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# E PA Response to Comment Document

April, 2016

EPA Reponses to Peer Reviewer Comments in the Peer Review Summary Report, July 28, 2015

Peer Review of the Draft Aquatic Life and Aquatic

Dependent Wildlife Selenium Water Quality Criteria for the San Francisco Bay and Delta (2014)2 

## EPA RESPONSE TO COMMENT DOCUMENT

Overall Document Organization and Structure

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 arrange and/or present the information? If so, please explain and describe.

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.

EPA: Thank you for your comments.

Re viewer 2 The format and conceptual 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 logica l. There seemed to be a richer discussion 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 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 through 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 the entire treatment.

EPA: Thank you. S ince birds are considered important eco

- recep tors in the San F rancisco estuary , EPA felt it was necessary to consider them in this site

- specific analysis.
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 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.3 EPA : EPA agrees that u ncertainty in the analysis is important. We have added information on uncertainty and sensitivity in the document.

Reviewer 3 The document is well constructed and relatively well written. While the document

(Chapter 2) separately addresses fate and expos ure (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 bioac cumulation 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 bett er 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 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 w eaknesses of the assumptions used in the model? It was difficult to find a specific section where validations of the models were provided.

EPA: Thank you for you r comments . EPA agrees that uncertainty a nalyse s would be useful; we have added information and discussion in the document.

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 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 20 10 and the CA Water Board TMDL documents for the North Bay can be the 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.

EPA: Th ank you for your comments.

Reviewer 5 I found the overall 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 d evelop a Se WQC for SFBD. One very minor comment, paginate the whole document rather than just within a section.

EPA: Thank you for your comment s.4 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 supportin g 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 ways to estimate toxicity benchmark valu es for key aquatic life species, many of which a re anadromous, in the estuary? Please explain.

Reviewer 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 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 competition 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 potentia lly competing 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 com parison 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.

EPA: EPA acknowledges your comment s concerning applying data from fresh water species to saltwater species. However, the freshwater species sensitivity distribution for the national criterion includes several anadromous fish, particularly at the sensitive end of the distribution. A lso, the available toxicity data indicate s l ittle difference in the sensitivity between freshwater, saltwater, and anadromous estuarine species of fish. Based on the concerns presented, the use of data for freshwater species is likely conservative for saltwater species, given that ionic content (i. e. , sulfate) of saltwater limits the bioavailability of selenite. Given the lack of specific data, and the uncertainty, using the national freshwater tissue criterion for the estuary is reasonable

.

Reviewer 2 Although the national freshwater selenium criterion was used, its use and adjustments

for the SFBD were reasonable and effectively incorporated. The challenge with some species of concern being anadromous is a difficult one and I wondered while reading the document whether an exposure ad justment for duration of time within the estuary or freshwater regions might have included more detail. Try as I might, 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 as sessment 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 not5 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  g/L and  g/kg is fine for fre shwater 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.)

EPA: Thank you for y our comments. Given the lack of specific data, with the exception of the available information on anadromous species, EPA believes it would not be sufficiently informative to solicit expert opinion on an iss u e tha t has a paucity of data

.

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 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 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 proje ction 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 reprod uction 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 al. 2014).

EPA: Thank you for your comments . EPA does not agree that selenium may be an endocrine disruptor in the sense that it is receptor

- based; the general scientific consensus is that excess selenium is involved with oxidative damage, but the evidence is not conclusive. D espite some uncertainty, EPA believes using the national freshwater tissue criterion for the estuary is reasonable

. 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 (derived fr om 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 e ndemic 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 yo ung 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.6 EPA: Medaka are freshwater species while anadromous fish are specifically adapted to a certain lifestyle and undergo major physiological changes when transitioning from freshwater to saltwater lifestyles. In the study of medaka, salinity may have been more of an acute stressor tha t affected homeostasis causing indirect effects manifested as developmental toxicity in offspring. If the medaka had been acclimated over time to a given salinity regime, as is the case for anadromous spec ies, the effects may have a more significant meani ng.
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 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.
EPA: The salinity of the San Francisco Bay and Delta ranges from freshwater (1 ppt) to marine (approximatel y 3 3 ppt); the conditions in the estuary are not hypersaline (above the salinity of seawater, or above 35 ppt). A key uncertain ty is the level of maturity of eggs and whether vitellogenesis is still actively occurring. If vitellogenesis is complete or nearly complete before entering the estuary, then only minimal amounts of selenium from diet in the estuary would be trans ferred t o eggs.
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).

EPA: A key issue is the species and their exposure to selenium in marine systems

. The document looks at salmonid smolts, since adults are semelparous and receive most ( almost all ) of their selenium exposure from a n ocean diet outside of the estuary before returning to spawn

. Salmonid smolts are exposed through diet in a freshwater

e nvironment until they transition to saltwater, and are then exposed through diet to selenium in the estuary for three months to a year before moving out into the ocean

. We have clarified this in the document.

