaso (2010) (both provided) indicate that populations and population densities of** Corbu la **appear to decline in wet years, and increase in dry years. The articles suggest that** Corbula **may be sensitive to flow into the estuary and/or the salinity of the estuary (and other factors). The model shows that when the system has higher K**  **d values**  **(rep resentative of dryer years), more selenium is available for bioaccumulation and more**  **selenium accumulates in the food chain (which would drive the draft criteria to protect the use downward), and thus, we are concerned with accounting for critically dry** 
**co nditions. Please comment on the articles and these statements.** 
All five reviewers responded to this question. The comments of four reviewers generally supported this

concern. One reviewer commented that, given the information about population dynamics and K d values, the focus on dry periods seemed appropriate. A second reviewer noted that the descriptions provided regarding wet and dry years and K d values appeared to be scientifically sound. A third reviewer agreed with EPA’s assessment that the available literature indicates that Corbula density and distribution is constrained by low salinity and that the system exhibits higher K d s during drier years, resulting in more selenium bioaccumulation higher in the food chain. He suggested that EPA monitor the system during exceptionally dry conditions and revise the site

- specific water quality criteria based on these new data, when available. He did not think it reasonable to speculate on how much K d s would change u nder such conditions and a priori increase the K d s in the models. The fourth reviewer noted that the Fuller et al. (2012) and Thompson and Parchaso (2010) studies were conducted before current critically dry conditions in California, and that incorporating recent data may help validate population relationships with the hydrograph. He also pointed out that lentic and lotic selenium dynamics for freshwater may not translate well to the marine sediment exposure pathways in the SFBD.
The fifth reviewer questio ned the use of K d values. He reiterated his point in Section 2 .7 that K d s are inappropriate in this scenario, and added that higher phytoplankton concentration factors in dry seasons would translate into higher selenium levels in Corbula predators. He also referenced his response to the next question (Section 2 .9) that the South Bay is likely less well flushed than waters to the north, meaning that applying models from other areas to the South Bay may be risky.

Reviewer Comments

Reviewer 1 Again, Kds are inappropriate here, but if phytoplankton CFs of Se are higher in dry seasons, then Corbula concentrations should be correspondingly higher then, and this would be reflected in higher Se levels in Corbula predators. Also, see comment just below

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29 (No. 9) on South Bay being less well flushed.

Reviewer 2 I do not have any helpful insights to provide about Corbula population changes relative to flow regime. Given the information about population dynamics and kd values, the focus on dry periods seems appropr iate.

Reviewer 3 I cannot comment on the life history of Corbula. The descriptions provided regarding wet and dry years and Kd values appear scientifically sound.

Reviewer 4 The work of Fuller et al. (2012) and Thompson and Parchaso (2010) predate the current CA critically dry conditions. Since the Fuller work appears based on ongoing BDMA assessments, incorporating the most recent data may help validate population relationships with the hydrograph which has experienced some extreme changes in recent years. With flow reductions in critically dry years, Se flux into the SFBD may also be reduced although existing sediment Se loading may provide Se exposure hysteresis and landward shift of the sedimentation zone at the salt

– fresh water interface of the estuary. Increased salinity into the landward reaches of the SFBD may shift Corbula populations with shifting salinity. Lentic/lotic Se dynamics that are understood for freshwater systems may not translate well to marine sediment exposure pathways observed in the SFBD, as stated in “more selenium is available for bioaccumulation and more selenium accumulates in the food chain.” A quick trend analysis of the most recent BDMA data may be sufficient to explore this concern.

Reviewer 5 I agr ee with EPA’s assessment that the available literature indicates the density and distribution of Corbula is constrained by low salinity (i.e., freshwater) and that the system exhibits higher Kds during drier years resulting in more Se bioaccumulation highe r in the food chain. To some extent, EPA has accounted for the inter

- annual variability by selecting the 75th percentile Kd for modeling. However, the possibility of higher Kds during exceptionally dry years or seasons cannot be ruled out. In the absence o f any data in such conditions, I think all EPA can do at this point is commit to monitoring the system next time such conditions occur and ensuring the option of revising the site

- specific WQC based on new data. I do not think it reasonable to speculate on how much Kds will change under such conditions and a priori increase the Kds in the models.

**2 .9**  **Transects: Discuss whether it is reasonable and representative to use the focused**  **seaward transects to model the clam**

**- based food webs, in order to eliminate t**  **he end**

  ** member variability at the ocean (at the Golden Gate Bridge, the entrance to San Francisco** **Bay). Does the geology of the focused area (a wide Suisun Bay flowing into a constricted Carquinez Strait), and the importance of the area (the location of ref**  **inery discharges), favor the use of focused transects to best represent the clam** 

**- based food web for the**  **estuary? Please discuss.**
All five reviewers provided responses, though two did not respond directly to the question. Three reviewers agreed with EPA’s a pproach of using focused seaward transects. One of them commented that using transects is a valuable way to explore sediment variability concerning flow and sedimentation dynamics in the SFBD; however, yearly hydrograph changes and critically dry periods m ay induce unacceptable variability

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30 in any model input. Another pointed out that EPA eliminated the K d s from near Golden Gate to reduce variability; a better rationale for eliminating data would be the presence or absence of relevant species of fish and bir ds. The other two reviewers did not respond directly to the question. One of them noted that the South Bay is likely less well flushed than waters to the north, meaning that applying models from other areas to the South Bay may be risky. The other pointed out that selenium has incredible geospatial movement, so focusing on specific areas may not be fruitful given SFBD’s complexity.

Reviewer Comments

Reviewer 1 I don’t have an opinion on this. It might be worth noting here that the South Bay is probably less well flushed than waters to the north, so applying modeling from other areas to the South Bay may be risky.

Reviewer 2 This decision does seem reasonable in my opinion.

Reviewer 3 The life history and ecology of Corbula is outside of my expertise. Given the complexity of the SFBD and the movement of organisms throughout its confines indicates that focus upon specific areas particularly with an element with incredible geospatial movement may not be fruitful.

Reviewer 4 Transects are a valuable way to explore sediment variability with regards to flow and sedimentation dynamics in the SFBD. Focused transects can help define food web variability that would result from geology and fresh

- salt water estuarine sedimentation processes. Yearly hydrograph cha nges and critically dry periods may induce unacceptable variability in any model input, however.

Reviewer 5 Yes, I generally agree with EPA’s decision to use the focused seaward transects to model the clam

- based food webs. The end

- member K d s clearly repr esent a set of conditions that differ from the focused area and the focused area is most relevant for exposure to both fish and bird species of interest. Having said that, as the document currently reads, it appears that EPA eliminated the K d s from near Go lden Gate simply to reduce variability. I think a better rationale for eliminated these data would be related to the presence/absence of relevant receptors (i.e., fish and birds). Are there species we should be concerned about in the outer Bay where K d s ap pear to be significantly higher? Some discussion of this issue in the document would be useful.

**Results and Application**

**2**

**. 10**  **Results: Discuss whether the model input and results scientifically support the water**  **quality criteria for the three food chains r epresented. Are there better ways to represent**  **the three food webs in the modeling? Please explain.**
All five reviewers responded to this question. Three reviewers noted that the model input and results are scientifically sound and support the water quality criteria for the three food chains represented. One of

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31 these reviewers suggested it would have been useful to find stable isotope

- based studies from which end member analyses could have been done to provide additional insights and, potentially, validation . Another reiterated that the SFBD is exceptionally well

- studied in regards to water flows, selenium, fish, and wildlife; the TTF model, dietary estimates, and selection of key species represent the current best available knowledge. The third reviewer poin ted out that one of the three food chains will ultimately drive the water quality criteria. Two reviewers had reservations. One doubted whether it was appropriate to apply toxicological results for clam

- eating fish as a surrogate for clam

- eating birds, because birds and fish have different sensitivities and possibly different toxic endpoints. The other reiterated that, by neglecting the movement of spawning females to freshwater habitats, the model underestimates exposure to selenium due to consumption of mixed trophic levels during vitellogenesis

.

Reviewer Comments

Reviewer 1 I have doubts whether it is appropriate to apply toxicological results for clam

- eating fish as a surrogate for clam

- eating birds. Birds and fish do not have the same sensitivity or necessarily the same toxic endpoints to particular toxicants. It may be mor e defensible to apply modeling results from clam

- eating fish to insect

- eating fish since the toxic end points in the fish would presumably be the same, or approximately the same. Probably the most relevant information that would be needed would be to have Se concentration in specific tissues following various dietary routes and a toxic response to Se concentrations in that tissue. Such data would be quite difficult to obtain, even in controlled experiments, however.

Reviewer 2 The model input and use of the three food webs do seem scientifically sound. The studies drawn upon relative to the trophic ecology of the key species are solid. I do wonder if there were any stable isotope

- based studies from which end member analyses might have been done. Such stud ies might have provided additional insights and perhaps a level of validation.

Reviewer 3 This has been addressed above. In summary, neglecting the movement of spawning females to freshwater habitats may under

- estimate exposure to Se due to consumption of mixed trophic levels during vitellogenesis. Examples would include forage fish species as dietary items; thus, adding another TTF.

Reviewer 4 The review document model input and results support the water quality criteria for the three food chains repres ented. The models and model inputs used appear to be the best available approach using peer

- reviewed data and approaches. The SFBD is an exceptionally well

- studied aquatic ecosystem with regards to water flows, Se, fish and wildlife. The TTF model, the die tary estimates, and the selection of key species all represent our best available knowledge. Clam eating fish represent a worse case exposure scenario due to the Se sediment dynamics in the SFBD and the migratory habits and thus lessened exposure scenario of aquatic birds in this ecosystem. In this regard, it is scientifically supportable to use the modeling results for the clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish, in addition to the clam

eating fish themselves. Ot her than applying safety factors to account for species

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32 differences in exposure and Se sensitivity (not recommended) there are no other common approaches that can be applied across species.

Reviewer 5 Yes, the proposed approach, model input and results a ll appear scientifically defensible for establishing water quality criteria protective of all three food chains. It was appropriate for EPA to evaluate all three chains, but ultimately one of these food chains will drive the WQC. It is not surprising that clam

- eating fish are the driver and it is scientifically defensible to use WQC derived from this model to protect all species in the system.

**Discuss whether it is scientifically supportable to use the modeling results for the clam**

  ** eating fish as a** **surrogate to protect clam**

**- eating birds and insect** 

**- eating fish (all three**  **food webs) in addition to the clam**

**- eating fish themselves. Discuss whether there are**  **other scientifically defensible ways to use the modeling results to protect all the categories of**  **species for the SFBD.**
All five reviewers responded to this question. Two reviewers reiterated their earlier comments (in response to 2 .10) that the models inputs and results are scientifically valid. The other three reviewers had reservations about using the modeling results. One reviewer also referenced his response to 2 .10, in which he doubted whether it is appropriate to apply toxicological results for clam

eating fish as a surrogate for clam

- eating birds, because birds and fish have different sensitivi ties and potentially different toxic endpoints. Another reviewer commented that the general approach of using clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish is not appropriate, but that in this particular instance invo lving the SFBD area, the protective value derived for clam

- eating fish would also be protective of fish

- eating birds and insect

- eating fish. The fifth reviewer emphasized that the model should be revised to include “inbound” adult salmonids as a food

- wed category due to the continued exposure to developing ova . He also suggested that EPA consider adding uncertainty factors for salinity and selenium interactions in species in which maternally exposed embryos are discharged in salt or brackish water.

Review er Comments

Reviewer 1 See response provided under 2

. 10

.

Reviewer 2 Using clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish does not seem the best general approach. However, in this particular instance involving the SFBD area, the calculations demonstrated (see quoted materials in the answer to Question 12 below) that the protective value derived for clam

- eating fish would also be protective of the fish

- eating birds and insect

- eating fish.

Reviewer 3 As mentioned above, revision or modification of the model to include “inbound” adult salmonids as a food

- web category is essential. Salmonids are clearly insect

- eating going out to sea, but are fish

- eating when returning. The rationale for this is the continued exposure to de veloping ova, which upon fertilization will be embryonic. In addition, the

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33 addition of uncertainty factors for salinity and Se interactions may also be warranted in species were maternally exposed embryos are discharged in salt or brackish water environmen ts.

Reviewer 4 See response provided under 2 .10.

Reviewer 5 See response provided under 2 .10.

**2 .11**  **Draft Criteria: The USGS Ecosystem** 

**- Scale Selenium model was originally developed and**  **validated for SFBD, and a considerable amount of site**

**- specific data**  **are available and are used to model the estuary. EPA is using the model results to inform the criteria**  **development process, and presents draft multi**

**- media criteria in Chapter 4. These criteria**  **are a whole body or muscle fish tissue value and a clam tissue value that directly reflect**  **selenium levels that are considered to be protective of aquatic biota; and corresponding chronic and intermittent water column values, as well as a particulate concentration**  **value to facilitate regulatory controls of selenium so urces.**  **Given the relevance and detail of the USGS model and the abundance of site**

**- specific data,**  **discuss whether the criteria in the different media are scientifically defensible and protective for this aquatic ecosystem.** 
All five reviewers responded to this question. Four reviewers said that the USGS model provides a defensible approach for generating protective criteria. Three reviewers commended the abundance of data available for the SFBD. One reviewer noted that the USGS Ecosystem

- Scale Selenium mode l is the gold standard for modeling, balancing interpolation and extrapolation with required knowledge of species

- specific and ecosystem

- specific dynamics and values.
The fifth reviewer held a different view. He described the criteria as “ an excellent fir st step in setting site

specific values ,” but pointed out that the criteria are focused on Corbula

- consuming predators, assuming these are the most sensitive species to selenium toxicity. Consequently, in his opinion, these criteria are more appropriately site

- and species

- specific criteria for sturgeon, and may not be protective of “in

- bound” salmonid offspring or broadcast spawning species in brack ish or saltwater environments.

Reviewer Comments

Reviewer 1 I think that the USGS model provides a defensibl e approach for generating protective criteria for wildlife exposed to Se in SF Bay. It seems to me that the same processes that operate in SF Bay would occur in other regions, so the approach taken here should, in principle, be applicable to other water bo dies as well. However, the SF Bay system is unusually well studied with respect to Se, and it is doubtful that these kinds of detailed data for Se in other waters would be available.

Reviewer 2 This seems to be an unusual situation in which a remarkable amount of site

- specific information exists and appropriate synthesis of that information has already been done. That greatly enhances the development of the WQC draft document. The area

- specific data and its use to produce predictive models is definitely d efensible, and from my reading of the documents, is protective.

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34 Reviewer 3 The criteria are certainly an excellent first step in setting site

- specific values. However, the criteria seem to be focused exclusively on Corbula consuming predators with the

ass umption that they are the most sensitive species with regard to Se toxicity. Consequently, this criteria is more appropriately a site and species

- specific criteria primarily toward sturgeon. While numerically the values may protect ocean

- bound salmonids, it is unclear whether “in

- bound” offspring would experience the same protection. Likewise, it is unclear the value would protect broadcast spawning species in brackish or saltwater environments.

Reviewer 4 In our current understanding of Se impacts and e ffects, the USGS Ecosystem

- Scale Selenium model is the gold standard for modeling, balancing interpolation/extrapolation with required knowledge of species specific and ecosystem specific dynamics and values. As presented in this review document, the crite ria in the different media are scientifically defensible and protective for this aquatic ecosystem.

Reviewer 5 Yes, given the abundance of both site

- specific and detail of the USGS model, the proposed criteria in different media are both scientifically de fensible and protective of the SFB aquatic ecosystem. I have been involved with several dozen site

- specific water quality criteria/standard projects and the amount of data and model development involved in deriving these site

- specific criteria far exceed ( by an order of magnitude in most cases) the level of information typically available in these efforts.

**2 .12**  **Translator (Permits): EPA regulations generally call for NPDES permit limits to be**  **expressed in terms of total recoverable values (40 CFR 122.45(c)). The model applied in**  **this document yields calculations of water column values in the dissolved form. For most metals, EPA recommends dissolved values for water quality criteria, because the**  **dissolved form better represents the bioavailable frac tion in the water column to aquatic**  **biota. However, for selenium, aquatic biota can take in the dissolved and particulate fractions in the water column, which are then moved into and up the food chain.** 

**For most metals, EPA allows a translator to be used on the dissolved criteria value, to**  **determine a total recoverable permit limit; the translator is the fraction of the total recoverable metal in the downstream water (downstream of a discharge) that is**  **dissolved.**

**Given that selenium has different bioaccumula tion dynamics, what is an appropriate**  **method to derive a translator? Explain your answer.**
All five reviewers responded to this question. Two reviewers agreed with EPA’s approach of setting the translator at 1.0. One reviewer endorsed this approach because, he noted, it is clear that both dissolved and particulate selenium are bioavailable and toxic to aquatic organisms. The other reviewer supported EPA’s selection of a translator of 1 because it equates total recoverable concentrations with notionally bioav ialable selenium concentrations; this is appropriate for selenium because total recoverable selenium is likely the most reflective of the selenium available to the filter feeders such as Corbula

.

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35 The other three reviewers expressed different opinions. One of them noted that not all of the total recoverable selenium can be considered bioavailable and suggested that Luoma et al. (1992) 3 has the most direct answer to the selenium translator challenge. Another disagreed with the assertion that “the dissolved fo rm better represents the bioavailable fraction in the water column to aquatic biota.” For most metals, he noted, it is the dietary source that tends to predominate as a source of metals for aquatic animals

— this is particularly the case in saline situations such as San Francisco Bay. The fifth reviewer pointed out that selenium can exist in many forms, with the inorganic forms (selenite and selenate) predominating in most discharges; it is difficult to determine a translator from particulate to dissolved for ms when the most toxic form is likely organic. Without the ability to measure the most toxic selenium species and understand the kinetics of transformation to organic forms, tremendous uncertainty exists in set ting a translator value. Consequently, additio nal modeling is necessary to estimate the transformation rates of inorganic to organic (particulate) in a site

- specific manner in which nutrient input and hydrology will likely play significant roles.

Reviewer Comments

Reviewer 1 I would disagree with the assertion that “the dissolved form better represents the bioavailable fraction in the water column to aquatic biota.” For most metals, it is in fact, the dietary source that tends to predominate as a source of metals for aquatic animals

— this is particular ly the case in saline situations such as SF Bay.

Reviewer 2 If I understand the question, it refers to the derivation of a protective value in terms of dissolved selenium. What seems to be the pertinent materials from two parts of the draft report are pasted below.

“Dissolved Selenium: To protect clam

- eating fish at an EC10 level, the predicted protective dissolved selenium estuarine water column concentration is between 0. 137 and 0.685 μg/L, or between approximately 0.1 and 0.7 μg/L , based on available data. Using the mean value of the 75th percentile K d s (3,966), the predicted protective dissolved selenium estuarine water column concentration is 0.244 μg/L, or approximatel y 0.2 μg/L. Based on these analyses, the protective dissolved selenium water column concentration selected is 0.2 μg/L . This value should protect existing species in the estuary most of the time, under the environmental conditions used in the modeling.