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, which 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).

EPA: Both the national freshwa ter selenium criterion and the proposed criteria for the San Francisco estuary do not consider and/or incorporate the marine dietary exposure to selenium. Although it is uncertain as to how much selenium returning salmon take up as they pass through the estua ry, it is likely very small in comparison to the dietary component take n up and delivered via maternal transfer to eggs during oogenesis and vitillogenesis which primarily (almost exclusively) occurs prior to entering the estuary.

Reviewer 4 In the SF B ay 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 presen ce of dissolved sulfate at the lowest trophic levels. With sedimentation however, sulfate reducing bacteria come into play in the sediment forming reduced sulfur7 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 effec t 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 Se as well) that would decrease sul fate 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.

EPA: Thank you for your comments and the proposed scientific rationale as to why the national fre shwater criterion would be reasonable.

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 mechanisms of action for Se, I can think of no reason to hypothesize that this might be the case.

EPA: Thank you for your comments

.

2 .3 Toxicity Benchmarks/Green Sturgeon: For green sturgeon in the SFBD, juven ile 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 ‘n o - effect’ concentration for growth or other effec ts, and is similar to the draft national whole body criteri on 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 ben chmark value of 8.1 mg/kg dw protective of the juvenile grow th endpoint for green sturgeon? Please explain your

answer.

Reviewer Comments

Reviewer 1 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 and these green sturgeon woul d appear to be just barely protected by the draft national benchmark value of 8.1 ppm.

EPA: EPA agrees that the difference between 8.0

- 8.1 mg/kg dw and 6

- 7 mg/kg dw is not significant. The study supports a whole body EC10 value of 6

– 8 mg/kg dw for juvenile growth and development (non

- reproductive effects) in both green and white sturgeon , given that effects would be expected above this range.

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 this8 distinction by using laboratory study results that allow inferences about the statistical population of tested individuals to suggest protection of the ecologic al 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 labo ratory

- 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 for a long time, but produce many eggs upon spawning. It is not a species for which an expedient heuristiclike “if you protect the individual’s most sensitive life stage, you protect the species population viability” can be confidently applied.

Fortunately , 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 demogra phic 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 rates that most influence the growth rate (log  ) 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 populatio n model 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 induce d fitness is not determined by the most sensitive life

- cycle trait. Funct. Ecol. 10:106

- 111.

EPA: If under your analysis of less critical vital rates the proposed criteria might be

o verprotective, since green sturgeon are listed as Federally threatened and populations in the system are dwindling, the proposed criteria could be considered reasonable and protective of the species.

EPA notes that the Linville ( 2006 ) study on white sturgeon has been added to the database to derive the national freshwa ter criterion. This significantly strengthe ns the assertion that the national value will be protective of green sturgeon , since it is based on a genus level surrogate of the green sturgeon

.

Reviewer 3 The estimated value (EC 5 ) 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.9 EPA: Thank you for your comments . (The estimated value is an EC10 value [an effect concentration affecting 10% of the species ’ population] determined from a regression analysis of the four most sensitive Genus Mean Chronic Values [ GMCVs ] and an extrapolation to the 5 th percentile of the distribution represented b y the tested genera.)

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 ± 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 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. 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 genetic variability limitations of De Riu et al. (2014) as well as their ob servation 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 protection of juvenile green sturgeon is qualitatively and quantitative ly 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 variability 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.10 EPA: Thank you for your comments

. EPA notes your concern of uncertainty in the De Riu et al. (2014) study , given that the exposure concentrations in diet w ere unrealistically high.

Reviewer 5 I disagree with the assertion that juvenile growth 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 s turgeon 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 threshold using the micro

- injection to maternal transfer ratio further increases the uncertainty in this analysis.

EPA: Micro

- injection is an un supportable route of exposure for toxicity tests, particularly with selenium which is available in several forms in organ ic matter, and which is regulated by organisms as a nutrient . Micro

- injection exposure contains significant uncertainty as it is usual ly only one type of selenium (selenomethionine) and the injection is a bolus dose instead of an acquisition over time through diet. A bolus dose may overwhelm the body’s metabolic response to selenium as its function as a nutrient.

I think it is clear tha t the draft national benchmark value of 8.1 mg/kg dw is protective 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 (Table 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.

EPA: Thank you for your comments

. The data in the Linville ( 2006 ) study supports an EC10 egg/ovary value of 16 mg/kg dw for white sturgeon

. Including the Linville (2006) study in the datase t for the draft national criterion resul ts in a whole body criterion of 8 mg/kg dw

. The De R i u et al. (2014) study shows the control green sturgeon had a whole body level of 6

– 7 mg/kg dw; this indicates that juvenile green sturgeon may have a similar sensitivity to selenium as juvenile white sturgeon at this whole body concentration level . This st rongly supports using the national freshwater thr eshold for the San Francisco estuary.11 2

. 4 Toxicity Benchmarks/Model: EPA u ses log

- logistic modeling to determine EC10 values from environmental data. FWS has suggested that a biphasic mo del (Beckon et al., 2008 and Br a i n 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, H ilton 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) c ontrol 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 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?

Reviewer Comments

Reviewer 1 I do not know.

(Declined to respond.)

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 numbe r of observations needed in the 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 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 effec t levels for selected representative/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 inform ation were available, a biphasic 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 see ms 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 biphas ic 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 u ncertainty 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, I12 suggest that formal methods be established to aid user s in deciding which model is best for their particular data set.

EPA: Thank you for your comments. EPA agrees that if sufficient dose levels in the range of essentiality are unavailable, the use of the biphasic model is inappropriate and if used, may lea d to bias

.

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 essential nutrients s hould 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.

EPA: Th ank you for your comments. EPA agrees that if sufficient data are not available to use a biphasic model, this type of model should not be used

. In those cases, EPA agrees that a standard log

- logistic model should 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 range of dosage required to explore effec ts 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 co nfounds 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

- re sponse 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 ... Howeve r, 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 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 measurement of health, growth, or fecundity rather than a narrower effect such

as e mbryonic 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 t o 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 )13 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 reproductive endpoints found in Se exposure limit the usefulness of the biphasic approach. Th us 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 oth er 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.

EPA: Thank you for your comments. EPA agrees that a log

- lo g regression is more appropriate than a biphasic model for the data from the published studies that have been reviewed . EPA acknowledges the citation from Beckon et al. ( 2008 ) concerning cautions against using the biphasic model, and the comment that s ele nium appears to have very poor regulatory homeostasis as an essential trace element compared to copper or manganese, and that this confounds the use of biphasic models for selenium

.

Reviewer 5 For some data sets, a biphasic model may better describe the d ata 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 quit e different . The data from Hilton et al. (1980) (Figure 23; USFWS 2008) is the clearest example of such a data set although this particular 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

- st andard” 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.

EPA: Thank you for your comments. EPA agrees that where sufficient and a ppropriate data exist, non

- standard models like biphasic models should be considered. EPA does not find that the data sets in the studies discussed includ e sufficient and /or appropriate data for utilization of a biphasic model.14

2.4 continued: Toxicity Bench m arks/Model :

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 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.

Reviewer Comments

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

(Declined to respond.)

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 biologic al systems.

EPA: Thank you for your comments. EPA agrees that if studies have sufficient data points in the lower dose regions, the use of a biphasic model may be more appropriate. However, for the studies reviewed, sufficient data in the lower dose ran ges does not exist and therefore, EPA supports the use of a standard log

- logistic model to determine EC10 values.

Reviewer 3 As mentioned above, a biphasic model would be preferred if the data were available to

provide adequate statistical power.

EPA: T hank you for your comments. Please s ee EPA r esponse to Reviewer 2.

Reviewer 4 See response provided under 2 .4. a

.

EPA: Thank you. Please s ee EPA response provided under 2.4.a.

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

EPA: Thank you. Please s ee EPA response provided under 2.4.a.15 2

. 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 supportable based on those diets (s ee specific questions below). Are ther e better ways to calculate TTFs for mi xed diets for the key species? Please explain.

Reviewer Comments

Reviewer 1 It is possible to mathematically calculate TTFs for mixed diets for a given 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 considerable 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 o f magnitude differences are seen, largely based on the variability in the metal concentrations in the different forms of prey. [see Mathews & Fisher, Sci. Total Environ. 407: 5156

- 5161 (2009).]

The goal of the site specific water quality criteria is to pro tect the system as a whole based on the available toxicity data for sensitive species. In this case, we have data for sturgeon, salmonids and birds a s sensitive receptors for selenium toxicity. These species, although consuming a mixed diet, do have docu mented “prey” preferences (e.g. sturgeon

- mollusc, and juvenile salmon

- insect), for which data is available. Since there are preferences, conservative assumptions are applied since there is uncertainty about other prey items in the diet. The result will t heoretically be protective, since the sensitivity of surrogates consuming the modeled diets containing selenium is representative (and maybe overly conservative) for other organisms in the system without data.

EPA: Thank you for your comments

. EPA acknowl edges that in nature, diet can vary greatly for a single species. For the San Francisco estuary , we have known sensitive species with known dietary preferences ; those species have been modeled using reasonably conservative assumptions in order to determin e protective criteria values to capture a range of consumption rates.