The modeling for clam

- eating birds and insect

- eating fish results in predicted protective dissolved selenium water column concentrations between 0.126 and 2.046 μg/L, or between approximately 0.1 and 2 μg/L. The lower end of this range (0.1 μg/L) is the same as the lower end of the range of protective values for clam

- eating fish (0.1 μg/L). Using the mean value of the 75th percentile K d s, (3,966), the predicted protective dissolved selenium water column concentration is 0.224 μg/L for scoter and scaup, or appr oximately 0.2 μg/L, the same predicted value for clam

- eating fish. These analyses indicate that if clam

- eating fish are protected, clam

- eating birds and insect

- eating fish should also be protected.

Particulate Selenium: To protect clam

- eating fish at an EC 10 level, the predicted

3 Luoma et al

. 1992

. Determination of selenium bi oavailability to a benthic bivalve from particulate and solute pathways. Environ. Sci. Technol. 26 (3) pp. 485

– 491

.

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36 protective particulate selenium concentration is 0.969 μg/g dw, or approximately 1 μg/g dw , based on available data. The modeling for clam

- eating birds and insect

- eating fish results in predicted protective particulate selenium conc entrations between 0.890 and 2.894 μg/g dw, or between approximately 1 and 3 μg/g dw

. The lower end of this range is approximately equal to the protective value for clam

- eating fish; if clam

- eating fish are protected, clam

- eating birds and insect

- eating fi sh should also be protected.

Clam Tissue: To protect clam

- eating fish at an EC10 level, the predicted protective selenium invertebrate (prey) tissue concentration is 7.4 μg/g dw; the predicted protective selenium Corbula tissue concentration is 6.6 μg/g dw , or approximately 7 μg/g dw , based on available data. The modeling for clam

- eating birds results in predicted protective Corbula selenium concentrations between 6.8 and 9.9 μg/g dw, or between approximately 7 and 10 μg/g dw. The lower end of this range is approximately equal to the predicted protective value for clam

- eating fish (6.8 vs 6.6 μg/g dw); if clam

- eating fish are protected, clam

- eating birds should also be protected. All predicted values have been rounded to one significant digit. The rounded va lues provide a reasonable prediction of the appropriate protective values of allowable dissolved water column selenium, particulate selenium, and prey tissue selenium concentrations that will protect clam

- eating fish and birds, and insect

- eating fish in th e estuary. And the sentences below are most relevant to this question. Form of Permit Limits: Although draft water column criteria values are expressed in dissolved selenium concentrations, water quality

- based permit limits, in most instances, are require d to be in total recoverable values (40 CFR §122.45(c)). For most metals, criteria are in dissolved values because the dissolved fraction provides a better representation of the biologically active portion of the metal than does the total or total

recovera ble fraction (USEPA, 1996). When water quality criteria are in the dissolved form, a translator can be used to determine a total recoverable permit limit. The translator is the fraction of the total recoverable metal in the downstream water that is dissolv ed (ibid). However, for selenium, both the dissolved and particulate fractions are bioavailable to the aquatic biota. Thus, we used a translator of 1 in developing the draft criteria, an appropriate assumption for the Bay and Delta.

Answer

The dissolved se lenium is much less relevant than bioavailable selenium in particulates so urging for a focus on dissolved Se would not be as helpful as for other elements and back calculation from tissue concentrations to total recoverable metals in lentic and lotic waters seems preferable. Of all of the conventional water concentrations measured, total recoverable selenium is likely the most reflective of the selenium available to the filter feeders such as Corbula

. The selection of a translator of 1 equates total re coverable concentrations with notionally bioavailable selenium concentrations. In the case of selenium, that is a sound and appropriate conservative approach. The variability in total, recoverable, and dissolved selenium remains problematic regardless of t he approach.

Reviewer 3 Se can exist in dissolved states in many forms with the inorganic forms (selenite and selenite) predominating most discharges. Thus, it is difficult to determine a translator

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37 from particulate to dissolved forms when the most toxic form of Se is likely organic. Without the ability to measure the most toxic species of Se (SeMe or SeCys, or other organic forms) and understand the kinetics of transformation to organic forms, tremendous uncertainty exists in set ting a translator value. Consequently, additional modeling is necessary to estimate the transformation rates of inorganic to organic (particulate) in a site

- specific manner which nutrient input and hydrology will likely play significant roles.

Reviewer 4 As with lead (Pb) exposu re in birds and fish, not all of the total recoverable Se can be considered bioavailable (e.g. Zia et al., In vitro and in vivo approaches for the measurement of oral bioavailability of lead (Pb) in contaminated soils: A review. Environmental Pollution. Vo lume 159, Issue 10, October 2011, Pages 2320

– 2327). Luoma et al 1992 (Determination of selenium bioavailability to a benthic bivalve from particulate and solute pathways. Environ. Sci. Technol., 1992, 26 (3), pp 485

– 491) has perhaps the most direct answer to the Se translator challenge.

Reviewer 5 I agree with EPA’s approach of setting the translator at 1.0 for Se. For divalent metals, the dissolved fraction is clearly the dominant bioavailable metal fraction with respect to toxicity. While there is consid erable evidence that particulate divalent metals are can be bioaccumulated, their toxic potency appears to be considerably less than the dissolved form in most cases. In contrast, for Se, it is clear that both dissolved and particulate Se are bioavailable and toxic to aquatic organisms. Consequently, it is appropriate to use a translator of 1.0 for Se.

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38 **2.13 Other Comments**  **Provided**

Reviewer Comments

Reviewer 5 Section 1, Page 11, Last Paragraph : There are numerous papers and reports indicating Se is the most dose

- sensitive nutrient, but I have yet to see a quantitative analysis supporting this statement. Several other metals also have very narrow ranges between essentiality and toxicity that are c omparable to Se. For example, Cu (for snails) and Zn (for daphnids) both have very narrow ranges between essential requirements and toxicity. Unless EPA is aware of a quantitative analysis supporting this statement I suggest deleting it.
Section 1, Page 13 , First Paragraph : “ppt” stands for parts per thousand, not trillion in this instance. Section 2, Page 8, First Paragraph : Risk is an integration of exposure and effect (i.e., sensitivity). Just because clam

- eating species have the highest exposure doesn’t necessarily mean they are most at risk. It depends on their sensitivity as well. Section 4, Page 11, First Paragraph : It is unclear why bioaccumulative based effects are of greater concern that other effects. Why would this type of effect justify a lower effect threshold? Regardless of the mechanism, the EC10 represents a 10% effect.

**3.0 NEW INFORMATION PROV**  **IDED BY REVIEWERS**

This section compiles all new information that reviewers provided in their individual comments that were separate from responses to t he charge questions in Section 2 .0

.

Reviewer Comments

Reviewer 3 Refere n ces Beckon, WN. Cary Parkins, C., Maximovich, A. and Beckon, AV . (2008). A General Approach to Modeling Biphasic Relationships. Environ. Sci. Technol. 42, 1308

- 1314. Eaton, DL and Gilbert SG (2013) Principles of Toxicology IN: Casarett and Doull’s Toxicology : The Basic Science of Poisons. (C. Klaassen Editor) McGraw Hill Publishers, New York, NY. pp13

- 48. Fan, XA, Klein, M, Flanagan

- Steet, HR, Steet, R. (2010). Select ive Yolk Deposition and Mannose Phosphorylation of Lysosomal Glycosidases in Zebrafish Journal of Biological Chemistry 285:32946

- 32953. Janz, D.M., D.K. DeForest, M.L. Brooks, P.M. Chapman, G. Gilron, D. Hoff, W.A. Hopkins, D.O. McIntyre, C.A. Mebane, V.P . Palace, J.P. Skorupa and M.Wayland. (2010). Selenium Toxicity to Aquatic Organisms in: Chapman PM, Adams WJ, Brooks ML, Delos CG, Luoma SN, Maher WA, Ohlendorf HM, Presser TS, Shaw DP (eds). Ecological

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39 Assessment of Selenium in the Aquatic Environment. S ETAC Press, Pensacola, FL, USA.

Linares

- Casenave, J. Linville, R. Van Eenennaam, JP, Muguet,JB and Doroshovy, SI. (2015). Selenium tissue burden compartmentalization in resident white sturgeon ( Acipenser transmontanus ) of the San Francisco bay delta estuar y Environmental Toxicology and Chemistry, Vol. 34, No. 1, pp. 152

– 160, 2015 Lavado, R., Shi, D. and Schlenk, D. (2012). Effects of salinity on the toxicity and biotransformation of l

- selenomethionine in Japanese medaka ( Oryzias latipes ) embryos: Mechanisms of oxidative stress. Aquatic Toxicology108:18

- 22. Linville RG. 2006. Effects of selenium on health and reproduction of white sturgeon Acipenser transmontanus ): Implications for San Francisco Bay

- Delta. PhD thesis. University of California, Davis, CA, USA. Kupsco, A. and Schlenk D. (2014). Mechanisms of Selenomethionine Developmental Toxicity and the Impacts of Combined Hypersaline Conditions on Japanese Medaka ( Oryzias latipes ). Environ. Sci. Technol. 2014, 48, 7062−7068. Rigby, MC., Lemly, AD, Gerads, R.( 2014). Fish toxicity testing with selenomethionine spiked feed

– what's the real question being asked? Environ. Sci. Processes Impacts, 2014, 16, 511

– 517 Thomas, JK and Janz DM (2014) In ovo exposure to selenomethionine via maternal transfer increases deve lopmental toxicities and impairs swim performance in F1generation zebrafish ( Danio rerio ) Aquatic Toxicology 152:20

- 29. USEPA, 2014: U.S. Environmental Protection Agency. 2014. External Review Draft, Aquatic Life Ambient Water Quality Criteria for Selenium

– Freshwater 2014. Office of Water, EPA 822

- P

- 14

- 001. Washington, D.C.

Reviewer 5 References Heinz, G. H., G. W. Pendelton, A. J. Krynitsky and L. G. Gold (1990). "Selenium accumulation and elimination in mallards." Arch. Environ. Contam. Toxicol. 19 : 374

- 379. Henny, C. J., D. D. Rudis, T. J. Roffe and E. Robinson

- Wilson (1995). "Contaminants and sea ducks in Alaska and the circumpolar region." Environ. Hlth. Per. 103 (4): 41

- 49. Hilton, J. W., P. V. Hodson and S. J. Slinger (1980). "The requirement and toxicity of selenium in rainbow trout ( Salmo gairdneri )." J. Nutr. 110 (12): 2527

- 2535.

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# A PPENDIX 

# A

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# R EVIEW ERS

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## Charge to External Peer Reviewers Contract No. EP

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- 19 January 2015

External Peer Review of Draft Aquatic Life and Aquatic

- Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014)

BACKGROUND The United States Environmental Protection Agency (EPA), Office of Water is charged with protecting ecological integrity and human he alth from adverse anthropogenic, water

- mediated effects, under the purview of the Clean Water Act and Safe Drinking Water Act. At this time, t he Agency is revising its Clean Water Act (CWA) section 304(a) recommended aquatic life water quality criterion fo r selenium to reflect the latest science. States may adopt EPA’s recommended criteria, use it to develop site specific criteria, or develop their own scientifically defensible criteria. Once adopted and approved, a State’s Water Quality Standards (WQS) are then used to determine the level of pollution control necessary to attain the aquatic life designated use in a waterbody and to assess whether the waterbodies are impaired. EPA Region 9, assisted by EPA HQ, has developed the Draft Aquatic Life and Aquati c

- Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014) , and is seeking independent, external peer review on the draft criteria. The external peer review draft selenium criterion is intended to protect the aquatic co mmunities of the San Francisco Bay Delta generally, but also focuses on aquatic

dependent waterfowl, consistent with current science and the available data for the Bay and Delta Region. The document is not intended to address concerns about selenium toxicity to human health, nor to selenium contamination in other areas outside the Bay and Delta; t herefore, comments on human health or selenium

- related aquatic issues (unless clearly relatable) are beyond the scope of this peer review. In addition, recen tly, the USEPA released a national external peer review draft of a selenium chronic criterion for the protecti on of freshwater aquatic life. This document will be provided as supporting information, but is undergoing its own peer review process, so the nat ional external peer review draft criterion is also beyond the scope of this review. Although selenium may cause acute toxicity, the most deleterious effect on aquatic organisms and aquatic dependent wildlife is due to its bioaccu mulative properties. Organi sms in aquatic environments exposed to selenium accumulate it primarily through their diet, and not directly through exposure to water (Chapman et al. 2010). Selenium toxicity occurs primarily through transfer to the eggs and subsequent reproductive effect s. Consequently, in harmony with the recommendations of expert panels (U.S. EPA 1998, Chapman et al. 2010) and with peer review and public comments on the U.S. EPA (2004) draft criterion, the Agency recently developed a national chronic criterion reflectiv e of the effects of selenium concentrations in the reproductive tissues of fish species. EPA developed draft selenium freshwater aquatic life fish tissue guidance values based on the empirically measured relationship between reproductive effects and fish tissue values from dietary exposure from a range of field and lab oratory studies (USEPA, 2014). Using a simplified set of equations derived from the U.S.

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- 4 Geological Survey (USGS) Ecosystem

- Scale Selenium Model 1 (Presser and Luoma, 2010), EPA calculated
wat er column values associated with the fish tissue values, for lentic and lotic systems. Since the most significant exposure pathway of selenium to species of concern in the San Francisco Bay and Delta is through diet, the current applicable freshwater crite ria (5 ug/L) may not adequately p rotect species in the estuary. In particular, in the San Francisco Bay and Delta, the clam

- based food webs dominant in the Bay and brackish Delta accumulate selenium at a much higher rate than insect

- based food webs. Potamo corbula amurensis (P. amurensis) 2 or Corbula , an introduced clam species, can now be found throughout the San Francisco estuary. Corbula are abundant in San Pablo Bay, and Suisun Bay and Marsh, and accumulate selenium at roughly three times the rate of sup planted nat ive clam species (Cohen, 2011). The amount of selenium

laden food in an organism’s diet will affect its level of exposure. In San Francisco Bay, predator species that prefer to feed on Corbula , such as diving birds and sturgeon, are exposed to h igher levels of bioaccumulated and bioconcentrated 3 selenium than species that feed mainly on insects or higher order species within an insect

- based food web. Where national criteria guidance values may not be sufficiently protective, other scientifically defensible methods may be used to develop water qual ity criteria (40 CFR §131.11). In this document, site

- specific selenium water quality criteria protective of aquatic life and aquatic

- dependent wildlife for the San Francisco Bay and Delta are developed t o address bioaccumulation through dietary exposure to protect the estuary’s diverse living resources. The criteria are intended to apply to all waters of the San Francisco Bay and Delta. These waters are located within the jurisdictions of the San Francisc o Bay Regional Water Quality Control Board (SFRWQCB) and the Central Valley Regional Water Quality Control Board (CVRWQCB) of the State of California.

MATERIAL PROVIDED BY EPA FOR THE PEER REVIEW
The following materials are available on a secure ERG FTP project site and include:

• Peer Review Document: External Peer Review Draft Aquatic Life and Aquatic

- Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014) an d Appendices

• Supporting Materials (provided for reference during the review ) (a) External Peer Review Draft Aquatic Life Ambient Water Quality Criterion for Selenium

– Freshwater 2014 : Main text. The external peer review draft selenium criterion document inc ludes toxicity test results and analyses used to derive an egg

- ovary criterion element, a whole

- body and muscle tissue criterion element, and two water

- column elements; and

1 The model is a predictive tool to delineate the fate and biological uptake of selenium in an aquatic ecosystem, and is discussed in detail in the document to be reviewed.
2 Also commonly known has Corbula amurensis (C. amurensis) . The species correct taxo nomic name is Potamocorbula amurensis (P. amurensis) . See : Huber, M. (2014 ). Potamocorbula amurensis (Schrenck, 1861). Accessed through: World Register of Marine Species at http: //www.marinespecies.org/aphia.php?p=taxdetails&id=397175 on 2014

- 09

- 17.
3 Bioconcentration is the process by which an organism accumulates a chemical in its tissue from direct exposure to its surroundings (non

- dietary exposure).

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- 5 (b) External Peer Review Draft Aquatic Life Ambient Water Quality Criterion for Selenium

– Freshwater 2014 : Appendices A

- K. The appendices contain supporting information, including the results of several selenium toxicity tests used to derive the tissue

- based criterion element and EPA’s interpretation of the test results, and methods, data and analyses used to derive water

column elements.
Note : Sections that are specifically relevant to the development of the SSC for the San Francisco Bay Delta are outlined in the charge questions

. (c) U.S. Geological Survey, by Theresa Presser and Sam Lu oma. 2010. Ecosystem

- Scale Selenium Modeling in Support of Fish and Wildlife Criteria Development for the San Francisco Bay

- Delta Estuary, California Administrative Report . Menlo Park, California Note : This is included as Appendix A of the peer review docu ment. (d) Theresa S. Presser and Samual N. Luoma. 2010 . A Methodology of Ecosystem

- Scale Modeling of Selenium

. Integrated Environmental Assessment and Management, v.6, no. 4. p. 685

- 710 (plus Supporting Information). Note: This is included as Appendix B in App endix A of the peer review document.

• Supporting Reference Material: EPA is also providing supplemental information related to Corbula amerensis , and a key fish species of concern in the Bay Delta, the white and green sturgeon ( Acipencer transmontanous and A. medirostrus ). This information was influential in development of the water column, particulate and clam tissue values by informing the analysis concerning the percentage of Corbula in diet for sturgeon (and thus the TTF value used in the model). (a) Nicola De Riu, Jang

- Won Lee, Susie S.Y. Huang, Giuseppe Moniello, Silas S.O. Hung. 2014. Effect of dietary selenomethionine on growth performance, tissue burden, and histopathology in green and white sturgeon. Aquatic Toxicology 148, 65

– 73 (b) Steven C. Zeug, Annie Brodsky, Nina Kogut, A. Robin Stewart, Joseph E. Merz. 2014 Ancient fish and recent invaders: white sturgeon ( Acipenser transmontanus ) diet response to invasive species

- mediated changes in a benthic prey assemblage. Marine Ecology Progress Series. DO I: 110.3354/meps11002. Accepted for publication. (c) Janet K. Thompson and Francis Parchaso, Corbula amurensis Conceptual Model. US Geological Survey, 2010 (d) Heather Fuller, Karen Gehrts, Dan Riordan, and Jan Thompson. 2012. The biomass of Corbula and Corbicula in the low salinity zone, August 2011 Poster presented at Interagency Ecological Program 2012 Annual Workshop (April 18

- 20)

CHARGE QUESTIONS Overall Document Organization and Structure

1. Please comment on the overall construction and clarity of the documen t, i.e., is the layout of the document logical and is the document clearly written? Are there better ways to arrange a nd/or present the information? If so, please explain and describe. Questions on Use of Ecosystem

- Scale Selenium Model

2. Overall Toxicity Benchmarks/Development: The salinity throughout the San Francisco Bay and Delta (SFBD) varies from fresh to brackish to marine, and many of the species (or close relatives of

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- 6 the species) evaluated for the draft national freshwater criterion (USEPA, 2014 pp 57

- 62; 78

- 79 provided as supporting m aterial), live in the estuary. Given these considerations, discuss whether it is reasonable to use the draft national freshwater selenium criterion (tissue elements) for aquatic life in the SFBD. Are there better way s to estimate toxicity benchmark values for key aquatic life species, many of which a re anadromous, in the estuary? Please explain.