Reviewer 2 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
uncerta inty of each component going into the various calculations could be incorporated into a Monte Carlo resampling routine to provide estimates of the uncertainty around each calculated TTF. The uncertainty is likely large relative to that variation in TTF val ues among species.16 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.

EPA: Thank you for your comments. EPA agrees that an end member analysis involving N, C and S stable isotopes would help to determine di etary components. A study using stable isotope analyses has been completed for white sturgeon that live in the estuary (Zeug et al., 2014) and is consi dered in the analysis; EPA is not aware of any other similar studies for the critical species that live in the estuary. E PA agrees that a discussion of uncertainty would be useful ; we have added information and discussion in the document. (See EPA respons e to q uestion 2.1.)

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 lik ely 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 document.

EPA: E PA agrees that the lifestage of the species is important and necessary; the document discusses juvenile salmonids as the endpoint associated with a TTF based on an insectivorous diet. Adult salmonids moving back into freshwater s from a marine environment have very limited dietary exposure to selenium in the estuary, since it is used mainly as a migratory corridor and staging area for salmon ids preparing to enter freshwater natal streams and rivers. Thus assigning a TTF to this species lifestage combinatio n would not be meaningful with regard to selenium exposure related to maternal transfer of selenium to eggs. We have clarified this in the document

.

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 scientific analyses

e xploring 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. The dietary informati on 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 feeding 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.

EPA : Thank you for your comments.

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 TTFs for mixed diets for the key species. Also see specific responses below.17 EPA : Thank you for your comments.

2.5 continued: Species and Diet: 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?

Reviewer Comments

Reviewer 1 This seems reasonable to me, but see my comment below (under “c”).

EPA: Thank you for your comment

.

Reviewer 2 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. F or 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 apparent incongruity.

b. Yes. Based on my review of the supplied materials and the discussions in the draft document, the diet mixes seem reasonable, including the di fferences between sturgeon and splittail consumptions of Corbula

.

EPA: T hank you for your comments. Most of the TTFs used in the analysis are based on (and/or validated using) matched field data sets , reflecting what is happening in the environment . One reason to explain the similarity in TTF values between fish and birds , even though cold

- blooded fish and warm

- blooded birds may have significantly different metabolic rates, is that in this case, fish size might ameliorate some of the metabolic differences , e.g., a 100+ pound sturgeon will need quite a bit of food to maintain its bodyweight, while a small bird, even if it has a much higher metabolic rate, may eat substantially less.

Reviewer 3 Based on the literature, these assumptions seem appropriate.

EP A: Thank you for your comment.

Reviewer 4 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. Witho ut clear and definitive data addressing system variability, such as the case for many organism’s diet, best informed estimates that18 balance what is known against what is unknown or unquantified, is a reasonable approach. This appears to be the approach tak en when the ; USFWS, 2008 and Feyrer et al. work is used:
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 split tail do not consume as much Corbula, and are therefore no t as much at

- risk as sturgeon.

EPA: Thank you for your comments . EPA has clarified in the document that even though splittail may eat up to 34% mollusks, a portion of which may include Corbula , it is less than the amount of Corbula that white sturgeon are estimated to consume.

Reviewer 5 The diet mixes proposed by USEPA are scientifically supportable, although I would not say

the available data precludes consideration of other dietary mixes. I t 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 risk. 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 for splittail is unknown.

EPA: Thank you for your comments . EPA has added information and discussion on uncertainty and sensit ivity in the document. EPA agrees that risk is a combination of exposure and effect. For splittail, studies indicate that diet is likely no greater than 34% clam

- based. The available studies on splittail do not indicate whether they are more or less sensitive to selenium than other species whose diet i s also clam

- based (e.g., white sturgeon).19

2.5 continued: Species and Diet: Specifically for Clam

- eating Fish :

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 SF BD 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 re ferences). 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 sturg eon.

Reviewer Comments

Reviewer 1 These questions are outside my expertise.

(Declined to respond.)

Reviewer 2 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 quantitatively include more details for exposure duration and frequency. The EPA document dealing with human risk assessment (EPA 540/1

- 89/002) includes expo sure duration and frequency in its calculation of intake. Given the lack of knowledge about selenium bioaccumulation kinetics in the sturgeon, this approach would likely not improve the accuracy of estimates. Perhaps a formal expert elicitation would impro ve future estimates.
EPA: Thank you for your comments. EPA agrees that including information on exposure duration and frequency of intake (diet) would improve our understanding of risk for migratory sturgeon , but these kinds of very specific data are not available

. We have added more detail in the document to clarify our assumptions concerning white and green adult and juvenile sturgeon.

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

- yolk precursor vitellogenin (Linville

2006: Janz et a l. 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. S tudies 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.

EPA: Different f ish species have dif f erent strategies for depositing vitellogenin into eggs prior to spawning ; zebrafish may not be representative of other fish species, particularly sturgeon

.
In the recent Linares

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

- vitellogenic indicating20 most fish did not have sexually mature gonadal development. It was not documented whether the animals were coming 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 have higher concentrations of Se.

EPA: A key uncertainty is whether selenium is being deposited from body burden to eggs via maternal transfer during vitellogenesis, or whether selenium is being deposited more directly through current diet, or a combination of the two pathways. EPA noted this issue in the document

.

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 observation that sturgeon use the “SFBD as a migrato ry 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 juvenile white and green sturgeon will be more a ffected 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 Kleckner, et al. 2010, suggest lower level risks f or juvenile growth toxic endpoints.

EPA: EPA has added discussion in the document concerning these issues to clarify what information currently exists.

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 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. H owever, I think we cannot rule out the potential for toxicologically significant 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 expo sure 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 conc ern as the document currently does.

EPA: Thank you for your comments

. EPA has added discussion in the document concerning these issues to clarify wh at information currently exists . We have also noted its uncertainty. However, f or selenium exposure in the estuary to be toxicologically significant, several key conditions must occur : 1) green sturgeon must consume a significant amount of selenium

- contaminated prey items over the course of their occupancy during migration, and 2) a pathway for maternal transfer of the current diet

- ba sed selenium must be present, i.e., immature/developing eggs are still predominant in the female during migratory processes in the estuary , and/or turnover of vitellogenin is occurring, as observed by on e reviewer above in zebrafish (note: a key issue here is that zebrafish have a different spawning strategy than sturgeon in the wild, but are easily manipulated in the lab, with unknown effects on the reproductive cycles when compared with wild population s )

. It is no t apparent that either of these conditions are occurring in the estuary, and we therefore d o not consider exposure to adult green sturgeon in the estuary to be toxicologically significant.21

2 .5 continued: Species and Diet: 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

.

Reviewer Comments

Reviewer 1 This definitely makes sense.

EPA: Thank you for your comment.

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

EPA: Thank you for your comment.

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

species.
(Declined to respond.)

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 c hoice and thus exposure potential from Corbula are beyond my area of expertise, d) it seems plausible and reasonable to assess exposure potential in this manner. My work with aquatic birds in this ecosystem (Möller, G. 1996.Biogeochemical Interactions Affe cting Hepatic Trace Element Levels in Aquatic Birds. Environmental Toxicology and Chemistry 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, th e tissue data for several of the sediment feeding birds demonstrated very high Se levels 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 expos ure and the potential for reproductive endpoints.

EPA: Thank you for your comment.22

Reviewer 5 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 of the rail diet (60%) were Corbula , would they become the driver of the proposed WQC? If so, what percentage Corbula in the diet cau ses this to be the case?

EPA: Thank you for your comments. Given the lack of Corbula’s preferred habitat overlap ping with rail feeding areas, the likelihood of rails c onsuming specifically more Corbula ( not mollusk s generally) is low ; and g iven the other mollusks h ave substantially lower TTFs, EPA does not believe substantial risk exists to the general population , and a highly exposed rail due to Corbula consumption would be an exception. EPA has included information and discussion on sensitivity in the document.

2.5 continued: d. continued: Species and Diet: Specifically for Clam

- eating Birds:

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 w inter 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 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.

Reviewer Comments

Reviewer 1 It st rikes 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 a t 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/100 ar senic (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.

EPA: Your concerns appear to reflect whether acute exposures to adult birds are toxic, whereas our question concerned whether selenium exposure s shortly prior to migration have the potential for maternal transfer at a later time when the birds reach23 breeding grounds. We have no evidence that the level of acute exposure s fro m clams in the estuary has led to death in these adult birds.

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

EPA: Thank you for your comments. EPA agrees that additional information concerning exposure duration and frequency may be helpful in r efining the approach in the future. We have added discussion in the document to reflect what is currently known about the migratory movements of scoter and scaup to help reduce uncertainty.

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

(Declined to resp ond.)

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

EPA: Thank you for your comments.

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 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 to 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 relat ively 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)

.

EPA: EPA has added infor mation and discussion in the document concerning what is currently know about the timing of selenium incorporation into eggs for fish species (sturgeon) and bird species (migratory ducks/waterfowl), as well as its depuration in fish species and bird specie s. As noted in the comment , e vidence indicates that selenium is depurated rapidly in waterfowl, and that marine duck species deposit less selenium into their eggs than freshwater ducks species.24

2.5 continued: Species and Diet: 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.

Reviewer Comments

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 probably account for much of the variabil ity that one sees in Se concentrations in predator fish.