3. Toxicity Benchmarks/Green Sturgeon: For green sturgeon in the SFBD, juvenile growth is most likely the most sensitive end point

. A recent study, De Riu et al. (2014) (provided), using green sturgeon 4 observed selenium concentrations of 6

– 7 mg/kg dw (whole body) in the control treatment, which appears to reflect essentially a ‘no

- effect’ concentration for growth or other eff ects, and is similar to the draft national whole body criteria of 8.1 mg/kg dw (U SEPA, 2014 pp. 57

- 62; 78

- 79). In light of this study (and any other relevant data on green sturgeon), is the draft national benchmark value of 8.1 mg/kg dw protective of the j uvenile grow th endpoint for green sturgeon? Please explain your

answer.

4. Toxicity Benchmarks/Model: EPA uses log

- logistic modeling to determine EC10 values from environmental data. FWS has suggested that a biphasic model (Beckon et al., 2008 and Brian an d Cousens, 1989, cited in review document) may be a better model to represent effects of selenium, since a biphasic model shows a more representative progression of effect to living species (selenium is a micronutrient, but is toxic in both deficit concent rations and excessive concentrations). Studies on selenium effects in the literature (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document) do not appear to consider this issue, and study designs do not appear to tak e the issue into account.

a. Given that many of the studies in the literature often use a small (or zero) control concentration of selenium, and a low level of effect is observed (reflective of a deficient concentration), is the response to increasing lev els of selenium (into the excessive toxic amounts) better represented using a biphasi c model or log

- logistic model? Would the slope of the regression be skewed in either model, due to incomplete modeling of deficit effects?

b. Discuss whether it would be r easonable and appropriate to use a biphasic model to determine EC10 values for studies in the literature on representative or key species for the SFBD (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document), or whethe r the results of using a standard log

- logistic model would produce more representative results.

5. Species and Diet: Discuss whether the appropriate key species and food chains (webs) have been identified and appro priately applied for the SFBD.

a. Discuss whether the diets of the key species chosen in each of the identified food webs are reasonable based on the literature (sources cited in review document) and whether the calculations of the Trophic Transfer Factors (TTFs) are scientifically support able based on those diets (s ee specific questions below). Are there better ways to calculate TTFs for mi xed diets for the key species? Please explain.

4 Green sturgeon larvae were obtained from the offspring of three males and one female originating from the Klamath River along the Pacific Coast.

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A-7 Specifically for Clam

- eating Fish:

b. Are the diet mixes (i.e., percentage of Corbula ) for adult white sturgeon, juvenile white and green sturgeon, and splittail scientifically supportable based on the available literature (Zeug et al., 2014, provided; USFWS, 2008 pp. 51

- 59, provided as supporting material; and Feyrer et al., 2003, cited i n review document) ? Is it scientifically supportable to postulate that splittail do not consume as much Corbula , and are therefore not as much at

- risk as sturgeon?

c. Recent literature indicates that green sturgeon are more sensitive to selenium than white sturgeon (De Riu et al., 2014, provided; and Silvestre et al., 2010, cited in review document). Studies have also shown that adult green sturgeon primarily use the SFBD as a migratory corridor to freshwaters for spawning (http://exxexpartnership.com/wp

content/uploads/2010/10/GreenSturgeon

- _1_.pdf , cited in review document). If it is known that egg maturation in adult green sturgeon is completed prior to entering the estuary, discuss whether it is scientifically supportable to conclude that adult white stu rgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFB D (please provide references). Please comment on and discuss the potential for selenium exposure of adult green sturgeon during migration to play a role in reproductive toxicity, given the current state of knowledge on the reproductive biology and life history of green sturgeon. Specifically for Clam

- eating Birds:

d. Discuss whether the diet mixes for the California Ridgway’s rail, scoter and scaup are scientifically defensible based on the literature (sources cited in review document).

Rails: Specifically, discuss whether it is scientifically supportable to assume that California Ridgeway’s rails do not consume a large percentage of Corbula, given that their littoral feeding habitat does not overlap with the preferred habitat of Corbula

. Scoter/Scaup: It has been observed that in the early part of the winter, scoter and scaup live mainly in the shallower, norther n parts of the Bay (Suisun Bay and San Pablo Bay) where Corbula are prevalent, and consume mostly Corbula

. However, in the latter part of the winter and early spring prior to migration, they move down to the deeper, Central Bay area where Corbula are not as available, and the scoter and scaup are thought to consume mostly herring that do not bioaccum ulate selenium as effectively. They then follow the coast north and continue to feed on herring prior to breeding and nesting. It appears that selenium moves directly from the diet of water birds into their eggs and not from internal tissue stores (Chapman et al., 2010). Given that scoter and scaup switch to a low selenium diet for a period prior to migration as well as during migration, and that selenium may be depurated at a higher rate during migration, and that scoter and scaup are likely to continue to feed on low selenium fish sources in the breeding and nesting grounds, is it reasonable to decrease the percentage of Corbula in scoter and scaup diet by 1⁄2 (fr om 90% to 45%), with respect to selenium exposure that could impact reproductive endpoints? Please discuss.

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- 8 Specifically for Insect

- eating Fish:

e. Are the diet mixes for SFBD steelhead, Chinook salmon and delta smelt used in the model scientifically supportable based on the literature (sources cited in review document)? Please explain.

6. Trophic Transfer Factors (TTFs): Discuss whether the TTF values taken from the literature for individual species based on their food prey are scientifically supporta ble, i.e., are the TTF factors in Table 4

- 3 (values taken from USGS, 2010, Figure 11 and pp. 21

– 24; Presser and Luoma, 2010, Table 3; and USEPA, 2014, pp. 71

- 77, each provided as supporting material) scientificall y supportable and appropriate? Are you aw are of any other or more applicable data?

The TTF for Corbula (17) was developed and discussed in USGS (2010) pp. 21

- 23 (provided as supporting material). Discuss whether this analysis is scientifically supportable. Would you recommend a different or bett er way to develop a site

- specific TTF for Corbula , given the available data? Are there additional data that the Agency should consider for developing a site

- specific TTF for Corbula ?

7. Partitioning Coefficients (K d s): In general, selenium is more bioavail able for accumulation into the food chain during dry/low flow (lentic) conditions, which is represented by higher K d values. Is it scientifically supportable to use the 75 th percentile of the K d values for each of the landward and seaward transects in the modeling, since data representing critical (very dry) conditions are not available? Would the use of median or mean K d values be more appropriate? Please explain your

answer.

8. Corbula Concentrations: Information in Fuller et al. (2012) and in Thompson an d Parchaso (2010) (both provided) indicate that populations and population densities of Corbula appear to decline in wet ye ars, and increase in dry years. The articles suggest that Corbula may be sensitive to flow into the estuary and/or the salinity of th e estuary (and other factors). The model shows that when the system has higher K d values (representative of dryer years), more selenium is available for bioaccumulation and more selenium accumulates in the food chain (which would drive the draft criteria t o protect the use downward), and thus, we are concerned with accounting for critically dry conditions. Please comment on the articles and these statements.

9. Transects: Discuss whether it is reasonable and representative to use the focused seaward transec ts to model the clam

- based food webs, in order to eliminate the end

- member variability at the ocean (at the Golden Gate Bridge, the e ntrance to San Francisco Bay). Does the geology of the focused area (a wide Suisun Bay flowing into a constricted Carquinez Strait), and the importance of the area (the location of refinery discharges), favor the use of focused transects to best represent the clam

ba sed food web for the estuary? Please discuss. Results and Application

10. Results: Discuss whether the model input and results scientifically support the water quality criteria for the three food chains represented. Are there better ways to represent the th ree food webs in the modeling? Please explain.

Discuss whether it is scientificall y supportable to use the modeling results for the clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish (all three food webs) in addition to

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- 9 th e clam

- eating fish themselves. Discuss whether there are other scientifically defen sible ways to use the modeling results to protect all the categories of species for the SFBD.

11. Draft Criteria : The USGS Ecosystem

- Scale Selenium model was originally developed and validated for SFBD, and a considerable amount of site

- specific data are a vailable and are used to model the estuary. EPA is using the model results to inform the criteria development process, and presents draft mult i

- media criteria in Chapter 4. These criteria are a whole body or muscle fish tissue value and a clam tissue value that directly reflect selenium levels that are considered to be protective of aquatic biota; and corresponding chronic and intermittent water column values, as well as a particulate concentration value to facilitate regulatory controls of selenium sources

. Given the relevance and detail of the USGS model and the abundance of site

- specific data, discuss whether the criteria in the different media are scientifically defensible and protective for this aquatic ecosystem.

12. Translator (Permits): EPA regulat ions generally call for NPDES permit limits to be expressed in terms of total recovera ble values (40 CFR 122.45(c)). The model applied in this document yields calculations of water column values in the dissolved form. For most metals, EPA recommends dissol ved values for water quality criteria, because the dissolved form better represents the bioavailable fraction in the water column to aquatic biota. However, for selenium, aquatic biota can take in the dissolved and particulate fractions in the water column , which are then mov ed into and up the food chain.
For most metals, EPA allows a translator to be used on the dissolved criteria value, to determine a total recoverable permit limit; the translator is the fraction of the total recoverable metal in the down stream water (downstream of a discharge) that is dissolved. Given that selenium has different bioaccumulation dynamics, what is an appropriate method to derive a translator? Explain your answer.

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# A PPENDIX 

# B

I NDIVIDUAL 

# R EVIEWER 

# C OMMENTS

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## COMMENTS SUBMITTED B Y

Reviewer 1

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- 5 Overall Document Organization and Structure

1. Please comment on the overall construction and clarity of the document, i.e., is the layout of the document logical and is the document clearly written? Are there better ways to arrange and/or present the information? If so, please explain and describe.
I found the writing to be quite good

— that is the layout of logical argument and the clarity of the statements made. Considering the many other documents I have seen, this document is much better written than many others.
Questions on Use of Ecosystem

- Scale Selenium Model

2. Overall Toxicity Benchmarks /Development: The salinity throughout the San Francisco Bay and Delta (SFBD) varies from fresh to brackish to marine, and many of the species (or close relatives of the species) evaluated for the draft national freshwater criterion (USEPA, 2014 pp 57

- 62; 7 8

- 79 provided as supporting material), live in the estuary. Given these considerations, discuss whether it is reasonable to use the draft national freshwater selenium criterion (tissue elements) for aquatic life in the SFBD. Are there better ways to estima te toxicity benchmark values for key aquatic life species, many of which are anadromous, in the estuary? Please explain.
It is not appropriate to apply Se bioaccumulation data from freshwater studies to estuarine or saline waters. This is because sulfate i s abundant in saline waters but not in fresh water environments. Thus, selenate, which comes into phytoplankton cells, at the base of the food chain, is not appreciably taken up by cells in seawater where the sulfate concentration exceeds that of selenate by 10 million times (approx.). Selenite is the main species of inorganic selenium that is acquired by marine phytoplankton, which can also take up organic selenides. Thus, selenate uptake in freshwater regions may be quite appreciable (due to the lack of

c ompetition from sulfate) but not in saline waters. However, once the Se is in organisms, it is not clear whether freshwater organisms would respond to potentially toxic levels in the same way as would estuarine organisms. The abundance of potentially compe ting ions in saline waters may result in different sensitivities for the estuarine organisms, but I am unaware of a rigorous comparison of animal sensitivities to a given tissue Se concentration among marine vs. freshwater organisms. The ideal comparison w ould be for a euryhaline species in which Se toxicity is compared for the same species at freshwater and estuarine salinities. I am unaware if such a comparison has been made.

3. Toxicity Benchmarks/Green Sturgeon: For green sturgeon in the SFBD, juvenile gro wth is most likely the most sensitive endpoint. A recent study, De Riu et al. (2014) (provided), using green sturgeon 1 observed selenium concentrations of 6

– 7 mg/kg dw (whole body) in the control treatment, which appears to reflect essentially a ‘no

- effe ct’ concentration for growth or other effects, and is similar to the draft national whole body criteria of 8.1 mg/kg dw (USEPA, 2014 pp. 57

- 62; 78

- 79). In light of this study (and any other relevant data on green sturgeon), is the draft national benchmark value of 8.1 mg/kg dw protective of the juvenile growth endpoint for green sturgeon? Please explain your answer.

The difference between 8.1 and 6

- 7 mg/kg is probably not significant, especially given the variability in these data and the fact that the 5 th percentile projection of 8.1 is a projection, not a hard number. Thus, the green sturgeon have Se concentrations are about equal to the 5 th percentile projection of 8.1 whole body criterion

1 Green sturgeon larvae were obtained from the offspring of three males and one female originating from the Klamath River along the Pacific Coast.

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- 6 and these green sturgeon would appear to be just barely protected by the draft national benchmark value of 8.1 ppm.

4. Toxicity Benchmarks/Model: EPA uses log

- logistic modeling to determine EC10 values from environmental data. FWS has suggested that a biphasic model (Beckon et al., 2008 and Brian and Cousens, 1989, cited in review document) may be a better model to represent effects of selenium, since a biphasic model shows a more representative progression of effect to living species (selenium is a micronutrient, but is toxic in both deficit concentrations and excessive concentrations). Studies on selenium effects in the literature (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document) do not appear to consider this issue, and study designs do not appear to take the issue into accou nt.

a. Given that many of the studies in the literature often use a small (or zero) control concentration of selenium, and a low level of effect is observed (reflective of a deficient concentration), is the response to increasing levels of selenium (into the excessive toxic amounts) better represented using a biphasic model or log

- logistic model? Would the slope of the regression be skewed in either model, due to incomplete modeling of deficit effects?

I do not know.

b. Discuss whether it would be reasonab le and appropriate to use a biphasic model to determine EC10 values for studies in the literature on representative or key species for the SFBD (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document), or whether the

r esults of using a standard log

- logistic model would produce more representative results.
I do not know and have no opinions on this.

5. Species and Diet: Discuss whether the appropriate key species and food chains (webs) have been identified and appropria tely applied for the SFBD.

a. Discuss whether the diets of the key species chosen in each of the identified food webs are reasonable based on the literature (sources cited in review document) and whether the calculations of the Trophic Transfer Factors (T TFs) are scientifically supportable based on those diets (see specific questions below). Are there better ways to calculate TTFs for mixed diets for the key species? Please explain.
It is possible to mathematically calculate TTFs for mixed diets for a giv en species, but I am not sure that it is worth doing so, even though many animals consume more than one prey item....that is, nature is more complex than models typically depict. The reason I have concerns in doing so for mixed diets is that there is conside rable variability for any one predator/prey combination. If one were to consider two or more prey items, the variability compounds itself and does not help pinpoint or quantify a more “real” TTF. An example of this sort of variability can be seen for 6 different metals in fish consuming diverse prey, where about an order of magnitude differences are seen, largely based on the variabi lity in the metal concentrations in the different forms of prey. [see Mathews & Fisher, Sci. Total Environ. 407: 5156

- 5161 (2009).]
Specifically for Clam

- eating Fish:

b. Are the diet mixes (i.e., percentage of Corbula ) for adult white sturgeon, juvenile wh ite and green sturgeon, and splittail scientifically supportable based on the available literature (Zeug et al., 2014, provided; USFWS, 2008 pp. 51

- 59, provided as supporting material; and Feyrer et al., 2003,

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- risk as sturgeon?
This seems reasonable to me, but see my comment below (under “c”).

c. Recent literature indicates that green sturgeon are more sensitive to selenium than white sturgeon (De Riu et al., 2014, provided; and Silvestre et al., 2010, cited in review document). Studies have also shown that adult green sturgeon primarily use the SFBD as a migratory corridor to freshwaters for spawning (http: //exxexpartnership.com/wp

content/uploads/2010/10/GreenSturgeon

- _1_.pdf , cited in review document). If it is known that egg maturation in adult green sturgeon is completed prior to entering the estuary, discuss whether it is scientifically supportable to conclude that adult white sturgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFBD (please provide references). Please comment on and discuss the potential for selenium exposure of adult green sturgeon during migration to play a role in reproductive toxicity, given the current state of knowledge on the reproductive biology and life history of green sturgeon.
These questions are outside my expertise.
Specifically for Clam

- eating Birds:

d. Discuss whether the diet mixes for the California Ridgway’s rail, scoter and scaup are scientifically defensible based on the literature (sources cited in review document). Rails: Specifically, discuss whether it is scientifically s upportable to assume that California Ridgeway’s rails do not consume a large percentage of Corbula, given that their littoral feeding habitat does not overlap with the preferred habitat of Corbula

. This definitely makes sense. Scoter/Scaup: It has been observed that in the early part of the winter, scoter and scaup live mainly in the shallower, northern parts of the Bay (Suisun Bay and San Pablo Bay) where Corbula are prevalent, and consume mostly Corbula . However, in the latter part of the winter and earl y spring prior to migration, they move down to the deeper, Central Bay area where Corbula are not as available, and the scoter and scaup are thought to consume mostly herring that do not bioaccumulate selenium as effectively. They then follow the coast north and continue to feed on herring prior to breeding and nesting. It appears that selenium moves directly from the diet of water birds into their eggs and not from internal tissue stores (Chapman et al., 2010). Given that scoter and scaup switch to a low s elenium diet for a period prior to migration as well as during migration, and that selenium may be depurated at a higher rate during migration, and that scoter and scaup are likely to continue to feed on low selenium fish sources in the breeding and nestin g grounds, is it reasonable to decrease the percentage of Corbula in scoter and scaup diet by 1⁄2 (from 90% to 45%), with respect to selenium exposure that could impact reproductive endpoints? Please discuss.
It strikes me as rather speculative to do so, and possibly not protective of these species. Bear in mind that animals do not respond to average concentrations of toxic substances in their tissues, but rather to whatever concentration they have in their tissue at any particular time. So, when they are fee ding on Corbula, their Se concentrations is high and at that time they are vulnerable. It is not appropriate to average

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- 8 the Se that they see, and respond to, by including herring for part of the time. Imagine if you drank one glass of water each day for 10 0 consecutive days, but only one of those glasses had a toxic level (concentration X) of arsenic. You would die after drinking that one glass of arsenic. You should not conclude that you would respond to X/100 arsenic (the average arsenic concentration of the ten glasses) and be safe. 99 of those glasses would be har mless, and one would be lethal. The same may occur with the Se in these birds.
Specifically for Insect

- eating Fish:

e. Are the diet mixes for SFBD steelhead, Chinook salmon and delta smelt used in the model scientifically supportable based on the literature (sources cited in review document)? Please explain.
I suppose so, but again, how much of any given diet these fish happen to consume in any one location and any one time depends on the abundan ce of those prey insects at that particular time and place. These things vary enormously and probably account for much of the variability that one sees in Se concentrations in predator fish.

6. Trophic Transfer Factors (TTFs): Discuss whether the TTF value s taken from the literature for individual species based on their food prey are scientifically supportable, i.e., are the TTF factors in Table 4

- 3 (values taken from USGS, 2010, Figure 11 and pp. 21

– 24; Presser and Luoma, 2010, Table 3; and USEPA, 2014, pp. 71

- 77, each provided as supporting material) scientifically supportable and appropriate? Are you aware of any other or more applicable data?
These TTFs look good to me.