EPA: Thank you for your comments . EPA has added a discussion on uncertainty to account for the variability of selenium in diet due to prey species; v ariability of selenium levels from (and in) prey species is a reflection of abundance, timing and location of predation

.

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 ecol ogy and habits.

EPA: Thank you for your comment.

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 deposition 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.

EPA : EPA has clarified its discussion in the document concernin g life stages and associated d iet mixes . EPA does not consider inbound salmonids in the analysis due to their minimal exposure to selenium in the estuary.

Reviewer 4 With several decades of monitoring, the insect diet mixes for SFBD insect eating fish ar e

e) scientifically supportable and well discussed and referenced in FWS, 2008.

EPA: Thank you for your comments.

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.

EPA: Thank you for your comments.25 2 .6 Trophic Transfer Factors (TTFs):

a. 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, 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?

Reviewer Comments

Reviewer 1 These TTFs look good to me.

EPA: Thank you for your comment.

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 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 se veral 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 subject area were found with a quick Google search. Some examples include the following:

Cloern, JE,EACanuel and D Harris. 2002. Stable carbon and nitrogen isotope composition of aquatic and terrestrial plants of the San Fra ncisco 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 isotope s. 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.En viron. Sci. Technol., 38 (17): 4519

– 4526
EPA: Thank you for your comments. Please s ee EPA r esponse to question 2. 5. b. concernin g TTF values for cold

- blooded and warm - blooded species. Please s ee EPA response to question 2.5 .a. concerning studies using stable isotope tracking to determine diet composition.26

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 (Fi gure 7; USEPA 2014).

EPA: Thank you for your comments . EPA has clarified its discussion in the document concerning life stages and associated diet mixes. EPA does not consider inbound adult salmonids in the analysis due to their minimal exposure to selen ium in the estuary.

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 w ould 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 an d cited in this reference and I am not aware of any additional analyses of this caliber and quality.

EPA: Thank you for your comments.

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 by USGS and adopted by EPA in this analysis.

One issue of concern is that EPA has o pted 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.
EPA: Thank you for your comments . The analysis for the San Francisco estuary looks at categories of species based on diet prefe rences. Although sturgeon may have a n estimated TTF of 0.8 with respect to its primary food source ( Corbula ) , it is not the only clam

- eating species; the average fish TTF of 1.1 is a reasonable, conservative estimate to represent all fish species in the c lam

- eating fish category

.27

2.6 continued: Trophic Transfer Factors (TTFs) :

b. 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 ?

Reviewer Comments

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

EPA: Thank you for your comment.

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 reinforces this conclusion of consistency. I can think of no better way to estimate TTF values. Supplementing the current i n formation 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, 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 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 du ring filtration can vary with the density of those particles in the waters. Some additional scrutiny of the uncertainty in the chosen values seems warranted.28 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 fr om the literature (living phytoplankton, AE = 60%; adsorbed on seston, AE = 40%; elemental, AE = 0%; Schlekat et al., 2004; Wang et al., 1996). The equation is: AE = (fraction organic particulate Se) (AE organic particulate Se) + (fraction adsorbed particu late 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 6 0%; 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 time discussing the variation expected in this and the resulting variation in AE.

K e Estimation



### “ We apply the e

fflux rate constant derived experimentally (Lee et al., 2006): k e = 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 th at 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

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 for C. amurensis of 17 in modeling scenarios here. The rang e 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. ”

EPA: Thank you for your comments. We have added additional detail and discussion in the document concerning the calculations for the Corbula TTF value.29

Reviewer 3 The site

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

EPA: Thank you for your comment.

Reviewer 4 See r esponse provided under 2 .6 [a].

EPA: Thank you for your comments.

Reviewer 5 See response provided under 2 .6 [a].

EPA: Thank you for your comments. Please see EPA r esponse to que stion 2.6

. a
.

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.

Reviewer Comments

Reviewer 1 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 betwee n 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 uptak e 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 phytoplankton, with chl orophytes 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 phytoplan kton assemblage, and these natural communities typically change with season (seasonal succession patterns among the phytoplankton communities) and nutrient concentrations.

EPA: EPA agrees that K d s (or CFs) can vary significantly within a system depending on season (i.e., water flow). Using a 75 th percentile K d value is intended to reasonably capture the variability, and provides a more conservative value for modeling low flows, which have been occurring in the estuary for the last several years . We have included a more detailed explanation in the document of our rationale, and have included the K d values in the sensitivity analysis to show how values will change using a different metric (e.g., mean or median, larger percentile). In response to the commen t that phytoplankton assemblages change with season and nutrient concentrations, EPA notes that trophic level 2 organisms (e.g., Corbula ) will consume and take up selenium from a variety of particulate/algal matter.30

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 applied . The conservative approach of using the 75% percentile value seems better than using the mean or median.