The TTF for Corbula (17) was developed and discussed in USGS (2010) pp. 21

- 23 (pr ovided as supporting material). Discuss whether this analysis is scientifically supportable. Would you recommend a different or better way to develop a site

- specific TTF for Corbula , given the available data? Are there additional data that the Agency shoul d consider for developing a site

- specific TTF for Corbula ?
I don’t know of any involving Corbula beyond what is here.

7. Partitioning Coefficients (K d s): In general, selenium is more bioavailable for accumulation into the food chain during dry/low flow (le ntic) conditions, which is represented by higher K d values. Is it scientifically supportable to use the 75 th percentile of the K d values for each of the landward and seaward transects in the modeling, since data representing critical (very dry) conditions are not available? Would the use of median or mean K d values be more appropriate? Please explain your

answer.
I think it is inappropriate to use Kds, or at least to call them Kds. This is because Kds assume that the element in question

— in this case, Se

— is in equilibrium between the dissolved and particulate phases. That may be the case for sediments, but it is not the case for suspended particles, which in many case would probably be phytoplankton, and I believe that this is the case to which the authors ar e referring. Se uptake by phytoplankton (and also other microorganisms at the base of the food chain). It is more appropriate to call them concentration factors. However, Se CFs can vary enormously (several orders of magnitude) among different types of phy toplankton, with chlorophytes being the lowest and diatoms and dinoflagellates among the highest (for selenite). As for median or mean CFs, I would instead use a range of values, since a

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- 9 mean for some types of phytoplankton would be wholly inappropriate fo r another phytoplankton assemblage, and these natural communities typically change with season (seasonal succession patterns among the phytoplankton communities) and nutrient concentrations.

8. Corbula Concentrations: Information in Fuller et al. (2012) an d in Thompson and Parchaso (2010) (both provided) indicate that populations and population densities of Corbula appear to decline in wet years, and increase in dry years. The articles suggest that Corbula may be sensitive to flow into the estuary and/or the salinity of the estuary (and other factors). The model shows that when the system has higher K d values (representative of dryer years), more selenium is available for bioaccumulation and more selenium a ccumulates in the food chain (which would drive the draft criteria to protect the use downward), and thus, we are concerned with accounting for critically dry conditions. Please comment on the articles and these statements.
Again, Kds are inappropriate her e, but if phytoplankton CFs of Se are higher in dry seasons, then Corbula concentrations should be correspondingly higher then, and this would be reflected in higher Se levels in Corbula predators. Also, see comment just below (No. 9) on South Bay being le ss well flushed.

9. Transects: Discuss whether it is reasonable and representative to use the focused seaward transects to model the clam

- based food webs, in order to eliminate the end

- member variability at the ocean (at the Golden Gate Bridge, the entrance to San Francisco Bay). Does t he geology of the focused area (a wide Suisun Bay flowing into a constricted Carquinez Strait), and the importance of the area (the location of refinery discharges), favor the use of focused transects to best represent the clam

- based food web for the estua ry? Please discuss.
I don’t have an opinion on this. It might be worth noting here that the South Bay is probably less well flushed than waters to the north, so applying modeling from other areas to the South Bay may be risky.
Results and Application

10. R esults: Discuss whether the model input and results scientifically support the water quality criteria for the three food chains represented. Are there better ways to represent the three food webs in the modeling? Please explain.
Discuss whether it is scien tifically supportable to use the modeling results for the clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish (all three food webs) in addition to the clam

- eating fish themselves. Discuss whether there are other scientifical ly defensible ways to use the modeling results to protect all the categories of species for the SFBD.
I have doubts whether it is appropriate to apply toxicological results for clam

- eating fish as a surrogate for clam

- eating birds. Birds and fish do not ha ve the same sensitivity or necessarily the same toxic endpoints to particular toxicants. It may be more defensible to apply modeling results from clam

- eating fish to insect

eating fish since the toxic end points in the fish would presumably be the same, or approximately the same. Probably the most relevant information that would be needed would be to have Se concentration in specific tissues following various dietary routes and a toxic response to Se concentrations in that tissue. Such data would be quite d ifficult to obtain, even in controlled experiments, however.

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- 10 11. Draft Criteria: The USGS Ecosystem

- Scale Selenium model was originally developed and validated for SFBD, and a considerable amount of site

- specific data are available and are used to model th e estuary. EPA is using the model results to inform the criteria development process, and presents draft multi

media criteria in Chapter 4. These criteria are a whole body or muscle fish tissue value and a clam tissue value that directly reflect selenium l evels that are considered to be protective of aquatic biota; and corresponding chronic and intermittent water column values, as well as a particulate concentration value to facilitate regulatory controls of selenium sources.
Given the relevance and detail of the USGS model and the abundance of site

- specific data, discuss whether the criteria in the different media are scientifically defensible and protective for this aquatic ecosystem.
I think that the USGS model provides a defensible approach for generat ing protective criteria for wildlife exposed to Se in SF Bay. It seems to me that the same processes that operate in SF Bay would occur in other regions, so the approach taken here should, in principle, be applicable to other water bodies as well. However, the SF Bay system is unusually well studied with respect to Se, and it is doubtful that these kinds of detailed data for Se in other waters would be available.

12. Translator (Permits): EPA regulations generally call for NPDES permit limits to be expressed in terms of total recoverable values (40 CFR 122.45(c)). The model applied in this document yields calculations of water column values in the dissolved form. For most metals, EPA recommends dissolved values for water quality criteria, because the dissolved form better represents the bioavailable fraction in the water column to aquatic biota. However, for selenium, aquatic biota can take in the dissolved and particulate fractions in the water column, which are then moved into and up the food chain. For most metals, EPA allows a translator to be used on the dissolved criteria value, to determine a total recoverable permit limit; the translator is the fraction of the total recoverable metal in the downstream water (downstream of a discharge) that is d issolved. Given that selenium has different bioaccumulation dynamics, what is an appropriate method to derive a translator? Explain your answer.
I would disagree with the assertion that “the dissolved form better represents the bioavailable fraction in the water column to aquatic biota.” For most metals, it is in fact, the dietary source that tends to predominate as a source of metals for aquatic animals

— this is particularly the case in saline situations such as SF Bay.

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## COMMENTS SUBMITTED BY
Reviewer 2

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## CHARGE QUESTIONS

Overall Document Organization and Structure

1. Please comment on the overall construction and clarity of the document, i.e., is the layout of the document logical and is the document clearly written? Are there better ways to arrange and/or present the information? If so, please explain and describe.

ANSWER
The format and conceptual flow are generally similar to those of the federal WQC

– Selenium draft, making it easily read and unders tood by those who have reviewed the federal treatment of the issue. In my opinion, the writing was clear and logical. There seemed to be a richer discussion and handling of uncertainties than in the federal document. It helped substantially to have signifi cant components of the material already published in the open literature (e.g., Luoma and Presser (ES&T 43:8483, 2009) and Presser and Luoma (IEAM 6:685, 2010). Those publications were polished and concise discussions of the central themes, especially the methodology applied for ecosystem

- scale modeling.
Unlike the federal document that focused on taxonomic groupings, this draft document categorized species first based on their ecological qualities such as trophic ecology and movement patterns. Species were considered based on how much they consumed high (e.g., bivalves) or low (e.g., insects) selenium prey. Diet composition, species movements and life histories were considered throughout the draft. This made it much easier to understand and logically move t hrough the materials. Whereas the federal draft document could not develop a comprehensive treatment of aquatic

- dependent wildlife (birds), the SFBD draft document was able to consider such important wildlife. This was a welcome addition that rounded

- out t he entire
treatment.
In my opinion, the draft SFBD document (and federal document) might have quantified the propagation of uncertainty more during the numerous computational steps so that the reader had a sound understanding with which to decide whether a ny modest differences in calculated values were real or simply reflective of the variation generated during the uncertain computations in the process. Question 3 below can be used as an example. Is the difference between 6

- 7 and 8.1 trivial relative to the uncertainty that emerges during computations? The 0.1 digit in the 8.1 suggests very high certainty that, given the details of the derivation, is dubious.

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- 14 Questions on Use of Ecosystem

- Scale Selenium Model

2. Overall Toxicity Benchmarks/Development: The salinity throughout the San Francisco Bay and Delta (SFBD) varies from fresh to brackish to marine, and many of the species (or close relatives of the species) evaluated for the draft national freshwater criterion (USEPA, 2014 pp 57

- 62; 78

- 79 provided

as s upporting material), live in the estuary. Given these considerations, discuss whether it is reasonable to use the draft national freshwater selenium criterion (tissue elements) for aquatic life in the SFBD. Are there better ways to estimate toxicity benchm ark values for key aquatic life species, many of which are anadromous, in the estuary? Please explain.

ANSWER
Although the national freshwater selenium criterion was used, its use and adjustments for the SFBD were reasonable and effectively incorporated. T he challenge with some species of concern being anadromous is a difficult one and I wondered while reading the document whether an exposure adjustment for duration of time within the estuary or freshwater regions might have included more detail. Try as I m ight, I could not think of an alternative that might have been materially more accurate. As an example, the EPA 540/1

- 89/002 for human risk assessment can incorporate more exposure duration and frequency details in its calculation of intake. But, given the lack of knowledge about bioaccumulation kinetics of the species of concern, this approach would likely not improve accuracy of estimates for the SFBD species. Perhaps a formal expert elicitation would further refine estimates.
As a very minor point relate d to the use of freshwater concepts and computations for the estuarine or marine regions of the SFBD, equating μ g/L and μ g/kg is fine for freshwater as done on page 11 for partition coefficients but water density differences in saline waters makes the equa ting of liters and kilograms slightly biased. (An average liter of Pacific seawater weighs roughly 1025 g, not 1000 g.)

3. Toxicity Benchmarks/Green Sturgeon: For green sturgeon in the SFBD, juvenile growth is most likely the most sensitive endpoint. A recent study, De Riu et al. (2014) (provided), using green sturgeon observed selenium concentrations of 6

– 7 mg/kg dw (whole body) in the control treatment, which appears to reflect essentially a ‘no

- effect’ concentration for growth or other effects, and is sim ilar to the draft national whole body criteria of 8.1 mg/kg dw (USEPA, 2014 pp. 57

- 62; 78

- 79). In light of this study (and any other relevant data on green sturgeon), is the draft national benchmark value of 8.1 mg/kg dw protective of the juvenile growth e ndpoint for green sturgeon? Please explain your answer.

ANSWER
The methods used in the federal draft criterion document and De Riu et al. (2014) focus on effects to individuals, not populations. Indeed, these documents often obfuscate this distinction by u sing laboratory study results that allow inferences about the statistical population of tested individuals to suggest protection of the ecological population . It is often the case that individual

- based metrics will be protective of populations but that could easily not be true for many species. This point was made very clearly by Kammenga et al. (1996) and others almost twenty years ago. Most laboratory

- derive d testing is done with species (“r

- strategists”) that are quite different from the green sturgeon. The sturgeon has a life history in which individuals take several years to mature, develop eggs over several years, do not spawn annually, live for a long ti me, but produce many eggs upon spawning. It is not a species for which an expedient heuristic

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- 15 like “if you protect the individual’s most sensitive life stage, you protect the species population viability” can be confidently applied.
Fortunately, because o f concerns of conservationists about the endangered green sturgeon, information has been gathered about the vital rates of most concern for this species, e.g., Beanesderfer et al (2007) and Heppell (2007). Beanesderfer et al. (2007) used demographic models to conclude, “ The model highlights the extreme sensitivity of a green sturgeon population to even small incremental increases in mortality where multiple ages are affected.” Heppell (2007) used a technique called elasticity analysis to identify vital rate s that most influence the growth rate (log λ ) of green sturgeon populations, concluding that “Elasticity analysis [demonstrated ] a high sensitivity of population growth rate to changes in the survival rate of subadult and adult fish.” The federal and SFBD proposed criteria focus on the less critical vital rate (reproduction and YOY) so they are likely protective and might even be overprotective.
Beamesderfer, RCP, ML Simpson, and GJ Kopp. 2007. Use of life history information in a population model of Sacr amento green sturgeon. Environ Biol Fish 79:315

- 337.
Heppell, SS. 2007. Elasticity analysis of green sturgeon life history. Environ Biol Fish 79:357

- 368.

Kammenga, JE, M Busschers, NM Van Straalen, PC Jepson, and J Baker. 1996. Stress induced fitness is no t determined by the most sensitive life

- cycle trait. Funct. Ecol. 10:106

- 111.

4. Toxicity Benchmarks/Model: EPA uses log

- logistic modeling to determine EC10 values from environmental data. FWS has suggested that a biphasic model (Beckon et al., 2008 and Br ian and Cousens, 1989, cited in review document) may be a better model to represent effects of selenium, since a biphasic model shows a more representative progression of effect to living species (selenium is a micronutrient, but is toxic in both deficit c oncentrations and excessive concentrations). Studies on selenium effects in the literature (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document) do not appear to consider this issue, and study designs do not appear to take the issue into account.

ANSWER
This concern crossed my mind several times during the review of the EPA draft federal WQC document. However, many of the data sets presented in that draft document were not designed to generate or sufficient for generating a reliable biphasic model. Exposures concentrations were not established to produce the number of observations needed in the region where the deviation from a conventional log

logistic model would be observed. So, the log

- logistic is generally t he best model if the data are inadequate for fitting a more complicated one.
The USFWS document (Beckon and Maurer, 2008) does contain relevant data sets (e.g., Figure 23 for weights of juvenile rainbow trout) that would allow a biphasic model to be fit. In such cases, the biphasic model does seem best. The supplied FWS report by Beckon (2009, Selenium effect levels for selected representative/surrogate species) has some examples illustrating my point. Figure 9 (salmon survival) and perhaps Figure 1 (malla rd hatchability) show data for which a biphasic model would be warranted. If additional supportive information were available, a biphasic model might be fit to the salmon survival data

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- 16 shown in Figure 10. A biphasic model for Figure 2 (mallard hatchability ) would be an over parameterization given the nature of the data set.
Given the above discussion, it seems that professional judgment might be used to decide which model is warranted. I suggest that more formal methods be codified to guide a user in decidi ng which model is best for their particular data set(s).

a. Given that many of the studies in the literature often use a small (or zero) control concentration of selenium, and a low level of effect is observed (reflective of a deficient concentration), is the response to increasing levels of selenium (into the excessive toxic amounts) better represented using a biphasic model or log

- logistic model? Would the slope of the regression be skewed in either model, due to incomplete modeling of deficit effects?

AN SWER
If one possessed a data set with which a biphasic model could be successfully fit, the biphasic model would be best. Obviously the slope derived from an inadequate data set for fitting the deficit response dynamics would be biased. But, if one forced a biphasic model onto an inadequate data set, the uncertainty in parameter estimates would increase. Many of the species response data sets illustrated in the federal draft document would be inadequate for fitting a biphasic model. As stated above, I sugge st that formal methods be established to aid users in deciding which model is best for their particular data set.

b. Discuss whether it would be reasonable and appropriate to use a biphasic model to determine EC10 values for studies in the literature on re presentative or key species for the SFBD (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document), or whether the results of using a standard log

- logistic model would produce more representative results.

ANSWER

Yes. F itting a biphasic model to data sets with enough points in the lower dose regions would result in a model that more accurately made predictions and conformed to our current understanding of the mechanisms of selenium influences on biological systems.

5. Sp ecies and Diet: Discuss whether the appropriate key species and food chains (webs) have been identified and appropriately applied for the SFBD.

a. Discuss whether the diets of the key species chosen in each of the identified food webs are reasonable based on the literature (sources cited in review document) and whether the calculations of the Trophic Transfer Factors (TTFs) are scientifically supportable based on those diets (see specific questions below). Are there better ways to calculate TTFs for mixed diets for the key species? Please explain.

ANSWER
I am not an expert on the trophic ecology of these species so the answer here is based on the information sent with the supplemental materials and that shown in tables of the draft SFBD document. Based on those data, the diet information appears to be reasonable. The TTF values seem well chosen; however, it might be useful to have some indication of the uncertainty associated with each estimate. In future reports, the

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One conventional addition would be to use end member analysis involving N, C and perhaps S stable isotopes to estimate dietary components for each key species. The UC

- Davis campus has an excellent facility to do the analyses and others have the required software such as the EPA’s IsoSource package. This being said, my judgment is that such an approach would not provide much better information than the one taken in the draft document.
Specifically for Clam

- eating Fish:

ANSWER
A brief clarification of one point would help relative to the general TTF values for clam

- eating fish and birds. The fish are cold

- blooded and the birds are warm

- blooded. The amount of selenium

- containing food that a fish consumes to maintain itself would be substantially less than that consumed by the warm

- blooded birds. Since selenium is accumulated mostly from food, it was confusing to me that the TTF values for fish were so close to those of birds. For fish and birds eating Corbula as 40

- 45% of their diet, Table 4

- 8 gives TTF fish = 1.1 and TTF duck egg = 1.8. Based on a physiological rule

- of

- thumb, my informal guess would have been a 5 - to 10

- fold difference, not the low 2

- fold difference in the tables. Clearly, there is an unexplained feature of the calculated TTF values that results in this ap parent incongruity.

b. Are the diet mixes (i.e., percentage of Corbula ) for adult white sturgeon, juvenile white and green sturgeon, and splittail scientifically supportable based on the available literature (Zeug et al., 2014, provided; USFWS, 2008 pp. 51

- 59, provided as supporting material; and Feyrer et al., 2003, cited in review document)? Is it scientifically supportable to postulate that splittail do not consume as much Corbula , and are therefore not as much at

- risk as sturgeon?

ANSWER

Yes. Based on m y review of the supplied materials and the discussions in the draft document, the diet mixes seem reasonable, including the differences between sturgeon and splittail consumptions of Corbula

.

c. Recent literature indicates that green sturgeon are more sensitive to selenium than white sturgeon (De Riu et al., 2014, provided; and Silvestre et al., 2010, cited in review document). Studies have also shown that adult green sturgeon primarily use the SFBD as a migratory corridor to freshwaters for spawning (http://exxexpartnership.com/wp

content/uploads/2010/10/GreenSturgeon

- _1_.pdf , cited in review document). If it is known that egg maturation in adult green sturgeon is completed prior to entering the estuary, discuss whether it is scientifically supportable to conclude that adult white sturgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFBD (please provide references). Please comment on and discuss the potential for selenium exposure of adult green sturgeon during migration to play a role in reproductive toxicity, given the current state of knowledge on the reproductive biology and life history of green sturge on.

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Yes. The judgment is sound that “ adult white sturgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon. ” As discussed above, one way of handling the migratory characteristics of each species would be to quant itatively include more details for exposure duration and frequency. The EPA document dealing with human risk assessment (EPA 540/1

- 89/002) includes exposure duration and frequency in its calculation of intake. Given the lack of knowledge about selenium bio accumulation kinetics in the sturgeon, this approach would likely not improve the accuracy of estimates. Perhaps a formal expert elicitation would improve future estimates.
Specifically for Clam

- eating Birds:

d. Discuss whether the diet mixes for the Calif ornia Ridgway’s rail, scoter and scaup are scientifically defensible based on the literature (sources cited in review document).
Rails: Specifically, discuss whether it is scientifically supportable to assume that California Ridgeway’s rails do not consum e a large percentage of Corbula , given that their littoral feeding habitat does not overlap with the preferred habitat of Corbula

.
ANSWER
Yes. This assumption seems defensible for the rail. Scoter/Scaup: It has been observed that in the early part of the winter, scoter and scaup live mainly in the shallower, northern parts of the Bay (Suisun Bay and San Pablo Bay) where Corbula are prevalent, and consume mostly Corbula . However, in the latter part of the winter and early spring prior to migration, they mov e down to the deeper, Central Bay area where Corbula are not as available, and the scoter and scaup are thought to consume mostly herring that do not bioaccumulate selenium as effectively. They then follow the coast north and continue to feed on herring pr ior to breeding and nesting. It appears that selenium moves directly from the diet of water birds into their eggs and not from internal tissue stores (Chapman et al., 2010). Given that scoter and scaup switch to a low selenium diet for a period prior to mi gration as well as during migration, and that selenium may be depurated at a higher rate during migration, and that scoter and scaup are likely to continue to feed on low selenium fish sources in the breeding and nesting grounds, is it reasonable to decrea se the percentage of Corbula in scoter and scaup diet by 1⁄2 (from 90% to 45%), with respect to selenium exposure that could impact reproductive endpoints? Please discuss.

ANSWER
Yes. It seems reasonable and is consistent with my earlier comments about adjusting intake estimates based on knowledge of exposure duration and frequency. But exposure frequency and duration might be considered more fully in the future as done with human risk assessment (EPA 540/1

- 89/002). The treatment in “D. Draft Criteria. A . Applicable Waters; Magnitude, Duration and Frequency” reflects the approach in the federal draft document. However, a more granular treatment of the duration/frequency of exposure issues could improve the accuracy of judgments in my opinion. In the futur e, additional bioaccumulation/ elimination pharmacokinetics models combined with knowledge of the migratory movement of the species between habitats differing in selenium levels might enhance the certainty in this judgment.

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- 19 Specifically for Insect

- eating Fish:

e. Are the diet mixes for SFBD steelhead, Chinook salmon and delta smelt used in the model scientifically supportable based on the literature (sources cited in review document)? Please explain.

ANSWER
Based on a review of the supplied documents and t abulations in the draft SFBD document, the diet mixes do seem sound. However, I am not an expert on fish trophic ecology and habits.

6. Trophic Transfer Factors (TTFs): Discuss whether the TTF values taken from the literature for individual species based o n their food prey are scientifically supportable, i.e., are the TTF factors in Table 4

- 3 (values taken from USGS, 2010, Figure 11 and pp. 21

– 24; Presser and Luoma, 2010, Table 3; and USEPA, 2014, pp. 71

- 77, each provided as supporting material) scientifi cally supportable and appropriate? Are you aware of any other or more applicable data?

ANSWER
The extraction and derivation of the TTF values seem well founded although the reason for such a small difference in TTF values for warm

- blooded birds and cold

- bo lded fish mentioned earlier is not apparent. The TTF value computations are straightforward and consistent with our understanding of trophic transfer of selenium. I do wonder if there is useful stable isotope information available for the trophic transfer for the key species in this report. Several such studies exist including those by authors of several supporting documents for this review. Perhaps their discussion was not prominent enough for me to recognize the inclusion of stable isotope information in the draft SFBD document. (A search of the 96 page draft pdf did not find the word “isotope.”) In the future, it might be useful to explore and discuss more the insights available from published stable isotope studies of these or similar species. These kind s of data might provide reinforcing detail to the estimated TTF values.
Numerous publications of stable isotope studies of the subject area were found with a quick Google search. Some examples include the following:
Cloern, JE,EA Canuel and D Harris. 2002. Stable carbon and nitrogen isotope composition of aquatic and terrestrial plants of the San Francisco Bay estuarine system. Limnol. Oceanogr., 47(3): 713

– 729

Croteau, MN, SN Luoma, and AR Stewart.2005. Trophic transfer of metals along freshwater food webs : Evidence of cadmium biomagnification in nature. Limnol. Oceanogr., 50(5): 1511

– 1519
Davis, JA et al. 2012. Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds. Environmental Research 119: 3

– 26
Gegrke, GE. 20 11. Sources of mercury to San Francisco Bay surface sediment as revealed by mercury stable isotopes. Geochimica et Cosmochimica Acta, 75:691

- 705

Stewart , AR et al. 2004. Food Web Pathway Determines How Selenium Affects Aquatic Ecosystems: A San Francisco Bay Case Study. Environ. Sci. Technol., 38 (17): 4519

– 4526

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- 20 The TTF for Corbula (17) was developed and discussed in USGS (2010) pp. 21

- 23 (provided as supporting material). Discuss whether this analysis is scientifically supportable. Would you recommend a different or better way to develop a site

- specific TTF for Corbula , given the available data? Are there additional data that the Agency should consider for developing a site

- specific TTF for Corbula ?

ANSWER
The TTF values are consistent with the federal draft document’s general approach. They are tailored very logically for the SFBD . Reading the relevant materials such as Luoma and Presser (2009) and Presser and Luoma (2010) for more details reinforces this conclusion of consistency. I can think of no better way to estimate TTF values. Supplementing the current information with stabl e isotope end member analyses might enhance insights. An expert elicitation exercise might improve TTF estimates if done carefully. Perhaps future reports could calculate and present the quantitative uncertainties in TTF estimates.
More specific comments c an be made below about the components (IR,AE, k e ) going into the calculations as discussed in the USGS(2010) document.

IR Estimation
“IR is determined by filtration rate (125 L/g clam/d, Cole et al., 1992) multiplied by C (median = 0.4 mg C/L) to achieve t he units (g C/g clam/d) in the suspended particulate material at each sampling. In the average condition in the estuary, clams ingest 5% of their body weight per day in C across all days for which data is available. At an average of 2% C in suspended parti culate material (again, the average across all data) they ingest 2.5 times their body weight per day in total suspended particulate material. If IR is calculated at each of three low river discharge months where data is available, the average is 1.7 g susp ended particulate material/g clam/d. Experience has indicated that the ingestion model is more accurate when actual outcomes are used (or averaged) for the generic situation (i.e., 1.7 g suspended particulate material/g clam/d) as compared to taking the av erage of each component of the outcome and calculating a generic average. Therefore, we recommend using 1.7 g suspended particulate material/g clam/d for modeling.”
Again I wonder about the variation in features such as filtration rates as a function of fa ctors like temperature or salinity. Until provided with contrary information, it would be reasonable for a reader to suppose that filtration rate varies substantially. Also variation associated with the general estimate of 0.4 mg C/L might be important to describe. Given the wide variation in k d values throughout the region of interest, this value might have substantial variation associated with it. Finally, according to classic Holling’s predator functional responses, the efficiency of removing particles d uring filtration can vary with the density of those particles in the waters. Some additional scrutiny of the uncertainty in the chosen values seems warranted.

AE Estimation
“The derivation of a refined site

- specific AE based on individualized bioavailabili ties of Selenium in suspended particulate material uses observed fractions of particulate organo

- Selenium, adsorbed Se, or elemental Se found in the estuary (Doblin et al., 2006) combined with individual AEs for those particulate Se species from the litera ture (living phytoplankton, AE = 60%; adsorbed on seston, AE = 40%; elemental, AE = 0%; Schlekat et

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- 21 al., 2004; Wang et al., 1996). The equation is: AE = (fraction organic particulate Se) (AE organic particulate Se) + (fraction adsorbed particulate Se) (AEa dsorbed particulate Se) + (fraction elemental particulate Se)(AEelemental particulate Se). For example, if a site

- specific sample of suspended particulate material collected in the estuary contains 45% Se in phytoplankton at an assumed AE of 60%; 30% Se ad sorbed on seston at an assumed AE of 40%; and 25% elemental Se in sediment at an assumed AE of 0%, then the composite AE = (0.45 x 0.6) + (0.30 x 0.40) + (0.25 x 0) = 0.39 or 39% AE.”
This manner of estimating AE seems reasonable although the variation in the distribution of selenium among the three phases will likely change temporally and spatially. Future documents might spend more time discussing the variation expected in this and the resulting variation in AE.

K e Estimation
“We apply the efflux rate con stant derived experimentally (Lee et al., 2006): ke = 0.03/d.”
Seems like a reasonable value chosen from a peer

- reviewed publication.

Calculations
“When we model for times when all data are available from the estuary, we use all data from that sampling da te. When we model generically we employ mean parameters.”
This is fine; however, insight might be enriched by more detail about the variation as well as the mean parameters. During the calculations, general decisions involving variation were made such as calculating values for specific regions or “ excluding April, 1999 transects data as out of the norm (i.e., El Niño condition in the estuary). ” Relative to the last decision, one could argue that El Niño years are normal occurrences and clams will be there during those times.
Nonetheless, the handling of the calculations is fine and the report does provide some useful information about the expected variation, that is, “ We assume a TTF C.amurensis of 17 in modeling scenarios here. The range of TTFs across all estuarine conditions was 14

- 26. These values are higher than laboratory

- derived values primarily because ingestion rates are higher in these field systems than in experiments. This is the first calculation of a field

- derived TTF for a marine bivalve speci es. ”

7. Partitioning Coefficients (K d s): In general, selenium is more bioavailable for accumulation into the food chain during dry/low flow (lentic) conditions, which is represented by higher K d values. Is it scientifically supportable to use the 75th per centile of the K d values for each of the landward and seaward transects in the modeling, since data representing critical (very dry) conditions are not available? Would the use of median or mean K d values be more appropriate? Please explain your

answer.

ANSWER

The natural variation in the K d values is quite high. The constrained transects have k d values from 712 to 7,725 and the landward transect models use k d values from 554 to 12,650. Table 8 in USGS (2010) indicates means that if used, would be unrepre sentative of the populations of K d values. In such a case, I would have suggested that a probabilistic approach be taken or that a conservative approach be applied. The conservative approach of using the 75% percentile value seems better than using the mea n or median.

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- 22 8. Corbula Concentrations: Information in Fuller et al. (2012) and in Thompson and Parchaso (2010) (both provided) indicate that populations and population densities of Corbula appear to decline in wet years, and increase in dry years. The art icles suggest that Corbula may be sensitive to flow into the estuary and/or the salinity of the estuary (and other factors). The model shows that when the system has higher K d values (representative of dryer years), more selenium is available for bioaccumu lation and more selenium accumulates in the food chain (which would drive the draft criteria to protect the use downward), and thus, we are concerned with accounting for critically dry conditions. Please comment on the articles and these statements.

ANSWER
I do not have any helpful insights to provide about Corbula population changes relative to flow regime. Given the information about population dynamics and k d values, the focus on dry periods seems appropriate.

9. Transects: Discuss whether it is reasonab le and representative to use the focused seaward transects to model the clam

- based food webs, in order to eliminate the end

- member variability at the ocean (at the Golden Gate Bridge, the entrance to San Francisco Bay). Does the geology of the focused area (a wide Suisun Bay flowing into a constricted Carquinez Strait), and the importance of the area (the location of refinery discharges), favor the use of focused transects to best represent the clam

- based food web for the estuary? Please discuss.

ANSWER

Thi s decision does seem reasonable in my opinion. Results and Application

10. Results: Discuss whether the model input and results scientifically support the water quality criteria for the three food chains represented. Are there better ways to represent the three food webs in the modeling? Please explain.

ANSWER
The model input and use of the three food webs do seem scientifically sound. The studies drawn upon relative to the trophic ecology of the key species are solid. I do wonder if there were any stable isotope

based studies from which end member analyses might have been done. Such studies might have provided additional insights and perhaps a level of validation. Discuss whether it is scientifically supportable to use the modeling results for the clam

- eat ing fish as a surrogate to protect clam

- eating birds and insect

- eating fish (all three food webs) in addition to the clam

- eating fish themselves. Discuss whether there are other scientifically defensible ways to use the modeling results to protect all the categories of species for the SFBD.

ANSWER
Using clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish does not seem the best general approach. However, in this particular instance involving the SFBD area, the calculations dem onstrated (see quoted materials in the answer to Question 12 below) that the protective value derived for clam

- eating fish would also be protective of the fish

- eating birds and insect

- eating fish.

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- 23 11. Draft Criteria: The USGS Ecosystem

- Scale Selenium model was originally developed and validated for SFBD, and a considerable amount of site

- specific data are available and are used to model the estuary. EPA is using the model results to inform the criteria development process, and presents draft multi

media cri teria in Chapter 4. These criteria are a whole body or muscle fish tissue value and a clam tissue value that directly reflect selenium levels that are considered to be protective of aquatic biota; and corresponding chronic and intermittent water column val ues, as well as a particulate concentration value to facilitate regulatory controls of selenium sources.

Given the relevance and detail of the USGS model and the abundance of site

- specific data, discuss whether the criteria in the different media are scie ntifically defensible and protective for this aquatic ecosystem.

ANSWER

This seems to be an unusual situation in which a remarkable amount of site

- specific information exists and appropriate synthesis of that information has already been done. That greatl y enhances the development of the WQC draft document. The area

- specific data and its use to produce predictive models is definitely defensible, and from my reading of the documents, is protective.

12. Translator (Permits): EPA regulations generally call for NPDES permit limits to be expressed in terms of total recoverable values (40 CFR 122.45(c)). The model applied in this document yields calculations of water column values in the dissolved form. For most metals, EPA recommends dissolved values for water quality criteria, because the dissolved form better represents the bioavailable fraction in the water column to aquatic biota. However, for selenium, aquatic biota can take in the dissolved and particulate fractions in the water column, which are then mov ed into and up the food chain.
For most metals, EPA allows a translator to be used on the dissolved criteria value, to determine a total recoverable permit limit; the translator is the fraction of the total recoverable metal in the downstream water (downst ream of a discharge) that is dissolved.
Given that selenium has different bioaccumulation dynamics, what is an appropriate method to derive a translator? Explain your answer.

ANSWER
If I understand the question, it refers to the derivation of a protective value in terms of dissolved selenium. What seems to be the pertinent materials from two parts of the draft report are pasted below.

“Dissolved Selenium: To protect clam

- eating fish at an EC10 level, the predicted protective dissolved selenium estuarine wa ter column concentration is between 0.137 and 0.685 μg/L, or between approximately 0.1 and 0.7 μg/L , based on available data. Using the mean value of the 75th percentile K d s (3,966), the predicted protective dissolved selenium estuarine water column concen tration is 0.244 μg/L, or approximately 0.2 μg/L. Based on these analyses, the protective dissolved selenium water column concentration selected is 0.2 μg/L . This value should protect existing species in the estuary most of the time, under the environmenta l conditions used in the modeling.
The modeling for clam

- eating birds and insect

- eating fish results in predicted protective dissolved selenium water column concentrations between 0.126 and 2.046 μg/L, or between approximately 0.1 and 2 μg/L. The lower end of this range (0.1 μg/L) is the same as the lower end of the range of protective values for clam

-

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- 24 eating fish (0.1 μg/L). Using the mean value of the 75th percentile K d s, (3,966), the predicted protective dissolved selenium water column concentration is 0. 224 μg/L for scoter and scaup, or approximately 0.2 μg/L, the same predicted value for clam

- eating fish. These analyses indicate that if clam

- eating fish are protected, clam

- eating birds and insect

- eating fish should also be protected.

Particulate Selenium : To protect clam

- eating fish at an EC10 level, the predicted protective particulate selenium concentration is 0.969 μg/g dw, or approximately 1 μg/g dw
, based on available data. The modeling for clam

- eating birds and insect

- eating fish results in predicted protective particulate selenium concentrations between 0.890 and 2.894 μg/g dw, or between approximately 1 and 3 μg/g dw

. The lower end of this range is approximately equal to the protective value for clam

- eating fish; if clam

- eating fish are pro tected, clam

- eating birds and insect

- eating fish should also be protected.

Clam Tissue: To protect clam

- eating fish at an EC10 level, the predicted protective selenium invertebrate (prey) tissue concentration is 7.4 μg/g dw; the predicted protective seleni um Corbula tissue concentration is 6.6 μg/g dw, or approximately 7 μg/g dw , based on available data. The modeling for clam

- eating birds results in predicted protective Corbula selenium concentrations between 6.8 and 9.9 μg/g dw, or between approximately 7 and 10 μg/g dw. The lower end of this range is approximately equal to the predicted protective value for clam

- eating fish (6.8 vs 6.6 μg/g dw); if clam

- eating fish are protected, clam

- eating birds should also be protected.
All predicted values have been ro unded to one significant digit. The rounded values provide a reasonable prediction of the appropriate protective values of allowable dissolved water column selenium, particulate selenium, and prey tissue selenium concentrations that will protect clam

- eatin g fish and birds, and insect

eating fish in the estuary.
And the sentences below are most relevant to this question.

Form of Permit Limits: Although draft water column criteria values are expressed in dissolved selenium concentrations, water quality

- based permit limits, in most instances, are required to be in total recoverable values (40 CFR §122.45(c)). For most metals, criteria are in dissolved values because the dissolved fraction provides a better representation of the biologically active portion of t he metal than does the total or total recoverable fraction (USEPA, 1996). When water quality criteria are in the dissolved form, a translator can be used to determine a total recoverable permit limit. The translator is the fraction of the total recoverable metal in the downstream water that is dissolved (ibid). However, for selenium, both the dissolved and particulate fractions are bioavailable to the aquatic biota. Thus, we used a translator of 1 in developing the draft criteria, an appropriate assumption for the Bay and Delta.

Answer
The dissolved selenium is much less relevant than bioavailable selenium in particulates so urging for a focus on dissolved Se would not be as helpful as for other elements and back calculation from tissue concentrations to tot al recoverable metals in lentic and lotic waters seems preferable. Of all of the conventional water concentrations measured, total recoverable selenium is likely the most reflective of the selenium available to the filter feeders such as Corbula

. The selec tion of a translator of 1 equates total recoverable concentrations with notionally bioavailable selenium concentrations. In the case of selenium, that is a sound and appropriate conservative approach. The variability in total, recoverable, and dissolved

se lenium remains problematic regardless of the approach.