EPA: Thank you for yo ur comments . EPA has added an analysis and discussion in the document concerning the distribution of K d values.

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 components within these systems (i.e. percentage of microalgae, peryphyton etc), one would think a 95 th percentile would be mor e conservative.

EPA : EPA has added an analysis and discussion in the document concerning the distribution of K d values , an d to clarify our rationale for using 75 th percentile values. The 95 th percentile would be more conservative but may incorporate outliers that are not representative of the normal distribution and seasonal variability of K d values for the system. EPA beli eves that using 75 th percentile K d value s reasonably represents a conservative approach to modeling probable wet and dry conditions in the estuary.

Reviewer 4 Without data, median or mean values build on absent data estimate that may

underestimate risk w ithout 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 estimates 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 analysi s for the 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 impa cting the SFBD hydrograph.

EPA: Thank you for your comments.

Reviewer 5 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 with comments). EPA should evaluate concentration dependency in their31 assessmen t 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 the model (i.e., 75 th percentile at each step), this would equate to a 98 th pe rcentile site/condition (assuming each step is independent), which I believe most would consider adequately protective.

EPA: Thank you for your comments. We feel that using 75 th percentile K d values and reasonable, conservative estimates of other variables in the model, the proposed criteria values are both reasonable and 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 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 (a nd 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 th e use downward), and thus, we are concerned with accounting for critically dry conditions. Please comment on the articles and these statements.

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

EPA: Please see EPA response to question 2.7.

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 appropriate.

EPA: Thank you for your comments.

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.

EPA: Thank you for your comments.

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 th e 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 for32 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 suffici ent to explore this concern.

EPA: EPA will continue to review all available information on the system to identify where the analysis can be improved. As the dry conditions in California continue, we will continue to review new data and consider adjustme nts to the analysis as necessary.

Reviewer 5 I agree 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 higher 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 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 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.

EPA: Thank you for your comments. EPA has and will continue to review all available data reflecting the cur rent dry conditions; if the dry conditions continue, EPA will consider adjus tments to the analysis as necessary.

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 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 ar ea (the location of refinery discharges), favor the use of focused transects to best represent the clam

- based food web for the estuary? Please discuss.

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.
(Declined to respon d.) EPA : EPA has clarified its rationale in the document for including the South Bay in the applicab le area of the water quality criteria.

Reviewer 2 This decision does seem reasonable in my opinion.

EPA: Thank you for your comment.

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 focus33 upon specific areas particularly with an element with incredible geospatial movement may not be fruitful.
(Declined to respond.) EPA: By modeling a smaller area, EPA can focus on the areas of greatest importance and limit complexity which helps determine appropriate criteria values.

Reviewer 4 Transects are a valuable way to explore sediment variability with regards to flow and

sedimentation dynam ics 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 changes and critically dry periods may induce unacceptable variability in any m odel input, however.

EPA: Thank you for your comments. EPA hopes that by focusing on important are as and modeling dry (conservative) conditions, we can determine appropriate and reasonable criteria values. EPA agrees that modeling critically dry or extremely wet conditions may introduce extreme results.

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 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 that, as the d ocument 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.

EPA: Thank you for your comments . EPA has added information and discussion

concern ing the presence/absence of relev ant species in the Central Bay near the Golden Gate, and clarified the rationale for using focused transects in the Suisun Bay

area.34 Results and Application

2

. 10 Results: a. 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.

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 more defensible to apply modeling results f rom 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 fol lowing 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.

EPA: EPA modeled the three food chains independently, then chose a set of result s that would reasonably protect all three food chains; we did not model one food chain as a surrogate for another.

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 studies might have provided additional insights and p erhaps a level of validation.

EPA: Thank you for your comments. Please see EPA response to question 2.5.a. concerning studies that use stable isotope analysis.

Reviewer 3 This has been addressed above. In summary, neglecting the movement of spawning

f emales 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.

EPA: As discussed in EPA’s response to question 2.5.e. and 2.6., EPA does not consider inbound adult salmonids in the analysis due to their minimal dietary exposure to selenium in the estuary ; adult salmonids use the ecosystem mainly as a migratory corridor. Sturgeon, although large, are ma inly bottom feeders and consume large amounts of Corbula

. Some sturgeon may also consume a small amount of small (forage) fish, but the selenium load from that would be minimal.

Reviewer 4 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 flo ws, 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 migr atory habits35 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, i n addition to the clam

eating fish 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.

EPA: Thank you fo r your response.

Reviewer 5 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 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.
EPA: Thank you for your response.

2.10 continued: Results:

b. 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

- eat ing 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.

Reviewer Comments

Reviewer 1 See response provided under 2

. 10 [a]

.

EPA: Please see EPA response to question 2.10

. a
.