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## COMMENTS SUBMITTED B Y

Reviewer 3

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- 27 CHARGE QUESTIONS
Overall Document Organization and Structure

1. Please comment on the overall construction and clarity of the document, i.e., is the layout of the document logical and is the document clearly written? Are there better ways to arrange and/or present the information? If so, please explain and describe.
The document is well constructed and relatively w ell written. While the document (Chapter 2) separately addresses fate and exposure (based on modeling) and effects in separate sections (Chapter 3), these are not clearly delineated in the outline. For example, the outline should separate environmental fat e and models used to assess particulate vs. dissolved concentrations from bioaccumulation models that estimate body burdens. While Figure 2

- 1 attempts to provide an overall conceptual a model, a more simplified model documenting the estimation of water cri teria from tissues would be a better representation, and would probably be better suited in Chapter 1.
Chapter 3 is relatively well

- written. However, more figurative descriptions for thresholds would provide better clarity. For example, copies of the spec ies sensitivity distribution (SSD) which were used to obtain EC10s would be very helpful. As a template, please see the EPA 2014 document.
As a minor editorial comment, the outline for Chapter 4 is missing a subheading C.
A chapter should be dedicated to Uncertainty Analyses at some point in the document. What are the strengths and weaknesses of the assumptions used in the model? It was difficult to find a specific section where validations of the models were provided.
Questions on Use of Ecosystem

- Scale Selenium Model

2. Overall Toxicity Benchmarks/Development: The salinity throughout the San Francisco Bay and Delta (SFBD) varies from fresh to brackish to marine, and many of the species (or close relatives of the species) evaluated for the draft national freshwater criterion (USEPA, 2014 pp 57

- 62; 78

- 79 provided as supporting material), live in the estuary. Given these considerations, discuss whether it is reasonable to use the draft national freshwater selenium criterion (tissue elements) for aquatic life in the SFBD. Are there better ways to estimate toxicity benchmark values for key aquatic life species, many of which are anadromous, in the estuary? Please explain.
It is clear that salinity values have significant varian ce throughout SF Bay and the Delta. Acclimation to hyper and hypo saline conditions has significant impacts on endocrine and physiological responses in anadromous fish. Two of the most sensitive toxicity benchmarks for selenium in freshwater are altered de velopment of offspring and diminished reproduction, both under endocrine control. The National Se criteria was estimated based on reproductive and developmental endpoints using a species distribution of 9 freshwater fish genera with an N=14 Genus Mean Chro nic Values (GMCVs) (EPA 2014). Most of the exposures included a dietary component, which would allow all forms of Se (organic species) to be present and transported to the gonad. The 5th percentile projection yielded criterion lower than the most sensitive fish species tested, brown trout ( Salmo trutta ) and Oncorhynchus , which has two anadromous species in SFBD (Steelhead and Chinook Salmon). Since at least two andromous species were evaluated with reproduction and developmental endpoints utilized in the ev aluation, the National value is likely conservative. However, some

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- 28 uncertainty exists with the value as some have suggested many of the studies used dietary selenomethionine as the primary source of Se, and this may underestimate Se toxicity as other organ ic forms may also contribute to the toxic responses observed in fish (Ridby et al. 2014).
In addition, there may be some underestimation in Saltwater acclimated animals. When embryos of Japanese medaka ( Oryzia latipes ) were acclimated to hypersaline condi tions and treated with concentrations of 0.05 mM SeMe (derived from concentrations observed in mosquito fish ( Gambuis affinis) from the San Joaquin River) for 12 hours (Kupsco and Schlenk 2014) and 24 hours (Lavado et al. 2012), significant enhancement of developmental toxicity was observed. While this species is not endemic to SFBD, it demonstrates that there may be significant differences in developmental toxicity between saltwater adapted fish and those of freshwater fish, particularly at early life stag es (Larvae, alevin, smolt). And since many anadromous fish at young ages must acclimate to hypersaline conditions in areas where exposure to Se may still occur either through prior maternal transfer in ovo, or via diet, combined exposure to both
stressors may occur, particularly in the SFBD.
Alternatively, since anadromous adult female fish are likely gravid prior to returning to freshwater to spawn, it is unknown whether acclimation to freshwater impairs endocrine signaling, which could affect maternal
tr ansfer of Se to offspring or have any reproductive impact on Se toxicity in the returning adults. The endocrine responses would not be due to accumulation or feeding preferences on the adult females but due to the effects of hypersaline conditions on the p hysiology and susceptibility of anadromous species.
Thus, it may be more appropriate to differentiate criteria based on returning adults (ocean to stream) or outgoing younger life stages (i.e. smolts; stream to ocean).
In addition, the assumption of the SFBD criteria assumes that for salmonids juvenile (fry, alevin, smolt) life stages are the more sensitive to Se toxicity and assumes dietary exposures via insects. The proposed SFBD criteria fails to recognize in ovo exposure within returning females, whic h is likely more critical (Thomas and Janz 2014). If in ovo exposure occurs, then models must incorporate a more complex food web (inclusion of fish to returning adults, rather than exclusively insects as in outgoing fish).

3. Toxicity Benchmarks/Green Sturg eon: For green sturgeon in the SFBD, juvenile growth is most likely the most sensitive endpoint. A recent study, De Riu et al. (2014) (provided), using green sturgeon 1 observed selenium concentrations of 6

– 7 mg/kg dw (whole body) in the control treatment , which appears to reflect essentially a ‘no

- effect’ concentration for growth or other effects, and is similar to the draft national whole body criteria of 8.1 mg/kg dw (USEPA, 2014 pp. 57

- 62; 78

- 79). In light of this study (and any other relevant data on green sturgeon), is the draft national benchmark value of 8.1 mg/kg dw protective of the juvenile growth endpoint for green sturgeon? Please explain your answer.
The estimated value (EC5) should be protective of growth for juvenile green sturgeon. This is because the National benchmark was based on the more sensitive response of reproduction/development. Since growth is likely a less sensitive endpoint, the predicted value should be conservative and protective. In addition, the National criteria is similar to the criteria obtained from Linville (2006), which also used a feeding study and offspring development to estimate tissue values in white sturgeon.

1 Green sturgeon larvae were obtained from the offspring of three males and one female originating from the Klamath River along the Pacific Coast.

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- 29 4. Toxicity Benchmarks/Model: EPA uses log

- logistic modeling to determine EC10 values from environmental data. FWS has suggested that a biphasic model (Beckon et al., 2008 and Brian and Cousens, 1989, cited in review document) may be a better model to represent effects of selenium, sin ce a biphasic model shows a more representative progression of effect to living species (selenium is a micronutrient, but is toxic in both deficit concentrations and excessive concentrations). Studies on selenium effects in the literature (Heinz et al., 19 89, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document) do not appear to consider this issue, and study designs do not appear to take the issue into account.

a. Given that many of the studies in the literature often use a small (or zero) control concentration of selenium, and a low level of effect is observed (reflective of a deficient concentration), is the response to increasing levels of selenium (into the excessive toxic amounts) better represented using a biphasic model or log

- l ogistic model? Would the slope of the regression be skewed in either model, due to incomplete modeling of deficit effects?
Se is clearly an essential nutrient and likely fits a “bi

- phasic” model showing non

- montonicity or a U

- shape (Eaton and Gilbert 2013)

. While this is likely the most accurate description of the relationship of Se to development, the data are significantly lacking to identify EC10 values. The Beckon et al. (2008) manuscript compares 3 log

- logistic models with varied EC10 estimates. For ea ch comparison there are limited data points showing the classic U

- shape that essential nutrients should have with only one point showing reduced hatch at low concentrations. Consequently, until studies can be conducted to provide statistically adequate dat a to generate a biphasic curve, standard log

- logistic modeling should still be utilized.

b. Discuss whether it would be reasonable and appropriate to use a biphasic model to determine EC10 values for studies in the literature on representative or key spec ies for the SFBD (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document), or whether the results of using a standard log

- logistic model would produce more representative results.
As mentioned above, a biphasic model would be preferred if the data were available to provide adequate statistical power.

5. Species and Diet: Discuss whether the appropriate key species and food chains (webs) have been identified and appropriately applied for the SFBD.

a. Discuss whether th e diets of the key species chosen in each of the identified food webs are reasonable based on the literature (sources cited in review document) and whether the calculations of the Trophic Transfer Factors (TTFs) are scientifically supportable based on thos e diets (see specific questions below). Are there better ways to calculate TTFs for mixed diets for the key species? Please explain.
Overall, the criteria focuses on ocean

- going early life stage organisms for the salmonid anadromous fish species. As discu ssed above, larval or Young of the Year fish moving from freshwater into saltwater (smolts) are likely to have a different diet (only one TTF) than adults moving back into freshwater to spawn (Mixture 4

- trophic level

- see Fig 7 USEPA, 2014). Specification o f the targeted life stage is necessary to refine the food chains proposed in this document.

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- eating Fish:

b. Are the diet mixes (i.e., percentage of Corbula ) for adult white sturgeon, juvenile white and green sturgeon, and splittail scientifically supportable based on the available literature (Zeug et al., 2014, provided; USFWS, 2008 pp. 51

- 59, provided as supporting material; and Feyrer et al., 2003, cited in review document)? Is it scientifically supportable to postulate that splittai l do not consume as much Corbula , and are therefore not as much at

- risk as sturgeon?
Based on the literature, these assumptions seem appropriate.

c. Recent literature indicates that green sturgeon are more sensitive to selenium than white sturgeon (De Riu et al., 2014, provided; and Silvestre et al., 2010, cited in review document). Studies have also shown that adult green sturgeon primarily use the SFBD as a migratory corridor to freshwaters for spawning (http://exxexpartnership.com/wp

content/uploads/2010 /10/GreenSturgeon

- _1_.pdf , cited in review document). If it is known that egg maturation in adult green sturgeon is completed prior to entering the estuary, discuss whether it is scientifically supportable to conclude that adult white sturgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFBD (please provide references). Please comment on and discuss the potential for selenium exposure of adult green sturgeon during migration to play a role in reproductive toxicity, given the current state of knowledge on the reproductive biology and life history of green sturgeon.
Since Se is likely transported to gonads via the egg

- yolk precursor vitellogenin (Linville 2006: Janz et al. 2010), one could assume that animals that do not require vitellogenin any longer would not continue to increase gonadal concentrations of Se. However, it is unclear whether vitellogenin is continually deposited into “mature” gonads of green sturgeon. Studies in zebrafish indicate vitellogenin is constantly turned over throughout embryogenesis (Han et al. 2010) which would argue diet

- derived Se would continue to accumulate in animals even after maturation of gonads.

In the recent Linares

- Casenave et al . 2015 publication, of 26 female white sturgeon collected between San Pablo Bay and Suisun Bay, 18 were pre

- vitellogenic indicating most fish did not have sexually mature gonadal development. It was not documented whether the animals were coming from saltw ater to freshwater for spawning or vice

- versa. If animals are returning to spawn, then it can presumed that gonadal development and selenium burdens would be higher than in animals exciting the estuary. Animals with vitellogenic oocytes did have higher con centrations of Se.
Specifically for Clam

- eating Birds:

d. Discuss whether the diet mixes for the California Ridgway’s rail, scoter and scaup are scientifically defensible based on the literature (sources cited in review document). Rails: Specifically, dis cuss whether it is scientifically supportable to assume that California Ridgeway’s rails do not consume a large percentage of Corbula, given that their littoral feeding habitat does not overlap with the preferred habitat of Corbula

. Scoter/Scaup: It has been observed that in the early part of the winter, scoter and scaup live mainly in the shallower, northern parts of the Bay (Suisun Bay and San Pablo Bay) where Corbula are prevalent, and consume mostly Corbula . However, in the latter part of the winter and early

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- 31 spring prior to migration, they move down to the deeper, Central Bay area where Corbula are not as available, and the scoter and scaup are thought to consume mostly herring that do not bioaccumulate selenium as effectively. They then follow the coast north and continue to feed on herring prior to breeding and nesting. It appears that selenium moves directly from the diet of water birds into their eggs and not from internal tissue stores (Chapman et al., 2010). Given that scoter and scaup swi tch to a low selenium diet for a period prior to migration as well as during migration, and that selenium may be depurated at a higher rate during migration, and that scoter and scaup are likely to continue to feed on low selenium fish sources in the breed ing and nesting grounds, is it reasonable to decrease the percentage of Corbula in scoter and scaup diet by 1⁄2 (from 90% to 45%), with respect to selenium exposure that could impact reproductive endpoints? Please discuss.

I cannot comment on this section as I am unfamiliar with the life histories of these avian species.
Specifically for Insect

- eating Fish:

e. Are the diet mixes for SFBD steelhead, Chinook salmon and delta smelt used in the model scientifically supportable based on the literature (sources cit ed in review document)? Please explain.
As discussed above, at least for salmonids, the diet mixes will differ based on the life

- stage of the animal. Returning adults will have a much larger forage fish component than insects and likely continual depositio n of Se into ova. In contrast, early life

- stage salmonids will have a greater insect component. The models should be revised to separate adult and early life stages.

6. Trophic Transfer Factors (TTFs): Discuss whether the TTF values taken from the literature for individual species based on their food prey are scientifically supportable, i.e., are the TTF factors in Table 4

- 3 (values taken from USGS, 2010, Figure 11 and pp. 21

– 24; Presser and Luoma, 201 0, Table 3; and USEPA, 2014, pp. 71

- 77, each provided as supporting material) scientifically supportable and appropriate? Are you aware of any other or more applicable data?
The TTFs appear valid and are scientifically supportable. However, as discussed ab ove, a 4 trophic level mixture should be used for adult returning salmonids (Figure 7; USEPA 2014).

The TTF for Corbula (17) was developed and discussed in USGS (2010) pp. 21

- 23 (provided as supporting material). Discuss whether this analysis is scientifi cally supportable. Would you recommend a different or better way to develop a site

- specific TTF for Corbula , given the available data? Are there additional data that the Agency should consider for developing a site

- specific TTF for Corbula ?

The site

- specif ic model used to calculate TTF for Corbula is scientifically sound.

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- 32 7. Partitioning Coefficients (K d s): In general, selenium is more bioavailable for accumulation into the food chain during dry/low flow (lentic) conditions, which is represented by higher K d values. Is it scientifically supportable to use the 75 th percentile of the K d values for each of the landward and seaward transects in the modeling, since data representing critical (very dry) conditions are not available? Would the use of median or mean K d values be more appropriate? Please explain your

answer.

The rationale for selection of the 75 th percentile is not clearly stated. Given the significant uncertainties in Kd as well as other components within these systems (i.e. percentage of microalgae, peryphyton etc), one would think a 95 th percentile would be more conservative.

8. Corbula Concentrations: Information in Fuller et al. (2012) and in Thompson and Parchaso (20 10) (both provided) indicate that populations and population densities of Corbula appear to decline in wet years, and increase in dry years. The articles suggest that Corbula may be sensitive to flow into the estuary and/or the salinity of the estuary (and other factors). The model shows that when the system has higher K d values (representative of dryer years), more selenium is available for bioaccumulation and more selenium accumulates in the food chain (which would drive the draft criteria to protect the use downward), and thus, we are concerned with accounting for critically dry conditions. Please comment on the articles and these statements.
I cannot comment on the life history of Corbula . The descriptions provided regarding wet and dry years and Kd valu es appear scientifically sound.

9. Transects: Discuss whether it is reasonable and representative to use the focused seaward transects to model the clam

- based food webs, in order to eliminate the end

- member variability at the ocean (at the Golden Gate Brid ge, the entrance to San Francisco Bay). Does the geology of the focused area (a wide Suisun Bay flowing into a constricted Carquinez Strait), and the importance of the area (the location of refinery discharges), favor the use of focused transects to best r epresent the clam

- based food web for the estuary? Please discuss.
The life history and ecology of Corbula is outside of my expertise. Given the complexity of the SFBD and the movement of organisms throughout its confines indicates that focus upon specific areas particularly with an element with incredible geospatial movement may not be fruitful.
Results and Application

10. Results: Discuss whether the model input and results scientifically support the water quality criteria for the three food chains repres ented. Are there better ways to represent the three food webs in the modeling? Please explain.

This has been addressed above. In summary, neglecting the movement of spawning females to freshwater habitats may under

- estimate exposure to Se due to consumptio n of mixed trophic levels during vitellogenesis. Examples would include forage fish species as dietary items; thus, adding another TTF.

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- 33 Discuss whether it is scientifically supportable to use the modeling results for the clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish (all three food webs) in addition to the clam

- eating fish themselves. Discuss whether there are other scientifically defensible ways to use the modeling results to protect all the categories of species fo r the SFBD.
As mentioned above, revision or modification of the model to include “inbound” adult salmonids as a food

web category is essential. Salmonids are clearly insect

- eating going out to sea, but are fish

- eating when returning. The rationale for this is the continued exposure to developing ova, which upon fertilization will be embryonic. In addition, the addition of uncertainty factors for salinity and Se interactions may also be warranted in species were maternally exposed embryos are discharged in s alt or brackish water environments.

11. Draft Criteria: The USGS Ecosystem

- Scale Selenium model was originally developed and validated for SFBD, and a considerable amount of site

- specific data are available and are used to model the estuary. EPA is using the model results to inform the criteria development process, and presents draft multi

media criteria in Chapter 4. These criteria are a whole body or muscle fish tissue value and a clam tissue value that directly reflect selenium levels that are considere d to be protective of aquatic biota; and corresponding chronic and intermittent water column values, as well as a particulate concentration value to facilitate regulatory controls of selenium sources.

Given the relevance and detail of the USGS model and t he abundance of site

- specific data, discuss whether the criteria in the different media are scientifically defensible and protective for this aquatic ecosystem.
The criteria are certainly an excellent first step in setting site

- specific values. However, t he criteria seem to be focused exclusively on Corbula consuming predators with the assumption that they are the most sensitive species with regard to Se toxicity. Consequently, this criteria is more appropriately a site and species

- specific criteria primar ily toward sturgeon. While numerically the values may protect ocean

- bound salmonids, it is unclear whether “in

- bound” offspring would experience the same protection. Likewise, it is unclear the value would protect broadcast spawning species in brackish or saltwater environments.

12. Translator (Permits): EPA regulations generally call for NPDES permit limits to be expressed in terms of total recoverable values (40 CFR 122.45(c)). The model applied in this document yields calculations of water column values in the dissolved form. For most metals, EPA recommends dissolved values for water quality criteria, because the dissolved form better represents the bioavailable fraction in the water column to aquatic biota. However, for selenium, aquatic biota can take in the dissolved and particulate fractions in the water column, which are then moved into and up the food chain. For most metals, EPA allows a translator to be used on the dissolved criteria value, to determine a total recoverable permit limit; the translator is the fraction of the total recoverable metal in the downstream water (downstream of a discharge) that is dissolved. Given that selenium has different bioaccumulation dynamics, what is an appropriate method to derive a translator? Explain your answer. Se can exist in dissolved states in many forms with the inorganic forms (selenite and selenite) predominating most discharges. Thus, it is difficult to determine a translator from particulate to dissolved forms when the most toxic form of Se is lik ely organic. Without the ability to measure the most toxic species of Se (SeMe or

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- 34 SeCys, or other organic forms) and understand the kinetics of transformation to organic forms, tremendous uncertainty exists in setting a translator value. Consequently, addi tional modeling is necessary to estimate the transformation rates of inorganic to organic (particulate) in a site

- specific manner which nutrient input and hydrology will likely play significant roles.

References
Beckon, WN. Cary Parkins, C., Maximovich, A . and Beckon, AV . (2008). A General Approach to Modeling Biphasic Relationships. Environ. Sci. Technol. 42, 1308

- 1314.
Eaton, DL and Gilbert SG (2013) Principles of Toxicology IN: Casarett and Doull’s Toxicology : The Basic Science of Poisons. (C. Klaasse n Editor) McGraw Hill Publishers, New York, NY. pp13

- 48.
Fan, XA, Klein, M, Flanagan

- Steet, HR, Steet, R. (2010). Selective Yolk Deposition and Mannose Phosphorylation of Lysosomal Glycosidases in Zebrafish Journal of Biological Chemistry 285:32946

- 32953.
Janz, D.M., D.K. DeForest, M.L. Brooks, P.M. Chapman, G. Gilron, D. Hoff, W.A. Hopkins, D.O. McIntyre, C.A. Mebane, V.P. Palace, J.P. Skorupa and M.Wayland. (2010). Selenium Toxicity to Aquatic Organisms in: Chapman PM, Adams WJ, Brooks ML, Delos CG, Luom a SN, Maher WA, Ohlendorf HM, Presser TS, Shaw DP (eds). Ecological Assessment of Selenium in the Aquatic Environment. SETAC Press, Pensacola, FL, USA.

Linares

- Casenave, J. Linville, R. Van Eenennaam, JP, Muguet,JB and Doroshovy, SI. (2015). Selenium tissu e burden compartmentalization in resident white sturgeon ( Acipenser transmontanus ) of the San Francisco bay delta estuary Environmental Toxicology and Chemistry, Vol. 34, No. 1, pp. 152

– 160, 2015
Lavado, R., Shi, D. and Schlenk, D. (2012). Effects of salin ity on the toxicity and biotransformation of l

selenomethionine in Japanese medaka ( Oryzias latipes ) embryos: Mechanisms of oxidative stress. Aquatic Toxicology108:18

- 22.
Linville RG. 2006. Effects of selenium on health and reproduction of white sturgeon A cipenser
transmontanus ): Implications for San Francisco Bay

- Delta. PhD thesis. University of California, Davis, CA, USA.
Kupsco, A. and Schlenk D. (2014). Mechanisms of Selenomethionine Developmental Toxicity and the Impacts of Combined Hypersaline Conditi ons on Japanese Medaka ( Oryzias latipes ). Environ. Sci. Technol. 2014, 48, 7062−7068. Rigby, MC., Lemly, AD, Gerads, R.(2014). Fish toxicity testing with selenomethionine spiked feed

– what's the real question being asked? Environ. Sci. Processes Impacts, 2014, 16, 511

– 517 Thomas, JK and Janz DM (2014) In ovo exposure to selenomethionine via maternal transfer increases developmental toxicities and impairs swim performance in F1generation zebrafish ( Danio rerio ) Aquatic Toxicology 152:20

- 29. USEPA, 2014: U.S. Environmental Protection Agency. 2014. External Review Draft, Aquatic Life Ambient Water Quality Criteria for Selenium

– Freshwater 2014. Office of Water, EPA 822

- P

- 14

- 001. Washington, D.C.

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## COMMENTS SUBMITTED B Y

Reviewer 4

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- 37 External Peer Review of Draft Aquatic Life and Aquatic

- Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014)

1. Overall Document Organization and Structure
Overall the document is well written and well organized. It could be enhanced with additional summary information concerning selenium flux, loading and discharge in this complex ecosystem, as well as additional discussion of water column concentrations and estuarine fresh

- salt water dynamics that impact Se sedimentation. The major routes of fish and avian wildlife dietary exposure are very well treated. USGS Professional Paper 1646, USGS 2010 and the CA Water Board TMDL documents for the North Bay can be th e source of some of this water column and loading information. Note: p13 “across the full range of bay salinities (<1 to 33 parts per trillion, ppt)” should be parts per thousand.
Questions on Use of Ecosystem

- Scale Selenium Model

2. Overall Toxicity Be nchmarks/Development:
In the SF Bay estuarine system, the interface of marine and freshwater from the Delta causes sedimentation of much of the freshwater suspended particulate load and many dissolved ions. The major concern of Se toxicological impact mod ulation would come from the presence of dissolved sulfate at the lowest trophic levels. With sedimentation however, sulfate reducing bacteria come into play in the sediment forming reduced sulfur compounds reacting with co

- precipitating dissolved metal sal ts and mineral adsorbents (see for example: Chambers, et al. Sulfate reduction and sediment metabolism in Tomales Bay, California. Biogeochemistry 1994, Volume 25, Issue 1, pp 1

- 18). Thus, it is reasonable to suggest that marine

freshwater interface sedime ntation caused by common ion effect and other solution processes, would increase the sedimentation of dissolved and suspended Se, forming the well

- recognized sediment Se exposure pathway of the SF Bay, while providing for a sulfate reduction pathway (and S e as well) that would decrease sulfate competition in selenium exposure as well as modifying Se oxidation state and chemical forms (see for example: Meseck & Cutter. 2012. Selenium Behavior in San Francisco Bay Sediments. Estuaries and Coasts (2012) 35:646

– 657). With sediment Se exposure as a prime pathway in this ecosystem, it is reasonable to use the draft national freshwater selenium criterion (tissue elements) for aquatic life in the SFBD.

3. Toxicity Benchmarks/Green Sturgeon:
De Riu et al. (2014) is an solid Se aquatic toxicity study (lacking genetic diversity due to green sturgeon listing and single egg donor), however the exposure diets of 0 (common 1

- 2 mg/kg Se diet formulation background), 50, 100 and 200 (2.2 ± 0.2, 19.7 ± 0.6, 40.1 ± 1.5, and 77 .7 ± 3.6 mg Se/kg dw tested) are a very high exposure range that lack clear environmental dietary relevance. Indeed Kleckner, et al. 2010 (Selenium Concentrations and Stable Isotopic Compositions of Carbon and Nitrogen in the Benthic Clam Corbula amurensis from Northern San Francisco Bay, California: May 1995

– February 2010. USGS Open

- File Report 2010

– 1252) observe a max Corbula Se concentration of 22 mg/kg dw. Thus there is really only a two point dose response curve (2.2 and 19.7 mg/kg) for the major dose

- response range dynamic in the SFBD area of interest for clam feeding fish. The data of Table 1 for fixed ration Growth Performance in De Riu et al. (2014) for the 0 and 50 exposure groups through 8 weeks appear to have very high variability and a very larg e 95%

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- 38 confidence interval that includes zero. The ANOVA used assumes normality but the data appeared skewed and may require transformation to explore effects estimation. The effect of time in this study is also not adequately explored. Thus the Control and 50 dose group data for %BWI/d as presented in Table 1 are far less than definitive and not justified to warrant the summary conclusion of the paper characterized as “the low SeMet diet (19.7 ± 0.6 mg Se/kg dw), which caused severe adverse effects in green sturgeon”. Hence De Riu et al. (2014) is not definitive as a single study for lower (<20 mg/kg Se) diet concentration growth effects in clam eating fish.
%BWI/d 2wk 4wk 6wk 8wk

0 control 4.5 ±1.8 (± 40%) 11.9 ± 6.1 (± 51%) 6.3 ± 15.9 (± 252%) 6.6 ± 14.9 (± 226%)

50 3.8 ± 3.9 (± 103%) 6.8 ± 8.4 (± 123%) 3.1 ± 14.8 (± 477%) 2.6 ± 16.0 (± 615%)

The control (2.2 mg/kg Se dw diet) green sturgeon total body Se at 4 weeks (6.5 ± 0.9) and 8 weeks (7.1 ± 0.9) have upper confidence bounds of 7.4 mg/kg and 8.0 mg/kg respectively and thus in close proximity to the draft national benchmark value of 8.1 mg/kg dw. Given the noted genet ic variability limitations of De Riu et al. (2014) as well as their observation of potential fixed ration study impacts to the rapid growth phase of juvenile green sturgeon, as well as expected routine laboratory sampling variability and method bias, the
p rotection of juvenile green sturgeon is qualitatively and quantitatively afforded by the draft national benchmark value.
In light of the lack of precision of the De Riu et al. (2014) study to benthic clam Se concentration range in this ecosystem, and the v ariability of the Table 1 data, the NOEL of 6

- 7 mg/kg dw (whole body) is protected by the draft national benchmark value of 8.1 mg/kg dw.

4. Toxicity Benchmarks/Model:
Biphasic models have good potential to address toxicological impacts from essential tra ce elements (ETEs). However the broad range of existing and published aquatic toxicology studies were not experimentally set up with the broad range of dosage required to explore effects with this model. Log

- logistic models are acceptable common practice, although all models have limitations. Selenium appears to have very poor regulatory homeostasis as an essential trace element, compared to for example copper or manganese, and this confounds the use of biphasic models for selenium. The 2008 work of Beckon notes that the complexity of dietary selenium exposure makes it a poor choice for biphasic modeling:
“Although biphasic relationships are common, it should not be assumed that dose

- response relationships are biphasic as a general rule, even for substances that are well known to cause biphasic responses. For example, dietary exposure to selenium is widely understood to have biphasic effects on the health and survival of animals ... However, although embryonic malformations are one of the effects of high levels of selenium, such defects are not known to be among the effects of selenium deficiency. Therefore, data relating selenium exposure to developmental defects ... may be

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- 39 best represented by a monotonic dose response model. Affecters of organisms are more likel y to exhibit biphasic dose

- response relationships if the effect or “endpoint” assessed is a general measurement of health, growth, or fecundity rather than a narrower effect such as embryonic deformities, liver lesions, or thrombosis. This is because broad measures of effect are more likely to represent a combination of individual beneficial low

- dose and deleterious high

- dose mechanisms or responses. A narrow end point is more likely to capture the consequence of a particular mechanism or response that may be only beneficial or only deleterious to the organism, and would be represented better by a monotonic dose

- response model.” (Beckon, et al. Environ. Sci. Technol. 2008, 42, 1308

– 1314)
As noted, biphasic models work best when the response tracked in the st udy appears in both deficiency and toxicity realms of exposure. The somewhat narrow toxic reproductive endpoints found in Se exposure limit the usefulness of the biphasic approach. Thus a) the Se dose response analysis is better represented log

logistic mo del. Skewing of the slope of the regression due to incomplete deficit dosing maybe unlikely since all experimental diets will have a baseline Se concentration from the protein and other constituents in the diet formulation prior to test agent fortification (i.e. addition of selenate, Se

- methionine or other quantified Se substance). Dietary formulations for deficiency studies are very difficult with ETEs since they are ubiquitous at low, often required, levels in many healthy plants and animals. The cautions of Beckon, et al. 2008 concerning the application of biphasic modeling to selenium suggest b) it is not reasonable and appropriate to use a biphasic model to determine EC10 values for studies in the literature on representative or key species for the SFBD . A standard log

- logistic model is appropriate and acceptable in the exploration of high dose Se reproductive toxicity.

5. Species and Diet:
The seminal works of Luoma and Presser have wonderfully characterized Se behavior, impacts and risks in the SFBD. Building on these works, the SFBD is exceptionally well characterized through several decades of modeling, samplings and scientific analyses exploring pathways and endpoints for selenium in this complex and important ecosystem. The body of SFBD work has b een thorough in its analysis of key species and the related food webs that contribute to our understanding of Se impacts. The dietary information for the key species analyzed are well cited and well explored. More recent work with sturgeon (Zeug et al, 201 4) fills data gaps with this key species. The resulting TTFs thus represent the use of best available data. Opportunistic feeding and food web dynamics related to the hydrograph and climate variability add variability to dietary understanding, however it i s unlikely that precise quantitative analysis that addresses the full range of variables is possible. Thus a) TTFs derived from best available information, such as done in the current analysis is generally scientifically supportable.

Specifically for Clam

- eating Fish:
The diet mixes appear to be representative of our current understanding of clam

- eating fish in the SFBD. Newer work such as Zeug et al., 2014 are valuable assets in modeling dietary exposure and thus TTFs. Without clear and definitive dat a addressing system variability, such as the case for many organism’s diet, best informed estimates that balance what is known against what is unknown or unquantified, is a reasonable approach. This appears to be the approach taken when the ; USFWS, 2008 a nd Feyrer et al. work is used:

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- 40 Diet: Splittail are benthic (bottom) feeders. Stomach contents from 70 splittail collected in Suisun Marsh between March 1998 and January 1999 indicate that their diet consisted mainly (43%) of unidentified material, probably detritus. The overbite clam (Asian clam), Potamocorbula amurensis, and other mollusks constituted 34% of the diet (Feyrer and Matern 2000, Feyrer et al. 2003).

Thus b) it is scientifically supportable to postulate that splittail do not consume as much C orbula, and are therefore not as much at

- risk as sturgeon.
While of value, De Riu et al., 2014 for reasons stated above, is neither definitive nor quantitatively precise in assessing green sturgeon Se exposure risk in the SFBD. If there is high confidence in the observation that sturgeon use the “SFBD as a migratory corridor to freshwaters for spawning” and that egg maturation is primarily complete before entering the estuary, then there is cause to c) scientifically support a conclusion that adult white s turgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFBD. The 0 and 50 group dose

- response data in De Riu et al., 2014 compared to the observed Corbula Se concentr ations in Kleckner, et al. 2010, suggest lower level risks for juvenile growth toxic endpoints.

Specifically for Clam

- eating Birds:
The review document presents a solid and defensible understanding of diet mix and this dietary exposure for the California Ridgway’s rail, scoter and scaup. While habitat choice and thus exposure potential from Corbula are beyond my area of expertise, d) i t seems plausible and reasonable to assess exposure potential in this manner. My work with aquatic birds in this ecosystem (Möller, G. 1996. Biogeochemical Interactions Affecting Hepatic Trace Element Levels in Aquatic Birds. Environmental Toxicology and C hemistry 15:1025

- 1033) suggests a complex dietary and environmental correlation of Cd

– Mn

– Se

– Hg

– As in vivo that may confound simple monotonic dose response models. Indeed, the tissue data for several of the sediment feeding birds demonstrated very high Se l evels compared to other species. While complex, d) it does appear reasonable to decrease the percentage of Corbula in scoter and scaup diet by one half for Se selenium exposure and the potential for reproductive endpoints.

Specifically for Insect

- eating Fish:
With several decades of monitoring, the insect diet mixes for SFBD insect eating fish are e) scientifically supportable and well discussed and referenced in FWS, 2008.

6. Trophic Transfer Factors (TTFs):

The TTFs taken from the work of Presser and Luoma, USGS and the 2014 Draft Criteria are to my knowledge the best available TTF values that could be applied in a SFBD model; I am not aware of any additional TTF values that would supplant this data. The additional Corbula TTF values developed in USGS 2010 pp21

- 23 is coherently presented and contains well supported assumptions (e.g. dissolved Se exposure is trivial). The USGS 2010 Corbula TTF analysis is explicitly developed and cited in this reference and I am not aware of any additional analyses of th is caliber and quality.

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- 41 7. Partitioning Coefficients (K d s):
Without data, median or mean values build on absent data estimate that may underestimate risk without cause. Using the 75th percentile of the Kd values seems to be an appropriately protective es timate, allowing for precaution in dry/low flow higher know risk conditions.

.

8. Corbula Concentrations:
The work of Fuller et al. (2012) and Thompson and Parchaso (2010) predate the current CA critically dry conditions. Since the Fuller work appears based on ongoing BDMA assessments, incorporating the most recent data may help validate population relationships with the hydrograph which has experienced some
extreme changes in recent years. With flow reductions in critically dry years, Se flux into the SFBD may also be reduced although existing sediment Se loading may provide Se exposure hysteresis and landward shift of the sedimentation zone at the salt

– fresh water interface of the estuary. Increased salinity into the landward reaches of the SFBD may shift Corbula populations with shifting salinity. Lentic/lotic Se dynamics that are understood for freshwater systems may not translate well to marine sediment exposure pathways observed in the SFBD, as stated in “more selenium is available for bioaccumulation and more selenium accumulates in the food chain.” A quick trend analysis of the most recent BDMA data may be sufficient to explore this concern.

9. Transects:

Tr ansects are a valuable way to explore sediment variability with regards to flow and sedimentation dynamics in the SFBD. Focused transects can help define food web variability that would result from geology and fresh

- salt water estuarine sedimentation proce sses. Yearly hydrograph changes and critically dry periods may induce unacceptable variability in any model input, however.

Results and Application

10. Results:
The review document model input and results support the water quality criteria for the three food chains represented. The models and model inputs used appear to be the best available approach using peer

reviewed data and approaches. The SFBD is an exceptionally well

- studied aquatic ecosystem with regards to water flows, Se, fish and wildlife. The TTF model, the dietary estimates, and the selection of key species all represent our best available knowledge. Clam eating fish represent a worse case exposure scenario due to the Se sediment dynamics in the SFBD and the migratory habits and thus lessened exposure scenario of aquatic birds in this ecosystem. In this regard, it is scientifically supportable to use the modeling results for the clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish, in addition to the clam

- eating f ish themselves. Other than applying safety factors to account for species differences in exposure and Se sensitivity (not recommended) there are no other common approaches that can be applied across species.

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- 42 11. Draft Criteria :

In our current understandi ng of Se impacts and effects, the USGS Ecosystem

- Scale Selenium model is the gold standard for modeling, balancing interpolation/extrapolation with required knowledge of species specific and ecosystem specific dynamics and values. As presented in this revi ew document, the criteria in the different media are scientifically defensible and protective for this aquatic ecosystem.

12. Translator (Permits):
As with lead (Pb) exposure in birds and fish, not all of the total recoverable Se can be considered bioavai lable (e.g. Zia et al., In vitro and in vivo approaches for the measurement of oral bioavailability of lead (Pb) in contaminated soils: A review. Environmental Pollution. Volume 159, Issue 10, October 2011, Pages 2320

– 2327). Luoma et al 1992 (Determination of selenium bioavailability to a benthic bivalve from particulate and solute pathways. Environ. Sci. Technol., 1992, 26 (3), pp 485

– 491) has perhaps the most direct answer to the Se translator challenge.

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## COMMENTS SUBMITTED B Y

Reviewer 5

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- 45 Peer Review of Draft Aquatic Life and Aquatic

- Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014)
Overall Document Organization and Structure

1. Please comment on the overall construction and clarity of the document, i.e., is the layout of the document logical and is the document clearly written? Are there better ways to arrange and/or present the information? If so, please explain and describe.

Response: I found the overall construction an d clarity of the document to be quite good. There was a nice logical progression beginning with background and then describing and assembling all the various components needed to develop a Se WQC for SFBD. One very minor comment, paginate the whole documen t rather than just within a section.
Questions on Use of Ecosystem

- Scale Selenium Model

2. Overall Toxicity Benchmarks/Development: The salinity throughout the San Francisco Bay and Delta (SFBD) varies from fresh to brackish to marine, and many of the specie s (or close relatives of the species) evaluated for the draft national freshwater criterion (USEPA, 2014 pp 57

- 62; 78

- 79 provided as supporting material), live in the estuary. Given these considerations, discuss whether it is reasonable to use the draft na tional freshwater selenium criterion (tissue elements) for aquatic life in the SFBD. Are there better ways to estimate toxicity benchmark values for key aquatic life species, many of which are anadromous, in the estuary? Please explain.

Response: Yes, I th ink it is reasonable to use the draft national freshwater selenium tissue criterion for SFBD. I am not aware of any evidence that suggests anadromous species are more or less sensitive to Se than freshwater species. Further, considering the mechanisms of a ction for Se, I can think of no reason to hypothesize that this might be the case.