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.

EPA: Thank you for your comments. (The analysis for San Francisco estuary does not include fish

- eating birds; it is assumed the reviewer is referring to clam

- eating birds.)

Reviewer 3 As mentioned above, revision or modification of the model to in clude “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 wil l 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 salt or brackish water environments.36 EPA: EPA does not consider inbound adult salmonids in the analysis due to their minimal exposure to selenium in the estuary as a migratory corridor

. Almost all of the selenium exposure to inbound salmonids is outside the estuary. In addition, a key step i s maternal transfer of selenium to the ova via vitellogenesis (not exposure to the developing ova) ; if maternal transfer of vitellogenin is ongoing during the migratory passage and staging, and adult salmon are actively feeding within the estuary during that process, then some dietary sele nium exposure from the estuary may take place. However, it would be much lower than full

- time residents of the estuary.

Reviewer 4 See response provided under 2 .10 .[a]

.

EPA: Thank you for your response.

Reviewer 5 See response provided under 2 .10 .[a].

EPA: Thank you for your response

.

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 i s 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 c onsidered 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 mode l and the abundance of site

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

Reviewer Comments

Reviewer 1 I think that the USGS model provides a defensible 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 bodies as w ell. 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.

EPA: Thank you for your comments. EPA agrees that the San Francisco estuary is well

studied , however the USGS model can be used in other places. For less studied areas, data gaps can filled by carefully selecting surrogate species and model variables.

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

- specific37 d ata and its use to produce predictive models is definitely defensible, and from my reading of the documents, is protective.

EPA: Thank you for your comments.

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

- specific crite ria 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 br ackish or saltwater environments.

EPA: Thank you for your comments. EPA focused on clam

- eating fish, clam

- eating birds, and insect

- eating fish (including juvenile salmonids) because they were identified as the most at

- risk set of species for this system (FWS , 2008; FWS, 2009; FWS, 2012), based on their sensitivity to selenium and their dietary exposure to selenium. EPA concurs with this asse ssment; adult salmon have minimal exposure, and other broadcast spawning species within the estuary have less expo sure and sensitivity than the clam

- eating fish and bird species that are discussed.

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

- Scale

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

EPA: Thank you for your comments.

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 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.

EPA: Thank you for your comments.38 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 fraction in the water colu mn 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 criteri a 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.

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 a nimals

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

EPA: For selenium, EPA agrees that the dissolved form does not better represent the bioavailable fraction, since particulate selenium is easily taken up into biota (e.g., by filter feeders). However, for permit purposes, a total recoverable value is needed, and the issue is how to translate the dissolved value into a total recoverable value for this waterbody, the San Francisco estuary.

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, t he 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 prot ective dissolved selenium estuarine water column concentration 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 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 protect ive 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

- eat ing fish should also be protected.39 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 protected, 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 concentratio n 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 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

- eating 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 di ssolved 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

re presentation of the biologically active portion of the 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 devel oping 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 a nd 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 avail able to the filter feeders such as Corbula

. The selection 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. T he variability in total, recoverable, and dissolved selenium remains problematic regardless of the approach.

EPA: Thank you for your comments.40

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 from particulate to dissolved forms when the most toxic form of Se is likely orga nic. 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.

EPA: Organic and inorganic forms of selenium can exist as di ssolved or particulate

. Organic forms are more readily available to biota than inorganic forms, but inorganic selenium (selenate and selenite) can be t ransformed into organic forms. Thus, all forms of selenium have the potential to be taken up into the fo od chain, although some forms will undergo a longer transformation process.

Both dissolved and particulate forms of selenium are bioavailable, and they transform back and forth in the system depending on the conditions in the system . Therefore, the
tran slator should equal 1, i.e., all dissolved selenium should be considered bioavailable as part of the total recoverable fraction.

Reviewer 4 As with lead (Pb) exposure 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. Volume 159, Issue 10, October 2011, Pages 2320

– 2327). Luoma et al 1992 (Determination of sel enium 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.

EPA: EPA does not agree; both dissolved and particulate s elenium can be bioavailable and toxic; some forms are more bioavailable than other forms, e.g., organo

- selenium is more available than selenite, but selenite can be transformed into organo

- selenium.

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 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, 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.

EPA: Thank you for your comments.41 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.42 New Information P rovided by R eviewers

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 References

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Approach to Modeling Biphasic Relationships. Environ. Sci. Technol. 42, 1308

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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.
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- Steet, HR, Steet, R. (2010). Selective Yolk Deposition and
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Linares

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– 160, 2015
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- Delta. PhD thesis. University of California, Davis, CA, USA.

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Rigby, MC., Lemly, AD, Gerads, R.(2014). Fish toxicity te sting with selenomethionine spiked feed

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