3. Toxicity Benchmarks/Green Sturgeon: For green sturgeon in the SFBD, juvenile growth is most likely the most sensitive endpoint. A recent study, De Riu et al. (2014) (provid ed), using green sturgeon 1 observed selenium concentrations of 6

– 7 mg/kg dw (whole body) in the control treatment, which appears to reflect essentially a ‘no

- effect’ concentration for growth or other effects, and is similar to the draft national whole body criteria of 8.1 mg/kg dw (USEPA, 2014 pp. 57

- 62; 78

- 79). In light of this study (and any other relevant data on green sturgeon), is the draft national benchmark value of 8.1 mg/kg dw protective of the juvenile growth endpoint for green sturgeon? Please explain your answer.

Response: I disagree with the assertion that juvenile gr owth is likely the most sensitive endpoint for green sturgeon. In general, larval abnormality is the most sensitive endpoint for fish. Using the micro

- injection to maternal transfer ratio for white sturgeon and applying it to green sturgeon suggests larval abnormality may be a more sensitive endpoint. I agree with EPA’s current assessment that while the FWS analysis suggests this may be the case, the uncertainty in this extrapolation precludes its use in setting a Se WQC. The fact that background Se in juve nile sturgeon is higher than the estimated whole body threshold using the micro

injection to maternal transfer ratio further increases the uncertainty in this analysis.

1 Green sturgeon larvae were obtained from the offspring of three males and one female origi nating from the Klamath River along the Pacific Coast.

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- 46 I think it is clear that the draft national benchmark value of 8.1 mg/kg dw is protecti ve of juvenile green sturgeon growth. The real concern is that this value is likely statistically indistinguishable from background Se in juvenile green sturgeon. Based on the error estimates for week 8 whole body measurements in the De Rui et al. study (T able 2), it is likely that at least one control sample exceeded the 8.1 mg/kg dw threshold. This raises concerns that some relatively large fraction (e.g., 30% based on n=3 from De Rui et al.) of background tissue measurements exceed the proposed Se WQC.

4. Toxicity Benchmarks/Model: EPA uses log

- logistic modeling to determine EC10 values from environmental data. FWS has suggested that a biphasic model (Beckon et al., 2008 and Brian and Cousens, 1989, cited in review document) may be a better model to repr esent effects of selenium, since a biphasic model shows a more representative progression of effect to living species (selenium is a micronutrient, but is toxic in both deficit concentrations and excessive concentrations). Studies on selenium effects in th e literature (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document) do not appear to consider this issue, and study designs do not appear to take the issue into account.

a. Given that many of the studies in the lite rature often use a small (or zero) control concentration of selenium, and a low level of effect is observed (reflective of a deficient concentration), is the response to increasing levels of selenium (into the excessive toxic amounts) better represented

us ing a biphasic model or log

- logistic model? Would the slope of the regression be skewed in either model, due to incomplete modeling of deficit effects?
b. Discuss whether it would be reasonable and appropriate to use a biphasic model to determine EC10 valu es for studies in the literature on representative or key species for the SFBD (Heinz et al., 1989, Hilton et al., 1980, and Hamilton et al., 1990, cited in review document), or whether the results of using a standard log

- logistic model would produce more representative results.

Response: For some data sets, a biphasic model may better describe the data and there is a potential mechanistic underpinning (i.e., Se essentiality) for why such a model would be appropriate. It is possible for model slopes to dif fer depending on the data set and the interpretation of what constitutes a 10% effect can be quite different. The data from Hilton et al. (1980) (Figure 23; USFWS 2008) is the clearest example of such a data set although this parti cular study is problematic because fish were fed an inorganic Se diet. In contrast, it is not clear that use of a biphasic model on data for Chinook salmon (Figure 11; USFWS 2008) and mallards (Figure 1; USFWS 2008) is more appropriate than a standard log

- logistic model. In general, I think EPA should consider use of “non

- standard” models if they better describe the data and there is a viable mechanism for why such a model should be used. In my opinion, only the Hilton et al. study meets both criteria.

5. S pecies and Diet: Discuss whether the appropriate key species and food chains (webs) have been identified and appropriately applied for the SFBD.

a. Discuss whether the diets of the key species chosen in each of the identified food webs are reasonable base d on the literature (sources cited in review document) and whether the calculations of the Trophic Transfer Factors (TTFs) are scientifically supportable based on those diets (see specific questions below). Are there better ways to calculate TTFs for mixed diets for the key species? Please explain.

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B- 47 Response: Yes, based on the literature provided the identified food webs are reasonable. No, I don’t think there are better ways to calculate TTFs for mixed diets for the key species. Also see specific responses below.
Specifically for Clam

- eating Fish:

b. Are the diet mixes (i.e., percentage of Corbula ) for adult white sturgeon, juvenile white and green sturgeon, and splittail scientifically supportable based on the available literature (Zeug et al., 20 14, provided; USFWS, 2008 pp. 51

- 59, provided as supporting material; and Feyrer et al., 2003, cited in review document)? Is it scientifically supportable to postulate that splittail do not consume as much Corbula , and are therefore not as much at

- risk as sturgeon?

Response: The diet mixes proposed by USEPA are scientifically supportable, although I would not say the available data precludes consideration of other dietary mixes. It would be useful to perform and provide the results of a sensitivity analysis on this issue. For example, if the sturgeon diet was 50% Corbula , how much lower would the proposed WQC need to be? I also agree that splittail do not consume as much Corbula as sturgeon, but do not agree this necessarily equates to them being at lower ri sk. Risk is an integration of exposure and effect (i.e., sensitivity). Given the limited studies on sturgeon and splittail in general, it is premature to conclude they are less or equally sensitive to Se compared to sturgeon. Therefore, the level of risk f or splittail is unknown.

c. Recent literature indicates that green sturgeon are more sensitive to selenium than white sturgeon (De Riu et al., 2014, provided; and Silvestre et al., 2010, cited in review document). Studies have also shown that adult green sturgeon primarily use the SFBD as a migratory corridor to freshwaters for spawning (http://exxexpartnership.com/wp

content/uploads/2010/10/GreenSturgeon

- _1_.pdf , cited in review document). If it is known that egg maturation in adult green sturgeon is comp leted prior to entering the estuary, discuss whether it is scientifically supportable to conclude that adult white sturgeon and juvenile white and green sturgeon will be more affected than adult green sturgeon from elevated levels of selenium in Corbula in the SFBD (please provide references). Please comment on and discuss the potential for selenium exposure of adult green sturgeon during migration to play a role in reproductive toxicity, given the current state of knowledge on the reproductive biology and life history of green sturgeon.

Response: I think given our understanding of adult green and white sturgeon use of SFBD, it is likely that juvenile white and green sturgeon will be more affected than adults of either species. I understand that it is likely green sturgeon eggs mature while adults are in the ocean and that the adults appear to primarily use SFBD as a migration corridor. However, I think we cannot rule out the potential for toxicologically significant Se exposure (with respect to the eggs) dur ing this migration. We simply don’t have any information on this issue and so it would be prudent not to rule out this potential exposure pathway. I don’t think there is enough information to address this issue in a quantitative manner, but it should be highlighted that this is a potentially significant uncertainty that needs further study rather than eliminating it as an issue for concern as the document currently does.

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- 48 Specifically for Clam

- eating Birds:

d. Discuss whether the diet mixes for the Californi a Ridgway’s rail, scoter and scaup are scientifically defensible based on the literature (sources cited in review document). Rails: Specifically, discuss whether it is scientifically supportable to assume that California Ridgeway’s rails do not consume a large percentage of Corbula, given that their littoral feeding habitat does not overlap with the preferred habitat of Corbula

. Response: While the 20% Corbula diet used in the model is not unreasonable given the available data, it is entirely speculative and could be either lower or higher. A sensitivity analysis would be useful to understand the implications of this assumption. If all of the mollusk component o f the rail diet (60%) were Corbula , would they become the driver of the proposed WQC? If so, what percentage Corbula in the diet causes this to be the case? Scoter/Scaup: It has been observed that in the early part of the winter, scoter and scaup live main ly in the shallower, northern parts of the Bay (Suisun Bay and San Pablo Bay) where Corbula are prevalent, and consume mostly Corbula . However, in the latter part of the winter and early spring prior to migration, they move down to the deeper, Central Bay area where Corbula are not as available, and the scoter and scaup are thought to consume mostly herring that do not bioaccumulate selenium as effectively. They then follow the coast north and continue to feed on herring prior to breeding and nesting. It ap pears that selenium moves directly from the diet of water birds into their eggs and not from internal tissue stores (Chapman et al., 2010). Given that scoter and scaup switch to a low selenium diet for a period prior to migration as well as during migratio n, and that selenium may be depurated at a higher rate during migration, and that scoter and scaup are likely to continue to feed on low selenium fish sources in the breeding and nesting grounds, is it reasonable to decrease the percentage of Corbula in sc oter and scaup diet by 1⁄2 (from 90% to 45%), with respect to selenium exposure that could impact reproductive endpoints? Please discuss.

Response: While I follow the thinking used by EPA in setting the Corbula diet at 45% for scoter and scaup, I’m not convi nced it is particularly accurate. In assessing potential exposure of green sturgeon, EPA asserted that sturgeon eggs mature while adults are in the open ocean where Se exposure is low. It seems a similar line of thinking should be used in assessing risks t o scoters and scaups. When are egg proteins deposited relative to the timing of duck feeding on Corbula . If Corbula feeding occurs during this period, then exposure should be high, if not, then there is no relevant exposure with respect to the SFB WQC. It should also be pointed out that even if exposure is relatively high, there is evidence that ducks depurate Se relatively rapidly (19 d half life for mallards; (Heinz et al. 1990) ) and marine ducks deposit a low percentage of Se in eggs relative to freshwater species (Henny et al. 1995)

. Specifically for Insect

- eating Fish:

e. Are the diet mixes for SFBD steelhead, Chinook salmon and delta smelt used in the model scientifically supportable based on t he literature (sources cited in review document)? Please explain.

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- 49 Response: The diets of SFBD steelhead, Chinook salmon and delta smelt are relatively well studied. These are probably the most reliable diet mixes of any of the species evaluated by EPA. Mos t importantly, there is high confidence that these species are not consuming mollusks.

6. Trophic Transfer Factors (TTFs): Discuss whether the TTF values taken from the literature for individual species based on their food prey are scientifically supportab le, i.e., are the TTF factors in Table 4

- 3 (values taken from USGS, 2010, Figure 11 and pp. 21

– 24; Presser and Luoma, 2010, Table 3; and USEPA, 2014, pp. 71

- 77, each provided as supporting material) scientifically supportable and appropriate? Are you awa re of any other or more applicable data?
The TTF for Corbula (17) was developed and discussed in USGS (2010) pp. 21

- 23 (provided as supporting material). Discuss whether this analysis is scientifically supportable. Would you recommend a different or bette r way to develop a site

- specific TTF for Corbula , given the available data? Are there additional data that the Agency should consider for developing a site

- specific TTF for Corbula ?

Response: In general, the TTFs taken from the literature and used in the W QC derivation are scientifically supportable. Specific to Corbula , yes I agree with the novel approach taken by USGS and adopted by EPA in this analysis.
One issue of concern is that EPA has opted to use a TTF fish of 1.1 in all cases despite species

- specific TTFs being available in some circumstances. For example, USGS derived a TTF for white sturgeon of 0.8. It is unclear why EPA selected to use a mean value from across species, as generally in WQC derivation, spe cific

specific data is given preference.
Also, see comments below on K d s and the need to consider concentration

- dependent TTFs.

7. Partitioning Coefficients (K d s): In general, selenium is more bioavailable for accumulation into the food chain during dry/lo w flow (lentic) conditions, which is represented by higher K d values. Is it scientifically supportable to use the 75 th percentile of the K d values for each of the landward and seaward transects in the modeling, since data representing critical (very dry) c onditions are not available? Would the use of median or mean K d values be more appropriate? Please explain your

answer.
Response: Yes, I think it is appropriate to use the 75 th percentile K d in the modeling given the variability in K d s both seasonally and annually, and the uncertainty regarding K d s during very dry conditions. One uncertainty with K d s that EPA has not considered is that they tend to be inversely related to exposure concentration (see Poster by DeForest et al. provided wi th comments). EPA should evaluate concentration dependency in their assessment and consider using a quantile regression approach for determining the 75 th percentile K d . It is also worth noting that if EPA were to use this type of approach at each step in t he model (i.e., 75 th percentile at each step), this would equate to a 98 th percentile site/condition (assuming each step is independent), which I believe most would consider adequately protective.

8. Corbula Concentrations: Information in Fuller et al. (20 12) and in Thompson and Parchaso (2010) (both provided) indicate that populations and population densities of Corbula appear to decline in wet years, and increase in dry years. The articles suggest that Corbula may be sensitive to flow into the estuary and /or the salinity of the estuary (and other factors). The model shows that when the system has higher K d values (representative of dryer years), more selenium is available for

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- 50 bioaccumulation and more selenium accumulates in the food chain (which would driv e the draft criteria to protect the use downward), and thus, we are concerned with accounting for critically dry conditions. Please comment on the articles and these statements.

Response: I agree with EPA’s assessment that the available literature indicate s the density and distribution of Corbula is constrained by low salinity (i.e., freshwater) and that the system exhibits higher K d s during drier years resulting in more Se bioaccumulation higher in the food chain. To some extent, EPA has accounted for the inter

- annual variability by selecting the 75 th percentile K d for modeling. However, the possibility of higher K d s during exceptiona lly dry years or seasons cannot be ruled out. In the absence of any data in such conditions, I think all EPA can do at this point is commit to monitoring the system next time such conditions occur and ensuring the option of revising the site

- specific WQC b ased on new data. I do not think it reasonable to speculate on how much K d s will change under such conditions and a priori increase the K d s in the models.

9. Transects: Discuss whether it is reasonable and representative to use the focused seaward transect s to model the clam

- based food webs, in order to eliminate the end

- member variability at the ocean (at the Golden Gate Bridge, the entrance to San Francisco Bay). Does the geology of the focused area (a wide Suisun Bay flowing into a constricted Carquinez Strait), and the importance of the area (the location of refinery discharges), favor the use of focused transects to best represent the clam

- based food web for the estuary? Please discuss.

Response: Yes, I generally agree with EPA’s decision to use the foc used seaward transects to model the clam

- based food webs. The end

- member K d s clearly represent a set of conditions that differ from the focused area and the focused area is most relevant for exposure to both fish and bird species of interest. Having said t hat, as the document currently reads, it appears that EPA eliminated the K d s from near Golden Gate simply to reduce variability. I think a better rationale for eliminated these data would be related to the presence/absence of relevant receptors (i.e., fish and birds). Are there species we should be concerned about in the outer Bay where K d s appear to be significantly higher? Some discussion of this issue in the document would be useful.
Results and Application

10. Results: Discuss whether the model input an d results scientifically support the water quality criteria for the three food chains represented. Are there better ways to represent the three food webs in the modeling? Please explain. Discuss whether it is scientifically supportable to use the modeling results for the clam

- eating fish as a surrogate to protect clam

- eating birds and insect

- eating fish (all three food webs) in addition to the clam

- eating fish themselves. Discuss whether there are other scientifically defensible ways to use the modeling res ults to protect all the categories of species for the SFBD.

Response: Yes, the proposed approach, model input and results all appear scientifically defensible for establishing water quality criteria protective of all three food chains. It was appropriate f or EPA to evaluate all three chains, but ultimately one of these food chains will drive the WQC. It is not surprising that clam

eating fish are the driver and it is scientifically defensible to use WQC derived from this model to protect all species in the system.

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- 51 11. Draft Criteria: The USGS Ecosystem

- Scale Selenium model was originally developed and validated for SFBD, and a considerable amount of site

- specific data are available and are used to model the estuary. EPA is using the model results to inform the criteria development process, and presents draft multi

media criteria in Chapter 4. These criteria are a whole body or muscle fish tissue value and a clam tissue value that directly reflect selenium levels that are considered to be protective of aquati c biota; and corresponding chronic and intermittent water column values, as well as a particulate concentration value to facilitate regulatory controls of selenium sources.
Given the relevance and detail of the USGS model and the abundance of site

- specific data, discuss whether the criteria in the different media are scientifically defensible and protective for this aquatic ecosystem.
Response: Yes, given the abundance of both site

- specific and detail of the USGS model, the proposed criteria in different me dia are both scientifically defensible and protective of the SFB aquatic ecosystem. I have been involved with several dozen site

- specific water quality criteria/standard projects and the amount of data and model development involved in deriving these site

- specific criteria far exceed (by an order of magnitude in most cases) the level of information typically available in these efforts.

12. Translator (Permits): EPA regulations generally call for NPDES permit limits to be expressed in terms of total recovera ble values (40 CFR 122.45(c)). The model applied in this document yields calculations of water column values in the dissolved form. For most metals, EPA recommends dissolved values for water quality criteria, because the dissolved form better represents th e bioavailable fraction in the water column to aquatic biota. However, for selenium, aquatic biota can take in the dissolved and particulate fractions in the water column, which are then moved into and up the food chain. For most metals, EPA allows a trans lator to be used on the dissolved criteria value, to determine a total recoverable permit limit; the translator is the fraction of the total recoverable metal in the downstream water (downstream of a discharge) that is dissolved.
Given that selenium has di fferent bioaccumulation dynamics, what is an appropriate method to derive a translator? Explain your answer.

Response: I agree with EPA’s approach of setting the translator at 1.0 for Se. For divalent metals, the dissolved fraction is clearly the dominant bioavailable metal fraction with respect to toxicity. While there is considerable evidence that particulate divalent metals are can be bioaccumulated, their toxic potency appears to be considerably less than the dissolved form in most cases. In contrast, f or Se, it is clear that both dissolved and particulate Se are bioavailable and toxic to aquatic organisms. Consequently, it is appropriate to use a translator of 1.0 for Se.

Other Comments
Section 1, Page 11, Last Paragraph : There are numerous papers and reports indicating Se is the most dose

sensitive nutrient, but I have yet to see a quantitative analysis supporting this statement. Several other metals also have very narrow ranges between essentiality and toxicity that are c omparable to Se. For example, Cu (for snails) and Zn (for daphnids) both have very narrow ranges between essential requirements and toxicity. Unless EPA is aware of a quantitative analysis supporting this statement I suggest deleting it.
Section 1, Page 13 , First Paragraph : “ppt” stands for parts per thousand, not trillion in this instance.

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- 52 Section 2, Page 8, First Paragraph : Risk is an integration of exposure and effect (i.e., sensitivity). Just because clam

- eating species have the highest exposure doesn’t necessarily mean they are most at risk. It depends on their sensitivity as well.
Section 4, Page 11, First Paragraph : It is unclear why bioaccumulative based effects are of greater concern that other effects. Why would this type of effect justify a lower effect threshold? Regardless of the mechanism, the EC10 represents a 10% effect.

References
Heinz, G. H., G. W. Pendelton, A. J. Krynitsky and L. G. Gold (1990). "Selenium accumulation and elimination in mallards." Arch. Environ. Contam. Toxicol. 19 : 374

- 379. Henny, C. J., D. D. Rudis, T. J. Roffe and E. Robinson

- Wilson (1995). "Contaminants and sea ducks in Alaska and the circumpolar region." Environ. Hlth. Per. 103 (4): 41

- 49. Hilton, J. W., P. V. Hodson and S. J. Slinger (1980). "The requirement and toxicity of selenium in rainbow trout ( Salmo gairdneri )." J. Nutr. 110 (12): 2527

- 2535.

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